Efficient Generation and Synthetic Applications of Alkyl-Substituted Siloxycarbenes: Suppression of Norrish-Type Fragmentations of Alkanoylsilanes by Triplet Energy Transfer

Acylsilanes have been known to undergo isomerization to siloxycarbenes under photoirradiation and the thus generated carbenes can be utilized for various synthetic reactions. But this carbene formation is not necessarily efficient with some alkanoylsilanes because Norrish-type fragmentations compete, which limit the synthetic utility of alkanoylsilanes as carbene precursors. In this study, generation of siloxycarbenes from alkanoylsilanes by visible-light-induced energy transfer was examined by using an Ir complex, [Ir{dF(CF₃)ppy}₂(dtbpy)]PF₆, and was successfully applied to the C−C coupling reactions with boronic esters or aldehydes. This methodology efficiently suppressed undesired Norrish-type reactions and broadened synthetic utility of alkanoylsilanes.     

Chemical Modification of Tryptophan Residues in Pullulanase

Tryptophan（Trp）residues in pullulanase have been chemically modified with N-bromossuccinimide（NBS）. The results of ultraviolet spectra indicated that there are 18 Trp residues in pullulanase and nine of them are located on the surface of the enzyme. Three of these Trp residues are none-essential residues which showed the fastest reaction speed by Zhou＇s plot. Two of the seven relative faster reacting residues are essential for the activity of the enzyme. The other eight are none-reactive residues with lowest reaction speed.     

Acylsilanes in Rhodium(III)‐Catalyzed Directed Aromatic C–H Alkenylations and Siloxycarbene Reactions with CC Double Bonds

Acylsilanes are known to undergo a 1,2‐silicon‐to‐oxygen migration under thermal or photochemical conditions to form siloxycarbenes. However, there are few reports regarding the application of siloxycarbenes in organic synthesis and surprisingly, their reaction with C? C double or triple bonds remains virtually unexplored. To facilitate such a study, previously inaccessible aromatic acylsilanes containing an ortho‐tethered C? C double bond were identified as suitable substrates. To access these key intermediates, we developed a new synthetic method utilizing a rhodium‐catalyzed oxidative Heck‐type olefination involving the application of an acylsilane moiety as a directing group. When exposed to visible‐light irradiation, the ortho‐olefinated acylsilanes underwent a smooth intramolecular cyclization process to afford valuable indanone derivatives in quantitative yields. This result paves the way for the development of new transformations involving siloxycarbene intermediates.     

聚半乳糖醛酸酶（PG2）中色氨酸残基的化学修饰

用化学修饰法以Ｎ－溴代琥珀酰亚胺作修饰剂，对聚半乳糖醛酸酶（ＰＧ２）中色氨酸（Ｔｒｐ）残基与酶活性的关系进行研究，发现１个ＰＧ２分子中有６个Ｔｒｐ残基，其中４个位于酶分子内部，２个位于酶分子表面，该发现通过表面荧光猝灭实验得到进一步证明，酶分子表面的２个Ｔｒｐ残基中，有１个为活性必需的氨基酸，它的修饰导致大部分酶活力丧失，底物保护实验进一步证明该活性必需的Ｔｒｐ可能位于酶的活性部位，酶被修饰后其圆     

提高TiO2可见光催化性能的改性方法

TiO₂光催化技术作为一种环境友好的污染治理技术,在废水废气净化、抗菌环保等领域有着广泛的应用前景。阻碍其应用的是它的大禁带宽度(E=3.2eV),不能有效地利用太阳能,因此研究开发可见光响应的TiO₂就成为当前光催化剂研究的关键课题。目前,国内外关于TiO₂光催化剂的改性技术日益完善,且日趋多样化。本文简单回顾了TiO₂光催化的发展历程及其反应机理,概述了提高TiO₂光催化性能的改性技术,主要包括金属离子掺杂、表面贵金属沉积、半导体复合、非金属掺杂以及金属络合物和染料光敏化等方法,可以将只能由紫外光激发的TiO₂光催化反应红移到可见光区域进行。针对各种改性方法列举了国内外应用的具体实例,提出TiO₂的改性是提高光催化反应效率的关键。同时,对TiO₂光催化技术目前存在的问题和发展前景做了简单的总结和展望。     

人纤维蛋白溶酶原中色氨酸残基的化学修饰

以Ｎ－溴代琥珀酰亚胺为修饰剂，对人纤维蛋白溶酶原（ＨＰｇ）中色氨酸（Ｔｒｐ）残基的分布及其与酶活力的关系进行了研究，发现每个ＨＰｇ分子有１９个Ｔｒｐ残基，５个位于分子表面：有２个是快反应残基，其中１个是活性必需的氨基酸，酶被修饰后其荧光光谱及圆二色谱发生了变化。     

菊粉酶中色氨酸残基的化学修饰及其荧光光谱

用N-溴代琥珀酰亚胺为修饰剂, 研究菊粉酶中的Trp残基的分布及其对酶生物学功能的影响, 为进一步研究菊粉酶结构与其功能之间的关系提供了新的信息.     

