True and false chirality and parity violation

Systems that exhibit distinguishable enantiomers under space inversion are not necessarily chiral. A new definition of chirality is proposed that enables true and false chirality to be distinguished. This definition is reinforced by a consideration of parity violation, which lifts only the degeneracy of the space-inverted enantiomers of truly chiral systems.     

The enantio-preferential stabilization of D-ribose from parity violation

Ab initio calculations show that a biologically important sugar, D-ribose, is energetically stabilized relative to its unnatural Lenantiomer by the parity-violating weak interactions. This preferential stabilization may account for the exclusive adoption of Dribose rather than its L-enantiomer in the RNA of terrestrial organisms.     

Streaming potential measurements as a characterization method for nanofiltration membranes

The streaming potentials of two different nanofiltration membranes were studied with several electrolyte solutions to investigate the influence of salt type and concentration on the zeta potential and kinetic surface charge density of the membranes. The zeta potentials decreased with increasing salt concentration, whereas the kinetic surface charge densities increased. The kinetic surface charge densities could be described by Freundlich isotherms, except in one case, indicating that the membranes had a negligible surface charge. The kinetic surface charge density observed was caused by adsorbed anions. Salt retention measurements showed different mechanisms for salt separation for the two investigated membranes. One membrane showed a salt retention that could be explained by a Donnan exclusion type of separation mechanism, whereas for the other membrane the salt rejection seemed to be a combination of size and Donnan excluion. Comparing the results obtained by the streaming potential measurements with those of the retention measurements, it could be concluded that the membrane with the highest kinetic surface charge density showed the Donnan exclusion type of separation, whereas the membrane with the lower surface charge density showed a separation mechanism that was not totally determined by Donnan exclusion, size effects seemed to play a role as well.     

Lactose-appended schizophyllan is a potential candidate as a hepatocyte-targeted antisense carrier

A schizophyllan (beta-1,3-glucan) derivative carrying lactose-appendages prepared by reductive amination can form stable macromolecular complexes with polynucleotides, shows excellent affinity with a lactose-binding lectin, and effectively mediates gene transfection into hepatocytes.     

Stereomutation tunneling switching dynamics and parity violation in chlorineperoxide Cl-O-O-Cl

In a search for efficient spectroscopic avenues toward experiments on molecular parity violation, we investigate the stereomutation tunneling processes in the axially chiral chlorine isotopomers of Cl2O2 by the quasi-adiabatic channel reaction path Hamiltonian (RPH) approach and the corresponding parity violating potentials by means of quantum chemical calculations including our recently developed Multiconfiguration linear response (MC-LR) approach to electroweak quantum chemistry. The calculated ground-state torsional tunneling splittings for all isotopomers of Cl2O2 are much smaller than the parity violating energy differences Delta(pv)E between the enantiomers of these molecules and therefore parity violation is predicted to dominate the quantum dynamics of stereomutation at low energies. We also compare these with torsional ground-state tunneling splittings and parity violating energy differences of the whole series of axially chiral HXYH(+) isotopomers (with X, Y= Cl(+), O, S, Se, Te). A comparison with our previous results for the homologous molecule Cl2S2 shows that for Cl2O2 a spectroscopic high-resolution analysis should be easier and the energy region of large tunneling splittings should be more easily accessible by IR excitation. We thus propose a scheme using "tunneling switching" with vibrational excitation in order to carry out the measurement of time-dependent parity violation in superposition states of initially well-defined parity. We discuss the advantages and drawbacks of such an experiment that can be carried out entirely in the IR spectral range (for Cl2O2 or related molecules).     

Large parity violation effects in the vibrational spectrum of organometallic compounds

Large parity violation effects of the order of 1 Hz are predicted for the vibrational spectrum of two organometallic species, Os(eta5-C5H5)(=CCl2)Cl(PH3) and Re(eta5-Cp*)(=O)(CH3)Cl. It should therefore be possible to detect such effects in molecules by high-resolution spectroscopy for the first time.     

The effect of parity violation on kinetic models of enantioselective autocatalysis

A detailed analysis of enantioselective autocatalytic reaction models is carried out using both deterministic and stochastic approaches. The models include the small differences between the total energies of enantiomers (DeltaE(PV) approximately 10(-13) J mol(-1)) that arise due to parity violation. Different possible orders of autocatalysis are considered, and the reasons why the predictions of the stochastic and deterministic approaches are different under certain conditions are explored. The continuous time discrete state (CDS) stochastic approach is clearly superior to the deterministic approach. It is concluded that the small difference between enantiomers caused by DeltaE(PV) cannot be amplified under conditions reasonable for the generation of biological chirality. It also seems highly unlikely that biological chirality was determined by any intrinsic difference between enantiomers.     

