Mass spectrometry of bisquinolizidine alkaloids: 2- and 17-cyano-substituted derivatives of sparteine and lupanine

The mass spectral fragmentations of 2-cyano-2-methylsparteine (1), 2-cyano-2-phenylsparteine (2), 2-cyano-2-(p-tolyl)sparteine (3), 17-cyanosparteine (4) and 17-cyanolupanine (5) were investigated. Fragmentation pathways, whose identification was assisted by accurate mass measurements and a correlation between the abundances of the M(+*) and the selected fragment ions of the investigated compounds, are discussed. The data obtained create the basis for distinguishing the structural metamers.     

Volumes of mixing 2,4-dimethylpyridine withn-alkanes

In continuation of our work on excess thermodynamic properties of non-electrolyte solutions containing pyridine bases withn-alkanes, we have determined excess molar volumesV ^E for 2,4-dimethylpyridine + C₆ to C₁₀ n-alkanes at 25°C. For the investigated systems noV ^E values were available in the literature for comparison with our data. The experimentalV ^E was used to test the Prigogine-Flory-Patterson theory (PFP), Extended Real Associated Solutions model (ERAS) and the Treszczanowicz-Benson method (TB).     

Equilibrium, FTIR, scanning electron microscopy and small wide angle X-ray scattering studies of chromates adsorption on modified bentonite

The study presents a discussion about the adsorption mechanism of chromate anions on bentonite modified by hexadecyltrimethylammonium bromide (HDTMA-Br). The formation of alkylammonium chromates: HDTMAHCrO₄, (HDTMA)₂Cr₂O₇ and to the lesser extent (HDTMA)₂CrO₄ at the water–bentonite interface is examined based on the Scanning Electron Microscopy and surface tension measurements. The histograms of HDTMA/Cr(VI) molar ratio on the bentonite surface, found from Scanning Electron Microscopy (SEM) measurements, show that for the majority of points of bentonite surface the value of this ratio is in 1–2 range. FTIR spectra of modified bentonite samples show the change from gauche to trans conformation in the surfactant arrangement in the clay interlayer accompanying its concentration increase.

In turn Small Wide Angle X-Ray Scattering (SWAXS) patterns evidently suggest incorporation of chromate anions into the interlamellar space of bentonite structure.     

Restricting the conformational heterogeneity of RNA by specific incorporation of 8-bromoguanosine

In an effort to reduce the conformational heterogeneity of RNA, the modified nucleobase 8-bromoguanosine (8BrG) was introduced into oligonucleotides having the hairpin tetraloop motif YNMG (Y = U or C and M = C or A). Purine nucleobases with bromine at position eight are known to preferentially adopt the syn conformation as nucleosides. The hairpin tetraloop motif YNMG was chosen as a model system because it has a syn guanosine at position four of the loop that is essential for thermodynamic stability. Thermodynamic and structural characterization of modified oligonucleotides with the hairpin sequences UUCG, CGCG, and CGAG by UV-melting and NMR spectroscopy revealed that 8BrG substitution has a small effect upon the hairpin conformation, while the duplex conformation is strongly destabilized (DeltaDeltaG degrees 37 approximately +4.7 kcal mol-1), thus inhibiting dimerization. These results support a model in which 8BrG substitution shifts the hairpin-duplex equilibrium constant toward the hairpin conformation by destabilizing the duplex. This methodology should be useful for limiting conformational heterogeneity in large RNAs, with potential applications in structural biology and enzymology.     

UV absorption spectra,kinetics, and mechanisms of the self reaction of CF3O2 radicals in the gas phase at 295 K

The ultraviolet absorption spectrum and the self reaction kinetics of CF₃O₂ radicals have been studied in the gas phase at 298 K using the pulse radiolysis technique. Long pathlength Fourier transform infrared (FTIR) spectroscopy was used to identify and quantify reaction products. Absorption cross sections were quantified over the wavelength range 215–270 nm. The measured cross section at 230 nm was; Errors represent statistical (2σ) together with our estimate of potential systematic errors. The absorption cross section data were then used to derive the observed self reaction rate constant for reaction (1), defined as ?d[CF₃O₂]/dt = 2k _obs[CF₃O₂]² k_lobs = (3.6 ± 0.9) × 10^?12 cm³ molecule^?1 s^?1. The only carbon containing product observed by FTIR spectroscopy was CF₃OOOCF₃. Consideration of the loss of CF₃O₂ radicals to form the trioxide CF₃OOOCF₃ allows derivation of the true bimolecular rate constant for reaction (1); k₁ = (1.8 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1. These results are discussed with respect to previous studies of the absorption spectra of peroxy radicals, the kinetics, and mechanisms of their self reaction. © John Wiley & Sons, Inc.     

