Well-defined Melting Point Research Articles

Enhancing RNA Payload and Temperature Stability and Activity with Cationic Peptide-Coated Zinc Oxide Nanoparticles.

The lipid nanoparticle (LNP) mRNA vaccine was first tested through clinic but suffered from relatively low RNA payloads and poor temperature stability. Our lab patented a protamine-coated particle approach for temperature-stabilizing DNA vaccines, translating this successfully to the clinic. In subsequent work, we have characterized RNA interaction and delivery by zinc oxide nanoparticles, filing a patent most recently entitled RNA-stabilizing nanoparticles, similarly utilizing protamine-coated zinc oxide nanoparticles for RNA. Here, we present this data for the first time. Briefly, ZnO, ZnO-protamine, and ZnO-protamine-RNA were characterized by size and zeta potential analyses and the RNA-loaded nanoparticles were visualized by transmission electron microscopy. UV spectroscopic analysis demonstrated up to 95-98% loading efficiency with protamine and approximately 75% loading efficiency with LL37, another cationic antiviral peptide. Elution of the RNA isolated from the particles afforded a calculation in three independent trials where RNA payloads ranged from 18 to 45 μg of RNA per 0.5 mg of coated particles. Circular dichroism (CD) analysis indicated that binding of RNA to ZnO NPs stabilized, enhancing the pattern with a clear dependence on the RNA:ZnO stoichiometry. Enhanced temperature stability was shown by differential scanning calorimetry (DSC), gel electrophoresis, and in vitro mRNA expression analysis. Using poly I:C RNA with a well-defined melting point (64.3 ± 0.32 °C), formation of the ZnO:RNA complex increased the RNA melting point (70.9 ± 0.62 °C). After refrigerated or room-temperature storage or incubation at 30, 40, or 50 °C, RNA comigration with the control RNA was recovered from all samples, exposed to either 14 or 100 nm ZnO, and coated with protamine. Furthermore, the ZnO-protamine-mRNA samples retained significantly higher expression activity when incubated at these elevated temperatures. Finally, the ZnO-protamine-mRNA was functionally active for in vitro translation, in cell extracts, and in cells for expression of GFP, luciferase, and COVID spike protein. These data support further preclinical development of ZnO-protamine-mRNA.

Experimental investigation on melting heat transfer of an organic material under electric field

In this paper the melting heat transfer process of n-octadecane when confined in a cylinder-cubic cavity under the influence of an electric field is experimentally investigated. n-octadecane is a typical organic phase change material (PCM) and possesses a well-defined melting point. The cylinder is subject to the simultaneous actions of electric potential and heating, while the bottom wall or the four sidewalls of cavity are grounded. The effects of the voltage's magnitude and polarity on the solid–liquid phase change heat transfer performance are studied. The dynamic evolutions of the melting front and liquid fractions, the measurement of velocity field and electric current–voltage characteristics, and the distribution of electric field are presented to understand the physical mechanism. It is observed that when the applied voltage is higher than a certain threshold charge injection at the cylinder takes places, and the resulting strong Coulomb force promotes melting. In addition, heat transfer enhancement is more significant when the charge injection takes place at a negative voltage. The strong electric field that surrounds the whole cylinder with the four grounded sidewalls would facilitate injection and accelerate phase change. In this case, the melting time can be reduced by up to 68.0% when the −25.0 kV is applied.

Near-infrared and tumor environment Co-activated nanoplatform for precise tumor therapy in multiple models

