Tailoring thermal conductivity of bulk graphene oxide by tuning the oxidation degree

The thermal conductivity of graphene oxides can be tailored by tuning oxidation degree due to the introduction of atomic- and nano-scale phonon scattering centers.     

Two new β-carboline-type alkaloids from Stellaria dichotoma var.lanceolata

Two new β-carboline-type alkaloids,dichotomine K(1) and dichotomine L(2),were isolated from the roots of Chinese medicinal plant Stellaria dichotoma L.var.lanceolata Bge.Structures of 1 and 2 were determined on the basis of chemical and spectroscopic means.     

PPLT倍频宽线宽掺镱双包层光纤放大激光

分别通过理论和实验研究了周期性极化的钽酸锂（PPLT）倍频宽线宽准连续掺镱双包层光纤放大激光.PPLT样品长为40 mm,极化周期为7.67 μm.基频光的中心波长为1064 nm,线宽约为6 nm.从基频光的光谱特性出发,利用超晶格倍频理论,解释了实验中获得的倍频温度与二次谐波功率之间的关系.在基频光的功率为2.2 W时,获得的宽线宽光纤激光倍频效率为1.8%.     

Polycondensation of Sebacic Acid with Primary and Secondary Hydroxyl Groups Containing Diols Catalyzed by Candida antarctica Lipase B

Abstract

The aliphatic polyesters are normally synthesized by ester interchange reactions or direct esterification of hydroxyacids or diacid/diol combinations. Biotransformation, utilizing the enzymes as catalysts, was accepted as an alternative route for the synthesis of aliphatic polyesters and offers various advantages compared with the conventional, metal-catalyzed polymerization reactions. Previous studies indicated that lipase-catalyzed polycondensation reactions between diols and diacids occurred preferentially at primary hydroxyl groups of diols, when diols contained both primary and secondary hydroxyl groups. In this work, we investigated lipase-catalyzed polycondensation of diacids and secondary hydroxyl group–containing diols, and successfully synthesized polyesters by polycondensation with secondary hydroxyl groups as well as primary hydroxyl groups. Various diols, glycerol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, and 2,4-pentanediol were tested for the polycondensation. The polymerization was achieved by heating a mixture of lipase B, sebacic acid, and the diols in anhydrous toluene at 100 °C for 72 h. The resulting polymers were characterized by ¹H and ¹³C NMR spectroscopy, Fourier transform–infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography.     

Polyethylene Glycol–Enhanced Chemoselective Synthesis of Organic Carbamates from Amines,CO2, and Alkyl Halides

An efficient and environmentally benign method for the synthesis of organic carbamates was developed. Amines, CO₂, and alkyl halides underwent a three-component reaction with the aid of K₂CO₃ and polyethylene glycol (PEG, MW = 400), affording the organic carbamates under ambient conditions. PEG could presumably act as a solvent and phase-transfer catalyst (PTC). Notably, the presence of PEG could also depress the alkylation of both the amine and the carbamate, thus resulting in enhanced selectivity toward the target carbamate.

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