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1.
Patrizia Scafato Francesca Caprioli Laura Pisani Daniele Padula Fabrizio Santoro Giuseppe Mazzeo Sergio Abbate France Lebon Giovanna Longhi 《Tetrahedron》2013
Three forms of chiroptical spectroscopies, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and optical rotatory dispersion (ORD) have been employed to study the configuration and conformational properties of the three molecules: (S)-3-phenylcyclopentanone, (S)-3-phenylcyclohexanone, and (S)-3-phenylcycloheptanone (including (S)-3-phenylcyclopentanone-2,2,5,5-d4 and (S)-3-phenylcyclohexanone-2,2,6,6-d4). ECD and VCD spectra in the mid-IR for the three molecular systems are marginally dependent on fine conformational details, as interpreted in terms of standard DFT computational methods, with common spectroscopic features to the three systems clearly identified. Accounting for vibronic coupling mechanisms reproduces the structuring of ECD n→π∗ band. The ORD curves are quite similar for the three types of molecules, but their interpretation highlights a crucial role played by conformations of the cycloalkanone ring in the case of (S)-3-phenylcycloheptanone. The same conclusions are reached by considering the VCD spectra in the CH-stretching region. 相似文献
2.
Yeasudhasan Christu Rajan 《Tetrahedron letters》2008,49(18):3023-3026
Enantiopure bis-chromanones were prepared from (S)-Binol and bromo esters via a Baylis-Hillman approach. Chiroptical studies indicate that the two-naphthyl units of the chromanone system are non-coplanar. 相似文献
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《Analytical letters》2012,45(20):1725-1733
Abstract A new simple and fast micro method has been established to determine the optical purity of a small amount of amino acids (0.1–1 μg/ml). The amino acids react readily with fluorescamine to form pyrrolinone-type chromophores, which show strong CD bands at 400–300 nm and much larger optical rotation than the free amino acids in the visible spectral range. 相似文献
5.
Yimei Yin Katsuyoshi Nishinari Hongbin Zhang Takahiro Funami 《Macromolecular rapid communications》2006,27(12):971-975
Summary: The existence of liquid‐crystalline (LC) phases in dilute methylcellulose solutions is demonstrated by exothermic peaks in differential scanning calorimetry (DSC) curves upon heating and is evidenced by a discontinuity of the dynamic storage modulus when the concentration of methylcellulose increases. This crystalline phenomenon is further confirmed by polarized light microscopy and optical rotatory dispersion measurements. It is found that the appearance of the LC formation is related to the temperature, concentration, and molecular weight of methylcellulose.
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Reinhold Tacke Thomas Kornek Tilman Heinrich Christian Burschka Martin Penka Melanie Pülm Christine Keim Ernst Mutschler Günter Lambrecht 《Journal of organometallic chemistry》2001,640(1-2):140-165
The C/Si/Ge-analogous compounds rac-Ph(c-C5H9)El(CH2OH)CH2CH2NR2 (NR2=piperidino; El=C, rac-3a; El=Si, rac-3b; El=Ge, rac-3c) and (c-C5H9)2El(CH2OH)CH2CH2NR2 (NR2=piperidino; El=C, 5a; El=Si, 5b; El=Ge, 5c) were prepared in multi-step syntheses. The (R)- and (S)-enantiomers of 3a–c were obtained by resolution of the respective racemates using the antipodes of O,O′-dibenzoyltartaric acid (resolution of rac-3a), O,O′-di-p-toluoyltartaric acid (resolution of rac-3b), or 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (resolution of rac-3c). The enantiomeric purities of (R)-3a–c and (S)-3a–c were ≥98% ee (determined by 1H-NMR spectroscopy using a chiral solvating agent). Reaction of rac-3a–c, (R)-3a–c, (S)-3a–c, and 5a–c with methyl iodide gave the corresponding methylammonium iodides rac-4a–c, (R)-4a–c, (S)-4a–c, and 6a–c (3a–c→4a–c; 5a–c→6a–c). The absolute configuration of (S)-3a was determined by a single-crystal X-ray diffraction analysis of its (R,R)-O,O′-dibenzoyltartrate. The absolute configurations of the silicon analog (R)-4b and germanium analog (R)-4c were also determined by single-crystal X-ray diffraction. The chiroptical properties of the (R)- and (S)-enantiomers of 3a–c, 3a–c·HCl, and 4a–c were studied by ORD measurements. In addition, the C/Si/Ge analogs (R)-3a–c, (S)-3a–c, (R)-4a–c, (S)-4a–c, 5a–c, and 6a–c were studied for their affinities at recombinant human muscarinic M1, M2, M3, M4, and M5 receptors stably expressed in CHO-K1 cells (radioligand binding experiments with [3H]N-methylscopolamine as the radioligand). For reasons of comparison, the known C/Si/Ge analogs Ph2El(CH2OH)CH2CH2NR2 (NR2=piperidino; El=C, 7a; El=Si, 7b; El=Ge, 7c) and the corresponding methylammonium iodides 8a–c were included in these studies. According to