Dissolution Of Molecules Research Articles

Calculation of Crystal-Solution Dissociation Constants.

The calculation of dissociation constants is an important problem in molecular biophysics. For such a calculation, it is important to correctly calculate both terms of the binding free energy; that is, the enthalpy and entropy of binding. Both these terms can be computed using molecular dynamics simulations, but this approach is very computationally expensive, and entropy calculations are especially slow. We develop an alternative very fast method of calculating the binding entropy and dissociation constants. The main part of our approach is based on the evaluation of movement ranges of molecules in the bound state. Then, the range of molecular movements in the bound state (here, in molecular crystals) is used for the calculation of the binding entropies and, then (using, in addition, the experimentally measured sublimation enthalpies), the crystal-to-vapor dissociation constants. Previously, we considered the process of the reversible sublimation of small organic molecules from crystals to vapor. In this work, we extend our approach by considering the dissolution of molecules, in addition to their sublimation. Similar to the sublimation case, our method shows a good correlation with experimentally measured dissociation constants at the dissolution of crystals.

Nanoscale Curvature of Nanocellulose Paper Promotes High Yield Spontaneous Formation of Giant Vesicles

Giant unilamellar vesicles (GUVs) have proven to be instrumental tools for a variety of biophysical experiments including among others, lipid membrane organization, membrane protein function, cytoskeleton mechanics, membrane division. To date, techniques to obtain adequate yields of vesicles require the application of electric fields or dissolution of molecules during growth and quantitative comparisons of the vesicles produced across these different growth conditions is unclear. In this work, we report quantitative measurements that i) show the nanoscale curvature and hydrophilic surface chemistry of nanocellulose paper promotes the highest yields of GUVs when compared to the other most commonly used techniques and ii) lead to the development of a thermodynamic model that unifies our observations and provides mechanistic insight into the growth process. The results from this work show the exciting potential of nanocellulose paper as a simple and scalable platform to manufacture large quantities of GUVs for biophysical interrogation as well as to open avenues in drug delivery and synthetic cells.

PRODUCTION OF EXTRACTS FROM VEGETABLE RAW MATERIALS BY CARBON DIOXIDE

The unique properties of supercritical carbon dioxide as a solvent are widely used for extraction. In supercritical media, the dissolution of molecules of various chemical nature is possible. The purpose of this investigation was to study the extraction process and obtain extracts from valuable regional plant materials by applying CO2 extraction under pre- and supercritical conditions. The objects of research were: ground seeds of melon, pumpkin and licorice roots, as well as mint leaves, mulberry and jida flowers. For extraction, a laboratory setup was used that allows extraction when the CO2 is supplied by a high-pressure plunger pump in the sub- and supercritical state using a heat pump. The pressure range is 3-15 MPa, temperatures 295–330 K, and the volumetric flow rate above the critical CO2 is 800–900 g. Experiments with ground seeds of melon and pumpkin showed that as a result of 4 sequentially performed extraction cycles on a single load with supercritical CO2 parameters ( 315–330 K; 3–7.5 MPa) the decrease in the mass of melon seeds was 90 g (pumpkins 80 g). During the total extraction time (2.5 hours), 20 kg of CO2 were pumped through the reactor (25 l at 290 K and 6.8 MPa), while the average oil content in the extract was 4 g per 1 kg of CO2 (3.0 g per 1 l of SС-CO2) In experiments with jida flowers, the maximum amount of solid extractable substance (2% by weight of the raw material) was obtained at a temperature in the extractor of 308 K and a pressure of 7.5 MPa. Upon extraction under critical conditions in collection 2, the liquid phase was absent; only a yellow-green paste was released in it. According to the results of experiments with mint leaves, the maximum yield of a greenish liquid was observed at T = 315 K and P = 4 MPa., Mulberry - at T = 306 K and P = 6.0 MPa. The results of the extraction of oils and extracts from ground seeds of melon, pumpkin and licorice roots, as well as mint leaves, mulberries and jida flowers confirm that the maximum yield of the extracted substance is achieved with supercritical CO2 parameters in the extractor (310 K, 7.5 MPa). When liquid CO2 is extracted (300 K and 6-8 MPa), up to 2% of a yellow substance is extracted, which does not differ in appearance from a supercritical extract.

