Ions In Molecules Research Articles

Pronounced nonlinear behavior of atomic collision sequences induced by keV-energy heavy ions in solids and molecules.

When an energetic ion hits a target consisting of atoms lighter than the projectile, the target configuration seen by the ion along its trajectory may differ significantly from the initial state. This nonlinear effect, which originates in rapidly moving recoil atoms, has been investigated by molecular-dynamics simulation mainly for the simple case where the target is a diatomic molecule. Nonlinear behavior has been distinguished from linear behavior by, respectively, switching on and off the interaction between target particles. Pronounced nonlinear effects have been found in energy loss and scattering angle of the ion; they have been classified roughly as clearing-the-way and blocking-the-way effects, depending on whether nonlinear behavior results in a low or high scattering probability. Effects on stopping power appear small for the small systems investigated. For ion-molecule collisions, the important conclusion is made that binary-scattering behavior need not be indicative of a spectator collision but may, if the ion mass exceeds the target mass, originate in the (nonlinear) clearing-the-way effect. The paper ends with a few results and tentative conclusions on ion-surface scattering with heavy ions.

Roles of the two copper ions in bovine serum amine oxidase.

With a view to obtaining information on the roles of the two copper ions in bovine serum amine oxidase (BSAO), spectroscopic and magnetic studies on several BSAO derivatives have been carried out. Cu-depleted BSAO (Cu-depBSAO) exhibits no enzyme activity and only a low absorption intensity at ca. 475 nm, which is the characteristic absorption maximum of the chromophore in BSAO. The binding of 1 mol of Cu to 1 mol of Cu-depBSAO slightly but definitely increases the enzyme activity and the absorptivity, although they are much lower than those of native BSAO. The incorporation of 2 mol of Cu into Cu-depBSAO gives rise to a similar high activity and absorptivity as those of the native enzyme. Electron paramagnetic resonance (EPR) spectra of the BSAO derivatives reveal that two copper ions in the enzyme molecule are environmentally identical. Titrations of BSAO, Cu-depBSAO, and Cu-half-depleted BSAO (Cu-half-depBSAO), containing 1 mol of copper per mole of protein, with phenylhydrazine (an inhibitor of BSAO) indicate that only 1 mol of phenylhydrazine reacts with 1 mol of the enzyme. In other words the enzyme possesses only one chromophore or one active site, though the molecule is composed of two electrophoretically identical subunits. The binding constants between phenylhydrazine and BSAO, Cu-depBSAO, or Cu-half-depBSAO were estimated to be 5 X 10(6), 5 X 10(4), and 1 X 10(5) M-1, respectively. The binding of phenylhydrazine to the chromophore is assisted by the presence of two copper ions by a factor of 100.(ABSTRACT TRUNCATED AT 250 WORDS)

Ionization potentials and structure of simple ionic compounds

From the analysis we have presented here, we can state that the mutual influence of ions in simple diatomic and triatomic molecules essentially comes down to polarization effects similar to the Stark shift of levels. An expression for the Stark shift, obtained within the framework of perturbation theory, is valid only for weak fields. However, experiments indicate that phenomena similar to the Stark shift of levels occur for rather strong intramolecular fields as well.

Each Phaseolus vulgaris isolectin exists in five electrophoretic forms related to the number of metal ions bound per molecule

Analysis of the pH 8.3 electrophoresis of the Phaseolus vulgaris seed lectins suggests that each of the five isolectins exists in five different forms. Incubations of the lectins in the presence of EDTA or of metal ions such as Mn 2+, Mg 2+, Co 2+ and Ni 2+ shows that their different electrophoretic behaviours are related to the binding of metal ions to the molecules. Determinations of the isolectin metal content by atomic absorption measurements demonstrate that at pH 8.3 their five electrophoretic forms are related to the number of subunits (0, 1, 2, 3 or 4) which contain metal ions in the tetrameric molecules.

