(-)-Menthol is a widely used flavoring ingredient present in mouthwash, foods, toothpaste, and cigarettes; yet, the pharmacological effects of menthol have not been widely studied. Mentholated cigarette smoking may increase the risk for lung cancer. Many African American smokers smoke mentholated cigarettes, and African Americans have a significantly higher incidence of lung cancer as compared with whites. There may be a relationship between the incidence of lung cancer and the type of cigarette smoked because the use of mentholated cigarettes by white smokers is significantly less and the incidence of lung cancer is less. The mechanism whereby (-)-menthol could increase the health risk of smoking is not known. The results of our in vitro studies herein show that (-)-menthol and synthetic congeners inhibit the microsomal oxidation of nicotine to cotinine and the P450 2A6-mediated 7-hydroxylation of coumarin. Replacement of the alcohol oxygen atom of menthol with other heteroatoms increased the potency of P450 2A6 inhibition. Thus, the K(i) value of (-)-menthol for inhibition of microsomal nicotine oxidation was 69.7 micro M but neomenthyl thiol possesses a K(i) value of 13.8 micro M. Menthylamine inhibited nicotine oxidation with a K(i) value of 49.8 micro M, but its hydroxylamine derivative gave an IC(50) value of 2.2 micro M. A series of 16 menthol derivatives and putative metabolites were procured or chemically synthesized and tested as inhibitors of P450 2A6. While highly potent inhibition of P450 2A6 was not observed for the menthol analogues examined, it is nevertheless possible that smoking mentholated cigarettes leads to inhibition of nicotine metabolism and allows the smoker to achieve a certain elevated dose of nicotine each day. This may be another example of self-medication to obtain the desired effect of nicotine.

Mid-infrared spectra of neat n-heptane at room temperature are presented over a pressure range from ambient to 70 kbar. The application of hydrostatic pressure induces frequency shifts, band splittings, and significant changes in the line shapes of internal vibrational modes both in liquid and in solid phases. The results are discussed in terms of the liquid-solid phase transition and changes of the population of molecular conformers. Evidence for a solid-solid phase transition near 30 kbar is also presented.

MS/MS of electrosprayed ions is shown to have the capacity to discriminate between peptides that differ by configuration about their alpha-carbons. It is not necessary for the peptides to possess tertiary structures that are affected by stereochemistry, since five epimers of the pentapeptide, H2N-Gly-Leu-Ser-Phe-Ala-OH (GLSFA) all display different collisionally activated dissociation (CAD) patterns of their protonated parent ions. The figure of merit, r, is a ratio of ratios of fragment ion abundances between stereoisomers, where r = 1 corresponds to no stereochemical effect. Values of r as high as 3.8 are seen for diastereomer pairs. Stereochemical effects are also seen for the diprotonated dodecapeptide H2N-Leu-Val-Phe-Phe-Ala-Glu-Asp-Val-Gly-Ser-Asn-Lys-OH (LVFFAEDVGSNK), a tryptic fragment from the amyloid beta-protein. Triply charged complexes of the protonated dodecapeptide with cobalt(II) ions undergo CAD at lower collision energies than do doubly protonated LVFFAEDVGSNK ions. Statistically significant (p < 0.01) differences between the all-L-dodecapeptide and the ones containing a d-serine or a D-aspartic acid are observed.

Protonated threonine and its allo diastereomer exhibit different proportions of collisionally activated dissociation (CAD) product ions. N-Methylation attenuates these differences. Water loss from protonated allo-threonine gives protonated trans-3-methylaziridinecarboxylic acid via an internal S(N)2 pathway, rather than protonated vinylglycine.