ChemInform Abstract: How Strong Is the GalliumGallium Triple Bond? Theoretical Compliance Matrices as a Probe for Intrinsic Bond Strengths.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

The Coordination of NiII and CuII Ions to the Polyhistidyl Motif of Hpn Protein: Is It as Strong as We Think?

Hpn, one of Helicobacter pylori′s nickel‐accessory proteins, is an amazingly peculiar protein: Almost half of its sequence consists of polyhistidyl (poly‐His) residues. Herein, we try to understand the origin of this naturally occurring sequence, thereby shedding some light on the bioinorganic chemistry of Hpn′s numerous poly‐His repeats. By using potentiometric, mass spectrometric, and various spectroscopic techniques, we studied the Ni^II‐ and Cu^II complexes of the wild‐type Ac‐THHHHYHGG‐NH₂ fragment of Hpn and of its six analogues, in which consecutive residues (His or Tyr) were replaced by Ala (Ala‐substitution or Ala‐scan approaches), thereby resulting in Ac‐TAHHHYHGG‐NH₂, Ac‐THAHHYHGG‐NH₂, Ac‐THHAHYHGG‐NH₂, Ac‐THHHAYHGG‐NH₂, Ac‐THHHHAHGG‐NH₂, and Ac‐THHHHYAGG‐NH₂ peptides. We found that the His4 residue is critical for both Ni^II‐ and Cu^II‐ion binding and the effectiveness of binding varies even if the substituted amino acid does not take part in the direct binding interactions.     

The Coordination of Ni(II) and Cu(II) Ions to the Polyhistidyl Motif of Hpn Protein: Is It as Strong as We Think?

Hpn, one of Helicobacter pylori's nickel-accessory proteins, is an amazingly peculiar protein: Almost half of its sequence consists of polyhistidyl (poly-His) residues. Herein, we try to understand the origin of this naturally occurring sequence, thereby shedding some light on the bioinorganic chemistry of Hpn's numerous poly-His repeats. By using potentiometric, mass spectrometric, and various spectroscopic techniques, we studied the Ni(II) - and Cu(II) complexes of the wild-type Ac-THHHHYHGG-NH(2) fragment of Hpn and of its six analogues, in which consecutive residues (His or Tyr) were replaced by Ala (Ala-substitution or Ala-scan approaches), thereby resulting in Ac-TAHHHYHGG-NH(2) , Ac-THAHHYHGG-NH(2) , Ac-THHAHYHGG-NH(2) , Ac-THHHAYHGG-NH(2) , Ac-THHHHAHGG-NH(2) , and Ac-THHHHYAGG-NH(2) peptides. We found that the His4 residue is critical for both Ni(II) - and Cu(II) -ion binding and the effectiveness of binding varies even if the substituted amino acid does not take part in the direct binding interactions.     

How Many Molecules are Required to Obtain a Steady Faradaic Current from Mediated Electron Transfer at a Single Nanoparticle on a Supporting Surface?

We investigate the chronoamperometric noise characteristics of electron‐transfer reactions occurring on single nanoparticles (NPs) and assemblies of well‐separated NPs on a supporting surface. To this end, we combine a formerly described expression for the steady‐state current of a single particle with the shot‐noise model and derive an expression for the signal‐to‐noise ratio as a function of bulk concentration and particle radius. Our findings are supported by random‐walk simulations, which closely match the analytical results.     

Can We Merge the Weak and Strong Tetrel Bonds? Electronic Features of Tetrahedral Molecules Interacted with Halide Anions

Using the orbital-free quantum crystallography approach, we have disclosed the quantitative trends in electronic features for bonds of different strengths formed by tetrel (Tt) atoms in stable molecular complexes consisting of electrically neutral tetrahedral molecules and halide anions. We have revealed the role of the electrostatic and exchange-correlation components of the total one-electron static potential that are determined by the equilibrium atomic structure and by kinetic Pauli potential, which reflects the spin-dependent electron motion features of the weak and strong bonds. The gap between the extreme positions in the electrostatic and total static potentials along the line linking the Tt atom and halide anion is wide for weak bonds and narrow for strong ones. It is in very good agreement with the number of minima in the Pauli potential between the bounded atoms. This gap exponentially correlates with the exchange-correlation potential in various series with a fixed nucleophilic fragment. A criterion for categorizing the noncovalent tetrel bonds (TtB) based on the potential features is suggested.     

