Anaesthetics physical properties

Physical Properties. All th e ethers are insoluble in water. The aliphatic ethers have strong characteristic odours, have anaesthetic properties and are extremely inflammable. 

Acetylene is a simple asphyxiant and anaesthetic. Pure acetylene is a colourless, highly flammable gas with an ethereal odour. Material of commercial purity has an odour of garlic. Its physical properties are shown in Table 8.4. 

Cinnamyl-Z-ecgonine has been obtained by acylation of Z-ecgonine with cinnamic anhydride. Esterification of this cinnamyl-derivative with methanol gave cinnamylcocaine (103). After the physical properties of cinnamylcocaine had been established it was subsequently isolated from Java coca leaves (109) and from Erythroxylum monogynum Roxb. (77). It has been reported (77) that cinnamylcocaine is devoid of mydriatic and anaesthetic properties. 

The structurally non-specific drugs include general anaesthetics, hypnotics together with a few bactericidal compounds and insecticides. However, it is important to note here that the biologieal characteristic of such drugs is solely linked with the physical properties of the molecules rather than the chemical feature. 

Later on, William Morton — a Boston dentist demonstrated the anaesthetic actions of diethyl ether in 1846 at the historical Ether Dome located at the Massachusetts General Hospital. In actual practice, the usage of diethyl ether followed by cyclopropane were withdrawn completely for being highly toxic amalgamated with equally dangerous physical properties, such as flammable and explosive. 

A good deal of faetual information has been accumulated in connection with physical properties together with bioehemical and physiological processes of anaesthetic agents, but unfortunately not a single theory proved and substantiated by experimental facts of anaesthesia is known. 

In another investigation of the comparative value of lipid and hydration hypotheses (Eger et aL 1969), the minimal anaesthetic concentrations of the following agents were plotted against the relevant physical properties carbon tetrafluoride, sulphur hexafluoride, nitrous oxide, xenon, cyclopropane, fluorexene (trifluoroethyl vinyl ether), diethyl ether, enflurane (see above), halothane, chloroform, and methoxyflurane (see above). (These anaesthetics have been arranged here in order of increasing lipid/water solubility.) The results of this study showed an excellent correlation between... 

Nitrous oxide (N20) was first prepared by Priestly in 1772. Its anaesthetic properties were described by Sir Humphrey Davy in 1800 and it was first used in clinical practice by Colton and Wells in 1844. Physical characteristics... 

Table 4.2 Physical and pharmacological properties of the ideal intravenous anaesthetic agent...

Thus, the amino-ester and the amino-amide series attribute a highly lipophilic property to the drug molecule and is beheved to afford a substantial contribution towards the binding of local anaesthetics particularly to the channel-receptor proteins. In other words, whatever structural modifications are intended to be carried out in this particular zone of the molecule, it would certainly reflect directly upon the physical and chemical characteristics thereby causing an appreciable alteration in its local anaesthetic profile ultimately. 

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