Wake formation by megaelectronvolt-per-nucleon bare H and He ions in large hydrocarbon molecules?

A new component is observed in \ensuremath{\sim}0\ifmmode^\circ\else\textdegree\fi{} electron cusp spectra produced by megaelectronvolt per nucleon ${\mathrm{H}}^{+}$ or ${\mathrm{He}}^{++}$ bombardment of hydrocarbon molecules with more than three C atoms. This component is narrower than, and different in skew and yield energy dependence from, electron capture or loss to the continuum processes, and has a width that is dependent on projectile Z. Of the presently proposed mechanism for single forward electron production, only wake production in the larger molecules cannot be eliminated, although wake model predictions agree just qualitatively with our experimental results.

Electronic Polarizability of Ions in Silver Halide Diatomics

AbstractThe electronic polarizability of ions in silver halide molecules is estimated including the influence of molecular environment. The calculation is also compared with results from other approaches. Finally some spectroscopic properties have been calculated to show the validity of the result of present calculation in the molecular environment.

Influence of solvent deuteration on the spectral-luminescent and generational properties of xanthene and oxazine dyes

Solving the problem of realizing the energetic potential of laser devices based on dye solutions involves making deliberate changes in such characteristics of the active medium as the magnitude of the induced pumping loss, the quantum yield of fluorescence, and the degree of photostability of the laser solutions. This approach presumes either the synthesis of new highly effective compounds or the improvement in the laser characteristics of already existing materials by the selection of the appropriate solvents or chemical additives [1-3]. In a series of works, an increase in the fluorescence quantum yield of certain dyes has been observed on passing from ordinary to deuterated solvents [4, 5]. Unfortunately, the literature includes no information on the attendant changes in laser characteristics of the active media, and also the question of the mechanisms suppressing the nonradiative transfer of the excitation energy in the isotropic substitution of deuterium for hydrogen ions in the solvent molecules remains quite unclear. In the present work, it is established that the use of deuterated ethyl and methyl alcohols leads to improvement in the laser efficiency of xanthene and oxazine dyes; especially favorable effects of solvent deuteration are seen in oxazine-9 (cresyl violet). It is shown that the change in spectroscopic constants controlling the processes of triplet-molecule formation and deactivation in the given materials is not much expressed, and the increase in generational characteristics of the dye solutions is due to slowing of the nonradiational internal-conversion processes S~ § So. Deuterated ethyl and methyl alcohols of analytical grade were used as the solvents; the hydrogen-containing alcohols were doubly distilled. The absorption and luminescence spectra of the dyes, preliminarily purified by the methods of recrystallizatio n and chromatography,

Modification of 5'-nucleotidase activity by divalent cations and nucleotides.

The 5'-nucleotidase activity of the purified cytoplasmic fraction preparation of bovine brain does not depend on the presence of the divalent metal ions Mg2+, Ca2+, and Cu2+ in the incubation medium. The Zn2+ ion (0.5 mM) causes total enzyme inhibition. Although EDTA and 8-hydroxyquinoline inhibit the 5'-nucleotidase from this source, it has not been possible to show the existence of metal ions in the enzyme molecule. The inhibition of 5'nucleotidase by EDTA is progressive and irreversible; when the enzyme is not preincubated with EDTA, the inhibition is overridden by metal ions. The purines (except xanthine, 0.3 mM), pyrimidines, and their nucleosides do not affect the 5'-nucleotidase activity. The nucleoside di- and triphosphates are competitive enzyme inhibitors against 5'-AMP as substrate. The Ki values of the diphosphates are lower than those determined for the corresponding triphosphates. The inhibition caused by the above nucleotides is reversed, partly or wholly, by Mg2+, depending on the molar ratio between the effectors. The inhibitory action of the -SH group reagents on the 5'-nucleotidase activity is weak and reversible.

