Change In Melting Temperature Research Articles

ThermoMutDB: a thermodynamic database for missense mutations.

Proteins are intricate, dynamic structures, and small changes in their amino acid sequences can lead to large effects on their folding, stability and dynamics. To facilitate the further development and evaluation of methods to predict these changes, we have developed ThermoMutDB, a manually curated database containing >14,669 experimental data of thermodynamic parameters for wild type and mutant proteins. This represents an increase of 83% in unique mutations over previous databases and includes thermodynamic information on 204 new proteins. During manual curation we have also corrected annotation errors in previously curated entries. Associated with each entry, we have included information on the unfolding Gibbs free energy and melting temperature change, and have associated entries with available experimental structural information. ThermoMutDB supports users to contribute to new data points and programmatic access to the database via a RESTful API. ThermoMutDB is freely available at: http://biosig.unimelb.edu.au/thermomutdb.

Selective laser sintering of polyamide 12/flame retardant compositions

In this work, various flame retardants (FR) and clays were added to polyamide 12 (PA12). The processability by Selective Laser Sintering (SLS), thermal behaviour and flame retardancy of these compounds were evaluated. The observations show an important impact on powder flowability of some formulations containing melamine cyanurate and melamine polyphosphate leading to difficulties during SLS process. The incorporation of FRs also leads to changes in melting and crystallization temperatures of polyamide as a function of the FR type. Furthermore, in order to evaluate the influence of the process on thermal properties of samples, a comparison between thermocompression (TC) and SLS techniques was performed for the formulations containing the flame retardants alone. The addition of flame retardants impacts the porosity of the SLS samples as a function of the FR type. For the additives which are able to melt during SLS process, a lower porosity was observed. Samples made by TC containing 30 wt% of ammonium polyphosphate, zinc diethylphosphinate and a pentaerythritol ester of methane phosphonic acid showed a better thermal stability and flame retardancy compared to the ones made by SLS, probably due to the porosity of the SLS samples and some degradation of the flame retardant by the laser beam. For the formulation containing only zinc borate, no difference was observed between TC and SLS. In order to evaluate possibly synergistic effects between flame retardants, binary and ternary formulations were prepared by SLS. On the whole, these formulations led to an improvement of flame retardancy compared to neat PA12. Moreover, XRD results showed the formation of borophosphates for binary and ternary formulations, indicating interactions between flame retardants. EDX results showed that at least 95% of the phosphorus remained in the residue for the formulations containing zinc borate, thus corroborating the results obtained by XRD. The partial substitution of zinc borate by kaolinite led to a further improvement of flame retardancy at the expense of a porosity increase in the samples.

Novel behavior in a polymer solution: the disappearance of the melting temperature (Tm) and enthalpy change (\u0394Hm) of the solvent

The phase change temperature and enthalpy change as a function of polystyrene (PS) concentration in dimethylformamide through a dynamic heating and quenching process were investigated. Cold crystallization, freezing and melting phenomena in a 10 wt% PS solution were all observed. Cold crystallization and melting phenomena were still observed in a 20 wt% solution. In a 30 wt% solution, all three phenomena disappeared without any solvent enthalpy changes, e.g., enthalpy changes at the melting temperature. The disappearance of both the melting temperature and the melting enthalpy change indicated that all polymer and solvent molecules in the 30 wt% solution existed only in the amorphous phase without any phase changes despite repeated heating and quenching processes. Thus, our results can provide a new approach for gelation through enthalpy changes and can be applied in the fabrication of porous membranes with a narrow distribution.

Optimization of polymer electrolytes with the effect of concentration of additives in PEO-NH4HF2 polymer electrolytes

