1 Sudhir R. - INFLIBNETshodhganga.inflibnet.ac.in/bitstream/10603/3871/8/08_chapter 1.pdfcontinuous...

1 Ph.D. Thesis Dave Sudhir R.


INTRODUCTION

The term supramolecular chemistry, which was coined by Jean-Marie Lehn1,

means “Chemistry beyond the molecule”2. While individual molecules consist of atoms joined

by covalent bond, supramolecular chemistry makes use of intermolecular interaction like

hydrogen bonds, π-stacking and electrostatic forces bringing molecules together to form larger

species3. Hydrogen bonding enables compounds containing electronegative functional groups to

interact with protons to form extended arrays. Molecules with aromatic rings can stack together

by virtue of π-π interactions. Electrostatic interactions include ion-ion, ion-dipole and dipole-

dipole interactions, where positively and negatively charged species associate. As

supramolecular chemistry focuses on how molecules interact with one another, there is emphasis

on complementarity and preorganization.4 Complementarity is the matching of a host molecule

to the electronic and geometric needs of a guest. One can design supramolecular complexes that

can behaves as molecular machines,5 such as shuttles, switches, and sensors. Within the field of

supramolecular chemistry Lehn6 distinguished between ‘supramolecule’ and ‘molecular

assemblies’. Supramolecules as were considered to be oligomers composed of a few components

assembled via specific intermolecular associations whereas in molecular assemblies, large

numbers of components assemble spontaneously into a structure that has reasonably well defined

microscopic organization and displays characteristics typical of macromolecules, e. g., fibre

formation, glass and melting transitions, chain entanglement and high property/ weight ratios7. It

is because they exhibit these typical properties that extended –chain molecular assemblies are

frequently referred to as ‘supramolecular polymers’.

Macrocyclic compound is an organic compound that contains a large ring. In the

organic chemistry of alicyclic compounds, a closed chain of 12 carbon (C) atoms is usually


regarded as the minimum size for a large ring. Macrocyclic compounds may be a single,

continuous thread of atoms or they may incorporate more than one strand or other ring systems

within the macrocycle or macro ring. Macrocyclic compounds play an important role in

supramolecular chemistry. The macrocyclic compound often contains heteroatoms like O, N, S,

and P or functional group that allow for the participation in intermolecular interactions. Crown

ether is an early example of macrocyclic compound, crown ethers are generally composed of

repeating ethylene units separated by noncarbon atoms such as oxygen but as more intricate

structures are prepared, nitrogen, sulfur, phosphorus, silicon, or siloxy residues are becoming

much more common. Charles Pedersen, who was a chemist working at Dupont, discovered a

simple method of synthesizing crown ether in 1967 (Figure 1) when he was trying to prepare a

complexing agent for divalent cations. Crown ethers have the remarkable property of

recognizing and binding specific metal cations in complex mixtures. Consequently, since their

discovery, crown ethers have found numerous applications in science and industry. In other

words, due to the fix size of cavity, crown ethers are more selective for metal ions. The

selectivity of the metal ion binding is controlled by changing the size of crown ether cavity and

by introducing the various combinations of the O, N, S, heteroatoms in the crown ether ring.

Attachment of different functional group to crown ethers give unique metal complexing

properties, due to their extensive ability to bind metal cations.8 The oxygen atoms of crown

ethers are ideally situated to coordinate with a cation in the interior of the ring, whereas the

exterior to the ring is hydrophobic. The result is that the complexed cation is soluble in nonpolar

solvents. The size of the interior of the crown ether determines the size of the cation it can

solvate. Therefore, 18-crown-6 has high affinity to potassium cation, 15-crown-5 for sodium


cation and 12-crown-4 for lithium cation. Pedersen, Lehn and Cram earned the nobel prize in

chemistry in 1987 for their pioneering work in macrocyclic field.

The oxygen atoms in the ring enable the macrocycle to coordinate alkali metal

cations.9 When one or two oxygen of crown ether is replaced with nitrogen atoms it is known as

aza crown ether. The unmetalled crown ethers show a collapsed ring structure in the solid state.

Preorganized macrocycles maintain their structure in the absence of metal10. That means the

macrocyclic compound is a cyclic compound having high molecular masses. Some other

macrocyclic compound like calixarenes, cyclodextrin, rotaxane and catanane are also included to

the list of crown ethers.

Aza crown ethers have especially been focused on as useful ligands because of

their versatility and applicability. The aza crown ethers have complexation properties that are

intermediate between those of all oxygen atoms of aza crown ethers which strongly complex

alkali and alkaline earths metal ions and those of all nitrogen cyclams which strongly complex

with heavy-metal cations. These mixed complexation property make the aza crown ethers

interesting to researchers in many areas. The property of aza crown ethers can be modified by

altering its donating side arms as well as macrocycle itself. The metal ion complexing ability of

aza crown can be significantly improved by functionalizing them with ligating sidearms. Aza

crown ethers which are chemically modified are very interesting molecules because; they can be

designed according to the need. The aza crown ethers have important applications in different

field.


Figure 1. 18-Crown-6 ether with K+ ion

Polymeric macrocyclic compound

The convergence of various polymers, which are substituted by attaching different

functional group and macrocyclic compounds like crown ethers, cryptands and calixarenes are

known as polymeric macrocyclic compound. The use of crown ethers and analogous compound

on a large scale for industrial purposes is inhibited by their expense. A potentially useful way

around this problem lies in attaching the crown ethers to a polymeric matrix and thus facilitating

it retrieval. Other benefits of polymeric supported aza crown ethers are that the properties of

these macromolecules do not change even after long term use. The insoluble cross-linked

polymer supported aza crown ethers are of considerable interest to the synthetic chemist. Such

polymers that can be used as starting materials for the preparation of solid supported catalyst and

ligands, have been recently reported.11

Supramolecular polymer

The field of supramolecular chemistry has been developed over the past 25

years by synthetic chemists. A SP (supramolecular polymer) is based on the reversible

association of many monomers through weak labile interactions self-assembling in to an infinite

network.12 Unlike finite supramolecular systems, whose synthons form thermodynamically

stable finite architectures, monomer synthons having multiple recognition sites complex ad


infinitum until all available synthons have been consumed. When the supramolecular recognition

is due to the coordination between a functionalized ditopic ligand and a ditopic metal complex

the metalla-supramolecular polymers are called coordination polymers (CP). Strong, highly

directional, reversible interactions are required to form liner supramolecular polymers.

