双自由基桥联双铜(Ⅱ)配合物的合成、结构、磁性和分子力学研究

合成和表征了双自由基桥联的双核铜配合物［Ｃｕ（ｈｆａｃ）_２］_２　ＰｈＢＮＭ,其中ｈｆａｃ为 六氟乙酰丙酮负离子,ＰｈＢＮＭ为２,５－二甲基－１,４－二（４,４,５,５－四甲基－３－氧化咪唑啉１－氧 基自由基）苯．配合物的晶体为单斜晶系, Ｃ２／ｃ空间群, ａ＝１．９０１２（４） ｎｍ, ｂ＝１．３７１８（３） ｎｍ, ｃ＝２．１６２ ０（４） ｎｍ,β＝９７．５５（３）°, Ｚ＝４． Ｘ射线衍射结果表明该配合物存在两种构象,其 比例为 ７：３．用分子力学 ＭＭＸ计算了这两种构象的能量分别为 Ｅ_１＝７４０ ｋＪ／ｍｏｌ,Ｅ２＝７７１ ｋＪ／ｍｏｌ．运用不同的自旋多重度作参数,通过ＣＮＤＯ／Ｋ对配合物中磁偶合体系的轨道能 量进行计算,当体系中成单电子为反铁磁偶合时,轨道能量较低,这与磁性测量及其理 论拟合结果一致。     

二维核磁共振波谱和分子力学方法计算香茶菜醛溶液中的…

采用二维核磁共振波谱完全归属了天然有机化合物香茶菜醛的＾１Ｈ和＾１３Ｃ ＮＭＲ化学位移，测定了部分质子的偶合常数，并用孤立自旋对近似方法质量处理香茶菜醛的相敏ＮＯＳＥＹ谱，根据１／γ＾６ｉｊ∝Ａｉｊ计算出相应的质子间距离。其溶液中的三维空间结构采用以ＮＭＲ结构参数为初始数据的ＷＵＰＨ计算程序和分子力学能量优化（ＭＭ２）完成计算。计算结果表明，得到的香茶菜醛在溶液中的三维空间结构反映了该化合物在溶液     

含MoFe3Se4类立方烷核芯簇合物的合成与结构表征

室温下［Ｅｔ_４Ｎ］_２ＭｏＳｅ_４, ＦｅＣｌ_２和 Ｒ_２ＮＣＳ_２Ｎａ在 ＤＭＦ和 ＣＨ_３ＣＮ混合溶剂中反应,得到含ＭｏＦｅ_３Ｓｅ_４核芯的Ｍｏ－Ｆｅ－Ｓｅ簇合物ＭｏＦｅ_３Ｓｅ_４（μ－Ｒ_２ＮＣＳ_２）_２（Ｒ_２ＮＣＳ_２）_４（Ｒ２＝Ｍｅ_２（１）,Ｅｔ_２（２）,Ｃ_４Ｈ_８（３））．化合物２的单晶Ｘ射线衍射分析表明,其分子结构为２个桥式和４个螫合Ｅｔ_２ＮＣＳ_２~－配体包围的一个扭曲类立方烷Ｍ_４Ｓｅ_４簇核对３个化合物的ＣＶ进行了表征,它们在ＤＭＳＯ溶液中的电化学行为表现出了多电子可逆的传递过程．     

用Mo（Ⅲ）络合物分裂N_2分子

用Ｍｏ（Ⅲ）络合物分裂Ｎ_２分子麻省理工学院的Ｃ．Ｅ．Ｌａｐｌａｚａ和Ｃ．Ｃ．Ｃｕｍｍｉｎｓ用配位数为３的Ｍｏｔ（Ⅲ）络合物Ｍｏ（ＮＲＡｒ）３［Ｒ＝Ｃ（ＣＤ３）２ＣＨ３；Ａｒ＝３，５－Ｃ６Ｈ３Ｍｅ２（Ｍｅ，－ＣＨ３）与Ｎ２反应，实现了将Ｎ２分子裂开还?..     

SYNTHESIS AND ~（183）W NMR CHARACTERIZATION OF A－β－Ge_2W_18Ti_6O_（77）~（14） HETEROPOLYANION

ＳＹＮＴＨＥＳＩＳ ＡＮＤ ~（１８３）Ｗ ＮＭＲＣＨＡＲＡＣＴＥＲＩＺＡＴＩＯＮ ＯＦ Ａ－β－Ｇｅ_２Ｗ_１８Ｔｉ_６Ｏ_（７７）~（１４） ＨＥＴＥＲＯＰＯＬＹＡＮＩＯＮ￥ＬｕＭＥＮＧ；ＪｉｎｇＦｕＬＩＵ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，...     

