Transition Melting Temperature Research Articles

High-purity 1,2-dimyristoyl-sn-glycero-3-phosphocholine: synthesis and emulsifying performance evaluation

Introduction1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) is a promising emulsifier for bioactive delivery systems, but its industrial applications are limited by the lack of cost-effective and scalable synthetic routes. The purpose of this study was to economically produce high-purity DMPC by replacing commonly used column chromatography methods and to evaluate the emulsifying performance.MethodsDMPC was synthesized from sn-glycero-3-phosphocholine using Steglich esterification followed by sequential recrystallization from ethyl acetate and acetone. The structure of DMPC was identified and its purity was confirmed using various spectroscopy and chromatography techniques. The emulsifying performance was evaluated by examining the effects of storage on the properties of o/w emulsions prepared using soybean oil with (i) soy PC, (ii) soy PC + DMPC (1:1, w/w), and (iii) DMPC as emulsifiers.ResultsThe chemical impurities formed during the synthesis of DMPC was removed, and its final purity was 96%, and the melt transition temperature was 37.6°C. No visible difference between the three emulsions (soy PC, soy PC+DMPC, and DMPC) was observed during two-week storage, and the DMPC-based emulsion was more stable than soy PC emulsion, showing smaller particle size distribution during 6 months.DiscussionThe highly pure DMPC was synthesized by an economical method, and DMPC-based emulsions demonstrated physicochemical stable, highlighting its potential for food and pharmaceutical industry-related applications. Our findings suggest that DMPC holds promise as an emulsifier with broad applications in the food industry.

Crafting sustainable solutions: architecting biodegradable copolymers through controlled ring-opening copolymerization.

Polylactic acid (PLA) is a biodegradable and biocompatible polymer with versatile applications in packaging and medicine. It is derived from lactic acid and thus represents an eco-friendly option sourced from renewable raw materials. Despite its advantages, PLA exhibits few drawbacks, such as brittleness and relatively high melting and glass transition temperatures. However, these limitations can be addressed through copolymerization with other monomers like ε-caprolactone (ε-CL), resulting in a composite material with improved physical properties. This paper comprehensively reviews achievements in PLA-PCL copolymerization using organometallic catalysts, discussing scientific findings and various copolymer architectures obtained, including random or block configurations. It also demonstrates various sustainable catalysts for achieving the required microstructure under mild reaction conditions without the aid of any external initiator.

Comparative study on the effects of chitosan, carrageenan, and sodium alginate on the film-forming properties of fish skin gelatin

Polysaccharides are commonly used to improve the film-forming properties of gelatin due to their wide range of sources, safety, and edible properties. However, there has been no systematic study comparing the effects of different polysaccharides on the film-forming properties of gelatin. Effects of chitosan, carrageenan, and sodium alginate on the optical properties, mechanical properties, thermal stability, hydrophilicity, and structure properties of gelatin films were systematically compared. Adding chitosan effectively reduced the ultraviolet transmittance of gelatin film. With an increase in chitosan concentration from 2 g/L to 8 g/L, the melting transition temperature (Tm) of gelatin film increased from 74 °C to 101 °C. Additionally, water vapor permeability decreased from 2.2 ± 0.23 (g.mm)/m2.h.kpa to 1.2 ± 0.18 (g.mm)/m2.h.kpa and water solubility decreased from 75% to 66%. Adding carrageenan and sodium alginate respectively increased the Tm of gelatin film to 92 °C and 84 °C; however, their addition reduced hydrophobicity and elongation at break for gelatin films. X-ray diffraction results suggested good compatibility between gelatin and all three polysaccharides while Fourier transform infrared spectrum results confirmed hydrogen bond interaction between gelatin and polysaccharides with a more orderly structure observed in gelatin films after adding polysaccharides.

Water Promotes Melting of a Metal-Organic Framework.

