染料敏化太阳能电池中Eosin Y在TiO2(101)表面的吸附构型及其对电子注入过程影响的理论研究

基于密度泛函理论计算分析了2种Eosin Y-TiO₂(101)吸附构型下的几何结构、 电子结构及电荷转移性质. 结果表明, Eosin Y以H构型吸附在TiO₂(101)表面时的体系总能量比B构型的高59.7 kJ/mol; Eosin Y以B构型吸附在TiO₂(101)表面时比以H构型吸附时的吸附能更高. 因此, B吸附构型更易形成. 此外, 还对电子注入动力学进行了模拟并对界面间的电荷转移进行了Bader定量分析. 结果显示, 与吸附H构型相比, B构型下的电子注入过程更迅速也更完全.     

Inorganic asymmetric synthesis: diastereoselective syntheses of mono- and dinuclear complexes containing octahedral, two-bladed propeller, bis(pyridine-2-aldehyde 2'-pyridylhydrazone)iron(II) stereocenters

A C2 hexadentate diester derived from (5-hydroxymethyl)pyridine-2-aldehyde 2'-pyridylhydrazone (5-HOCH2PAPHY) and an enantiomerically pure (aS)-spirane dicarboxylic acid diastereoselectively reacts with iron(II) benzenesulfonate in methanol to furnish a 20% diastereomeric excess (de) of a two-bladed propeller, octahedral iron complex in which the P configuration of the newly created (+/-)-[Fe(PAPHY)2](2+) stereocenter predominates; when the reaction mixture is heated under reflux for 12 h, however, the excess of the diastereomer having the P configuration at iron increases to 80%, as determined by (1)H NMR spectroscopy. The configuration at iron in the major diastereomer of the complex was determined by comparison of the circular dichroism spectrum of the deprotonated complex with that of a related complex of known configuration. Repositioning of the hydroxymethyl group of the pyridine-2-aldehyde from the 5- to the 6-position produced a C2-spirane ligand that generates a double-stranded diiron(II) helicate in >99% de. Single crystal X-ray structure determinations of the racemates of the protonated and deprotonated helicates revealed that the complexes crystallize diastereoselectively, that is, two ligand strands of a S configuration generate two octahedral iron(II) stereocenters of P configuration to give a dinuclear metal helicate of P configuration and vice versa for the ligand of a R configuration.     

Effects of molecular configuration of a chiral trimeric phenylene vinylene on its liquid crystalline properties

Based on an analysis of the ~1H NMR,FT-IR,UV-vis spectra,a chiral trimeric phenylene vinylene derivative(ChTPV) synthesized by a Wittig reaction was determined to have a trans-cis configuration, and it could be isomerized to the trans-trans isomer when treated with iodine.The melting point of ChTPV with a trans-trans configuration increased by 162.1℃compared to the trans-cis isomer,and the ChTPV with trans-trans configuration exhibited the typical liquid-crystalline texture of the smectic A in the heating process.The results indicated that the molecular configuration can influence the formation of the liquid crystalline phase of ChTPV.     

Transport of water dissolved oxygen in polymers via electrochemical technique

Transport properties of polymer membranes for dissolved oxygen in a liquid-membrane-liquid configuration were investigated by using an electrochemical technique based on the use of the Clark oxygen electrode. The oxygen permeability and the diffusivity coefficient in a polymer-water system can be determined accurately by appropriate choice of the experimental conditions. Polymers that do not absorb water such as polyethyleneterephtalate (PET) and bioriented polypropylene (OPP) were tested for permeation experiments in both gas-membrane-gas and liquid-membrane-liquid configuration. Data obtained in the liquid-membrane-liquid configuration with the electrochemical technique show excellent agreement with those obtained with the gas-membrane-gas configuration. The permeability of water saturated Kapton® polyimide (PI) for dissolved oxygen was also evaluated and compared with data obtained in the gas-membrane-gas configuration.     