Otherwise, the polymer gel forms microphase-separated structure. The repeat units of the

molecular assembly must only interact with their intended partners. In hydrogen-bonded

supramolecular polymer system where there is no anisotropy, single or double hydrogen bonds

are not sufficiently stable to allow self-assembly to occur. High purity monomers must be used in

preparing supramolecular polymers because monofunctional impurities or unreacted repeat units

cap the growing polymer chain. A first step towards the synthesis of supramolecular polymers

was taken as far back as 1984. While studying the liquid crystalline behavior of polymeric

gycols, Lenz and coworkers prepared dicarboxylic acid derivatives of glycol polymers13 hoping

to obtain liquid crystals by varying the position of mesogenic group and flexible spacers along

the polymer chain. Adjacent acid groups were found to have hydrogen bond, doubling the length

of the mesogenic groups and giving stiffer, more anisotropic, liquid crystals.

The first truly main chain supramolecular polymer was self-assembled by

Lehn et al.14 using uracil (A) and 2, 6 diaminopyridine (B). The polymer consisted of a

molecular assembly composed of an equimolar mixture of repeat units bearing uracil (A) and 2,6

diaminopyridine (B) groups, which are associated via triple hydrogen bonding. This polymer

adopted a well-defined structure and displayed physical properties similar to conventional

polymers. Ka of polymer is approximately 103 M-1 in apolar solvents. These polymers had liquid

crystalline behavior and a helical pitch owing to the chirality of the tartarate backbone. This

study and others relied on a small number of repeated H-bonding interactions to give interesting


solution properties such as liquid crystallinity or light harvesting15. No complications have been

reported regarding its long-term stability. For these reasons, it has become a benchmark in the

field of supramolecular polymer chemistry. Since then increasing interest has developed in

extended self-assembled structure such as one dimensional chains, two-dimensional sheets and

three-dimensional networks. Much research into supramolecular polymers has been concerned

with preparing liquid crystalline molecular assemblies that display similar characteristics to that

prepared by Lehn’s polymers.

Meijer and coworkers16 have designed derivatives of the ureidopyrimidinone

motif for use as an associating end group to overcome the limitation imposed by weak

interactions mentioned previously. Ureidopyrimidinones offer strong, directional hydrogen

bonding, and have been shown to form dimers following a predictable recognition and assembly

process. Polymer derived from ureidopyrimidinones may also have potential for preparing soft

materials whose flow properties can be accurately controlled. Viscoelasticity in polymers arises

from entanglements between chains. While conventional high molecular weight polymers are

elastic, they have long relaxation times. Ka of dimerization is approximately 108 M-1 in apolar

solvents, 17, 18. SPs with polymeric properties in both concentrated and dilute solutions, with

improved polymeric properties, allowed for processing in to the quadruple H-bonded array

stabilized by favorable secondary H-bonding interactions. Meijer’s polymer and its analogues,

such as telechelic polysiloxanes, -ethers, -esters, -ethylene/butylenes and –carbonates,19 were

shown to have viscoelastic properties similar to those of traditional polymers.


Figure 2. Ureidopyrimidione supramolecular polymer.

Shortly after Meijer’s seminal work, Zimmerman and co-workers20, 21 have

designed comparable systems with similar association strengths. These novel materials have

found a range of everyday applications such as adhesives, inks, printing, cosmetics, personal

care, coating and advanced applications such as tissue engineering22 and plastic electronics.

Cates and co-workers23 have proposed a model for the rheological behavior

of ‘living’ polymers having reversible bonds which has been shown to be applicable to model

ureidopyrimidinone polymers. These supramolecular polymers offer the possibility that the

structure can adapt to changing environmental stresses after systhesis24.

Bailar began working25, 26 on inorganic CPs (coordination polymers) almost

40 years ago. Since this time much of the work on CPs has been on crystal engineering and

solid-state structures and applications. These early CPs were not very soluble and often rigid

frameworks, which easily degrade in solution making them difficult to characterize and process

in solution27, 28.

Common ligand donor atoms are N, O or S, and pyridine is the simplest

ligand for CP formation in the solid-state, but its Ka is usually weak for a reasonable DP (Degree


of Polymerization) in soloution29. Other common coordination motifs chelate the metal ion

increasing the Ka of the metal-ligand interaction through cooperative and entropic effects29.

Many different CP systems using different ligands and/or metal centers have been reported and

have been thoroughly reviewed30. Therefore, only several important reports in this area will be

highlighted. Many early CPs are thermodynamically and kinetically stable, making them inert

and essentially irreversible polymeric species, thus deviating from the relevant definition of SP.

Rehahn and coworkers31, 32 have reported a soluble CP assembled from

phenanthroline ligand and chelated with Cu+ or Ag+ salts in to robust CP architectures in non-

competitive solvents giving kinetically labile species with chain-like polymeric solution

properties.

Hunter and co-workers33, 34 have used the well-studied coordination of the dye

molecule porphyrin (Figure 3). Synthesized labile self-associated pyridyl functionalized co-

porphyrin monomeric synthons with Ka approximately 106-108 M-1, Hunter’s CP showed the

characteristic traits of a SP in solution. The length of these robust and massive polymers could be

modulated by concentration changes and chain stopper impurities34.

Figure 3. Pyridyl-porphyrin co-coordination polymer


Schubert and coworkers35 have done extensive work with tpy (Terpyridine)

ligands generating water soluble telechelic tpy poly (ethylene oxide) (tpyPEO) CPs. tpyPEO CPs

showed potential applications in water purification, food processing, mining and cosmetics. By

employing and substituting a variety of different metal centers (Ka of Zn2+=Cd2+<Fe2+<Ru2+)

Schubert could tune the photo physical and physical properties of the system.

