Improvement of electron capture efficiency by resonant excitation

A novel pulse sequence improving the efficiency for electron capture dissociation (ECD) of an unmodified Fourier transform ion cyclotron resonance (FTICR) mass spectrometer by more than an order of magnitude is presented. Commercially available FTICR instruments are usually equipped with a filament-based electron source producing an electron beam that has a rather small cross section. An ideal overlap between the rotating ion cloud and the electron beam appears to be a prerequisite for a high ECD efficiency. A reduced interception of the ion cloud and the electron beam is probably due to the contribution of the magnetron motion to the trajectory of the ions, resulting in a precession about the z-axis of the instrument. By increasing the kinetic energy and therefore increasing the cyclotron radii of the precursor ions by resonant excitation, the overlap of the rotating ion cloud with the electron beam is improved. By use of this protocol the efficiency of electron capture is substantially increased and consequently the acquisition time of ECD spectra is reduced significantly. The capability of resonant excitation of the precursor ions during the irradiation with electrons is demonstrated for standard peptides. This approach is particularly valuable for analysis and characterization of O-glycosylated peptides. In addition to amino acid sequence information, the attachment site of the labile glycan moiety is determined, and also radical-site-induced fragmentations of the glycosidic bonds are observed.     

Some new ring-D seco steroids

The Beckmann fragmentation product, 3-methoxy-17-oxo-16,17-secoestra-1,3,5(10)-trien-16-nitrile (2) has been reduced by LAH giving the expected 3-methoxy-17-hydroxy-16,17-secoestra-1,3,5(10-trien-16-amine hydrochloride (3) and 3-methoxy-17-oxa-D-homoestra-1,3,5(10)-trien-16-ol (4), by a presumed neighbouring group participation of 17-OH group in the intermediary formed 16-imino derivative (A). The structure of 4 has been proved by an alternative synthetic route by reducing 3-methoxy-17-oxa-D-homoestra-1,3,5(10)-trien-16-one (7) with di-iso-butylaluminium hydride.     

Study of the Retention Behavior of Newly Synthesized s-Triazine Derivatives in RP TLC Systems,and the Lipophilicity of the Compounds

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of nine newly synthesized s-tri-azines has been studied by thin-layer chromatography on C18/UV254...     

Development and prevalidation of a method for phenol determination by solid-phase spectrophotometry

A simple, sensitive and rapid solid-phase spectrophotometric procedure was developed for the determination of traces of phenol with 4-aminoantipyrine as a reagent (AAP-SPS), and the optimal experimental conditions were established. This method was performed by sorption and direct absorbance measurements of the product phenol-AAP sorbed on the anion-exchanger Dowex 1-X4 (0.2 g) at 495 nm (absorption maximum) and 700 nm (non-absorption wavelength). The sensitivity offered by the AAP-SPS procedure was higher by a factor of 40 compared with the respective conventional spectrophotometric method. Metrological characteristics were established using a prevalidation strategy. The AAP-SPS procedure is characterized by a linear calibration function in the working range of 0.05–0.50 μmol, low standard deviation of procedure (±0.012), low limit of determination (0.021 μmol), and favorable random (±0.85 to ±11.27%) and systematic deviations (−4.55 to +11.50%). Moreover, the accuracy of the system investigated by the recovery test is acceptable (99–102%). Favorable working and performance characteristics make the new SPS method ideal for phenol monitoring in pharmaceutical preparations as well as other matrices.     

Cyclic chronopotentiometry of nickel(II) at mercury electrodes in acidic perchlorate solutions: Case of higher order nonregenerative reactions following electron transfer

The reduction of Ni²⁺ ions at mercury electrodes in acidic perchlorate solutions, at perchlorate concentrations below 0.2 M, is characterized by absence of kinetic control in the preceding step, and by a complex reaction mechanism following the electron transfer. This reaction sequence is known to involve intermetallic compound formation between Ni and Hg and is best described, as shown here, by a parallel second and third order kinetic scheme. Apparent rate coefficients for this kinetic scheme were determined using cyclic chronopotentiometric data and fitting by digital simulation. A linearization test of computed kinetic rate coefficients versus the number of transitions permits quantitative tests of validity of assumptions made.     