In the present work, nanocomposite polymer electrolyte films were prepared by solution casting technique using nanosized fumed silica to polyethylene oxide (PEO)-based polymer electrolytes containing ammonium bifluoride (NH4HF2). The ionic conductivity of 1.19 × 10−5 S cm−1 has been observed at room temperature (25°C) for 3 wt% fumed silica in PEO-10 wt% NH4HF2 polymer electrolytes after which the conductivity was observed to decrease. Furthermore, the addition of high dielectric constant plasticizer propylene carbonate (PC) in the optimized composition of nanocomposite polymer electrolytes has increased the number of charge carriers by the large dissolution of ionic salt, amorphous content, and hence the ionic conductivity. Maximum ionic conductivity obtained at room temperature was found to be 1.55 × 10−4 S cm−1 in the case of PEO-10 wt% NH4HF2-3 wt% fumed silica-0.3 (ml) PC polymer electrolytes which is five orders of magnitude higher than that of the polymer host material. Temperature-dependent ionic conductivity, activation energy, and dielectric constant studies have been described for all the compositions of polymer electrolytes. Ionic conductivity and dielectric constant studies were determined from impedance data. Polymer electrolytes containing both fumed silica and PC highlight that there is no phase transition in the polymer electrolyte and temperature dependence of ionic conductivity in the temperature range is of almost Arrhenius type. The lowest activation energy value for the highest conducting polymer electrolyte was found to be 0.172 eV. Change in melting temperature, % crystallinity ( χc), and mechanical properties have also been observed in polymer electrolytes containing fumed silica as well as PC as studied by Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TGA) and universal testing machine, respectively.

A Thermoplastic Polyurethane /Nanosilica Composite via Melt Mixing Process and its Properties

This investigation reports the preparation and properties of thermoplastic polyurethane/silica nanocomposite prepared via melt mixing process. In this case, nanosilica at different loading was mixed with a polyester-based thermoplastic polyurethane (TPU). The dispersion of nanofiller was studied by the SEM and TEM analyses. The nanocomposite with optimal dispersion of nanofiller has better filler-polymer interaction that has been confirmed by the FT-IR study. TPU with 1 phr of nanosilica loading showed better tensile properties. DSC study revealed that incorporation of fumed silica in the TPU matrix does not substantially affect the refinement of TPU crystallite, and thus resulted in an insignificant change in glass transition temperature (Tg) and crystalline melting temperature of the nanocomposite. TGA study also confirmed enhanced onset degradation temperature and maximum degradation temperature (Tmax) for optimal nanosilica composite. The final degradation temperature and char content also increased with an increase in fumed silica content. Water contact angle (WCA) study revealed that hydrophilicity of the nanocomposite increased with the incorporation of fumed silica.

Study on heat transfer performance of a solar double-slope PCM glazed roof with different physical parameters

The glazed roof has better lighting performance and is widely used in modern building design. However, its poorer heat insulation performance can decrease indoor thermal comfort. Therefore, the interlayer of insulating glazed roof is injected with phase change material (PCM) to improve the indoor thermal environment of building and reduce the energy consumption, while obtain sufficient indoor light. Based on enthalpy method, a numerical heat transfer model of double-slope PCM glazed roof was established and verified in this paper. The heat transfer performance of double-slope hollow glazed roof and double-slope PCM glazed roof were compared. Finally, the design of double-slope PCM glazed roof in hot summer and cold winter area was optimized by further studying the roof angle, phase change layer thickness, glazing layer thickness, the melting temperature and phase change latent heat of PCM. The results show that the suitable melting temperature is 26–30 °C under the typical climate of hot summer and cold winter in Wuhan. Increasing the thickness of phase change layer and glazing layer can improve the thermal insulation performance of the roof, but the former effect is more significant. Moreover, a smaller roof angle within a certain range can reduce the amount of solar radiation received by the roof, and a larger latent heat energy of PCM can absorb more solar radiation to improve the heat transfer performance of the roof.

Biocomputing label-free security system based on homogenous ligation chain reaction-induced dramatic change in melting temperature for screening single nucleotide polymorphisms

The development of smart platform with accurate, inexpensive and reliable detection of single-nucleotide polymorphisms (SNPs) has long been concerned in the fields of medical diagnosis and basic research. Here, we present a ligation chain reaction (LCR)-based sensing system for the cost-effective screening of SNPs by simply conducting DNA melting analysis. No chemical modification is required and the signaling operation is accomplished in homogeneous solution, circumventing the complex modification process and possibly compromised enzymatic activity associated with heterogeneous materials, such as quantum dot (QD) and gold nanoparticle (GNP). Due to the enzymatic catalysis and high fidelity of ligase, the system is capable of executing signal amplification, providing a high sensitivity and selectivity. KRAS gene is easily recognized and the site-specific mutation of guanine (G) to adenine (A), thymine (T) or cytosine (C) is accurately screened. Moreover, the excellent reliability was demonstrated by blind test and recovery test. LCR-based signaling mechanism was further used to develop the biocomputing security system, and two logic gates consisting of four single-stranded DNAs (ssDNAs) offer a double insurance to protect the information against illegal invasion, guaranteeing the reliability of output information. Once in the absence of one essential factor, the security system was always locked regardless of target key, serving as a novel strategy to ensure the safety of output information at molecular level. As a proof-of-concept scheme, this contribution introduces new insight into the development of DNA security systems and the exploitation of powerful signal transduction strategy suitable for rapid and convenient disease diagnosis.

