Determination Of Melting Points Research Articles

Green Synthesis of Quinazolinones via Selective Electro‐oxidation Using Iron Electrode and NaCl Electrolyte as an Eco‐friendly Electrolyte

AbstractPrimary alcohols 2(a–h) and o‐aminobenzamides 1(a–h) can be selectively oxidized electrochemically to yield dihydroquinazolinone 4(a–h) and quinazolinones 5(a–h) in an efficient and chemoselective manner. This methodology employs sodium chloride (NaCl) 3(a) as a co‐catalyst and electricity as the oxidizing agent, utilizing cost‐effective and commercially available materials such as Graphite anode, Iron (Fe) cathode, and isopropyl alcohol (iPrOH) as a solvent and weak base. The synthesis yields various quinazolinone derivatives with diverse structural characteristics in good quantities, showcasing the method‘s broad applicability. This approach facilitates the production of a range of dihydroquinazolinones and quinazolinones (24 examples), highlighting its versatility and compatibility with different functional groups. Characterization of the synthesized derivatives included CHN analysis, 1HNMR spectroscopy, and determination of melting points.

Is it possible to overheat ice? The activated melting of TIP4P/Ice at solid–vapour coexistence.

A widely accepted phenomenological rule states that solids with free surfaces cannot be overheated. In this work we discuss this statement critically under the light of the statistical thermodynamics of interfacial roughening transitions. Our results show that the basal face of ice as described by the TIP4P/Ice model can remain mechanically stable for more than one hundred nanoseconds when overheated by 1 K, and for several hundreds of nanoseconds at smaller overheating despite the presence of a significant quasi-liquid layer at the surface. Such time scales, which are often of little experimental significance, can become a concern for the determination of melting points by computer simulations using the direct coexistence method. In the light of this observation, we reinterpret computer simulations of ice premelting and show that current results for the TIP4P/Ice model all imply a scenario of incomplete surface melting. Using a thermodynamic integration path, we reassess our own estimates for the Laplace pressure difference between water and vapour. These calculations are used to measure the disjoining pressure of premelting liquid films and allow us to confirm a minimum of the interfacial free energy at finite premelting thickness of about one nanometer.

Alloy Crystal Structure and Volumetric Mass Density Analysis

Volumetric mass density and changes in crystal structure analysis of Sn-xBi alloy and Sn-xBi-yAl alloys have been conducted to enhance our understanding of these materials. The Sn-xBi alloy, with various compositions including Sn-0Bi, Sn-10Bi, Sn-30Bi, Sn-52Bi, and Sn-70Bi, and the Sn-xBi-yAl alloys, with compositions including Sn-52Bi-0.05Al, Sn-52Bi-0.11Al, Sn-52Bi-0.14Al, Sn-52Bi-0.19Al, and Sn-52Bi-0.25Al, were synthesized for this research. The selection of Sn-xBi-yAl compositions was based on the optimal composition of Sn-xBi alloys, specifically Sn-52Bi, which possesses the lowest melting point at 142.8°C. The determination of melting points was carried out using the Differential Scanning Calorimetry (DSC) method. Crystal structure characterization was accomplished using X-ray diffraction (XRD) techniques, with subsequent analysis performed through the Generalized Structure Analysis System (GSAS) method. These investigations are pivotal as they provide insights into the material properties and structural changes in Sn-xBi and Sn-xBi-yAl alloys, which have significant implications in various industrial applications and technological advancements. The results of this research are expected to contribute to the optimization of these alloy systems, leading to improved performance and potential innovations in materials science and engineering.

Crystallinity and perfection in ethylene vitrimers probed by combined calorimetry, scattering, and time-domain NMR

The kinetics of crystallization and crystal-crystal transformations in ethylene vitrimers are studied by time-domain NMR. These vitrimers previously exhibited polymorphic transition of crystal structures, which are shown here to be distinguishable by NMR via their dipolar line widths based upon different proton densities and fast internal motions. The conditions under which the polymorphs are formed and interconvert are identified via time-resolved NMR experiments, with a focus on recrystallization after full and partial melting. DSC experiments are used to clarify an unexpected superheating effect, which challenges the determination of actual melting points. We further identify a strong memory effect in isothermal (re)crystallization. Implications of the dynamic nature of the vitrimers in relation to the kinetics of crystallization are discussed. We find that internal perfecting of crystals, enabled by the vitrimeric exchange process, can have a large effect on the DSC-detected melting enthalpy without change in overall crystallinity.

