Physical Chemistry Flashcards
Define atomic number
The number of protons in each atom of an element
Define atom
The smallest part of an element that can take part in a chemical reaction
Define an element
A group of atoms all having the same atomic number
Define a molecule
A combination of atoms which is the smallest unit of a chemical substance that can exist whilst still retaining the properties of the original substance
Define atomic mass
The mass of one mole of an element
Define a mole
A constant number (6.022 x10^23) of atoms or molecules
What are isotopes
Elements with different numbers of neutrons but the same atomic number (same number of protons)
Where are the atomic and mass numbers shown in relation to the element letter
Atomic number subscript
Mass number superscript
What are the electron shells of an atom labelled
Innermost K the
L M N O P Q
Maximum capacity of the k, l m and n electron shells
K 2
L 8
M 18
N 32
What is valency
The number of atoms of hydrogen that one atom of an element can combine with or replace
The number of electrons an atom can loose or gain to gain stability - with by loosing in ionic bonding or sharing in convalent bonding. Depends on the electron configuration.
What is the valency of carbon? Why is this important
Valency of 4
It is very versatile, can either loose or gain 4 electrons to achieve electrical stability .
How does an ionic bond work
An atom donates an electron to another giving both stable outer shells but opposite charges resulting in attraction
What electron configurations confir stability
Full shells
Pairs
Octets
What is a dative bone
A type of covalent bond where both electrons come from the same atom
Occurs when loan pairs of electrons are in the outer shell in the unbonded state
What is the shape characteristics of ionic and covalent bonds
Ionic have no electron sharing thus bond non directional and no particular shape
Covalent have distinct shapes
What type of substances do ionic and covalent bonded molecules form
Ionic - usually solid, usually crystalline, easily dissolvable, hard to vapourise
Covalent - usually highly volatile liquid or gas, not readily soluble in water, readily vapourised
What are van der waals forces
Electrons not rigidly fixed thus attracted to charges so distribution becomes uneven producing a dipole thus undergo attraction and repulsion to similar neighbouring molecules
What are hydrophobic bonds, why do they form
How can it be overcome
Grouping of areas of uniform charge (not polar) as don’t bond to hydrogen bonds, thus energy required to split uniform bond would be greater than the energy produced by formation of new ones (as no new ones form). There is no direct attraction between the hydrophobic areas, just lack of attraction of water!
Vigerous mixing for example gives the energy to overcome the hydrogen bonds temporarily
What is an emulsion
Mixture of two or more immiscible liquids, one existing as particles within another
How is propofol held in emulsion
Propofol molecule surrounded by phospholipids in a micelle
Strength of main intermolecular bonds
Covalent - 50-150kJ/mol
Ionic - 5-10kj/mol
Hydrogen - 2-5kJ/mol
Van der waals - 0.5kJ/mol
What is the implication of covalent bonds in pharmacology
Very strong and hard to break, require catalyst or enzyme to split eg. Metabolism of entire drug:receptor complex or replacement of receptor
What is the relationship between force of attraction of a bond and distance for ionic and van der waals
Ionic: force directly proportional to 1/distance^2
Vdw: force directly proportional to 1/distance^7
Very close vdw repel due to nearby electron groups
What are oxidation and reduction
Why called oxydation?
Oxidation - loss of electrons
Reduction - gain of electrons
Oxydation can also be considered as gain of a proton e.g. local anaesthetic ionisation
Loosing an electron means you need to give it to an electron acceptor eg forming a bond with oxygen
What is diffusion
The movement of molecules or ions within a gas or solution down concentration and electrical gradients until those gradients disappear resulting in an even distribution of all molecules or ions within the container
What is the law of gaseous diffusion? What is it?
Grahams law
Rate directly proportional to 1/sqroot density
At given temp and pressure
What is the key property of ionised vs non ionised drug and vica versa
Ionised water soluble
Non ionised can cross membranes
What is the dissociation equation for a weak acid
What is the relationship with pH
HA reversible H+ + A-
pH = pKa + log 10 [A-]/[HA]
What is pKa
Negative log of dissociation constant
The pH at which drug is 50% ionised
How does ionic dissociation relate to thiopental
What is its pKa
pKa 7.8
Made up in an alkaline solution pH11 so ionised and soluble
Enters acidic body and becomes unionised so can penetrate membranes and have effect on CNS
What is a partition coefficient
Numerical constant that is the ratio AT EQUILIBRIUM or the concentrations of that substance in two adjacent compartments separated by an interface through which the substance readily passes
The interface can be a physical boundary such as a cell membrane or a liquid gas interface
What are the Ostwald partition coefficients
How do they reach equilibrium
The blood gas coefficient of a gas at 37oC
Gases travel down their partial pressure gradient until pp is equal in both compartments (which usually means different concentrations to obtain that equal pp)
By Ostwald partition coefficients what influences the concentration of a molecule for a given partial pressure in a particular compartment
What about the amount of the molecule?
