A ground state morphed intermolecular potential for the hydrogen bonded and van der Waals isomers in OC:HI and a prediction of an anomalous deuterium isotope effect

An extended analysis of the noncovalent interaction OC:HI is reported using microwave and infrared supersonic jet spectroscopic techniques. All available spectroscopic data then provide the basis for generating an accurately determined vibrationally complete semiempirical intermolecular potential function using a four-dimensional potential coordinate morphing methodology. These results are consistent with the existence of four bound isomers: OC-HI, OC-IH, CO-HI, and CO-IH. Analysis also leads to unequivocal characterization of the common isotopic ground state as having the OC-HI structure and with the first excited state having the OC-IH structure with an energy of 3.4683(80) cm(-1) above the ground state. The potential is consistent with the following barriers between the pairs of isomers: 382(4) cm(-1) (OC-IH/OC-HI), 294(5) cm(-1) (CO-IH/CO-HI), 324(3) cm(-1) (OC-IH/CO-IH), and 301(2) cm(-1) (OC-HI/CO-HI) defined with respect to each lower minimum. The potential is also determined to have a linear OC-IH van der Waals global equilibrium minimum structure having R(e)=4.180(11) A?, θ(1)=0.00(1)°, and θ(2)=0.00(1)°. This is differentiated from its OC-HI ground state hydrogen bound structure having R(0)=4.895(1) A?, θ(1)=20.48(1)°, and θ(2)=155.213(1)° where the distances are defined between the centers of mass of the monomers and θ(1) and θ(2) as cos(-1)[(1/2)] for i=1 and 2. A fundamentally new molecular phenomenon - ground state isotopic isomerization is proposed based on the generated semiempirical potential. The protonated ground state hydrogen-bonded OC-HI structure is predicted to be converted on deuteration to the corresponding ground state van der Waals OC-ID isomeric structure. This results in a large anomalous isotope effect in which the R(0) center of mass distance between monomeric components changes from 4.895(1) to 4.286(1) A?. Such a proposed isotopic effect is demonstrated to be a consequence of differential zero point energy factors resulting from the shallower nature of hydrogen bonding at a local potential minimum (greater quartic character of the potential) relative to the corresponding van der Waals global minimum. Further consequences of this anomalous deuterium isotope effect are also discussed.     

Evaluation of methods to cap molecular fragments in calculating energies of interaction in avian pancreatic polypeptide

The accuracy of the determination of the energy of interaction between Phe20 and the Pro5-Thr6-Tyr7-Pro8 complex inside the hydrophobic core of avian pancreatic polypeptide was investigated using three capping strategies for molecular fractionation with conjugated caps and DFT quantum chemical calculations at the BHandHLYP/cc-pVTZ level of theory. The most accurate determination resulted from acetylation of the alpha-amino group combined with methyl amidation of the alpha-carbonyl group with relative deviations less than 10%. Combinations of hydrogenation of the alpha-amino group with the replacement of the alpha-carbonyl group with a hydrogen and the hydrogenation of the alpha-amino group with methylation of the alpha-carbonyl group were less accurate, leading to relative deviations up to 35%. Choice of capping methods depends on the structural features of the polypeptide system, the desired accuracy and the available computational resources.     

Thermoanalytical method for studying the guest content in cyclodextrin inclusion complexes

The interaction of cypermethrin with β-cyclodextrin was investigated using different (coprecipitation, suspension, kneading and ‘melting in solution’) complexation methods and qualifying the resulted complexes by UV-spectrophotometry, thermal methods (TG, DTG and DSC) and X-ray powder diffraction. The total guest content of complexes can be measured by UV-spectrophotometry in aqueous ethanol solution, while the uncomplexed guest fraction of samples can be determined by DSC based on a previous calibration curve, which was found between the melting enthalpy change of cypermethrin and the guest content of physical mixture samples. The combination of both analytical methods enables the determination of really complexed guest content.     

Titanium Dioxide/Electrolyte Solution Interface: Electron Transfer Phenomena

Electron transfer between a titanium dioxide/electrolyte solution interface has been studied. As found by other researchers of similar interfaces (TiO(2)- and ZnO-electrolyte solution), a slow consumption of OH(-) ions takes place in this type of interface. A theoretical model has been developed for calculating the change in the Fermi energy of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by the decrease of the difference between their Fermi energies. A kinetic constant (upsilon) is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion. Copyright 2000 Academic Press.     

The microwave and millimeter-wave spectra of hypochlorous acid

To permit atmospheric monitoring of the molecule, the microwave spectra of two isotopic species of hypochlorous acid, HOCl, have been measured in the frequency range 8–650 GHz. Three b-type branches and an a-type Q branch have all been measured for the first time; improved measurements have been made for the a-type R branches. The analysis has included combination differences of earlier high-resolution infrared spectra to give accurate values for all rotational constants, five quartic and five higher degree centrifugal distortion constants, as well as the chlorine nuclear quadrupole and spin-rotation coupling constants. From the Stark effect, accurate values have also been obtained for both components of the molecular dipole moment. A table of transition frequencies of potential use in atmospheric monitoring is presented.     

Multicomponent Magnetically Soft Alloy with High Glass-forming Ability and Improved Castability

A new alloy exhibiting high glass-forming ability was developed with the composition Fe_70.7C_6.7P_10.4B₅Si_1.1Mn_0.1Cr₂Mo₂Ga₂. This alloy exhibited excellent castability enabling net-shape-casting. The samples were prepared by copper-mould casting in conical rod form which has a small diameter of 3 mm, a large diameter of 4 mm, and a length of 54 mm, as well as in ring form with an outer diameter of 26 mm, an inner diameter of 18 mm and a thickness of 1 mm. The B _S and H _C values in DC conditions determined for the ring sample in the as-cast state are 0.45 T and 1.7 A/m, respectively, and for the ribbon in the as-cast state 0.5 T and 3.8 A/m, respectively. On the basis of the measured properties, large industrial use of this new alloy can be predicted.     

Dichlorocarbene Addition to

In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway.     

A three-body approach to the effective nucleon-nucleon interaction

The problem of the effective nucleon-nucleon interaction is formulated in a three-body model. The interaction of two nucleons and a heavy core having internal excitations is described by means of Faddeev-type coupled equations. The elimination of the excited states of the core leads to a set of coupled equations with an effective kernel which incorporates the effect of the eliminated degrees of freedom. An exactly soluble model is constructed and solved. The exact and an approximate solution are compared. The comparison demonstrates the applicability of the model for the investigation of problems connected with the effective nucleon-nucleon interaction.