A vacuum-ultraviolet (VUV) circular-dichroism (CD) spectrophotometer usable down to 140 nm was constructed using synchrotron radiation and applied to the structural analyses of various saccharides, amino acids, and proteins in aqueous solutions. Most monosaccharides and disaccharides exhibited a positive CD peak around 170 nm, depending on anomeric and axial/equatorial configurations of hydroxy groups, trans–gauche configurations of hydroxymethyl groups, and the type of glycosidic linkage. The VUVCD spectra of glycosaminoglycans sensitively reflected the characteristic contributions of constituent functional groups in the VUV region. L-Isomers of amino acids showed two successive positive peaks around 200 and 180 nm, depending on the types of side chains. The VUVCD spectrum of alanine theoretically calculated using a time-dependent density functional theory revealed the important role of hydration for stabilizing the alanine structure. The VUVCD spectra of native proteins down to 160 nm improved the predictive accuracy for the contents, numbers of segments, and sequences of α-helices and β-strands. These secondary-structure analyses were also successfully applied to various types of nonnative proteins. The obtained results demonstrate that synchrotron-radiation VUVCD spectroscopy is a powerful technique for the structural analysis of biomolecules in aqueous solution, and hence could open a new field in structural biology.
A vacuum-ultraviolet circular-dichroism spectrophotometer usable down to 140 nm in solution was constructed using synchrotron radiation. This device enhanced capabilities for the structural analysis of biomolecules based on high-energy chromophores, and hence could open a new field in structural biology.
A peptide thioester is a key building block for protein synthesis by a ligation method, such as the thioester method and native chemical ligation. Combining these ligation methods offers flexibility in the choice of the condensation sites in a sequential ligation strategy. We describe herein a novel strategy, in which native chemical ligation followed by the thioester method are utilized, based on the use of a peptide containing a Cys–Pro ester (CPE) autoactivating unit at the C-terminus as a peptide thioester precursor. This sequential ligation strategy was applied to the synthesis of histone H3, which consists of 135 amino acid residues and contains a trimethyl Lys9 residue.
A novel sequential ligation strategy, in which native chemical ligation followed by the thioester method was performed, based on the use of the CPE peptide, was applied to the synthesis of histone H3 containing a trimethyl Lys9 residue.
We synthesized and determined the crystal structure of a novel pyrogallolaldehyde derivative with a 5-dimethylaminomethyl group. In solution, this compound underwent autoxidation to form unidentified blue species under ambient conditions. Electrochemical measurements revealed that addition of a base promoted the autoxidation, whereas addition of an acid effectively suppressed it. Using p-toluenesulfonic acid, we isolated a hydroxy-rich salphen-type Schiff base ligand as an ammonium salt of the acid. We obtained several transition-metal complexes of this ligand that retained its antioxidant stability. We discuss the spectroscopic and electrochemical properties of these complexes in comparison with analogous complexes without a 5-dimethylaminomethyl group.
Calcium hydroxyapatite (Hap) particles were produced using a microreactor, and the relationship between the morphology of the Hap particles and the synthesis conditions using a microreactor was investigated. Sheet-like Hap particles could be produced continuously using a microreactor, whereas only rod-like Hap particles were produced by a batch method. The Ca/P atomic ratio of the Hap particles produced by microreactor processing was 1.40–1.46, which was lower than the stoichiometric value of 1.67. This result suggests that the Hap particles produced by microreactor processing were calcium-deficient. The size of the sheet-like Hap particles increased, and the length of b and c axes of the Hap particles increased as the mixing efficiency of the microreactor increased, whereas the length of a axis remained almost unchanged. The X-ray diffraction patterns revealed that the lattice constant of the c axis increased while that of the a axis decreased as the mixing efficiency of the microreactor increased and they came close to data reported in a previous study. The size and shape of Hap particles produced by microreactor processing significantly depend on the mixing efficiency of the microreactor.
The low-frequency spectra of normal anthracene and anthracene-d10 in the solid state were measured by a high-resolution terahertz spectrometer. We observed the isotope shift of the vibrational frequency in the THz frequency region at 5 K. The vibrational mode assignment was performed based on the DFT calculation for the isolated species and observed isotope shifts. We also conducted solid-state DFT calculations using CRYSTAL09 to confirm the mode assignment. The correlation field splitting for the intramolecular mode due to the dipole–dipole interaction is quantitatively discussed.
Crystallization of 4′-diethylamino-3-hydroxyflavone (1) yields two polymorphic crystals. One is monoclinic, space group P21/n (1a), and the other triclinic, P1 (1b). In both crystals, the two adjacent molecules form a dimeric unit by two intermolecular O–H···O hydrogen bonds. The hydrogen-bonded dimer in crystal 1a is nearly planar, whereas that in crystal 1b is centrically twisted, having cis-like and trans-like conformations for the terminal carbon atoms at the diethylamino group.
