Influence of the R-substituents on the properties of [Ni(R2pipdt)(dmit)] complexes and crystal structure where R = CH2C6H5

[Ni(R2pipdt)(dmit)], (R2pipdt = 1,4-disubstituted-piperazine-3,2-dithione, R = CH2C6H5; dmit = 1,3-dithiole-2-thione-4,5-dithiolate) (1b) has been prepared and characterised and the properties compared with those of the known complex 2b belonging to the same class where R = Pr i. Cyclic voltammetry of 1b and 2b was carried out and compared with that of the respective R2pipdt ligand precursors (1a and 2a ). The nature of the R-groups of the pipdt ligand exerts an effect on the redox potentials and confirmed the position of the LUMO as mainly on the R2pipdt part of the complex. Accordingly the low frequency absorption, assigned to the HOMO-LUMO transition which has inter-ligand charge-transfer character, is found for 1b at lower frequency when compared to the corresponding transition of 2b. In situ EPR was carried out on electroreduced radical species of the R2pipdt ligand precursors (1a, 2a ) and corresponding complexes (1b, 2b ). This revealed considerable delocalisation of the unpaired electron on the R2pipdt ligand in 1b and 2b with coupling constants to N and H comparable with those of 1a and 2a . Complex 1b crystallised in the space group Pnma and shows an essentially planar complex (with out-of-plane R groups) pi stacked at a distance of 3.65(1) A. Such a one-dimensional structure is not achieved in the case of 2b, where the complex units are almost parallel and head-to-tail with each other forming dimers and this difference in solid-state packing is apparent in the diffuse reflectance spectrum of each. Plane-wave DFT calculations for 1b revealed a highly one-dimensional band structure with considerable band dispersion along the direction of greatest molecular interaction via pi-stacking.     

Mechanism of quinol oxidation by ferricenium produced by light excitation in reaction centers of photosynthetic bacteria

The kinetics and thermodynamics of cyclic electron transfer through the isolated reaction center protein of photosynthetic bacterium Rhodobacter sphaeroides were determined in detergent (Triton X-100) solution. The redox reactions between the reducing (ubiquinol-0 or ubiquinol-10) and oxidizing species (ferricenium, ferricytochrome, or ferricyanide) produced chemically or by light excitation of the protein were monitored by absorption changes of the reactants and by acidification of the solution accompanied with the disappearance of the quinol. The bimolecular rate constants of reactions of anionic ubiquinol-0 with different oxidizing agents showed large variation: 5 x 10(8) M(-1) s(-1) for ferricenium, 3.5 x 10(5) M(-1) s(-1) for ferricyanide, and 1.5 x 10(5) M(-1) s(-1) for ferricytochrome. Although the redox partners were created in pairs by the same protein promptly after light excitation, their bimolecular redox reaction was not observed even in the case of the fastest reacting partners of ferricenium and ubiquinol-0. Instead, they equilibrate with the corresponding (donor and acceptor) pools before the electron is transferred. The (logarithms of the) observed rate constants of quinol oxidation showed steep pH-dependence for water soluble ubiquinol-0 (slope +1) and mild pH-dependence for hydrophobic ubiquinol-10 (slope approximately 0.25). Combined with studies of the ionic strength dependence of the rate, it was concluded that the electron-transfer pathways of ubiquinol-0 and ubiquinol-10 oxidation started from their anionic and neutral forms, respectively. The mild pH-dependence of the rate of ubiquinol-10 oxidation came from the electrostatic interactions between ferricenium and the pH-dependent surface charges of the reaction center. The results help to understand, monitor, and design (cyclic) electron flow in bioenergetic proteins.     

A novel highly stereoselective synthesis of 2,3-disubstituted 3H-quinazoline-4-one derivatives

[structure: see text]. An efficient three-step synthesis of chiral 3H-quinazoline-4-one derivatives from commercial materials is disclosed. The Mumm reaction of imidoyl chloride with alpha-amino acids followed by reductive cyclization affords enantiomerically pure (ee >93%) quinazoline-4-ones in good overall yield. A comparison with existing approaches indicates that this method is superior for hindered substrates.     

l-Proline-catalyzed direct intermolecular asymmetric aldol reactions of 1-phenylthiocycloalkyl carboxaldehydes with ketones. Easy access to spiro- and fused-cyclobutyl tetrahydrofurans and cyclopentanones

[reaction: see text] Acid-catalyzed ring expansion of chiral cyclopropyl and cyclobutyl derivatives for the synthesis of carbo- and heterocyclic compounds is reported. The starting materials have been successfully prepared by l-proline-catalyzed direct asymmetric aldol reactions of 1-phenylthiocycloalkyl carboxaldehydes with ketones.     