Correlation between C-H and C-C spin-spin coupling constants and s character of hybrids calculated by the maximum overlap method

For some thirty hydrocarbons the s character of hybrids obtained by the application of the maximum overlap method have been correlated with C-H and C-C spin-spin coupling constants. The following relationships were obtained: $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}} = 1079a_{{\text{CH}}}^{\text{2}} /(1 + S_{{\text{CH}}}^{\text{2}} ) - 54.9$$ , $$J_{{\text{C}}_{\text{1}}^{{\text{13}}} - {\text{C}}_{\text{2}}^{{\text{13}}} } = 1020.5a_{{\text{C}}_{\text{1}} }^2 a_{{\text{C}}_{\text{2}} }^{\text{2}} /(1 + S_{{\text{CC}}}^{\text{2}} ) - 8.2$$ . Here the coupling constants are expressed in cps units. In the calculation of the maximum overlap hybrids either the experimental bond lengths or a standard bond lengths were used. For the \(J_{{\text{C}}^{{\text{13}}} - {\text{H}}}\) and \(J_{{\text{C}}^{{\text{13}}} - {\text{H}}} \) coupling constants the standard deviations are 0.9 cps and 1.9 cps respectively. It has been suggested that the large additive constant in the \(J_{{\text{C}}^{{\text{13}}} - {\text{H}}}\) correlation may be attributed to the ionic character of C-H bonds. A good agreement with the experimental data strongly supports the idea that the Fermi contact term and the hybridization are dominant factors in determining carbon-hydrogen and carbon-carbon spin-spin coupling constants across one bond, at least in hydrocarbons.     

Development of novel antioxidants: design,synthesis, and reactivity

We are attempting to develop novel synthetic antioxidants aimed at retarding the effects of free-radical induced cell damage. In this paper we discuss the design strategy and report the synthesis of seven novel antioxidants, including six catechols and a benzylic phenol. The bond dissociation enthalpy (BDE) for the most active (weakest) OH bond in each molecule was calculated by theoretical methods, as well as the BDE for the semiquinone radical. Reaction rates with the nitrogen-centered free radical DPPH(*) were measured in ethyl acetate. The log of k(DPPH) for bimolecular reaction correlated well with the primary BDE. The correlation between rate constants and calculated BDEs shows that the BDE is a good predictor of antioxidant activity with DPPH(*), suggesting that our design criteria are useful and that these compounds should undergo further testing in cell cultures and in animal models.     

Mössbauer spectroscopic and X-ray diffraction study of the thermal decomposition of natural siderite and goethite

Thermal decomposition of natural siderite and goethite has been studied using Mössbauer spectroscopy and X-ray diffraction. Hematite and magnetite were the principal compounds formed during high temperature treatment of siderite. Natural goethite transformed to hematite at high temperatures. The crystal structures, stoichiometry and the nuclear magnetic properties of Fe-oxides formed are discussed.     

Synthesis of novel, potentially biologically active dibenzosuberone derivatives

Novel representatives of the important group of biologically active dibenzosuberone derivatives were prepared: 3,7-dibromo-5-(dimethylaminoethyl- oxyimino)-10,11-dihydro-5H-dibenzo[a,d]cyclohepta-1,4-diene (1), 3,7-dibromo-5-(3- dimethylaminopropylidene)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene (2) and 1,7- dibromo-5-(3-dimethylaminopropylidene)-10,11-dihydro-5H-dibenzo-[a,d]-cycloheptene (3). These compounds are potential tricyclic antidepressants (TCAs), which are still the most frequently prescribed antidepressants in many countries.