Changes in single K+ channel behavior through the lipid phase transition

We show that the activity of an ion channel is strictly related to the phase state of the lipid bilayer hosting the channel. By measuring unitary conductance, dwell times, and open probability of the K+ channel KcsA as a function of temperature in lipid bilayers composed of POPE and POPG in different relative proportions, we obtain that all those properties show a trend inversion when the bilayer is in the transition region between the liquid disordered and the solid ordered phase. These data suggest that the physical properties of the lipid bilayer influence ion channel activity likely via a fine tuning of its conformations. In a more general interpretative framework, we suggest that other parameters such as pH, ionic strength, and the action of amphiphilic drugs can affect the physical behavior of the lipid bilayer in a fashion similar to temperature changes resulting in functional changes of transmembrane proteins

Effect of the Addition of Proteins and Hydrocolloids on the Water Mobility in Gluten-Free Pasta Formulations

In a gluten free pasta formulation (suitable for celiac people), the influence of each constituent has a major importance on the final product quality, especially water and hydrocolloids contents used to replace the gluten matrix. The presence of hydrocolloids and proteins in dough may modify the availability of water to interact with starch in the gelatinization process. The aim of the present work was to investigate the effect of the addition proteins and hydrocolloids addition on the water-starch interaction using a triangular mixture design. Basic dough formula consisted in a mixture of corn starch and flour (4:1, 53.5%), 1%NaCl, and 3% sunflower oil, water (35.48-39.5%), gums (xanthan and locust bean gums, 2:1 ratio, 0.512-2.519%), and proteins (dry egg and ovoalbumin mixtures, 10:1 ratio, 0.683-6.704%) Combinations of gums, proteins, and water were used in a simplex-centroid design with constrains. Modulated differential scanning calorimetry was used to study starch gelatinization and the amount of unfrozen water in the samples; thermograms were obtained between -50ºC and 140ºC (heating rate 5ºC/min, modulated at ±1ºC, period of 60s). Regarding the process of gelatinization, a biphasic endotherm was observed; when the free water content of the dough was progressively reduced (0.94 to 0.42g H2O/ g dough), endotherms shifted to higher temperatures (onset from 56.7ºC to 63.1ºC, first peak from 75.1ºC to 77.6ºC) following a linear relationship. The response surface analysis of the unfrozen water content of the complex composite system as a function of the concentration of proteins, hydrocolloids, and water led to a “saddle” type surface, involving interactions between components.Facultad de Ciencias ExactasCentro de Investigación y Desarrollo en Criotecnología de AlimentosFacultad de Ingenierí

Effect of the Addition of Proteins and Hydrocolloids on the Water Mobility in Gluten-Free Pasta Formulations

In a gluten free pasta formulation (suitable for celiac people), the influence of each constituent has a major importance on the final product quality, especially water and hydrocolloids contents used to replace the gluten matrix. The presence of hydrocolloids and proteins in dough may modify the availability of water to interact with starch in the gelatinization process. The aim of the present work was to investigate the effect of the addition proteins and hydrocolloids addition on the water-starch interaction using a triangular mixture design. Basic dough formula consisted in a mixture of corn starch and flour (4:1, 53.5%), 1%NaCl, and 3% sunflower oil, water (35.48-39.5%), gums (xanthan and locust bean gums, 2:1 ratio, 0.512-2.519%), and proteins (dry egg and ovoalbumin mixtures, 10:1 ratio, 0.683-6.704%) Combinations of gums, proteins, and water were used in a simplex-centroid design with constrains. Modulated differential scanning calorimetry was used to study starch gelatinization and the amount of unfrozen water in the samples; thermograms were obtained between -50ºC and 140ºC (heating rate 5ºC/min, modulated at ±1ºC, period of 60s). Regarding the process of gelatinization, a biphasic endotherm was observed; when the free water content of the dough was progressively reduced (0.94 to 0.42g H2O/ g dough), endotherms shifted to higher temperatures (onset from 56.7ºC to 63.1ºC, first peak from 75.1ºC to 77.6ºC) following a linear relationship. The response surface analysis of the unfrozen water content of the complex composite system as a function of the concentration of proteins, hydrocolloids, and water led to a “saddle” type surface, involving interactions between components.Facultad de Ciencias ExactasCentro de Investigación y Desarrollo en Criotecnología de AlimentosFacultad de Ingenierí

Setup of Modulated Temperature FTIR technique to investigate thermal transitions of polymers

