Photochlorination of tetramethylsilane and hexamethyldisilane in the gas phase

Preliminary studies of the reaction of chlorine with tetramethylsilane and hexamethyldisilane in the gas phase show that the photochlorination of tetramethylsilane is complex, giving different products from the corresponding reaction in solution and having an explosion boundary. At pressures below the explosion boundary the main products are ethylene, hydrogen chloride, dimethylchlorosilane, and more highly chlorinated methylsilanes. Above the explosion boundary main products after explosion are methane, acetylene, ethylene, hydrogen chloride, and silicon tetrachloride. Hexamethyldisilane reacts rapidly with chlorine in the dark, as it does in solution, forming mainly trimethylchlorosilane along with similar products to those found with tetramethylsilane. Subsequent photochlorination of trimethylchlorosilane follows a similar course to that of tetramethylsilane in the gas phase. Tentative mechanisms involving “hot” molecules are suggested.     

Vinylidene complexes of transition metals : III. Derivatives of cyclopentadienyltricarbonyl rhenium with phenylvinylidene ligands. Crystal and molecular structure of Cp(CO)2Re[CC(Ph)C(Ph)CH2]Re(CO)2Cp

The novel complexes CpRe(CCHPh)(CO)₂ and Cp₂Re₂(μ-CCHPh)(CO)₄ containing a terminal and a bridging phenylvinylidene ligand respectively and the binuclear complex Cp(CO)₂Re[CC(Ph)C(Ph)CH₂]Re(CO)₂Cp were obtained in the reaction of CpRe(CO)₃ with PhCCH.According to an X-ray study of the latter complex the unusual bridging ligand is η¹-bonded to one Re atom and η²-bonded to the other.     

Electrochemical behaviour of mono- and oligonucleotides I. Effects of charge and configuration of adenine mononucleotides on their adsorption at the mercury—solution interface

A systematic study of the adsorption and interfacial behaviour of the adenine mono-nucleotides (5′-AMP, 3′-AMP, cyclic 3′,5′-AMP, 5′-ADP and 5′-ATP) and adenosine for comparison at the HMDE has been carried out at pH 3.4 to 3.5. Thus, the N(1) of the adenine moiety is protonated to a major extent.The adsorption was followed by single sweep voltammetry (measurement of the time integral of the reduction peak of the adsorbed adenine moiety) and by a.c. voltammetry (out-of-phase component of the a.c. response being proportional to the differential double layer capacity). In this paper the situation corresponding to a “dilute” adsorption layer existing at low bulk concentrations is studied for various degrees of coverage. The potential dependence of the coverage is of bell shaped type with an extended maximum region around the potential of electrocapillary maximum (E_ecm) of the blank. For the same bulk concentration the coverage decreases in the series AMP, ADP, ATP, i.e. with increasing negative charge of the nucleotide, and at the same time the potential range of adsorption narrows. Among the monophosphates the coverage decreases in the series 3′-AMP, 5′-AMP, cyclic 3′,5′-AMP. The variations are connected with the varying charge of the mononucleotides and with the possibilities for interactions with adjacent molecules in the adsorption layer.At elevated bulk concentrations above a threshold value a substantial increase in coverage occurs around E_ecm as due to strong interactions between the adsorbed base moieties a rather compact film is formed.     

Some structural systematics in metal carbonyl cluster chemistry

The recently developed electron-counting rules for condensed polyhedral metal carbonyl clusters have been utilised to develop a systematic approach for enumerating the structural alternatives for metal cluster compounds which are isoelectronic. The more usual cluster degradation and aggregation processes are represented in a matrix form which relates the change in electron count to the number of new bonds formed (or broken). The matrices for cluster degradation and aggregation are represented in a complementary fashion so that the search for isoelectronic clusters greatly simplified. The utility of the approach is illustrated by reference to some recent examples from metal carbonyl cluster chemistry.     

Double asymmetric induction in benchrotrene derivatives

Attachment of a Cr(CO)₃ moiety to one of the aromatic rings in rigid diaryl ketones of very low prochirality followed by addition of a chiral and optically pure reagent leads to satisfactory asymmetric induction ~40%. Asymmetric induction is smaller in the case of acyclic systems.     

Cleavage by halogens of carbon—cobalt bonds in organometallic complexes of cobalt(III) : III. Kinetics and mechanism of the reactions of organobis(dimethylglyoximato)cobalt(III) complexes with iodine in chloroform

The kinetics of the reaction between organocobaloximes, RCo(DH)₂H₂O, and iodine have been investigated. They reveal the participation of an RCo(DH)₂H₂O · I₂ intermediate which undergoes intramolecular transalkylation and acts as an electrophile towards a second organocobaloxime molecule. The trend in reactivity as the R group is varied is discussed.     

The system copper-tellurium

The system copper-tellurium was investigated by DTA, DSC, and X-ray methods. A phase diagram with the phases Cu_2?xTe (33.5–36.2 mole% Te), Cu_3?xTe₂ (40–41 mole%), and CuTe was constructed. In the homogeneity ranges of the nonstoichiometric phases several superstructures were observed. The lattice parameters and d values of some of these phases are given.     

Polarographic determination of α-amylase activity

The enzyme α-amylase splits blue starch in fragments bearing electroactive groups which exhibit two waves in the pulse polarograms. This behaviour is the basis of the polagraphic determination of bacterial and human serum α-amylase activity. The differential pulse mode is more sensitive by a factor of 25 as compared with normal pulse polarography. With serum α-amylase, protein adsorption disturbs the determination of low activities.     

Concerning the Thermal Diastereomerization of the Green Fluorescent Protein Chromophore

Summary. Two model compounds for the green fluorescent protein chromophore were prepared. One of them incorporates the natural 4-hydroxybenzylidene group of the natural tyrosin derived chromophore, the other one bears a methyl group instead of the hydroxy group. Whereas the photochemically prepared (E)-diastereomer of the first compound very effectively reverted thermally (room temperature) to the thermodynamically stable (Z)-diastereomer, the (E)-diastereomer of the second derivative proved to be stable even at elevated temperatures for more than a day. This finding can be rationalized by constructing the appropriate resonance structures showing that only in the first case an effective delocalization enables partial single bond character of the benzylidene double bond. From the standpoint of chemical etiology, only Nature’s choice of the tyrosin derived chromophore of the green fluorescent protein provides an efficient radiationless thermal relaxation channel for the unwanted photo-diastereomerization product formed after excitation besides the dominating fluorescence channel of its chromophore.     

Separation and concentration of molybdenum(VI) and tungsten(VI) with chelating ion-exchange resins containing sulphur ligands

Three chelating ion-exchange resins based on macroreticular polyacrylonitrile-divinylbenzene copolymers with thioglycollic acid and cysteine as functional groups have been tested for separation of molybdenum(VI) and tungsten(VI). On a short column of the thioglycollic acid resin, molybdenum(VI) and tungsten(VI) can be selectively sorbed from pH-4.3 acetate buffer and eluted with 2M hydrochloric acid and a mixture of 0.1M sodium hydroxide and 0.1M sodium chloride, respectively, with quantitative recovery even at very low concentrations. Simulated sea-water samples have been analysed.