ST Molecules Research Articles

High-energy-density metallized gel propellant by hydrogen-bonded polymer-small molecules for enhanced stability and shear-thinning performance

Metallized gel propellants with high metal content hold significant potential for enhancing the energy properties of hydrocarbon fuels. However, achieving an optimal balance between storage stability and atomization characteristics poses a significant challenge. In this study, we successfully synthesized metallized gel propellants that exhibit exceptional stability and remarkable shear-thinning properties by utilizing cooperative hydrogen bonding between polymer octanoyl cellulose and the small Thixatrol ST molecule. Through meticulous mixture design and formulation optimization, the metallized gel propellants demonstrated noteworthy characteristics, including a high calorific value of 48.48 MJ/kg, an impressive dynamic stability index of 89.12%, a surface tension of 23.21 mN/m, and sustained stability for at least six months under resting conditions. The metallized gel propellant, containing 50 wt% boron particles, exhibited a density 1.54 times higher than pure kerosene, meeting the requirements for enhancing specific impulse in rocket and ramjet engines. Moreover, optimized samples with varying boron concentrations were evaluated for their rheological properties and atomization behavior. The results revealed that the inclusion of boron particles increased the viscosity of the metallized gels. Consequently, the sample with 50 wt% boron exhibited modified viscosity-flow behavior, resulting in the formation of larger gel droplets during atomization. Finally, the metallized gel propellant demonstrated successful ignition in ramjet engine experiments. We anticipate that the cooperative hydrogen bonding between the polymer and small molecule will pave the way for the development of high-content metallized gel propellants with exceptional stability and superior shear thinning performance.

A Carboxyl-Functionalized Covalent Organic Framework Synthesized in a Deep Eutectic Solvent for Dye Adsorption.

Instead of using organic solvents, a deep eutectic solvent (DES) composed of tetrabutylammonium bromide and imidazole (Bu4 NBr/Im) was employed as a solvent for the first time to synthesize covalent organic frameworks (COFs). Due to the low vapor pressure of the Bu4 NBr/Im-based DES, a new carboxyl-functionalized COF (TpPa-COOH) was synthesized under environmental pressure. The as-synthesized TpPa-COOH has open channels, and the DES can be removed completely from the pores. The dye adsorption performance of TpPa-COOH was examined for three organic dyes with similar molecular sizes: one anionic dye (eosin B, EB) and two cationic dyes (methylene blue, MB and safranine T, ST). TpPa-COOH showed an excellent selective adsorption effect on MB and ST. The electronegative keto form in TpPa-COOH might help to form electrostatic and π-π interactions between the π-stacking frameworks of TpPa-COOH and the positive plane MB and ST molecules. The adsorption isotherms of MB and ST on TpPa-COOH were further investigated in detail, and the equilibrium adsorption was well modeled by using a Langmuir isotherm model. Together with hydrogen bonding, TpPa-COOH showed higher adsorption capacity for ST than for MB (1135 vs. 410 mg g-1 ). These results could provide a guidance for the green synthesis of adsorbents in removing organic dyes from wastewater.

Theoretical modeling of the interaction of phenylacetylene and styrene molecules with Pd{111}

The DFT-PBE method was used to calculate the structural and energy characteristics of all possible adsorption complexes of phenylacetylene (PA) and styrene (St) molecules with the Pd{111} surface. According to the calculations, the acetylene group of the PA molecule in the energetically preferred complexes is bound to three or four Pd atoms and the plane of the phenyl ring is parallel to the Pd surface. In the case of deficiency of fcc sites, the phenyl ring of the PA molecule is displaced from the Pd{111} surface. The number of Pd atoms required for the compact adsorption of two PA molecules is the same as that for the adsorption of one St molecule.

Theoretical Designs of Photoresponsive Energy-Storage Materials Based on Attachment of π-Conjugated Molecules onto Sulfur-Doped Graphene

Introducing heteroatom active sites and functional units is essential for achieving high-performance graphene in potential applications of optoelectronic devices and sustainable solar-heat energy conversion/storage. Density functional theory calculations with long-range van der Waals effects (vdW-DF2) were performed to study the electronic structures and energy storage/release of graphene through sulfur (S)-doping and physisorption of π-conjugated photoresponsive molecules, trans/cis-azobenzene (AB) derivatives with an electron-donating substituent group and trans/cis-stilbene (ST), respectively. With the increase of the S-doping concentration from 0.4 to 0.8 atom/nm2, the band gap of graphene exhibits the enhanced metallic characteristics with a direct-to-indirect transition. Although AB and ST molecules have different unsaturated bridge bonds, −N═N– versus −CH═CH–, physisorption of these two photoresponsive molecules onto the graphene can both broaden the band gap to about 0.02 eV, as a result of the π–...

