Comments on the design of chemical libraries for screening

Different representations of molecules, based ondistinct sets of properties can yield differentperspectives of the issues involved in library design.In particular, different chemical representations cangive rise to very different estimates of requiredlibrary sizes. We provide a preliminary mathematicalframework that examines the size of libraries requiredto adequately sample the spaces corresponding to somecommonly used property sets. Introduction ofconformational flexibility is also discussed as ameans of increasing coverage of chemical libraries,while at the same time considering the thermodynamicconsequences of flexibility upon detectable activity.Our theoretical analysis reveals that the propertyspaces currently in use are extremely large andunlikely to provide adequate discrimination amongcompounds.     

Emission spectra and stimulated emission characteristics of [N2]2--N2 molecular dimer

It has been proved by ab initio calculation and theoretical analysis that there exist [N2]2--N2 molecular dimers with D2h symmetry group, and there also exists an electric dipole excimer-like transition a1B2g→a1B3u. The theoretical spectra accord with the experimental results for transition a1B2g→a1B3u. The stimulated emission characteristic of N2 molecular dimer was researched through the microwave excited highly pure nitrogen and the method of amplified spontaneous emission. The experimental results show that N2 molecular dimer has stimulated emission characteristics when the microwave power is more than 100 W and the N2 pressure is in the range from 260 Pa to 2200 Pa.     

含胺基功能性单体的聚合研究 XIV.含二甲氨基丙烯酰类衍生物与过硫酸钾引发体系引发的丙烯酰胺聚合

N-(N′,N′-二甲氨基亚甲基)甲基丙烯酰胺、甲基丙烯酸N,N二甲氨基乙酯、可聚合叔胺、氧化还原引发体系、超高分子量聚丙烯酰胺     

紫外光降解-离子色谱法测定液晶材料中有机分子上的碱、碱土金属和铵

采用紫外光降解－离子色谱法测定了液晶材料中的阳离子。研究了样品光降解的条件，H2O2及酸的影响，样品基体有机物的去除，并对直接水溶样品，超声提取样品和光解样品和光解样品测定结果进行了对比。结果表明：3种样品中均含有Na^ ,NH4^ ,K^ ,Mg^2 ,Ca^2 5种阳离子，但光解样品中5种阳离子的含量分别是超声提取及直接水溶样品中含量的3．5－19．7倍和10．6－46．6倍。对液晶样品进行光解测定阳离子时无需加入H2O2氧化，光解后无需对样品进行酸化。Na^ ,NH4^ ,K^ 在光解1.5h时响应值达到最大，Mg^2 ,Ca^2 在2h时光解最完全。5种阳离子加标回收率为71．5％－107．6％。本方法对测定有机化合物上结合的阳离子有一定的参考价值。     

On the contribution of higher-order excitations to correlation energies: The ground state of the water molecule

Using the results of a configuration interaction calculation reported by Rosenberg and Shavitt, we derive an approximation to the correlation energy which may be associated with the sum to infinite order of all linked diagrams involving singly- and doubly-excited states. This result is compared with that obtained by calculation of the energy through third-order. The fourth-order linked diagrams involving quadruply-excited states are computed. It is shown that there is a considerable degree of cancellation between the fourth-order linked diagram energy terms involving doubly-excited intermediate states only and those which contain quadruply-excited states.     

Revised interpretations of the available x-ray data for B-DNA

Comparisons are made between calculations based on the double-helix and side-by-side models of DNA and data taken from the available x-ray diffraction measurements of the B form of DNA. The SBS model invoked here is an improvement on the one which was published earlier. In our estimation the fibre diffraction patterns do not significantly favour either model. However, the DH model is incompatible with the on-axis form of the cylindrically-averaged Patterson function, whereas the SBS model is compatible (this result is relatively insensitive to appreciable modifications to the SBS structure)—the crucial question is whether the quality of the data is sufficient to make this finding significant. It is shown that the maximum expected effect on the fibre pattern, of exchanging A-T base pairs for G-C base pairs, is less than the probable experimental error.     

Symmetry adaption

The matrix of force constants of a symmetric molecule is reduced to its invariants (nearly diagonal form). For the case of distance dependent potentials these invariants are expressed by the derivations of the potentials and geometric factors. For the purpose of parametrization the inversions of these formulae are derived. The general equilibrium condition and the elimination of the translational and rotational coordinates are discussed. The example of the tetrahedral AB₄ structure is worked out.