Influence of chlorine and potassium additives on the catalytic properties of reduced Mo?Ni and Cr?Ni complex compounds

Chlorine and potassium are introduced during the preparation of Mo–Ni and Cr–Ni complex compounds by using nickel chloride and potassium molybdate or dichromate as starting materials. The resulting compounds are isomorphous with a series of complexes prepared with nickel nitrate and ammonium heptamolybdate or dichromate, previously described. The influence of the presence of chlorine and of potassium on the properties of the catalysts obtained by reduction of these compounds by hydrogen is investigated. Potassium-containing catalysts show a behavior similar to copper based catalysts.

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How does mechanism of biosorption determine the differences between the initial and equilibrium adsorption states?

The analysis of various models assumed to represent the influence of pH on heavy metals biosorption equilibrium is presented. It shows that all of them lead to the same mathematical expressions (e.g. the Langmuir or the Flory adsorption isotherm equations) when the pH effects are neglected. Even if considering the pH effects, some of them (competitive adsorption and ion-exchange models, for instance) still lead to analogical expressions for sorption isotherm equations. The accepted mechanism of biosorption may, however, influence strongly the differences between the initial and equilibrium states of biosorption system.     

Strong interactions between copper halides and unsaturated systems: new metallocycles? Or the importance of deformation

The complexes formed by CuF with CC double and triple bonds have been studied at the MP2 and CCSD(T) computational levels. The interaction of CuF with acetylene, ethylene and their fluoro derivatives is very strong, with interaction energies close to those of conventional covalent bonds. Hence, these complexes could be actually viewed as a new kind of metallocycles, with significantly strong Cu-C linkages. All electronic indexes analyzed by means of the AIM, ELF and NBO formalisms, indicate that the strength of the interaction should increase with the number of fluorine substituents in both series of compounds. Surprisingly, however, although both series of compounds exhibit the same bonding arrangements, they follow opposite stability trends and the expected increase of the interaction energies with the number of fluorine substituents is only observed in the acetylene series. The reason for this unexpected behavior is once more associated with the effects triggered by the distortion of the interacting subunits. Deformation not only has a direct energetic cost but dramatically affects the intrinsic properties of the interacting systems.     

Syntheses and Structures of a New Tetrazylphosphonate Ligand and the Coordination Polymer Based on Zn~(Ⅱ)

A novel tetrazylphosphonate ligand, namely ethyl 4-(2-ethyl-2H-1,2,3,4-tetrazol-5-yl) benzylphosphonate(Et-L), was designed and successfully achieved from p-cyano benzyl chloride, based on which a zinc coordination polymer(1) with a 2D layer structure has been hydrothermally synthesized and structurally characterized by elemental analysis, IR, TGA and X-ray single-crystal diffraction. The colorless block crystals of H_2L·H_2O were also obtained under the same hydrothermal conditions, which belongs to monoclinic system, space group P2_1/c with a = 13.3141(7), b = 5.1650(3), c = 21.9839(18) ?, β = 115.307(5)°, V = 1366.69(15) ?~3, Z = 4, D_c = 1.391 mg/cm~(-3), Mr = 349.58, F(000) = 600, R = 0.0748 and wR = 0.1917 for 2392 observed reflections(I 2σ(I)). The colorless block crystals of complex 1([Zn(L)(H_2O)]_n) also belong to monoclinic system, space group P2_1/c with a = 22.7464(10), b = 6.0430(3), c = 9.7704(4) ?, β = 92.525(4)°, V = 1341.70(10) ?~3, Z = 4, D_c = 1.731 mg/cm_(-3), M_r = 349.58, F(000) = 712, R = 0.0596 and wR = 0.1688 for 2357 observed reflections(I 2σ(I)). Only the oxygen atoms of phosphonic group are coordinated with the metal zinc probably because the hydrogen atom of tetrazole has been substituted by ethyl group. Photoluminescence properties of the complex are also investigated.     

