Improved description of the orbital relaxation effect by practical use of the self‐energy

The self‐energy shift in the orbital relaxation (OR) term of the polarization propagator complete through the second‐order is presented. In combination with the optimal damping parameter in the OR term, the modified propagator produces the excitation energy of the coupled‐cluster with singles and doubles (CCSD) accuracy. The self‐energy shift requires the floating‐point operation of , where N refers to the magnitude of the molecular size. Because the second‐order polarization propagator requires the floating‐point operation of , the additional computational effort to construct the self‐energy is negligibly small. Numerical results are shown for several molecules including glycine, 2,3,5,6‐tetrafluorobenzene, and naphthalene, and promising agreements with those of CCSD are confirmed within less than 0.2 eV. The basis set dependence is also tested for the water molecule using aug‐cc‐pV NZ (N = D–7), where this newly developed approach mimics the behavior of the CCSD values. The self‐energy shifting for the second‐order response matrix in combination with the use of a dumping parameter is efficiently implemented for calculations of medium‐sized molecular systems, including glycine and naphthalene. The developed approach provides CCSD‐like accuracy at a more affordable computational expense. © 2014 Wiley Periodicals, Inc.     

Poly(D,L-lactide-co-glycolide)/hydroxyapatite core-shell nanosphere. Part 2: Simultaneous release of a drug and a prodrug (clindamycin and clindamycin phosphate)

The novel concept of a simultaneous, controlled release of a drug and a prodrug with different physico-chemical properties was applied in order to prolong the release period of antibiotics and estimate their high local concentrations, which are the necessary preconditions for the treatment of some chronic infection diseases. For this purpose poly(D,L-lactide-co-glycolide)/hydroxyapatite (PLGA/HAp) core-shell nanostructures were used as the carrier of clindamycin-base, as a drug, and clindamycin-2-phosphate, as a prodrug model. As a result, a two-step release was observed: the controlled release of the more soluble phosphate form and the sustained release of the less-soluble base form of clindamycin, resulting in a high overall concentration of the released drug during the period of 30 days in vitro. The HAp phase within the PLGA core-shells, applied as a drug carrier, delayed the process of the degradation of the polymer; however, the presence of the drug affected the process of degradation and this influence was the dominant factor in the control over the degradation of the polymer phase of PLGA/HAp and the consequent kinetics of the drug release.     

Structure, solution chemistry, antiproliferative actions and protein binding properties of non-conventional platinum(II) compounds with sulfur and phosphorus donors

Twelve Pt(II) complexes with cis-PtP(2)S(2) pharmacophores (where P(2) refers to two monodentate or one bidentate phosphane ligand and S(2) is a dithiolato ligand) were prepared, characterized and evaluated as potential antiproliferative agents. The various compounds were first studied from the structural point of view; afterward, their solubility properties as well as their solution behaviour were analyzed in detail. Antiproliferative properties were specifically evaluated against A2780 human ovarian carcinoma cells, either resistant or sensitive to cisplatin. For comparison purposes similar studies were carried out on four parent cis-dichloro bisphosphane Pt(II)complexes. On the whole, the cis-PtP(2)S(2) compounds displayed significant antiproliferative properties while the cis-PtP(2)Cl(2) (cis-dichloro bisphosphane Pt(II)) compounds revealed quite poor biological performances. To gain further insight into the molecular mechanisms of these bisphosphane Pt(II) compounds, the reactions of selected complexes against the model protein cytochrome c were investigated by ESI-MS and their adduct formation explored. A relevant reactivity with cyt c was obtained only for cis-PtP(2)Cl(2) compounds, whereas cis-PtP(2)S(2) compounds turned out to be nearly unreactive. The obtained results are interpreted and discussed in the frame of the current knowledge of anticancer platinum compounds and their structure-activity-relationships. The observation of appreciable antiproliferative effects for the relatively inert cis-PtP(2)S(2) compounds strongly suggests that these compounds will undergo specific activation within the cellular environment.     

Noncovalent interaction-driven stereoselectivity of copper(II) complexes with cyclodextrin derivatives of L- and D-carnosine

L-Carnosine (β-alanyl-L-histidine, LCar) is the most widely and abundantly distributed copper(II)-coordinating endogenous dipeptide. Though its physiological role has not been completely understood yet, many functions have been proposed for this compound. LCar might be crucial in the potential reduction or prevention of several pathologies in which the metal ions are thought to be involved. The potential therapeutic applications of LCar are drastically limited because of hydrolysis by specific dipeptidases (carnosinases). D-Carnosine (DCar), the enantiomer of the naturally occurring dipeptide, shows the same properties as those of LCar, but it is not hydrolyzed by carnosinases. Chemical modification of LCar has been proposed as a promising strategy to reduce its enzymatic hydrolysis; conjugation of a carbohydrate moiety may also improve site-specific transport to different tissues, which would enhance the peptide bioavailability. On this basis, we have functionalized DCar with β-cyclodextrin (CDDCar) and characterized the compound via NMR. The copper(II) binding properties of the new DCar derivative were investigated by spectroscopic techniques (UV-vis, circular dichroism, electron paramagnetic resonance) and potentiometric measurements. The results surprisingly revealed a pronounced difference from the analogous LCar derivative (CDLCar), especially concerning the dimeric species. The spectroscopic data show that this stereoselectivity is driven by noncovalent interactions, namely, hydrogen bonds, CH-π interactions, and steric and hydrophobic effects of the cyclodextrin cavity.     

