Structural Characterization of Chemical Species in Solution by a Theoretical Analysis of XANES Spectra

A theoretical analysis method using a discrete variational X (DV-X) molecular orbital (MO) calculation, based on electron transition from an inner orbital to an unoccupied orbital, is introduced to analyze X-ray absorption near-edge structure (XANES) spectra in a lower energy region below the X-ray absorption edge. The computational procedure is described in detail and the evaluation of an obtained result is also explained. Applications of this method are presented for Cu(II) ions in liquid ammonia, macrocyclic Cu(II) complex in aqueous solution, and Al(III) ions in aqueous solution.     

Linear silver clusters in aqueous solution (clusterites): radiation-induced chemical synthesis and properties

The formation and properties of the products of the radiation-induced chemical reduction of silver ions in aqueous solutions containing sodium polyacrylate were investigated. The absorption spectra of these species exhibit a band at 290 mn and a band in the visible region. The latter shifts from 470 nm to -800 nm with time or after the addition of silver ions. The species obtained (clusterites) arc linear silver clusters bound to the carboxyl groups of the ion exchanger. The red shift of the visible band is due to the increase in their size. The mechanism of the formation and the structure of the clusterites are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1429–1435, June, 1996.     

Colloidal copper in aqueous solutions: radiation-chemical reduction,mechanism of formation,and properties

Colloidal copper has been obtained by -irradiation of aqueous solutions of copper (II) perchlorate in the presence of alcohol and polyethyleneimine (PEI). The sols are spherical particles about 4 nm in diameter, which are quickly oxidized by oxygen or other oxidants. When Cu^II is not entirely incorporated into the complex with PEI, disproportionation of Cu^I aqua complexes formed affords the metal, along with Cu₂O. Reduction of the PEI complex of Cu^I by hydrated electrons gives only colloidal copper. The copper ions can be reduced on the surface of silver sols. Optical parameters of the resulting bimetallic particles have been studied. The presence of copper ions leads to broadening of the absorption band associated with the silver sols and shifts it to the UV region, which is due to the transfer of electrons from copper to silver. Three copper monolayers are enough to cause plasmon absorption of colloidal copper.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 25–30, January, 1994.     

Reactions of aminals of conjugated ω-dimethylaminoaldehydes with coumarin derivatives

The reactions of aminals of conjugated -dimethylaminoaldehydes with various derivatives of 4-methyl- or 3-acetyl coumarins produce -dimethylaminopolyenones containing coumarin fragments. Unlike the starting coumarins, these polyenones practically do not fluoresce. Dialkyl-substituted coumarins with hydroxyl groups in positions 5 or 7 react with -dimethylaminoacrolein aminal to give salts consisting of 1 mole of doubly charged dimethylaminopropenylidenedimethylammonium cations and 2 moles of phenoxide ions (derived from the starting coumarins). The structure and the properties of the salts in solutions have been studied by absorption and fluorescence spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 537–543, March, 1995.The authors are grateful to I. V. Komlev for providing coumarins3 and4.     

Investigation of the metal binding site in methionine aminopeptidase by density functional theory

All methionine aminopeptidases exhibit the same conserved metal binding site. The structure of this site with either Co²⁺ions or Zn²⁺ions was investigated using density functional theory. The calculations showed that the structure of the site was not influenced by the identity of the metal ions. This was the case for both of the systems studied; one based on the X-ray structure of the human methionine aminopeptidase type 2 (hMetAP-2) and the other based on the X-ray structure of the E. colimethionine aminopeptidase type 1 (eMetAP-1). Another important structural issue is the identity of the bridging oxygen, which is part of either a water molecule or a hydroxide ion. Within the site of hMetAP-2 the results strongly indicate that a hydroxide ion bridges the metal ions. By contrast, the nature of the oxygen bridging the metal ions within the metal binding site of eMetAP-1 cannot be determined based on the results here, due to the similar structural results obtained with a bridging water molecule and a bridging hydroxide ion.     

Inclusion of Organic Cations by Calix[n]arenes

Calix[n]arenes represent an interestingclass of preorganized aromatic hostsexhibiting an enhanced ability forcation- interaction. Recent resultsobtained with the complexation of variouscalix[n]arenes and five structural typesof organic cations, namely ammonium ions,quaternary ammonium ions, phosphonium ions,iminium ions and tropylium ions are reviewed.The influence of both the guest structure and theshape and flexibility of the hosts on the complexstability in the gas phase and (mainly) in solutionis considered.     