Two deformation paths in fission of light actinides

The correlation among the fission threshold energy, the scission configuration and the mass yield distribution has been studied in proton-induced fission of light actinides. It was found that there exist at least two fission paths from the threshold region to the scission. The elongated scission configuration is related with the fission process that goes over a higher threshold energy and results in a symmetric mass division mode, while the compact scission configuration with the process that experiences a lower threshold and ends up with an asymmetric mass division mode.     

Determination of the anomeric configuration of glycosyl esters of nucleoside pyrophosphates and polyisoprenyl phosphates by fast-atom bombardment tandem mass spectrometry

Collision-induced dissociation of the deprotonated molecules of glycosyl esters of nucleoside pyrophosphates and polyisoprenyl (dolichyl and polyprenyl) phosphates results in distinct fragmentation patterns that depend on cis-trans configuration of the phosphodiester and 2″ (or 2′, respectively)-hydroxyl groups of the glycosyl residue. At the collision-offset voltage of 0. 5 V, sugar nucleotides with cis configuration produce only one very abundant fragment of nucleoside monophosphate, whereas compounds with trans configuration give weak signals for nucleoside di- and mono-phosphates and their dehydration products. These fragmentation patterns are largely preserved at higher collision energy, with the exception that, for sugar nucleotides with trans configuration, the characteristic signals are much more abundant and a novel diagnostic fragment of [ribosyl(deoxyribosyl)-5′-P₂O₅ — H]^? is generated. In the case of polyisoprenyl-P-sugars, polyisoprenyl phosphate ion is the only fragment observed for compounds with trans configuration, whereas in compounds with cis configuration, this ion is accompanied by another abundant fragment, which is derived from the cleavage across the sugar ring and corresponds to [polyisoprenyl-PO₄-(C₂H₃O)]^?. The relative intensity ratio of the latter ion to the [polyisoprenyl-HPO₄]^? ion is close to 1 for compounds with cis configuration, but it is only about 0. 01 for compounds with trans configuration. This ratio may serve, therefore, as a diagnostic value for determination of the anomeric configuration of glycosyl esters of polyisoprenyl phosphates. It is proposed that the observed differences in fragmentation patterns of cis-trans sugar nucleotides and polyisoprenyl-P-sugars could be explained in terms of kinetic stereoelectronic effect, and a speculative mechanism of fragmentation of compounds with trans configuration is presented. For compounds with cis configuration, formation of a hydrogen bond between the C-2″(2′) hydroxyl and the phosphate group could play a crucial role in directing the specific fragmentation reactions. Consequently, the described empirical rules would hold only for compounds that have a free 2″(2′)-hydroxyl group and no alternative charge location. Owing to its simplicity, sensitivity, and tolerance of impurities, fast-atom bombardment-tandem mass spectrometry represents a suitable method for determination of the anomeric linkage of glycosyl esters of nucleoside pyrophosphates and polyisoprenyl phosphates if the absolute configuration of glycosyl residue is known and the compound fulfills the above-mentioned requirements.     

Adsorption of acicular particles at liquid-fluid interfaces and the influence of the line tension

In this paper, the adsorption energy of an acicular (prolate and cylindrical) particle onto a liquid-fluid interface and the effect of the line tension are investigated. The results show that, without line tension, acicular particles always prefer to lie flat in the plane of the interface. However, line tension plays a significant role in determining the adsorption of an acicular particle. First, the line tension creates an energy barrier for the adsorption of particles onto an interface. The planar configuration has a larger energy barrier due to the longer contact line. Therefore, the particles prefer to enter the interface in a homeotropic configuration and then rearrange to a planar configuration or an oblique configuration with a small tilt angle. Second, for prolate particles, an energy maximum occurs at some tilt angles when the line tension is large. Therefore, once the prolate particle is adsorbed on the interface in a homeotropic configuration or with a larger tilt angle, it must conquer an energy barrier to rearrange to a planar configuration. For cylindrical particles, when the line tension is higher, the planar configuration will not be the most energy-favorable configuration. The cylindrical particles prefer to stay in the interface with a small tilt angle.     