Wurthner36 and coworkers have reported that the perylene bisimide retained 95%

fluorescence after self assembling showing that the Zn2+ metal center acts only as a cohesive unit

within the CP due to its closed-shell electronic configuration. However, upon the addition of an

iron (II) salt to the monomer synthons the resultant solution retained the physical polymeric

properties but the fluorescence was rapidly and irreversibly quenched, due to metal to ligand

charge transfer of the structural and functional Fe2+ to the perylene chromophore. Meijer’s

systems are difficult to obtain using standard covalent protocols. As in the case of Wurthner's

polymers, the Fe2+ centers again acted as both structural and functional components giving a red-

shifted absorbance from the OPV.

Recently, Rowan and coworkers37 have carried out elegant studies with tpy

(Terpyridine)-like CPs taking these systems to a new functional level. He fabricated stimuli

responsive 3-D gel networks38 and also processed 1-D CPs in to self-supporting films and fibers

with interesting properties much like Meijer,s UPy (Ureidopyrimidone) H-bonded SP systems.

Rowan’s end functionalized low molecular weight poly(p-phenylene ethynylene)s (PPE)s or

poly(tetrahydrofuran) with the tpy ligand analog 2,6-bis(1’-methylbenzimidazolyl)-Cd2+ metal

ion salt into high molecular weight supramolecular PPVs. These conjugated systems have strong

absorbance and photoluminescence characteristics well suited for a variety of applications. Much

like other conjugated systems, difficulties are experienced in synthesizing and purifying defect


free materials and solution processing of these rigid structures. Therefore, high molecular weight

SP PPEs self-assembled from low molecular weight PPE appears to be a good strategy. After

self-assembly of CPs from either Zn2+ or Fe2+ salts, the CPs was completely quenched in both the

solution and solid-state. The processability of these materials makes them very attractive due to

their luminescent properties.

Finally merging these two realms of self-assembled polymers are the compounds

reported by Schubert et al39 that combine both H-bonding and metal-ligand interactions to give

hybrid SPs. The SP formed from low molecular weight monomeric synthons had poor solubility

due to high charge density of the metal centers in the hybrid polymer. By incorporating a high

molecular weight caprolactone poly (ester) spacer between the orthogonal recognition units, the

charge density is spread out in this revised system, therefore solubility and thus processability

was dramatically improved.

Polymeric crown ethers

Talanova et al.40 reported a crown ether polymer consisting of dibenzo-18-crown-

6 bound to crosslinked polystyrene through a piperazine moiety (Figure 4). The piperazine

moiety is studied by first bonding to chlorometylated crosslinked polystyrene and the

dibenzocrown ether after immoblilizing onto it by reaction with formaldehyde. Both Pd(II) and

Pt(II) are soft ions and do not typically form complex with hard (oxygen-containing) crown

ethers. However, the anionic chlorides [PdCl4]2- and [PtCl4]2- were found to form ion pairs with

the crown ether-alkali cation complex when the resin was contacted with K2PdCl4 and K2PtCl4 in

solutions of varying KCl concentrations. The resin had a greater sorption capacity for K2PdCl4

than K2PtCl4. It was estimated that the dibenzo-18-crown-6 resin was able to bind one [PtCl4]2-

and up to two [PdCl4]2- per crown ether unit, the latter perhaps occurring due to the formation of


chloride-bridged anionic complexes [PdnCl2n+2]2- and Pt(II) in competitive studies from a

solution of 0.50 M KCl, though Pt(II) was complexed to a greater extent.

Figure 4. Polystyrene immobilized dibenzo 18-crown-6 ether

Pethrick et al.41 prepared crown ether resins with the crown moiety in the

backbone by reaction of dianhydrides to give polymers of varying flexibility. Dibenzo-18-crown-

6 was mono nitrated at each of the benzene rings with concentrated nitric acid in acetic acid. The

cis (4, 4’)-dinitro isomer was isolated and converted to the diamine by reduction with hydrazine

monohydrate. The polyamic acids were formed by subsequent reaction with ex-polyamic acids at

225 °C which led to dehydration (Figure 5) had a greater binding ability with alkali and alkaline

earth metals in aqueous solutions than its polyimide analogue. The carboxylic acid residues on

the former contributed to its increased uptake and the loss of conformational mobility in the

polyimide further reduced the latter’s uptake. The selectivities from 1M aqueous solutions of the

chloride salts followed the trend K>Rb>Na>Li>Cs and Ca>Sr>Ba>Mg. A 15-crown-5/polyamic

acid displayed selectivities of Na>K>Li, Rb>Cs and Ca>Mg>Sr>Ba. When metal binding

studies were done using the same resins in methanol solution, the metal ion capacities increased.

This was attributed to the ions decreased affinity for methanol relative to water. The uptake

trends in methanol were generally consistent with those in aqueous solution.


Figure 5. Linear dibenzo-18-crown-6/ polyamic acid

Shinkai and coworkers42 have reported immobilized dibenzo 24-crown-8 and

azobenzene on polymer support, p-chlorometylated polystyrene beads (Figure 6). The

immobilized azo benzene -24-crown-8-azobenzene bridge on cross-linked poly-styrene beads

and attempted to photocontrol the complexation ability of the immobilized polymer dibenzo-24-

crown-8 unit toward cesium ion. The forgoing results consistently suggest that, the photoinduced

trans-to-cis isomerization of the azobenzene moiety is capable of changing the conformation of

the crown ether in to a more stretched one which has poor ion-binding ability relative to the

normal crown ether. Therefore, the binding ability of the crown ether immobilized as the

Azobenzene Bridge in the polymer support can be controlled by an on-off light switch.

Figure 6. Immobilized azobenzene-crown-azobenzene in polystyrene support


Soluble as well as immobilized crown ethers and other cation binding ligands

have been extensively employed in studies of mediated ion transports and anion activated

catalysis43-45. Smid et al.46 have reported benzo 15-crown-5 and bezo-18-crown-6 ligands

anchored to cross-linked polystyrene resins (Figure 7). Binding property of sodium and

potassium picrate to immobilized polystyrene and polymethacrylate supported benzo 15-crown-5

and benzo 18-crown-6 ethers are studied.

