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We report quantum mechanical calculations of excitation functions (relative reaction cross sections) for the F+HD reaction. We include three potential energy surfaces and an accurate treatment of all couplings (non-adiabatic, spin-orbit, and Coriolis). Comparison with experimental results [Dong, Lee, and Liu, J. Chem. Phys., 113, 3633 (2000)] show excellent agreement for the DF product channel and an improved but not perfect agreement for the HF product channel. In the former case, when weighted by the (16%) fractional population of the spin-orbit excited state (F*) in the beam, the overall reactivity of the F* is small (∼5%). For the HF product channel and with the same (16%) fractional weight, F* reactivity makes a contribution of ∼12% in the high-energy tail of the resonance peak. As a result, averaging over the population of F spin-orbit states in the beam changes the shape of the resonance. The greater the fraction of F* in the beam, the less pronounced will be the resonance modulation of the reaction excitation function. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In the present work we address a simple, rapid and quantitative analytical method for detection of different proteins present in biological samples. For this, we proposed the model of titration of double protein (TDP) and its relevant leverage theory relied on the retardation signal of chip moving reaction boundary electrophoresis (MRBE). The leverage principle showed that the product of the first protein content and its absolute retardation signal is equal to that of the second protein content and its absolute one. To manifest the model, we achieved theoretical self-evidence for the demonstration of the leverage principle at first. Then relevant experiments were conducted on the TDP-MRBE chip. The results revealed that (i) there was a leverage principle of retardation signal within the TDP of two pure proteins, and (ii) a lever also existed within these two complex protein samples, evidently demonstrating the validity of TDP model and leverage theory in MRBE chip. It was also showed that the proposed technique could provide a rapid and simple quantitative analysis of two protein samples in a mixture. Finally, we successfully applied the developed technique for the quantification of soymilk in adulterated infant formula. The TDP-MRBE opens up a new window for the detection of adulteration ratio of the poor food (milk) in blended high quality one. [ABSTRACT FROM AUTHOR]

A series of random poly(hexamethylene succinate- co -hexamethylene fumarate) (PHSF) samples was synthesized through a two-step reaction process, and their properties were systematically studied using wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The crystal modification of polyester changes from monoclinic to orthorhombic after substituting hexamethylene succinate (HS) units by hexamethylene fumarate (HF) units, and the chain conformation changes from all-trans to gauche. The copolyesters were found to be in a particular case as strict isomorphism in a limited composition range, adopting the same crystal modification when HF content ranged from 19 to 100 mol%. The melting point of the copolyester increases almost linearly with increasing molar content of HF, and the melting enthalpy hardly changes. Interestingly, FTIR results suggest that a special hydrogen-bonding interaction, in “C C–H···O C–C C” form, forms in the crystalline phase of PHSF and poly(hexamethylene fumarate) (PHF). The strong hydrogen-bonding interaction might be responsible for the transformation of conformation from all-trans to gauche in hexamethylene segments, and triggers the variation of crystal modification. [ABSTRACT FROM AUTHOR]

The results of a theoretical study of the reaction mechanism for the neutral hydration of ketene, HC=C=O + ( n + 1) HO → CHCOOH + nHO ( n = 0-4), in solution are presented. All structures were optimized and characterized at the MP2(fc)/6-31 + G* level of theory, and then re-optimized by MP2(fc)/6-311 ++G**, and the effect of the bulk solvent is taken into account according to the conductor-like polarized continuum model (CPCM) using the gas MP2(fc)/6-311 ++G** geometries. Energies were refined for five-water hydration at higher level of theory, QCISD(T)(fc)/6-311 ++G**//MP2(fc)/6-311 ++G**. In the combined supermolecular/continuum model, one water molecule directly attacks the central C-atom, and the other four explicit water molecules are divided into two groups, one acting as catalyst(s) by participating in the proton transfer to reduce the tension of proton transfer ring, and the other being placed near the non-reactive oxygen or carbon atom in order to catalyze the hydration by engaging in hydrogen-bonding to the substrate (the so-called cooperative effect). Between the two possible nucleophilic addition reactions of water molecule, across the C=O bond or the C=C bond, the former one is preferred. Our calculations suggest that the favorable hydrolysis mechanism of ketene involves a sort of eight-membered ring transition structure formed by a three-water proton transfer loop, and a cooperative dimeric water near the non-reactive carbon-atom. The best-estimated in the present paper for the rate-determining barrier in solution, $$ \Updelta G_{\text{sol}}^{ \ne } $$ (298 K), is about 58 kJ/mol, reasonably close to the available experimental result. [ABSTRACT FROM AUTHOR]