Acylsilanes in Iridium‐Catalyzed Directed Amidation Reactions and Formation of Heterocycles via Siloxycarbenes

Exposing ortho‐amido aroylsilanes to visible light or heat leads to cyclization reactions that provide N‐heterocyclic compounds via siloxycarbenes as key intermediates. The previously unreported starting materials have been prepared by directed amidations of aromatic acylsilanes in the presence of an iridium catalyst followed by N‐alkylation.     

Visible-Light Assisted Covalent Surface Functionalization of Reduced Graphene Oxide Nanosheets with Arylazo Sulfones

We present an environmentally benign methodology for the covalent functionalization (arylation) of reduced graphene oxide (rGO) nanosheets with arylazo sulfones. A variety of tagged aryl units were conveniently accommodated at the rGO surface via visible-light irradiation of suspensions of carbon nanostructured materials in aqueous media. Mild reaction conditions, absence of photosensitizers, functional group tolerance and high atomic fractions (XPS analysis) represent some of the salient features characterizing the present methodology. Control experiments for the mechanistic elucidation (Raman analysis) and chemical nanomanipulation of the tagged rGO surfaces are also reported.     

Chemical Modification and Fluorescence Spectrum of Tryptophan Residues in Pullulanase

IntroductionPullulanase(E.C.3.2.1.41)is a debranchingenzyme that can hydrolyze theα-1,6glucosidic bondsin pullulan,amylopectin,andβ-limit dextrin[1].It iswidely applied to starch industry and in the manufactu-ring of malt syrup,high-purity glucose,and f…     

在不同激发波长下的单壁碳纳米管的拉曼光谱研究

采用直流电弧法制备单壁碳纳米管样品,用457.5和632.8nm两种不同的激发光分别测得单壁碳纳米管的正常拉曼光谱和共振拉曼光谱.通过理论分析得到了单壁碳纳米管的直径分布,进一步推测了其类型及结构参数;对单壁碳纳米管的正切拉伸模的成分进行了归属.在632.8nm激发波长下得到了IG/ID值随激光功率变化的曲线,认为在2.5mW时,单壁碳纳米管缺陷的结构可能发生了改变.在用457.5nm波长激发的单壁碳纳米管的拉曼光谱中,首次发现了1421cm-1的拉曼谱峰.     

Chemical Modification of Tryptophan Residues in Superoxide Dismutase from Camellia Pollen and Its Fluorescence Spectrum

The amino acid composition of the superoxide dismutase（SOD） from camellia pollen was measured and the tryptophan（Trp） residues were modified by using N-bromosuccinimide（NBS）. The results show that there are 21 Trp residues in an SOD molecule and seven of which are located on the surface of the enzyme. By researching the fluorescence spectra of the native SOD and the modified SOD, we have found that the emission wavelength of Trp is at 335 nm and the fluorescence intensity will decrease when the enzyme is modified. The results also show that potassium iodide（KI） can significantly quench the fluorescence of the native SOD, but it has a less pronounced effect on the modified enzyme. Glycerin as a surface activation reagent can stabilize the fluorescence of the modified enzyme.     

Fast and Cysteine-Specific Modification of Peptides,Proteins and Bacteriophage Using Chlorooximes

This work reports a novel chlorooxime mediated modification of native peptides and proteins under physiologic conditions. This method features fast reaction kinetics (apparent k₂=306±4 M⁻¹s⁻¹ for GSH) and exquisite selectivity for cysteine residues. This cysteine conjugation reaction can be carried out with just single-digit micromolar concentrations of the labeling reagent. The conjugates show high stability towards acid, base, and external thiol nucleophiles. A nitrile oxide species generated in situ is likely involved as the key intermediate. Furthermore, a bis-chlorooxime reagent is synthesized to enable facile Cys-Cys stapling in native peptides and proteins. This highly efficient cysteine conjugation and stapling was further implemented on bacteriophage to construct chemically modified phage libraries.     

Ge‐Mediated Modification in Ta3N5 Photoelectrodes with Enhanced Charge Transport for Solar Water Splitting

Ta₃N₅ is a promising photoanode candidate for photoelectrochemical water splitting, with a band gap of about 2.1 eV and a theoretical solar‐to‐hydrogen efficiency as high as 15.9 % under AM 1.5 G 100 mW cm^?2 irradiation. However, the presently achieved highest photocurrent (ca. 7.5 mA cm^?2) on Ta₃N₅ photoelectrodes under AM 1.5 G 100 mW cm^?2 is far from the theoretical maximum (ca. 12.9 mA cm^?2), which is possibly due to serious bulk recombination (poor bulk charge transport and charge separation) in Ta₃N₅ photoelectrodes. In this study, we show that volatilization of intentionally added Ge (5 %) during the synthesis of Ta₃N₅ promotes the electron transport and thereby improves the charge‐separation efficiency in bulk Ta₃N₅ photoanode, which affords a 320 % increase of the highest photocurrent comparing with that of pure Ta₃N₅ photoanode under AM 1.5 G 100 mW cm^?2 simulated sunlight.     

