bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemo‐Enzymatic Synthesis of Optically Active Amino Acids and Peptides
Authors: Chen Shui‐Tein , Wang Kung‐Tsung 
Published: May 2015

AbstractThe industrial alkaline protease, alcalase, is stable and active in a high concentration of organic solvents and useful as a biocatalyst for (i) diastereoselective hydrolysis of peptide esters and preparation of racemization‐free peptides; (ii) selective incorporation of esters of D‐amino acid into peptides in t‐butanol via a selective hydrolysis of esters of D,L‐amino acid, followed by using the unhydrolyzed D‐esters as a nucleophile in a kinetically controlled peptide bond formation; (iii) resolution of esters of amino acid in 95% t‐butanol/5% water, followed by saponification of the unreacted esters to offer both enantiomers with high yield and optical purity; (iv) completely resolve amino‐acid esters with high yield and optical purity via in situ racemization of the unreacted antipode catalyzed by pyridoxal 5‐phosphate; (v) cryobioorganic synthesis of peptides with increased yields 15%–40% of peptide bond formation by reaction at 5 °C instead of 25–30 °C of a kinetically controlled enzymatic reaction in alcohols.
A Correlation between CH Bond Activation Barrier and Singlet‐Tripet Energy Gap of Transition Metal Complex‐Density Functional Study on CpML Insertion into CH4
Authors: Su Ming‐Der , Chu San‐Yan 
Published: May 2015

AbstractThe density functional calculation with B3LYP/LANL2DZ method showed that the singlet‐triplet splitting (ΔE51 = Etriplet – Esinglet) of 16‐electron CpML (M = Rh, Ir; L = CH2, CO, SH2, PH3) correlates well with the activation barrier for its oxidative addition reaction into methane. A qualitative model of the configuration mixing has been used to interpret the correlation.
Theory of Vibrational Predissociation Spectroscopy
Authors: Chang R. , Jiang J. C. , Hsieh P.‐J. , Chang H.C. , Lin S. H. 
Published: May 2015

AbstractA theory of vibrational predissociation spectroscopy is developed based on the adiabatic approximation that separates the oscillations of the high frequency vibron and low frequency phonon. We find that some properties such as dissociation energy and the number of phonon modes have significant influence on the temperature dependent spectra. Thus a comparison between the present theory and experiment would be a useful approach in determining these properties.
Reactions of Difluorosilylene with Amines, Phosphines and Halomethanes The First Evidence of the Insertion of Difluorosilylene into Tetrafluorosilane
Authors: Chang Chih‐Wei , Liu Chao‐Shiuan , Lee Chi‐Young 
Published: May 2015

AbstractThe reactions of SiF2/SiF4 with amines, phosphines and various halomethanes were studied. The results show that in the presence of strong Lewis base (Et3N, HNEt2, PR3, PR2Cl), SiF2 inserts initially into SiF4 to form Si2F6, which was followed by subsequent reactions leading to products containing SiF3 groups. This is the first report of the insertion of SiF2 into SiF4. When the reactants were a weaker base (such as RPCl2, CX3Br, X=F, Cl), insertion of SiF2 into P‐Cl and C‐Br bonds became predominant.
Polyene Cyclization Promoted by the Cross Conjugated α‐Carbalkoxy Enone System. An Efficient Approach to Highly Functionalized Decalins
Authors: Liu Hsing‐Jang , Sun Daqing , Shia Kak‐Shan 
Published: May 2015

AbstractThe cross conjugated α‐carbalkoxy enone system was found to be an excellent promoter for polyene cyclization. Under mild conditions, the reaction occurred readily with a high degree of regio‐ and stereoselectivity. Based on this facile process, an efficient method for the construction of highly functionalized decalin derivatives has been developed.
The Attempted Generation of 3,4‐Didehydrofuran
Authors: Wu Yong‐Ming , Yang Xiao‐Ping , Xue Feng , Mak Thomas C. W. , Wong Henry N. C. 
Published: May 2015

