Anaesthetics
Introduction
 Loss of consciousness
 Surgery
 Blockage of conduction in nerves
 Early anaesthetics Nitrous oxide
 Ether
 Side effects
 Modern anaesthetics Trichloroethylene
 Halothane
First Connection
Hydrogen Bonding
Chapter 4-Structures and Properties of Substances
 4.3-Intermolecular Forces in Liquids and Solids
 Intermolecular Forces
 Hydrogen Bonding
Eg) N, O, F
Hydrogen Bonds in Anaesthetics
 Anaesthetic
 Structure
 Stability
 Function
 Electronegative atoms + hydrogen atom
 halogens
 aromatic rings
 sulphur atoms
Second Connection
Strong Acids + Strong Bases
Weak Acids + Weak Bases
pH
pKa
Chapter 8- Acids, Bases, and pH
Chapter 9- Aqueous Solutions and Solubility Equilibria
 8.2-The Equilibrium of Weak Acids and Bases:
 pH-the exponential power of hydronium ions
 acid dissociation constant, Ka
 pKa = pH + log [AH]/[A-]
 9.1-The Acid-Base Properties of Salt Solutions:
Sophia Tang
 Salts that Dissolve and Form Acidic Solutions
-weak bases and strong acids dissolve in water
Third Connection
Equilibrium
Chapter 7- Reversible Reactions and Chemical Equilibrium
 7.1- Recognizing Equilibrium
 Equilibrium
 7.4- Predicting the Direction of a Reaction
 Le Chatelier’s principle
 “A dynamic equilibrium tends to respond so as to relieve the effect of any change in the
conditions that affect the equilibrium.”
 The effects of changing conditions on a system at equilibrium
 Increasing [reactant] or decreasing [product], toward products
 Decreasing [reactant] or increasing [product], toward reactants
1. To Produce Anaesthetics
 Prepared as weak bases
 Manufacture: powdered solids
(poor solubility in water)
 + Acid
Salt
 Stable solution
 Acidic anaesthetics solutions
2.












After Injection
RN, RNH+
Equilibrium vs. pH of the solution
Acidic surrounding medium(low pH):
[H3O+] increases
combined with RN
shifts to the left
[RNH+] increases
Basic surrounding medium(high pH):
low [H3O+]
release H+
shift to the right
[RN] increases
3. Diffusion (nerve cell)
Lipid membrane
Outside the neuron: RN
Inside the neuron: RNH+ (positively charged)
Diffusion
 Outside the membrane:
 [uncharged base]
 equilibrium
right
 uncharged base formed
 Inside the membrane:
 equilibrium
left
 [cations]
 RNH+ : bind to Na+ channels
 More RN outside of the cell
4. Idea pKa of an anaesthetics
 pKa (dissociation constant) :
pH – number of RN = number of RNH+
 pH of normal body tissue - 7.4
 Idea pKa of an anaesthetic - 7.4
 Higher pKa, lower [uncharged base], slower diffusion
Mepivicaine
Etidocaine
Articaine
Lidocaine
Prilocaine
Bupivicaine
Procaine
pKa
Onset in minutes
7.6
7.7
7.8
7.9
7.9
8.1
9.1
2 to 4
2 to 4
2 to 4
2 to 4
2 to 4
5 to 8
14 to 18