Figure 7. Polystyrene bound benzo 18-crown-6 ethers

Koshima and coworkers47 have reported the adsorption behaviour of iron(III),

gallium(III), thallium (III), and antimony (V) metal ions on the commercial available poly

(dibenzo 18-crown-6) resin. Satisfactory separation of the above mentioned metal ions has been

achieved from polymer loaded columns. Adsorption of iron (III), gallium (III) and antimony (V)

were efficiently adsorbed from the high concentrate hydrochloric acid and the adsorption

behavior of the metals was similar to the extraction behavior with a chloroform solution of

dibenzo 18-crown-6 48, 49 Iron(II) was not adsorbed and the gold (III) and thallium (III) were

efficiently adsorbed from the hydrochloric acid solutions of low acidity. The capacities of poly

(DB18C6) for metals were found to be 0.9-1.7 mmol g-1.


Warshawsky et al.50 have studied the binding abilities of polymer supported

pseudocrown ethers prepared by reacting poly(ethylene or propylene glycols) with crosslinked

chloromethylated poly-styrene under Williamson ether synthesis conditions. The polymeric

pseudocrown ethers were studied for their ability to complex Au(III), Fe(III) and Zn(II) as

chlorides, bromides and iodides from acidic solutions. The number of oxygen atoms contained in

the polymeric pseudocrown ether with fourteen oxygen atoms was found to perform best with

AuCl-4, FeCl-

4 and ZnCl2- due to its large cavity size. The mechanism entails oxonium salt

formation between the acid and the pseudocrown ethers followed by anion exchange with the

transition metal halide. Complexation with the size of the anion matches the calculated cavity

size of the pseudocrown ether. The polymers with nine and ten oxygen atoms also performed

well with the anions. No complexation was found with macrocycles having less than four oxygen

atoms.

Blanton et al51 have synthesized novel polymer bound benzo 15-crown-5 ether and

polymer bound tin reagents in which both reactive sites are on the same polymer matrix,

(Figure 8). The 2% divinyl benzene cross-linked polystyrene containing crown ether and

organotin dichloride appendages, as cocatalystic system, are applied for reducing alkyl halides to

alkenes. In addition, when multiple functional groups are placed on the same polymer support,

the overall activity of catalytic system is comparably more than polymeric system, which contain

one of the reactive sites.


(a) (b)

Figure 8. (a) Divinylbenzene crown-linked polystyrene bounded benzo crown ether (b) Polymer bound tin reagent.

Many of the researchers have prepared high molecular weight poly (amide crown

ethers) based on the interfacial polycondensation reaction of diamino dibenzo-18-crown-6 and

different aromatic and aliphatic diacid chlorides52,53. Crowns ether which are in the range of 30

and higher membered rings have the ability to bind two metal ions per cavity54.

Delaviz et al.55 have synthesized high molecular weight novel and well defined

poly (amide crown ethers) (Figure 9) which contain the semi rigid large 32 membered

macrocycle in the main chain. Novel semiaromatic polyamides with a 32 membered crown ether

moiety in the main chain are insoluble in any solvents, the insolubility is attributed to in situ

threading of linear segments of one polymer chain through the macrocyclic cavity of another

during polymerization, which is most likely the result of permanent physical entanglements

arising from threading of the macrocycles by the polyamide segments as they form, leading to an

insoluble network.


Figure 9. Poly (ester crown ether)

Dai et al.56 have synthesized crown ether substituted phenylenevinylene oligomers

(CE-OPV) (Figure 10) using a Witting or Horner-Wadsworth-Emmons Reaction. The resulting

crown polymer is shown strong fluorescence emission at 515 nm. The photo- and

electroluminescent properties of the CE-OPV is a class of highly photoluminescent material

which was investigated using fluorescence, UV-Vis, and optical multichannel spectrometers. The

spectroscopic results indicate unusual optoelectronic properties for electroluminescent

application. They were also demonstrated the LED structure of ITO/CE-OPV/Al.

Figure 10 Crown ether phenylenevinylene oligomers

Bowman and coworkers57 have synthesized polymeric pseudocrown ether

networks (Figure 11) which were formed in situ by the photopolymerization of poly (ethylene

glycol) diacrylate PEGDA/transition metal complexes. The synthesized polymeric pseudocrown

ethers are inexpensive because the starting materials are common and also nontoxic because

these systems are polymeric and therefore nonbioavailable. Classical crown ethers are effective

in ion separation and may be bioavailable and can cause adverse effect in living system. The


metal-monomer complexation have led to a near to circular conformation of the monomer in

which the two reactive end groups are brought into close proximity and the probability of

intermolecular cyclization is increased. They have also studied the complexation of Co (II),

Ni (II), Zi (II), Cd (II), Cr (III), Cu (II), Nd (III), and Li (III) with polymeric pseudocrown.

Figure 11 Polymeric pseudocrown ether

Kimura and coworkers58 have synthesized polymer carrying bis-crowned

malachite green derivatives, which was obtained by copolymerization of vinyl monomer bearing

a bis-crowned malachite green moiety with several widely used vinyl monomers. The polymers

carrying bis-crowned malachite green moiety are very different from the corresponding

monomeric analogue in the metal ion complexation and photochromism. The synthesized

polymeric crowned malachite green derivatives have been found to be selective for complexation

ability towards Na+, K+, Cs+ and Li+. The ion selectivity of polymeric malachite green

derivatives is shown quite different from their corresponding monomeric analogues. They

observed that the malachite green moiety can be affected dramatically by their polymer rheology

under dark and UV-irradiated conditions.

The polymers have well defined structure for the purpose of self-assembly. In

recent years, a variety of polymers carrying crown ethers have been reported. The crown ethers


are a part of a main chain, or pendent groups anchored to a polymer backbone or terminal groups

of a macromolecular chain, their synthetic methods were reviewed by Yagci59.

Feng and coworkers60,61 have synthesized two armed crown ether contained

polymers by ATRP (Atom Transfer Radical Polymerization) of styrene, acrylate butyl acrylate,

and methyl methacrylate using bis[4’-(2-bromobutyryl)]dibenzo-18-crown-6 BBDC/CuBr/bpy

initiation system. Well defined two-armed crown polymers have been self-assembled in presence

of potassium cations and different morphologies have been observed when the polymer is

obtained. The AFM images indicate that polymer film with holes was formed for poly MMA.

Poly styrene with different molecular weight resulted in different self-assembly studies. It is

proposed that the morphologies are formed through accumulation of crown ether moieties. The

morphologies are the result of energy competition between crown ether moieties and polymer

chains.

