Interconversion Process Research Articles

Protein expression changes induced in murine peritoneal macrophages by Group B Streptococcus

Protein expression changes induced in thioglycolate-elicited peritoneal murine macrophages (M Phi) by infection with type III Group B Streptococcus (GBS) are described. Proteins from control M Phi and M Phi incubated 2 h with live or heat-inactivated GBS were separated by 2-DE. Proteins whose expression was significantly different in infected M Phi, as compared with control cells, were identified by MS/MS analysis. Changes in the expression level of proteins involved in both positive and negative modulation of phagocytic functions, stress response and cell death were induced in M Phi by GBS infection. In particular, expression of enzymes playing a key role in production of reactive oxygen species was lowered in GBS-infected M Phi. Significant alterations in the expression of some metabolic enzymes were also observed, most of the glycolytic and of the pentose-cycle enzymes being down-regulated in M Phi infected with live GBS. Finally, evidence was obtained that GBS infection affects the expression of enzymes or enzyme subunits involved in ATP synthesis and in adenine nucleotides interconversion processes.

Ultrafast Dynamics of the Low-Lying 3MLCT States of [Ru(bpy)2(dppp2)]2+

The solvent dependence of the excited state dynamics of [Ru(bpy)(2)(dppp2)](2+) (bpy = 2,2'-bipyridine, dppp2 = pyrido[2',3':5,6]pyrazino[2,3-f][1,10]phenanthroline) were investigated using ultrafast transient absorption spectroscopy. In contrast to the "DNA light-switch" complex [Ru(bpy)(2)(dppz)](2+) (dppz = dipyrido[3,2-a:2',3'-c]phenzine), the structurally related [Ru(bpy)(2)(dppp2)](2+) exhibits discrete formation of the lowest-lying (3)MLCT(dis) (MLCT = metal-to-ligand charge transfer) state from the higher-energy (3)MLCT(prox) state in the picosecond time scale. In (3)MLCT(dis) and (3)MLCT(prox), the transferred electron is localized on the portion of the dppp2 ligand distal and proximal to the metal, respectively. The greater dipole moment of (3)MLCT(dis) compared to (3)MCLT(prox), together with the ability of the dppp2 ligand to hydrogen bond, results in a strong dependence of the kinetics of the interconversion process on solvent polarity, decreasing from 67 to 26 ps in CH(2)Cl(2) and CH(3)CN, respectively. Similarly, the lifetime of the emission of the lowest energy state of [Ru(bpy)(2)(dppp2)](2+) also decreases from 273 to 35 ns in the same solvents. In CH(3)CH(2)OH, both the rate of interconversion and the decay of (3)MLCT(dis) are significantly faster, 6.7 ps and 1.7 ns, respectively. Such dependence of the excited state properties is not observed for [Ru(bpy)(2)(dppz)](2+). The results are consistent with the relative stabilization of (3)MLCT(dis) of the dppp2 complex in CH(3)CN compared to CH(2)Cl(2) due to solvent polarity, which may be further stabilized by hydrogen bonding in CH(3)CH(2)OH.

Weak interaction rate Coulomb corrections in big bang nucleosynthesis

We have applied a fully relativistic Coulomb wave correction to the weak reactions in the full Kawano/Wagoner big bang nucleosynthesis (BBN) code. We have also added the zero-temperature radiative correction. We find that using this higher accuracy Coulomb correction results in good agreement with previous work, giving only a modest $\ensuremath{\sim}0.04%$ increase in helium mass fraction over correction prescriptions applied previously in BBN calculations. We have calculated the effect of these corrections on other light element abundance yields in BBN, and we have studied these yields as functions of electron neutrino lepton number. This has allowed insights into the role of the weak neutron-proton interconversion processes in the setting of the neutron-to-proton ratio during the BBN epoch. We find that the lepton capture processes' contributions to this ratio are only second order in the Coulomb correction.

