Application of the method of increments to the adsorption of CO on the CeO2(110) surface

We have combined an embedded-cluster model with an extension of the method of increments to treat the adsorption of molecules on a surface. In this way we are able to investigate the physisorption of CO on CeO(2)(110) at the MP2, MP4(SDTQ), and CCSD(T) levels with only moderate computational costs. We find that, at the CCSD(T) level, 25% of the adsorption energy originates from electron correlation. The interactions of the CO molecule with its five nearest cerium and oxygen neighbors in the surface layer make the largest contributions to the electron correlation. Approximately 97% of the adsorption-induced electron correlation energy part of the adsorption energy is recovered by the method of increments (in our chosen expansion), at the MP2 level.     

The Thermal Diastereomerization of the Tryptophane-Derived Green Fluorescent Protein Chromophore

Summary. Two model compounds for the tryptophane variant of the green fluorescent protein chromophore containing a 3-indolyl and 2-pyrrolyl moiety were prepared. For the first one the (Z)-diastereomer was found to be more stable than the (E)-diastereomer by 5.7 kJ mol⁻¹. It could be photo-diastereomerized and its thermal equilibration was studied, whereas the second one underwent photo-destruction. From an Arrhenius plot an activation barrier for the (E) to (Z) diastereomerization of 85.6 kJ mol⁻¹ could be determined. Thus, it could be demonstrated that in contrast to the corresponding phenyl derivative studied recently the tyrosine- and tryptophane-derived chromophores of the green fluorescent protein are amenable to fast thermal diastereomerization, which is of fundamental importance for the fluorescence and photoswitching processes in the corresponding proteins.     

Photoinduced energy and electron transfer processes in hexapyropheophorbide a- fullerene [C(60)] molecular systems

The photophysical properties of the novel hexapyropheophorbide a (P6), and hexakis (pyropheophorbide a)-C60 (FP6) were studied and compared with those of hexakis (pyropheophorbide a)-fullerene [5:1] hexaadduct (FHP6). It was found that after light absorption the pyropheophorbide a molecules in all three compounds undergo very efficient energy transfer as well as partly excitonic interactions. The last process results in the formation of energy traps, which could be resolved experimentally. For P6, due to shorter distances between neighboring dye molecules, stronger interactions between pyropheophorbide a units than for FHP6 were observed. As a consequence, the excitation energy is delivered rapidly to traps formed by stacked pyropheophorbide a molecules resulting in the reduction of fluorescence, intersystem crossing, and singlet oxygen quantum yields compared to the values of FHP6. For FP6 the reduction of these values is much stronger due to an additional fast and efficient deactivation process, namely photoinduced electron transfer from pyropheophorbide a to the fullerene moiety. Consequently, FP6 can be considered as a combination of a light-harvesting system consisting of several separate pyropheophorbide a molecules and a charge-separating center.     

Smectic liquid single crystal elastomers

In the liquid crystalline (I.c.) state the backbone of l.c-polymers has to adapt an anisotropic conformation that is consistent with the I.c.-phase structure. For macroscopically uniformly aligned samples this anisotropic backbone conformation can be obtained by applying a suitable mechanical field on chemically crosslinked I.c-polymers. Introducing the network anisotropy a priori by synthesis, stable macroscopically aligned I.c.-networks can be realized. We have called these networks Liquid Single Crystal Elastomers (LSCE) because their physical properties resemble that of organic or inorganic single crystals.     

Abtrennung und Bestimmung des Fluorid-Ions mit Hilfe siliciumorganischer Verbindungen

Zusammenfassung Fluorid läßt sich aus sauren wäßrigen Lösungen nach Reaktion mit Triäthyl-silanol, Diäthyl-silandiol, Dimethyl-phenyl-silanol oder Diphenyl-silandiol bzw. den entsprechenden Chlorverbindungen ausschütteln; dabei können zahlreiche organische Lösungsmittel verwendet werden. Die Umsetzung zu den Fluor-silanen verläuft verhältnismäßig langsam, kann aber durch hohe Säurekonzentrationen beschleunigt werden.Als Fluor-silan-Verbindung in der organischen Phase gelöstes Fluorid läßt sich mit halbgesättigter Natriumhydrogencarbonat-Lösung wieder aus der organischen Lösung entfernen, doch verläuft auch diese Reaktion recht langsam. Es ist einfacher, das Fluorid als Triäthyl-fluorsilan auszuschütteln und in der organischen Lösung gas-chromatographisch oder massenspektrometrisch zu bestimmen.Die Abtrennung des Fluorids durch Ausschütteln als siliciumorganische Verbindung wird nur durch Zirkonium und hohe Konzentrationen an Kieselsäure, Thorium oder Vanadium(V) gestört.

---

Summary The reaction products of fluoride with triethyl-silanol, diethyl-silane-diol, dimethyl-phenyl-silanol, and diphenyl-silane-diol or with the corresponding chlorosilanes can be extracted from acid aqueous solutions by many different organic solvents. The velocity of this reaction is rather slow, but increases in solutions of high acidity.Fluoride can be back-extracted from organic fluorosilane solutions by half-saturated sodium hydrogencarbonate. Yet, this process is slow, too. Preferably, fluoride will be determined as triethyl-fluoro-silane directly in the organic phase by gas chromatography or mass spectrometry.The extraction of fluoride by means of these organosilicon compounds is specific; it is interfered with partly by zirconium and by high concentrations of silica, thorium, and vanadium.