Abstract4‐Trimethylsilyl‐3(2H)‐furanone (4) was converted to 4‐trimethylsilyl‐3‐furyl triflate (5). An attempted generation of 3,4‐didehydrofuran (3a) from 5 was unfruitful. On the other hand, 3,4‐bis(trimethylsilyl)furan (6) was also converted to 4‐trimethylsilyl‐3‐furylphenyliodonium triflate (7c) and its fluoride‐promoted elimination pathway might involve a biradical intermediate 3b.
Chemistry of Hypusine Formation on Eukaryotic Initiation Factor 5A in Biological Systems
Authors: Chen Kuang Yu , Jao David L. 
Published: May 2015

AbstractHypusine, an unusual amino acid, is derived from the hydrolysis of eukaryotic initiation factor 5 A (eIF‐5A), the only cellular protein known to contain hypusine residue. Hypusine residue is formed through a spermidine‐dependent posttranslational modification of eIF‐5A at a specific lysine residue. Each mature eIF‐5A molecule contains only one hypusine. Hypusine formation on eIF‐5A is essential for cell survival and proliferation. The biochemistry of hypusine formation has been actively investigated in a number of leading laboratories during the past decade. The precise functional role of eIF‐5A remains a mystery. This paper reviews recent progress in the study of the biochemistry of hypusine formation and offers speculation on the possible function of eIF‐5A.
Ion‐Solvent Interaction of Biunivalent Electrolytes in Dioxane‐Water Mixtures from Conductivity Data at Different Temperatures
Authors: Bakr Moustafa Farag , El‐Wahab Mohamed Abd Allah Abd 
Published: May 2015

AbstractThis paper presents the conductivity measurements for some alkaline earth metal salts MgCl2, MgBr2, Mg(NO3)2, CaCl2, CaBr2 and Ca(NO3)2 by which the ion‐solvent interactions are reported in the concentration range in dioxane‐water mixtures at mass fraction of 0, 3, 10, 20 and 30% at 30°, 35°, 40° and 45°C ± 0.01.The conductance data were analyzed for the limiting molar conductivity, Ao, by the Fuoss‐Edelson conductivity equation for the 2:1 unsymmetrical electrolytes. The results were discussed in terms of the solute‐solvent interaction from the temperature coefficient of Walden product, Λoη of the electrolyte solutions. Moreover, Λoη was found to exhibit a linear relationship with the dielectric constant, ϵ, of the dioxane‐water mixtures. The study gives information regarding the ion‐solvent interactions from the mobilities and Walden product of the ions in the solvent. The ions appear to interact appreciably and the ion‐solvent interaction tends to increase in the order Ca > Mg for the same anion while for the anions, the trend decreases in the order Cl− < Br− < No−3.
Aristolochic Acids as a Defensive Substance for the Aristolochiaceous Plant‐Feeding Swallowtail Butterfly, Pachliopta aristolochiae interpositus
Authors: Wu Tian‐Shung , Leu Yann‐Lii , Chan Yu‐Yi 
Published: May 2015

AbstractThe chemical constituents isolated from every stage of the Taiwanese swallowtail butterfly, Pachliopta aristolochiae interpositus, were studied and compared with the constituents of the insect feeding plant, A. cucurbitifolia. Two aristolochic acid derivatives (1 and 4) and three aristolactam analogues (5, 6, and 7) were isolated from the larval osmeterial fluid and larvae of the insect. In addition, four purines (2, 3, 13, and 14), one indole alkaloid (11), one steroid (10), two benzenoids (8 and 9) and allantoin (12) were also isolated from the insect. Among these compounds, aristolochic acid ‐I (AA‐I, 1) was detected in all life stages of the insect, especially in the larval osmeterial fluid. The studies confirm that the toxic AAs are used as larval feeding stimulants and deterrent allomones against birds.
Flavonoid Glycosides from Terminalia catappa L.
Authors: Lin Yun‐Lian , Kuo Yueh‐Hsiung , Shiao Ming‐Shi , Chen Chien‐Chih , Ou Jun‐Chih 
Published: May 2015

