Atoms, ions, molecules y macromolecules - La Factoría...
Transcript of Atoms, ions, molecules y macromolecules - La Factoría...
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Atoms, ions, molecules y macromolecules
Master of Crystallography and Crystallization – 2012 T02 – Mathematical, Physical and Chemical basis of
Crystallography
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Elements, Atoms and Ions The Chemical elements, their names and symbols,
are collected on the PERIODIC TABLE
Dmitri Mendeleev (1834 - 1907)
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Atoms of Cooper on a surface of silicium.
• An Atom is the smallest particle of an element mantaining
all chemical properties of the element itself.
Distance = 1.8 nanometers (1.8 x 10-9 m)
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COMPOSITION Of the ATOM
The atom is mainly empty space
• Protons (p+) – electric charge + – mass = 1.672623 x 10-24 g – relative mass = 1.007 units of atomic mass (amu) may be rounded to 1
• Electrons (e-) – electric charge - – relative mass = 0.0005 amu
may be rounded to 0
• Neutrons (no) – without electric charge – mass = 1.009 amu may be rounded to 1 – Has a spin momentum of 1/2
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Atomic Number, Z
13
Al
26.981
Atomic Number
Atomic Symbol
AVERAGE Atomic Mass
Mass Number, A
• # protons + # neutrons
• An atom of boron may have A = 5 p + 5 n = 10 amu
• The Atomic Mass is the AVERAGE of the atomic masses.
A
Z
10
5B
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Isotopes
• An element (same Z) different mass number (A)
• Boron-10 (10B) has 5 p y 5 n
• Boron-11 (11B) has 5 p y 6 n 10B
11B
0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu
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IONS
• IONS are atoms or groups of atoms charged positive
o negatively.
– Removing an electron of one atom produces a CATION
with positive charge.
– adding an electron to an atom produces an ANION with
negative charge.
Mg --> Mg2+ + 2 e- F + e- --> F-
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Neutrons: fision vs espallation
180-200 MeV/useful neutron Ideally suited as a Continous Source
35-40 MeV/useful neutron (Hg 1.3 GeV protons) Ideally suited for pulsed operation.
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X Rays vs Neutrons
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A First Approximation to interprete the bond
• At the beginnig of the XX century, the scientist Lewis, observing the little reactivity of the noble gases (structure of 8 electrons in the last level), suggested that the atomos to bonding “tend” to adquire a distribution of valence electrons equal to that of the closest noble gas.
8-ELECTRON RULE
Clasification of the elements
acording to the 8-electron rule.
• Metals: low electronegativity, low energy of ionization. Tendency to give electrons.
• Non metals: High electronegativity. Tendency to get electrons
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Depending on the type of atoms joining:
• Metal – Non metal: one gives and other accepts
electrons (cations and anions)
• Non metal – Non metal: both accept electrons,
share electrons
• Metal – Metal: both give electrons
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Ionic Bond • The Ionic compound is formed by reacting one metal
with a non metal.
• The atomos of the metal lose electrons (producing a cation) whic are accepted by the non metal (producing an anion).
• The ions of different charge attract electricaly eachother, ordering itselves to form and ionic network. The Ionic compounds are not made of molecules.
• The bond results of the natural force of atraction stablished among ions with oposite charges.
• That forces of attraction keep them united, forming a compound of ionic type.
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Ionic Bond between Cl and Na: formation of the ions Cl- and Na+
Ionic Networks
NaCl CsCl
The compounds joint by ionic bonds when are periodicaly ordered usually form crystals.
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Properties of Ionic compounds
• High melting and boiling points.
• Soluble in water
• Non electrical conductivity in solid state, but good conductors in solution or melted (Chemical Reaction: electrolisis)
• These are rigid substances, the atempts of bend, fold or deformation lead to break the crystal (fragility)
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Metallic Bond
• The metalic substances are made of atomos of the same metallic element (low electronegativity).
• The atoms of the metallic element may lose some electrons, producing one cation or “metallic rest”.
• Producing at the same time a Cloud or sea of electrons: set of free electrons, delocalized, which do not belong to any particular atoms.
• The cations repel each other, but are attacted by the sea of electrons existing among them. This is the way to form a metallic network: metalic sustances neither are formed by discrete molecules.
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The model of the cloud of electrons represents the metal as a set of cations occupaying the fixed positions of the network, being the free electrons moving easily, without being confinated/attached to any especific cation.
