Accepted Manuscript

The influence of native and methylated β-cyclodextrin on the electroreduction

of nitrophenyl glycosides

Tomasz Gubica, Maciej Mazur, Łukasz Szeleszczuk, Andrzej Temeriusz,

Marianna Kańska

PII: S1572-6657(13)00167-7

DOI: http://dx.doi.org/10.1016/j.jelechem.2013.04.005

Reference: JEAC 1236

To appear in: Journal of Electroanalytical Chemistry

Received Date: 11 August 2012

Revised Date: 31 March 2013

Accepted Date: 4 April 2013

Please cite this article as: T. Gubica, M. Mazur, Ł. Szeleszczuk, A. Temeriusz, M. Kańska, The influence of native

and methylated β-cyclodextrin on the electroreduction of nitrophenyl glycosides, Journal of Electroanalytical

Chemistry (2013), doi: http://dx.doi.org/10.1016/j.jelechem.2013.04.005

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1

The influence of native and methylated β-cyclodextrin on the electroreduction of

nitrophenyl glycosides

Tomasz Gubicaa,*, Maciej Mazurb, Łukasz Szeleszczuka, Andrzej Temeriuszb,

Marianna Kańskab,c

aDepartment of Physical Chemistry, Faculty of Pharmacy, Medical University of Warsaw,

Banacha 1, 02-097 Warsaw, Poland

bFaculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

cSecond Faculty of Medicine with the English Division and the Physiotherapy Division,

Medical University of Warsaw, Żwirki i Wigury 61, 02-091 Warsaw, Poland

*Corresponding author

Tel./fax: + 48 22 5720950

E-mail address: tomasz.gubica@wum.edu.pl (T. Gubica)

Abstract

The effect of native and methylated β-cyclodextrin on electrochemical processes of a series of

nitrophenyl glycosides (o-, m-, and p-nitrophenyl -D-galactopyranosides, as well as p-

nitrophenyl -D-galacto-, -D-gluco-, -D-manno-, -L-fuco-, and -L-fucopyranosides) in

alkaline aqueous solutions on the mercury electrode was evaluated. The totally different

influence of native and methylated β-cyclodextrin on electroreduction of nitrophenyl

glycosides was discovered. According to electrochemical measurements (cyclic voltammetry

and chronocoulometry) as well as theoretical method (molecular modelling) inclusion

complexes are formed between both cyclodextrins and nitrophenyl glycosides. Although the

2

inclusion processes took place for both cyclodextrins, the source of their different influence

on the electrode processes is connected with their different abilities of nitro radical anion

(de)stabilisation.

Keywords: Nitrophenyl glycoside; Cyclodextrin; Cyclic voltammetry; Chronocoulometry;

Molecular modelling; Inclusion complex.

1. Introduction

Nitrobenzene (Ph–NO2) and other more complicated aromatic nitro compounds have been

extensively studied electrochemically on the mercury electrode and the data obtained are

reviewed herein [1-25]. Ph–NO2 in neutral aqueous solutions in the absence of inhibitors

undergoes the four-electron reduction to phenylhydroxylamine (Ph–NHOH) according to the

following equation:

Ph–NO2 + 4e- + 4H+ → Ph–NHOH + H2O (1)

The above process splits into two processes in alkaline solutions or in the presence of

inhibitors [19-21], or by adding aprotic co-solvents [22-25]. The first split process is

connected with a one-electron reduction of Ph–NO2 to nitro radical anion ( −•− 2NOPh ). The

second process is connected with a three-electron reduction of −•− 2NOPh to Ph–NHOH. This

reaction proceeds according to the following equation:

−•− 2NOPh + 3e- + 3H2O → Ph–NHOH + 4OH- (2)

3

The current paper is a continuation of our previous studies focused on electrochemical

investigations into nitrophenyl derivatives of different saccharides [26-28]. We studied the

electrode processes of nitrophenyl glycosides (R–NO2) in neutral aqueous solutions in the

absence of inhibitors [27]. Even though the electrode processes of R–NO2 and Ph–NO2 were

similar to each other under the same experimental conditions, several parameters (peak

currents and potentials, and formal potentials) varied significantly between R–NO2 and Ph–

NO2. Those differences were attributed to different molecular structures of R–NO2 [27].