AbstractUnder the inhibition of Cu+2‐induced LDL oxidation‐guided fractionation, two new flavone glycosides with galloyl substitution were isolated from the dried fallen leaves of Terminalia catappa L. Their structures were established as apigenin 6‐C‐(2″‐O‐galloyl)‐β‐D‐glucopyranoside (1) and apigenin 8‐C‐(2″‐O‐galloyl)‐β‐D‐glucopyranoside (2), together with four known flavone glycosides, isovitexin, vitexin, isoorientin, and rutin, on the basis of spectroscopic method. Compounds 1 and 2 showed significant antioxidative effects. Their IC50 were 2.1 and 4.5 μM, respectively.
Secoiridoids Glycosides from Some Selected Jasminum SPP
Authors: Shen Ya‐Ching , Chen Chih‐Fan , Gao Jianjun , Zhao Changqi , Chen Ching‐Yeu 
Published: May 2015

AbstractSecoiridoid glycosides of three oleaceaous plants are described. Fractionation of the ethanolic extracts of Jasminum nitidum Skan, J. giraldii Diels and J. sambac (L.) Ait. var. trifoliatum Hort. (Oleaceace) resulted in the isolation of syringalactones A (1) and B (2), oleoside 7,11‐dimethyl ester (3), jasminoside (7), jaslanceosides B (8), sambacoside A (9) and molihuaside D (10). The structures of these secoiridoid glycosides were elucidated on the basis of spectral methods. Chemotaxonomy for plants of Jasminum is also discussed.
Structure‐Reactivity Relationships as Probes for the Inhibition Mechanism of Cholesterol Esterase by Aryl Carbamates. I. Steady‐State Kinetics
Authors: Lin Gialih , Lai Cheng‐Yue , Liao Wei‐Cheng , Kuo Bing‐Hong , Lu Chun‐Ping 
Published: May 2015

AbstractFor substituted phenyl‐N‐butyl carbamates (1) and 4‐nitrophenyl‐N‐substituted carbamates (2), linear relationships between values of NH proton chemical shift (δNH), pKa, and logk[OH] and Hammett substituent constant (σ) or Taft substituent constant (σ*) are observed. Carbamates 1 and 2 are pseudo‐substrate inhibitors of porcine pancreatic cholesterol esterase. Thus, the mechanism of the reaction necessitates that the inhibitor molecule and the enzyme form the enzyme‐inhibitor tetrahedral species at the Ki step of the reaction and then form the carbamyl enzyme at the kc step of the reaction. Linear relationships between the logarithms of Ki and kc for cholesterol esterase by carbamates 1 and σ are observed, and the reaction constants (ρs) are −3.4 and −0.13, respectively. Therefore, the above reaction forms the negative‐charge tetrahedral species and follows the formation of the relatively neutral carbamyl enzymes. For the inhibition of cholesterol esterase by carbamates 2 except 4‐nitrophenyl‐N‐phenyl carbamate and 4‐nitrophenyl‐N‐t‐butyl carbamate, linear relationships of ‐logKi and logkc with σ* are observed and the ρ* values are −0.50 and 1.03, respectively. Since the above reaction also forms the negative‐charge tetrahedral intermediate, it is possible that the Ki step of this reaction is further divided into two steps. The first Ki step is the development of the positive‐charge at the carbamate nitrogen from the protonation of the carbamate nitrogen. The second Ki step is the formation of the tetrahedral intermediate with the negative‐charge at the carbonyl oxygen. From Arrhenius plots of a series of inhibition reactions by carbamates 1 and 2, the isokinetic and isoequilibrium temperatures are different from the reaction temperature (25°C). Therefore, the observed ρ and ρ* values only depend upon the electronic effects of the substituents. Taken together, the cholesterol esterase inhibition mechanism by carbamates 1 and 2 is proposed.
The Chemical Constituents from the Heartwood of Eucalyptus Citriodora
Authors: Lee Ching‐Kuo , Chang Ming‐Huey 
Published: May 2015

AbstractNineteen compounds were isolated from the CHCl3 soluble portion of the heartwood of Eucalyptus citriodora. These compounds included trans‐calamenene (1), T‐muurolol (2), α‐cadinol (3), 2β‐hydroxy‐α‐cadinol (4), 4‐hydroxy‐3,5‐dimethoxybenzaldehyde (5), 4‐hydroxy‐3,5‐dimethoxybenzoic acid (6), linoleic acid (7), squalene (8), α‐tocopherol (9), erythrodiol (10), morolic acid (11), betulonic acid (12), cycloeucalenol (13), cycloeucalenol vernolitate (14), β‐sitosterol (15), β‐sitosteryl‐β‐D‐glucopyranoside (16), β‐sitostenone (17), yangambin (18), sesamin (19). Among them, 14 is a new compound. The structures of these compounds were elucidated on the basis of spectroscopic evidence.
Effects of Gamma Radiation on Various Polyimides
Authors: Liu Daniel Chun‐Hung , Liaw Der‐Jang , Liaw Been‐Yang , Tsai Chih‐Hung , Ho Jinn‐Hsuan , Ho Tong‐Ing 
Published: May 2015

