bluuebunny/crossref_metadata_2025_split huggingface dataset:
Folding Structures of Isolated Peptides as Revealed by Gas‐Phase Mid‐Infrared Spectroscopy
Authors: Bakker Joost M. , Plützer Christian , Hünig Isabel , Häber Thomas , Compagnon Isabelle , von Helden Gert , Meijer Gerard , Kleinermanns Karl 
Published: January 2005

AbstractTo understand the intrinsic properties of peptides, which are determined by factors such as intramolecular hydrogen bonding, van der Waals bonding and electrostatic interactions, the conformational landscape of isolated protein building blocks in the gas phase was investigated. Here, we present IR‐UV double‐resonance spectra of jet‐cooled, uncapped peptides containing a tryptophan (Trp) UV chromophore in the 1000–2000 cm−1 spectral range. In the series Trp, Trp‐Gly and Trp‐Gly‐Gly (where Gly stands for glycine), the number of detected conformers was found to decrease from six (Snoek et al., PCCP, 2001, 3, 1819) to four and two, respectively, which indicates a trend to relaxation to a global minimum. Density functional theory calculations reveal that the OH in‐plane bending vibration, together with the NH in‐plane bending and the peptide CO stretching vibrations, is a sensitive probe to hydrogen bonding and, thus, to the folding of the peptide backbone in these structures. This enables the identification of spectroscopic fingerprints for the various conformational structures. By comparing the experimentally observed IR spectra with the calculated spectra, a unique conformational assignment can be made in most cases. The IR‐UV spectrum of a Trp‐containing nonapeptide (Trp‐Ala‐Gly‐Gly‐Asp‐Ala‐Ser‐Gly‐Glu) was recorded as well and, although the IR spectrum is less well‐resolved (and it probably results from different isomers), groups of amide I (peptide CO stretching) and amide II (NH in‐plane bending) bands can still be recognised, in agreement with predictions at the AM1 level.
Primary sclerosing cholangitis as a cause of false positive bile duct brushing cytology: Report of two cases.
Authors: Layfield Lester J. , Cramer Harvey 
Published: January 2005

AbstractPrimary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease of unknown etiology characterized by ongoing inflammation, destruction, and fibrosis of intrahepatic and extrahepatic bile ducts. Irregular narrowing and dilation of the biliary duct system produces the characteristic beaded pattern seen on cholangiogram. Malignant degeneration resulting in cholangiocarcinoma is a well‐recognized sequela of PSC. Bile duct brushing cytology is the primary screening technique for cholangiocarcinoma. It is associated with a relatively low sensitivity but high specificity. Few false positive bile duct brushings have been reported in the literature, with the majority of these having occurred in a background of PSC. We report two patients with PSC in whom bile duct brush cytologies were falsely positive for carcinoma. Diagn. Cytopathol. 2005;32:119–124. © 2005 Wiley‐Liss, Inc.
Evolutionary origin of the feather epidermis
Authors: Sawyer Roger H. , Rogers Loren , Washington Lynette , Glenn Travis C. , Knapp Loren W. 
Published: January 2005

AbstractThe formation of scales and feathers in reptiles and birds has fascinated biologists for decades. How might the developmental processes involved in the evolution of the amniote ectoderm be interpreted to shed light on the evolution of integumental appendages? An Evo–Devo approach to this question is proving essential to understand the observation that there is homology between the transient embryonic layers covering the scale epidermis of alligators and birds and the epidermal cell populations of embryonic feather filaments. Whereas the embryonic layers of scutate scales are sloughed off at hatching, that their homologues persist in feathers demonstrates that the predecessors of birds took advantage of the ability of their ectoderm to generate embryonic layers by recruiting them to make the epidermis of the embryonic feather filament. Furthermore, observations on mutant chickens with altered scale and feather development (Abbott and Asmundson [1957] J. Hered. 18:63–70; Abbott [1965] Poult. Sci. 44:1347; Abbott [1967] Methods in developmental biology. New York: Thomas Y. Crowell) suggest that the ectodermal placodes of feathers, which direct the formation of unique dermal condensations and subsequently appendage outgrowth, provided the mechanism by which the developmental processes generating the embryonic layers diverged during evolution to support the morphogenesis of the epidermis of the primitive feather filament with its barb ridges. Developmental Dynamics 232:256–267, 2005. © 2005 Wiley‐Liss, Inc.
Potential role of thioredoxin in immune responses in intestinal lamina propria T lymphocytes
Authors: Sido Bernd , Giese Thomas , Autschbach Frank , Lasitschka Felix , Braunstein Jutta , Meuer Stefan C. 
Published: January 2005