一阶紫外导数光谱PLS法直接同时测定硝酸根和亚硝酸根

用偏最小二乘（ＰＬＳ）法解析了ＮＯ_３~－和ＮＯ_２~－混合体系的一阶紫外导数光谱，提出了直接同时测定环境水样中ＮＯ_３~－－Ｎ和ＮＯ_２~－－Ｎ的计算分析法。该法对ＮＯ_３~－和ＮＯ_２~－来说，最低检测浓度分别为９×１０~（－８）和２×１０~（－７）ｍｏｌ·Ｌ~（－１），精密度（ＲＳＤ）分别为２．０５％和２．１２％。用于测定合成水样，平均相对误差在４％以内；用于测定环境水样，结果与标准法相吻合。     

RS－联萘酚膦酰胺晶体结构及与其SS体分子力学计算结果的比较

测定了Ｏ，Ｏ（２，２′－联萘基）－Ｎ－（α－苯基乙基）膦酰胺（简称联萘酚膦酰胺，ＤＮＰＡ）ＲＳ体与乙醇形成的分子化合物晶体结构。晶体学数据为：Ｃ＿（２８）Ｈ＿（２２）ＮＯ＿３Ｐ·Ｃ＿２Ｈ＿５ＯＨ，Ｍｒ＝４９７．５，单斜晶系，Ｐ２＿１空间群，α＝９．３５９（２），ｂ＝１２．８０６（３），ｃ＝１１．６４１（Ａ），β＝１１１．６２（３）°，Ｚ＝２，Ｖ＝１２９４．０（５）（Ａ）３，Ｄｃ＝１．２７７ｇ／ｃｍ￣３，ＭｏＫａ（λ＝０．７１０７３Ａ）射线，μ＝０．１３６ｍｍ￣（－１），可观测数据３８７１个，Ｆ（０００）＝５２４，Ｒ＝０．０３５，Ｒｗ＝０．０４２。分子间以氢键相连接。ＲＳ体晶体结构与分子力学方法计算得到的ＳＳ体构象比较，发现这一对非对映体构象的差别由联萘基一边的构型决定。     

SYNTHESES， CHARACTERIZATION AND CATALYSIS OF （dppe）Rh（μ－CO）_2M（CO）_3（M＝CR，Mo，W） CARBONYL COMPOUNDS

ＳＹＮＴＨＥＳＥＳ，ＣＨＡＲＡＣＴＥＲＩＺＡＴＩＯＮ ＡＮＤ ＣＡＴＡＬＹＳＩＳ ＯＦ （ｄｐｐｅ）Ｒｈ（μ－ＣＯ）_２Ｍ（ＣＯ）_３（Ｍ＝ＣＲ，Ｍｏ，ｗ）ＣＡＲＢＯＮＹＬ ＣＯＭＰＯＵＮＤＳ￥ＣｈａｎｇＰｉｎｇＳＨＡＯ；ＪａｉｅＹｕＷＡＮＧ；ＸｉｕＺ...     

H＋NF_2→NF（α）＋HF反应的从头算研究

本文用量子化学从头算法对Ｈ＋ＮＦ_２→ＮＦ（α）＋ＨＦ反应进行了理论研究，采用ＭＰ_２（ＦＵＬＬ）／６－３１Ｇ（ｄ）方法计算了反应物、产物、中间体和过渡态的构型参数和振动频率，然后用Ｇａｕｓｓｉａｎ－２理论计算了各物种的精确能量，计算结果表明：反应在单重态势能面上进行，电子激发态ＮＦ（α）通过复合－消除机理产生，用Ｇ２理论计算２９８Ｋ下反应的焓变为－１１９．４ｋＪ／ｍｏｌ，过渡态比反应物能量低９８．４ｋＪ／ｍｏｌ．中间体ＨＮＦ２是势能面的最低点，比反应物的能量低３１３．５ｋＪ／ｍｏｌ．     