Fe
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Properties of the metallic substances
• Elevated melting and boiling points
• Insoluble in water
• Excellent electrical conductors even in solid state (only get warm: physical change). Conductivity is higher at low temperature.
• May be easily deformed without break
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Covalent Bond Covalent compounds originates by Sharing Electrons
among non metallic atoms.
Electrons highly localized.
This type of bonds is stablished among a group of special atoms, called the non metallic elements.
Their atoms have simmilar forces of electrical attraction, for that reason share valence electrons
when participate in one bond of such type.
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Covalent Bond and Molecules
• Atoms bonded by covalent bonds form individual particles maned molecules.
• So, a molecule is any stable set of two or more atoms bonded covalently, but many may have hundreds or thousands of bonded atoms.
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• Covalent bonding allows the formation of molecules of elements (H2, O2, N2), when cambinating atomos of the same element, and molecules of compounds (H2O, CH4, when combining atoms of diferent elements.
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• Covalent normal bond:
– Simple or Multiple: doble o triple
• Bond Polarity :
– Apolar or Polar
• Covalent dative or coordinated bond
• May be present in different agregation states. Intermolecular forces?
• Soluble: apolar molecules – apolar solvents
• Insoluble: apolar molecules – polar solvents
• In general Non electrical conductors.
• Have very variable melting and boiling temperatures.
Different types of covalent bonds:
The properties of covalents compounds are:
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Covalent Molecules • When the bond is apolar: apolar molecules (H2, O2, F2…)
• When the bond is polar:
– Polar Molecules (HCl, H2O...) (Permament dipoles)
– Apolar Molecules (CO2) (space symetry)
O ─ C ─ O δ+ δ- δ-
In the CO2 exist polar covalent bonds and, nevertheless, the covalent molecule is not polar. This is due of the linear estructure of the molecule cancellanting the effects of both dipoles of the C-O bonds.
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There Exist molecules, or are really giant structures?
• Covalent Networks
• Covalent Molecules (Small - Macromolecules)
Diamond: tetraedra of carbon atoms
Grafite: layers of carbon atoms
The union between atoms sharing
electrons is very strong, very dificult
to break. The shared electrons are highly
localized.
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Topological Characterization of Bonds
maxima, minima and saddle points critical points
x, y,z Electron density, : derivable function
r r
x, r
y, r
z
r c 0
Gradient zero: neccesary condition for maximum,
minimum or saddle point
H r
2
x2
2
x y
2
xz
2
y x
2
y2
2
yz
2
z x
2
z y
2
z 2
Range (): number of non zero eigenvalues
Signature (): N. positive - N. negative eigenvalues
mathematical nature
(, )
denomination
(Bader´s theory)
maximum (3, -3) tridimensional atractor
second order saddle point (3, -1) bond critical point
first order saddle point (3, 1) ring critical point
minimum (3, 3) cage critical point
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Alows to derive the nature of the bond from the electron density
Type of interaction and bond multiplicity
From the density at the bond critical point, b
Bond Anisotropy
Bond Elipticity,
1
2
2
1
2
1
1
012
1
n
2
22.012
1
n
character of the three membered rings
High elipticity
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Electron Density:
(r) = ... ({r,s})*({r,s})dVdS
Spatial coordinates Wavefunction of many electrons
Hohenberg&Kohn (1964):
1) The electron density defines univocally the electronic fundamental state of
atoms, molecules and crystals.
2) The electron density provides a minimum of the energy functional.