Piperidinium and Pyrrolidinium Ionic Liquids as Precursors in the Synthesis of New Platinum Catalysts for Hydrosilylation

Six new air-stable anionic platinum complexes were synthesized in simple reactions of piperidinium [BMPip]Cl or pyrrolidinium [BMPyrr]Cl ionic liquids with platinum compounds ([Pt(cod)Cl2] or K2[PtCl6]). All these compounds were subjected to isolation and spectrometric characterization using NMR and ESI-MS techniques. Furthermore, the determination of melting points and thermal stability of the above derivatives was performed with the use of thermogravimetric analysis. The catalytic performance of the synthesized complexes was tested in hydrosilylation of 1-octene and allyl glycidyl ether with 1,1,1,3,5,5,5-heptamethyltrisiloxane. The study has shown that they have high catalytic activity and are insoluble in the reaction medium which enabled them to isolate and reuse them in consecutive catalytic cycles. The most active complex [BMPip]2[PtCl6] makes it possible to conduct at least 10 catalytic runs without losing activity which makes it an attractive alternative not only to commonly used homogeneous catalysts, but also to heterogeneous catalysts for hydrosilylation processes. The activity of the studied catalysts is also affected by the kind of anion and, to some extent, the kind of cation.

Using fiber-optic sensors to give insight into liquid-solid phase transitions in pure fluids and mixtures

Fiber optic sensors offer a new and unique way to detect and analyze phase transitions, due to their small thermal mass and inert material. This paper presents and demonstrates a dual-sensor system to detect and analyze phase transitions in pure water and aqueous ethanol mixtures. With a multi-mode interferometer based on a thin-core fiber, and a fiber Bragg grating sensor, it is possible to differentiate between refractive index, temperature and strain in the sample system. The three parameters supply important information during a phase transition, but also in the characterization of the liquid and solid phases. Binary mixtures at non-eutectic concentrations are expected to separate into a solid phase consisting of only one constituent, and the sensors are demonstrated to be able to estimate the concentration in the remaining liquid phase. For pure water and low ethanol concentrations, the progression of the phase transition was found to be limited by heat transfer, whereas for higher concentrations the process becomes mass transfer limited. In pure water, strain due to thermal expansion of the ice hinderes temperature measurements in the solid phase. The reflection-based geometry enables insertion probes that measure the properties inside the samples, with little or no disturbance of the system. By interpreting the sensor response in a known system, the sensing capabilities in unknown substances can be evaluated. The sensor system is able to capture the dynamics of the phase transition, which can be difficult to predict theoretically due to the multitude of contributing effects. Analysis of the combined signal from the two sensors enables the determination of the ethanol mixture melting points in agreement with the literature, within the uncertainty of the system (0.25 K).

A machine learning workflow for molecular analysis: application to melting points

Computational tools encompassing integrated molecular prediction, analysis, and generation are key for molecular design in a variety of critical applications. In this work, we develop a workflow for molecular analysis (MOLAN) that integrates an ensemble of supervised and unsupervised machine learning techniques to analyze molecular data sets. The MOLAN workflow combines molecular featurization, clustering algorithms, uncertainty analysis, low-bias dataset construction, high-performance regression models, graph-based molecular embeddings and attribution, and a semi-supervised variational autoencoder based on the novel SELFIES representation to enable molecular design. We demonstrate the utility of the MOLAN workflow in the context of a challenging multi-molecule property prediction problem: the determination of melting points solely from single molecule structure. This application serves as a case study for how to employ the MOLAN workflow in the context of molecular property prediction.

The N-terminal peptide of the transglutaminase-activating metalloprotease inhibitor from Streptomycesmobaraensis accommodates both inhibition and glutamine cross-linking sites.