Water is one of the most reactive and abundant molecules on Earth, and it is thus crucial to understand its reactivity with various material families. One of the big unknown questions is how water in liquid and vapor forms impact the fast-emerging class of metal-organic frameworks (MOFs). Here, we discover that high-pressure water vapor drastically modifies the structure and hence the dynamic, thermodynamic, and mechanical properties of MOF glasses. In detail, we find that an archetypical MOF (ZIF-62) is extremely sensitive to heat treatments performed at 460 °C and water vapor pressures up to ∼110 bar. Both the melting and glass transition temperatures decrease remarkably (by >100 °C), and simultaneously, hardness and Young's modulus increase by up to 100% under very mild treatment conditions (<20 bar of hydrothermal pressure). Structural analyses suggest water to partially coordinate to Zn in the form of a hydroxide ion by replacing a bridging imidazolate-based linker. The work provides insight into the role of hot-compressed water in influencing the structure and properties of MOF glasses and opens a new route for systematically changing the thermodynamics and kinetics of MOF liquids and thus altering the thermal and mechanical properties of the resulting MOF glasses.

Structural and biophysical characterization of PadR family protein Rv1176c of Mycobacterium tuberculosis H37Rv

Rv1176c of Mycobacterium tuberculosis H37Rv belongs to the PadR-s1 subfamily of the PadR family of protein. Rv1176c forms a stable dimer in solution. Its stability is characterized by a thermal melting transition temperature (Tm) of 39.4 °C. The crystal structure of Rv1176c was determined at a resolution of 2.94 Å, with two monomers in the asymmetric unit. Each monomer has a characteristic N-terminal winged-helix-turn-helix DNA-binding domain. Rv1176c C-terminal is a coiled-coil dimerization domain formed of α-helices α5 to α7. In the Rv1176c dimer, there is domain-swapping of the C-terminal domain in comparison to other PadR homologs. In the dimer, there is a long inter-subunit tunnel in which different ligands can bind. Rv1176c was found to bind to the promoter region of its own gene with high specificity. M. smegmatis MC2 155 genome lacks homolog of Rv1176c. Therefore, it was used as a surrogate to characterize the functional role of Rv1176c. Expression of Rv1176c in M. smegmatis MC2 155 cells imparted enhanced tolerance towards oxidative stress. Rv1176c expressing M. smegmatis MC2 155 cells exhibited enhanced intracellular survival in J774A.1 murine macrophage cells. Overall, our studies demonstrate Rv1176c to be a PadR-s1 subfamily transcription factor that can moderate the effect of oxidative stress.

Torsional Strain Enabled Ring-Opening Polymerization towards Axially Chiral Semiaromatic Polyesters with Chemical Recyclability.

The development of new chemically recyclable polymers via monomer design would provide a transformative strategy to address the energy crisis and plastic pollution problem. Biaryl-fused cyclic esters were targeted to generate axially chiral polymers, which would impart new material performance. To overcome the non-polymerizability of the biaryl-fused monomer DBO, a cyclic ester Me-DBO installed with dimethyl substitution was prepared to enable its polymerizability via enhancing torsional strain. Impressively, Me-DBO readily went through well-controlled ring-opening polymerization, producing polymer P(Me-DBO) with high glass transition temperature (Tg >100 °C). Intriguingly, mixing these complementary enantiopure polymers containing axial chirality promoted a transformation from amorphous to crystalline material, affording a semicrystalline stereocomplex with a melting transition temperature more than 300 °C. P(Me-DBO) were capable of depolymerizing back to Me-DBO in high efficiency, highlighting an excellent recyclability.

Torsional Strain Enabled Ring‐Opening Polymerization towards Axially Chiral Semiaromatic Polyesters with Chemical Recyclability

AbstractThe development of new chemically recyclable polymers via monomer design would provide a transformative strategy to address the energy crisis and plastic pollution problem. Biaryl‐fused cyclic esters were targeted to generate axially chiral polymers, which would impart new material performance. To overcome the non‐polymerizability of the biaryl‐fused monomer DBO, a cyclic ester Me‐DBO installed with dimethyl substitution was prepared to enable its polymerizability via enhancing torsional strain. Impressively, Me‐DBO readily went through well‐controlled ring‐opening polymerization, producing polymer P(Me‐DBO) with high glass transition temperature (Tg &gt;100 °C). Intriguingly, mixing these complementary enantiopure polymers containing axial chirality promoted a transformation from amorphous to crystalline material, affording a semicrystalline stereocomplex with a melting transition temperature more than 300 °C. P(Me‐DBO) were capable of depolymerizing back to Me‐DBO in high efficiency, highlighting an excellent recyclability.