18-冠醚-6的构象研究

以柔性大分子１８－冠醚－６为研究对象，将ＭＮＤＯ法所得的三种构象的静电势电荷用于分子力学计算，得到了三种构象的能量，同时计算了电负性电荷，亦将其用于分子力学计算，将两种计算结果进行比较发现，有可能将电负性作为分子力学、分子动力学计算的力场参数。     

X-ray Crystal Structure and Molecular Mechanics Calculations of (2,6-iso-dipropyl-phenylamide) Dimethyl ( tetra-methylcyclopenta-dienyl ) Silane Titanium Dichloride

Crystal and molecular structure of (2,6-dipropylphenylamide) dimethyl (tetra-methyl cyclopentadienyl) silane titanium dichloride (I) was fully characterized by X-ray diffraction. The crystal is obtained from a mixture of ether/hexane as orthorhombic, with a = 12.658 (3) (A), b = 16.62 (3)(A), c = 11.760 (2)(A), V = 2474.2 (9)(A) 3, Z = 4, space group Pnma, R = 0.0399. Componud I compose of the π-bounded ring with its dimethylsilyl-dipropyl phenyl amido group and the two terminal chloride atoms coordinated to central metal to form a so-called constrained geometry catalyst (CGC) structure. The result of molecular mechanics (MM) calculations on compound I shows that bond lengths and bond angles from the MM calculation are comparable to the data obtained from the X-ray diffraction study. The relation of the structure of CGCs and their catalytic activity by MM calculations is also discussed.     

X-ray Crystal Structure and Molecular Mechanics Calculations of (2,6-iso-dipropyl-phcnylamidc) Dimethyl (tetra-methylecyclopenta- dienyl)Silane Titanium Dichloride

ExperimentalSynthesisofitToI.sg(4mmol.)TiCI,.THFin25mLTHFwasaddedI.sg(4mmol.)dilithium(2,6-propylphenylamide)dimethyl(tetra-methylcyclopentadienyl)silaneandthemixturewasallowedtostirforIhour,then0.639AgCI(4mmol.)wasadded.After4hoursstirring,thesolventwasmovedandtheresiduewasextractedwithdiethylether.Theetherextractwasfilteredandevaporatedtodrynesstogive0.409yellowcrystallinesolid,yield41%.'H-NMR(C,D,)f0.48(6H),l.I2(6H),l.49(6H),l.98(6H).2.18(6H),and3.04(2H).Asuitablesinglecrystalwa…     

DETERMINATION OF THREE-DIMENSIONAL STRUCTURE OF CODEINE BY NMR MOLECULAR GRAPHICS TECHNIQUES

In this paper, we describe a method for calculating the three-dimensional structure ofantagonist drug codeine by means of one- and two-dimensional NMR and computer tech-niques. The calculation of molecular mechanics is based on NMR data, so we call it NMRmolecular graphics (NMRMG). With codeine as a demonstration. we find that the molecularstructure data from NMRMG are in quite good agreement with those by X-ray diffractionmeasurement. NMRMG can be utilized to study configuration and conformation of naturalproducts, especially rigid structure compounds in solution.     

Conformation and configuration of tertiary amines via GIAO-derived (13)C NMR chemical shifts and a multiple independent variable regression analysis.

The (13)C chemical shifts of six tertiary amines of unambiguous conformational structure are compared to predicted (13)C NMR chemical shifts obtained via empirically scaled GIAO shieldings for geometries from MM3 molecular mechanics calculations. An average deviation, absolute value of Deltadelta(av), of 0.8 ppm and a maximum deviation, absolute value of Deltadelta(max), of 2.8 ppm between predicted and experimental (13)C shifts of the six tertiary amines of unambiguous structure are found. In several cases of tertiary amines subject to rapid exchange, where experimental (13)C shifts at room temperature are weighted averages of multiple conformers, a comparison of calculated (13)C shifts of all reasonable MM3 predicted conformers with experimental (13)C shifts via a multiple independent variable regression analysis provides an efficient method of determining the major and minor conformers. The examples presented are 2-methyl-2-azabicyclo[2.2.1]heptane and 1,6-diazabicyclo[4.3.1]decane, which each have two expected contributing structures, and 2-(diethylamino)propane and 1,8-diazabicyclo[6.3.1]dodecane, where ten and seven low-energy conformers, respectively, are predicted by MM3 calculations.     

