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101.
Hen-egg-white lysozyme (HEWL) crystals does not differ from small molecule crystals in respect to diffusion limited growth but differ substantially as far as lattice bound strength is concerned. 相似文献
102.
A novel structure type has been established as a result of studying a non-merohedral microtwin of polyoxovanadate (K2ZnV5O14) by X-ray diffractometry (R = 0.0595). The new compound, synthesized under hydrothermal conditions in the ZnCl2–K2CO3–V2O5–H2O system, is characterized as follows: a = 8.066(5) Å, b = 8.117(5) Å, c = 9.236(5) Å, β = 105.287(5)°, sp. P21/m, Z = 2, ρcalcd = 3.54 g/cm3. Edge-shared five-core “clusters” consisting of vanadium octahedra, between which ZnO4 tetrahedra (sharing vertices with octahedra) are located, form two-dimensional two-layer anion packets of the (ZnV5O14)2– composition, alternating along the c axis with layers of potassium atoms. Structural peculiarities determine the morphology and color of new-phase crystals. 相似文献
103.
Estimating phylogenetic trees is an important problem in evolutionary biology, environmental policy, and medicine. Although trees are estimated, their uncertainties are generally discarded in statistical models for tree-valued data. Here, we explicitly model the multivariate uncertainty of tree estimates. We consider both the cases where uncertainty information arises extrinsically (through covariate information) and intrinsically (through the tree estimates themselves). The latter case is applicable to any procedure for tree estimation, and thus has broad relevance to the entire field of phylogenetics. The importance of accounting for tree uncertainty in tree space is demonstrated in two case studies. In the first instance, differences between gene trees are small relative to their uncertainties, while in the second, the differences are relatively large. Our main goal is visualization of tree uncertainty, and we demonstrate advantages of our method with respect to reproducibility, speed, and preservation of topological differences compared to visualization based on multidimensional scaling. The proposal highlights that phylogenetic trees are estimated in an extremely high-dimensional space, resulting in uncertainty information that cannot be discarded. Most importantly, it is a method that allows biologists to diagnose whether differences between gene trees are biologically meaningful or due to uncertainty in estimation. 相似文献
104.
105.
A titration method is developed that titrant is added continuously to the analyte by electromigration through an ion exchange membrane. A constant rate of the titrant addition is achieved by keeping the electric current constant. Analyte amount then is proportional to the titration time. The method is applied to the most widely used titrations with a visual end point indication. 相似文献
106.
A new iron(II) orthophosphate K[Fe(PO4)] has been obtained by hydrothermal synthesis and its crystal structure was determined by single‐crystal X‐ray diffraction: space group P21/n, Z = 8, a = 9.6199(10), b = 8.6756(8), c = 10.8996(13) Å, β = 115.577(8)° at 193 K, R = 0.023. FeII shows coordination numbers (CN) 4 (distorted tetrahedral) and CN 5 (distorted trigonal bipyramidal). The [FeO4] and [FeO5] units form together with the [PO4] tetrahedra a microporous 3D para‐framework with open channels along the a and b directions. The potassium ions positioned in the channels show CN 7 and 8. The structural relations within the morphotropic row of non‐isotypic K[M(PO4)] structures (M = Zn, Ni, Mn, Fe) are discussed on the basis of common basic structural units. 相似文献
107.
Pistelli L Noccioli C Giachi I Dimitrova B Gevrenova R Morelli I Potenza D 《Natural product research》2005,19(8):783-788
Two new triterpenoids, lup-20(29)-en-3 alpha, 28-diol (1) and lup-20(29)-en-3 alpha, 28,30-triol (2), have been isolated from aerial parts of Bupleurum flavum, a native plant of the Eastern Mediterranean area (Bulgaria, Greece, and Turkey). Their structures were elucidated by spectral analysis. The known compounds betulin, betulinic acid, jasminol, together with the lignan nemerosin and eight flavonoids (kaempferol, isokaempferide, gossipetin, quercetin, luteolin, isorhamnetin 3-O-beta-D-glucopyranoside, isorhamnetin 3-rutinoside, and rutin) were also characterized. 相似文献
108.
Dimitrov S Dimitrova G Pavlov T Dimitrova N Patlewicz G Niemela J Mekenyan O 《Journal of chemical information and modeling》2005,45(4):839-849
A stepwise approach for determining the model applicability domain is proposed. Four stages are applied to account for the diversity and complexity of the current SAR/QSAR models, reflecting their mechanistic rationality (including metabolic activation of chemicals) and transparency. General parametric requirements are imposed in the first stage, specifying in the domain only those chemicals that fall in the range of variation of the physicochemical properties of the chemicals in the training set. The second stage defines the structural similarity between chemicals that are correctly predicted by the model. The structural neighborhood of atom-centered fragments is used to determine this similarity. The third stage in defining the domain is based on a mechanistic understanding of the modeled phenomenon. Here, the model domain combines the reliability of specific reactive groups hypothesized to cause the effect and the domain of explanatory variables determining the parametric requirements in order for functional groups to elicit their reactivity. Finally, the reliability of simulated metabolism (metabolites, pathways, and maps) is taken into account in assessing the reliability of predictions, if metabolic activation of chemicals is a part of the (Q)SAR model. Some of the stages of the proposed approach for defining the model domain can be eliminated depending on the availability and quality of the experimental data used to derive the model, the specificity of (Q)SARs, and the goals of their ultimate application. The performance of the proposed definition of the model domain is tested using several examples of (Q)SARs that have been externally validated, including models for predicting acute toxicity, skin sensitization, and biodegradation. The results clearly showed that credibility in predictions of QSAR models for chemicals belonging to their domain is much higher than for chemicals outside this domain. 相似文献
109.
G. Wendt K. Hagenau R. Dimitrova Z. Popova Ch. Dimitrov 《Reaction Kinetics and Catalysis Letters》1986,31(2):383-388
The catalytic activity of synthetic and natural nickel exchanged mordenites of different compositions has been investigated in dimerization of n-butenes at high pressure in the liquid phase. High selectivities to n-octenes and methylheptenes were found. It is suggested that the mordenite channel structure influences the product distribution.
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110.
G. V. Kiriukhina O. V. Yakubovich O. V. Dimitrova A. S. Volkov 《Crystallography Reports》2016,61(5):796-804
The crystal structure of Rb2Mn3(H2O)2[P2O7]2, a new phase obtained in the form of single crystals under hydrothermal conditions in the MnCl2–Rb3PO4–H2O system, is determined by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.0270): a = 9.374(2), b = 8.367(2), c = 9.437(2) Å, ß = 99.12(2)°, space group P21/c, Z = 2, Dx = 3.27 g/cm3. A correlation between the unit-cell parameters and the size of cations forming the crystal structures of isostructural A2M3(H2O)2[P2O7]2 diphosphates (A = K, NH4, Rb, or Na; M = Mn, Fe, Co, or Ni) is revealed. It is shown that, due to the topological similarity, the structures of diphosphates and orthophosphates of the farringtonite structural type can undergo mutual transformations. 相似文献