Chemotherapy based on anti-tumor drugs is one of the most commonly utilized approaches for tumor treatment. However, the uncontrollable toxicity of these drugs to healthy tissue, insufficient therapeutic efficiency and chemotherapeutic resistance induced by hypoxic environment in most types of solid tumors still limited the clinical application of chemotherapy. Herein, a smart nanoplatform responsive to near-infrared (NIR) light and tumor-specific microenvironment is developed for precise and effective tumor therapy via chain procedures of rapid hypoxia inhibition, promoted catalytic medicine and low-resistance chemotherapy. The concept is demonstrated by co-encapsulating ferroferric oxide nanoparticles (Fe3O4 NPs, photothermal agent and catalyst), calcium peroxide (CaO2, H2O2/O2 generator) and paclitaxel (PTX, anticancer drug) into an enzyme and thermal breakable capsule, which contained a bilayer shell of hyaluronic acid (HA) and lauric acid (LA). The HA layer serves as tumor target agent to guide the nanoplatform to accumulate in tumor tissue, which would be subsequently degraded by the over-expressed hyaluronidase to expose LA layer for further activation by NIR irradiation. Due to the well-defined melting point of LA at 44°C and excellent photothermal property of Fe3O4, the LA layer undertakes a NIR-triggered phase-change to release the encapsulated therapeutic agents (CaO2, Fe3O4 and PTX) for controllable tumor therapy. The exposed CaO2 would react with water or acid in tumor cells to produce O2 and H2O2, where the O2 not only press PTX out of the capsule to accelerate its release, but reverse the hypoxic environment to inhibit the hypoxia-induced drug resistance for enhanced chemotherapy. The H2O2 would be further converted to cytotoxic hydroxyl radical by Fe3O4via catalytic medicine (Fenton reaction), resulting in an enhanced anticancer activity.Near-infrared and tumor environment co-activated nanoplatform, Effective hypoxia inhibition, Promoted catalytic medicine, Low-resistance chemotherapy, Precise tumor therapy via chain activities

Combined thermal analysis of fluid plasticizers

The paper deals with the study of plasticizers using different thermal methods. The literature data on the melting points of plasticizers proved uncertain; we intended to gather the data by other methods, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermally stimulated discharge (TSD). Results of ten plasticizers are demonstrated. During this work, we found that most of plasticizers have no well-defined melting point, and the solidification of plasticizer is similar to the glass transition of polymers. Only the di-n-butyl-phthalate showed regular crystallization. Thermally stimulated discharge current (TSD) method revealed that these compounds have several transitions –dispersion ranges assigned to different molecular motions.

Comparison of two DSC-based methods to predict drug-polymer solubility

The aim of the present study was to compare two DSC-based methods to predict drug-polymer solubility (melting point depression method and recrystallization method) and propose a guideline for selecting the most suitable method based on physicochemical properties of both the drug and the polymer. Using the two methods, the solubilities of celecoxib, indomethacin, carbamazepine, and ritonavir in polyvinylpyrrolidone, hydroxypropyl methylcellulose, and Soluplus® were determined at elevated temperatures and extrapolated to room temperature using the Flory-Huggins model. For the melting point depression method, it was observed that a well-defined drug melting point was required in order to predict drug-polymer solubility, since the method is based on the depression of the melting point as a function of polymer content. In contrast to previous findings, it was possible to measure melting point depression up to 20 °C below the glass transition temperature (Tg) of the polymer for some systems. Nevertheless, in general it was possible to obtain solubility measurements at lower temperatures using polymers with a low Tg. Finally, for the recrystallization method it was found that the experimental composition dependence of the Tg must be differentiable for compositions ranging from 50 to 90% drug (w/w) so that one Tg corresponds to only one composition. Based on these findings, a guideline for selecting the most suitable thermal method to predict drug-polymer solubility based on the physicochemical properties of the drug and polymer is suggested in the form of a decision tree.

A Eutectic Mixture of Natural Fatty Acids Can Serve as the Gating Material for Near-Infrared-Triggered Drug Release.

A smart release system responsive to near-infrared (NIR) light is developed for intracellular drug delivery. The concept is demonstrated by coencapsulating doxorubicin (DOX) (an anticancer drug) and IR780 iodide (IR780) (an NIR-absorbing dye) into nanoparticles made of a eutectic mixture of naturally occurring fatty acids. The eutectic mixture has a well-defined melting point at 39 °C, and can be used as a biocompatible phase-change material for NIR-triggered drug release. The resultant nanoparticles exhibit prominent photothermal effect and quick drug release in response to NIR irradiation. Fluorescence microscopy analysis indicates that the DOX trapped in the nanoparticles can be efficiently released into the cytosol under NIR irradiation, resulting in enhanced anticancer activity. A new platform is thus offered for designing effective intracellular drug-release systems, holding great promise for future cancer therapy.

