Photoaffinity labeling of bovine rhodopsin

Photoaffinity labeled (3-diazoacetoxy)-9-cis-retinal (1) and (9-methylenediazoacetoxy)-9-cis-retinal (20) were synthesized and bound to absorption maxima at 465 and 460 nm respectively. Binding studies established that synthetic retinals 1 and 2 bind to the natural binding site and that the integrity of the diazoacetoxy photoaffinity label is preserved in the process. Incorporation of 3-(O¹⁴COCHN₂)-labeled 9-cis retinal could be conveniently carried out in high yield using apomembrane solubilized in CHAPS as detergent to afford the pigment analog in a pure form. Photolysis of the diazoacetoxy group within the binding site led to 15–20%, crosslinking of rhodopsin as estimated by using radiocarbon containing labeled retinal 1 thus showing that this synthetic retinal is suitable for photoaffinity labeling of the active site in rhodopsin. Subsequent experiments to establish the site(s) of crosslinking by sequencing studies will then contribute to our knowledge of the structure of rhodopsin.     

Cumulative yields of short-lived isotopes of barium in the spontaneous fission of252Cf

Cumulative yields of short-lived/barium isotopes^{139, 141, 142}Ba have been determined in the spontaneous fission of²⁵²Cf, using fast radiochemical separation and gamma-ray spectrometry.¹⁴²Ba yield is reported for the first time. The measured cumulative yields are converted to chain yields, assuming normal charge distribution systematics for comparision with the literature data.     

Improved highly efficient synthesis of α,β-acetylenic ketones. Nature of the intermediate from the reaction of lithium acetylide with boron trifluoride etherate

A wide variety of α,β-acetylenic ketones were synthesized in very high yields via an exceptionally facile intermolecular reaction of lithium alkynyltrifluoroborates and carboxylic acid anhydrides.     

Nucleotide. XV. Synthese und Eigenschaften von 2′-O-t-Butyldimethylsilyl-5′-O-monomethoxytritylribonucleosid-3′-phosphotriestern,Ausgangssubstanzen für Oligonucleotid-Synthesen

Nucleotides. XV. Synthesis and Properties of 2′O-t-Butyldimethylsilyl-5′-O-monomethoxytritylribonucleoside-3′-phosphotriesters, Starting Materials for Oligonucleotide Syntheses The syntheses of two types of fully blocked ribonucleoside 3′-phosphotriesters 6–14 have been achieved in excellent yields from 2′-O-t-butyldimethylsilyl-5′-O-monomethoxytrityl-ribonucleosides 1–5 by phosphorylation with 2-chloro- and 2,5-dichlorophenylphosphorodichloridate respectively and subsequent treatment by cyanoethanol to 6 , 8 , 10 , 12 and 14 and by p-nitrophenylethanol to 7 , 9 , 11 and 13 . These phosphotriesters are valuable starting materials for oligonucleotide syntheses due to the fact that the corresponding phosphotriesters 15–23 with free HO? C(5′) could be obtained by detritylation and the 3′-phosphodiester triethylammonium salts 24–32 by deblocking of the cyanoethyl and the 2,5-dichlorophenyl group respectively. All newly synthesized compounds have been characterized by UV.-and NMR.-spectra as well as C, H, N elementary analyses.     

Intramolecular interactions between chalcogen atoms: organoseleniums derived from 1-bromo-4-tert-butyl-2,6-di(formyl)benzene

[structure: see text] The synthesis and characterization of a series of low-valent organoselenium compounds derived from 1-bromo-4-tert-butyl-2,6-di(formyl)benzene (22) is described. The synthesis of diselenide 25 was achieved by the lithiation route whereas bis(4-tert-butyl-2,6-di(formyl)phenyl) diselenide (26) was synthesized by treating 22 with disodium diselenide. A series of monoselenides (27, 28, and 29) was obtained by facile nucleophilic substitution of bromine in 22, using the corresponding selenolates as nucleophiles. The halogenation reactions of bis(4-tert-butyl-2,6-di(formyl)phenyl) diselenide (26) did not afford the corresponding selenenyl halides but resulted in the isolation of an unexpected cyclic selenenate ester 34 as a product. The selenide 32 was synthesized by the treatment of dimethoxymethyl diselenide with trilithiated 2-bromo-5-tert-butyl-N,N'-di(phenyl)isophthalamide. The existence of potential Se...O intramolecular nonbonding interactions was examined by IR, (1)H, and (77)Se NMR spectroscopy, X-ray crystallography, and computational studies. The X-ray crystal structures of 26 and 27, having two ortho formyl groups, reveal the absence of any Se...O interactions. However, the Se...O interactions were observed in the selenenate ester 34 where one of the formyl groups has been utilized for the selenenate ring formation. The crystal structures of 26 and 27 exhibited intermolecular short-range C-H...Se interactions (hydrogen bonding). Although there are four heteroatoms in carbamoyl moieties ortho to selenium capable of forming a five-membered ring on intramolecular coordination, no such intramolecular Se...X (X = N, O) interaction was observed in the crystal structure of 32. The density functional theory calculations at the B3LYP/6-31G* level predicted that for all the diformyl systems (47a-c, 48a-c), the anti,anti conformer (when both formyl oxygen atoms point away from the selenium) is more stable. This preference was found to be reversed in the monoformyl-substituted systems (50a,b, 51a,b), where the syn conformer (when formyl oxygen is near the selenium) is energetically more favorable than the anti conformer.     

