Stepwise Melting Research Articles

All-In-One OsciDrop Digital PCR System for Automated and Highly Multiplexed Molecular Diagnostics.

Digital PCR (dPCR) holds immense potential for precisely detecting nucleic acid markers essential for personalized medicine. However, its broader application is hindered by high consumable costs, complex procedures, and restricted multiplexing capabilities. To address these challenges, an all-in-one dPCR system is introduced that eliminates the need for microfabricated chips, offering fully automated operations and enhanced multiplexing capabilities. Using this innovative oscillation-induced droplet generation technique, OsciDrop, this system supports a comprehensive dPCR workflow, including precise liquid handling, pipette-based droplet printing, in situ thermocycling, multicolor fluorescence imaging, and machine learning-driven analysis. The system's reliability is demonstrated by quantifying reference materials and evaluating HER2 copy number variation in breast cancer. Its multiplexing capability is showcased with a quadruplex dPCR assay that detects key EGFR mutations, including 19Del, L858R, and T790M in lung cancer. Moreover, the digital stepwise melting analysis (dSMA) technique is introduced, enabling high-multiplex profiling of seven major EGFR variants spanning 35 subtypes. This innovative dPCR system presents a cost-effective and versatile alternative, overcoming existing limitations and paving the way for transformative advances in precision diagnostics.

Two-dimensional ionic liquids with an anomalous stepwise melting process and ultrahigh CO2 adsorption capacity

Ultrathin ionic liquid (IL) films have shown wide applications in the chemistry and materials fields. However, the structure feature and quantitative controlling mechanism of thin IL films have rarely been reported to date. Here, computational simulations combined with scanning tunnel microscope experiments are used to quantify the structure and function of the thinnest possible IL films, two-dimensional (2D) ILs, which consist of 2D ordered mono-ionic IL structures. Interestingly, the 2D ILs exhibit anomalous stepwise melting processes, involving localized rotated, out-of-plane flipped, and fully disordered states, which are different from 3D ILs. Meanwhile, a theoretical model and temperature-surface phase diagram are constructed to evaluate the critical stepwise melting behaviors. Furthermore, the 2D ILs also possess ultrahigh CO 2 adsorption capabilities and structural robustness during the CO 2 adsorption-desorption process. These findings are promising for the rational design of an IL-solid interface for CO 2 -capture-fixation chemistry and related applications. • 2D ionic liquid with ordered mono-ionic structure • The anomalous stepwise melting processes of 2D ionic liquids is revealed • A theoretical model is developed to evaluate the critical melting points • The 2D ionic liquids possess extremely high CO 2 adsorption capabilities Combining STM experiments and molecular dynamics simulations, Wang et al. investigate 2D ionic liquids that exhibit anomalous stepwise melting processes and superhigh CO 2 adsorption capacity. The 2D modification technique may provide a strategy for the precise control and function design of liquids.

Evolution of V-containing phases during preparation of Al-based Al−V master alloys

Al-based Al−V master alloys were prepared by both the stepwise heating melting experiment and stepwise melting cooling experiment with rapid solidification to investigate the transformation of V-containing phases which gave different effects on microstructures and properties of commercial Al alloys and Ti alloys, as both melting and solidification processes affect the evolution of V-containing phases largely. The results showed that the raw Al−50wt.%V alloy consisted of needle-like Al3V phase and Al8V5 phase (matrix), while petal-like Al3V, needle-like Al7V and plate-like Al10V phase were present in the Al−V master alloys. The metastable Al7V phase was evolved from Al3V phase and then evolved into Al10V phase during melting process. The number of Al10V phase increased with the decrease of temperature in the range of 800−1000 °C. Petal-like Al3V phases could be transformed from Al8V5 phase, pre-precipitated from Al−V molten liquid during melting process and precipitated directly during rapid solidification, respectively.