The developing of selective alkali metal ion sensors is a subject of much current

interest. A clinically useful detection technology should have two key criteria. It should comprise

a recognition moiety with sufficient ionic selectivity and an integral transducer to convert the

concentration of the target electrolyte in to a measurable change.

Mayes and coworker61 have synthesized metal ion-sensitive holographic sensor

for Na+ and K+ by copolymerization of hydroxyether crown ether with hydroxylethyl

methacrylate and the cross-linker ethylene dimethacrylate to form polymeric hydrogel film. A

variety of different polymer hydrogel composition resulted which are covalently bounded with

12-crown-4, 15-crown-5 and 18-crown-6 by pendent functionality. These have been used to

characterize the volume changes when films bind a variety of different monovalent and divalent

metal ions. The film composition has been optimized in reflection holograms. The behavior of


hologram containing 12-crown-4, 15-crown-5 and 18-crown-6 to bind Li+, Na+ and K+ ion have

been investigated over wide concentration ranges.

Since that time a wide range of polymeric crown ethers has been synthesized and

reviewed. In the family of crown ether, medium size of oxo crown ethers have received limited

attention, only Okahara et al.62 have reported several of these compounds, like 2, 11-dioxo-18-

crown-6, 2-oxo-12-crown-4, and 2-oxo-21-crown-7.

Peters and coworker63 have synthesized polymers by powerful and simple

cyclization technique. A new synthetic route was established to the oxo-crown ethers and the

polymerization of oxo crown ethers with ring sizes of 12, 18 and 21. Polymerization has been

carried out in presence of SnOct2 as catalyst and alcohol as initiator. The used polymerization

technique facilitates the introduction of end groups to the polymer. When an alcohol is mixed

with monomer and catalyst, this alcohol acts as initiator and is thus introduced into the polymer

as an end group.

Isotope effect has been found in such complexation reaction with crown ethers

and a number of studies on the isotope effects has been reported. Jepson et al.64 have investigated

calcium isotope effects by breakthrough technique of column chromatography through polymer-

bound ligands of iminodiacetate, cryptand and 18-crown-6. Kim et al.65 have synthesized a resin

having monobenzo-15-crown-5 as a functional group and performed lithium isotope separation

by column chromatographic method.

Zinc is considered as a useful material for cooling water treatment in light water

nuclear power plants. The trace amount of soluble zinc injected in the coolant water

reduces 60Co in water piping system. The zinc injected reactor water has been investigated by

EPRI (Electric Power Research Institute) and GE (General Electric)66.


Ban and coworkers67 have reported isotope separation of zinc by using polymer-

supported crown ether resin packed glass columns. Break through technique of chromatography

has been studied by feeding a zinc chloride solution in to the column. Polymer supported crown

ether resin was produced by sorbing 4, 4’ (5’) bis (t-butylcyclohexano)-18-crown-6 in a

polymeric porous adsorbent68. The concentration of zinc isotope has been determined by flame

analysis with AAS. The largest isotope separation coefficient, 1.0 × 10-3, has been obtained.

After the discovery of polymer light-emitting diodes (LEDs) in 1990, a wide

range of conjugated polymers have been developed as electroluminescent materials69, most of

these materials, polymer containing phenylene vinylene (PV) are well studied.70 The

photoluminescence (PL) and electroluminescence (EL) properties of synthesized poly (p-

phenylenevinylene) derivative containing 18-crown-6 (C-PPV) have been reported by

Yagci et al.59 PL and EL properties of C-PPV have been characterized. C-PPV shows high PL

quantum yield and is independent of temperature. The polymer has been introduced for light

emitting diodes (LEDs). By using C-PPV emissive material the single layer light emitting device

showed a low turn-on voltage (3V).

The polymer light-emitting electrochemical cell (LEC) is a different approach to

fabricate the light emitting devices from conjugated semiconducting polymers71. Active layer of

a LEC contains a blend of conjugated luminescent polymer and solid electrolyte. First LECs

were prepared by Pei et al.72 A complex of PEO (poly ethylene oxide) and lithium triflate

(LiCF3SO3) were added to luminescent polymer, such as PPV [poly(phenylenevinylene)] or its

soluble derivative poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene]. However,

these systems showed a strong tendency to phase separation, and the different chemical

structures of luminescent polymers and PEO (Poly Ethylene Oxide). In recent years, much effort


has been devoted to develop novel luminescent polymers and new solid electrolytes to overcome

this problem.

Li and coworkers73 have synthesized the three novel copolymers containing

alternating 1,4-bis(phenylethenyl) benzene, 1,4-bis(phenylethenyl)-2,5-dimethoxybenzene or

1,5-bis(phenylethenyl)naphthalene PPV-like [poly(p-phenylenevinylene)] chromophore and

crown ether spacers within the polymer backbone by using the Witting polycondensation

reaction (Figure 12). Synthesized crown polymer exhibit good thermal stability and show blue

light emission in solution. This light emission is responsible for the changing in the PL spectra of

the thin films. The PL and EL color tuning is realized in these copolymers by changing the

structure of the chromophore. CE spacers in these copolymers contribute to the increasing ionic

conductivity and the improvement in the morphology of the active layers.

Figure 12. Poly (dibenzo -24-crown-6-co-1,5- divinylnaphthalene)

Sakai and coworkers74 synthesized a novel optically inactive poly(phenyl

isocyanate) derivative bearing a benzo18-crown-6 as a host group by the anionic polymerization

of 4’-isocyanatobenzo 18-crown-6 (Figure 13). The host-guest complexation study of polymer

and chiral guest like perchloric acid salts of amino acids are investigated. In the circular

dichroism spectra of PPI-CE in presence of various chiral guests i.e., the perchloric acid salt of

different amino acids, large cotton effect were observed between the range from 240 nm to


340 nm, due to the adsorption of the polymer backbone. Therefore, it was observed that the

induced CDs were based on the structure of the main chain.

Figure 13. Poly(phenyl isocyanate) derivative bearing a benzo18-crown-6

The synthesis of well-defined nanostructures of conjugated polymer like poly(p-

phenylene vinylene) (PPV), such as nanotubes and nanowires, is of considerable interest in the

design of novel functional materials and nanoelectronic devices, such as nanosensors75 and

nanotransistors76. Well-defined nanosized materials have been used for the understanding of the

effects of interchain interactions on the conjugated polymers77.

