Chromium-Salophen as a Soluble or Silica-Supported Co-Catalyst for the Fixation of CO2 Onto Styrene Oxide at Low Temperatures

Addition of a soluble or a supported CrIII-salophen complex as a co-catalyst greatly enhances the catalytic activity of Bu4NBr for the formation of styrene carbonate from styrene epoxide and CO2. Their combination with a very low co-catalyst:Bu4NBr:styrene oxide molar ratio = 1:2:112 (corresponding to 0.9 mol% of CrIII co-catalyst) led to an almost complete conversion of styrene oxide after 7 h at 80°C under an initial pressure of CO2 of 11 bar and to a selectivity in styrene carbonate of 100%. The covalent heterogenization of the complex was achieved through the formation of an amide bond with a functionalized {NH2}-SBA-15 silica support. In both conditions, the use of these CrIII catalysts allowed excellent conversion of styrene already at 50°C (69 and 47% after 24 h, respectively, in homogeneous and heterogeneous conditions). Comparison with our previous work using other metal cations from the transition metals particularly highlights the preponderant effect of the nature of the metal cation as a co-catalyst in this reaction, that may be linked to its calculated binding energy to the epoxides. Both co-catalysts were successfully reused four times without any appreciable loss of performance.

Studies of Conformational Changes of Tubulin Induced by Interaction with Kinesin Using Atomistic Molecular Dynamics Simulations

The transition between strong and weak interactions of the kinesin head with the microtubule, which is regulated by the change of the nucleotide state of the head, is indispensable for the processive motion of the kinesin molecular motor on the microtubule. Here, using all-atom molecular dynamics simulations, the interactions between the kinesin head and tubulin are studied on the basis of the available high-resolution structural data. We found that the strong interaction can induce rapid large conformational changes of the tubulin, whereas the weak interaction cannot. Furthermore, we found that the large conformational changes of the tubulin have a significant effect on the interaction of the tubulin with the head in the weak-microtubule-binding ADP state. The calculated binding energy of the ADP-bound head to the tubulin with the large conformational changes is only about half that of the tubulin without the conformational changes.

The Inter-Nucleon Up-to-Down Quark Bond and its Implications for Nuclear Binding

This paper describes an interesting and potentially significant phenomenon regarding the properties of up and down quarks within the nucleus, specifically how the possible internucleon bonding of these quarks may affect the bonding energy of the nuclear force. A very simple calculation is used, which involves a bond between two internucleon up and down quarks. This simple calculation does not specify the shape or structure for the nucleus, rather this calculation only examines the energy of all possible internucleon up-to-down bonds that may be formed within a quantum nucleus. A comparison of this calculated binding energy is made to the experimental binding energy with remarkably good results. The potential significance and implications of this noteworthy finding are discussed.

Structure Model Analysis Of Phosphorylation Dependent Binding And Sequestration Of SARS-COV-2 Encoded Nucleocapsid Protein By Protein 14-3-3

Phosphorylation of serines 197 and 206 of SARS-COV-2 Nucleocapsid protein (NCp) enhanced the stability and binding efficiency and sequestration of NCp to Protein 14-3-3 by increasing the Stability Energy (ΔGstability energy) and Binding Energy (ΔΔGbinding energy) from ~545 Kcal/mol to ~616 Kcal/mol, and from 108 Kcal/mol to ~228 Kcal/mol respectively. The calculated Binding Energy Difference (ΔΔGbinding energy difference) between dephospho-NCp-14-3-3 complex and phospho-NCp-13-3-3 complex was ~72 Kcal/mol. Phosphorylations of serines 186, 197, 202 and 206, and threonines 198 and 205 NCp also caused an increase in the Stability Energy (ΔGstability energy) and Binding Energy (ΔΔGbinding energy) from ~545 Kcal/mol to ~617, 616, 583, 580, 574, 564 and 566 Kcal/mol and from ~108 Kcal/mol to ~228, 216, 184, 188, 184, 174 and 112 Kcal/mol respectively. Phosphorylation of NCp on serines 197 and 206 caused a decrease in Stability Energy and Binding Energy from ~698 Kcal/mol to 688 Kcal/mol, and from ~91 Kcal/mol to ~82 Kcal/mol for the dimerization of NCp. These results support the existence of a phosphorylation dependent cellular mechanism to bind and sequester NCp.

Cordination Compound of Dimethyltin(IV) with N,N,N’N’-Tetraethylethylenediamine: Speciation and Theoretical approach

The formation equilibria of the dimethyltin(IV) complexes with of N,N,N’,N’-tetraethylethylenediamine (Et4en) in solution were investigated. The stoichiometry and stability constants of the complexes formed in solution phase were determined at different temperatures (15 oC – 35 oC) and in solutions of dioxane-water mixtures of different compositions (15% - 62.5%). The accepted model is composed of the 110, 111, 11-1 and 11-2 species. The thermodynamic parameters H and S associated with the protonation of N,N,N`,N`-tetraethylethylendiamine (Et4en) and its complex formation with the dimethyltin(IV) species were determined. The complex formation reaction is exothermic. The equilibrium constant for the displacement of N,N,N’,N’-tetraethylethylenediamine coordinated to dimethyltin(IV) by some selected DNA constituents was calculated. The Keq values clearly indicate the ability of DNA to displace the coordinated Et4en from its dimethyltin(IV) complex. The nucleotides IMP and GMP have the highest values. The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program. Also the vibrational frequencies of the ligands and complexes were computed for the optimized geometries. The results shows that there is no imaginary frequencies as found in the calculated vibrational frequencies. The binding energies of the dimethyltin(IV) complexes were calculated. All calculated binding energy values are negative.

