Effect Of Molecular Mobility Research Articles

Preheat Compression Molding for Polyetherketoneketone: Effect of Molecular Mobility

Preheat Compression Molding for Polyetherketoneketone: Effect of Molecular Mobility

Dicarboxylic acid as a linker to improve the content of amorphous drug in drug-in-polymer film: Effects of molecular mobility, electrical conductivity and intermolecular interactions

Amorphous solid dispersion (ASD) is a well-established approach to improve the dissolution rate of the drugs with low water solubility. However, the application of the ASD was hindered by the low drug content and high risk of re-crystallization of drugs. The purpose of this research was to develop an ASD film with high content of amorphous olanzapine (OLN) for oral delivery. To overcome the high crystallization tendency of OLN in polyvinyl alcohol (PVA) films, three dicarboxylic acids (succinic acid (Suc), fumaric acid (Fum) and malic acid (Mal)) were introduced in the drug-in-polymer system as linkers between the drug and the polymer. The influence of the linkers on the re-crystallization of OLN in PVA films was evaluated by polarized light microscopy (PLM) and x-ray diffraction (XRD). Then, the possible mechanisms of crystallization inhibition were discussed based on the results of dielectric spectroscopy (DES), differential scanning calorimetry (DSC), attenuated total reflectance Fourier transform infrared (ATR-FTIR), Raman spectroscopy and molecular modeling. Finally, the effect of the linkers on the in vitro dissolution of the OLN-in-PVA films was studied in simulant saliva, and the in vivo performance of the optimal formulation was evaluated in rats. The results showed that OLN-in-PVA film have lower molecular mobility, lower electrical conductivity and stronger intermolecular interactions with the existence of Mal, which led to a better crystallization inhibition of OLN in PVA films. The re-crystallization of OLN in PVA films decreased the dissolution rate of OLN in simulant saliva. The in vivo performance of the optimal formulation was similar with that of OLN solution in rats. This study introduced a novel strategy to reduce the risk of drug re-crystallization in ASD, and also provided a deeper insight into the mechanisms of crystallization inhibition in ASD. The results will improve the judicious selection of excipients in pharmaceutical formulations.

Molecular Mobility Effect on Magnetic Interactions in All-Organic Paramagnetic Liquid Crystal with Nitroxide Radical as a Hydrogen-Bonding Acceptor.

We synthesized new chiral all-organic liquid crystalline (LC) compounds with nitroxide (NO) and hydroxy (OH) groups, which form intermolecular hydrogen bonds between the NO and OH groups. The LC compounds show hexagonal columnar phases at room temperature, which solidify as LC glasses at low temperature. The experimental magnetic susceptibility of each of the compounds in the LC and isotropic phases is larger than that theoretically estimated on the simple assumption about the amount of the spins, whereas it accords with the theoretical one in the LC glass state. It is called magneto-LC effects. The difference between experimental and theoretical magnetic susceptibilities gradually increases as temperature increases through the LC glass state-to-LC phase transition. It suggests that molecular mobility is one of the origins of the magneto-LC effects.

Origin of toughness in β-polypropylene: The effect of molecular mobility in the amorphous phase

This study aims to explore the origin of toughness in β-phase isotactic polypropylene (i-PP). Samples of commercial-grade i-PP, both neat and nucleated with a specific β-nucleating agent (N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide), were subjected to a combination of structure-sensitive methods and fracture mechanical testing. In addition to common structural characterisation methods, solid-state NMR data were collected to obtain information about the dynamics of the polymer segments as well as the structure. In particular, temperate-induced transformation between the free and constrained amorphous phase was monitored by variable-temperature 13C MAS NMR, whereas T1ρ(1H) relaxation was used to estimate correlations times of segmental motions. Lower thermodynamic stability of rigid amorphous fraction was found in the β-crystalline systems. In contrast helical chains in crystalline and constrained amorphous phase were found to be more restrained in the α-crystalline system. Overall, the results indicate larger restrictions in chain mobility in the amorphous phase of the α-polymorphic PP system than in that of the β-crystalline ones.

