A density functional theory study on the Ag<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>H (<Emphasis Type="Italic">n</Emphasis> = 1–10) clusters

Density functional GGA-PW91 method with DNP basis set is applied to optimize the geometries of Ag _n H (n = 1–10) clusters. For the lowest energy geometries of Ag _n H (n = 1–10) clusters, the hydrogen atom prefers to occupy the two-fold coordination bridge site except the occupation of single-fold coordination site in AgH cluster. After adsorption of hydrogen atom, most Ag _n structures are slightly perturbed and only the Ag₆ structure in Ag₆H cluster is distorted obviously. The Ag–Ag bond is strengthened and the strength of Ag–H bond exhibits a clear odd–even oscillation like the strength of Au–H bond in Au _n H clusters, indicating that the hydrogen atom is more favorable to be adsorbed by odd-numbered pure silver clusters. The adsorption strength of small silver cluster toward H atom is obviously weaker than that of small gold cluster toward H atom due to the strong scalar relativistic effect in small gold cluster. The pronounced odd–even alternation of the magnetic moments is observed in Ag _n H systems, indicating that the Ag _n H clusters possess tunable magnetic properties by adsorbing hydrogen atom onto odd-numbered or even-numbered small silver cluster.     

Studies on the interaction of achiral cationic pseudoisocyanine with chiral metal complexes

The effect of chiral metal complexes ([Co(en)(3)]I(3)·H(2)O, cis-[CoBr(NH(3))(en)(2)]Br(2), K[Co(edta)]·2H(2)O and [Ru(phen)(3)](PF(6))(2)) on the polymer-bound J-aggregates in aqueous mixtures of pesudoisocyanine (PIC) iodine and poly(acrylic acid, sodium)(PAAS) have been studied by UV-vis absorption, circular dichroism (CD) and fluorescence spectra. At low concentration, the PIC monomers could self-assemble to form supermolecules by binding to each of the COO(-) groups on the polymer chains through electrostatic interactions. After the addition of chiral metal complexes to the formed PIC-PAAS J-aggregates, we found that only the chiral multiple π-conjugated phenanthroline metal complexes could transfer their metal-centered chiral information to the formed J-aggregates. The chiral J-aggregates showed a characteristic induced circular dichroism (ICD) in the visible region of J-band chromophore, and the ICD signals depend on the absolute configuration, concentration of the chiral multiple π-conjugated metal complexes, as well as temperature. More interestingly, the supramolecular chirality of the polymer supported PIC J-aggregates could be memorized even after the addition of an excess opposite chiral complex enantiomers. This is in sharp contrast to the behavior in the high concentrated NaCl induced PIC-J aggregates, in which the optical rotation of a mixture of two enantiomers varies linearly with their ratio.     

Library of second-generation cycloruthenated compounds and evaluation of their biological properties as potential anticancer drugs: passing the nanomolar barrier

A library of 32 organoruthenium compounds has been synthesised. Known and novel C-N cyclometalated compounds as well as N-C-N and N-N-C pincer derivatives of this metal have been used in this purpose. Most of the compounds have been tested for their in vitro antitumoral behaviours, good to excellent activities have thus been found. Several of the newly synthesized compounds pass the symbolic barrier of the nanomolar range for their IC(50) indicating a critical improvement. The level of activity is tentatively correlated to physicochemical properties of the compounds such as their Ru(III/II) redox potential and their lipophilicity (log P).     

The adsorptions of silver-doped small gold clusters toward carbon monoxide molecule

An all-electron scalar relativistic calculation on Au _n AgCO (n = 1–12) clusters has been performed using density functional theory with the generalized gradient approximation at PW91 level. The introduction of impurity silver weakens the adsorption, and, however, promotes the reactivity enhancement of CO molecule. The CO molecule is relatively more favorable to be adsorbed by the odd-numbered Au _n Ag clusters with closed-shell electronic structure. The values of chemical hardness indicate that the Au _n AgCO cluster is less stable than the corresponding Au _n+1CO cluster chemically. This picture of the influence of impurity silver on the adsorption behavior of Au _n Ag (n = 1–12) clusters toward CO molecule is consistent with previous experimental work (Haeck et al. in J Phys Chem A 115:2103, 2011), in which the cluster’s reaction probability toward CO molecule is reduced upon substitution of gold atoms for silver and the clusters with closed electronic shell are the most reactive toward CO molecule.     

Effective asymmetric synthesis of the key chiral building blocks of 20(S)- and 20(R)-camptothecins

Abstract  

An effective diastereoselective synthesis of (S)-N,N-diethyl-2-formyl-2-(methoxymethoxy)butanamide and (S)-2-formyl-2-(methoxymethoxy)butanoic acid ethyl ester, which are two key chiral building blocks for the synthesis of 20(S)-camptothecins, has been developed by employing an asymmetric bromolactonization using (R)-proline. The (R) compounds were also synthesized to obtain 20(R)-camptothecin.     

