Dependence Of Melting Temperature Research Articles

Thermostability of DNA Complexes with Mitoxantrone at Small Fillings

Thermostability of DNA complexes with anti-tumorous compound — mitoxantrone — at 0.011[Formula: see text]M and 0.11 M NaCl ionic strengths of solution by spectrophotometric and microcalorimetric methods has been studied. It was shown that at small fillings when one molecule of mitoxantrone corresponds to 250 or more base pairs of DNA, the thermostability of complexes strongly depends on the solution’s ionic strength; moreover, at an ionic strength of 0.011 M NaCl the melting temperature dependence on mitoxantrone concentration passes through a minimum. In the mentioned region of mitoxantrone concentration the melting enthalpy of the complexes increases linearly with mitoxantrone concentration enhancement. The observed phenomenon, which is not observed for ethidium bromide complexes with DNA, is qualitatively explained by the increasing of coil-shaped state of DNA–mitoxantrone complex due to additional freedom of rotation of mitoxantrone side groups.

Size-dependent cohesive energy, melting temperature, and Debye temperature of spherical metallic nanoparticles

It is necessary to theoretically evaluate the thermodynamic properties of metallic nanoparticles due to the lack of experimental data. Considering the surface effects and crystal structures, a simple theoretical model is developed to study the size dependence of thermodynamic properties of spherical metallic nanoparticles. Based on the model, we have considered Co and Cu nanoparticles for the study of size dependence of cohesive energy, Au and Cu nanoparticles for size dependence of melting temperature, and Cu, Co and Au nanoparticles for size dependence of Debye temperature, respectively. The results show that the size effects on melting temperature, cohesive energy and Debye temperature of the spherical metallic nanoparticles are predominant in the sizes ranging from about 3 nm to 20 nm. The present theoretical predictions are in agreement with available corresponding experimental and computer simulation results for the spherical metallic nanoparticles. The model could be used to determine the thermodynamic properties of other metallic nanoparticles to some extent.

Melting behaviour of the candidate minerals for planetary models

The discovery of super-Earths and extra solar giant planets has made high pressure physics relevant for determining the formation and composition of these planets.We have developed a model to determine the pressure dependence of melting temperature, Tm and the Debye temperature, ΘD of materials utilizing Grüneisen parameter, ξ and the bulk modulus, B as the basic ingredients. The formalism has been applied to estimate the pressure dependence of melting temperature and Debye temperature of one of the candidate minerals such as quartz (stishovite, SiO2). The pressure range used in the present study is 0-6000GPa commensurate with the interior pressures of giant exoplanets. The results show an excellent agreement with the available experimental and other theoretical results.

Comment on “Re-exploring the double-melting behavior of semirigid-chain polymers with an in-situ combination of synchrotron nanofocus X-ray scattering and nanocalorimetry” by Ivanov et al. [European Polymer Journal 81 (2016) 598–606.

Ivanov et al., European Polymer Journal 81 (2016) 598–606, conclude that “the phenomenon of the double (or multiple) melting behavior [in poly(trimethylene terephthalate) (PTT)] is not necessarily coupled to the melting–recrystallization processes and can be observed even in the absence of any recrystallization”. To further clarify this long standing issue, the multiple-melting behavior of isothermally crystallized PTT was examined using differential scanning calorimetry (DSC) and fast scanning chip calorimetry (FSC) in a wide range of heating rates (0.1Ks−1–60,000Ks−1). The critical heating rate to suppress recrystallization, βcritical, was determined as 2000Ks−1 from the analysis of heating rate dependence of melting temperature. Melting peaks observed below βcritical are due to the melting of recrystallized crystals, which are formed during slow heating. On the other hand, above βcritical, a single endothermic peak originated from the melting of initially formed crystals is observed. The result of thermal analysis strongly suggests that a single population of crystals is formed during isothermal crystallization of PTT. The heating rate of 1000Ks−1, as used by Ivanov et al., was therefore not fast enough to suppress recrystallization.

Effect of size and shape on melting and superheating of free standing and embedded nanoparticles

A simple model is proposed to study the size and shape dependence of melting and superheating of nanomaterials. The size dependence of melting temperature of free standing spherical nanosolids viz. Ag, Au, Al and Zn nanowire as well as embedded nanoparticles Pb and Ag is reported. The formulation is used to study the effect of shape on melting temperature during reduction of size. The different shapes of nanomaterials viz. film, icosahedral, wire, spherical, hexahedral, octahedral and tetrahedral are considered. The size and shape dependence of surface atoms, total number of atoms and their ratio is computed. The results obtained are compared with the available experimental data and discussed in the light of recent investigations. A good agreement between model predictions and experimental data supports the validity of the formulation developed. It is concluded that in addition to the size, the shape of nanomaterials also plays an important role during the behaviour of nanomaterials.

