[en] Optimal motion for a robot manipulator is obtained by nonlinear programming. The objective of optimal motion is minimizing energy consumption of manipulator arm with fixed traveling time in the presence of obstacles. The geometric path is not predetermined. The total trajectory is described in terms of cubic B-spline polynomials and the coefficients of them are obtained to minimize a specific performance index. Obstacle avoidance is performed by the method that the square sum of penetration growth distances between every obstacles and robot links is included in the performance index with appropriate weighting coefficient. In all examples tested here, the solutions were converged to unique optimal trajectories from different initial ones. The optimal geometric path obtained in this research can be used in minimum time trajectory planning. (author)

[en] Proton and charge transfers in water solvent have been an issue in the quantum dynamics and energetics of (H₂O)_n clusters. we studied state-to-state correlation curves of the ground and excited states for H₃O dissociating into (H₂O + H). For the dissociation reaction, the molecular orbitals and geometric structures at each internuclear distance were optimized using the restricted open-shell Hartree-Fock method (ROHF), keeping C_2υ symmetry

[en] The geometrical structures, potential energy surfaces, and energetics for the ligand exchange reactions of tetracoordinated platinum (PtY₂L₂ : Y, L=Cl^-, OH^-, OH₂, NH₃) complexes in the ligand-solvent interaction systems were investigated using the ab initio Hartree-Fock (HF) and Density Functional Theory (DFT) methods. The potential energy surfaces for the ligand exchange reactions used for the conversions of (PtCl₄ + H₂O) to [PtCl₃(H₂O) + Cl^-] and [Pt(NH₃)₂Cl₂ + H₂O] to [Pt(NH₃)₂Cl(H₂O) + Cl^-] were investigated in detail. For these two exchange reactions, the transition states ([PtY₂L₂ ···L']) correspond to complexes such as (PtCl₄ ···H₂O) and [Pt(NH₃)₂Cl₂ ···H₂O], respectively. In the transition state, ([PtCl₄ ···H₂O] and [Pt(NH₃)₂Cl₂ ··· H₂O]) have a kind of 6-membered (Pt-Cl···HOH···Cl) and (Pt-OH···Cl···HN) interactions, respectively, wherein a central Pt(II) metal directly combines with a leaving Cl^- and an entering H₂O. Simultaneously, the entering H₂O interacts with a leaving Cl^-. No vertical one metal-ligand interactions ([PtY₂L₂ ···L']) are found at the axial positions of the square planar (PtY₂L₂) complexes, which were formed via a vertically associative mechanism leading to D_3h or C_2v-transition state symmetry. The geometrical structure variations, molecular orbital variations (HOMO and LUMO), and relative stabilities for the ligand exchange processes are also examined quantitatively. Schematic diagrams for the dissociation reactions of {PtCl₄(H₂O)n(n = 2,4)} into {PtCl₃(H₂O)_(n-2) + Cl^-(H₂O)₂} and the binding energies {PtCl₄(H₂O)n(n = 1-5)} of PtCl₄ with water molecules are drawn

[en] The jet-cooled m-cyanobenzyl radical was generated for the first time in a jet from m-tolunitrile seeded in a large amount of inert carrier gas He and vibronically excited using a pinhole-type glass nozzle in a corona excited supersonic expansion. The position of the origin band was measured from the well-resolved visible emission spectra in the D_1 → D_0 transition. From the comparison with other isomers, it has also been found that the trends are similar to those of chlorobenzyls, xylyls, and tolunitriles. Transient species such as molecular ions and molecular radicals are of considerable interest in chemistry because they are believed to play an important role in chemical reaction as intermediates. Many techniques have been developed to find an ideal environment suitable to produce and preserve the radicals for the spectroscopic work. Of the methods employed, upersonic jet expansion with a large amount of inert carrier gases has been proved to be effective in the gas phase. However, the nature of high reactivity and short lifetime of free radicals has certainly slowed their experimental study in free jet

[en] Potential energy curves and internuclear (M-X) distance variations for dissociation reactions of [MX_4]"2"- into ([MX_3]"- + X"-) have been calculated using ab initio Hartree-Fock (HF), second order Moller-Plesset perturbation (MP2), and Density Functional Theory (DFT) methods with a triple zeta plus polarization (TZP) basis set. The equilibrium geometrical structures of [MX_4]"2"- are optimized to tetrahedral geometry for [NiX_4]"2"- and square planar geometry for ([PdX_4]"2"- and [PtX_4]"2"-). The bond (M-X) distances of [NiCl_4]"2"-, [NiBr_4]"2"-, [PdCl_4]"2"-, [PdBr_4]"2"-, [PtCl_4]"2"-, and [PtBr"4]"2"- at the DFT level are 2.258, 2.332, 2.351, 2.476, 2.367, and 2.493 A, respectively. The dissociation energies for the bond dissociation of ([MX_3]"-···X"-) at the DFT level are found to be 4.73 eV for [NiCl_4]"2"-, 4.89 eV for [NiBr_4]"2"-, 4.93 eV for [PdCl_4]"2"-, 5.57 eV for [PdBr_4]"2"-, 5.44 eV for [PtCl_4]"2"-, and 5.87 eV for [PtBr_4]"2"-. As the (M···X) distance of ([MX_3]"-···X"-) increases, the distance variation (Rt) of trans (M-X) bond at the trans-position is shorter than those (Rc) of two cis (M-X) bonds at the cisposition. Simultaneously the atomic charge variation of trans-X atom is more positive than those of equilibrium [MX_4]"2"- structures, while the variation of leaving X group is more positive