Cloning polymer single crystals through self-seeding

In general, when a crystal is molten, all molecules forget about their mutual correlations and long-range order is lost. Thus, a regrown crystal does not inherit any features from an initially present crystal. Such is true for materials exhibiting a well-defined melting point. However, polymer crystallites have a wide range of melting temperatures, enabling paradoxical phenomena such as the coexistence of melting and crystallization. Here, we report a self-seeding technique that enables the generation of arrays of orientation-correlated polymer crystals of uniform size and shape ('clones') with their orientation inherited from an initial single crystal. Moreover, the number density and locations of these cloned crystals can to some extent be predetermined through the thermal history of the starting crystal. We attribute this unique behaviour of polymers to the coexistence of variable fold lengths in metastable crystalline lamellae, typical for ordering of complex chain-like molecules.

Crystalline particles from self-assembled divinyl oligomers

Ethylene glycol dimethacrylate (EGDMA) and/or triethylene glycol dimethacrylate (TEGDMA) oligomers formation was catalyzed in aqueous medium by horseradish peroxidase (HRP) in the presence of H 2O 2 at room temperature. EGDMA and/or TEGDMA oligomers were characterized by means of gel permeation chromatography, infrared vibrational spectroscopy and 1H NMR spectroscopy. Self-assembling of oligomers led to right-angled crystalline particles, as evidenced by scanning electron microscopy and differential scanning calorimetry. EGDMA, TEGDMA and EGDMA- co-TEGDMA oligomers synthesized in the presence of HRP–H 2O 2 system presented pendant vinyl groups along the chains, good solubility in chloroform, and well-defined melting point. These features evidenced few cross-linking or cyclization and revealed that the catalytic properties of HRP led to oligomeric materials with new characteristics.

Melting and phase transformation of hardmetal powders

Hardmetals are excellent tool materials that are made of WC–Co powder mixture by liquid phase sintering. The sintering occurs above 1320°C, the melting point of the eutectics formed by the components, and the melt acts as the binder phase for the WC grains. Efforts are made to reduce grain coarsening during heat treatment because fine-grained materials have considerably better mechanical properties. One possible way might be the use of powders with grain size ranging from 10 to 100 nm. When experiments were carried out with such powders, it was found that they have no well-defined melting point. Individual grains melt at different temperature values, sometimes much below the eutectic temperature given in the equilibrium phase diagram. Solidification also may occur below the equilibrium melting point resulting in different compositional variations. A possible explanation of this phenomenon is given based on the high specific surface of the ultrafine powders.

Hartite from Bilina

In the Bilina Mine (Czech Republic), a very chemically pure material corresponding to hartite was found as a product of distillation into the pelosiderite nodule during coalification of a lignite seam in the Miocene or later. The amount of the material available allowed characterizing this natural mineral equivalent of the hydrocarbon (+)-phyllocladane [16alpha (H)-phyllocladane] thoroughly. Elementary analysis of hartite from Bilina gave C = 87.45 wt% and H = 12.55 wt%, which corresponds to the formula C 20 H 34 . The IR spectrum demonstrated the presence of gem-dimethyl groups (doublet delta s CH 3 at 1369 and 1383 cm (super -1) ). Other bands indicated the presence of methyl and methylene groups. NMR studies showed that the hydrocarbon (hartite) molecule contains four CH 3 groups, nine CH 2 groups, four CH groups, and three quaternary carbon atoms. The sample exhibits a well-defined melting point between 71 and 71.5 degrees C. Measurements of optical rotation gave [alpha ] D = +24.2 degrees (CHCl 3 , c = 0.7). Lattice parameters from single-crystal study measured at 293(2) K were a = 11.407 (1), b = 20.952 (2), c = 7.4060 (8) Aa, alpha = 93.941 (9) degrees , beta = 100.750 (8) degrees , and gamma = 80.499 (9) degrees . The crystal system is triclinic with space group Pl, Z = 4, V = 1713.8 (3) Aa 3 . Densities are D m = 1.04 g/cm 3 and D x = 1.064 g/cm 3 , respectively. Isotopic composition of C in hartite from Bilina gave delta 13 C (sub (PDB)) = -24.4(1) per mil, a common value for coal and organic sedimentary material derived from higher plants.

