Rise In Melting Temperature Research Articles

NMR characterization and ligand binding site of the stem-loop 2 motif from the Delta variant of SARS-CoV-2.

The stem-loop 2 motif (s2m) in SARS-CoV-2 (SCoV-2) is located in the 3'-UTR. Although s2m has been reported to display characteristics of a mobile genomic element that might lead to an evolutionary advantage, its function has remained unknown. The secondary structure of the original SCoV-2 RNA sequence (Wuhan-Hu-1) was determined by NMR in late 2020, delineating the base-pairing pattern and revealing substantial differences in secondary structure compared to SARS-CoV-1 (SCoV-1). The existence of a single G29742-A29756 mismatch in the upper stem of s2m leads to its destabilization and impedes a complete NMR analysis. With Delta, a variant of concern has evolved with one mutation compared to the original sequence that replaces G29742 by U29742. We show here that this mutation results in a more defined structure at ambient temperature accompanied by a rise in melting temperature. Consequently, we were able to identify >90% of the relevant NMR resonances using a combination of selective RNA labeling and filtered 2D NOESY as well as 4D NMR experiments. We present a comprehensive NMR analysis of the secondary structure, (sub)nanosecond dynamics, and ribose conformation of s2m Delta based on heteronuclear 13C NOE and T 1 measurements and ribose carbon chemical shift-derived canonical coordinates. We further show that the G29742U mutation in Delta has no influence on the druggability of s2m compared to the Wuhan-Hu-1 sequence. With the assignment at hand, we identify the flexible regions of s2m as the primary site for small molecule binding.

Masterbatch of Chitosan Nanowhiskers for Preparation of Nylon 6,10 Nanocomposite by Melt Blending.

Composite materials have been extensively studied to optimize properties such as lightness and strength, which are the advantages of plastics. We prepared a highly concentrated (30 wt %) nylon/chitosan nanowhisker (CSW) masterbatch by blending nylon 6,10 and CSW by solvent casting to achieve high dispersion efficiency while considering an industrial setting. Subsequently, 0.3 wt % nylon/CSW nanocomposites were prepared with a large quantity of nylon 6,10 via melt blending. During preparation, the materials were stirred in the presence of formic acid at different times to investigate the effect of stirring time on the structure of the CSW and the physical properties of the composite. The formation of nanocomposites by the interactions between nylon and CSW was confirmed by observing the change in hydrogen bonding using FT-IR spectroscopy and the rise in melting temperature and melting enthalpy through differential scanning calorimetry. The results demonstrated increases in complex viscosity and shear thinning. The rheological properties of the composites changed due to interactions between CSW and nylon, as indicated by the loss factor. The mechanical properties produced by the nanocomposite stirred for 1.5 h were superior, suggesting that formic acid caused minimal structural damage, thus verifying the suitability of the stirring condition.

Development of lead free solder for electronic components based on thermal analysis

In the post COVID-19 virus era, online teaching and work from home have develop a common trends so the demand of electronic component rapidly increases. The development of lead-free solder has grown rapidly because various environmental legislations have enforced laws to restrict the use of Lead (Pb), Mercury (Hg) and Cadmium (Cd), etc because this is hazardous materials. In electronic and electrical industries. Many lead-free solder composition such as Sn - Bi, Sn - Cu, Sn - Zn, Sn - Ag, Zn - Bi, Sn – Ag - Cu, Sn – Zn - Bi, Sn – Cu - Bi, Sn – Cu - Ni etc. have been developed as a replacement of Sn - Pb solder. Researcher are facing challenges due to rise in melting temperature in lead-free solder (LFS) and the formation of intermetallic compound. This review paper aimed to summarise the thermal properties of lead free solders (LFS) and analyse the effect of addition of various elements and reinforcement in Sn based lead free solder (LFS).

Investigation of the Effect of Filler Concentration on the Flow Characteristics of Filled Polyethylene Melts

