Adams methods for neutral functional differential equations

Summary In this paper Adams type methods for the special case of neutral functional differential equations are examined. It is shown thatk-step methods maintain orderk+1 for sufficiently small step size in a sufficiently smooth situation. However, when these methods are applied to an equation with a non-smooth solution the order of convergence is only one. Some computational considerations are given and numerical experiments are presented.     

Suppression of deleterious effects of free silanols in liquid chromatography by imidazolium tetrafluoroborate ionic liquids

Silica-based stationary phases are commonly used in liquid chromatography, but their surface acidity causes known problems, especially when separating basic compounds. Deleterious effects of free silanols are not fully removed by standard prevention procedures consisting in adding alkylamines or other amino quenchers to the eluents. We found that ionic liquids of the imidazolium tetrafluoroborate class, added to mobile phases at concentrations of 0.5-1.5% (v/v), blocked silanols and provided excellent thin-layer chromatographic separations of strongly basic drugs which were otherwise not eluted, even with neat acetonitrile as the mobile phase. The silanol suppressing potency of imidazolium tetrafluoroborates was demonstrated to markedly exceed that of the standard mobile phase additives, like triethylamine, dimethyloctylamine and ammonia. The proposed new mobile phase additives were also demonstrated to provide reliable lipophilicity parameters of base drug analytes as determined by gradient mode of high-performance liquid chromatography. By applying the readily available and environmentally friendly imidazolium tetrafluoroborate ionic liquids, simple and efficient means of improvement of liquid chromatographic analysis of organic bases were elaborated.     

Protective effects of vitamin E against CCl<Subscript>4</Subscript>-induced hepatotoxicity in rabbits

The influence of CCl₄ on the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), the value of the total antioxidant status (TAS), and the concentration of malonic dialdehyde (MDA) and glutathione (GSH) was monitored in plasma or whole blood of rabbits. The administration of CCl₄ caused the increase of the SOD activity to approximately 150 % and the decrease in the activity of GPx and GR by about 50 %. These changes were accompanied with the increase in TAS value and MDA concentration and the decrease of GSH concentration. The effect of CCl₄ was suppressed by the previous 7 days lasting or simultaneous administration of vitamin E. Oxidative stress caused by CCl₄ was accompanied by the development of reactive oxygen forms, especially superoxide radical anion.     

Sensitive spectrophotometric determination of gallium with bromopyrogallol red in the presence of surfactants

Gallium in the presence of surfactants (NTGE and CTA) forms with BPR a violet ternary complexes with λ_max at 615 and 625 nm, respectively, with molar absorptivities of 7.0 × 10⁴ and 1.3 × 10⁵ liters mol^?1 cm^?1. These complexes can be advantageously used for the determination of gallium. The molar ratio of gallium to BPR, which is 1:1 in the binary complex, increases to 1:3 in the ternary complex. The presence of surfactants changes the number of BPR molecules bonded to gallium. This is the main factor in the increase in color intensity. Numerous metals interfere. Gallium can be separated by extraction of gallium from 7 M hydrochloric acid with diisopropyl ether.     

Redox-iodometry: a new potentiometric method

A new iodometric method for quantifying aqueous solutions of iodide-oxidizing and iodine-reducing substances, as well as plain iodine/iodide solutions, is presented. It is based on the redox potential of said solutions after reaction with iodide (or iodine) of known initial concentration. Calibration of the system and calculations of unknown concentrations was performed on the basis of developed algorithms and simple GWBASIC-programs. The method is distinguished by a short analysis time (2–3 min) and a simple instrumentation consisting of pH/mV meter, platinum and reference electrodes. In general the feasible concentration range encompasses 0.1 to 10^–6 mol/L, although it goes down to 10^–8 mol/L (0.001 mg Cl₂/L) for oxidants like active chlorine compounds. The calculated imprecision and inaccuracy of the method were found to be 0.4–0.9% and 0.3–0.8%, respectively, resulting in a total error of 0.5–1.2%. Based on the experiments, average imprecisions of 1.0–1.5% at c(Ox)>10^–5 M, 1.5–3% at 10^–5 to 10^–7 M, and 4–7% at <10^–7 M were found. Redox-iodometry is a simple, precise, and time-saving substitute for the more laborious and expensive iodometric titration method, which, like other well-established colorimetric procedures, is clearly outbalanced at low concentrations; this underlines the practical importance of redox-iodometry.

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An erratum to this article is available at .     