Stepwise Homogeneous Melting of Benzene Phase I at High Pressure

We investigate, using molecular dynamics simulations, the spontaneous homogeneous melting of benzene phase I under a high pressure of 1.0 GPa. We find an apparent stepwise transition via a metastable crystal phase, unlike the direct melting observed at ambient pressure. The transition to the metastable phase is achieved by rotational motions, without the diffusion of the center of mass of benzene. The metastable crystal completely occupies the whole space and maintains its structure for at least several picoseconds, so that the phase seems to have a local free energy minimum. The unit cell is found to be unique—no such crystalline structure has been reported so far. Furthermore, we discuss the influence of pressure control on the melting behavior.

Critical Role of the Spacer Length of Gemini Surfactants on the Formation of Ionic Liquid Crystals and Thermotropic Behavior.

Numerous reports have shown that the self-assembling properties of 12-s-12 bis(quaternary ammonium) gemini surfactants in aqueous solution are significantly influenced by s, the number of methylene groups in the covalent spacer. However, the role played by s on the phase behavior of the single compounds has not been investigated in a similarly systematic way. Here, we report on the thermotropic phase behavior of the anhydrous compounds with s = 2-6, 8, 10, and 12, resorting to differential scanning calorimetry (DSC), polarized light microscopy (PLM), and X-ray diffraction (XRD). All of the compounds show a stepwise melting behavior, decomposing at 200 °C. As the spacer length increases, nonmonotonic trends are observed for the thermodynamic parameters of the thermotropic phase transitions, mesophase formation, and solid-state d00l spacings. In particular, the number and type of mesophases (ordered smectic phases and/or fluid smectic liquid crystals) depend critically on s. Further, upon heating molecules with s < 8 decompose before the liquid phase, while those with long spacers, s = 8-12, reach the isotropization (clearing) temperature, hence forming both ionic liquid crystals and ionic liquid phases. We demonstrate that the melting behavior and type of ionic mesophases formed by gemini molecules can be usefully manipulated by a simple structural parameter like the length of the covalent linker.

Direction-dependent secondary bonds and their stepwise melting in a uracil-based molecular crystal studied by infrared spectroscopy and theoretical modeling

Three types of supramolecular interactions are identified in the three crystallographic directions in crystals of 1,4-bis[(1-hexylurac-6-yl) ethynyl]benzene, a uracil-based molecule with a linear backbone. These three interactions, characterized by their strongest component, are: intermolecular double H-bonds along the molecular axis, London dispersion interaction of hexyl chains connecting these linear assemblies, and π–π stacking of the aromatic rings perpendicular to the molecular planes. On heating, two transitions happen, disordering of hexyl chains at 473 K, followed by H-bond melting at 534 K. The nature of the bonds and transitions was established by matrix-isolation and temperature-dependent infrared spectroscopy and supported by theoretical computations.

Unraveling the Stepwise Melting of an Ionic Liquid.

Differential scanning calorimetry, X-ray diffraction, and Raman spectroscopy were used to reveal the premelting events precursors of melting of the ionic liquid triethylsulfonium bis(trifluoromethanesufonyl)imide, [S222][NTf2]. On heating the crystalline phase of [S222][NTf2], melting occurs along a sequence of at least three steps. First, the crystalline long-range order breaks down, but local order is retained. The second step is characterized by conformational freedom of the ethyl chains of cations related to premelting of nonpolar domains, and the complete melting finally occurs when anions acquire conformational freedom. This work provides a microscopic view on the mechanism of melting of [S222][NTf2] in line with the picture of melting taking place as a sequence of structural changes. The results of this work shed light on the understanding of the complex melting process of ionic liquids.

Modeling of DFT quality neural network potential for sodium clusters: Application to melting of sodium clusters (Na20 to Na40)

The present work demonstrates the use of computationally inexpensive neural network (NN) potential for studying global optimizations and phase transitions in small to medium sized sodium clusters with DFT accuracy. Accuracy of NN potential has been tested by performing global optimizations in the size range of 16–40atoms. We performed Monte Carlo (MC) simulations using NN potential to study the melting behaviour. Melting study in the size range of 20–40atoms shows a characteristic premelting peak and a main melting peak. Our results using NN potentials support the idea of stepwise melting in small Na clusters (Aguado, 2011).

