Ultraviolet absorption spectra of α-nitroso β-naphthol and its copper chelate

From a comparative study of the U.V. absorption spectra of α-nitroso-β-naphthol and of β-naphthol in neutral ethanol and in the presence of 0.1N HClO₄ and 0.1N KOH respectively, evidence in favour of the quinone-oxime structure of α-nitroso-β-naphthol has been presented. The spectrum of the copper chelate of α-nitroso-β-naphthol indicates a planar configuration of the complex with considerable resonance between the quinonoid and benzenoid structures of the ligand.     

Molecular configuration of α-furil

X-ray diffraction studies on α-furil single crystals reveal that the two parts of the molecule are connected with a twofold symmetry axis perpendicular to the C-C single bond connecting the two carbonyl groups. The dihedral angles between the two halves of the molecule and the carbonyl/furan moieties are 46.7° and 2.7°, respectively.     

Davydov splitting in the polarized absorption spectra of single crystals of some copper complexes of α-amino acids

This paper presents the absorption spectra observed with polarized light of the single crystals of the copper complexes of L-alanine and DL--aminobutyric acid.The spectra are interpreted by the crystal-field theory.

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Zusammenfassung Es werden die Absorptionsspektren angegeben, welche mit Hilfe polarisierten Lichts an Einkristallen der Kupferkomplexe von L-Alanin und DL--AminobuttersÄure beobachtet wurden.Die Spektren wurden an Hand der Kristallfeldtheorie gedeutet.

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Résumé On donne les spectres d'absorption observés, à l'aide de lumière polarisée, aux cristaux uniques des complexes de cuivre du L-alanine et de l'acide DL--aminobutyrique.Les spectres sont interprétés suivant la théorie du champ cristallin.

     

Molecular configuration of α-naphthil

X-ray crystallographic studies on the molecular structure of α-naphthil reveal that the intercarbonyl dihedral angle is 87.29° whereas the naphthalene groups make angles of 4.26° and 6.98° with the respective carbonyl planes. The two naphthalene moieties are twisted about their central bonds.     

Triplet—triplet absorption and polarization spectra of phenazine

Employing laser photoselection spectroscopy, the triplet—triplet (T—T) polarization spectrum over the visible portion of the spectrum of phenazine was recorded. The strong T—T absorption band located in the violet portion of the spectrum is differently polarized from the flat band stretching from the blue to the red portion of the spectrum. This indicates the presence of two electronic transitions. The portion located in the violet spectral region is long-axis-polarized and presents the ³B⁻_3g ← ³B⁺_2u transition and the long-wavelength portion to the short-axis-polarized ³A⁻_1g ← ³B⁺_2u transition.     

Infra-red spectra of α-CrPO4-type phases

Infra-red spectra of polycrystalline samples of α-CrPO₄, RhPO₄ and CrAsO₄, the only known phases belonging to the α-CrPO₄ structural type, were recorded and briefly discussed with the aid of a factor group analysis.     

IR absorption spectra and structure of 4-cyano-4′,-p-alkoxybiphenyls

The IR absorption spectra of 4-cyano-4,-p-alkoxybiphenyls were investigated experimentally (in the range 100–3200 cm^–1 at 100–400 K), and they were interpreted on the basis of a calculation of the frequencies, forms, and intensities of the normal vibrations of various conformers of the propyloxycyanobiphenyl molecule. Temperature and phase changes in the parameters of the IR spectrum are explained by a change in the conformational composition and intermolecular interactions in the investigated liquid crystals.Institute of Physics, Ukrainian Academy of Sciences. Saratov State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 105–111, January–February, 1993.     

Mechanism of Formation and Molecular Structure of α-Halothioacetones

The mechanism of formation of -halo thioketones in reactions of haloacetones with H₂S in the presence of HCl was studied by quantum-chemical methods. The cause of failure in attempted preparation of iodo thioketone by this procedure was elucidated. The stereoelectronic structure and capability for 1,3-proto- tropic rearrangements of -halothioacetones were studied.     

