The magnetic hyperfine field of bromine in iron by NMR/ON

Nuclear magnetic resonance of⁸²Br oriented at low temperature in iron has been observed with a sample prepared by ion implantation atT<0.2 K. The asymmetric resonance signal can be decomposed in a broad background signal and a narrow line of FWHM=1.8 (4) MHz which can be attributed to⁸²Br in undisturbed substitutional sites of Fe. From the center frequency of this narrow line (B _ext=0)=201.86(13) MHz we derive the magnetic hyperfine field asB _hf(BrFe)=81.38(6) T. This value is considerably larger than the result of theoretical calculations.     

3',4'-trans-linked bicyclic nucleosides locked in S-type conformations

A novel class of 3',4'-trans-linked bicyclic nucleosides with locked S-type furanose conformations is introduced by synthesis of two model derivatives; one was obtained by cyclic ether formation and the other by ring-closing metathesis methodology.     

Preparation of stationary phases for open-tubular capillary electrochromatography using the sol-gel method

Capillary electrochromatography requires the deposition of a stationary phase inside the capillary. In this paper the sol-gel method is proposed for this purpose. The gels were prepared externally and injected into a fused-silica capillary, where anchorage to the capillary wall was possible through condensation reactions between the silanol groups of the capillary wall and the residual silanol groups the gel. Contrary to a commonly used practice, alkaline pretreatment of the inner capillary wall prior to the introduction and anchoring of the gel was found to be only marginally effective in improving the mechanical stability of the column. The influence of various parameters, such as the pH, the water content, the presence of alcohol (ethanol) on the formation of tetraethoxysilane (TEOS)-n-octyltriethoxysilane (C8-TEOS) hybrid gels of varied composition is discussed. The pH and the amount of water present were found to be the determining factors in the preparation of a stable gel with the desired mechanical and chromatographic properties. By carrying out the gel formation at 80 degrees C, capillary columns could be produced in 2.5 h. While an acidic pH was required during (external) gel formation, subsequent treatment of the gel inside the capillary with an alkaline solution ('aging') was found to improve separation and stationary phase capacity significantly. The capillary columns were subsequently used to separate a mixture of polycyclic aromatic hydrocarbons in less than 3 min.     

Spectral properties of diode-pumped non-planar monolithic Nd:YAG ring lasers

The coherence length of a single-frequency monolithic Nd:YAG ring laser is determined by using a highly unbalanced all-fiber Mach-Zehnder interferometer. A coherence length larger than 1500km and a 3 dB linewidth less than 60 Hz is estimated.Furthermore, an easy method to measure the temperature dependence on several laser parameters is described. This method is based on the laser emission in multiple axial modes, which is enforced by coherent optical feedback. A model explaining the multimode behaviour is presented.     

One-Step Synthesis of Monolithic Silica Nanocomposites in Fused Silica Capillaries

The ideal way to prepare efficient, yet robust stationary phases for microanalytical high-resolution methods such as capillary chromatography and electrochromatography remains to be defined. In this contribution a one step sol-gel process is proposed for the production of monolithic, macroporous nanocomposite phases in fused silica capillaries, which require no additional derivatization, since they already bear the interactive (C8) moieties. The effect of the catalyst, the water content, the pH, as well as that of certain additives on monolith formation and porosity is investigated. Volume shrinkage and a tendency to crack were the major obstacles to overcome. Homogeneous stationary phases could be produced by applying a pH gradient during sol formation, thereby changing the catalytic principle from acidic (0.1 M HCl) to basic (gradual formation of OH^– as a consequence of the hydrolysis of N-methylformamide). Gelation/coacervation of suchgels could be induced by the addition of N,N-diethylamine. The water content during sol formation was determined as decisive for pore formation, with 250% of the amount theoretically needed for complete hydrolysis of all precursors giving optimal results. The volume shrinkage problem during xerogel formation was resolved by integrating dialkyldialkoxysilane units (dimethyldiethoxysilane 35 mol%) into the silica network.     

Investigation of conditions allowing the synthesis of acrylamide-based monolithic microcolumns for capillary electrochromatography and of factors determining the retention of aromatic compounds on these stationary phases

The influence of the cross-linker (concentration), the porogen (lyotrophic salt) and the solvent type as well as the type and concentration of up to three "functional", i.e., interactive monomers on the morphology and the chromatographic properties of acrylamide-based hydrophilic monoliths are investigated. High total monomer concentrations favored polymers with a rigid rather than gel-like structure. High cross-linker concentrations also favor the formation of a nodular structure. The addition of a lyotrophic salt favors the formation of small nodules especially at higher monomer concentration; the pore size of the polymer can also be modulated through the salt concentration. Suitable monoliths were further investigated as potential stationary phases for capillary electrochromatography (CEC). Depending on the type and concentration of the monomers, plate numbers between 50,000 and 100,000 were routinely obtained. The standard deviation of the run-to-run reproducibility was below 2% and that of the batch-to-batch reproducibility below 5%. A set of nine hydrophobic and polar aromatic compounds (all noncharged) was used to investigate the retention mechanism. Possible candidates for chromatographic interaction and retention in these monoliths are the hydrophobic polymer backbone itself and the alkyl, carbonyl, hydroxy, amino, amide, and charged groups introduced by the various functional monomers. Judging from our results, the carbonyl and the hydroxy functions, as well as the hydrophobic polymer backbone can be supposed to be the main sites of interaction. The charged but also the alkyl functions seem to be less important in this regard. The polymerization conditions and especially the composition of the reaction mixture have a strong influence on the behavior of the final column.