Increase In Enthalpy Change Research Articles

Synergistic effect of phytic acid and eggshell bio-fillers on the dual-phase fire-retardancy of intumescent coatings applied on cellulosic substrates

Cellulosic substrates, including wood and thatch, have become icons for sustainable architecture and construction, however, they suffer from high flammability because of their inherent cellulosic composition. Current control measures for such hazards include applying intumescent fire-retardant (IFR) coatings that swell and form a char layer upon ignition, protecting the underlying substrate from burning. Typically, conventional IFR coatings are opaque and are made of halogenated compounds that release toxic fumes when ignited, compromising the roofing's aesthetic value and sustainability. In this work, phytic acid, a naturally occurring phosphorus source extracted from rice bran, was used to synthesize phytic acid-based fire-retardants (PFR) via esterification under reflux, along with powdered chicken eggshells (CES) as calcium carbonate (CaCO3) bio-filler. These components were incorporated into melamine formaldehyde resin to produce the transparent IFR coating. It was revealed that the developed IFR coatings achieved the highest fire protection rating based on UL94 flammability standards compared to the control. The coatings also yielded increased LOI values, indicative of self-extinguishing properties. A 17 °C elevation of the IFR coating's melting temperature and a significant ∼172% increase in enthalpy change from the control were observed, indicating enhanced fire-retardancy. The thermal stability of the coatings was improved, denoted by reduced mass losses, and increased residual masses after thermal degradation. As validated by microscopy and spectroscopy, the abundance of phosphorus and carbon groups in the coatings' condensed phase after combustion indicates enhanced char formation. In the gas phase, TG-FTIR showed the evolution of non-flammable CO2, and fire-retardant PO and P–O–C. Mechanical property testing confirmed no reduction in the adhesion strength of the IFR coating. With these results, the developed IFR coating exhibited enhanced fire-retardancy whilst remaining optically transparent, suggestive of a dual-phase IFR protective mechanism involving the release of gaseous combustion diluents and the formation of a thermally insulating char layer.

Effects of dual modification on thermal, structural and pasting properties of taro (Colocasia esculenta L.) starch

In this study, organic taro starch was submitted to dual modification: the first modification was by heat-moisture treatment (HMT), which totalled nine treatments, combining three moisture levels (13, 19 and 25%), three time intervals (45, 60 and 75 min) and a temperature of 120 °C, and the second modification was by ultrasound (US), which was applied for 30 min at 60% amplitude (frequency of 20 kHz) for all the samples. The morphology of the granules did not show major changes; the relative crystallinity decreased after HMT and increased after the second treatment by US, varying between 26.9 and 32.7%. The Rapid Visco Analyser (RVA) profile showed a decrease in all parameters, except for the pasting temperature. The gelatinisation showed an increase in enthalpy change for all the HMT-modified samples, up to 14.8 J g−1. Moreover, an extension of the gelatinisation range also occurred, suggesting a higher stability in relation to heating; the values ranged from 9.3 (native sample) to 16.7 J g−1 for the HMT-modified sample. The dual-modified samples resulted in a lower gelatinisation temperature range and a decrease in enthalpy change; 4.1 J g−1 was the lowest value. The chemometric approach resulted in a better understanding of the behaviour of the samples modified by dual modification.

Interactions of the AT1 antagonist valsartan with dipalmitoyl-phosphatidylcholine bilayers

Valsartan is a marketed drug with high affinity to the type 1 angiotensin (AT1) receptor. It has been reported that AT1 antagonists may reach the receptor site by diffusion through the plasma membrane. For this reason we have applied a combination of differential scanning calorimetry (DSC), Raman spectroscopy and small and wide angle X-ray scattering (SAXS and WAXS) to investigate the interactions of valsartan with the model membrane of dipalmitoyl-phosphatidylcholine (DPPC). Hence, the thermal, dynamic and structural effects in bulk as well as local dynamic properties in the bilayers were studied with different valsartan concentrations ranging from 0 to 20mol%. The DSC experimental results showed that valsartan causes a lowering and broadening of the phase transition. A splitting of the main transition is observed at high drug concentrations. In addition, valsartan causes an increase in enthalpy change of the main transition, which can be related to the induction of interdigitation of the lipid bilayers in the gel phase. Raman spectroscopy revealed distinct interactions between valsartan with the lipid interface localizing it in the polar head group region and in the upper part of the hydrophobic core. This localization of the drug molecule in the lipid bilayers supports the interdigitation view. SAXS measurements confirm a monotonous bilayer thinning in the fluid phase, associated with a steady increase of the root mean square fluctuation of the bilayers as the valsartan concentration is increased. At high drug concentrations these fluctuations are mainly governed by the electrostatic repulsion of neighboring membranes. Finally, valsartans' complex thermal and structural effects on DPPC bilayers are illustrated and discussed on a molecular level.

