Computational and experimental studies of the conformational reactions of 1,3,5-tris(pentaphenylphenyl)benzene

Computational analyses of the five possible functional group rotations in 1,3,5-tris(pentaphenylphenyl)benzene (1) were conducted at three disparate levels of theory: AM1, HF/STO-3G, and B3LYP/6-31G(d). The ground state and transition state structures were located for all of the conformational reactions, and the free energies of activation for these processes were calculated. In addition, compound 1 was resolved by low-temperature chromatography on a chiral support, and its barrier to racemization was determined by dynamic chromatography. These computational and experimental results are compared with data from dynamic NMR studies of 1 in the literature.     

A new spectroscopic tool for surface layer analysis: multiple-angle incidence resolution spectrometry

A series of application studies of infrared multiple-angle incidence resolution spectrometry (IR-MAIRS) have been reported since it was first proposed as a unique technique for analyzing molecular orientation in thin films on an optically transparent substrate, and both expected and unexpected benefits of IR-MAIRS have been revealed. In this review, cutting-edge application studies are summarized systematically, and the principle of MAIRS is explained from a new point of view.     

A cyclic group action on resolutions of quadruple systems

We prove that the necessary conditions for a quadruple system with a cyclic resolution to exist are sufficient for all possible v and all .     

The first pure LambdaHT rotamer of a complex with a cis-[metal(nucleotide)2] unit: a cis-[Pt(amine)2(nucleotide)2] LambdaHT rotamer with unique molecular structural features

cis-[PtA2(nucleotide)2] complexes (A2 stands for two amines or a diamine) have been extensively investigated as model compounds for key cisplatin-DNA adducts. All cis-[metal(nucleotide/nucleoside)2] complexes with guanine and related purines characterized in the solid state thus far have the DeltaHT conformation (head-to-tail orientation of the two bases and right-handed chirality). In sharp contrast, the LambdaHT conformation (left-handed chirality) dominates in acidic and neutral aqueous solutions of cis-[PtA2(5'-GMP)2] complexes. Molecular models and solution experiments indicate that the LambdaHT conformer is stabilized by 5'-phosphate/N1H hydrogen-bond interactions between cis nucleotides with the normal anti conformation. However, this evidence, while compelling, is indirect. At last, conditions have been defined to allow crystallization of this elusive conformer. The structure obtained reveals three unique features not present in all other cis-[PtA2(nucleotide)2] solid-state structures: a LambdaHT conformation, very strong hydrogen-bond interactions between the phosphate and N1H of cis nucleotides, and a very small dihedral angle between the planes of the two guanines lying nearly perpendicular to the coordination plane. These new results indicate that, because there are no local base-base repulsions precluding the LambdaHT conformer, global forces rather than local interactions account for the predominance of the DeltaHT conformer over the LambdaHT conformer in the solid state and in both inter- and intrastrand HT crosslinks of oligonucleotides and DNA.     

Iterative tandem catalysis of secondary diols and diesters to chiral polyesters

The well-known dynamic kinetic resolution of secondary alcohols and esters was extended to secondary diols and diesters to afford chiral polyesters. This process is an example of iterative tandem catalysis (ITC), a polymerization method where the concurrent action of two fundamentally different catalysts is required to achieve chain growth. In order to procure chiral polyesters of high enantiomeric excess value (ee) and good molecular weight, the catalysts employed need to be complementary and compatible during the polymerization reaction. We here show that Shvo's catalyst and Novozym 435 fulfil these requirements. The optimal polymerization conditions of 1,1'-(1,3-phenylene) diethanol (1,3-diol) and diisopropyl adipate required 2 mol% Shvo's catalyst and 12 mg Novozym 435 per mmol alcohol group in the presence of 0.5 M 2,4-dimethyl-3-pentanol as the hydrogen donor. With these conditions, chiral polyesters were obtained with peak molecular weights up to 15 kDa, an ee value up to 99% and with 1-3 % ketone end groups. Also with the structural isomer, 1,4-diol, a chiral polyester was obtained, albeit with lower molecular weight (8.3 kDa) and slightly lower ee (94%). Aliphatic secondary diols also resulted in enantio-enriched polymers but at most an ee of 46 % was obtained with molecular weights in the range of 3.3-3.7 kDa. This low ee originates from the intrinsic low enantioselectivity of Novozym 435 for this type of secondary aliphatic diols. The results presented here show that ITC can be applied to procure chiral polyesters with good molecular weight and high ee from optically inactive AA-BB type monomers.     

