Highly Efficient α‐Sialylation by Virtue of Fixed Dipole Effects of N‐Phthalyl Group: Application to Continuous Flow Synthesis of α(2‐3)‐and α(2‐6)‐Neu5Ac‐Gal Motifs by Microreactor

Highly α‐selective sialylation of sialic acid N‐phenyltrifluoroacetimidate with various galactose and lactose acceptors has been achieved by introducing the C‐5 N‐phthalyl group on the donor. The “fixed dipole effect” of the N‐phthalyl group was proposed to explain the high reactivity and α‐selectivity. The microfluidic system was applied to the present α‐sialylation, which is amenable to large‐scale synthesis. The N‐phthalyl group was removed by treatment with methylhydrazine acetate, for which protocol can be readily applied to the synthesis of a variety of sialic acid‐containing oligosaccharides.      

Synthesis and Molecular Properties of Acceptor‐Substituted Squaraine Dyes

A broad series of more than 20 acceptor‐substituted squaraines was synthesized that feature different acceptor functionalities at the central squaraine four‐membered ring. The influence of these acceptor units on the reactivity of semisquaraine precursors and stability of the respective squaraines were explored. Thereby the dicyanovinyl group was found to be the most versatile acceptor group that enabled various modifications at the donor moiety of the squaraine scaffold, leading to an extended series of dicyanovinyl‐functionalized squaraines. The variation of donor units afforded a set of NIR fluorophores that cover a wavelength region from the visible at about 650 nm far into the NIR up to 920 nm with fluorescence quantum yields between 0.93 and 0.11 and outstanding optical brightness. This excellent optical property is related to a rigid molecular scaffold that is fixed in an all‐cis configuration by the additional dicyanovinyl acceptor unit. The change of the molecular symmetry from C_2h to C_2v upon functionalization of the squaraine core with dicyanovinyl acceptor group has been confirmed in solution by electro‐optical absorption (EOA) spectroscopy, revealing permanent ground‐state dipole moments μ_g in the range between 4.3 and 6.4 D. These dipole moments direct an antiparallel packing of the molecules in the solid state according to single‐crystal X‐ray analyses achieved for four dicyanovinyl‐functionalized squaraines. The structural properties, the EOA results, as well as the band shapes of the optical spectra indicate that these polymethine dyes are cyanine‐type chromophores. It is worth noting that the orientation of the dipole moment vectors is orthogonal to the orientation of the transition dipole moment vectors, which is an uncommon but characteristic feature of this rather novel class of polymethine dyes. With regard to applications of these dyes in organic solar cells, their redox properties were also studied by cyclic voltammetry.     

Valence state parameters of all transition metal atoms in metalloproteins—development of ABEEMσπ fluctuating charge force field

To promote accuracy of the atom‐bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc‐Zn, Y‐Cd, and Lu‐Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO‐3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy. © 2014 Wiley Periodicals, Inc.     

Cooperativity and cluster growth patterns in acetonitrile: A DFT study

Cooperativity in intermolecular interactions and cluster growth patterns of acetonitrile has been studied using M06L density functional theory. Cyclic, ladder‐type, stacked, cross‐stacked, and mixed patterns are studied. Total interaction energy (E_int) and interaction energy per monomer (E_m) show maximum stability and cooperativity in stacked clusters followed by cross‐stacked ones. As cluster size increased, magnitude of E_m showed significant increase. Compared to E_m of dimer (?2.97 kcal/mol), the increase is 2.6‐fold for 27mer . Higher stabilization in larger clusters is attributed to strong cooperativity in intermolecular C? H···N and dipolar interactions. Enhanced cooperativity in stacked structures is supported by atoms‐in‐molecule electron density (ρ) data. Sum of ρ at intermolecular bond critical points is the highest for stacked clusters. Further, area of negative‐valued molecular electrostatic potential is linearly related with E_int and showed the lowest value in stacked followed by cross‐stacked clusters, indicating maximum utilization of lone pair density and maximum cooperativity in such growth patterns. A red shift in the average C? N stretching frequencies with increase in the number of monomers and its direct correlation with E_int in stacked clusters also supported their stability. Further, two known crystal patterns of acetonitrile (α and β) with 16 monomers are optimized and compared with the most stable hexadecamer pattern and are found to show lower values for E_int and E_m compared to the latter. Based on this result, we predict the existence of a third crystal pattern for acetonitrile which will be more ordered and more stable than α and β forms. © 2014 Wiley Periodicals, Inc.     

