Dynamics of a Strongly Coupled Polaron

We study the dynamics of large polarons described by the Fröhlich Hamiltonian in the limit of strong coupling. The initial conditions are (perturbations of) product states of an electron wave function and a phonon coherent state, as suggested by Pekar. We show that, to leading order on the natural time scale of the problem, the phonon field is stationary and the electron moves according to an effective linear Schrödinger equation.     

Optimal estimates on free boundary propagation in thin-film flow

We present a method for the derivation of lower bounds on free boundary propagation for the thin-film equation, one of the most prominent examples of a higher-order degenerate parabolic equation. In particular, we obtain sufficient conditions for instantaneous forward motion of the free boundary, upper bounds on waiting times, as well as lower bounds on asymptotic propagation rates. Our estimates coincide (up to a constant factor) with the previously known reverse bounds and are therefore optimal. To the best of our knowledge, these results constitute the first lower bounds on free boundary propagation for any higher-order degenerate parabolic equation. Our technique is based on new monotonicity formulas for solutions to the thin-film equation which involve weighted entropies with singular weight functions. It turns out that our method is not restricted to the thin-film equation, but also applicable to other higher-order parabolic equations like quantum drift-diffusion equations. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization, spectrophotometric and electrochemistry studies,and DNA cleavage of copper(II) complexes of a new azacrown bis-macrocycle and its mono-cyclic analogue

A new azacrown bis-macrocycle (5) and its mono–cyclic analogue (7) were synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, DEPT ¹³C NMR, MS, and elemental analysis. The reaction with copper(II) nitrate yielded the corresponding complexes, formulated as Cu(5)(NO₃)₂·3H₂O (8), and Cu(7)(NO₃)₂·2.5H₂O (9). Also the stoichiometries of the complexes were determined in alcoholic solution and the results show that for both complexes the ratio of ligand to metal was 1:1 in methanol. The redox behavior of both complexes has been studied by cyclic voltammetry in DMF. Cyclic voltamogram of 8 shows quasi-reversible Cu^II/Cu^I redox couple whereas 9 shows a reversible Cu^II/Cu^I redox couple. Mono- and bis-macrocycle copper(II) complexes (8 and 9 respectively) cleaved plasmid pGS2 DNA by using an oxidative mechanism with 3- mercaptopropionic acid (MPA) as the reductant under aerobic conditions. The bis-macrocycle copper(II) complex 8 showed higher cleavage efficiency than their mono-macrocycle analogue 9 at the same Cu²⁺ concentration.     

Fluorescent signaling based on sulfoxide profluorophores: application to the visual detection of the explosive TATP

The first visual fluorescence-based assay for the peroxide explosive triacetone triperoxide (TATP) is described. The assay is based on a conceptually new fluorescence signaling mechanism, in which nonemissive pyrenyl sulfoxide profluorophores are oxidized to visibly emissive pyrenyl sulfones. Although not without limitations, these first-generation fluorescent probes can provide a visual response to ca. 100 nmol of TATP. In addition, the success of this assay suggests the potential for broader application of aryl sulfoxides in fluorescent chemosensing.     

Identification and characterization of a new family of catalytically highly active imidazolin-2-ylidenes

A new class of easily accessible and stable imidazolin-2-ylidenes has been synthesized where the side chains are comprised of substituted naphthyl units. Introduction of the naphthyl groups generates C 2 -symmetric ( rac) and C s- symmetric ( meso) atropisomers, and interconversion between the isomers is studied in detail both experimentally and computationally. Complete characterization of the carbenes includes rare examples of crystallographically characterized saturated NHC structures. Steric properties of the ligands and an investigation of their stability are also presented. In catalysis, the new ligands show versatility comparable to the most widely used NHCs IMes/SIMes or IPr/SIPr. Excellent catalytic results are obtained when either the NHC salts (ring-opening alkylation of epoxides), NHC-modified palladium compounds (C-C and C-N cross-couplings), or NHC-ruthenium complexes (ring-closing metathesis, RCM) are employed. In several cases, this new ligand family provides catalytic systems of higher reactivity than that observed with previously reported NHC compounds.     