1,1′-Diaminoferrocene (3) was conveniently synthesized by employing a Gabriel synthesis in two steps starting from 1,1′-dibromoferrocene (1). Compound 1 was reacted with 2.5 equivalents of phthalimide in the presence of Cu2O using 4-picoline as a solvent to give 1,1′-diphthalimidoferrocene (2) in a moderate yield. Hydrazinolysis of 2 in EtOH afforded 3 in good yields of ca. 70%. The subsequent reaction of 3 with two equivalents of ethyloxalyl chloride in THF gave the diethyl ester of N,N′-ferrocenylene bis(oxamic acid) (1,1′-fcbaH2Et2, 4). The solution obtained by treating 4 with two equivalents of n-Bu4NOH in H2O was added to a solution of Pd(AcO)2 in THF to give the palladium complex [n-Bu4N]2[Pd(1,1′-fcba)] (5) in ca. 80% yield. The compounds 2–4 were characterized by 1H, 13C NMR and IR spectroscopy as well as elemental analysis and the heterobinuclear complex 5 by 1H NMR and IR spectroscopy, elemental analysis and by a single-crystal X-ray diffraction study.
Lectins are important not only as biological functional molecules but as useful probes for glycan analysis. Here, we developed fluorescent-labeled lectins showing fluorescence changes upon ligand-binding. BODIPYFL-aminophenylalanine was incorporated at eight respective positions near the ligand-binding site of a sialic acid-binding lectin in response to UAG codon in a cell-free translation system. Fluorescence imaging of SDS-PAGE gel indicated the successful expression of the fluorescent-labeled lectins containing BODIPYFL-linked amino acid. Fluorescence spectral measurements revealed that the fluorescent-labeled lectins showed significant increases in the fluorescence intensity upon the binding of sialyllactose for all the incorporation positions. Particularly, the fluorescence intensity increased 3.7-fold for the labeled lectin at Thr38 position. The increase in the fluorescence intensity could occur because the fluorescence of BODIPYFL is quenched by amino acid residues located near the ligand-binding site in the absence of ligand, but the ligand-binding reduces the fluorescence quenching by removing the BODIPYFL moiety from the ligand-binding site. The W31F substitution decreased the fluorescence change of the labeled lectin, suggesting that the Trp31 residue may partially contribute to the ligand-dependent quenching. The present strategy will be utilized for producing various fluorescent-labeled lectin probes showing ligand-dependent fluorescence change.
A kinetic study on nucleophilic displacement reactions of O-ethyl O-4-nitrophenyl phenylphosphonothioate (an insecticide called EPN) with alkali-metal ethoxides (EtOM; M = Li, Na, K, and K/18-crown-6-ether) is reported. Dissection of pseudo-first-order rate constant (kobsd) into the second-order rate constants for the reaction of EPN with the dissociated EtO− (kEtO - ) and ion-paired EtOM (kEtOM) has revealed that the reactivity increases in the order kEtOLi < kEtO - < kEtONa < kEtOK < kEtOK/18-crown-6-ether, indicating that Li+ inhibits the reaction while the other M+ ions behave as a Lewis acid catalyst in the order Na+ < K+ < 18C6-complexed K+. The contrasting M+ ion effects have been explained in terms of the hard and soft acids and bases (HSAB) principle, since EPN, as a polarizable P=S centered electrophile, would exert a weak interaction with Li+ (a hard acid) but a strong interaction with the 18C6-complexed K+ ion (a soft acid). M+ ions catalyze the current reaction by increasing the electrophilicity of the reaction center. EPN is less reactive than O-4-nitrophenyl diphenylphosphinothioate but is more reactive than O-4-nitrophenyl O,O-diethyl thiophosphate. Factors governing the reactivity of these P=S centered electrophiles are discussed.
Dry reforming reactions have important environmental implications, since they can utilize and/or mitigate greenhouse gases. An experimental study was carried out to prepare suitable catalysts for dry reforming of methane. The Ni/γ-Al2O3 supported catalysts with strontium as a promoter (0.00–2.25 wt %) were prepared by a wet impregnation method. Various experimental techniques such as N2 adsorption–desorption isotherm, H2-TPR, CO2-TPD, XRD, TGA, O2-TPO, and SEM were applied for characterization of fresh and spent catalysts. The results of characterizations and catalyst activity test revealed that addition of Sr in Ni/γ-Al2O3 catalyst has dual effect; it improves the metal support interaction as well as enhances the Lewis basicity of the catalyst. This boost in basicity favors the chemisorption and dissociation of CO2 over the catalyst which in turn decreases the coke deposition. Amongst all tested catalysts, best results in terms of coke suppression were attained when 0.75% Sr loading was used, which showed 3.8% weight loss, less than half of that of the parent Ni–Al catalyst (8.2 wt %).
The influence of support electrolyte on the electrochemical degradation of formic acid was studied on boron-doped diamond (BDD) electrodes. Experimental data are compared with a theoretical model, which is based on organic degradation via hydroxyl radicals under current or mass transport controlled regimes depending on the difference between the applied and limiting current. The kinetics of the different reactions involved in the process is also briefly studied. It is shown that when sulfuric acid is used as support electrolyte, the reactions involving electro-generated peroxodisulfate anions during the degradation of formic acid are highly dependent on temperature. For this reason, the influence on the overall process of the chemical reaction between these anions and formic acid tends to increase with increasing temperatures and when the electrolysis becomes controlled by mass transport. However, it is proven that degradation of formic acid in the bulk occurs under current controlled regime as well. Furthermore, it is shown that the use of sulfuric acid as support electrolyte enhances the degradation of formic acid at high temperatures and when the process is controlled by mass transfer compared to other inert support electrolytes.