Asymptotic quantum yield of triplet sensitized decomposition

The asymptotic quantum yield of triplet energy transfer is found by calculating the fraction of acceptor molecules with energy above the minimum energy for decomposition. This is done by allowing for a statistical energy distribution among the internal modes in the collision complex. It is found that for a monatomic triplet donor most of the triplet energy is transferred to the acceptor molecule, while for a polyatomic donor molecule only a fraction of it is available for future decomposition of the acceptor.     

Triglyceride determination with use of an enzyme thermistor

The application of a split-flow type of enzyme thermistor for determining triglycerides is described. The device measures the protonation heat produced when a triglyceride is passed through a column containing triacyl glycerol lipase covalently bound to controlled-pore glass beads. The time required for a determination is less than 5 min, and the calibration graph for a triolein standard is linear up to 5 mM. The procedure is used for determining triglycerides in human blood sera and is compared with a conventional spectrophotometric method.     

A Water-Soluble Polymer-Lumefantrine Conjugate for the Intravenous Treatment of Severe Malaria

Uncomplicated malaria is effectively treated with oral artemisinin-based combination therapy (ACT). Yet, there is an unmet clinical need for the intravenous treatment of the more fatal severe malaria. There is no combination intravenous therapy for uncomplicated due to the nonavailability of a water-soluble partner drug for the artemisinin, artesunate. The currently available treatment is a two-part regimen split into an intravenous artesunate followed by the conventional oral ACT . In a novel application of polymer therapeutics, the aqueous insoluble antimalarial lumefantrine is conjugated to a carrier polymer to create a new water-soluble chemical entity suitable for intravenous administration in a clinically relevant formulation . The conjugate is characterized by spectroscopic and analytical techniques, and the aqueous solubility of lumefantrine is determined to have increased by three orders of magnitude. Pharmacokinetic studies in mice indicate that there is a significant plasma release of lumefantrine and production its metabolite desbutyl-lumefantrine (area under the curve of metabolite is ≈10% that of the parent). In a Plasmodium falciparum malaria mouse model, parasitemia clearance is 50% higher than that of reference unconjugated lumefantrine. The polymer-lumefantrine shows potential for entering the clinic to meet the need for a one-course combination treatment for severe malaria.     

Gas bubbles in simulation and experiment

An experimental setup for the examination of single bubbles, rising in a liquid, is presented. Its main part is a rotating chamber, in which the bubble is spatially stabilized by a balance of buoyancy, drag, and lift forces. This allows for long observation periods in time. Experimental results are presented for air bubbles in silicone oil. The experimental results are validated by a comparison with numerical simulations. A modified, mass-conserving level-set method is used for the representation of the free interface, while an immersed-boundary formulation is engaged for the conservation equations. The agreement between experiment and simulation, and to available correlations from literature, is found to be perfect. It is shown that the influence of the liquid shear due to the rotation is negligible. Also, for the presented liquid system, no influence by Marangoni stresses could be found, which makes the system of air and silicone oil a good choice for validation purposes.     

Statistical mechanical theory for steady state systems. V. Nonequilibrium probability density

The phase space probability density for steady heat flow is given. This generalizes the Boltzmann distribution to a nonequilibrium system. The expression includes the nonequilibrium partition function, which is a generating function for statistical averages and which can be related to a nonequilibrium free energy. The probability density is shown to give the Green-Kubo formula in the linear regime. A Monte Carlo algorithm is developed based upon a Metropolis sampling of the probability distribution using an umbrella weight. The nonequilibrium simulation scheme is shown to be much more efficient for the thermal conductivity of a Lennard-Jones fluid than the Green-Kubo equilibrium fluctuation method. The theory for heat flow is generalized to give the generic nonequilibrium probability densities for hydrodynamic transport, for time-dependent mechanical work, and for nonequilibrium quantum statistical mechanics.     