Electroreduction of Pd(II) Complexes with α-Alanine on a Palladium Electrode

The kinetics of electroreduction of Pd(II) complexes with -alanine, Pd(ala)₂, is studied on a rotating Pd disk electrode in solutions of pH 8–13 containing large excess of -alanine and various supporting electrolytes (NaF, Na₂SO₄, NaClO₄). On a Pd electrode, complexes Pd(ala)₂ undergo reduction at potentials much more negative than on an Hg electrode. This is attributed to the chemisorption of water on the Pd electrode, which hampers adsorption of Pd(ala)₂ that take part in the slow electrochemical stage. As with the Hg electrode, perchlorate ions hinder the Pd(ala)₂ reduction on a Pd electrode. Studying adsorption of Pd(ala)₂ on a Pd electrode is hampered by parallel processes of hydrogen adsorption and absorption.     

The effect of Fe(II) ions on the 1,10-phenanthroline and neocuproine intercalates of γ-zirconium phosphate

1,10-Phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neocuproine), and 4,7-dimethyl-1,10-phenanthroline have been intercalated between layers of -zirconium phosphate (-ZrP). The observed interlayer distances are not a simple function of the size of guest molecules. Despite the fact that -ZrP takes up very few Fe²⁺ ions, the phen and neocuproine intercalates do take up some Fe²⁺ ions without further changes in the interlayer distances. The chemical environments around Fe²⁺ ions between layers of the intercalates were investigated by⁵⁷Fe Mössbauer spectroscopy. A fairly large fraction of the Fe²⁺ ions was found to be in a high-spin state. The low-spin [Fe(phen)₃]²⁺ ions are also ion exchanged on -ZrP, with the expansion of the interlayer up to 19.9 Å.     

Some interelement interferences in the chemical analysis of intermetallic γ′ phase isolates using AAS method

The determination of elements such as Ti, Ta and Nb is a complicated analytical task regardless of the applied methods and research techniques. Flame atomic absorption analysis is a relatively simple and quick method for the determination of major and minor elements in phase isolates. The paper presents the results of some revealed chemical interferences during determination of the above mentioned elements in intermetallic phase isolates.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Synthesis of γ-zirconium phosphate by the fluoro-complex method and the intercalation behavior of some α-diimines

The ammonium form of -zirconium phosphate has been synthesized by the direct precipitation method from fluorozirconate solution in the presence of ammonium dihydrogen phosphate. The hydrogen form Zr(HPO₄)₂ · 2H₂O, was obtained by acid treatment of the ammonium form -Zirconium phosphate , Zr(HPO₄)₂ · H₂O, with a relatively large particle size resulted from fluorozirconate solution in the presence of concentrated orthophosphoric acid. The intercalation behavior of such -diimines as 2,2-bipyridine (bpy) and 1,10-phenanthroline (phen) toward -zirconium phosphate was investigated, and it was found that about 0.2 mol of bpy and 0.5 mol of phen have been incorporated respectively per one mol of the host, with the expansion of interlayer distances. Further incorporation of Cu(H) ions into the interlayer space of these intercalates was possible. The bpy intercalate took up more Cu(II) ions than -zirconium phosphate, indicating that effective pillars are constructed between layers and the ion exchange of Cu(II) ions is facilitated thereby.     

Reactions of excited fullerenes C60 and C70 studied by mass spectrometry

The transformation of the mass spectra of the laser-desorbed C₆₀ and C₇₀ samples with a successive increase in the laser power, resulting in an increase in the degree of excitation of C₆₀ (C₇₀) and in the number of the particles in the laser plume, was studied. Unusual metastable clusters (C₆₀ + C₂) and (C₇₀ + C₂) are formed even at a minimum laser power and begin to dissociate after 0.5 s following a short (3 ns) laser pulse. An increase in the laser power results in the appearance of peaks of metastable clusters C₆₂ (C₇₂) with the statistically normal lifetime without a delay of dissociation. A further increase in the laser power produces metastable clusters C_60k–2n and C_70k–2n (k = 2, 3) formed without a lag from the dimers and trimers of C₆₀ (C₇₀) by the ejection of a number of C₂ required for the stabilization of the C₂ molecules. The peak of C₇₀ appears simultaneously with the appearance of the (C₆₀)_2–2n peaks upon the laser desorption of pure C₆₀. These findings provide evidence for the growth of the excited fullerene clusters by coalescence and subsequent stabilization due to the ejection of a small fragment rather than by the implantation of C₂ into the fullerene framework. This mechanism of cluster growth should be taken into consideration in modeling fullerene formation in an electric arc reactor, because the clusters formed under these conditions have a substantial excess internal energy.     

Metal ion interaction with dimethyl phosphate anion

The influence of metal ions on the conformation of dimethyl phosphate anion around its O-P bonds, has been studied theoretically. The perturbation caused due to metal ions like Na⁺ and Mg²⁺ seems to affect the free dimethyl phosphate anion conformation to a considerable extent. In particular, the fully extended conformation becomes much more favourable in the metal ion dimethyl phosphate complex.     

