Intraframework potential energy function of zeolites

Potential energy functions suitable for the (Cs_1–xNa_xT₂O₄)-A type zeolite family were obtained from the known crystal structure of Cs₇Na₅-A zeolite. Using these potential functions, several other crystal structures in these family were obtained by molecular mechanical calculations. The activation energy - to -cage transmission of the H₂ molecule and the void volume of Cs₃Na₉-A zeolite were calculated.     

应用分子图形学、分子力学、量子化学及静电势研究农药分子结构与性能关系(X)──磺酰脲分子内旋转通道的分子力学研究

磺酞豚分子是一类极其重要的低毒超高效除草剂，有着十分重要的用途．研究分子的空间结构对于了解分子的构效关系十分重要．最近，我们测定的一系列分子的晶体结构［‘－’1表明，分子1、2、3晶体结构的空间群分别为PZ；儿、Pz、Pz，说明晶体中分别有对称元素（对称面或者对称中心），分子以对映体的形式存在于晶体中．由于磺酸豚分子本身不存在手性原子，由此推断磺酷服分子在晶体中存在的对映异构体是由内旋转阻碍产生的，因而应是构象异构体．本项研究工作的目的是应用分子力学方法，计算阻碍内旋转的能垒，从而找出分子内旋转时的最低…     

MECHANICS AND THE EVOLUTION AND FUNCTIONAL MORPHOLOGY OF CONCHOSTRACAN CARAPACE MECHANICS AND THE EVOLUTION AND FUNCTIONAL MORPHOLOGY OF CONCHOSTRACAN CARAPACE

Conchostracans, with a laterally compressed body enclosed between two symmetric valves, live swimming in fresh or brackish water. The carapace valve has a number of growth bands with various sculptures. The general trend of sculptural evolution is from smooth to punctate-minute polygon-medium reticulation-large reticulation, while these punctate, polygonal and various reticulate patterns may separately develop into various radial ridges. The development of sculpture can be well explained by mechanical principle. Functional morphology of carapace is discussed in the light of mechanics in this paper.     

STEREOCHEMISTRY OF (R)-2-METHYLAZIRIDINE COMPLEXES OF COBALT(III) AND DIMERIZATION OF THE LIGAND

Abstract

A cobalt(III) complex containing (R)-2-methylaziridine (R-meaz), [Co(R-meaz)(NH₃)₅]³⁺, was prepared and the two diastereomers arising from the presence of the chiral nitrogen atom (N(R) and N(S)) were separated by column chromatography. Molecular mechanics calculations estimated the N(R)-isomer to be more stable. This result was supported by the x-ray structure determination of the more abundant (ca. 94%) isomer, N(R)-[Co(R-meaz)(NH₃)₅]Br₃H₂O. Crystal data: monoclinic, P2₁, a = 7.357(1), b = 9.780(1), c = 10.426(1) Å, μ = 93.58(1)°, V= 748.7(3) ų, Z= 2. Kinetic studies of isomerization (epimerization) between the two isomers revealed that inversion at the nitrogen center was very slow (5 × 10^?2 M^?1 S^?1at 25 °C). The small rate constant seems to be related to the strained three-membered structure of the meaz ligand. The reaction of Na₃[Co(N0₂)6] and R-meaz yielded a complex containing two dimerized R-meaz chelates, trans-[Co(NO₂)2(di-R-meaz)₂] (di-R-meaz =RR)-α,2-dimethyl-l-aziridineethanamine). The crystal strucrure of trans-[Co(NO₂)₂ (di-R-meaz)₂]C1O₄H₂O was established by x-ray crystallography. Crystal data: orthorhombic, P2₁2₁2₁, a = 11.784(6), b = 21.023(9), c = 8.608(7) Å, V = 2133(2) ų, Z = 4.     

Percycloalkylated cyclohexanes: attempted synthesis of a trispropellane

The acid catalyzed rearrangement of two cyclohexanols of spiroannelated four-membered rings has been studied. In accordance with molecular mechanics calculations, far-reaching reorganizations with formation of unsaturated hexacyclic systems, including a fully cycloalkylated cyclohexene with a bispropellane partial structure, were observed. Attempts to convert this bispropellane to a trispropellane failed.     

Barriers to Internal Rotation and Conformational Behaviour of the MESO and D,L Isomers of Pt(II) Complexes with Antitumour Activity

Abstract

The conformational behaviour of a series of ring substituted (ortho-Cl, F and meta or para OH) Pt(II) complexes of general formula [(1,2-hydroxyphenyl)ethylenediamine]PtL₂ [L ? Cl, 1] has been studied by molecular mechanics (MM) methods. Preferred orientations of the phenyl rings, which are important for the complexes′ biological activity, were obtained by calculations of rotational energies about C_sp3?C_ar bonds for all theoretically possible isomers and conformers, meso-λ (R,S/S,R-λ), meso-δ (R,S/S,R-δ), d,l-δ (S,S/R,R-λ) and d,l-λ (S,S/R, R-δ). The influence of the ring substituents and the conformation type on the positions of the energy minima and barriers to rotations about C_sp3?C_ar and C_ar-O(H) bonds were investigated in detail. Theoretical predictions were compared with the experimental results where appropriate.     

Modeling the cluster formation during infrared and ultraviolet matrix-assisted laser desorption ionization of oligonucleotides in succinic acid matrix with molecular mechanics

A large succinic acid (HOOC(CH₂)₂COOH) matrix containing 7 × 7 × 7 unit cells with guest oligonucleotide AGCAGCT was modeled with molecular dynamics simulation for infrared matrix-assisted laser desorption ionization. We simulated the laser heating of the succinic acid (this data is still missing from the literature) with λ=2.94 μm infrared laser pulses and compared it to ultraviolet excitation. We did this in order to elucidate the cluster formation of succinic acid in the gas phase in itself and around the analyte. At this wavelength, the laser energy is coupled into the matrix through the OH vibrations of the carboxyl groups. The most pronounced difference we observed at 1,500 K simulation is that infrared heating generates about 10–15 more succinic acid molecules bound to the analyte in noncovalent complex form than the ultraviolet mode, which generates about 2 molecules thus bound. We report energy redistribution within the matrix between the host and guest species as well as other dynamical properties. The parameter and topology data for succinic acid that we used are reported and ready for use in CHARMM computer code environment for simulation. Revised: 12 October 2001 / Accepted: 27 February 2002 / Published online: 13 June 2002