The porphyrin photosensitizer, meso-Tetra (4-N-methylpyridyl) porphine tetraperchlorate binds to calf thymus DNA by intercalation and by external electrostatic association. This was concluded from the results of measruements involving Scatchard analysis, viscometry, thermal denaturation, and circular dichroism.

The interactions of two positional isomers and one analogue of meso-tetra (4-N-methylpyridyl) porphine, with the synthetic polynucleotides poly[d(A-T)] . poly[d(A-T)] and poly[d(G-C)] . poly[d(G-C)] have been investigated by circular dichroism. All four porphyrins were found to bind to the polynucleotides as shown by the induction of circular dichroism in their Soret bands. Furthermore, the sign of the induced ellipticity reflects selective occupation of binding sites by the porphyrin ligands. The conformational lability of poly[d(A-T)] X poly[d(A-T)] was found to be appreciable as micromolar amounts of meso-substituted 4-N-methylpyridyl, 3-N-methylpyridyl, and p-N-trimethylanilinium porphines induced a CD spectrum similar but not identical to that of DNA in the Z-form, i.e. a negative band at 280 nm and a positive band at 259 nm. The effect of porphyrin binding to poly[d(G-C)] X poly[d(G-C)] was less pronounced and dissimilar to that seen in the AT polymer.

Proton nuclear magnetic resonance and circular dichroism studies were carried out on aqueous solutions of the tetrapeptide Asp-Lys-Thr-Gly (which appears as a bend at residues 35-38 of alpha-chymotrypsin) and its sequence variants Gly-Thr-Asp-Lys, Asp-Lys-Gly-Thr, and Lys-Thr-Gly-Asp; the N and C termini of all four tetrapeptides were blocked with CH3CO and NHCH3 groups, respectively. The spectroscopic data suggest that bend conformations may exist, to some extent, among the distributions of conformations in the first, third, and fourth, but not in the second, tetrapeptide. This result is consistent with empirical probabilities for the prediction of bend conformations in proteins. Conformational energy calculations on these four tetrapeptides support the indications from the experimental data. It thus appears that, because of short-range interactions, the tendency toward bend formation exists in short peptides, provided that both the composition and amino acid sequence are energetically favorable for bend formation.

The Chlorarachniophyceae are unicellular eukaryotic algae characterized by an amoeboid morphology that may be the result of secondary endosymbiosis of a green alga by a nonphotosynthetic amoeba or amoeboflagellate. Whereas much is known about the phylogeny of chlorarachniophytes, little is known about their physiology, particularly that of their lipids. In an initial effort to characterize the lipids of this algal class, four organisms from three genera were examined for their fatty acid and sterol composition. Fatty acids from lipid fractions containing chloroplast-associated glycolipids, storage triglycerides, and cytoplasmic membrane-associated polar lipids were characterized. Glycolipidassociated fatty acids were of limited composition, principally eicosapentaenoic acid [20:5(n-3)] and hexadecanoic acid (16:0). Triglyceride-associated fatty acids, although minor, were found to be similar in composition. The polar lipid fraction was dominated by lipids that did not contain phosphorus and had a more variable fatty acid composition with 16:0 and docosapentaenoic acid [22:5(n-3)] dominant along with a number of minor C 18 and C 20 fatty acids. Crinosterol and one of the epimeric pair poriferasterol/stigmasterol were the sole sterols. Several genes required for synthesis of these sterols were computationally identified in Bigelowiella natans Moestrup. One sterol biosynthesis gene showed the greatest similarity to SMT1 of the green alga, Chlamydomonas reinhardtii. However, homologues to other species, mostly green plant species, were also found. Further, the method used for identification suggested that the sequences were transferred to a genetic compartment other than the likely original location, the nucleomorph nucleus.

Ionic and covalent derivatives of the chlorine analogue of the nonbasic, weakly coordinating triflate ion, Cl3CSO3(-) or "trichlate" ion, have been prepared and compared with the corresponding more strongly coordinated chloroacetates, Cl(x)CH(3-x)CO(2)M (x = 1-3), using 35Cl NQR (nuclear quadrupole resonance) spectroscopy. The (35)Cl NQR frequencies of all types of derivatives are sensitive to the nature of the metal ion or Lewis acid and are most sensitive in the case of monochloroacetates. In covalent (including zirconocene) derivatives, the average NQR frequencies fall as the Pauling electronegativity of M falls. The results for ionic derivatives contrast with previous results for ionic hexachlorometalates: the average (35)Cl NQR frequencies drop sharply as the ionic radius of the group 1 cation increases. Ab initio Gaussian 98 computations at the B3LYP/6-311++G(3df,3pd) level on isolated XCH2CO2M (M = Li, Na, K; X = F, Cl) molecules duplicate this trend, showing increasing polarization of the C-Cl bond and smaller electric field gradients for larger group 1 ions; the relevance of this to the solid state polymerization of chloroacetates (Herzberg, O.; Epple, M. Eur. J. Inorg. Chem. 2001, 1395-1406) is discussed. We have prepared the dihydrate and monohydrate of trichlic acid, Cl3CSO3H. Although trichlates have the highest average NQR frequencies of any of these salts, the NQR frequencies of trichlic acid dihydrate are anomalously lower than those of trichloroacetic acid, which suggests that it is a strong acid, ionized in the solid state to H5O2+ and Cl3CSO3(-) ions.