bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self‐ and hetero‐association of sterically hindered tertiary alcohols
Authors: Lomas John S. 
Published: June 2005

AbstractSelf‐association constants for 2,2,4,4‐tetramethyl‐3‐alkylpentan‐3‐ols are so small as to be negligible in comparison with hetero‐association constants for the same alcohols with a moderately strong base. Equilibrium constants were determined by the NMR titration method for the hydrogen bonding association of this and two other series of sterically hindered alcohols with pyridine, in benzene as solvent. Steric effects are small even when the 3‐alkyl substituent is very bulky. The acidity of the OH hydrogen in 2,2,4,4‐tetramethyl‐3‐phenylpentan‐3‐ols increases slightly with the electron‐withdrawing ability of the para substituent (Hammett reaction constant, 0.3). The syn rotamer of a 2‐methyl derivative, where the methyl and OH groups are close, has a lower association constant than the anti rotamer. In the case of 2,2,4,4‐tetramethyl‐3‐(2‐thienyl)pentan‐3‐ols a second approach, based on the variation of the syn/anti ratio with the pyridine concentration, gives results concordant with those of the NMR method. The association constants predict accurately syn/anti ratios and syn OH proton chemical shifts in neat pyridine. The unusually large temperature coefficients of OH proton shifts in pyridine are due in part to the variation of the association constant. Copyright © 2005 John Wiley & Sons, Ltd.
Controlled/living polymerization of methacrylamide in aqueous media via the RAFT process
Authors: Vasilieva Yulia A. , Scales Charles W. , Thomas David B. , Ezell Ryan G. , Lowe Andrew B. , Ayres Neil , McCormick Charles L. 
Published: June 2005

AbstractThe polymerization of methacrylamide (MAM) was performed in aqueous media via reversible addition fragmentation chain transfer (RAFT) polymerization with the dithiobenzoate chain‐transfer agent (CTA) 4‐cyanopentanoic acid dithiobenzoate (CTP) and 4,4′‐azobis(4‐cyanopentanoic acid) (V‐501) as initiator. The polymerization in unbuffered water at 70 °C with a CTP/V‐501 ratio of 1.5 was controlled for the first 3 h, after which the molecular weight distribution broadened and a substantial deviation of the experimental from the theoretical molecular weight occurred, presumably because of a loss of CTA functionality at longer polymerization times. Conducting the polymerization in an acidic buffer afforded a well‐defined homopolymer (Mn = 23,800 g/mol, Mw/Mn = 1.08). To demonstrate the controlled/living nature of the system, a block copolymer of MAM and acrylamide was successfully prepared (Mn = 33,800 g/mol, Mw/Mn = 1.25) from a polymethacrylamide macro‐CTA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3141–3152, 2005
Synthesis and characterization of novel fluoride‐releasing monomers. II. Dimethacrylates containing bis(aminodiacetic acid) and their ternary zirconium fluoride complexes
Authors: Xu Xiaoming , Ding Xingzhe , Ling Long , Burgess John O. 
Published: June 2005

AbstractNovel dimethacrylate monomers containing bis(aminodiacetic acid) chelating ligands with or without additional hydroxyl groups were synthesized, starting from 2,2‐bis(4‐hydroxy‐3‐methylphenyl)propane. The structures of the monomers were characterized by electrospray mass spectrometry (ESMS), 1H NMR, and 13C NMR. The structures and relative stability of fluoride‐releasing monomers containing one or more ternary zirconium fluoride complex moieties were studied by ESMS. The most stable ternary zirconium fluoride complex was in the form of [LZrF]−, where H4L is the monomer containing bis(aminodiacetic acid) without additional hydroxyl groups. The synthesized monomer was photopolymerized with camphorquinone and 1‐phenyl‐1,2‐propane‐dione as initiators and N,N‐dimethylaminoethyl methacrylate as the accelerator. The fluoride release, fluoride recharge, compressive strength, and flexure strength were tested on the experimental dental composite containing 13.7 wt % synthesized monomer and three commercial flowable dental composites. The results showed that the experimental composite has significantly higher fluoride release and recharge capabilities than the commercial flowable composites. The compressive strength was comparable to that of the commercial materials. The water sorption and solubility met the requirement of the ISO Specification 4049. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3153–3166, 2005
Synthesis and characterization of poly(ethylene glycol) polymers functionalized by terminal tributyltin carboxylate moieties
Authors: Angiolini Luigi , Caretti Daniele , Mazzocchetti Laura , Salatelli Elisabetta , Willem Rudolph , Biesemans Monique 
Published: June 2005