Stepwise Melting Model for the Formation Mechanism of Ni Catalyst Nanoparticles for Carbon Nanotube Growth

Different thicknesses of Ni films were deposited on Si substrates and heat treated at 973 and 1073 K. The results showed that Ni nanopartides with different diameters and shapes were formed from different thicknesses. To find the mechanisms of the Ni nanoparticle formation from Ni nanofilms, our previous model on the heterogeneous transformation of Ni nanofilms to nanoparticles and geometrical and kinetic calculations were used and compared with the experimental results. It was found that the mechanism for formation of particles is a stepwise melting of layers of specific thickness, dependent upon the working temperature, e.g., 0.5 nm thick layers at 1073 K. Nanofilms transform to nanoparticles which do not exceed 150 nm in diameter and 40° in wetting angle. Films with a thickness of more than 12.9 nm show a different behavior. The predictions are in excellent agreement with the experimental results.

Stepwise Melting in Na41+: A First-Principles Critical Analysis of Available Experimental Results

Current experimental techniques for measuring the heat capacity of size-selected and isolated atomic clusters are based on dissociation and differ in the critical step of deducing internal energy changes from the dissociation measurements. The heat capacity of Na41+ has been measured by two different techniques with uneven results: one suggests a gradual melting process with a featureless heat capacity; the other reports the first observation of two-step melting in sodium clusters. Here, we report first-principles molecular dynamics simulations of the melting transition in Na41+, including an approximate account of quantum atomic delocalization effects. Our work aims to help in the resolution of the experimental discrepancies. The results provide support for a stepwise melting process, which is induced by a hierarchical structure of the energies of local minima in the potential enery landscape.

The influence of thermal history on the physical behavior of poly(ethylene glycol) (PEG)

Objectives: To investigate the influence of thermal history on the physical behavior of poly(ethylene glycol) (PEG), commonly used as a pharmaceutical excipient.Materials and methods: Rheological investigations together with SEM imaging and solid state analysis by XRPD and DSC were used to characterize PEG as starting material, as well as PEG:lactose monohydrate granules. For granulation experiments PEG 6000 was used and for further investigations of physicochemical properties, three Mw of PEG (3000–10000) with different thermal histories obtained by melting the PEG followed by solidification with specific cooling rates.Results and discussion: More uniform granules were obtained when fast cooled PEG was used as binder. XRPD suggested similar crystallinity for the different Mw and thermal history did not influence the results drastically. However, rheological analysis and DSC measurements indicated different melting behavior dependent on the Mw of PEG. PEG 6000 and 10000 were affected by the thermal treatment where stepwise melting was observed with slower cooling rate probably due to increased formation of extended structures.Conclusions: Increased cooling rate gives rise to increased randomness, more folded structure of PEG, which reflects in the outcome of the granulation process.

Stepwise melting of a model glass former under confinement

The equilibrium thermodynamics of a binary Lennard-Jones model glass former are investigated using exchange Monte Carlo simulations, covering the crystalline and amorphous regions of configuration space in appropriate temperature ranges. We investigate both bulk and film mixtures, the latter being confined between noninteracting flat walls. Both the bulk and film systems exhibit a principal heat capacity peak at the melting point, but confinement leads to a significant depression in the melting temperature by about 25%. Microcanonical caloric curves, as well as analysis of the probability distributions of a bond-orientational order parameter, show that this transition has first-order character. However, the film system shows additional features at lower temperatures, which are interpreted in terms of localized partial melting, perpendicular to the confining walls and near the walls, with some increase in layering. This premelting is associated with local minima on the underlying potential energy surface that are not supported by the bulk system.

Crystal structures and phase transitions of long-chain n-alkylammonium bromide monohydrates

The crystal structures of five long-chain n-alkylammonium bromide monohydrates, with carbon chain lengths ranging from 13 to 18, were determined. n-Tridecylammonium bromide monohydrate 1, n-tetradecylammonium bromide monohydrate 2, n-pentadecylammonium bromide monohydrate 3, n-hexadecylammonium bromide monohydrate 4, and n-octadecylammonium bromide monohydrate 5, all crystallise in layered structures, and the same hydrogen bonding network is observed for the odd- and even carbon chain compounds. Comparison of an anhydrous and a hydrated n-alkylammonium bromide structure indicate that the structures differ in alkyl chain tilt angle, methylene subcell packing as well as hydrogen bonding network. The thermotropic phase transitions exhibited by the hydrates were investigated viaDSC and TGA, and indicate stepwise melting behaviour through a number of high temperature phases, including a liquid crystalline phase.