PHB production by Bacillus megaterium strain MNSH1-9K-1 using low-cost media.

Plastics are widely used for diverse applications due to their versatility. However, their negative impact on ecosystems is undeniable due to their long-term degradation. Thus, there is a rising need for developing eco-friendlier alternatives to substitute fossil-based plastics, like biopolymers. PHA are synthesized intracellularly by microorganisms under stressful conditions of growth and have similar characteristics to conventional polymers, like their melting point, transition temperatures, crystallinity, and flexibility. Although it is feasible to use biopolymers for diverse industrial applications, their elevated production cost due to the supplies needed for microbiological procedures and the low productivity yields obtained have been the main limiting factors for their commercial success. The present study assessed the ability of Bacillus megaterium strain MNSH1-9K-1 to produce biopolymers using low-cost media from different kinds of fruit-peel residues. The results show that MNSH1-9K-1 can produce up to 58 g/L of PHB when grown in a medium prepared from orange-peel residues. The data obtained provide information to enhance the scalability of these kinds of biotechnological processes.

Star-PCL shape memory polymer (SMP) scaffolds with tunable transition temperatures for enhanced utility.

Thermoresponsive shape memory polymers (SMPs) prepared from UV-curable poly(ε-caprolactone) (PCL) macromers have the potential to create self-fitting bone scaffolds, self-expanding vaginal stents, and other shape-shifting devices. To ensure tissue safety during deployment, the shape actuation temperature (i.e., the melt transition temperature or Tm of PCL) must be reduced from ∼55 °C that is observed for scaffolds prepared from linear-PCL-DA (Mn ∼ 10 kg mol-1). Moreover, increasing the rate of biodegradation would be advantageous, facilitating bone tissue healing and potentially eliminating the need for stent retrieval. Herein, a series of six UV-curable PCL macromers were prepared with linear or 4-arm star architectures and with Mns of 10, 7.5, and 5 kg mol-1, and subsequently fabricated into six porous scaffold compositions (10k, 7.5k, 5k, 10k★, 7.5k★, and 5k★) via solvent casting particulate leaching (SCPL). Scaffolds produced from star-PCL-tetraacrylate (star-PCL-TA) macromers produced pronounced reductions in Tm with decreased Mnversus those formed with the corresponding linear-PCL-diacrylate (linear-PCL-DA) macromers. Scaffolds were produced with the desired reduced Tm profiles: 37 °C < Tm < 55 °C (self-fitting bone scaffold), and Tm ≤ 37 °C (self-expanding stent). As macromer Mn decreased, crosslink density increased while % crystallinity decreased, particularly for scaffolds prepared from star-PCL-TA macromers. While shape memory behavior was retained and radial expansion pressure increased, this imparted a reduction in modulus but with an increase in the rate of degradation.

The influence of mixing time on the structure and thermophysical characteristics of systems based on polyethylene glycol and organomodified montmorillonite

The structure and thermophysical properties of polymer nanocomposite systems based on polyethylene glycol and organomodified montmorillonite were studied using the methods of X-ray structural analysis and differential scanning calorimetry. From the data of X-ray structural analysis, it was found that the optimal degree of delamination of montmorillonite, which corresponds to the maximum interlayer distance, occurs in 3-5 minutes. A further increase in the mixing time has no significant effect on the structural characteristics of the nanocomposite. On the basis of calorimetric studies, it is shown that the melting and glass transition temperatures, as well as the degree of crystallinity, reach critical values at 3 min of treatment, after which they remain unchanged. It was established that the time of extruder mixing is optimal. At the same time, the maximum intercalation takes place, which leads to an impact on the final functional characteristics of the polymer-organoclay system. It was established that extruder mixing during 3 min is optimal.

