Plumage colour mutations and melanins in the feathers of the Japanese quail: a first comparison.

The absorbance of melanin content from dorsal feathers was compared between wild-type Japanese quail and nine other quail plumage colours determined by single mutations in one of seven genes: extended brown (MC1R), yellow (ASIP), silver (MITF), lavender (MLPH), roux (TYRP1), imperfect albinism (SLC45A2) and rusty. As compared with wild-type quail, all mutations but extended brown decreased total melanins. The largest decrease was observed in quail with one of the dilution mutations at TYRP1, MLPH or SLCA45A2. No difference in eumelanins was found between the 10 plumage colours. Despite visible colour differences, homozygous and heterozygous mutants at MITF, or the two imperfect albino (white) and cinnamon (pale yellow) alleles at SLC45A2, could not be differentiated on the basis of melanins. In contrast, the two white phenotypes caused by mutations at MITF and SLC45A2, or the two reddish plumage colours caused by the roux and rusty non-allelic mutations had different total melanin contents. The results showed that rusty was not likely to be a dilution mutation.

Retention mechanism for ion-pair chromatography with chaotropic reagents.

During the last decade, the extensive use of ion-pair chromatography (IPC) in protein, peptides and basic drugs applications prompted chromatographers to evaluate new additives, since traditional ion-pairing reagents (IPRs) are not usually compatible with LC-MS hyphenation and tend to stick very strongly to the stationary phase, thereby impairing the initial column properties. Chaotropic salts received a great share of credit as tentative IPRs, since they proved to be able to mimic the role of classical IPRs, thereby increasing the retention of oppositely charged analytes. Very few quantitative theoretical studies faced the retention modelling when chaotropic additives are made use of in a chromatographic system and, unfortunately, they used a stoichiometric approach. We hereby debate the present state of the theory and illustrate the first attempt to explain the retention mechanism in the presence of chaotropic reagents in RP-HPLC at a thermodynamic level. We quantitatively validate this model for typical positively and negatively charged analytes as well as for ionic liquid, zwitterionic and neutral analytes.

Use of lipophilic ion adsorption isotherms to determine the surface area and the monolayer capacity of a chromatographic packing, as well as the thermodynamic equilibrium constant for its adsorption.

A method that champions the approaches of two independent research groups, to quantitate the chromatographic stationary phase surface available for lipophilic ion adsorption, is presented. For the first time the non-approximated expression of the electrostatically modified Langmuir adsorption isotherm was used. The non approximated Gouy-Chapman (G-C) theory equation was used to give the rigorous surface potential. The method helps model makers, interested in ionic interactions, determine whether the potential modified Langmuir isotherm can be linearized, and, accordingly, whether simplified retention equations can be properly used. The theory cultivated here allows the estimates not only of the chromatographically accessible surface area, but also of the thermodynamic equilibrium constant for the adsorption of the amphiphile, the standard free energy of its adsorption, and the monolayer capacity of the packing. In addition, it establishes the limit between a theoretical and an empirical use of the Freundlich isotherm to determine the surface area. Estimates of the parameters characterising the chromatographic system are reliable from the physical point of view, and this greatly validates the present comprehensive approach.

Extended thermodynamic approach to ion interaction chromatography: a thorough comparison with the electrostatic approach, and further quantitative validation.

The most reliable literature experimental results, concerning retention behavior of charged molecules, in the presence of an ion-interaction reagent (IIR), were used to obtain a further quantitative validation of a new theory. The present work emphasizes the fact that the extent to which electrostatic interactions, ion pair formation in the adsorbed and the mobile phases, and adsorption competitions are one more important than the other depends on experimental conditions. Further insight into the meaning of the linearity of the log k vs. log [IIR] plot, which is common to many theoretical models, is given. The experimental conditions under which the linearity of this plot can be expected not only practically, but also theoretically, are elucidated. The dependence of the ratio of retention factors with and without IIR in the eluent on the analyte nature, which cannot be predicted by the electrostatic approach, was explained and tracked. The difference between the actual surface potential and that predicted by the electrostatic approach is also rationalized. The model is also theoretically shown to be able to elucidate the enantioselective retention mechanism, in the presence of chiral counter ions.

Extended thermodynamic approach to ion interaction chromatography.

The chromatographic behavior of charged analytes in ion interaction chromatography (IIC) is theoretically investigated. The chemical modifications of the stationary and mobile phases in the presence of ion interaction reagent (IIR) are theoretically shown to change the partition coefficient for charged molecules. The most reliable literature experimental results concerning retention behavior of charged molecules in IIC were used to test the new theory. Retention equations are compared with those that can be obtained from the most important retention models in IIC. The present exhaustive retention model, which is well-founded in physical chemistry, goes further than the previous ones whose retention equations can be viewed as limiting cases of the present theory. The present extended thermodynamic approach reduces to stoichiometric or electrostatic retention models if the surface potential or pairing equilibria are respectively neglected. Moreover, it is able to quantitatively explain experimental evidences that cannot be rationalized by the existing retention models.