同型二聚体肽模型的二维红外光谱

利用一个同型二聚体模型,甲酰胺二聚体,模拟一对肽基团.用量子化学从头计算考察了二聚体中酰胺-I带振动模式之间的振动耦合及其在空间的行为. 研究发现C=O伸缩振动耦合以静电作用为主,耦合有效距离能超过10 oA. 一维和二维红外光谱的激子模拟计算表明,耦合常数的空间依赖性能够清楚地表现在光谱特征中. 这些结果意味着多肽中C=O伸缩振动模式能够在很远的距离相互耦合并产生振动态的离域化.     

Adsorption of three selected flavonoids with humic fraction-modified silica gel in hexane: A mechanism study

Three selected flavonoids, commonly found in spices, red-purple fruits, and vegetables, were adsorbed on humic fraction-modified silica gel in hexane. The percentage of adsorption in hexane for all examined analytes was nearly 100% after 1 hr, as a result of the strong dipole–dipole interaction. The increasing amount of adsorbent involved in the process improved the percentage of adsorption, which in turn shortened the time needed to reach the maximum by providing more binding sites. However, adsorption was not observed in other liquid phases under the same conditions, such as acetonitrile and ethyl ether. The mechanism leading to the adsorption was explored chromatographically, as well as by fourier transform infrared spectroscopy (FTIR) and theoretical simulations.     

Novel Synthesis of N‐Methyl Spiropyrrolidines by 1,3‐Dipolar Cycloaddition Reaction of Azomethine Ylides

A series of novel N‐methyl spiropyrrolidines have been synthesized in good yield by the cycloaddition reaction of azomethine ylides generated by a decarboxylative route from sarcosine and paraformaldehyde with conformationally locked s‐trans enone functionality present in the (E)‐3‐arylidene‐4‐chromanone as dipolarophiles. The structure of the title compound was established by spectroscopic techniques.     

Multireference calculations on low-lying states and the X~3 Π_u -~3 Π_g absorption spectra of indium dimers

Multireference configuration interaction calculations are carried out on 11 Λ-S low-lying electronic states of indium dimers. The states are investigated with spin-orbit pseudopotentials via the state-interacting method, and characterized by fitted spectroscopic constants based on computed potential energy curves. The vibrational structures of the double-potential well 0+g (I) ( 3 Σ g ) state are also analyzed. The experimentally observed absorption spectrum centred at ～ 13000cm-1 is simulated and assigned to X 3 Πu (v=0)-3Πg transition according to the present ab initio calculations on transition energies and dipole moment functions.     

The transient scattering mechanism of dipole array with reflector

The transient backscattering mechanisms of a dipole array with reflector have been investigated from different aspects： time-domain, frequency-domain, and combined time-frequency domain, using 4 × 8 dipole arrays with reflector as an example. The data of scattering from the arrays under the incidence of Gaussian pulses are obtained by finite differential time domain method. The influences of the array structural parameters, incident wave parameters, and incident angles on the waveforms, spectrum, and time-frequency representations of the backscattered fields of the arrays are analysed and conclusions are drawn. From these characteristics and conclusions, it is possible to deduce the array structure inversely from the backscattered field.     

Theoretical study of the <Superscript>1,3</Superscript>Σ<Superscript>+</Superscript> states of the NaH molecule in the adiabatic and diabatic representations

Adiabatic and diabatic study for all the states dissociating below the ionic limit [i.e., Na (3s, 3p, 4s, 3d, 4p, 5s, 4d, and 4f) + H (1s)] in ¹Σ⁺ and ³Σ⁺ symmetries are presented. Adiabatic results are also reported for ^1,3Π and ^1,3Δ symmetries. Pseudo-potential, operatorial core-valence correlation, and full valence CI approaches combined with an efficient diabatization procedure are used in these ab initio calculations. Our vibrational-level spacings and spectroscopic constants are in good agreement with the available experimental data for the low-lying states. Diabatic potentials and dipole moments are analyzed, revealing the strong imprint of the ionic state in the ¹Σ⁺ adiabatic states. The hydrogen electron affinity correction was taken into account by the use of the efficient diabatization method. This leads to a better agreement with the available experimental data. Experimental suggestions are also given for the higher excited states based on their unusual behavior.