The role of interfacial chemistry and interactions in the dynamics of thermosetting polyurethane–multiwalled carbon nanotube composites at low filler contents

Acid-oxidized multiwalled carbon nanotubes (MWCNTs) were introduced into a polyurethane (PU) matrix at low filler levels (0.01–0.25 wt%) through either van der Waals or covalent interactions, and their glass transition dynamics using dynamic mechanical analysis and laser-interferometric creep rate spectroscopy was investigated. The nanocomposites reveal substantial impact on the PU glass transition dynamics, which depends on the nanotube content and type of interfacial interactions. The pronounced dynamic heterogeneity within the glass transition covering 200 °C range and the displacement of main PU relaxation maxima from around 0 to 80–140 °C were registered. The results are treated in the framework of chemical inhomogeneity, constrained dynamics effects, and different motional cooperativities. The peculiariaties of the glass transition dynamics in the composites are reflected in their dynamic and static mechanical properties, in particular a two- to threefold increase in modulus and tensile strength for the covalent interfacial interaction of MWCNTs with PU.     

Ion–micelle interactions and the modeling of reactivity in micellar solutions of simple zwitterionic sulfobetaine surfactants

Aqueous micellar solutions of sulfobetaine surfactants provide a simple physical–chemical system for investigating the origin and consequences of the specific interactions of anions with a model zwitterionic interface. Studies of ground-state reaction kinetics in micellar solutions of these surfactants provide a window into some of the more intriguing aspects of both anion and cation interactions with a zwitterionic micelle surface. Recent molecular dynamics simulations paint a more physically reasonable picture of the zwitterionic micelle–water interface than that usually depicted in the literature and should contribute to our future understanding of the factors that contribute to specific anion binding.     

Parsing of the free energy of aromatic–aromatic stacking interactions in solution

We report an analysis of the energetics of aromatic–aromatic stacking interactions for 39 non-covalent reactions of self- and hetero-association of 12 aromatic molecules with different structures and charge states. A protocol for computation of the contributions to the total energy from various energetic terms has been developed and the results are consistent with experiment in 92% of all the systems studied. It is found that the contributions from hydrogen bonds and entropic factors are always unfavorable, whereas contributions from van-der-Waals, electrostatic and/or hydrophobic effects may lead to stabilizing or destabilizing factors depending on the system studied. The analysis carried out in this work provides an answer to the questions “What forces stabilize/destabilize the stacking of aromatic molecules in aqueous-salt solution and what are their relative importance?”     

The calculation of Cs and Rb conductivities in the region of liquid–plasma transition

The conductivity and thermal conductivity of Cs and Rb are calculated in the liquid phase and in the region between the plasma (gas) and the liquid states. The last area is located at the temperatures higher than the critical one, near the critical point. The Ziman formalism originated from the liquid metal theory was used for the calculations. The results of present calculations were compared with available experiments and calculations of other researchers. It was found that the liquid state formalism can be applied to expanded liquid Cs and Rb at densities higher than the critical one, but another type of models is necessary at lower densities.     

Investigations of the hydrophobic and hydrophilic interactions in polymer–water systems by ATR FTIR and Raman spectroscopy

ATR FTIR and Raman spectra of polymers containing amide groups in the main chain and in the side chain and of the amide low-molecular-weight model compounds in water media were measured. The hydrophobic and hydrophilic interactions of the dissolved compounds with the neighboring water molecules are reflected in the wavenumbers of the CH₃ stretching and of the Amide I and II vibrations. The possibility of the existence of β-sheet-like structures in polypeptides surrounded by water molecules is also discussed.     

Enthalpies of mixing and intermolecular interactions in the 1-octanol-dimethylformamide system at 298–318 K

The heat effects of solution of N,N-dimethylformamide (DMF) and 1-octanol (OctOH) in the DMF (1)-OctOH (2) system are measured over the range of compositions using a variable-temperature isothermal-shell calorimeter at 298, 308, and 318 K. The partial molar enthalpies of the binary mixture components and the enthalpies and heat capacities of mixing are determined. It is found that the amide-alcohol mixing is strongly endothermic and very weakly depends on temperature. The enthalpy and specific heat parameters of binary and ternary interactions between the DMF molecules in OctOH and the OctOH molecules in DMF are determined in terms of the virial expansion technique, and it is shown that the two nonelectrolytes exhibit a tendency to homoassociation.     

Temporal resolution of protein–protein interactions in the live-cell plasma membrane

We have recently devised a method to quantify interactions between a membrane protein (“bait”) and a fluorophore-labeled protein (“prey”) directly in the live-cell plasma membrane (Schwarzenbacher et al. Nature Methods 5:1053–1060 2008). The idea is to seed cells on surfaces containing micro-patterned antibodies against the exoplasmic domain of the bait, and monitor the co-patterning of the fluorescent prey via fluorescence microscopy. Here, we characterized the time course of bait and prey micropattern formation upon seeding the cells onto the micro-biochip. Patterns were formed immediately after contact of the cells with the surface. Cells were able to migrate over the chip surface without affecting the micropattern contrast, which remained constant over hours. On single cells, bait contrast may be subject to fluctuations, indicating that the bait can be released from and recaptured on the micropatterns. We conclude that interaction studies can be performed at any time-point ranging from 5 min to several hours post seeding. Monitoring interactions with time opens up the possibility for new assays, which are briefly sketched in the discussion section.     

