bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of the acceptor conjugation length and composition on the electrical memory characteristics of random copolyimides
Authors: Kurosawa Tadanori , Lai Yi‐Cang , Yu An‐Dih , Wu Hung‐Chin , Higashihara Tomoya , Ueda Mitsuru , Chen Wen‐Chang 
Published: December 2012

AbstractResistive‐switching memories based on copolyimides (coPIs), PI‐NTCDIX and PI‐BTCDIX, with different compositions of 4,4′‐diamino‐4″‐methyltriphenylamine (AMTPA), 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, and N,N′‐bis‐(4‐aminophenyl)‐1,8:4,5‐naphthalenetetracarboxydiimide (NTCDI) or N,N′‐bis‐(4‐aminophenyl)‐1,2:4,5‐benzenetetracarboxydiimide (BTCDI) have been developed. By varying the feed ratio of monomers, PI‐NTCDIX and PI‐BTCDIX showed tunable optical and electronic properties through the charge transfer (CT) between AMTPA and NTCDI or BTCDI. The memory devices based on PI‐NTCDIX exhibited the tunable electrical bistability from the volatile dynamic random access memory to nonvolatile write once read many memory characteristics as the NTCDI composition increased. The OFF/ON electrical switching transition was mainly attributed to the CT mechanism for the charge separated high conductance, based on the analysis of model compounds and density functional theory calculation. Also, the volatility of the memory device depended on the stability of CT complex. The long conjugation and high electron affinity of the NTCDI moiety stabilized the radical anion generated in the CT complex and prevented the recombination of segregated radical species even through applying the high positive or negative voltage. On the other hand, the memory devices based on PI‐BTCDIX showed a rather unique behavior compared with those based on PI‐NTCDIX. At the low BTCDI composition, the device exhibited volatile memory property. However, no switching behavior was observed at the high BTCDI composition due to the low highest occupied molecular orbital energy level of BTCDI. Combining these results and our previous study on perylenebisimide (PBI), we concluded that memory characteristics could be tailored by changing the conjugation length (PBI > NTCDI > BTCDI) and the acceptor composition in random coPIs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
An enhanced host–guest electro‐optical polymer system using poly(norbornene‐dicarboximides) via ROMP
Authors: Yu Feng , Spring Andrew M. , Li Lu , Qiu Feng , Yamamoto Kazuhiro , Maeda Daisuke , Ozawa Masaaki , Odoi Keisuke , Yokoyama Shiyoshi 
Published: December 2012

AbstractHigh glass transition temperature poly(N‐cyclohexyl‐5‐norbornene‐2,3‐dicarboximide)s (NDI)s prepared by ring opening metathesis polymerization yielded polymers with a narrow polydispersity and well‐controlled molecular weight materials when using the Grubbs first generation initiator. Polymers produced using the Grubbs second generation initiator could not be controlled easily. By initiator selection it was also possible to synthesize polymers with either 98 or 52% trans microstructures. These materials were employed as electro‐optic (EO) polymer hosts for high molecular hyperpolarizability (β) phenyl vinylene thiophene vinylene bridge chromophores. This chromophore was modified by the incorporation of a tert‐butyldiphenylsilane group. The addition was able to further increase its EO coefficient (r33) to reach 93 pm/V in a trans rich poly(NDI) produced by the Grubbs first generation initiator, compared to a benchmark chromophore / polymer combination. We investigated in detail the relationship between polymer microstructure and their absolute molecular weight on forming the best host–guest with the high β chromophore. Our results indicate that by utilizing a very simple host–guest system a high r33 can be realized. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Materials for the preparation of polymer pen lithography tip arrays and a comparison of their printing properties
Authors: Zhong Xiao , Bailey Nevette A. , Schesing Kevin B. , Bian Shudan , Campos Luis M. , Braunschweig Adam B. 
Published: December 2012

