Synthesis of carbenes through substitution reactions at a carbene center

An (amino)(phosphino) carbene can be transformed into (amino)(phosphonio) carbenes, which undergo nucleophilic intermolecular as well as intramolecular substitution reactions at the carbene center. A variety of carbenes can be synthesized starting from a single carbene precursor. The resulting gamut of electronic and steric effects possible should open the way not only to a detailed study of the mechanism, but also to the subsequent improvement of catalytic reactions that involve carbene-transition metal complexes.     

Stable versions of transient push-pull carbenes: extending lifetimes from nanoseconds to weeks

A (phosphanyl)(trifluoromethyl)carbene is shown to be stable for weeks in solution at temperatures up to -30 degrees C. Its chemical behavior exactly matches that of its transient congeners, even to the extent that subtle effects, such as the recently discovered weak pi interaction with aromatics, are observed. The influence of substituents on the structure of push-pull carbenes is demonstrated by a single-crystal x-ray diffraction study of a (phosphanyl)[2, 6-bis(trifluoromethyl)phenyl]carbene. The lifetime of these molecules makes them accessible to a wider range of standard techniques, allowing their chemical and physical behaviors to be studied in more detail than was previously possible.     

Facile splitting of hydrogen and ammonia by nucleophilic activation at a single carbon center

In possessing a lone pair of electrons and an accessible vacant orbital, singlet carbenes resemble transition metal centers and thus could potentially mimic their chemical behavior. Although singlet di(amino)carbenes are inert toward dihydrogen, it is shown that more nucleophilic and electrophilic (alkyl)(amino)carbenes can activate H2 under mild conditions, a reaction that has long been known for transition metals. However, in contrast to transition metals that act as electrophiles toward dihydrogen, these carbenes primarily behave as nucleophiles, creating a hydride-like hydrogen, which then attacks the positively polarized carbon center. This nucleophilic behavior allows these carbenes to activate NH3 as well, a difficult task for transition metals because of the formation of Lewis acid-base adducts.     

Asymmetric hydrogenation of unfunctionalized, purely alkyl-substituted olefins

Asymmetric hydrogenation of olefins is one of the most useful reactions for the synthesis of optically active compounds, especially in industry. However, the application range of the catalysts developed so far is limited to alkenes with a coordinating functional group or an aryl substituent next to the double bond. We have found a class of chiral iridium catalysts that give high enantioselectivity in the hydrogenation of unfunctionalized, trialkyl-substituted olefins. Because these catalysts do not require the presence of any particular functional group or aryl substituent in the substrate, they considerably broaden the scope of asymmetric hydrogenation.     

Cyclopropenylidenes: from interstellar space to an isolated derivative in the laboratory

Like many of the molecular species that have been detected in the interstellar medium, the singlet carbene cyclopropenylidene (C3H2) has been presumed to be too unstable to isolate in the laboratory. However, by appending pi-electron-donating amino groups to the triangular skeleton, we prepared a cyclopropenylidene derivative that is stable at room temperature. In contrast to previously isolated carbenes, this compound does not require a heteroatom adjacent to the electron-deficient carbon to confer stability. Despite the presence of amino groups, the geometric parameters of the cyclic skeleton, revealed by x-ray crystallography, are only slightly perturbed relative to those of the calculated structure of unsubstituted cyclopropenylidene. Stable cyclopropenylidene derivatives might thus serve as models for a better understanding of the formation of carbon-bearing molecules in the interstellar medium.     

小麦籽粒氨基酸碳氮稳定同位素的测定与分析

 【目的】利用气相色谱-燃烧-同位素比值质谱仪（gas chromatography-combustion-isotope ratio mass spectrometry,GC-C-IRMS）测定小麦籽粒氨基酸碳氮稳定同位素组成。【方法】以小麦临汾50744为材料,水解得到其籽粒蛋白质氨基酸,将氨基酸标准样品以及小麦籽粒氨基酸衍生化为N-新戊酰基,O-异丙醇（N-pivaloyl-isopropyl,NPP）氨基酸酯,利用GC-C-IRMS测定其碳氮稳定同位素组成。【结果】氨基酸标准样品的碳氮同位素组成分析表明,NPP氨基酸酯的平均重现性δ13C为0.47‰,δ15N为0.28‰,并没有产生大的同位素分馏,因此δ13C和δ15N都能得到满意的测定结果。运用GC-C-IRMS测定了小麦临汾50744籽粒蛋白质氨基酸的稳定碳氮同位素的自然丰度,其中δ13C的变化范围在-28.7‰到-34.7‰,δ15N的变化范围为-6.2‰到9.5‰。采用系统聚类分析进行分类,根据δ13C可以将氨基酸分为两类;根据δ15N可以将氨基酸分为三类。【结论】运用GC-C-IRMS结合NPP氨基酸酯衍生物可以测定小麦籽粒氨基酸的稳定碳氮同位素,这对于揭示氨基酸代谢途径的差异以及逆境胁迫下氨基酸的合成差异具有重要的意义。     

