Circular dichroism spectra of trans-chalcone epoxides

The electronic absorption and CD spectra of (−)-trans-chalcone epoxide and its derivatives with methyl and alkoxy substituents at the ortho-positions of the aromatic rings have been measured. The spectra have been assigned with help of the energies, oscillatory strengths, and rotatory strengths of the singlet transitions obtained from DFT calculations. The features of the CD spectra, indicative of the absolute configuration, are the carbonyl n–π¹ band and two further strong bands assigned to the overlapping signals of π–π¹ and n_epoxy–π¹ excitations.     

Circular dichroism of some sesquiterpene lactones of the germacrane type

The CD spectra of a series of germacranolides have been considered, and the parameters of the Cotton effects observed have been correlated with the stereochemistries of the compounds studied. The applicability for germanocranolides of the Waddell-Stocklin-Geissman rule is discussed.Deceased.Institute of the Chemistry of Plant Substances of the Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 176–179, March–April, 1986.     

Circular dichroism of the products of the amination of lactones

The circular dichroism method has been used to study the products of the amination of sesquiterpene lactones containing α-methylene-γ-lactone groupings. Analysis of the results obtained has shown that in all the lactones considered the amination reaction takes place with the predominant formation of one of the possible stereochemical forms of the product of the addition of the amine to the exomethylene group of the lactone ring, namely, that having the 11S configuration.     

Circular dichroism—LXIII : Third-sphere contribution to the R-band cotton effect of lactones

The Cotton effect within the n→π* band of the lactone chromophore of the halo lactones 3a-c, prepared from (1S)-2-bromo adamantanedione-4.8 (1) is positive and can be used to determine unequivocally the sign of third-sphere contributions of the appropriate sector rule. An “axial” halogen (Cl, Br, I) substituent in a β-position to the keto group of these halogeno oxa-homoadamantanediones gives an antioctant contribution to the Cotton effect of the carbonyl chromophore as observed earlier for the corresponding halogeno-adamantanones.     

火菇素的圆二色性与溶液二级结构

为了弄清火菇素蛋白的结构与功能的关系并揭示抗癌机理,使其更好地发挥临床作用,测定了火菇素的圆二色性,并用蛋白质二级结构解析程序分析了火菇素的溶液二级结构。火菇素远紫外圆二色性的研究表明,其水溶液在208nm处表现为宽大负峰,最大平均残基摩尔椭圆度[θ]~2~0~8=-6574deg·cm^2·dmol^-^1,在223nm处为肩,经二级结构解析程序计算分析,火菇素的二级结构和二硫键和芳香氨基酸对火菇素圆二色性的贡献分别为77.4%和22.6%,二级结构的组成为：α-螺旋19.7%,β-折叠和β-转角50.1%,无规卷曲和γ-转角30.2%。火菇素二级结构对pH,SDS和乙醇有一定的稳定性,在pH4.6～9.4范围内,火菇素的结构几乎不发生变化,但在碱性太强的环境中火菇素发生不可逆变性,火菇素对热变性很敏感。     

Circular dichroism spectra and absolute configuration of some aryl methyl sulfoxides

The absorption and circular dichroism (CD) spectra of three aryl sulfoxides, i.e. (-)-(S)-1-naphthyl methyl sulfoxide, (S)-1, (-)-(S)-1-(2-methyl)naphthyl methyl sulfoxide, (S)-2 and (-)-(S)-9-phenanthryl methyl sulfoxide, (S)-3, have been interpreted by means of the coupled oscillator model formulated by DeVoe. Theoretical spectra have been calculated starting from input geometries provided by molecular mechanics (MMX) calculations and by employing standard spectroscopic parameters to describe the allowed transitions of the aromatic and the sulfoxide chromophores. The satisfactory agreement between the predicted and experimental spectra allows us to confirm the configurational assignment of these compounds as (-)/(S). The analysis of CD spectra, affording the right assignment of the absolute configuration (AC) of the alkyl aryl sulfoxides, then offers a practical alternative to the more complex vibrational circular dichroism spectroscopy and ab initio optical rotation calculation techniques that have been used very recently to assign the AC of (-)-2 and (-)-3.     