AbstractPolymer Pen Lithography (PPL) uses an array of polymeric tips, typically composed of poly(dimethyl siloxane), to transfer ink onto a surface and create patterns of soft molecules with micrometer to nanometer feature dimensions. In this study, tip arrays were fabricated from poly(methyl methacrylate), poly([methyl methacrylate]‐co‐[butyl methacrylate]), and poly(3‐mercaptopropylmethylsiloxane), and used to pattern 1‐mercaptohexadecanoic acid onto Au surfaces to determine the fidelity of pattern transfer by PPL as a function of the mechanical properties of the materials. It was found that the dependence between the applied force and feature edge length correlates directly to the mechanical properties of each of the polymers used to fabricate the tip arrays, where stiffer polymers have a reduced dependence between the applied force and feature size. This study demonstrates that PPL tip arrays can be composed of a wide variety of materials whose choice is determined by the desired printing application. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Insulin analog with additional disulfide bond has increased stability and preserved activity
Authors: Vinther Tine N. , Norrman Mathias , Ribel Ulla , Huus Kasper , Schlein Morten , Steensgaard Dorte B. , Pedersen Thomas Å. , Pettersson Ingrid , Ludvigsen Svend , Kjeldsen Thomas , Jensen Knud J. , Hubálek František 
Published: December 2012

AbstractInsulin is a key hormone controlling glucose homeostasis. All known vertebrate insulin analogs have a classical structure with three 100% conserved disulfide bonds that are essential for structural stability and thus the function of insulin. It might be hypothesized that an additional disulfide bond may enhance insulin structural stability which would be highly desirable in a pharmaceutical use. To address this hypothesis, we designed insulin with an additional interchain disulfide bond in positions A10/B4 based on Cα‐Cα distances, solvent exposure, and side‐chain orientation in human insulin (HI) structure. This insulin analog had increased affinity for the insulin receptor and apparently augmented glucodynamic potency in a normal rat model compared with HI. Addition of the disulfide bond also resulted in a 34.6°C increase in melting temperature and prevented insulin fibril formation under high physical stress even though the C‐terminus of the B‐chain thought to be directly involved in fibril formation was not modified. Importantly, this analog was capable of forming hexamer upon Zn addition as typical for wild‐type insulin and its crystal structure showed only minor deviations from the classical insulin structure. Furthermore, the additional disulfide bond prevented this insulin analog from adopting the R‐state conformation and thus showing that the R‐state conformation is not a prerequisite for binding to insulin receptor as previously suggested. In summary, this is the first example of an insulin analog featuring a fourth disulfide bond with increased structural stability and retained function.
Hepatitis E virus capsid protein assembles in 4M urea in the presence of salts
Authors: Yang Chunyan , Pan Huirong , Wei Minxi , Zhang Xiao , Wang Nan , Gu Ying , Du Hailian , Zhang Jun , Li Shaowei , Xia Ningshao 
Published: December 2012

AbstractThe hepatitis E virus (HEV) capsid protein has been demonstrated to be able to assemble into particles in vitro. However, this process and the mechanism of protein–protein interactions during particle assembly remain unclear. In this study, we investigated the assembly mechanism of HEV structural protein subunits, the capsid protein p239 (aa368–606), using analytical ultracentrifugation. It was the first to observe that the p239 can form particles in 4M urea as a result of supplementation with salt, including ammonium sulfate [(NH4)2SO4], sodium sulfate (Na2SO4), sodium chloride (NaCl), and ammonium chloride (NH4Cl). Interestingly, it is the ionic strength that determines the efficiency of promoting particle assembly. The assembly rate was affected by temperature and salt concentration. When (NH4)2SO4 was used, assembling intermediates of p239 with sedimentation coefficient values of approximately 5 S, which were mostly dodecamers, were identified for the first time. A highly conserved 28‐aa region (aa368–395) of p239 was found to be critical for particle assembly, and the hydrophobic residues Leu372, Leu375, and Leu395of p239 was found to be critical for particle assembly, which was revealed by site‐directed mutagenesis. This study provides new insights into the assembly mechanism of native HEV, and contributes a valuable basis for further investigations of protein assembly by hydrophobic interactions under denaturing conditions.
A simple criterion for gas chromatography/mass spectrometric analysis of thermally unstable compounds, and reassessment of the by‐products of alkyl diazoacetate synthesis
Authors: Kornilova Tatiana A. , Ukolov Anton I. , Kostikov Rafael R. , Zenkevich Igor G. 
Published: December 2012