The effect of molecular mobility on electronic transport in carbon nanotube-polymer composites and networks

A multiscale modeling approach to the prediction of electrical conductivity in carbon nanotube (CNT)–polymer composite materials is developed, which takes into account thermally activated molecular mobility of the matrix and the CNTs. On molecular level, a tight-binding density functional theory and non-equilibrium Green's function method are used to calculate the static electron transmission function in the contact between two metallic carbon nanotubes that corresponds to electron transport at 0 K. For higher temperatures, the statistical distribution of effective contact resistances is considered that originates from thermal fluctuations of intermolecular distances caused by molecular mobility of carbon nanotube and the polymer matrix. Based on this distribution and using effective medium theory, the temperature dependence of macroscopic electrical resistivity for CNT-polymer composites and CNT mats is calculated. The predicted data indicate that the electrical conductivity of the CNT-polymer composites increases linearly with temperature above 50 K, which is in a quantitative agreement with the experiments. Our model predicts a slight nonlinearity in temperature dependence of electric conductivity at low temperatures for percolated composites with small CNT loading. The model also explains the effect of glass transition and other molecular relaxation processes in the polymer matrix on the composite electrical conductivity. The developed multiscale approach integrates the atomistic charge transport mechanisms in percolated CNT-polymer composites with the macroscopic response and thus enables direct comparison of the prediction with the measurements of macroscopic material properties.

Effect of molecular mobility on coupled enzymatic reactions involving cofactor regeneration using nanoparticle-attached enzymes

Cofactor-dependent multi-step enzymatic reactions generally require dynamic interactions among cofactor, enzyme and substrate molecules. Maintaining such molecular interactions can be quite challenging especially when the catalysts are tethered to solid state supports for heterogeneous catalysis for either biosynthesis or biosensing. The current work examines the effects of the pattern of immobilization, which presumably impacts molecular interactions on the surface of solid supports, on the reaction kinetics of a multienzymic system including glutamate dehydrogenase, glucose dehydrogenase and cofactor NAD(H). Interestingly, particle collision due to Brownian motion of nanoparticles successfully enabled the coupled reactions involving a regeneration cycle of NAD(H) even when the enzymes and cofactor were immobilized separately onto superparamagnetic nanoparticles (124 nm). The impact of particle motion and collision was evident in that the overall reaction rate was increased by over 100% by applying a moderate alternating magnetic field (500 Hz, 17 Gs), or using additional spacers, both of which could improve the mobility of the immobilized catalysts. We further observed that integrated immobilization, which allowed the cofactor to be placed in the molecular vicinity of enzymes on the same nanoparticles, could enhance the reaction rate by 1.8 fold. These results demonstrated the feasibility in manipulating molecular interactions among immobilized catalyst components by using nanoscale fabrication for efficient multienzymic biosynthesis.

Study of effect of molecular mobility in chromatophore membranes of the bacterium E. shaposhnikovii on processes of photoinduced electron transport using the NMR-Spin-Echo method with isotope substitution and dehydration

The effect of dehydration and (2)H2O/H2O isotope substitution on electron transport reactions and relaxation of proton-containing groups was studied in chromatophore membranes of Ectothiorhodospira shaposhnikovii. During dehydration (including isotope substitution of hydrate water) of preliminarily dehydrated isolated photosynthetic membranes there was a partial correlation between hydration intervals within which activation of electron transport from high-potential cytochrome c to photoactive bacteriochlorophyll dimer P890 of photosynthetic reaction center and variation of spin-lattice and spin-spin proton relaxation time was observed. Partial correlation between hydration intervals can be considered as evidence of correlation between mobility of non-water proton-containing groups with proton relaxation frequency approximately 10(8) sec(-1) with efficiency of electron transfer at the donor side of the chain.

