Comparison between Gibbs free energy minimization and mass action law for a multitemperature plasma with application to nitrogen

This paper gives all the necessary physical equations to determine the composition and the thermodynamic properties in a multitemperature plasma utilizing two different methods: the first method is based on Gibbs free energy minimization and the second is based on the resolution of the mass action law. The lowering terms of the ionization potential and thermodynamic properties are given for a multitemperature plasma using the Debye-Hückel approximation. Numerical application is made to a nitrogen plasma.     

A Statistical Mechanical View of the Determination of the Composition of Multi‐Temperature Plasmas

It is important that plasma composition is calculated in a manner consistent with statistical mechanics, particularly since the Boltzmann equation is the basis from which transport coefficients and the fluiddynamic equations are derived. It is shown from statistical mechanical considerations based on the Boltzmann equation and the Htheorem that it is (i) not possible for a plasma to have more than one temperature in equilibrium in the absence of external forces and gradients, and (ii) not possible to draw conclusions about the change in entropy of a plasma in the presence of external forces and gradients. Derivations of the twotemperature Saha equation, and more generally calculations of the composition of a multitemperature plasma, that are based on entropy maximization are therefore invalid. A thermodynamic derivation of the composition of a multitemperature plasma that is consistent with the statistical mechanical results is presented. The derivation shows that the equilibrium composition of a plasma can be correctly calculated by minimization of the internal or free energy.     

Ab initio conformational analysis of 1,3-propanedithiol

By carrying out Hartree-Fock full, symmetry unconstrained geometry optimizations on the 25 symmetrically unique staggered conformers, using the 4-31+G^* basis set it was found that, on the Hartree-Fock level, gTTg and gTTg′ are the lowest energy rotamers in 1,3-propanedithiol. We also found a number of clear conformational trends. Intramolecular hydrogen bonding was found to be of minor importance. The introduction of electron correlation yields a stabilization of the rotamers with one or two gauche SCCC arrangements relative to those with less gauche SCCC arrangements. Consistent with this, we find that on the MP2 level the most stable conformers are gGGg′ and gGGg.     

Complexes of Zn(2+), Cd(2+), and Hg(2+) with 2-(alpha-Hydroxybenzyl)thiamine Monophosphate Chloride

The binding sites of Zn(2+), Cd(2+), and Hg(2+) in complexes with 2-(alpha-hydroxybenzyl)thiamine monophosphate chloride, (LH)(+)Cl(-), have been investigated in the solid state [2-(alpha-hydroxybenzyl)thiamin monophosphate chloride monoprotonated at the phosphate group and protonated at N(1)' is denoted as (LH)(+)Cl(-); therefore, the ligand monoprotonated at the phosphate group and deprotonated at N(1)' is L]. Complexes of formulae MLCl(2), M(LH)Cl(3), and (MCl(4))(2)(-)(LH)(2)(+) (M = Zn(2+), Cd(2+), and Hg(2+)) were isolated in aqueous and methanolic solutions, depending on pH. The crystal structure of the complex of formula HgL(2)Cl(2) was solved, together with that of the free ligand (LH)(+)Cl(-), by X-ray crystallography. HgL(2)Cl(2) crystallizes in C2/c, with a = 32.968(6) ?, b = 7.477(2) ?, c = 21.471(4) ?, beta = 118.19(1) degrees, V = 4665(2) ?(3), and Z = 4. (LH)(+)Cl(-) crystallizes in Cc, with a = 10.951(3) ?, b = 17.579(4) ?, c = 13.373(3) ?, beta = 105.36(2) degrees, V = 2482.4(10) ?(3), and Z = 4. Mercury(II) binds to the N(1') of the pyrimidine ring. Both ligands are in the S conformation [Phi(T) = -98.1(9) degrees and Phi(P) = 176.1(10) degrees for HgL(2)Cl(2) and Phi(T) = 104.1(5) degrees and Phi(P) = 171.9(6) degrees for (LH)(+)Cl(-)]. (31)P and (13)C NMR spectra, together with vibrational spectra (IR/Raman), are used to deduce the binding sites of the metal and the protonation states of the ligand at various pH values. It is found that solid-state (31)P NMR spectroscopy is particularly useful in characterizing these complexes as the (31)P shielding tensors are sensitive to the state of the phosphate group. On the other hand, the (31)P NMR spectra indicate that direct bonding between Zn(2+) and Cd(2+) to the phosphate can occur under certain preparation conditions. Solid-state (13)C NMR and vibrational (IR/Raman) spectroscopic results are also in agreement with the other techniques.     

