Surface tension measurements show that chaotropic salting-in denaturants are not just water-structure breakers ( ABSTRACTSince the salting-in agents guanidinium chloride, urea, and lithium perchlorate increase the surface tension of water, the salting-in phenomenon does not reflect easier cavity formation in water. Therefore, these salting-in agents must be directly contributing to the solvation of a solute such as benzene in water, probably by a direct solvation interaction. The increased surface-tension effects do not overbalance these solvation effects since they are smaller than the large surfacetension increases with lithium chloride, a typical salting-out agent. The salting-in agent tetra-n-butylammonium chloride differs in that it lowers the surface tension of water. Thus, it probably contributes both to easier cavity formation and to direct solvation of the substrate. The previous findings that most salting-in agents switch to become salting-out agents in other polar solvents such as ethylene glycol and formamide but that tetra-n-butylammonium chloride does not switch in these solvents can be understood in terms of relative polarities.

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Using the chromomagnetic interaction Hamiltonian with proper account for the SU (3) flavor symmetry breaking, we have performed a schematic study on the masses of S−wave heavy tetraquarks as bq bq (q denotes u, d, s quark). It is found that the numeral results for bu b d or bd bū with 1 + quantum number are 10612 MeV and 10683 MeV respectively, which are well compatible with the recent detected charged bottomonium-like Z b (10610) and Z b (10650). Theoretically, we also investigate the possible tetraquark states of 1 ++ and 2 + due to the charge conjugation as the potential candidates for the updating experiments.

The cyclic hexadepsipeptide framework of enniatin B was identified as a template matching the beta-turn tripeptide of tendamistat. The modified analog 1 was synthesized as a tendamistat mimic and compared to the acyclic derivative 2 and the tripeptide Ac-Try-Arg-Tyr-OMe. These compounds were assembled from the dimeric esters 3-5. As an inhibitor of alpha-amylase, 1 is twice as potent as 2 and comparable to the tripeptide. NMR studies of 1 reveal four conformers in equilibrium in a 50:25:15:10 ratio; the ring conformation of the major component is similar to that of the enniatin B template, with the cis geometry of the alpha-hydroxyisovaleryl-N-methylvaline amide linkage; the other conformers differ in the position or presence of the cis amide linkage.

Folding type‐specific secondary structure propensities of 20 naturally occurring amino acids have been derived from α‐helical, β‐sheet, α/β, and α+β proteins of known structures. These data show that each residue type of amino acids has intrinsic propensities in different regions of secondary structures for different folding types of proteins. Each of the folding types shows markedly different rank ordering, indicating folding type‐specific effects on the secondary structure propensities of amino acids. Rigorous statistical tests have been made to validate the folding type‐specific effects. It should be noted that α and β proteins have relatively small α‐helices and β‐strands forming propensities respectively compared with those of α+β and α/β proteins. This may suggest that, with more complex architectures than α and β proteins, α+β and α/β proteins require larger propensities to distinguish from interacting α‐helices and β‐strands. Our finding of folding type‐specific secondary structure propensities suggests that sequence space accessible to each folding type may have differing features. Differing sequence space features might be constrained by topological requirement for each of the folding types. Almost all strong β‐sheet forming residues are hydrophobic in character regardless of folding types, thus suggesting the hydrophobicities of side chains as a key determinant of β‐sheet structures. In contrast, conformational entropy of side chains is a major determinant of the helical propensities of amino acids, although other interactions such as hydrophobicities and charged interactions cannot be neglected. These results will be helpful to protein design, class‐based secondary structure prediction, and protein folding. © 1998 John Wiley & Sons, Inc. Biopoly 45: 35–49, 1998