In this paper, we report the electrochemical study of a series of R–NO2 (Table 1) in

alkaline aqueous solution in the absence or in the presence of native and methylated β-

cyclodextrins (β-CD and Me-β-CD, respectively) (Table 2). Cyclodextrins (CDs) are known

to form inclusion complexes with R–NO2 [29-31] and other aromatic nitro compounds [32-

34]. CDs also inhibit electrode reactions [35-36]. We hypothesised that by addition of CDs to

the electrochemical bath we would be able to control the mechanism of the redox reaction by

tuning the direct microenvironment of the molecule. Squella et al. [37] showed that the

electrochemically generated nitro radical anion is destabilised even by weakly acidic protons.

β-CD possesses free hydroxyl groups which are proton donors while Me-β-CD has

functionalised hydroxyl groups which are not proton donors. Therefore, we expected a

different mechanism of R–NO2 reduction in the presence of those two CDs.

According to our knowledge this is the first report in the literature on controlling the nitro

compounds redox reaction in supramolecular systems through (de)stabilisation of the nitro

radical anion by optimising the intermolecular protonation of the radical. Our findings are

extremely important from the point of view of possible applications, e.g. in targeted drug

delivery and catalysis.

4

2. Experimental

2.1. Nitrophenyl glycosides (R–NO2)

2.1.1. o-Nitrophenyl β-D-galactopyranoside (1), m-nitrophenyl β-D-galactopyranoside (2)

and p-nitrophenyl β-D-galactopyranoside (3).

The synthesis and full analytical data for these compounds were reported earlier [27].

2.1.2. p-Nitrophenyl α-D-galactopyranoside (4)

This compound was purchased from Koch-Light Laboratories Ltd.

2.1.3. p-Nitrophenyl α-D-glucopyranoside (5), p-nitrophenyl α-D-mannopyranoside (6), p-

nitrophenyl α-L-fucopyranoside (7), and p-nitrophenyl β-L-fucopyranoside (8)

These compounds were purchased from Sigma-Aldrich Chemie GmbH.

2.2. Cyclodextrins (CDs)

2.2.1. β-cyclodextrin (β-CD)

This compound was purchased from Sigma-Aldrich Chemie GmbH. -CD was dried in

vacuum before use in the presence of P2O5 at the temperature of 60ºC.

2.2.2. Methylated β-cyclodextrin (Me-β-CD)

The synthesis and full analytical data for heptakis(2,3,6-tri-O-methyl)cyclomaltoheptaose

(Me-β-CD) were reported earlier [38].

2.3. Electrochemical measurements

The electrochemical behaviour of nitrophenyl glycosides were investigated using cyclic

voltammetry and chronocoulometry. The measurements were carried out with a CH Instrument

(Austin, TX, USA), model 660 electrochemical analyser connected to a computer using a

three-electrode cell with a water jacket at 25.0±0.1oC. A static mercury drop electrode (A

0.01055 cm2) was used as the working electrode, while platinum foil (2 cm2) served as the

5

counter electrode. All the potentials were measured against a saturated sodium calomel electrode

(SSCE). Doubly distilled and deionised water (Milli-Q, Millipore, Austria) was used for

preparation of the solutions. The substances used for preparation of Britton-Robinson buffer:

Na2HPO4·12H2O, CH3COONa·3H2O, Na2B4O7·10H2O, NaOH (from POCh, Gliwice, Poland),

70% HClO4 and NaClO4·H2O (supporting electrolyte) (from Fluka) were commercial chemicals

of analytical grade.

The cyclic voltammetric curves (CVs) were recorded over a potential range from –0.1 to –

1.8 V vs the SSCE electrode using different scan rates in the range from 0.02 to 1.0 V·s-1. The

measurements were carried out in the presence of Britton-Robinson buffer at pH 11 containing

0.5 M NaClO4 with the reactant concentrations equal to 1 10-4 or 2.5 10-4 M.

For the following processes: R–NO2 → R–NHOH, −•−→− 22 NORNOR ,

NHOHRNOR 2 −→− −• , R–NHOH → R–NO, and R–NO → R–NHOH the potentials of the

associated peaks I, Ia, Ib, II, and III (Epc(I), Epc(Ia), Epc(Ib), Epa(II), Epc(III), respectively) were

evaluated. The error of measurements of potentials was equal to ±0.003 V.