RATIONALEA principal limitation of gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) is the thermal instability of analytes. We propose that the injector and column temperatures should not exceed the atmospheric pressure boiling point, without decomposition, of the highest homologue of the series being analyzed, instead of the time‐consuming procedure of obtaining chromatograms using different temperatures.METHODSA series of thermally unstable diazocarbonyl compounds, alkyl diazoacetates (predicted limit of stability approx. 140 °C, the boiling point of ethyl diazoacetate), was selected for GC/MS analysis using standard equipment. Different GC separation conditions were selected so that the retention temperatures of target compounds were both below and above 140 °C.RESULTSAnalyzing alkyl diazoacetates within their thermal stability range permitted reanalysis of their typical synthesis by‐products. No dialkyl fumarate or maleate impurities, principal decomposition products which have often been reported previously, were found. Instead, alkyl esters of glycolic acid nitrate, O2NOCH2CO2R, and 'pseudo‐dimeric' products, ROCO[C2H3NO]CO2R, were discovered for the first time.CONCLUSIONSAvoiding the decomposition of thermally unstable organic compounds during GC and/or GC/MS analysis requires estimating their degradation temperature limits. This limit can be estimated as being equal to the atmospheric pressure boiling point of the highest homologue in the homologous series under consideration that does not decompose on boiling. Copyright © 2012 John Wiley & Sons, Ltd.
High‐throughput liquid chromatography/mass spectrometry method for the quantitation of small molecules using accurate mass technologies in supporting discovery drug screening
Authors: Ding Xiao , Ghobarah Hesham , Zhang Xiaolin , Jaochico Allan , Liu Xingrong , Deshmukh Gauri , Liederer Bianca M. , Hop Cornelis E. C. A. , Dean Brian 
Published: December 2012

RATIONALEDrug discovery samples are routinely analyzed using liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods on triple quadrupole mass spectrometers employing multiple reaction monitoring (MRM). In order to improve analysis throughput, quantitation of small molecules on a quadrupole time‐of‐flight (QqTOF) instrument using TOF scan and high‐resolution MRM (MRM‐HR) modes was evaluated in this study.METHODSCassette dosed plasma and brain samples from nine compounds were extracted using a protein precipitation method. Separation was achieved by reversed‐phase liquid chromatography. Mass spectrometric analysis was performed using TOF scan and high‐resolution MRM approaches on a QqTOF mass spectrometer with turbo‐ionspray ionization. Results were compared to those obtained on a triple quadrupole mass spectrometer.RESULTSThe dynamic range varied depending on compounds and instruments and was similar between the MRM on QqQ and full TOF scan mode on QqTOF. Linear or quadratic regression and 1/x2 weighting were used. Resolution on the QqTOF instrument was around 32000 and mass accuracy was within 4.4 ppm. The MRM‐HR method showed better sensitivity compared to the TOF scan method, and was comparable to the MRM on a QqQ mass spectrometer. Assay accuracy was within ±25%.CONCLUSIONSA TOF scan method allowed the use of the generic method without compound‐specific optimization and was an alternative choice for routine high‐throughput quantitation of small molecules. The MRM‐HR method on the QqTOF showed good sensitivity which was comparable to that obtained by the MRM method on the triple quadrupole mass spectrometer. Copyright © 2012 John Wiley & Sons, Ltd.
Combination of Edman degradation of peptides with liquid chromatography/mass spectrometry workflow for peptide identification in bottom‐up proteomics
Authors: Lobas Anna A. , Verenchikov Anatoly N. , Goloborodko Anton A. , Levitsky Lev I. , Gorshkov Mikhail V. 
Published: December 2012