Mass cultivation of various algal species and their evaluation as a potential candidate for lipid production

Microalgae have been proposed as a promising source for biodiesel production. Focusing on algal strains for biodiesel production, efforts should be made to search new strains. Experiments were carried out to investigate the effects of growth parameters (nutrients, pH, light, aeration and temperature) and the oil percentage of eight algal strains (Chlorella sp., Cladophora sp., Hydrodictylium sp., Oedogonium sp., Oscillatoria sp., Spirogyra sp., Stigeocolonium sp., Ulothrix sp.). Results show that 6.5–7.5 is the optimum pH for the growth of all algal species. Temperature showed a greater variation (25°40°C). Ulothrix sp. gave more biomass productivity and is the most suitable strain for biodiesel production due to higher oil percentage (62%). Least biomass production was observed for Stigeocolonium sp. and least oil content was obtained from Hydrodictylium sp. It was observed that among these eight algal strains for biodiesel production, Ulothrix and Chlorella are the most promising algae species.     

Lifetime measurements of some TmI odd parity levels

Eleven new lifetimes of odd parity excited energy levels in four configurations: 4f ¹² 5d 6s6p, 4f ¹² 6s² 6p, 4f ¹³ 5d6s and 4f ¹³ 6s7s of atomic thulium have been mesured with atomic-beam laser spectrocopy. Two pulsed dye lasers are used for stepwise excitation and the time-resolved fluorescence decay was used to determine lifetime values. The accuracy of the measurements is about 10%.     

Steps towards molecular parity violation in axially chiral molecules. I. Theory for allene and 1,3-difluoroallene

In view of exploring possibilities for an experimental investigation of molecular parity violation we report quantum-chemical calculations of the parity-conserving and parity-violating potentials in the framework of electroweak quantum chemistry in allene C3H4 and 1,3-difluoroallene C3H2F2, which is nonplanar and axially chiral in the electronic ground state but expected to be nearly planar and achiral in several electronically excited states. The parity-violating potentials Epv for allene and 1,3-difluoroallene calculated with the multiconfiguration linear-response (MC-LR) approach of Berger and Quack [J. Chem. Phys. 112, 3148 (2000)] show qualitatively similar behavior as a function of torsional angle tau with maximum values of about 0.5 pJ mol(-1) for C3H4 and 2 pJ mol(-1) for C3H2F2. However, in the latter case they are asymmetrically shifted around tau=90 degrees , with a nonzero value at the chiral equilibrium geometry resulting in a parity-violating energy difference between enantiomers DeltapvE=Epv(P)-Epv(M)=1.2 pJ mol(-1) (equivalent to about 10(-13) cm(-1)). The calculated barrier heights corresponding to the nonrigid (multiple, and in part chiral) transition states in 1,3-difluoroallene fall in the range of 180-200 kJ mol(-1). These high barriers result in hypothetical tunneling splittings much smaller than DeltapvE and thus parity violation dominates over tunneling for the stereomutation dynamics in 1,3-difluoroallene. Therefore, DeltapvE is predicted to be a spectroscopically measurable energy difference. Two of the lower excited electronic states of C3H2F2 (1A and 3A) are calculated to be planar or quasiplanar, allowing, in principle, for spectroscopic state selection of states of well-defined parity. The results are discussed in relation to possible schemes of measuring parity violation in chiral molecules.     

High resolution spectroscopy of methyltrioxorhenium: towards the observation of parity violation in chiral molecules

Originating from the weak interaction, parity violation in chiral molecules has been considered as a possible origin of biohomochirality. We have proposed the observation of molecular parity violation using the two-photon Ramsey fringes technique on a supersonic beam. As a first step in this direction, a detailed spectroscopic study of methyltrioxorhenium (MTO) has been undertaken. It is an ideal test molecule as the achiral parent molecule of chiral candidates for a parity violation experiment. For the (187)Re MTO isotopologue, a combined analysis of Fourier transform microwave and infrared spectra as well as ultra-high resolution CO(2) laser absorption spectra enabled the assignment of 28 rotational lines and 71 rovibrational lines, some of them with a resolved hyperfine structure. A set of spectroscopic parameters in the ground and first excited state, including hyperfine structure constants, was obtained for the ν(as) antisymmetric Re=O stretching mode of this molecule. This result validates the experimental approach to be followed once a chiral derivative of MTO is synthesized, and shows the benefit of the combination of several spectroscopic techniques in different spectral regions, with different set-ups and resolutions. The first high resolution spectra of jet-cooled MTO, obtained on a set-up being developed for the observation of molecular parity violation, are shown, which constitutes a major step towards the targeted objective.     

Honey as a candidate reference material for trace elements.

