Breakup of 42 MeV 7Li projectiles in the fields of 12C and 197Au nuclei

Inclusive cross sections of α particles and tritons from the breakup of 42 MeV ⁷Li by ¹²C and ¹⁹⁷Au targets are presented and analysed in the framework of the Serber model. Spectral distortions due to the targets and relevant reaction mechanisms are discussed.     

3-amino-1,2,4-benzotriazine 4-oxide: characterization of a new metabolite arising from bioreductive processing of the antitumor agent 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine).

Tirapazamine (1) is a promising antitumor agent that selectively causes DNA damage in hypoxic tumor cells, following one-electron bioreductive activation. Surprisingly, after more than 10 years of study, the products arising from bioreductive metabolism of tirapazamine have not been completely characterized. The two previously characterized metabolites are 3-amino-1,2,4-benzotriazine 1-oxide (3) and 3-amino-1,2,4-benzotriazine (5). In this work, 3-amino-1,2,4-benzotriazine 4-oxide (4) is identified for the first time as a product resulting from one-electron activation of the antitumor agent tirapazamine by the enzymes xanthine/xanthine oxidase and NADPH:cytochrome P450 oxidoreductase. As part of this work, the novel N-oxide (4) was unambiguously synthesized and characterized using NMR spectroscopy, UV-vis spectroscopy, LC/MS, and X-ray crystallography. Under conditions where the parent drug tirapazamine is enzymatically activated, the metabolite 4 is produced but readily undergoes further reduction to the benzotriazine (5). Thus, under circumstances where extensive reductive metabolism occurs, the yield of the 4-oxide (4) decreases. In contrast, the isomeric two-electron reduction product 3-amino-1,2,4-benzotriazine 1-oxide (3) does not readily undergo enzymatic reduction and, therefore, is found as a major bioreductive metabolite under all conditions. Finally, the ability of the 4-oxide metabolite (4) to participate in tirapazamine-mediated DNA damage is considered.     

Thiochromenone-Annelated Heterocycles: Regioselective Synthesis of Furo[3,2-b]-thiochromen-9-ones

Summary.  A number of hitherto unreported furo[3,2-b]thiochromenone derivatives were regioselectively synthesized in good yields starting from 3-allyloxy-thiochromenones. Received September 18, 2000. Accepted (revised) November 15, 2000     

An Audio Analogy To FT-NMR and FT-IR Spectroscopy

The principles behind the operation of a nuclear magnetic resonance spectrometer and an infrared spectrophotometer were fairly easy to explain to students fifteen years ago. As NMR and IR instruments became FTIR and FTNMR instruments, students understanding of these important chemical tools became vague to nonexistent. Furthermore, the task of a teacher to explain them to the students became more difficult. The audiofrequency analogy presented here is offered as a plausible technique for presenting these difficult ideas to chemistry students.     

A genetic algorithm for the structural optimization of Morse clusters

This article describes the application of a genetic algorithm for the structural optimization of 19–50-atom clusters bound by medium-range and short-range Morse pair potentials. The GA is found to be efficient and reliable for finding the geometries corresponding to the previously published global minima [Doye JPK, Wales DJ (1997) J Chem Soc Faraday Trans 93: 4233]. Using the genetic algorithm, only a relatively small number of energy evaluations and minimizations are required to find the global minima. By contrast, a simple random search algorithm often cannot find the global minima of the larger clusters, even after many thousands of searches. Received: 27 October 1999 / Accepted: 7 December 1999 / Published online: 19 April 2000     

Caractérisation spectrale de la forme de Jordan

Soit , où désigne l'ensemble des matrices n×n à coefficients complexes. Nous montrons qu'on peut complètement caractériser la forme de Jordan de A en examinant le polynôme caractéristique de tA+X pour tous les tC et tous les . Ceci nous permet de donner une démonstration plus élémentaire d'un théorème de Baribeau et Ransford sur les transformations holomorphes de qui préservent le spectre.

Denote by the set of complex n×n matrices, and let . We give a variational, purely spectral characterization of the Jordan form of A by examining the characteristic polynomial of the perturbed matrices tA+X for tC and . This allows us to give a more elementary proof of a theorem of Baribeau and Ransford on spectrum-preserving holomorphic maps on .     