Single-step chronocoulometric experiments were used to determine the surface

concentration of the adsorbed reactants. The chronocoulometric Q-t curves were described

using the following equation:

Adsdl2/1

2/1pox

2/1ox QQ

tcnFAD2Q ++=

π (3) [39]

where oxD and oxc describe diffusion coefficients and concentrations of reactants,

respectively, whereas Qdl and QAds stand for the charge of the double layer and the charge of

the adsorbed reactant, respectively.

6

2.4. Molecular modelling

The Gaussian09 software package [40] was used for the theoretical calculations. The

geometry optimisations were performed using the AM1 semiempirical method [41]. The

effect of solvation was applied using the polarizable continuum model (PCM) [42]. The

harmonic frequencies were calculated in order to confirm that the structures are not in the

transitional state. Only positive frequencies confirm that the obtained structures were in

minima.

3. Results and discussion

3.1. Electrochemical behaviour of nitrophenyl glycosides (R–NO2) in the absence of

cyclodextrins (CDs)

The electrochemical behaviour of R–NO2 on the mercury electrode was studied under basic

conditions. The following representative nitrophenyl glycosides were chosen in this study: o-,

m-, and p-nitrophenyl -D-galactopyranosides (1-3, respectively), p-nitrophenyl -D-

galactopyranoside (4), p-nitrophenyl -D-glucopyranoside (5), p-nitrophenyl -D-

mannopyranoside (6), p-nitrophenyl -L-fucopyranoside (7), and p-nitrophenyl -L-

fucopyranoside (8). For structural formulas of R–NO2 under investigation see Table 1.

The consecutive voltammograms of o-nitrophenyl -D-galactopyranoside (1) at the

concentration of 2.5×10-4 M are shown in Figure 1. In the first scan a reduction peak at ca

−0.6 V (peak I) is seen. This peak is attributed to a four-electron reduction of the nitro

compound to its hydroxylamine derivative (R−NHOH). With the reverse polarisation a new

oxidation peak is observed at ca −0.25 V (peak II) which is due to oxidation of R−NHOH to

the corresponding nitrozo derivative (R−NO). In the second scan the R−NO is again reduced

at ca −0.28 V (peak III) while peak I is slightly diminishing in consecutive scans. The above

electrochemical pattern is operative for all the other glycosides under investigation (2-8).

7

We analysed further the peak currents as a function of square root of scan rate, ν1/2, or scan

rate, v, to find out whether the redox processes are affected by adsorption of the glycosides on

the mercury surface. The dependence of the peak I currents for 1-8 as a function of ν1/2 is

shown in Figure 2. For all the compounds the peak I currents increase monotonically with the

ν1/2 but the relationship is not linear as predicted by the Randles-Sevcik equation for the

diffusive electrode processes. Moreover, the peak I currents are not linear with the v (Figure

S1, Supplementary content), which excludes the purely adsorptive phenomena. This suggests

that the diffusion is affected by adsorption of the glycosides on the electrode surface. A

similar behaviour was also observed for peaks II and III where the currents are linear neither

with ν1/2 nor ν (Figures S2-S5, Supplementary content).

In order to confirm the conclusions based on voltammetry data we performed a

chronocoulometric analysis of the R−NO2 reduction for selected reactants (6-8). The electrode

was first conditioned at −0.4 V, being followed by a potential pulse at −1.0 V for 0.03 s. The

recorded charge values were then plotted versus t1/2 and the linear parts of the curves were

fitted and extrapolated to t = 0 to determine the charge associated with the adsorbed species.

The representative chronocoulometric curves are shown in Figure S6 (Supplementary

content). Assuming the four-electron reaction these data were recalculated to obtain the

surface concentration of the adsorbed R−NO2. The values of surface concentration of 6-8

determined from the coulometric analysis are 1.7×10-10, 1.7×10-10, and 1.6×10-10 mol/cm2,

respectively.