these experiments, all the C/Si/Ge analogs behaved as simple competitive antagonists at M1–M5 receptors. The receptor subtype affinities of the individual carbon, silicon, and germanium analogs 3a–8a, 3b–8b, and 3c–8c were similar, indicating a strongly pronounced C/Si/Ge bioisosterism. The (R)-enantiomers (eutomers) of 3a–c and 4a–c exhibited higher affinities (up to 22.4 fold) for M1–M5 receptors than their corresponding (S)-antipodes (distomers), the stereoselectivity ratios being higher at M1, M3, M4, and M5 than at M2 receptors, and higher for the methylammonium compounds (4a–c) than for the amines (3a–c). With a few exceptions, compounds 5a–c, 6a–c, 7a–c, and 8a–c displayed lower affinities for M1–M5 receptors than the related (R)-enantiomers of 3a–c and 4a–c. The stereoselective interaction of the enantiomers of 3a–c and 4a–c with M1–M5 receptors is best explained in terms of opposite binding of the phenyl and cyclopentyl ring of the (R)- and (S)-enantiomers. The highest receptor subtype selectivity was observed for the germanium compound (R)-4c at M1/M2 receptors (12.9-fold). 相似文献
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The performance of time-dependent density functional theory (TDDFT) for calculations of long-range exciton circular dichroism (CD) is investigated. Tetraphenylporphyrin (TPP) is used as a representative of a class of strongly absorbing chromophores for which exciton CD with chromophore separations of 50 Å and even beyond has been observed experimentally. A dimer model for TPP is set up to reproduce long-range exciton CD previously observed for a brevetoxin derivative. The calculated CD intensity is consistent with TPP separations of over 40 Å. It is found that a hybrid functional with fully long-range corrected range-separated exchange performs best for full TDDFT calculations of the dimer. The range-separation parameter is optimally tuned for TPP, resulting in a good quality TPP absorption spectrum and small DFT delocalization error (measured by the curvature of the energy calculated as a function of fractional electron numbers). Calculated TDDFT data for the absorption spectra of TPP are also used as input for a ‘matrix method’ (MM) model of the exciton CD. For long-range exciton CD, comparison of MM spectra with full TDDFT CD spectra for the dimer shows that the matrix method is capable of producing very accurate results. A MM spectrum obtained from TPP absorption data calculated with the nonhybrid Becke88–Perdew86 (BP) functional is shown to match the experimental brevetoxin spectrum ‘best’, but for the wrong reasons. 相似文献
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Jie Ren Dan Zhao Shi-Jie Wu Jie Wang Yun-Jing Jia Wen-Xin Li Hua-Jie Zhu Fei Cao Wan Li Charles U. Pittman Xiang-Jiu He 《Tetrahedron》2019,75(9):1194-1202
The absolute configuration of cepharanthine (1), a strongly bioactive bisbenzylisoquinoline alkaloid exhibiting 12 specific bioactivities without any reported negative side-effects, has been reassigned from (1R,1′S) to (1R,1′R) using quantum theory. The absolute configurations (ACs) of 13 other analogues of 1 were also systematically reassigned. Six quaternary salts were prepared from 1 and one exhibited strong anti-bacterial activity against Bacillus subtilis with MIC 0.31?μM, while Ciprofloxacin, the positive control medicine was 3.88?μM. This work established the critical importance of correlating chiroptical experimental spectra with their quantum mechanically predicted spectra for accurate stereogenic center assignments. 相似文献
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Prof.Dra M. L. García O. Valls S. García M. Baucells M. Roura G. Lacort 《Colloid and polymer science》1987,265(3):267-270
The ORD spectra of three types of glycogen in salt solutions at different concentrations, pH and ionic strength values were determined to investigate the influence of these variables on the rotatory power.The ORD curves obtained with the samples recently prepared correspond to positive monotone dispersion curves, similar to available data for the other polysaccharides.Once the mutarotation equilibrium is attained a maximum is observed at 210±10 nm. The rotatory power decreases with the elapsed time and in some cases, it is possible to find a change in the sign of these curves. Such a phenomenon may be attributed to conformational changes in the monomer units constituting the macromolecule.A considerable increase in the rotatory power is found at pH extreme values.The dispersion constant,ORDER="0">
c
, was calculated by means of a modified Drude equation and results indicate that theORDER="0">
c
value is higher for muscle glycogen in the mussel species, suggesting a higher degree of asymmetry in this macromolecule. 相似文献