Computational and experimental evidence of through-space NMR spectroscopic J coupling of hydrogen atoms

J coupling in NMR spectroscopy is conventionally associated with covalent bonds. A noncovalent contribution often called through-space coupling (TSC) has been observed for heavy atoms. In this study, the TSC was detected and analyzed for the more common (1)H-(1)H coupling as well. In synthesized model molecules the hydrogen positions could be well controlled. For several coupling constants the through-space mechanism was even found to be the predominant factor. The nature and magnitude of the phenomenon were also analyzed by density functional computations. Calculated carbon- and hydrogen-coupling maps and perturbed electronic densities suggest that the aromatic system strongly participates in the noncovalent contribution. Unlike covalent coupling, which is usually governed by the Fermi contact, TSC is dominated by the diamagnetic term comprising interactions of nuclei with the electron orbital angular momentum. The computations further revealed a strong distance and conformational dependence of TSC. This suggests that the through-space coupling can be explored in molecular structural studies in the same way as the covalent one.     

Secondary processes in atmospheric pressure chemical ionization–ion trap mass spectrometry: a case study of orotic acid

Atmospheric pressure chemical ionization is known for producing unusual artifacts of the ionization process in some cases. In this work, processes occuring in atmospheric pressure chemical ionization/MS of orotic acid that afforded ions accompanying protonated and deprotonated orotic acid molecules in the spectra were studied. Two processes ran in parallel in the ion source: decarboxylation of neutral orotic acid and collision‐induced dissociation of its protonated or deprotonated form. A procedure discerning pre‐ionization decomposition and post‐ionization dissociation by manipulating ion source parameters was proposed. Experiments with isotopically labeled solvents confirmed ion–molecule reactions of the product of collision‐induced dissociation of protonated orotic acid with solvent molecules in the ion source and even under vacuum in the ion trap. Copyright © 2012 John Wiley & Sons, Ltd.     

Electrophoretic and chromatographic evaluation of transgenic barley expressing a bacterial dihydrodipicolinate synthase

Nutritional quality of human and animal foodstuffs is determined by the content of essential amino acids. Barley is the fourth most important cereal of the world and the second most important cereal grown in the Czech Republic. Cereal grains such as barley contain insufficient levels of some essential amino acids, especially lysine. Dihydrodipicolinate synthase is the key enzyme involved in the regulatory step for lysine biosynthesis. Two constructs pBract214::sTPdapA and pBract214::mdapA containing the dapA gene from Escherichia coli coding for the bacterial dihydrodipicolinate synthase were used for transformation of barley. An Agrobacterium-mediated technique was used for transformation of immature embryos of spring barley cv. Golden Promise. Transgenic barley plants of the T0 and T1 generations were evaluated by PCR, real-time PCR, gel electrophoresis, and Western blot. Amino acid content was analyzed by HPLC after HCl hydrolysis. The lysine content in leaves of the T1 generation plant no. 5/5 was 50% higher than in wild-type plants; the lysine content in seeds of T2 generation plant no. 5/16 was 30% higher than in wild-type seeds of spring barley cv. Golden Promise.     

A hint on the correlation between cellulose fibers polymerization degree and their thermal and thermo-oxidative degradation

The degree of polymerization is one of the main parameters reflecting cellulose ageing. Viscometry is a method frequently used for determination of cellulose fibers polymerization degree, however, sample preparation and viscosity measurement are demanding, time consuming and do not provide reproducible results. In this study, the relationship between polymerization degree of cellulose fibers obtained by viscosity measurement and their degradation parameters obtained by thermal analysis were investigated. Differential scanning calorimetry provided values of effective combustion heat and thermogravimetry (TG) was used for the determination of temperatures and associated mass losses during the cellulose degradation. Effective combustion heat did not show any correlation with degree of polymerization of investigated cotton fabrics. In contrast, results from TG suggested several promising nonlinear correlations which could be used as a hint to develop a method useful for quick determination of cotton fabrics polymerization degree. The most promising correlations with cellulose polymerization degree were found for both rates of thermal and thermo-oxidative degradations.     