Breaking symmetry: spontaneous resolution of a polyoxometalate

A chiral polyoxometalate [Hf(PW11O39)2]10- (1) has been prepared and structurally characterized. It crystallizes in the chiral space group P2(1)2(1)2, as a conglomerate of two enantiomerically pure crystals in the absence of any chiral source. The absolute configuration of 1 was determined from the Flack parameter by X-ray crystallography. The structure of 1 comprises two lacunary [PW11O39]7- units, each functioning as a tetra-dentate ligand sandwiching an 8-coordinate HfIV centre in a distorted square antiprismatic geometry. Optically active crystals of both enantiomers were spectroscopically distinguishable by means of solid state circular dichroism spectroscopy. This hafnium-substituted polyoxometalate (POM), 1, shows that spontaneous chiral resolution, a rare phenomenon, can be operable in POM systems.     

Validation of the concentration profiles obtained from the near infrared/multivariate curve resolution monitoring of reactions of epoxy resins using high performance liquid chromatography as a reference method

This paper reports the validation of the results obtained by combining near infrared spectroscopy and multivariate curve resolution-alternating least squares (MCR-ALS) and using high performance liquid chromatography as a reference method, for the model reaction of phenylglycidylether (PGE) and aniline. The results are obtained as concentration profiles over the reaction time. The trueness of the proposed method has been evaluated in terms of lack of bias. The joint test for the intercept and the slope showed that there were no significant differences between the profiles calculated spectroscopically and the ones obtained experimentally by means of the chromatographic reference method at an overall level of confidence of 5%. The uncertainty of the results was estimated by using information derived from the process of assessment of trueness. Such operational aspects as the cost and availability of instrumentation and the length and cost of the analysis were evaluated. The method proposed is a good way of monitoring the reactions of epoxy resins, and it adequately shows how the species concentration varies over time.     

表面高分辨弹性反冲探测分析

在中国原子能科学研究院 HI- 1 3串列加速器上建立了用 Q3D磁谱仪动量分析和ΔE- E粒子分辨对材料表面进行高分辨的弹性反冲探测分析技术 .用 1 0 0 Me V12 7I对 C/Li F多层样品的深度分布分析表明 ,表面分辨达到 1 .2 nm.所建立的ΔE(气体 ) - E(半导体 )望远镜探测器可同时分析从轻至中重的所有元素 .实测了新光电材料 Ga N,La2 Sr Cu O4 超导膜和新超硬材料 C3N4 (Si)等样品. High resolution depth profiling technique with elastic recoil detection analysis has been developed at the HI 13 tandem accelerator of CIAE. A depth resolution of 1.2 nm was achieved at the surface of the samples with the Q3D magnetic spectrometer and the focal plane detector. From light to medium heavy elements were simultaneous analyzed with a small Δ E E telescope. The method was applied to depth profile analysis of C/LiF multilayers, La 2SrCuO 4 superconductor and GaN foil samples.     

用于活体人眼视网膜观察的自适应光学成像系统

利用自适应光学技术,研制了两套活体人眼视网膜高分辨力成像系统,在实时校正人眼波前误差的基础上,实现活体人眼视网膜细胞尺度的高分辨力成像。这两套系统分别采用19和37单元小型压电变形反射镜作为波前校正元件,哈特曼-夏克(Hartmann-Shack)波前传感器测量波前误差,用眼底反射的半导体激光作为波前探测的信标。在用计算机控制自适应光学系统实现人眼波前误差校正后,触发闪光灯照明视网膜,用CCD相机记录视网膜的高分辨力图像。校正后的残余波前误差的均方根值已分别小于1／6和1／10波长,相当于视网膜上成像分辨力分别为3．4μm和2．6μm,接近衍射极限。试验表明37单元系统的成像质量更好。     

A versatile computer‐controlled high‐resolution LBIC system

This paper presents the design of versatile equipment for obtaining laser‐beam‐induced current (LBIC) images which allows the study of large surfaces as well as conversion areas of a few micrometers. The modular optomechanical design enables the user to modify the size of the irradiation spot by simply changing the microscope objective used as focal lens, albeit within the limits set by the wavelength. The use of an appropriate calculation algorithm makes it possible to rely on a computerized system to adjust the distance at which the focusing lens must be placed with respect to the sample plane. The possibility of working at micrometer resolution allows one to obtain very significant information for the study of irregularities, manufacturing defects, impurities, grain boundaries, dislocations, recombination centers, etc. in photovoltaic wafers. Copyright © 2004 John Wiley & Sons, Ltd.