The study reported in this thesis provides information about the inhibition and catalysis of procaine in the absence and presence of three types of micelle-forming surfactants, anionic, cationic and nonionic. The effect of ionic surfactants between 1X10-5 -8X10-2M and 0.1%-3% W/V for mixed alkyltrimethyl ammonium bromide on the rate of hydrolysis of procaine was investigated at 40º, 50º, 60º and 70ºC in case of nonionic surfactants, the effect of Tween 20, 40, and 60 between 0.2%-2.0% and tween 80 between 0.1%-0.8% W/V was also studies at these temperatures. The work was carried out in the presence of carbonate bicarbonate buffer at pH 9.20. The effect of neutralinorganic electrolytes (Sodium chloride and lithium sulphate) on the rate of hydrolysis of procaine in the absence and presence of sodium dodecyl suphate (SDS) and cetyltrimethyl ammonium bromide (CTAB), was also investigated
The CMCs of ionic surfactants under various sets of conditions were determined. CMCs were found to be increased by increasing the temperature in all cases which could be dur to a thermal agitation decreasing adhesion between monomers; so shifting the equilibrium to favor the monomeric species. The values of CMCs were unaffected by the temperature in presence of nonionic surfactants in the region 40º-70ºC. Moreover, the CMC was found to decrease markedly as the hydrophobic part of the surfactant was increased
Kinetic studies in the presence of ionic micelles reveal that above CMCs the rate of hydrolysis of procaine decreases. The order of a retardation effect of micellar solutions was found to be anionic surfactant> cationic surfactants which suggests the difference in reaction of the drug in the micellar phase and in the bulk phase and or the differences of the partitioning behavior of the drug between these two phases. The longer hydrocarbon chain of ionic surfactants gave more protection of drug (procaine) from hydrolysis. Nonionic surfactants speed the rate of hydrolysis of procaine and exhibits catalytic effect in the order of tween 20 < Tween 40 < Tween 60 < Tween 80
Maximum stabilization of procaine was obtained in presence of sodium tetradecyl sulphate of concentration 6X10-2M with shelf-life of 57.92 days at 25ºC. The inhibitory effects of anionic and cationic surfactants resulting from columbic interactions was explained on the following grounds.
(i) Adsorption of the ester molecules at the surface of the ionic micelles and then deep penetration into micellar core of anionic micelles resulting more inhibition of the hydrolysis
(ii) A change in the polarity of water at the micellar surface as well as of the water in the micellar core than the water in bulk
(iii) Presence of high density of charge groups of the micellar surface in an environment of low polarity.
(iv) Larger sphere model of anionic micelles with a large sphere area allowing grater penetration of ester molecules into the micelles accounting more inhibition than cationic micelles
In partitioning profiles there has always been a break in the region 2X10-2 -3X10-2 ionic surfactants with the exception of sodium octylsulphate. The rate of hydrolysis in presence of SDS, CTAB and Tween 80 were found to be independent of the ester concentration giving support to the idea of constant partitioning, Lithium sulphate was found to be much potent inhibitor of SDS amongst various systems studied
The energy of activation above CMC gradually increases both in presence of anionic and cationic surfactants. Greater increase in enthalpy change for anionic surfactants compared to cationic surfactants would suggest a stronger interaction between anionic surfactants and procaine molecule. This leads to greater possibility of inhibition
A more negative entirely change suggests that the molecules are activated prior to reaction and must undergo into an orderly state