Affinity of the molecule for the constituents of the compartment
Amount also influenced by size of the compartment
What is the blood gas coefficient for sevoflurane
What does this mean
0.69
At equilibrium for every 1% sevoflurane in gas there will be 0.69% in the blood
What is osmosis
The passage of solvent through a semipermeable membrane separating two compartments having different concentrations of solutes to which the membrane is impermeable.
What is osmotic pressure
The pressure required to stop the movement of solvent across a semipermeable membrane
Differentiate osmolality and osmolarity
Osmolality is concentration by mass of solution (mOsm kg-1 H2O)
Osmolarity is concentration by volume of solvent (mOsm L-1)
What is mannitol
Why is it an effective osmotic diuretic
A high molecular weight alcohol
It is filtered at the glomerulus and not reabsorbed. It has high osmotic potential so draws water after it.
What is an isomer
A chemical compound that has the same empirical molecular formulae but differing physical or chemical properties
Define a structural isomer
Types
Presence of different structures with the same empirical molecular formulae
Chain isomer - carbon skeleton varies between isomers with same functional groups
Position isomer - component atoms or functional groups are in different positions on an identical carbon skeleton
Functional group isomerism - change in functional group - eg alcohol to ether
What is dynamic isomerism
Another name
Example
Tautomerism
Variant of functional group isomerism where two isomers exist in dynamic equilibrium
Changes in the environment can change this equilibrium eg ph
Eg thiopental and nitrous oxide
What is stereoisomerism
Types
Same molecular formula, carbon skeleton and structure but different spatial arrangement. All molecular bonds are the same but arrangement different
Optical isomerism
Geometric (cis-trans) isomerism
What is optical isomerism
Requirements
Atoms which are at least tetravalent (four bonds) with different groups of atoms on each bond
Has a chiral centre (usually a carbon). If two of the groups are interchanged then it forms a non-superimposable mirror image of the original.
What do optical isomers produce
Features
Separate enantiomers
Different cysteine structures and rotate polarised light in the opposite direction.
How can stereoisomers be classified
Handedness (prioritising groups around chiral centre based on atomic number). can be right handed (R or D) or left handed (L or S) - note s for sinister, as in left handed people are the sinister. D is for dexter.
Can also be classified by rotation of light - clockwise rotation is symboled with + or d, anti-clockwise rotation is symbolised with - or l. Note you can be either handedness with either rotation (eg D- or D+)
What handedness are most carbohydrates?
What about proteins?
Most carbohydrates are right handed (eg D+glucose = dextrose)
Most amino acids are left handed (except for glycine which has no chiral centre and some right handed amino acids in bacterial cell walls)
What are the potential pharmacological effects of different enantiomers
Different potencies
Different side effects
Naturally occurring receptors are often steriospecific cancelling out one of the enantiomers form having an effect
Most drug level measurements doesn’t distinguish stereoisomers and thus needs to be accounted for in pharmacokinetic calculations
Elimination may also differ between enantiomers, as can metabolite activity
Redundant enantiomer (eg R bupivicaine) can still cause unwanted effects
What is the term for a non superimposable non mirror image sterioisomer? What are the subcategories
Diastereomer
Isomers with multiple chiral centres
Cis-trans isomers
What is a geometric isomer
Atomic orientational variation around a double bond
If the main parts of each half are in the same side of the bond it’s cis (or e) , on opposite it’s trans (or z)
What geometric isomerisation is exhibited by mivicurium
Two double bonds with geometric isomerism so can be
Cis cis
Cis trans
Trans trans
What is the difference between cis and racemic atricurium
Cis atricurium supposedly causes less histamine release
Which main plasma proteins are involved in drug transport
Albumin
Globulin
Molecular weight of albumin
69,000 daltons
Features of albumins drug binding sites
Multiple and non specific
Facility for many weak bonds (hydrogen, hydrophobic, vdw)
Factors that can effect drug:plasma protein binding
Amount of protein - can be influenced by surgery, trauma, mi, ca, ra
Abnormalities in protein structure
PH
Presence of other drugs
In what cases are changes in protein binding of drugs producing more pronounced effects?
In highly protein bound drugs
In less protein bound drugs large changes need to occur before any effect is noted.