A series of dithieno[3,2-b:2′,3′-d]phospholes with a perfluorophenyl substituent at the phosphorus center has been synthesized. Further cross-coupling reactions with additional fluorinated phenyl groups afforded extended conjugated materials with different substitution patterns. Investigation of the optoelectronic properties of the materials revealed smaller highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) gaps for the extended materials that were also confirmed by theoretical density functional theory (DFT) calculations. These further indicated that the LUMO levels experience a more significant drop in energy than the respective HOMO levels. This fact can be attributed to the strongly electron-withdrawing nature of the fluoroaryls. In addition, the absolute energies of the frontier orbitals depend on the position of the fluoro substituents in the terminal aryl groups, with meta-positioned fluoro atoms having the strongest effect. Electrochemical investigations as well as theoretical calculations toward the electron affinity of the extended, highly fluorinated dithienophospholes revealed promising features that may prove useful for application as n-type semiconductors in corresponding organic field-effect transistors (OFETs). [ABSTRACT FROM AUTHOR]

Three identity nucleophilic substitution reactions at tetracoordinated silicon atom with inversion and retention pathways: Nu + SiH3Cl → Nu + SiH3Cl[Nu = (1)Cl−, (2) LiCl, and (3) (LiCl)2], are investigated using the G2M(+) theory. Our results show that changing the nucleophile can shift the mechanism (favorable pathway), stepwise from a single-well PES for reaction 1, via a double-well PES for reaction 2, to a triple-well PES for reaction 3, indicating the importance of steric and electronic effects on the SN2@Si. [ABSTRACT FROM AUTHOR]

The origin of enhanced reactivity of α-nucleophiles in SN2 reactions was examined on the basis of computational results at the high level G2(+) method for 22 gas-phase reactions: Nu- + RCl → RNu + Cl- [R = Et and i-Pr; Nu- = HO-, CH3O-, HS-, Cl-, Br-, NH2O-, HOO-, FO-, HSO-, ClO-, and BrO-]. The results clearly indicate the existence of the α-effect, whose size varies depending on the R group and the identity of the α-atom. The α-effect is larger for i-PrCI than EtCI, and for an α-nucleophile with a harder α-atom. Analyses of the present results, together with previously reported ones for MeF and MeCI reactions, reveal that several rationales so far presented to explain the α-effect, such as thermodynamic product stability, transition state (TS) tightness, electrostatic interaction, ET rationale, and polarizability, cannot explain the observed size of the α-effect. The importance of deformation energy on going from the reactant to the TS is presented. [ABSTRACT FROM AUTHOR]

The mechanism of the isomerization of nitrosomethane to formaldoxime catalyzed by neutral molecule (H2O and HCOOH) has been investigated at the level of B3LYP/6-311+G**. Calculated results indicate that the rearrangement from nitrosomethane to more stable trans-formaldoxime can proceed via two different reaction channels, but the favorable reaction pathway catalyzed by water and formic acid is different from the one in the catalyst-free reaction. It is more favorable that the tautomeric reaction involves the formation of cis-formaldoxime and a subsequent rotation about the N–O bond to form trans-formaldoxime in the catalyzed reaction. The activation energy of rate-determining step was reduced from 197.9 kJ/mol to 138.7 kJ/mol in the water-catalyzed reaction and 79.6 kJ/mol in the formic acid-catalyzed reaction, respectively, due to the catalysis of hydroxylic groups, but the catalysis of more acidic hydroxyl group in the latter system has been shown to be more efficient. [ABSTRACT FROM AUTHOR]

The original article to which this notice refers was published in the International Journal of Quantum ChemistryInt J Quantum Chem (2006). [ABSTRACT FROM AUTHOR]