Elucidating the Open and Active Conformation of Human 5‐Lipoxygenase

Human 5‐Lipoxygenase (5‐LOX) is an enzyme that responds to the call for inflammation by initiating the synthesis of leukotrienes involved in asthmatic and allergic reactions and acts to sustain inflammatory reactions. Acting at the nuclear membrane in leukocytes, 5‐LOX oxygenates its lipid substrate arachidonic acid to leukotriene A4. The structure of 5‐LOX was solved in a closed conformation with helix‐α2 shortened and two large hydrophobic residues from the helix corking the active site. Most other animal lipoxygenase structures were solved with an elongated helix‐α2 allowing for an open conformation of the active site. Our goal is to study the molecular determinants important for the transition from a closed to open structure. We used site‐directed mutagenesis of helix‐α2 residues to favor either a more opened or closed conformation. We also used inhibitors to probe the conformational flexibility of 5‐LOX by testing susceptibility to cleavage by limited proteolysis and changes in melting temperature by differential scanning fluorimetry. So far, we have observed that by mutating key residues to encourage a closed conformation, 5‐LOX was less susceptible to proteolysis and melted at a higher temperature. We also showed that by mutating the same residues to encourage an open conformation, 5‐LOX was more susceptible to proteolysis. When bound to a competitive inhibitor nordihydroguaiaretic acid (NDGA), 5‐LOX melts at significantly lower temperatures and appears more susceptible to proteolytic cleavage. However, mutations that stabilize the closed conformation reduce these NDGA‐induced effects. By enhancing the presence of a closed or open conformation by mutagenesis, our results continue to hint at the structural significance of the elongated helix‐α2 in 5‐LOX dynamics. Determination of a structure of 5‐LOX in an open conformation will enable understanding of substrate acquisition and inhibitor binding. An open conformation of 5‐LOX could aid in structure‐based drug design and would foster the development of new therapies for inflammatory disorders.

Multi-Material 3D Printed Shape Memory Polymer with Tunable Melting and Glass Transition Temperature Activated by Heat or Light.

Shape memory polymers are attractive smart materials that have many practical applications and academic interest. Three-dimensional (3D) printable shape memory polymers are of great importance for the fabrication of soft robotic devices due to their ability to build complex 3D structures with desired shapes. We present a 3D printable shape memory polymer, with controlled melting and transition temperature, composed of methacrylated polycaprolactone monomers and N-Vinylcaprolactam reactive diluent. Tuning the ratio between the monomers and the diluents resulted in changes in melting and transition temperatures by 20, and 6 °C, respectively. The effect of the diluent addition on the shape memory behavior and mechanical properties was studied, showing above 85% recovery ratio, and above 90% fixity, when the concentration of the diluent was up to 40 wt %. Finally, we demonstrated multi-material printing of a 3D structure that can be activated locally, at two different temperatures, by two different stimuli; direct heating and light irradiation. The remote light activation was enabled by utilizing a coating of Carbon Nano Tubes (CNTs) as an absorbing material, onto sections of the printed objects.

