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Molecular Mobility (molecular + mobility)
Selected AbstractsWide-ranging molecular mobilities of water in active pharmaceutical ingredient (API) hydrates as determined by NMR relaxation timesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2008Sumie Yoshioka Abstract In order to examine the possibility of determining the molecular mobility of hydration water in active pharmaceutical ingredient (API) hydrates by NMR relaxation measurement, spin,spin relaxation and spin,lattice relaxation were measured for the 11 API hydrates listed in the Japanese Pharmacopeia using pulsed 1H-NMR. For hydration water that has relatively high mobility and shows Lorentzian decay, molecular mobility as determined by spin,spin relaxation time (T2) was correlated with ease of evaporation under both nonisothermal and isothermal conditions, as determined by DSC and water vapor sorption isotherm analysis, respectively. Thus, T2 may be considered a useful parameter which indicates the molecular mobility of hydration water. In contrast, for hydration water that has low mobility and shows Gaussian decay, T2 was found not to correlate with ease of evaporation under nonisothermal conditions, which suggests that in this case, the molecular mobility of hydration water was too low to be determined by T2. A wide range of water mobilities was found among API hydrates, from low mobility that could not be evaluated by NMR relaxation time, such as that of the water molecules in pipemidic acid hydrate, to high mobility that could be evaluated by this method, such as that of the water molecules in ceftazidime hydrate. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4258,4268, 2008 [source] Relationship between ice recrystallisation rates and the glass transition in frozen sugar solutionsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2002Steve Ablett Abstract The increase in ice crystal size that occurs through recrystallisation when many frozen products such as ice cream and frozen desserts are stored is one of the major factors contributing to the perceived deterioration of the product by the consumer. In order to reduce the rate of deterioration, a detailed understanding of the fundamental mechanism is needed. This study demonstrates that ice recrystallisation rates in a series of frozen sugar solutions are strongly correlated with the molecular mobilities of the water and solute molecules as measured by time domain nuclear magnetic resonance. The study also demonstrates that the proximity to the glass transition temperature as described by state diagrams correlates well with the measured ice recrystallisation rates. The temperature dependence in these systems is described by Williams, Landel and Ferry theory. © 2002 Society of Chemical Industry [source] The glass transition approach to determination of drying protocols for colour stability in dehydrated pear slicesINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 9 2005Hang-Ing Ling Summary Colour stability in dehydrated fruit is often attained by use of sulphite treatment to inhibit browning during processing and storage. However, colour stability may be able to be conferred on products by ensuring that the molecular mobility is restricted in dried fruit by drying to sufficiently low moisture to raise the glass transition temperature (under mild conditions). Pear slices were dehydrated at a low temperature (40 °C) to a low final moisture content (below 5%) after it was shown that, for a moisture content of 22% (which is the moisture content of commercial dehydrated pears) pretreatment with sulphite would be necessary to stabilise the colour. The use of longer drying regimes resulted in a moisture content where the food matrix would be closer to the glassy state and conferred colour stability on the dehydrated product compared to a product containing more moisture. For these low-moisture products, pretreatment with sulphite would not be necessary to preserve colour stability. [source] Effect of physico-chemical and molecular mobility parameters on Staphylococcus aureus growthINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 8 2003Elena Vittadini Summary The role played by water activity, ,mobility' and physico-chemical properties of the media in modulating microbial response has been the object of large debate in the scientific community. In this study, Staphylococcus aureus growth parameters (lag phase and cell density at 24 h) in brain heart infusion (BHI) and BHI:NaCl (1:1) were analysed in their correlation with physico-chemical/mobility parameters descriptive of the media [solid content, aw, kinematic