AbstractThioredoxin (TRX) is a ubiquitous oxidoreductase with strong co‐cytokine, chemoattractant and anti‐apoptotic activities. TRX expression was found to be particularly elevated in the intestinal mucosa, where its physiologic function is entirely unknown. Here, we demonstrate a high level of TRX expression in lamina propria T cells (LP‐T) as opposed to autologous peripheral blood T lymphocytes (PB‐T). Addition of recombinant human TRX (rhTRX) to PB‐T enhances TRX gene expression. This autoregulation involves the calcineurin signaling pathway, as rhTRX antagonizes the cyclosporine A (CsA)‐ and tacrolimus‐mediated suppression of TRX gene expression. Similarly, rhTRX reverses the suppression of IL‐2 mRNA production by CsA and enhances cytokine production preferentially in prestimulated cells. The differential TRX expression in LP‐T versus PB‐T may thus contribute to the high‐level, CsA‐resistant IL‐2 production characteristic for CD2‐stimulated LP‐T. Inversely, inactivation of TRX in LP‐T through inhibition of TRX reductase abolishes cytokine gene expression. TRX may play a key role in the specialized intestinal microenvironment in amplifying immediate immune responses of LP‐T whenever appropriate costimulation of LP‐T is provided.
The functional avidity of virus‐specific CD8+ T cells is down‐modulated in Borna disease virus‐induced immunopathology of the central nervous system
Authors: Engelhardt Karin R. , Richter Kirsten , Baur Karen , Staeheli Peter , Hausmann Jürgen 
Published: January 2005

AbstractBorna disease virus (BDV) infection of the central nervous system (CNS) leads to severe neurological symptoms in susceptible MRL mice. The disease is mainly mediated by CD8+ T cells specific for the immunodominant epitope TELEISSI in the BDV nucleoprotein. In this study, TELEISSI/MHC class I tetramers were used to directly visualize antigen‐specific CD8+ T cells. We found that on average approximately 30% of the ex vivo analyzed CD8+ T cells in the CNS of diseased mice were specific for TELEISSI. Unexpectedly, the frequency of tetramer‐reactive brain‐derived CD8+ T cells doubled following overnight culture in the absence of antigen. The majority of CD8+ T cells showed enhanced tetramer binding without up‐regulation of T cell receptor surface expression. The frequency of IFN‐γ‐secreting CD8+ T cells after antigen‐specific stimulation was higher in overnight cultures than in freshly isolated BDV‐specific brain lymphocytes, and enhanced tetramer binding correlated with elevated sensitivity to lower levels of peptide antigen in cytotoxicity assays. These results indicate that the functional avidity of virus‐specific CD8+ T cells was down‐modulated in vivo. Thus, quantification of tissue‐infiltrating CD8+ T cells by the tetramer technique must be interpreted with caution as it may underestimate the real frequency of antigen‐specific CD8+ T cells.
Synergistic increases in intracellular Ca2+, and the release of MCP‐1, RANTES, and IL‐6 by astrocytes treated with opiates and HIV‐1 Tat
Authors: El‐Hage Nazira , Gurwell Julie A. , Singh Indrapal N. , Knapp Pamela E. , Nath Avindra , Hauser Kurt F. 
Published: January 2005

