1,720,992 research outputs found
Polysaccharide solutions and gels: Isothermal dehydration study by dynamic calorimetric experiments with DSC
No full textThe isothermal dehydration of aqueous biosystems is a relevant topic in food, pharmaceutical and cosmetic industry and has been recently investigated for the assessment of a model calorimetric set-up and for the characterization of the parameters featuring the experimental calorimetric curve.
In this study, the experimental Differential Scanning Calorimetry (DSC) data obtained under controlled conditions in isothermal mode have been collected on the dehydration of films consisting of solutions and gels of alginate, hydroxypropylmethylcellulose (HPMC), trehalose and mixtures thereof. Based on the proportionality between the calorimetric heat flow and water activity (aw) of solutions of known aw, the values calculated from calorimetry have been compared to those obtained with classic hygrometric measurements revealing a good consistency between the methods. Furthermore, the experimental data were mathematically turned into desorption isotherms, providing a continuous description of the water activity down to the low water activity limit. This experimental method represents an innovative approach to support other consolidated analytical techniques in the physico-chemical characterization of aqueous systems and, more importantly, a step forward in the determination of water activity as a continuous measurement in a timeframe far shorter than that necessary with other instruments (e.g., hygrometers)
Pellicle Biofilm Formation in Burkholderia cenocepacia J2315 is Epigenetically Regulated through WspH, a Hybrid Two-Component System Kinase-Response Regulator
Full text linkThe chemosensory signal transduction system Wsp regulates biofilm formation and related phenotypes by influencing cyclic-di-GMP (c-di-GMP) levels in bacterial cells. This is typically achieved by activation of the diguanylate cyclase WspR, through phosphorylation of its phosphoreceiver domain. The Wsp system of Burkholderia cenocepacia J2315 is in one operon with the hybrid response regulator/histidine kinase wspH, but lacks the diguanylate cyclase wspR which is located in a different operon. The expression of wspH, the first gene in the B. cenocepacia Wsp operon as well as pellicle biofilm formation are epigenetically regulated in B. cenocepacia J2315. To investigate whether WspH regulates pellicle biofilm formation, several mutants with altered expression of wspH were constructed. Mutants with increased expression of wspH showed accelerated pellicle biofilm formation, reduced swimming motility and increased c-di-GMP levels. This was independent of WspR phosphorylation, showing that WspR is not the cognate response receiver for histidine kinase WspH. IMPORTANCE Biofilms are surface-attached or suspended aggregates of cells, that are problematic in the context of bacterial infections, as they provide protection from antibiotic treatment. Burkholderia cenocepacia can colonize the lung of immunocompromised patients and forms biofilms that increase its recalcitrance to antibiotic treatment. Pellicles are biofilms which form at an air-liquid interface to take advantage of the higher oxygen concentrations in this environment. How quickly pellicles are formed is crucial for the fitness of obligate aerobic bacteria such as B. cenocepacia. Cyclic-di-GMP (c-di-GMP) levels determine the transition between planktonic and biofilm lifestyle, and WspH controls c-di-GMP production. WspH is therefore important for the fitness of B. cenocepacia in environments with gradients in oxygen concentration, such as the human lung
Microwave generated solid dispersions containing ibuprofen
No full textThe purpose of this study was to apply the attractive technique of the microwaves irradiation (MW) for the preparation of solvent-free solid dispersions (SD). In particular, the microwave technology has been
considered in order to prepare an enhanced release dosage form for the poorly soluble drug Ibuprofen (IBU), employing PVP/VA 60/40 (PVP/VA 64) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as hydrophilic
carriers. Their physico-chemical characteristics and dissolution properties were compared to the corresponding
physical mixtures and the drug alone. The results of physico-chemical characterization attested
a correspondence of the solid state of the drug before and after irradiation treatment and that an amorphous
form of the drug was obtained. This result, together with the presence of the hydrophilic polymers
determined a remarkable enhancement of the in vitro dissolution rate of the drug suggesting that the
microwave technique could be considered as a new and interesting method to prepare drug–polymer
systems
Water evaporation from gel beads. A calorimetric approach to hydrogel matrix release properties.