Circular dichroism spectra of 1,2,3,4,5,6-Hexahydro-2,6-methano-3-benzazocines

Circular dichroism curves of levorotatory 1,2,3,4,5,6-hexahydro-2,6-methano-3-benzazocin-8-ol derivatives have been determined and correlated with stereochemical features. Compounds with the rectus configuration at C-6 were found to exhibit negative extrema for the long wavelength phenolic π → π* transition. The remaining Cotton effects have been ascribed to specific aromatic π → π* transitions.     

Optical rotatory dispersion and circular dichroism. LXXV. Circular dichroism of some aryl-amino acids

CD. curves have been recorded for α-aryl-α-amino acids, esters and amides related to α-phenylglycine, α-phenyl-alanine and their N-dimethyl derivatives, and for the corresponding α-cyclohexyl-α-amino acids and esters. Compounds with the (S)-configuration at the single asymmetric carbon atom give strong positive Cotton effects near 220 nm. The conformations of the acids are discussed and compared with those of other α-amino acids.     

Circular dichroism of 5α-deuteriocholesta-1,3-diene

Replacement of the 5α-hydrogen by deuterium in 5α-cholesta-1,3-diene decreased the Δ at 262 nm (in hexane) from ?2.37 ± 0.06 to ?2.18 ± 0.04.     

Investigation of the circular dichromism spectra of bromine-substituted nucleic acid fragments II. Circular dichroism spectra of 5-bromine-substituted pyrimidine nucleotides

Summary The CD spectra of 5-bromine-substituted derivatives of nucelotides of uracil and cytosine, namely the ribo- and 2-deoxyribonucleoside 5-monophosphates, have been obtained in neutral, acid, alkaline, and alcoholic solutions. Three CEs have been recorded in the 220–300 nm region, corresponding to -* transitions in the B_2u, B_1u, and E_1ua bands. It has been concluded that an intramolecular hydrogen bond exists between 0–2 and the 2-hydroxyl in the 5-bromine-substituted ribonucleotides of uridine and cytidine. A transition of the conformational type localized at a pH equal to the pK value of the heterocyclic base has been detected for 5-bromo-UMP and UMP. On comparing the main characteristic of the CD spectra of the compounds investigated with the spectra of the unbrominated analogs given in the literature, it has been concluded that the halogenation of a pyrimidine base in position 5 does not fundamentally change the ratio of the most probable rotational stereomers, and the compounds investigated have the anti conformation in solution.Institute of Molecular Genetics, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 204–208, March–April, 1979.     

Circular dichroism spectra of the inclusion complexes of phlorizin in cyclodextrins

Two aromatic rings of a phlorizin molecule form inclusion complexes with -CD and -CD. Induced circular dichroism spectra of these complexes have been measured to estimate the orientation of the two aromatic rings in the hydrophobic space of CDs. Apparent complex formation constants have been also estimated for each complex. It is concluded that phlorizin forms a stronger inclusion complex with -CD than with -CD.     

Investigation of the circular dichroism spectra of bromine-substituted nucleic acid fragments I. Circular dichroism spectra of 8-bromine-substituted purine nucleotides

Summary The CD spectra of 8-bromo-AMP, 8-bromo-dAMP, 8-bromo-GMP, and 8-bromo-dGMP in acid, neutral, and alkaline media and, in some cases, in methanol have been obtained. In the 200–300 nm region three Cotton effects have been recorded which correspond to -* in the B_2u, B_1u, and E_1ua bands (280–265, 240–250, and 200–220 nm, respectively). The CD spectra obtained differ from the spectra known in the literature for unbrominated compounds of this class. It has been shown that in ribonucleotides the syn conformation is stabilized by the formation of an intramolecular hydrogen bond with the participation of the ribose 2-hydroxyl and the N₃ atom of the purine base. The 5-phosphate group in the molecule of a purine nucloside of the syn type changes the CD profile, particularly in the short-wave region of the spectrum, as compared with the CD spectra of the unbrominated analogs given in the literature.Institute of Molecular Genetics, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 199–204, March–April, 1979.     