Abstract All polymeric slurries that have a high concentration of filler are shear thinning. Shear thinning is an important characteristic of polymers, filled and unfilled, because it enables an increase in the throughput, shear rate in a die or an injection molding system without having to use substantially more power to increase the flow rate. Newtonian fluid-based slurries show an increase in shear thinning as the concentration of “filler” increases above the percolation threshold. As particle maximum packing concentration is approached the slurries begin to approach a perfect pseudoplastic fluid. In some cases, the shear thinning characteristics of a filled polymer do not increase substantially as the filler loading is increased. This is a quite different response than in Newtonian fluid-based slurry. Therefore, it is important to understand the materials engineering interactions that control shear thinning so that process flow models can better predict the performance of filled polymer systems. Highly filled polymers can have processing issues, including high screw shaft torque, energy consumption, die pressure and melt temperature rise. Previous theoretical developments and experimental evaluations of highly filled polymer melts showed that the rheology can be effectively described with a percolation model. In this work, capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide fillers are reported using percolation theory concepts. The theoretical treatment of the rheology as a particulate percolating system with power-law behavior is used to analyze capillary rheometer data. The observed effects of resin molecular weight, filler type and size on rheology are described. Engineers that design and debottleneck polymer processes need to utilize the polymer viscosity at the minimum process shear rate to determine the smallest motor that will allow the process to run; in addition, the shear thinning characteristics of the polymer are used to indicate how much increased production may be possible with a given motor size. Thus, some examples of expected effects on melt processing are also presented.

Increasing thermal stability of glutamate decarboxylase from Escherichia. coli by site-directed saturation mutagenesis and its application in GABA production

Gamma-amino butyric acid (GABA) is an important bio-product used in pharmaceuticals, functional foods, and a precursor of the biodegradable plastic polyamide 4 (Nylon 4). Glutamate decarboxylase B (GadB) from Escherichia. coli is a highly active biocatalyst that can convert l-glutamate to GABA. However, its practical application is limited by the poor thermostability and only active under acidic conditions of GadB. In this study, we performed site-directed saturation mutagenesis of the N-terminal residues of GadB from Escherichia coli to improve its thermostability. A triple mutant (M6, Gln5Ile/Val6Asp/Thr7Gln) showed higher thermostability, with a 5.6 times (560%) increase in half-life value at 45 °C, 8.7 °C rise in melting temperature (Tm) and a 14.3 °C rise in the temperature at which 50% of the initial activity remained after 15 min incubation (T1550), compared to wild-type enzyme. Protein 3D structure analysis showed that the induced new hydrogen bonds in the same polypeptide chain or between polypeptide chains in E. coli GadB homo-hexamer may be responsible for the improved thermostability. Increased thermostability contributed to increased GABA conversion ability. After 12 h conversion of 3 mol/L l-glutamate, GABA produced and mole conversion rate catalyzed by M6 whole cells was 297 g/L and 95%, respectively, while those by wild-type GAD was 273.5 g/L and 86.2%, respectively.

Flow Behavior of PP-Polymer Nanocomposites in Capillary and Injection Molding Dies

Abstract For simulation of thin-wall injection molding, accurate viscosity data measured at shear rates up to 800,000 s−1 and more are important, but not available in any commercial material database. Such data can be measured on conventional injection molding machines with the help of a rheological mold, which is constructed like a standard injection mold with interchangeable dies. It enables operators to measure viscosity in time on their own machines at practically relevant shear rates (from 102 s−1 to 2 × 106 s−1). A special feature allows measuring the pressure dependency of viscosity using closed-loop counter pressure control. Experimental data are evaluated taking into account the melt temperature rise due to dissipative heating. Using capillary dies having different diameters, D, and length-to-diameter L/D ratios, a full rheological characterization has been carried out for a polypropylene-filled nanocomposite, and the experimental data have been fitted both with a viscous model (Cross) and a viscoelastic one (the Kaye – Bernstein, Kearsley, Zapas/Papanastasiou, Scriven, Macosko or K-BKZ/PSM model). Four injection molding dies have been also used to reach apparent shear rates up to 800,000 s−1. Particular emphasis has been given on the pressure-dependence of viscosity. It was found that only the viscoelastic simulations were capable of reproducing the experimental data well, while any viscous modeling always underestimates the pressures, especially at the higher apparent shear rates and L/D ratios.

Rational Design of Disulfide Bonds Increases Thermostability of a Mesophilic 1,3-1,4-β-Glucanase from Bacillus terquilensis.

