Absolute configuration of C2-symmetric spiroselenurane: 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole

The enantiomers of 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole have been separated on a chiral preparative chromatographic column. The experimental vibrational circular dichroism (VCD) spectra have been obtained for both enantiomers in CH(2)Cl(2). The theoretical VCD spectra have been obtained by means of density functional theoretical calculations with the B3 LYP density functional. From a comparison of experimental and theoretical VCD spectra, the absolute configuration of an enantiomer with positive specific rotation in CH(2)Cl(2) at 589 nm is determined to be R. This conclusion has been verified by comparing results of experimental optical rotatory dispersion (ORD) and electronic circular dichroism (ECD) to predictions of the same properties using the B3 LYP functional for the title compound.     

Solid-state,optical-rotation measurements on macromolecules using powder-suspensions

Summary We report techniques for measuring optical rotation of suspended solids, including dissymmetric molecular crystals (e.g. sodium chlorate and bromate), synthetic polymers, polypeptides and biopolymers. Examples include poly(triphenylmethyl methacrylate), poly-S-lactide, poly-L-hydroxyproline, hemocyanine, cellulose acetate andRNA. The results indicate that optical rotation measurements are sensitive to differences in secondary structure and can serve as a probe for structural differences between solid-state and solution.

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Messung der optischen Rotation von Makromolekülen im Festzustand unter Verwendung von Pulversuspensionen

Zusammenfassung Es wird über eine Methode zur Messung der optischen Rotation von Festkörpern in Suspensionen berichtet, wobei dissymetrische Kristalle (z. B. Natriumchlorat und -bromat), synthetische Polymere, Polypeptide und Biopolymere behandelt werden. Die Beispiele umfassen Poly(triphenylmethylmethacrylat), Poly-S-lactid, Poly-L-hydroxyprolin, Hemocyanin, Celluloseacetat undRNA. Die Ergebnisse zeigen, daß die optischen Rotationen bezüglich Unterschiede in der Sekundärstruktur empfindlich sind und daß diese Messungen als ein Maß für Strukturunterschiede zwischen Festzustand und Lösung herangezogen werden können.

     

A new method for the derivation of exact vibration-rotational kinetic energy operator in internal coordinates

An efficient angular momentum method is presented and used to derive analytic expressions for the vibration-rotational kinetic energy operator of polyatomic molecules.The vibration-rotational kinetic energy operator is expressed in terms of the total angular momentum operator J,the angular momentum operator J and the momentum operator p conjugate to Z in the molecule-fixed frame Not only the method of derivation is simpler than that in the previous work,but also the expressions ot the kinetic energy operators arc more compact.Particularly,the operator is easily applied to different vibrational or rovibrational problems of the polyatomic molecules by variations of matrix elements Gn of a mass-dependent constant symmetric matrix     

Symmetry numbers and chemical reaction rates

This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i) if the reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers for reactants and/or transition states and, (iv) if there is an internal rotation of part of the molecular system. All these four situations are treated systematically and analyzed in detail in the present article. We also include a large number of examples to clarify some complicated situations, and in the last section we discuss an example involving an achiral diasteroisomer.     

Development and validation of HPLC methods for enantioseparation of mirtazapine enantiomers at analytical and semipreparative scale using polysaccharide chiral stationary phases

Novel HPLC methods were developed for the analytical and semipreparative resolution of new antidepressant drug mirtazapine enantiomers. At analytical scale, the separation of the mirtazapine enantiomers was investigated using both cellulose and amylose tris(3,5-dimethylphenylcarbamate) (CDMPC and ADMPC) chiral stationary phases under normal-phases and polar organic modes. Good baseline enantioseparation was achieved using cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phases under both normal-phases and polar organic modes. Furthermore, the elution order of mirtazapine enantiomic pairs was found reversed by changing the stationary phase from the amylose-based ADMPC–CSPs to its cellulose-based counterpart, CDMPC–CSPs. The validation of the analytical methods including linearity, limit of detection (LOD), limit of quantification (LOQ), recovery and precision, together with the semipreparative resolution of mirtazapine racemate were carried out using cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phases and methanol as mobile phase without any basic additives under polar organic mode. At analytical scale, the elution times of both enantiomers were less than 6 min at normal temperature and 1.0 ml/min, with the separation factor () 1.99 and the resolution factor (Rs) 3.56. Then, the analytical methods were scaled up to semipreparative loading to obtain small quantities of both mirtazapine enantiomers. At semipreparative scale, about 16 mg/h enantiomers could be isolated and elution times of both enantiomers were less than 10 min at 2.0 ml/min. To increase the throughput, the technique of boxcar injections was used. One enantiomer ((−)-(R)-mirtazapine) was isolated with purity of >99.9% e.e. and >98.0% yield and another ((+)-(S)-mirtazapine) was isolated with purity of >97.0% e.e. and >99.0% yield. In addition, optical rotation and circular dichroism (CD) spectroscopy of both mirtazapine enantiomers isolated were also investigated.     

Electrochemical dimerization of phenacyl bromides N-acylhydrazones—a new way to 1-N-acylamino-2,5-diaryl-pyrroles

Cathodic reduction of phenacyl bromides N-acyl hydrazones lead to dimeric 1,4-diaryl-1,4-butanedione di-N-acylhydrazones, which give the corresponding 1-N-acylamino-2,5-diarylpyrroles in good yields.     

测量圆盘转动惯量产生误差的曲线研究

结合三线摆实验的基本过程,进行实验数据的采集。利用投影法来测量圆盘的转角大小,借助于matlab的cftool工具箱,对数据进行曲线拟合,对测出来的二组数据拟合,得到转角与百分差曲线图。通过误差的大小比较,得出圆盘转动惯量测量值与理论值的百分差随转角变化最接近于三次曲线。     

New tetraphenylpyridinium-baseci luminogens with aggregation-induced emission characteristics

The research on aggregation-induced emission （AIE） has drawn increasing interests in the past decade. With the efforts scientists paid, a variety of AIE systems have been developed, among which the tetraphenylethelene and silole derivatives are the most studied. Development of new AIE systems could further enrich the AIE molecules and promote the development of AIE area. In this communication, we prepared a new AIE system based on 1,2,4,6-tetraphenylpyridinium ions according to the restriction of intramolecular rotation mechanism. These molecules could be facilely synthesized via one-step and one-pot reaction. The ionic AIE-active molecules could find wide application in sensing and optoelectronic areas.     

Fluid inertia effects in ferrofluid squeeze film between a sphere and a plate

On the ground of the ferrohydrodynamic model proposed by Shliomis  and , the present study investigates the influences of fluid inertia forces on the ferrofluid squeeze film between a sphere and a plate in the presence of external magnetic fields. According to the results, the effects of fluid inertia forces enhance the load capacity and prolong the approaching time for the ferrofluid sphere–plate system. Further numerical results for the load capacity are also provided in a table for engineering applications.