AbstractRecent evidence suggests that injection drug users who abuse heroin are at increased risk of CNS complications from human immunodeficiency virus (HIV) infection. Opiate drugs may intrinsically alter the pathogenesis of HIV by directly modulating immune function and by directly modifying the CNS response to HIV. Despite this, the mechanisms by which opiates increase the neuropathogenesis of HIV are uncertain. In the present study, we describe the effect of morphine and the HIV‐1 protein toxin Tat1‐72 on astroglial function in cultures derived from ICR mice. Astroglia maintain the blood‐brain barrier and influence inflammatory signaling in the CNS. Astrocytes can express μ‐opioid receptors, and are likely targets for abused opiates, which preferentially activate μ‐opioid receptors. While Tat alone disrupts astrocyte function, when combined with morphine, Tat causes synergistic increases in [Ca2+]i. Moreover, astrocyte cultures treated with morphine and Tat showed exaggerated increases in chemokine release, including monocyte chemoattractant protein‐1 (MCP‐1) and regulated on activation, normal T cell expressed and secreted (RANTES), as well as interleukin‐6 (IL‐6). Morphine‐Tat interactions were prevented by the μ‐opioid receptor antagonist β‐funaltrexamine, or by immunoneutralizing Tat1‐72 or substituting a nontoxic, deletion mutant (TatΔ31‐61). Our findings suggest that opiates may increase the vulnerability of the CNS to viral entry (via recruitment of monocytes/macrophages) and ensuing HIV encephalitis by synergistically increasing MCP‐1 and RANTES release by astrocytes. The results further suggest that astrocytes are key intermediaries in opiate‐HIV interactions and disruptions in astroglial function and inflammatory signaling may contribute to an accelerated neuropathogenesis in HIV‐infected individuals who abuse opiates. © 2004 Wiley‐Liss, Inc.
The reactions of tellurium tetrachloride with aliphatic monoketones
Authors: O'Brien Daniel H. , Irgolic Kurt J. , Huang Chang‐Kai 
Published: January 2005

AbstractThe reactions of 13 aliphatic ketones with tellurium tetrachloride has been studied with proton, carbon‐13, and tellurium‐125 NMR. Tellurium tetrachloride adds electrophilically to the α‐carbon of the enol to form ketonyl tellurium trichlorides. Unsymmetric ketones gave mixtures of isomeric ketonyl tellurium trichlorides. Steric hindrance determines which ketonyl tellurium trichlorides form. Except for the ketonyl tellurium trichloride from 2‐butanone, tellurium reacts preferentially with the least substituted α‐carbon. Six methyl alkyl ketones also yielded appreciable amounts of diketonyl tellurium dichlorides. In all diketonyl tellurium dichlorides, tellurium is bonded to less hindered methylene carbons.
Ambident electrophilicity of O,O‐diethyl‐S‐phenyl phosphorothiolate
Authors: Garbers Hendrik V. , Modro Tomasz A. 
Published: January 2005

AbstractReaction between O,O‐diethyl‐S‐phenyl phosphorothiolate and lithium dialkylamides results in the displacement of the PhS substituent by the R2N group. With Grignard reagents, the same substrate gives products of the nucleophilic substitution at both the phosphorus and the sulfur atom.
Reaction of (t‐BuGaCl2)2 with Ar′PHLi (Ar′ = 2,4,6‐t‐Bu3C6H2): Preparation of the chloride‐bridged dimer (t‐BuGa(Cl)P(H)Ar′)2
Authors: Cowley Alan H. , Jones Richard A. , Mardones Miguel A. , Atwood Jerry L. , Bott Simon G. 
Published: January 2005

AbstractThe reaction of (t‐BuGaCl2)2 with Ar′P(H)Li (AR′ = 2,4,6‐t‐Bu3C6H2) affords the chloride‐bridged dimer [t‐BuGa(Cl)P(H)Ar′]2 (1). The structure of 1 has been established by X‐ray crystallography. Compound 1, C44H78Cl2Ga2P2, crystallizes in the monoclinic space group P21/n with Z = 2, a = 10.468(1), b = 14.967(1), c = 16.182(2) Å, and Å = 94.48(1)β. The reaction of 1 with t‐BuLi is described.
Efficient deanilidation of phosphoranilidates by the use of nitrites and acetic anhydride
Authors: Nishino Shigeyoshí , Nagato Yasuhiro , Hasegawa Yoshihiro , Yamamoto Hisanao , Kamaike Kazuo , Ishido Yoshiharu 
Published: January 2005

