The mechanism of electrochemical reduction of tricarbonylchromium-tropylium tetrafluoroborate in acetonitrile

The mechanism of electrochemical reduction of tricarbonylchromium-tropylium tetrafluoborate has been investigated in anhydrous MeCN together with that of the free tropylium tetrafluoborate. The bi-(cycloheptatrienyl), free and bis complexed with Cr(CO)₃ is the reduction product of the macroscale electrolysis of the free and complexed cations respectively. However, the mechanism of formation of the two dimers is different: the free dimer is formed through a radical-cation coupling mechanism; in constrast, the complexed dimer is produced by the coupling of the tricarbonylchromiumcycloheptatrienyl anion with the starting cation.     

Reduction stereospecifique de complexes aziridinyl-cetones-bromure de zinc

Specific reduction of ketoaziridine is obtained by NaBH₄ in protic solvent. The ketoaziridine must be previously complexed by ZnBr₂. Crystal structure determination shows that the complex is formed by two molecules of ketoaziridine and that no complexation between the nitrogen and the ketogroup is possible.     

A mild radical procedure for the reduction of B-alkylcatecholboranes to alkanes

A mild radical-mediated reduction of organoboranes is reported. The reducing agent is methanol complexed by the Lewis acidic B-methoxycatecholborane.     

Volumetric titration of iron (III)-salts with disodium EDTA, using FeII-cacotheline as indicator

Summary A volumetric method has been developed for the determination of iron (III) with disodium EDTA, using a mixture of cacotheline and iron(II) as indicator. The titration of the iron (III) salt is carried out in a buffered solution ofph 4–5 in carbon dioxide atmosphere with magnetic stirring, until a pink color appears. The pink color is due to the reduction of cacotheline by ferrous-EDTA. The reduction occurs only when all the iron (III) is complexed by EDTA. The end point is sharp and the method has been found to give results accurate to±0.3 to±0.5 percent.     

Chromium complexed carbinols as highly effective auxiliaries for use in asymmetric induction : reduction of α-ketoesters

High percentages of asymmetric induction are obtained during reduction of pyruvate and phenylglyoxylate esters of chromium complexed carbinol $\text{1a}$: 75% with NaBH₄ and 85% to 90% with L-selectride.     

Gold electroless reduction in nanosized channels of thiol-modified SBA-15 material

A new procedure for the preparation of high aspect ratio Au nanowires utilizing gold electroless reduction in the hexagonally ordered, thiol-modified nanosized channels of the SBA-15 material is reported. Two different Au precursors were adsorbed onto pedant thiol groups, covalently bonded to the mesoporous silica surface, and used as seeds to grow extended Au nanostructures by treatment in Au electroless reduction bath. It is shown that the dimensions and the assembly of the Au seeds are important parameters for the subsequent electroless reduction process. The [AuCl4]- ions complexed to the TOAB molecules assembled on the thiol-modified mesoporous surface of the SBA-15 material are suitable precursors for the subsequent gold electroless reduction. The resulting structures are several micrometer long Au nanowires with uniform diameters of about 5 nm, having large single-crystalline domains. The TEM results clearly show that the growth of the Au nanowires is templated by the channel structure of the SBA-15 material.     

An electrochemical study on interaction of copper ions with three isomers,picolinic, nicotinic and isonicotinic acids at physiological pH

The electrochemical behaviors of copper ions complexed with picolinic, nicotinic and isonicotinic acids (2-, 3- and 4-pyridinecarboxylic acids) in Britton–Robinson buffer (pH 7.4) was studied by polarographic and voltammetric techniques on a mercury electrode. This study showed that the reduction of complexed copper ions in the presence of nicotinic acid (NA) was carried out in two one-electron steps [Cu(II)/Cu(I) and Cu(I)/Cu(0)] whereas this cathodic process in the presence of picolinic acid (PA) or isonicotinic acid (INA) occurred in one two-electron step [Cu(II)/Cu(0)]. The stability of the Cu(I) complex can be sourced from the positions of carboxylate substituents on these isomeric ligands, binding to the copper center.     

