C-H...N and C-H...S hydrogen bonds--influence of hybridization on their strength

Simple complexes connected through C-H...S and C-H...N interactions are investigated: CH4...NH3, C2H4...NH3, C2H2...NH3, CH4...SH2, C2H4...SH2, and C2H2...SH2. Ab initio and DFT calculations are performed (SCF, MP2, B3LYP) using different basis sets up to the MP2/aug-cc-pVQZ//MP2/aug-cc-pVDZ level of approximation. The Bader theory is applied since MP2/6-311++G(d,p) wave functions are used to find and to characterize bond critical points in terms of electron densities and their Laplacians. The influence of hybridization on the properties of C-H...S and C-H...N systems is also studied showing that the strength of such interactions increases in the following order: C(sp3)-H...Y, C(sp2)-H...Y, C(sp)-H...Y, where Y = S, N--it is in line with the previous findings on C-H...O hydrogen bonds. The results also show that CH4...SH2 and C2H4...SH2 complexes should be rather classified as van der Waals interactions and not as hydrogen bonds. The frequency associated with the C-H stretch of C(sp3)-H...S is blue-shifted.     

Square, hexagonal, and row phases of PTCDA and PTCDI on Ag-Si(111)square root(3) x square root(3)R30 degrees

We have investigated the ordered phases of the perylene derivatives perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) and the imide analogue PTCDI on the Ag-Si(111)square root(3) x square root(3)R30 degrees surface using scanning tunneling microscopy. We find that PTCDA forms square, hexagonal, and herringbone phases, which coexist on the surface. The existence of a square phase on a hexagonal surface is of particular interest and is a result of a near commensurability between the molecular dimensions and the surface lattice. Contrast variations across the square islands arise from PTCDA molecules binding to different sites on the surface. PTCDI on Ag-Si(111)square root(3) x square root(3)R30 degrees forms extended rows, as well as two-dimensional islands, both of which are stabilized by hydrogen bonding mediated by the presence of imide groups. We present models for the molecular arrangements in all these phases and highlight the role of hydrogen bonding in controlling this order.     

强外电场作用下二甲基硅酮的分子结构和激发态

The ground states of dimethyl siloxane under different intense electric fields ranging from - 0. 04 to 0. 04 a. u. are optimized using density functional theory DFT / B3P86 at 6-311 ++ G（d,p）level. The excitation energies and oscillator strengths under the same intense applied electric fields are calculated employing the revised hybrid CIS-DFT method. The result shows that the electronic state,molecular geometry,total energy,dipole moment and excitation energy are strongly dependent on the field strength and behave asymmetry to the direction of the applied electric field. As the electric field changes from - 0. 04 to 0. 04 a. u. ,the bond length of Si-O increases whereas the bond length of Si-C decreases because of the charge transfer induced by the applied electric field. The dipole moment of the ground state decreases linearly with the applied field strength. However,the dipole moment of molecule changes from positive to negative as the inverse electric field increase to - 0. 03 a. u. Further increase of the inverse electric field results in an increase of the total energy of the molecule. The dependence of the calculated excitation energies on the applied electric field strength is fitting well to the relationship proposed by Grozema. The excitation energies of the first five excited states of dimethyl siloxane decrease as the applied electric filed increases because the energy gap between the HOMO and LUMO become close with the field,which shows that the molecule is easy to be excited under electric field and hence can be easily dissociated.     

外电场作用下三元环状水分子团簇的特性研究

The influence of an external field on the ground states energy and dipole moment of the cyclic water trimer is investigated. Employing the Hartree-Fork method with basis sets 3-21G. The field-induced H-F force including the internal and external forces and clusters equilibrium structures under balance of this force are analyzed. The external field is varied in the 0.001~0.01 a.u. range. It is shown that the magnitude of the external electric field has important effects on these characteristics of the cyclic water trimer. The energy was found to decrease and the dipole moment to increase with the increasing external field. The change of the electronic population of every atom leads the electrostatic field to vary accordingly.     

Solution self-assembly, spontaneous deprotonation, and crystal structures of bipyrazolate-bridged metallomacrocycles with dimetal centers