AbstractReagent systems of sodium– and tetrabutylammonium nitrite–acetic anhydride were proved to be extremely efficient for the deanilidation of nucleoside 3′‐phosphoranilidates, whose reactions were rapid with the former and instant with the latter. It was further found that the reagent system is applicable to oligonucleotide synthesis provided that the exocyclic amino groups of 2′‐deoxyadenosine, 2′‐deoxyguanosine, and 2′‐deoxycytidine were protected by succinylation.
2‐Aminopyridiniomethylphosphonite: A hydrogen‐bonded polymer from the hydrolysis of 1,3,4‐diazaphospholo[1,2‐a]pyridine
Authors: Litvinov Igor A. , Karaghiosoff Konstantin , Schmidpeter Alfred , Zabotina Elena Y. , Dianova Evelina N. 
Published: January 2005

AbstractCondensation of 2‐aminopyridine and chloromethyldichlorophosphane yields 1,3,4‐diazaphospholo[1,2‐a]pyridine 2. Methanol adds to 2 while diethylamine does not; with additional elemental sulfur, in both cases the sulfides 4, 6 of the respective adducts are formed. Hydrolysis of 2 specifically opens the PN‐bond and gives the zwitterionic 2‐aminopyridinio‐methylphosphonite 7. The compound crystallizes with one molecule water in the monoclinic space group P21/c with a = 25.490(7)Å, b = 7.365(4)Å, c = 9.088(3)Å, β = 100.06(3)°, and Z = 8 with two independent molecules of 7 and of water. In the crystal hydrogen bonds connect the molecules of 7 to form double‐chain structured polymers. The individual double‐chains are linked to each other by hydrogen‐bonded water molecules.
Synthesis, characterization, and in vitro antitumor activity of some tin(IV)–oxygen and tin(IV)–sulfur heterocycles
Authors: Bouâlam Mohammed , Willem Rudolph , Biesemans Monique , Mahieu Bernard , Gielen Marcel 
Published: January 2005

AbstractThe synthesis of diorganotin(IV) derivatives of thiosalicylic acid, of 3‐aza‐2‐thiosalicylic acid, and of several related compounds is reported. Their characterization by 1H, 13C, and 119Sn NMR, Mössbauer, and mass spectrometry is described. The in vitro antitumor activity of selected derivatives against two human tumoral cell lines is discussed.
Unsymmetrical and symmetrical diphosphazane ligands derived from o‐phenylene phosphorochloridite
Authors: Babu Ruppa P. Kamalesh , Krishnamurthy Setharampattu S. , Nethaji Munirathinam 
Published: January 2005

AbstractTwo new diphosphazane ligands, PriN(PPh2)(PO2C6H4) (1) and PriN{P(O2C6H4)}2 (3), have been synthesized and characterized by spectroscopic data. The structure of 1 has been confirmed by single crystal X‐ray diffraction. Crystal data: Monoclinic, C2/c, Z = 16, a = 34.149(5) Å, b = 9.717(6) Å, c = 29.439(5) Å, β = 125.11(2)°, V = 7991 Å3, R = 0.058, Rw = 0.061. This compound shows two different P–N bond lengths (1.654 (4) and 1.743(4) Å) and a P–N–P angle of 120.7(2)°. Variable temperature 31P NMR measurements for 1 and 3 throw light on the nature of the conformers present in solution.
Sodium arenetellurolate‐catalyzed reduction of nitroalkanes to oximes
Authors: Ohe Kouichi , Uemura Sakae 
Published: January 2005

AbstractTreatment of aliphatic nitro compounds with NaBH4 in alkaline ethanol in the presence of a catalytic amount of diaryl ditelluride at 25°C for 5–20 h produces the corresponding oximes, generally as a mixture of E/Z isomers, in fair to good yields. Arenetellurolate anion (ArTe−) generated in situ is suggested to be the active species for the reduction.
13C Chemical shifts and 13C15N coupling constants of some 15N‐labelled bridgehead nitro compounds
Authors: Della Ernest W. , Janowski Wit K. , Kasum Bruno , Kirkbride K. Paul , Shirley Neil J. 
Published: January 2005

AbstractMeasurement of the 13C NMR spectra of the bridgehead nitro compounds 1a–5a has been performed. It is found that one‐bond 13C15N coupling is not necessarily a reflection of the degree of s character of the bridgehead carbon exocyclic bonding orbital. Although the magnitude of vicinal coupling to the bridgehead carbon increases, in accordance with the number of three‐bond pathways available for transmission of spin information, coupling is actually reduced by opposing contributions from through‐space intramolecular orbital interactions.
Amperometric enzyme‐modified electrodes based on tetrathiafulvalene derivatives for the determination of glucose
Authors: Lee H. S. , Liu L.‐F. , Hale P. D. , Okamoto Y. 
Published: January 2005