钒取代Keggin型杂多酸的多层组装和电催化性能研究

用层层组装的方法在4-氨基苯甲酸预修饰的玻碳电极上交替沉积过渡金属钒取代的杂多酸H₃PW₆V₆O₆-40(简称PW₆V₆)和联吡啶锇取代的聚乙烯吡啶(QPVP-Os).用表面等离子体共振(SPR)技术和循环伏安(CV)法对多层膜进行了表征.结果表明,多层膜的生长均匀,平均厚度为2.88nm.还研究了多层膜对亚硝酸根(NO₂^-)和溴酸根(BrO₃^-)的催化还原活性.     

Control of stepwise radial complexation in dendritic polyphenylazomethines

The fourth generation of a dendritic polyphenylazomethine (DPA G4) has 2, 4, 8, and 16 imine groups in the first, second, third, and fourth shells, respectively (total, 30 imine groups). DPA G4 can trap 30 equiv of SnCl(2) molecules, because the imine group is complexed with SnCl(2) at a ratio of 1:1. During addition of 30 equiv of SnCl(2) to DPA G4, four shifts in the isosbestic point were observed in the UV-vis spectra, and the amount of SnCl(2) added in each step is in agreement with the number of imine groups in each shell of DPA G4. This result shows that the complexation of the imine groups in DPA G4 with SnCl(2) occurs stepwise in the order of the first, second, third, and fourth shells. The unique stepwise complexation was also observed in DPA G2 and G3 as two and three shifts of the isosbestic point, respectively. The stepwise complexation was supported by TEM, NMR, and a novel shell-selective reduction (SSR) method for imines. An expansion in the molecular size of DPA G4 by the complexation was revealed by molecular modeling and TEM measurements. The stepwise complexation is caused by the different basicity of the imine groups between the shells, which was supported by the chemical shifts of the peaks attributed to the imine carbons in the (13)C NMR spectra. The gradients in the basicity were controlled by the introduction of electron-withdrawing or -releasing groups to the core of the dendrimers; the core imines were complexed last in DPAs having a 2,3,5,6-tetrafluoro or 2,5-dichlorophenyl core due to the low basicity of the core imines. The different complexation pattern was also clearly confirmed by the SSR method.     

One-pot Synthesis of Pd/Azo-polymer as an Efficient Catalyst for 4-Nitrophenol Reduction and Suzuki-Miyaura Coupling Reaction

The porous polymer matrix with good stability and confined microenvironment is considered as ideal support to stabilize isolated metal centers for catalysis. Herein, we report a “one-pot” method to prepare a kind of palladium complexed with azo porous organic polymer nanospheres (Pd-azo-POPs). The method combines the synthesis of azo-POPs with the reduction of the Pd ion, where azo serves as an anchoring group to limit the growth of Pd. The unique structure is conductive to the formation of a uniform active center and provides improved electron transfer. Pd-azo-POPs-80 exhibits a high catalytic activity and cycling stability both in 4-nitrophenol reduction and Suzuki-Miyaura coupling. The k_nor for the 4-nitrophenol reduction was 174.7 min⁻¹ mM⁻¹ and the conversion remains above 90% after 6 cycles. Meanwhile, the yield was still up to 94.5% after 5 cycles for the Suzuki-Miyaura coupling reaction of benzene derivatives with I/Br under mild conditions.     

Prediction of the reduction potential of tris(2,2′‐bipyridinyl)iron(III/II) derivatives

The reduction potentials of a tris(2,2′‐bipyridinyl)iron (III/II) and iron(III/II) couples complexed with 2,2′‐bipyridinyl derivatives in acetonitrile are predicted using density functional theory. The calculation protocol proposed by Kim et al. (Kim, J. Park, Y. S. Lee, J. Comput. Chem. 2013, 34, 2233) showing reliable performance for the reduction potential is used. The four kinds of the functional groups, a methoxy group, a methyl group, a chlorine atom, and a cyanide group, are substituted at the ligands to examine the electronic effect on the reduction potential. Electron donating/withdrawing effect is analyzed by comparing the reduction potential having different substituents at the same position. The influence of the geometrical strain on the reduction potential is investigated. The good correlation between the experimental results and the calculated results is obtained. Not only the general trend, but also the detailed phenomena are correctly reproduced. The maximum deviation from the experimental value is 0.083 V for the methyl substitution at the position 4. The mean absolute error for the seven couples is 0.047 V. The difference of the reduction potential between the chlorine atom substituted at the positions 4 and 5, 0.1 V, is well described. The difference between the CN and the Cl substitution of 0.318 and 0.228 V for the position 4 and 5 is correctly obtained as 0.325 and 0.213 V, respectively. The simple linear relation between the lowest unoccupied molecular orbital (LUMO) energy of the Fe(III) complexes in solution and the calculated reduction potentials is obtained with the R² of 0.977. © 2014 Wiley Periodicals, Inc.     

