Concentration dependence of diffusion coefficient at various molecular weights and temperatures

Adsorption study on the formation of interfacial layers based on birch glucuronoxylans

Glucuronoxylans (GX), particularly crude fractions obtained by pressurized hot water extraction of birch wood, act as potent emulsifiers and stabilizers against physical separation and lipid oxidation. Herein, we studied the adsorption of GX on hydrophobic interfaces to correlate their multicomponent character towards the formation of interfacial layers in emulsions. Dynamic interfacial tension (DIFT) and quartz crystal microgravimetry with dissipation monitoring (QCM-D) were applied to various GX fractions and the results compared with those from cellulose-based emulsifiers. The roles of residual lignin and polysaccharides are discussed considering the formation of interfacial layers during emulsification. The DIFT of the different GXs reached quasi-equilibrium faster as the lignin concentration increased, implying a correlation between the rate of adsorption and the residual lignin content. The effect of NaCl addition was more pronounced in polysaccharide-rich fractions, indicating that the polysaccharide fraction modulated the effect of ionic strength. QCM-D showed that despite the fast adsorption exhibited by the lignin-rich GX extract in the DIFT curves, the adsorbed materials were lightweight, suggesting that the polysaccharide fraction built the bulk of the interfacial layer. These results provide a foundation towards understanding the role of GX in interfacial stabilization beyond traditional plant-based counterparts.

A comprehensive study of the effect of elevated temperature on the extractability and rate of exaggerated and exhaustive extractions of medical devices

The effectiveness of an elevated temperature on the thermodynamic and kinetic properties of the solvent extraction of medical devices is evaluated in this study. The main objective of the current work is to specifically address the question of how effective a temperature of 50 °C, relative to 37 °C, is in improving the extractability and rate of the exaggerated and exhaustive extractions of medical devices. The extractability at equilibrium is related to the extraction partition coefficient, while the extraction rate is related to the corresponding diffusion coefficient. The partition and diffusion coefficients (or the enthalpies of extraction and diffusional activation energies) of solid-liquid extractions for different polymeric materials, solvents, and types of extractables entities at different temperatures are compiled comprehensively from extensive publications in the literature. The collected partition and diffusion coefficients at different temperatures are used to derive the partition enthalpies and diffusional activation energies in this study. The combined 209 partition enthalpies and 262 diffusional activation energies are then used to calculate the ratios of the partition and diffusion coefficients, when the extraction temperature increases from 37 °C to 50 °C. It is concluded from the study that the maximum improvement in extracted chemical amount with this specific temperature increase is about 3-fold, but the median improvement is only 16%. The most probable improvement is 25%. The maximum improvement (or decrease) in extraction time is 3.2-fold by the change in the diffusional coefficient, but the median value is 1.9-fold. The most probable decrease in extraction time is 2.4-fold. The collected data also allow the calculation of the ratio of the diffusion coefficient for a 10 °C increase, and the results are compared with the "factor 10 rule" in the literature on the relationship between the diffusion coefficient and temperature. The explicit conclusions of the study certainly provide evidences (not assumptions) in designing practical and cost-effective exaggerated and exhaustive extractions in the chemical characterization of medical devices, taking into considerations of extraction cycle time, temperature-dependent chemical stability, and the number of repeated extractions.

Polyzwitterion fast and slow mode behavior are coupled to phase separation as observed by dynamic laser light scattering

A model zwitterionic polysulfobetaine, poly(3-(acrylamidopropyl-dimethyl-ammonium) propyl-1-sulfonate) (pAPAPS), phase separates upon cooling and exhibits an upper critical solution temperature (UCST) behavior with no added salt in deuterium oxide solutions. Dynamic light scattering measurements indicate the presence of distinct fast and slow diffusive modes, where the fast mode is interpreted as a collective diffusion coefficient and the slow mode is attributed to the diffusion of multi-chain dynamic clusters. The relative population of fast and slow modes varies systematically with temperature and concentration. A clustering temperature (T*) was assigned when the slow mode first appeared upon cooling. The slow mode then increases in relative scattering amplitude as the phase boundary is approached. The fast mode exhibits a concentration dependence above T* consistent with the virial expansion in the collective diffusion. The sign of the virial coefficient (kd) is negative, even in the good solvent region above the expected Flory temperature (Θ ≈ 39 °C), a behavior distinct from synthetic neutral polymers in organic solvents. The onset of multi-chain clustering at T < T* coincides with the poor solvent regime (T < Θ). Attractive dipolar interactions due to the zwitterionic sulfobetaine groups in pAPAPS are suggested as the origin of the multi-chain clusters with no salt. Upon the addition of 100 mM NaCl, the slow mode is suppressed, and the hydrodynamic radius is consistent with polyzwitterion chain dimensions in a dilute solution. We find that concentration dependent diffusion is highly linked to the theta temperature and the emergence of dynamic clusters as the polymer goes from good to poor solvent on approach to the UCST. The slow mode in the semidilute regime is reported along with preliminary small-angle neutron scattering data that show salt reduces clustering and leads to predominantly chain scattering.

