Laser desorption of DNA oligomers larger than one kilobase from cooled 4-nitrophenol

A unique matrix system consisting mostly of 4-nitrophenol has shown to be very effective for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of large DNA oligomers when a cooled sample stage was used to prevent the sublimation of this matrix under vacuum. Using this 4-nitrophenol matrix with UV laser desorption, detection of picomole quantities of DNA oligomers containing up to approximately 800 nucleotides was routinely achieved. The effectiveness of this matrix was further demonstrated by the observation of a double-stranded DNA oligomer larger than 1000 base pairs, seen as a denatured single-stranded species, with a molecular ion mass exceeding 300 000 Da. The potential applications of 4-nitrophenol as a matrix for DNA sizing are discussed.     

Anomalous Nitration Reactions of Halotropones and Tribromotropolone

Nitration of 2-bromo or 2-chlorotropone gave a new compound, 2,7-dinitrotropone: The halegen atom on the 2-position was displaced by the nitro group through an electrophilic substitution reaction. Nitration of 3,5,7-tribromotropolone gave 3,7-dibromo-5-nitropolone: the nitro group again displaced the bromine atom at position 5.     

Mass Spectra of N-Arylglycines and Substituted Aniline-N,N-Diacetic Acids

The electron impact mass spectra of eleven N-arylglycines and seven substituted aniline-N,N-diacetic acids were obtained under 70 eV and 14 eV ionization energies. The fragmentation patterns are similar to those of α-amino acids except for the degree of cleavage. The dehydration process of the diacetic acids may be considered as the characterestic process for this group of compounds.     

Trifluoromethanesulfonyl azide: an efficient reagent for the preparation of α-cyano-α-diazo carbonyls and an α-sulfonyl-α-diazo carbonyl

The reaction scope of trifluoromethanesulfonyl azide in diazo transfer reactions was extended to include the preparation of α-cyano-α-diazo-carbonyls, phenyl sulfonyl diazoacetophenone and diethyl diazomalonate in high yields. The effect of the bases used in the diazo transfer reactions were found to have a dramatic influence on the success of the reaction with pyridine being the base of choice.     

高效液相色谱和热重分析在树形聚酰胺胺合成中的应用

优化了聚酰胺胺树形分子合成工艺条件，采用HPLC和热重分析（TG）相结合的方法对所合成的树形聚酰胺胺进行分析与表征；HPLC的分析表明，在各不同代的目标化合物中，均有反应物单体存在，在高代产物中除了含有少量反应物外，还有少量的低代数分子；TG分析表明，产物中小分子反应物占的比例很少，一般为2％－3％左右，如果将减压蒸馏后的产物重新进行真空干燥，对半代树形大分子，能进一步有效除去小分子反应物，而对于整数代树形大分子，则效果并不理想。     

Mesoporous silica anchored Ru catalysts for highly enantioselective hydrogenation of beta-ketoesters

Recyclable and reusable mesoporous silica anchored Ru catalysts based on 4,4'-substituted BINAPs were synthesized and used for the hydrogenation of beta-alkyl beta-ketoesters with up to 98.6% e.e. and beta-aryl beta-ketoesters with up to 95.2% e.e.     

Photocrosslinking of copolymers of vinyloxyethyl methacrylate–styrene initiated by sulfonium salts. I. Transient species formed on photolysis of sulfonium salt

Benzyl cation was detected by transient absorption spectroscopy with a spectroscopic multichannel analyzer on pulse excitation (fourth harmonic of Nd:YAG laser, 266 nm; 10 ns fwhm) of benzyl(4-hydroxyphenyl) methylsulfonium hexafluoroantimonate(BSS) in 1,2-dichloroethane (EDC). The benzyl cation was long-lived (lifetime, 59 ms) at room temperature and quenched by a vinyl ether compound. The formation of the benzyl cation as active species on photolysis of BSS is in contrast to the formation of Brønsted acids in other sulfonium salts so far reported. © 1992 John Wiley & Sons, Inc.     

镧对Rhizoctonia solani的毒力及其致病酶活性的影响

采用琼脂平板生长速率法及液体培养基培养测定了La对立枯丝核病菌(Rhizoctoniasolani)的抑制作用和毒力,并测定了其对病菌胞外的果胶酶、蛋白酶和纤维素酶等几种致病酶的活性的影响。结果表明,随着La浓度升高,对病菌菌丝生长的抑制作用增强,固体培养上所测定的对病菌的EC50和EC95分别为171.9和667.7mg·L-1;在液体培养基中所测定的EC50和EC95分别为111 4和500 7mg·L-1。在一定浓度范围内,La提高了单位量菌丝所产生3种致病酶的活性,但由于对菌丝生长量的强烈抑制,使病菌胞外3种致病酶的总量或总活性受到抑制,减低了病菌的致病力。     

Synthesis of a novel spiro bisphosphinamidite ligand for highly enantioselective hydrogenation

A novel chiral bisphosphinamidite ligand SpiroNP has been synthesized. The rhodium complex of this ligand has been found to be highly active and enantioselective in the asymmetric hydrogenation of (Z)-2-acetamidoacrylic acid derivatives and α,β-unsaturated carboxylic acid derivatives.     

Novel Phenomenon of Oxygen-to-oxygen Silyl Migration in Directed Aldol Reaction

The phenomenon of migration of the silyl groups from α-oxygen to β-oxygen in sodium aldol reaction was observed for the first time in this paper.