Molecular Structure of α-Phenylselanyl-α-Acetylmethylenen Triphenylarsenium

1mTRODUCrIONAsWittigreactionplayedanimPOrtantroleinanolefinationmethod,anumberofrelevantinvestigationshavebeendone.Ifanorganoseleniumgroupisintroducedintoylide,itmaybepossibletoconnecttheorganoseleniumgroupwithmanyorganicmoleculesbyWittigreaction,obtainingalotoforganoseleniumcompounds,suchasa-seleno--a,g-unsaturatedcomPOunds.Althougha-selenophosphoniumylidesweresynthesized,a--electron--attractlug--groupsubstituteda-scienophosphoniurnylidescannotundergoWittigreaction(l'2}.Consideringthatt…     

Evolution of thermal disorder in the absorption and Raman spectra of all-trans-β-carotene

The temperature-dependent visible absorption and resonant Raman spectra of all-trans-β-carotene extremely diluted in dimethyl sulfoxide are investigated to clarify the effects of temperature on conjugated polyenes. The visible absorption and Raman spectra are found to blueshift with increasing temperature. The blueshift in polyenes is attributed to the decrease in the liquid density and the concomitant decrease in the refractive index by the Lorentz–Lorenz relation. We demonstrate that visible absorption is reproduced well by simple Franck–Condon analysis using a single Huang–Rhys factor over a temperature range. The analysis reveals features of temperature dependence in terms of important spectral parameters, such as line width, Raman scattering cross section and Huang–Rhys factor.     

Investigation of hydration of α-amino acids by means of absorption millimeter spectroscopy

The hydration indexes for 19 protein -amino acids are measured by means of absorption millimeter spectroscopy (AMS) at 31.42 GHz. The plot of the hydration indexes on the area of surface of aliphatic amino acid molecules accessible for water is a straight line located above the points corresponding to aromatic or polar amino acids. The contribution of nonpolar groups in the hydration index is greater than that of polar groups provided that their accessible surface areas are equal. The contribution to hydration of -OH and-CONH₂ groups in Ser. Gin, and Asn coincides in sign with that of pure hydrophobic hydration but the value of the contribution is significantly smaller. The change in mobility of water molecules, which is the basis of the AMS method, may serve as the physicochemical foundation for the construction of a new hydrophobicity scale for amino acids comparable with the already existing scales.Deceased September 2, 1995.Translated fromIzvestiya Akodemii Nauk. Seriya Khimicheskaya, No. 3, pp. 618–622, March, 1996.     

Fluorescence and excitation spectra of cinnamyl and α-styryl radicals

Radiolysis of solutions in alkane glasses at 77 K provides a convenient source of radicals derived from olefins, either by loss or by gain of a hydrogen atom. Fluorescence excitation spectroscopy has been used to trace absorption bands of radicals related to benzyl. Spectra of cinnamyl (1-phenyl-allyl) radicals derived from allyl-benzene, 1- and 2-phenyl-butadiene, are reported. Attempts at observing atropyl(2-phenyl-allyl) radicals were unsuccessful. The assignment of thermoluminescent emission of phenyl-acetylene solutions to α-styryl radicals is supported by their excitation spectra. Diphenyl acetylene gives similar phenyl-α-styryl radicals.     

π* ← n and π* ← π absorption spectra of aminopyrazine

π* ← n and π* ← π absorption spectra of aminopyrazine have been recorded and analysed assuming C_s symmetry for the molecule.     

Vibrational spectra and intermolecular potential of the α-form crystal of glycine

Polarized Raman and far i.r. spectra of glycine and N-deuterated glycine crystallized in the α-form were recorded. The normal coordinate analysis of the optical active intra- and intermolecular vibrations of the α-form crystal of glycine was carried out. A modified Urey—Bradley type intramolecular potential was adopted. The observed factor group splittings were elucidated fairly well by using the intermolecular potential including the exchange repulsion—dispersion interaction between non-bonded atoms and the Coulomb interaction. The stretching potential for the hydrogen bonds was found to contribute appreciably to the lattice frequencies.     

K–edge X–ray absorption spectra of argon in sputtered aluminum films

We have measured K–edge X–ray absorption spectra of argon in sputtered aluminum films at a synchrotron radiation facility (the Photon Factory). We found that the energy and shape of white line change when the film is annealed at 500 °C and the spectrum becomes resembling that of argon implanted in silicon. From the analyses of the X–ray absorption spectra and TEM observation we concluded that argon exists as very small atom clusters with a diameter less than 1 nm or exist as isolated atoms in the as–sputtered aluminum film, and that the size of the clusters become as big as 10 nm diameter when the film is heated.     