Spontaneous molecular orientation of polyimides induced by thermal imidization (4): Casting- and melt-induced in-plane orientation

Driving forces of in-plane chain orientation of polyimides (PIs) and their precursors were discussed and the mechanisms were proposed. A polyimide precursor, poly(amic acid) (PAA) derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) with p-phenylenediamine (PDA) showed a certain degree of in-plane orientation in its solution-casting process and clear molecular weight dependence. The results allowed us to propose the casting-induced in-plane orientation mechanism of the rigid PAA chains. The imidization-induced in-plane orientation mechanism was also discussed by investigating how residual solvent content influences the degree of in-plane orientation of resultant PI films. The results suggested that the magnitudes of the PI chain in-plane orientation are dominated by a combined effect of the initial PAA orientation, apparent stretching based on a great thickness decrease, and the molecular mobility during thermal imidization. In a system derived from s-BPDA with 2,2′-bis(trifluoromethyl)benzidine (TFMB), the effect of molecular mobility during thermal imidization was predominant when cured under usual thermal conditions owing to the presence of the trifluoromethyl groups contributing to weakened intermolecular interaction. In s-BPDA/TFMB and s-BPDA/m-TOL systems (m-TOL = m-tolidine), a melt-induced in-plane orientation phenomenon was observed at temperatures corresponding to their T g’s when the extents of in-plane chain orientation ( f values) were monitored as a function of temperature in the stepwise heating process. This behavior is very curious because there are no appreciable dimensional, morphological, and structural changes as some driving forces just above the T g of s-BPDA/TFMB.

Significance of Local Mobility in Aggregation of β-Galactosidase Lyophilized with Trehalose, Sucrose or Stachyose

The purpose of this study is to compare the effects of global mobility, as reflected by glass transition temperature (T(g)) and local mobility, as reflected by rotating-frame spin-lattice relaxation time (T(1rho)) on aggregation during storage of lyophilized beta-galactosidase (beta-GA). The storage stability of beta-GA lyophilized with sucrose, trehalose or stachyose was investigated at 12% relative humidity and various temperatures (40-90 degrees C). beta-GA aggregation was monitored by size exclusion chromatography (SEC). Furthermore, the T(1rho) of the beta-GA carbonyl carbon was measured by (13)C solid-state NMR, and T(g) was measured by modulated temperature differential scanning calorimetry. Changes in protein structure during freeze drying were measured by solid-state FT-IR. The aggregation rate of beta-GA in lyophilized formulations exhibited a change in slope at around T(g), indicating the effect of molecular mobility on the aggregation rate. Although the T(g) rank order of beta-GA formulations was sucrose < trehalose < stachyose, the rank order of beta-GA aggregation rate at temperatures below and above T(g) was also sucrose < trehalose < stachyose, thus suggesting that beta-GA aggregation rate is not related to (T-T(g)). The local mobility of beta-GA, as determined by the T(1rho) of the beta-GA carbonyl carbon, was more markedly decreased by the addition of sucrose than by the addition of stachyose. The effect of trehalose on T(1rho) was intermediate when compared to those for sucrose and stachyose. These findings suggest that beta-GA aggregation rate is primarily related to local mobility. Significant differences in the second derivative FT-IR spectra were not observed between the excipients, and the differences in beta-GA aggregation rate observed between the excipients could not be attributed to differences in protein secondary structure. The aggregation rate of beta-GA in lyophilized formulations unexpectedly correlated with the local mobility of beta-GA, as indicated by T(1rho), rather than with (T-T(g)). Sucrose exhibited the most intense stabilizing effect due to the most intense ability to inhibit local protein mobility during storage.

Explanation of the Crystallization Rate of Amorphous Nifedipine and Phenobarbital from Their Molecular Mobility as Measured by 13C Nuclear Magnetic Resonance Relaxation Time and the Relaxation Time Obtained from the Heating Rate Dependence of the Glass Transition Temperature

