The effective hydrodynamic radius in the Stokes-Einstein relation is not a constant

Variants based on the assumption of effective hydrodynamic radius being a constant are usually adopted to test the Stokes-Einstein(SE)relation.The rationality of the assumption is examined by performing molecular dynamics simulations with the truncated Lennard-Jones-like(TLJ)model,Kob-Andersen model and ortho-terphenyl(OTP)model.The results indicate the assumption is generally not established except for special case.The effective hydrodynamic radius is observed to increase with decreasing temperature for TLJ model but is decreased for Kob-Andersen and OTP model;and which is almost a constant for TLJ particle with enough rigidity.The variant of SE relation D~Th is invalid for the three models except for the TLJ particle with enough rigidity.We propose similar inconsistency may be also existed in other liquids and the assumption should be critically evaluated when adopted to test the SE relation.

NMR relaxation and diffusion studies to probe the motional dynamics of risperidone within PLGA microsphere

The present study aims to investigate the motional dynamics of risperidone within polylactic co-glycolic acid(PLGA)microsphere by employing solution state'H and 19F nuclear magnetic resonance(NMR)measurements.Risperidone,a second-generation fluorinated antipsychotic drug used for the treatment of schizophrenia is commercially marketed as PLGA microsphere formulation resulting in prolonged release of the drug in solution.Although the current trend in the pharmaceutical market is to develop drug formulation with long-acting release(LAR)products,complete physicochemical characterization of such formulations are scarce.Especially the effects of microsphere encapsulation on the motional properties and diffusion behavior of the drugs are not discussed adequately in any of the earlier reports.We therefore,have employed NMR relaxation and diffusion measurements to decipher the interaction of PLGA cavity water with risperidone.A detailed analysis of NMR relaxation rates confirmed the event of encapsulation and the presence of local motion in the non-fluorinated end of risperidone.Further,the relaxation data indicated a significant alteration in 19F chemical shift anisotropy(CSA)and CSA/dipole-dipole(DD)cross-correlated relaxation mechanism and decreased effect of solvent relaxation pointing out reduced water concentration within the microsphere cavity.'H and 19F diffusion coefficients of risperidone led to the information about hydrodynamic radius of risperidone in free and encapsulated states.Measurement of hydrodynamic radius supported the presence of limited water in PLGA cavity allowing higher translational mobility of risperidone after the encapsulation.

ADSORPTION OF PROTEIN ON NANOPARTICLES

The adsorption of protein on nanoparticles was studied by using dynamic light scattering tomeasure the hydrodynamic size of both pure protein and nanoparticles adsorbed with differentamounts of protein. The thickness of the adsorbed protein layer increases as proteinconcentration, but decreases as the initial size of nanoparticles. After properly scaling thethickness with the initial diameter, we are able to fit all experimental data with a single mastercurve. Our experimental results suggest that the adsorbed proteins form a monolayer on thenanoparticle surface and the adsorbed protein molecules are attached to the particle surface atmany points through a possible hydrogen-bonding. Our results also indicate that as proteinconcentration increases, the overall shape of the adsorbed protein molecule continuously changesfrom a flat layer on the particle surface to a stretched coil extended into water. During thechange, the hydrodynamic volume of the adsorbed protein increases linearly with proteinconcentration.

SOLVENT QUALITY AND SOLUTION BEHAVIOR OF NYLON 12

The refractive index increment, dynamic and static laser light scattering, intrinsic viscosity [η] and Huggins constant （KH） of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 10-60℃. The intrinsic viscosity, Rn, Rg, A2, and （〈 S 〉2）^1/2 （calculated from viscosity data） and ＂a＂ values of nylon 12 are found to be higher in m-cresol than in sulphuric acid. All these parameters decrease with the increase in water contents in sulphuric acid. The refractive index increment, KH and activation energy show an opposite trend to that of [η]. The intrinsic viscosity, RH, Rg, A2, and （〈 S 〉2）^1/2 have maximum values around 30-40℃ in sulphuric acid/water system, whereas in m-cresol they fall at about 20℃. It has been concluded that the variation in size, interaction parameter （second virial coefficient）, [η] and KH of the polymer solutions with the alteration in solvent composition and temperature are the out come of change in thermodynamic quality of solvents, selective adsorption, hydrogen bonding and conformational transitions. It has also been concluded that the increase in temperature first enhances the quality of the solvent, encourages hydrogen bonding and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. However, the addition of water to sulphuric acid continuously deteriorates the solvent quality. This characteristic of the solvent system brings conformational changes in the polymer especially at low temperatures.