AbstractA number of tetrathiafulvalene (TTF) derivatives have been synthesized and tested as electron transfer mediators in glucose oxidase‐based amperometric biosensors. Using cyclic voltammetry and stationary potential experiments, it is shown that several of these derivatives can effectively mediate electron transfer from the reduced flavin adenine dinucleotide redox centers of glucose oxidase to a conventional carbon paste electrode. An insoluble polymeric electron relay system, based on the covalent attachment of TTF moieties to a highly flexible siloxane polymer, is also shown to facilitate a flow of electrons from the enzyme to the electrode. The resulting glucose biosensors function efficiently over a clinically relevant range of glucose concentrations.
Cyclic SN compounds and phosphorus reagents: Part X. Synthesis and characterization of phosphinimino‐substituted SN heterocycles
Authors: Thomas C. J. , Rao M. N. Sudheendra 
Published: January 2005

AbstractRoom temperature reactions of S4N4 with (amino) diphenylphosphines, (R)Ph2P, have basically yielded two different types of SN heterocycles under two different stoichiometric conditions. Phosphiniminocyclotrithiatriazenes, (R)Ph2PNS3N3 (R = C4H8N, C5H10N, C6H12N, CH3NC4H8N, (C6H11)2 N, and (C6H5CH2)2N) have been obtained (yield 45–76%) from a 1:2 mole ratio (S4N4:(R)Ph2P) reaction, while the disubstituted S4N4 derivatives, 1,5‐[Ph2(R)PN]2S4N4 (R = C4N8N, C5H10N, and C6H12N) have been obtained (yield 30–45%) only from a 1:3.5–4 mole ratio reaction. All the 1,5‐[Ph2(R)PN]2S4N4 derivatives prepared in this study undergo a room temperature solution phase transformation to the corresponding (R)Ph2PNS3N3 heterocycles.
Ir‐spectroscopic evidence for NaSiO and KSiO in solid argon
Authors: Köppe Ralf , Schnöckel Hansgeorg 
Published: January 2005

AbstractCondensation of SiO with sodium or potassium, respectively, leads to the formation of Na+(SiO)− and K+(SiO)−. The SiO force constant is reduced to 6.15 mdyn/Å and 6.30 mdyn/Å with respect to uncoordinated SiO (f = 9.0 mdyn/Å). From these results a similar type of bonding can be concluded for the charge transfer complexes Ag+(SiO)− and Ag+(SiS)− published recently.
Proximity effect in the oxidation of dithiols with 3‐methyllumiflavin
Authors: Nagata Toshiyuki , Fujimori Ken , Oae Shigeru 
Published: January 2005

AbstractRates of oxidation of various dithiols with 3‐methyllumiflavin to afford the corresponding cyclic disulfides have been examined at various pH values in 30% aqueous ethanol at 30°C. 1,3‐Propanedithiol, which affords 1,2‐dithiolane, has been found to be the most reactive among several dithiols tested in this oxidation. Kinetic results clearly show that highly strained 1,2‐dithiethanes are formed as primary products in the oxidation of vic‐dithiols with 3‐methyllumiflavin.
Stereoselective synthesis of (2Z)‐cinnamanilides via desulfonylation of (2E)‐α‐amido‐α,β‐unsaturated sulfones by sodium hydrogen telluride
Authors: Huang Xian , Pi Jin‐Hong , Huang Zhi‐Zhen 
Published: January 2005

Abstract(2E)‐α‐Amido‐α,β‐unsaturated sulfones, which are easily prepared by the condensation of α‐amido‐sulfones with aldehydes, can be desulfonylated by sodium hydrogen telluride to give (2Z)‐cinnamanilides with excellent stereoselectivity and in good yields.
Equilibrium and kinetic studies of reactions of 2‐methyl‐2‐propanesulfenic acid
Authors: Okuyama Tadashi , Miyake Katsuji , Fueno Takayuki , Yoshimura Toshiaki , Soga Shinichi , Tsukurimichi Eiichi 
Published: January 2005