Luo et al.78 have reported poly(p-phenylene vinylene) substituted 18-crown-6

polymer (CPPV) to form nanoribbons through the assembly of a conjugated polymers induced

by K+ in a chloroform solution and proposed the formation mechanism for the nanoribbons. The

growth mechanism of the nanorods to the nanoribbons was observed. The length of the

nanoribbons on their photo physical properties has been studied. The formation of more dredges

between the free K+ ions and the protruding cilia of the nanorods which leads to the connection

of the nanorods at their ends, producing nanorods can be analyzed and disguised through the

AFM height measurement.


Gibson and coworkers79 have synthesized novel poly (amide crown ethers)

(Figure 14), by direct polycondensation reactions of bis(5-carboxy-1,3-phenylene)

-32-crown-10 (BCP32C10) with 4,4’-oxydianiline (ODA) and bis[4-(m-aminophenoxy)

phenylphosphine oxide (m-BAPPO). These semiaromatic polyamides contains a 32 membered

crown ether moiety in main chain. These polymers with semirigid 32-membered crown ethers in

the main chain are insoluble in any solvent. The insolubility is attributed to permanent physical

entanglements arising from threading of the macrocycles by the polyamide segments as they

form, leading to an insoluble network. In 2004 same group have reported bis(5-carboxy-1,3-

phenylene)-(3x+2)-crown-x ethers [BCP(3x+2)] with 26-membered (BCP26C8), 20-membered

(BCP20C6) and 14 membered (BCP14C4) and was utilized to investigate further the proposed

topological branching via in situ treading during polymerization. In addition they have

synthesized two poly (amide crown ethers) using condensation of BCP32C8 with ODA and m-

BAPPO which is soluble in dipolar and aprotic solvent. The solubility and molecular weight

distribution of aramide based on 26-, 20- and 14- membered crown ether have been investigated.

The self treading is observed in studies, which lead to polypseudorotaxanes, polyrotaxanes, and

polycatenane because the mechanical linked structures dependent upon the crown ether cavity.

Figure 14. Polyamide crown ether

The separations of many isotopes were carried out on experiment based

complex formation of metal ions with crown ether by using the liquid-liquid extraction. By


liquid-liquid extraction it is difficult to separate the isotopes, because the distribution coefficient

is too small. Impregnating the resin through crown ethers is unsuitable for long term use and

cannot be used in presence of organic solvents, since the crown ether is not bonded chemically.

Otake and coworkers80 have developed the benzo 15-crown-5 ether resin based

on the phenol type resin (Figure 15). The diameter and shape of this resin was controlled by

synthesizing the resin in the high porous silica beads support. The lithium isotope fractionation

by chromatography using the synthesized crown ether resin was confirmed. However, the

adsorption of lithium ion on this resin decreases with time period because only few crown ether

bonded with the main chain of resin, and many crown ether get only tangled in the phenol resin.

Figure 15. Structure of phenol type 15-crown-5 resin

The fixation of carbon dioxide (CO2) in to the organic compounds is very

important from an economical and an environmental point of view81. The CO2 is a prominent

green house gas. Yamamoto et al82 have reported the relationship between the ring size of crown


ether and Li+ salt catalyst, which increased the fixation of CO2 in to oxirane group on the

copolymer containing the crown ether. Copolymer containing crown ether have been

synthesized by using methacrylate derivatives of 12-crown-4 to 16-crown-5 series and the

derivatives copolymerized with glycidyl methacrylate under the radical conditions. Obtained

copolymers were applied for fixation of carbon dioxide. In the fixation, the crown ether moiety

was thought to contribute to the salvation and activation of lithium salts. Among crown ethers

with several ring sizes, the combination of LiBr and 14-crown-4 showed the most effective

catalytic activity.

Tang and coworker83 have synthesized a polymeric crown via the reaction

between amino group in chitosan and –CHO in 4’-formyl benzo-crown ether. The adsorption

behavior for lead and cadmium by FAAS has been studied. Furthermore, the best analysis

conditions also have been investigated, this new method was applied to the determination

environmental samples. The detection limits of lead and cadmium are found to be 0.5 µg L-1 and

0.04 µg L-1 and the standard deviations of lead and cadmium are 3.1 % and 2.8% respectively.

Polymeric aza crown ether

Sahim and coworkers84 have reported the synthesis and the phase-transfer

catalytic activities of polystyrene resins containing aza crown ether moieties and hydroxyl

groups adjacent to the macro rings (Figure 16). Immobilized lariat aza crown ethers has been

prepared by the reaction of crosslinked polystyrene resins containing epoxy groups with mono

aza 15-crown-5 and mono aza 18-crown-6. Microporous crosslinked polystyrene resins

containing epoxy group to synthesize the polymer supported aza crown ether have been prepared

by suspension polymerization of styrene, divinylbenzene and vinylbenzyl glycidyl ether. These


immobilized lariat aza crown ether catalysts have shown higher activity for the halogen

exchange reactions and exhibited good activity than corresponding catalyst without the hydroxyl

group; these results suggested that the K+ ion is bound by the cooperative coordination of the

crown ether ring donors and the hydroxyl group in the side arm.

Figure 16. Polystyrene supported mono aza 18-crown-6 ether

The cation based photoinduced electron transfer (PET) has been explored

extensively in the recent past85. These type of molecular devices attached to polymer bead and

capable of sensing cations can be applied for quantitative determination and qualitative

detection of metal ions. The development of polymer bead attached sensors as reusable cation

sensors is of contemporary interest86.

Maitra and coworkers87 have synthesized bile acid based photoinduced electron

transfer (PET) sensor for alkali metal ions and immobilized on Merrifield resin

and on tentagel (Figure 17). They attempted a simple, general, and effective strategy to

immobilize and utilize such sensors on polymer beads in aqueous environment. Due to the

attachment of Merrifield resin, the PET based cation sensor work as reusable cation sensor. The

florescence property has been studied of the polymer bead attached sensor. The fluorescence of

the sensors was enhanced through the binding of cations. The sensor bead worked efficiently in

nonpolar solvents, but the detection of K+ in polar solvent remained a challenge. The sensor bead


after the treatment of KClO4 in presence of methanol did not show the fluorescence enhancement

because of Merrifield resin does not swell in to the methanol. Thus the K+ is not able to penetrate

into resin.