RATIONALEHigh‐throughput methods of proteomics are essential for identification of proteins in a cell or tissue under certain conditions. Most of these methods require tandem mass spectrometry (MS/MS). A multidimensional approach including predictive chromatography and partial chemical degradation could be a valuable alternative and/or addition to MS/MS.METHODSIn the proposed strategy peptides are identified in a three‐dimensional (3D) search space consisting of retention time (RT), mass, and reduced mass after one‐step partial Edman degradation. The strategy was evaluated in silico for two databases: baker's yeast and human proteins. Rates of unambiguous identifications were estimated for mass accuracies from 0.001 to 0.05 Da and RT prediction accuracies from 0.1 to 5 min. Rates of Edman reactions were measured for test peptides.RESULTSA 3D description of proteolytic peptides allowing unambiguous identification without employing MS/MS of up to 95% and 80% of tryptic peptides from the yeast and human proteomes, respectively, was considered. Further extension of the search space to a four‐dimensional one by incorporating the second N‐terminal amino acid residue as the fourth dimension was also considered and was shown to result in up to 90% of human peptides being identified unambiguously.CONCLUSIONSThe proposed 3D search space can be a useful alternative to MS/MS‐based peptide identification approach. Experimental implementations of the proposed method within the on‐line liquid chromatography/mass spectrometry (LC/MS) and off‐line matrix‐assisted laser desorption/ionization (MALDI) workflows are in progress. Copyright © 2012 John Wiley & Sons, Ltd.
A comparison of pretreatment methods for the analysis of phosphate oxygen isotope ratios in bioapatite
Authors: Grimes Vaughan , Pellegrini Maura 
Published: December 2012

RATIONALEThe integrity of the biological phosphate oxygen isotope (δ18Op) signal is thought to be contingent upon the complete removal of competing sources of oxygen such as associated organic matter. A range of pretreatment methods to purify phosphate material from competing sources of oxygen has been reported, with contradictory evidence on the usefulness and efficiency of one or another. Yet, a systematic comparison of these techniques for bioapatite phosphate has not been conducted.METHODSChemical and thermal pretreatment techniques were tested for their effectiveness at removing organic matter and the likelihood that they modify original δ18O values. The test was performed in inorganic (synthetic apatite and a phosphorite rock) and organic (bone and tooth tissues) phosphate materials for which we had an expectation of the actual original δ18Op value. Analysis of nitrogen content (wt.%), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy were employed.RESULTSWe detected variable efficiency at removing organic matter between pretreatment methods with no correlation to any specific structural change. The δ18Op results showed considerable variation between samples pretreated with the different methods and the untreated samples, with a compositional range of up to 4.5 ‰ in the bone samples. Variations of the δ18Op values within error were found for tooth enamel, phosphorite rock and inorganic apatite.CONCLUSIONSWe recommend a cautious approach when interpreting and comparing δ18Op data from bone samples treated with different pretreatment protocols. In general, the untreated samples seem to show δ18Op values closer to the expected ones. According to our results, pretreatment is completely unnecessary in highly mineralized tissues. Copyright © 2012 John Wiley & Sons, Ltd.
Analytical challenges in the quantitative determination of 2H/1H ratios of methyl iodide
Authors: Feakins Sarah J. , Rincon Miguel , Pinedo Paulina 
Published: December 2012