1,3–1,4-β-glucanase is an important biocatalyst in brewing industry and animal feed industry, while its low thermostability often reduces its application performance. In this study, the thermostability of a mesophilic β-glucanase from Bacillus terquilensis was enhanced by rational design and engineering of disulfide bonds in the protein structure. Protein spatial configuration was analyzed to pre-exclude the residues pairs which negatively conflicted with the protein structure and ensure the contact of catalytic center. The changes in protein overall and local flexibility among the wild-type enzyme and the designated mutants were predicted to select the potential disulfide bonds for enhancement of thermostability. Two residue pairs (N31C-T187C and P102C-N125C) were chosen as engineering targets and both of them were proved to significantly enhance the protein thermostability. After combinational mutagenesis, the double mutant N31C-T187C/P102C-N125C showed a 48.3% increase in half-life value at 60°C and a 4.1°C rise in melting temperature (Tm) compared to wild-type enzyme. The catalytic property of N31C-T187C/P102C-N125C mutant was similar to that of wild-type enzyme. Interestingly, the optimal pH of double mutant was shifted from pH6.5 to pH6.0, which could also increase its industrial application. By comparison with mutants with single-Cys substitutions, the introduction of disulfide bonds and the induced new hydrogen bonds were proved to result in both local and overall rigidification and should be responsible for the improved thermostability. Therefore, the introduction of disulfide bonds for thermostability improvement could be rationally and highly-effectively designed by combination with spatial configuration analysis and molecular dynamics simulation.

Plasmid DNA mono-ion complex stabilized by hydrogen bond for in vivo diffusive gene delivery.

Our original concept of the mono-ion complex (MIC) between plasmid DNA (pDNA) and a monocationic biocompatible polymer has been stabilized by hydrogen bond formation. To form the hydrogen bond with pDNA, ω-amide-pentylimidazolium end-modified poly(ethylene glycol), that is, APe-Im-PEG, has been synthesized. Agarose gel retardation assay and circular dichroism measurement have revealed that the MIC between pDNA and APe-Im-PEG has been stabilized by the hydrogen bond between pDNA and the ω-amide group and that the stable MIC has surprisingly further migrated into gel, as compared with naked pDNA. The rise of melting temperature suggests that the specific hydrogen bond forms between an adenine-thymine base pair and the ω-amide group. The resulting pDNA MIC with APe-Im-PEG has enhanced gene expression by intramuscular administration in mice, as compared with a poly(ethylenimine) polyion complex (PIC). These results suggest that the pDNA MIC is diffusive in vivo administration site, as compared with pDNA PICs. Our methodology for MIC stabilization by a ω-amide group is expected to offer superior supramolecular systems to those by ubiquitous PICs for in vivo diffusive gene delivery.

Slip Heating in Die Drool with Viscous Dissipation

Abstract Plastics can build-up on the die lip during extrusion. This phenomenon is called die drool and can be costly for plastics producers, requiring periodic shutdowns for die cleaning. Die drool has been attributed to the cohesive fracture of the melt into a drool layer and a bulk layer. The bulk layer slips on the drool layer after fracture, resulting in heating at the slip interface, called slip heating. The heat generated through slip heating can contribute to polymer thermal degradation, and to the die drool degradation. The impact of slip heating on die temperature rise has been investigated by neglecting viscous dissipation (Gilbert and Giacomin, 2014). This work considers viscous dissipation and its importance to slip heating. We find that viscous dissipation and slip heating contribute equally to the melt temperature rise, and we conclude with a worked example showing the importance of these two heating sources during polymer processing. We also develop two sufficient conditions for the accurate use of our results, Pé ≤ 1 and ∂Θ/∂ς ≪ ∂2Θ/∂ζ2.

CFD Analysis of the Frame Invariance of the Melt Temperature Rise in a Single-screw Extruder

Abstract In analytical analyses for single-screw extruders the simplified approach of rotating the barrel and keeping the screw fixed is often used instead of rotating the screw and fixing the barrel. Although the flow field is independent of the reference frame, as has already been shown to a satisfactory degree (Rauwendaal et al., 1997), the question of the dependence of the melt temperature rise on the reference frame is still being challenged, e.g. Campbell et al. (2001, 2008). In this work we develop a finite-volume CFD code allowing for the three-dimensional simulation of the flow and temperature rise in both reference frames. The question of frame invariance is addressed by simulating the flow of a Newtonian-like polycarbonate both in a two-dimensional cross-section of a single-screw extruder and in a three-dimensional model with two full turns of the screw. Our results show that the kinematics and the melt temperature rise are equal for screw- and barrel-rotation and thus independent of the reference frame. Furthermore, the presence of a clearance flow has a negligible influence on the temperature rise.