Relation of 3HV fraction and thermomechanical properties of poly(3–hydroxybutyrate–co–3–hydroxyvalerate) produced by Azotobacter vinelandii OP

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has attracted substantial attention as a promising material for industrial applications. In this study, different PHBV films with distinct 3-hydroxyvalerate (3HV) contents produced by Azotobacter vinelandii OP were evaluated. The 3HV fraction ranged from 18.6 to 36.7 mol%, and the number-average molecular weight (Mn) was between 238 and 434 kDa. In the bioreactor, a 3HV fraction (36.7 mol%) and an Mn value of 409 kDa were obtained with an oxygen transfer rate (OTR) of 12.5 mmol L−1 h−1. Thermal analysis measurements showed decreased melting (Tm) and glass transition (Tg) temperatures, and values with relatively high 3HV fractions indicated improved thermomechanical properties. The incorporation of the 3HV fraction in the PHBV chain improved the thermal stability of the films, reduced the polymer Tm, and affected the tensile strength. PHBV film with 36.7 mol% 3HV showed an increase in its tensile strength (51.8 MPa) and a decrease in its Tm (170.61 °C) compared with PHB. Finally, scanning electron microscopy (SEM) results revealed that the PHBV film with 32.8 mol% 3HV showed a degradation upon contact with soil, water, or soil bacteria, showing more porous surfaces after degradation. The latter phenomenon indicated that thermomechanical properties played an important role in biodegradation.

Chemically recyclable polyolefin-like multiblock polymers.

Polyolefins are the most important and largest volume plastics produced. Unfortunately, the enormous use of plastics and lack of effective disposal or recycling options have created a plastic waste catastrophe. In this work, we report an approach to create chemically recyclable polyolefin-like materials with diverse mechanical properties through the construction of multiblock polymers from hard and soft oligomeric building blocks synthesized with ruthenium-mediated ring-opening metathesis polymerization of cyclooctenes. The multiblock polymers exhibit broad mechanical properties, spanning elastomers to plastomers to thermoplastics, while integrating a high melting transition temperature (Tm) and low glass transition temperature (Tg), making them suitable for use across diverse applications (Tm as high as 128°C and Tg as low as -60°C). After use, the different plastics can be combined and efficiently deconstructed back to the fundamental hard and soft building blocks for separation and repolymerization to realize a closed-loop recycling process.

Development of poly(methyl methacrylate)/poly(lactic acid) blend as sustainable biomaterial for dental applications

Poly(lactic acid) (PLA) is gaining popularity in manufacturing due to environmental concerns. When comparing to poly(methyl methacrylate) (PMMA), PLA exhibits low melting and glass transition temperature (Tg). To enhance the properties of these polymers, a PMMA/PLA blend has been introduced. This study aimed to investigate the optimal ratio of PMMA/PLA blends for potential dental applications based on their mechanical properties, physical properties, and biocompatibility. The PMMA/PLA blends were manufactured by melting and mixing using twin screw extruder and prepared into thermoplastic polymer beads. The specimens of neat PMMA (M100), three different ratios of PMMA/PLA blends (M75, M50, and M25), and neat PLA (M0) were fabricated with injection molding technique. The neat polymers and polymer blends were investigated in terms of flexural properties, Tg, miscibility, residual monomer, water sorption, water solubility, degradation, and biocompatibility. The data was statistically analyzed. The results indicated that Tg of PMMA/PLA blends was increased with increasing PMMA content. PMMA/PLA blends were miscible in all composition ratios. The flexural properties of polymer blends were superior to those of neat PMMA and neat PLA. The biocompatibility was not different among different composition ratios. Additionally, the other parameters of PMMA/PLA blends were improved as the PMMA ratio decreased. Thus, the optimum ratio of PMMA/PLA blends have the potential to serve as novel sustainable biomaterial for extensive dental applications.

Analysis of differential scanning calorimetry (DSC): determining the transition temperatures, and enthalpy and heat capacity changes in multicomponent systems by analytical model fitting

We have developed an analytical method to quantitatively analyze differential scanning calorimetry (DSC) experimental data. This method provides accurate determination of thermal properties such as equilibrium melting temperature, latent heat, change of heat capacity which can be performed automatically without intervention of a DSC operator. DSC is one of the best techniques to determine the thermal properties of materials. However, the accuracy of the transition temperature and enthalpy change can be affected by artifacts caused by the instrumentation, sampling, and the DSC analysis methods which are based on graphical constructions. In the present study, an analytical function (DSCN(T)) has been developed based on an assumed Arrhenius crystal size distribution together with instrumental and sample-related peak broadening. The DSCN(T) function was successfully applied to fit the experimental data of a substantial number of calibration and new unknown samples, including samples with an obvious asymmetry of the melting peak, yielding the thermal characteristics such as melting and glass transition temperature, and enthalpy and heat capacity change. It also allows very accurate analysis of binary systems with two distinct but severely overlapping peaks and samples that include a cold crystallization before melting.