As can be seen, for all glycosides under investigation the surface concentrations are

roughly 1.7×10-10 mol/cm2, which corresponds to ca 100 Å2. Assuming that the geometrical

area occupied by a typical R−NO2 is equal to ca 70 Å2, we estimate that the surface coverage

is roughly 70 %.

8

From the above data the following scenario is emerging. The R−NO2 is diffused to the

electrode surface where a fraction of the molecules becomes adsorbed. The electron transfer

occurs from both the adsorbed and non-adsorbed species and results in transformation of the

nitro compounds to a R−NHOH/R−NO redox couple. The voltammetric data suggest that

some of the R−NHOH and R−NO products stayed adsorbed while the other were diffused off

the mercury surface.

3.2. Electrochemical behaviour of nitrophenyl glycosides (R–NO2) in the presence of

cyclodextrins (CDs)

3.2.1. Methylated β-cyclodextrin (Me-β-CD)

We studied further the effect of CDs on the electrode reactions of 1-8. The consecutive

voltammograms of o-nitrophenyl -D-galactopyranoside (1) (c = 2.5×10-4 M) in the absence

and in the presence of Me-β-CD (c = 2.5×10-5 M) are shown in Figure 3.

In the presence of Me-β-CD the electrode processes of R−NO2 are strongly affected as

compared with the reaction in the absence of this additive. The CVs for other R−NO2 under

investigation were similar to the above example. For all glycosides the separation of peak I

into two processes was observed. The first separated process (peaks Ia and V) is connected

with a one-electron reduction of the nitro group to the radical anion ( −•−→− 22 NORNOR ).

This reduction is described by the equation which is analogous to Eqn (1). The second

process, separated from peak I, (peak Ib) is connected with a three-electron reduction of the

nitro radical anion ( −•− 2NOR ) to R−NHOH. This process is described by the equation which

is analogous to Eqn (2). Another peak IV is also observed at potential near –1.4 V in the CVs.

It is likely connected with desorption of Me-β-CD from the mercury electrode. An analogous

peak IV was observed in the absence of reactants but in the presence of Me-β-CD (Figure S7,

9

Supplementary content). The potential of this voltammetric peak is also coincident with the

desorption peak on differential capacitance curves recorded for Me-β-CD [36].

We evaluated further the minimal concentration of Me-β-CD when separation of peak I

was observed. Therefore, the electrode reactions of 1 were observed with simultaneous

titration by Me-β-CD. The data obtained from this titration are presented in Figure 4.

The separation of peak I depends on both the sweep rate and the Me-β-CD concentration.

For the lowest sweep rate used (0.02 V·s-1) the R−NO2/R−NHOH electrode process is

separated into two processes (peaks Ia and Ib were observed) at a Me-β-CD concentration as

low as 10-5 M. For higher sweep rates the separation of peak I occurred at higher CD

concentrations.

We analysed further the dependence of the peaks Ia and Ib currents on the ν1/2 and ν

(Figures S8-S15, Supplementary content). For peaks Ia and Ib both types of plots are non-

linear and they sometimes change slope with the sweep rate. This confirms that the

mechanism of the redox reaction is rather complicated. In a few cases, the dependences of the

peak Ia currents vs v (for higher sweep rates) seem to be vs vn where n > 1 (Figures S10 and

S11, Supplementary content). On the other hand, with the increase of the sweep rate the peak

Ib current increases typically up to 0.5 V·s-1 and then rapidly decreases (Figures S14 and S15,

Supplementary content). It appears that for slow sweep rates there is a full separation of four-

electron reduction of the nitro group into generation of −•− 2NOR and its subsequent

reduction to R−NHOH in a three-electron process. However, for higher sweep rates (from 0.5

V·s-1) the non-separated four-electron reduction of R–NO2 to R–NHOH occurs together with

the separation of this process.

The analysis of the currents of peaks II and III associated with the R−NHOH/R−NO redox

reaction also leads to the conclusion that the diffusion of this couple is affected by adsorption

10

on the electrode surface – the peak currents are linear neither with ν1/2 nor ν (Figures S16-S23,

Supplementary content).

