Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

J. Appl. Cryst.の発刊に際して

Anion recognition chemistry has grown from its beginnings in the late 1960s with positively charged ammonium cryptand receptors for halide binding to, at the end of the millennium, a plethora of charged and neutral, cyclic and acyclic, inorganic and organic supramolecular host systems for the selective complexation, detection, and separation of anionic guest species. Solvation effects and pH values have been shown to play crucial roles in the overall anion recognition process. More recent developments include exciting advances in anion-templated syntheses and directed self-assembly, ion-pair recognition, and the function of anions in supramolecular catalysis.

Anion Recognition and Sensing: The State of the Art and Future Perspectives

介绍了Kirk—Othmer Encyclopedia of Chemical Technology（化工技术百科全书）（第五版）电子图书网络版数据库，并对该数据库使用方法和检索途径作出了说明，且结合实例简单地介绍了该数据库的检索方法。

Kirk-Othmer Encyclopedia of Chemical Technology数据库介绍及实例

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Two ligands have been synthesized by derivatisation of cyanuric chloride: 6-(diethylamino)-2,4-disulfanyl-1,3,5-triazine (H2SSta) 1 and 6-(diethylamino)-2-hydroxo-4-sulfanyl-1,3,5-triazine (H2OSta) 2 have been characterised by X-ray crystallography, which shows intermolecular hydrogen bonding in the solid state, leading to dimers of 1 and ribbons of 2. On reaction with metal salts both ligands undergo oligomerisation reactions. Compound 1 reacts with nickel chloride to form a mononuclear complex, [Ni{(Sta)S(S2ta)}] 3. In 3 two triazine ligands have reacted, to form a tetradentate ligand in which two triazine rings are bridged by a sulfur group, with a co-ordinated disulfide group present on one ring and a co-ordinated thiolate on the second. Compound 2 reacts with cobalt(II) chloride to form a cage complex, [Co6NaO(OStaH)7{S(Ota)2}2(O2CPh)2(H2O)2] 4. This complicated structure contains two polydentate ligands formed by linking triazine groups through a bridging sulfur. The cage contains four cobalt(II) and two cobalt(III) sites which are assigned by bond length considerations. The compound [Co(OSta)3] 5 co-crystallises with 4, and its structure has also been determined.

Inter-ligand reactions: in situ formation of new polydentate ligands

Dialkylammonium Ion/Crown Ether Complexes: The Forerunners of a New Family of Interlocked Molecules

The modes of action of the commercial solvent extractants used in extractive hydrometallurgy are classified according to whether the recovery process involves the transport of metal cations, Mn+, metalate anions, MXxn−, or metal salts, MXx into a water-immiscible solvent. Well-established principles of coordination chemistry provide an explanation for the remarkable strengths and selectivities shown by most of these extractants. Reagents which achieve high selectivity when transporting metal cations or metal salts into a water-immiscible solvent usually operate in the inner coordination sphere of the metal and provide donor atom types or dispositions which favour the formation of particularly stable neutral complexes that have high solubility in the hydrocarbons commonly used in recovery processes. In the extraction of metalates, the structures of the neutral assemblies formed in the water-immiscible phase are usually not well defined and the cationic reagents can be assumed to operate in the outer coordination spheres. The formation of secondary bonds in the outer sphere using, for example, electrostatic or H-bonding interactions are favoured by the low polarity of the water-immiscible solvents.

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Peter A. Tasker

Papers

Inter-ligand reactions: in situ formation of new polydentate ligands

Dialkylammonium Ion/Crown Ether Complexes: The Forerunners of a New Family of Interlocked Molecules

Solvent extraction: the coordination chemistry behind extractive metallurgy

Pseudorotaxanes Formed Between Secondary Dialkylammonium Salts and Crown Ethers

Pseudorotaxanes formed between secondary dialkylammonium salts and crown ethers