Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Spin labelling of human erythrocytes with nitroxide radicals

Summary Human erythrocytes were labelled with nitroxide, the spin label SYNVAR 101, under various experimental conditions. A study was made of the influence of antireductants on the labelling efficiency and the kinetics of the radical decay during the labelling process. The antireductant hydrogen peroxide was effective in suppressing the decay, whereas ferricyanide was not very effective in this role. The nitroxide radical concentration in a nondialyzed plasma suspension of spin-labelled erythrocytes continuously decayed exponentially with a time constant of 35 min. Nitroxide radicals in nondialyzed plasma exhibited a similar decay to a final residual value which was small relative to the initial concentration. Dialyzing the plasma raised the residual concentration to three quarters of the initial value without changing the decay time.

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Riassunto Eritrociti umani sono marcati con ossido di azoto, il marchio di spin SYNVAR 101, in varie condizioni sperimentali. Si è fatto uno studio dell’influenza degli agenti antiriducenti sulla capacità di marcare e sulla cinetica del decadimento dei radicali durante il processo di marcatura. Il perossido d’idrogeno antiriducente era efficacie nel sopprimere il decadimento, mentre il ferrocianuro non era molto efficacie in questo roulo. La concentrazione dei radicali dell’ossido di azoto in una sospensione di plasma non dializzato degli eritrociti marcati secondo lo spin decade continuamente in maniera esponenziale con una costante di tempo di 35 min. I radicali dell’ossido di azoto nel plasma non dializzato esibiscono un decadimento simile al valore residuo finale che era piccolo in relazione alla concentrazione iniziale. Dializzare il plasma aumenta la concentrazione residua a tre quarti del valore iniziale senza cambiare il tempo di decadimento.

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Резюме В различных эксрериментальных условиях метятся человеческие эритроциты с окисью азота. Исследуются влияния антивосстановителя на эффективность нанесения метки и кинетику распада радикалов в процессе нанесения метки, Перекись водорода, как антивосстановитель, является эффективной для подавления распада, тогда как феррицианид не очень эффективен в этой. Концетрация радикалов окиси азота в суспензии недиализированной плазмы эритроцитов со спиновой меткой уменьшается эксоненциально с временной постоянной, равной 35 мин. Радикалы окиси азота в недиализированной плазме обнаруживают аналогичный распад, причем конечная остаточная величина концентрации оказывается малой по сравнений с начальной концентрацией. Диализация рлазмы увеличивает остаточную концентрацию до трех четвертых начальной без изменения времени распада.

     

An on-line voltammetric analyzer for trace metals in wastewater

Differential-pulse anodic stripping voltammetric and differential pulse polarographic techniques were adapted to an on-line analytical system to measure trace levels of metals in a waste- water stream. Chromium, nickel, zinc, cadmium, lead and copper were determined automatically for several days to characterize a wastewater stream and detection limits were typically near 50 μg l^?1.     

Behavior of oil droplets on an electrified solid metal surface immersed in ionic surfactant solutions

The present study investigates the change in the shape of oil droplets immersed in an ionic surfactant solution when the droplets are in contact with metal surfaces to which an electrical potential is applied. The three-phase system of aqueous solution-oil-steel was subjected to low-voltage electric potentials, which resulted in sometimes dramatic changes in droplet shape and wetting. This electric potential was applied to the conductive steel surface directly, and the counter electrode was immersed in the solution. Changes in both the shape and wetting extent of hexadecane and phenylmethyl polysiloxane were observed for voltages between +/-3.0 V in both sodium dodecyl sulfate and cetyl trimethylammonium bromide solutions. The droplets' behavior was opposite to what would be expected for traditional electrowetting. In one instance, hexadecane droplets in sodium dodecyl sulfate solutions with a voltage of -3.0 V, a rapid and repeating droplet elongation and detachment was observed. Additionally, the impact of the observed phenomena on electrowetting enhanced ultrasonication is presented to demonstrate the potential improvements in industrial ultrasonic cleaning processes. The observations lead to the possibility of employing simple electrowetting techniques in the removal of oil from metal surfaces in a manner that could greatly improve the environmental and economic performance of aqueous cleaning techniques.     

Thermo field dynamics in the treatment of the nuclear pairing problem at finite temperature

The use of the thermo field dynamics, in dealing with the study of nuclear properties at finite temperature, is discussed for the case of a nuclear Hamiltonian which includes a single-particle term and a monopole pairing residual two-body interaction. The rules of the thermo field dynamics are applied to double the Hilbert space, thus accounting for the thermal occupation of single-particle states, and to construct dual spaces, both for single-particle (BCS) and collective (RPA) degrees of freedom. It is shown that the rules of the thermo field dynamics yield to a temperature dependence of the equations describing quasiparticle and phonon excitations which is similar to the one found in the more conventional finite temperature Wick's theorem approach, namely: by dealing with thermal averages.     

