Concepts and approaches to in situ luminescence dating of Martian sediments

In this paper we present the concept of a robotic instrument for in situ luminescence dating of near-surface sediments on Mars. The scientific objectives and advantages to be gained from the development of such an instrument are described, and the challenges presented by the Mars surface environment to the design and operation of the instrument are outlined.     

Carbohydrate Mimetics: A New Strategy for Tackling the Problem of Carbohydrate-Mediated Biological Recognition

Useful strategies for the design of molecules to mimic carbohydrates have been developed over the past few years. Mimics of the target may contain new functional groups, a new scaffold, or both (in the schematic representation the natural ligand is shown on the left and the modified version on the right). Many examples of successful carbohydrate mimetics that interfere with sugar–protein and sugar–nucleic acid interactions are known.     

Tantal und Niob

Ohne Zusammenfassung     

New Insights into the Mechanism and an Expanded Scope of the Fe(III)-Mediated Vinblastine Coupling Reaction

A definition of the scope of aromatic substrates that participate with catharanthine in an Fe(III)-mediated coupling reaction, an examination of the key structural features of catharanthine required for participation in the reaction, and the development of a generalized indole functionalization reaction that bears little structural relationship to catharanthine itself are detailed. In addition to providing insights into the mechanism of the Fe(III)-mediated coupling reaction of catharanthine with vindoline suggesting the reaction conducted in acidic aqueous buffer may be radical mediated, the studies provide new opportunities for the preparation of previously inaccessible vinblastine analogs and define powerful new methodology for the synthesis of indole-containing natural and unnatural products.     

Hot bands in jet-cooled and ambient temperature spectra of chloromethylene

Rotationally resolved spectra of several bands lying to the red of the origin of the A(1)A" - X (1)A' band system of chloromethylene (HCCl), were recorded by laser absorption spectroscopy in ambient temperature and jet-cooled samples. The radical was made by excimer laser photolysis of dibromochloromethane, diluted in inert gas, at 193 nm. The jet-cooled sample showed efficient rotational but less vibrational cooling. Analysis showed that the observed bands originate in the (upsilon(1),upsilon(2),upsilon(3)) = (010), (001), and (011) vibrational levels of the ground electronic state of the radical, while the upper-state levels involved were (000), (010), (001), and (011). Vibrational energies and rotational constants describing the rotational levels in the lower-state vibrational levels were determined by fitting to combination differences. The analysis also resulted in a reevaluation of the C-Cl stretching frequency in the excited state and we find E(001)' = 13 206.57 or 926.17 cm(-1) above the A(1)A" (000) rotationless level for HC(35)Cl. Scaled ab initio potential energy surfaces for the A and X states were used to compute the transition moment surface and thereby the relative intensities of different vibronic transitions, providing additional support for the assignments and permitting the prediction of the shorter wavelength spectrum. All the observed upper state levels showed some degree of perturbation in their rotational energy levels, particularly in K(a) = 1, presumably due to coupling with near-resonant vibrationally excited levels of the ground electronic state. Transitions originating in the low-lying a(3)A" were also predicted to occur in the same wavelength region, but could not be identified in the spectra.     

Sub-Doppler spectroscopy of mixed state levels in CH(2)

Perturbations in the 7(16) and 8(18) mixed singlet/triplet levels of a??(1)A(1)(0,0,0) methylene, CH(2), have been reinvestigated by frequency-modulated laser sub-Doppler saturation spectroscopy. The hyperfine structure was completely resolved for both the predominantly singlet and the predominantly triplet components of these mixed rotational levels using b??(1)B(1)-a??(1)A(1) optical transitions near 12?200?cm(-1) with megahertz resolution. The mixing coefficients were obtained from the observed hyperfine splittings and a two-level deperturbation model. The analysis also determines the energy separation of the unperturbed zero-order levels and the unperturbed hyperfine splittings for the triplet perturbing levels 6(15) X??(3)B(1)(0,3,0) and 9(37) X??(3)B(1)(0,2,0).     

Fluorescence,fluorescence-excitation and absorption spectra of trans-1-(2-anthryl)-2-phenylethene conformers

Fluorescence spectra of trans-1-(2-anthryl)-2-phenylethene (APE) obtained under varying conditions of excitation wavelength and oxygen concentration in toluene are resolved into two distinct components by application of principal component analysis with self-modeling (PCA-SM). Self-modeling is guided by the constraint that Stem-Volmer quenching plots for the individual conformers be independent of excitation wavelength. The same process applied on a matrix of fluorescence-excitation spectra leads to resolved conformer-specific fluorescence-excitation spectra. Consistency between the fluorescence and the fluorescence-excitation spectrum of each conformer is established. The fluorescence-excitation spectr and literature fluorescence quantum yields are used to resolve the UV absorption spectrum of APE. The pure conformer spectra obtained in this work are compared with those from earlier PCA-SM treatments in which self-modeling procedures were based on the Lawton and Sylvestre nonnegativity constraint and on a maximal spectral dissimilarity constraint.     

On close to linear cocycles

If we have a flow and a cocycle on this flow, , then is called close to linear if can be written as the direct sum of a linear (constant) cocycle and a cocycle in the closure of the coboundaries. Many of the desirable consequences of linearity hold for such cocycles and, in fact, a close to linear cocycle is cohomologous to a cocycle which is norm close to a linear one. Furthermore in the uniquely ergodic case all cocycles are close to linear. We also establish that a close to linear cocycle which is covering is cohomologous to one with the special property that it can be extended by piecewise linearity to an invertible cocycle from to itself. This implies that a suspension obtained from a close to linear cocycle is isomorphic to a time change of the suspension obtained from the identity cocycle.