To gain further insight into the effect of molecular mobility on the crystallization rate of amorphous drugs, the mean relaxation times of amorphous nifedipine and phenobarbital were calculated based on the Adam–Gibbs–Vogel (AGV) equation, using the parameters D, T0, and Tf, derived from the heating rate dependence of the glass transition temperature (Tg) of the amorphous drugs and heat capacity of the drugs in the amorphous and crystalline states. These relaxation times were compared with the crystallization rate of amorphous nifedipine and phenobarbital reported previously. The spin‐lattice relaxation time (T1) and the spin‐lattice relaxation time in the rotating frame (T1ρ) of phenobarbital and nifedipine carbons were also determined. The temperature dependence of the crystallization rate of nifedipine and phenobarbital on the Tg was coincident with that of the mean relaxation time calculated according to the AGV equation within experimental error, indicating that the crystallization of nifedipine and phenobarbital is largely correlated with molecular mobility at the temperatures studied. A 13C nuclear magnetic resonance relaxation study indicated that the molecular motion of nifedipine and phenobarbital in the mid‐kHz frequency range became significant at temperatures higher than Tg−20 and Tg, respectively. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:798–806, 2001

Radiation-Induced Electron Transport Processes in Polymeric Dielectrics (A Review)

Recent results that have been obtained in studying the radiation-induced conductivity of low-polar polymeric dielectrics are surveyed. Major attention is given to the analysis of the kinetic behavior of radiation-induced current under different irradiation conditions. The effects of molecular mobility, morphology, and radiation-chemical processes on the transport of radiation-generated charges are considered. The relaxation model and its application to describing the kinetics of excess-charge transport in polymers are discussed.

2. タンパク質凍結乾燥製剤の安定性に及ぼす分子運動性の影響に関する検討(セミナー : 生物資源の保存)

2. タンパク質凍結乾燥製剤の安定性に及ぼす分子運動性の影響に関する検討(セミナー : 生物資源の保存)

Monte-Carlo simulation of free-radical decay as a probe of local and collective dynamics in polymer molecules

Abstract The effect of molecular mobility on the stability of free radicals in amorphous polymers was investigated by a Monte-Carlo (MC) method. Crank, crankshaft-like, kink and double kink were used as the various types of movements of submolecular structures. This work introduces the librational motions of these structures and formulates the methodology for their incorporation into the MC method. The results show that the presence of librational motion significantly influences both transfer and the decay of free radicals.

Stearyl poly(ethylene oxide) grafted surfaces for preferential adsorption of albumin Part 2. The effect of molecular mobility on protein adsorption

The adsorption of plasma proteins (fibrinogen and albumin) from buffer onto polystyrene-graft-(stearyl-poly(ethylene oxide)) (PS- g-SPEO) was investigated by radioiodine labeling of proteins using the iodine monochloride method. The molecular mobility of poly(ethylene oxide) grafts was determined by ESR spectroscopy, and the effects of PEO mobility on the ability of PS- g-SPEO to resist the non-specific protein adsorption have been studied. The non-specific adsorption of fibrinogen was found to decrease with increasing PEO mobility, whereas the interfacial energies lack significant correlation to the protein adsorption. The elastic restoring force seems much more important than hydrophobic interaction in PS- g-SPEO/protein interfaces. The high molecular mobility of PEO side chain is supposed to be the key effect on the protein-resistant properties of PS- g-SPEO. The protein adsorption results also reveal that the molecular mobility of PEO has a quite important role in developing albumin preferential materials. A high albumin preferential adsorption layer has been developed by immobilizing the stearyl end groups onto high mobile PEO chains.

Temperature dependence of bimolecular reactions associated with molecular mobility in lyophilized formulations.