Modification of a neuronal network direction using stepwise photo-thermal etching of an agarose architecture

Control over spatial distribution of individual neurons and the pattern of neural network provides an important tool for studying information processing pathways during neural network formation. Moreover, the knowledge of the direction of synaptic connections between cells in each neural network can provide detailed information on the relationship between the forward and feedback signaling. We have developed a method for topographical control of the direction of synaptic connections within a living neuronal network using a new type of individual-cell-based on-chip cell-cultivation system with an agarose microchamber array (AMCA). The advantages of this system include the possibility to control positions and number of cultured cells as well as flexible control of the direction of elongation of axons through stepwise melting of narrow grooves. Such micrometer-order microchannels are obtained by photo-thermal etching of agarose where a portion of the gel is melted with a 1064-nm infrared laser beam. Using this system, we created neural network from individual Rat hippocampal cells. We were able to control elongation of individual axons during cultivation (from cells contained within the AMCA) by non-destructive stepwise photo-thermal etching. We have demonstrated the potential of our on-chip AMCA cell cultivation system for the controlled development of individual cell-based neural networks.

Formation and disappearance of the rigid amorphous fraction in semicrystalline polymers revealed from frequency dependent heat capacity

For semicrystalline polymers the observed relaxation strength at glass transition is often significantly smaller than expected from the non-crystalline fraction. This observation leads to the introduction of a rigid amorphous fraction (RAF) which does not contribute to the heat of fusion or X-ray crystallinity nor to the relaxation strength at glass transition. The RAF is non-crystalline and in a glassy state at temperatures above the common glass transition. Complex heat capacity in the high frequency limit allows for the measurement of base-line heat capacity also at temperatures above the glass transition. From that the temperature and time dependence of the RAF can be obtained. For PC, PHB and syndiotactic polypropylene (sPP) it is possible to study the creation and disappearance of the RAF in situ during isothermal crystallization and on stepwise melting. If crystallization is not limited by the stability (melting point) of the crystals to be formed the total RAF is created during the isothermal crystallization. Simultaneously with the melting of the smallest crystals the RAF disappears. For these polymers vitrification and devitrification of the non-crystalline material detected as the RAF at glass transition is structural (conformational) and not temperature induced. The formation of the last growing crystals, which melt first, are responsible for the vitrification of the amorphous material around them and, consequently, by that they limit their own growth.

Novel lipid-based colloidal dispersions as potential drug administration systems - expectations and reality

Colloidal drug carriers offer a number of potential advantages as delivery systems for, for example, poorly soluble compounds. The first generation of colloidal carriers, in particular liposomes and sub-micron-sized lipid emulsions, are, however, associated with several drawbacks which so far have prevented the extensive use of these carriers in drug delivery. As an alternative colloidal delivery system melt-emulsified nanoparticles based on solid lipids have been proposed. Careful physicochemical characterization has demonstrated that these lipid-based nanosuspensions (solid lipid nanoparticles) are not just “emulsions with solidified droplets”. During the development process of these systems interesting phenomena have been observed, such as gel formation on solidification and upon storage, unexpected dynamics of polymorphic transitions, extensive annealing of nanocrystals over significant periods of time, stepwise melting of particle fractions in the lower-nanometer-size range, drug expulsion from the carrier particles on crystallization and upon storage, and extensive supercooling. These phenomena can be related to the crystalline nature of the carrier matrix in combination with its colloidal state. Observation of the supercooling effect has led to the development of a second new type of carrier system: nanospheres of supercooled melts. This novel type of colloidal lipidic carrier represents an intermediate state between emulsions and suspensions. Moreover, these dispersions are particularly suited to the study of the basic differences between colloidal triglyceride emulsions and suspensions. For many decades drug carriers have represented the only group of colloidal drug administration systems. Nowadays a fundamentally different group of dispersions is also under investigation: drug nanodispersions. They overcome a number of carrier-related drawbacks, such as limitations in drug load as well as side effects due to the matrix material of the carrier particles. Utilizing this concept virtually insoluble drugs can be formulated as colloidal particles, of solid or supercooled nature. For example, coenzyme Q10 (Q10) has been successfully processed into a dispersion of a supercooled melt. Droplet sizes in the lower nanometer range and shelf lives of more than 3 years can easily be achieved for Q10 dispersions. The drug load of the emulsion particles reaches nearly 100%.