No full textHydrogels are characterized by properties which make them ideal candidates for applications in several fields, such as drug delivery, biomedicine, and functional foods. Molecular diffusion out of a hydrogel matrix depends on their hydrodynamic radii and the mesh sizes within the matrix of the gel. A quantitative experimental and mathematical understanding of interactions, kinetics, and transport phenomena within complex hydrogel systems assists network design by identifying the key parameters and mechanisms that govern the rate and extent of solute release. In this article a calorimetric differential scanning calorimetry (DSC) study reports on the approach to parallel water effusion from a hydrogel matrix to the release of a model protein. The measurement of the water evaporation is taken as the simplest routine determination of a phenomenon that is basically due to a diffusive process through the porous structure of the gel and thermodynamically governed by the difference in the water chemical potential inside and outside of the bead. The analysis of the experimental calorimetric curves is made with the purpose of extracting several numerical parameters characteristic of each curve. The rationale is to develop a simple methodology to understand the release properties of the porous structure of the complex gel matrix by means of DSC
Marine Polysaccharides in Microencapsulation and Application to Aquaculture: “From Sea to Sea”
No full textThis review’s main objective is to discuss some physico-chemical features of polysaccharides as intrinsic determinants for the supramolecular structures that can efficiently provide encapsulation of drugs and other biological entities. Thus, the general characteristics of some basic polysaccharides are outlined in terms of their conformational, dynamic and thermodynamic properties. The analysis of some polysaccharide gelling properties is also provided, including the peculiarity of the charged polysaccharides. Then, the way the basic physical chemistry of polymer self-assembly is made in practice through the laboratory methods is highlighted. A description of the several literature procedures used to influence molecular interactions into the macroscopic goal of the encapsulation is given with an attempt at classification. Finally, a practical case study of specific interest, the use of marine polysaccharide matrices for encapsulation of vaccines in aquaculture, is reported
Physico-chemical properties of aqueous drug solutions: From the basic thermodynamics to the advanced experimental and simulation results
No full textThe physical chemical properties of aqueous solutions of model compounds are illustrated in relation to hydration
and solubility issues by using three perspectives: thermodynamic, spectroscopic and molecular dynamics
simulations. The thermodynamic survey of the fundamental backgrounds of concentration dependence and
experimental solubility results show some peculiar behavior of aqueous solutions with several types of similar
solutes. Secondly, the use of a variety of experimental spectroscopic devices, operating under different experimental
conditions of dimension and frequency, has produced a large amount of structural and dynamic data on
aqueous solutions showing the richness of the information produced, depending on where and how the experiment
is carried out. Finally, the use of molecular dynamics computational work is presented to highlight how
the different types of solute functional groups and surface topologies organize adjacent water molecules differently.
The highly valuable contribution of computer simulation studies in providing molecular explanations
for experimental deductions, either of a thermodynamic or spectroscopic nature, is shown to have changed the
current knowledge of many aqueous solution processes. While this paper is intended to provide a collective view
on the latest literature results, still the presentation aims at a tutorial explanation of the potentials of the three
methodologies in the field of aqueous solutions of pharmaceutical molecules
Preparation, characterization and dehydration of micro- and nano-particles based on alginate gel.
No full text
Thermal behavior of water in micro-particles based on alginate gel.
No full textAlginate has been established as a very versatile material in the preparation of hydrogel capsules for trapping therapeutic biomolecules and cells. The physico-chemical properties, the mechanism and the processing of gel formation are now well established. In the frame of a project aiming at the exploitation of encapsulation of therapeutic proteins in alginate gel particles, the procedure of preparation, characterization, gel-drying and re-hydrating has been explored for the shelf-life of the encapsulated biomolecules. Here, the results of a calorimetric study on the freezing and dehydration process of alginate micro-capsules is presented. The work aims at the description of water state(s) and its removal under “controlled conditions” in the presence of bioprotectant sugars
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