Synthesis and X-ray structure analysis of benzoic acid [1-(6-methyl-2,4-dioxo-3,4-dihydro-2H-pyran-3-yl)eth-(E)-ylidene]-hydrazide with a water molecule (C15H14N2O4?H2O)

The crystal structure of the title compound has been determined by X-ray diffraction methods. It crystallizes in the monoclinic space group P2₁/n with cell parameters a = 7.097(1) Å, b = 19.257(1) Å, c = 10.893(1) Å, = 106.17(2), V = 1429.8(3) ų and Z = 4. The final reliability index is 0.059 for 2419 observed reflections. The molecule comprises of two six- membered rings which are abridged together through a network of C–N, N–N and C–N bonds. There are three keto functional groups and two methyl groups at various locations of the molecule. The C9 atom of methyl group and O2 of the keto group are deviated significantly from the mean plane of the molecule. Both the six-membered rings are planar and it is evident from the magnitude of their exocyclic torsion angles. The molecular structure is stabilized by few intra and intermolecular hydrogen bonds.     

Novel method to characterize the hydrolytic decomposition of biopolymer surfaces

Present pharmaceutical research is focused on the development, modification and characterisation of new drug delivery systems. Among the many different substances, biodegradable polymers and copolymers are of practical importance, especially if their degradation byproducts are non-toxic. The polymeric drug carriers are not easily wettable by water or aqueous solutions, i.e. they are hydrophobic. This surface hydrophobicity is unfavourable for keeping drug carriers circulating in the blood long enough to release the drug so that it reaches its target. Therefore, copolymers with components of different hydrophobicity were introduced, to make them less hydrophobic and hence more suitable for drug delivery in the human body. Exploratory experiments with one homopolymer, , -poly(lactic acid), , -PLA and two of its copolymers, , -poly(lactic/glycolic acid), and , -PLGA with 85/15 and 50/50 copolymer ratios were carried out. Films of these substances were prepared by dip coating onto hydrophobic and hydrophilic substrates. The changes in wettability of the polymer layers, caused by the direct contact with an aqueous environment (soaking the samples in distilled water), have been studied to model the hydrolytic decomposition of polymer surfaces and to follow the changes in their wettability by dynamic contact angle measurements in a non-destructive manner. It was found that each polymer film became less hydrophobic (dynamic contact angles decreased) and more heterogeneous as the decomposition progressed with time. Increasingly significant decreases in contact angles were observed for the copolymer films containing 15 and 50% glycolic acid, during the 50–80-day-long study. These findings were supported by gel chromatographic analysis of the soaking liquids. It was concluded that the homopolymer layer of , -PLA was the most resistant to hydrolysis and the stability of copolymer films decreased with increasing glycolic acid ratio in the copolymers. This is accordance with the fact that the less crystalline poly(glycolic acid) is more hydrophilic and hence less resistant to hydrolytic decomposition, than the poly(lactic acid). The effect of pH on the rate of hydrolysis of polymer films was also established; the influence of pH on the decomposition was best demonstrated, again, for the copolymer with 50/50 component ratio. The outcome of these experiments showed that the contact angle measuring method enables us to detect, follow and interpret the hydrolytic decomposition of biopolymer substances in a non-invasive manner.     

An eigenvalue method on group decision

I.ThePrincipleofGEMInthefollowing,wewi1levaluatenobjectsB,,B1,"-,B,bygroupdecisionsupportsystemGwhichconsistsofmexpertsS,,S,,..',S..Letx',E[I,J](f=1,2'...,mlj=l,2,"',n)betheevaluationvalueofthejthobjectBjestimatedbythei-tllexpertS'.Thelargerxqis,themoreop…     

Precise measurement of hyperfine coupling in CH F based on nuclear spin conversion

A new method is proposed for the experimental determination of the hyperfine coupling in molecules. The method is based on the level-crossing effect in the spin isomer conversion in alternating electric fields. An experiment performed with the ¹³CH₃F molecules has revealed the strength of the off-diagonal in K () nuclear spin-spin coupling kHz, which is only by kHz larger than the theoretical value calculated on the basis of the molecular structure. Received 25 January 2000 and Received in final form 11 May 2000     

