Ko-Ki Kunimoto

A comparative vibrational and NMR study of cis-cinnamic acid polymorphs and trans-cinnamic acid.

The IR and Raman spectra of the two polymorphic forms (58 degree- and 68 degree-forms) of cis-cinnamic acid were measured, and the spectral differences discussed on the basis of the crystal structures of the two forms. The IR bands related to the COOH group differ in the frequencies and band shape, reflecting differences in the hydrogen bonding between the two modifications. These spectra were compared with those of trans-cinnamic acid. The IR, Raman, and NMR spectra of the isotopic compounds, including the deuterated and 13C analogs of the cis and trans acids, were also recorded in the solid state and in solution to confirm the spectral assignments.

Characterization of microbial poly (ε-l-lysine) by FT-IR, Raman and solid state 13C NMR spectroscopies

Abstract The molecular structure and conformation of microbial poly(e- l -lysine) (M-e-PL) produced by a variant of Streptomyces albulus were studied by means of FT-IR, FT-Raman and solid-state 13C NMR spectroscopies. Vibrational results indicate that M-e-PL assumes a β-sheet conformation in the solid state. Solid state 13C NMR spectra of the crystalline and the amorphous components were observed separately and the degree of crystallinity was estimated to be 63%. A plausible conformation model was proposed.

Molecular structure and vibrational spectra of phenolphthalein and its dianion

Infrared (IR) and Raman spectra of phenolphthalein (PP) and its dianion form (sodium and potassium salts) were studied both in the solid state and in aqueous solution. Band assignments were carried out on the basis of the isotope shifts of the ring deuterated and 13C-substituted derivatives. Spectral analyses reveal that the PP dianion exists as mixtures of the benzenoid form (colorless) and the quinonoid form (colored) in the solid state and in aqueous solution, while the neutral PP solely takes the gamma-lactone form. This work provides the first vibrational spectroscopic evidence for the coexistence of the two species in the PP dianions.

Crystal structures and conformations of 5-benzyl-2-thiohydantoin and its 1-acetylated derivative

ABSTRACT The crystal structures of 5-benzyl-2-thiohydantoin (5-BTH) and 1-acetyl-5-benzyl-2-thiohydantoin (1-Ac-5-BTH) have been determined by X-ray diffraction. In the 5-BTH crystals, the enantiomeric (R)- and (S)-5-BTH molecules are connected to form cyclic dimers via the hydrogen bonds of the thioamide and the amide moieties. On the other hand, the intermolecular hydrogen bonds in 1-Ac-5-BTH crystals form an infinite chain. These differences in the hydrogen bond pattern are also discussed in the IR and Raman spectra. The ab initio molecular orbital calculations (Gaussian 03) with 6-31G(d,p) basis set were carried out for 5-BTH and 1-Ac-5-BTH to get the preferred conformation.

Molecular structure (monomeric and dimeric) and hydrogen bonds in 5-benzyl 2-thiohydantoin studied by FT-IR and FT-Raman spectroscopy and DFT calculations.

In the present work the structural and spectral characteristics of 5-benzyl-2-thiohydantoin (5-BTH) have been studied by methods of infrared, Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) employing B3LYP with complete relaxation in the potential energy surface using 6-311G++(d,p) basis set. Our results support the hydrogen bonding pattern proposed by reported crystalline structure. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. UV-vis spectrum of the compound was recorded in methanol solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using PCM and 6-311++G(d,p) basis set. In addition, the thermodynamic properties of the compound were calculated at different temperatures and corresponding relations between the properties and temperature were also studied.

Experimental (FT-IR, FT-Raman, NMR) and theoretical spectroscopic properties of intermolecular hydrogen bonded 1-acetyl-2-thiohydantoin polymorphs

In this work, use of FT-Raman, FT-IR and (13)C NMR spectroscopies have been made for the full characterization of 1-acetyl-2-thiohydantoin (ACTH). A detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis using single scaling factor. Our results support the hydrogen bonding pattern proposed in the reported crystalline structure. Good reproduction of experimental values is obtained and % error is small in majority of the cases. Isotropic chemical shifts were calculated using gauge-invariant atomic orbital (GIAO) along with several thermodynamic parameters.

Crysatl and Molecular Structures of Racemic and Chiral 4-Phenyl-1,3-thiazolidine-2-thiones

The crystal and molecular structures of (rac)- and (S)-4-phenyl-1,3-thiazolidine-2-thiones (4-PTT) have been studied by X-Ray diffraction and ab initio MO calculations at the level of HF/6-31G*. In racemic crystals, the thioamide groups of the enantiomeric (R)- and (S)-4-PTT pairs are hydrogen-bonded around a crystallographic center of symmetry to form a planar cyclic dimer. On the other hand, in (S)-4-PTT crystals, a cyclic dimer through the hydrogen bonding is formed between the two independent molecules (molecules A and B) in the asymmetric unit and its geometry is distorted.

Extraction of arbutin and its comparative content in branches, leaves, stems, and fruits of Japanese pear Pyrus pyrifolia cv. Kousui

Arbutin is a tyrosinase inhibitor and is extensively used as a human skin-whitening agent. This study investigated the optimum conditions for extracting arbutin by ultrasonic homogenization from discarded branches pruned from Japanese pear (Pyrus pyrifolia cv. Kousui) trees. The arbutin content was measured in the branches and also in the leaves, stems, fruit peel, and fruit flesh.

5-Isopropyl-5-methyl-2-sulfanylidene­imidazolidin-4-one

In the title compound, C7H12N2OS, the 2-sulfanylideneimidazolidin-4-one moiety is nearly planar, with a maximum deviation of 0.054 (2) Å. In the crystal, a pair of N—H⋯O hydrogen bonds and a pair of N—H⋯S hydrogen bonds each form a centrosymmetric ring with an R 2 2(8) graph-set motif. The enantiomeric R and S molecules are alternately linked into a tape along [1-10] via these pairs of hydrogen bonds.

Ring-chain tautomerism of halogenated phenolphthaleins: Vibrational spectroscopic and semiempirical MO study

Ring-chain tautomerism of halogenated phenolphthaleins and the effect of the halogen substitution have been studied by vibrational spectroscopic and semiempirical MO methods. The vibrational spectra indicate that the content of the colored species (carboxylate form) increases on the substitution of the isobenzofuranone ring, whereas the colorless species (lactone form) becomes dominant on the substitution of phenolic rings. MO calculations have revealed that the substitution of either ring does not change the basic property of the electronic transition of the colored species and that the relative stability of both forms is dependent on the substitution type in accord with the results of the vibrational study.