viscosity, 17O NMR (R2, Pbw and )]. In these high moisture content, liquid and ,homogeneous' media S.aureus growth related to all the physico-chemical and molecular mobility parameters analysed in a similar manner and it was found to be influenced more significantly by added NaCl than by the physico-chemical and molecular mobility of the media. Staphylococcus aureus growth parameters correlated better with aw (relatively independent of NaCl concentration) than with any other parameter considered in this study. [source] Poly(butylene terephthalate)/clay nanocomposite compatibilized with poly(ethylene- co -glycidyl methacrylate).JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Abstract Poly(butylene terephthalate) (PBT)/clay nanocomposite was prepared by blending PBT and commercial modified montmorillonite clays via a extruder by using poly(ethylene- co -glycidyl methacrylate) (PEGMA) as a compatibilizer (PBT/PEGMA/Clay). PEGMA and clay were also blended with PBT to prepare PBT/PEGMA and PBT/Clay, respectively. The morphology was investigated by wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The clays were aggregated together and phase separation was observed in PBT/Clay. The clays were exfoliated in PBT/PEGMA/Clay. The equilibrium melting temperature was estimated by linear and nonlinear Hoffman-Weeks relation. The influence of the PEGMA and clay on the PBT crystallizable ability was also investigated by Avrami model and undercooling (difference between crystallization and equilibrium melting temperature). Hoffman-Lauritzen relation was used to estimate chain fold surface free energy. The exfoliated silicates cause a large number nucleus center to enhance the crystallization in PBT/PEGMA/Clay. The presence of PEGMA can react with the PBT and an increase in viscosity would reduce molecular mobility and crystallization in PBT/PEGMA. The aggregated clays have a confinement effect on the segmental motion of PBT and hinder the crystallization in PBT/Clay. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effects of Water-Glycerol and Water-Sorbitol Interactions on the Physical Properties of Konjac Glucomannan FilmsJOURNAL OF FOOD SCIENCE, Issue 2 2006Lai Hoong Cheng ABSTRACT Konjac glucomannan (KGM)-edible films were prepared with different amounts of glycerol or sorbitol as a plasticizer. Films were characterized by moisture sorption isotherm, and following conditioning at different relative humidities, by differential scanning calorimetry and tensile tests. Moisture and polyols (sorbitol and glycerol) were found to plasticize KGM-based films with respect to their tensile properties. However, thermal properties and water sorption capacity (WSC) of polyolplasticized KGM films were found to vary with water activity (aw), namely at low aw (< 0.6), WSC and melting enthalpy were decreased with increasing in polyol content and the opposite was true at higher aw (>0.6). This was attributed to extensive interactions between plasticizer and KGM that reduced the available active site (-OH groups) for water adsorption. The presence of polyols at low aw appeared to suppress crystalline structures due probably to restricted molecular mobility. These effects were diminished when the moisture content was >20%. [source] Glass Transition and Food Technology: A Critical AppraisalJOURNAL OF FOOD SCIENCE, Issue 7 2002M. Le Meste ABSTRACT: Most low water content or frozen food products are partly or fully amorphous. This review will discuss the extent to which it is possible to understand and predict their behavior during processing and storage, on the basis of glass transition temperature values (Tg) and phenomena related to glass transition. Two main conclusions are provisionally proposed. Firstly, glass transition cannot be considered as an absolute threshold for molecular mobility. Transport of water and other small molecules takes place even in the glassy state at a significant rate, resulting in effective exchange of water in multi-domains foods or sensitivity to oxidation of encapsulated materials. Texture properties (crispness) also appear to be greatly affected by sub-Tg relaxations and aging below Tg. Secondly, glass transition is only one among the various factors controlling the kinetics of evolution of products during storage and processing. For processes such as collapse, caking, crystallization, and operations like drying, extrusion, flaking, Tg data and WLF kinetics have good predictive value as regards the effects of temperature and water content. On the contrary, chemical/biochemical reactions are frequently observed at temperature below Tg, albeit at a reduced rate, and WLF kinetics may