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ABSTRACT:
Jobs plot or continuous variation method is used to estimate the stoichiometry in cyclodextrin complexation. Cyclodextrin complexation is well known as widely acceptable technique for improving the poor physicchemical properties of BCS class II and class IV drugs. The stoichiometry of the inclusion complex is given by the number of guest and host molecules present in the supramolecular complex/inclusion system. The most common stoichiometry is 1:1, implying the inclusion of a single guest molecule. Now-a-days jobs plot is replaced by phase-solubility study. Jobs plot deals with spectral methods mainly for molecular modelling study of drugs and bioactives.
KEYWORDS: cyclodextrin, complexation, jobs plot, phase solubility study
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INTRODUCTION:
In cyclodextrin complexation jobs plot is used for determination of the Stoichiometry for preparation of binary/ternary complex. The theoretical aspect of cyclodextrin complexation contributes in understanding the molecular recognition, molecular interactions and the role of different structural factors of the guest molecule. The stoichiometry plays a vital role in complexation. Without stoichiometric ratio of guest and host; it would be difficult to prepare complex. According to literatures and datas, it is stated and considered that both on experimental grounds and molecular dynamics calculations the efficient stoichiometry for complexation is 1:2 guest: host, providing best effect. Stoichiometry can be estimated by spectral method. Through stoichiometry and or phase solubility study following parameters relevant to complexation can be determined -
a. Stability constant
b. Complexation efficiency
c. Coefficient of regression
d. Intrinsic solubility of guest
e. Solubilizing efficiency
The stoichiometry/stoichiometric ratio
The stoichiometry of the inclusion complex is given by the number of guest [G] and host [H] molecules present in the supramolecular complex/inclusion system. The general notation being GnHm; The most common stoichiometry is 1:1 (G:H), implying the inclusion of a single guest molecule. However, several other stoichiometries like G1H2, G2H1, G2H2, G1H3, G3H1, etc., can also be encountered. Besides 1:1 stiochiometry, the formation of the G1H2 complex may be due to two successive equilibriums, the simultaneous presence of 1:1 and 1:2 complexes is also frequently mentioned.
JOBs Method
The first method used for determination of the stoichiometry of inclusion complexes was Job's method given by Mr. Job in year 1928. It is also known as the continuous variation method. In this...