Possible biotransformation reactions of polynuclear Pt(II) complexes

The reactions of the two complexes BBR3464 [{trans-PtCl(NH3)2}2{mu-trans-Pt(NH3)2(NH2(CH2)6NH2)2}](4+) and BBR3610 [{trans-PtCl(NH3)2}2{mu-C2H4(NH2(CH2)6NH2)2}](4+) and the corresponding diaqua complexes with the nucleophiles thiourea (tu) and l-methionine (l-Met), were investigated under pseudo-first-order conditions as a function of concentration and temperature, using UV-vis spectrophotometric and stopped-flow techniques. 1H NMR spectroscopy was used to follow the stepwise substitution of the chloro ligands by guanosine-5'-monophosphate under second-order conditions. For the sulfur donor containing nucleophiles (tu and l-Met), a second reaction step, the displacement of the labilized amine chain linker, as a result of the strong trans-effect of tu and l-Met, was found. The activation parameters for all reactions studied suggest an associative substitution mechanism. The displacement of the chain linker by S-donor nucleophiles illustrates the limit of application of polynuclear complexes with monodentate aliphatic amine bridges and primary ammines, in agreement with previous studies reported in the literature.     

Narrowness implies uniformity

This paper is about varietiesV of universal algebras which satisfy the following numerical condition on the spectrum: there are only finitely many prime integersp such thatp is a divisor of the cardinality of some finite algebra inV. Such varieties are callednarrow. The variety (or equational class) generated by a classK of similar algebras is denoted by V(K)=HSPK. We define Pr (K) as the set of prime integers which divide the cardinality of a (some) finite member ofK. We callK narrow if Pr (K) is finite. The key result proved here states that for any finite setK of finite algebras of the same type, the following are equivalent: (1) SPK is a narrow class. (2) V(K) has uniform congruence relations. (3) SK has uniform congruences and (3) SK has permuting congruences. (4) Pr (V(K))= Pr(SK). A varietyV is calleddirectly representable if there is a finite setK of finite algebras such thatV= V(K) and such that all finite algebras inV belong to PK. An equivalent definition states thatV is finitely generated and, up to isomorphism,V has only finitely many finite directly indecomposable algebras. Directly representable varieties are narrow and hence congruence modular. The machinery of modular commutators is applied in this paper to derive the following results for any directly representable varietyV. Each finite, directly indecomposable algebra inV is either simple or abelian.V satisfies the commutator identity [x,y]=x·y·[1,1] holding for congruencesx andy over any member ofV. The problem of characterizing finite algebras which generate directly representable varieties is reduced to a problem of ring theory on which there exists an extensive literature: to characterize those finite ringsR with identity element for which the variety of all unitary leftR-modules is directly representable. (In the terminology of [7], the condition is thatR has finite representation type.) We show that the directly representable varieties of groups are precisely the finitely generated abelian varieties, and that a finite, subdirectly irreducible, ring generates a directly representable variety iff the ring is a field or a zero ring.     

Elucidating the mechanism of cis double bond formation in epothilone biosynthesis

The epothilones, originally isolated from the myxobacterium Sorangium cellulosum, are macrocyclic compounds that are synthesized by a modular polyketide synthase, an enzyme complex composed of six large, multifunctional proteins. The penultimate intermediates in epothilone production, and the products of the PKS-catalyzed reactions, are epothilones D and C, which contain a 12,13-cis-double bond. The 12 and 13 positions of epothilones are generated during the fourth elongation step that is governed by module 4. Module 4 does not contain a dehydratase (DH) domain, which is required for dehydration to create the double bond. A DH domain, present in module 5 and presumed to act in the fifth elongation step at the 10 and 11 positions, was proposed to act as well to generate the 12,13-cis-double bond. Inactivation of the DH domain in module 5 resulted in the production of 10,11-dehydro-13-hydroxyepothilone D as the major product, confirming that DH5 is required for 12,13 dehydration. A mechanistic model based on domain skipping and modular stuttering is presented to explain the basis for the iterative DH5 activity observed.     

Ultrasound-assisted vapor generation of mercury

Cold vapor generation arising from reduction of both Hg²⁺ and CH₃Hg⁺ occurs using ultrasonic (US) fields of sufficient density to achieve both localized heating as well as radical-based attack in solutions of formic and acetic acids and tetramethylammonium hydroxide (TMAH). A batch sonoreactor utilizing an ultrasonic probe as an energy source and a flow through system based on a US bath were optimized for this purpose. Reduction of CH₃Hg⁺ to Hg⁰ occurs only at relatively high US field density (>10 W cm⁻³ of sample solution) and is thus not observed when a conventional US bath is used for cold vapor generation. Speciation of mercury is thus possible by altering the power density during the measurement process. Thermal reduction of Hg²⁺ is efficient in formic acid and TMAH at 70 °C and occurs in the absence of the US field. Room temperature studies with the batch sonoreactor reveal a slow reduction process, producing temporally broad signals having an efficiency of approximately 68% of that arising from use of a conventional SnCl₂ reduction system. Molecular species of mercury are generated at high concentrations of formic and acetic acid. Factors affecting the generation of Hg⁰ were optimized and the batch sonoreactor used for the determination of total mercury in SLRS-4 river water reference material.     