Metallocyclo‐ and Polyphosphazenes Containing Gold or Silver: Thermolytic Transformation into Nanostructured Materials

A cyclotriphosphazene bearing two 4-oxypyridine groups on the same phosphorus atom, gem-[N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4)(2)] (I), and its analogous polymer [{NP(O(2)C(12)H(8))}(0.7){NP(OC(5)H(4)N-4)(2)}(0.3)](n) (II), have been used to prepare gold or silver, cyclic and polymeric, metallophosphazenes. The following complexes, gem-[N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{ML})(2)] (ML=Au(C(6)F(5)) (1) or Au(C(6)F(5))(3) (2)), [N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{AuPPh(3)})(2)][NO(3)](2) (3), and [N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{AgPPh(2)R})(2)][SO(3)CF(3)](2) (R=Ph (4) or Me (5)) have been obtained. Complexes 1 and 4 are excellent models for the preparation of the analogous polymers [{NP(O(2)C(12)H(8))}(0.7){NP(OC(5)H(4)N-4{ML})(2)}(0.3)](n) (ML=Au(C(6)F(5)) (P1), Ag(OSO(2)CF(3))PPh(3) (P2)). All complexes have been characterized by elemental analysis, various spectroscopic methods, and mass spectrometry. The polymers were further investigated by thermochemical methods (thermogravimetric analysis) and differential scanning calorimetry. For compounds 1-5 and for the starting phosphazene I, a mixture of different stereoisomers may be expected. The stereochemistry in solution has been studied by variable-temperature NMR spectroscopy studies, which provided evidence for interconversion processes that involve changes in the chirality of a 2,2'-dioxybiphenyl group. A single-crystal X-ray analysis of the gold complex 2 confirmed not only the proposed structure, but also S,S and R,R configurations at the two biphenoxy-substituted phosphorus centers, in contrast to those observed for the precursor I. Pyrolysis of these new metallophosphazenes was also studied. Notably, pyrolysis of the gold derivatives gave macroporous metallic gold sponges without the requirement of either an external reducing agent or a porous support. These materials were all characterized by XRD, TEM, SEM, and energy-dispersive X-ray spectroscopy.

Dynamic interconversion of chiral oxime compounds in gas chromatography

A number of chiral oxime compounds have been synthesised and their gas chromatographic analysis on both a polyethelene glycol phase column and two chiral column phases was investigated. Of particular interest to this work is the observation of dynamic interconversion behaviour, both in a single dimensional analysis, and by using comprehensive two-dimensional gas chromatography (GC × GC). A number of non-chiral compounds were studied as a means to understand the nature of the behaviour observed. As expected, the achiral compound on both the wax column and the chiral column generated two isomeric compounds—the E and Z isomers. On the wax column, a characteristic interconversion zone representing the dynamic process was observed, with extent of interconversion dependent on the conditions used. For the chiral compounds, two isomers and the interconversion zone were exhibited on the wax column, however on the chiral column 4 isomeric peaks were found—the (R) and (S) enantiomers of each of the E and Z isomers. In the case of the chiral column, the extent of interconversion was negligible, and this appears to correlate with the use of low polarity columns. In order to encourage dynamic interconversion, a polyethylene glycol column was coupled to the chiral column, by placing it either before or after the chiral column. In this case a monitor detector was employed between the two columns in order to isolate the effects of the first column from the behaviour on the second. In a further study, the most appropriate column arrangement from the earlier study was placed into a comprehensive two-dimensional gas chromatography instrument, with a wax-phase column in the second dimension. The unique location of peaks for each of the molecules in 2D space and patterns for the interconversion processes is interpreted phenomenologically.

Ab Initio and DFT Study of the Conformational Energy Hypersurface of Cyclic Gly-Gly-Gly

The multidimensional conformational potential energy hypersurface (PEHS) of cyclic Gly-Gly-Gly (1,4,7-triazonane-2,5,8-trione) was comprehensively investigated at the Hartree-Fock (RHF/6-31G(d)) level of theory. The equilibrium structures, their relative stability, and the transition state (TS) structures involved in the conformational interconversion pathways were analyzed. aug-cc-pVTZ//B3LYP/6-311++G** single point calculations predict a trans-cis-cis conformation as the energetically preferred form for this compound. However, all of the levels of theory employed here predicted that two forms, a trans-cis-cis and a cis-cis-cis (crown), of conformers contribute significantly to the equilibrium mixture at room temperature. The conformational interconversion between the global minimum and the symmetric cis-cis-cis crown form requires 12.49 kcal/mol at the RHF 6-31G(d) level of theory, whereas the conformational interconversion between the cis-cis-cis crown and cis-cis-cis boat form requires 18.70 kcal/mol. An exploratory topological analysis of the PEHS was also carried out. Our results allow us to form a concise idea about the internal intricacies of the PEHSs of these cyclic tripeptides, describing the conformations as well as the conformational interconversion processes in these hypersurfaces.