FCl:PCX complexes: old and new types of halogen bonds

MP2/aug'-cc-pVTZ calculations have been performed to investigate the halogen-bonded complexes FCl:PCX, for X = NC, CN, F, H, CCH, CCF, CH(3), Li, and Na. Although stable complexes with a F-Cl···P halogen bond exist that form through the lone pair at P (configuration I), except for FCl:PCCN, the more stable complexes are those in which FCl interacts with the C≡P triple bond through a perturbed π system (configuration II). In complexes I, the nature of the halogen bond changes from traditional to chlorine-shared and the interaction energies increase, as the electron-donating ability of X increases. The anionic complex FCl:PC(-) has a chlorine-transferred halogen bond. SAPT analyses indicate that configuration I complexes with traditional halogen bonds are stabilized primarily by the dispersion interaction. The electrostatic interaction is the most important for configuration I complexes with chlorine-shared halogen bonds and for configuration II complexes except for FCl:PCNa for which the induction term is most important. The F-Cl stretching frequency is red-shifted upon complexation. EOM-CCSD/(qzp,qz2p) spin-spin coupling constants have been obtained for all FCl:PCX complexes with configuration I. (1)J(F-Cl) decreases upon complexation. (2X)J(F-P) values are quadratically dependent upon the F-P distance and are very sensitive to halogen-bond type. (1X)J(Cl-P) tends to increase as the Cl-P distance decreases but then decreases dramatically in the chlorine-transferred complex FCl:PC(-) as the Cl-P interaction approaches that of a covalent Cl-P bond. Values of (1)J(F-Cl) for configuration II are reduced relative to configuration I, reflecting the longer F-Cl distances in II compared to those of the neutral complexes of I. Although the F-P and Cl-P distances in configuration II complexes are shorter than these distances in the corresponding configuration I complexes, (2X)J(F-P) and (1X)J(Cl-P) values are significantly reduced, indicating that coupling through the perturbed C-P π bond is less efficient. The nature of F-P coupling for configuration II is also significantly different, as evidenced by the relative importance of PSO, FC, and SD components.     

Enantioselective synthesis and stereoselective rearrangements of enol ester epoxides

Enol esters can be epoxidized with high enantioselectivities using the fructose-derived chiral ketone 1 as catalyst and Oxone as oxidant. A detailed study of enantiomerically enriched enol ester epoxides has revealed that the acid-catalyzed rearrangement can proceed through two distinct pathways, one with retention of configuration and the other with inversion. The competition between the two pathways is highly dependent upon the nature of the acid catalyst. A strong acid favors retention of configuration and a weak acid favors inversion of configuration. Under thermal conditions, these epoxides rearrange highly stereoselectively with inversion of configuration. Either enantiomer of an alpha-acyloxy ketone can be formed from one enantiomer of an enol ester epoxide by judicious choice of reaction conditions.     

振动圆二色谱在轴手性β-双咔啉N—O衍生物立体化学研究中的应用

采用振动圆二色谱(VCD)方法研究了一个具有高度催化活性的轴手性结构的双咔啉N—O化合物的立体化学结构. 在B3LYP/6-311+G(d)水平上得到的计算结果表明, 对于具有负旋光值的双咔啉N—O化合物化合物, 其绝对构型是aS. 同时, 分别计算了双咔啉N—O化合物的电子圆二色谱(ECD)和旋光值, 并与实验结果进行了比较. 在化合物结构完全正确条件下, VCD, ECD和旋光数据均表明, 具有负旋光值的该化合物的绝对构型是aS.     