Mass spectrometric behaviour of carboxylated polyethylene glycols and carboxylated octylphenol ethoxylates

Mass spectrometric behaviour of mono- and di-carboxylated polyethylene glycols (PEGCs and CPEGCs) and carboxylated octylphenol ethoxylates (OPECs) are discussed. The tendency for ionisation (deprotonation, protonation and cationisation by alkali metal cations) of carboxylated PEGs was compared with that of non-carboxylated correspondents by using both secondary ion mass spectrometry (SIMS) and electrospray ionisation (ESI). The fragmentation of the PEGCs and CPEGCs is discussed and also compared with their neutral correspondents, PEGs. The B/E mass spectra were recorded, using secondary ion mass spectrometry as a method for generation, for deprotonated and protonated molecules and molecules cationised by alkali metal cations. The fragmentation behaviour of PEGs is found to be different from that of CPEGCs, The presence of carboxylic groups may be confirmed not only by the determination of molecular weights of the ethoxylates studied, but also on the basis of the fragment ions formed. The metastable decomposition of the [OPEC-H](-) ions proceed through the cleavage of the bond between the octylphenol moiety and the ethoxylene chain leading to the octylphenoxy anions. It permits determination of the mass of the hydrophobic moiety of the studied carboxylated alkylphenol ethoxylate. ESI mass spectra recorded in the negative ion mode were found to be more suitable for the determination of the average molecular weight of carboxylated ethoxylates than SI mass spectra.     

Photoinjection studies of ion-implantation-induced electron traps in MOS structures

Trapping centers related to P⁺ and B⁺ ions implanted in the SiO₂ layer as well as traps introduced into SiO₂ during boron implantation through the oxide into the silicon substrate have been investigated. The internal photoemission method has been used to estimate their capture cross section and total densityN _t .     

Relativistic virial theorem for diatomic molecules. Application to H 2 +

Summary The virial theorem for a molecule in the relativistic clamped-nuclei approximation is derived. The individual energy contributionsA (momentum energy),B (mass energy),T=A+B (kinetic energy) andV (potential energy) are expressed in terms ofE, E/R (derivate w.r.t. the nuclear coordinates) and the relativistic correction E/² (derivative w.r.t. Sommerfield's fine-structure constant ). IfE and E/R are known as functions of , then all individual energy terms are also known as functions of . As an example, numerical results for H ₂ ⁺ are presented. The relativistic and nonrelativistic potential energy curves and the paradoxical behavior of their different contributions are analyzed and interpreted in both the largeR and shortR ranges.Dedicated to Professor W. Kutzelnigg on the occasion of his 60th birthday     

Kinetics and Mechanism of Chromium(III)-oxalates-2-hydroxynicotinate and Chromium(III)-oxalates-3-hydroxypicolinate Aquation in HClO4 Solutions

New chromium(III) complexes, [Cr(C₂O₄)₂(2-hnic)]²⁻ and [Cr(C₂O₄)₂(3-hpic)]²⁻ (where 2-hnic = O,O′-bonded 2-hydroxynicotinic acid and 3-hpic = N,O-bonded 3-hydroxypicolinic acid), were obtained and characterized in solution. The acid-catalyzed aquation of the both complexes leads to liberation of the appropriate pyridinecarboxylic acid and formation of cis-[Cr(C₂O₄)₂(H₂O)₂]⁻. Kinetics of these reactions were studied spectrophotometrically in the 0.1–1.0 M HClO₄ range, at I = 1.0 M. In the case of [Cr(C₂O₄)₂(2-hnic)]²⁻, a slow chelate-ring opening at the Cr–O (phenolate) bond is followed by a fast Cr–O (carboxylate) bond breaking. The rate law: k_obs = k_HQ_H[H⁺] was established, where k_H is the acid-catalyzed rate constant and Q_H is the protonation constant of the coordinated phenolate oxygen atom. In the case of [Cr(C₂O₄)₂(3-hpic)]²⁻, the reversible chelate-ring opening at Cr–N bond is followed by the rate determining step – the one-end bonded ligand liberation. The rate law for the first step was determined: k_obs = k₁+k₋₁/Q₁[H⁺], where k₁ and k₋₁ are the rate constants of the chelate-ring opening and closure and Q₁ is the protonation constant of the pyridine nitrogen atom. The aquation mechanisms are proposed and the effect of ligand coordination mode on complex reactivity is discussed.     

Fine tuning the structure of the Cu2+ complex with the prion protein chicken repeat by proline isomerization

The interaction between the single hexarepeat unit of chicken prion protein [ChPrP(54-59)] and Cu(II) was investigated by NMR, finding different coordination modes for the trans/trans and cis/trans isomers.