AbstractFour polyimides (PIa‐PId) containing 4,4′‐hexafluoroisopropylidene‐bisphthalic anhydride (6FDA) units in the backbone were prepared via one‐step synthesis. The effects of different doses of gamma radiation from a cobalt‐60 source are studied. The irradiated and the unirradiated polyimides are characterized by using tensile strength, infrared (IR), viscosity, differential scanning calorimeter (DSC), and gel permeation chromatography (GPC). All polyimides show the increase of tensile strength and elongation at low doses (>350 Mrad). The molecule weights decrease as the irradiation doses increase. All samples showed a drastic degradation of the mechanical and thermal properties at doses above 1400 Mrad. Samples irradiated at a dose of 2800 Mrad were completely brittle. The major difference of the radiation effect of the polyimides depends largely on their structural differences. PId with an extra hexafluoroisopropylidene moiety is most sensitive to irradiation at high doses.
Femtosecond Dynamics of Hydrogen Bonds in Liquid Water: A Real Time Study
Authors: Lascoux Noelle , Gallot Guilhem , Hache Francois , Gale Geoffrey Mitchell , Bratos Savo , Leicknam Jean‐Claude 
Published: May 2015

AbstractAn experiment is described to study temporal variations of the hydrogen bond length in diluted HDO/D2O solutions. The principles of this laser spectroscopic experiment are explained first. The construction of a laser source generating 150 fs pulses in the 2.5‐4.5 μm spectral region at a 10 μJ power level is detailed next. The OH stretching band is reproduced for different excitation frequencies and different pump‐probe delay times. A theory, based on statistical mechanics of nonlinear optical processes, is proposed to calculate the lowest two spectral moments. A new effect is reported, the delay dependent vibrational solvatochromism. It is shown how this effect can be exploited to follow temporal variations of the OH…O bond length directly, in real time. Initially elongated hydrogen bonds were found to contract with time and to reach the equilibrium lengths. The corresponding times scales are of the order of 700 fs. No bond oscillations are observed.
Photodissociation Dynamics of Chloroiodomethane in Acetonitrile Studied by Ultrafast Pump‐Probe Spectroscopy
Authors: Tarnovsky Alexander N. , Wall Magnus , Rasmusson Marcus , Pascher Torbjörn , Åkesson Eva 
Published: May 2015

AbstractWe have studied the photodissociation dynamics of chloroiodomethane (CH2ICl) in acetonitrile by ultrafast pump‐probe spectroscopy. The reaction was initiated using a femtosecond pulse at 266 nm and the transient absorption was measured out to delays of 300 ps over a spectral region from 330 to 850 nm. The photodissociation leads to formation and subsequent vibrational cooling of a product species, which we suggest is the isomer of chloroiodomethane, CH2Cl‐I, likely produced via in‐cage recombination between the nascent fragments CH2Cl and I.
Femtosecond Two‐Dimensional Infrared Spectroscopy
Authors: Hochstrasser Robin M. , Asplund Matthew C. , Hamm Peter , Ge Nien‐Hui 
Published: May 2015

AbstractThe dynamics occurring amongst the structures of peptides and small proteins present significant questions that are not readily addressed by conventional methods. Multiple pulse infrared experiments provide a promising alternative. The time resolution is easily fast enough to intercept the structures on different parts of the free energy surfaces. This paper reviews how infrared spectroscopy can be optimized by stretching it into two dimensions thereby making it possible to separately examine and assign the cross peaks arising from the interaction of different amide oscillators in the molecule. A variety of approaches such as pump/probe, self‐heterodyned pump/probe, three pulse photon echo and spectrally resolved echoes are described which are analogous to magnetic resonance schemes.
Metal Imido Complexes (M=Ti, W) Containing 2‐(Dimethylaminomethyl)pyrrole: Synthesis and the Crystal Structures of ButN=TiCIPy2[2‐Me2NCH2(C4H3N)] and PhN=WCl3[2‐Me2NCH2(C4H3N)]
Authors: Huang Jui‐Hsien , Chi Liang‐Sheng , Huang Feng‐Mau , Kuo Pei‐Cheng , Zhou Chong‐Chin , Lee Gene‐Hsiang , Peng Shie‐Ming 
Published: May 2015

