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171.
N. I. Shuikin I. F. Bel'skii A. T. Balaban K. D. Nenitsesku 《Russian Chemical Bulletin》1962,11(3):452-454
Summary By hydrogenation in the vapor phase on a platinum catalyst at 200–210° we have formed from 2-acetyl-3-alkyl-5-methylfurans the 2,6-dimethyl-4-alkyltetrahydropyranes with yields of 40–45%. 相似文献
172.
Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids
Marioara Bem Marilena Vasilescu Miron T. Caproiu Constantin Draghici Adrian Beteringhe Titus Constantinescu Mircea D. Banciu Alexandru T. Balaban 《Central European Journal of Chemistry》2004,2(4):672-685
An interesting observation was made when studying the S
N
Ar reaction between several 4-aryloxy-7-nitrobenzofurazans (2) and several amino acids leading to the apparition of detectable fluorescence from the substitution products3. Acidic amino acids reacted very slowly=while basic amino acids react fastest with2 having an unsubstituted phenyl or a 4-formyl-phenyl Ar group. Amongst neutral amino acids, proline reacts fastest at room
temperature after 100 min. With2 having a methoxy-subtituted Ar group. 相似文献
173.
Schalk O Brands H Balaban TS Unterreiner AN 《The journal of physical chemistry. A》2008,112(8):1719-1729
The photophysics of 5,10,15,20-tetra-p-tolyl-21H,23H-porphyrin (TTP-H2) and 5,10,15,20-tetra-p-tolyl-porphyrinato zinc II (ZnTTP) have been investigated by means of pump-probe and transient anisotropy experiments. After excitation to the Q band, the molecules were probed by NIR pulses in the range between 950 and 1350 nm in order to study states of gerade symmetry in the vicinity of the Soret band. Examination of transient spectra and anisotropy delivered the first direct observation and the excitation energies of the two lowest so-called dark states. The experimental results were compared with predictions from theoretical calculations. 相似文献
174.
Balaban TS Berova N Drain CM Hauschild R Huang X Kalt H Lebedkin S Lehn JM Nifaitis F Pescitelli G Prokhorenko VI Riedel G Smeureanu G Zeller J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(30):8411-8427
A number of new porphyrins equipped with complementary triple hydrogen-bonding groups were synthesized in good yields. Self-assembly was investigated by NMR spectroscopy, dynamic light scattering (DLS), and atomic force microscopy (AFM). These artificial antenna systems were further characterized by stationary and time-resolved fluorescence techniques to investigate several yet unsolved questions on the mechanism of excitation energy transfer (EET) in supramolecular systems. For example, the photophysics of a simple D--U[triple chemical bond]P--A dyad was studied, in which donor D and acceptor A are ZnII- metalated and free-base porphyrins, respectively, and U (uracyl) and P (2,6-diacetamidopyridyl) are complementary hydrogen-bonding groups linked by flexible spacers. In this dyad, the EET occurs with about 20 % efficiency with a lifetime of 14 ps. Reversal of the nonsymmetric triple hydrogen-bonding groups to give a A--U[triple chemical bond]P--D construct results in an EET efficiency of about 25 % and a lifetime of 19 ps. Thus, there is a slight directionality of EET mediated by these asymmetric triple hydrogen-bonding units tethered to flexible spacers. In polymeric systems of the type P-D-P[triple chemical bond]U-A-U[triple chemical bond]P-D-P, or U-D-U[triple chemical bond]P-A-P[triple chemical bond]U-D-U, the EET efficiency doubles as each donor is flanked by two acceptors. Because doubling the probability of photon capture doubles the EET efficiency, there is no energy amplification, which is consistent with the "antenna effect". For these polymeric systems, AFM images and DLS data indicate large rodlike assemblies of a few hundred nanometers, whereas the components form much smaller aggregates under the same conditions. To understand the importance of the flexible hydrogen-bonding zipper, three different covalently bridged D-B-A molecules were synthesized in which the bridge B is a rigid steroidal system and the same ester chemistry was used to link the porphyrins to each end of the steroid. The geometry inferred from molecular modeling of D-B-A indicates geometric similarities between B and some conformations of the --P[triple chemical bond]U-- supramolecular bridge. Although the EET efficiency is a factor of two greater for the steroidal systems relative to the supramolecular dyads, the rate is 50-80 times slower, but still slightly faster than that predicted by F?rster-type mechanisms. Circular dichrosim (CD) spectra provide a conformational sampling of the porphyrin groups appended on the steroidal skeleton, thus allowing an estimation of the orientation factor kappa for the transition dipole moments, which significantly affects the EET rate. We conclude that the flexible hydrogen-bonded linked systems are adaptive and have variable geometries with foldamers in which the D and A groups can approach well under 1 nm. In these folded conformations, a rapid EET process occurs, probably also involving a Dexter-type exchange mechanism, thus explaining the fast EET relative to the rigid steroidal compounds. This study predicts that it is indeed possible to build large supramolecular antennas and the component design and supramolecular dynamics are essential features that dictate EET rates and efficiencies. 相似文献
175.
