Search results for "Perch"
showing 10 items of 1084 documents
EFFECTS OF SENSITIZED AND UNSENSITIZED LONGWAVE U.V.-IRRADIATION ON THE SOLUTION PROPERTIES OF DNA
1971
— Two types of photoreactions occur in DNA irradiated in aqueous systems with longwave u.v.-light (Λ > 295 nm), namely, (a) thymine dimerization, and (b) single- and double-strand breakage of the sugar phosphate backbone; these two reactions are unrelated. The presence of acetophenone as a photosensitizer caused an increase in dimerization by a factor of 16, and an increase in single-strand breaks by a factor of 4. The number of thymine dimers per single-strand break is about 100 in the sensitized and 25 in the unsensitized reaction. The alteration of the radius of gyration of DNA molecules is that expected by the degradation observed. At the same time the change in hyperchromicity is very …
Complexation of planar, organic, five-membered cations with crown ethers
2000
Complexation of six aromatic, nitrogen-containing cations with various crown ethers has been studied using 1H NMR, mass spectrometric and crystallographic methods. Hydrogen bonding appears to be the most important interaction in complexation, but minor effects such as π-stacking or cation–π interactions have also been observed. The stability constants of five different imidazolium perchlorate ·crown ether complexes and five other similar cation·DB18C6 complexes were determined by 1H NMR titration in acetonitrile solution. The stability of these complexes in solution and in the gas phase is discussed. The crystal structures of seven complexes were determined in order to study complexation in…
Homochiral self-assembly of biocoordination polymers: anion-triggered helicity and absolute configuration inversion
2015
The different natures of the weakly coordinating anions – triflate or perchlorate – in the Cu2+-mediated self-assembly of cytidine monophosphate nucleotide play a fundamental role in the homochiral resolution process, yielding one-dimensional copper(II) coordination polymers of opposite helicity that can be easily inverted, in a reversible way, by changing the nature of the anion as revealed by circular dichroism experiments both in solution and in the solid state.
Crystal structure of copper(II) cimetidine sulphate nonahydrate. Cation distortion and structure isomerism in three copper(II) cimetidine complexes
1988
Abstract In the crystalline state, the complex [Cu(CM) 2 ]SO 4 ·9H 2 O (CM = cimetidine) is constituted of two-dimensional cations[Cu(CM) 2 2+ ] n separated by SO 4 2− anions and water molecules. As in the related complexes [Cu(CM) 2 ](ClO 4 ) 2 and [Cu(CM) 2 ](NO 3 ) 2 , the copper atom lies in a strongly distorted octahedral CuN 4 S 2 environment. The distortion is quite different from one complex to another (cation distortion isomerism). In the title compound the CuS bond is unusually long (2.91 A). Unlike the title compound, the [Cu(CM) 2 2+ ] n cations in the perchlorate and nitrate salts are one-dimensional infinite chains characterized by different conformations of the cimetidine mo…
A quantitative study of substituent effects on oxidative cyclization of some 2-aryl-substituted aldehyde thiosemicarbazones induced by ferric chlorid…
1999
As a development of our previous work, we performed a kinetic study of the oxidative cyclization reaction of some 2,4-diaryl-substituted aldehyde thiosemicarbazones 1a-n induced by ferric chloride and by cupric perchlorate. The results of cyclization of 1a-n were compared to those of the corresponding 2-methyl derivatives. The kinetic data were analyzed by means of the Hammett's equation.
Ion pair association in isodielectric mixtures at 25�C
1974
Conductance measurements of potassium perchlorate and iodide have been carried out on the following mixtures: methanol-ethylene carbonate, acetone-ethylene carbonate, acetonitrile-ethylene carbonate, sulfolane-ethylene carbonate, isodielectric with water; and in benzene-sulfolane, benzene-acetonitrile, ethanol-sulfolane, isodielectric with methanol. The extent of ionic association at a given concentration in two solvents of the same dielectric constant is greater in the aprotic solvent.
Influence of solvent structure on ion pair association: The conductance of potassium perchlorate in ethylene carbonate-acetonitrile mixtures at 25�C
1974
The conductance of potassium perchlorate in mixtures of ethylene carbonate and acetonitrile covering the range 82.6 ≥ D ≥ 36.0 in dielectric constant has been measured. The Walden products in these aprotic solvents are approximately one-half as large as the products for the same salt in isodielectric mixtures of water and tetramethylene sulfone. This alters the distribution between electrostatic and hydrodynamic terms in the theoretical conductance function in such a way that the calculated association constants for potassium perchlorate are much smaller in the aprotic mixtures.
Selenoproteins, cholesterol-lowering drugs, and the consequences: revisiting of the mevalonate pathway.
2004
3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) and peroxisome proliferator-activated receptor alpha activators (fibrates) are the backbone of pharmacologic hypercholesterolemia and dyslipidemia treatment. Many of their clinical effects, however, are still enigmatic. This article describes how a side road of the mevalonate pathway, characterized in recent years, can rationalize a major fraction of these unexplained observations. This side road is the enzymatic isopentenylation of selenocysteine-tRNA([Ser]Sec) (Sec-tRNA), the singular tRNA to decode the unusual amino acid selenocysteine. The functionally indispensable isopentenylation of Sec-tRNA requires a unique interm…
Alkyl and Aryl Substituted Corroles. 1. Synthesis and Characterization of Free Base and Cobalt Containing Derivatives. X-ray Structure of (Me4Ph5Cor)…
2001
The synthesis, spectroscopic properties, and electrochemistry of six different alkyl- and aryl-substituted Co(III) corroles are presented. The investigated compounds contain methyl, ethyl, phenyl, or substituted phenyl groups at the eight β-positions of the corrole macrocycle and four derivatives also contain a phenyl group at the 10-meso position of the macrocycle. Each cobalt corrole undergoes four reversible oxidations in CH2Cl2 containing 0.1 M tetra-n-butylammonium perchlorate and exists as a dimer in its singly and doubly oxidized forms. The difference in potential between the first two oxidations is associated with the degree of interaction between the two corrole units of the dimer …
Synthesis, properties and crystal structure of an N-cyano-N′-methyl-N″-[2-{(5-methyl-1H-imidazol-4-yl)-methylthio}ethyl]guanidi
1985
Abstract A Cu(II) complex has been prepared with N-cyano-N′-methyl-N′'-[2-{(5-methyl-1H-imidazol-4-yl)-methylthio}ethyl]guanidine, cimet