Fast multipole method for three-dimensional systems with periodic boundary condition in two directions

We derived a new expression for the electrostatic interaction of three-dimensional charge-neutral systems with two-dimensional periodic boundary conditions (slab geometry) using a fast multipole method (FMM). Contributions from all the image cells are expressed as a sum of real and reciprocal space terms, and a self-interaction term. The reciprocal space contribution consists of two parts: zero and nonzero terms of the absolute value of the reciprocal lattice vector. To test the new expressions, electrostatic interactions were calculated for a randomly placed charge distribution in a cubic box and liquid water produced by molecular dynamics calculation. The accuracy could be controlled by the degree of expansion of the FMM. In the present expression, the computational complexity of the electrostatic interaction of N-particle systems is order N, which is superior to that of the conventional two-dimensional periodic Ewald method for a slab geometry and the particle mesh Ewald method with a large empty space at an interface of the unit cell. © 2020 Wiley Periodicals, Inc.     

Controlled Reduction of Carboxamides to Alcohols or Amines by Zinc Hydrides

New protocols for controlled reduction of carboxamides to either alcohols or amines were established using a combination of sodium hydride (NaH) and zinc halides (ZnX₂). Use of a different halide on ZnX₂ dictates the selectivity, wherein the NaH‐ZnI₂ system delivers alcohols and NaH‐ZnCl₂ gives amines. Extensive mechanistic studies by experimental and theoretical approaches imply that polymeric zinc hydride (ZnH₂)_∞ is responsible for alcohol formation, whereas dimeric zinc chloride hydride (H?Zn?Cl)₂ is the key species for the production of amines.     

ESEEM study of the location of spin-polarized chlorophyll-quinone radical pair in membrane-oriented spinach photosystems I and II complexes

Light-induced spin-polarized radical pairs, P700⁺A₁ ^? in spinach photosystem (PS) I particles and P680⁺Q_A ^? in Zn-substituted PS II core complexes, in oriented membranes were studied by pulsed electron paramagnetic resonance (EPR). Based on the determined distance of 25.2 ± 0.2 Å between P700 and A₁, the angular dependence of the spin-polarized electron spin echo envelope modulation (ESEEM) spectra on the magnetic field suggests that the angle between $R_{P700 - {\rm A}_1 } $ , the radius-vector connecting P700 and A₁, and the membrane normaln was 24 ± 4° in PS I particles. Obtained angle and distance of P700-A₁ axis suggested Q_K side in the molecular geometry of cofactors presented in a recent X-ray crystallography of cyanobacterial PS I reaction center to be an active branch of electron transfer. The distance between P680 and Q_A was determined to be 27.4 ± 0.3 Å for a nonoriented PS II. The angle between $R_{P680 - Q_{\rm A} } $ , the radius-vector connecting P680 and Q_A, andn was determined to be 21 ± 5°. The angle of P680-Q_A axis was close to that of 20° of P870-Q_A axis reported in X-ray analysis of the purple bacterial reaction center crystal.     

Nuclear magnetic resonance spectra of carbanions—VI. Cumyl-, α-methylbenzyl- and benzyl carbanions

The proton magnetic resonance spectra of the three title carbanions have been observed in THF with potassium as a counter ion. The ortho-protons in the α-methylbenzyl carbanion are nonequivalent at room temperature. This shows that the α-carbon in this carbanion is in the near-sp² configuration. The aromatic proton chemical shifts of the benzylpotassium obtained here are at higher shielding than those of benzyllithium reported previously by Sandel and Freedman. This seems to arise from the different ionic nature of the bonds between carbon and metal in the carbanions.     

Supramolecular ion channels from a transmembrane bischolic acid derivative showing two discrete conductances

Bischolic acid derivative 1 linked by m-xylylene dicarbamate at the 3,3'-position was synthesized and the single ion channel properties were examined. Compound 1 showed two clearly distinct conductances, 9.5 (type A) and 25.3 pS (type B), under 500 mM KCl symmetric salt conditions, whereas various conductances, ranging from 5-20 pS, were observed in the tetramethylether analogue reported previously. Results indicate that the replacement of four methylether groups with hydroxyls at the 7, 7', 12, and 12' positions in the bischolic acid framework influences the stability of aggregated (supramolecular) ion channel structures. Ion permeability ratios (potassium/chloride and potassium/sodium) for each type of channel were also determined.     

Vernodalidimers A and B, novel orthoester elemanolide dimers from seeds of Vernonia anthelmintica

Two novel elemanolide dimers, vernodalidimers A (1) and B (2), possessing a rare tricyclic ortho ester moiety, were isolated from the seeds of Vernonia anthelmintica. Their structures were elucidated by 1D and 2D NMR data and CD spectra. Vernodalidimers A (1) and B (2) exhibited potent cell growth inhibitory activity against HL-60 cells (IC₅₀ 0.72 and 0.47 μM, respectively).     

Molecular mechanics (MM3) calculations on lithium amide compounds

The MM3 force field has been extended to deal with the lithium amide molecules that are widely used as efficient catalysts for stereoselective asymmetric synthesis. The MM3 force field parameters have been determined on the basis of the ab initio MP2/6-31G* and/or DFT (B3LYP/6-31G*, B3-PW91/6-31G*) geometry optimization calculations. To evaluate the electronic interactions specific to the lithium amides derived from the diamine molecules properly, the Lewis bonding potential term for the interaction between the lithium atom and the nonbonded adjacent electronegative atom such as nitrogen was introduced into the MM3 force field. The bond dipoles were evaluated correctly from the electronic charges on the atoms calculated by fitting to the electrostatic potential at points selected. The MM3 results on the molecular structures, conformational energies, and vibrational spectra show good agreement with those from the quantum mechanical calculations.     

A tensor product of the Steinberg module and a certain simple kG(pr)-module

Let G be a connected, semisimple, and simply connected algebraic group defined and split over the finite field of order p, and let G(q) be the corresponding finite Chevalley or twisted group, where q = p^r. Recently, Anwar determines the direct sum decomposition of the tensor product of the rth Steinberg module and a simple G-module with a (p,r)-minuscule highest weight λ. In this paper, we determine that of the tensor product regarded as a module for G(q) under some weak assumptions for λ.     

Low-temperature phase of Li2FeSiO4: crystal structure and a preliminary study of electrochemical behavior

A nearly single-phase of a low-temperature (LT) phase of Li(2)FeSiO(4) is prepared by a hydrothermal method at 150 °C. We report the detailed crystal structure of LT-Li(2)FeSiO(4) (S.G. Pmn2(1)) by applying Rietveld/MEM analysis to the synchrotron XRD pattern. LT-Li(2)FeSiO(4) shows 150 mA h g(-1) as the positive electrode materials of rechargeable batteries.