be obscured by other factors. [source] Prediction of onset of crystallization in amorphous pharmaceutical systems: Phenobarbital, nifedipine/PVP, and phenobarbital/PVPJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2010Vincent Caron Abstract The aim of this work is to determine if a stability testing protocol based on the correlations between crystallization onset and relaxation time above the glass transition temperature (Tg) can be used to predict the crystallization onsets in amorphous pharmaceutical systems well below their Tg. This procedure assumes that the coupling between crystallization onset and molecular mobility is the same above and below Tg. The stability testing protocol has been applied to phenobarbital, phenobarbital/polyvinylpyrrolidone (PVP) (95/5, w/w), and nifedipine/PVP (95/5, w/w). Crystallization onsets have been detected by polarized light microscopy examination of amorphous films; molecular mobility has been determined by dielectric relaxation spectroscopy above Tg and by both isothermal calorimetry and modulated differential scanning calorimetry below Tg. We find that small amounts of PVP significantly retard re-crystallization. This dramatic effect of PVP is not related to mobility, so this approach applies, at best, to extrapolation of high temperature data on a given formulation to low temperatures. Variation in molecular mobility at these concentrations of PVP is not the dominant factor in determining variation in propensity for re-crystallization from glassy systems; we suggest surface interactions between PVP and nuclei and/or small crystals slowing growth control variation in crystallization kinetics between formulations. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3887,3900, 2010 [source] Wide-ranging molecular mobilities of water in active pharmaceutical ingredient (API) hydrates as determined by NMR relaxation timesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2008Sumie Yoshioka Abstract In order to examine the possibility of determining the molecular mobility of hydration water in active pharmaceutical ingredient (API) hydrates by NMR relaxation measurement, spin,spin relaxation and spin,lattice relaxation were measured for the 11 API hydrates listed in the Japanese Pharmacopeia using pulsed 1H-NMR. For hydration water that has relatively high mobility and shows Lorentzian decay, molecular mobility as determined by spin,spin relaxation time (T2) was correlated with ease of evaporation under both nonisothermal and isothermal conditions, as determined by DSC and water vapor sorption isotherm analysis, respectively. Thus, T2 may be considered a useful parameter which indicates the molecular mobility of hydration water. In contrast, for hydration water that has low mobility and shows Gaussian decay, T2 was found not to correlate with ease of evaporation under nonisothermal conditions, which suggests that in this case, the molecular mobility of hydration water was too low to be determined by T2. A wide range of water mobilities was found among API hydrates, from low mobility that could not be evaluated by NMR relaxation time, such as that of the water molecules in pipemidic acid hydrate, to high mobility that could be evaluated by this method, such as that of the water molecules in ceftazidime hydrate. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4258,4268, 2008 [source] Role of thermodynamic, molecular, and kinetic factors in crystallization from the amorphous stateJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2008Chandan Bhugra Abstract Though there is an advantage in using the higher solubility amorphous state in cases where low solubility limits absorption, physical instability poses a significant barrier limiting its use in solid oral dosage forms. Unlike chemical instability, where useful accelerated stability testing protocols are common, no methodology has been established to predict physical instability. Therefore, an understanding of the factors affecting crystallization from the amorphous state is not only important from a scientific perspective but also has practical applications. Crystallization from the amorphous matrix has been linked to the molecular mobility in the amorphous matrix and recent research has focused on developing the link between these two fundamental properties of glass forming materials. Although researchers have been actively working in this area for some time, there is no current review describing the present state of understanding of crystallization from the amorphous state. The purpose of this review therefore is to examine the roles of different factors such as molecular mobility, thermodynamic factors, and the implication of different processing condition, in crystallization from the amorphous state. We believe an increased understanding of the relative contributions of molecular mobility and processing conditions are vital to increased usage of the amorphous state in solid oral dosage forms. