Electron spin resonance studies of d5 ions (Fe3+ and Mn2+) in lead oxide-lead halide glasses

Electron spin resonance (ESR) of d5 ions (Fe3+ and Mn2+) has been investigated in PbO---PbF2 and PbO---PbCl2 glasses in wide ranges of composition. ESR spectra of d5 ions in these glasses exhibit significant differences which we have attributed to at least three important causes: (i) The ionic potentials of Fe3+ and Mn2+ are different. Hence Fe3+ ions tend to acquire their own environment while Mn2+ ions take up substitutional (Pb2+ ion) positions. (ii) The sizes and nephelauxetic behaviours of O2- and F- ions are similar. Thus even when there is a mixed anionic coordination, the environment of Mn2+ ions is highly symmetrical in oxyfluoride glasses. The Mn2+ spectra in oxychloride glasses are considerably different. (iii) Increase in halide ion concentration increases the ionicity of lead-ligand bonding and favours a more symmetrical environment around dopant ions in halide-rich glasses. The features in ESR spectra have been interpreted in the light of known behaviour of d5 ions in glasses and also in the context of known structural features of PbO---PbX2 glasses. Dopant ions appear to cluster at high concentrations although isolated low-symmetry sites are still observed. Effects of crystallization and annealing upon ESR spectra have also been investigated.

Interaction of Metal Ions with 2'-Deoxyribonucleotides. Crystal and Molecular Structure of a Cobalt(l1) Complex with 2'-Deoxyinosine 5'-Monophosphate

The crystal structure of the cobalt( 11) complex with 2'-deoxyinosine 5'-monophosphate (5'- dlMP), [Co(5'-dlMP) (H,0),]-2H20, has been analysed by X-ray diffraction. The complex crystallizes in the space group P2,2,2, with a = 6.877(3), b = 10.904(2), c = 25.421 (6) A, and Z = 4. The structure was solved by the heavy-atom method and refined to an R value of 0.043 using 1 776 unique reflections. The cobalt ion binds only to the 6-oxopurine base of the nucleotide at the N(7) position, the octahedral co-ordination of the metal being completed by five water oxygens. The phosphate oxygens are involved in hydrogen bonding with the co-ordinated water molecules. The structure is closely similar to that of the corresponding ribonucleotide complex. The nucleotide has the energetically preferred conformation: an anti base, a C(3') -endo sugar pucker, and a gauche-gauche conformation about the C(4')-C( 5') bond. The significance of sugar puckering in the monomeric complexes of general formula [ M (5'-nucleotide) (H20),] is explained in terms of the structural requirements for metal-water-phosphate bridging interactions.

Configuration mixing in the s-hole states of metal ions

Configuration interaction calculation have been carried out on the s-hole states of Mn2+ Fe2+ (both high- and low-spin configurations). Co2+, Ca2+, K+ and Na+ including configurations involving virtual orbitals. The results show good agreement with the multiplet structures found in X-ray photoelectron spectra of these ions.

Requirement for calcium ions in mycobacteriophage I3 DNA injection and propagation

Ca2+ ions are absolutely necessary for the propagation of mycobacteriophage I3 in synthetic medium. These ions are required for successful infection of the host and during the entire span of the intracellular development of the phage. A direct assay of the phage DNA injection using 32[P] labelled phage, showns that Ca2+ ions are necessary for the injection process. The injection itself is a slow process and takes 15 min to complete at 37°C. The bacteria infected in presence of Ca2+ tend to abort if the ions are subsequently withdrawn from the growth medium. The effect of calcium withdrawal is maximally felt during the early part of the latent period; however, later supplementation of Ca2+ ions salvage phage production and the mature phage progeny appear after a delayed interval, proportional to the time of addition of Ca2+.

Coordination Behaviour of Imino Hydrazone Ligands towards Nickel (II) and Copper (II) Ions

The complexing ability of a new series of ligands, β-N-arylimine hydrazones, toward Ni (II) and Cu (II) ions has been studied. The isolated complexes are characterised on the basis of elemental analysis, spectroscopic methods and magnetic susceptibility measurements. The ligands are notentially bidentate in character coordinating to divalent metal ions through the N1 and N5 nitrogens. Square planar geometry of the metal ions is suggested on the basis of experimental evidence.

