Ho-Hi Lee

Polymorphism of phenylpyruvic acid studied by IR, Raman and solid state 13C NMR spectroscopy

Abstract Polymorphs I and II of phenylpyruvic acid are obtained as mixtures of both crystal forms or relatively pure crystals, from different solvents. Polymorph I is more stable than polymorph II at room temperature. Spectral characteristics of these polymorphs are discussed on the basis of IR, Raman and solid state 13 C NMR spectra. Also, the assignment of the IR features observed in the 1600–1700 cm −1 region is re-investigated by referring to the spectra of heavy-atom substituted derivatives. It is suggested that the CO stretching band is split by the crystal field for both polymorphs.

Synthesis and Conformation of Monodispersed Oligo(ε-L-Lysine)mers Studied by Cd and IR Spectroscopies

Abstract A series of monodispersed oligo(e-L-lysine)mers (2-, 4-, 6-, and 8-mers), which provides a fragment structure of microbially produced poly(e-L-lysine) (e-PLL), was synthesized by the liquid phase method. Conformations of the oligopeptides were studied using circular dichroism and infrared spectra, and compared with the results of e-PLL. The pH variation study of the CD spectra suggested that the oligopeptides exhibited a β-sheet conformation in water at pH elevated above the pKa of the α-amino group. A CD band intensity at 215 nm for the high pH solution was dependent on the number of lysine residues in the oligopeptides, indicating an increased interchromophore interaction in a higher oligopeptide. IR spectra measured in D2O supported the pH induced conformational change for the oligopeptides and e-PLL.

Trypsin-catalyzed synthesis of the arginyl-arginine dipeptide froml-arginine ethyl ester

SummaryTrypsin has been found to catalyze oligomerization ofl-arginine ethyl ester in aqueous reaction media. More than 40% of the substrate has been converted mostly to arginyl-arginine under the optimized reaction conditions (pH 10; [trypsin]≥10μM; [substrate]≥0.5M).

Molecular Structure and Dimerization of d-Cycloserine in the Solid State

Abstract d-cycloserine (CS) is transformed into cis-3, 6-bis(aminooxymethyl)-2, 5-piperazinedione (CS-dimer) in the solid state under a humid atmosphere. This dimerization process was followed by measuring the IR bands characteristic of CS and CS-dimer. The reaction was accelerated by the presence of increased water vapor. The X-ray analysis of CS monohydrate (CS · H2O) revealed that the CS molecules exist as a zwitter ion where the α-amino N atom is protonated and the amide N atom is deprotonated in the crystal. Participation of water molecules was suggested in the dimerization of CS.

Solid state structures of phenylpyruvates as studied by high resolution 13C NMR spectroscopy

Abstract High resolution solid state 13 C NMR measurements were made on phenylpyruvic acid and its sodium, lithium and calcium salts, using the total suppression of spinning side bands and the dipolar diphasing technique. The spectra of their 2- 13 C enriched analogs were also recorded. The NMR data were discussed by reference to the solution spectra, and the following definitive evidence was obtained: the acid, the hydrated sodium and lithium salts and the dehydrated sodium salt take the enol, the diol and the keto form, respectively, but the hydrated calcium salt exists in the keto form. The 13 C NMR signal of the gem -diol carbon was found to appear at 98 ppm. The calcium salt has two doublets at 166 and 134 ppm which originate from the carbons C(1) and C(4); this splitting suggests that the carboxylate group and/or the phenyl ring in the phenylpyruvate anion are oriented in two different ways.

IR Study on Aqueous Solution Behavior of D-Cycloserine

Abstract IR spectra were measured for an antitubercular agent, D-cycloserine (CS), and the hydrolyzate, β-aminooxy-D-alanine (AOA) and the dimer, cis-3, 6-bis(aminooxymethyl)-2, 5-piperadinedione (CS-dimer) at various pHs in aqueous solutions. Molecular species existing in the ionic equilibria were characterized by the pH dependence of the spectra. Band assignments were carried out by reference to the spectra of D20 solutions and those of related compounds. Spontaneous transformation of CS to CS-dimer was observed by the IR spectra for the neutral aqueous solution. The spectral evidence suggested that the non-ionic form of CS plays a key role in the dimerization process.

Keto-Enol Tautomerism of Mono-Substituted Phenylpyruvic Acids as Studied by NMR and PM3 Calculation

Abstract Keto-enol tautomerism of mono-substituted phenylpyruvic acids has been studied by the 1H and 13C NMR spectra. The equilibrium constants and the kinetic parameters for the tautomerism were obtained from the spectral data. The equilibrium constants are strongly dependent on the position of the substitution; the values for the o-substituted PPAs are several times greater than those of the m- or p-substituted derivatives. The PM3 calculations have been carried out to obtain the information on the preferred conformations of the tautomers and on the mechanism for the tautomerism. The results suggest the involvement of a solvent molecule in the equilibrium process.

Structure of 3-phenyl-2-thiopyruvic acid as studied by FT-IR, FT-RAMAN, and NMR spectroscopies

Abstract FT-IR, FT-Raman and High Resolution NMR spectra of 3-phenyl-2-thiopyruvic acid (PTPA) have been measured in solution and in the solid state. Spectral assignments were carried out by referring to data of PTPA derivatives including para-substituted PTPAs, PTPA-d5 and PTPA disulfide. All of the spectral evidences coherently point out that PTPA exists exclusively as the ene-thiol form both in solution and in the solid state. Detailed spectral features of PTPA were discussed in comparison with those of phenylpyruvic acid.

PEG-papain catalyzed synthesis of a Kyotorphin derivative in aqueous organic media

SummaryPEG-papain catalyzed synthesis of a Kyotorphin derivative has been investigated in aqueous organic solvents using Bz-Tyr-OEt and Arg-OMe as substrates. PEG-papain has shown increased resistance to high pH and high ethanol concentration; 42 % of Bz-Try-OEt has been converted to Bz-Tyr-Arg-OH under the optimized reaction condition (pH 7.0–9.0; 40 % EtOH).

Molecular structure of methyl phenylpyruvates studied by 1H NMR and IR spectroscopies and quantum mechanical calculations

Abstract Molecular structure of methyl phenylpyruvate (MPP) and its p -substituted derivatives has been investigated by 1 H NMR and IR spectroscopies. The spectral data point out that MPPs take the enol form both in solution and in the solid state. The ab initio calculations were carried out in order to get information on the configurational and conformational preferences in the enol form. It is suggested from the calculation that the inter- and intra-molecular hydrogen bondings between the enol OH group and the ester C  O group are important for stabilization of the conformer.