Analysis of optical absorption spectra of transition metal cluster ions by the spin-polarized DV-Xα method

Optical absorption spectra of cobalt cluster ions, Co _n ⁺ , and vanadium cluster ions, V _n ⁺ , were analyzed by a theoretical calculation based on the spin-polarized DV-Xα method, and their electronic and geometric structures were obtained. Relative absorption cross section associated with each electronic transition was calculated; the calculation enables a qualitative comparison of calculated spectrum with a measured one not only in its transition energy but also in its intensity profile. This analysis shows that Co ₄ ⁺ , Co ₃ ⁺ , and V ₄ ⁺ have, respectively, a tetrahedral structure with a bond distance of 2.00Å, an equilateral triangle with a bond distance of 2.30Å, and a distorted tetrahedral structure with five bonds having a distance of 2.34 Å and one of 2.89Å. The differences in the population between majority and minority spins (spin-difference) evaluated from the electronic structure thus obtained were 2.0, 1.7, and zero per atom in Co ₃ ⁺ , Co ₄ ⁺ , and V ₄ ⁺ , respectively. These spin differences indicate a ferromagnetic and an antiferromagnetic spin-coupling in the cobalt and vanadium cluster ions, respectively.     

The Molecular Basis of the Interaction of Cyclophilin A with α-Synuclein

Peptidylprolyl isomerases (PPIases) catalyze cis/trans isomerization of prolines. The PPIase CypA colocalizes with the Parkinson's disease (PD)-associated protein α-synuclein in cells and interacts with α-synuclein oligomers. Herein, we describe atomic insights into the molecular details of the α-synuclein/CypA interaction. NMR spectroscopy shows that CypA catalyzes isomerization of proline 128 in the C-terminal domain of α-synuclein. Strikingly, we reveal a second CypA-binding site formed by the hydrophobic sequence ⁴⁷GVVHGVATVA⁵⁶, termed PreNAC. The 1.38 Å crystal structure of the CypA/PreNAC complex displays a contact between alanine 53 of α-synuclein and glutamine 111 in the catalytic pocket of CypA. Mutation of alanine 53 to glutamate, as found in patients with early-onset PD, weakens the interaction of α-synuclein with CypA. Our study provides high-resolution insights into the structure of the PD-associated protein α-synuclein in complex with the most abundant cellular cyclophilin.     

Molecular dynamics studies of α-helix stability in fibril-forming peptides

Diseases associated with protein fibril-formation, such as the prion diseases and Alzheimer’s disease, are gaining increased attention due to their medical importance and complex origins. Using molecular dynamics (MD) simulations in an aqueous environment, we have studied the stability of the α-helix covering positions 15–25 of the amyloid β-peptide (Aβ) involved in Alzheimer’s disease. The effects of residue replacements, including the effects of Aβ disease related mutations, were also investigated. The MD simulations show a very early (2 ns) loss of α-helical structure for the Flemish (Aβ(A21G)), Italian (Aβ(E22K)), and Iowa (Aβ(D23N)) forms associated with hereditary Alzheimer’s disease. Similarly, an early (5 ns) loss of α-helical structure was observed for the Dutch (Aβ(E22Q)) variant. MD here provides a possible explanation for the structural changes. Two variants of Aβ, Aβ(K16A,L17A,F20A) and Aβ(V18A,F19A,F20A), that do not produce fibrils in vitro were also investigated. The Aβ(V18A,F19A,F20A) initially loses its helical conformation but refolds into helix several times and spends most of the simulation time in helical conformation. However, the Aβ(K16A,L17A,F20A) loses the α-helical structure after 5 ns and does not refold. For the wildtype Aβ(1–40) and Aβ(1–42), the helical conformation is lost after 5 ns or after 40 ns, respectively, while for the “familial” (Aβ(A42T)) variant, the MD simulations suggest that a C-terminal β-strand is stabilised, which could explain the fibrillation. The simulations for the Arctic (Aβ(E22G)) variant indicate that the α-helix is kept for 2 ns, but reappears 2 ns later, whereafter it disappears after 10 ns. The MD results are in several cases compatible with known experimental data, but the correlation is not perfect, indicating that multimerisation tendency and other factors might also be important for fibril formation.