AbstractA titanium imido complex, ButN=TiClPy2[2‐Me2NCH2‐(C4H3N)] 1, was synthesized through metathesis by reacting ButN=TiCl2Py3 with lithium 2‐(dimethylaminomethyl) pyrrolate (LLi) in diethyl ether at room temperature. The dark brown red crystals were obtained from a concentrated diethyl ether solution of compound 1at −20°C and the monoclinic crystal shows a distorted octahedral structure with two pyridines taking trans positions. Hydrolysis ButN=TiCl2Py3 with 2,2′‐methylene‐bis(6‐t‐butyl‐4‐methylphenol) (HO∼∼CH2∼∼OH)generates a bis phenoxide titanium complex, (O∼∼CH2∼∼O)TiCl2Py 2, by eliminating one equivalent of ButNH2. Similarly, the reaction of LH with PhN=WCl4(OEt2) in diethyl ether at room temperature generates PhN=WCl3(L) 3, in moderate yield. 3has been characterized by NMR spectroscopies and X‐ray crystallography.
Synthesis of β‐D‐Glucopyranosyl(1→3)‐1‐thiol‐β‐glucosamine Disaccharide Derivative as Building Block for the Synthesis of Hyaluronic Acid
Authors: Lin Chun‐Cheng , Hsu Tzu‐Sui , Lu Kuo‐Cheng , Huang I‐Ting 
Published: May 2015

AbstractA practical synthetic method for the title disaccharide 2 is described. Glycosylation using thioglycoside as acceptor and glycosyl imidate as donor was performed with trimethylsilyltriflate as the promoter.
An Interesting Isomerization: Synthesis of Mesoionic 5‐Arylamino‐1,3,4‐Thiadiazolium‐2‐Thiolates by Using ω‐Bromo‐ω‐(1H‐1,2,4‐Triazol‐1‐yl)acetophenone as Catalyst
Authors: Chang‐HuChu  , Hui Xin‐Ping , Xu Peng‐Fei , Zhang Zi‐Yi , Li Zhi‐Chun , Liao Ren‐An 
Published: May 2015

AbstractMesoionic 5‐arylamino‐1,3,4‐thiadiazolium‐2‐thiolates 7a‐f were prepared by the isomerization of 5‐arylamino‐1,3,4‐thiadiazol‐2‐thiones 5a‐f by using ω‐bromo‐ω‐(1H‐1,2,4‐triazol‐1‐yl)acetophenone 6 as catalyst. All the structures of mesoionic synthesized were confirmed by elemental analyses, 1H NMR, IR and MS spectral data. We have also determined the x‐ray photoelectron spectroscopy (XPS) of the mesoionic and their precursors. A comparison of XPS spectra between the mesoionic and their precursors showed that the charge separation in mesoionic is distinctly larger than in their precursors.
Studies on Polyfunctionalised Heteroaromatics: Synthesis of Several New Cinnoline and Pyrido[3,4‐c]pyridazine Derivatives
Authors: Barsy Magda A. 
Published: May 2015

AbstractOne‐pot reaction of ethyl 2‐aryhydrazono‐3‐oxobutyrates with cyanoacetamide afforded pyridazine and pyridine derivatives, which were found to be excellent precursors for the synthesis of different cinnolines and pyrido[3,4‐c]pyridazines, respectively.
Heterocyclic Fused Rings with Bridgehead Nitrogen Atoms: Single‐Step Synthesis of Azolo[1″,2″:1′,2′]pyrido[5′,6′:5,4]pyrimido[1,6‐a]benzimidazole; Pyrido[1,2‐a]benzimidazole; Pyrido[4″,5″:2′,3′]pyrido[6′,5′:4,5]pyrimido‐[1,6‐a]benzimidazole and Polysubstituted Pyridine Derivatives
Authors: Raslan M. A. 
Published: May 2015

