Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies

Electronic excitation energy transfer (EET) rates in rylene diimide dyads are calculated using second-order approximate coupled-cluster theory and time-dependent density functional theory. We investigate the dependence of the EET rates on the interchromophoric distance and the relative orientation and show that Forster theory works quantitatively only for donor-acceptor separations larger than roughly 5 nm. For smaller distances the EET rates are over- or underestimated by Forster theory depending on the respective orientation of the transition dipole moments of the chromophores. In addition to the direct transfer rates we consider bridge-mediated transfer originating from oligophenylene units placed between the chromophores. We find that the polarizability of the bridge significantly enhances the effective interaction. We compare our calculations to single molecule experiments on two types of dyads and find reasonable agreement between theory and experiment.     

Nitraza-/Oxa-Propylene- and Hydrazonemethylene-Bridged 1,2,4-Nitraminotriazoles and Selected Salts

Two new bridged nitraminotriazoles with bridging oxapropylene and nitrazapropylene moieties were synthesized, and converted into several salts, as well as from the hydrazonemethylene bridged nitraminotriazole. All compounds were fully characterized by NMR and IR spectroscopy, elemental analysis as well as differential thermal analysis. The sensitivity towards friction and impact were determined according to BAM standard technics and the energetic properties were calculated by using the EXPLO5 computer code. The neutral compounds as well as the various salts were examined in terms of their physicochemical properties and detonation performance to each other and compared to the commonly used secondary explosive RDX.     

Selected Nitrocarbamates of Glycerine & Co. and the First Acetylene Derivative

A simple two step synthesis route for the preparation of several energetic multivalent nitrocarbamates of easily available alcohols is presented. The carbamates were obtained by the reaction of the alcohols and the reactive reagent chlorosulfonyl isocyanate (CSI) with subsequent aqueous work‐up. The nitration of the carbamates was performed with mixed acid (nitric and sulfuric acid). The thermal stabilities were explored by using differential scanning calorimetry and the energies of formation were calculated on the CBS‐4M level of theory, as well as several detonation and propulsion parameters for the application as energetic materials. All compounds were fully characterized and discussed in addition with single X‐ray diffraction.     

Tumor selectivity at short times following systemic administration of a liposomal temoporfin formulation in a murine tumor model

Meso-tetra(hydroxyphenyl)chlorin (mTHPC) (INN: Temoporfin) is one of the most potent photodynamically active substances in clinical use. Treatment protocols for Temoporfin-mediated photodynamic therapy often rely on drug-light intervals of several days in order for the photosensitizer to accumulate within the target tissue, though tumor selectivity is limited. Here, the mTHPC localization was studied at 2-8 h following systemic administration of a liposomal Temoporfin formulation (0.15 mg kg(-1) b.w.) in HT29 human colon adenocarcinoma in NMRI nu/nu mice. Photosensitizer distribution within tumor and internal organs was investigated by means of high performance liquid chromatography following chemical extraction, as well as in situ fluorescence imaging and point-monitoring fluorescence spectroscopy. For tumor tissue, the Temoporfin concentrations at 4 h (0.16+/-0.024 ng mg(-1)) and 8 h (0.18+/-0.064 ng mg(-1)) were significantly higher than at 2 h (0.08+/-0.026 ng mg(-1)). The average tumor-to-muscle and the tumor-to-skin selectivity were 6.6 and 2, respectively, and did not vary significantly with time after photosensitizer injection. In plasma, the Temoporfin concentration was low (0.07+/-0.07 ng mg(-1)) and showed no significant variation with time. Our results indicate a rapid biodistribution and clearance from the bloodstream. Within the same type of organ, data from both fluorescence methods generally exhibited a significant correlation with the extraction results.     

Single-shot experiments for the acquisition of coherence-transfer functions in real time.

Simple pulse sequences are introduced that make it possible to acquire experimental Hartmann-Hahn transfer functions for arbitrary multiple-pulse sequences in a single shot. With this approach it is possible to study the detailed dependence of coherence-transfer functions on experimental parameters in real time.     

In Situ Characterization of Polymorphic Forms: The Potential of Raman Techniques

The use of hot-stage Raman microscopy — the direct coupling of Raman spectroscopy and thermomicroscopy — is demonstrated for the drug substances paracetamol and lufenuron.Paracetamol is a well-known analgesic and antipyretic drug, for which three polymorphic forms are currently known. Lufenuron is a benzoylphenyl urea derivative that has been classified as a chitin synthesis inhibitor. It is indicated for the use in pets for the prevention and control of flea population and used in crop protection for the control of Lepidoptera, Western Flower thrips and rust mites. It is the first time that the polymorphism of lufenuron is addressed. All known modifications of paracetamol and lufenuron were produced and identified by hot-stage Raman microscopy. A close correlation of thermal and spectroscopic information was achieved by this combination of techniques.For lufenuron a series of new polymorphic forms were found and characterized. Raman spectroscopy allowed to identify the thermodynamic stable form A as the one which is marketed in tablets.This revised version was published online in November 2005 with corrections to the Cover Date.     

Offset dependence of homonuclear hartmann-hahn transfer based on residual dipolar couplings in solution state NMR

The offset dependence of homonuclear Hartmann-Hahn transfer is markedly different if a given multiple-pulse sequence is applied to dipolar coupled spins or to isotropically coupled spins. The different offset dependence of the transfer efficiency is studied by numerical simulations of a multiple-pulse sequence and by the analytical treatment of a simple model experiment.