A novel nano-porous aluminum substrate with anodizing treatment to encapsulate 1-tetrapropanol as composite phase change materials for thermal energy utilization

In this study, an innovative matrix material has been designed and prepared for supporting phase change materials (PCMs) to optimize the thermal property of composite PCM. The abandoned thin-slice aluminum substrate (TS-AS) is etched electrochemically into porous layer with peak-valley structure via anodizing surface treatment, nano-porous Al2O3 film growing on the TS-AS surface is used to encapsulate 1-tetrapropanol (1-TD) to prepare nano-porous TS-AS/1-TD composite PCM. According to thermal properties test results, the melting temperature and phase change latent heat (PCHL) of TS-AS/1-TD composite are 36.9 °C and 97.4 J/g, and its thermal conductivity is enhanced by 560.0% compared to pure 1-TD by introducing porous TS-AS, both these thermal properties show excellent sustainability maintaining only ±1.4% variation even after 400 times melting/freezing thermal cycles, while the composite PCM performs good thermal stability beyond 144.7 °C, which enables them to behave as thermal energy absorbing materials applied to cooling the generated heat from running precision device. Besides, the anodizing mechanism inspires the further optimization of aluminum substrate or other metal substrates by regulating porous layer morphology and thickness.

Development of binary eutectic organic phase change materials for solar thermal energy storage systems

Solar thermal energy storage unit anchored fatty acids as Phase Change Materials (PCMs) having narrow range of transition temperature and high latent heat of fusion. In this paper, a new novel eutectic PCM was developed by using a fatty acid (acetamide) and non-paraffin organic PCM (acetanilide) for a sharp melting point and high latent heat of fusion. The optimized eutectic PCM may be used for middle temperature range solar thermal energy storage systems. The binary mixture of acetamide and acetanilide at various compositions by mass ratio (wt%) was prepared and optimized experimentally for lowest value of melting point at a eutectic mixture composition of 60 wt% of acetamide and 40 wt% of acetanilide. Eutectic PCM was analyzed by Differential Scanning Calorimetry (DSC) and Field-Emission Scanning Electron Microscopy (FE-SEM). DSC results revealed that optimized eutectic PCM has a sharp melting point of 65.37°C and high latent heat of fusion of 224.67 kJ/kg. Accelerated thermal cycle testing of optimized eutectic PCM was performed for 100 melting and freezing cycles and change in melting temperature and latent heat of fusion was acceptable.

Rheological, physical, and mechanical properties of chicken skin gelatin films incorporated with potato starch

The aim of this study was to investigate the rheological, physical, and mechanical properties of chicken skin gelatin film forming solutions (FFSs) and films incorporated with potato starch. Chicken skin gelatin-based FFSs with various potato starch concentrations (0, 2, 4, 6, 8, and 10%, w/w) were prepared via casting technique. The dynamic viscoelastic properties of FFS were measured, and film characterization in terms of physical and mechanical properties was conducted. Potato starch incorporation with chicken skin gelatin-based FFS resulted in improvement of viscous behavior (G″ > G′). As potato starch concentration increased, the tensile strength, elongation at break, and elastic modulus values of chicken skin gelatin-based films also increased (p < 0.05). Additionally, increasing the concentration of potato starch caused incremental changes in water vapor permeability and melting temperatures (Tm), but a reduction in water solubility (p < 0.05). In addition, the surface smoothness and internal structure of composite films improved via potato starch incorporation. The incorporation of potato starch was also found to provide good barrier properties against ultraviolet and visible light, but did not significantly influence the transparency values of composite films. Overall, chicken skin gelatin film with 6% potato starch concentration incorporation was the most promising composite film, since it was found to exhibit optimal performance in terms of physical properties.

Epigenetic modification of cytosines fine tunes the stability of i-motif DNA.

i-Motifs are widely used in nanotechnology, play a part in gene regulation and have been detected in human nuclei. As these structures are composed of cytosine, they are potential sites for epigenetic modification. In addition to 5-methyl- and 5-hydroxymethylcytosine modifications, recent evidence has suggested biological roles for 5-formylcytosine and 5-carboxylcytosine. Herein the human telomeric i-motif sequence was used to examine how these four epigenetic modifications alter the thermal and pH stability of i-motifs. Changes in melting temperature and transitional pH depended on both the type of modification and its position within the i-motif forming sequence. The cytosines most sensitive to modification were next to the first and third loops within the structure. Using previously described i-motif forming sequences, we screened the MCF-7 and MCF-10A methylomes to map 5-methylcytosine and found the majority of sequences were differentially methylated in MCF7 (cancerous) and MCF10A (non-cancerous) cell lines. Furthermore, i-motif forming sequences stable at neutral pH were significantly more likely to be epigenetically modified than traditional acidic i-motif forming sequences. This work has implications not only in the epigenetic regulation of DNA, but also allows discreet tunability of i-motif stability for nanotechnological applications.

