An epidemiological profile of vitiligo in Calcutta is presented. Prevalence data were gathered from 15,685 individuals drawn from the general population; pedigree data were collected through 293 vitiligo patients. The overall prevalence of vitiligo is about 5 per 1,000 individuals. There are no significant sex or age differences in prevalence rates. About a 4.5-fold increase in prevalence is observed among close biological relatives of affected individuals. There is, however, no clearcut correspondence between relative risks and kinship coefficients. There are no significant differences in the frequencies of various types of vitiligo between probands with and without positive family history. The overall mean and modal ages of onset are about 22 years and 15 years, respectively. The mean ages among males (24.8 years) and females (19.3 years) are significantly different.

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Vancomycin, a macrocyclic antibiotic, is an amphoteric glycopeptide produced by Streptomyces orientalis which has proven to be a viable chiral selector for high performance liquid chromatograph (HPLC) (D. W. Armstrong, Y. Tang, S. Chen, Y. Zhou, C. Bagwill and J-R. Chen, Anal. Chem. (1994; 66: 1473). While it is related to other glycopeptide antibiotics, vancomycin has a number of unique structural features, including 18 stereogenic centers, five aromatic rings, and two side chains one of which is a carbohydrate dimer. Therefore, a vancomycin-based stationary phase appears to be multimodal in that it can be utilized in both normal-phase and reversed-phase liquid chromatography. Consequently, the enantiomeric separation may be operative via several mechanisms, including pi-pi complexation, dipole stacking, inclusion, hydrogen bonding, or combinations of these interactions. LC/MS/MS is a powerful tool for quantitative analysis when evaluated on the basis of speed, specificity, reliability and sensitivity. For these reasons, the present paper explored the feasibility of bonded macrocyclic glycopeptide phases for chiral LC/MS/MS quantitative analysis. Methylphenidate was used as a model compound. A rapid chiral bioanalytical method (<7.5 min) for the determination of the enantiomers of methylphenidate was developed. A lower limit of quantification (LLOQ) of 87 pg/mL was attained for the human plasma assay. This is to our knowledge the first example of enantioselective reversed-phase LC/MS/MS for methylphenidate. The chiral column was relatively cost effective and exhibited excellent performance with no separation deterioration observed after approximately 2500 injections.

Epimers of methylcyclohexanol are distinguished by their relative gas-phase acidities (AG°acid) obtained by a kinetic method which is based on the relative rates of competitive fragmentations of cluster ions. The estimated AG°acid values for cw-2-methylcyclohexanol, tmnj-2-methylcyclohexanol, cw-4-methylcyclohexanol, and trans-4-methylcyclohexanol are 364.1 ± 0.1, 365.1 ± 0.1, 365.1 ± 0.1, and 366.2 ± 0.1 kcal/mol, respectively. These results illustrate the high sensitivity of the kinetic method to small differences in gas-phase acidity (±0.1 kcal/mol using the triple-quadrupole mass spectrometer) and the fact that it allows the distinction of isomeric compounds. The difference in acidities of the epimers is explained by steric decompression due to hyperconjugation which involves contributions by the hydride-ketone ion/molecule complex. 1,3-Diaxial interactions are relieved in the course of hyperconjugation as the axial alkoxide adopts a quasi-equatorial orientation and so increases the acid strength of the cis alcohols. The greater acidity of the 2-substituted over the 4-substituted alcohols is due to interactions of the oxygen atom with the vicinal methyl group. Changes in the type of alcohol groups involved in hydrogen bonding to the proton have a discernible influence on the relative rates of competitive dissociation of the proton-bound dimers. This is reflected in the susceptibility to dissociation, expressed as an effective temperature, which is largest for metastable dissociations of the proton-bound cluster ion comprising a primary alcohol proton-bound to a secondary alcohol and smallest when two secondary alcohols comprise the cluster ion. These changes are due to differences in the vibrational states of the proton-bound dimers.