Enhancing the Water Stability of Al‐MIL‐101‐NH2 via Postsynthetic Modification

The resistance of metal–organic frameworks towards water is a very critical issue concerning their practical use. Recently, it was shown for microporous MOFs that the water stability could be increased by introducing hydrophobic pendant groups. Here, we demonstrate a remarkable stabilisation of the mesoporous MOF Al‐MIL‐101‐NH₂ by postsynthetic modification with phenyl isocyanate. In this process 86 % of the amino groups were converted into phenylurea units. As a consequence, the long‐term stability of Al‐MIL‐101‐URPh in liquid water could be extended beyond a week. In water saturated atmospheres Al‐MIL‐101‐URPh decomposed at least 12‐times slower than the unfunctionalised analogue. To study the underlying processes both materials were characterised by Ar, N₂ and H₂O sorption measurements, powder X‐ray diffraction, thermogravimetric and chemical analysis as well as solid‐state NMR and IR spectroscopy. Postsynthetic modification decreased the BET equivalent surface area from 3363 to 1555 m² g^?1 for Al‐MIL‐101‐URPh and reduced the mean diameters of the mesopores by 0.6 nm without degrading the structure significantly and reducing thermal stability. In spite of similar water uptake capacities, the relative humidity‐dependent uptake of Al‐MIL‐101‐URPh is slowed and occurs at higher relative humidity values. In combination with ¹H‐²⁷Al D ‐HMQC NMR spectroscopy experiments this favours a shielding mechanism of the Al clusters by the pendant phenyl groups and rules out pore blocking.     

Variant superfield representations

We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields.     

Exponential averaging for traveling wave solutions in rapidly varying periodic media

Reaction diffusion systems on cylindrical domains with terms that vary rapidly and periodically in the unbounded direction can be analyzed by averaging techniques. Here, using iterated normal form transformations and Gevrey regularity of bounded solutions, we prove a result on exponential averaging for such systems, i.e., we show that traveling wave solutions can be described by a spatially homogenous equation and exponentially small remainders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ab Initio Structure/Reactivity Investigations of Illudin‐Based Antitumor Agents: A Model for Reaction in vivo

(Hydroxymethyl)acylfulvene (HMAF, irofulven; 4 ), a third‐generation derivative of a natural product extracted from the mushroom Omphalotus illudens, is selectively toxic towards certain forms of malignant tumors. Conversion of HMAF and cognates to stable aromatic derivatives is triggered by thiol attack in vitro and in vivo. Quantum‐chemical methods predict well the structure for several functionalized derivatives of irofulven as compared to known X‐ray crystallographic structures. Computational reaction profiles for thiol attack and aromatic rearrangement of irofulven and illudin S, a toxin from which irofulven is derived, provide insight into HMAF's selectivity and toxicity. Methods used include hybrid density‐functional theory (HDFT), Hartree? Fock (HF), and Møller? Plesset second‐order perturbation theory (MP2). Solvent effects have been explored by means of the new continuum‐solvation method, COSab, presented in an accompanying paper.     

Standing waves, clustering, and phase waves in 1D simulations of kinetic relaxation oscillations in NO+NH3 on Pt(1 0 0) coupled by diffusion

The Lombardo–Imbihl–Fink (LFI) ODE model of the NO+NH₃ reaction on a Pt(1 0 0) surface shows stable relaxation oscillations with very sharp transitions for temperatures T between 404 and 433 K. Here we study numerically the effect of linear diffusive coupling of these oscillators in one spatial dimension. Depending on the parameters and initial conditions we find a rich variety of spatio-temporal patterns which we group into four main regimes: bulk oscillations (BOs), standing waves (SW), phase clusters (PC), and phase waves (PW). Two key ingredients for SW and PC are identified, namely the relaxation type of the ODE oscillations and a nonlocal (and nonglobal) coupling due to relatively fast diffusion of the kinetically slaved variables NH₃ and H. In particular, the latter replaces the global coupling through the gas phase used to obtain SW and PC in models of related surface reactions. The PW exist only under the assumption of (relatively) slow diffusion of NH₃ and H.     

Über die katalytische Hydrierung von Chinolen

Zusammenfassung Bei der katalytischen Hydrierung von freien Chinolen werden unter Wasserstoffaufnahme hydroaromatische Verbindungen gebildet, während bei den Chinolen andere Reduktionsmethoden, sowie bei den Chinolacetaten auch die katalytische Hydrierung zur Ausbildung von aromatischen Körpern führen.Unserem verehrten Lehrer, Herrn Prof. Dr.F. Wessely, in Dankbarkeit zum 60. Geburtstag gewidmet.     

Stereochemistry and the use of H2/D2 mixtures as probes into the mechanism of hydrogenations catalyzed by cationic rhodium (DIPHOS) complexes

The stereochemistry of the hydrogenation of 4-tert-butylmethylenecyclohexane (1) and the use of D₂ or D₂/H₂ mixtures in place of H₂ furnishes evidence that hydrogenations using the catalyst precursor [Rh(DIPHOS)(COD)]⁺BF ₄ ⁻ proceed via more than one mechanism. This evidence includes the effect of changes in pressure and added triethylamine upon the kinetics and isomerization of 1, as well as the distribution of the added deuterium in the products of the reaction of 1 or norbornene with either D₂ or H₂/D₂ mixtures. That an alkene necessarily causes the equilibration of H₂/D₂ mixtures, although it need not involve any of the alkenes’s hydrogen atoms (e.g., norbornene), provides a clue to the process by which the mononuclear mechanism proposed by Halpern, which is dominant near one atmosphere of H₂, merges into another with increasing pressure. It has been proposed that the cationic complex [Rh(DIPHOS)S₂]⁺ is transformed in the presence of an alkene and hydrogen into a binuclear hydrido complex, such as those described by Sivak and Muetterties (1979) and Fryzuk (1982), which represent a far more active catalyst than its mononuclear precursor. Such an intermediate should readily catalyze the H₂-D₂ equilibration and the isomerization of an alkene in the presence of D₂ without necessarily introducing deuterium into the product. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 88–97. Deceased. The text was submitted by the authors in English. This work was conducted at the University of Arkansas.     

THE EFFECTS OF THROMBOXANE INHIBITORS ON THE MICROVASCULAR AND TUMOR RESPONSE TO PHOTODYNAMIC THERAPY

Abstract— Vascular stasis and tissue ischemia are known to cause tumor cell death in several experimental models after photodynamic therapy (PDT); however, the mechanisms leading to this damage remain unclear. Because previous studies indicated that thromboxane release is implicated in vessel damage, we further examined the role of throm-boxane in PDT. Rats bearing chondrosarcoma were injected with 25 mg/kg Photofrin® (intravenously) 24 h before treatment. Light (135 J/cm ² , 630 nm) was delivered to thc tumor area after injection of one of the following inhibitors: (1) R68070: a thromboxane synthetase inhibitor; (2) SQ-29548: a thromboxane receptor antagonist; and (3) Flunarizine: an inhibitor of platelet shape change. Systemic thromboxane levels were determined. Vessel constriction and leakage were evaluated by intravital microscopy. Tumor response was assessed after treatment. Thromboxane levels were decreased more than 50% with SQ-29548 as compared to controls. Thromboxane levels in animals given R68070 and Flunarizine remained at baseline levels. SQ-29548 and R68070 reduced vessel constriction compared to controls, while Flunarizine totally prevented vessel constriction. R68070 and SQ-29548 inhibited vessel permeability compared to PDT controls; Flunarizine did not. Animals given these inhibitors showed markedly reduced tumor cure. These results indicate that the release of thromboxane is linked to the vascular response in PDT.