Electrochemical olefin epoxidation employing an iron(IV)porphyrin/trisbipyridineruthenium(III) polymer catalyst

A porphyrin molecule containing four meso-appended 2,2'-bipyridyl ligands has been prepared. Each bipyridine is attached to the porphyrin core at the 4-position (pseudo-para to one of the pyridine nitrogens). Subsequently, each of the four bipyridines was complexed with a RuL2(2+) moiety and iron coordinated in the porphyrin core. When L = 4-vinyl-4'-methyl-2,2'-bipyridine, reduction of the ruthenium centers resulted in the formation of robust electroactive polymer films which deposited on the electrode surface. In the presence of aqueous acid, these films electrocatalytically epoxidize cyclohexene at positive potentials from the formal iron(IV) oxidation state. Although product analysis has only been conducted for cyclohexene, the catalytic activity extends to a large variety of olefins including ethylene and propylene.     

SINGLET OXYGEN FORMATION BY SENSITIZATION OF FUROCOUMARINS COMPLEXED WITH, OR BOUND COVALENTLY TO DNA

Abstract— The formation of singlet molecular oxygen (¹O₂) by sensitization of the furocoumarins 5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP) and psoralen complexed with DNA was investigated. From the results it is concluded that 5-MOP complexed with native DNA is able to generate ¹O₂, even in a larger extent than 5-MOP free in solution. Also, with 8-MOP and especially with psoralen, ¹O₂ formation by the complexed compound could be observed. The ¹O₂ formation sensitized by covalently bound furocoumarin was demonstrated with psoralen as a model compound. 4',5'-Dihydropsoralen, a model compound for the UVA light absorbing 4',5'monoadducts of furocoumarins to DNA, is also able to generate ¹O₂.     

60-CO organic complexes formed in the seawater by the addition of amino acids and their pretreatment for chemical analysis

By sodium nickel ferrocyanide coprecipitation, 60Co and 137Cs are simultaneously collected by nearly 99% recoveries from the unaged seawater. But this coprecipitation is not effective for the recovery of the 60Co complexed with organic ligands which would exist in natural seawater. In order to obtain the effective recoveries for these complexed 60Co, various pretreatments were investigated by using model samples containing the 60Co aged with several amino acids. In the acidification of these samples by nitric acid as 1 pretreatment, a large portion of these complexed 60Co was dissociated, especially by heating samples at 90-95 degrees C. The recoveries of 60Co were ranging from 90 to 97%. On the other hand, the usage of potassium peroxodisulfate (4.0 x 10(-4)-2.0 x 10(-2) M) as another pretreatment method elevated the recoveries of these complexed 60Co by more than 99% by heating samples above 90 degrees C. These 2 pretreatment methods were also effective for recoveries of 137Cs ion.     

离子-电子导电中呈现协同效应的互穿网络聚合物

用2,4-甲苯二异氰酸酯将蓖麻油及聚乙二醇(PEG)偶联成聚氨酯,同时通过自由基聚合使2-乙烯基吡啶(VP)与蓖麻油的双键共聚,生成互穿网络聚合物(IPN),其产率及凝胶含量大多超过93%,力学性能很好.当IPN与LiClO₄络合后呈现离子导电现象;与TCNE或TCNQ络合后产生电子导电,与LiClO₄及TCNE(TCNQ)络合后,呈现比上述两种导电率更大且具有协同效应的混合导电率,在25℃混合电导率可达到10^-3～10^-2S/cm.     

A new solvent extraction scheme for the separation of platinum,palladium, rhodium and iridium

A new scheme is proposed for the separation of platinum, palladium, rhodium and iridium in hydrochloric acid solutions, by solvent extraction. Platinum and palladium are complexed with 2-mercaptobenzothiazole and potassium iodide and simultaneously extracted into chloroform, thus separating them from rhodium and iridium. Palladium is separated from platinum by extracting its dimethylglyoxime complex into chloroform, while rhodium is separated from iridium by extracting its 2-mercaptobenzothiazole complex into chloroform after reduction with tin(II) chloride.     