Multi-elemental analysis of non-food packaging materials by inductively coupled plasma-time of flight-mass spectrometry

Commercial non-food packaging materials of four different matrices (paper, low density polyethylene (LDPE), polyethylene-polypropylene (PE-PP) and high density polyethylene (HDPE)) were examined for the content of Cr, Ni, Cu, Zn, As, Mo, Cd, Sb, Ba, Hg, Tl, Pb and U. The examined samples (0.17–0.35 g) were digested in HNO₃ and H₂O₂ (papers, LDPE and PE-PP) and in HNO₃, H₂SO₄ and H₂O₂ (HDPE) using microwave assisted high pressure system. The inductively coupled plasma-time of flight-mass spectrometry (ICP-TOFMS) has been employed as the detection technique. All measurements were carried out using internal standardization. Yttrium and rhodium (50 ng g⁻¹) were used as internal standards. The detection and quantification limits obtained were in the range of 0.005 ng g⁻¹ (⁵²Cr) to 0.51 ng g⁻¹ (⁶⁶Zn) and 0.015 μg g⁻¹ (⁵²Cr) to 2.02 μg g⁻¹ (⁶⁶Zn) of dry mass, respectively. The evaluated contents (mg kg⁻¹) of particular elements in the examined materials were as follows: 0.22–219; <1.05–9.03; 1.25–112; <2.02–449; <0.98–<1.30; <0.36–2.06; <0.29–113; <0.22–44.1; <0.06–57.4; <0.66–<0.88; <0.08–0.24; <0.13–1222 and <0.08–0.44 for Cr, Ni, Cu, Zn, As, Mo, Cd, Sb, Ba, Hg, Tl, Pb and U, respectively.     

Potentiometric, spectroscopic, electrochemical and DFT characterization of oxovanadium(IV) complexes formed by citrate and tartrates in aqueous solution at high ligand to metal molar ratios: the effects of the trigonal bipyramidal distortion in bis-chelated species and biological implications

The complexation of VO(iv) ion with citrate (L(3-)), d-, l- and dl-tartrate (L(2-)) at high ligand to metal molar ratios was studied in aqueous solution through the combined application of potentiometric, spectroscopic (UV-vis and EPR) and electrochemical (cyclic voltammetry) techniques. Unlike in equimolar solution, mononuclear and not dinuclear species are formed with the binding of carboxylate-COO(-) and alcoholate-O(-) donors yielding mono- and bis-chelated species with VOLH, VOL, VOLH(-1) and VOL(2)H(-2) composition; for tartrates also the "sugar-like" (O(-), O(-)) coordination is involved in the vanadium binding at basic pH values giving rise to the formation of VOL(2)H(-3) and VOL(2)H(-4) complexes. Among the species formed, VOL(2)H(-2) is characterised by a strong distortion towards the trigonal bipyramid with the two V-O(alcoholate) bonds in the equatorial and the two V-O(carboxylate) bonds in the axial positions. The geometry and electronic absorption spectra of such complexes were simulated by DFT methods and it was found that in aqueous solution the distortion follows the steric hindrance of the substituents on the alpha-carbon atom and the hydrophobicity of the ligands. The results were compared with those displayed by simple alpha-hydroxycarboxylates (glycolate, 2-hydroxyisobutyrate, 2-ethyl-2-hydroxybutyrate and benzilate). The trigonal bipyramidal distortion was correlated with the values of: i) Deltalambda = lambda(2) - lambda(3), where lambda(2) and lambda(3) are the central bands in the electronic absorption spectrum; ii) |A(x) - A(y)|, where A(x) and A(y) are the (51)V hyperfine coupling constants along the x and y axes in the anisotropic EPR spectrum; iii) the half-wave potential E(1/2) of oxidation of VO(iv) to the corresponding VO(2)(v) species in the cyclic voltammogram. Finally, a discussion on the possible form of VO(iv)-citrate complexes in blood serum is presented, where it is found that the most relevant species under physiological conditions should be [VO(citrH(-1))](2-).     

NMR and molecular modeling study, as complementary techniques to capillary electrophoresis method to elucidate the separation mechanism of linezolid enantiomers

NMR study and molecular modeling were performed to improve the level of understanding of the chiral recognition process occurring between linezolid and anionic single-isomer cyclodextrin-heptakis-(2,3-diacetyl-6-sulfato)-beta-cyclodextrin (HDAS-beta-CD). NMR spectrometry allowed to estimate the stoichiometry of the complexes between HDAS-beta-CD and S- or R-linezolid and to determine the binding constants. The 1:1 complex stoichiometry was detected in millimolar concentrations and the mode of binding was proposed. The binding constants Ka of the complexes were of the order of 30-80 M(-1). Molecular dynamic simulations of 40ns for four complexes and calculations of binding free energies were performed. These calculations allowed determining the mode of binding of linezolid to HDAS-beta-CD and explaining the binding enantioselectivity.     

Resolution of the vertical and horizontal heterogeneity of adsorbed collagen layers by combination of QCM-D and AFM

Collagen (type I from calf skin) adsorption on polystyrene (PS) and plasma-oxidized polystyrene (PSox) was studied, using a quartz crystal microbalance with energy dissipation measurements (QCM-D) and atomic force microscopy (AFM) in tapping mode. Radio-labeled collagen was used to measure the adsorbed amount and the ability of adsorbed collagen to exchange with molecules in the solution. The results show that the collagen adlayer consists of two parts: a dense and thin sheet in which fibrils are formed (directly observed by AFM) and an overlying thick layer (up to 200 nm) containing protruding molecules or bundles which are in very low concentration but modify noticeably the local viscosity. The thickness and viscosity of the semi-liquid adlayer both increase with adsorption time and collagen concentration. Fibril formation near the surface also increases with time and collagen concentration and occurs more readily on PS compared to PSox. Radiochemical measurements show that this may be related to the larger mobility of molecules adsorbed on PS, presumably owing to a smaller number of binding points.