The new thioantimonate(V) (C3H10N)[NiSbS4(C6H18N4)]

Turquoise crystals of the title salt, propyl­ammonium di‐μ‐thio‐1:2κ⁴S‐di­thio‐2κ²S‐tris(2‐amino­ethyl)­amine‐1κ⁴N‐anti­mony(V)­nickel(II), (C₃H₁₀N)[NiSbS₄(C₆H₁₈N₄)] or [PAH][Ni(tren)SbS₄] [where tren is tris(2‐amino­ethyl)­amine and PA is propyl­amine], were synthesized under solvothermal conditions by reacting [Ni(tren)₂]Cl₂, Sb and S in a solution of PA. The Ni^II ion is octahedrally surrounded by four N atoms of the tetradentate tren mol­ecule and by two S atoms of the tetrahedral [Sb^VS₄]^3? anion, thus forming the anionic [Ni(tren)SbS₄]^? part of the compound. Charge balance is achieved through the PAH⁺ cation. An extended intermolecular hydrogen‐bonding network is observed between the anion and the cation.     

Determination of total mercury in biological samples using flow injection CVAAS following tissue solubilization in formic acid

Total mercury in biological samples was determined by flow injection (FI) cold vapour atomic absorption spectrometry (CVAAS) following tissue solubilization with formic acid. A mixture of potassium bromide and potassium bromate was used to decompose organomercury compounds prior to their reduction with sodium borohydride. A gold amalgam system was used to achieve lower detection limits when required. National Research Council Canada certified reference materials dogfish liver (DOLT-3), dogfish flesh (DORM-2) and lobster hepatopancreas (TORT-2), as well as oyster tissue (NIST SRM 1566b) and mussel tissue (NIST SRM 2976) were used to assess the accuracy of the method. The method of standard additions provided the most accurate results. Limit of detection (LOD) for Hg in the solid sample of 0.001 and 0.01 μg g⁻¹ were achieved with and without amalgamation, respectively. The precision of measurement for 1.6 ng ml⁻¹ methylmercury was 2.7% using the amalgam system.     

CEPA calculations on open-shell molecules. III. Potential curves for the six lowest excited states of He2 in the vicinity of their equilibrium distances

CEPA-PNO and PNO-CI calculations have been performed for the potential energy curves of the He ₂ ⁺ ground state and the six lowest excited states of He₂ in the range of 1.4 a₀ ≤R ≤ 3.5 a₀. The calculated equilibrium distances as well as the spectroscopic constants are in very good agreement with molecular constants as derived experimentally from the rotation-vibration spectrum of He₂ by Ginter, except for thec ³∑ _g ⁺ state. This latter discrepancy is probably due to an “obligatory” hump in thec ³∑ _g ⁺ state occurring at 3.5 a₀ which cannot be properly treated in our calculation. The relative energetic positions of the six lowest states and their ionization energies are reproduced by our calculations with an accuracy of 0–400 cm⁻¹. Extrapolation of our results to infinite basis sets leads to estimates of the dissociation energies of He₂ excited states which cannot be measured spectroscopically because of the humps in all these states.     

The potential of autofluorescence for the detection of single living cells for label-free cell sorting in microfluidic systems

A novel method for studying unlabeled living mammalian cells based on their autofluorescence (AF) signal in a prototype microfluidic device is presented. When combined, cellular AF detection and microfluidic devices have the potential to facilitate high-throughput analysis of different cell populations. To demonstrate this, unlabeled cultured cells in microfluidic devices were excited with a 488 nm excitation light and the AF emission (> 505 nm) was detected using a confocal fluorescence microscope (CFM). For example, a simple microfluidic three-port glass microstructure was used together with conventional electroosmotic flow (EOF) to switch the direction of the fluid flow. As a means to test the potential of AF-based cell sorting in this microfluidic device, granulocytes were successfully differentiated from human red blood cells (RBCs) based on differences in AF. This study demonstrated the use of a simple microfabricated device to perform high-throughput live cell detection and differentiation without the need for cell-specific fluorescent labeling dyes and thereby reducing the sample preparation time. Hence, the combined use of microfluidic devices and cell AF may have many applications in single-cell analysis.