Epitope affinity chromatography and biophysical studies of monoclonal antibodies and recombinant antibody fragments

Peptide epitope affinity chromatography is a powerful technique for the purification of antibodies. This study aims to demonstrate the versatility of the technique and to show how biophysical techniques such as circular dichroism (CD) and fluorescence quenching (FQ) can aid the rational design of affinity ligands and characterization of antibody-based reagents. The performance of a number of peptide ligands for the purification of a range of different antibodies and recombinant fragments is investigated by automated fast-protein liquid chromatography. Purified products are analyzed for purity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. They are then radiolabelled and the immunoreactivity is determined. Ligands are analyzed for secondary structural characteristics by CD and for binding affinity by FQ. Finally, a study is performed to investigate the thermal stability of a recombinant antibody fragment by CD analysis. It is found that simple ligand modifications such as the introduction of a C-terminal cysteine residue can improve purification performance. The FQ studies show that the modified peptide has a higher affinity for antibody. The CD analysis shows that it has a tendency to dimerize because of the formation of disulfide bonds. The versatility of epitope affinity is demonstrated through the purification of a recombinant diabody (dbFv) and by the use of a separate peptide matrix for the purification of an unrelated antibody. All studies result in antibody preparations of high purity and immunoreactivity. The CD analysis of the dbFv shows that it is denatured at 37 degrees C and is therefore unsuitable as a targeting reagent for use in humans in its present form. It is concluded that epitope affinity chromatography coupled with biophysical analyses plays an important role in the production and characterization of antibody-based reagents for targeted diagnosis and therapy of human diseases.     

Determination of the reference value of nitrogen mass fraction in the reference material of Polish soil

Ensuring a traceability and meaningful of a measurements is one of the most important stages of each analysis, each measurement. It is especially important for measurement of the environmental samples, like soil, which is a very complex matrix. A certified reference materials (CRMs) should be routinely used for this purpose. The paper discusses the procedure for preparation of the soil samples for certification as CRM. As for agricultural reasons there is a growing demand for CRMs regarding a nitrogen mass fraction in the Polish soil, we prepared such a material and established the reference value with associated measurement uncertainty. Homogeneity and stability of the material were shown to be appropriate for the intended purpose. The presented approach can also be used in a process of manufacture of a laboratory reference material, which can be used for a routine quality control.     

Statistical mechanical theory for steady-state systems. III. Heat flow in a Lennard-Jones fluid

A statistical mechanical theory for heat flow is developed based upon the second entropy for dynamical transitions between energy moment macrostates. The thermal conductivity, as obtained from a Green-Kubo integral of a time correlation function, is derived as an approximation from these more fundamental theories, and its short-time dependence is explored. A new expression for the thermal conductivity is derived and shown to converge to its asymptotic value faster than the traditional Green-Kubo expression. An ansatz for the steady-state probability distribution for heat flow down an imposed thermal gradient is tested with simulations of a Lennard-Jones fluid. It is found to be accurate in the high-density regime at not too short times, but not more generally. The probability distribution is implemented in Monte Carlo simulations, and a method for extracting the thermal conductivity is given.     

Fragility of supercooled liquids from differential scanning calorimetry traces: theory and experiment

Starting from the Debye model for frequency-dependent specific heat and the Vogel-Fulcher-Tammann (VFT) model for its relaxation time, an analytic expression is presented for the heat capacity versus temperature trace for differential scanning calorimetry (DSC) of glass transitions, suggesting a novel definition of the glass transition temperature based on a dimensionless criterion. An explicit expression is presented for the transition temperature as a function of the VFT parameters and the cooling rate, and for the slope as a function of fragility. Also a generalization of the results to non-VFT and non-Debye relaxation is given. Two unique ways are proposed to tackle the inverse problem, i.e., to extract the fragility from an experimental DSC trace. Good agreement is found between theoretically predicted DSC traces and experimental DSC traces for glycerol for different cooling rates.     