Amphiphilic Molecular Brushes with Regular Polydimethylsiloxane Backbone and Poly-2-isopropyl-2-oxazoline Side Chains. 2. Self-Organization in Aqueous Solutions on Heating

The behavior of amphiphilic molecular brushes in aqueous solutions on heating was studied by light scattering and turbidimetry. The main chain of the graft copolymers was polydimethylsiloxane, and the side chains were thermosensitive poly-2-isopropyl-2-oxazoline. The studied samples differed in the length of the grafted chains (polymerization degrees were 14 and 30) and, accordingly, in the molar fraction of the hydrophobic backbone. The grafting density of both samples was 0.6. At low temperatures, macromolecules and aggregates, which formed due to the interaction of main chains, were observed in solutions. At moderate temperatures, heating solutions of the sample with short side chains led to aggregation due to dehydration of poly-2-isopropyl-2-oxazoline and the formation of intermolecular hydrogen bonds. In the case of the brush with long grafted chains, dehydration caused the formation of intramolecular hydrogen bonds and the compaction of molecules and aggregates. The lower critical solution temperature for solutions of the sample with long side chains was higher than LCST for the sample with short side chains. It was shown that the molar fraction of the hydrophobic component and the intramolecular density are the important factors determining the LCST behavior of amphiphilic molecular brushes in aqueous solutions.

Mathematical analysis-based feasibility study of pre-emptive medicine for Staphylococcus aureus infectious disease: Early detection and antibiotic-free maintenance therapy

Global efforts are being made to achieve the clinical implementation of pre-emptive medicine for Staphylococcus aureus (S. aureus) infectious disease, which will realize both early detection at the pre-symptom stage and bacteriostatic therapy by antibiotic-free medicine in a future. Several research groups proposed the intercellular signal transduction factor (auto-inducing peptide: AIP) antibody, the synthesised AIP analogues and a cyclic depsipeptide with high constitutional similarity to AIP as a candidate of the pre-emptive medicine for S. aureus infectious disease. In this paper, to evaluate a validity of them, we mathematically explored both a pre-symptom associated with the pathogenic expression process of S. aureus and several therapeutic targets that delay or suppress the appearance of the pre-symptom. The stochastic mathematical analysis identified a peak of fluctuation in intracellular AgrD concentration as the pre-symptom. Moreover, employing parameter sensitivity analysis, the enhancement of binding inhibition between AgrC receptor and AIP was identified as effective therapeutic target. Based on these findings, we evaluated a feasibility of above-mentioned candidates, and concluded that the continuous application of AgrC receptor antagonists, such as the synthesised AIP analogues and a cyclic depsipeptide with high constitutional similarity to AIP, is useful as pre-emptive medicine for S. aureus infectious disease.

A model of cell biological signaling predicts a phase transition of signaling and provides mathematical formulae

A biological signal is transmitted by interactions between signaling molecules in the cell. To date, there have been extensive studies regarding signaling pathways using numerical simulation of kinetic equations that are based on equations of continuity and Fick’s law. To obtain a mathematical formulation of cell signaling, we propose a stability kinetic model of cell biological signaling of a simple two-parameter model based on the kinetics of the diffusion-limiting step. In the present model, the signaling is regulated by the binding of a cofactor, such as ATP. Non-linearity of the kinetics is given by the diffusion fluctuation in the interaction between signaling molecules, which is different from previous works that hypothesized autocatalytic reactions. Numerical simulations showed the presence of a critical concentration of the cofactor beyond which the cell signaling molecule concentration is altered in a chaos-like oscillation with frequency, which is similar to a discontinuous phase transition in physics. Notably, we found that the frequency is given by the logarithm function of the difference of the outside cofactor concentration from the critical concentration. This implies that the outside alteration of the cofactor concentration is transformed into the oscillatory alteration of cell inner signaling. Further, mathematical stability kinetic analysis predicted a discontinuous dynamic phase transition in the critical state at which the cofactor concentration is equivalent to the critical concentration. In conclusion, the present model illustrates a unique feature of cell signaling, and the stability analysis may provide an analytical framework of the cell signaling system and a novel formulation of biological signaling.

Hydrodynamic Behavior of High Molar Mass Linear Polyglycidol in Dilute Aqueous Solution

Six high molar mass polyglycidol samples were obtained by fractionation of polyglycidol synthesized by means of cationic polymerization of ethoxyethyl glycidyl ether followed by cleavage of the protective groups. The fractions covering the molar mass range from 0.1 to 2.4 x 10(6) were studied by dynamic and static light scattering. The weight-average molar masses (Mw), second virial coefficients (A2), radii of gyration (Rg), diffusion coefficients (D0), hydrodynamic radii (Rh), and dynamic virial coefficients (kDphi) were determined for the single coil in dilute aqueous solution at 25 degrees C, and scaling equations were established. It was found that polyglycidol in water does not exhibit the expected asymptotic good solvent behavior. The scaling exponents for A2, D0, and Rh are even closer to those for polymer coils in marginal solvents than to the expected ones in the excluded-volume region. The values of the interpenetration parameter, psi, and kDphi are far from reaching limiting values even for the fractions of the highest molar masses. The scaling exponent for Rg as well as the Rg/Rh ratio, which was found to increase with increasing molar mass, imply elongated coil conformation in the high molar mass region.