Isomerization dynamics of the 2-phenylazo-1,3-dimethylimidazolium cation photoexcited to the S2 (π, π*) state as studied by transient absorption spectroscopy in the time domain of 10(-13) to 10(3) seconds

Photoinduced isomerization of a novel photochromic cation, [2PA-Mmim](+) (2-phenylazo-1,3-dimethylimidazolium cation), was studied by optical spectroscopic methods. The UV-Vis absorption spectra of the [2PA-Mmim](+) cation show two prominent bands starting around 410 and 520 nm, corresponding to the S(0)-S(2) (π, π*) and S(0)-S(1) (n, π*) transitions, respectively. The photoisomerization mechanism is studied by femtosecond time-resolved transient absorption experiments performed after S(0)-S(2) (π, π*) excitation in several solvents with different viscosity, including ionic liquids. The transient absorption signals at two representative wavelengths were fitted by bi-exponential functions, which yield four decay components. The photoisomerization mechanism is discussed in light of the relaxation schemes available for azobenzene. Only one of the components depends on the solvent viscosity and it changes from 1.2 ps (dichloromethane, 0.4 cP) to 5.6 ps ([Bmim][BF(4)], 93 cP). This component is assigned to a molecule at the S(1) state, which is responsible for the "rotational" isomerization. The weak dependence on the solvent viscosity of this component is explained in terms of local change in the viscosity as a result of local heating due to excess energy released at S(2)-S(1) internal conversion. The other three components of ～0.4, 1.0 and 10 ps are attributed to relaxation processes of the molecule at S(2), S(1) and S(0) states, respectively. The quantum yields for the forward E-Z photoisomerization are ～0.15 after S(2) excitation. The backward Z-E isomerization is slow with a lifetime of 1 hour and an activation energy of 91 kJ mol(-1) through an "inversion" mechanism.     

Thermochemistry of Alane Complexes for Hydrogen Storage: A Theoretical and Experimental Investigation

Knowledge of the relative stabilities of alane (AlH(3)) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for 38 alane complexes with NH(3-n)R(n) (R = Me, Et; n = 0-3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH(2-n)R(n) (R = Me, Et; n = 0-2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine-alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine and obtaining upper limits of ΔG° for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the alane complex. On the basis of this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an alane-based hydrogen storage system.     

Biological Activity of Amidino-Substituted Imidazo [4,5-b]pyridines

A series of cyano- and amidino-substituted imidazo[4,5-b]pyridines were synthesized using standard methods of organic synthesis, and their biological activity was evaluated. Biological evaluation included in vitro assessment of antiproliferative effects on a diverse selection of human cancer cell lines, antibacterial activity against chosen Gram-positive and Gram-negative bacterial strains, and antiviral activity on a broad panel of DNA and RNA viruses. The most pronounced antiproliferative activity was observed for compound 10, which contained an unsubstituted amidino group, and compound 14, which contained a 2-imidazolinyl amidino group; both displayed selective and strong activity in sub-micromolar inhibitory concentration range against colon carcinoma (IC₅₀ 0.4 and 0.7 μM, respectively). All tested compounds lacked antibacterial activity, with the exception of compound 14, which showed moderate activity against E. coli (MIC 32 μM). Bromo-substituted derivative 7, which contained an unsubstituted phenyl ring (EC₅₀ 21 μM), and para-cyano-substituted derivative 17 (EC₅₀ 58 μM) showed selective but moderate activity against respiratory syncytial virus (RSV).     

Accelerating flames in tubes—an analysis

Flame acceleration in tubes is studied. A tube filled with flammable mixture is closed at one end and open to the atmosphere at its second end. When ignition takes place near the closed end, it is well-known from experiments that the flame may accelerate, oscillate and eventually reach considerable speeds. A one-dimensional analysis is presented, based upon the assumption that the flame front propagates at a speed that is small compared to the speed of sound. The analysis leads to a construction of the complete unsteady solution. Results from the analysis and from a numerical simulation are compared. They are similar enough to validate the analysis. The tube acoustics are set in motion by the expansion of the fluid due to ignition at the closed end. Subsequently, both spectrum and amplitude evolve because of the motion of the temperature interface, and because of forcing by the flame front, which the analysis precisely quantifies. Oscillations in the front position are strong enough to result in flow reversal. In addition, the induced periodic acoustic acceleration of the temperature and density interface will periodically make the flame front Rayleigh–Taylor unstable, which should result in the dramatic increase in the propagation speed seen in experiments.     

Low-power 1:16 DEMUX and one-chip CDR with 1:4 DEMUX using InP-InGaAs heterojunction bipolar transistors

Using InP-InGaAs heterojunction bipolar transistor (HBT) technology, we have successfully designed and fabricated a low-power 1:16 demultiplexer (DEMUX) integrated circuit (IC) and one-chip clock and data recovery (CDR) with a 1:4 DEMUX IC for 10-Gb/s optical communications systems. The InP-InGaAs HBTs were fabricated by a nonself-aligned process for high uniformity of device characteristics and producibility. The 1:16 DEMUX IC and the one-chip CDR with the 1:4 DEMUX IC consist of approximately 1200 and 460 transistors, respectively. We have confirmed error-free operation at 10 Gb/s for all data outputs of both ICs. The 1:16 DEMUX IC and the one-chip CDR with the 1:4 DEMUX IC consume only 1 W and 950 mW, respectively. These results demonstrate the feasibility of InP-InGaAs HBTs for low power high-integration optical communication ICs.