Synthesis and Crystal Structure of a Model for the Active Sites of Fe-only Hydrogenases： [Fe2（SCH2）2N（3-PhCF3）（CO）6]2

A model compound for the active sites of Fe-only hydrogenases,[Fe2(SCH2)2N(3-PhCF3)(CO)6]2,has been synthesized and structurally characterized by single-crystal X-ray diffraction.It crystallizes in tetragonal,space group P43,with a = 12.6324(3),b = 12.6324(3),c=24.0453(12) (A),V = 3837.1(2) (A)3,Z = 4,Fe4S4N2C30O12F6H16,Mr= 1062.09,Dc= 1.839 g/cm3,μ(MoKa) = 1.791 mm-1,F(000) = 2112,T= 293(2) K,Flack = 0.034(9),R= 0.0282 and wR =0.0685 for 8148 observed reflections with I ＞ 2σ(I).In the title compound,each Fe1 atom is coordinated by three terminal carbonyl C atoms (Fe-C:1.783(3)～ 1.816(3)(A)),two bridging S atoms (Fe-S:2.2609(7)～2.2757(8)(A)) and another Fe atom (Fe-Fe 2.5011(5) (A)),adopting a distorted octahedral geometry with trans angles ranging from 152.45( 11 ) to 157.77(10)°.     

Angles in Complex Vector Spaces

The article reviews some of the (fairly scattered) information available in the mathematical literature on the subject of angles in complex vector spaces. The following angles and their relations are considered: Euclidean, complex, and Hermitian angles, (Kasner's) pseudo-angle, the Kähler angle (synonyms for the latter used in the literature are angle of inclination, characteristic deviation, holomorphic deviation, holomorphy angle, Wirtinger angle, slant angle).     

A markov-modulated M/M/1 queue with group arrivals

We study anM/M/1 group arrival queue in which the arrival rate, service time distributions and the size of each group arrival depend on the state of an underlying finite-state Markov chain. Using Laplace transforms and matrix analysis, we derive the results for the queue length process, its limit distribution and the departure process. In some special cases, explicit results are obtained which are analogous to known classic results.     

Preferential surface segregation of homopolymer and copolymer blend films

Surface film properties of the homopolymers polystyrene (PS), poly(methyl methacrylate) (PMMA), poly(butyl methacrylate) (PBMA) and the copolymer poly(methyl methacrylate)-co-poly(butyl methacrylate) (PMMA-co-PBMA) and their blends with PS have been examined by atomic force microscopy (AFM) and contact angle measurements. The total and the Lifshitz-van der Waals, acid and base components of the surface free energy together with the work of adhesion and its components, the cohesive energy density and the solubility parameters of the homopolymer, copolymer and blend films were determined. Films of about 3 μm were considered. The results are discussed in terms of surface migration mechanisms based on surface free energy and solubilities of the polymers in the solvent, toluene in this paper. AFM imaging and contact angles revealed surface enrichment at the air polymer interface of PBMA for both the PS/PBMA blend and the copolymer PMMA-co-PBMA, whereas the PS/PMMA and PS/PMMA-co-PBMA blend film surfaces show island-like phase-separated structure of typical size 27.4-86.5 nm in diameter and 6.9-15.6 nm in height for PS/PMMA, while for PS/ PMMA-co-PBMA film surface the typical size is 49.6-153.3 nm in diameter and 1.6-14.2 nm in height.     

Neutron production at the heavy ion research facility in Lanzhou

In this work,the neutron radiation field at Heavy Ion Research Facility in Lanzhou (HIRFL) was investigated.Total neutron yields,spectra and angular distributions in the bombardment of various thick targets by 12C and 18O ions with energies up to 75 MeV/u were obtained using the activation method.The neutron dose equivalent rates of 60 MeV/u 18O on various thick targets at different angles were measured with a modified A-B remmeter.Our results are compared with those of other reports.     

Stereology of dihedral angles

The paper presents a short survey of stereological problems concerning dihedral angles, their solutions and applications, and introduces a graph for determining the distribution functions of planar angles under the hypothesis that dihedral angles in ³ are of the same size and create a random field.