E[] = G[] + ENe [] + Eee[] + Exc []
kinetic energy electron- electron energy
electron-nuclear energy change and correlation energy
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Five characteristics of the atomic and molecular
interactions :
(rb), 2 (rb), g (rb), v (rb), E (rb)
Ee(r) = g (r) + v (r)
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Atomic and molecular interactions characterized in terms
of bond critical points (acording to Bader, Bianchi, Espinosa, Macchi, Tsirelson y otros)
covalent and covalent-polar bonds
Vb << 0
gb << Vb
Eb << 0
Dative bonds
Vb < 0
gb Vb
Eb < 0
Metallic bonds
Vb < 0
gb Vb
Eb < 0
Ionic bonds
Vb < 0
gb Vb
Eb 0
vdW and H-bonds
Vb < 0
gb Vb
Eb 0
‘Shared’ Interactions
ρb > 0.5 eÅ-3, 2 ρ<0
‘Closed-shell’ Interactions
ρb < 0.5 eÅ-3, 2 ρ>0
Increase of gb, Vb, Eb
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Sources of Electron densities:
1) Experiments of X-ray diffraction:
2) Theoretical :Calculation
- Four Circles Diffractometers
- Diffractometers equipped with area detectors (imaging plate or
CCD)
-non-empiric Hartree-Fock and methods based on
theTheory of the Density Functional
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Dynamic electron density analysis:
Space of Nuclear Configurations Equivalence Relation, E
Same Characteristic set of CP
Molecular Structure
B = 0.2 Å2
B = 0.0 Å2
C C
Topological Peculiarities of the conventional Fourier maps
Shared Interactions
ρb > 0.5 eÅ-3, 2 ρ<0
Closed-shell Interactions
ρb < 0.5 eÅ-3, 2 ρ>0
Deensity at the bond Critical Point, b
- non-covalent: 0.3 e/Å3 b 0.6 e/Å3
- Ionic or hightly polar covalent: 0.6 e/Å3 b 0.9 e/Å3
- Covalent Bonds 0.9 e/Å3 b 3.0 e/Å3
- simple: b < 2.0 e/Å3
- double: b ~ 2.0 e/Å3
- triple : b ~ 2.5 e/Å3
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Bond paths
electron density
ridges created by
the gradient lines,
which go through
the bond CP and
connect some
nuclei
NaCl: ρ(r) field with bond paths and bond CP
Bond CP
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Electron Density Modeling
Atomic Coordinates
Thermal displacement parameters
Electron Density parameters
Fmodel(q) = F [ {x,y,x}n, {Uij, Cijk, Dijkl }n, { P, κ }n ]
Σ w q [F experim (q) - F model (q)]2 minimum
Least Square fit
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Properties which can be derived from electron density
Electrostatic potential
Electron diffraction
Quadrupole
electric moments
Optical measurements
Inner-crystal electric
field
Electric field gradient
NMR, NQR, Mössbauer
spectroscopy
Diamagnetic
susceptibility
Magnetic
measurements
Dipole electric atomic
and molecular
moments
Electrostatic atomic
and molecular
interaction energy
DFT
Kinetic electron
energy
Electron
density
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Clasification of the Chemical Compounds
• They may be clasified into two large groups:
• 1.- Organic Compounds and
• 2.- Inorganic Compounds.
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Inorganic Compounds
• Are those formed by any of elements different of Carbon, including carbon in some special cases (CO2 y el CO).
• Water (H2O), the table salt(NaCl), the saltpeter/nitre (NaNO3) or the sodium bicarbonate (NaHCO3) are some examples of inorganic compounds.
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Organic Compounds • Contain carbon as main element. • Besides contain elements as hydrogen, oxygen,
nitrogen and, less frecuently, phosphorus and sulphur.
• CHONPS • Except CO2 and CO
• Sucrose, is an example of Organic Molecule, a carbohydrate un this particular case.
• Other organic compounds important to life are, the fates, the vitamins and the nucleic acids, including DNA and RNA.
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Macromolecules in nature
• Are large molecules and, besides, of high estructural complexity.
• Macromolecules may be clasified, atending to their origen, in Natural and Synthetic.
• Biomolecules, which are the molecules constituents of the living organisms, are mainly made of the following elements: carbon, hydrogen, oxygen, and nitrogen.
The main biomolecules are: Carbohydrates, Lipids, Proteins and Nucleic Acids.
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Chemical elements on the living organisms
H, C, O, y N constitute thr 96.5% weight of a living organism
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Carbohydrates.
• Play energetic and estructural functions.
• Are made by the union of basic units called monosacarids.
• Acording to the number of basic units they contain, may be clasified as:
• Monosacarids: basic unit.
• Oligosacarids : between 2 and 10 monosacarids.
• Polisacarids : more than 10.
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Lipids.
• Are organic macromolecules containing carbon, hydrogen and oxygen,
• Functions: energetics and estructurals.
• One of most particular characteristics of the lipids is their insolubility in water.
• Examples:
• Colesterol,
• Saturated and insaturated fats and
• hormones as testosterone.
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Proteins. • Are the most abundant macromolécules.
• Have various functions:
• Antibodies, participating in the defense of the organism;
• Enzimes which acelerate the speed of the chemical reactions of the cells;
• Estructurals, by forming part of different tissues as the skin, nails and hears;
• Hormonal, regulation of growing, levels of sugar in blood, etc.
