Etude en RMN du carbone 13 de dicoumarols substitués

The ¹³C n.m.r. spectrum of the bridge substituted dicoumarols are interpreted in order to obtain structural information for quantitative structure-activity relationships. The results are in agreement with those obtained by ¹H n.m.r. These dicoumarols exhibit double restricted rotation around both bridge bonds.     

Rearrangement thermique des adduits du tetracyanoethylene de 2H-pyrannes

The addition of tetracyanotehylene to 2H-pyrans 1 results in a mixture of two isomeric adducts 6. The thermal decomposition of the compounds 6 gives rise to both a small percentage of the retro Diels-Alder, and a new mode of evolution leading to a mixture of furans (E+Z) 7. A detailed interpretation of the ¹³C spectra of the compounds 7 was established by comparison with the ¹³C spectra of 2,5-diphenylfuran and trans-stilbene. The structure 7 is confirmed by chemical degradation.     

Zur Theorie der ebenen,instationären Unterschallströmung um ein schwingendes Profil im Kanal

Summary The mixed boundary value problem for the determination of the velocity potential of an unsteady perturbation flow past an oscillating thin profile in an inviscid compressible gas at subsonic speeds is treated. After the separation of the wave-like terms in the Fourier expansions of the reduced potential, satisfying the Helmholtz wave equation, the boundary value problem for the remaining potential is transformed into a functional equation of the generalized Wiener-Hopf type by means of the Laplace transform. The familiar Wiener-Hopf technique leads to a linear system of infinitely many unknowns which can be solved by iteration for not too small profile lengths. Finally, two analytic expressions for the reduced potential in terms of different kernel functions and formulae for the lift and moment acting on the profile are written down.

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Diese Arbeit enthält einen Teil der von der Mathematisch-Naturwissenschaftlichen Fakultät der Universität des Saarlandes am 30. Oktober 1963 angenommenen Habilitationsschrift des Verfassers.     

Carbon-13 spin–lattice relaxation in some polyfluoroaromatic compounds

Carbon-13 chemical shifts, spin-lattice relaxation times and nuclear Overhauser enhancement factors are reported for five polyfluoroaromatic compounds at 28°C. In all cases the relaxation of the fluorine bearing carbon is predominantly dipolar. Effective correlation times are smaller than those of the analogous benzene derivatives by a factor of 3–4, in qualitative agreement with predictions from the Stokes–Einstein diffusion theory. The T₁ values for the para-carbon of monosubstituted fluorobenzenes is clearly shorter than the T₁ values for the ortho- and meta-carbons. This phenomenon was traced to anisotropic tumbling, and D∥ and D⊥ diffusion coefficients were computed using Woessner's equations for molecules assumed to behave like symmetric rotors about their C₂ in-plane principal symmetry axis. Equal tumbling ratios, D∥/D⊥, were found in this way for toluene and perfluorotoluene.     

Synthesis,Electrochemical, and Optical Properties of New Fluorescent,Substituted Thieno[3,2-b][1]Benzothiophenes

The synthesis, electrochemical and optical properties of three fluorescent substituted thieno[3,2-b][1]benzothiophenes (TBT) derivatives, including 3-methoxythieno[3,2-b][1]benzothiophene (3-MeO-TBT), 2,3-dimethylthieno[3,2-b][1]benzothiophene (2,3-diMe-TBT), and 6-methoxythieno[3,2-b][1]benzothiophene-2-carboxylate (6-MeO-TBT-2-COOMe), were investigated. The oxidation potential values varied between 1.40 and 1.20 V/SCE according to the electronic substituent effect, and electropolymerization attempts, performed in 0.1 M LiClO₄ acetonitrile solution, led to the formation of very thin films of poly(3-MeO-TBT) and poly(2,3-di-Me-TBT). Electronic absorption spectra, fluorescence excitation and emission spectra, fluorescence quantum yields (Φ_F) , lifetimes (τ_F), and other photophysical parameters of the three new TBT derivatives were measured in DMSO solutions at room temperature. For the methyl-and methoxy-substituted TBT derivatives, the fluorescence emission peak were slightly red shifted relative to that of unsubstituted TBT (Δλ_em = 1–12 nm) whereas, in the case of 6-MeO-TBT-2-COOMe, a rather strong red-shift (Δλ_em = 73 nm) was attributed to the existence of a “push-pull” electronic interaction of the MeO and COOMe groups. All Φ_F values were rather high, varying between 0.11 and 0.35, according to the substituent effect. Fluorescence decays were mono-exponential and τ_F values were very short, ranging between 0.11 and 0.30 ns for the substituted TBT derivatives until study.     

SELEX and dynamic combinatorial chemistry interplay for the selection of conjugated RNA aptamers

SELEX (for Systematic Evolution of Ligands by Exponential enrichment) has proven to be extraordinarily powerful for the isolation of DNA or RNA aptamers that bind with high affinity and specificity to a wide range of molecular targets. However, the modest chemical functionality of nucleic acids poses some limits on the versatility of aptamers as binders and catalysts. To further improve the properties of aptamers, additional chemical diversity must be introduced. The design of chemical modifications is not a trivial task. Recently, dynamic combinatorial chemistry (DCC) has been introduced as an alternative to traditional combinatorial chemistry. DCC employs equilibrium shifting to effect molecular evolution of a dynamic combinatorial library of molecules. Herein, we describe an original process that combines DCC and SELEX for the in vitro selection of modified aptamers which are conjugated to chemically diverse small-molecules. Its successful application for the selection of small-molecule conjugated RNA aptamers that bind tightly to the transactivation-response (TAR) element of HIV-1 is presented.     

Radiative heat transfer at nanoscale: Closed-form expression for silicon at different doping levels

Radiative heat transfer at the nanoscale is becoming an important technological issue with the development of nano electromechanical systems (NEMS). In this article, we derive asymptotic expressions to compute near-field radiative heat transfer between two planes of silicon. We identify two physical mechanisms that give the dominant contribution at small gaps. For intrinsic and low-doped silicon, the main contribution is due to evanescent waves coming from propagating waves undergoing frustrated total internal reflections at the interfaces. For doping levels larger than N_e=10¹⁶ cm^?3 surface mode coupling contributes to the heat transfer. Asymptotic expressions are also given in that case. In all cases, we compare analytical formulas with exact numerical calculations when varying the temperature and the doping concentration. We also give their range of validity.     

Solvent Effects on the NMR Chemical Shifts of Imidazolium-Based Ionic Liquids and Cellulose Therein

The interactions of ionic liquids (IL) with solvents usually used in liquid-state nuclear magnetic resonance (NMR) spectroscopy are studied. The ¹H- and ¹³C-NMR chemical shift values of 1-n-butyl-3-methyl (BM)- and 1-ethyl-3-methyl (EM)-substituted imidazolium (IM) -chlorides (Cl) and -acetates (Ac) are determined before and after diluting with deuterated solvents (DMSO-d₆, D₂O, CD₃OD, and CDCl₃). The dilution offers structural modifications of the IL due to the solvents capacity to ionization. For further investigation of highly viscous cellulose dopes made of imidazolium-based IL, solid-state NMR spectroscopy enables the reproducibility of liquid-state NMR data of pure IL. The correlation of liquid- and solid-state NMR is shown on EMIM-Ac and cellulose/EMIM-Ac dope (10 wt %).