Next we studied the adsorption of selected R−NO2 onto the electrode surface in the

presence of Me-β-CD using chronocoulometry. The electrode was first conditioned at −0.4 V

which was followed by a potential pulse at −1.8 V for 0.07 s. The determined surface

concentrations are 0.4×10-10, 0.5×10-10, and 0.5×10-10 mol/cm2 for 6-8, respectively.

One can see that the surface concentrations are roughly three times lower than the

respective values determined in the absence of Me-β-CD. This may be due to competitive

adsorption of CD onto the electrode surface. It is well established that Me-β-CD strongly

adsorbs onto the mercury surface in the potential range from −0.4 to −1.2 V [36]. In fact, we

observe desorption peaks of Me-β-CD at −1.4 V on cyclic voltammograms as discussed

above. We assume therefore that it is the adsorbed CD that impedes the adsorption of R−NO2

onto the electrode surface. In one of our recent papers on adsorption of nitrophenyl

derivatives of β-cyclodextrin onto the mercury electrode we showed that the surface

concentrations are typically ca 0.5×10-10 mol/cm2 [26]. This value is similar to surface

concentrations recovered in the present paper for R−NO2 in the presence of Me-β-CD. If this

is not pure coincidence, one should speculate that R−NO2 may form 1:1 inclusion complexes

with Me-β-CD onto the mercury electrode and that is why similar surface concentration

values were obtained for both the nitro compound and cyclodextrin.

According to literature data [29-31] the R−NO2 form inclusion complexes with CDs. In

order to visualise the 3D geometry of inclusion complexes between selected R−NO2 (1-3)

with Me-β-CD we performed quantum chemical calculations using Gaussian09 software

package (Figure 5). The sugar moieties of 1-3 are accommodated inside the molecular cavity

of Me-β-CD, whereas nitrophenyl groups do not penetrate it fully and they are close to the

shallower rim of the host molecule (where seven methoxy groups are present).

11

It seems that the Me-β-CD/R−NO2 complex adsorbs from the solution onto the mercury

surface where the electrochemical reduction of the nitro group occurs. Since R−NO2 is

included into Me-β-CD cavity, the closest surrounding for the nitro group are methoxy groups

from host molecules. The methoxy groups cannot act as donors of protons for −•− 2NOR .

Therefore, −•− 2NOR can be stabilized, especially so as the reactions take place at pH 11.

These conditions (the adsorption phenomena and the lack of proton donors near the nitro

group) are responsible for separation of the four-electron reduction into two processes.

3.2.2. β-cyclodextrin (β-CD)

As we observed considerable influence of Me-β-CD on the electrochemical reduction of

R−NO2 we were interested to find out whether β-CD, a compound that can also form

inclusion complexes with reactants, exhibits similar effects. It is worth noting that 1-3

penetrate the molecular cavity of β-CD in a totally different way in comparison with Me-β-

CD (Figure 6). This time, the nitrophenyl groups accommodate the molecular cavity of the

host molecule, while sugar moieties are situated near the shallower rim of β-CD. Nitro groups

are situated close to the wider rim of the host molecule and therefore they can interact with

fourteen hydroxyl groups of β-CD situated at this rim.

We performed cyclic voltammetry of R−NO2 in the presence of β-CD under the same

experimental conditions as for Me-β-CD and observed practically no effect on the

electrochemical behaviour in comparison with CV in the absence of cyclodextrins. For that

reason we increased the concentration of β-CD by three orders of magnitude in comparison

with Me-β-CD and studied electroreduction of 1-8. A representative cyclic voltammogram is

shown in Figure 7. R−NO2 in the presence of β-CD undergo the same electrode reactions

connected with peaks I-III as in the absence of CDs. However, pronounced differences were

observed in currents and potentials of peaks between those two cases. In the presence of β-

12

CD, the reduction of R−NO2 to R−NHOH (peak I) was observed at more negative potentials

(Table 3). On the other hand, no separation of peak I was observed as for Me-β-CD.

