Spectroscopic investigation of fluoroiodomethane, CH2FI: Fourier-transform microwave and millimeter-/submillimeter-wave spectroscopy and quantum-chemical calculations

Guided by theoretical predictions, the rotational spectrum of fluoroiodomethane, CH(2)FI, has been recorded and assigned. Accurate values are reported for the ground-state rotational constants, all quartic, sextic, and two octic centrifugal-distortion constants. The hyperfine structure of the rotational spectrum was thoroughly investigated using a Fourier-transform microwave spectrometer and the Lamb-dip technique in the millimeter-/submillimeter-wave region, thus allowing the accurate determination of the complete iodine quadrupole-coupling tensor and of the diagonal elements of the iodine spin-rotation tensor. Relativistic effects turned out to be essential for the accurate theoretical prediction of the dipole moment and quadrupole-coupling constants and were accounted for by direct perturbation theory and a spin-free four-component treatment based on the Dirac-Coulomb Hamiltonian. The relativistic corrections to the dipole moment amount to up to 34% and to the iodine quadrupole-coupling tensor to about 15-16% of the total values.     

Intrinsic stability and hydrogen affinity of pure and bimetallic nanowires

A density functional theory study of the intrinsic stability of pure and bimetallic wires is presented. Several bimetallic combinations forming one-atom thick wires are studied. An explanation for the experimental instability of Cu wires in contrast to the stability of Au and Ag wires is given, which relies on the higher surface energy of the former. All the possible intercalations between Ni, Pd, Pt, Cu, Ag, and Au are studied. The bimetallic wires AuCu and AuAg were found to be the most stable ones. The reactivity of the latter two systems is also examined using hydrogen adsorption as a microscopic probe. It was found that at the inter-metal interface, up to second neighbors, Cu and Ag become more reactive and Au becomes more inert than the corresponding pure wires. These results are explained within the d-band model.     

Thermochemistry of 2,2′-dipyridil N-oxide and 2,2′-dipyridil N,N′-dioxide. The dissociation enthalpies of the N−O bonds

In this paper, the first, second and mean (N?O) bond dissociation enthalpies (BDEs) were derived from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, ${\mathrm{\Delta }}_{\text{f}}{H}_{\text{m}}^{°}(\text{g})$, at T = 298.15 K, of 2,2′-dipyridil N-oxide and 2,2′-dipyridil N,N′-dioxide. These values were calculated from experimental thermodynamic parameters, namely from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, ${\mathrm{\Delta }}_{\text{f}}{H}_{\text{m}}^{°}(\text{cr})$, at T = 298.15 K, obtained from the standard molar enthalpies of combustion, ${\mathrm{\Delta }}_{\text{c}}{H}_{\text{m}}^{°}$, measured by static bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from Knudsen mass-loss effusion method.     

Efficient refolding of a hydrophobic protein with multiple S-S bonds by on-resin immobilized metal affinity chromatography

The efficient refolding of recombinant proteins produced in the form of inclusion bodies (IBs) in Escherichia coli still is a complicated experimental problem especially for large hydrophobic highly disulfide-bonded proteins. The aim of this work was to develop highly efficient and simple refolding procedure for such a protein. The recombinant C-terminal fragment of human alpha-fetoprotein (rAFP-Cterm), which has molecular weight of 26 kDa and possesses 6 S-S bonds, was expressed in the form of IBs in E. coli. The C-terminal 7× His tag was introduced to facilitate protein purification and refolding. The refolding procedure of the immobilized protein by immobilized metal chelating chromatography (IMAC) was developed. Such hydrophobic highly disulfide-bonded proteins tend to irreversibly bind to traditionally used agarose-based matrices upon attempted refolding of the immobilized protein. Indeed, the yield of rAFP-Cterm upon its refolding by IMAC on agarose-based matrix was negligible with bulk of the protein irreversibly stacked to the resin. The key has occurred to be using IMAC based on silica matrix. This increased on-resin refolding yield of the target protein from almost 0 to 60% with purity 98%. Compared to dilution refolding of the same protein, the productivity of the developed procedure was two orders higher. There was no need for further purification or concentration of the renatured protein. The usage of silica-based matrix for the refolding of immobilized proteins by IMAC can improve and facilitate the experimental work for difficult-to-refold proteins.     

