Light particles emission and incomplete fusion in heavy ion collisions

Light particles emission in heavy-ion collisions is considered in terms of direct-reaction mechanisms. The extreme high-energy part of the inclusive spectrum of light particles is shown to arise essentially from the stripping mechanism while the usually observed maximum of the spectrum is formed by a superposition of several mechanisms. The significance is emphasized of the heavy-fragment stripping in the synthesis of the exotic superheavy nuclei.     

Positron annihilation in dextro and laevo amino acid

High-precision positron lifetime spectra in tryptophan do not confirm the pronounced asymmetries in the interaction of positrons from radioactive sources with the d and l forms that were reported earlier and quoted as a cause for the the evolution of living matter with laevo amino acids.     

Radical chemistry of glucosamine naphthalene acetic acid and naphthalene acetic acid: a pulse radiolysis study

Free radical‐induced oxidation reactions of glucosamine naphthalene acetic acid (GNaa) and naphthalene acetic acid (Naa) have been studied using pulse radiolysis. GNaa was synthesized by covalently attaching Naa on glucosamine. Hydroxyl adduct (from the reaction of hydroxyl radicals (^●OH) at the naphthalene ring) was identified as the major transient intermediate (suggesting that the ^●OH reaction is on the naphthalene ring) and is characterized by its absorption maxima of 340 and 400 nm. Both GNaa and Naa undergo similar reaction pattern. The bimolecular rate constants determined for the reactions are 4.8 × 10⁹ and 8.9 × 10⁹ dm³ mol^?1 s^?1 for GNaa and Naa respectively. The mechanism of reaction of ^●OH with GNaa was further confirmed using steady‐state method. Radical cation of GNaa was detected as an intermediate during the reaction of sulfate radical (SO₄^●?) with GNaa (k₂ = 4.52 × 10⁹ dm³ mol^?1 s^?1). This radical cation transforms to a ^●OH adduct at higher pH. The radical cation of GNaa is comparatively long lived, and a cyclic transition state by neighboring group participation accounts for its stability. The oxy radical anion (O^●?) reacts with GNaa (k₂ = 1.12 × 10⁹ dm³ mol^?1 s^?1) mainly by one‐electron transfer mechanism. The reduction potential values of Naa and GNaa were determined using cyclic voltammetric technique, and these are 1.39 V versus NHE for Naa and 1.60 V versus NHE for GNaa. Copyright © 2014 John Wiley & Sons, Ltd.     

Light and heavy hadron masses in a relativistic quark potential model with diquark clustering

Meson masses are calculated in the quark model with a phenomenological spin-dependent potential of form motivated by QCD. For comparison, the potential is used in two different wave equations, both of which incorporate the feature of relativistic two-body kinematics. The masses of light and heavy pseudoscalar and vector mesons are calculated in the model with only a small number of adjustable parameters, and good qualitative agreement with experiment is obtained. The masses of diquarks are calculated without any additional parameters, using the same potential as for mesons except for a QCD color factor. Then baryon masses are calculated, also without additional parameters, in an approximation in which a baryon is a composite of a quark and a diquark. Again the results are in good qualitative agreement with experiment. Both wave equations yield similar solutions, although there are differences in detail. One distinctive feature of the model is that quark current masses are used as input, and effective constituent quark masses are obtained as a result of the calculation.     

New chromogenic substrates of human neutrophil cathepsin G containing non-natural aromatic amino acid residues in position P1 selected by combinatorial chemistry methods

Specificity of human cathepsin G was explored using combinatorial chemistry methods. Deconvolution of a tetrapeptide library, where 5-amino-2-nitrobenzoic acid served as a chromophore attached at the C-terminus, yielded the active sequence Phe-Val-Thr-Tyr-Anb^5,2-NH₂. This sequence was used for a second-generation library with the general formula Ac-Phe-Val-Thr-X-Anb^5,2-NH₂, where position X was replaced with several amino acids: l-pyridyl- alanine (Pal), 4-nitro-l-phenylalanine (Nif), 4-amino-l- phenylalanine (Amf), 4-carboxy-l-phenylalanine (Cbf), 4-guanidine-l-phenylalanine (Gnf), 4-methyloxycarbonyl- l-phenylalanine (Mcf), 4-cyano-l-phenylalanine (Cyf), Phe, Tyr, Arg and Lys. Specificity ligand parameters, k _cat and K _M, with human cathepsin G were determined for all chromogenic substrates synthesized. The highest value of the specificity constant (k _cat/K _M) was obtained for a substrate with the Gnf residue in position P₁. This peptide was 10 times more active than the second most active substrate which contained the Amf residue. The following order of potency was established: Gnf > > Amf > Tyr = Phe > Arg= Lys > Cyf. Substrate specificity for cathepsin G is greatly enhanced when an aromatic side chain and a strong positive charge are incorporated in residue P₁.     