The respective dependences of the peak I current, Ipc(I), on the square root of sweep rate

are depicted in Figure 8. As in previous cases, the plots are non-linear suggesting a

complicated mechanism of the redox reaction.

We investigated further the adsorption of R−NO2 onto the mercury surface in the presence

of β-CD by chronocoulometry. The potential was stepped from −0.4 V to −1.8 V during 0.07

s. The determined surface concentrations of selected glycosides, that is, 6-8, are 0.6×10-10,

0.6×10-10, and 0.4×10-10 mol/cm2, respectively.

The surface concentrations are considerably lower than those recorded in the absence of β-

CD. Moreover, these values are only slightly higher than those for Me-β-CD (even though the

comparisons are difficult due to different concentrations of the CDs in bulk solution).

The decreased adsorption of R−NO2 in the presence of β-CD is interpreted as the effect of

co-adsorption of β-cyclodextrin on the electrode surface. Similarly as for Me-β-CD we

postulate that the inclusion complex between R−NO2 and β-CD is adsorbed onto the mercury

surface where it follows the electrochemical reaction. However, in this case the one-electron

process is not separated from the reduction of R−NO2 to R−NHOH. The possible reason for

this might be the protonation of −•− 2NOR by protons available from hydroxyl groups of β-

CD. Consequently, in this case the −•− 2NOR is not stabilized and the reversible couple

R−NO2/ −•− 2NOR is not observed.

4. Conclusions

We have shown that two structurally similar cyclodextrins, Me-β-CD and β-CD, affect the

electrochemical reduction of a series of nitrophenyl glycosides in a different way. In the first

case even a small addition of Me-β-CD (1/10 of the concentration of the nitro compound)

13

affects on the mechanism of electroreduction. This results in the separation of the four-

electron reduction into the generation of radical anion ( −•− 2NOR ) and its transformation to

the hydroxylamine derivative (R−NHOH). On the other hand, the addition of -CD at the

same concentration has no observable effect on electroreduction of R−NO2. However,

increasing the β-CD concentration three orders of magnitude in comparison with Me-β-CD

allows one to observe some slight changes on voltammetric curves like a decrease of peak

currents or changes of peak potentials. Regardless of these effects, no separation of reduction

peak I was observed. The inclusion complexes between R−NO2 and CDs are adsorbed onto

the mercury surface where they follow electrochemical reduction. The electroreduction of

those complexes is different between β-CD and Me-β-CD due to the possibility of

protonation of −•− 2NOR by free hydroxyl groups present in β-CD. In the case of Me-β-CD,

hydroxyl groups are substituted by methoxy groups which cannot serve as proton donors. The

protonation of −•− 2NOR destabilizes it, therefore the reduction of R−NO2 leads to R−NHOH

in one step.

Acknowledgements

The authors are grateful to Prof. Z. Galus and Dr. J. Stroka (University of Warsaw) for their

scientific support. The authors also thank Dr. B. Krasnodębska-Ostręga and Prof. J.

Golimowski (University of Warsaw) for providing the mercury electrode. Financial support

from the Ministry of Science and Higher Education (1 TO9A 001 30) and the University of

Warsaw (120000 501/64-BST-163266) is gratefully acknowledged.

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16

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17

Highlights: >Cyclodextrins (CDs) affect electroreduction of nitrophenyl glycosides (R�NO2). >Reduction of R�NO2 proceeds as one process in the presence of native β-CD. >Reduction of R�NO2 is separated in the presence of methylated β-CD. >Methylated β-CD stabilizes nitro radicals, whereas native β-CD destabilizes them.

Figure 1. Cyclic voltammograms (CVs) of o-nitrophenyl -D-galactopyranoside (1) at the

concentration of 2.510-4

M in 0.5 M NaClO4 and 0.04 M Britton-Robinson buffer at pH 11.

The 1st sweep (black dotted curve), the 2

nd sweep (red solid curve), and the 3

rd sweep (green

dashed curve). Scan rate 0.1 V∙s-1

.

Figure(s)

Figure 2. The dependence of the cathodic peak I current, –Ipc(I), on the square root of the

scan rate, v1/2

, for 1-8.