We studied the temperature dependence of acetyl transfer between aspirin and sulfadiazine, a bimolecular reaction, in lyophilized formulations at temperatures near the glass transition temperature (Tg) and NMR relaxation-based critical mobility temperature (Tmc), to further understand the effect of molecular mobility on chemical degradation rates in solid pharmaceutical formulations. The temperature dependence of the hydrolysis rates of aspirin and cephalothin in lyophilized formulations was also studied as a model of bimolecular reactions in which water is a reactant. Degradation of lyophilized aspirin-sulfadiazine formulations containing dextran and various amounts of water at temperatures ranging from 1 degrees C to 80 degrees C was analyzed by HPLC. The degradation of cephalothin in lyophilized formulations containing dextran and methylcellulose was also analyzed at temperatures ranging from 10 degrees C to 70 degrees C. Acetyl transfer in lyophilized aspirin--sulfadiazine formulations containing dextran exhibited a temperature dependence with a distinct break around Tmc, which may be ascribed to a change in the translational mobility of aspirin and sulfadiazine molecules. The hydrolysis of aspirin and cephalothin in lyophilized formulations, which is also a bimolecular reaction, did not show a distinct break, suggesting that water diffusion is not rate-limiting. The diffusion barrier of water molecules in lyophilized formulations appears to be smaller than the activational barrier of the hydrolysis of aspirin and cephalothin based on the results of this study that the temperature dependence of the hydrolysis rate is almost linear regardless of Tmc and Tg. On the other hand, the diffusion barrier of aspirin and sulfadiazine molecules appears to be comparable to the activational barrier of the acetyl transfer reaction between these compounds, resulting in nonlinear temperature dependence.

Effect of molecular mobility on the deformation characteristics of polycaproamide fibres

The deformation characteristics of PCA fibres are a function of the deformation temperature to a significant degree. The character of the curves of E(e), Emax(t), σb(t), and eb(t) indicate a pronounced change in the mechanical properties of PCA fibres not only in “thawing” of segmental mobility in amorphous regions of the polymer, but also in passage of crystallites into the mesomorphic state, which is characterized by pronounced weakening of interchain interactions in the crystallites. The first segment of σ(e) is only observed in the curves for PCA fibres in the glassy state. In activation of segmental mobility, the σ(e) curves only contain the second and third segments.

Effect of molecular mobility on kinetics of an electrochemical Langmuir-Hinshelwood reaction

A simple model to study the kinetics of a Langmuir-Hinshelwood surface reaction is developed and applied to the oxidation of a complete monolayer of CO molecules at a metal/electrolyte interface in a potential-step experiment. A dramatic influence of the molecular mobility on the reaction kinetics is found. The present model is able to connect the simple Langmuir-Hinshelwood kinetics to that predicted by Kolmogoroff-Avrami theory since it includes them as the two limiting cases of high and low mobility, respectively.

The effect of molecular mobility on spin exchange in dinitroxylpinacol

An ESR study of the biradical, 4,4-bis-2,2,6,6-tetramethyl-4-hydroxy-piperidyl-1-oxyl is reported. The effect of molecular mobility in a viscous environment on spin exchange dynamics is investigated.

Crystallization kinetics during hot-drawing of poly(ethylene terephthalate) film: strain-rate/draw-time superposition

We have investigated the influence of strain rate during hot-drawing of poly(ethylene terephthalate) on the kinetics of overall crystallization and of crystal growth normal to the 010 and 100 planes. Drawing was at 90°C and at various strain rates between 0.01 s −1 and 2.1 s −1. We found that changing strain rate simply shifts the crystallization rate curves along the log time axis, that the shift factor and the strain rate are related by a power law, and that the value of the exponent reflects the relative influence of two effects of molecular mobility : relaxation of orientation and enhancement of crystallization. The relative importance of these two effects was found to be different in different crystallographic growth directions : normal to the 100 planes, they almost exactly compensate each other; normal to the 010 planes, the relaxation effect dominates. By defining an ‘equivalent time’ for crystallization, degree of crystallinity at any strain rate can be predicted from knowledge of either draw time or draw ratio. A similar treatment permits prediction of crystallite size.

Effect of molecular mobility on the decay of free radicals in amorphous polymers: a Monte Carlo study

An algorithm has been formulated for studying the diffusion-controlled reactions in amorphous polymers. A method has been proposed based on molecular mobility and leading to migration of radical centres, their approach and decay. In a volume of dimensions 70 × 100 × 123 A ̊ , using boundary periodic conditions, an amorphous polymer system and free radicals are simulated on a diamond lattice by the Monte Carlo method. Owing to crank, kink and crankshaft motions, some of them approach one another and decay. A change in the concentration of free radicals with time and temperature has been observed by the method described.