Search results for "dynamics"
showing 10 items of 9782 documents
Thermodynamics of cyclodextrin-star copolymer threading-dethreading process
2015
We investigated the interactions of a star-like copolymer with cyclodextrins (CD) with different cavity size. Direct measurements of thermodynamic properties were done, and the application of proper molecular models was useful for the interpretation of the involved phenomena. The CD–copolymer inclusion complexes were characterized by isothermal titration calorimetry. The copolymer aggregation induced by temperature was investigated by differential scanning calorimetry, volume and compressibility measurements. The behavior of the ternary T1107/CD/water mixture was interpreted considering competing equilibria. The investigated systems showed an interesting temperature responsive behavior so t…
Cyclodextrin/surfactant inclusion complexes: An integrated view of their thermodynamic and structural properties
2021
Cyclodextrins (CDs) play an important role in self-assembly systems of amphiphiles. The structure of CDs provides distinguished physicochemical properties, including the ability to form host-guest complexes. The complexation affects the properties of guest molecules and can produce supramolecular aggregates with desirable characteristics for fundamental and practical applications. Surfactants are particularly attractive host molecules due to their wide variety, availability, responsiveness to different stimuli, and high relevance in different fields, e.g. medical, cosmetic, pharmaceutical, and food industries. The tendency of organization in higher-order supramolecular aggregates arises the…
Pressure dependence in the methyl vinyl ketone + OH and methacrolein + OH oxidation reactions: an electronic structure study.
2005
High-level electronic structure calculations were carried out for the study of the reaction pathways in the OH-initiated oxidations of methyl vinyl ketone (MVK) and methacrolein (MACR). For the two conformers of MVK (called synperiplanar and antiperiplanar), the addition channels of OH to the terminal and central carbon atom of the double bond dominate the overall rate constant, whereas the abstraction of the methyl hydrogen atoms has no significant kinetic role. In the case of MACR, only the antiperiplanar conformer is important in its reactivity. In addition, the lower Gibbs free energy barrier for MACR corresponds to the aldehydic hydrogen abstraction reaction, which will be somewhat mor…
A Novel Gas Chromatographic Method to Measure Sorption of Dense Gases into Polymers
2006
A novel experimental approach to determine the solubility of gaseous compounds inside polymers is here described. The method is based on the gas chromatographic determination of the composition of the fluid phase at equilibrium with the polymer. To take into account the effect of the volume swelling on the measurement a suitable probe, nonabsorbable by the polymer, was added to the fluid phase. Under the adopted configuration the apparatus can operate up to 35 MPa and 80°C. This experimental technique has been used to determine the solubility of carbon dioxide in poly(vinylidene fluoride) using argon as a probe. The latter was chosen because it is negligibly absorbed by the polymer and does…
Studying the role of protein dynamics in an SN2 enzyme reaction using free-energy surfaces and solvent coordinates
2013
Conformational changes are known to be able to drive an enzyme through its catalytic cycle, allowing, for example, substrate binding or product release. However, the influence of protein motions on the chemical step is a controversial issue. One proposal is that the simple equilibrium fluctuations incorporated into transition-state theory are insufficient to account for the catalytic effect of enzymes and that protein motions should be treated dynamically. Here, we propose the use of free-energy surfaces, obtained as a function of both a chemical coordinate and an environmental coordinate, as an efficient way to elucidate the role of protein structure and motions during the reaction. We sho…
Thermodynamically induced shear degradation
1988
The shear degradation of polymers in semiconcentrated solutions is viewed as a function of solvent quality. It is shown that the deterioration of the thermodynamic quality of the solvent leads to a marked flow resistance due to an increasing number of contacts between the chains. This may be probed by viscosimetric measurements as well as by degradation experiments (“thermodynamically induced shear degradation”). For a detailed discussion of this phenomenon the experimental setup for the mechanochemical experiment is outlined first, followed by a survey of the kinetics of chain scission. Finally, experiments mostly obtained on polystyrene in the theta-solvent trans-decalin are discussed. Th…
Temperature and pressure dependence of phase separation of trans-decahydronaphthalene/polystyrene solution
2004
Abstract The cloud-point temperatures (Tcl’s) of trans-decahydronaphthalene (TD)/polystyrene (PS, Mw=270 kg/mol) solutions were determined by light scattering measurements over a range of temperatures (1–16 °C), pressures (100–900 bar), and compositions (4.2–21.6 vol% polymer). The system phase separates upon cooling and the Tcl was found to increase with the rising pressure for the constant composition. In the absence of special effects this finding indicates positive excess volumes. The special attention was paid to the demixing temperatures as a function of the pressure for the different polymer solutions and the plots in the T-volume fraction plane and P-volume fraction plane. The cloud…
Interactions between proteins and poly(ethylene-glycol) investigated using molecular dynamics simulations
2017
Poly(ethylene-glycol) (PEG) is a polymer used to coat therapeutic preparations, like drugs or drug nanocarriers, and improve their efficacy. This effect is probably due to a reduction of the interactions of the coated species with the host organism. Nevertheless, experiments show that PEGylated materials do interact with the surrounding biological milieu, and in particular with blood proteins. Here, we use atomistic molecular dynamics simulations to characterize the interactions between the polymer and several blood proteins. In these simulations, the proteins are immersed in a mixture of PEG and water molecules. We observe how PEG distributes around the protein surface and measure PEG-prot…
The protein dynamical transition does not require the protein polypeptide chain
2011
We give experimental evidence that the main features of protein dynamics revealed by neutron scattering, i.e., the “protein dynamical transition” and the “boson peak”, do not need the protein polypeptide chain. We show that a rapid increase of hydrogen atoms fluctuations at about 220 K, analogous to the one observed in hydrated myoglobin powders, is also observed in a hydrated amino acids mixture with the chemical composition of myoglobin but lacking the polypeptide chain; in agreement with the protein behavior, the transition is abolished in the dry mixture. Further, an excess of low-frequency vibrational modes around 3 meV, typically observed in protein powders, is also observed in our mi…
Interactions Between Blood Proteins and Nanoparticles Investigated Using Molecular Dynamics Simulations
2019
In the development of new therapeutic agents based on nanoparticles it is of fundamental importance understanding how these substances interact with the underlying biological milieu. Our research is focussed on simulating in silico these interactions using accurate atomistic models, and gather from these information general pictures and simplified models of the underlying phenomena. Here we report results about the interactions of blood proteins with promising hydrophilic polymers used for the coating of therapeutic nanoparticles, about the salt dependent behavior of one of these polymers (poly-(ethylene glycol)) and about the interactions of blood proteins with silica, one of the most used…