Surface Modification of Nanometer Silica by N, N''''dicyclohexyl- carbodiimide Mediated Amidation

Nanometer silica has gained ever more attention for its superior properties over conventional micrometer particles and has been widely used as a filler in the manufacture of paints, rubber, plastics and so on1. However it is difficult to get silica mono- dispersed in the matrix due to heavy agglomeration. Surface modification through organic reactions is an efficient way to improve the dispersibility and compatibility with the matrix, thus improving the mechanical properties of the composite…     

Fast and Stable N-Terminal Cysteine Modification through Thiazolidino Boronate Mediated Acyl Transfer

We report a novel conjugation of N-terminal cysteines (NCys) that proceeds with fast kinetics and exquisite selectivity, thereby enabling facile modification of NCys-bearing proteins in complex biological milieu. This new NCys conjugation proceeds via a thiazolidine boronate (TzB) intermediate that results from fast (k₂: ≈5000 m ⁻¹ s⁻¹) and reversible conjugation of NCys with 2-formylphenylboronic acid (FPBA). We designed a FPBA derivative that upon TzB formation elicits intramolecular acyl transfer to give N-acyl thiazolidines. In contrast to the quick hydrolysis of TzB, the N-acylated thiazolidines exhibit robust stability under physiologic conditions. The utility of the TzB-mediated NCys conjugation is demonstrated by rapid and non-disruptive labeling of two enzymes. Furthermore, applying this chemistry to bacteriophage allows facile chemical modification of phage libraries, which greatly expands the chemical space amenable to phage display.     

用燐光寿命变化分析血中游离色氨酸

全血用三氯醋酸(TCA)去蛋白的上清液中加入不同量色氨酸(x),测燐光寿命(τ).以加入色氨酸与燐光寿命变化回归方程与应用推导的公式。x_0=τ_i-bx_i)/b,计算血中游离色氨酸(x。)为 11.1μg/mL.与文献报道的一致.     

色氨酸及其主要代谢产物的分离和在生物样品中的测定

建立以乙酸缓冲系统和甲醇作流动相、电化学和紫外检测器联用的高效液相色谱法,分离和测定了色氨酸经5-羟色胺和犬尿酸原两条主要代谢途径的8种代谢物。使用三氯乙酸作离子对试剂以延长3-羟犬尿酸原的保留时间,分析了流动相pH值和三氯乙酸浓度对各物质分离的影响及检测条件。结果表明,pH值及三氯乙酸浓度对各物质保留时间有明显影响,可作为控制分离的主要因素。此外,对生物样品中各物质分离和检测条件进行了讨论。     

Catch,Modify and Analyze: Methods of Chemoselective Modification of Cysteine-Containing Peptides

One effective solution in the analysis of complex mixtures, including protein or cell hydrolysates, is based on chemoselective derivatization of a selected group of compounds by using selective tags to facilitate detection. Another method is based on the capture of the desired compounds by properly designed solid supports, resulting in sample enrichment. Cysteine is one of the rarest amino acids, but at least one cysteine residue is present in more than 91% of human proteins, which clearly confirms its important role in biological systems. Some cysteine-containing peptides may serve as significant molecular biomarkers, which may emerge as key indices in the management of patients with particular diseases. In the current review, we describe recent advances in the development of cysteine-containing peptide modification techniques based on solution and solid phase derivatization and enrichment strategies.     

Fast and Stable N‐Terminal Cysteine Modification through Thiazolidino Boronate Mediated Acyl Transfer

We report a novel conjugation of N‐terminal cysteines (NCys) that proceeds with fast kinetics and exquisite selectivity, thereby enabling facile modification of NCys‐bearing proteins in complex biological milieu. This new NCys conjugation proceeds via a thiazolidine boronate (TzB) intermediate that results from fast (k₂: ≈5000 m ^?1 s^?1) and reversible conjugation of NCys with 2‐formylphenylboronic acid (FPBA). We designed a FPBA derivative that upon TzB formation elicits intramolecular acyl transfer to give N‐acyl thiazolidines. In contrast to the quick hydrolysis of TzB, the N‐acylated thiazolidines exhibit robust stability under physiologic conditions. The utility of the TzB‐mediated NCys conjugation is demonstrated by rapid and non‐disruptive labeling of two enzymes. Furthermore, applying this chemistry to bacteriophage allows facile chemical modification of phage libraries, which greatly expands the chemical space amenable to phage display.