Figure(s)

Figure 3. Cyclic voltammograms (CVs) of p-nitrophenyl α-L-fucopyranoside (7) in the

absence (black dotted curve) and in the presence (red solid curve) of Me--CD (at the

concentration of 2.510-5

M) The reactant concentration of 2.510-4

M in 0.5 M NaClO4 and

0.04 M Britton-Robinson buffer at pH 11. Scan rate 0.02 V∙s-1

.

Figure(s)

Figure 4. The dependence of peaks I and Ia potentials (Epc(I) and Epc(Ia), respectively) versus

the Me--CD concentration for o-nitrophenyl -D-galactopyranoside (1). The solutions

contained 110-4

M reactant in 0.5 M NaClO4 and 0.04 M Britton-Robinson buffer at pH 11.

Scan rates: 0.02 (); 0.2 (■); and 0.7 (▲) V·s-1

.

Figure(s)

(a)

(b)

(c)

Figure 5. Optimized (Gaussian09) molecular structures of inclusion complexes between host

molecule Me-β-CD and guest molecules 1-3: (a)-(c), respectively.

Figure(s)

(a)

(b)

(c)

Figure 6. Optimized (Gaussian09) molecular structures of inclusion complexes between host

molecule β-CD and guest molecules 1-3: (a)-(c), respectively.

Figure(s)

Figure 7. Cyclic voltammograms (CVs) of p-nitrophenyl -D-galactopyranoside (3) in the

absence (black dotted curve) and in the presence (red solid curve) of -CD (at the 100-times

excess). The reactant concentration of 2.510-4

M in 0.5 M NaClO4 and 0.04 M Britton-

Robinson buffer at pH 11. Scan rate 0.1 V∙s-1

.

Figure(s)

Figure 8. The dependence of the cathodic peak I current, –Ipc(I), on the square root of the

scan rate, v1/2

, for 1-8 in the presence of β-CD.

Figure(s)

18

Table 1. Structural formulas of nitrophenyl glycosides (R−NO2) under investigation.

Abbreviation Chemical name Structural formula

1 o-Nitrophenyl -D-

galactopyranoside O

O

OHOH

NO2CH2OHHO

2 m-Nitrophenyl -D-

galactopyranoside O

O

OHOH

NO2

CH2OHHO

3 p-Nitrophenyl -D-

galactopyranoside O

O

OHOH

NO2

CH2OHHO

4 p-Nitrophenyl α-D-

galactopyranoside O

OHOH

O

NO2

CH2OHHO

5 p-Nitrophenyl α-D-

glucopyranoside

O

OHOH

O

NO2

CH2OH

HO

19

6 p-Nitrophenyl α-D-

mannopyranoside O

OH

OH

O

NO2

CH2OH

HO

7 p-Nitrophenyl α-L-

fucopyranoside O

O

OH

OH

CH3

NO2

HO

8 p-Nitrophenyl -L-

fucopyranoside

NO2

O

OOH

OH

CH3

HO

20

Table 2. Structural formulas of native and methylated β-cyclodextrin.

Abbreviation Chemical name Structural formula

-CD β-cyclodextrin

O

O

OH

7

HOHO

Me- -CD Methylated β-cyclodextrin

O

O

MeO

OMe

7

MeO

21

Table 3. The values of the cathodic peak I potentials, Epc(I), of R–NO2 in the absence and in

the presence (2.5×10-2 M) of -CD. The solutions contained: 1-8 at a concentration of

2.5×10-4 M, supporting electrolyte 0.5 M NaClO4 and 0.04 M Britton-Robinson buffer at pH

11. Scan rate 0.1 V·s-1.

R–NO2 In the absence of -CD In the presence of -CD

1 –0.591 –0.638

2 –0.638 –0.682

3 –0.712 –0.767

4 –0.709 –0.747

5 –0.705 –0.771

6 –0.702 –0.748

7 –0.704 –0.731

8 –0.714 –0.750

43.

OO

OHOH

NO2CH2OHHO

O

O

MeO

OMe

7

MeO

Graphical Abstract:

+

Graphical Abstract (for review)