On-column trace enrichment by sequential frontal and elution electrochromatography II. Enhancement of sensitivity by segmented capillaries with z-cell configuration--application to the detection of dilute samples of moderately polar and nonpolar pesticides

An on-column trace enrichment method for capillary electrochromatography of dilute samples is described. It involves the sequential use of frontal and elution electrochromatography on a segmented capillary column comprising of two contiguous segments each packed with a different sorbent. While the entering segment is for preconcentration by frontal electrochromatography the second segment is much longer and is meant for separation of the enriched analytes in the subsequent elution electrochromatography step. The preconcentration segment is usually packed with a sorbent that affords the highest affinity towards the solutes of interest while the separation segment is packed with a stationary phase that exhibits the highest selectivity and separation efficiency for the analytes. The detection is performed in the UV using a z-cell configuration for achieving an increased path length for detection. The effectiveness of this on-column trace enrichment is demonstrated on dilute samples of moderately polar solutes (e.g., carbamate insecticides) and nonpolar solutes (e.g., pyrethroid insecticides). Under optimal frontal and elution electrochromatography conditions. 817- and 1100-fold sensitivity increase are achieved for permethrin (a pyrethroid insecticide) and methiocarb (a carbamate insecticide), respectively, with a UV detector. The method is demonstrated with real water samples (e.g., tap and lake water samples) spiked with carbamate and pyrethroid insecticides. The limits of detection for the pesticides achieved in tap and lake waters reached 10(-8) to 10(-9) M.     

Wetting: Inverse Dynamic Problem and Equations for Microscopic Parameters

Movement of a liquid meniscus in a low-diameter capillary while it is being filled or emptied is considered. The liquid is nonvolatile. Assuming low Reynolds number and low capillary number, the liquid-gas interface shape is studied. Angles of inclination of this boundary to the solid near the contact line are small. Consideration is given to the inverse problem in wetting dynamics: to establish an analytic expression for the universal constant that influences the dynamics of a three-phase contact line. Inverse relations for microscopic parameters in terms of macroscopic measured values obtained in experiments with a meniscus moving through a capillary are derived. The inverse relations are substantiated independently. To do so, numerical experiments for a van der Waals liquid have been carried out, using the de Gennes model of partial wetting. General formulas for microparameters agree well with numerical experiments. The article provides the similarity criterion which influences the wetting in the case of a van der Waals liquid meniscus. The inverse dynamic problem for both an advancing and a receding meniscus is solved. A relation for the critical speed of meniscus recession is proposed. Two contact angles for a meniscus are discussed. Behavior of dynamic contact angles in the vicinity of the critical speed is studied. One of the angles is shown to vanish at less than the critical speed, and the other one, exactly at the critical speed. In the case of an advancing meniscus the equations for microparameters are valid for both partial and complete wetting. The proposed inverse expression for complete wetting allows determination of the maximum precursor film thickness and its dependence on the motion speed (also determination of the Hamaker constant in the case of a van der Waals liquid). Copyright 2000 Academic Press.     

Quantum mechanical reactive scattering theory

In this article we briefly discuss a number of promising approaches to the formulation of a general, numerically exact, quantum mechanical theory of fully three-dimensional reactive atom-diatom collisions. It is noted that the ability to treat the three-dimensional H + H₂ exchange reactions is pre-requisite to any demonstration of the success of a general quantum mechanical formalism for reactivescattering. However, it is also noted that the time has come for any such theory to further demonstrate the ability to go beyond this basic, elementary atom-diatom exchange reaction. It is speculated that there now exist a number of approaches which can potentially provide such a general framework for quantum reactive scattering theory. Finally, a new generalizationof the Faddeev formalism for such systems, which is capable of inclusion ofthree body forces with a completely general form for the potential surface, is presented.     

A theoretical model for evaluation of configurational entropy of mixing with respect to shape and size of particles

A general method of evaluation of configurational entropy of a liquid mixture is presented. It is based on a generalized lattice model with no restrictions due to particle shape being introduced. A general formula for the entropy is derived. Achieved results open a way for a rigorous analysis of particle shape effect on mixing process. As an example, a new formula for the entropy of mixing of hard spheres in continuous space is derived which may respect a physical bound for packing ratio. A systematic approach to improve the model accuracy is proposed. The resultant alternative models are discussed in details. A comparison with literature data and the Mansoori-Carnahan-Starling formula is presented. Very good agreement is shown.     