---

---

Dissertation, Mainz 1967.

---

Wir danken Herrn Prof. O. Süs, Wiesbaden-Biebrich, für wertvolle Ratschläge, Herrn Prof. W. Fischer, Hannover, und den Farbenfabriken Bayer AG, Leverkusen, für freundliche Überlassung von Scandiumoxid bzw. Diphenyl-dichlorsilan und von komplexen Fluoriden. Wir danken dem Bundesministerium für wissenschaftliche Forschung für großzügige Gewährung von Sachmitteln.     

Low-temperature formation of cubic β-PbF2: precursor-based synthesis and first-principles phase stability study

A precursor-based approach to the cubic β-phase of PbF(2) was developed and allowed the preparation of this high-temperature phase well below the temperature for transition from the orthorhombic α- to the cubic β-phase. The formation of β-PbF(2) from the molecular precursors Pb[Se(C(6)H(2)(CF(3))(3))](2) and Pb(C(6)H(2)(CF(3))(3))(2) is facilitated by the presence of several short PbF contacts in these molecules. The cubic form of PbF(2) was obtained as macroscopic crystals as well as nanoparticulate powder. Its formation at relatively low temperature suggested a theoretical re-investigation of the phase stabilities of the two polymorphs. The theoretical results from the Kohn-Sham density functional theory indicate that the energy content for the β-phase is slightly lower than the one for the α-phase, by 0.5-1.7 kJ mol(-1) depending on the density functional used (zero-point vibrational energy correction included).     

Allosteric and Chelate Cooperativity in Divalent Crown Ether/Ammonium Complexes with Strong Binding Enhancement

A thorough thermodynamic analysis by isothermal titration calorimetry of allosteric and chelate cooperativity effects in divalent crown ether/ammonium complexes is combined with DFT calculations including implicit solvent on the one hand and large‐scale molecular dynamics simulations with explicit solvent molecules on the other. The complexes studied exhibit binding constants up to 2×10⁶ m ^?1 with large multivalent binding enhancements and thus strong chelate cooperativity effects. Slight structural changes in the spacers, that is, the exchange of two ether oxygen atoms by two isoelectronic methylene groups, cause significantly stronger binding and substantially increased chelate cooperativity. The analysis is complemented by the examination of solvent effects and allosteric cooperativity. Such a detailed understanding of the binding processes will help to efficiently design and construct larger supramolecular architectures with multiple multivalent building blocks.     

Substituent size effects in lewis base induced reductions in organolanthanide chemistry

The reaction of the tripodal 1,3,5-trialkyl-1,3,5-triazacyclohexanes (L=cyclo-[N(R)CH(2)](3) , R=Et, iPr, tBu), with [Sm(AlMe(4))(3)] resulted in the formation of divalent samarium complexes of the constitution [{L(n)Sm(AlMe(4))(2)}(m)] (n, m=1,2) under ethane extrusion. These compounds were characterised by single-crystal X-ray diffraction and elemental analyses. Simultaneous occurrence of Lewis base induced reduction and C--activation reactions is observed. The ratio of products depends on the bulkiness of the N-alkyl substituent R. The reaction of [Sm(AlMe(4))(3)] with 1,3,5-triisopropyl-1,3,5-triazacyclohexane (TiPTAC) in benzene afforded the inversion-symmetric dimer [{(TiPTAC)(η(3)-AlMe(4))Sm}(2)(μ(2)-AlMe(4))(2)], whereas in toluene the pseudo-samarocene [(TiPTAC)(2)Sm(η(1)-AlMe(4))(2)] was obtained. The trisaluminate [(TiPTAC)Sm{(μ(2)-Me)(Me(2) l)}(2)(μ(3)-CH(2))(2)AlMe(2))] was found to be the C--activation product. In the case of the particular bulky 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane (TtBuTAC), the reaction led to the formation of the dimeric [{(TtBuTAC)(η(3)-AlMe(4))Sm}(2)(μ(2)-AlMe(4))(2)] even in toluene in comparably high yields. The decrease of the steric demand to ethyl groups in 1,3,5-triethyl-1,3,5-triazacyclohexane (TETAC) afforded the samarocene-like [(TETAC)(2) Sm(η(1)-AlMe(4))(2)] in lower yields. The resulting divalent samarium compounds are found to be stable with respect to reagents like dinitrogen, conjugated olefins and polycyclic aromatic systems.     

Reduction products of dinuclear [Rh2Cl2(CO)2 {μ-(PhO)2PN(Et)P(OPh)2}2]. Crystal structure of [Rh2HgCl(μ-H)(CO)2 {μ-(PhO)2PN(Et)P(OPh)2}2]

Treatment of [Rh₂Cl₂(CO)₂ {μ-(PhO)₂PN(Et)P(OPh)₂}₂] with various reducing agents gives a number of products, the type depending on the conditions employed. The products isolated include [Rh₂(CO)₂{μ-(PhO)₂PN(Et)P(OPh)₂}₂], [Rh₂(CO)₃{μ-(PhO)₂PN(Et)P(OPh)₂}₂],and [Rh₂HgCl(μ-H)(CO)₂{μ-(PhO)₂PN(Et)P(OPh)₂}₂]; the structure of the last complex was determined by X-ray diffraction.