The role of metals in the initiation and the development of malignant transformation

The concentration of metal ions in DNA molecules of a malignant growth is higher than in the norm. The genetic consequences appearing in the DNA molecule as a result of mutations of certain type and of the penetration of metal ions into its structure are considered. The present state of investigation of metal influence upon the structural and thermodynamic properties of DNA, histones and chromatin in the norm and in the malignant transformation is considered. Metals endogen-bound with DNA leave the latter susceptible to the influence of X-rays and certain antitumor preparations. The change in the physical properties (electronic density distribution, thermostability) of DNA, histones and their complexes in the case of cancer are interpreted from the view-point of the influence of endogen-bound metal ions on the structure and cooperative properties of these molecules. The change of dipole moments of DNA sites after the incorporation of certain bivalent metal ions has been established using computation methods. The change in histone structure under the influence of metals has been demonstrated experimentally using X-ray diffraction and spectral methods. The predicted changes in chromatin structure and thermodynamic properties under the influence of metal ions have been confirmed by direct calorimetric and spectral investigations. A general analysis of the available data is given. The program of investigations required in this field is laid out.

The effect of molecular vibration on charge transfer between H2+and H2

Charge transfer between H2+ ions in specific vibrational states and H2 molecules has been investigated within the energy range 8-1000 eV using photoelectron-photoion coincidence spectroscopy. Results up to the sixth vibrational level show that cross sections vary significantly with vibrational energy in a complicated manner which is not in accord with multistate impact parameter theory.

Electronic polarizabilities, ionic radii, and repulsive potential parameters for diatomic alkali halide molecules

The electronic polarizabilities of ions in diatomic alkali halide molecules calculated using the Seitz–Ruffa energy level analysis are found to agree closely with those recently estimated by Brumer and Karplus utilizing the exchange perturbation theory. A sensible test of these polarizabilities has been presented by calculating the molecular properties like dipole moments. Ionic radii for alkali and halogen ions appropriate to diatomic molecules are determined using the relation between size and effective nuclear charges. The radii thus evaluated are found to be nearly additive and reproduce the internuclear distances within about ± 0.10 Å for all the alkali halide molecules except for RbF and CsF. An analysis of interaction energies in alkali halide molecules is presented by adopting two potential forms for the repulsive energy showing, respectively, the inverse power dependence and exponential dependence on internuclear distance. The additivity of repulsive potential parameters is discussed in the light of recent investigations. The results for the molecular constants obtained from the exponential form are in much better agreement with experiment than those estimated from the inverse power form.

The effective dipole polarizabilities of the ions in MX molecules

The effective dipole polarizabilities of the ions in MX molecules

Spectral and Electron Paramagnetic Resonance Investigations of Copper(II) Complexes of Linear-Chain Fatty Diacids

Electron paramagnetic resonance spectra of polycrystalline copper complexes of butanedioic, pentanedioic, hexanedioic, heptanedioic, and decanedioic acids are presented, together with 77 K electronic spectra. The complexes are formulated as dimeric copper carboxylate units linked into infinite chains. Monomer impurities are also present and increase in quantity with the length of the diacid. The monomer and dimer signals occur at very different field strengths, but the g values calculated from the S = 1 2 spectra are similar to those calculated from the S = 1 spectra. The EPR method can thus be used to locate copper ions in possible biological frameworks and to study the geometry around the metal sites. The distortion from axial symmetry around the copper increases with the length of the diacid, as shown by the observed zero-field splitting parameters. Gaussian analysis of the optical absorptions yields information used with EPR data to calculate covalency and Fermi contact terms. Sodium, potassium, and lithium salts transform the dimeric polymers into monomeric polymers. The presence of magnetic exchange interactions in copper dicarboxylates is discussed and thereby shown to be of interest in the study of copper ions in molecules of biological importance containing carboxylate groups.