Streptomycesmobaraensis is a key player for the industrial production of the protein cross-linking enzyme microbial transglutaminase (MTG). Extra-cellular activation of MTG by the transglutaminase-activating metalloprotease (TAMP) is regulated by the TAMP inhibitory protein SSTI that belongs to the large Streptomyces subtilisin inhibitor (SSI) family. Despite decades of SSI research, the binding site for metalloproteases such as TAMP remained elusive in most of the SSI proteins. Moreover, SSTI is a MTG substrate, and the preferred glutamine residues for SSTI cross-linking are not determined. To address both issues, that is, determination of the TAMP and the MTG glutamine binding sites, SSTI was modified by distinct point mutations as well as elongation or truncation of the N-terminal peptide by six and three residues respectively. Structural integrity of the mutants was verified by the determination of protein melting points and supported by unimpaired subtilisin inhibitory activity. While exchange of single amino acids could not disrupt decisively the SSTI TAMP interaction, the N-terminally shortened variants clearly indicated the highly conserved Leu40-Tyr41 as binding motif for TAMP. Moreover, enzymatic biotinylation revealed that an adjacent glutamine pair, upstream from Leu40-Tyr41 in the SSTI precursor protein, is the preferred binding site of MTG. This extension peptide disturbs the interaction with TAMP. The structure of SSTI was furthermore determined by X-ray crystallography. While no structural data could be obtained for the N-terminal peptide due to flexibility, the core structure starting from Tyr41 could be determined and analysed, which superposes well with SSI-family proteins. ENZYMES: Chymotrypsin, EC3.4.21.1; griselysin (SGMPII, SgmA), EC3.4.24.27; snapalysin (ScNP), EC3.4.24.77; streptogrisin-A (SGPA), EC3.4.21.80; streptogrisin-B (SGPB), EC3.4.21.81; subtilisin BPN', EC3.4.21.62; transglutaminase, EC2.3.2.13; transglutaminase-activating metalloprotease (TAMP), EC3.4.-.-; tri-/tetrapeptidyl aminopeptidase, EC3.4.11.-; trypsin, EC3.4.21.4. DATABASES: The atomic coordinates and structure factors (PDB 6I0I) have been deposited in the Protein Data Bank (http://www.rcsb.org).

Estimation of melting points of fatty acids using homogeneously hybridized support vector regression

This work develops a hybridized support vector regression (HSVR)-based model for accurate estimation of melting points of fatty acids using their molecular weights and the number of carbon–carbon double bond as descriptors. The development of HSVR-based model is characterized with two stages. The first stage involves training and testing SVR using test-set-cross validation technique with molecular weights and the number of carbon–carbon double bond as descriptors, while the second stage utilizes the estimated melting points obtained from the first stage as descriptor for further training and testing of SVR. The proposed hybrid system therefore demonstrates a better predictive and generalization ability than ordinary SVR. Furthermore, the melting points of sixty-two fatty acids estimated using the proposed HSVR-based model show persistence closeness with the experimental values than the results of other existing predictive models for fatty acids melting points estimation such as Guijie et al. model and Guendouzi model. The developed HSVR-based model is also characterized with higher value of coefficient of correlation and lower value of mean absolute error than that of the existing predictive models. Superiority of the developed HSVR-based model over the existing predictive models in terms of the ease of obtaining its descriptors and the accuracy of its estimates is advantageous to unravel estimation challenges associated with determination of fatty acids melting points.

SYNTHESIS AND IDENTIFICATION OF SOME HYDROXAMIC DERIVATIVES AND STUDYING THEIR THERMO AND PHOTO DEGRADATION

The aim of this research is to prepare and study the kinetics effect of temperature and photochemical reactions of the hydroxamic acid derivatives of diethyl succinate through the interaction of alkyl halides and diethyl succinate in the presence of strong base. The transformation of ester to hydroxamic acid derivatives by the direct interaction between the ester hydroxyl amine hydrochloride in the presence of sodium hydroxide. Identification of the prepared compounds by determination of molecular weights and melting points . In addition to I.R and U.V spectroscopic absorption of the prepared compounds . Effect of temperature on the dissociation constant of hydroxamic acids derivatives in aqueous solutions. Ionic conductivity of these solutions were measured at different temperatures. It is found that the value of the dissociation constant of hydroxamic acid derivatives increase with temperature. The effect of radiation on the dissociation constant of hydroxamic acid derivatives through the preparation of series of solutions . Then these solutions were exposed to radiation at the wave length (λ=254nm), then the ionic conductivity was measured at different times and the dissociation constant (Ka, pK) was determined. It is found that dissociation constant increased with will time increment .

