Interatomic Interactions
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- Created by: LBCW0502
- Created on: 02-02-18 12:15
Why are forces relevant to pharmacy (3)?
Efficacy of a drug is determined by how strongly it interacts with target receptor. Ability of drug to go cross cell membranes is controlled by interaction of drug/molecules in membrane. Drug formulations rely on interactions between drugs/carrier
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What is a force?
Any agent that causes a change in the motion of a free body or causes stress in a fixed body
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What is the equation for force?
Force = mass x acceleration (force causes object with mass to accelerate) - Quantum mechanics, F = exchange of gauge bosons
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What are the four fundamental interactions?
Gravity, strong nuclear interactions, weak nuclear interactions and electromagnetic interactions
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Describe features of gravity
Purely attractive, longest range, weakest (strength = 1)
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What is the inverse square law for gravity?
F = G (m1m2)/r^2
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What is the value of G?
6.67 x 10^-11 N.m^2/kg^2
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Describe features of strong nuclear interactions
Holds nucleus together, strongest (strength = 10^38), shortest range (10^-15 m)
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Describe features of weak nuclear interactions
Weaker (strength = 10^25), short range (10^-18 m), involved in decay of nuclear particles (radioactivity)
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Describe features of electromagnetic interactions
Coulomb law, strength (10^36), infinite range
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What is the inverse square law for electromagnetic interactions?
F = k (q1q2)/r^2
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Give examples of electromagnetic interactions (4)?
Holds electrons near nucleus in atoms. Hold atoms to form molecules/crystals. Hold molecules to form cells. Keeps solid objects solid
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Describe features of solids (2)
High density, each molecule locked
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Describe features of liquids (3)
High density, molecules not locked, able to flow
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Describe features of gases (3)
Low density, widely separated particles, disordered motion
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Matter is held together by what type of forces?
Intermolecular forces
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Gases condensing into liquids is due to which type of force?
An attractive force
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Matter not collapsing is due to which type of force?
A repulsive force
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Liquids being compressed is due to which type of force?
Repulsive force (short-ranged and strong)
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Describe aspects of the potential energy curve
F = -dU/dr. When the potential energy is decreased, there is an increase in stability (small energy/increased stability)
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Describe features of the intermolecular potential curve
Consists of repulsion and attractive curves (converge at longer distances). Axes with energy against distance
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What is the Pauli exclusion priniciple?
Electron orbitals start interactions (repulsive force has a quantum mechanical origin)
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What is the Pauli exclusion priniciple?
Electron orbitals start interactions (repulsive force has a quantum mechanical origin)
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Describe features of the hard-sphere potential
Graph with axes separation distance against intermolecular potential U. At separation distance of sigma, the repulsion is dominant and there are no interactions. U = infinity when r < sigma and U = 0 when r > sigma
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Give examples of chemical bonds (2)
Covalent bonds and ionic bonds
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Give examples of physical forces (4)
Coulombic interaction. Van der Waals forces. Hydrogen bonds. Hydrophobic interactions.
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Describe features of the covalent bond
Sharing of one (or more) pair of electrons between two atoms. Very strong (~30-100 x 10^-20 J >> kBT). Two major theories are valence bond theory and MO theory
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Describe features of the ionic bond
Two or more atoms lose or gain electrons to form an ion e.g. LiF
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Which type of forces are involved in tabletting?
Compact formation. Bond formation. Uses van der Waals interactions
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Explain why water and oil do not mix
Oil droplets are hydrophobic and water molecules are hydrophilic. Hydrocarbons in oil droplets are unable to form H bonds with water molecules. Oil droplets disrupt structure in water. Decrease in S/increase in G (unstable). H bonds in water strong
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What is used to allow oil and water to mix?
Surfactants
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Describe features of molecular recognition and drug design
E.g. lock and key model. Key actors include H bonding, hydrophobic forces and electrostatic interaction
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What other phenomena don't involve bond breaking/making (4)?
Adsorption (physiosorption/catalysis/separation science). Crystal engineering. Helix structure of DNA. 3D structure of proteins
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Describe features of Coulombic interaction
Strong (~100x10^-20 J>> kBT). U(rij) = qiqj/4ne0rij (Coulombic potential) - application to Hb
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What is the permittivity of a medium?
An intensive physical property that describes how an electric field affects and is affected by the medium (forces between ions in crystal or solution - screening involved)
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How is the Coulombic interaction relevant to pharmacy?
Charged drugs interact with water (dipoles). Strong binding between drugs and target receptors with opposite charges. Good solvent used no charged drugs cannot cross lipidic cell membranes easily
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Describe features of van der Waals forces
Force between unchanged, weakly interacting atoms/molecules. Weaker than Coulombic forces (~10^-20 J ~ kBT)
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What are the three types of van der Waals forces?
Dipole-dipole, dipole-induced dipole, dispersion (London forces)/induced dipole-induced dipole
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What is a dipole?
An uneven balance of electrons between two atoms (positive end and negative end)
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What is the electric dipole moment?
mu = ql
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What is van der Waals potential?
-C/r^6 (attraction)
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Why does dew form on a cool morning?
Dipole formed between oxygen and water...
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Describe features of an induced dipole
Polar molecule induces dipole on adjacent non-polar molecule. mu* = alpha x E
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What is polarizability?
Ability to form instantaneous dipoles
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Describe features of dispersion/London forces
Induced dipole-induced dipole (van der Waals potential) - liquid N2: condenses with huge electron density due to ID-ID forces
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Describe features of hydrogen bonding
Association between electronegative atom (N, O, F) and an H atom. Electronegative atoms are H bond donors (e.g. OH, NH2, NH3) or acceptors (C=O, NH2, NHR2, NR3). Directional, water properties, biological systems, DNA, proteins
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What is the strength of hydrophobic interactions?
~10^-20 J
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Describe features of computational chemistry (modelling)
Data on: geometrics (bond angles/length/torsional angles), energies, charge and bulk properties
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What is the theory of quantum mechanics?
Fundamental theory that extends Newtonian mechanics to sub-atomic level
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What is the theory of molecular mechanics?
Uses Newtonian mechanics to model molecular systems. Atoms (balls) connected by springs. No bond making/breaking. Basis for computer simulation methods (e.g. molecular dynamics)
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Describe features of bond stretching
Harmonic oscillator used to model bond. Hooke's law
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Describe features of bond angle
U = k0/2(0-0.)^2 (bond bending equation)
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Describe features of torsional potential (rotation)
Eclipsed cos(n.0-0) = 1 (k theta). Staggered cos (n.180 - 0) = -1 (0 or k theta)
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What is the Lennard-Jones potential?
Equation. Combines repulsion and attraction. There is 2^1/6 x sigma separation distance when U = 0
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Give uses of models in computer simulations
Biopharmaceutics (bilayers/membranes/vesicles), crystal engineering, nucleation etc.
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Other cards in this set
Card 2
Front
What is a force?
Back
Any agent that causes a change in the motion of a free body or causes stress in a fixed body
Card 3
Front
What is the equation for force?
Back
Card 4
Front
What are the four fundamental interactions?
Back
Card 5
Front
Describe features of gravity
Back
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