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1329,1349, 2008 [source] Drying-induced variations in physico-chemical properties of amorphous pharmaceuticals and their impact on stability (I): Stability of a monoclonal antibody,JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2007Ahmad M. Abdul-Fattah Abstract The present study was conducted to investigate the impact of drying method and formulation on the storage stability of IgG1. Formulations of IgG1 with varying levels of sucrose with and without surfactant were dried by different methods, namely freeze drying, spray drying, and foam drying. Dried powders were characterized by thermal analysis, scanning electron microscopy, specific surface area (SSA) analysis, electron spectroscopy for chemical analysis (ESCA), solid state FTIR, and molecular mobility measurements by both isothermal calorimetry and incoherent elastic neutron scattering. Dried formulations were subjected to storage stability studies at 40°C and 50°C (aggregate levels were measured by size exclusion chromatography initially and at different time points). Both drying method and formulation had a significant impact on the properties of IgG1 powders, including storage stability. Among the drying methods, SSA was highest and perturbations in secondary structure were lowest with the spray-dried preparations. Sucrose-rich foams had the lowest SSA and the lowest protein surface accumulation. Also, sucrose-rich foams had the lowest molecular mobility (both fast dynamics and global motions). Stability studies showed a log-linear dependence of physical stability on composition. Preparations manufactured by "Foam Drying" were the most stable, regardless of the stabilizer level. In protein-rich formulations, freeze-dried powders showed the poorest storage stability and the stability differences were correlated to differences in secondary structure. In stabilizer-rich formulations, stability differences were best correlated to differences in molecular mobility (fast dynamics) and total protein surface accumulation. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:1983,2008, 2007 [source] Dielectric studies of molecular motions in amorphous solid and ultraviscous acetaminophenJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2005G.P. Johari Abstract The dielectric permittivity and loss spectra of glassy and ultraviscous states of acetaminophen have been measured over the frequency range 10 Hz,0.4 MHz. The relaxation spectra show an asymmetric distribution of times expressed in terms of the Kohlrausch exponent, ,, which remains constant at 0.79,±,0.02 over the 305,341 K range. The dielectric relaxation time increases on cooling according to the Vogel,Fulcher,Tammann equation. However, the values of the parameters are considerably different from the values deduced from earlier work by other researchers using the heat capacity of ultraviscous acetaminophen and relating it to its molecular mobility. The calorimetric glass softening temperature of 296 K obtained from differential scanning calorimetry is close to the value measured from dielectric relaxation. The equilibrium permittivity of ultraviscous acetaminophen decreases on heating like that of a normal dipolar liquid, as anticipated from the Curie law. But, its value decreases rapidly with time when it begins to crystallize. The equilibrium permittivity of this crystal phase is ,3.1 at 300 K and increases with temperature, which indicates a partial, orientational-disordering of its structure. The results show limitations of the procedures used in the modeling of the kinetics of molecular motions, that is, estimating physical stability, using thermodynamic considerations based on thermal analyses of the amorphous solid phase of acetaminophen. