Performance of fluorescence correlation spectroscopy for measuring diffusion and concentration.

Fluorescence correlation spectroscopy (FCS) has become an important tool for measuring diffusion, concentration, and molecular interactions of cellular components. The interpretation of FCS data critically depends on the measurement set-up. Here, we present a rigorous theory of FCS based on exact wave-optical calculations. Six of the most important optical and photophysical factors that influence FCS are studied: fluorescence anisotropy, cover-slide thickness, refractive index of the sample, laser-beam geometry, optical saturation, and pinhole adjustment. Our theoretical framework represents a general attempt to link all relevant parameters of the experimental set-up with the measured correlation function.     

Studies in negative ion mass spectrometry. VII—Negative ion mass spectra of copper (II) β-diketonate complexes

Electron capture processes in a series of copper (II) β-diketonate complexes of formula Cu[R¹COCHCOR²]₂ (where R¹ is an alkyl, perfluoroalkyl or aryl group and R² either an alkyl or aryl group) have been examined. Molecular anions, ligand ions and some novel rearrangement ions have been observed with these compounds. Relative intensities of fragment ions were dependent on the substituents R¹, R² as well as the electron energy and compound pressure in the ion source. By operating the mass spectrometer at compound pressures of c. 4×10^?6 Torr and higher, reproducible negative ion mass spectra (free from any significant ion-molecule contributions) have been obtained for all compounds of the series.     

Blood clot dissolution dynamics simulation during thrombolytic therapy

Nonocclusive blood clots only partially fill blood vessels and together with the adjacent vessel wall form a channel through which blood flows at usually much higher velocities than in normal vessels. Our aim was to find a theoretical explanation for the experimentally observed fact that fast flowing blood through the channel has a large effect on the increase of the clot dissolution rate compared to the dissolution rate in the absence of flow. Blood flow through the channel increases transport of dissolution agents to the clot and also exerts large forces to the surface of the clot along the channel. Proposed is a model for clot dissolution which assumes that the clot dissolution rate is proportional to the forces of flowing blood to the surface of the clot multiplied by the average blood velocity. The model has been verified by fitting to experimental magnetic resonance imaging data obtained by dynamical magnetic resonance microscopy of clots dissolved by recombinant tissue plasminogen activator in an artificial blood flow system.     

Short and diverse route toward complex natural product-like macrocycles

[reaction: see text] A general strategy toward macrocyclic compounds using multicomponent reaction (MCR) chemistry, e.g., Passerini and Ugi variants, and ring-closing metathesis (RCM) is introduced. The corresponding bifunctional isocyanides carboxylic acids bearing a terminal olefin are easy to prepare from the corresponding commercially available starting materials. Advantageously, this strategy allows fast access to a diverse conformational space of natural product-like macrocycles and could thus be of interest in the discovery of novel bioactive agents.     

The influence of ligand substituents and donor atom sets on the gas phase electron attachment reactions of bis-chelates of nickel(II)

Electron attachment reactions and negative ion mass spectra which were obtained under negative chemical ionization conditions have been examined for a series of 21 nickel(II) bis-chelates of formula Ni[R¹CXCHCYR²]₂. Three ligand donor atom sets (X, Y), respectively O₄, O₂S₂, S₄ were investigated for each of the substituent combinations, viz.: R¹=CH₃, CF₃ or C₂H₅O, R²=CH₃; R¹=C₆H₅, CH₃ or CF₃, R²=C₆H₅; and R¹ = R² = tert?C₄H₉. While the ligand substituent combinations exerted considerable influence over the various ion decomposition reactions, the relative molecular ion stabilities were largely dependent on the ligand donor atom sets and followed the sequence O₄? O₂S₂>S₄ for most substituent combinations. Rationalizations are offered in terms of reductive electron capture reactions involving metal-based orbitals, as well as the increasing stabilities of reaction products as sulphur is incorporated into the ligand donor atom sets. A comparison is also given of negative ion mass spectral data obtained under electron impact conditions as well as negative chemical ionization conditions when methane was used as an electron energy moderating gas.     

Linear extension diameter of subposets of Boolean lattice induced by two levels

The linear extension diameter of a finite poset P is the diameter of the graph on all linear extensions of P as vertices, two of them being adjacent whenever they differ in exactly one (adjacent) transposition. Recently, Felsner and Massow determined the linear extension diameter of the Boolean lattice B, and they posed a question of determining the linear extension diameter of a subposet of B induced by two levels. We solve the case of the 1st and kth level. The diametral pairs are obtained from minimal vertex covers of so called dependency graphs, a new concept which may be useful also for the general case.     

Literatur

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