Synthesis and Selected Transformations of 1H‐Imidazole 3‐Oxides Derived from Amino Acid Esters

A series of new optically active 1H‐imidazole 3‐oxides 5 with a substituted acetate group at N(1) as the chiral unit were prepared by the reaction of α‐(hydroxyimino) ketones, α‐amino acid methyl esters, and formaldehyde. In an analogous reaction, ethyl 2‐(hydroxyimino)‐3‐oxobutyrate and 1,3,5‐trialkylhexahydro‐1,3,5‐triazines gave 3‐oxido‐1H‐imidazole‐4‐carboxylates 14 , which easily rearranged into the 2‐oxo derivatives 15 . Selected examples of N‐oxides 5 could be transformed into the corresponding 2,3‐dihydro‐1H‐imidazole‐2‐thione derivatives 10 via a ‘sulfur‐transfer reaction’, and the reduction of the histidine derivative 5i with Raney‐Ni yielded the optically active 2,3‐bis(imidazolyl)propanoate 12 . Furthermore, reaction of the (1H‐imidazol‐1‐yl)acetates with primary amines yielded the corresponding acetamides.     

Specific colorimetric detection of cyanide triggered by a conformational switch in vitamin B12

"Base on"/"base off" coordination of the intramolecular bound benzimidazole nucleobase of vitamin B 12 allows the specific colorimetric detection of millimolar concentrations of cyanide in water. In various competition experiments, it was demonstrated that up to 12 different anions as well as a 1000-fold excess of Cl (-) over CN (-) do no interfere with the sensor. An 8-fold increased sensitivity in the "naked eye" detection of CN (-) was observed when water was replaced by MeOH/H 2O (5%) as a solvent.     

Synthesis and Conformational Analysis of Pentapeptides Containing Enantiomerically Pure 2,2‐Disubstituted Glycines

The synthesis and conformational analysis of model pentapeptides with the sequence Z‐Leu‐Aib‐Xaa‐Gln‐Valol is described. These peptides contain two 2,2‐disubstituted glycines (α,α‐disubstituted α‐amino acids), i.e., Aib (aminoisobutyric acid), and a series of unsymmetrically substituted, enantiomerically pure amino acids Xaa. These disubstituted amino acids were incorporated into the model peptides via the ‘azirine/oxazolone method’. Conformational analysis was performed in solution by means of NMR techniques and, in the solid state, by X‐ray crystallography. Both methods show that the backbones of these model peptides adopt helical conformations, as expected for 2,2‐disubstitued glycine‐containing peptides.     

Preparation of 3-Bromo-1,2,4,5-tetrazine

In this synthetic procedure, a seven-step protocol for the preparation of monosubstituted 3-bromo-1,2,4,5-tetrazine is presented. The procedure features efficient transformations and purification methods starting from commercially readily available starting materials and affords the title compound on a gram scale with 13 % overall yield in reliable purity (>97 %). Detailed experimental procedures, supported by images and additional notes, allow the preparation of a valuable advanced building block, enabling further applications in bioconjugation, protein labelling, bio-orthogonal chemistry, heterocycle syntheses, high energy materials, and drug release, among others.     

Half-sandwich para-cymene ruthenium(II) naphthylazophenolato complexes: Synthesis,molecular structure,light emission,redox behavior and catalytic oxidation properties

A series of conformationally rigid half-sandwich organoruthenium(II) complexes with the general formula [(η⁶-p-cymene)RuCl(L)] (where L = mono anionic 2-(naphthylazo)phenolato ligands) have been synthesized from the reaction of [{(η⁶-p-cymene)RuCl}₂(μ-Cl)₂] with a set of 2-(naphthylazo)phenolato O,N-donor ligands. All the ruthenium complexes were fully characterized by FT-IR, ¹H NMR, and UV–Vis spectroscopy as well as elemental analysis. In dichloromethane solution all the metal complexes exhibits characteristic metal-to-ligand charge transfer bands (MLCT) and emission bands in the visible region. The molecular structure of one of the complexes [Ru(η⁶-p-cymene)(Cl)(L2)] (2) was determined by X-ray crystallography. Electrochemical data of all the ruthenium complexes show a two metal centered voltammetric responses with respect to Ag/AgCl at scan rate 100 mV s⁻¹. Further, the complex (2) efficiently catalyzes the oxidation of a wide range of alcohols to their corresponding carbonyl compounds in the presence of N-methylmorpholine-N-oxide (NMO) up to 97%.