Quantum control of internal conversion in 24-vibrational-mode pyrazine

Quantum control of the S(2)-->S(1) internal conversion in a complete 24-mode dimensionality model of pyrazine is demonstrated. The fully quantum mechanical study makes use of the recently developed "QP algorithm" for performing accurate computations of projected quantum dynamics and the role of overlapping resonances in control. The results are extremely encouraging, demonstrating active control over internal conversion so as to almost completely suppress the process over time scales of approximately 50-100 fs [well in excess of the natural internal conversion times (approximately 20 fs)] or to accelerate it to complete internal conversion in less than 5 fs. A number of new diagnostics are introduced to demonstrate the significance of overlapping-resonance contributions to control. Control is far better than for a reduced dimensionality model of pyrazine, presumably because of the increased degree of overlap between bound state resonances existing in the full dimensionality case.     

A triazene-based new photolabile linker in solid phase chemistry

An extension of the T2 linker methodology by showing its applicability as a photocleavable linker is reported. Photocleavage was carried out with 355 nm UV laser irradiation (3ω Nd-YAG) in methanol/diethyl ether and is suitable for protected amino acid derivatives, as well as simple small organic molecules including resin-bound biotin. The linker is stable under a wide range of conditions with the exception of strongly acidic media.     

有机分子偶氮苯在高岭石表面吸附研究

利用Gaussian 98软件,采用量子化学从头算计算方法,研究有机分子偶氮苯在高岭石表面的吸附作用.不同位置的吸附结果比较表明,吸附后体系稳定性强弱及电子发生转移的可能性大小依次是平行于硅氧烷表面、平行(010)面、平行[AlO4]八面体表面.芳香环上的π键和硅氧烷表面的O原子均相互作用,电子从偶氮苯上的C和N原子流向高岭石表面的O原子.对吸附复合物进行了X射线粉末衍射(XRD)、红外光谱(FTIR)测试及结构分析,结果表明,偶氮苯吸附到高岭石的硅氧烷表面.     

A base labile handle for solid phase organic chemistry

Several arylsulfonamides have been synthesised on solid phase using a new base labile handle. Cleavage from the solid support is accomplished by oxidation of the sulfide to the sulfone, followed by β-elimination in base media.     

黄酮体化合物抗肿瘤活性的量子化学研究

本文对黄酮类化合物抗肿瘤活性进行了量子化学研究。采用从头算方法计算了黄酮体化合物的电荷分布，并基于电荷分布提出了黄酮体化合物表现抗肿瘤活性时与受体作用的模型：A环与受体的负电荷中心结构，C环与受体的正电荷中心结合，其他部分通过氢键与受体发生作用，氢键在受体的作用中起到很大的作用。     

桂皮酰异丁胺类化合物定量构效关系的量子化学研究

桂皮酰胺类化合物具有多种生理作用。目前研究较多的主要在抗惊作用方面。以往的研究表明,桂皮酰胺类化合物的抗惊作用与苯环上取代基及酰胺氮原子上取代基有关。其中桂皮酰异丁胺类化合物有较强的抗惊生物活性。而苯环取代基与酰胺间存在合理搭配问题。为了研究此类化合物的结构与抗惊作用的关系,并为进一步改造结构提供数据。本文采用量子化学从头算方法对此类化合物进行了计算,探讨了这类化合物的量化参数与抗惊生物活性之间的关系。图1给出了这些化合物的结构式。     

Quantum chemistry beyond Born–Oppenheimer approximation on a quantum computer: A simulated phase estimation study

We present an efficient quantum algorithm for beyond‐Born–Oppenheimer molecular energy computations. Our approach combines the quantum full configuration interaction method with the nuclear orbital plus molecular orbital method. We give the details of the algorithm and demonstrate its performance by classical simulations. Two isotopomers of the hydrogen molecule (H₂, HT) were chosen as representative examples and calculations of the lowest rotationless vibrational transition energies were simulated. © 2016 Wiley Periodicals, Inc.     