Figure 17 Fluorescent cation sensor bead

The polymer-supported polyazamacrocycle compounds have some important

potential applications88. Some immobilized polyamine fragments have interacted with a variety

of species such as neutral molecule, transition metal ions, and organic and inorganic anions,

these interaction are depending on the pH of the medium. Different polymers have been prepared

and the potential applications of those in separation processes, environmental science and

technologies,89 biomimeic chemistry90 and catalysis91 have been studied.

Altava and coworker92 have reported different crosslinking agents and porogens

were used to prepare a series of monolithic polymers prepared with vinylic tetrazacrown

monomers. Crosslinking agents were DVB, ethylene glycol dimethacrylate (EGDMA) and

ethylene glycol dimethacrylate (EDADMA), the porogens were dimethyl sulfoxide (DMSO),

dodecanol and toluene. Grafting of the same azacrowns onto chloromethylated polystyrene


resulted in multipoint bonding (Figure 18) which would significantly decrease ionic accessibility

in to the polymer. Metal ion studies with the monoliths consisted of equimolar amounts of the

perchlorate salts of Na(I), Zn(II), Cu(II) and Ni(II) at pH 6 and demonstrated that all were

selective for Cu(II). The monolith prepared with EDADMA and DMSO was also able to

complex Ni(II). A benzocrown monolith complexed significant amounts of Na(I) as prepared

with DVB and DMSO, when examined for their ion binding affinities in a solution of equimolar

amounts of Na(I), K(I), Cs(I), Ni(II), Fe(II) and Hg(II). The benzo-containing azacrown moiety

was also studied for their ability to extract anions.

Figure 18. Benzo 18-aza crown-4 bound to polystyrene through four sites

Miyagawa and coworkers93 have reported a water soluble neutral poly

(phenylacetylene) bearing the bulky aza 18-crown-6 ether pendants (Figure 19). The polymer has

been induced a one-handed helix by using L- and D-amino acids and chiral amino alcohol

through host-guest interaction in water. Poly (phenylacetylene) can trap an achiral benzoxazole

cyanine dye in the cavity inside the polymer in acidic water, which exhibit an induced circular

dichroism in the cyanine dye chromophore region, and the helical poly (phenylacetylene)

induced by chiral molecules can serve as a novel template for supramolecular chirality induction


in the achiral cyanine dye. The results indicated a new and promising approach for producing

supramolecular helical structures from achiral molecules based on the self assembly of organic

dyes assisted by a one-handed helicity induction in a dynamically racemic helical poly

(phenylacetylene).

Figure 19. Poly (phenyacetylene) bearing bulky aza 18-crown-6 ether

In the formation and elimination of barium sulfate scale, considerable efforts

have been invested for a long time. For example the sea water is used as injection fluid in oil-

producing locations often lead to closing of wells as result of BaSO4-scale formation94. BoZHOU

et al.95 have synthesized water soluble EDTA-diazacrown ether polymers by reaction of EDTA

dianhydride with diazacrown ether (Figure 20). The effect of crown ether ring in polymer chains

on the solubilization of BaSO4 to water has been investigated by comparison with ring-free

analogue. Solubilization capabilities of the polymers was determined by known equipment and

method at pH=10 by the addition of tetrabutyl ammonium hydroxide. The results show that the

EDTA-diazacrown ether polymer is an efficient solubilizer of BaSO4 and the highest

solubilization efficiency of the BaSO4 to water is up to 72.5%.


Figure 20. EDTA diazacrown ether polymer

Kimura and coworkers96 have synthesized crowned spirobenzopyran moiety at

the side chain(Figure 21) and studied their metal ion complexing property, photochromism in the

presence of metal ions, and their applicability to photoresponsive ion-conducting materials. A

comparison is also made with the corresponding monomeric crowned spirobenzopyran and the

copolymers incorporating crown ether and spirobenzopyran moieties independently. On the other

hand, polymers incorporating spirobenzopyran side chains are useful tools for photochemical

control of polymer rheology. Therefore, the combinations of crown ether and spirobenzopyran

moieties in polymers have some advantages over their corresponding mono-meric analogue in

materials applications.

Figure 21. Spirobenzopyran vinyl polymers


Aza thiacrown ethers immobilized onto poly(glycidyl methacrylate) and its thiirane

analogue (glycidyl methacrylate) and its thirane analogue (pGMA-O and pGMA-S, respectively)

have been reported by Van de water et al.97(Figure 22). The aza thiacrown moiety contained one

nitrogen and four sulfur atoms. The crown monomer was formed by reaction of the BOC-

protected HN(CH2SCH2CH2SH)2,deprotection, and immobilization onto pGMA-O or pGMA-S

through nucleophilic attack by the amine moiety on the three-membered ring. Non-competitive

and competitive metal ion studies were performed using metal salts in buffer solutions at pH

values of 0.9-2.3 and 2.5-6.0. in competitive binding studies using the chloride forms of Cu(II),

Cd(II), Zn(II), Co(II) and Ni(II), pGMA showed an affinity for Cu(II) which increased with pH

and a concomitant decrease in Cd(II) affinity. A competitive study with nitrate form of Ag(I),

Cu(II), Cd(II) and Zn(II) showed that the resin selectively complexed significant amounts of

Ag(I) from all pH solution. pGMA-S was also studied under non-competitive and competitive

conditions (though in the absence of Ag(I) since the –SH group in the ring-opened thirane has a

affinity for silver ions regardless of whether there is a crown moiety adjacent to it), under- non-

competitive conditions. The resin had a high affinity for Cu(II) relative to Cd(II), ZN(II), Co(II),

Ni(II) and Ca(II), which increased with pH. The amount of Cd(II) and Zn(II) complexed also

increased with pH though to a much lesser degree. Under competitive conditions with the same

metal ions as above (except Ca(II), pGMA-S selectively complexed Cu(II) and the capacity

increased with increasing pH.


X=O, S

Figure 22. Poly (thia) glycidyl-supported 16-azathiacrown-5.