Supported palladium nanomaterials as catalysts for petroleum chemistry: 2. Kinetics and specific features of the mechanism of selective hydrogenation of phenylacetylene in the presence of carbon-supported palladium nanocatalyst

The selective hydrogenation of phenylacetylene (PhA) into styrene (St) in the presence of a palladium nanocatalyst has been investigated. Salient features of this reaction have been revealed, such as independence of the PhA hydrogenation and St hydrogenation (after exhaustion of PhA) rates from the PhA and St concentrations, respectively; their nearly first-order dependence on the hydrogen pressure; and the first order in catalyst loading. The experimental results obtained according to a special plan have been processed using computer programs for various reaction mechanisms. It has been found that adequate description is achieved for the only scheme involving the adsorption one to two PhA and/or St molecules and one to two hydrogen molecules on the active site of the same type. The presence of one hydrogen molecule on the active site leads to the hydrogenation of PhA to St or St to ethylbenzene (EB). In the presence of two adsorbed hydrogen molecules, PhA is selectively hydrogenated to St and nonselectively hydrogenated directly to EB. It has been shown that the nature of the selectivity of the palladium catalyst is determined by the thermodynamics of competitive adsorption of PhA and St. The activation energies of the individual steps of the process have been determined.

The molecular configuration of a DOPA/ST monolayer at the air-water interface: a molecular dynamics study.

In this study, surface pressure-area isotherms for N-stearoyldopamine (DOPA) and 4-stearylcatechol (ST) monolayers are obtained by means of molecular dynamics simulations and compared to experimental isotherms. The difference between DOPA and ST is an amide group, which is present in the alkyl tails of DOPA molecules. We find a large difference between the isotherms for DOPA and ST monolayers. Upon using TIP4P/2005 for water and OPLS force fields for the organic material and a relatively large system size, the simulated results are found to be consistent with experiments. With molecular dynamics simulations, the configurations of molecules in the monolayers can be directly analyzed. When the surface pressure is high, a regular molecular orientation is observed for ST molecules, whereas regular orientations are only observed in local domains for DOPA molecules. The differences between DOPA and ST monolayers are attributed to the amide groups in DOPA molecules, which are useful for both steric effects and the formation of hydrogen bonds in the DOPA monolayers. This study clearly demonstrates that hydrogen bonds, due to the presence of the amide group in DOPA, are the cause of the disorder in its Langmuir monolayers. Thus, the conclusion may be helpful in making ordered organic monolayers in the future.

Monolayers (Langmuir films) behavior of multi-component systems composed of a bile acid with different sterols and with their 1:1 mixtures

Different physicochemical properties of Langmuir films (monolayers) composed of 10 mixed systems of a bile acid, deoxycholic acid (DC) with various plant sterols, such as stigmasterol (Stig), β-sitosterol (Sito) and campesterol (Camp) and a stanol, cholestanol (Chsta) in addition to an animal sterol, cholesterol (Ch) [these sterols and Chsta are abbreviated as St] and DC with 1:1 St mixtures; (Ch + Chsta), (Ch + Stig), (Stig + Chsta), (Ch + Sito) and (Ch + Camp) on the substrate of 5 M aqueous NaCl solution (pH 1.2) at 25 °C, were investigated in terms of mean surface area per molecule ( A m), the partial molecular area (PMA), surface excess Gibbs energy (Δ G (ex)), interaction parameter ( I p) as well as activity coefficients ( f 1 and f 2) in 2-D phase of each binary (or ternary) component system and elasticity (Cs −1) of formed films; these were analyzed on the basis of the respective surface pressure ( π) versus A m isotherms as a function of mole fraction of Sts ( X st) in the DC/St(s) mixtures at discrete surface pressures. Notable findings are: (i) all the binary component systems did form patched film type monolayers consisting of (a) DC-dominant film solubilizing a trace amount of St molecules and (b) St dominant film dissolving a small amount of DC molecules, (ii) DC in 2-D phase exhibited a transition from LE film to LC film at a constant pressure ( π C 1 ) accompanied by compression and (iii) Δ G (ex) as well as I p was found to be greatly dependent on (a) the combinations of DC with different St species and (b) to be markedly varied by a difference in mixing ratio of DC to Sts. Compressibility (or elasticity) analyses and fluorescence microscopy images could support the above findings as well as interpretation.