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2207,2223, 2005 [source] Self-association of cromolyn sodium in aqueous solution characterized by nuclear magnetic resonance spectroscopyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2004Xuan Ding Abstract The major objective of this study was to investigate and characterize the solution properties of cromolyn sodium (in D2O or D2O/H2O phosphate buffer at pH 7.5) using nuclear magnetic resonance (NMR) spectroscopy. The self-association of cromolyn molecules was examined primarily via one-dimensional 1H and 13C, and two-dimensional homonuclear NOESY NMR. Significant spectral shifts were observed for a majority of cromolyn 1H and 13C resonances, and are attributed to inter-molecular ring-stacking association accompanied by intra-molecular conformational changes. The critical self-association concentration was determined to be 10 mg/mL at pH 7.5 and 25°C by measuring the chemical shift of a specific cromolyn 1H resonance. The observed magnitude and sign changes of NOESY correlations indicate the formation of cromolyn aggregates with restricted molecular mobility. Mesomorphic liquid crystal formation is suggested by uniformly pronounced line broadening in concentrated cromolyn solutions; the transition concentration was approximately 60 mg/mL at 25°C, which is consistent with literature findings based on other techniques. A stronger tendency toward association was observed at lower temperature but aggregation appeared to be independent of pH. Lastly, it was concluded that self-association of cromolyn is promoted by the presence of monovalent cations as a result of reduced electrostatic repulsive forces. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:1351,1358, 2004 [source] Multiscale approach to investigate the radiochemical degradation of epoxy resins under high-energy electron-beam irradiationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2006N. Longiéras Abstract A multiscale investigation of the degradation mechanism of two epoxy systems exposed to electron-beam irradiation under a helium atmosphere was carried out with a variety of analytical methods, including high-resolution solution- and solid-state NMR spectroscopy, NMR relaxometry, infrared spectroscopy, sterical exclusion chromatography, and differential scanning calorimetry. As a first step, we studied a linear phenoxy polymer, poly(2-hydroxyether of bisphenol A), which provided a basis for the investigation of the degradation of a more complex, insoluble epoxy,amine network, diglycidyl ether of bisphenol A/triethylene tetramine. Among different structural modifications, the main degradation process was shown to produce in both cases a chain scission. For the phenoxy resin, the hydroxypropylidene moiety was identified as the fragile site leading to the formation of two phenolic chain ends and acetone and isopropyl alcohol as low-molecular-weight products. All methods, ranging from molecular to supramolecular scales, were shown to correlate both qualitatively and quantitatively. Experimental results obtained with diglycidyl ether of bisphenol A/triethylene tetramine evidenced a different degradation scheme occurring at the ethylene amine part and producing a dangling vinyl amine as the major degradation product. A selective increase in the molecular mobility at this site was confirmed by a two-dimensional, local-field wide-line separation experiment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 865,887, 2006 [source] Effects of Abstinence From Alcohol on the Broad Phospholipid Signal in Human Brain: An In Vivo 31P Magnetic Resonance Spectroscopy StudyALCOHOLISM, Issue 8 2001M. R. Estilaei Background: In vivo phosphorus magnetic resonance spectroscopy (31P MRS) at a magnetic field strength of 1.5 T allows measurement of fairly mobile membrane phospholipids in the human brain. We previously showed that subjects who are heavy drinkers had a smaller signal and a shorter transverse relaxation time (T2) of white matter phospholipids than light drinkers, which suggested lower concentrations and molecular mobility of phospholipids in heavy drinkers. The purpose of the present study was to measure if such chronic alcohol-induced white matter tissue changes are persistent in long-term abstinent alcoholics. Methods: Fourteen abstinent alcoholics (mean age 45 years, seven men and seven women) were studied by localized 31P MRS in the centrum semiovale and were compared with 13 male, alcohol-dependent, heavy drinkers and 23 nondependent light drinkers (17 men, 6 women) of similar age. Methods for measurements of the broad membrane phospholipid signal and its relaxation time were described previously. Results: Phospholipid concentrations and relaxation times in alcoholics abstinent for an average of 31 months were not significantly different from those measured in light drinkers. The contribution of fast and slowly relaxing signal components to the broad phospholipid signal, however, was still different in abstinent alcoholics compared with light drinkers. No effects of sex or of family history of alcoholism were noted on any of our spectroscopic measures within the light-drinking or abstinent groups. Conclusions: Most of our results suggest at least