Determination of Complete Melting and Surface Premelting Points of Silver Nanoparticles by Molecular Dynamics Simulation

A molecular dynamics simulation based on the embedded-atom method was conducted at different sizes of single-crystal Ag nanoparticles (NPs) with diameters of 4 to 20 nm to find complete melting and surface premelting points. Unlike the previous theoretical models, our model can predict both complete melting and surface premelting points for a wider size range of NPs. Programmed heating at an equal rate was applied to all sizes of NPs. Melting kinetics showed three different trends that are, respectively, associated with NPs in the size ranges of 4 to 7 nm, 8 to 10 nm, and 12 to 20 nm. NPs in the first range melted at a single temperature without passing through a surface premelting stage. Melting of the second range started by forming a quasi-liquid layer that expanded to the core, followed by the formation of a liquid layer of 1.8 nm thickness that also subsequently expanded to the core with increasing temperature and completed the melting process. For particles in the third range, the 1.8 nm liquid laye...

SYNTHESIS AND IDENTIFICATION FOR SOME FERRIC COMPLEXES OF HYDROXAMIC ACID.

The aim of this research is to prepare and identification of the hydroxamic acid derivatives of diethyl succinate which are considered as selective ligands of the Iron (III) . The synthesis of hydroxamic acid derivatives was performed as described in the preparation of the complex of ferric ion( Fe3+) with hydroxamic acid compound and other compounds through the interaction of hydroxamic acid compound with ferric chloride FeCl3 in the presence of basic medium. Identification of the prepared compounds through determination of molecular weights and melting points as will as I.R and U.V spectroscopic absorption. .Also, determination stoichiometric ratio between the derivatives of hydroxamic acids compounds and ferric ion( Fe3+ ) by using the mole – ratio method showed that the ratio between metal and ligand is (1:3) (metal : ligand) .

Investigations into the polymorphic properties of N,N-dimethyltryptamine by X-ray diffraction and differential scanning calorimetry

The powerful psychoactive features of N,N-dimethyltryptamine (DMT) have sparked the imagination of many research disciplines for several decades. One of the key chemical features associated with compound identity is the determination of melting points. The descriptions of both melting points and morphology associated with DMT free base have long been a source of interest and discussion, especially when considering that these values encountered in the scientific literature range dramatically between 38–40°C and 73–74°C, respectively. Such variations in reported melting points suggest that DMT may exist in two or more polymorphic forms and it was the aim of this study to examine the potential polymorphism of DMT via X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC), including fast scan DSC. DMT samples were prepared following extraction from Mimosa tenuiflora inner barks or by laboratory synthesis and then its crystals were recrystallized from solutions of the alkaloid using either hexane or acetonitrile. Irrespective of source, crystals originating from synthesis were predominantly white crystals obtained using crystallization from hexane, whereas yellow samples following recrystallization with acetonitrile. Irrespective of source or solvent, two polymorphs appeared to exist with melting points, determined by DSC, of 57°C to 58°C for Form I and 45°C to 46°C for Form II. Estimates for their enthalpies were 91.9±2.4Jg−1 for Form I and 98.3±2.8Jg−1 for Form II. Form II converted to Form I during DSC; conversion was thus prevented by fast scanning rates of 100°Cmin−1. A transition temperature (Tg) in the range −21°C (2°Cmin−1) to −13°C (100°Cmin−1) was determined depending on DSC scanning rate. Its closeness to the melting point indicates a tendency of Form II to convert to Form I on storage, a phenomenon that was also facilitated by grinding. This study indicates that the presence of differently colored DMT free base crystals obtained from recrystallization might also point towards the existence of polymorphs rather than just the presence of impurities.

