Semisynthesis II - formation of a covalently linked 1–12/106–129 -fragment of hen egg-white lysozyme

Methoxycarbonylsulphenyl chloride has been shown to cleave reduced Hen egg-white lysozyme into two fragments, rather than the 1–12, 13–105 and 106–129 fragments which would have been anticipated. The covalently linked 1–12/106–129 and 13-105 fragments are produced by initial cleavage at methionines 12 and 105 resulting in the generation of two homoserine lactone residues in place of the methionines. The homoserine lactone at position 12 then couples to the alpha amino group of asparagine-106 to give a covalently linked 1–12/106–129 fragment which has been characterised by a variety of techniques.     

Spherulitic growth of hen egg-white lysozyme crystals

In protein crystallography, spherulites are considered the result of a failed crystallization experiment. Understanding the formation of these structures may contribute to finding methods to prevent their formation. Here, we present an in situ study on lysozyme spherulites grown from sodium nitrate and sodium thiocyanate solutions, investigating their morphology and growth kinetics using optical microscopy. In a morphodrom, we indicate the conditions at which spherulites form for the lysozyme-nitrate system, showing that liquid-liquid phase separation is not a prerequisite to form sheaflike spherulites and that supersaturation is not the only factor determining their creation. Despite their sheaflike morphology, the spherulites all appear to be formed through heterogeneous nucleation. The spherulites are of a new polymorphic form and are less stable than the monoclinic form. For a single needle, growth kinetics indicate surface processes to be the rate-limiting step during growth, but for an entire spherulite volume, diffusion still plays a role. Spherulites simulated by using a time-dependent, tip-splitting model are found to compare well to experimentally observed spherulites.     

Charge-transfer interaction of some pyridinium salts with hen egg-white lysozyme

The charge-transfer interaction of pyridinium salts with lysozyme and L-tryptophan has been investigated by visible absorption, circular dichroism and fluorescence spectroscopy. Four quaternized and substituted pyridinium salts were used as electron acceptors. L-tryptophan was used as a model compound of electron donor for the purpose of the comparison with lysozyme. The binding constants obtained from absorption and circular dichroism spectra were 2.0–13 M^–1 and the sequence of the magnitude was found as EPCl(1-ethylpyridinium chloride) < MPCl(1-methylpyridinium chloride) < MNCl(1-methylnicotinamide chloride) < MNMCl(1-methyl-3-carbomethoxypyridinium chloride), which could be explained by the electron affinity of the pyridinium salt. The fluorescence spectra of lysozyme and L-tryptophan in the absence and presence of pyridinium salts were interpreted by Stern-Volmer plot. The static constants thus determined were in agreement with the binding constants obtained by other methods.     

12,52-二羟基-15,55-二甲基-14,16,34,36,54,56,74,76-八硝基-2,4,6,8-四氧桥连-1,3,5,7（1,3）-杯[4]芳烃的合成

以1,5-二氟-2,4-二硝基苯和3,4,5-三甲氧基甲苯为起始原料,经环化、甲基化、硝化和去甲基化反应,合成了一种新型杯芳烃衍生物,其结构经¹H NMR,¹³C NMR,¹⁵N NMR和元素分析表征。      

Palladium-catalyzed syntheses of condensed cyclopentanes. The crystal and molecular structure of 3-benzylidenpentacyclo[9.2.1.5,8.11,11.02,10.04,9]-pentadecane

New syntheses of condensed cyclopentanes are described, based on insertion into a sufficiently stable PdC bond of molecules able to provide an easy reductive elimination step. These reactions are highly stereoselective. Interesting features are revealed by the X-ray investigation of the title compound, which was obtained in good yield from β-bromostyrene and norbornene. The structural parameters are reported; the molecule adopts the conformation with the bridging carbon atoms of the two norbornanes trans with respect to the mean plane of the cyclopentylidene ring. The condensed cyclopentane system is highly symmetric. The phenyl group is twisted out of the plane of the cyclopentylidene ring by 25.3°.     

Molecular structure of methyl-10,14,19,19-tetramethyl-4-oxo-20-oxahexacyclo [15.3.1.16.18.06.15.09.14017.21]docosane-10-carboxylate

The synthesis of methyl-10,14,19,19-tetramethyl-4-oxo-20-oxahexacyclo[15.3.1.1^6.18.0^6.15.0^9.140^17.21] docosane-10-carboxylate III is performed and its molecular structure is determined. Compound III C₂₇H₄₀O₄ crystallizes in the monoclinic system with the cell parameters as follows: a = 12.8081(11) ?, b = 7.0384(6) ?, c = 12.8904(12) ?, β = 105.828(2)^o, P2₁ space group, Z = 2, d = 1.273 mg/m³.     

BF分子X1∑+,A1∏和B1∑+电子态的势能函数

使用SAC/SAC-CI和D95++,6-311++g,6-311++g**及D95(d)基组,分别对BF分子的基态X1∑+、第一简并激发态A1∏和第二激发态B1∑+的平衡结构和谐振频率进行优化计算.对所有计算结果进行比较,得出6-311++g**基组为最优基组.运用6-311++g**基组和SAC方法对基态X1∑+,SAC-CI方法对激发态A1∏和B1∑+进行单点能扫描计算,并用正规方程组拟合Murrell-Sorbie函数,得到相应电子态的势能函数解析式,由得到的势能函数计算了与X1∑+,A1∏和B1∑+态相对应的光谱常数,结果与实验数据较为一致.     