AbstractNovel polymeric derivatives of various average molecular weights bearing tributyltin carboxylate moieties as terminal groups have been prepared by esterification with bis(tributyltin) oxide of the corresponding poly(ethylene glycol)s functionalized with dimethylenecarboxylic end groups. Low‐molecular‐weight compounds have also been synthesized, with the aim of investigating the influence of the polymeric chain on tin properties. As investigated by Sn NMR and Fourier transform infrared, the metal center appears to be completely tetracoordinated in chloroform solution at room temperature, whereas at low temperature, the tin atom undergoes a fast exchange between intramolecular pentacoordination with the ethereal oxygen atoms and the unassociated form. In the solid state, even at room temperature, all the polymeric products exhibit both tetracoordination and pentacoordination at tin, the latter achieved by interaction with both ethereal and carbonyl oxygens. The thermal behavior of the series of compounds indicates the presence of crystalline domains in the material, which can be ascribed either to intermolecular interactions at tin, giving rise to organometal aggregates, or to the formation of an ordered phase induced by the presence of the macromolecular chain, depending on the more or less elevated relative concentration of the organotin moieties in the sample. These findings are also confirmed by the X‐ray diffractions patterns of the investigated products. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3091–3104, 2005
Development of an efficient route to hyperbranched poly(arylene ether sulfone)s
Authors: Himmelberg Patrick , Fossum Eric 
Published: June 2005

AbstractA two‐step route to an AB2 monomer that underwent polymerization via nucleophilic aromatic substitution to afford hyperbranched poly(arylene ether sulfone)s (HB PAES) was developed. The synthesis of 3,5‐difluoro‐4′‐hydroxydiphenyl sulfone (4) was accomplished by the reaction of 3,5‐difluorophenylmagnesium bromide with 4‐methoxyphenylsulfonyl chloride, followed by deprotection of the phenol group with HBr in acetic acid. The polymerization of 4 in the presence of 3,4,5‐trifluorophenylsulfonyl benzene or tris(3,4,5‐trifluorophenyl)phosphine oxide as a core molecule afforded HB PAES with number‐average molecular weights ranging from 3400 to 8400 Da and polydispersity index values ranging from 1.5 to 4.8. The presence of cyclic oligomeric species, formed by an intramolecular cyclization process, was a contributing factor to the relatively low molecular weights. The degree of branching (DB) of the HB PAES samples was estimated by a comparison of the 19F NMR spectra of the polymer samples with those of a series of model compounds, and DB values ranging from 0.51 to 0.70 were determined. The glass‐transition temperatures for the HB PAES samples were in the range of 205–222 °C, as determined by differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:3178–3187, 2005
High resolution electron microscopy of ordered polymers and organic molecular crystals: Recent developments and future possibilities
Authors: Martin David C. , Chen Jihua , Yang Junyan , Drummy Lawrence F. , Kübel Christian 
Published: June 2005

AbstractHigh Resolution Electron Microscopy (HREM) has made it possible to directly image the detailed organization of a variety of polymers and organic molecular crystals. For organic materials it is imperative to use low dose techniques that minimize the structural reorganizations that inevitably occur during electron beam irradiation. This article reviews recent developments in low dose HREM from our own laboratory and elsewhere. The developments in closely related microstructural characterization techniques are also reviewed. In the future, the ability to correct the spherical aberration of the objective lens, the use of low voltages to increase contrast, and the use of time‐resolved techniques are expected to open new avenues for the ultrastructural investigations of organic materials. New sample preparation techniques, such as the ability to make thin samples by focused ion beam (FIBs), to cut samples with an oscillating diamond knife, and to more conveniently prepare cryogenically solidified specimens, are also expected to be of increasing importance. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1749–1778, 2005
Free volume and water vapor transport properties of temperature‐sensitive polyurethanes
Authors: Ding X. M. , Hu J. L. , Tao X. M. , Wang Z. F. , Wang B. 
Published: June 2005