AbstractA one‐step synthesis of the title compounds by the reaction of arylidene‐lH‐benzimidazol‐2‐ylacetonitriles 1a‐d with 2‐cyanomethylbenzimidazole derivatives 2a,b is reported.
Dissociation Kinetics of Cerium(lll) Complexes of Macrocyclic Polyaza Polycarboxylate Ligands TETA and DOTA
Authors: Chang C. Allen , Liu Yuh‐Liang 
Published: May 2015

AbstractThe acid‐catalyzed dissociation rate constants of the cerium(III) complexes of 1,4,8,11‐tetraazacyclo‐tetradecane‐1,4,8,11‐tetraacetic acid (TETA) and 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) have been determined at four different temperatures (i.e., 25.0°C,32.0°C,39.0°C,45.0°C) in aqueous media (μ = 0.10 M, HCl/KCl) to obtain additional kinetic data and to evaluate possible effects of ligand pre‐organization for metal ion complexation. The rates are much faster for Ce(TETA)− than for Ce(DOTA)−, indicating the lower thermodynamic stability of the former. In the presence of excess strong acid, 0.1‐1.0 MHCl, the dissociation reactions follow the rate law: ‐d[ML]T/dt = (kd + kH[H+])[ML]T and ‐d[ML]T/dt = (kH[H+] + kH2[H+]2)[ML]T, respectively, where kd is acid‐independent dissociation reaction rate constant and kH and kH2 are the respective dissociation rate constants for the pathways involving monoprotonated and diprotonated species. The rate activation parameters, ΔH≠, ΔS≠ and ΔG≠, for each dissociation pathway have been obtained and their values are consistent with the proposed mechanisms. In particular, the rate difference between Ce(TETA)−and Ce(DOTA)− for the monoprotonated complex dissociation pathway is mainly due to difference in ΔHH≠. It has been concluded that ligand pre‐organization results in more stable complexes and slower complex dissociation rates.
Protein Folding and β‐Sheet Proteins
Authors: Kumar Thallampuranam Krishnaswamy Suresh , Sivaraman Thirunavukkarasu , Samuel Dharmaraj , Srisailam Sampath , Ganesh Gopal , Hsieh Hui‐Chu , Hung Kuo‐Wei , Peng Ho‐Jen , Ho Meng‐Chiao , Arunkumar Alphonse Ignatius , Yu Chin 
Published: May 2015

AbstractThe aim of this comprehensive review is to critically evaluate the progress in research in the area of protein folding. In the first section, we discuss the various models proposed to explain the protein folding paradox. In the succeeding section of the review, a detailed account of the developments in our understanding of the folding path ways of β‐sheet proteins is provided.
Time‐Resolved Phase Transitions of the Nanocrystalline Cubic to Submicron Monoclinic Phase in Mn2O3‐ZrO2
Authors: Lajavardi Manouchehr , Kenney Donald J. , Lin Sheng Hsien 
Published: May 2015

AbstractThe nanocrystalline cubic phase of zirconia was found to be thermally stabilized by the addition of 3 to 40 mol % manganese. The nanocrystalline cubic, tetragonal and monoclinic phases of zirconia stabilized with manganese (III)oxide (Mn‐Stabilized Zirconia) were prepared by thermal decomposition of carbonate and hydroxide precursors. Both the crystallization and isothermal phase transitions associated with Mn‐SZ were studied using high temperature x‐ray diffraction and x‐ray diffraction of quenched samples. Cubic Mn‐SZ initially crystallized and progressively transformed to tetragonal, and monoclinic structures above 700°C. The nanocrystalline cubic Mn‐SZ containing 25 mol % Mn was found to have the greatest thermal stability, retaining its cubic form at temperatures as high as 800°C for periods up to 25 hours. Higher than 40 mol %, cubic Mn2O3 was found to coexist with cubic Mn‐SZ. The crystallite sizes observed for the cubic, tetragonal and monoclinic Mn‐SZ phases ranged from 50 to 137, 130 to 220, and 195 to 450 Å respectively, indicating, for ZrO2, that particle size was a primary factor in determining its polymorphs. The classical Avrami equation for nucleation and growth was applied to the observed phase transformations.