Ab initio evaluation of bond orders and valence numbers in some substituted benzenes

Mayer's definition of bond order and valence number of an atom in a molecule in the ab initio SCF theory have been applied to calculate bond orders and valence numbers using different ab initio methods for some fluorobenzenes. The results have been discussed in the light of Mulliken population analysis. The traditional view that the valency of an atom is directly related to the atomic charge is found to be invalid in the present ab initio calculations.     

元素最高价态无机含氧酸氧化能力次周期性讨论

从原子轨道能量差异对杂化轨道成键后强度影响的角度对元素最高价态无机含氧酸氧化能力次周期性现象进行了讨论，提出了一些新的看法，半定量地解释了这一现象。     

Classical chemical concepts from ab initio SCF calculations

Alternative definitions of bond order, valency, gross orbital populations and total atomic charge for SCF wavefunctions are compared. It is found that there are sound theoretical and numerical reasons for preferring definitions based on the Löwdin density matrix.     

Fragile structured layers on surfaces in highly concentrated solutions of electrolytes of various valencies

In the present study a dynamic mode of atomic force microscopy for force measurements was employed to investigate the hydration repulsion force between charged surfaces in highly concentrated electrolyte solutions of NaCl, MgCl₂ and LaCl₃. A strong dependence of this repulsive force on the approaching rate of surfaces, the prehistory of their contact and the valency of cations was demonstrated. The phenomena were strongly pronounced in the cases of high scan rates, large surfaces and cations of high valency. The results obtained indicate that a fragile structure composed of water molecules, ions and hydrated ions exists outside of the primary layer of water molecules and ions adsorbed firmly on surfaces.     

Ab-initio SCF study of the nature of bonding in neutral and cationic silicon hydrides and analogous carbon compounds

The nature of bonding in a number of neutral and cationic silicon hydrides has been studied on the basis of atomic charge (q_A), valency (V_A), molecular valency (V_M) and localised molecular orbitals (LMO). Several structural isomers of each species have been considered. It is found that the most stable isomer is generally associated with maximum q_si and minimum V_si and V_M. Protonation of the neutral hydrides leads to an increase in the positive charge of Si, and in molecular valency. The bonding characteristics of the most stable isomers of the silicon hydrides have been compared with that of analogous hydrocarbons. It has been observed that the difference in bonding stems mainly from the highly electro-positive nature of the Si atom which prefers to form three-centre rather than multiple bonds. The molecular hardness parameters (η) have also been calculated. The most stable isomers of silicon hydrides are generally associated with maximum η. The HSAB principle has been tested by considering some hydrogenation and proton transfer reactions. It is qualitatively satisfied in both cases.     

Valency and molecular structure

Valency is defined for each molecular orbital. The molecular orbital valency values are shown to be a good measure of the bonding nature of the molecular orbital. Comparisons are made with photoelectron spectral studies and Mulliken overlap population analysis.The variation of molecular valency and molecular orbital valency with bond angle is studied. It is found that for all the molecules presently considered, energy is linearly related to valency and that the molecular valency reaches a maximum at the equilibrium bond angle. It is also shown that the molecular orbital valency can serve as a quantitatively reliable ordinate for Mulliken-Walsh diagrams.     

On the density matrix definition of valency

In a recent article Gopinathan and Jug have proposed a definition of atomic valency which had previously been given by Armstrong, Perkins and Stewart for closed shell molecules. The validity and interpretation of this definition for open shell systems is discussed. A new parameter for structural analysis, the free electron index, is presented.We want to acknowledge the computer time made available by Centro de Estudios Superiores para el Procesamiento de la Informatión (CESPI) de la Universidad National de La Plata and many useful suggestions made by the referees of this paper.     

Influence of mixed and multivalent counterions in overcharging of DNA-like spherocylindrical macroions

The influence of multivalent and mixed valency counterions on the ground-state energetics of overscreening of a core DNA-like model (sphero)cylindrical macroion is investigated using an earlier developed energy minimization numerical simulation algorithm. The effects of mono-, di-, tri-, and tetravalent counterions, and mixed valency (mono- plus di-) counterions are compared and contrasted. It is seen that the depth of the minimum in the excess ground-state energy (over the neutral reference state) versus the number of overcharging counterions increases as counterion valency changes from mono- to tetra- testifying to the efficiency of the overcharging process due to multivalent counterions. The influence of (i) the presence of mixed valency counterions and (ii) counterion size on the energetics is also investigated.     