Abstract2‐Methyl‐2‐propanesulfenic acid readily undergoes self‐condensation to give S‐t‐butyl 2‐methyl‐2‐propane‐thiosufinate. Rates of the reaction were measured in aqueous acetonitrile solution by use of NMR and UV spectroscopy. The reaction is second order in the substrate. The half‐life in a neutral aqueous solution is about 150 hours at 35°C when the initial substrate concentration is 0.003 M. The rate is proportional to acid concentration in the range 0.004–0.2 M. In alkaline solution, the main reaction is self‐condensation but some side reactions also seem to occur. The disappearance of the substrate does not follow satisfactory second‐order kinetics, but the second‐order rate constants obtained by the time‐lag method show a maximum around pH 10–11. The pKa (10.47) of the sulfenic acid was obtained at 14°C from a sig‐moid curve of the initial absorbances (240 nm) determined by extrapolation of the time‐dependent curve.
An observable model for the SN2 transition state [1a]. Hypervalent trigonal bipyramidal carbon (10‐C‐5) [1b]
Authors: Forbus T. R. , Martin J. C. 
Published: January 2005

AbstractDicationic 10‐C‐5 species 14, formally two‐electron oxidation products of 1,8‐bis(arylthio)‐9‐(2,6‐dimethoxyaryl)‐10‐phenylanthracenes, are prepared and characterized by NMR spectroscopy. Evidence is presented for a bis‐sulfonium structure containing a hypervalent trigonal bipyramidal (TBP) carbon atom. Dicationic species 14, prepared by the reaction of the appropriate diol with strong acid in liquid sulfur dioxide or sulfurylchlorofluoride, are stable for indefinite periods at room temperature in these solutions. Structural features common to these compounds which stabilize the TBP geometry sufficiently to allow their direct observation are as follows: (a) electronegative apical ligands (sulfonium sulfur atoms), (b) five‐membered rings linking each apical position to an equatorial position, (c) geometric constraints built into the tridentate ligand in a pattern designed to stabilize TBP, relative to tetrahedral carbon, (d) three relatively electropositive (sigma‐donor) equatorial ligands, which decrease the effective electronegativity of the central carbon atom of the threecenter bond, (e) a strain‐free, bidentate π‐acceptor equatorial ligand with its π‐axis parallel with the electron‐rich three‐center four‐electron bond axis, and (f) possible residual aromaticity (bis‐ipso‐aromaticity) in the equatorial six‐membered ring incorporating the hypervalent carbon atom.A low‐temperature19F NMR study of 14b sets an upper limit for ΔG≠−100°C of ca. 4 kcal/mol for a hypothetical process which would interconvert unsymmetrical species 30 and 30′ if such a tautomeric mixture were to represent the structure of 14. Evidence against such a tautomeric equilibrium is adduced from the upfield shift of 0.65 ppm observed for the proton meta to the two methoxyl substituents of dication 14a relative to the comparable proton in 21a, the model dication lacking one of the two arylthio substituents of 14a. This is most easily explained by postulating a nucleophilic interaction of the second thioaryl group in 14 at the hypervalent, 10‐C‐5 carbon.
New cascade molecules centered about phosphorus
Authors: Engel Robert , Rengan Kasthuri , Chan Ching‐See 
Published: January 2005

AbstractCascade molecules in which the branch points are phosphonium ion sites have been synthesized bearing phosphorus in a variety of oxidation states at the core. In addition to the previously reported phosphonium ion core species, these new cascade molecules include those bearing phosphine, phosphine oxide, and phosphorane cores.
The origin of the sulfone in photooxidations involving sulfurane intermediates
Authors: Clennan Edward L. , Yang Kang 
Published: January 2005

AbstractThe photooxidations of γ‐hydroxysulfides which give abnormally high yields of sulfones have been investigated. This unusual result is attributed to the potent trapping ability of a hydrogen bonded sulfoxide intermediate. This suggestion is supported by measuring the ability of a γ‐hydroxysulfoxide to trap the persulfoxide formed in the photooxidation of diethyl sulfide and by careful analysis of the reaction composition as a function of time.