Phthalocyanines core-modified by P and S and their complexes with fullerene C60: DFT study

Phthalocyanines (Pcs) and their derivatives have attracted a lot of attention because of their both biological importance and technological applications. The properties of Pcs can be tuned by replacing the central atom, by modifying the periphery of phthalocyanine ring, and by changing the meso-atoms. One more promising pathway for modifying Pcs and their derivatives can be the core-modification, or substitution of the core isoindole nitrogen(s) by other elements. Motivated by the results obtained for some core-modified porphyrins, we investigated computationally complete core-modification of regular Zn phthalocyanine (ZnPc) with P and S. We performed density functional theory studies of the structures, charges, and frontier molecular orbitals of P-core-modified and S-core-modified ZnPcs, ZnPc(P)4 and ZnPc(S)4, using both B3LYP and two dispersion-corrected functionals. Also, we studied computationally formation of complexes between the fullerene C60 and ZnPc(P)4 and ZnPc(S)4. Both ZnPc(P)4 and ZnPc(S)4 show strong bowl-like distortions similar to the results obtained earlier for ZnP(P)4 and ZnP(S)4. The size of the “bowl” cavity of the both core-modified Pcs is essentially the same, showing no dependence on the core-modifying element. For ZnPc(S)4, the HOMO is quite different from those of ZnPc and ZnPc(P)4. When the fullerene C60 forms complexes with the ZnPc(P)4 and ZnPc(S)4 species in the gas phase, it is located relatively far (4.30–5.72 Å) from the one of the P-centers and from the Zn-center of ZnPc(P)4, whereas with ZnPc(S)4 C60 forms relatively short bonds with the Zn-center, varying from ca. 2.0 to ca. 3.0 Å. The very strong deformations of both the ZnPc(P)4 and ZnPc(S)4 structures are observed. The calculated binding energy at the B3LYP/6-31G* level for the C60-ZnPc(P)4 complex is quite low, 1.2 kcal/mol, which agrees with the quite long distances fullerene - ZnPc(P)4, whereas it is noticeably larger, 13.6 kcal/mol, for the C60-ZnPc(S)4 complex which again agrees with the structural features of this complex. The binding energies of the complexes optimized using the dispersion-corrected functionals, CAM-B3LYP and wB97XD, are significantly larger, varying from ca. 14 till 52 kcal/mol which corresponds with the shorter distances between the fullerene and ZnPc(X)4 species.

Dioxygen binding to Fe-MOF-74: microscopic insights from periodic QM/MM calculations

Accurate MOF-FF parameter sets were determined for the ferrous and ferric forms of an iron-based metal–organic framework (MOF) called Fe-MOF-74. For this purpose, density functional theory (DFT) calculations were applied to truncated cluster models of Fe-MOF-74, and the DFT-calculated geometries and energy derivatives were used for the force-field parameterization. The resultant parameter sets performed remarkably well in reproducing the experimentally determined structure of the MOF. We also performed periodic quantum mechanics (QM) / molecular mechanics (MM) calculations employing a subtractive scheme called ONIOM, with the optimized MOF-FF parameters used for the MM calculations, in an attempt to evaluate the binding energies between O2 and several Fe-MOF-74 variants. The calculated binding energy for Fe-MOF-74 agreed very well with the experimental value, and QM/MM geometry optimization calculations confirmed that the O2-bound complex has a side-on geometry. Our calculations also predicted that, when the two neighboring iron ions around the O2-binding site are replaced with other metal ions (Mg2+, Ni2+, Zn2+, Co2+, or Mn2+), there are noticeable variations in the binding energy, indicating that these substituted metal ions affect the O2 binding indirectly.

Protein sequences bound to mineral surfaces persist into deep time

Proteins persist longer in the fossil record than DNA, but the longevity, survival mechanisms and substrates remain contested. Here, we demonstrate the role of mineral binding in preserving the protein sequence in ostrich (Struthionidae) eggshell, including from the palaeontological sites of Laetoli (3.8 Ma) and Olduvai Gorge (1.3 Ma) in Tanzania. By tracking protein diagenesis back in time we find consistent patterns of preservation, demonstrating authenticity of the surviving sequences. Molecular dynamics simulations of struthiocalcin-1 and -2, the dominant proteins within the eggshell, reveal that distinct domains bind to the mineral surface. It is the domain with the strongest calculated binding energy to the calcite surface that is selectively preserved. Thermal age calculations demonstrate that the Laetoli and Olduvai peptides are 50 times older than any previously authenticated sequence (equivalent to ~16 Ma at a constant 10°C).

Properties Predicting of Transition Metal-Doped Anatase TiO2

The binding energy of anatase TiO2, in which the Ti was substituted by other transition metals in the 4th, 5th and 6th periods of the periodic system of the elements, has been calculated by using first principles method. The doping limits of V, Cr, Zr, Nb, Mo and W are 61.5%, 39.7%, 88.2%, 100.0%, 65.0%, and 63.2%, respectively predicted by the calculated binding energy, while the doping limits of other transition metals are much lower. So, these transition metals can easily be doped into the anatase structure theoretically while it is difficult for the others. And the band structure and density of states (DOS) of V, Cr, Zr, Nb, Mo and W doped anatase TiO2 have also been calculated and analyzed.