AbstractSegmented polyurethanes (PU) with crystalline soft segments were prepared with different crystalline polyols as soft segments. Morphology and microstructure of the PUs were investigated using Differential Scanning Calorimetry (DSC), Wide‐angle X‐ray Diffraction (WAXD), and Positron Annihilation Lifetime Spectra (PALS). Water vapor transport properties of the PU membranes were measured in the temperature range of crystal melting of their soft segments. Dependence of free volume of the PUs on temperature and the relationship between the free volume and water vapor permeability of the PU membranes were investigated. The results show that the mean free volume size and fractional free volume increase more rapidly in the temperature range of crystal melting than in other temperature intervals. In the specified temperature range, water vapor permeability of the polyester based PU membranes increases significantly, caused by the steep increase in free volume, due to crystal melting of the soft segments. Water vapor permeability of the polyester based PUs exhibits approximately direct correlation with the fractional free volume within the temperature range of crystal melting. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1865–1872, 2005
Unique rheological behavior of rubber based nanocomposites
Authors: Sadhu Susmita , Bhowmick Anil K. 
Published: June 2005

AbstractMontmorillonite clay (N) based nanocomposites were prepared using three different grades of acrylonitrile butadiene rubber (NBR) (19%, 34%, and 50% acrylonitrile contents), styrene butadiene rubber (SBR), and polybutadiene rubber (BR). Rheological study was carried out on these nanocomposites at three different temperatures (110 °C, 120 °C, and 130 °C) over a range of shear rates for comparison. The results showed that the shear viscosity decreased with increasing shear rate and incorporation of the unmodified (N) and the modified (OC) fillers up to a certain loading, when the results were compared with the gum rubber. This effect became more prominent with increasing polarity of the rubber. The die swell, on the other hand, decreased with loading of N and OC. With increasing filler volume fraction, the die swell further decreased. Decrease of viscosity with concomitant decrease of die swell is unique in such systems. Consecutive runs of the same sample over different shear rates increased the viscosity. The results were explained with the help of X‐Ray Diffraction (XRD) data and Transmission Electron Microscopy (TEM).© 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1854–1864, 2005
Direct Si oxidation with fluorine incorporation using an argon excimer VUV source
Authors: Yu J. J. , Boyd I. W. 
Published: June 2005

AbstractDirect Si oxidation using an Ar excimer VUV source without substrate heating has led to the rapid growth of oxide layers, with a film thickness of 8 nm being obtained for only 10 min VUV irradiation. With fluorine incorporation, the film thickness was further increased to 21 nm. The 1073 cm–1 absorption band in the infrared spectra for the Si–O stretching vibration was shifted to a higher wavenumber up to 1096 cm–1 while its full width at half maximum (FWHM) was reduced from 64 to 54 cm–1. The resulting SiOF films were OH‐free. The rapid Si oxidation could be caused by the highly reactive O (1S) generated by VUV photons, the availability of more Si dangling bonds produced from the replacement of Si in the Si–Si bond by F, and more VUV‐induced O3 formation at low substrate temperatures. Fluorine incorporated into the Si–O network was directly provided by the VUV dissociated PTFE materials in the reaction chamber. The F contents in the SiOF films could be controlled by varying the VUV source parameters such as the excimer gas pressure. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transport in high mobility amorphous wide band gap indium zinc oxide films
Authors: Martins R. , Barquinha P. , Pimentel A. , Pereira L. , Fortunato E. 
Published: June 2005

AbstractThis paper discusses the electron transport in the n‐type amorphous indium–zinc–oxygen system produced at room temperature by rf magnetron sputtering, under different oxygen partial pressures. The data show that the transport is not band tail limited, as it happens in conventional disordered semiconductors, but highly dependent on its ionicity, which explains the very high mobilities (≥60 cm2 V–1 s–1) achieved. The room temperature dependence of the Hall mobility on the carrier concentration presents a reverse behaviour than the one observed in conventional crystalline/polycrystalline semi‐conductors, explained mainly by the presence of charged structural defects in excess of 4 × 1010 cm–2 that scatter the electrons that pass through them. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Recurrence relations for matrix elements of few‐body correlated wave functions
Authors: Harris Frank E. 
Published: June 2005