Flocculation and coalescence of droplets in oil-in-water emulsions formed with highly hydrolysed whey proteins as influenced by starch

The effects of added unmodified amylopectin starch, modified amylopectin starch and amylose starch on the formation and properties of emulsions (4 wt.% corn oil) made with an extensively hydrolysed commercial whey protein (WPH) product under a range of conditions were examined. The rate of coalescence was calculated based on the changes in the droplet size of the emulsions during storage at 20 degrees C. The rates of creaming and coalescence in emulsions containing amylopectin starches were enhanced with increasing concentration of the starches during storage for up to 7 days. At a given starch concentration, the rate of coalescence was higher in the emulsions containing modified amylopectin starch than in those containing unmodified amylopectin starch, whereas it was lowest in the emulsions containing amylose starch. All emulsions containing unmodified and modified amylopectin starches showed flocculation of oil droplets by a depletion mechanism. However, flocculation was not observed in the emulsions containing amylose starch. The extent of flocculation was considered to correlate with the rate of coalescence of oil droplets. The different rates of coalescence could be explained on the basis of the strength of the depletion potential, which was dependent on the molecular weight and the radius of gyration of the starches. At high levels of starch addition (>1.5%), the rate of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase caused by the starch.     

Supercritical fluid chromatographic analysis of polyprenols in Ginkgo biloba L

A supercritical fluid chromatographic (SFC) procedure for the quantitation of three major polyprenols present in the leaves of Ginkgo biloba was developed. In contrast to previously reported high-performance liquid chromatographic (HPLC) methods, the SFC method does not require extensive pre-purification for polyprenol analysis. The SFC analytical procedure described shows a very broad range of linearity and detects many known polyprenol isoprenologs with baseline separation. Dodecaprenol was used as the internal standard. The coefficient of variation of the method was 5.8% for the quantitation of C₈₅, C₉₀ and C₉₅ polyprenols. The SFC assay results showed that the content of polyprenols in ginkgo leaves were higher than the previously published values. In addition, the chromatogram of the highly concentrated leaf extract revealed the presence of an isoprenolog (C₁₂₀) not previously detected by HPLC methods.     

2020 Roadmap on two-dimensional nanomaterials for environmental catalysis

This roadmap demonstrates a series of two-dimensional nanomaterials, such as graphene, black phosphorus, oxides, layered double hydroxides, chalcogenides, bismuth-based layered compounds, MXenes, metal organic frameworks, covalent organic frameworks, and others, for environmental catalysis.     

Synthesis and spectral studies ofo-hydroxyacetophenone (N-benzoyl)glycyl hydrazone and some of its lanthanide(III) complexes

Summary o-Hydroxyacetophenone (N-benzoyl)glycyl hydrazone (o-HABzGH) has been characterized by i.r.,¹H n.m.r.,¹³C n.m.r. and mass spectral studies, and its complexes of the types [Ln(o-HABzGH)Cl₂(H₂O)₂]Cl and [Ln(o-HABzGH–2H)OH(H₂O)₃], where Ln=La, Pr, Nd, Sm and Eu, have been synthesized. The structures of the complexes have been studied by conductance, magnetic, electronic, i.r.,¹H n.m.r. and¹³C n.m.r. spectral techniques. The hypersensitive bands of the electronic spectra suggest coordination numbers six and seven around Nd^III in its adduct and neutral complexes respectively. I.r. and n.m.r. spectral data suggest a neutral bidentate behaviour for the ligand in the adducts and a dinegative tridentate nature in the neutral complexes.     

Photochemical and thermal transformations of carboxylic dithiocarbamic anhydrides and acyl xanthates

The reaction of diphenylchloroacetyl chloride with different dithiocarbamates gave the corresponding dithiocarbamic anhydrides. Under analogous conditions, dithiocarbamyl phenylacetic acids and dithiocarbamyl acetic acids were formed from the reaction of dithiocarbamates with phenylchloroacetyl chloride and chloroacetyl chloride, respectively. O-Ethyl S-acyl xanthates were formed from the reaction of potassium O-ethyl xanthate with diphenylacetyl chloride, diphenylchloroacetyl chloride, cyclopentylphenylacetyl chloride and triphenylacetyl chloride. Photolysis of dithiocarbamic anhydrides gave a mixture of products consisting of 1,2-dichlorotetraphenylethane, carbon monoxide and the corresponding thiocarbamoyl sulfides. Acyl xanthates, on the other hand, gave carbon monoxide and the corresponding substituted ethane derivatives. When dithiocarbamic anhydrides were refluxed in hydroxylic solvents such as methanol, ethanol and n-propanol, the corresponding dithiocarbamyl acetates were formed. Thermal decomposition of acyl xanthates gave carbon disulfide and the corresponding esters.