Direct construction of novel exo′-selective spiropyrrolidine bisoxindoles via a three-component 1,3-dipolar cycloaddition reaction

An efficient synthesis of novel exo′-selective spiropyrrolidine bisoxindoles has been achieved via a three-component 1,3-dipolar cycloaddition reaction. The azomethine ylides generated in situ from substituted isatin and primary α-amino acid methyl ester (or primary α-amino acids) reacted with the Knoevenagel adducts of substituted isatin to furnish novel spiropyrrolidine bisoxindoles in high yields (up to 99%). The structure and relative stereochemistry of cycloadducts were confirmed by single crystal X-ray diffraction. The possible mechanism was proposed and the cycloaddition proceeded via exo′-transition state.     

Effects of image charges, interfacial charge discreteness, and surface roughness on the zeta potential of spherical electric double layers

We investigate the effects of image charges, interfacial charge discreteness, and surface roughness on spherical electric double layer structures in electrolyte solutions with divalent counterions in the setting of the primitive model. By using Monte Carlo simulations and the image charge method, the zeta potential profile and the integrated charge distribution function are computed for varying surface charge strengths and salt concentrations. Systematic comparisons were carried out between three distinct models for interfacial charges: (1) SURF1 with uniform surface charges, (2) SURF2 with discrete point charges on the interface, and (3) SURF3 with discrete interfacial charges and finite excluded volume. By comparing the integrated charge distribution function and the zeta potential profile, we argue that the potential at the distance of one ion diameter from the macroion surface is a suitable location to define the zeta potential. In SURF2 model, we find that image charge effects strongly enhance charge inversion for monovalent interfacial charges, and strongly suppress charge inversion for multivalent interfacial charges. For SURF3, the image charge effect becomes much smaller. Finally, with image charges in action, we find that excluded volumes (in SURF3) suppress charge inversion for monovalent interfacial charges and enhance charge inversion for multivalent interfacial charges. Overall, our results demonstrate that all these aspects, i.e., image charges, interfacial charge discreteness, their excluding volumes, have significant impacts on zeta potentials of electric double layers.     

Generation of Optical Millimeter Wave Using Two Cascaded Polarization Modulators Based on Frequency Octupling Without Filtering

Abstract

An approach to generate an optical millimeter wave is introduced with frequency octupling using two cascaded polarization modulators followed by polarizers, respectively. By adjusting the modulation indexes of polarization modulators, only the ±4th-order sidebands are generated with a pure spectrum. Since no filter is needed, the proposed technique can be used to generate a frequency-tunable millimeter wave with a large frequency-tunable range. To prove the feasibility of the proposed approach, a simulation is conducted to generate an 80-GHz millimeter wave, and then its transmission performance is checked.     

Generalized function projective (lag, anticipated and complete) synchronization between two different complex networks with nonidentical nodes

Generalized function projective (lag, anticipated and complete) synchronization between two different complex networks with nonidentical nodes is investigated in this paper. Based on Barbalat’s lemma, some sufficient synchronization criteria are derived by applying the nonlinear feedback control. Although previous work studied function projective synchronization on complex dynamical networks, the dynamics of the nodes are coupled partially linear chaotic systems. In our work, the dynamics of the nodes of the complex networks are any chaotic systems without the limitation of the partial linearity. In addition, each network can be undirected or directed, connected or disconnected, and nodes in either network may have identical or different dynamics. The proposed strategy is applicable to almost all kinds of complex networks. Numerical simulations further verify the effectiveness and feasibility of the proposed synchronization method. Numeric evidence shows that the synchronization rate is sensitively influenced by the feedback strength, the time delay, the network size and the network topological structure.     

Gene Clone and Characterization of a Novel Thermostable β-Galactosidase with Transglycosylation Activity from Thermotoga naphthophila RUK-10

We cloned and expressed a new recombinant β-galactosidase(TN0949) from Thermotoga naphthophila RKU-10 with the pET28a(+) vector system in Escherichia coli BL21(DE3), and determined its catalytic capability to synthesize alkyl glucosides. The recombinant enzyme was purified to a single band via heat treatment and Ni²⁺-NTA affinity chromatography. The molecular mass of the recombinant enzyme was estimated to be 79 kDa with sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE). TN0949 can hydrolyze o-nitrophenyl β-D- galactopyranoside at the optimum pH and temperature of 6.5 and 80 ℃, respectively. TN0949 can also hydrolyze lactose at the optimum pH and temperature of 5.2 and 80 ℃, respectively. The K_m values for the hydrolyses of o-nitrophenyl β-D-galactopyranoside and lactose were 0.82 and 83.65 mmol/L, respectively. TN0949 was stable over a wide range of pH(3.0 to 7.0) after 24 h of incubation. The half-lives of TN0949 at 75, 80 and 85 ℃ were 22, 6 and 1.33 h, respectively. The enzyme displayed the capability to use lactose as the transglycosylation substrate to synthesize butyl galactopyranoside and hexyl galactopyranoside, indicating its suitability as a candidate industrial biocatalyst.