We revisited the π‐electron ring partitions in catacondensed benzenoids and re‐examined structural regularities reported for the ring partitions in these compounds, seeking the origin of the observed regularities. We examined the distribution of the π‐electron ring partitions by counting the contributions arising from benzene rings having different assigned numbers of π‐electrons. This has led to a better insight into the underlying structure of the π‐electron ring partitions and also to a novel and unique π‐electron “signature” of individual rings in benzenoid hydrocarbons. The physical interpretation of the local π‐electron ring partition represents the local π‐electron density of benzenoid molecules, and is not an alternative index of local aromaticity as one may erroneously assume. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
176.
Fatma Hamurcu Ayla Balaban Gündüzalp Servet ?ete Birgül Erk 《Transition Metal Chemistry》2008,33(1):137-141
Metal complexes derived from amides; N,N′-bis(2-thiophenecarboxamido)-1,3-diamino propane (1) and N,N′-bis(2-furancarboxamido)-1,3-diaminopropane (2) were characterized by elemental analysis, spectral (NMR, FT-IR, LC-MS) methods, magnetic moment, molar conductance, and TGA/DTA
studies. The complexes were dimeric and have the general formula [ML.Clm.(H2O)n]2Cl2 where M=Cu(II), Zn(II), Co(III); m = 1, 2; n = 0, 1. The antimicrobial activities of the amides and their complexes were studied against the bacteria; Escherichia coli (ATCC 11230), Yersinia enterocolitica (ATCC 1501), Bacillus magaterium (RSKK 5117), Bacillus cereus (RSKK 863), Bacillus subtilis (RSKK 863) and yeast; Candida albicans (ATCC 10239). 相似文献
177.
Alexandru T. Balaban Douglas J. Klein William A. Seitz 《International journal of quantum chemistry》1996,60(5):1065-1068
A discussion is presented for possible diamond-lattice-based structures containing holes that can be filled with metal atoms or ions. To allow the formation of coordinative bonds to the metal, some carbon atoms should be replaced by heteroatoms (with nitrogen preferred, but in some cases oxygen or other heteroatoms may be considered). Two types of holes that may lead to the formation of coordinative bonds are discussed in detail: tetrahedral holes for four such bonds and quasi-octahedral holes for six such bonds. In turn, when suitably arranged in a translationally symmetric manner, these holes may resemble open or closed pores in foams; when they are open, the “channels” may lead to interesting properties with regard to metallic conductivity or superconductivity. © 1996 John Wiley & Sons, Inc. 相似文献
178.
179.
The aim of this study was to investigate the changes in carbohydrate components and the crystalline structure in hemp bast
fibers by adding ethyl acetate to acetic acid/water pulping processes. It was found that ethyl acetate added to acetic acid/water
process had a positive effect on yield, viscosity and carbohydrate components in pulp. It was assumed that the delignification
ratio increased by adding ethyl acetate to aqueous acetic acid pulping. Xylose content in hemp bast fibers was affected more
negatively in the ethyl acetate/acetic acid/water process than in the acetic acid/water one. Crystallinity and crystallite
size were higher in pulp sample obtained by the acetic acid/water process without ethyl acetate. 相似文献
180.
Tadeusz Balaban Joel Feldman Horst Kn?rrer Eugene Trubowitz 《Journal of statistical physics》2009,134(5-6):839-857
We develop a power series representation and estimates for an effective action of the form $$\ln\frac{\int e^{f(\phi,\psi)}d\mu(\phi)}{\int e^{f(\phi,0)}d\mu(\phi)}$$ Here, f(φ,ψ) is an analytic function of the real fields φ(x),ψ(x) indexed by x in a finite set X, and d μ(φ) is a compactly supported product measure. Such effective actions occur in the small field region for a renormalization group analysis. The customary way to analyze them is a cluster expansion, possibly preceded by a decoupling expansion. Using methods similar to a polymer expansion, we estimate the power series of the effective action without introducing an artificial decomposition of the underlying space into boxes. 相似文献