Current trends in leather science

Abstract In preparing the second edition of ‘Tanning Chemistry. The Science of Leather.’, the literature was updated and the content was revised and reviewed. Here, the new findings are presented and discussed. Notable developments include the necessary rethinking of the mechanism of sulfide unhairing because of new understanding of the aqueous chemistry of sulfide species. Revision upwards of the value of the second pKa for sulfide species ionisation means that S2− cannot exist in an aqueous medium, so the unhairing species in hair burn reactions is HS−. Although the technology remains the same, this means the mechanisms of associated reactions such as immunisation must be revised. Rawstock preservation has benefitted from studies of the potential role of materials from plants which accumulate salt, but which also contribute terpene compounds. There is also further discussion on the continuing issue of chromium (VI) in the leather industry. The application to processing of new solvents, ionic liquids and deep eutectics, is the coming technology, which offers transforming options for new chemistries and products. Renewed interest in vegetable tanning and methods of wet white processing are current trends. Also, within the topic of reagent delivery is processing in a solid medium of plastic beads. Graphical abstrac

Hypothesis Aromatic-aromatic interactions in structures of proteins and protein-DNA complexes: a study based on orientation and distance

Abstract: Interactions between the aromatic amino acid residues have a significant influence on the protein structures and protein-DNA complexes. These interactions individually provide little stability to the structure; however, together they contribute significantly to the conformational stability of the protein structure. In this study, we focus on the four aromatic amino acid residues and their interactions with one another and their individual interactions with the four nucleotide bases. These are analyzed in order to determine the extent to which their orientation and the number of interactions contribute to the protein and protein-DNA complex structures. Background: Aromatic compounds are unsaturated cyclic and planar molecules that contain an aromatic ring. They possess additional stability as a result of the arrangement of the π -electrons situated above and below the plane of the aromatic ring. These electrons give rise to what is known as a π-electron cloud over the ring. Aromaticity is a chemical property associated with such cyclic and planar compounds and is attributed to these π-electrons which are free to cycle around the circular arrangements of atoms found in the aromatic moieties. It can be considered as a manifestation of cyclic delocalization and resonance which is found in planar ring systems such as benzene [1, 2]. The flat face of an aromatic ring has a partial negative charge owing to these π electrons. Out of the 20 amino acids found in protein structures, four are aromatic. They are phenylalanine, tyrosine, tryptophan and histidine [3]. The interactions that take place between the sidechains of the aromatic amino acid residues are referred to as aromatic-aromatic interactions. Formally, aromatic-aromatic interactions are defined as pairs of interacting aromatic residues which satisfy the following criteria: (i) the centers of th