Drug-Induced Phase Separation in Polyelectrolyte Microgels

Polyelectrolyte microgels may undergo volume phase transition upon loading and the release of amphiphilic molecules, a process important in drug delivery. The new phase is “born” in the outermost gel layers, whereby it grows inward as a shell with a sharp boundary to the “mother” phase (core). The swelling and collapse transitions have previously been studied with microgels in large solution volumes, where they go to completion. Our hypothesis is that the boundary between core and shell is stabilized by thermodynamic factors, and thus that collapsed and swollen phases should be able to also coexist at equilibrium. We investigated the interaction between sodium polyacrylate (PA) microgel networks (diameter: 400–850 µm) and the amphiphilic drug amitriptyline hydrochloride (AMT) in the presence of NaCl/phosphate buffer of ionic strength (I) 10 and 155 mM. We used a specially constructed microscopy cell and micromanipulators to study the size and internal morphology of single microgels equilibrated in small liquid volumes of AMT solution. To probe the distribution of AMT micelles we used the fluorescent probe rhodamine B. The amount of AMT in the microgel was determined by a spectrophotometric technique. In separate experiments we studied the binding of AMT and the distribution between different microgels in a suspension. We found that collapsed, AMT-rich, and swollen AMT-lean phases coexisted in equilibrium or as long-lived metastable states at intermediate drug loading levels. In single microgels at I = 10 mM, the collapsed phase formed after loading deviated from the core-shell configuration by forming either discrete domains near the gel boundary or a calotte shaped domain. At I = 155 mM, single microgels, initially fully collapsed, displayed a swollen shell and a collapsed core after partial release of the AMT load. Suspensions displayed a bimodal distribution of swollen and collapsed microgels. The results support the hypothesis that the boundary between collapsed and swollen phases in the same microgel is stabilized by thermodynamic factors.

Thermodynamic properties of hydroxypropyl-β-cyclodextrin/guest interaction: a survey of recent studies

For many years, cyclodextrins (CDs) have been the object of attention for their capability of improving the stability, solubility and bioavailability of numerous molecules of interest, including drugs and nutraceuticals. They have low toxicity and for this reason have been employed for different routes of administration, including oral, ocular, nasal and parenteral. Among them, the hydroxypropyl-β-cyclodextrin (HP-β-CD) is the least toxic. Several physicochemical methodologies have been employed for studying cyclodextrin/guest interaction, but isothermal titration calorimetry (ITC) is the only one capable of simultaneously providing the binding constant, ΔH°, ΔS°, ΔG° and the binding stoichiometry. Here, we present the state of the art of ITC studies applied to HP-β-CD/guest complexes, discussing selected publications of the last five years, highlighting the thermodynamic factors that are decisive for optimal encapsulation.

On the porosity of ridge keel (with reference to V.V. Kharitonov’s paper)

The article discusses whether the model of loose granular medium is applicable to the analysis of physical processes in the ridge keel. It is argued that the model is not valid for dealing with a number of problems such as the evolution of the ridge keel. It is also suggested that the decrease in keel porosity in time is primarily caused by thermodynamic factors.

The Influence of Modern Refrigerants on Environmental Protection

The aim of reviewing information was characterizing in the labor factor using in refrigeration technology is and their impact on the environment. The development of the refrigeration industry occurred thanks to progress towards coolants. The most important aspect of using of refrigerators is their impact on health and human life, and atmosphere. By caring for health, the European Union achieves legal rights. Research on thermodynamic factors pose a wide field of work for many scientists and are the most popular, new information, that can be used in practice.

Statistical analysis of C–H activation by oxo complexes supports diverse thermodynamic control over reactivity

Statistical analysis of transition metal oxo mediated C–H activation indicates that thermodynamic factors dictate reactivity and that the energetics of proton and electron transfer have effects independent of the free energy of the reaction.