Oxo-tricyano complexes of molybdenum(IV) and tungsten(IV) with bidentate Schiff bases

Summary The reaction of [M(CN)₄O(OH₂)]^2– (M = Mo or W) with 2-acetylpyridine and methyl-or butyl-amine in a water-MeOH mixture gave [M(CN)₃O(L-L)]^- (L-L= Schiff base ligand), isolated as [AsPh₄]⁺ salts. The complexes have been characterized by elemental analysis, and electronic, i.r. and¹H-n.m.r. spectroscopy. The Schiff base ligands complex in a bidentate manner through the two nitrogen atoms giving mixed-ligand compounds similarly to 2,2-bipyridyl or 1,10-phenanthroline.On leave from the Faculty of Chemistry, Jagiellonian University, Kraków.     

Mercurimetric determination of chloride with diphenylcarbazide disodium disulfonate as an indicator

A procedure is given for the use of diphenylcarbazide disodium disulfonate as an indicator in the direct titration of chloride with mercuric nitrate. By adding ferric nitrate to form the carbazone and an inert green substance to serve as a color screen, a sharp and reversible endpoint changing from green to grey to purple is obtained. Studies were made on the indicator reaction and other factors, such as mercuric chloride concentration, pH, volume, temperature and the effect of various added salts. The pH must be adjusted to 1.8 to 2.0 for best results. A series of ten determinations on a sample gave a standard deviation of ±0.16 part per thousand.     

Conformational flexibility of ribosomal decoding-site RNA monitored by fluorescent pteridine base analogues

Conformational transitions in ribosomal decoding-site RNA have previously been monitored by replacement of flexible adenine bases with fluorescent 2-aminopurine (2AP). Here, we have studied pteridine base analogues 3-methylisoxanthopterin (3MI) and 6-methylisoxanthopterin (6MI) as fluorescent labels for the investigation of conformational changes in the decoding site that are triggered by ligand binding. The higher quantum yield of 3MI and 6MI along with their relatively red-shifted excitation and emission wavelengths renders the pteridines interesting alternatives to 2AP for the establishment of ligand-binding assays for RNA based on fluorescence labelling.     

Alexander Naumovich Frumkin*

Russian Journal of Electrochemistry -     

Photosensitization of the sunscreen octyl p-dimethylaminobenzoate by UVA in human melanocytes but not in keratinocytes.

Sunscreens penetrate human epidermis and modify the biology of proliferating cells. This study addressed the question whether the UV response of cultured human cells is affected by direct treatment with nontoxic levels of sunscreens. Cell survival following exposure to UVC or unfiltered UBV was not altered by preincubation with 25 micrograms/mL of octyl p-dimethylaminobenzoate (o-PABA), 2-ethylhexyl p-methoxycinnamate (EHMC) or oxybenzone. However, UVA or UVB filtered to reproduce the solar UV spectrum penetrating to the basal layer of the epidermis, highly sensitized cells to killing by o-PABA but not by its hydrolysis product, 4-dimethylaminobenzoic acid. Sensitization was found in all cell types tested, except normal keratinocytes, and could be prevented by certain antioxidants particularly pyruvate and the hydroxyl radical scavenger mannitol. o-PABA and EHMC applied without UV reduced the adherence of cells. The results indicate that sunscreens may increase cell mobility and the combination of o-PABA with solar UV may selectively damage melanocytes in the skin.     

Tris-[3-hydroxy-1,2-dimethyl-pyridin-4(1H)-onato]cobalt(III)

The preparation and properties of tris-[3-hydroxy-1,2-dimethyl-pyridin-4(1H)-onato]cobalt(III) are described. The structure of the fac isomer has been established by X-ray diffraction techniques. Solvation characteristics of this complex have been assessed through solubility measurements in methanol–water mixtures. The complex is very inert in neutral solution but undergoes acid-catalysed aquation at lower pHs.