XAFS spectral analysis of the cadmium coordination geometry in cadmium thiolate clusters in metallothionein

We report the combination of measurement and prediction of X-ray absorption fine structure (XAFS) data, where the term XAFS refers to the overall spectrum that encompasses both the X-ray Absorption Near Edge Structure (XANES) region as well as the Extended X-ray Absorption Fine Structure (EXAFS) region, to evaluate the cadmium thiolate cluster structures in the metalloprotein metallothionein. XAFS spectra were simulated using coordinates from molecular models of the protein calculated by molecular mechanics/molecular dynamics (MM3/MD), from NMR analyses, and from analysis of X-ray diffraction data. XAFS spectra were also simulated using the coordinates from X-ray crystallographic data for [Cd(SPh)4]2-, CdS, [Cd2(mu-SPh)2(SPh)4]2-, and [Cd4(mu-SPh)6(SPh)4]2-. The simulated XAFS data that were calculated using the FEFF8 program closely resemble the experimental data reported for [Cd(SPh)4]2-, CdS, [Cd2(mu-SPh)2(SPh)4]2-, [Cd4(mu-SPh)6(SPh)4]2-, rabbit liver metallothionein cadmium alpha-domain (Cd4-alpha MT), and cadmium rabbit liver betaalpha metallothionein (Cd7-betaalpha MT). MM3 force field parameters were modified to include cadmium-sulfur bonding and were initially set to values derived from published X-ray diffraction and EXAFS experimental data. The force field was further calibrated and adjusted through comparison between experimental spectra taken from the literature and simulated XAFS spectra calculated using the FEFF8 program in combination with atomic coordinates from MM3/MD energy minimization. MM3/MD techniques were used with the calibrated force field to predict the high-resolution structure of the metal clusters in rabbit liver Cd7-MT. Structures for Cd3S9 (beta) MT and Cd4S11 (alpha) MT domains from MM3/MD calculations and those previously reported for Cd7-MT on the basis of 1H and 113Cd NMR data were compared. Structural differences between the different models for these cadmium thiolate clusters were evident. Combining the measurement and simulation of XAFS data provides an excellent method of assessing, modeling, and predicting metal-binding sites in metalloproteins when X-ray absorption spectroscopy (XAS) data are available.     

Spectral characterization of self-assemblies of aldopyranoside amphiphilic gelators: what is the essential structural difference between simple amphiphiles and bolaamphiphiles?

An aldopyranoside-based gelators (dodecanoyl-p-aminophenyl-beta-D-aldopyranoside)s and [1,12-dodecanedicarboxylic-bis(p-aminophenyl-beta-D-aldopyranoside)]s 1-4 were synthesized, and their gelation ability was evaluated in organic solvents and water. Simple aldopyranoside amphiphiles 1 and 2 were found to gelate organic solvents as well as water in the presence of a small amount of alcoholic solvents. More interestingly, not only extremely dilute aqueous solutions (0.05 wt%) of the bolaamphiphiles 3 and 4, but solutions of 3 and 4 in several organic solvents could be gelatinized. These results indicate that 1-4 can act as versatile amphiphilic gelators. We characterized the superstructures of the aqueous gels and organogels prepared from 1-4 using SEM, TEM, NMR and IR spectroscopy, and XRD. The aqueous gels 1 and 2 formed a three-dimensional network of puckered fibrils diameters in the range 20-200 nm, whereas the aqueous gels 3 and 4 produced filmlike lamellar structures with 50-100 nm thickness at extremely low concentrations (0.05 wt%). Powder XRD experiments indicate that the aqueous gels 1 and 2 maintain an interdigitated bilayer structure with a 2.90 nm period with the alkyl chain tilted, while the organogels 1 and 2 take a loosely interdigitated bilayer structure with a 3.48 nm period. On the other hand, the aqueous- and the organogels 3 and 4 have 3.58 nm spacing, which corresponds to a monolayered structure. The XRD, 1H NMR and FT-IR results suggest that 1-4 are stabilized by a combination of the hydrogen-bonding, pi-pi interactions and hydrophobic forces.     