Investigation of the Melting Thermodynamics of a DNA 4-Way Junction: One Base at a Time

DNA four-way junctions are branched structures that form between two homologous chromosomes. These junctions play key roles during several cellular processes, including meiosis and DNA double-stranded break repair, however their mechanism of formation and separation are not well understood, particularly with respect to branch migration. We have investigated the thermodynamic stability of the DNA four-way junction J3 using the fluorescent pteridine nucleoside analogues, 6-MAP and 6-MI, which provide site-specific information on the melting process. We have incorporated these probes at different locations throughout the junction to determine the influence of position on junction stability. Preliminary fluorescence data suggest that the central region of the four-way junction, a region under much torsional strain, is in fact more stable than previously hypothesized. We have also investigated the relative stability of the different arms, by incorporating probes on each arm approximately the same distance from the junction center. These results are compared with those predicted from coarse-grained simulations of the junction using the 3 sites per nucleotide (3SPN.2) model. Already, we have demonstrated the ability of this model to reproduce many experimentally determined aspects of DNA junction structure and stability, including the temperature dependence of melting on salt concentration, the bias between open and stacked conformations, the relative populations of conformers at high salt concentration, and the inter-duplex angle between arms. We are now using a replica-exchange molecular dynamics approach to evaluate the fraction of bonded bases along each arm of the junction over the temperature range associated with melting. This approach allows us to determine base-by-base the local melting temperature along the arm. We specifically compare the patterns of melting observed experimentally with those obtained from the coarse-grained simulations.

Melting of aluminum with ideal or defect lattice: Molecular dynamics simulations with accounting of electronic heat conductivity

In this work, the atomistic simulations of rapid melting of aluminum are performed. We use the two-temperature approach separately describing the ionic and electronic subsystems of crystal. Both ideal and defect states of initial lattice are considered. The dependence of melting temperature on pressure is investigated in the simulations of thermal equilibrium establishment in the systems with plate interphase boundaries. Non-equilibrium melting of aluminum is studied in simulations with the constant rate of heat energy supply. The maximal temperatures of overheated material before complete melting are obtained in dependence of energy supply rate. Presence of initial defects of lattice substantially decreases the overheating of material. Electronic heat conductivity significantly accelerates the thermal equilibrium establishment in systems with interphase boundaries and decreases the drop of temperature after beginning of melting in the systems with constant rate of heating.

Analysis of flow induced crystallization through molecular stretch

Abstract In this work, specific experiments on an isotactic polypropylene are carried out, aiming to investigate the flow induced crystallization and the final morphology. The viscoelastic nature of the polymer is described by a non-linear Maxwell model applied to the conformation tensor. Shear stress evolutions, recorded during step shear isothermal experiments, are satisfactory described considering the molecular stretch, i.e. the difference between the two main eigenvalues of the conformation tensor. In the general model, the effect of temperature, pressure, and crystallinity are taken into account. Furthermore, a modeling framework is proposed to describe flow-induced crystallization of isotactic polypropylene. The spherulitic growth rate is analyzed on the basis of a flow dependent equilibrium melting temperature, using the molecular stretch as the key parameter. A phenomenological correlation of the nucleation rate with growth rate is observed. By combining the morphological models, both for nucleation and growth rate, for flow induced crystallization is possible to explain the effect of shear rate and shearing times in different experimental results, and potentially in the simulation of polymer processing.

Thermal and physical properties of titanium oxide at high pressure

We have investigated the pressure dependence of the thermal and physical properties of titanium oxide (rutile) by utilizing the semi-empirical relation developed following the Lindemann's melting law. Grüneisen parameter and the bulk modulus are the basic inputs of the empirical relation. The formalism has been applied to estimate the pressure dependence of melting temperature, Debye temperature, viscosity, conductivity and diffusivity of rutile. The pressure range used in the present study is 0–20GPa. The results show that the properties of TiO2 as a function of pressure are close to linear at low pressures (P≤6.0GPa) but starts deviating from being linear for (P>6.0GPa). Similar trends are also exhibited for viscosity, thermal conductivity, and diffusivity.