New Apparatus: A Reflected Light Melting-Point Apparatus

Abstract Melting-point determinations in organic chemistry laboratories have traditionally been made by observation of the material in a capillary tube, suspended in various liquid baths. The utilisation of the high conductivity of copper in gas-heated and later electrically-heated copper blocks, gave the advantages of determination of melting-points over wide temperature ranges, without fumes and corrosion, and of close observation of the melting material by means of a lens. Such blocks have been described by many workers1, and when used with a thermometer calibrated in the block against A.R. chemicals such as those listed by Vogel2, give melting-points which are reproducible and accurate. A disadvantage of blocks, however, has been that the necessary illumination of the sample has been achieved by light shining through the block and thus directly into the observer’s eye. In a modification developed in the laboratories of May and Baker, Ltd., and now made available by Townson and Mercer, Ltd., two horizontal holes are drilled in the block so as to converge on the thermometer bulb. The sample is arranged immediately in front of the bulb and illuminated through one of the horizontal tubes by a shaded 6-volt bulb; the surface of the thermometer bulb aids in reflecting light through and round the sample, which is viewed by means of a lens adjusted at the other horizontal hole. This gives an extremely clear view of the behaviour of even a single crystal without eye-strain, particularly when a series of determinations is made in succession. The apparatus now commercially available as “Type 2” is compact and at the same time embodies a number of refinements in the electrical circuit designed to facilitate the determination of all melting-points. The block, adjustable for height, is mounted on a vertical rod rising from the back of a sheet metal case. The top of this case bears an ebonite panel on which is mounted a self-cleaning rotary switch, a spring-loaded push button, and a movable jack with three sockets marked H, L and M. The rotary switch selects the tappings on the transformer and thus the temperature to which the block is to be heated; the jack controls the rate of rise in temperature the sockets corresponding to high, low and medium rates, medium being regarded as normal. The spring-loaded button, when depressed, gives an approximately 50 per cent. increase in wattage input to the heating windings over the value for the maximum input from the highest tapping on the rotary switch, and thus enables quick heating of the block for readings at higher temperatures. The spring loading ensures that no damage can be done to electrical windings or thermometer, since the observer must be present while it is operated and it cannot therefore be left on by mistake. The tappings have been arranged for smooth transfer before the rate of rise on the next lowest one has become slow and the instrument has been designed to cool at such a rate that after switching off there is not an undue delay before the next determination can be made.

Determination of S–L phase transitions under gas pressure

The use of super-critical fluids as media for the formation of powdered materials is one of recent developments of supercritical fluid technologies. Driving force for understanding and design of a high pressure micronization processes is the knowledge of solid–liquid–gas (S–L–G) equilibrium. The results of experimental research verify the theory that the type of S–L–G equilibrium could be used to predict the applicability of high pressure micronization and to optimize the choice of operation parameters. It is very important to understand the influence of pressure on the melting point of the substance in the presence of gas and phase equilibrium data of the system. This work aims to review the published literature dealing with determination of melting points under pressure. Paper describes different methods and apparatus for the determination of S–L–G transitions and different systems substance/super-critical fluids.

A NEW CLASS OF IONIC SOLVENTS, ELECTROLYTES AND ENGINEERING FLUIDS BASED ON 1,3-ALKYLMETHYL-1,2,3-BENZOTRIAZOLIUM SALTS

A new series of ionic liquids based on 1,3-alkylmethyl-1,2,3-benzotriazolium cation has been prepared. The spectroscopic, physical and electrochemical characteristics of this family of salts have been investigated with respect to potential usage as ionic solvents, electrolytes and engineering fluids. Incorporation of diverse anions including weak coordinating anion and pseudohalide with this benzotriazolium cation produces ionic liquids with advantageously low melting points and good thermal stability. Thermal analyses of these very stable salts included the determination of melting points (-65 to 164 oC) and decomposition temperatures (up to 291 oC). The electrochemical windows of representative benzotriazolium species has been investigated by cyclic voltammetry and determined to be ~ 3 V. The X-ray single crystal and spectroscopic studies revealed that weak hydrogen-bonding interactions between the benzotriazolium ring protons and the anions are present both in the solid state as well as in solution. Keywords: ionic liquids, X-ray single crystal, thermal analysis, electrochemical analysis, benzotriazolium salt