Alcohols,ethers, carbohydrates,and related compounds. III. The 1,2-dimethoxyethane system

Ethylene glycol, its dimethyl ether, and some related compounds have been studied using the MM4 molecular mechanics force field. The MM4 calculated structural and energetic results have been brought into satisfactory agreement with a considerable number of experimental data and MP2/6-311++G(2d,2p) ab initio calculations. The heats of formation of these compounds are also well calculated. The MM4 ethylene glycol conformations in particular are in good agreement, both geometrically and in terms of energy, with those from the ab initio calculations. The corresponding dimethyl ether is of special interest, because it has been suggested that the trans-gauche conformation is unusually stable due to the hydrogen bonding of a hydrogen on a methyl group with the more distant oxygen. It is shown in the present work that while this conformation is more stable than might have been expected, the energy is adequately calculated by MM4 without using any hydrogen bonding between the Cbond;H bond and the oxygen. If such hydrogen bonding occurs, it amounts to no more than about 0.5 kcal/mol in energy, and is too small to detect with certainty. Additionally, energetic relationships in trans-1,2-dimethoxycyclohexane, 1,3,5,7-tetraoxadecalin, and 3-methoxytetrahydropyran have been studied, and the calculated results are compared with experimental information, which is adequately reproduced.     

First-principles simulations of the <Superscript>27</Superscript>Al and <Superscript>17</Superscript>O solid-state NMR spectra of the CaAl<Subscript>2</Subscript>Si<Subscript>3</Subscript>O<Subscript>10</Subscript> glass

The local and medium-range structure of the 20CaO·20Al₂O₃·60SiO₂ glass generated by classical molecular dynamics simulations has been compared to NMR experiments by computing the ²⁷Al and ¹⁷O NMR parameters and NMR spectra from first-principles simulations. The calculation of the NMR parameters (chemical shielding and quadrupolar parameters), which are then used to simulate solid-state MAS and 3QMAS NMR spectra, is achieved by the gauge including projector augmented-wave and the projector augmented-wave methods on the DFT-PBE relaxed structure. The NMR spectra calculated with the present approach are found to be in excellent agreement with the experimental data, providing an unambiguous view of the local and medium-range structure of aluminosilicate glasses.     

Alcohols,ethers, carbohydrates,and related compounds. II. The anomeric effect

The anomeric effect has been studied for a variety of compounds using the MM4 force field, and also using MP2/6-311++G(2d,2p) ab initio calculations and experimental data for reference purposes. Geometries and energies, including conformational, rotational barriers, and heats of formation were examined. Overall, the agreement of MM4 with the experimental and ab initio data is good, and significantly better than the agreement obtained with the MM3 force field. The anomeric effect is represented in MM4 by various explicit terms in the force constant matrix. The bond length changes are accounted for with torsion-stretch elements. The angle changes are accounted for with torsion-bend elements. The energies are taken into account with a number of torsional terms in the usual way. A torsion-torsion interaction is also of some importance. With all of these elements included in the calculation, the MM4 results now appear to be adequately accurate. The heats of formation were examined for a total of 12 anomeric compounds, and the experimental values were fit by MM4 with an RMS error of 0.42 kcal/mol.     

Dynamic structures of phosphodiesterase-5 active site by combined molecular dynamics simulations and hybrid quantum mechanical/molecular mechanical calculations

Various quantum mechanical/molecular mechanical (QM/MM) geometry optimizations starting from an x-ray crystal structure and from the snapshot structures of constrained molecular dynamics (MD) simulations have been performed to characterize two dynamically stable active site structures of phosphodiesterase-5 (PDE5) in solution. The only difference between the two PDE5 structures exists in the catalytic, second bridging ligand (BL2) which is HO- or H2O. It has been shown that, whereas BL2 (i.e. HO-) in the PDE5(BL2 = HO-) structure can really bridge the two positively charged metal ions (Zn2+ and Mg2+), BL2 (i.e. H2O) in the PDE5(BL2 = H2O) structure can only coordinate Mg2+. It has been demonstrated that the results of the QM/MM geometry optimizations are remarkably affected by the solvent water molecules, the dynamics of the protein environment, and the electronic embedding charges of the MM region in the QM part of the QMM/MM calculation. The PDE5(BL2 = H2O) geometries optimized by using the QM/MM method in different ways show strong couplings between these important factors. It is interesting to note that the PDE5(BL2 = HO-) and PDE5(BL2 = H2O) geometries determined by the QM/MM calculations neglecting these three factors are all consistent with the corresponding geometries determined by the QM/MM calculations that account for all of these three factors. These results suggest the overall effects of these three important factors on the optimized geometries can roughly cancel out. However, the QM/MM calculations that only account for some of these factors could lead to considerably different geometries. These results might be useful also in guiding future QM/MM geometry optimizations on other enzymes.