Effect of multiple recycling on properties of poplar fiber reinforced high density polyethylene wood-plastic composites

Wood-plastic composites have developed rapidly in recent years and are used in various fields, so their recycling is crucial. This research aims to understand the recyclability of poplar fiber (PF) reinforced high density polyethylene (HDPE) wood-plastic composites. The PF/HDPE composites were prepared by melt blending and injection molding process, and were recycled six times. The composites were subjected to mechanical tests, thermogravimetric analysis, differential scanning calorimetry and water absorption tests. The surface and tensile fracture surface of the composites were also observed by scanning electron microscope. The results showed that after recycling, the mechanical properties of PF/HDPE composites decreased and the flexural modulus decreased the most. The thermal stability of the composite gradually increased with the increase of recycling times. Recycling also improved crystallinity and crystallization and melting rates, but there is no significant change in crystallization and melting temperature. The water absorption of the recycled composites was reduced, and the waterproof performance is improved. Scanning electron microscopy revealed that the surface and interface defects of the composites were reduced by recycling, and PF was better combined with HDPE. Experimental results show that the performance change of the recycled composites is within an acceptable range and have application value in some fields.

A theoretical study on the size and morphology dependency of integral melting enthalpy and entropy of nanomaterials

Due to the fact that the melting process of nanomaterials is carried out with the continuous change of melting temperature, previous equations of differential melting enthalpy and entropy are unable to reflect their thermodynamic behaviors of actual melting process. On the basis of our previous work, theoretical calculations were conducted on the size and morphology dependent integral melting enthalpy and entropy of nano-sized Au, Ag and Sn and reasonable agreements with experimental results were observed. In addition, the integral melting enthalpy and entropy were also compared with the corresponding differential quantities. The differences between integral and differential melting enthalpy are mainly determined by the surface area and the interfacial tension, and the melting entropy by the surface area and the temperature coefficient of interfacial tension. The findings are able to deepen our understanding of the size and morphology dependent melting thermodynamics of nanomaterials and to further develop the thermodynamic theory of phase transitions of nanomaterials.

Physicochemical Properties of the Phosphoryl Guanidine Oligodeoxyribonucleotide Analogs

This work describes the basic physicochemical properties of phosphoryl guanidine oligonucleotides (PGOs)—a new type of DNA analog with a partially or totally uncharged backbone. Replacement of the negatively charged oxygen atom with an electroneutral 1,3-dimethylimidazolidine-2-imine (DMI) group is shown to influence the hydrophobicity of oligonucleotide, its electrophoretic mobility, and UV absorption spectra. Thermal stability of DMI-containing DNA-duplexes was studied in aqueous solutions with different ionic strength. It is determined that, in the case of low ionic strength, the presence of DMI groups significantly enhances the thermal stability of the duplex. In the case of nearly physiological condition (0.1 M NaCl, 10 mM MgCl2) or higher ionic strength, DMI groups do not affect the duplex stability or even slightly reduce it (melting temperature changes, on average, by –1.2°C per one DMI group). An important feature of totally uncharged PGO is its ability to form the duplex effectively regardless the ionic strength, even in deionized water. In addition, according to CD data, DMI groups do not disturb the double helix structure of DNA, maintaining it in the B form.

A robust model for quantitative prediction of the silencing efficacy of wild-type and A-to-I edited miRNAs

ABSTRACTMicroRNAs (miRNAs) are small non-coding RNAs that play essential roles in the regulation of gene function by a mechanism known as RNA silencing. In a previous study, we revealed that miRNA-mediated silencing efficacy is correlated with the combinatorial thermodynamic properties of the miRNA seed–target mRNA duplex and the 5´-terminus of the miRNA duplex, which can be predicted using ‘miScore’. In this study, a robust refined-miScore was developed by integrating the thermodynamic properties of various miRNA secondary structures and the latest thermodynamic parameters of wobble base-pairing, including newly established parameters for I:C base pairing. Through repeated random sampling and machine learning, refined-miScore models calculated with either melting temperature (Tm) or free energy change (ΔG) values were successfully built and validated in both wild-type and adenosine-to-inosine edited miRNAs. In addition to the previously reported contribution of the seed–target duplex and 5´-terminus region, the refined-miScore suggests that the central and 3´-terminus regions of the miRNA duplex also play a role in the thermodynamic regulation of miRNA-mediated silencing efficacy.