The feasibility of producing and certifying new certified reference materials (CRMs) for trace elements in honey was investigated. Preliminary steps for preparation of candidate materials are performed at the Institute for Reference Materials and Measurements, Joint Research Centre of the European Commission (EC-JRC-IRMM). Two different types of honey, Acacia and Eucalyptus, were tested for determination of 10 trace elements. To each type of honey was added a given amount of high purity deionized water to obtain aqueous solutions with an acceptable degree of homogeneity which would require only minimal manipulation before analysis. Average values obtained for the trace elements by means of inductively coupled plasma-based techniques were as follows (in microg/ kg +/- SD): Acacia honey, As, 1.10+/-0.20; Cd, 0.328+/-0.035; Cr, 1.90+/-0.22; Cu, 67.0+/-5; Fe, 215+/-30; Hg, < 0.75; Mn, 82.1+/-6.2; Ni, 21.0 3.0; Pb, 2.30+/-0.25; Se, 9.10+/-1.2; Zn, 167+/-22; Eucalyptus honey, As, 5.99+/-0.10; Cd, 0.592+/-0.074; Cr, 1.50+/-0.07; Cu, 219 24; Fe, 1008+/-114; Hg, <0.75; Mn, 1009+/-51; Ni, 11.3+/-1.5; Pb, 5.00+/-0.40; Se, 5.60+/-0.91; Zn, 791+/-91. When these 2 pilot materials are ready, the certification project will be launched in full compliance with current rules set by EC-JRC-IRMM. If the project is successful, the new CRMs will be put primarily at the disposal of the National Reference Laboratories for trace elements.     

Crosslinked and quaternized poly(4-vinylpyridine)/polypyrrole composite as a potential candidate for the detection of low humidity

Poly(4-vinylpyridine) was crosslinked and quaternized with 1,4-bromobutane to form a polyelectrolyte humidity sensitive film on an interdigitated gold electrode, which was further coated with a layer of polypyrrole by a facile method of vapor phase polymerization. The composite so prepared was characterized by UV-vis spectroscopy and scanning electron microscopy. The investigations on the humidity sensitive properties of the composite revealed that it exhibited an impedance as low as 10(5) Omega even at 0%RH due to the existence of intrinsic conducting polypyrrole, thus conquering the difficulties in measuring low humidity with resistive-type humidity sensors. The impedance of the composite changed linearly with humidity in the range of 0-60%RH with good sensitivity. In addition, its response time (t(90%)) for adsorption and desorption between 33% and 97%RH was estimated to be 33 s and 110 s, respectively, and a hysteresis of 5%RH was observed. All these suggest it is promising as a sensitive material for low humidity detection. The effect of concentration and ratio of oxidizing agent to doping agent, polymerization temperature of pyrrole on the humidity sensitive properties of the composite have been investigated. A sensitive mechanism of the composite was proposed by taking into account the contribution of both the intrinsic electronic conduction and ionic conduction.     

Hydrophobic interaction and hydrogen bonding cooperatively confer a vancomycin hydrogel: a potential candidate for biomaterials

Antibiotic hydrogels based on a vancomycin (Van) derivative, formed by self-assembling Van-pyrene (1) in water, using the pi-pi interaction of pyrene moieties and hydrogen bonding of Vans, promise a new way to make novel biomaterials.     

Mimotopes of viral antigens and biologically important molecules as candidate vaccines and potential immunotherapeutics

Antigen recognition by antibodies or ligand-receptor interactions involve small areas of the molecule named epitopes that are normally conformational in nature. The availability of combinatorial peptide libraries has provided a powerful tool for selecting novel sequences which mimic conformational epitopes (mimotopes) either structurally and/or immunologically. These mimotopes can be particularly useful in a number of situations, including: the development of vaccines against tumors, infectious diseases or allergic conditions; the design of molecules which can act as agonists or antagonists of various biologically-important molecules; and for the development of diagnostic assays. This article reviews the authors work on the application of combinatorial peptide libraries to identify mimotopes of protective B-cell epitopes from various pathogens, and the search for molecules able to block the biological activities of TNF-alpha, a cytokine which plays a key role in inflammation.     

Novel application of LiCoO_2 as a high-performance candidate material for supercapacitor

Electrochemical performances of LiCoO2 as a candidate material for supercapacitor are systematically investigated. LiCoO2 nanomaterials are synthesized via hydrothermal reaction with consequent calcination process. And the particle size increases as the calcination temperature rises.LCO-650 sample with the largest particle size displays the maximum capacitances of 817.5 Fg-1with the most outstanding capacity retention rate of 96.8% after 2000 cycles. It is shown that large particle size is beneficial to the electrochemical and structural stability of Li CoO2 materials. We speculate that the micron-sized waste LiCoO2 materials have great potential for supercapacitor application. It may provide a novel recovered approach for spent LIBs and effectively relieve the burdens on the resource waste and environment pollution.     

An efficient heteropolyacid catalyzed acylation of pyruvate esters to alpha-acyloxyacrylate esters as potential candidate monomers for bio-based polymers

Alpha-acyloxyacrylate esters were efficiently synthesized from pyruvate esters and carboxylic anhydrides under mild conditions. These esters are potential candidate monomers for bio-based polymers with high durability and transparency. Tungsten-based Keggin type heteropolyacids, especially H(3)PW(12)O(40), worked more effectively as catalysts for this reaction than other typical acids.