Search results for "Adduct"

Influence of DNA Repair on Nonlinear Dose-Responses for Mutation

2013

Recent evidence has challenged the default assumption that all DNA-reactive alkylating agents exhibit a linear dose-response. Emerging evidence suggests that the model alkylating agents methyl- and ethylmethanesulfonate and methylnitrosourea (MNU) and ethylnitrosourea observe a nonlinear dose-response with a no observed genotoxic effect level (NOGEL). Follow-up mechanistic studies are essential to understand the mechanism of cellular tolerance and biological relevance of such NOGELs. MNU is one of the most mutagenic simple alkylators. Therefore, understanding the mechanism of mutation induction, following low-dose MNU treatment, sets precedence for weaker mutagenic alkylating agents. Here, …

Organocatalytic enantioselective aminoalkylation of pyrazol-3-ones with aldimines generated in situ from α-amido sulfones

2019

Herein, an efficient asymmetric aminoalkylation of pyrazolones with α-amido sulfones catalyzed by a quinine-derived squaramide in dichloromethane/aqueous media has been established. A variety of chiral amines were obtained with high yields (up to 98%) and excellent enantioselectivities (up to 99% ee). The corresponding products are transformed into optically active acetylated pyrazoles after treatment with Ac2O/Et3N, because of the instability of some adducts. The reaction tolerates a wide range of α-amido sulfones and different pyrazolones.

Styrene Metabolism, Genotoxicity, and Potential Carcinogenicity

2006

This report reviews styrene biotransformation, including minor metabolic routes, and relates metabolism to the genotoxic effects and possible styrene-related carcinogenicity. Styrene is shown to require metabolic activation in order to become notably genotoxic and styrene 7,8-oxide is shown to contribute quantitatively by far the most (in humans more than 95%) to the genotoxicity of styrene, while minor ring oxidation products are also shown to contribute to local toxicities, especially in the respiratory system. Individual susceptibility depending on metabolism polymorphisms and individual DNA repair capacity as well as the dependence of the nonlinearity of the dose-response relationships …

Study of a medium-size biological molecular association by means of a pair potential semiempirical approach: β-carboline-lumiflavin

1985

The molecular association between some substituted β-carbolines and a model flavin, lumiflavin, has been studied by means of a semiempirical approach proposed by Fraga based on a 1/R expansion of atom-atom pair potentials. Only stacked minima have been considered because of their possible biological interest. The calculations characterize 15 different minimum stacked conformations, most of them occurring in the complexes considered. The structural and energetic effects of 1–Me, 6–OH and 7–OH substituents of β-carboline are discussed. An equilibrium conformation involving geometric overlap between the pteridinic portion of flavin and the indole group of β-carboline is predicted to be the mos…

Probing cluster structures with sensor molecules: methanol adsorbed onto gold clusters

1998

Abstract Structural, dynamical and electronic properties of the adducts formed by adsorbing methanol onto size-selected gold clusters are investigated using infrared multiple-photon dissociation spectroscopy of trapped Au n + CH 3 OH, n ⩽15, in conjunction with Car–Parrinello calculations. The C–O stretching vibration of the attached sensor molecule changes discontinuously as a function of cluster size, which is traced back to a change in dimensionality of the cluster structure.

Complexes of organometallic compounds. XLVI. Synthesis of adducts formed by organotin(IV) trichlorides with 1,2-bis(diphenylphosphino)ethane, and the…

1977

Abstract Adducts between RSnCl 3 (R = Me, Bu n , Oct n , Ph) and 1,2-bisz(diphenylphosphino)ethane, DPE, have 1:1 composition. In Mossbauer spectroscopic experiences at variable absorber temperature the area under the resonant peaks, A, has been measured for RSnCl 3 ·DPE, R = Me, Ph; slopes plots of in A vs. T suggest strong coupling between Mossbauer atoms, which has been interpreted in terms of solid state polymeric structures, due to DPE acting as a bridging bis-monodentate ligand. Infrared data indicate the covalency of SnCl bonds. Three possible structural isomers of octahedral type are then proposed, one having trans -P 2 and two cis -P 2 atoms. A choice between these structures has …

Molecular and Crystal Structures of TeCl4-Allylalcohol and -Allylacetate Adducts

2001

Molecular structure of Te(OMe)4.ClTe(OMe)3, a model for ligand exchange between Te(IV) centers.

2001

ClTe(OiPr)3 could be prepared from stoichiometric amounts of TeCl4 and Te(OiPr)4, a reaction that requires the exchange of ligands between different Te centers. Ligand redistribution between telluranes was studied, and rapid exchange of -Cl and -OR (R = Me, iPr) ligands in solutions of several binary mixtures of Te(OMe)4, Te(OiPr)4, ClTe(OMe)3, and ClTe(OMe)3, and ClTe(OiPr)3 was established by multinuclear NMR spectroscopy. The solid-state structure of Te(OMe)4.ClTe(OMe)3, the first structurally characterized adduct between different telluranes, was investigated by single-crystal X-ray diffraction. It exhibits a very short Te-O...Te bridge between the two Te centers and additional Te...O a…

Infrared and Mössbauer studies on adducts R3SnOH · R3MX (M = Sn, Pb; X = Pseudohalide)

1975

Abstract The synthesis of the solid adducts Me3SnOH · Me3 SnNCO, Me3SnOH · Me3SnNCS, Me3SnOH · Me3PbN3, Ph3SnOH · Ph3SnN3 is reported. The compounds have been investigated by infrared and Mossbauer spectroscopy. Their structure probably consists of polymeric OH-R3Sn-X-R3Sn(Pb) chains in which hydroxyl and pseudohalide (X) groups are bridging pentacoordinate tin atoms. In contrast to the triphenyl compound, the trimethyl derivatives show evidence of hydrogen bonding between adjacent chains.

Di‐ and Trivalent Ytterbium Complexes Containing Linked Amino‐ and Amidocyclopentadienyl Ligands

2003

Reactions of the aminocyclopentadienes (C5Me4H)SiMe2NHR (R = Et, allyl, nPr, tBu) with [YbI2(THF)2] in the presence of two equivalents of potassium 1,2-diphenylethenide in THF at room temperature gave the diamagnetic half-sandwich complexes [Yb(η5-C5Me4SiMe2NHR)Ln(μ-I)]2 (L = THF, n = 2, L = DME, n = 1). The tert-butylamido derivative [Yb(η5-C5Me4SiMe2NHtBu)(THF)2(μ-I)]2 was characterized by X-ray structural analysis as a dinuclear complex containing a nonchelating aminocyclopentadienyl ligand. Deprotonation of the aminocyclopentadiene (C5H4tBu)SiMe2NHtBu with two equivalents of potassium 1,2-diphenylethenide in THF, followed by reaction with [YbI2(THF)2] at 60 °C, gave the trivalent ytterb…