Nakajima et al.98 have prepared a tetraazacrown unsaturated analogue of 14-

crown-4 (2,7,12,14-tetramethyl-1,4,8, 11- tetraaza-cyclotetradeca-1,5,7,12-tetraene) which was

immobilized on to a crossliked poly(iodomethyl-styrene) by stirring the azacrown ether with the

beads in the presence of pyridine (Figure. 23). It was examined for metal ion binding properties

using 10-3 M aqueous solutions of Cu(II) and Ni(II) acetate. The resin was selective for Cu(II) at

pH 5.6, no significant amount of Ni(II) was complexed. The affinity of the resin for Cu(II)

increased with increasing pH over the range 3.5-5.6 and decreased with increasing solution ionic

strength. The loading capacity though, was consistently low, approximately 0.23 mmol/g, in

solution of varying ethanol content, the Cu(II) capacity of the poly(azacrown) increased as the

ethanol content increased, reaching a value of 0.73 mmol/g from a solution of absolute ethanol,

this may be ascribed to easier desolvation of the metal ion and thus an increased apparent affinity

of the ligand for the ion.


Figure 23. Polystyrene- immobilized tetra methyl-1, 4, 8, 11-cyclo-tetradeca-1,5,7, 12-tetraene.

Sherrington99 have reported azacrown ethers with both nitrogen and oxygen donor

atoms were supported on poly(glycidyl methacrylate) and its thio analogue (pGMA-O and

pGMA-S, respectively) through nucleophilic reaction at the epoxide or thioepoxide ring by the

crown nitrogen. Azacrown ethers with five donor atoms were studied under non-competitive and

competitive conditions in buffered solutions. Polymer-supported azacrown ether with one

nitrogen and four oxygen atoms was bonded to both pGMA-O and pGMA-S. Under non-

competitive conditions pGMA-O and pGMA-O had a greater affinity for Ag (I) with increasing

pH and it complexed Cd(II) at pH values from 1.2 to 5.5. The pGMA-S resin was moderately

selective for Cu(II) from a solution of Cu(II), Cd(II) and Zn(II) and Ca(II) from a solution of

Cu(II), Cd(II), Zn(II) and Ca(II) over the pH range 1.2-5.5. The level of complexation increased

with increasing pH. The polymer had little affinity for Cu(II), Zn(II), Co(II) and Ni (II). The

pGMA-S resin had a greater affinity for Cu(II) over Cd (II) with increasing pH and no significant

affinity for Zn(II), Co(II), or Ni (II). The pGMA-S resin had a greater affinity for Cu (II) over Cd

(II) with increasing pH and no significant affinity for Zn(II), Co(II), or Ni(II). The pGMA-O

resin was contacted with a solution of the chloride salts of Cu(II), Cd (II), Zn(II), Co(II) and

Ni(II) and a solution of the nitrate salts of Ag(I), Pb(II), Cu(II), Cd(II) and Zn(II). With the

chlorides, the resin was selective for Cd(II), the amount of Cd(II) or Ag(I) complexed increased

with increasing pH.


Aim and scope

Polymeric crown ethers, aza crown ethers and other Finite Molecular Architectures have

been reviewed from literature. The literature work on polymeric crown ether and aza crown ether

reveals that only very less number of polymeric crown ethers and aza crown ethers have been

synthesized to achieve column chromatographic separation and solid phase extraction of metal

ions. Crown ethers and other macrocycles are well known ligands for various metal cations. Aza

crown ethers have especially been focused on as useful ligands because of their versatility and

applicability. The mixed presence of N and O donors makes the macrocycle more interesting in

many research areas. The attachment of appropriate polymer matrix to aza crown ether enhances

the separation process and complexing ability of aza crown ether. Most of the polymers have

been reported with crown ethers whereas only few polymers are reported with diazacrown ethers

and mono aza crown ethers. Further, there are no reports on the synthesis of polymeric crown

ethers based on dibenzo 18-crown-6. And hence in the present investigation for the first time an

attempt is made to immobilize monoaza dibenzo 18-crown-6 on different polymeric materials

which could provide the efficiency of separation of polymeric adsorbents coupled with the

complexing ability of aza group and the specificity of crown ether. The immobilized aza crown

ethers on different polymeric media can be useful in separation of various metal ions.


Present Investigation

In the present investigation, four new polymeric macrocyclic compounds are

synthesized by immobilizing the mono aza dibenzo 18-crown-6 with four types of polymers viz.

functionlized XAD-4 resin, Merrifield resin, polyacryloyl chloride resin and polymethacryloyl

chloride resin moiety to prepare the polymeric macrocycles. Synthesized polymeric macrocycles

are targeted for solid phase extraction of various metal cations.

XAD-4[mono aza dibenzo 18-crown-6] (XAD-4[MADB18C6]) was

synthesized by linking of mono aza dibenzo 18-crown-6 ether and chloroformoyled styrene-

divinyl benzene copolymer (XAD-4 resin). The synthesized XAD-4[MADB18C6] was

demonstrated for the solid phase extraction of trivalent rare earth metals (REEs) La (II), Nd (II)

and Sm (II) and preconcentration and separation of binary and ternary mixtures of La (II), Nd

(II) and Sm (II). The mono aza dibenzo 18-crown-6 ether attached to Merrifield resin was used

in the solid phase extraction of Fe (II) and Cu (II). The polyacrylo-mono aza dibenzo 18-crown-6

(PA-MADB18C6) and polymethacrylo-mono aza dibenzo 18-crown-6 (PM-MADB18C6) were

synthesized by linking of functionalized poly(methacrylic acid) and poly(acrylic acid) to mono

aza dibenzo 18-crown-6 ether. The synthesized poly acrylo-mono aza dibenzo 18-crown-6 (PA-

MADB18C6) and poly methacrylo-mono aza dibenzo 18-crown-6 (PM-MADB18C6) aza crown

polymers were applied for solid phase extraction of alkaline earth metals and preconcentration

and separation alkaline earth metals (beryllium, magnesium, calcium, strontium and barium).

The binary and ternary mixtures of beryllium, magnesium, calcium, strontium and barium have

been separated by PA-MADB18C6 and PM-MADB18C6. The plausible applications of the

polymeric macrocycles synthesized for the real sample analysis have been explored.


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