Ultrafast time‐resolved studies of the photochemistry of diazo carbonyl compounds

AbstractThe rich photochemistry of diazo carbonyl compounds in solution has been extensively studied by ultrafast transient absorption spectroscopy with UV–Vis and mid‐IR detection. Both, stepwise (carbene mediated) and concerted Wolff rearrangement (WR) mechanisms have been confirmed for cyclic and acyclic diazo carbonyl precursors. Cyclic diazo‐carbonyl compounds are structurally locked in a syn conformation and mainly follow the concerted mechanism, however, a stepwise pathway does slightly contribute to the overall WR process, contrary to Kaplan's rule. With acyclic diazo ester carbonyl compounds, the WR process is dominated by the stepwise mechanism. A carbene–carbene interconversion process and singlet to triplet carbene intersystem crossing (ISC) processes are discussed in this review. The growth of secondary species (cations, ylides, OH insertion product) emerging from an interaction between a singlet carbene and solvent molecules has been characterized by picosecond time‐resolved UV–Vis transient absorption spectroscopy. Carbene reactivity results in shortening of the singlet carbene lifetime relative to more inert solvents. The quantum yield of diazo decomposition can be deduced from partial ground state bleach recovery using ultrafast time‐resolved IR spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd.

Group 4 Post-metallocene Complexes Incorporating Tridentate Silyl-Substituted Bis(naphthoxy)pyridine and Bis(naphthoxy)thiophene Ligands: Probing Systems for “Oscillating” Olefin Polymerization Catalysis

New bulky silyl ortho-substituted tridentate 2,6-bis(naphthol)pyridine ({ONOSiR3}H2, SiR3 = SiPh3, SiMe2tBu) and 2,5-bis(naphthol)thiophene ({OSOSiPh3}H2) pro-ligands were synthesized via a four-step approach. The solid-state structures of pro-ligands {ONOSiPh3}H2 (3a) and {OSOSiPh3}H2 (3b) were established by X-ray diffraction analysis. Both types of ligands were introduced onto group 4 metal centers (M = Ti, Zr, Hf) using straightforward one-step alkane, amine, or alcohol elimination protocols. Dibenzyl {ONOSiPh3}M(CH2Ph)2 (M = Ti, 4a; Zr, 5a; Hf, 6a) and {ONOSiMe2tBu}M(CH2Ph)2 (M = Ti, 4b; Zr, 5b), diamido {ONOSiPh3}Hf(NMe2)2 (7a and 7a·(NHMe2)), and di(isopropoxy) {ONOSiPh3}Ti(OiPr)2 (8a) complexes were authenticated using NMR spectroscopy and X-ray crystallography methods for some of them. In the solid state, complexes 4a, 4b, and 6a feature rac-like binding of the ligand, while ligands in complexes 5b and 7a·(NHMe2) are meso-like coordinated. The solution structures of 4b and 5b were investigated by VT NMR spectroscopy, which revealed that both complexes exist as rac and meso stereoisomers, which interconvert (activation parameters: 4b, ΔH⧧ = 12.9(7) kcal·mol−1 and ΔS⧧ = −3(1) cal·mol−1·K−1; 5b, ΔH⧧ = 13.4(8) kcal·mol−1 and ΔS⧧ = −7(1) cal·mol−1·K−1). A mechanism for this interconversion process, implying straightforward racemization, was proposed on the basis of DFT computations at the B3LYP (BP86) level, with computed activation barriers for Ti, Zr, and Hf complexes of 11.4 (10.1), 12.5 (11.2), and 12.2 (11.1) kcal·mol−1, respectively. The catalytic activity of dibenzyl and diamido precursors in homopolymerization of propylene and ethylene, upon activation with MAO, “dried-MAO”, and [Ph3C](B(C6F5)4]/Al(iBu)3, has been explored as well.