Efficient determination of crystallisation and melting points at low cooling and heating rates with novel computer controlled equipment

We studied melting and solidification points of 14 pure solvents and two ionic liquids with a recently constructed automatic computer-controlled equipment, which is able to record simultaneously temperature–time functions of up to 30 samples at very low heating and cooling rates down to 1.5 K · h −1. The effects of viscosity of the studied samples and of carbon fibres as an added crystallisation aid were also investigated. Equilibrium temperatures for the solid–liquid phase transition are in accordance with literature for materials that were often checked, such as acetonitrile, showing the quality of our new equipment, whereas the value of the transition temperature of some other materials differed from published results. It is shown that both the viscosity of the material and carbon fibres as crystallisation aids have an effect on supercooling. The value given for the equilibrium point of the ionic liquid trioctylmethylammonium trifluorocetate T tr = (285.62 ± 0.1) K is new.

Cyclohexanone-aniline-formaldehyde resins - synthesis and characterization

Cyclohexanone-aniline-formaldehyde resins, which contain functional groups in the polymeric chain, were prepared by acid catalysis condensation. Mixture of toluene and N-methylpyrrolidone was used both as reaction medium and as carrier for aqueous condensation. The resins were characterized by determination of melting points, viscosity measurement and elemental analysis (contents of nitrogen, N%). Their structure was established by means of IR and 1 H NMR spectroscopy. The obtained polymers have low molecular weights and a moderate solubility in medium and highly polar organic solvents. Thermal studies pointed out that these polymers undergo 2-5% weight loss up to 210°C for resins with low content of aniline, whereas weight loss starts at 220-240°C for resins with low content in cyclohexanone. Activation energy for the thermal degradation is observed to be within the range 37.6-41.7 kJ/mol.

Thermal characterization of polycarbonate/polycaprolactone blends

In this work, we prepared blends of bisphenol A polycarbonate (PC) and poly(∈-caprolactone) (PCL) in a wide composition range by melt mixing and solution mixing. Two different molecular weights of PCL were used (nominally, 10.000 g/mol, PCL10, and 80.000 g/mol, PCL80). The thermal behavior of both systems was studied via differential scanning calorimetry under dynamic and isothermal conditions. The blends were miscible in the entire composition range in the liquid and amorphous states, as indicated by the single glass-transition temperature (T g ) exhibited by both the PC/PCL10 and PC/PCL80 blends. The compositional variation of the T g was accurately described by the Fox equation for the PC/PCL80 blends, whereas slight deviations from this equation were exhibited by the PC/PCL10 blends. For blend compositions containing 40% or more PCL, either one or both blend components crystallized. Crystallization occurred during cooling from the melt or during subsequent heating in the form of cold crystallization. Although PCL crystallization was reduced and its crystallization rate decreased with the addition of PC, PCL was a very effective macromolecular plasticizer for PC, to the extent that crystallization during the scan was detected for some blend compositions. Isothermal crystallization experiments allowed the determination of equilibrium melting points (T o m ) by the Hoffman-Weeks extrapolation method. A T o m depression was found for both PCL and PC components as the content of the other blend component was increased. The Avrami equation was closely obeyed by both blend components during the isothermal overall crystallization kinetics up to crystalline conversion degrees of 60-70% and with values of Avrami indices ranging from 3 to 4, depending on the crystallization temperature employed.

Determination of melting points for A2B6 compounds

A new technique of rapid heating, recording both the melting and evaporation processes in an open system was proposed to determine the melting points of A2B6 (A=Zn, Cd) compounds. The different melting character and temperatures were detected for the equiatomic and non-stoichiometric composition of A2B6. A fit of these data to previously obtained results was considered and the reasons for their discrepancy were discussed.