玩具、铅笔中可溶性砷、锑、硒的形态分析

对玩具、铅笔中可溶性砷、锑、硒的形态分析方法进行了研究,对原子荧光光谱法测定不同价态砷、锑、硒的方法进行了优化,建立了砷、锑、硒的原子荧光光谱形态分析方法。该方法样品加标回收率为82.0%~110.0%,测定结果的相对标准偏差为1.35%~2.22%(n=10)。     

Theoretical study of degree of covalency in some CoF6(n-) complexes (n = 4, 3, and 2)

On the basis of a high-quality LCAO MO SCF calculation, covalency versus ionicity of a Co–F bond in the CoF₆(n-) complexes, where n = 4, 3, and 2, is discussed. The overlap and gross atomic populations, delocalization of certain MOS, and the charge densities in the bond region as well as around F's all indicate that the covalency increases as n decreases or the valency of Co increases in these complexes.     

Valency. II. Applications to molecules with first-row atoms

A quantum chemical definition of valency proposed in Part I is used to calculate the valency of carbon, nitrogen, oxygen, lithium, beryllium and boron in a number of compounds with the SINDO1 method. It is demonstrated that consistency of the basis set is necessary for comparable results. The general features of valency and bonding in these molecules are discussed. The π-electron concept of free valence is generalised to sigma systems and atoms in molecules are classified as subvalent, normal or hypervalent. The relation between valency and natural hybrid occupancy is illustrated. The symmetry properties of natural hybrid orbitals are discussed by means of group theory. A preliminary attempt is made to relate covalency and covalent reactivity. Bond indices and the σ, π character of bonds are obtained by a suitable partitioning and projection of valency into bonding and antibonding contributions. Alexander von Humboldt Fellow 1982–83.     

Photoemission studies of BaPb1?xBixO3 and Ba1?yKyBiO3 crystals

Summary Potassium and lead substituted single and polycrystalline material was examined by X-ray diffraction, X-ray topography, nonresonant microwave absorption, UPS and XPS. A covalent model instead of an ionic one is proposed. We find no evidence for a mixed valency of Bi. The valency of the Bi atoms at the unequivalent sites is close to +3. No density of states at the Fermi level has been detected.     

Double-layer phenomena in electrochemistry: controversial views on some fundamental notions related to electrified interfaces

The problem of the distinction between the so-called free charge and the thermodynamic (total) charge of electrodes was discussed in the light of the relevant IUPAC definitions calling attention to the strict relationships existing between charge and mass balances during the formation of a double layer at electrodes or/and particles. It is demonstrated that the origins of controversial views concerning partial charge transfer and electrosorption valency, notions widely used nowadays in the electrochemical literature, could be ascribed to confusion of the free and thermodynamic charges. Although there are, even if sporadic, evidences and theoretical considerations in the literature proving that electrosorption valency as usually defined is an extrathermodynamic and self-contradictory concept, it is widely used by many authors for the interpretation of electrosorption phenomena. One of the most important aims of the present work was to demonstrate that independent of the thermodynamic considerations, the concept of electrosorption valency cannot be reconciled with elementary laws of electrochemistry. On the basis of analysis of real processes occurring in the interfacial layer of electrodes it was urged to avoid the treatment of some double-layer phenomena in terms of electrosorption valency in order to eliminate far-reaching misinterpretations leading to serious contradictions.     

The role of Mn in the electronic structure of Ba3Ti2MnO9

The energy loss near edge structure (ELNES) of the O-K, Ti-L₂₃ and Mn-L₂₃ edges have been recorded in hexagonal Ba₃Ti₂MnO₉ with an energy resolution of 0.10-0.20 eV using a monochromator on a commercial transmission electron microscope (TEM) and compared with a tetragonal BaTiO₃ reference sample. The formal valency and symmetry of Mn have been determined using atomic multiplets calculations and its effect on the electronic structure of BaTiO₃ has been interpreted through a molecular-orbital model.     

Probing the Nature of the Cluster Effect Observed with Synthetic Multivalent Galactosides and Peanut Agglutinin Lectin

We designed a set of multi‐galactosides with valencies ranging from one to seven and different spacer‐arm lengths. The compounds display a high structural homology for a strict assessment of multivalent phenomena. The multimers were first evaluated by an enzyme‐linked lectin assay (ELLA) toward the peanut agglutinin (PNA). The binding affinity was shown to be dependent on the spacer‐arm length, and cluster effects were observed for the galactosides bearing the shortest and the longest linkers. The latter compounds were shown to be much more potent PNA cross‐linkers in a “sandwich assay”. Dynamic light scattering (DLS) experiments also revealed the formation of soluble aggregates between heptavalent derivatives with medium or long linkers and the labeled PNA. ELLA experiments performed with valency‐controlled clusters and labeled lectins are therefore not always devoid from aggregative processes. The precise nature of the multivalent interaction observed by ELLA for the compounds bearing the shortest linkers, which are unable to form PNA aggregates, was further investigated by atomic force microscopy (AFM). The galactosides were grafted onto the tip of a cantilever and the PNA lectin onto a gold surface. Similar unbinding forces were registered when the valency of the ligands was increased, thus showing that the multimers cannot interact more strongly with PNA. Multiple binding events to the PNA were also never observed, thus confirming that a chelate binding mode does not operate with the multivalent galactosides, probably because the linkers are too short. Altogether, these results suggest that the cluster effect that operates in ELLA with the multimers is not related to additional PNA stabilizations and can be ascribed to local concentration effects that favor a dynamic turnover of the tethered galactosides in the PNA binding sites.     