AbstractThis article considers the matrix elements arising from the use of wave functions containing exponentials in all the interparticle distances. Special cases (with some vanishing parameters) correspond to the use of the Hylleraas basis. For the three‐body (sometimes called two‐electron) correlated wave function, we present new recurrence relations that complement the formula of Sack, Roothaan, and Kolos. One of these is a sum rule that could also be used for downward recursion; the other is suitable for recursion in the usual (upward) recursive process. Formulas connecting matrix elements in the four‐body (three‐electron) problem are also derived; their use confirms the recurrence relations recently published by Pachucki, Puchalski, and Remiddi for the Hylleraas basis and provides a new sum rule for matrix elements in the general correlated exponential basis. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Ordering the complements of trees by the number of maximum matchings
Authors: Yan Weigen , Yeh Yeong‐Nan , Zhang Fuji 
Published: June 2005

AbstractA “perfect matching” of a graph G with n vertices is a set of ⌊n/2⌋ independent edges of G. In the present study, we succeeded in determining the trees whose complements have the extremal number of “perfect matchings” for two different group of trees. Some further problems are also posed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Geometry and stability of fullerene cages: C24 to C70
Authors: Chang Y. F. , Zhang J. P. , Sun H. , Hong B. , An Z. , Wang R. S. 
Published: June 2005

AbstractThe electronic structures and geometries of all even carbon fullerenes were investigated theoretically using density functional theory (DFT) at the B3LYP/6‐31G* level. Based on geometries, energies, and aromaticities, the potential relationship between geometry factors and stability has been investigated systematically. The extra stability of C60 has been confirmed by the shorter average bond length, smaller angle strain, widest energy gap, larger binding energy, and dissociation energy. Furthermore, C32 and C50 are predicted to have higher aromaticity due to larger negative nucleus independent chemical shift (NICS) values, whereas C60 displays a weak aromaticity. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Density functional theory study of the interaction between 3‐nitro‐1,2,4‐triazole‐5‐one and ammonia
Authors: Fang Guo‐Yong , Xu Li‐Na , Hu Xin‐Gen , Li Xin‐Hua 
Published: June 2005

AbstractTwo fully optimized geometries of 3‐nitro‐1,2,4‐triazol‐5‐one (NTO)–NH3 complexes have been obtained with the density function theory (DFT) method at the B3LYP/6‐311++G** level. The intermolecular interaction energy is calculated with zero point energy (ZPE) correction and basis set superposition error (BSSE) correction. The greatest corrected intermolecular interaction of the NTO–NH3 complexes is −37.58 kJ/mol. Electrons in complex systems transfer from NH3 to NTO. The strong hydrogen bonds contribute to the interaction energies dominantly. Natural bond orbital (NBO) analysis is performed to reveal the origin of the interaction. Based on vibrational analysis, the changes of thermodynamic properties from the monomer to complexes with the temperature ranging from 200 K to 800 K have been obtained using the statistical thermodynamic method. It is found that two NTO–NH3 complexes can be produced spontaneously from NTO and NH3 at normal temperature. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
High turbulence liquid chromatography online extraction and tandem mass spectrometry for the simultaneous determination of suberoylanilide hydroxamic acid and its two metabolites in human serum
Authors: Du Lihong , Musson Donald G. , Wang Amy Qiu 
Published: June 2005

AbstractA reliable and sensitive method incorporating high turbulence liquid chromatography (HTLC) online extraction with tandem mass spectrometry (MS/MS), for simultaneous determination of suberoylanilide hydroxamic acid (SAHA) and its two metabolites, SAHA‐glucuronide (M1) and 4‐anilino‐4‐oxobutanoic acid (M2), in human serum, has been developed to support clinical studies. The HTLC technology significantly reduces the time required for sample clean‐up since sample extraction and analysis are performed online. Clinical samples, internal standards (IS) and buffer are transferred into 96‐well plates using a robotic liquid handling system. A 20 µL aliquot of prepared sample is directly injected into the HTLC/LC‐MS/MS system where the matrix is rapidly washed away to waste and the analytes are retained on the narrow‐bore extraction column (0.5 × 50 mm), using an aqueous mobile phase at 1.5 mL/min. Analytes are then eluted from the extraction column and transferred to the analytical column using a gradient mobile phase prior to detection by MS/MS. Interference with determination of SAHA from in‐source dissociation of M1 is eliminated by the chromatographic separation. The resolution of SAHA and M1 did not change for more than 1500 serum sample injections by applying an acid wash (15% acetic acid) on the extraction column. The linear calibration ranges for SAHA, M1, and M2 are 2–500, 5–2000, and 10–2000 ng/mL, respectively. Assay intraday validation was conducted using five calibration curves prepared in five lots of human control serum. The precision expressed as relative standard deviation (RSD) is less than 6.8% and accuracy is 94.6–102.9% of nominal values for all three analytes. Assay specificity, freeze/thaw stability, storage stability, and matrix effects were also assessed. Copyright © 2005 John Wiley & Sons, Ltd.
Fragmentations of isomeric sulfated monosaccharides using electrospray ion trap mass spectrometry
Authors: Minamisawa Toshikazu , Hirabayashi Jun 
Published: June 2005