Nell'attività di ricerca dottorale è stata sviluppata una nuova tecnica d’indagine spettroscopica (Modulated Temperature Infrared Spectroscopy, MTFTIR) ed applicata allo studio delle transizioni termiche di polimeri. La tecnica permette lo studio delle variazioni conformazionali e strutturali delle singole macromolecole coinvolte nelle transizioni di fase dei materiali, differenziando inoltre transizioni all’equilibrio termodinamico da stati transienti di non-equilibrio. Ad una prima fase di messa a punto dell’apparato sperimentale e delle metodiche sono susseguiti studi su tre polimeri, il polipropilene isotattico, il polietilentereftalato ed il poli(L-lattide). I risultati MTFTIR, accoppiati ad analisi calorimetriche, hanno evidenziato dei comportamenti peculiari delle catene polimeriche nelle fasi vetrose, liquide e cristalline dei materiali, non indagabili o difficilmente distinguibili mediante altre tecniche sperimentali

Reversible melting and crystallization of short and long flexible chain molecules by Temperature-modulated calorimetry

Melting and crystallization of linear, flexible molecules of different lengths was studied by temperature-modulated differential scanning calorimetry, TMDSC. Various techniques for TMDSC with single and multifrequency modulations have been analyzed to optimize the conditions for the present study. The finally chosen method involved a quasi-isothermal mode with a temperature amplitude of 0.5 K and a period of 60 s (frequency = 0.167 Hz). The interpretation of the reversible and irreversible melting was developed by comparison of a variety of different modes of analysis (sinusoidal, sawtooth, and complex sawtooth). The analyzed molecules ranged from n-paraffins, oligomeric fractions of polyethylene and poly(oxyethylene) to macromolecules of polyethylene. The most important discovery was that there is a critical chain length for reversible melting and crystallization of small, flexible molecules at 10 nm or about 75 backbone chain atoms. Below this chain length, melting and crystallization is reversible under the given conditions of analysis and in the presence of primary crystal nuclei. Above this chain length, the crystallization requires a degree of supercooling which becomes constant for 200 chain atoms or more at a value of 6.0 !10 K. This critical chain length sets a lower limit for the need of supercooling, a characteristic property of flexible polymers. This result was then applied to resolving the problem of the existence of a small amount of reversible melting in polymers, discovered about five years ago. The following was shown: chain segments with melting temperatures equal to oligomers of less than the critical chain length can crystallize and melt reversibly, even when contained within the metastable structure of semicrystalline polymers. Above this chain length, longer segments can only show reversible melting when a molecular nucleus remains on the crystal surface after partial melting. The short-chain segments have been seen in linear-low-density polyethylene. The longer segments in the main melting peak of polyethylene. These observations are combined with the knowledge derived from the ATHAS data bank to propose three reversible and three irreversible calorimetric contributions to the heat capacity of flexible macromolecules

Effect of the Addition of Proteins and Hydrocolloids on the Water Mobility in Gluten-Free Pasta Formulations

In a gluten free pasta formulation (suitable for celiac people), the influence of each constituent has a major importance on the final product quality, especially water and hydrocolloids contents used to replace the gluten matrix. The presence of hydrocolloids and proteins in dough may modify the availability of water to interact with starch in the gelatinization process. The aim of the present work was to investigate the effect of the addition proteins and hydrocolloids addition on the water-starch interaction using a triangular mixture design. Basic dough formula consisted in a mixture of corn starch and flour (4:1, 53.5%), 1%NaCl, and 3% sunflower oil, water (35.48-39.5%), gums (xanthan and locust bean gums, 2:1 ratio, 0.512-2.519%), and proteins (dry egg and ovoalbumin mixtures, 10:1 ratio, 0.683-6.704%) Combinations of gums, proteins, and water were used in a simplex-centroid design with constrains. Modulated differential scanning calorimetry was used to study starch gelatinization and the amount of unfrozen water in the samples; thermograms were obtained between -50ºC and 140ºC (heating rate 5ºC/min, modulated at ±1ºC, period of 60s). Regarding the process of gelatinization, a biphasic endotherm was observed; when the free water content of the dough was progressively reduced (0.94 to 0.42g H2O/ g dough), endotherms shifted to higher temperatures (onset from 56.7ºC to 63.1ºC, first peak from 75.1ºC to 77.6ºC) following a linear relationship. The response surface analysis of the unfrozen water content of the complex composite system as a function of the concentration of proteins, hydrocolloids, and water led to a “saddle” type surface, involving interactions between components.Facultad de Ciencias ExactasCentro de Investigación y Desarrollo en Criotecnología de AlimentosFacultad de Ingenierí