RATIONALEA published method to determine the hydrogen isotope (2H/1H) ratios of methoxyl groups, cleaved from lignin by hydroiodic acid (HI), calls for the analysis of methyl iodide (CH3I). However, analysis of halogenated compounds by gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/P/IRMS) yields incomplete conversion into H2 and unwanted HX products post‐pyrolysis.METHODSWe tested analytical capabilities when measuring a pure CH3I standard using a GC Isolink pyrolysis furnace at 1420 °C and a DELTA VPlus™ isotope ratio mass spectrometer, both by Thermo Scientific. We added and tested the efficacy of either a secondary reduction furnace containing heated metals or a cold trap to eliminate unwanted HI prior to IRMS analysis for 2H/1H determinations.RESULTSWhile 94% of the hydrogen in CH3I is converted into H2 in GC/P/IRMS, 6% yields HI. The use of either a secondary reduction furnace or cold trap can eliminate HI. However, secondary reduction is untenable given changes in reduction/transmission efficiency and 2H/1H drift. A cold trap provides a pragmatic solution: the δ2H values of −97 ‰ were measured from injections of 23–57 µg of CH3I to a precision of 4.5 ‰ (n = 26), within the error of the offline measurements.CONCLUSIONSWe have refined an earlier method to measure the δ2H values of CH3I by GC/P/IRMS by adding a cold trap to remove HI. This approach should facilitate future experimentation with the measurement of CH3I liberated from natural samples for potentially diverse applications including forensic sourcing of wood and tree‐wood‐based reconstructions of source water. Copyright © 2012 John Wiley & Sons, Ltd.
Direct analysis in real time high‐resolution mass spectrometry for high‐throughput analysis of antiparasitic veterinary drugs in feed and food
Authors: Martínez‐Villalba Anna , Vaclavik Lukas , Moyano Encarnación , Galceran Maria Teresa , Hajslova Jana 
Published: December 2012

RATIONALEDirect analysis in real time (DART) is a novel ionization technique that has been demonstrated in numerous applications as a useful tool for fast and convenient mass spectrometry (MS)‐based analysis of complex samples. In this study, the feasibility of DART ionization coupled to a high‐resolution mass spectrometer utilizing an orbitrap mass analyzer (orbitrap MS) for high‐throughput analysis of antiparasitic veterinary drugs was explored.METHODSTo obtain the best DART‐orbitrap MS performance, stepwise optimization of instrumental parameter settings, such as ionization gas temperature and mass resolving power, was performed. The optimized method was applied to feed and bovine milk samples previously extracted following a QuEChERS‐like strategy.RESULTSMost antiparasitic drugs could be analyzed following the described method. Positive DART ionization provided the protonated molecules [M+H]+; in negative DART ion mode, deprotonated molecules [M–H]– were observed. As an exception, polyether ionophores could be observed as the sodiated adducts [M+Na]+. Samples of milk and feed were extracted using a modified QuEChERS method for the determination of benzimidazoles and coccidiostats respectively and quantification was carried out by matrix‐matched calibration curves.CONCLUSIONSThe combination of an analysis time of less than 1 min per sample and the possibility to acquire accurate masses under high mass resolving power (HR) makes the DART‐HRMS technique an effective tool for rapid qualitative screening of antiparasitic veterinary drugs. Additionally, the results obtained in this study demonstrated the feasibility of this approach to quantify target analytes at levels down to 1 µg kg–1 for benzimidazolic compounds in milk and 0.25 mg kg–1 for coccidiostats in chicken feed. Copyright © 2012 John Wiley & Sons, Ltd.
Influence of matrix effect on the performance of the method for the official residue control of non‐steroidal anti‐inflammatory drugs in animal muscle
Authors: Olejnik Małgorzata , Jedziniak Piotr , Szprengier‐Juszkiewicz Teresa , Żmudzki Jan 
Published: December 2012

RATIONALEDuring the development and validation of mass spectrometry based method in residue control analysis, it is recommended to evaluate the level of the matrix effect. Often its level is relatively high, despite extensive sample purification.METHODSThe matrix effect in the method for the determination of non‐steroidal anti‐inflammatory drugs in animal muscle was tested using a post‐extraction addition technique. The experiment was performed to assess the impact of chromatographic conditions and design of ion source on the results. Additionally, the impact of phospholipids was tested.RESULTSThe matrix effect signal varied from 36% (64% ion suppression) to 192% (92% ion enhancement), depending on the analyte and species. The internal standard corrected matrix effect was generally lower but was still high for some analytes. Both chromatographic conditions and ion source design have influence on the level of matrix effect; however, this effect was no longer observed after compensation with internal standards.CONCLUSIONSCurrently, no commonly accepted criteria exist for the interpretation of results of determination of matrix effects; such criteria have been proposed in this paper, based on guidelines for bioanalytical methods and results of the study. Copyright © 2012 John Wiley & Sons, Ltd.