Anwendung der dynamischen Remissionsspektroskopie zur Ermittlung kinetischer Daten von Reaktionen disperser Stoffe

Journal of Thermal Analysis and Calorimetry - Auf der Grundlage von Remissionsgrad-Temperatur-Kurven mit dynamischer Temperaturführung wird ein Verfahren zur Ermittlung von...     

Organometallic 4π Ligands as Building Blocks of Clusters

Abstract

The chemistry of RP-bridged clusters may be interpreted in terms of coordinatively stabilized antiaromatic organometallic 4π ligands. The idea of regarding these 4π entities (cf. A – C) as the central constituents of clusters is a synthetically rewarding approach.     

Sers investigation on the homologeous series of a cyanine dye adsorbed on silver colloidal particles

The Surface Enhanced Raman Scattering (SERS) on the first three representatives of the homologeous series of 3,3′-diethyl-2,2′-benzthiacyanines adsorbed on silver colloids was investigated in the blue-green excitation region. In spite of their different absorption wave lengths, i.e. different resonance Raman scattering (RRS) -conditions, the dyes showed very similar scattering intensities in SERS-experiments. This can be explained by a balancing superposition of RRS and a surface enhancement where the latter will be smaller under RRS-conditions than in the case of a more “normal” RS of the adsorbed dye.     

Laser heating of biological tissue with blood vessels: Modeling and clinical trials

The spatial distribution of the energy absorbed by a unit volume of a laser-irradiated biological tissue is calculated by the Monte Carlo method. Based on these calculations, the temperature fields in biological tissues subjected to laser radiation at 810 nm are modeled. The temperature fields in subcutaneous blood vessels are modeled separately taking into account the inhomogeneous volumetric distribution of heat sources inside the vessels. The results of the modeling showed that laser heating can be efficiently used both for small-diameter and large vessels. Experimental clinical trials of therapy of vascular skin changes by pulsed diode laser radiation (at 810 nm) confirmed these results.     

Kinetische Untersuchungen zur nichtisothermen Zersetzung von Festköpern im Hochvakuum am Beispiel von Kobalt-Pyridin-Komplexen

On the example of the non-isothermal decomposition of pyridine complexes of Co(II)Cl_under high-vacuum conditions, a method is demonstrated for determining kinetic parameters without assumptions concerning the dependence of the rate of reaction on the concentration. There are significant differences between decomposition under high-vacuum and atmospheric conditions. Experimental results can be described quantitatively assuming a rate-controlling desorption of surface-bound pyridine molecules in equilibrium with molecules in the interior of the crystallites.     

Picosecond time-resolved spectroscopic studies of a monomer—dimer system of 3,3′-diethyl thiacarbocyanne iodide in aqueous solution

Transient absorption in the blue and near-infrared and bleaching of 3,3'-diethyl thiacarbocyanine iodide monomers and dimers weres studied. The monomer excited-state lifetime is 145 ± 10 ps, the recovery time of the dimers is 460 ± 50 ps. An intermediate state with a rise time of 80 ps and decay time of 500 ps has been detected between 670 and 730 nm.     

Zur Kenntnis des Faktors F430 aus methanogenen Bakterien: Struktur des porphinoiden Ligandsystems

Factor F430 from Methanogenic Bacteria: Structure of the Porphninoid Ligand System A structure is proposed for F430M, a non-cristalline methanolysis product of isolates of the nickel-containing, porphinoid factor F430 from Methanobacterium thermoautotrophicum. Crucial to the structure determination are five incorporation experiments with M. thermoautotrophicum (strain Marburg) in which the specifically mono-¹³C-labeled biosynthetic precursors (2-¹³C), (3-¹³C), (4-¹³C)-, (5-¹³C) ALA (ALA = δ-amino-levulinic acid) and L-(methyl-¹³C)methionine were incorporated into F430 with high efficiency. The ¹³C-NMR,-spectra of the specifically labeled F430M samples derived therefrom, together with the UV./VIS. spectral data of F430M, contain all the information necessary for the deduction of the constitution of the F430M chromophore, assuming the established pattern of porphinoid biosynthesis to be operative in F430 biosynthesis. ¹H-NMR. spectroscopy and, in particular, ¹H-NMR.-NOE-difference spectroscopy corroborates and completes the constitutional assignments and, furthermore, makes possible an almost complete derivation of the molecule's relative configuration. Schemes 3 and 4 summarize the results of ¹H-NMR. spectroscopy, presenting them within the context of the proposed structure for F430M. The assignment of absolute configuration implied in the formula is given preference because of F430M's very close structural and (assumed) biosynthetic relationship to sirohydrochlorin and vitamin B₁₂ (with respect to ring C, the assignment is based on degradative evidence). According to the proposed structure, the nickel complex F430M possesses an uroporphinoid (Type III) ligand skeleton with an additional carbocyclic ring and a chromophore system not previously encountered among natural porphinoids. It can be considered to be a (tetrahydro) derivative of the corphin system, combining structural elements of both porphyrins and corrins.     

Sers excitation profile investigation of a cyanine dye adsorbed on silver colloidal particles

An excitation profile investigation of 3,3′-diethyl-2,2′-benzthiatrimethinecyanine adsorbed on silver sol shows, for the pure surface enhancement, a relative minimum near the dye absorption (about 550 nm) and a strong increase for yellow-red wavelengths, which is explained qualitatively in terms of an “electromagnetic” model.     

Thermische und spektroskopische Untersuchungen zur Wassersorption an Alkalihalogeniden

Investigations on the extension of the diffuse reflectance spectroscopy by means of the dilution method of KORTÜM show the decisive influence of water sorption on the dilution substances, particularly on their absolute reflectance. Water sorption is investigated on alkali halides (NaCl and LiF) as dilution substances by gravimetric, thermal desorption and reflectance methods. Sorption gravimetry gives data on the quantities of adsorbed substances and the time function of adsorption processes, thermal desorption on chemical binding of adsorbed molecules and reflectance spektroscopy on the molar absorptivity of adsorbed water molecules.     

Topographical analyses of homonuclear multiple bonds between main group elements

Recent experiments have resulted in the completion of the series of Group 14 and Group 15 element double-bond systems, R(n)E=ER(n) (E = C - Pb, n = 2; E = N - Bi, n = 1). Furthermore, new families of multiple-bonded species have been discovered, such as the radical anion [RSnSnR](-) , the close ion pairs [RE(mu2Na)2ER] (E = Ge,Sn), and a digallyne [RGa(mu2Na)2GaR] for which a Ga=Ga triple bond was formulated. Some of these compounds show classical multiple bond features (i.e. the dipnictogens RE=ER, E=N-Bi) in the sense that planar structures with short E-E distances are observed. However, many (i.e. R2E=ER2, E = Si - Pb) do not behave as expected for compounds with multiple bonds. They have trans bent structures, show enormous variation in their E-E distances, and some dissociate easily under E-E bond cleavage in solution. These properties raised doubts as to whether these compounds can be formulated as multiple-bonded systems. Using the electron localization function (ELF) it is possible to clearly show the topographical similarities between classical and nonclassical multiple bonds; ELF divides these systems into unslipped (classical) and slipped (nonclassical) systems. ELF can also be employed to confirm the nonexistence of multiple bonds. Therefore, topographical analyses using ELF are useful to categorize a bonding system. In particular, the bonds in the heavier Group 14 double systems and the Ga-Ga bond in digallyne are clearly shown by this method as slipped double and triple bonds, respectively.