The Electrooxidation of Tetracycline at Acetylene Black Electrode in the Presence of Sodium Dodecyl Sulfate

The electrooxidation of tetracycline (TC) at acetylene black electrode has been studied in the presence of sodium dodecyl sulfate (SDS). Tetracycline (TC) exhibited very sensitive oxidation peak in this system. The peak current was proportional to TC concentration, and the detection limit was 1.2×10-8 mol/L. The system was used to the determination of TC in Pharmaceuticals.     

从作物根际分离的多粘芽孢杆菌固氮作用的研究

用乙炔还原法，研究了从作物根际分离的５１株多粘芽孢杆菌的固氮作用，结果表明：２８株在有氧条件下培养能合成固氮酶并固氮，其中ＨＷ－１菌株固氮酶活性达７８．３×１０－６ｍｏｌＬ－１ｈ－１．该菌株固氮活性在对数生长后期（３６ｈ）最高，最适固氮培养条件是３５℃和ｐＨ８．０．该菌株在有５％氧气的条件下培养时，固氮活性最高，在初始培养和乙炔还原体系中分别注入５０％氧气仍能检测到乙炔还原活性．培养基中ＮＨ＋４阻遏该菌株固氮酶合成，但对已合成的固氮酶活性无影响．     

乙萘酚在纳米银/壳聚糖-乙炔黑复合修饰电极上的电化学行为及测定

制备了纳米银/壳聚糖(AgCS)与乙炔黑(AB)复合修饰电极(AgCS-AB/GCE),用紫外可见分光光度法、扫描电镜法对AgCS进行表征,用交流阻抗法对不同电极进行表征,用循环伏安法(CV)研究了乙萘酚(β-N)在AgCS-AB/GCE上的循环伏安行为。结果表明,在pH 6.5的PBS缓冲液中,β-N在该修饰电极上出现一明显氧化峰,在60~240 mV/s扫速范围内,β-N的氧化峰电流(I pa)与对应扫速平方根(v1/2)呈良好的线性关系,表明β-N在该电极上的电化学过程为受扩散控制的不可逆过程。计算了电极过程的动力学参数,运用方波伏安法测定不同浓度β-N的方波伏安曲线,结果表明β-N的氧化峰电流与其浓度在3.0×10-7~2.0×10-4mol/L范围内呈良好线性关系(r=0.996),检出限(S/N=3)为1.24×10-7mol/L,加标回收率为99%~105%。     

Quantum-chemical models of KOH(KOBut)/DMSO superbasic systems and mechanisms of base-promoted acetylene reactions

The mechanisms of fundamental base-promoted acetylene reactions, namely, nucleophilic addition to the triple C ≡ C bond (vinylation) and nucleophilic addition of acetylenic carbanion to a carbonyl group (ethynylation), are addressed using three models of different complexity—pentasolvate, monosolvate, and anionic—which describe the catalytic superbasic systems MOH(OBu^t)/DMSO (suspensions of alkali hydroxides or tert-butoxides in dimethyl sulfoxide). The above acetylene reactions and sequential transformations of reagents arranged by the superbasic center are modeled within the framework of the most complete pentasolvate model, in which the superbase is represented by the KOH·5DMSO (KOBu^t·5DMSO) complexes. We have developed approaches to the construction of simplified models (monosolvate and anionic) to describe transformations in complex systems. The mechanisms of cascade assemblies of 6,8-dioxabicyclo[3.2.1]octanes, cyclopentenones, and furan cycles from ketones and acetylenes in the superbasic environment are investigated using a uniform B2PLYP/6-311+G**//B3LYP/6-31+G* approach, and the energy profiles of these different carbo- and heterocycles are analyzed.     

Geometric Requirements for Hydrocarbon Catalytic Sites on Platinum Surfaces

Vibrational spectroscopic measurements and density functional calculations were used to identify a preferential catalytic mechanism for the transformation of acetylene, HC? CH, to vinylidene, C? CH₂, on surfaces of Pt‐Sn ordered alloys. In this mechanism, two adjacent Pt atoms adsorb an acetylene molecule and a third neighboring Pt atom is required for stabilizing the reacting H atom during the transformation. Therefore, unlike a direct H shift along the C? C bond in organometallic compounds with a single transition‐metal atom, this mechanism has a geometric site requirement of three adjacent Pt atoms in the form of a three‐fold site. The same geometric site requirement is identified for preferential C? H bond cleavage of acetylene with the formation of adsorbed C? CH and H species. In the absence of three‐fold Pt sites, the reaction mechanism changes, and reactions of H transfer and C? H bond cleavage are suppressed.     