Determination of the anomeric configuration of glycosyl esters of nucleoside pyrophosphates by fast-atom bombardment tandem mass spectrometry

Very low energy collision-induced dissociation of the deprotonated molecules of glycosyl esters of nucleoside pyrophosphates results in distinct fragmentation patterns that depend on the cis-trans configuration of the phosphodiester and 2″-hydroxyl groups of the glycosyl residue. In tandem mass spectrometry, sugar nucleotides with cis configuration produce only one, very abundant fragment that corresponds to nucleoside monophosphate, whereas nucleotides with trans configuration give weak signals for the nucleoside di- and monophosphates and their dehydration products. This empirical rule holds for sugar nucleotides that have a free 2″-hydroxyl group and no alternative charge location. Owing to its simplicity, sensitivity, and tolerance of impurities, fast-atom bombardment-tandem mass spectrometry represents a suitable method for determination of the anomeric linkage of glycosyl esters of nucleoside pyrophosphates if the absolute configuration of glycosyl residue is known and the compound fulfills the above-mentioned requirements.     

Bijvoet in solution reveals unexpected stereoselectivity in a Michael addition

The absolute configuration of small crystallizable molecules can be determined with anomalous X-ray diffraction as shown by Bijvoet in 1951. For the majority of compounds that can neither be crystallized nor easily be converted into crystallizable derivatives, stereocontrolled organic synthesis is still required to establish their absolute configuration. In this contribution, a new fundamental methodology for resolving the absolute configuration will be presented that does not require crystallization. With residual dipolar coupling enhanced NMR spectroscopy, ensembles of a limited number of structures are created reflecting the correct conformations and relative configuration. Subsequently, from these ensembles, optical rotation dispersion (ORD) spectra are predicted by DFT calculations and compared to experimental results. The combination of these two steps reveals the absolute configuration of a flexible molecule in solution, which is a big challenge to chiroptical methods and DFT in the absence of NMR spectroscopy. Here the absolute stereochemistry of the product of a new Michael addition, synthesized via a niobium(V) chiral enolate, will be elucidated by using the new methodology.     

Stable molecular configuration in crystalline carboxylic acids

The stable (lower enthalpy) molecular configurations of propionic, butyric, Jeric and lauric acids in the crystalline state have been examined via their atom-atom potentials. It was found that the cis configuration is more stable than the trans configuration for propionic, butyric and valeric acids, and that the trans configuration is more stable than the cis configuration for lauric acid, in accord with a previous IR spectral analysis. The potential energy of benzoic acid was recalculated using the positions of atoms given by Speakman, and indicates that the A form is more stable than the B form, in agreement with the results of previous work.     

完全活性空间组态相互作用能量的拟合和外推

完全活性空间组态相互作用计算与完全活性空间中的活性电子数和活性轨道数有关,但完全活性空间组态相互作用的能量不是活性电子数和活性轨道数的单调递减函数,因此活性轨道数和活性电子数不能用来外推完全活性空间组态相互作用的能量。为此,我们定义了一个新的变量:活性空间中的最大未占满轨道数。我们对一系列单重态、双重态和三重态分子进行了完全活性空间组态相互作用的计算,并利用活性空间中的活性电子数和最大未占满轨道数这两个变量,对这些基态能量进行了拟合和外推,拟合的均方根误差都在10~(-6)数量级。外推能量的精度优于MP4,对小分子体系,其精度高于CCSD。外推的完全的组态相互作用(FCI)能量值和实际计算的FCI值也很接近。另外,我们还利用外推能量来优化双原子分子的平衡键长,并计算谐振频率,其精度优于CASSCF。     

Synthesis and absolute configuration of substituted morpholines

We studied methods of stereospecific synthesis that enabled us to obtain variously substituted morpholinic compounds and to determine their absolute configuration. From a study of the chiroptical properties of synthetic N-[2-pyridyl-N-oxide] derivatives of optically active morpholines, it was possible to correlate the sign of the Cotton effect with the absolute configuration. This correlation agrees with that previously established for derivatives of the piperidine type. By evaluating the various contributions to the Cotton effect of substituents in positions 2 and 3, we established the absolute configuration of bicyclic compounds condensed in the two positions mentioned above.     