[en] The solvolysis rate constants of piperonyloyl chloride (1) in 27 different solvents are well correlated with the extended Grunwald-Winstein equation, using the N_T solvent nucleophilicity scale, Y_Cl solvent ionizing scale, and I aromatic ring parameter with sensitivity values of 0.30 ± 0.05, 0.71 ± 0.02, and 0.60 ± 0.04 for l, m, and h, respectively. The solvent kinetic isotope effect values (SKIE, k_MeOH/k_MeOD and k_{50%MeOD-50%D2O}) of 1.16 and 1.12 were also in accord with the values for the S_N1 mechanism and/or the dissociative S_N2 mechanism. The product selectivity values (S) for solvolysis of 1 in alcohol/water mixtures were in the range of 0.5 to 1.9, which is also consistent with the proposed unimolecular ionization mechanism

[en] The solvolysis rate constants of 2,4-dimethoxybenzenesulfonyl chloride (1) in 30 different solvents are well correlated with the extended Grunwald-Winstein equation, using the N_T solvent nucleophilicity scale and Y_Cl solvent ionizing scale, with sensitivity values of 0.93 ± 0.14 and 0.65 ± 0.06 for l and m, respectively. These l and m values can be considered to support a S_N2 reaction pathway. The activation enthalpies (ΔH^≠) were 12.4 to 14.6 kcal·mol^-1 and the activation entropies (ΔS^≠) were -15.5 to -32.3 cal·mol^-1·K^-1, which is consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effects (SKIE) were 1.74 to 1.86, which is also in accord with the SN₂ mechanism and was possibly assisted using a general-base catalysis. The values of product selectivity (S) for solvolyses of 1 in alcohol/water mixtures was 0.57 to 6.5, which is also consistent with the proposed bimolecular reaction mechanism. Third-order rate constants, k_ww and k_aa, were calculated from the rate constants (k_obs), together with k_aw and k_wa calculated from the intercept and slope of the plot of 1/S vs. [water]/[alcohol]. The calculated rate constants, k_calc (k_ww, k_aw, k_wa and k_aa), are in satisfactory agreement with the experimental values, supporting the stoichiometric solvation effect analysis

[en] A new colorimetric sensors containing thiourea (1-(4-nitrophenyl)-3-quinolin-6-ylthiourea: 1) and urea(1-(4- nitrophenyl)-3-quinolin-6-ylurea: 2) moieties for fluoride were designed and synthesized. These simple receptors were characterized their stoichiometry, and investigates the mechanism of their selectivity as anion receptors. The addition of tetrabutylammonium fluoride salts to the solution of receptors caused a dramatically and clearly observable color changes from colorless to yellow. To examine their application as anion receptors by UV-vis and ¹H NMR spectroscopy results revealed their higher selectivity for fluoride ion than other anions. The receptors and fluoride ion formed a 1:1 stoichiometry complex through strong hydrogen bonding interactions in the first step, followed by a process of deprotonation in presence of an excess of F^- in DMSO solvent

[en] This work demonstrates the ability of quasielastic neutron scattering (QENS) to measure the dynamics associated with counterions in perfluorosulfonate ionomers (PFSIs). PFSI membranes were prepared by neutralizing with hydrogenated alkyl ammonium counterions. Counterion dynamics were measured using the High-Flux Backscattering Spectrometer at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). Long-range mobility of the counterions was closely linked with the α-relaxation in these materials measured by dynamic mechanical analysis (DMA). The counterion motions in the membrane were found to follow a mechanism of random jump-diffusion within a confined spatial region with diffusion coefficients on the order of 10^-7 cm² s^-1. These data are presented along with variable temperature X-ray scattering investigations of the melting behavior of these materials. Altogether, the data presented here show the link between the onset of long-range counterion mobility and the mechanical properties of these materials. These data provide further fundamental understanding of the link between electrostatic interactions and dynamics in PFSI materials.

[en] Dimeric metallamacrocycles of 2 : 2 (metal-to-ligand) stoichiometry, [Pd{α,ω-bis(diphenylphosphino)oligothienylene} Cl_2]_2 1-3 were prepared from a self-assembly reaction of [Pd(CH_3CN)_2Cl_2] and α,ω-bis- (diphenylphosphino)oligothienylene in 90-94% yields. The structures of metallamacrocycles 1-3 were determined by X-ray diffraction. 1 crystallizes in the monoclinic space group P2_1/n with a/A = 12.0737(13), b/A = 17.1993(18), c/A = 13.0951(14) and β / .deg. = 101.505(2). 2 crystallizes in the triclinic space group P with a/A = 10.2634(4), b/A = 19.7855(9), c/A = 21.0851(9), α / .deg. = 63.1010(10), β / .deg. = 86.5880(10), γ / .deg. = 81.2280(10). 3 crystallizes in the triclinic space group P with a/A = 10.4353(19), b/A = 13.482(3), c/A = 13.816(3), α / .deg. = 108.027(4), β / .deg. = 90.461(4), γ / .deg. = 93.261(4). The UV spectra of 1-3 were characterized