Ab Initio Excited State Properties and Dynamics of a Prototype σ-Bridged-Donor−Acceptor Molecule

The photophysical and dynamical properties of the donor-(sigma-bridge)-acceptor molecule N-phenylpiperindone-malondinitrile are investigated by second-order approximate coupled cluster (CC2) and time-dependent density functional theory (TDDFT). The study is based on optimized equilibrium geometries for ground and excited states as well as on ab initio molecular dynamics simulations. While CC2 and DFT both predict ground state geometries that are consistent with the crystal structure, equilibrium geometries for the fluorescent charge transfer (CT) state are qualitatively different between CC2 and TDDFT. CC2 reproduces the experimental results for vertical excitations (within 0.3 eV) and provides an orbital assignment of the experimental absorption bands that is supported by experiments. Using CC2, a good agreement is also found for fluorescence energies (within 0.1-0.6 eV). At contrast, CT absorption and fluorescence energies are strongly underestimated by TDDFT using the semi-local functional PBE but improved agreement is found for the hybrid functional PBE0. However, for both functionals, TDDFT fails to predict an equilibrium geometry of the intradonor excited state because of mixing between this state and an artificially low-lying CT state during the optimization. This is an example where the well documented CT failure of TDDFT affects properties of other locally excited states. The minimum of the intradonor locally excited state was therefore only located by the CC2 method. The internal conversion (IC) process from a locally excited donor state to the CT state is simulated by excited state ab initio molecular dynamics based on CC2 and where nonadiabatic transitions are described using the Landau-Zener approximation. We find the IC process to occur a few tens of femtoseconds after excitation. The simulation provides a detailed description of the atomic rearrangements in electron donor and acceptor that drive the interconversion process.

Determination of enantiomerization barriers of hypericin and pseudohypericin by dynamic high‐performance liquid chromatography on immobilized polysaccharide‐type chiral stationary phases and off‐column racemization experiments

Direct enantiomer separation of hypericin, pseudohypericin, and protohypericin was accomplished by high-performance liquid chromatography (HPLC) using immobilized polysaccharide-type chiral stationary phases (CSPs). Enantioselectivities up to 1.30 were obtained in the polar-organic elution mode whereby for hypericin and pseudohypericin Chiralpak IC [chiral selector being cellulose tris(3,5-dichlorophenylcarbamate)] and for protohypericin Chiralpak IA (chiral selector being the 3,5-dimethylphenylcarbamate of amylose) gave favorable results. Enantiomers were distinguished by on-line electronic circular dichroism detection. Optimized enantioselective chromatographic conditions were the basis for determining stereodynamic parameters of the enantiomer interconversion process of hypericin and pseudohypericin. Rate constants delivered by computational simulation of dynamic HPLC elution profiles (stochastic model, consideration of peak tailing) were used to calculate averaged enantiomerization barriers (DeltaG(enant)(#)) of 97.6-99.6 kJ/mol for both compounds (investigated temperature range 25-45 degrees C). Complementary variable temperature off-column (i.e., in solution) racemization experiments delivered DeltaG(enant)(#) = 97.1-98.0 kJ/mol (27-45 degrees C) for hypericin and DeltaG(enant)(#) = 98.9-101.4 kJ/mol (25-55 degrees C) for pseudohypericin. An activation enthalpy of DeltaH(#) = 86.0 kJ/mol and an activation entropy of DeltaS(#) = -37.7 J/(K mol) were calculated from hypericin racemization kinetics in solution, whereas for pseudohypericin these figures amounted to 74.1 kJ/mol and -82.6 J/(K mol), respectively. Although the natural phenanthroperylene quinone pigments hypericin and pseudohypericin as well as their biological precursor protohypericin are chiral and can be separated by enantioselective HPLC low enantiomerization barriers seem to prevent the occurrence of an excess of one enantiomer under typical physiological conditions--at least as long as stereoselective intermolecular interactions with other chiral entities are absent.