Measuring raft size as a function of membrane composition in PC-based systems: Part II--ternary systems

The heterogeneity of cell membranes, specifically the presence of lipid rafts, has been hypothesized to play a role in a large number of cellular processes. Although extensive work has been carried out to show the function of lipid rafts in these processes, the characterization of lipid rafts has proven to be extremely difficult. It is known that raft size is relevant to the function of cellular processes and that raft coalescence may be a driving factor for these processes; however, it remains unclear what factors influence raft size and coalescence in natural cell membranes. In this work, we study two ternary model phospholipid and cholesterol systems using two steady-state fluorescent techniques to detect and characterize membrane domains. Domain size is determined through the use of a model to relate experimental F?rster resonance energy transfer (FRET) measurements to domain size. Domains in the range of 3-15 nm were detected in a dioleoylphosphatidylcholine-dipalmitoylphosphatidylcholine-cholesterol (DOPC-DPPC-Chol) system, while only a very small region containing domains was detected in a 1-palmitoyl-2-oleoyl-phosphatidylcholine-dipamitoylphosphatidylcholine-cholesterol (POPC-DPPC-Chol) system. In addition, the polarity-dependent emission maximum shift of the acceptor 1-myristoyl-2-[12-[(5-dimethylamino-1-naphthalenesulfonyl)amino]dodecanoyl]-sn-glycero-3-phosphocholine (DAN-PC) was used to detect the type of liquid phase(s) present in the membrane. It was found that, even in the case in which no two-phase coexistence was observed (POPC-DPPC-Chol), two liquid phases are present, although not necessarily in coexistence. These steady-state fluorescent techniques provide a method for detecting the presence of very small domains in model membranes and provide previously inaccessible detail about the phase behavior of these two systems.     

Optical biosensors as a tool for early determination of absorption and distribution parameters of lead candidates and drugs

Specific molecular interactions provide a fundamental mechanism for selectivity in every aspect of biological structure and function. The ability to measure quantitatively such interaction properties across a wide range of affinity, size, and purity is a growing need. A short review on the use of the optical biosensor techniques is presented, focused on its application for determining the absorption and distribution parameters of drugs and lead compounds. The basic biosensor technology principles are described together with some immobilization methods commonly used for the preparation of selective and specific biosensor surfaces for assays. Some relevant research topics in the field of small molecule recognition phenomena are presented as examples, including binding to plasma proteins, and binding to lipid membranes, in the frame of ADME (absorption, distribution, metabolism and excretion) parameter determinations. These applications demonstrate the applicability of such techniques to the study of low mass compounds and illustrates their potential for the screening of libraries of compounds with regard to their binding to target bio-molecules as part of drug development.     

Determination of chlorinated acid herbicides in vegetation and soil by liquid chromatography/electrospray-tandem mass spectrometry

The method presented uses reversed-phase liquid chromatography with negative electrospray ionization and tandem mass spectrometry to analyze 9 chlorinated acid herbicides in soil and vegetation matrixes: clopyralid, dicamba, MCPP, MCPA, 2,4-DP, 2,4-D, triclopyr, 2,4-DB, and picloram. A 20 g portion is extracted with a basic solution and an aliquot acidified and micropartitioned with 3 mL chloroform. Vegetation samples are subjected to an additional cleanup with a mixed-mode anion exchange solid-phase extraction cartridge. Two precursor product ion transitions per analyte are measured and evaluated to provide the maximum degree of confidence in results. Average recoveries for 3 different soil types tested ranged from 72 to 107% for all compounds with the exception of 2,4-DB at 56-99%. Average recoveries for the 3 different vegetation types studied were lower and ranged from 53 to 80% for all compounds.     

Experimental and numerical investigation of temperature fluctuations in the near-wall region of an optical reciprocating engine

Accurate prediction of in-cylinder heat transfer processes within internal combustion engines (ICEs) requires a comprehensive understanding of the boundary layer effects in the near-wall region (NWR). This study investigates near-wall temperature fluctuations of an optical reciprocating engine using a combined approach of planar laser-induced fluorescence (PLIF) thermometry and numerical conjugate heat transfer modeling. Single-line excitation of toluene and subsequent one-color emission detection is employed for PLIF thermometry, while large-eddy simulations (LES) using commercial CFD software (CONVERGE v2.4.18) is utilized for modeling. The PLIF signal is calibrated to predicted in-cylinder temperatures from a GT-POWER simulation, and precision uncertainty of temperature is found to be ±1.5 K within the calibration region. Near-wall temperature fluctuations are determined about the multi-cycle mean, and the development of thermal stratification is captured in the NWR under motored and fired conditions during the compression stroke. Regions of the largest cycle-to-cycle temperature fluctuations are identified closer to the in-cylinder head surface indicating the unsteadiness of the thermal boundary layer. Analysis includes an assessment of cyclic variability of near-wall temperature fluctuation, and the effects of compression on temperature fluctuations. Additionally, thermal stratification is found to be similar under motored and fired conditions before ignition timing. Lastly, spatial correlation analysis of temperature fluctuations is performed in the wall-normal direction, and it reveals higher correlations under fired conditions. Spatial correlations experience an initial drop outside of the buffer layer in the NWR, and the location of the drop is well captured in the simulations. Analysis of fluctuating temperatures needs to be extended to fluctuations about the spatial average temperature which directly affects the spatial thermal gradients relevant to engine heat transfer.