In vitro and in vivo evaluation of 177Lu- and 90Y-labeled E. coli heat-stable enterotoxin for specific targeting of uroguanylin receptors on human colon cancers

The human E. coli heat-stable enterotoxin (ST(h), amino acid sequence N1SSNYCCELCCNPACTGCY19) binds specifically to the guanylate cyclase C (GC-C) receptor, which is present in high density on the apical surface of normal intestinal epithelial cells as well as on the surface of human colon cancer cells. Analogs of ST(h) are currently being used as vectors targeting human colon cancers. Previous studies in our laboratory have focused on development of 111Indium-labeled ST(h) analogs for in vivo imaging applications. Here, we extend the scope of this work to include targeting of the therapeutic radionuclides 90Y and 177Lu. The peptide DOTA-F19-ST(h)(1-19) was synthesized using conventional Fmoc-based solid-phase techniques and refolded in dilute aqueous solution. The peptide was purified by RP-HPLC and characterized by MALDI-TOF MS and in vitro receptor binding assay. The DOTA-conjugate was metallated with nonradioactive Lu(III)Cl3 and Y(III)Cl3, and IC50 values of 2.6+/-0.1 and 4.2+/-0.9 nM were determined for the Lu- and Y-labeled peptides, respectively. 177Lu(III)Cl3 and 90Y(III)Cl3 labeling yielded tracer preparations that were inseparable by C18 RP-HPLC, indicating that putative differences between Lu-, Y- and In coordination spheres are not observed in the context of labeled ST(h) peptides. In vivo biodistribution studies of the 177Lu-labeled peptide in severe combined immunodeficient (SCID) mice bearing T-84 human cancer tumor xenografts showed rapid clearance from the bloodstream, with >90 %ID in the urine at 1 h pi. Localization of the tracer within tumor xenografts was 1.86+/-0.91 %ID/g at 1 h pi, a value higher than for all other tissues with the exception of kidney (2.74+/-0.24 %ID/g). At 24 h pi, >98 %ID was excreted into the urine, and 0.35+/-0.23 %ID/g remained in tumor, again higher than in all other tissues except kidney (0.91+/-0.46 %ID/g). Biodistribution results at 24 h pi for the 90Y-labeled peptide mirrored those for the 177Lu analog, in agreement with the identical behavior of the labeled analogs by C18 RP-HPLC. These results demonstrate the ability of 177Lu- and 90Y-labeled ST(h) molecules to specifically target GC-C receptors expressed on T-84 human colon cancer cells.

Two-Dimensional Mixtures of Stearic Acid and Partially Fluorinated Amphiphilic Molecule: A Grazing Incidence X-ray Diffraction Study

We report a grazing incidence X-ray diffraction (GIXD) study of mixed Langmuir monolayers of stearic acid (ST) and a fluorinated amphiphilic molecule (FEP). The mixing behavior of the two components was investigated at two different surface pressures, 5 and 30 mN/m. The ST molecules are found to be in the L2 mesophase at 5 mN/m and in the LS mesophase at 30 mN/m, whereas the FEP molecules appear disordered. In the mixture, the GIXD measurements, associated with previous thermodynamical and optical microscopy results, show that in the whole range of molar ratio, the two molecules are completely phase-separated. Also, we observed at 5 mN/m, relaxation in the pure ST monolayer and in the mixtures rich in ST; the tilt angle of the molecules and the rectangular distortion of the 2D-lattice decrease. By comparing mixed films and pure ST films, this relaxation could be correlated to the size of the domains.