The stereodynamics of 1,2‐dipropyldiaziridines

N-alkylated trans-diaziridines are an intriguing class of compounds with two stereogenic nitrogen atoms which easily interconvert. In the course of our investigations of the nature of the interconversion process via nitrogen inversion or electrocyclic ring opening ring closure, we synthesized and characterized the three constitutionally isomeric diaziridines 1,2-di-n-propyldiaziridine 1, 1-isopropyl-2-n-propyldiaziridine 2, and 1,2-diisopropyldiaziridine 3 to study the influence of the substituents on the interconversion barriers. Enantiomer separation was achieved by enantioselective gas chromatography on the chiral stationary phase Chirasil-beta-Dex with high separation factors alpha (1-isopropyl-2-n-propyldiaziridine: 1.18; 1, 2-diisopropyldiaziridine: 1.24; 100 degrees C 50 kPa He) for the isopropyl substituted diaziridines. These compounds showed pronounced plateau formation between 100 and 150 degrees C, and peak coalescence at elevated temperatures. The enantiomerization barriers DeltaG(double dagger) and activation parameters DeltaH(double dagger) and DeltaS(double dagger) were determined by enantioselective dynamic gas chromatography (DGC) and direct evaluation of the elution profiles using the unified equation implemented in the software DCXplorer. Interestingly, 1-isopropyl-2-n-propyldiaziridine and 1,2-diisopropyldiaziridine exhibit similar high interconversion barriers DeltaG(double dagger) (100 degrees C) of 128.3 +/- 0.4 kJ mol(-1) and 129.8 +/- 0.4 kJ mol(-1), respectively, which indicates that two sterically demanding substituents do not substantially increase the barrier as expected for a distinct nitrogen inversion process.

Structural and dynamic characterization of the upper part of the HIV-1 cTAR DNA hairpin

First strand transfer is essential for HIV-1 reverse transcription. During this step, the TAR RNA hairpin anneals to the cTAR DNA hairpin; this annealing reaction is promoted by the nucleocapsid protein and involves an initial loop–loop interaction between the apical loops of TAR and cTAR. Using NMR and probing methods, we investigated the structural and dynamic properties of the top half of the cTAR DNA (mini-cTAR). We show that the upper stem located between the apical and the internal loops is stable, but that the lower stem of mini-cTAR is unstable. The residues of the internal loop undergo slow motions at the NMR time-scale that are consistent with conformational exchange phenomena. In contrast, residues of the apical loop undergo fast motions. The lower stem is destabilized by the slow interconversion processes in the internal loop, and thus the internal loop is responsible for asymmetric destabilization of mini-cTAR. These findings are consistent with the functions of cTAR in first strand transfer: its apical loop is suitably exposed to interact with the apical loop of TAR RNA and its lower stem is significantly destabilized to facilitate the subsequent action of the nucleocapsid protein which promotes the annealing reaction.

Secretory proteins of human seminal vesicles and their relationship to lipids and sugars: Sekretorische Proteine der menschlichen Bläschendrüse und ihre Beziehungen zu Lipiden und Zuckern

Proteins secreted by human seminal vesicles are strongly positively charged. Cellulose acetate electrophoresis show how the presence of two protein bands of vesicular origin (N3 and N4). When studied on SDS-PAGE there are three main bands of molecular weight 67, 45 and 40 kDa, respectively. These proteins may be separated by a chromatographic process using gel filtration on Sephadex G 25 M and ion exchange chromatography on CM and SP Sephadex C 50. Fructose, secreted by seminal vesicles, is excreted with specific proteins and these complexes take part to coagulum formation. During liquefaction glucose appears progressively and fructose is released from complexes with proteins. Interconversion processes that transform fructose into glucose, originate from prostatic secretion. In man, the liquefaction process seems to be not due to proteolysis, but by the way of other mechanisms that transform vesicular proteins of very high molecular weight into sub-units with lower molecular weights in the first minutes after ejaculation. In species other than man, i.e. lemurian, fructose takes part in the coagulation process with other components (albumin, ions, -SH groups). Cholesterol appears to be in relation with proteins which have high molecular weights. Half of phospholipid content of seminal plasma is probably free. Incubation of seminal plasma with spermatozoa show that these cells use triglycerides for their metabolism. The ratio between cholesterol and phospholipids is an important marker for the capacitation-decapacitation process.

Direct Arylation Mediated by Palladium Complexes with Rigid Phosphine-Functionalized N-Heterocyclic Carbenes