Triad resonant wave interactions in electrically charged jets

Nonlinear instability in electrically charged jets is studied using the governing electro-hydrodynamic equations describing stretching and thinning of a liquid jet. A jet flow system subject to both space and time evolving disturbances is considered. At the linear stage, the Rayleigh and conducting jet flow instability modes are uncovered.Nonlinear instability in the flow is explored via triad resonant waves which uncover favorable operating modes not previously detected in the linear study of the problem. In particular, the jet radius is significantly reduced, and the electric field of the jet is properly oriented under the nonlinear study. It is found that taking into account the resonance triad modes provides a better mathematical description of a jet that stretches and thins due to tangential electric field effects. Both linear and nonlinear instability results in the jet flow system are presented and discussed.

Biopolymer-stabilized emulsions on the basis of interactions betweenβ-lactoglobulin andι-carrageenan

ι-Carrageenan andβ-lactoglobulin(β-lg)stabilized oil-in-water(O/W)emulsions,which can be used for the oral administration of bioactive but environmentally sensitive ingredients,have been successfully prepared.The effects of protein/polysaccharide ratios,total biopolymer concentration,environmental stress(thermal processing and sonication),and pH on the complex formation betweenι-carrageenan andβ-lactoglobulin have been investigated.We found thatβ-lactoglobulin andι-carrageenan stabilized emulsions can be formed at pH values of 6.0,4.0,and 3.4.However,the microstructures of emulsions stabilized byβ-lactoglobulin andι-carrageenan was identified by optical microscopy,and it indicated that the emulsion prepared at pH 6.0 flocculated more extensively,while its hydrodynamic radius was much bigger than those prepared at pH 4.0 and 3.4.Regarding rheological properties,the emulsion of pH 6.0 showed a more solid-like behavior but with a lower viscosity than those of pH 4.0 and 3.4.The optimum concentration ranges forβ-lg andι-carrageenan to form stable emulsions at pH 4.0 and 3.4 were 0.3 wt-%-0.6 wt-%and 0.4 wt-%-0.7 wt-%,respectively.

Dissolution and enzymatic hydrolysis of casein micelles studied by dynamic light scattering

The effects of temperature,ionic strength,and enzymatic hydrolysis on the average hydrodynamic radius(Rh)of casein micelles in phosphate buffer were studied by using dynamic light scattering.The results showed that the average Rh value of casein micelles decreased irreversibly during the heating,decreased with the increase of ionic strength in lower ionic strength solution(less than 0.05 mol/L),but opposite in higher ionic strength solution(above 0.1 mol/L).The Rh value of casein increased rapidly during the process of enzymatic hydrolysis,and the structural model of casein micelles in the enzymatic hydrolysis process was also proposed,i.e.the casein micelle changed from compact sphere into unfolded and regularly flocky peptides.

Advantage of Fluorescence Correlation Spectroscopy for the Study of Polyelectrolytes

The advantage of fluorescence correlation spectroscopy to study single chain behavior of polyelectrolytes has been demonstrated by checking the coil-to-globule transition ofpoly 2-vinylpyridine with the change ofpH value in aqueous solution. The ultra-high sensitivity of FCS allows measurement at extreme dilution where the effect of electrostatic interaction between the chains is greatly suppressed. The results exposed first-order conformation tran- sition of P2VP as detected by FCS while inter-chain aggregation occurred in the experiments of dynamic light scat- tering.