Characterisation and performance assessment of semi-solid dispersions using surface active lipidic carriers

Semi-solid dispersions offer many advantages in the delivery of poorly soluble drugs. However, there is limited understanding of the mechanisms by which in vitro dissolution and in vivo bioavailability is enhanced. Low melting point lipidic carrier excipients demonstrate properties beneficial to formulation of these systems despite presenting further challenge in their characterisation. The physicochemical properties of semi-solid dispersions comprising the lipidic carrier Gelucire 44114 with the poorly soluble drugs ibuprofen, indometacin and piroxicam were investigated. Conventional differential scanning calorimetry demonstrated dissolution effects, the slow rate allowing crystalline drug to dissolve within the molten lipid during analysis giving unreliable data regarding the presence of solid crystalline drug in proportion to that existing as a molecular dispersion. Hyper DSC was not definitively found to eliminate these effects; however they were reduced, giving a more accurate estimation of the drug solubility within the lipid. The drugs demonstrated different affinities for the lipid with subsequent effects on the extent of interaction. The presence of drug in the lipid demonstrated a significant inhibitory effect on the lipid crystallisation temperature, with QIMTDSC demonstrating a more extended crystallisation than expected. The dissolution properties of all drugs were enhanced when formulated into semi-solid dispersions with Gelucire 44/14, most notably with the low loaded systems. These low loaded systems, however, demonstrated an increased affinity for atmospheric moisture. Aging effects on the semi-solid dispersions were observed with ibuprofen and indometacin systems in which the drug was found to exist partially as a molecular dispersion. Piroxicam however, which had very limited miscibility with the lipid, was found to exhibit few aging effects over time. Overall, the formulated semi-solid dispersions with Gelucire 44114 achieved the ultimate goal of successfully enhancing the aqueous dissolution of poorly soluble drugs, however more research is needed in order to relate this successfully to in vivo bioavailability.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Melting and crystallization of paraffins as model compounds for linear macromolecules by temperature-modulated calorimetry (TMC)

Paraffins of sufficient chain length can serve as model compounds for flexible macro molecules. They crystallize almost completely and do not suffer from chain folding as long as their chain length is less than about 37 nm. The melting and crystallization of n-paraffins, C50H102 (n pentacontane, C50), C44H90 (n-tetratetracontane, C44), and C26H54 (n-hexacontane, C26) was analyzed as such model compounds with both a standard differential scanning calorimetry (DSC) and a temperature-modulated DSC (TMDSC) using sawtooth modulation and quasi-isothermal modulation with very small temperature amplitude (0.05 K). Melting and crystallization of C50 and C44 showed practically no superheating or supercooling, respectively, i e, with heating and cooling rates up to 12 K min\u27\u27 the onsets of the corresponding transitions occurred at the same temperature. Similarly, the isotropization of the condis crystals of C26 and the ordering of the melt to the condis crystals are detected at practically the same temperature without superheating and supercooling. The observation of no supercooling for crystallization was confirmed by visual inspection using hot-stage microscopy and a melting-point apparatus. Only the transition on cooling of the C26 condis crystal, which results in fully-ordered crystals, shows a supercooling of 4.0 K when nuclei are not present To make the link to linear macromolecules, polyethylene of molar mass 15520 Da (PE15520) and oligomers of 2150 Da (PE2150) and 560 Da molar mass (PE560) were analyzed in same manner, using standard DSC only. The PE560 has a molar mass close to the paraffin C40 and also shows almost no supercooling for crystallization from the melt, while PE2150 (»C153) and PE15520 (=C1106) need atypical degree of supercooling for polymer, namely «10 K, assumed to be due to molecular nucleation. Due to the well-known chain folding, which starts with C294 (37 nm molecular length), the melting temperature of PE15520 is lower than that expected for equilibrium, extended-chain crystals of this molar mass (411.9 K), and even lower than that for PE2150 which grows as an extended chain crystal and melts at a temperature close to the equilibrium melting temperature of 397.2 K. The apparent heat capacity measurements using quasi-isothermal TMDSC with 0.05 K amplitude, revealed that melting of C50 was completed within 1.0 K, isotropization of C26 -within less than 0.6 K, and melting of C44 within 4.3 K. But 62-78% of total transitions of C26 and C50 occurred over a much narrower temperature range of 0.1 K or less. A reversing melting in the paraffins was detected by TMDSC and integral analysis was proven to be a useful tool for quantitative analysis of the thermal transition, specially of samples exhibiting multiple transitions like C26