Strapped Porphyrins as Model Systems for Atropisomeric Photosensitizer Drugs

The time dependence of atropisomer interconversion has limited the pursuit of single atropisomer drug candidates, even in circumstances where one atropisomer presents favorable biological activity over another. Moderate interconversion energy barriers risk compromising drug stability. As a result, examples of atropisomerically pure drugs in current clinical use are rare. However, in recent years, there has been a shift towards the development of single, stable atropisomer drug candidates with enhanced activity. Consequently, development of methods which effectively restrict rotation in a configuration which favors activity is highly beneficial. The picket fence porphyrin α₄ atropisomer configuration has been previously demonstrated to improve the cell internalization of the pre-clinical drug, redaporfin, applied in photodynamic therapy. In this work, the α₄ configuration was modelled with novel porphyrin photosensitizers through strapped moieties which effectively fixed the atropisomeric configuration. The stable cis-αα configuration demonstrated enhanced cell membrane permeation, effectively predicting the behavior of the α₄ configuration and indicates that strapped porphyrins can serve as stable model systems for the investigation of photoactive drugs.     

Synthetic approaches to phomactins: Late stage stereochemical and reactivity issues

Oxidation of a 15-methylenebicyclo[9.3.1]pentadeca-3,7-dien-14-ol with a 10-phenylsulfonyl substituent provided a 14-oxobicyclo[9.3.1]pentadeca-1(15),3,7-triene-15-carbaldehyde that on reduction with DIBAL-H was converted into a 15-hydroxymethylbicyclo[9.3.1]pentadeca-1(15),3,7-triene-14-ol with the relative configuration at C14 required for incorporation into a synthesis of phomactin A. The oxidation and reduction of an analogous 3,4-epoxide that lacked the 10-phenylsulfonyl group gave a diol with the opposite relative configuration at C14. However, the TPAP oxidation and DIBAL-H reduction of a 14-hydroxy-15-methylene-3,4-epoxide that still had the 10-phenylsulfonyl group gave a diol with the required configuration at C14 although the expected spontaneous participation of the 14-hydroxyl group in an intramolecular epoxide ring-opening was only observed under Lewis acidic conditions.     

Stability considerations of the capillary condensation within a cylindrical pore

A proof of the stability of the unduloid configuration within a cylindrical pore is given. The proof involves calculus of variation techniques and in particular the theory of the problem of Bolza is used. It is shown that the unduloid configuration is stable to small disturbances provided dV/dκ < 0, where V represents the volume of the configuration and κ is the curvature of the configuration. If this condition is not satisfied the unduloid configuration is unstable.     

Assignment of absolute configuration of cyclic secondary amines by NMR techniques using Mosher's method: a general procedure exemplified with (-)-isoanabasine

A general procedure to determine the absolute configuration of cyclic secondary amines with Mosher's NMR method is demonstrated, with assignment of absolute configuration of isoanabasine as an example. Each Mosher amide can adopt two stable conformations (named rotamers) caused by hindered rotation around amide C--N bond. Via a three-step structural analysis of four rotamers, the absolute configuration of (-)-isoanabasine is deduced to be (R) on the basis of Newman projections, which makes it easy to understand and clarify the application of Mosher's method to cyclic secondary amines. Furthermore, it was observed that there was an unexpected ratio of rotamers of Mosher amide derived from (R)-isoanabasine and (R)-Mosher acid. This phenomenon implied that it is necessary to distinguish the predominant rotamer from the minor one prior to determining the absolute configuration while using this technique.     

Configuration space partitioning and matrix buildup scaling for the vibrational configuration interaction method

The accurate computation of anharmonic vibrational states for medium to large molecules is a requirement for the detailed understanding of nonlinear multidimensional infrared spectra and the dynamical information encoded in them. The vibrational configuration interaction (VCI) method constitutes a particularly promising tool in this respect. It is generally hampered though by its unfavorable scaling with respect to system size. We analyze the scaling behavior of several well‐known as well as some new approximate VCI schemes in detail, which are complementary to the class of configuration selection schemes developed recently. We find that the combination of a configuration space partitioning, possibly based on configuration selection, with energetic thresholding and resonance screening provides an efficient scheme for the reduction of computational effort involved in VCI calculations while at the same time maintaining sufficient accuracy for the vibrational energies. © 2012 Wiley Periodicals, Inc.