Simple electrostatic models for vibrating unsymmetrical triatomic molecules and triatomic ions

Bond charge, point-dipole models are used to derive simple universal relations,Kθθ=0.0435 (K11K22)1/2 −0.0086 (K 11 + K22), andKθθ = 0.11 (K11K22)1/2 −0.0055 (K11 +K22), between the bond stretching force constantsK11 andK22 and bond bending force constantKθθ for linear and bent unsymmetrical triatomic molecules respectively. The relations are shown to be approximately valid for a number of molecules. An extension of the models to include charged species (ions) in triatomic molecules is also presented and tested, giving good results.

Dielectric properties of moist cellulose

AbstractThe dielectric constant ϵ′ and the dielectric loss ϵ″ for cellulose fiber were measured over a frequency band 0.2 to 10 Mc/sec and a temperature range from −20 to 80°C. Also, the variation of the dielectric behavior with relative humidity was measured at 25°C. From these data, both the specific resistivity Rs and the dissociation energy U0 were calculated. The results showed that the dielectric constant increased with frequency and temperature. This may be due to the increase in the rotation and the polarization of the flexible part in the fiber. The variation of the dielectric loss with temperature showed a maximum absorption corresponding to the β‐relaxation. For the moist fiber, it is found that as the relative humidity increases, the dielectric constant and the dielectric loss increase. This increase may be due to the presence of polar water molecules, to the freeing of the polar groups, and to the freeing of the ions in the fiber molecule as well as to the increase in the number of OH− and H+ ions resulting from the ionization of water. A relation between the dielectric constant and resistivity at different humidities is represented graphically. From this relation, it is found that the dissociation energy is equal to 0.318 × 10−12 and 5.46 × 10−12 erg below and above 52% RH, respectively.

Outer-Shell Rearrangement in Highly Stripped Core Ions in Molecules

Outer-Shell Rearrangement in Highly Stripped Core Ions in Molecules

The role of metal ions in proteins and other biological molecules.

The application of new and improved physical, chemical , and analytical methods over the past decade to the role of metal ions in biological systems has resulted in many advances in a difficult field. This review will try to summarize some of these developments as well as mention some of the problems.

Resonances in Electron Impact on Diatomic Molecules

In this review we present the energies, configuration, and other properties of resonances (also called compound states and temporary negative ions) in diatomic molecules. Much of the information is presented in the form of tables and energy level diagrams. Vibrational, rotational, and electronic excitation are discussed whenever these processes have given information on resonances; often these excitation processes proceed via resonances. The paper is divided according to molecular species (${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, CO, NO, ${\mathrm{O}}_{2}$), but the main conclusions are discussed by the nature of the processes involved.

Charge changing cross sections for heavy ions in complex molecules: the failure of an 'additive' rule

Electron capture and loss cross sections have been measured for 12 MeV iodine ions passing through H2, N2, O2, CO2, N2O, CH4 and (CH2)3O. It is shown that, in contrast to recent data for fast hydrogen beams, it is not possible in this case to predict the cross sections in a complex molecular target by summing contributions from the measured cross sections of its constituent atoms.

Far-Infrared Magnetic Resonance in Fe(III) and Mn(III) Porphyrins, Myoglobin, Hemoglobin, Ferrichrome A, and Fe(III) Dithiocarbamates

Far-infrared spectroscopic techniques are used to study the magnetic resonance of Fe(III) and Mn(III) ions in molecular sites with large axial and rhombic ligand fields. Measurements of transmission spectra over the range 3–100 cm−1 are discussed for a group of polycrystalline compounds, including several biological complexes, at temperatures between 1.3 and 50°K and in applied magnetic fields up to 50 kOe. The spectra show magnetic resonance absorptions which are consistent with a number of cases of the spin-Hamiltonian formulation, and the spin-Hamiltonian parameters (D, E ≳ 1 cm−1) are directly obtained from the spectra. The observation of resonances due to high-spin Mn(III) and to the ferromagnetic resonance of ((C2H5)2NCS2)2 Fe(III)Cl is reported. These measurements show that present far-infrared techniques offer a direct method for the investigation of the effects of large ligand fields on paramagnetic ions in molecules.