Is there a relationship between protein thermal stability and the denaturation heat capacity change?

It is shown the non-occurrence of a correlation between the values of the denaturation temperature and those of the denaturation heat capacity change for a set of 13 proteins possessing the ‘SH3-type’ fold from both mesophilic and thermophilic microorganisms. This seems to be a rather general result, because, fixed the size and the folding pattern, the denaturation heat capacity change is a nearly constant quantity, within the uncertainty limits of experimental determinations, regardless of the thermal stability of the protein. A precise definition of the thermodynamics of the hydrophobic effect is presented to clarify that the above finding does not imply that the hydrophobic effect does not play a role in the extra-thermal stability of thermophilic and hyperthermophilic proteins.     

Helical Self-Assembly of Optically Active Phthalocyanine Derivatives: Effect of Zn?O Coordination Bond on Morphology and Handedness of Nanostructures

Two optically active phthalocyanine derivatives with eight peripheral chiral (S)-4′-(2-methylbutoxy)biphenyl moieties on the β-position of the phthalocyanine ring are synthesized. The circular dichroism (CD) spectra show signals in the Q absorption region for both compounds 1 and 2 in chloroform solution, indicating the effective chiral-information transfer from the peripheral chiral (S)-4′-(2-methylbutoxy)biphenyl side chains to the phthalocyanine chromophore at the molecular level. Their self-assembling properties are further investigated by using electronic absorption and Fourier transform infrared spectroscopy, transmission electronic microscopy, scanning electronic microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Experimental results reveal the effect of the metal-coordination bond on molecular packing models in these nanostructures, which in turn results in the self-assembled nanostructures with different morphologies, from nanosheets for 1 to helical nanofibers for 2 . In addition, good semiconducting properties of the nanostructures fabricated from phthalocyanine derivatives 1 and 2 are revealed by current–voltage measurements.     

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

One of the landmark achievements of quantum chemistry, specifically of MO-based methods that include electron correlation, was the precise calculation of the barrier for the hydrogen-exchange reaction (B. Liu, J. Chem. Phys. 1973, 58, 1925; P. Siegbahn, B. Liu, J. Chem. Phys. 1978, 68, 2457). This paper reports an accurate calculation of this barrier by two recently developed VB methods that use only the eight classical VB structures. To our knowledge, the present work is the first accurate ab initio VB barrier that matches an experimental value. Along with the accurate barrier, the VB method provides accurate bond energies and diabatic quantities that enable the barrier height to be analyzed by the VB state correlation diagram approach, VBSCD (S. Shaik, A. Shurki, Angew. Chem. 1999, 111, 616; Angew. Chem. Int. Ed. Engl. 1999, 38, 586). This is a proof of principal that VB theory with appropriate account of dynamic electron correlation can achieve quantitative accuracy of reaction barriers, and still retain a compact and interpretable wave function. A sample of S(N)2 barriers and dihalogen bonding energies, which are close to CCSD(T) and G2(+) values, show that the H(3) problem is not an isolated case, and while it is premature to conclude that VB theory has come of age, the occurrence of this event is clearly within sight.     

How deep is the potential well confining a protein in a specific conformation? A single-molecule study on temperature dependence of conformational change between 5 and 18 K

The fluorescence excitation spectrum of a single chromophore molecule in a photosynthetic pigment-protein complex is known to change in time at liquid helium temperature. The spectral change reflects a conformational change of the protein to which the chromophore binds. This work follows the temporal behavior of the spectrum of a single chromophore in the temperature range between 5 adn 18 K. The temperature dependence reveals two types of conformational change of the protein, i.e., thermally activated motions over a potential barrier of ca. 0.1 kJ/mol and temperature-independent motions of tunneling of a proton.