Reactions of cyclopalladated azobenzenes with xanthates and dithiocarbamates. Spectral characterisation and electrochemical studies of the products

Binuclear chloro-bridged cyclopalladated azobenzenes [Pd(A)Cl]₂ (A = ortho-metallated azobenzene or its derivatives) have been reacted with aqueous AgNO₃ to yield aquo-derivatives followed by the addition of xanthates, or dithiocarbamates (RCS₂ ^–) to synthesise ternary complexes, [Pd(A)(RCS₂)]. These complexes occur as configurational isomers and their compositions have been established by ¹H-n.m.r. spectroscopy. Cyclic voltammetric studies show azo reduction at negative and thiol oxidation at positive potentials relative to s.c.e., respectively. Dissociation of RCS₂ ^– under the electrode field is chemically supported by using a sulfide extractor, HgCl₂, Hg(OAc)₂, or AgOAc, to precipitate out the binuclear [Pd(A)Cl]₂/[Pd(A)(OAc)]₂ complexes.     

The synthesis of novel nonclassical reversed bridge quinazoline antifolates as inhibitors of thymidylate synthase

2‐Amino‐6‐methyl‐5‐(pyridin‐4‐ylsulfanyl)‐3H‐quinazolin‐4‐one ( 3 , AG337) a lipophilic thymidylate synthase inhibitor, is currently in clinical trials as an antitumor agent. On the basis of the crystal structure of 3 and the classical inhibitor 10‐propargyl‐5,8‐dideazafolic acid ( 1 , PDDF) with thymidylate synthase, we designed and synthesized a series of nonclassical 2‐amino‐6‐substituted‐3H‐quinazolin‐4‐ones 4–13 , with a variety of electron withdrawing groups in the side chain (with the exception of compound 4 ). Molecular modeling indicates that these reversed bridge (N9–C10) 6‐substituted analogues orient their side chain C10‐substituent such that it lies between that of 1 and 3 . These compounds were obtained by reduc tive amination of 6‐aminoquinazoline 16 and the appropriate aryl aldehyde 17 or aryl ketone 18 . For ana logues 11–13 , the yield depended on the substitutents on the aryl ketone 18 (comparison of 11 and 13 ). With the exception of analogue 13 , all the compounds in the series were poor inhibitors of thymidylate synthase from Lactobacillus casei, Pneumocystis carinii and human sources.     

Self-Assembled Nanofibrillar Aggregates with Amphiphilic and Lipophilic Molecules

Summary: This article gives a review on self-assembled nanofibrillar aggregates such as helical, twisted ribbon-like and tubular forms, those are produced in aqueous bilayer membrane and organogel systems. Two common features necessary for the chemical structure that yields special morphology are a chiral carbon atom and moieties feasible for intermolecular interactions although there are some exceptions. In aqueous systems, a hydrophobic effect is also an essential driving force for molecular aggregates in aqueous solution systems but almost disappear in organic media. More positive intermolecular interactions play an important role in molecular aggregation in organic media. Hydrogen bonding interaction is especially effective and many organogelators are classified into this category. Some lipophilic peptides have been investigated not only as organogelators but also with respect to their self-assembling behaviors. This latter property gives them distinct advantages compared with conventional gel systems because the gels include highly-ordered structures supramolecular functions like aqueous lipid membranes through molecular orientation. This article also introduces applicability of the organogel system.     

Dimensional reduction of a piezoelectric composite rod

In the present paper, a new generalized Timoshenko model is constructed for a composite rod with embedded or attached piezoelectric materials. This model is applicable to composite rods without prescribed electric potential along the lateral surfaces. The Variational-Asymptotic Method (VAM) is applied as a mathematical tool to carry out the dimensional reduction process. The present reduced model captured the effects of dielectric as well as the polarization of the piezoelectric material, which justifies its coupled electromechanical nature. First, the three-dimensional electromechanical enthalpy is asymptotically approximated by VAM using the slenderness of the rod as the small parameter and subsequently an equivalent one-dimensional electromechanical enthalpy is developed. Energy terms, which are asymptotically correct up to the second order are kept in the approximate enthalpy expression. For engineering applications, the approximate enthalpy is then transformed into a generalized Timoshenko model which has the traditional six mechanical degrees of freedom along with an extra one-dimensional electric degree of freedom.