Molecular and crystal structure of 23,24,25,26,27,29,30-heptamethyl-19,28-oxahexacyclo[15.13.18.017,18.013,14.08,9.05,10]tetracos-3-yl acetate

The molecular structure of 23,24,25,26,27,29,30-heptamethyl-19,28-oxahexacyclo[15.13.18.0^17,18.0^13,14.0^8,9.0^5,10]tetracos-3-yl acetate III. Compound III C₃₂H₅₂O₃ crystallizes in the monoclinic crystal system with the unit cell parameters a = 13.265(15) ?, b = 6.481(7) ?, c = 32.274(4) ?, β = 99.333(2)°, space group C2, Z = 4, d = 1.176 g/cm³. Original Russian Text Copyright ? 2009 by N. I. Medvedeva, O. B. Flechter, and A. A. Korlyukov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 2, pp. 399–401, March–April, 2009.     

Potential energy curve of 1Σ+ Li+/He

The potential energy curve of the system Li⁺/He has been determined with moderately large basis sets for 0.5 ? r ? 10.0 a₀ both at the SCF level and including correlation. The present SCF results predict a deeper well (?0.00248 au) at a smaller r(3.66 a₀) compared with earlier calculations. Correlation deepens the well further (?0.00274 au), but pulls it inward slightly (3.63 a₀). In the repulsive part the calculated curve lies above the experimental one, especially at shorter distances. A similar behavior has been noted in the systems Li⁺/H₂, Li⁺/CO and Li⁺/N₂, suggesting that the experimental determinations may underestimate the interaction in this region by 10–20%.     

Radiative lifetimes of the CO a′3Σ+, b3Σ+, c3Π, d3Δ and B1Σ+ states. Absolute emission cross sections for t

Radiative lifetimes have been measured for the CO a′³Σ⁺(ν′=4–9), b³Σ⁺(ν′= 0), c³Π(ν′=0), d³Δ(ν′=1–16) and B¹Σ⁺(ν′= 0) states. Our experimental values, arranged in the same order, are 7–10 μs, 56 ns, 16 ns, 3–7.5 μs, 34 ns. Some of these values disagree with the results of previous experiments. To our opinion this is due to an incomplete identification of the emission spectrum in regions where many bands may overlap, dependent on the applied spectral resolution. For the a′Σ⁺?a³Π and d³Δ?a³Π emissions effective cross sections for quenching by CO molecules are given. In connection with the identification of the spectrum, absolute emission cross sections for electrons incident on CO have been measured for the b³Σ⁺?a³Π and c³Π?a₃Π transitions. For an electron energy, corresponding to the maximum of the excitation function we find cross sections of 5.94 (?1.2) × 10^?18 cm² and 0.630 (? 0.13) × 10^?18 cm², respectively.     

The interaction of anionic azo dyes with hen egg-white lysozyme: 2

In continuation of our preceding study, this report describes pH and ionic strength dependences of the binding constants of six anionic azo dyes to lysozyme, the competitive binding of the dyes with the substrate analogues of lysozyme and the change in the circular dichroism of lysozyme by the dye binding. The binding constants were obtained from the difference spectra of visible absorption. With an increase in pH from 5.0 to 7.0 the constants for the dyes (1st of the two modes of the binding of a dye named D3) are reduced. The increase in ionic strength from 0.1 to 0.2 also reduces the values of the constant. Competitive binding was found between D3 and the analogues, but not for the other dyes. The change in the circular dichroism due to the electronic perturbation of tryptophyl residues in lysozyme was found. From these evidences, Lys 33 in lysozyme is pinpointed as the most credible binding site for the dyes (1st mode binding of D3). An unspecified location near the subsiteB in lysozyme is addressed for 2nd mode binding of D3.     

The interaction of anionic azo dyes with hen egg-white lysozyme: 1

The interactions between seven anionic azo dyes and hen egg-white lysozyme were investigated by means of visible absorption spectroscopic and lytic activity measurements. The dyes, for which no report on the interaction has appeared so far, were bound with lysozyme to different extents as a result of the differences in their chemical structures. Although most of the dyes formed 11 complex with lysozyme, two of them behaved differently. From the measurements of the absorption, lytic inhibition toward cell walls and competitive binding with substrate analogues, it was concluded that a major binding site of these dyes on lysozyme is a charged lysine residue in the vicinity of the subsitesD, E andF, and, in the case of a dye that forms 21 complex with lysozyme, and additional binding site is in the vicinity of the subsite B.     

Molecular structure of 8-carboxy-18-chloro-14-hydroxy-20-isopropyl-16-methoxy-4,8-dimethyl-15-oxaoctacyclo-[11.7.1.03,1204,9012,19014,18016,21017,20]henicosane

The structure of 8-carboxy-18-chloro-14-hydroxy-20-isopropyl-16-methoxy-4,8-dimethyl-15-oxaoctacyclo[11.7.1.0^3,120^4,90^12,190^14,180^16,210^17,20]henicosane has been determined by single crystal X-ray diffraction. Original Russian Text Copyright ? 2008 by R. R. Fazlyev, G. F. Vafina, and F. Z. Galin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 6, pp. 1179–1181, November–December, 2008.