Pressure and temperature behavior of thermoplastic polymer melts during high‐pressure expansion injection molding

AbstractThe development of expansion injection molding as new technology for producing thin plastic parts has raised questions about polymer melt behavior in the process of rapid high pressure compression and expansion. To investigate those phenomena, the new in‐line injection molding machine mounted measurement system has been developed. Measuring nozzle equipped with hydraulically driven closing bolts and contact fast response pressure and infrared temperature sensors enabled us to measure the compression and expansion of polymer melts at different starting conditions. Results presented for high impact polystyrene and polyamide show that polymer melt temperature rise is linearly dependent on compression pressure as well as it is dependent on compression speed. Comparable effect of temperature fall has been recorded during the polymer expansion, resulting in no noticeable loss of dissipation energy during this reversible process. Measurements have been compared with modified 2‐domain Tait equation of state. Curve fitting analysis to manufacturer's material data show that measurements fit well with the model, even at very high compression speeds. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

一軸伸長におけるポリイソプレンゴムの結晶化と融解

The crystallization and the melting of vulcanized isoprene rubber under uniaxial deformation have been studied by the measurements of the stress, strain-temperature relation. The melting temperature increases approximately linearly with nominal stress for the rubbers crystallized at a fixed temperature and stress condition. It has been shown that the main origin of the rise in melting temperature with stress is the work of contraction upon melting rather than the entropy reduction on deformation in the molten state. The crystallization rate monotonically increases with nominal stress above the melting stress at a given temperature, while it shows a maximum against temperature at a given stress. The relation between the temperature and the nominal stress at the onset of crystallization is satisfactorily reproduced by the simplified kinetic model.

Crystallization and Melting of Polyisoprene Rubber under Uniaxial Deformation

The crystallization and the melting of vulcanized isoprene rubber under uniaxial deformation have been studied by the measurements of the stress−strain−temperature relation. The melting temperature increases approximately linearly with nominal stress for the rubbers crystallized at a fixed temperature and stress condition. It has been shown that the main origin of the rise in melting temperature with stress is the work of contraction upon melting rather than the entropy reduction on deformation in the molten state. The crystallization rate monotonically increases with nominal stress above the melting stress at a given temperature, while it shows a maximum against temperature at a given stress. The relation between the temperature and the nominal stress at the onset of crystallization is satisfactorily reproduced by the simplified kinetic model.

The effect of a new type of pin mixing section on the performance of a single‐screw extruder

AbstractThe effect of a holed‐pin mixing section on the performance of a single screw extruder was investigated and compared with a free flight and a normal pin mixing section, using a practical single‐screw extruder. The effect of axial distance between two pins in a holed‐pin mixing section on performance was also studied. Mixing ability was quantified using the statistical approach of carbon black concentration distribution in the extruded film mixed with a carbon black masterbatch. The results indicate that a free flight gives the lowest melt temperature rise, pressure drop, and driver power, but the worst mixing; a holed‐pin mixing section has better mixing ability, lower melt temperature rise, and lower driver power than a normal pin mixing section does; the value of the pressure drop of the two types of pin mixing sections is approximately identical. A longer axial distance between the two pins in a holed‐pin mixing section gives better mixing and lower melt temperature rise than a shorter one; however, when the distance is longer than a critical value, the improvement of mixing is not so outstanding; for different axial distances between two pins, no great change in pressure drop was found and the extrusion throughput has almost no great relation to the axial distance.

Synthesis and characterization of poly(urethane‐sulfone)s

AbstractEight poly(urethane‐sulfone)s were synthesized from two sulfone‐containing diols, 1,3‐bis(3‐hydroxypropylsulfonyl)propane (Diol‐333) and 1,4‐bis(3‐hydroxypropylsulfonyl)butane (Diol‐343), and three diisocyanates, 1,6‐hexamethylene diisocyanate (HMDI), 4,4′‐diphenylmethane diisocyanate (MDI), and tolylene diisocyanate (TDI, 2,4‐ 80%; 2,6‐20%). As a comparison, eight polyurethanes were also synthesized from two alkanediols, 1,9‐nonanediol and 1,10‐decanediol, and three diisocyanates. Diol‐333 and Diol‐343 were prepared by the addition of 1,3‐propanedithiol or 1,4‐butanedithiol to allyl alcohol and subsequent oxidation of the resulting sulfide‐containing diols. The homopoly(urethanesulfone)s from HMDI and MDI are semicrystalline, and are soluble in m‐cresol and hot DMF, DMAC, and DMSO. The copoly(urethane‐sulfone)s from a 1/1 molar ratio mixture of Diol‐333 and Diol‐343 with HMDI or MDI have lower crystallinity and better solubility than the corresponding homopoly(urethane‐sulfone)s. The poly(urethane‐sulfone)s from TDI are amorphous, and are readily soluble in m‐cresol, DMF, DMAC, and DMSO at room temperature. Differential scanning calorimetry data showed that poly(urethane‐sulfone)s have higher glass transition temperatures and melting points than the corresponding polyurethanes without sulfone groups. The rise in glass transition temperature is 20–25°C while the rise in melting temperature is 46–71°C. © 1994 John Wiley & Sons, Inc.