Circular dichroism spectra of straight chain mono-olefins. Assignment of ethylene transitions

The circular dichroism spectra of three optically active alkenes, S, 3-methyl-1-pentene, S,4-methyl-1-hexene and S,5-methyl-1-heptane have been measured in the spectral region 200-140 nm in the gas phase. An intense CD band which does not have a well defined analogue in the absorption was observed in all three compounds and is assigned as π → σ_(CH)^*. A second prominent CD band at higher energy is assigned as σ_(CH) → π^*. The assignments of low frequency CD bands are discussed.     

Circular dichroism spectra of DNA hairpins studied by the green function method

The circular dichroism (CD) spectrum of a large biological molecule represented as an array of interacting chromophores is investigated. The configuration-averaged Green function formalism is developed to describe the CD and absorption spectra. The perturbation theory expansion is derived for absorption and CD spectra in the case of strong interaction of chromophores with their environment (solvent and/or internal dynamics) compared to their interaction with each other. We apply this formalism to study CD spectra of DNA hairpins.     

Circular dichroism spectra of planar chiral 2-substituted ferrocenecarboxaldehydes and 2-ferrocenyl-1,1-dicyanoethylenes

Circular dichroism spectra of a series of planar chiral 2-substituted ferrocene carboxaldehydes and 2-ferrocenyl-1,1-dicyanoethylenes are reported. They show Cotton effects associated with intramolecular charge transfer transitions and are related to the absolute configuration of these compounds.     

Circular dichroism and electronic spectra of 2,2′-dimethyl-1,1′-binaphthyl anion radical

The circular dichroism and electronic spectra of the 2,2′-dimethyl-1,1′-binaphthyl anion radical have been studied. The assignments of the complicated absorption bands of the species were made with the aid of the signs in the circular dichroism spectrum and the dihedral angle of the anion radical was set in the range 100°–110°.     

Optical activity of lactones and lactams—IV : Chiroptical properties of 4-imidazolidinones

The chiroptical properties of 4-imidazolidinones are reviewed. Several optically active compounds were obtained from amides and N-methylamides of corresponding N-acylamino acids. The origin of the two lowest energy electronic transitions is considered. The equilibrium between the two envelope conformations of heterocyclic ring was observed by means of NMR and CD spectra. The spectra of the compounds with non-protected amino group are affected by n → σ^* transition involving nitrogen lone pair.     

Circular dichroism in the angle-resolved C 1s photoemission spectra of gas-phase carvone enantiomers

The inner-shell C 1s photoionization of randomly oriented molecules of the chiral compound carvone has been investigated using circularly polarized synchrotron radiation up to 30 eV above threshold. Binding energies of the C=O and CH2= carbon 1s orbitals were determined to be 292.8+/-0.2 and 289.8+/-0.2 eV, respectively. The remaining C-H C 1s levels substantially overlap under an intense central peak centered at 290.5+/-0.2 eV. The angle-resolved photoemission from the carbonyl carbon C=O core orbital in pure carvone enantiomers shows a pronounced circular dichroism of approximately 6% at the magic angle of 54.7 degrees to the light beam propagation direction. This corresponds to an expected 0 degrees -180 degrees forward-backward electron emission asymmetry of approximately 10%. On changing between the R and S enantiomers of carvone the sense or sign of the asymmetry and associated dichroism effectively reverses. The observed circular dichroism, and its energy dependence, is well accounted for by calculations performed in the pure electric dipole approximation.