Impact of Multimeric Ferrocene-containing Cyclodecapeptide Scaffold on Host-Guest Interactions at a β-Cyclodextrin Covered Surface

Among non-covalent bonds, the host-guest interaction is an attractive way to attach biomolecules to solid surfaces since the binding strength can be tuned by the nature of host and guest partners or through the valency of the interaction. For that purpose, we synthesized cyclodecapeptide scaffolds exhibiting in a spatially controlled manner two independent domains enabling the multimeric presentation of guest molecules on one face and the other face enabling the potential grafting of a biomolecule of interest. In this work, we were interested in the β-cyclodextrin/ferrocene inclusion complex formed on β-CD monolayers functionalized surfaces. By using surface sensitive techniques such as quartz crystal microbalance and surface plasmon resonance, we quantified the influence of the guest valency on the stability of the inclusion complexes. The results show a drastic enhancement of the affinity with the gradual increase of guest valency. Considering that the sequential binding events are equal and independent, we applied the multivalent model developed by the Huskens group to extract intrinsic binding constants and an effective concentration of host.     

Tuning chemotactic responses with synthetic multivalent ligands

BACKGROUND: Multivalent ligands have been used previously to investigate the role of ligand valency and receptor clustering in eliciting biological responses. Studies of multivalent ligand function, however, typically have employed divalent ligands or ligands of undefined valency. How cells respond to multivalent ligands of distinct valencies, which can cluster a signaling receptor to different extents, has never been examined. The chemoreceptors, which mediate chemotactic responses in bacteria, are localized, and clustering has been proposed to play a role in their function. Using multivalent ligands directed at the chemoreceptors, we hypothesized that we could exploit ligand valency to control receptor occupation and clustering and, ultimately, the cellular response. RESULTS: To investigate the effects of ligand valency on the bacterial chemotactic response, we generated a series of linear multivalent arrays with distinct valencies by ring-opening metathesis polymerization. We report that these synthetic ligands elicit bacterial chemotaxis in both Escherichia coli and Bacillus subtilis. The chemotactic response depended on the valency of the ligand; the response of the bacteria can be altered by varying chemoattractant ligand valency. Significantly, these differences in chemotactic responses were related to the ability of the multivalent ligands to cluster chemoreceptors at the plasma membrane. CONCLUSIONS: Our results demonstrate that ligand valency can be used to tune the chemotactic responses of bacteria. This mode of regulation may arise from changes in receptor occupation or changes in receptor clustering or both. Our data implicate changes in receptor clustering as one important mechanism for altering cellular responses. Given the diverse events modulated by changes in the spatial proximity of cell surface receptors, our results suggest a general strategy for tuning biological responses.     

Periodicity in the formulae of carbonyls and the electronic basis of the Periodic Table

The basis of the Periodic Table is discussed. Electronic configuration recurs in only 21 out of the 32 groups. A better basis is derived by considering the highest classical valency (v) exhibited by an element and a new measure, the highest valency in carbonyl compounds (v*). This leads to a table based on the number of outer electrons possessed by an atom (N) and the number of electrons required for it to achieve an inert (noble) gas configuration (N*). Periodicity of these is nearly complete. The new basis helps to settle the question of the best form of table and related issues.     

Studies on State and Structure of Noble Metals in Electrocatalyst Made by Coprecipitation Method

The electrocatalysts of Pt/C,PtRu/C and Ru/C were prepared by the impregnation method.The facet characterization.The dispersion and the particle size for the catalysts were determined by means of X-ray diffraction and transmission electron microscopy,X-ray photoelectron spectroscopy was also used to analyze the state and the valency of the noble metals.The results show that the particle size was in nanometer range and the binary metals have come into being an alloy.The platinum in the catalysts existed in zero valency.The valency of the ruthenium on the surface is different from that in the body,while the ruthenium on the surface existed in oxide-form.PtRu/C and Pt/C are of good activity of the electrooxidation of hydrogen except Ru/C.PtRu/C is more tolerant of CO than Pt/C,and CO is only adsorbed on Pt.