Excluded-volume effect of inert macromolecules on the melting of nucleic acids

It is shown on the basis of the excluded-volume effect that inert macromolecules may be expected to suppress the dissociation of double-helical nucleic acids into single helices and thus to raise the melting point of the double helix. The rise in melting temperature of the ribonucleic acid [poly(I).poly(C)] caused by dextran polymers and by poly(ethylene oxide) is described and compared with the theoretical prediction. Good agreement was found in respect of the extent of the rise in melting point and in respect of its dependence upon polymer length. An additional dependence upon the identify of the polymer was attributed to detailed effects of shape in solution.

Study on crystallization of nylon-6 (polycapramide): Part 2. Effect of molecular weight on isothermal crystallization kinetics

Further studies of the kinetics of primary isothermal crystallization of fractions of nylon-6 with viscosity-average molecular weights ranging from 17 000 to 49 000 are reported. The results were analysed in terms of the Avrami equation to give rate constants and the mechanism of crystallization. In accordance with theoretical assumptions the crystallization rate decreased as molecular weight and temperature increased within the investigated range of molecular weight and crystallization temperature. The relation between the logarithm of half-time of crystallization and the molecular weight is linear. The Avrami exponent n depends on the crystallization temperature and molecular weight of the fractions. Above 210°C the Avrami exponent n was constant and equal to 4–6 for various fractions, corresponding to spherical and sheaf-like growth from sporadic nucleation. Below 210°C, n was equal to 2.8–5, corresponding to spherical and sheaf-like growth from pre-determined nuclei. It has been found that the Avrami exponent n depends on the molecular weight starting from the limiting value of 32 500. For fractions with a lower molecular weight, the exponent n was not dependent on that parameter. Above that value exponent n decreased as the molecular weight increased for all crystallization temperatures. For all samples, assuming n = 4 and rise of crystallization temperature is accompanied by rise of melting temperature, linear relations for log K against T m T(ΔT) and T 2 m T(ΔT) 2 were obtained.

Theory of deformation and strain‐induced crystallization of an elastomeric network polymer

AbstractA new theory of deformation and strain induced crystallization of network polymers has been developed. The effects of lattice vacancies, variation in distribution of trans and gauche bond conformations in stretched amorphous polymers, and the crystallite orientation in the partially crystalline stretched vulcanizate were considered in the evaluation of their partition functions. Stress‐extension ratio relationships were evaluated for the amorphous and semicrystalline polymers. The rise in melting temperature due to strain induced crystallization is discussed. The new theory seems to be in closer agreement with the actual strain‐induced crystallization process than earlier research.

Crystallization in Stretched Polymer Networks. I. trans-Polychloroprene

Abstract Changes in tensile stress afford a simple means of studying the rates of crystallization and the melting temperatures in crosslinked polymers subjected to simple extension. The form and magnitude of the stress changes in networks of trans-polychloroprene are closely similar to those observed for cis-1:4-polyisoprene and cis-l:4-polybutadiene networks. They are in accord with the formation of oriented crystallites and incompatible with folded chain crystallization at extensions as low as 15 per cent. It seems likely that the present networks do not crystallize by chain folding even in the unstretched state. The large increases in rate of crystallization with extension are approximately accounted for by corresponding increases in the equilibrium melting temperature. Direct measurements of the melting temperature show similar rises with extension. The rise in melting temperature is in good agreement with Flory's theoretical treatment of oriented crystallization at extension ratios of three and higher (when the crystallite orientation is complete) for three networks having different degrees of crosslinking. When referred to a constant segmental mobility, namely, that obtaining at Tg+50° C, the rates of crystallization at various extensions obey a common dependence upon the degree of supercooling. This relation is in fair accord with theories of nucleation kinetics, except at the lowest temperatures where there is some indication of the appearance of a new crystal form.

The use of deuterium oxide for the detection of water-binding of helical structures in nucleic acids and in polynucleotides

Collation of the H-water-bridge theory and the thesis that the D-bond is stronger than the H-bond leads to the expectation that the melting temperature values of nucleic acids at low ionic strengths should be higher in D2O than in H2O. This has been confirmed in the case of salmon-sperm DNA over the pH range of 4.5–7.5 at 10−3 ionic strength. The further expectation that under certain conditions D2O substitution should result not only in rise in melting temperature but also in increased hypochromicity has been confirmed using synthetic polynucleotides.