A series of nanosized cavity-containing bipyrazolate-bridged metallomacrocycles with dimetal centers, namely, {[(bpy)M]8L4}(NO3)8 [L=3,3',5,5'-tetramethyl-4,4'-bipyrazolyl, Pd, Pt; 1,4-bis-4'-(3',5'-dimethyl)-pyrazolylbenzene), Pd; and 1,4-bis-4'-(3',5'-dimethyl)-pyrazolylbiphenyl, Pd], {[(phen)M]8L4}(NO3)8 [L=3,3',5,5'-tetramethyl-4,4'-bipyrazolyl, Pd, Pt; 1,4-bis-4'-(3',5'-dimethyl)-pyrazolylbenzene, Pd; and 1,4-bis-4'-(3',5'-dimethyl)-pyrazolylbiphenyl, Pd], {[(bpy)Pd]6L3}(NO3)6 [L=1,4-bis-4'-(3',5'-dimethyl)-pyrazolylbenzene,], {[(phen)Pd]6L3}(NO3)6 [L=1,4-bis-4'-(3',5'-dimethyl)-pyrazolylbenzene,], {[(bpy)Pd]4L2}(NO3)4 [L=1,3-bis-4'-(3',5'-dimethyl)-pyrazolylbenzene, and 1,2-bis-4'-(3',5'-dimethyl)-pyrazolylbenzene,], and {[(phen)Pd]4L2}(NO3)4 [L=1,3-bis-4'-(3',5'-dimethyl)-pyrazolylbenzene, and 1,2-bis-4'-(3',5'-dimethyl)-pyrazolylbenzene,] (where bpy=2,2'-bipyridine and phen=1,10-phenanthroline) have been synthesized through a directed self-assembly approach that involves spontaneous deprotonation of the 1H-bipyrazolyl ligands in aqueous solution. These complexes, with weak Pd(II)...Pd(II) or Pt(II)...Pt(II) interactions, have been characterized by elemental analysis, 1H and 13C NMR, cold-spray ionization or electrospray ionization mass spectrometry, UV-visible spectroscopy, and luminescence spectroscopy. Complexes and have also been characterized by single-crystal X-ray diffraction analysis.     

Unfolding of heptameric co-chaperonin protein follows "fly casting" mechanism: observation of transient nonnative heptamer

Protein recognition and binding play a fundamental role in living systems but sometimes also result in pathological aggregates. To probe the coupling between folding and binding in a homoheptameric system, we have characterized the time-resolved unfolding/disassembly mechanism of human co-chaperonin protein 10 (cpn10) by a combination of experimental and computational methods. The results from both approaches are in excellent agreement and make obvious that the kinetic process is three-state: an initial polypeptide-unfolding step, resulting in a non-native heptamer, is followed by a slower heptamer-dissociation step. This demonstrates that the barriers on the kinetic free-energy landscape are defined by thermodynamic stability. cpn10 is one of few, and the only heptameric, experimentally characterized system that follows the "fly casting scenario" of molecular recognition.     

Novel Fluorescent Chemosensor for Detection of F− Anions Based on a Single Functionalized Pillar[5]arene Iron(III) Complex

Novel fluorescent chemosensor with good selectivity for F^? anion was designed and synthesized. The sensor has a bearing on a single functionalized pillar[5]arene and Fe³⁺ metal complex (PN‐Fe), which showed prominent fluorescent response for F^? anion over other common anions (Cl^?, Br^?, I^?, AcO^?, HSO4^?, H₂PO₄^?, ClO₄^?, CN^? and SCN^?). These results were evaluated by fluorescent method. The detection limit of PN‐Fe to F^? was calculated to be 2.50×10^?7 mol/L. Moreover, the sensor PN‐Fe³⁺ might serve as a recyclable component in sensing materials.     

Electrochemical Behavior and Voltammetric Determination of Curcumin at Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of curcumin by using a electrochemically reduced graphene oxide (ERGO) modified glass carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The electrochemical behaviors of curcumin at ERGO/GCE were investigated by cyclic voltammetry, suggesting that the ERGO/GCE exhibits excellent electrocatalytic activity towards curcumin, compared with bare GCE and GO/GCE electrodes. The electrochemical reaction mechanisms of curcumin, demethoxycurcumin and bisdemethoxycurcumin at the ERGO/GCE were also investigated and discussed systematically. Under physiological condition, the modified electrode showed linear voltammetric response from 0.2 μM to 60.0 μM for curcumin, with the detection limit of 0.1 μm. This work demonstrates that the graphene‐modified electrode is a promising strategy for electrochemical determination of biological important phenolic compounds.     

Tailoring Thermodynamics and Kinetics for Hydrogen Storage in Complex Hydrides towards Applications

Solid‐state hydrogen storage using various materials is expected to provide the ultimate solution for safe and efficient on‐board storage. Complex hydrides have attracted increasing attention over the past two decades due to their high gravimetric and volumetric hydrogen densities. In this account, we review studies from our lab on tailoring the thermodynamics and kinetics for hydrogen storage in complex hydrides, including metal alanates, borohydrides and amides. By changing the material composition and structure, developing feasible preparation methods, doping high‐performance catalysts, optimizing multifunctional additives, creating nanostructures and understanding the interaction mechanisms with hydrogen, the operating temperatures for hydrogen storage in metal amides, alanates and borohydrides are remarkably reduced. This temperature reduction is associated with enhanced reaction kinetics and improved reversibility. The examples discussed in this review are expected to provide new inspiration for the development of complex hydrides with high hydrogen capacity and appropriate thermodynamics and kinetics for hydrogen storage.