Interdigitation and vesicle-to-micelle transformation induced by a local anesthetic tetracaine in phospholipids bilayers

The phase transitions of distearoyl- (DSPC), dipalmitoyl- (DPPC) and dimyristoyl-phosphatidylcholine (DMPC) bilayer membranes were observed by means of differential scanning calorimetry as a function of the concentration of a local anesthetic tetracaine hydrochloride (TC·HCl). The depression of both temperatures of the main- and pre-transition, which is accompanied by a decrease in enthalpy changes for both transitions, was observed initially by the addition of TC·HCl. Bilayer interdigitation, which is accompanied by an increase in enthalpy change for the main transition from the interdigitated gel phase to the liquid crystalline phase, was followed by disappearance of the pretransition. The TC·HCl concentration necessary for the bilayer interdigitation was found to be 10, 21 and 6 mmol kg −1 for DSPC, DPPC and DMPC bilayers, respectively, which was not consistent with the order of acyl-chain length of lipids. Biphasic interactions for the interdigitation, that is, repulsive interaction between polar head groups and van der Waals attractive interaction between hydrophobic chains of lipids, were discussed. On the other hand, vesicle-to-micelle transformation, which is accompanied by a cooperative decrease in enthalpy change for the main transition, was observed at higher concentration of TC·HCl and was confirmed by the vesicle size determined by the dynamic light scattering. The longer the acyl-chain length of lipids, the higher the TC·HCl concentration necessary for the vesicle-to-micelle transformation.

State diagram of potato starch–water mixtures treated with high hydrostatic pressure

Potato starch–water mixture was treated with high hydrostatic pressure (HHP) of up to 1.2 GPa, and effect of starch content (10–70% (w/w)) on HHP-gelatinization was investigated by differential scanning calorimetry (DSC). Depending on the treatment pressure and potato starch content, DSC thermograms showed decrease in enthalpy change of heat gelatinization reflecting the progress of HHP-gelatinization and increase in enthalpy change of re-gelatinization of retrograded starch. From the viewpoint of the enthalpy changes, physically modified state of HHP-treated potato starch–water mixtures was classified as follows: no change, partial gelatinization, complete gelatinization, partial gelatinization and retrogradation, and complete gelatinization and retrogradation. A state diagram of potato starch–water mixtures (treatment pressure vs. starch content) was presented.

Thermodynamic Consequences of Single-mutation on Association of an Antibody with Its Specific Antigen: The Case of HyHEL-10-hen Lysozyme Complex

Abstract The interactions between protein antigen and its specific antibodies with one-point mutation have been investigated using isothermal titration calorimetry. Some mutation led to the increase in enthalpy change, and others to the decrease. Contributions of each amino acid to the interaction could be classified with two types, i.e., enthalpic and entropic.

Thermodynamic Consequences of Grafting Enhanced Affinity toward the Mutated Antigen onto an Antibody: THE CASE OF ANTI-LYSOZYME ANTIBODY, HyHEL-10

In order to address the mechanism of enhancement of the affinity of an antibody toward an antigen from a thermodynamic viewpoint, anti-hen lysozyme (HEL) antibody HyHEL-10, which also recognize the mutated antigen turkey lysozyme (TEL) with reduced affinity, was examined. Grafting high affinity toward TEL onto HyHEL-10 was performed by saturation mutagenesis into four residues (Tyr(53), Ser(54), Ser(56), and Tyr(58)) in complementarity-determining region 2 of the heavy chain (CDR-H2) followed by selection with affinity for TEL. Several clones enriched have a Phe residue at site 58. Thermodynamic analyses showed that the clones selected had experienced a greater than 3-fold affinity increase toward TEL in comparison with wild-type Fv, originating from an increase in negative enthalpy change. Substitution of HyHEL-10 HTyr(58) with Phe led to the increase in negative enthalpy change and to almost identical affinity for TEL in comparison with mutants selected, indicating that mutations at other sites decrease the entropy loss despite little contribution to the affinity for TEL. These results suggest that the affinity of an antibody toward the antigen is enhanced by the increase in enthalpy change by some limited mutation, and excess entropy loss due to the mutation is decreased by other energetically neutral mutations.