Protein–polysaccharide associative interactions in the design of tailor-made colloidal particles

This article reviews some recent advances in the use of diverse protein–polysaccharide associative interactions in the design of colloidal particles having potential to be used for both fortification of food colloids with health-promoting bioactive compounds with better control of their physical stability and breakdown within the gastrointestinal tract. Protein–polysaccharide associative interactions are discussed in the following aspects: (i) the formation of micro- and nanoparticles for the delivery of health promoting ingredients (nutraceuticals); (ii) the controlled gastrointestinal fate of colloidal particles; (iii) the formation of biopolymer-based particles as fat replacers; and (iv) the behavior of colloidal particles as stabilizers of emulsions and foams. The first aspect concerns soluble protein–polysaccharide complex particles (electrostatic nanocomplexes, complex coacervates, covalent conjugates), mixed hydrogel particles, and nanoemulsion-based delivery systems.     

Acid–base interactions and swelling of cellulose fibers in organic liquids

Drago’s acid–base approach was used to quantify the hydrogen bonding interactions in solvent swelling of cellulose fibers. The fiber swelling was correlated with acid–base, dispersive interactions and solvent molar volume. The acid–base interaction potentials of solvents were expressed in terms of their electron pair donor and acceptor numbers. The acid–base interaction terms of cellulosic materials were determined by using: (1) Flory–Huggins; (2) multiple regression models. We have used the swelling data of Mantanis and coworkers, which were based on the equilibrium liquid holding capacities of various compressed fibers in water and series of organic solvents. According to our interpretations, acid–base interactions and molar volume parameters were the major contributors to the overall solubility parameter. Acid–base interaction terms were balanced in alpha-cellulose sample. However spruce wood and sulfite pulp samples were more acidic than basic and therefore swollen better in organic basic solvents. For a good swelling behavior solvent must have high electron pair donor number/acceptor number ratio and high electron pair donor number–acceptor number difference.     

Mutual enhancing effects of the σ-hole interactions and halogen/hydrogen-bonded interactions in the iodine-ylide containing complexes

The region of positive electrostatic potentials (σ-hole) has been found along the extension of the C–I bond in the iodine-ylide CH₂IH, which suggests that the iodine-ylide could interact with nucleophiles to form weak, directional noncovalent interactions. MP2 calculations confirmed that the I···N σ-hole interaction exists in the CH₂IH···NCX (X = H, F, Cl, Br, I) bimolecular complexes. The NCCl···CH₂IH···NCX (X = H, F, Cl, Br, I) termolecular complexes were constructed to investigate the weakly bonded σ-hole interactions to be strengthened by Cl···C halogen bond. And then, the NCY···CH₂IH···NCCl (Y = H, F, Cl, Br, I) termolecular complexes were designed to investigate the enhancing effects of the I···N σ-hole interaction on the Y···C halogen/hydrogen-bonded interactions. Accompany with the mutual enhancing processes of the σ-hole interactions and halogen/hydrogen-bonded interactions in the iodine-ylide containing termolecular complexes, both the I···N σ-hole interactions and Y···C halogen/hydrogen-bonded interactions become more polarizable.     

The role of dipole—dipole interactions in the formation of the structure of amorphous Teflon AF2400 and complexation of acetone with perfluorodioxolane rings

FTIR spectroscopy investigation have shown that the contact of acetone with the film of Teflon AF2400 led to changes in the intensities of some absoption bands of the polymer and to the splitting of the stretching vibration band ν_C=O of acetone. The theoretical vibration spectrum of a model of AF2400 repeat unit was obtained. It is in good agreement with the experimental spectrum of the film of this polymer. The bands, whose intensities change during the contact of the AF2400 film with acetone, belong to the stretching and deformation vibrations of the C-F bond of the dioxolane ring as a whole. Structural, energy, and electron characteristics of a complex of acetone with the perfluorodioxolane ring were calculated by the B3LYP/6-31G(d) method. The dipole-dipole character of interaction of acetone with the repeat unit of AF2400 with the involvement of the whole dioxolane ring was demonstrated. The polarizabilies of the C=O bonds in acetone and the C-F bonds in the dioxolane ring of the polymer are substantially changed, which is in good agreement with the experimental IR spectrum of the AF2400 film that had been in the contact with acetone. The results of quantum chemical and molecular dynamics calculations testify the orthogonal-block structure of the chains in AF2400, which explains great stiffness and a large free volume of this polymer.     