New phosphine-functionalized N-heterocyclic carbene ligand precursors (L1H·I and L2H·I) were prepared. The former compound contains a PPh2 moiety, whereas the latter one has a more electron-donating PCy2 group. A reaction of L1H···I with PdCl2 in the presence of base afforded the complex PdL1ClI. An interconversion process between the two structural isomers of PdL1ClI was observed by variable-temperature NMR. The coalescence temperature (Tc) is at 368 K with the free energy of activation (ΔG⧧) found to be 68.9 kJ mol−1. A similar reaction of L2H·I with PdCl2 produced a mixture of PdL2ClI, PdL2Cl2, and PdL2I2. Unlike PdL1ClI, PdL2ClI undergoes a much faster exchange between the two structural isomers. Pure PdLI2 (L = L1 and L2) can be obtained by adding NaI in the reaction mixture to facilitate ligand exchange. [PdL(CH3C≡N)2](BF4)2 were also prepared straightforwardly by salt metathesis reactions. In total, seven new palladium complexes of L were structurally characterized, and in each of these structures an anagostic interaction exists between the palladium center and one of the diastereotopic methylene protons. The interaction also exists in solution, as evidenced by the downfield NMR shift of the proton. The new complexes PdLI2 and [PdL(CH3C≡N)2](BF4)2 show mediocre activities in benchmark Suzuki coupling reactions under conventional and microwave heating. They are, however, highly promising in mediating direct arylation of phenyl halides and diphenylacetylene, affording 9-benzylidene-9H-fluorene in good yields.

Dynamic 1H NMR study around the heteroaryl–carbon and carbon–carbon single bonds and also around carbon–carbon double bond in a particular phosphorous ylide involving a 2-methyl indole

For the first time, a series of separate dynamic 1H NMR effects are reported at different temperatures within a particular phosphorous ylide involving a 2-methyl indole namely dimethyl 2( N-2-methyl indole-1-yl)-3-(triphenyl phosphoran ylidene) butandioate. These effects are attributed to restricted rotation around the heteroaryl–carbon and carbon–carbon single bonds and also around carbon–carbon double bond. Rotational energy barrier (Δ G #) for their interconversion process of rotational isomers equals (55.33, 49.91 and 70.16) ± 2 kJ mol −1, respectively.

Mechanism of action of cyclophilin A explored by metadynamics simulations

Peptidyl prolyl isomerases (PPiases) are ubiquitous enzymes that catalyze the interconversion of the cis and trans isomers of the peptidyl prolyl bond. Their action is crucial in several biological processes as, for instance, in cellular signalling and in the onset of several diseases. In the HIV-1 capside protein (CA), such process takes place in the uncoating and recruitment of the virion and is catalyzed by cyclophilin A (CypA). Previous studies identified several residues that play an important role in the trans/cis interconversion process. However, the role of some active site residues remains still obscure, since their catalytic importance depend crucially on the stabilization of both ground and transition states. Here, we report the results of classical AMBER99 calculations on a substrate fragment of the capside protein (the /HAGPIA/ peptide) in aqueous solution and in complex with CypA. By applying replica exchange metadynamics, we calculate the free energy profile of the isomerization process in both cases as a function of several reaction coordinates. We find that CypA catalyzes only one isomerization pathway in the trans-to-cis direction and enhances the stability of a particular cis conformer. Based on our computational results, we propose a novel hypothesis for the working mechanism of cyclophilin A that explains, for the first time, all the available data and awaits further experimental tests.

Solution Structure and Dynamics, Stability, and NIR Emission Properties of Lanthanide Complexes with a Carboxylated Bispyrazolylpyridyl Ligand

The complexation behavior of the ligand 2,6-bis{3-[N,N-bis(carboxymethyl)aminomethyl]pyrazol-1-yl}-pyridine, L, toward lanthanide cations was investigated throughout the series. Potentiometric titration experiments on L (0.1 M KCl) revealed the presence of four protonation steps in the 2-12 pH domain, associated with the protonation of the two tertiary amine nitrogen atoms and with two of the four carboxylate functions. The stability constants for the formation of the [LnL](-) complexes (Ln = La, Nd, Eu, Ho, and Lu) were determined in water and evidenced a hill-shaped complexation trend along the series, with log K increasing from 14.56(9) (La) to 16.68(2) (Ho) and decreasing to 15.42(2) (Lu). Geometry optimizations showed the [LnL](-) complexes (Ln = La, Nd, Eu, Ho, Yb, and Lu) adopting a C(2) symmetry with the symmetry axis going through the metal atom and the nitrogen atom of the central pyridine ring, leading to the presence of Delta and Lambda helical enantiomers. Analysis of the calculated Ln-O and Ln-N bond lengths showed a marked deviation from the expected values at the end of the series, which accounts for the observed decreased complexation affinity. (1)H and (13)C NMR experiments in D(2)O (room temperature) showed the shortening of the bond distances in [LnL](-) complexes from La to Lu to be accompanied by a rigidification of the structure, leading to a decreased C(2) symmetry for the Lu complex compared to C(2v) for La. This decreased symmetry was attributed to a slow Delta <--> Lambda interconversion that was followed by variable-temperature (13)C NMR experiments on the Lu complex. The activation parameters determined by line broadening analysis for this interconversion process point to an associatively assisted interconversion process. The (1)H NMR spectrum of the paramagnetic [YbL](-) complex was investigated in D(2)O, and a lanthanide induced shift analysis showed good agreement between the observed paramagnetic chemical shifts and those calculated from the DFT optimized structures using a dipolar model, especially when solvent effects are taken into account. The UV-vis absorption and near-infrared luminescence spectra of the Pr, Nd, Er, and Yb complexes were measured in water and showed the complexation pocket provided by the ligand to be well-suited for the protection of the cations, all of them displaying typical Ln-centered emission spectra, the Yb complex having a relatively long lifetime of 3.0 micros in water.