Ground state correlations in the BCS treatment of a monopole pairing Hamiltonian

The treatment of a monopole pairing Hamiltonian, in the quasiparticle basis and with the inclusion of ground state correlations, is discussed. The theoretical procedure is based on the BCS method supplemented by a variational treatment of ground state correlations. A significant improvement in the results is found, for ground state energies, when the comparison between correlated, BCS and exact values is performed. Results are discussed for one and two level model configurations.     

Computable error bounds for pointwise derivatives of a Neumann problem

In this paper we discuss the recovery of derivatives and thecomputation of rigorous and useful upper bounds for the pointwiseerror in the recovered derivatives, for finite element approximationsof the Laplace equation with Neumann boundary conditions, especiallyat points close to or on a smooth, curved boundary. We analyzethe dipole image technique for the case of curved boundaries,and show how to compute reliable recovered derivatives and errorbounds even in the limiting case of points lying on the curvedboundary. Numerical experiments show reasonably tight errorbounds for points both close to and away from a curved boundary.     

Electrohydrodynamic Velocity and Pumping Measurements in Water and Alcohols

Bubble and particle velocities in water and alcohols, under the influence of an electric field, were investigated in this work. Air bubbles were injected into the liquids through an electrified metal capillary insulated by glass with its tip left exposed. The end of the capillary from which the bubbles were released was conical in shape. Due to an electric field formed between the noninsulated capillary tip and a ground electrode immersed in the solvent, small bubbles were formed and used as tracers for the electrohydrodynamic (EHD) flow field. The pressure inside the capillary was measured for all liquids used in this study. For water, ethanol, and n-propanol, it was found that, at relatively low applied voltage, the pressure increases with voltage, reaches a maximum (pressure breakpoint), and then sharply decreases. This behavior is a result of the competition between the electric force appearing at the interface and the force due to the EHD flow near the capillary tip. The electric force tends to increase the pressure inside the capillary, while the EHD flow tends to decrease this pressure. For isopropanol and butanol, the pressure breakpoint was not observed in the range of voltage applied in the experiments. The EHD flow velocity was measured by using microbubbles and particles as flow tracers. An adaptive phase-Doppler velocimeter was employed to measure the velocity of bubbles, while the velocity of particles was measured by trajectory visualization of fluorescent particles. A discrepancy was observed between the two methods because of the location at which the measurements were made. It was found that average velocities of both bubbles and particles increase linearly with applied voltage. Experiments were also conducted to investigate pumping of water, which is a result of the EHD velocity near the capillary tip. The pumping flow rate was linearly related to the applied voltage and agreed well with EHD velocity measurements obtained from particle trajectories. Copyright 2000 Academic Press.     

Thermodynamic method for prediction of surfactant-modified oil droplet contact angle

A model applying surfactant self-assembly theory and classical thermodynamics has been developed to aid in the prediction of solid surface cleaning by aqueous surfactant solutions. Information gained from a combination of surfactant self-assembly behavior and cleaning system parameters, such as oil species, surfactant type, temperature, alkalinity, and solid surface type has been shown to provide insight into surface cleaning. The model combines minimization of free energy, pertinent component distribution mechanisms, and surfactant self-assembly processes to provide a methodology for the predicting of oil droplet contact angles. Such predictive capabilities will allow for the development of beneficial environmental and economic changes to industrial and commercial surface cleaning and degreasing processes. Results from the model will be compared to experimental data to verify the capability of the theory to account for the effect of solutions parameters on oil droplet behavior. The model, while approximate in nature, has shown a remarkable quantitative predictive ability.     

Liposome-templated supramolecular assembly of responsive alginate nanogels

Nanosized gel particles (nanogels) are of interest for a variety of applications, including drug delivery and single-molecule encapsulation. Here, we employ the cores of nanoscale liposomes as reaction vessels to template the assembly of calcium alginate nanogels. For our experiments, a liposome formulation with a high bilayer melting temperature (Tm) is selected, and sodium alginate is encapsulated in the liposomal core. The liposomes are then placed in an aqueous buffer containing calcium chloride, and the temperature is raised up to Tm. This allows permeation of Ca2+ ions through the bilayer and into the core, whereupon these ions gel the encapsulated alginate. Subsequently, the lipid bilayer covering the gelled core is removed by the addition of a detergent. The resulting alginate nanogels have a size distribution consistent with that of the template liposomes (ca. 120-200 nm), as confirmed by transmission electron microscopy and light scattering. Nanogels of different average sizes can be synthesized by varying the template dimensions, and the gel size can be further tuned after synthesis by the addition of monovalent salt to the solution.