木质素二聚体模型化合物热解机理的量子化学研究

β-O-4连接是木质素主体结构单元之间的主要联结方式。采用密度泛函理论方法B3LYP,在6-31G (d, p)基组水平上,对β-O-4型木质素二聚体模型化合物(1-愈创木基-2-(2-甲氧基苯氧基)-1,3丙二醇)的热解反应机理进行了研究。提出了三种热解反应途径:C_β-O键均裂的后续反应、C_α-C_β键均裂的后续反应以及协同反应。对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化,计算了各热解反应途径的标准动力学参数。分析了各种主要热解产物的形成演化机理以及热解过程中温度对热解机理的影响。计算结果表明,C_β-O键的均裂反应和协同反应路径(1)和(3)是木质素二聚体热解过程中主要的反应路径,而C_α-C_β键的均裂反应和协同反应路径(2)和(5)是主要的竞争反应路径;热解的主要产物是酚类化合物如愈创木酚、1-愈创木基-3-羟基丙酮、3-愈创木基-3-羟基丙醛、愈创木基甲醛和乙烯等。在热解低温阶段协同反应是热解过程中的主要反应形式,而在高温阶段自由基均裂反应是热解过程的主要反应形式。     

Microwave-assisted solid phase conversion study of Meldrum's acid to ethylenetetracarboxylic dianhydride (C6O6)

Utilization of microwave irradiation provides an effective method for fast synthesizing of some important compounds. Microwave-assisted solid phase is an especial class in chemical synthesis. By the use of MW-irradiation on chemicals, sometimes interesting results can be seen. The synthesis of the interesting molecule ethylenetetracarboxylic dianhydride (C₆O₆) was attempted with a few different methods. In this study, the microwave-assisted solid phase conversion of Meldrum's acid to ethylenetetracarboxylic dianhydride was reported. This conversion was characterized by FT-IR, GC/MS and NMR spectroscopy results.     

Ab initio based surface-hopping dynamics study on ultrafast internal conversion in cyclopropanone

Cyclopropanone exhibits an intriguing phenomenon that the fluorescence from the S(1) state disappears below 365 nm. This is ascribed to the ultrafast S(1) → S(0) internal conversion process via conical intersection, which deprives opportunity of the fluorescence emission. In this work, we have used ab initio based surface hopping dynamics method to study vibrational-mode-dependent S(1) → S(0) internal conversion of cyclopropanone. A new conical intersection between the S(1) and S(0) states is determined by the state-averaged CASSCF/cc-pVDZ calculations, which is confirmed to play a critical role in the ultrafast S(1) → S(0) internal conversion by the nonadiabatic dynamics simulations. It is found that the internal conversion occurs more efficiently when the initial kinetic energies are distributed in the four vibrational modes related to the C═O group, especially in the C-O stretching and the O-C-C-C out-of-plane torsional modes. Meanwhile, the S(1) lifetime and the time scale of the S(1) → S(0) internal conversion are estimated by the ab initio based dynamics simulations, which is consistent with the ultrafast S(1) → S(0) internal conversion and provides further evidence that the ultrafast internal conversion is responsible for the fluorescence disappearance of cyclopropanone.     

Semiclassical initial value representation study of internal conversion rates

Internal conversion is an inherently quantum mechanical process. To date, "on the fly" computation of internal conversion rates is limited to harmonic approximations, which would seem to be especially unsuitable, given that the typical transition to the ground electronic state occurs at energies which are far from the harmonic limit. It is thus of interest to study the applicability of the semiclassial initial value representation (SCIVR) approach which is in principle amenable to on the fly studies even with "many" degrees of freedom. In this paper we study the applicability of the Herman-Kluk (HK) SCIVR to a model system with two coupled and anharmonic degrees of freedom. We find that (a) the HK SCIVR is a good approximation to the exact quantum dynamics; (b) computation of the first order correction to the HK-SCIVR approximation corroborates the accuracy; (c) by studying a large parameter range, we find that the harmonic approximation is mostly unsatisfactory; and (d) for the specific model used, the coupling between the modes was found to be relatively unimportant. These results imply that the HK-SCIVR methodology is a good candidate for on the fly studies of internal conversion processes of "large" molecules.     

Selenol protecting groups in organic chemistry: special emphasis on selenocysteine Se-protection in solid phase peptide synthesis

The appearance of selenium in organic synthesis is relatively rare, and thus examples in the literature pertaining to the masking of its considerable reactivity are similarly uncommon. Greene's Protecting Groups in Organic Synthesis, the standard reference for the state of the art in this arena, offers no entries for selenium protective methodology, in stark comparison to its mention of the great variety of protecting groups germane to its chalcogen cousin sulfur. This scarcity of Se-protection methods makes it no less interesting and pertinent toward the construction of selenium-containing organic systems which do indeed require the iterative blocking and de-blocking of selenol functionalities. A selenium-containing system which is especially relevant is selenocysteine, as its use in Solid Phase Peptide Synthesis requires extensive protection of its selenol side chain. This review will attempt to summarize the current state of understanding with regard to selenium protection protocol in organic synthesis. Moreover, it will provide a special emphasis on selenocysteine side chain protection, comprising both the breadth of functionality used for this purpose as well as methods of deprotection.     