Characterizing the fuel-specific combustion chemistry of acetic acid and propanoic acid: Laminar flame propagation and kinetic modeling studies

In order to study the combustion chemistry of carboxyl functionality, the laminar burning velocity of acetic acid/air and propanoic acid/air mixtures was investigated in a high-pressure constant-volume cylindrical combustion vessel at 423 K, 1 atm and equivalence ratios of 0.7–1.4. Experimental results reveal that the flame propagation of propanoic acid flame is much faster than that of acetic acid flame, especially under rich conditions, and the laminar burning velocity of propanoic acid/air mixtures peaks at richer conditions than that of acetic acid. The present theoretical calculations for the isomerization and decomposition of propanoic acid radicals indicate that the primary radical products are HOCO, H and C₂H₅, while those in acetic acid flame are CH₃ and OH based on previous studies. A kinetic model of the two acids was developed mainly based on previous and the present theoretical calculation results. It could reasonably capture the measured laminar burning velocities of acetic acid/air and propanoic acid/air mixtures in this work, as well as the previous experimental data in literature. Based on the present model, CH₃- and ketene-related pathways play an important role in acetic acid flames. Under rich conditions, ketene is mostly converted to CH₃ via CH₂CO+HCH₃+CO, and the chain-termination reaction of CH₃+H(+M)=CH₄(+M) is enhanced, which strongly inhibits the propagation of rich acetic acid flames. In contrast, C₂H₅ and ethylene chemistry play an important role in propanoic acid flames. Rich conditions promote the decomposition of C₂H₅, yielding ethylene and H, which can facilitate the flame propagation. This can explain the shift of the peak laminar burning velocity of propanoic acid/air mixtures towards a slightly richer condition compared with that of acetic acid/air mixtures.     

Swift heavy ion irradiation effects on carbonyl and trans-vinylene groups in high and low density polyethylene

In this work, we have studied the effects of swift heavy ion irradiation on the creation of new functional groups in high and low density polyethylene (HDPE and LDPE). Polymers were irradiated with different ions (6.77 MeV He and 47 MeV Li) and fluences. The induced changes were analyzed by Fourier transform infrared (FTIR) spectroscopy. Creation and damage cross sections for some groups were compared for two different types of PE.     

Differentiation of isomeric amino acid residues in proteins and peptides using mass spectrometry

Characterization and differentiation of isomers in biological macromolecules using mass spectrometry is one of the most significant challenges facing scientists in the field. The capability of high-resolution MS instruments along with the development of new fragmentation methods now provides the ability to indirectly differentiate between some isomers. This ability has enabled mass spectrometry to evolve into a multidisciplinary technique incorporating areas such as pharmaceutical research, proteomics, polymer science, medicine, environmental chemistry, and recently archeology. This article aims to review recent developments in mass spectrometry methodologies in the identification of structural and spatial isomers in biological macromolecules, such as aspartic acid and isoaspartic acid (Asp/IsoAsp), leucine and isoleucine (Leu/Ile), glutamic acid and γ-glutamic acid, and D/L enantiomers. ? 2012 Wiley Periodicals, Inc. Mass Spec Rev 31:609-625, 2012.     

EPR study of radiation-induced radicals in glutaric and amino acid derivatives in solid state

Gamma radiation-induced radicals of 2-methylglutaric acid (2MG), diethyl amino malonate hydrochloride (DEAMHCl), ethyl malonate monoamide have been investigated at room temperature by the electron paramagnetic resonance technique. The type of radicals formed and their room temperature stability were evaluated. Three different radicals have been detected. The free radicals formed in compounds were attributed to the HOOCCH₃?CH₂CH₂ COOH, CH₃?HCO₂CHNH₂COCH₂CH₃ HCl and NH₂COCH₂COO?HCH₃ radicals, respectively. The results were found to be in good agreement with the existing literature data and theoretical predictions conformation.     