Characterization and properties of the charge transfer complex of carbazole derivatives

The purpose of this work is to characterize the charge transfer complex (CTC) formed between one carbazolic derivative and an organic electron acceptor, and to compare some physicochemical properties. We have used either poly ( N-vinylcarbazole) or poly( N-butylcarbazole) or again 3,3′-diethyl-9,9′-dicarbazole (DÉC) as a donor, and one of the following as acceptor: tetracyanoethylene (TCNE), 2,4,7-trinitro-9-fluorenone (TNF), 1,4-naphthoquinone (NQ) or 2,3-dicyano-1,4-naphthoquinone (DCNQ). The characterization of the CTC has been made following two methods: optical spectroscopy or differential scanning calorimetry (DSC). In fact, when the optical absorption of the CTC corresponds to a well-defined peak, its characterization by optical spectroscopy leads to the determination of some intrinsic properties such as equilibrium constant, molar extinction coefficient, etc. On the contrary, if the optical absorption is indiscernible of the absorption peaks of acceptor or donor alone, we have shown that use of DSC allows us to characterize the formation of CTC measuring the fusion enthalpy of the CTC. These determinations are only described, in this paper, in the case of the dimer DEC as a donor which possesses a well-defined melting point. The CTC between DEC and each acceptor has been characterized in this way.

Radiation-induced effects on alternative fuels

After the so-called energy crisis occurred in the 70's 1 several macromolecules have been investigated as alternative energy and chemical feed stocks. Among several possibilities coal has received special attention due to its large proven reserves as well as the similarity between the products obtained by its processing and crude oil. 2-5 One of the constituents present in crude oil and coal-derived products is composed of brown solids, brittle, without a well-defined melting point named asphaltenes. 6 They are isolated from liquid fuels by precipitating the benzene-soluble material with hydrocarbons such as pentane or hexane. 7 In previous publications we have studied the effects of X-ray irradiation on solvent refined coal, 8 asphaltenes 9 and asphaltols. 1~ Using a proper analytical method based on liquid chromatography, developed in our laboratory, ix the irradiation products were studied. As a generall rule it was found that X-ray irradiation can promote decomposition of the macromolecules investigated thus producing lower molecular weight products including hydrocarbons. 8-I~ In the present work the chemical effects of y-ray irradiation of asphaltenes produced from coal are reported.

A novel silicon-containing copolymer for near-u.v. resist

N-(4-hydroxyphenyl)maleimide/allyltrimethylsilane copolymer (PHAMS) was synthesized as a novel near-u.v. resist when containing diazonaphthoquinone sulphonate chloride. The chain-stiffening effect of the cyclic maleimide group was responsible for high temperature stability. A high glass transition temperature of 226° and a thermal decomposition temperature of 418° were found for PHAMS; a well-defined melting point was not observed because of its low crystallinity. The prepared resist could produce high contrast images at dose of 42.4 mJ/cm 2. Microlithographic positive images were obtained stable to temperatures above 200°. Excellent solubility in aqueous base was observed with PHAMS having 9.3 wt% silicon content and an oxygen-plasma etching rate of 1:10.5 compared to that of hard-baked HPR-204 (believed to be a novolac-type resin; baked at 200° for 30 min as a coating on silicon wafer).

Metal-catalyzed alkynylation of brominated polyphenylenes. Thermoset precursors of high-density monolithic glassy carbon

Abstract : The functionalization of brominated polyphenylenes with several alkynes is described. The bromide groups on the polymer were replaced with terminal alkynes using a Pd/Cu catalyst system. Substitution of nearly all the original bromide locations was achieved. The functionalized polymers, freely soluble in THF, exhibited high char yields of up to 89% on thermolysis to 900 deg C under a nitrogen atmosphere. Several of the functionalized polymers, derived from brominated polyphenylenes with approximately equal amounts of meta- and para-linkages, flowed on heating. The polymer that was functionalized with phenylacetylene exhibited a well-defined melting point at approximately 200 deg C and flowed to produce a monolithic disk of glassy carbon. The amount of acetylenic crosslinking units in the polymers functionalized with phenylacetylene appears to be directly related to the char yields of the functionalized polymers. Predominantly meta-linked brominated polyphenylenes were also functionalized with a number of terminal alkynes and though high char yields of up to 86% were observed, these materials offered no improvements in flow properties. The structure/property relationships and material applications are discussed.