Divalent carbon intermediates: laser photolysis and spectroscopy

A brief review is given of the structures of an important class of reactive intermediates, divalent carbon species (carbenes). The electronic properties of carbenes force an unusual electronic character upon these species that, in turn, leads to intriguing physical and chemical properties. Because of the fleeting nature of carbenes, which are extraordinarily reactive, direct investigation of their structural and chemical behavior has presented a challenge to the experimentalist. The application of spectroscopic and ultrafast laser techniques has met this challenge. With the use of laser methods, along with conventional techniques, quantitative evaluation of the energetics, dynamics, and reactivities of a variety of carbenes has been possible.     

L-半胱氨酸—植酸缔合显色体系的研究

植酸和半胱氨酸的显色反应。在ｐＨ＝１００的ＮＨ３－ＮＨ４Ｃｌ缓冲体系中,植酸与半胱氨酸可以形成稳定的缔合物,缔合物的最大吸收波长为５７０ｎｍ。该体系操作方便、灵敏度高,具有很好的显色可逆性,其它氨基酸不干扰半胱氨酸的鉴定,用于混合样品中半胱氨酸的定性鉴定,结果满意。     

Synthesis and characterization of a neutral tricoordinate organoboron isoelectronic with amines

Amines and boranes are the archetypical Lewis bases and acids, respectively. The former can readily undergo one-electron oxidation to give radical cations, whereas the latter are easily reduced to afford radical anions. Here, we report the synthesis of a neutral tricoordinate boron derivative, which acts as a Lewis base and undergoes one-electron oxidation into the corresponding radical cation. These compounds can be regarded as the parent borylene (H-B:) and borinylium (H-B(+.)), respectively, stabilized by two cyclic (alkyl)(amino)carbenes. Ab initio calculations show that the highest occupied molecular orbital of the borane as well as the singly occupied molecular orbital of the radical cation are essentially a pair and a single electron, respectively, in the p(π) orbital of boron.     

Design and application of electron-transporting organic materials

Operating lifetime is the main problem that complicates the use of polymeric light-emitting diodes (LEDs). A class of electron transport (ET) polymers [poly(aryl acrylate) and poly(aryl ether)s] is reported in which moieties with high electron affinities are covalently attached to stable polymer backbones. Devices based on poly(p-phenylenevinylene) (PPV) prepared with these materials exhibited a 30-fold improvement in stability and, in one case, dramatically lower (10 volts versus about 30 volts) operating voltage relative to those having conventional ET layers. The current-carrying capacity of indium tin oxide-PPV-polymeric ET layer-aluminum LEDs was also increased by a factor of 30. These improvements lead to an enhancement in power efficiency of nearly an order of magnitude. Choosing polymers with high glass transition temperatures increases device lifetime.     

Detection and Characterization of the Cumulene Carbenes H2C5 and H2C6

Two cumulene carbenes, H2C5 and H2C6, were detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. Their rotational and leading centrifugal distortion constants were determined with high accuracy, such that the entire radio spectrum can now be calculated. Like the known carbenes H2C3 and H2C4, both molecules have singlet electronic ground states and linear carbon-chain backbones. They can be produced in sufficiently high concentrations in the laboratory that their electronic spectra, expected to lie in the visible, should be readily detectable by laser spectroscopy. The microwave spectra of other, more exotic isomers may be detectable as well.     

Automated chemical synthesis of a protein growth factor for hemopoietic cells, interleukin-3

Interleukin-3 (IL-3), a protein of 140 amino acids, was chemically synthesized by means of an automated peptide synthesizer and was shown to have the biological activities attributed to native IL-3. Assays of synthetic analogues established that an amino terminal fragment has detectable IL-3 activity, but that the stable tertiary structure of the complete molecule was required for full activity. The results demonstrate that automated peptide synthesis can be applied to the study of the structure and function of proteins.     

Characterization of a helical protein designed from first principles

The question of how the primary amino acid sequence of a protein determines its three-dimensional structure is still unanswered. One approach to this problem involves the de novo design of model peptides and proteins that should adopt desired three-dimensional structures. A systematic approach was aimed at the design of a four-helix bundle protein. The gene encoding the designed protein was synthesized and the protein was expressed in Escherichia coli and purified to homogeneity. The protein was shown to be monomeric, highly helical, and very stable to denaturation by guanidine hydrochloride (GuHCl). Thus a globular protein has been designed that is capable of adopting a stable, folded structure in aqueous solution.     