Fast Interpretation Of 3D Liquid Chromatography Signals: Application To The Study Of Organic Matter In Wastewaters

Abstract

The aim of this work is to propose a very simple method for the selection and interpretation of the relevant individual spectra of a set of absorbance spectra, as for example in a 3D chromatogram. The method is based on the rank computation of the matrix of experimental values, after or during a chromatographic run. From a classical chromatographic system with a rapid scanning spectrophotometer (diode array detector for example), a computer is used for data acquisition of absorbances of the whole UV spectrum, and later computation. Firstly, acquisition is performed until the end of the elution and then the program gives the number and the corresponding spectra of relevant fractions. If another run is needed, for a different sample for example, the procedure makes it possible to check whether the detection signal is independent of the previous spectra. Different applications are presented for the study of organic matter in wastewaters by low pressure liquid chromatography.     

A quantitative contour analysis of axisymmetric vesicles spontaneously adhering onto a substrate

The determination of membrane-substrate profile for adherent vesicle using confocal reflectance interference contrast microscopy (C-RICM) has pushed for the need of advanced mechanics model for interpreting adhesion mechanisms. In this work, a model for vesicles or cells adhesion is established, the governing equation is derived from the variation of the potential energy at the cohesive zone. A closed-form solution is found for vesicle spontaneously adheres to a substrate when its shear modulus, micro vanishes. Based on the model and C-RICM experiments the magnitude of the adhesion force is calculated for a lipid vesicle adheres to a glass substrate.     

Determination of formaldehyde in frozen fish with formaldehyde dehydrogenase using a flow injection system with an incorporated gel-filtration chromatography column

A flow injection analysis (FIA) system for determination of formaldehyde in frozen fish products is described. The system provides a rapid and selective determination of formaldehyde in aqueous fish extracts by the combination of a deproteinization procedure and a stopped-flow enzymatic approach in a FIA system. The FIA system is furnished with a gel-filtration chromatography column for on-line removal of the proteins from the extract before the enzymatic analysis is performed. Compared with the standard methods for determination of formaldehyde in fish products the present method is much faster and less affected by interferences. The limit of detection for the proposed method is 2.5 mg/l of formaldehyde. The sampling frequency is about 10 determinations per hour.     

Monte Carlo estimation of kinetic parameters in polymerization reactions

A general method for estimating kinetic parameters in polymerization reactions using Monte Carlo simulation to represent the models of the reactions is developed. From a statistical point of view, the procedure is a Bayesian one in which a posterior probability density surface (PPDS) is calculated for points on a grid in the parameter space. A smoothing function is fitted to the PPDS, then a posterior probability region, which is similar to a confidence region, is calculated for the parameters. An application to a relatively trivial example, the Mayo–Lewis copolymerization model is shown in detail. Many other potential applications are suggested.     

ABSINTH: a new continuum solvation model for simulations of polypeptides in aqueous solutions

A new implicit solvation model for use in Monte Carlo simulations of polypeptides is introduced. The model is termed ABSINTH for self-Assembly of Biomolecules Studied by an Implicit, Novel, and Tunable Hamiltonian. It is designed primarily for simulating conformational equilibria and oligomerization reactions of intrinsically disordered proteins in aqueous solutions. The paradigm for ABSINTH is conceptually similar to the EEF1 model of Lazaridis and Karplus (Proteins 1999, 35, 133). In ABSINTH, the transfer of a polypeptide solute from the gas phase into a continuum solvent is the sum of a direct mean field interaction (DMFI), and a term to model the screening of polar interactions. Polypeptide solutes are decomposed into a set of distinct solvation groups. The DMFI is a sum of contributions from each of the solvation groups, which are analogs of model compounds. Continuum-mediated screening of electrostatic interactions is achieved using a framework similar to the one used for the DMFI. Promising results are shown for a set of test cases. These include the calculation of NMR coupling constants for short peptides, the assessment of the thermal stability of two small proteins, reversible folding of both an alpha-helix and a beta-hairpin forming peptide, and the polymeric properties of intrinsically disordered polyglutamine peptides of varying lengths. The tests reveal that the computational expense for simulations with the ABSINTH implicit solvation model increase by a factor that is in the range of 2.5-5.0 with respect to gas-phase calculations.