Synthesis, spectroscopy, computational study and prospective biological activity of two novel 1,3,2-diazaphospholidine-2,4,5-triones

The preparation of two new 1,3,2-diazaphospholidine-2,4,5-triones is reported. Thus, 2-chloro-1,3,2-diazaphospholidine-2,4,5-trione [ClP(O)(NHC(O)C(O)NH) ( I)] and 2-benzylamino-1,3,2-diazaphospholidine-2,4,5-trione [C 6H 5CH 2NHP(O)(NHC(O)C(O)NH) ( II)] have been synthesized by the reaction of POCl 3 with the corresponding carboxylic diamide salts. The characterization of the compound I was performed by multinuclear ( 1H, 13C, 31P) NMR and FTIR spectroscopies, elemental analysis and also mass spectrometry. Both compounds show two signals at room temperature in the low field region of the 1H NMR spectrum, which collapsed to a single peak when the temperature is increased. Dynamic NMR ( 1H DNMR) and quantum chemical studies were performed to gain insight from this conversion process. The free activation energies, calculated at the coalescence temperatures are 18.51 and 17.45 kcal/mol for compounds ( I) and ( II), respectively, which are associated with a tautomeric interconversion process, most likely between the lactam and lactim forms. The relative energy, molecular geometry and vibrational properties of several plausible tautomers were analyzed by using quantum chemical calculations at the HF/6-311G** and B3LYP/6-311++G** levels of the theory. The nuclear magnetic shielding tensors have been calculated for both tautomeric forms using the gauge independent atomic orbital (GIAO) method at the B3LYP/6-311++G(3df,2p) level of approximation. A biological activity prediction using the PASS software shows that compound ( I) can be characterized by a superb anti-HIV activity whereas compound ( II) is a very good antineoplastic.

Solid-state electrochemistry of LDH-supported polyaniline hybrid inorganic–organic material

The solid-state electrochemistry of a Zn–Al layered double hydroxide-supported polyaniline material (LDH-PANI) in contact with aqueous electrolytes is described. Interconversion processes between different forms (emeraldine, protoemeraldine, leucoemeraldine, nigraniline and pernigraniline) of the LDH-supported polyaniline units are involved in redox processes. This material exhibits significant variations of impedance upon application of different conditioning potentials, acting as an electrochemical frequency filter. Using Fe (CN) 6 4 - as redox probe, LDH-PANI can be used as a chemical–electrochemical information processing system equivalent to different combinational logic circuits integrating AND, NOT and OR gates.

The interconversion mechanism between TcO3+ and TcO2 + core of 99mTc labeled amine-oxime (AO) complexes

Density functional theory, employing B3LYP/DZVP and B3LYP/6-31G*(LANL2DZ for Tc), has been used to investigate the interconversion mechanism between formal TcO3+ and TcO2 + core of 99mTc labeled amine-oxime (AO) complex, in which two water molecules have been used to simulate the possible interconversion process. The obtained results indicate that the length of amine-amine hydrocarbon backbone of AO ligand has a significant influence on the stabilities of formal TcO3+ and TcO2 + complex. The interconversion process between TcO–BnAO and TcO2–BnAO has been amply discussed, which releases the useful information for the further investigation of the structure and hypoxic mechanism of 99mTc-HL91.