原始林内紫果云杉种群的数量动态

本文将紫果云杉种群看作是由不同径级林木所组成的群体,借以Leslie矩阵描述其数量动态情况,由此得种群Leslie矩阵的特征根λ=1.028,对应特征向量亦即种群稳定的径级组成为:(9941,783,556,393,280,116,32,8)。结果表明:在原始林内,紫果云杉种群结构较为稳定,呈增长稳定型;经预测,种群未来的结构组成与现在的相似。     

Isolation of an unidentified agent from the respiratory tract of chickens

A relatively stable filterable virus, not previously described, which hemagglutinated red blood cells of chickens, was isolated from the tracheae of birds suffering from an unusually severe outbreak of infectious laryngotracheitis. The latter disease concealed the infection caused by the new hemagglutinating agent, which was shown to cause, by itself, a mild and transient illness in susceptible chickens. Preliminary studies indicate that the new agent may be a new entity of the myxovirus group.     

玉米新不育胞质WBMs的利用潜力研究

 在广州、武汉两地多次对华中农业大学玉米研究室新近从我国地方群体“巫溪”中发现的玉米雄性不育细胞质WBMs进行育性和细胞质效应观察。结果表明,WBMs是一个不育性及恢复性稳定、无明显不良细胞质效应的Ⅰ、Ⅱ级S组雄性不育胞质,它作为可在玉米雄性不育育种和生产中应用的新不育胞质,将丰富我国有限的可利用的玉米雄性不育细胞质资源,应用前景广阔。     

转lrp基因生菜氨基酸营养分析

以转lrp(lysinc-rich protein gene)基因的转基因T_0和T_1代生菜为材料,非转基因生菜植株为对照,研究包括赖氨酸在内的所有氨基酸的变化情况.结果表明:lrp可以在生菜体内正常表达,在2个世代都可提高生菜中赖氨酸的含量,同时,其他必需氨基酸的含量并没有变化.     

不同品种橡胶籽中氨基酸及无机元素定性和定量分析

橡胶籽是大戟科乔木植物-三叶橡胶的有性繁殖器官,它是褐色并带有银灰色斑纹的椭圆形种子。橡胶籽作为橡胶树的副产物在很长一段时间里只是少量被用来育种其余的均没有被开发利用。橡胶籽仁是一种含油量很高的油料作物,并且粗蛋白含量丰富,含有赖氨酸、组氨酸、缬氨酸、苏氨酸、亮氨酸、苯丙氨酸等必须氨基酸。橡胶籽主要由棕榈酸、亚油酸、亚麻酸、油酸和硬脂酸等成分组成,富含不饱和脂肪酸,营养丰富,具有很高的利用价值。本篇文章将利用ICP-MS等设备对不同品种的橡胶籽中的氨基酸和无机元素进行定性和定量分析,比较不同橡胶籽的氨基酸和无机元素种类与含量差异,并为下一步的研究及橡胶籽产品开发提供理论依据。     

大豆预处理对提升酱油氨基酸得率的影响

[目的]通过对大豆进行预处理,提高酱油中氨基酸含量,从而提升酱油氨基酸得率。[方法]以完整颗粒的大豆做为对照样,确定大豆的最佳破碎程度,再在不同时机对大豆进行破碎,确定大豆的最佳破碎时机。[结果]试验得出,对照样的大豆做出的大曲酶活达1 762 U/g,对应天然油氨基酸为9.0 g/L,出油量为2 400 g/kg,随着大豆的破碎程度越严重,出油量越少。而将大豆打碎程度为1颗大豆破碎成1~2瓣,虽出油量减少,但天然油氨基酸提升至10.1 g/L,提升幅度为12.0%,氨基酸得率有一定的提升;再将大豆在不同时机破碎成1~2瓣,在冷却后将大豆打碎,其天然油氨基酸最高,且出油量也不受影响,酱油氨基酸得率最高,较对照组提升13.3%。[结论]大豆制作酱油时的最佳预处理方式为:破碎程度为将1颗大豆破碎成1~2瓣;破碎时机为在冷却后进行破碎。     

The DNA binding domain of the rat liver nuclear protein C/EBP is bipartite

C/EBP is a rat liver nuclear protein capable of sequence-specific interaction with DNA. The DNA sequences to which C/EBP binds in vitro have been implicated in the control of messenger RNA synthesis. It has therefore been predicted that C/EBP will play a role in regulating gene expression in mammalian cells. The region of the C/EBP polypeptide required for direct interaction with DNA has been identified and shown to bear amino acid sequence relatedness with the product of the myc, fos, and jun proto-oncogenes. The arrangement of these related amino acid sequences led to the prediction of a new structural motif, termed the "leucine zipper," that plays a role in facilitating sequence-specific interaction between protein and DNA. Experimental tests now provide support for the leucine zipper hypothesis.