An investigation of the structure of a porous substance by NMR cryodiffusometry

Cryoporosimetry and diffusometry, along with traditional techniques, are used to determine the characteristics of porous media. In real systems characterized by a pore-size distribution and a complex geometry of the pore space, the possibilities of these methods are limited. To obtain more data on the structure of the pore space, it was suggested that these approaches be combined in a unified experimental technique called cryodiffusometry. A concept of this technique lies in the investigation of self-diffusion in liquid-containing regions in the course of sequential stepwise melting of a substance precrystallized in pores. Possibilities of cryodiffusometry were demonstrated by investigating of the pore structure of gypsum stone as an example. An analysis of the data obtained showed that pores of the sample are shaped like layers characterized by an equally probable alignment in space. The layers are longer than 40 μm and vary in thickness from 200 to more than 1000 A; in this case, regions of different thickness are randomly distributed over the layer. The thinner the layer, the more the shape of layer portions of different thicknesses deviates from spherical.

A thermophysical study of the melting process in alkyl chain metal n-alkanoates: The thallium (I) series

The peculiar thermal behavior of the thallium(I) n-alkanoates series (consisting in several transitions between polymorphic and mesomorphic phases) in comparison with other metallic n-alkanoates series is stated. The allowance of highly accurate adiabatic heat capacity data permits a study of the CH2 contributions to the lattice heat capacity curve at low temperature. Moreover, in this series an anomalous gradual enhancement of the lattice heat capacity has been interpreted from vibrational spectroscopy results as a noncooperative effect due to the internal hindered rotation of the alkyl chain (formation of gauche defects, even in the solid state). The thermodynamics of the “stepwise melting process” from the totally ordered solid at low temperature to the isotropic liquid is based on a revised lattice heat-capacity curve. This was used to evaluate the energy and entropy not only of the clear first order transitions present in the series but also of the described noncooperative effect. The CH2 enthalpy and entropy contribution for this series is estimated and a comparison with the published values for other series is carried out. Moreover, the texture of the mesophases is revealed by polarized light microscopy.

Determination of Trace Elements in an Arctic Ice Core by ICP/MS with a Desolvated Micro-concentric Nebulizer.

Concentrations of trace elements in an ice core obtained in the polar region have been determined by inductively coupled plasma mass spectrometry (ICP-MS) . For trace metals in the ice core, sample uptake and high sensitivity for analysis are also important due to the limited volume of sample and the low concentrations of analytes. A desolvated micro-concentric nebulizer (MCN-6000), which is a recent development and offers high nebulizer efficiency at low sample consumption volume, in combination with ICP-MS, permitted multi-element determination of ppt levels of Al, V, Cr, Fe, Cu, Zn, As, Ag, Cd, Pb and U within a 2ml sample from a ice core obtained from the Vestfonna ice cap (89° 58' N, 21° 02' E) in Nordaustlandet, Svalbard. The contamination on the ice core exterior was removed with a stepwise melting process. The concentrations of Al, Fe, Cu, Zn and Pb were determined from the results of this analysis.

Effect of various ions on the stepwise melting of plasmid DNA.

The effect of anions and cations on the stepwise melting of plasmid DNA was studied by means of differential scanning calorimetry. The melting profiles of DNA are different depending upon the type of anions; oxoacids and non-oxoacids. With an increase in the concentration of cations, the melting temperature of DNA increases, passes through a maximum, and then decreases.