Ferroelectricity in solid state chemistry

This article discusses some state-of-the-art aspects of solid state chemistry within the context of ferroelectric materials such as oxides, fluorides and oxyfluorides, whose crystalline networks include octahedra. Structural considerations make it possible to determine the origin of the ferroelectricity and to predict the existence of polar properties in new families. Crystallographic distortions of different nature lead to highly variable transition sequences. Ferroelectricity is often associated with ferroelasticity. The Curie temperature is linked to the composition and to the chemical bond. In this respect, several factors are to be considered, e.g. size, coordination and configuration of the cations, covalence of bonds, order-disorder, etc. Physical studies are very useful: first, the dielectric characteristics and their variations with temperature, frequency and electric field are typical of ferroelectrics; second, the pyroelectric, piezoelectric, electro-optical and non-linear optical properties are among the most effective. Various types of materials (single crystals, ceramics, thin films) are used nowadays in a wide range of applications. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASferroelectricity / solid state chemistry     

Quantum chemistry in parallel with PQS

This article describes the capabilities and performance of the latest release (version 4.0) of the Parallel Quantum Solutions (PQS) ab initio program package. The program was first released in 1998 and evolved from the TEXAS program package developed by Pulay and coworkers in the late 1970s. PQS was designed from the start to run on Linux‐based clusters (which at the time were just becoming popular) with all major functionality being (a) fully parallel; and (b) capable of carrying out calculations on large—by ab initio standards—molecules, our initial aim being at least 100 atoms and 1000 basis functions with only modest memory requirements. With modern hardware and recent algorithmic developments, full accuracy, high‐level calculations (DFT, MP2, CI, and Coupled‐Cluster) can be performed on systems with up to several thousand basis functions on small (4‐32 node) Linux clusters. We have also developed a graphical user interface with a model builder, job input preparation, parallel job submission, and post‐job visualization and display. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

Quantum chemistry study on B14, B,and B14H

The structure of B₁₄, B, and B₁₄H in octahedral symmetry has been investigated by ab initio calculations at the STO-3G and 4–31G levels. The relationship of molecular orbitals among them has been analyzed and it can be found that the number of valence bonding orbitals of high borane obeys the Wade rule. The similarities and difference between boron clusters and carbon clusters are also discussed. © 1994 John Wiley & Sons, Inc.     

Quantum chemistry study on cation structures of fluorinated and chlorinated germanes and their radicals

The structures and vibrational frequencies of cations of fluorinated and chlorinated germanes and radicals (GeHxXy+, X = F, Cl; x + y = 1-4) and protonated germanes are investigated theoretically at B3LYP/6-31+G(2df,p) level. For GeH2, GeHX, GeH2X, GeHX2, and germanes, the most stable cationic structures are largely distorted from their neutral ones and all can be viewed as ion complexes between a Ge-centered cation and a neutral atom or diatom. The ionization potentials, appearance energies, and proton affinities are obtained at Gaussian-3(CC) levels. Cations with the lowest energy (and adiabatic ionization potentials (in eV)) are Ge+-H2 (2B2, 8.94), Ge+-FH (9.42), Ge+-ClH (9.45), GeH3(+) (8.01), GeF+-H2 (7.71), GeCl+-H2 (8.01), GeF+-FH (7.69), GeCl+-ClH (7.80), GeH2(+)-H2 (10.45), GeH2(+)-FH (10.32), GeHF+-FH (10.64), GeF2(+)-FH (11.40), GeF4(+) (15.22), GeH2(+)-ClH (10.29), GeHCl+-ClH (10.33), GeCl2(+)-ClH (10.43), and GeCl4(+) (11.48). The most stable protonated germanes (and proton affinities (in kJ/mol, 0 K)) are GeH3(+)-H2 (658.3), GeH3(+)-FH (672.5), GeH2F+-FH (634.2), GeHF2(+)-FH (583.4), GeF3(+)-FH (516.3), GeH3(+)-ClH (672.7), GeH2Cl+-ClH (652.6), GeHCl2(+)-ClH (637.5), and GeCl3(+)-ClH (624.4), respectively. The G3 atomization energies of fluorinated Ge-species are found to be significantly different from G3X and G4 ones, and this may merit further investigation.