Optimizing BiOCl concentration for enhanced LDPE performance: Investigation of structure, thermal stability, and optical characteristics

This research article presents a comprehensive study on enhancing the structural, thermal alongside optical properties of LDPE by incorporating BiOCl nanoparticles. LDPE nanocomposites were synthesized using the solvent casting technique, employing different concentrations of BiOCl (3, 5, and 7 wt.%) nanoparticles. BiOCl demonstrated crystalline anisotropic growth along the (110) plane under solvothermal treatment, enhancing the interfacial interaction with LDPE chains. This interaction reduces electrostatic inter-chain interactions, promoting alignment and crystallization of molecular chains and yielding a smooth morphology. The optimal BiOCl concentration is determined to be 5 wt.%, as higher concentrations lead to nanoparticle aggregations and weak interactions. Raman spectroscopy shows broadened intensity peaks in the nanocomposite with increasing BiOCl concentrations, indicating the presence of defects and oxygen vacancies. These findings offer promising prospects for photocatalytic applications. The thermal analysis reveals enhanced thermal stability, fire resistance, and insulation in the nanocomposites compared to pure LDPE. The incorporation of BiOCl increases activation energy, melting, and glass transition temperatures, highlighting their positive impact on enhancing the thermal properties of LDPE. The red shift in absorption peaks of LDPE nanocomposites indicates π-delocalization, suggesting small band gaps. Additionally, higher weight percentages of BiOCl nanoparticles in the LDPE matrix result in increased absorption intensities in the UV region, providing enhanced UV radiation protection, with a maximum absorption of 96% of UV light. The results include improved interaction, morphology, alignment, thermal stability, fire resistance, and UV protection of BiOCl: LDPE nanocomposite, with potential for diverse industries.

Inexpensive Production of Poly (3‑hydroxybutyrate‑co‑ 3‑hydroxyvalerate) from Bacillus megaterium PP-10 Using Pineapple Peel Waste

Pineapple peel waste has recently been interested in being utilized as a low-cost carbon source in PHA biosynthesis to reduce the production cost of PHA. The production of copolymer Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] by the new Bacillus megaterium PP-10 was investigated. The bacteria were grown in a mixture of pineapple peel hydrolysate (PPH) and 3-hydroxyvalerate (3HV) precursor such as sodium propionate or sodium valerate at ratios of 1:1. Remarkably, the microbial growth and PHBV production in a mixture of PPH and sodium valerate exhibited higher biomass and higher PHA amount than that of sodium propionate, accounted about 2.40 ± 0.07 g/L of DCW and 0.71 ± 0.03 g/L of PHA concentration (PHA content of 29.6%DCW). Moreover, to control the 3HV molar fraction in PHBV, various sodium valerate concentration from 2 to 18 g/L was supplemented with PPH, and the result showed that the 3HV fraction increased linear trend with an increase in valerate concentration and was in the range between 6-35 mol%HV. In contrast, a maximum PHA concentration of 1.65 ± 0.04 g/L content (about 49%DCW) was obtained when B. megaterium PP-10 was cultivated in 18 g/L of total reducing sugar in PPH with 2 g/L of sodium valerate at 12 h of cultivation. Finally, the produced PHBV containing 20 mol%HV was further determined by some thermal properties and found that it possessed the melting and glass transition temperatures of 148°C and -10°C, respectively. Therefore, PHBV synthesized by B. megaterium PP-10 with various 3HV fractions was an excellent choice for biopolymer production.

Interaction of G-quadruplex Forming DNA Aptamers with PAMAM Dendrimers Studied by Dynamic Light Scattering and UV-VIS Spectrophotometry.