AbstractElectrospray ionization combined with ion trap mass spectrometry (ESI‐ITMS) is a powerful tool for structural analysis of complex carbohydrates. Although its application to sulfated glycans has been limited so far, it should provide critical information, such as sulfate positions, on their structures. In this work, MSn spectra of nine monosulfated monosaccharides, consisting of five hexoses and four N‐acetylhexosamines, were measured in negative ion mode to find basic fragmentation rules for sulfated sugars. Two pairs of positional isomers with respect to sulfation, i.e., Gal4S and Gal6S, and GalNAc4S and GalNAc6S, showed characteristic fragmentation patterns in MS3, and could be discriminated from one another by the appearance of particular diagnostic fragment ions that characterize individual isomers. It was also demonstrated that, even if a mixture of these positional isomers was analyzed, the proportion of each species could be estimated through analysis of the abundance ratios of the diagnostic ions. However, 3‐O‐sulfated saccharides (Glc3S and GlcNAc3S) gave a single abundant diagnostic ion in MS2 corresponding to the hydrogensulfate ion, [OSO3H]−, and this characteristic clearly differentiated them from their positional isomers. In contrast, 6‐O‐sulfated diastereomers consisting of two groups, Glc6S, Man6S, Gal6S, and GlcNAc6S, GalNAc6S, could not be discriminated by the types of fragment ions; however, the abundance ratios of particular fragment ions differed significantly between Glc(NAc)6S and Gal(NAc)6S. Since ESI‐ITMS yielded large quantities of useful information on structures of monosulfated hexoses and N‐acetylhexosamines in an extremely simple and reproducible manner, establishment of a comprehensive strategy based on ESI‐ITMSn appears to be a promising technique for structural elucidation of sulfated complex carbohydrates. Copyright © 2005 John Wiley & Sons, Ltd.
Analysis of the composition of immunoconjugates using size‐exclusion chromatography coupled to mass spectrometry
Authors: Lazar Alexandru C. , Wang Lintao , Blättler Walter A. , Amphlett Godfrey , Lambert John M. , Zhang Wei 
Published: June 2005

AbstractRecombinant monoclonal antibody drug products play an increasingly important role in the treatment of various diseases. Antibodies are large, multi‐chain proteins and antibody preparations often contain several molecular variants, which renders them heterogeneous. The heterogeneity is further increased in immunoconjugates prepared by covalently linking several drug molecules per antibody molecule. As part of the product characterization, the molecular weights of the antibodies or their drug conjugates need to be measured. Electrospray ionization mass spectrometry (ESI‐MS) is well suited for the analysis of recombinant antibodies and immunoconjugates. Sample preparation is an important element of ESI‐MS analysis, in particular samples need to be freed of interfering charged species, such as salts and buffer components. In this paper, Amicon centrifugal filters, reversed‐phase high‐performance liquid chromatography (HPLC), and size‐exclusion HPLC were evaluated for sample desalting. Size‐exclusion HPLC, using aqueous acetonitrile as the mobile phase, directly coupled to ESI‐MS provided the best performance and was optimized for the study of immunoconjugates. The results showed that antibodies carrying covalently linked maytansinoid molecules generated charge envelope profiles that differ from those of the non‐conjugated antibody. For the determination of the distribution of the various conjugate species in an immunoconjugate sample prepared by randomly linking in the average 3.6 drug molecules per antibody molecule, the experimental conditions needed to be carefully selected to allow acquisition of the whole spectrum containing the charge envelopes of all species. Copyright © 2005 John Wiley & Sons, Ltd.