Search results for "race."
showing 10 items of 4442 documents
New tracer compounds for secondary organic aerosol formation from β-caryophyllene oxidation
2013
Abstract Five products from β-caryophyllene oxidation (β-caryophyllonic acid (I), 3,3-dimethyl-2-(3-oxobutyl)cyclobutanecarboxylic acid (βCA198) (II), β-nocaryophyllonic acid (III), β-caryophyllinic acid (IV), and 2-(2-carboxyethyl)-3,3-dimethylcyclobutanecarboxylic acid (βCA200) (V)) were synthesized and their structures confirmed by nuclear magnetic resonance spectroscopy. Reaction chamber experiments with β-caryophyllene at two different ozone mixing ratios were performed and the carboxylic acid oxidation products in the particle phase were characterized by APCI–MS and HPLC–ESI–MS. All five synthesized acids were found as β-caryophyllene oxidation products in the reaction chamber aerosol…
Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)
2012
Chirality can have a decisive influence on the molecular structure formation upon self-assembly on surfaces. In this paper, we study the structures formed by enantiopure (M)-heptahelicene-2-carboxylic acid ((M)-[7]HCA) on the calcite (10 (1) over bar4) cleavage plane under ultrahigh vacuum conditions. Previous noncontact atomic force microscopy studies have revealed that the racemic mixture of (M)-[7]HCA and (P)-[7]FICA (1:1) self-assembles into well-defined molecular double rows that are oriented along the calcite [01 (1) over bar0] direction. Here, we investigate the enantiopure (M)[7]HCA compound, resulting in distinctly different molecular structures upon deposition onto calcite (10 (1)…
A molecular electron density theory study of the mechanism, chemo- and stereoselectivity of the epoxidation reaction of R -carvone with peracetic acid
2019
The epoxidation reaction of R-carvone 8 with peracetic acid 9 has been studied within the molecular electron density theory at the B3LYP/6-311(d,p) computational level. The chemo- and stereoisomeric reaction paths involving the two C–C double bonds of R-carvone 8 have been studied. DFT calculations account for the high chemoselectivity involving the C–C double bond of the isopropenyl group and the low diastereoselectivity, in complete agreement with the experimental outcomes. The Baeyer–Villiger reaction involving the carbonyl group of R-carvone 8 has also been analysed. A bonding evolution theory analysis of the epoxidation reaction shows the complexity of the bonding cha…
Relationships Between Dimorphism, Cell Wall Structure, and Surface Activities in Candida albicans
1991
Most cells are covered with a complex network of interacting molecules that form the extracellular matrix. These molecules (proteins and polysaccharides) are secreted locally and interact among themselves to form an organized structure outside the cell plasma membrane. In unicellular eukaryotic organisms and plant cells, this structure is reinforced to withstand osmotic changes in the external environment, giving rise to the so-called cell wall.
Organo-phosphorus compounds—LXVI
1970
Abstract The recemization kinetics of (+)-methyl-n-propylphenylphosphine were studied in several solvents of widely varying polarity. The recemization followed first order kinetics in every solvent with approximately equal activation energies of 30 ±3 kcal/mole. The rate of racemization showed no dependence on solvent polarity and could not be correlated with any known solvent parameters. The unusually slow racemization in caproic acid and in tributyl borate were attributed to partial salt and adduct formation respectively.
On the Occurrence of Caffeoyltartronic Acid and Other Phenolics in Chondrilla juncea
1993
Abstract Caffeoyltartronic acid and other eleven phenolic com pounds were identified in the MeOH extract of Chondrilla juncea: the flavonoids luteolin, luteolin-7-glucoside, luteolin-7-galactosylglucuronide and quercetin-3-galactoside; the phenolic acids protocatechuic, caffeic, chlorogenic, isochlorogenic and isoferulic and the coumarins cichoriin and aesculetin. The taxonomic im plications of these com pounds have been discussed.
A micellar liquid chromatographic method for quality control of pharmaceutical preparations containing tricyclic antidepressants
2002
Micellar liquid chromatography methods for quality control of pharmaceutical preparations (capsules, pills, tablets, injections) containing the tricyclic antidepressants amineptine, amitriptiline, clomipramine, doxepin, imipramine, melitracen and nortriptyline alone or together with other CNS drugs like diazepam, medazepam and perphenazine are described. The methods using micellar solutions of cetyltrimethylammonium bromide as mobile phases and UV detection are rapid and reproducible. Due to the versatility of interactions in micellar liquid chromatography, it is possible determine highly hydrophobic compounds such as TCAs in a short time using mobile phases containing low organic solvent c…
Novel, potent calmodulin antagonists derived from an all-dhexapeptide combinatorial library that inhibitin vivocell proliferation: activity and struc…
2000
: Calmodulin is known to bind to various amphipathic helical peptide sequences, and the calmodulin–peptide binding surface has been shown to be remarkably tolerant sterically. d-Amino acid peptides, therefore, represent potential non-hydrolysable intracellular antagonists of calmodulin. In the present study, synthetic combinatorial libraries have been used to develop novel d-amino acid hexapeptide antagonists to calmodulin-regulated phosphodiesterase activity. Five hexapeptides were identified from a library containing over 52 million sequences. These peptides inhibited cell proliferation both in cell culture using normal rat kidney cells and by injection via the femoral vein following part…
Assays of Proteasome-Dependent Cleavage Products
2005
The degradation of misfolded, aged, or no longer needed cytosolic proteins depends largely on the ubiquitin-proteasome system. Proteasomes degrade their substrates into fragments of 3-20 amino acids. Human 20S proteasomes can be purified from human erythrocytes by batch adsorption to DEAE-cellulose, ammonium sulfate precipitation, anion-exchange fast protein liquid chromatography (FPLC), and glycerol density gradient ultracentrifugation. 20S proteasomes purified by this method are suitable for the in vitro digestion of synthetic peptides as well as full-length proteins. The degradation products produced by proteasomes are separated by reversed-phase HPLC using an acetonitrile gradient. The …
1990
The determination of average molecular weights and the characterization of molecular weight distributions by the ratio of the weight- to number-average molecular weights Mw/Mn from sedimentation equilibrium in the ultracentrifuge are described. The essential measurement of the density profile of the mixed solvent is conducted according to Munk (Macromolecules15, 500 (1982)). Special evaluation of the polymer band in the equilibrium allowed to deduce from the observed concentration profile Mw and Mn of a series of poly(methyl methacrylate) samples and thus to characterize the molecular weight distribution of the samples.