The complexes of G-quadruplex forming DNA thrombin binding aptamers (TBA) and polyamidoamine dendrimers (PAMAM) were studied with the aim to form a model targeted drug delivery system. Hydrodynamic diameter, zeta potential and melting temperature (Tm ) were investigated by dynamic light scattering and UV-VIS spectrophotometry. Non-covalent adsorption by means of electrostatic interaction between positively charged amino groups of dendrimers (+) and negatively charged phosphate groups of aptamers (-) has driven the formation of aggregates. The size of complexes was in the range of 0.2-2 μm and depended on the type of dispersant, charge ratio (+/-) and temperature. Raising the temperature increased the polydispersity, new smaller size distributions were observed indicating the G-quadruplex unfolding. The melting transition temperature of TBA aptamer was affected by the presence of amino-terminated PAMAM rather than carboxylated succinic acid PAMAM-SAH dendrimer, thus supporting the electrostatic nature of interaction that disturbed denaturation of target-specific quadruplex aptamer structure.

Calibrating the Composition of a Copolymer

In collaboration with Isao Noda, I have been using Raman spectroscopy to study the properties of the bioplastic polyhydroxybutyrate hexanoate (PHBHx), which depend on the percentage of hexanoate (which produces propyl side branches to the polymer chain). The percentages of hexanoate determine the maximum crystallinity that the polymer can experience, and that determines its physical and chemical properties, which include its optical clarity, dyability, flexibility, and thermal properties (melting and glass transition temperature). It is useful to have an easy way to determine the composition; in this column, we describe how Raman spectroscopy was used to show that this is feasible at an accuracy greater than expected.

Температурні залежності модуля Юнга металів з різними кристалічними гратками у широком діапазоні температур

The known temperature dependences of the modulus of normal elasticity E, mainly of metals with different types of crystal lattices, were analyzed. The dependences of E/E0 on T/Tm and on T/Tpt are considered, where E0 is the modulus of elasticity extrapolated to 0 K, and Tm and Tpt are the melting and phase transition temperatures of the material, respectively. The difference in shape and slope of temperature dependences E/E0 of materials with bcc and fcc crystal lattices from materials with hcp crystal lattice is shown. If for the first two types of lattices, the dependences can be described by a second degree polynomial with coefficients close to 0,21 and 0,3, then the temperature dependences of the modulus of elasticity of titanium, zirconium, and its alloys are mostly linear and are significantly lower than the first ones due to the anisotropy of temperature changes of the lattice parameters a and c. The dependence of E/E0 on the c/a ratio is plotted for a number of hcp metals for two levels of T/Tpt, and the area of the best c/a values for creating materials with increased thermal elasticity is shown. The relationship between the dependences of E/E0 on E/E0 and the ratio of diffusion coefficients on E/E0 and examples of their use for the analysis of deformation mechanisms at high temperatures are shown. Keywords: temperature dependence of the modulus of elasticity, crystal lattic parameters.

Temperature-Induced Effects on the Structure of Gramicidin S.

We report on the structure of Gramicidin S (GS) in a model membrane mimetic environment represented by the amphipathic solvent 1-octanol using one-dimensional (1D) and two-dimensional (2D) IR spectroscopy. To explore potential structural changes of GS, we also performed a series of spectroscopic measurements at differing temperatures. By analyzing the amide I band and using 2D-IR spectral changes, results could be associated to the disruption of aggregates/oligomers, as well as structural and conformational changes happening in the concentrated solution of GS. The ability of 2D-IR to enable differentiation in melting transitions of oligomerized GS structures is attributed to the sensitivity of the technique to vibrational coupling. Two melting transition temperatures were identified; at Tm1 in the range 41-47 °C where the GS aggregates/oligomers disassemble and at Tm2 = 57 ± 2 °C where there is significant change involving GS β-sheet-type hydrogen bonds, whereby it is proposed that there is loss of interpeptide hydrogen bonds and we are left with mainly intrapeptide β-sheet and β-turn hydrogen bonds of the smaller oligomers. Further analysis with quantum mechanical/molecular mechanics (QM/MM) simulations and second derivative results highlighted the participation of active GS side chains. Ultimately, this work contributes toward understanding the GS structure and the formulation of GS analogues with improved bioactivity.