Quantitative understanding of two distinct melting kinetics of an isothermally crystallized poly(ether ether ketone)

Abstract The multiple melting peaks of isothermally crystallized poly(ether ether ketone) were investigated by fast-scanning chip calorimetry over a wide range of heating rates from 500 to 60,000 K s −1 . The analysis of heating rate dependence of melting temperatures revealed that there are two crystal populations with distinct melting kinetics for the samples prepared at different crystallization temperatures, 170 °C ≤ T iso ≤ 270 °C. For each T iso , the two melting temperatures of the metastable crystals without prior reorganization or superheating (i.e. zero-entropy-production melting temperatures) were constantly 20 K and 30 K, respectively, higher than T iso . We first discuss this behavior quantitatively based on the Lauritzen-Hoffman nucleation approach. Finally we conclude that these increases in temperature are linked to the number of stems which construct the secondary surface nuclei. The existence of two crystal populations can be caused by differences in the stability of the crystal or “local” differences in the free energy of the surrounding melt.

Holliday Junction Thermodynamics and Structure: Coarse-Grained Simulations and Experiments.

Holliday junctions play a central role in genetic recombination, DNA repair and other cellular processes. We combine simulations and experiments to evaluate the ability of the 3SPN.2 model, a coarse-grained representation designed to mimic B-DNA, to predict the properties of DNA Holliday junctions. The model reproduces many experimentally determined aspects of junction structure and stability, including the temperature dependence of melting on salt concentration, the bias between open and stacked conformations, the relative populations of conformers at high salt concentration, and the inter-duplex angle (IDA) between arms. We also obtain a close correspondence between the junction structure evaluated by all-atom and coarse-grained simulations. We predict that, for salt concentrations at physiological and higher levels, the populations of the stacked conformers are independent of salt concentration, and directly observe proposed tetrahedral intermediate sub-states implicated in conformational transitions. Our findings demonstrate that the 3SPN.2 model captures junction properties that are inaccessible to all-atom studies, opening the possibility to simulate complex aspects of junction behavior.

Holliday Junction Thermodynamics and Structure: Comparisons of Coarse-Grained Simulations and Experiments

The DNA Holliday junction plays a vital role in genetic recombination and DNA repair. All-atom simulations of DNA junctions have proved challenging, owing to the substantial size and time scales required to examine conformational changes or junction melting. Here, we combine simulations and experiments to evaluate the possibility of using the 3SPN.2 model, a coarse-grained molecular representation designed to mimic B-DNA, to reproduce the properties of a DNA four-way Holliday junction. We find that the model reproduces our experimental measurements of the junction melting temperature dependence on salt concentration to within 3%. The model reproduces the bias between open and stacked conformations, as well as the relative population of stacked isomers at high salt concentration. We further predict the population of the iso-I and iso-II forms is nearly independent of salt concentration. We directly observe proposed tetrahedral intermediate sub-states implicated in conformational transitions, suggesting that these conformations, rather than planar open states, facilitate these transitions. Finally, we compare our results for inter-duplex angle (IDA) with previous fluorescence experiments and all-atom calculations based on the AMBER force field. We find a close correspondence between the average IDA of our all-atom and coarse-grained simulations, but find that the “arms” of the junction in the 3SPN.2 model exhibit larger fluctuations, apparently due to the implicit nature of solvent and ion interactions. Our findings demonstrate that the 3SPN.2 model captures junction properties that are not presently accessible to all-atom studies, opening the possibilities to simulate complex aspects of junction behavior.

Nanodisc-Tm: Rapid functional assessment of nanodisc reconstituted membrane proteins by CPM assay

Membrane proteins are generally unstable in detergents. Therefore, biochemical and biophysical studies of membrane proteins in lipidic environments provides a near native-like environment suitable for membrane proteins. However, manipulation of proteins embedded in lipid bilayer has remained difficult. Methods such as nanodiscs and lipid cubic phase have been developed for easy manipulation of membrane proteins and have yielded significant insights into membrane proteins. Traditionally functional reconstitution of receptors in nanodiscs has been studied with radioligands. We present a simple and faster method for studying the functionality of reconstituted membrane proteins for routine characterization of protein batches after initial optimization of suitable conditions using radioligands. The benefits of the method are•Faster and generic method to assess functional reconstitution of membrane proteins.•Adaptable in high throughput format (≥96 well format).•Stability measurement in near-native lipid environment and lipid dependent melting temperatures.

A theoretical model to study melting of metals under pressure

On the basis of the thermal equation-of-state a simple theoretical model is developed to study the pressure dependence of melting temperature. The model is then applied to compute the high pressure melting curve of 10 metals (Cu, Mg, Pb, Al, In, Cd, Zn, Au, Ag and Mn). It is found that the melting temperature is not linear with pressure and the slope [Formula: see text] of the melting curve decreases continuously with the increase in pressure. The results obtained with the present model are also compared with the previous theoretical and experimental data. A good agreement between theoretical and experimental result supports the validity of the present model.