Effects of metal salts on polymerization. Part VII. Radical polymerization and spectra of vinylpyridine in the presence of cobaltous chloride

The radical polymerizability of vinylpyridines in the presence of cobaltous chloride was studied in DMF solution, and the results were correlated with the spectroscopic data obtained for methanol solution. In general, the behavior of vinylpyridine complexed with cobaltous chloride is qualitatively the same as that of zinc complexes reported previously. The rates of polymerization were enhanced by the addition of cobaltous chloride when 4-vinylpyridine(4-VP) or 2-methyl-5-vinylpyridine(MVP) was the monomer, whereas the polymerization of 2-vinylpyridine(2-VP) was retarded by cobaltous chloride. The monomer reactivity of all the vinylpyridines was also enhanced by complex formation as studied by copolymerization with styrene. The enhancement of reactivity of 4-VP complexed with cobaltous chloride is somewhat smaller than that of the corresponding zinc complex.     

Inhibition of peroxyoxalate chemiluminescence by intercalation of fluorescent acceptors between DNA bases

We have examined the ability of different fluorescent DNA dyes to become chemically excited by the peroxyoxalate chemiluminescent reaction. The intercalating dyes ethidium bromide and propidium iodide, and the bis-intercalating dyes ethidium homodimer-1, benzoxazolium-4-pyridinium dimer-1 and benzoxazolium-4-quinolinium dimer-1, exhibit an intense chemiluminescence when they are excited by the bis(2,4,6-trichlorophenyl)oxalate (TCPO)-H2O2 reaction in the absence of DNA. However, the chemiluminescence of these dyes is very low when they are bound to double-stranded DNA (dsDNA). In contrast, the minor groove-binding dye Hoechst 33258 excited by the TCPO-H2O2 reaction shows approximately the same chemiluminescence intensity when it is free in solution or complexed with dsDNA. Structural alterations or partial dissociation of dsDNA-bis-intercalating dye complexes produced by the addition of acetone, NaCl, MgCl2 or the cationic surfactant cetyltrimethylammonium bromide increases the chemiluminescence intensity. A moderate chemiluminescence intensity is observed when bis-intercalating dyes are complexed with single-stranded DNA. Our results indicate that the energy from the intermediates produced in the peroxyoxalate chemiluminescent reaction cannot be efficiently transferred to fluorescent dyes complexed with DNA; chemiexcitation is almost completely inhibited when dyes are buried in the dsDNA structure by intercalation between the base pairs.     

Fluorescent stilbene,diene and triene surfactants as probes of reactivity in amylose inclusion complexes

The surfactant diphenylbutadiene and diphenylhexatriene derivatives, trans,trans-1-[4-(3-carboxypropyl)-phenyl]-4-[4-butylphenyl]-1,3-butadiene (4B4A) and trans, trans, trans-1-[4-(3-carboxypropyl)-phenyl]-6-[4-butylphenyl]-1,3,5-hexatriene (4H4A), respectively, have been found to form highly fluorescent inclusion complexes with amylose in aqueous dimethylsulfoxide. The fluorescence of the complexed guests is comparable in efficiency to that of some intrachain surfactant trans-stilbenes and greater than that of earlier-studied monosubstituted stilbenes. Dissociation constants (K_d^*) for the inclusion complexes are shown to be mainly determined by the effective chain length for several comparable surfactants. A preliminary study of quenching of the excited singlet of 4H4A indicates that the complexed probe is less reactive towards a variety of quenchers by roughly one order of magnitude.     

CDK4与靛玉红及其衍生物复合物结构的模建

细胞周期蛋白依赖性激酶(Cyclin-dependent Kinases, CDKs)是细胞周期调控的重要因子, 也是治疗癌症的一类重要的药物靶标. 靛玉红是传统中药当归龙荟丸中治疗慢性疾病的有效成分, 靛玉红及其衍生物5-磺酸基-靛玉红对CDKs具有有效的抑制作用. 以获得晶体结构的CDK2与5-磺酸根-靛玉红的复合物为模板, 通过同源模建和分子对接的方法构建出的CDK4与靛玉红及其衍生物的结合模式. 结合CDK4与两种抑制剂的复合物结构, 解释了靛玉红和衍生物5-磺酸基-靛玉红之间抑制活性的差别, 同时也分析了5-磺酸基-靛玉红对CDK2和CDK4不同选择性的原因. 所建CDK4结构为进一步进行基于结构的抗癌药物设计提供了合理的模型.