partial recovery of chronic alcohol-induced white matter phospholipid damage with long-term abstinence. They offer myelination changes and/or dendritic rearborization as a possible mechanism for the commonly observed white matter volume gain with prolonged abstinence. But the results also suggest a persistent abnormality in the nature and/or physical properties of white matter phospholipids in long-term abstinent alcoholics. [source] Degradation kinetics of beetroot pigment encapsulated in polymeric matricesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 8 2001George S Serris Abstract Kinetic studies on the degradation of water-soluble beetroot pigment, mainly consisting of the betalain betanin, encapsulated in three different matrices (pullulan and two maltodextrin samples differing in their molecular weight) were carried out under various water activity (aw,=,0.23, 0.43, 0.64, 0.75 and 0.84) and temperature (30, 40 and 50,°C) conditions. The water sorption behaviour of these materials was also examined. Degradation of the pigment was monitored by absorbance measurements at 537,nm (,max of betanin). The highest values of the rate constants for degradation were observed at an intermediate water activity level (aw,=,0.64) for all matrices and all three storage temperatures examined. An attempt to relate the degradation kinetics to the molecular mobility of the wall material was not successful. Pigment losses were observed even at temperatures below the glass transition temperature (Tg) of the polymeric matrices, although degradation was largely slowed down in the glassy state. In the vicinity of the Tg zone, where all polymers go through a glass , rubber transition, there was not a distinct change in the reaction rate, which could reflect the pronounced changes in molecular mobility of the wall material. In fact, some of the lower degradation rates were observed mostly under conditions where the matrices were fully plasticised (ie rubbery) and ,collapsed', implying that the degradation kinetics is not governed by factors related only to the physical state of the polymeric wall material. © 2001 Society of Chemical Industry [source] Conformation analysis and molecular mobility of ethylene and tetrafluoroethylene copolymer using solid-state 19F MAS and 1H , 19F CP/MAS NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2004Keitaro Aimi Abstract The changes in the conformation and molecular mobility accompanied by a phase transition in the crystalline domain were analyzed for ethylene (E) and tetrafluoroethylene (TFE) copolymer, ETFE, using variable-temperature (VT) solid-state 19F magic angle spinning (MAS) and 1H , 19F cross-polarization (CP)/MAS NMR spectroscopy. The shifts of the signals for fluorines in TFE units to higher frequency and the continuing decrease and increase in the T1,F values suggest that conformational exchange motions exist in the crystalline domain between 42 and 145 °C. Quantum chemical calculations of magnetic shielding constants showed that the high-frequency shift of TFE units should be induced by trans to gauche conformational changes at the CH2CF2 linkage in the E,TFE unit. Although the 19F signals of the crystalline domain are substantially overlapped with those of the amorphous domain at ambient probe temperature (68 °C), they were successfully distinguished by using the dipolar filter and spin-lock pulse sequences at 145 °C. The dipolar coupling constants for the crystalline domain, which can be estimated by fitting the dipolar oscillation behaviors in the 1H , 19F CP curve, showed a significant decrease with increasing temperature from 42 to 145 °C. This is due to the averaging of 1H19F dipolar interactions originating from the molecular motion in the crystalline domain. The increase in molecular mobility in the crystalline domain was clearly shown by VT T1,F and 1H , 19F CP measurements in the phase transition temperature range. Copyright © 2004 John Wiley & Sons, Ltd. [source] Nitroxide spin probe study of probe size, hydrogen bonding and polymer matrix rigidity effects on poly(acrylic acid)/poly(ethylene oxide) complexesMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003Li Tan Abstract An electron spin resonance (ESR) spin probe study was performed on 1 : 1 by weight poly(acrylic acid) (PAA)/poly(ethylene oxide) (PEO) complex over the 100,450 K temperature range with a series of tetramethylpiperidyloxy-based spin probes. Measurements of the parameters T5mT, Ta and Td demonstrated the effects of probe size and the strength of hydrogen bonding. The probes in the series Tempone, Tempo, Tempol and Tamine (respectively 4-oxo-, unsubstituted, 4-hydroxy- and 