Detection and identification of thyreostats in the thyroid gland by gas chromatography-mass spectrometry

Because thyreostatic compounds, also named thyreostats, are banned in Europe (directive 86/469/EEC), methods have to be developed to prevent the illegal use of these substances. The analytical procedure described herein involves the detection and identification at the low ng g⁻¹ level of the main thyreostats known to be used for growth promotion by gas chromatography coupled to mass spectrometry (GC-MS). The assay is based on a liquid/liquid extraction of the thyroid gland, derivatization with pentafluorobenzyl bromide (PFBBr), purification on a silica solid phase extraction column and finally a trimethylsilylation prior to GC-MS. Good thyreostat recoveries were obtained (from 40% to 70%) as well as at acceptable repeatability. The target analytes were detectable below the 1 ng g⁻¹ level on a quadrupole mass spectrometer with negative chemical ionization (NCI) using ammonia as reagent gas and the selected ion monitoring (SIM) acquisition mode. This limit of detection was also reached in the SIM high resolution mode. An improved specificity (more diagnostic ions) was obtained under electronic impact (EI) conditions and positive chemical ionization (PCI) with methane as reagent gas. Identification of thyreostats according to the EU (European Union) criteria (93/256/EEC decision) was made on the basis of two independent GC-MS techniques; the limit of identification was close to 5 ng g⁻¹ for most thyreostats, which represents a real improvement for their control.     

Single molecule modulation spectroscopy of conjugated polymers

This paper describes a new single molecule spectroscopy approach for the investigation of triplet-triplet and singlet-triplet interactions in conjugated polymers. The technique involves the irradiation of isolated single, mulitchromophoric, conjugated polymer molecules by a repetitive sequence of variable-intensity microsecond time scale excitation pulses. The fluorescence intensity is synchronously time-averaged for thousands of cycles of the pulse sequence to yield a high signal-to-noise fluorescence transient on the microsecond time scale. The transient can be analyzed with kinetic models to obtain quantitative information about the kinetics of triplet-triplet exciton annihilation and the quenching of singlet excitons by triplet excitons in conjugated polymers.     

Quantum bits with polyacetylene

The dynamics of a polyacetylene single chain as a system for possible physical implementations of quantum bits is determined. This novel proposition is studied by varying intensity and duration of application of an electric field as well as the intensity, number, and position in the polymer chain of impurity molecules. The behavior of soliton pairs, whose associated energy levels form the quantum bit, is analyzed. The chain is modeled by a modified Pariser-Parr-Pople Hamiltonian extended to include the effects of an external electric field and the parameters of the impurity molecules. The effect of the variation of the field and impurities on the separation of the energy levels associated with soliton pairs is analyzed by numerical integration of the equations of motion. Two different approaches for controlling the separation of levels are presented, and their features compared. First, the use of changes in the electric field to control the distance (and ultimately coupling) between two solitons moving freely on the chain or captured by the potential generated by the impurity molecules. Second, the change in the intensity of the impurities alone, with no application of an external field. We have found that the effect of the use of the field on the separation of levels is much smaller than the one obtained by changes in the parameters of the impurity molecules, which eventually led us to achieve quantum bit behavior in a polyacetylene chain. The influence of the field and impurity parameters in the energy levels is determined, as well as their role in the coupling of the two solitons on the chain. Critical values for distance between solitons, intensity of field, and impurities that determine whether a pair of solitons can work as a quantum bit are obtained.     

On carboxylate as a leaving group at the active site of Mo nitrogenase: electrochemical reactions of some MO and W carboxylates, formation of mono-, di- and tri-hydrides and the detection of an MoH2(N2) intermediate

A carboxylate ligand can function as a leaving group at a reduced molybdenum dihydride centre and this exposes a site at which dinitrogen or other small molecules can bind ; dihydrogen loss occurs after substrate binding ; protic attack intercepts carboxylate loss affording a trihydride intermediate which can partake in a hydrogen evolution cycle : it is suggested that carboxylate loss from the reduced Mo centre of nitrogenase might similarly lead to substrate binding and thence obligatory evolution of H₂.     

Influence of common ions during ultrafiltration of mixtures: Part I. Common anions mixtures

A lot of experiments were investigated to show the behaviour of an ultrafiltration membrane during the filtration of pure salt solutions. What happens when the filtered solution contains several ions?

In this paper, results are given concerning the filtration of mixtures of two salts solutions, salts with a common anion: NaCl + CaCl₂ and Na₂SO₄ + CaSO₄.

The surface charge of the membrane is characterized by streaming potential measurements and rejection rates by means of chromatography. These results confirm the adsorption of divalent ions on the surface and a good selectivity for divalent cations.