Vibrational structure of complex compound emission spectra measured by dynamical photon flux fluctuations as predicted in quantum theory of irreversible processes

The 10 K emission spectrum of Cs₂TeBr₆ was measured by recording the fluctuating photon flux. Since this fluctuation, according to the theory, is due to the dynamic coupling of the molecular system to the environment controlling the dissipation of energy, it should depend on the frequency of the emitted photons. By this, the vibrational structure of the transition has been resolved which could not be obtained by usual emission spectroscopy.Dedicated to Professor Dr. H. Hartmann, Frankfurt am Main, on the occasion of his seventieth birthday     

Das “Angular Overlap”-Modell für niedersymmetrische Koordinationsverbindungen

Zusammenfassung Eine kurze Ableitung des Angular Overlap-Modells wird gegeben. Das Modell wird auf zweikernige Übergangsmetallkomplexe vom Typ L₅M-O-ML₅ angewandt. Die Parametrisierung vond-Orbitalwechselwirkungen liefert fürD _4h-Symmetrie die Orbitalreihenfolgee _g<b _2g=b _1u<e _u ^* <a _1g ^* <b _1g=b _2u<a _2u ^* . Aus dem Orbitalschema lassen sich die magnetischen (intramolekularer Antiferromagnetismus) und die optischen Eigenschaften (Elektronenspektren) erklären, die sich von den gewinkelten Molekülen wesentlich unterscheiden. Der im linearen Cr-Komplex neu auftretende Bandentyp wird einem Übergang einesd-Elektrons in ein Molekülorbital zugeordnet, das über die Cr-O-Cr-Bindungsregion delokalisiert ist.

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Angular overlap treatment of low symmetry complexesII. Binuclear complexes with a linear oxygen bridge

A short derivation of the Angular Overlap model is presented. It is applied on binuclear transition metal complexes of the type L₅M-O-ML₅. A parametrization ofd-orbital interactions forD _4h symmetry yields the energy ordere _g<b _2g=b _1u<e _u ^* <a _1g ^* <b _1g=b _2u<a _2u ^* . From the orbital scheme the magnetic (intra molecular antiferromagnetism) and optical properties (electron spectra) are explained, which are different from corresponding molecules with angled structure. The new type of bands found in the spectrum of the linear Cr complex is assigned to a transition of ad electron into a molecular orbital which is delocalized over the Cr-O-Cr bond moiety.

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Résumé Une brève représentation du modèle Angular Overlap est donnée. Le modèle est appliqué aux composés binucléaires de groupes de transition du type L₅M-O-ML₅. La parametrization des interactions des orbitalesd pour la symétrieD _4h donne les énergies d'orbitalese _g<b _2g=b _1u<e _u ^* <a _1g ^* <b _1g=b _2u<a _2u ^* . Cette série peux expliquer les propriétés magnétiques (antiferromagnétisme intramoléculaire) et optiques, qui sont différent de molécules avec structure angulaire. Le nouveau type des bandes trouvé dans le spectre du complex linéaire Cr est assigné à la transition d'un électrond dans une orbitale moléculaire qui est délocalisée sur la région de liaison Cr-O-Cr.

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Dem Andenken von Herrn Professor Hans-Ludwig Schläfer gewidmet.

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Herrn Prof. Dr. Hans-Ludwig Schläfer, der das Thema dieser Arbeit anregte, danke ich an dieser Stelle nochmals herzlich für viele wertvolle Diskussionen. Der Deutschen Forschungsgemeinschaft, Bad Godesberg, sei für die Bereitstellung finanzieller Mittel gedankt.     

Magnetic behavior of the oxide spinels: Li0.5Fe2.5−2x Al x Cr x O4

In order to study the effect of substitution of Fe³⁺ by Al³⁺ and Cr³⁺ in Li_0.5Fe_2.5O₄ on its structural and magnetic properties, the spinel system Li_0.5Al _x Cr _x Fe_2.5?2x O₄ (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and ⁵⁷Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al³⁺ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5).     

Gas analysis with IR-diode laser spectrometers

Summary An IR laser diode spectrometer of modular design with micro-processor control is presented. It consists of laser source (vibration decoupled refrigerator with temperature control unit and laser power supply), mode filter, open-path and detector modules, and electronics for the data evaluation. For quantitative gas analysis the diode is tuned by periodic current pulses over the frequency range of a selected spectral line. The determination of the gas concentration is based on the measurement of the extinction of the signal integrated over the absorption line profile (integrative spectroscopy). As an example the measurement of the atmospheric minor constituent carbon monoxide is described for an open path of 50 m.

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Gasanalyse mit IR-Diodenlaser-Spektrometern

Zusammenfassung Ein modular aufgebautes, mikroprozessor-gesteuertes IR-Diodenlaser-Spektrometer wird vorgestellt. Es besteht aus dem Laser-Modul (vibrationsentkoppelter Kühler mit Temperaturregler und Laserstromversorgung), dem Modenfilter, der Meßstrecke und dem Detektor-Modul und der Auswerteelektronik. Für die quantitative Gasanalyse wird die Laserdiode mit periodischen Stromimpulsen derart durchgestimmt, daß der Frequenzbereich der jeweils ausgewählten Spektrallinie während des Impulses durchlaufen wird. Die Bestimmung der Gaskonzentration beruht auf der Messung der Extinktion, integriert über das Profil der betreffenden Absorptionslinie (Integrativspektroskopie). Als Anwendungsbeispiel wird die Messung des atmosphärischen Spurengases Kohlenmonoxid auf einer 50m langen Fernmeßstrecke beschrieben.