4-amino-2,2,6,6,-tetramethylpiperidine -1-oxyl) displayed noticeable increases in the hydrogen-bonding effect, as indicated by Ta and Td. These increases correlated with increasing hydrogen bond acceptor strength. On the other hand, as the probe size became larger, T5mT gradually increased due to the free volume decrease. These effects were analyzed using the established theoretical relationship of T5mT to probe volume expressed by f. Meanwhile, in order to investigate the effect of polymer matrix rigidity, a similar study was performed with a nitroxide spin probe, 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (Tempo), on PAA/PEO complexes of different weight compositions. The quantitative fast motion fraction in the composite ESR spectrum was calculated. The influence of changes in the composition of PAA on the molecular mobility was characterized by changes of the spectral parameters and ,c. The molecular mobility was shown to diminish with increasing content of PAA in PAA/PEO blends duo to the restriction of the polymer matrix rigidity increase. Copyright © 2003 John Wiley & Sons, Ltd. [source] Collagen dynamics in articular cartilage under osmotic pressureNMR IN BIOMEDICINE, Issue 8 2006Göran Zernia Abstract Cartilage is a complex biological tissue consisting of collagen, proteoglycans and water. The structure and molecular mobility of the collagen component of cartilage were studied by 13C solid-state NMR spectroscopy as a function of hydration. The hydration level of cartilage was adjusted between fully hydrated (,80 wt% H2O) and highly dehydrated (,30 wt% H2O) using the osmotic stress technique. Thus, the conditions of mechanical load could be simulated and the response of the tissue macromolecules to mechanical stress is reported. From the NMR measurements, the following results were obtained. (i) Measurements of motionally averaged dipolar 1H,13C couplings were carried out to study the segmental mobility in cartilage collagen at full hydration. Backbone segments undergo fast motions with amplitudes of ,35° whereas the collagen side-chains are somewhat more mobile with amplitudes between 40 and 50°. In spite of the high water content of cartilage, collagen remains essentially rigid. (ii) No chemical shift changes were observed in 13C cross-polarization magic angle spinning spectra of cartilage tissue at varying hydration indicating that the collagen structure was not altered by application of high osmotic stress. (iii) The 1H,13C dipolar coupling values detected for collagen signals respond to dehydration. The dipolar coupling values gradually increase upon cartilage dehydration, reaching rigid limit values at ,30 wt% H2O. This indicates that collagen is essentially dehydrated in cartilage tissue under very high mechanical load, which provides insights into the elastic properties of cartilage collagen, although the mechanical pressures applied here exceed the physiological limit. Copyright © 2006 John Wiley & Sons, Ltd. [source] Monitoring cytotoxic tumour treatment response by diffusion magnetic resonance imaging and proton spectroscopyNMR IN BIOMEDICINE, Issue 1 2002Risto A. Kauppinen Abstract Exposure of tumours to anti-cancer drugs, gene or radiation therapy consistently leads to an increase in water diffusion in the cases expressing favourable treatment response. The diffusion change coincides cytotoxic cell eradication and precedes volume reduction in drug or gene therapy-treated experimental tumours. Interestingly, the recent studies from human brain tumour patients undergoing chemotherapy show similar behaviour of diffusion, suggesting important application for MRI in patient management. In this review observations from diffusion MRI and MRS in the tumours during cytotoxic treatment are summarized and the cellular mechanisms affecting molecular mobility are discussed in the light of tissue microenvironmental and microdynamic changes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Morphology and mechanical properties of impact modified polypropylene blendsPOLYMER ENGINEERING & SCIENCE, Issue 11 2008Nathan Tortorella Isotactic polypropylene (PP) has been reactively blended with various grades of an ethylene,octene copolymer (EOC) in a twin-screw extruder. Free radical polymerization of styrene and a multifunctional acrylate during melt extrusion has resulted in an enhancement of mechanical properties over the binary blend. The reactive blend exhibits a notched Izod impact strength over 12 times that of pure polypropylene and greater than double the performance of the binary blend. Electron microscopy shows that by grafting onto the polymers, elastomer particle size and