Quantum concentration for the liquid phase of elements

The novel concept of quantum concentration for the liquid phase of elements was introduced which indicates the number of possible states of atoms per unit volume. A simplified thermodynamic energy model for a solid–liquid phase transition is used to define the quantum concentration for the liquids. Values of quantum concentration for liquid phase of most of elements were calculated and analyzed. It was revealed that the metalloids such as boron, silicon, germanium, antimony, tellurium and bismuth exhibited a highest value of quantum concentrations compared with other elements. Several physical and chemical properties of substances (such as melting temperature and free energy) can be calculated using these data. The size dependence of melting temperatures of Au, Pb and Sn spherically symmetric nanoparticles were calculated and compared well with experimental data and theoretical model based on generalized Gibbs–Thomson predictions.

Multiscale approach for studying melting transitions in CuPt nanoparticles.

A multiscale approach, based on the combination of CALPHAD and molecular dynamics (MD) simulation, is applied in order to understand the melting transition taking place in CuPt nanoalloys. We found that in systems containing up to 1000 atoms, the morphology adopted by the nanoparticles causes the icosahedral CuPt to melt at temperatures 100 K below that of the other morphologies, if the chemical composition contains less than 30% of Pt. We show that the solid-to-liquid transition in CuPt nanoparticles of a radius equal to or greater than 3 nm could be studied using classical tools.

Influence of expansion cooling regime on morphology of poly(ε‐caprolactone) foams prepared by pressure quenching using supercritical CO2

Creation of foam structures from hydrolytically degradable poly(ε‐caprolactone) (PCL) is a current task in biomaterial research. One example are degradable scaffolds. The thermodynamic and kinetic conditions in a supercritical CO2 (scCO2) supported foaming process of PCL can influence the resulting morphology of the foam. PCL foaming with scCO2 was systematically investigated in the pressure range from 78 to 200 bar at temperatures between 25°C and 50°C with the help of a view cell. PCL foams could be obtained at both conditions above the pressure dependent melting temperature as well as below this temperature, i.e. from supercooled melt states. Differential scanning calorimetry investigations of the PCL foam samples were used for the analysis of the relationship between pore morphology and foaming conditions. Three characteristic regions could be distinguished in the PCL/CO2 phase diagram. Only when the foaming was conducted above the critical temperature of CO2, a significant influence of the depressurization rate could be observed. Here, an increase in the quenching rate resulted in a decreasing pore size while the pore density was found to increase. Copyright © 2014 John Wiley & Sons, Ltd.

Thermodynamic approach to the size dependence of the melting temperatures of films

The size dependence of melting temperature T m of metallic films (tin and copper) on different substrates, including amorphous carbon and another refractory metal (i.e., the dependence of T m on film thickness h) is investigated. It is found that the effect of the interfacial boundary can result in the growth of T m for thin metallic films on carbon substrates with a reduction in film thickness h. For a system with a metallic film on a metallic substrate, the size dependence of T m is less pronounced and T m falls with a reduction in h.

Laser sintering of separated and uniformly distributed multiwall carbon nanotubes integrated iron nanocomposites

Uniform distribution of carbon nanotubes (CNTs) in metal matrix during additive manufacturing of nanocomposites is always a challenge since the CNTs tend to aggregate in the molten pool. In this study, Multiwall carbon nanotubes (MWNTs) were separated and distributed uniformly into iron matrix by laser sintering process. MWNTs and iron powders were mixed together by magnetic stir, coated on steel 4140 surface, followed by laser sintering. Due to the fast heating and cooling rate, the CNTs are evenly distributed in the metal matrix. The temperature field was calculated by multiphysics simulation considering size effects, including size dependent melting temperature, thermal conductivity, and heat capacity. The SEM, TEM, and XRD were used to understand the laser sintering of CNT integrated nanocomposites. The results proved the feasibility of this technique to synthesize MWNTS integrated metal matrix nanocomposites.

Modelling ignition temperature and burning time of a single aluminium nanoparticle

A mathematical model is developed for the burning of a single nanosized aluminium particle in air. First, based on thermal definition, the ignition temperature of single Al is obtained. For this purpose, the interpolation method is used for the conduction of heat loss rate in the transition regime; the chemical heat generation rate is described by a single term Arrhenius ignition model; the Gibbs-Thomson equation for an isolated spherical solid particle is utilised for modelling the size dependent melting temperature of nanoparticles; and the size dependent activation energy is also obtained. The theoretical result shows that the ignition temperature is slightly higher than the melting temperature. With the assumption of constant particle size and the use of the `Taffanel and le Floch' condition, the burning time of a single aluminium particle is achieved. According to the obtained results, as particle size decreases or pressure increases, the reaction rate increases.