Effect of ionic strength on the transfer of 1-pyrenemethyl-3β-hydroxy-22,23-bisnor-5-cholenate between bilayer vesicles containing phosphatidylserine

The influence of ionic strength or the concentration of K + ([K +]) of the aqueous phase on the spontaneous transfer of cholesterol between negatively charged bilayer vesicles composed of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylserine (DPPS) (1:1, mole:mole) was studied using a pyrene-labelled cholesterol analogue, 1-pyrenemethyl-3β-hydroxy-22,23-bisnor-5-cholenate (PMC), as the probe. The decrease in PMC excimer fluorescence was best fitted to a bi-exponential function. Increasing [K +] from 0.1 M to 0.3 M had little effect on the shorter half-time (1.4 ± 0.2 min) but increased the longer half-time from 16.3 ± 1.9 min to 26.7 ± 2.1 min. Fluorescence quenching and titration of an interface-located fluorophore, 1-anilinonaphthalene-8-sulfonic acid (ANS) revealed an increase in interfacial hydrophobicity upon increasing in ionic strength. The physical state of the acyl chains was not affected by ionic strength as indicated by a constant PMC excimer:monomer fluorescence intensity ratio. However, an increase in enthalpy change of the lipid phase transition from 15.7 kJ/mol ([K +] = 0.1 M) to 21.3 kJ/mol ([K +] = 0.3 M), together with a slight increase in the transition temperature, implies that interactions between adjacent molecules in the charged lipid bilayer vesicles became stronger at higher ionic strength. Our results suggest that the van der Waals attraction between PMC and phospholipid molecules could be affected by conformation changes in the charged head group region brought about by changes of ionic strength in the aqueous phase, with consequent effects on the desorption of cholesterol from the bilayer surface.

DISTRIBUTION OF DISPERSE DYES BETWEEN n-HEPTANE AND MIXED SOLVENTS

In the previous paper2) it was concluded that the treatment of polyolefine with bromine gas resulted in the introduction of polar groups, such as C-Br, C-O and C=O. The object of this paper is to investigate the mode of action of these groups to the dyeing properties of the polymer.Isotherms were measured for the distribution of model disperse dyes (azobenzene, p-aminoazobenzene and 4-amino-4′-nitroazobenzene) between water and various organic solvents at 50°, 60° and 70°C. The solvents with similar chemical constitution to the modified polyolefine fiber were selected, such as brominated n-heptane, mixture of n-heptane with 2-heptanone, n-heptylalcohol, butylether or heptene-1. From the results the thermodynamic parameters were calculated for the process of the transfer of unit mole of dye from n-heptane to the mixed solvents.The unitary free energy changes were all negative for the dye transfer from n-heptane into mixed solvent phase. This indicates that the disperse dyes are more stable in the mixed solvents than in n-heptane. From the thermodynamic parameters obtained in this paper the interaction between the dyes and polar groups in the mixed solvents is discussed. An introduction of an amino group in azobenzene molecule caused a marked increase in enthalpy change. This suggests that a main source of the stability of the dye in the mixed solvents might be hydrogen-bonds between dye molecules and polar groups in the solvents.

DISTRIBUTION OF DISPERSE DYES BETWEEN <i>n</i>-HEPTANE AND CHLORINATED <i>n</i>-HEPTANE

Isotherms were measured for distributions of model disperse dyes (benzene, azobenzene, p-amino-azobenzene, p-nitroazobenzene, 4-amino-4′-nitroazobenzene, 4-N-methylamino-4′-nitroazobenzene, and 4-N, N-dimethylamino-4′-nitroazobenzene) between water and n-heptane and between water and 3.5% chlorinated n-heptane at various temperatures. From the results the thermodynamic parameters were calculated for the process which consists of the transfer of one mole of the dye molecule from n-heptane to 3.5% chlorinated n-heptane.Dye in n-heptane (mole fraction) → Dye in 3.5% chlorinated n-heptane (mole fraction)The unitary free energy changes accompanied by the process were all negative. This indicates that the dye molecules were more stable in chlorinated n-heptane than in n-heptane. From the thermodynamic parameters obtained in this work the interaction between the dye molecule and chlorinated n-heptane molecule was discussed. It was concluded that the ability of the chlorine atom of chlorinated n-heptane to form hydrogen-bonds with proton-donating groups of the dye molecule might be a main source of the stability of the dye molecule in chlorinated n-heptane.The fact that an introduction of an amino group into the dye molecule caused a marked increase in enthalpy change supported this conclusion.