Light charged particle emission in 485 MeV 56Fe + 197Au reactions: Correlations with heavy fragments and relationships to spin and lifetime

Emission of ⁴He and ¹H has been studied in reactions of 485 MeV ⁵⁶Fe + ¹⁹⁷Au, using low-threshold detector arrays for light charged particles, and two heavy-fragment trigger detectors placed at symmetrically opposite angles with respect to the beam direction. The light charged particles were measured both in singles and in coincidence with heavy products of deeply inelastic and fission reactions detected near the grazing angle. Statistical model analyses of the data show that most of the ⁴He/¹H intensity is due to evaporation from energy equilibrated emitters both in deeply inelastic and fission reactions. In deeply inelastic reactions, the observed ⁴He/¹H emission can be attributed to evaporation from the post-scission reactant-like products, while in fusion-like fission reactions evaporation from pre- and post-scission sources are observed in comparable amounts. Angle-integrated multiplicities for ₄He and ¹H are deduced for each source of emission, and are compared with results from similar systems. The experimental ⁴He/¹H multiplicity ratios indicate roughly equal probability for ⁴He and ¹H evaporation from a given excited source. The observation of pre-scission ⁴He/¹H in fusion-like fission reactions supports the notion that thermal equilibration and subsequent particle evaporation proceed more rapidly than the collective motions that drive the system toward fission. Conversely, the lack of appreciable ⁴He/¹H emission from pre-scission sources in deeply inelastic reactions implies that the interaction times are short compared to the time required for particle evaporation.     

QED corrections for the valence electron in the heavy and superheavy metal atoms from the 11 and 12 groups

The first-order QED corrections for valence electron are investigated for the neutral Ag, Rg and their neighbours of the Mendeleev Periodic Table within the framework of the Dirac-Hartree-Fock method. The including of SE effects in such procedure was done first for superheavy atoms. The obtained results provide the limit of the accuracy for the modern relativistic theoretical calculations for the superheavy elements and open the discussion about the accuracy of the QED corrections in the superheavy elements themselves.     

Lipid spin labeling and NMR study of interaction between polyadenylic acid: polyuridilic acid duplex and egg phosphatidylcholine liposomes. Evidence for involvement of surface groups of bilayer,phosphoryl groups and metal cations

Hydrophobic spin labeling of fatty acyl residues at 5-, 12- or 16-positions of phosphatidylcholine liposomes reveals the involvement of surface moieties of bilayer (up to fifth carbon atom of fatty acyl) into interaction with polyadenylic acid: polyuridilic acid duplex and magnesium ions.³¹P NMR spectra of this system demonstrate participation of nucleotide phosphoryl groups and metal cations in ternary complexation.     

Morphology and protonic conductivity of the polyurethanes with acid groups in the flexible segment

Thermal transitions, morphology and electric conductivity of polyurethanes that contain acid (COOH) groups bound to their polyether (poly(tetramethylene oxide)) chains and hard urethane segments of various length have been studied by means of calorimetry, wide- and small-angle X-ray scattering and a.c. conductivity in wide range of frequencies (0.1 Hz–1 MHz) and temperature (−100 to 100°C). It was shown that the polyurethanes are basically microphase-separated systems whose polyether-rich matrix contain from 20 to 25% of the hard urethane fragments. The protonic conductivity of the materials decreases with decreasing the polyether phase in the system.     

Advancements in tetronic acid chemistry. Part 2: Use as a simple precursor to privileged heterocyclic motifs

This work highlights the literature of one of the most valuable moieties in the field of organic chemistry. In this review, the chemistry of tetronic acid as a simple precursor to privileged heterocyclic motifs is described. The synthetic procedures of different fused heterocycles incorporating a furan moiety are described. Fused heterocycles are classified as bicyclic, tricyclic, tetracyclic and spiro-fused pyran derivatives.     

Metal/electrolyte surface chemistry: The adsorption of nitric acid and water on Ag(110)

The adsorption of HNO₃/H₂O mixtures on Ag(110) was investigated to learn more about the chemistry of the metal/electrolyte interface. The experiments were performed in ultrahigh vacuum (UHV) using thermal desorption spectroscopy (TDS), low energy electron diffraction (LEED), and electron stimulated desorption ion angular distribution (ESDIAD) over temperatures of 80–650 K and coverages of 0–10 monolayers (ML). As this is the first known study of HNO₃ in UHV, the mass spectrometer cracking pattern for HNO₃ is here reported. HNO₃ adsorbs irreversibly on the clean surface at 80 K and loses its acidic proton to form an adsorbed surface nitrate (NO₃) below 150 K. The saturation amount of adsorbed NO₃ is 0.4 ± 0.1 ML for which adsorption occurs in either a normal or split c(2 × 2) structure. N03 is stable on the surface up to 450 K beyond which it decomposes directly to gaseous NO₂ and NO and adsorbed atomic oxygen. NO₃ decomposition is first order with an activation energy E_a = 151±4 kJ mol⁻¹ and a pre-exponential factor of A = 10^15.4±0.4s⁻¹. NO₃ stabilizes adsorbed H₂O by about 8 kJ mol⁻¹ and is hydrated by as many as three H₂O molecules. Multilayers of HNO₃/H₂O desorb at 150–220 K and show evidence of extensive hydrogen bonding and hydration interactions. No evidence for HNO₃-induced corrosion or other surface damage was detected in any of these experiments.