Phase equilibrium measurements for semi-clathrate hydrates of the (CO2 + N2 + tetra-n-butylammonium bromide) aqueous solution system

The application of semi-clathrate hydrate formation technology for gas separation purposes has gained much attention in recent years. Consequently, there is a demand for experimental data for relevant semi-clathrate hydrate phase equilibria. In this work, semi-clathrate hydrate dissociation conditions for the system comprising mixtures of {CO₂ (0.151/0.399 mole fraction) + N₂ (0.849/0.601 mole fraction) + 0.05, 0.15, and 0.30 mass fraction tetra-n-butylammonium bromide (TBAB)} aqueous solutions have been measured and are reported. An experimental apparatus which was designed and built in-house was used for the measurements using the isochoric pressure-search method. The range of conditions for the measurements was from 277.1 K to 293.2 K for temperature and pressures up to 16.21 MPa. The phase equilibrium data measured demonstrate the high hydrate promotion effects of TBAB aqueous solutions.     

Metal-metabolomics of microalga Chlorella sorokiniana growing in selenium- and iodine-enriched media

The microalga Chlorella sorokiniana has been used to accumulate selenium and iodine from culture media enriched with these elements as a first stage in the production of supplemented foods. The microalgal colony was grown in a conventional culture medium containing iodine (KI) at concentrations in the range of 150?C4000 ??g mL^?1. Similar experiments were performed with selenium (SeO ₄ ^2? ) at concentrations in the range of 20?C500 ??g mL^?1. The concentration of iodine and selenium in the culture medium was analytically monitored daily and the viability of the colony was checked by biomass concentration measurement and by evaluation of the total content of chlorophyll and carotenoids. In addition, photosynthetic activity and the number of cells were also monitored. Iodine accumulation in the algal biomass increased rapidly with time and reached a steady state after 4 h of exposure. With Se exposure the colony viability decreased, although the culture grew well with concentrations of the element of 50 ??g mL^?1 in the culture medium; this experiment produced Se-enrichment in the alga (3 ??g g^?1) within 100 h. Sequential extraction of an algal pellet was performed in order to separate Se compounds according to their affinity with the following solvents: hot water to recover low molecular mass Se species, enzymatic extraction with driselase for species associated with the cell wall, sodium dodecyl sulphate (SDS) for water insoluble selenoproteins and, finally, enzymolysis with lipase and pronase that release and fragment residual selenoproteinsproducing compounds with low molecular mass. Size-exclusion chromatography (SEC) coupled with an ICP-MS detector showed the preponderance of Se-containing molecules with low molecular mass, possibly seleno-amino acids. Only a peak of low intensity located at 10 min was observed in the SDS extract that could be associated with a protein with molecular mass of 67 kDa. Finally, analysis of the aqueous extract of alga by reverse-phase chromatography with inductively-coupled plasma mass-spectrometry (RPC-ICP-MS) detection revealed the presence of selenocysteine (SeCys₂), selenomethylselenocysteine (SeMetSeCys), selenomethionine (SeMet), and Se(VI), particularly the last two species.     

Antioxidant activity of o-bisphenols: the role of intramolecular hydrogen bonding

A kinetic and thermodynamic investigation on the antioxidant activity of 2,2'-methylenebis(6-tert-butyl-4-methylphenol) (2), 2,2'-ethylidenebis(4,6-di-tert-butylphenol) (3), and 4,4'-methylenebis(2,6-di-tert-butylphenol) (4) are reported. EPR studies of the equilibration between 3 or 4 and a reference phenol, and the corresponding phenoxyl radicals, allowed us to determine the O-H bond dissociation enthalpy (BDE) of the O-H bond as 81.2 and 81.1 kcal/mol in 3 and 4, respectively. Despite this similarity, the absolute rate constants for the reaction with peroxyl radicals, determined by autoxidation studies under controlled conditions, indicate that the o-bisphenols 2 and 3 behave as excellent antioxidants while the p-bisphenol 4 is less effective by a factor of 64 and 22, respectively. FT-IR spectroscopy and product studies suggest that the very good antioxidant activity of the o-bisphenols largely arises from both the reduced steric crowding about the hydroxyl group and the stabilization of the aroxyl radical due to the formation of an intramolecular hydrogen bond between the residual OH and the oxygen radical center.     

JOC Recent Reviews, Number 81

Reviews are listed in order of appearance in the sources indicated. In multidisciplinary review journals, only those reviews which fall within the scope of this Journal are included. Sources are listed alphabetically in three categories: regularly issued review journals and series volumes, contributed volumes, and other monographs. Titles are numbered serially, and these numbers are used for reference in the index. Major English-language sources of critical reviews are covered. Encyclopedic treatises, annual surveys such as Specialist Periodical Reports, and compilations of symposia proceedings are omitted. This installment of Recent Reviews covers principally the early part of the 2006 literature. Previous installment: J. Org. Chem. 2006, 71(7), 2926-34.     

Yttrium-86 Is a Positron Emitting Surrogate of Gadolinium for Noninvasive Quantification of Whole-Body Distribution of Gadolinium-Based Contrast Agents

Gadolinium-based contrast agents (GBCAs) are used to provide diagnostic information in clinical magnetic resonance (MR) examinations. Gadolinium (Gd) has been detected in the brain, bone and skin of patients, months and years following GBCA administration, raising concerns about long term toxicity. Despite increased scrutiny, the concentration, chemical form and fate of the retained gadolinium species remain unknown. Importantly, the whole body biodistribution and organ clearance of GBCAs is poorly understood in humans. Gadolinium lacks suitable isotopes for nuclear imaging. We demonstrate that the yttrium-86 isotope can be used as a gadolinium surrogate. We show that Gd and their analogous Y complexes have similar properties both in solution and in vivo, and that yttrium-86 PET can be used to track the biodistribution of GBCAs over a two-day period.     