Thermal Behavior of Sr(II) and Ba(II)‐Diclofenac Complexes in Solid State: Study of the Dehydration and Thermal Decomposition

Solid state compounds of general formula Sr(Diclof)₂·5.7H₂O and Ba(Diclof)₂·4.8H₂O were obtained. Thermogravimetry (TG), differential scanning calorimetry (DSC), X‐ray diffraction powder patterns and microscopy analysis were used to characterize these compounds. Details concerning the dehydration and thermal decomposition as well as data of kinetic parameters have been described here. The kinetic behaviors of these stages were evaluated from several heating rates with samples masses of 2 and 5 mg in open crucibles under a nitrogen atmosphere. The results of the present study improve the knowledge on these compounds including their dehydration and thermal stability. The obtained data depend on the mass of the sample which results in two kinetic behavior patterns.     

Chemiluminescence as a PDT light source for microbial control

The photodynamic therapy (PDT) is a combination of using a photosensitizer agent, light and oxygen that can cause oxidative cellular damage. This technique is applied in several cases, including for microbial control. The most extensively studied light sources for this purpose are lasers and LED-based systems. Few studies treat alternative light sources based PDT. Sources which present flexibility, portability and economic advantages are of great interest. In this study, we evaluated the in vitro feasibility for the use of chemiluminescence as a PDT light source to induce Staphylococcus aureus reduction. The Photogem? concentration varied from 0 to 75 μg/ml and the illumination time varied from 60 min to 240 min.The long exposure time was necessary due to the low irradiance achieved with chemiluminescence reaction at μW/cm2 level. The results demonstrated an effective microbial reduction of around 98% for the highest photosensitizer concentration and light dose. These data suggest the potential use of chemiluminescence as a light source for PDT microbial control, with advantages in terms of flexibility, when compared with conventional sources.     

Redox Mechanisms of Nodularin and Chemically Degraded Nodularin

The electrochemical behaviour of Nodularin (NOD), a hepatotoxic cyclic pentapeptide, was studied at a glassy carbon electrode. NOD electrochemical oxidation is an irreversible, pH‐independent process, involving the transfer of one electron. Upon incubation in different pH electrolytes, chemical degradation of NOD was electrochemically detected by the appearance of a new oxidation peak. The chemically degraded NOD (cdNOD), undergoes an irreversible, pH‐dependent oxidation, and its redox products are reversibly oxidised. The charge transfer properties of cdNOD as well as of its redox metabolites were investigated. Mechanisms for NOD oxidation, NOD chemical degradation and oxidation of cdNOD and its metabolites were proposed.     

Validation of a digestion system using a digester block/cold finger system for the determination of lead in vegetable foods by electrothermal atomic absorption spectrometry

This paper presents the validation of a system for sample digestion using a digester block/cold finger to determine the lead content in vegetables by electrothermal atomic absorption spectrometry (ETAAS). After mineralization, lead contents were determined by ETAAS using a calibration curve based on aqueous standards prepared in 2.60 M nitric acid solutions containing 5 microg ammonium phosphate as chemical modifier. A pyrolysis temperature of 900 degrees C and atomization temperature of 2000 degrees C were used. This method allowed the determination of lead with a characteristic mass of 35 pg; LOD and LOQ of 0.6 and 2 nglg, respectively, were found. The precision was investigated in terms of reproducibility and repeatability. Reproducibility was estimated by analysis of nine different portions of a certified reference material (CRM) of spinach leaves, and the repeatability was determined through the analysis of nine aliquots of the same solution. The reproducibility and repeatability were found to be 4.27 and 2.94% RSD, respectively. The accuracy was confirmed by analysis of whole meal flour, spinach leaves, and orchard leaves CRMs, all furnished by the National Institute of Standards and Technology. Lead contents were measured using the newly developed technique in 11 different potato samples. The lead contents ranged from 12.80 to 69.27 ng/g, with an average value of 28.59 ng/g. These values were in agreement with data reported in the literature.     

Stereochemical dependence of 3JCH coupling constants in 2-substituted 4-t-butyl-cyclohexanone and their alcohol derivatives

Theoretical and experimental studies on (3)J(C2H6eq) NMR spin-spin coupling constants in both the 2-X-4-t-butyl-cyclohexanone (X = H, CH(3), F, Cl, and Br) and in their alcohol derivatives series are reported. Results thus found are rationalized in terms of the transmission of the Fermi contact contribution to such couplings. To this end, dependencies of (3)J(C2H6eq) couplings versus the C(2)-C(1)-C(6) angle are compared in both series for equatorial and axial X orientations. The main trend is described in terms of the rear lobes interaction. Besides, for X = halogen atom in equatorial orientation a rather strong interaction between oxygen and halogen lone pairs is observed, and its influence on (3)J(C2H6eq) couplings is discussed and rationalized in terms of different Fermi contact transmission pathways.