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 70th birthday     

DNA-Diagnostik genetisch bedingter Erkrankungen

Ohne Zusammenfassung

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DNA-Diagnosis of diseases of genetic origin

     

What a Difference an OH Makes: Conformational Dynamics as the Basis for the Ligand Specificity of the Neomycin‐Sensing Riboswitch

To ensure appropriate metabolic regulation, riboswitches must discriminate efficiently between their target ligands and chemically similar molecules that are also present in the cell. A remarkable example of efficient ligand discrimination is a synthetic neomycin‐sensing riboswitch. Paromomycin, which differs from neomycin only by the substitution of a single amino group with a hydroxy group, also binds but does not flip the riboswitch. Interestingly, the solution structures of the two riboswitch–ligand complexes are virtually identical. In this work, we demonstrate that the local loss of key intermolecular interactions at the substitution site is translated through a defined network of intramolecular interactions into global changes in RNA conformational dynamics. The remarkable specificity of this riboswitch is thus based on structural dynamics rather than static structural differences. In this respect, the neomycin riboswitch is a model for many of its natural counterparts.     

Non-empirical calculations on diatomic transition metals. I. An investigation of various orbital contraction schemes of gaussian basis sets on the SCF level for Zn2

Ab initio SCF LCAO MO calculations with various contracted primitive gaussian basis sets were performed using Zn₂ as an example. When improving the basis set, polarization functions are shown to be more important for a proper reproduction of the repulsive potential curve, than a complete relaxation of the orbital contraction. This is considered to be true for all diatomics although for Zn₂ at larger internuclear distances no varr der Waals minimum is obtained on the SCF level.     

Nonempirical calculations on diatomic transition metals. II. RHF investigation of lowest closed-shell states of homonuclear 3d transition-metal dimers

Potential-energy curves of the 3d dimer series Sc₂ through Cu₂ are calculated for the lowest closed-shell states within the nonempirical RHF formalism using limited basis sets of minimal to near-double-zeta–plus-polarization size. Calculated spectroscopic constants are compared to semiempirical results as well as to experimental estimates. The possibility for closed- or open-shell ground states is discussed for each dimer. For diatomic Sc and Cu a detailed study of basis set effects on calculated molecular constants is carried out.     

Pyridylpyrrolides as alternatives to cyclometalated phenylpyridine ligands: synthesis and characterization of luminescent zinc and boron pyridylpyrrolide complexes

The synthesis, structure, and properties of six luminescent pyridylpyrrolide complexes and the first structural characterization of pyridylpyrrolide metal complexes are reported. A series of new zinc complexes, bis(pyridylpyrrolyl)zinc, (R2PyrPy)2Zn (R = Me, Et, iPr, tBu, and Ph), that vary in their substituents on the pyrrole ring (Me, Et, iPr, tBu, and Ph), were prepared. Pyrrole substitution produced small structural changes in the complexes and affected the fluorescence properties very little. The zinc complexes were found to be luminescent, emitting at 495 nm (Phi = 0.32, 0.32 0.31, 0.19 and 0.57, respectively). A boron analog, (Me2PyrPy)BF2, was prepared and was found to share the luminescent properties with the zinc complexes, emitting at 505 nm (Phi = 0.22), but not their water-sensitivity. A total of four crystal structures are reported, tBu2PyrPyH, (Me2PyrPy)2Zn, (tBu2PyrPy)2Zn, and (Me2PyrPy)BF2. tBu2PyrPyH crystallizes as a doubly hydrogen bonded dimer with non-coplanar pyridine and pyrrole rings. The solid-state structures of (Me2PyrPy)2Zn and (tBu2PyrPy)2Zn revealed that despite the large change in steric bulk, the two compounds have very similar structures. The structure of (Me2PyrPy)BF2 showed changes that are expected with the interaction between a smaller atom (B as compared to Zn). Molecular orbital calculations were performed on Me2PyrPyH, (Me2PyrPy)BF2, and (Me2PyrPy)2Zn using Gaussian 98 methods. It was found that the main transition (HOMO-LUMO) for all three molecules is a pi-->pi* transition and that in the inorganic complexes, the metal atom (zinc or boron) present has very little effect on transition, evidence that the optical properties are largely ligand based and that the B or Zn atom's main effect is lowering of the LUMO relative energy.     

Effects of electrolyte and pH on the behavior of cross-linked films of ferrocene-modified poly(ethylenimine)

Ferrocene redox polymers based on the coupling of ferrocenecarboxaldehyde to both linear and branched poly(ethylenimine) (PEI) have been prepared to investigate the effects of pH, electrolyte, and cross-linking on electron charge transport and film swelling. The redox behavior of both ferrocene-modified linear PEI and ferrocene-modified branched PEI was investigated by cyclic voltammetry, while electron diffusion coefficients reported for PEI-based redox polymers were determined by electrochemical impedance spectroscopy. In phosphate solutions at pH>7, cross-linked films of both redox polymers exhibited multiple redox wave behavior and were unstable. In contrast, in non-phosphate solutions, cross-linked films exhibited stable electrochemical behavior and fast electron transfer in solutions with pH<11. Gel swelling experiments suggested that the multiple wave behavior and instability exhibited in either phosphate solutions or at high pH in non-phosphate solutions were related to a combination of film collapse and electrolyte binding within the hydrogel. The electron diffusion coefficients for these polymers are on the order of 10-8 (mol cm(-2) s(-1/2)), which are approximately 40 times greater than other ferrocene-modified polymers. Incorporation of the enzyme, glucose oxidase, into these films demonstrated that these redox polymers were able to electrically communicate with the enzyme's flavin adenine dinucleotide (FAD) redox centers. Glucose sensors based on these films exhibited enzyme saturation current densities that ranged from 240 to 480 microA/cm2 in response to glucose, which were dependent upon the supporting electrolyte and pH. The sensitivity of these sensors at 5 mM glucose ranged from 10 to 48 microA.cm(-2).mM(-1).