Identification of a binding region onEscherichia coli heat-stable enterotoxin to intestinal guanylyl cyclase C

The heat-stable enterotoxin (ST), produced by Escherichia coli, causes acute diarrhea in infants and domestic animals by activation of the intestinal membrane-bound receptor, guanylyl cyclase C. We have investigated a region on the ST molecule, which is recognized by the receptor, by introducing a photochromophore, p-azidophenylalanine (Pap), into three different regions of STp(4–17), which has the full toxic activity. Each ST analog bound to the receptor, but only STp(4–17) containing a Pap residue at position 11 in the central portion of the ST molecule, showed a high efficiency in the reaction which cross- linked with the receptor by UV radiation. These data clearly demonstrate that the region of the ST molecule encompassing the Asn11 residue directly interacts with the receptor.

Surface properties of mixed phospholipid—stearylamine monolayers and their interaction with a non-ionic surfactant (poloxamer)

Surface pressure and surface potential studies of phosphatidylcholine—stearylamine (PL-ST) monolayers were performed in the presence and absence of poloxamer in the aqueous phase. For pure PL, the surface pressure area (π- A) isotherm was found to be independent of whether the monolayer was obtained by continuous compression or by aliquot adding. In sharp contrast to PL, ST molecules orient vertically when compressed under dynamic conditions and have a tilted configuration when compressed at constant area. Mixed PL-ST monolayers exhibit a non-ideal behavior which results in a significant increase in surface potential above that corresponding to the pure compounds. This deviation from ideality is mainly due to strong interactions between the positively charged ST head group and a phospholipid polar group occurring in the electric double layer. As revealed by surface pressure measurements, poloxamer molecules seem to be unable to penetrate into the mixed PL-ST monolayers, even when the molar ratio of ST to PL is 0.74. The surface potential data do not corroborate the surface pressure data. An important increment of the surface potential of these monolayers observed on the injection of poloxamer into the aqueous subphase can thus be attributed to the interaction occurring at the level of the hydrophilic groups of the spread lipid.

<i>Escherichia coli </i>Heat-Stable Enterotoxins and Their Receptors

The family of ST has grown to include closely related toxins produced by a number of organisms. The core sequence of these toxins can bind specifically and reversibly to a receptor found in the microvillus membranes of the intestinal cell brush border. As a result of a specific binding event, the ST can stimulate fluid secretion via receptor-mediated stimulation of guanylate cyclase. The structure of the ST molecule has been partially obtained through a variety of techniques. It is apparent that in the near future, key amino acids and sequence regions of these toxins will be found that will identify the requirements for toxicity. The ST are ideal probes to study the secretory system of intestinal cells since they are not cytotoxic. The receptor for ST has been extensively studied and its purification and characterization will yield important insight into the reversal of toxin-mediated diarrheas, and possibly into the nonpathological secretory process. As yet, the nature of the 54,000-57,000 and 68,000-75,000 dalton binding proteins identified by cross-linking studies are not known. When purified ST-binding peptides and other components of the secretory cascade will become available, they will provide better insight into the actual dynamics of the ST receptor-guanylate cyclase complex secretory pathway.

Vascular permeability activity in Escherichia coli heat-stable enterotoxin.

Purified heat-stable enterotoxin (ST) prepared from supernatants of Escherichia coli strain 53402 A-1, isolated from a patient with diarrhea, caused an increase in the permeability of the small blood vessels of the skin of adult rabbits after intracutaneous injection. Increased permeability was manifested by localized accumulation of intravenously injected blue dye at the injection sites. Permeability factor (PF) activity reached a peak 1 h after injection, and recovery of normal permeability was nearly complete in 3 h. Residual PF activity had disappeared by 24 h. Dose-response curves demonstrated a straight-line relationship between the logarithm of the dose and mean blueing diameter over a range of 3 to 12 mm. The PF assay was less sensitive that the suckling mouse assay, and adult rabbits varied in their sensitivity to the PF effect. Five to 100 mouse units of ST were required to consistently evoke strong and unequivocal blue lesions of 7 mm or more in diameter. PF activity was reduced 50 to 70% by heating at 70 degrees C for 30 min, 60 to 80% by boiling for 30 min, and 95 to 98% by autoclaving for 15 min, but it was unaffected by treatment with cholera antitoxin. These findings are consistent with the notion that PF activity is a property of the ST molecule itself. This PF assay cannot be used for the detection of ST in crude culture supernatant fluid because of low sensitivity and the presence of nonspecific PF effects of culture media and other E. coli products.