Оптимальность и точность компьютерных вычислений свободной энергии Гиббса гидратации молекул в континуальных моделях сольватации

  In this paper, computer simulations of dissolving some small organic molecules: methanol (CH3OH), ethanol (CH5OH), acetamide (H3CC(O)NH2), methanethiol (CH3SH), methylamine (CH3NH2), chloromethane (CH3Cl) in water and calculations of the Gibbs free energy of hydration are performed. Calculations of the free energy of hydration are carried out within the framework of two well-known continuum solvation models: Solvation Model of Density (SMD) and Conductor-like Polarizable Continuum Model (CPCM). The quantum-mechanical part of the calculations is performed by the method of the hybrid density functional b3lyp and the restricted Hartree-Fock method. A comparative assessment of the accuracy and timing of calculations using different methods has been carried out. The versatility, high accuracy, and low consumption of calculation time using the SMD in a frame of the density functional method b3lyp are shown. In comparison with experimental data, errors of the values of the free Gibbs energy of dissolution of molecules in water are not exceeded 20 percent. The two modified CPCM models demonstrate worse results regarding accuracy and time consumption than the SMD approach. In this case, the restricted Hartree-Fock method turns out to be preferable compared to the density functional method b3lyp.

Stability of hexa(ethylene glycol) SAMs towards the exposure to natural light and repeated reimmersion

We investigate the stability of HS(CH2)11(OCH2CH2)6CH3 self assembling monolayers (hexa(ethylene glycol) SAMs) on gold regarding reimmersion and exposure to natural light over long periods of time up to several months. With polarisation modulation infrared spectroscopy we were able to monitor significant changes in the fingerprint region (900–1800cm−1) of the absorption modes of the SAMs, starting after a few days of exposure to natural light. We observed an exponential intensity decrease of modes indicating helical conformation of the SAM, as well as an exponential increase of modes indicating esters and formates suggesting a degradation of the SAM. X-ray photoelectron spectra of carbon C1s and sulphur S2p confirm the chemical nature of those changes. SAMs stored without light exposure show a drastically decreased change in the infrared spectra. In addition, we could find substantial conformational changes upon repeated drying and reimmersion in EtOH, manifesting in an intensity decrease of the absorption modes indicating hexa(ethylene glycol) molecules in helical conformation. Since the XPS data do not show changes in the chemical structure, we assume disordering effects and dissolution of molecules in solution. Our results suggest that SAMs can be stored over long periods of time in air without major changes if light exposure is avoided.

Husk-like microcapsule formation in material self-assembly

Solid microspheres, that were phase-separated in aqueous suspensions of thermal heterocomplex molecules made by heating a mixture of amino adds, transformed into husk-like microcapsules as pH increased. The transformation from solid microspheres into microcapsules proceeded at two different time scales. Rapid dissolution of thermal heterocomplex molecules fi'om the outer surfaces only during a short period was followed by slow dissolution of those molecules from their inside. The difference of the rates of dissolution led to the formation ofmicrocapsules carrying smaller inner kernels as remnants. Thermal heterocomplex molecules from amino acids consisted of many different kinds of chemical species whose distinction could be identified by isoelectric electrofocussing When the aqueous environment in which those heterocomplex molecules were made had a sutficiently low pH value, most of those thermal products could participate in formation of solid microspheres. As the pH value of the environment increased, supramolecules as the members of the solid particles were gradually dissolved into the solution by disconnecting both intaand inter-molecular bonding. Those dissolved molecular species then suffered conformational changes depending upon the pH value of the solution. Some of the molecular species decreased their diffusion coefticient due to pH-dependent conformational changes, and could aggregate onto the parental particles again. Sfight differences in the diffusion coefficients of those molecular species that varied their conformations led to a wide variety of morphological structures. Various microstructures that could have served as matrices for prebiotic chemical syntheses could be diverse. Our present observation suggests that a wide variety of microstructures of prebiotic significance could be conceivable depending upon how the pH value of the aqueous environment developed historically on the primitive earth.