Metal ions in molecular association of porphyrins

Molecular association of porphyrins and their metal derivatives has been recognized as one of the important properties for many of their biological functions. The association is classified into (i) self-aggregation, (ii) intermolecular association and (iii) intramolecular association. The presence of metal ions in the porphyrin cavity is shown to alter the magnitudes of binding constants and thermodynamic parameters of complexation. The interaction between the porphyrin unit and the acceptor is described in terms of π-π interaction. The manifestation of charge transfer states both in the ground and excited states of these complexes is shown to influence the rates of excited state electron transfer reactions. Owing to paucity of crystal structure data, the time-averaged geometries of many of these complexes have been derived from magnetic resonance data.

Intermolecular potentials in the dimer, the excimers, and the dimer ions of ethylene

Calculations are reported on the interaction energies in the dimer, the excimers, and the dimer ions of ethylene. The various a- and u-electron terms for different conformations of the dimeric species are determined by using the exchange perturbation method. The results predict that the singlet excimer and the dimer cation are stable primarily because of the large magnitude of the exciton-resonance and charge-resonance terms, respectively, while the neutral dimer, the triplet excimer, and the dimer anion are weakly stable. The variations of the various energy terms with conformations suggest that these dimeric species cannot have identifical structure.

A study of interaction between two He+ ions in terms of the electronic forces

The potential energy curve of the He2+2 system dissociating into two He+ ions is examined in terms of the electronic force exerted on each nucleus as a function of the internuclear separation. The results are compared with the process of bond-formation in H2 from the separated atoms.

Korteweg-De Vries Equation for Non-Linear Ion-Acoustic Waves in a Plasma with Negative Ions

The theoretical analysis, based on the perturbation technique, of ion-acoustic waves in the vicinity of a Korteweg-de Vries (K-dV) equation derived in a plasma with some negative ions has been made. The investigation shows that the negative ions in plasma with isothermal electrons introduced a critical concentration at which the ion-acoustic wave plays an important role of wave-breaking and forming a precursor while the plasma with non-isothermal electrons has no such singular behaviour of the wave. These two distinct features of ion waves lead to an overall different approach of present study of ion-waves. A distinct feature of non-uniform transition from the nonisothermal case to isothermal case has been shown. Few particular plasma models have been chosen to show the characteristics behaviour of the ion-waves existing in different cases

Non-enzymatic reactions involving vitamin B6: Spectroscopic investigations on the effect of pH and metal ions on the decyclization reactions of the pyridoxal-histamine cyclized Schiff base

The effect of pH and metal ions (Cu2+, Zn2+, Cd2+, Mn2+, Cr3+, Co3+, and Mg2+) on the decyclization reactions of pyridoxal-histamine cyclized Schiff base has been studied using electronic spectroscopy. The study reveals that the cyclization reaction is irreversible with respect to pH and metal ions. Interest in this work derives from the possible involvement of cyclization reactions in the inhibitory activity of a number of pyridoxal-dependent enzymes.

Intensity Oscillation in the Corona as Observed during the Total Solar Eclipse of 29 March 2006

We obtained the images of the eastern part of the solar corona in the Fe xiv 530.3 nm (green) and Fe x 637.4 nm (red) coronal emission lines during the total solar eclipse of 29 March 2006 at Manavgat, Antalya, Turkey. The images were obtained using a 35 cm Meade telescope equipped with a Peltier-cooled 2k x 2k CCD and 0.3 nm pass-band interference filters at the rates of 2.95 s (exposure times of 100 ms) and 2.0 s (exposure times of 300 ms) in the Fe xiv and Fe x emission lines,respectively. The analysis of the data indicates intensity variations at some locations with period of strongest power around 27 s for the green line and 20 s for the red line. These results confirm earlier findings of variations in the continuum intensity with periods in the range of 5 to 56 s by Singh et al. (Solar Phys. 170, 235, 1997). The wavelet analysis has been used to identify significant intensity oscillations at all pixels within our field of view. Significant oscillations with high probability estimates were detected for some locations only. These locations seem to follow the boundary of an active region and in the neighborhood, rather than within the loops themselves. These intensity oscillations may be caused by fast magneto-sonic waves in the solar corona and partly account for heating of the plasma in the corona.