Studies on thermal,spectral, magnetic and biological properties of new Ni(II), Cu(II) and Zn(II) complexes with a bismacrocyclic ligand bearing an aromatic linker

Novel complexes of M₂LCl₄·nH₂O type (M:Ni, n = 4; M:Cu, n = 3 and M:Zn, n = 0; L: ligand resulted from 1,4-phenylenediamine, 3,6-diazaoctane-1,8-diamine and formaldehyde one-pot condensation) were synthesized and characterised by microanalytical, ESI–MS, IR, UV–Vis, ¹H NMR and EPR spectra, magnetic data at room temperature and molar conductivities as well. The electrochemical behaviour of complexes was investigated by cyclic voltammetry. Simultaneous TG/DTA measurements were performed in order to evidence the thermal behaviour of the obtained complexes. Processes such as water elimination, fragmentation and oxidative degradation of the organic ligand as well as chloride elimination occurred during thermal decomposition. The antimicrobial assays demonstrate that the compounds exhibited good antibacterial activity, especially against S. aureus and E. coli strains, the most active being the copper(II) complex, which also exhibited the most prominent anti-biofilm effect, suggesting its potential use for the development of new antimicrobial agents. The biological activity was correlated with log P _ow values. All complexes disrupt the membrane integrity of HCT 8 tumour cells.     

Thermal behaviour of some novel antimicrobials based on complexes with a Schiff base bearing 1,2,4-triazole pharmacophore

A series of complexes of type [ML(CH₃COO)(OH₂)₂] (M: Co, Ni; HL: 2-[(E)-1H-1,2,4-triazol-3-ylimino)methyl]phenol)) and [M₂L₂(CH₃COO)₂(OH₂)_n] (M: Cu, n = 2; M: Zn, n = 0) were synthesised by template condensation. The compounds were characterised with microanalytical, ESI–MS, IR, electronic, EPR spectra and magnetic data at room temperature. Based on the IR and ESI–MS spectra, a dinuclear structure with the acetate as bridge was proposed for Cu(II) and Zn(II) complexes. The dinuclear structure of Cu(II) complex is also consistent with both magnetic behaviour and EPR spectrum. The thermal analyses have evidenced processes as water elimination, acetate decomposition, as well as oxidative degradation of the Schiff base. The final decomposition product was the most stable metal oxide as indicated by powder X-ray diffraction. The cobalt and copper compounds exhibited a broad spectrum of antibacterial activity towards both planktonic and biofilm-embedded cells. The complexes exhibit a low cytotoxicity except for Cu(II) species that induces the early apoptosis for the HEp 2 cells.     

Plasmon coupling of R6G-linked gold nanoparticle assemblies for surface-enhanced Raman spectroscopy

This paper presents the study of surface-enhanced Raman scattering (SERS) for Rhodamine 6G (R6G)-linked gold (Au) assemblies. The nano-assemblies fabricated with Au nanoparticles, having diameters (D) of ～5–40 nm, possessed interparticle gaps of ～0.03–0.2D, respectively. The R6G-linked Au assemblies displayed weak spectral shifts of localized surface plasmon resonance (LSPR) mode at shorter wavelength region and large fractional red-shifts Δλ ～ 0.07–0.47λ_o at longer wavelength region. The resonant spectral coupling of the nano-assemblies LSPR mode at the longer wavelength region and the optical excitation at ～785 nm, in addition to the highly localized hot spots, could support the large SERS enhancement of R6G-linked Au assemblies.     

Correlation of the EPR properties of perchlorotriphenylmethyl radicals and their efficiency as DNP polarizers

Water soluble perchlorinated trityl (PTM) radicals were found to be effective 95 GHz DNP (dynamic nuclear polarization) polarizers in ex situ (dissolution) (13)C DNP (Gabellieri et al., Angew Chem., Int. Ed. 2010, 49, 3360). The degree of the nuclear polarization obtained was reported to be dependent on the position of the chlorine substituents on the trityl skeleton. In addition, on the basis of the DNP frequency sweeps it was suggested that the (13)C NMR signal enhancement is mediated by the Cl nuclei. To understand the DNP mechanism of the PTM radicals we have explored the 95 GHz EPR characteristics of these radicals that are relevant to their performance as DNP polarizers. The EPR spectra of the radicals revealed axially symmetric g-tensors. A comparison of the spectra with the (13)C DNP frequency sweeps showed that although the solid effect mechanism is operational the DNP frequency sweeps reveal some extra width suggesting that contributions from EPR forbidden transitions involving (35,37)Cl nuclear flips are likely. This was substantiated experimentally by ELDOR (electron-electron double resonance) detected NMR measurements, which map the EPR forbidden transitions, and ELDOR experiments that follow the depolarization of the electron spin upon irradiation of the forbidden EPR transitions. DFT (density functional theory) calculations helped to assign the observed transitions and provided the relevant spin Hamiltonian parameters. These results show that the (35,37)Cl hyperfine and nuclear quadrupolar interactions cause a considerable nuclear state mixing at 95 GHz thus facilitating the polarization of the Cl nuclei upon microwave irradiation. Overlap of Cl nuclear frequencies and the (13)C Larmor frequency further facilitates the polarization of the (13)C nuclei by spin diffusion. Calculation of the (13)C DNP frequency sweep based on the Cl nuclear polarization showed that it does lead to an increase in the width of the spectra, improving the agreement with the experimental sweeps, thus supporting the existence of a new heteronuclear assisted DNP mechanism.