Fluoroform-derived CuCF3 for low-cost, simple, efficient, and safe trifluoromethylation of aryl boronic acids in air

Easy does it: Aryl boronic acids undergo smooth and selective trifluoromethylation with low-cost fluoroform-derived CuCF(3) in DMF in non-dried air. The reaction occurs under mild conditions (1?atm, room temperature), exhibits unprecedented functional-group tolerance, and affords trifluoromethylated aromatic compounds in up to 99?% yield.     

Size resolved infrared spectroscopy of Na(CH3OH)n (n = 4-7) clusters in the OH stretching region: unravelling the interaction of methanol clusters with a sodium atom and the emergence of the solvated electron

Size resolved IR action spectra of neutral sodium doped methanol clusters have been measured using IR excitation modulated photoionisation mass spectroscopy. The Na(CH(3)OH)(n) clusters were generated in a supersonic He seeded expansion of methanol by subsequent Na doping in a pick-up cell. A combined analysis of IR action spectra, IP evolutions and harmonic predictions of IR spectra (using density functional theory) of the most stable structures revealed that for n = 4, 5 structures with an exterior Na atom showing high ionisation potentials (IPs) of ~4 eV dominate, while for n = 6, 7 clusters with lower IPs (~3.2 eV) featuring fully solvated Na atoms and solvated electrons emerge and dominate the IR action spectra. For n = 4 simulations of photoionisation spectra using an ab initio MD approach confirm the dominance of exterior structures and explain the previously reported appearance IP of 3.48 eV by small fractions of clusters with partly solvated Na atoms. Only for this cluster size a shift in the isomer composition with cluster temperature has been observed, which may be related to kinetic stabilisation of less Na solvated clusters at low temperatures. Features of slow fragmentation dynamics of cationic Na(+)(CH(3)OH)(6) clusters have been observed for the photoionisation near the adiabatic limit. This finding points to the relevance of previously proposed non-vertical photoionisation dynamics of this system.     

Control of CO2 adsorption heats by the Al distribution in FER zeolites

Proper combination of template and optimized reaction conditions provides zeolite FER with homogeneous distribution of Al in the framework; this results in a new zeolite adsorbent exhibiting a constant heat of CO(2) adsorption.     

Monomeric organoantimony(III) sulphide and selenide with terminal Sb-E bond (E = S, Se). Synthesis, structure and theoretical consideration

NCN chelated monomeric chalcogenides, LSbE (E = S (1), Se (2), L = 2,6-bis[N-(2',6'-dimethylphenyl)ketimino]phenyl), were synthesized and characterized with the help of elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction analyses. The terminal Sb-E (E = S, Se) bonds in 1 and 2 were subjected to theoretical investigation and the results are compared with the hypothetical molecules, PhSb=E (E = S, Se, Te), and earlier reported analogues.     

Structure and properties of glasses in ZnO-P2O5-TeO2 system

Glasses in the ternary ZnO-P₂O₅-TeO₂ system were prepared and studied in two compositional series (100 − x)[0.5ZnO-0.5P₂O₅]-xTeO₂ (X-series) and 50ZnO-(50 − y)P₂O₅-yTeO₂ (Y-series) within the concentration range of x = 0-60 and y = 0-40 mol% TeO₂. Their structure was studied by Raman and ³¹P MAS NMR spectroscopies. The incorporation of TeO_x units into the structural network is associated with the depolymerisation of phosphate chain structure as revealed by both methods. At a high TeO₂ content isolated PO₄ tetrahedra are formed in the structure of glass series Y, while diphosphate O₃P-O-PO₃ groups are present in the structure of the glass series X. In the structure of glass series Y tellurium atoms form predominantly TeO₃ trigonal pyramids, whereas in the X glass series TeO₄ trigonal bipyramids prevail in the glass structure. The addition of TeO₂ to the parent zinc metaphosphate glass results in a decrease of glass transition temperature in both compositional series associated with the replacement of stronger P―O bonds by weaker Te―O bonds.