First total synthesis of neurotrophic diacetylene tetrol (−)-petrosiol D

The first total synthesis of the natural product (−)-petrosiol D has been achieved in a linear fashion. Sharpless asymmetric epoxidation, base induced elimination reaction for the formation of chiral propargyl alcohol and Cadiot–Chodkiewicz coupling reaction are the key steps utilized for the synthesis.     

RADIATION INDUCED SOLID-STATE POLYMERIZATION OF ACETYLENEDICARBOXYLIC ACID

ABSTRACT

Radiation induced solid-state polymerization of acetylenedicarboxylic acid was carried out at room temperature in open atmosphere and under vacuum conditions. The gray colored powder polymer obtained was insoluble in most common solvents but only partially soluble in DMSO and THF. The limiting conversion to polymer was about 5%. The polymer was characterized by IR, UV, DP-MS, DSC, TGA, and XRD. The mechanism of polymerization was elucidated from the available data. Polymerization followed a free radical mechanism. However, before the addition of monomer molecules to the growing chain, at least one of the carboxylic groups of the monomer breaks away as CO or CO₂. The formation of side group cyclization takes place. At least one of the bonds in the side cyclic group is an etheric bond. The DSC, TGA, and XRD results showed that the polymer was partially crystalline and showed no melting up to 1200°C. The mechanism of polymerization and assigned chain structure was studied by the direct pyrolysis mass spectrometric method.

The crystal structure of monomer and polymer was investigated by the XRD method. Both monomer and crystalline polymer were monoclinic with similar cell parameters. Thus, the polymerization follows a topotactic mechanism. The unpolymerized monomer retains its crystal structure and, therefore, CO or CO₂ in the monomer molecule has to be eliminated before polymerization could take place.     

Soft Scorpionate Hydridotris(2-mercapto-1-methylimidazolyl) borate) Tungsten-Oxido and -Sulfido Complexes as Acetylene Hydratase Models

A series of W^IV alkyne complexes with the sulfur-rich ligand hydridotris(2-mercapto-1-methylimidazolyl) borate) (Tm^Me) are presented as bio-inspired models to elucidate the mechanism of the tungstoenzyme acetylene hydratase (AH). The mono- and/or bis-alkyne precursors were reacted with NaTm^Me and the resulting complexes [W(CO)(C₂R₂)(Tm^Me)Br] (R=H 1 , Me 2 ) oxidized to the target [WE(C₂R₂)(Tm^Me)Br] (E=O, R=H 4 , Me 5 ; E=S, R=H 6 , Me 7 ) using pyridine-N-oxide and methylthiirane. Halide abstraction with TlOTf in MeCN gave the cationic complexes [WE(C₂R₂)(MeCN)(Tm^Me)](OTf) (E=CO, R=H 10 , Me 11 ; E=O, R=H 12 , Me 13 ; E=S, R=H 14 , Me 15 ). Without MeCN, dinuclear complexes [W₂O(μ-O)(C₂Me₂)₂(Tm^Me)₂](OTf)₂ ( 8 ) and [W₂(μ-S)₂(C₂Me₂)(Tm^Me)₂](OTf)₂ ( 9 ) could be isolated showing distinct differences between the oxido and sulfido system with the latter exhibiting only one molecule of C₂Me₂. This provides evidence that a fine balance of the softness at W is important for acetylene coordination. Upon dissolving complex 8 in acetonitrile complex 13 is reconstituted in contrast to 9 . All complexes exhibit the desired stability toward water and the observed effective coordination of the scorpionate ligand avoids decomposition to disulfide, an often-occurring reaction in sulfur ligand chemistry. Hence, the data presented here point toward a mechanism with a direct coordination of acetylene in the active site and provide the basis for further model chemistry for acetylene hydratase.     

Density Functional Theory Study of the Adsorption of C2H2 on the Cu/Pt(111) Bimetallic Surfaces

We applied periodic density-functional theory to investigate the adsorption of C2H2 on the Cu/Pt bimetallic and monometallic surfaces, including Cu-Pt-Pt and Pt-Cu-Pt representing the monolayer Cu on the Pt surface and subsurface Cu in the Pt surface, respectively. For the Pt(111) and Pt-Cu-Pt surfaces, C2H2 is preferentially a 3-fold "parallel-bridge" configuration, and a "μ-bridge" structure exists above the Cu(111) and Cu-Pt-Pt surfaces. The adsorption energy of C2H2 on these surfaces decreases in the order Pt(111) > Cu-Pt-Pt > Pt-Cu-Pt > Cu(111). The analysis of density of states, charge, and vibrational frequencies showed obviously weakening of the adsorbed C-C bond and high sp2 character on the carbon atom. Furthermore, when the top-layer compositions are equal, the nearer the EF d-band center is, the larger the C2H2 adsorption energy will be.