Random existence of charge ordered stripes and its influence on the magnetotransport properties of La0.6Sr0.4MnO3 perovskite substituted with diamagnetic ions at Mn sublattice

Phase-singular solid solutions of La0.6Sr0.4Mn1-yMeyO3 (0 <= y <= 0.3) [Me=Li1+, Mg2+, Al3+, Ti4+, Nb5+, Mo6+ or W6+] [LSMey] perovskite of rhombohedral symmetry (space group: R (3) over barc) have been prepared wherein the valence of the diamagnetic substituent at Mn site ranged from 1 to 6. With increasing y-content in LSMey, the metal-insulator (TM-I) transition in resistivity-temperature rho(T) curves shifted to low temperatures. The magnetization studies M(H) as well as the M(T) indicated two groups for LSMey. (1) Group A with Me=Mg, Al, Ti, or Nb which are paramagnetic insulators (PIs) at room temperature with low values of M (< 0.5 mu(B)/Mn); the magnetic transition [ferromagnetic insulator (FMI)-PI] temperature (T-C) shifts to low temperatures and nearly coincides with that of TM-I and the maximum magnetoresistance (MR) of similar to 50% prevails near T-C (approximate to TM-I). (2) Group-B samples with Me=Li, Mo, or W which are FMIs with M-s=3.3-3.58 mu(B)/Mn and marginal reduction in T-C similar to 350 K as compared to the undoped LSMO (T-C similar to 378 K). The latter samples show large temperature differences Delta T=T-c-TM-I, reaching up to similar to 288 K. The maximum MR (similar to 60%) prevails at low temperatures corresponding to the M-I transition TM-I rather than around T-C. High resolution lattice images as well as microscopy analysis revealed the prevalence of inhomogeneous phase mixtures of randomly distributed charge ordered-insulating (COI) bistripes (similar to 3-5 nm width) within FMI charge-disordered regions, yet maintaining crystallographically single phase with no secondary precipitate formation. The averaged ionic radius < r(B)>, valency, or charge/radius ratio < CRR > cannot be correlated with that of large Delta T; hence cannot be used to parametrize the discrepancy between T-C and TM-I. The M-I transition is controlled by the charge conduction within the electronically heterogeneous mixtures (COI bistripes+FMI charge disordered); large MR at TM-I suggests that the spin-ordered FM-insulating regions assist the charge transport, whereas the T-C is associated with the bulk spin ordered regions corresponding to the FMI phase of higher volume fraction of which anchors the T-C to higher temperatures. The present analysis showed that the double-exchange model alone cannot account for the wide bifurcation of the magnetic and electric transitions, contributions from the charge as well as lattice degrees of freedom to be separated from spin/orbital ordering. The heterogeneous phase mixtures (COI+FMI) cannot be treated as of granular composite behavior. (c) 2008 American Institute of Physics.

Experimental studies on new particle formation and ions

Atmospheric aerosol particles have significant climatic effects. Secondary new particle formation is a globally important source of these particles. Currently, the mechanisms of particle formation and the vapours participating in this process are, however, not truly understood. The recently developed Neutral cluster and Air Ion Spectrometer (NAIS) was widely used in field studies of atmospheric particle formation. The NAIS was calibrated and found to be in adequate agreement with the reference instruments. It was concluded that NAIS can be reliably used to measure ions and particles near the sizes where the atmospheric particle formation begins. The main focus of this thesis was to study new particle formation and participation of ions in this process. To attain this objective, particle and ion formation and growth rates were studied in various environments - at several field sites in Europe, in previously rarely studied sites in Antarctica and Siberia and also in an indoor environment. New particle formation was observed at all sites were studied and the observations were used as indicatives of the particle formation mechanisms. Particle size-dependent growth rates and nucleation mode hygroscopic growth factors were examined to obtain information on the particle growth. It was found that the atmospheric ions participate in the initial steps of new particle formation, although their contribution was minor in the boundary layer. The highest atmospheric particle formation rates were observed at the most polluted sites where the role of ions was the least pronounced. Furthermore, the increase of particle growth rate with size suggested that enhancement of the growth by ions was negligible. Participation of organic vapours in the particle growth was supported by laboratory and field observations. It was addressed that secondary new particle formation can also be a significant source of indoor air particles. These results, extending over a wide variety of environments, give support to previous observations and increase understanding on new particle formation on a global scale.