Synthesis and antileishmanial evaluation of thiazole orange analogs

Cyanine compounds have previously shown excellent in vitro and promising in vivo antileishmanial efficacy, but the potential toxicity of these agents is a concern. A series of 22 analogs of thiazole orange ((Z)-1-methyl-4-((3-methylbenzo[d]thiazol-2(3H)-ylidene)methyl)quinolin-1-ium salt), a commercial cyanine dye with antileishmanial activity, were synthesized in an effort to increase the selectivity of such compounds while maintaining efficacy. Cyanines possessing substitutions on the quinolinium ring system displayed potency against Leishmania donovani axenic amastigotes that differed little from the parent compound (IC50 12–42 nM), while ring disjunction analogs were both less potent and less toxic. Changes in DNA melting temperature were modest when synthetic oligonucleotides were incubated with selected analogs (ΔTm ≤ 5 °C), with ring disjunction analogs showing the least effect on this parameter. Despite the high antileishmanial potency of the target compounds, their toxicity and relatively flat SAR suggests that further information regarding the target(s) of these molecules is needed to aid their development as antileishmanials.

Fabrication and Characterization of Carboxymethyl Starch/Poly(l-Lactide) Acid/β-Tricalcium Phosphate Composite Nanofibers via Electrospinning.

A natural polymer of carboxymethyl starch (CMS) was used in combination with the inorganic mineral of β-Tricalcium Phosphate (β-TCP) and Poly l-lactide (PLLA) to prepare composite nanofibers with the potential to be used as a biomedical membrane. β-TCP contents varied in the range of 0.25% to 1% in the composition of PLLA and CMS. A mixed composition of these organic and inorganic materials was electro-spun to produce composite nanofibers. Morphological investigation indicated that smooth and uniform nanofibers could be produced via this technique. The average of the nanofiber diameters was slightly increased from 190 to 265 nm with the β-TCP content but some agglomeration of particles began to impede in the fiber at a higher content of β-TCP. It was observed that the fibers were damaged at a higher content of β-TCP nanoparticles. With the presence of higher β-TCP, the wettability of the PLLA was also improved, as indicated by the water contact angle measurement from 127.3° to 118°. The crystallization in the composite decreased, as shown in the changes in glass transition (Tg) and melting temperature (Tm) by differential scanning calorimeter (DSC) and X-ray diffraction analysis. Increases in β-TCP contributed to weaker mechanical strength, from 8.5 to 5.7 MPa, due to imperfect fiber structure.

Eco-friendly lightweight filament synthesis and mechanical characterization of additively manufactured closed cell foams

Environmentally pollutant fly ash cenospheres (hollow microballoons) are utilized with most widely consumed, relatively expensive high density polyethylene (HDPE) for developing lightweight eco-friendly filament for 3D printing of closed cell foams. Cenospheres (20, 40 and 60 by volume %) are blended with HDPE and subsequently extruded in filament to be used for 3D printing. Cenosphere/HDPE blends are studied for melt flow index (MFI) and rheological properties. MFI decreases with cenospheres addition. Complex viscosity, storage and loss modulus increase with filler loading. DSC results on the filament and printed samples reveal increasing crystallization temperature and decreasing crystallinity % with no appreciable change in peak melting temperature. Cooling rate variations exhibit crystallinity differences between the filament and the prints. CTE decreases with increasing cenosphere content resulting in lower thermal stresses and under diffusion of raster leading to non-warped prints. Micrography on freeze fractured filament and prints show cenospheres uniform distribution in HDPE. Intact cenospheres lower the foam density making it lightweight. Tensile tests are carried out on filaments and printed samples while flexural properties are investigated for 3D prints. Cenospheres addition resulted in improved tensile modulus and decreased filament strength. Tensile and flexural modulus of printed foams increases with filler content. Results are also compared with injection molded samples. Printed foams registered comparable tensile strength. Specific tensile modulus is noted to be increased with cenospheres loading implying weight saving potential of 3D printed foams. Property map reveals printed foams advantage over other fillers and HDPE composites synthesized through injection and compression molding.