Microcapsule formation in self-assembly of thermal heterocomplex molecules from amino acids

Solid microspheres that were phase-separated in aqueous suspensions of thermal heterocomplex molecules made by heating a mixture of proline and aspartic acid transformed into husk-like microcapsules as pH increased. The transformation from solid microspheres into microcapsules proceeded at two different time scales. Rapid dissolution of thermal heterocomplex molecules from the outer surfaces only during a short period was followed by slow dissolution of those molecules from their inside. The difference of the rates of dissolution led to the formation of microcapsules carrying smaller inner kernels as remnants.

Preparation, characterization and pharmaceutical application of linear dextrins. I. Preparation and characterization of amylodextrin, metastable amylodextrins, and metastable amylose.

The linear dextrin amylodextrin was prepared by enzymatic hydrolysis from waxy maize. Four metastable amylodextrins were prepared by complexation with different volatile organic compounds. All products showed partial dissolution into water at room temperature, because of dissolution of molecules with a lower DP. X-ray diffractometry revealed a helical conformation with six glucose units per turn for amylodextrin and metastable amylodextrins prepared with small molecules, and a helical conformation with seven glucose units per turn for metastable amylodextrins prepared with larger molecules. All metastable amylodextrins showed a helix with reduced distance between two turns as compared to amylodextrin. Metastable amylose, prepared from Amylose V, showed a helical conformation again with a reduced distance between two turns compared to Amylose V. FTIR analysis indicated a more flexible conformation for Amylose V and metastable amylose than for the amylodextrins.

Influence of composition, crystallization conditions and melt phase structure on solid morphology, kinetics of crystallization and thermal behavior of binary polymer/polymer blends

AbstractResults of an investigation on the morphology, the crystallization and the thermal behavior of several binary crystallizable blends are reported. The composition, molecular mass and crystallization conditions strongly influence the crystallization and the thermal behavior as well as the overall morphology of crystallizable binary blends. Quantities such as nucleation density (N), radial growth rate (G) of spherulites, overall rate of crystallization (K), and equilibrium melting temperature (Tm) are strongly dependent upon composition, crystallization conditions, and molecular mass of components. The type of dependence is to be related to the physical state of the melt, which, at the crystallization temperature, is in equilibrium with or coexists with the developing solid phase. In the ease of compatible blends such as poly(ethylene oxide)/poly(methyl methacrylate) the depression observed for G and Tm is mainly to be attributed to the diluent effect of the non‐crystallizable component. For such a blend it is found that, after crystallization, the non‐crystallizable component is trapped in intralamellar regions increasing the distance between adjacent lamellae. Depression of G, in the case of incompatible blends such as isotactic polypropylene/rubbers is mainly accounted for by rejection and deformation of rubber drops. The coexistence during crystallization of different processes such as molecular fractionation and segregation, preferential inclusion or dissolution of molecules with lower molecular mass and/or high degree of steric disorder of the crystallizable component in the phase rich in non‐crystallizable component and vice versa may explain some minima observed in the plots of T and Tm, vs. composition in the case of blends semicompatible in the melt. It was found that the addition of a second non‐crystallizable component causes drastic variations on some morphological and structural quantities of the semicrystalline matrix (isotactic polypropylene or nylon 6) such as the shape, dimensions, and regularity of spherulites and interspherulite boundary regions and lamella and interlamella thickness. In some cases the formation of new boundary lines connecting occluded particles are also observed. Such phenomena may have great importance on crack propagation and on impact behavior as well as on the tensile mechanical properties of binary blends characterized by a semicrystalline polymer component with a relatively high Tg and a rubber‐like component with a lower Tg.