• It is important to point out that, normaly, proteins DO NOT act as a source of energy.
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Nucleic Acids. • These macromolecules are especialy important to the living
organisms, because thay store and transport the genetic message.
• There exist two types of Nucleic Acids:
desoxirribonucleic acid (DNA) and the ribonucleic (RNA).
ADN is the most important nucleic acid. It contains all genetic information to determine the color of your eyes, whether your hair is straight or curl, and even the pattern of your fingerprints.
• ARN, is formed from the DNA and transports the information to allow cells syntesize all their proteins.
• Both DNA and RNA are formed by basic units called nucleotids.
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- Are the most abundant biologic macromolecules.
- Are present in all cell and everywhere within the cell.
- There exist thousans of different types and sizes of proteins.
- Exhibit an amasing number and diversity of functions.
Proteins.
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Each organism may biuld proteins using a base of 20 defferent aminoacids
Enzimes poisons
Hormones colagen (skin, bones)
Antibodies receptors
Transporters hemoglobin
Proteins of milk
Queratine (horns, scales, hairs, wool, nails)
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•an amino group (-NH2)
•a carboxilo group (-COOH)
•an atomo of H
•a characteristic group R (lateral chain)
Basic estructural Units of proteins
a- aminoacids
connected carbon aatom
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POLAR
NON POLAR
The difference among then is based in size, electric charge, hydrofobicity
aliphatic
aromatic
charged positively
negatively
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• Proteins of all living organisms are build by 20 aminoacids covalentely bonded in different combinations and sequences.
• Due to that each of these aminoacids have diferent lateral chains, with different chemical properties, this group of 20 molecules may be considered as the ALFABET to WRITE the language of the proteins.
• Thanks to this variety the cells may produce proteins with Physical and functional propierties fully different
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Aminoacids with aliphatic lateral chains
Glicina (Gly, G)
Alanina (Ala, A)
Valina (Val, V)
Leucina (Leu, L)
Isoleucina (Ile, I)
Prolina (Pro, P)
Glicina (Gly, G)
Alanina (Ala, A)
Valina (Val, V)
Leucina (Leu, L)
Isoleucina (Ile, I)
Prolina (Pro, P)
Fenilalanina (Phe, F)
Tirosina (Tyr, Y)
Triptofano (Trp, W)
Aminoacids whith aromatic lateral chains
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Sulphur containing lateral chains
Cisteína (Cys, C)
Metionina (Met, M)
SH
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Aminoacids with positively charged (+) lateral chains
Lisina (Lys, K)
Arginina (Arg, R)
Histidina (His, H)
pKa=10.8 pKa=12.5 pKa=6.0
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Aminoacids with negatively charged (-) latetral chains
Glutamato (Glu, E)
Aspartato (Asp, D)
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Such subunits linked by AMIDE BOND or PEPTIDIC BOND provide the structure of proteins
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The skeleton of the whole protein is made by repetition of the N-Ca-C. This unit propagates bonded by peptidic bonds
Bonded to the polipeptidic skeleton we find, hydrogens of the amino group, oxygens of the carbonil group and hydrogens and the lateral chains of the alpha carbons.
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Proteins are macromolecules which may contain from 400 to 25,000 residues
MW between 5,000 y 700,000
Ser Gly
Tyr
Ala
Leu
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The aminoacid sequence of a protein are genetically determined :
The nucleotids sequence of DNA codifies a
Complementary sequence of nucleotids on the RNA
Which determines the aminoacids sequence of the protein
Espacial structure function
mutations genetic alterations
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Electric dipole Trans position
CHARACTERISTICS OF THE PEPTIDIC BOND
Double bond character
These 6 atoms are on the same plane
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Sheets
a Helix
a Helix (left)
Gráfico de Ramachandran
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Conformation of the proteins
All proteins have a NATIVE state, a characteristic tridimensional form known as CONFORMATION.