Photometric determination of palladium with the inclusion complex 1,2-Diaminoanthraquinone-β-cyclodextrin as ligand

1,2-Diaminoanthraquinone forms a 11 inclusion complex with-cyclodextrin in aqueous media and at different pH. This can be employed to solubilize the anthraquinone in water for use as a ligand for metal ions. This ligand can be used to determine palladium at trace levels spectrophotometrically. The limit of detection is 11 ng/ml and the R.S.D. is 2.1%. The performance can be improved by using derivative spectrometry.     

Induced circular dichroiism spectra of benz[b]anthracene included inβ-cyclodextrin

The assignment of the absorption spectra of benz[b]anthracene (1) is reported by measuring the induced circular dichroism spectra of the -cyclodextrin complex with1. It is concluded from the signs of the induced circular dichroism bands that the first absorption band (20.4–30.9×10³ cm^–1) has the transition dipole moment perpendicular to the long axis and the second absorption band (30.9–37.2×10² cm^–1) has the transition dipole moment parallel to the long axis of1. Our assignments are in complete agreement with earlier assignments. The induced circular dichroism spectra exhibit Cotton splittings at 19.1×10³ and 42.8×10³ cm^–1. It can be concluded from Cotton splittings of the induced circular dichroism spectra that the association of two 1:1 inclusion complexes forms a ground-state dimer.     

Improvement of fat digestion in rats by dimethyl-β-cyclodextrin

Heptakis-(2,6-di-O-methyl)--cyclodextrin (DIMEB), a compound having a great water-solubility enhancing effect on lipids via inclusion complex formation was investigated as a potential bile-substituting agentin vivo in rats. The normal fat digestion was inhibited by ligating the bile duct. 3-H-Stearic acid or edible oil were administered orally to rats and the effect of simultaneously administered DIMEB on the lipid absorption was studied by measuring the blood radioactivity level or plasma triglyceride and free fatty acid concentrations. The lipid absorption was significantly improved by DIMEB. Accordingly, it seems to be a new fat digestion and absorption enhancing drug, i.e. a possible bile-substituting agent.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Effect of medium on the equilibrium of cationic σ- and π-complexes: interconversion of 1-pentafluorophenylthio-1,2-dimethyl-acenaphthylenium and 1,2-dimethylacenaphtylene-1,2-S-pentafluorophenylepisulphonium ions

The equilibrium of 1-pentafluorophenylthio-1,2-dimethylacenaphthylenium and 1,2-dimethylacenaphthylene-1, 2-S-pentafluorophenylepisulphonium ions in different media has been investigated by¹H and¹³C NMR spectroscopy using isotope perturbation. It has been found that this equilibrium is weakly sensitive to variation in the medium.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1057–1060, June, 1993.     

Calculation of some electronic excited states of formaldehyde

The optimized MO's of several excited states of formaldehyde have been calculated by means of a large basis set of modified Gaussian functions; particular attention has been paid to the * transition. The total energy of the various states has been obtained as the sum of the SCF and correlation energies; the last one has been calculated as a functional of the electronic density. The calculated values for the transition energies are in good agreement with the experiment. A strong interaction of the * state with the continuum is evidentiated; this fact can justify the absence of the * band in the absorption spectrum.     

Optimisation of Supercritical Carbon Dioxide Systems for Complexation of Naproxen : Beta-Cyclodextrin

Supercritical carbon dioxide (scCO₂)offers several attractive scenarios for thepharmaceutical processing as an alternativeto aqueous and organic solvents. In thiswork naproxen, a widely used non steroidalanti-inflammatory drug with analgesic andanti-inflammatory properties, was chosenas a model drug. Its complexation with cyclodextrinsimproves the rate and extent of dissolutionof the drug, increase its rate of absorption and mayreduce the unpleasant side-effects of the drug.The interest in using this supercritical technologyled us to develop an experimental unit for the useof supercritical CO₂ as a processing medium forthe complexation of naproxen with beta cyclodextrin (CD).     

Novel techniques for plasma diagnostics: Electron paramagnetic resonance and laser-induced fluorescence spectroscopy

Diagnostic techniques for low-pressure, cold plasmas have mostly been limited to emission and mass spectrometry. Herein, the techniques of gas-phase electron paramagnetic resonance and laser-induced fluorescence spectroscopy are briefly reviewed. Particular attention is paid to their attributes which make them good candidates for plasma diagnostic tools. It is found that gas-phase electron paramagnetic resonance can be used to determine and monitor the absolute concentration of a number of important plasma species, e.g., free radicals and atoms. Laser-induced fluorescence can also monitor, with even more sensitivity, but perhaps not so well absolutely, the concentrations of many plasma species, e.g., free radicals, metastable excited states, and molecular ions.