Pharmacophore-based database mining for probing fragmental drug-likeness of diketo acid analogues

A number of the structurally diverse chemical compounds with functional diketo acid (DKA) subunit(s) have been revealed by combined online and MoStBiodat 3D pharmacophore-guided ZINC and PubChem database screening. We used the structural data available from such screening to analyse the similarities of the compounds containing the DKA fragment. Generally, the analysis by principal component analysis and self-organizing neural network approaches reveals four families of compounds complying with the chemical constitution (aromatic, aliphatic) of the compounds. From a practical point of view, similar studies may reveal potential bioisosteres of known drugs, e.g. raltegravir/elvitegravir. In this context, it seems that mono-halogenated aryl substructures with para group show the closest similarity to these compounds, in contrast to structures where the aromatic ring is halogenated in both ortho- and para-locations.     

气相色谱-负化学源质谱联用法测定水产品及食用油中氟乐灵的残留量

建立了一种可用于水产品及食用油中氟乐灵残留量分析的分散型固相萃取-气相色谱-负化学离子源质谱方法。水产品及食用油经乙腈提取,4 ℃冷藏后,采用分散型固相萃取法净化,由气相色谱-负化学离子源质谱选择离子监测技术进行测定与确证,同位素内标法定量。在1~40 μg/L范围内氟乐灵农药的线性关系良好;方法定量限（LOQ）为0.02 μg/kg;对鳗鱼、烤鳗、梭子蟹、小龙虾、猪油和橄榄油等6种复杂基质进行1.0、2.0和3.0 μg/kg等3个水平的添加回收试验,平均回收率均处于80%~100%之间,RSD≤10.3%;无干扰现象出现。该方法可作为水产品及食用油中氟乐灵残留检测的确证方法。     

无机热化学数据库中卤化物高温熵的计算机预报

在W. M. Latimer估算化合物标准熵的方法的基础上,建立了卤化物高温熵的计算机预报方法。作为试验,未参加训练的18个卤化物高温熵的预报值与实验值作了对照,其偏差均小于20焦耳/度·摩尔,即与若干卤化物标准熵的实验误差相近。     

可倾瓦径向滑动轴承支承的转子系统瞬态响应计算

研究了可倾瓦径向滑动轴承支承的转子系统瞬态响应的计算方法,提出了可倾瓦径向滑动轴承非线性滑膜力计算的数据库方法,将可倾瓦与轴颈的结构和运动参数归结到三个参数中,建立了起可倾瓦的非线性油膜力数据库,通过精确插值到每一运动参数组合下轴承提代的油力和轴瓦上所受的油膜力矩。     

Strategies for the determination of pharmacophoric 3D database queries

Strategies are described for constructing pharmacophoric 3D database queries, based on aseries of active and inactive analogs. The results are highly selective database queries, whichare consistent with the generally accepted pharmacophore for a number of systems. Thefoundation of these strategies is the method of Mayer, Naylor, Motoc and Marshall [J.Comput.-Aided Mol. Design, 1 (1987) 3] for inferring a unique binding geometry forangiotensin-converting enzyme (ACE) inhibitors. The strategies described here generalize theirapproach to cases where the chemical features responsible for binding are not a prioriapparent, and to cases where the binding geometry deduced by that method is not unique. Thekey new insight, the selectivity principle, is to rank the multiple solutions produced by themethod of Mayer et al. by their selectivity, a value that is related to the proportion of adatabase that is returned as a database hit list. Retrospective analyses are described for D2-antagonists, ACE inhibitors, fibrinogen antagonists, and 2-antagonists.     

关系数据库的数字水印新技术

提出一种能嵌入有意义水印信息并可由用户定义各种约束的水印算法CAMW（Constraints Allowahie Meaningful Watermark Algorithm），该算法将水印信息映射成二进制串，并把每个水印信息位重复嵌入多次，最后经选举过程确定出完整的水印，较大地提高了正确提取水印的概率，CAMW不仪使嵌入水印的数据能有效保持关系数据的语义特征，而且有很强的鲁棒性，仿真试验表明能有效抵御子集删除，子集添加，数据修改等多种攻击。     

On the stability of queueing systems under precedence restrictions for the service of customers

We consider queueing systems under precedence-based queueing disciplines and derive conditions for the stability of the system. The precedence restrictions are posed on customers' service in a way that a service can start only if some previous customers are served completely and some later customers arrived already. The stability depends on the interarrival times only through their means and the stability condition splits into two terms: with respect to a typical customer, one is representing the influences of future arrivals and one is representing the influences of past arrivals.     

Fluorines in tetrafluoromethane as halogen bond donors: Revisiting address the nature of the fluorine's σhole

It has been demonstrated in several instances that the 0.001 a.u. (electrons per bohr³) isodensity mapped electrostatic surface potentials on the fluorines along the outermost extensions of the C? F covalent bonds in tetrafluoromethane (CF₄) are entirely negative, they are thereby unable to engage in σ_hole bonding interactions with the negative sites on another molecules. In this study, we have attempted at resolving this controversy by performing various high‐level electronic structure calculations with Quadratic Configuration Integrals of Singles and Doubles QCISD(full), second‐order Møller–Plesset MP2(full), and 12 other Density Functional Theory (DFT) based functionals with and without dispersion corrections, all in conjunction with the 6–311++G(2d,2p) basis set. The results achieved with all the levels of theory utilized suggest that the fluorine's σ_holes in CF₄ are positive regardless of the 0.001‐, 0.0015‐, and 0.002‐a.u. isodensity mapped electrostatic surfaces examined. Because of this specific quality, the fluorines in CF₄ have displayed their capacities to form not only 1:1 clusters with the Lewis bases such as water (H₂O), ammonia (NH₃), formaldehyde (H₂C?O), hydrogen fluoride (HF), and hydrogen cyanide (HCN), but also 1:2, 1:3, and 1:4 clusters with the latter three randomly chosen Lewis bases. Various topological and nontopological features obtained from applications of atoms in molecules, noncovalent interaction reduced‐density‐gradient and natural bond orbital analytical tools reveal that the N···F, O···F, and F···F long‐ranged interactions developed between the interacting monomers in H₃N···FCF₃, H₂O···FCF₃, and (Y? D)_n=1–4···F₄C (Y? D = H₂C?O, HCN, and HF) are reminiscent of halogen bonding. The nonadditive cooperative and anticooperative energetic effects emerged on cluster formations are discussed in detail. © 2015 Wiley Periodicals, Inc.     

GC-MS/NCI稳定同位素稀释技术检测动物源性食品中氯霉素的残留量

建立了一种用于各种动物源性食品中氯霉素残留量的气相色谱-负化学离子源质谱(GC-MS/NCI)检测方法。以氘代氯霉素(D5-CAP)为内标物,用乙酸乙酯对各类样品中的氯霉素进行提取,用正己烷和40 g/L NaCl溶液液液分配除脂肪,基质复杂的样品再用Oasi HLB固相萃取柱净化,经硅烷化衍生后由GC-MS/NCI在选择离子监测模式下进行测定。多数样品在0.2,0.5,1.0μg/kg3个添加水平下氯霉素的回收率处于87.8%和107.0%之间,相对标准偏差(RSD)不大于8.5%。方法在2.0~80.0μg/L范围内有良好的线性关系,基质复杂样品中氯霉素残留的检出限达到0.1μg/kg,基质简单样品的检测限可达0.05μg/kg。方法适合各种动物源性食品中氯霉素残留量的确证分析。