The conformation can be described in terms of different structural levels
1ry, 2ry, 3ry and 4ry structures
Tridimensional Ordering
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Concerns the ordering of the covalent skeleton of the polypeptidic chain,
GIVEN BY THE SEQUENCE OF aminoacids
1ry Structure
Will be determining the tridimensional ordering to be adopted by the protein
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Different forces participate in the estabilization of the peptidic skeleton in order to reach the
tridimensional conformation
Hydrogen bonds
Hidrofobic interactions
Electroestatic atraction
NON COVALENT
COVALENT S-S Bidges
2ry, 3ry and 4ry Structures
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• a - helix (like a cylinder)
• - sheet (fold)
• Turns (, , )
• Random coil (desordered)
Different spacial dispositions or 2ry
structures
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Conformation a-helix
link C=O of rn
with N-H of rn+4
ALL RESIDUES GET BONDED by H-bond in the same polipeptidic chain
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Conformation - Sheet fold
Antiparallel
Parallel
- Sheet fully extended !
H bond between the NH and CO groups of different polipeptidic chains
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Turns
1/3 of the aminoacids are found on turns or loops where the CHAINS INVERT the their
direction
turns
The C=O group of one residue n bonded by H bond with the NH group of residue (n+3)
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3ry Structure
Concerns the way in which the polipeptidic
chain folds or curvs itself to produce the folded o compact structure
of the soluble proteins
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Forces participating in the estabilization of the terciary structure
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Cisteine, with sulphur containing lateral chains (S), may oxidate and form S-S BRIDGES
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4ry Structure
Only present in proteins with more than
one polipeptidic chain
May participate covalent and non covalent bonds
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CONFORMATION OF PROTEINS
hierarchic structure
Sequence of aminoacids of the peptidic skeleton and S-S
Array / distribution / ordering of the skeleton and lateral chains of the
protein in space
Describes the tridimensional order of the
protein
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What happen during the heating of the proteins ?
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Consists in the loss of the quaternary, terciary and
secondary structures, by breaking the bridges sosteinig such
structure
All proteins denaturalized have the same conformation
Very opened and with a maximum interaction with the solvent
A water soluble protein when denaturalized become insoluble and precipitates
Denaturation may be produced by changes temperature (> 60-70 ºC)
variations of pH.
salinity
In some cases, if the initial conditions are restablished, a denaturalized protein may return to the previous folding o conformation, that process is called renaturation.
MANY PROTEINS ONLY KEEP ITS BIOLOGIC ACTIVITY WITHIN A LIMITED FLUCTUATION OF pH AND TEMPERATURE
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* La Naturaleza del Enlace Químico. L. Pauling, (1939) ¡A clasic!
* Atomo. I. Asimov, (1992). Ed. Plaza-Janés ¡On the way to become a clasic!
* Física Cuántica: Atomos, Moléculas, Sólidos, Núcleos y Partículas.
R. Eisberg, (1992, 16ª re-impresión 2002). Ed. Limusa
* Construyendo con Átomos y Moléculas. Indigo, (2006). Ed. Eudeba
* Enlaces Químicos. A.L. Companion, (2008). Ed. Reverté.
* Electrones, Neutrinos y Quarks. F.J. Indurain, (2001). Ed. Crítica (Collection Drakontos)
* Partículas Elementales. G.T. Hooft, (2008). Ed. Crítica (Collection Drakontos)
* An Introduction to the Electronic Structure of Atoms and Molecules. R.F.W. Bader, (1970).
* Atoms in Molecules. A Quantum Theory.
R.F.W. Bader, (1994). Ed. Oxford University Press.
* Density-Functional Theory of Atoms and Molecules.
R.G. Parr & Y. Weitao, (1994). Ed. Oxford University Press
* Bonding and Structure of Molecules and Solids.
D.G. Pettifor, (1995). Ed. Oxford University Press
* Physics of Atoms and Molecules.
B.H. Bransden & C.J. Joachain, (2003, 2ª edición) Ed. Prentice Hall.
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* The Chemist's Guide to Valence Bond Theory.
S.S. Shaik & P.C. Hiberty, (2007). Ed. Wiley-Interscience
* The Quantum Theory of Atoms in Molecules.
C.F. Matta & R.J. Boyd, (2007). Ed. Wiley-
VCH
* The Chemical Bond: A Fundamental Quantum-Mechanical Picture.
T. Shida, (2008, 2ª edition corrected). Ed. Springer
On the Chemical Bond (antecedents-history):
http://platea.pntic.mec.es/~jrodri5/web_enlaces_quimicos/antecedentes.htm
On molecular structures. Links to various “books” electronics and pages on several aspects of chemical bond(formulas, characteristics, figures, geometries, etc..) http://www.uhu.es/quimiorg/estructuraweb.html