interparticle distance decrease, while particle shape becomes less spherical. The acrylate is crucial to achieve superior performance, as infrared spectra correlate an increase in graft yield to improvements in stress,strain behavior and impact strength. In addition, melt flow index (MFI) and melt strength data indicate a reduction in unwanted side reactions of polypropylene and the presence of long-chain branching. Dynamic-mechanical analysis reveals that the reaction promotes miscibility between polypropylene and the EOC and reduces molecular mobility at their glass-transition temperatures. Mechanical properties, graft yield, and MFI are shown to be highly dependent upon the elastomer's concentration, density, and molecular weight, initiator and monomer concentration, as well as processing temperature. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Effect of organic additives on formation and structure of polyelectrolyte-oppositely charged surfactant complexes,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2006J. A. Zakharova Abstract Effect of butanol and Triton X-100 on formation, supramolecular organization and local dynamics of poly(N -ethyl-4-vinylpyridinium)-dodecyl sulfate complexes have been studied by UV spectroscopy, high-speed sedimentation, laser light scattering and electron spin resonance (ESR) spectroscopy. It was found that solubilization of butanol promotes aggregation of the complex species in solution and results in contraction of the region in which water-soluble complexes are formed. On the contrary, highly aggregated complexes disaggregate up to molecularly dispersed state upon addition of Triton X-100. It was found that under the experimental conditions neither butanol (up to 3,wt%) nor Triton X-100 ([Triton X-100]/[sodium dodecylsulfate],,,1:1) cause destruction of the complexes. The results of ESR spin probe and spin label studies show that in both cases supramolecular realignments are accompanied by a slight increase of the local molecular mobility of surfactant ions in the complex micelles, segmental mobility of polyelectrolyte being unchanged. Copyright © 2006 John Wiley & Sons, Ltd. [source] Polycarbonate/SiC nanocomposites,influence of nanoparticle dispersion on molecular mobility and gas transport,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2-3 2005Martin Böhning Abstract Plasma synthesized silicon carbide (SiC) nanoparticles were dispersed in dichloromethane/poly(bisphenol-A-carbonate) (PC) solutions by high power ultrasonification. Samples were then prepared by film casting under well adapted preparation conditions. The influence of the SiC nanoparticles on the molecular mobility of the PC is studied by dielectric relaxation spectroscopy. No effect on the cooperative segmental mobility (glass transition) was detected. But the relaxation region corresponding to localized fluctuations is strongly broadened and the activation energy is reduced with increasing nanoparticle concentration. The most significant change was observed in the relaxation region between , - and , -process. The gas transport properties of these nanocomposite films are characterized in terms of permeability, diffusivity and solubility. Results can be interpreted based on an altered local free volume distribution and a change of molecular mobility of the polymer matrix near the nanoparticle surface which is in agreement with the dielectric results. Concentration dependent CO2 permeation experiments reveal a significant reduction of plasticization effects in the nanocomposites compared to the pure PC. Copyright © 2005 John Wiley & Sons, Ltd. [source] High-Resolution Solid-State NMR Studies on Uniformly [13C,15N]-Labeled UbiquitinCHEMBIOCHEM, Issue 9 2005Karsten Seidel Abstract Understanding of the effects of intermolecular interactions, molecular dynamics, and sample preparation on high-resolution magic-angle spinning NMR data is currently limited. Using the example of a uniformly [13C,15N]-labeled sample of ubiquitin, we discuss solid-state NMR methods tailored to the construction of 3D molecular structure and study the influence of solid-phase protein preparation on solid-state NMR spectra. A comparative analysis of13C,,13C,, and13C, resonance frequencies suggests that13C chemical-shift variations are most likely to occur in protein regions that exhibit an enhanced degree of molecular mobility. Our results can be refined by additional solid-state NMR techniques and serve as a reference for ongoing efforts to characterize the structure and dynamics of (membrane) proteins, protein complexes, and other biomolecules by high-resolution solid-state NMR. [source] | ||||||||||||||||