The study of cell wall structure and cellulose–cellulase interactions through fluorescence microscopy

The efficient decomposition of biomass into carbohydrates for the sustainable generation of biofuels has become the focus of much research. Yet, limited understanding exists on how the enzymes that catalyze the biochemical conversion of biomass, such as cellulases, interact with cellulose microfibrils and how cellulose structure is changed by cellulolytic enzymes. This has spurred the application of high-resolution imaging techniques, such as atomic force microscopy or fluorescence microscopy, to visualize the biomolecular interactions and structural changes that occur at the micro/nanoscale. In particular, fluorescence microscopy offers advantages such as high sensitivity and the ability to monitor species under biologically relevant conditions. Furthermore, the introduction of techniques, such as single molecule or super-resolution fluorescence microscopy, has allowed imaging biomolecules and macromolecular structures with near molecular resolution. These advantages make fluorescence microscopy ideally suited for the study of cell wall structure and cellulose–cellulase interactions. The application of fluorescence microscopy has already yielded key insights into the arrangement of structural polysaccharides in the plant cell wall, the reversibility and binding kinetics of cellulases, their molecular motion on crystalline cellulose, and the structural changes that occur as cellulose is depolymerized by cellulases. Yet, the application of fluorescence to study cellulose–cellulase interactions remains limited. This review aims at (1) providing an overview of fluorescence microscopy techniques suitable for the study of cellulose–cellulase interactions; (2) the applications of these techniques to date and the key insights obtained; and (3) the opportunities for future studies of the interaction of cell wall degrading enzymes with cellulosic materials.     

The strength and selectivity of perfluorinated nano-hoops and buckybowls for anion binding and the nature of anion-π interactions

Perfluorinated cycloparaphenylenes (F-[n]CPP, n = 5–8), boron nitride nanohoop (F-[5]BNNH), and buckybowls (F-BBs) were proposed as anion receptors via anion-π interactions with halide anions (Cl⁻, Br⁻ and I⁻), and remarkable binding strengths up to −294.8 kJ/mol were computationally verified. The energy decomposition approach based on the block-localized wavefunction method, which combines the computational efficiency of molecular orbital theory and the chemical intuition of ab initio valence bond theory, was applied to the above anion-π complexes, in order to elucidate the nature and selectivity of these interactions. The overall attraction is mainly governed by the frozen energy component, in which the electrostatic interaction is included. Remarkable binding strengths with F-[n]CPPs can be attributed to the accumulated anion-π interactions between the anion and each conjugated ring on the hoop, while for F-BBs, additional stability results from the curved frameworks, which distribute electron densities unequally on π-faces. Interestingly, the strongest host was proved to be the F-[5]BNNH, which exhibits the most significant anisotropy of the electrostatic potential surface due to the difference in the electronegativities of nitrogen and boron. The selectivity of each host for anions was explored and the importance of the often-overlooked Pauli exchange repulsion was illustrated. Chloride anion turns out to be the most favorable anion for all receptors, due to the smallest ionic radius and the weakest destabilizing Pauli exchange repulsion.     

Influence of the addition of Cr in the microstructure and in the phase transformation temperatures of Cu–Al–Be–Nb–Ni alloys

Journal of Thermal Analysis and Calorimetry - Cu–Al–Be polycrystalline SMAs modified with the addition of inoculants show improved ductility, which accredits them for technological...     

The interactions between cholesterol and phospholipids located in the inner leaflet of humane erythrocytes membrane (DPPE and DPPS) in binary and ternary films—The effect of sodium and calcium ions

The studies on the influence of cholesterol on phospholipids accumulated in inner leaflet of membrane are performed rather rarely, especially in the presence of electrolytes, which are present in membrane environment. Therefore, in this work the interactions between cholesterol and saturated phosphatidylethanolamine (PE) and phosphatidylserine (PS) were studied in binary (phospholipid/cholesterol) and ternary (PS/PE/cholesterol) monolayers in the presence and absence of sodium and calcium ions. The composition of ternary films was estimated to reflect the proportion of PSs to PEs in inner layer of human erythrocyte membrane. The influence of electrolytes on pure PS and PE films was also analyzed. It was found that both sodium and calcium ions affect the condensation of DPPS films, and influence the interactions in DPPS/cholesterol monolayers. On the other hand, no effect of these ions on DPPE films as well as on DPPE/cholesterol interactions in the mixed systems was observed. The results obtained for ternary mixtures prove that in the presence of Na⁺ the interactions between the lipids are more favorable than in the absence of these ions. This is in contrast to the effect of Ca²⁺. All the results were thoroughly analyzed in the context of the structure of polar heads of the investigated phospholipids.     

Protein–polysaccharide interactions and aggregates in food formulations

The protein–polysaccharide combinations that lead to electrostatic complex and coacervate formation are the object of extensive research using both layer-by-layer and mixed emulsion approaches. The protein–polysaccharide conjugates demonstrated interesting physicochemical properties as stabilizers and emulsifiers, as well as texture modifiers in food products. Furthermore, they are potential optimal nutrient delivery systems. Their complex behavior due to several factors such as pH, ionic strength, concentration, heat, and mechanical treatments is the main reason behind the continuous growth of the research field. The review is reporting some recent advances on the topic, along with an overview of the possible interactions between protein and polysaccharide, from Maillard reaction to enzymatic cross-linking passing through coacervates.     

Spectroscopic and electrochemical studies of cocaine–opioid interactions

The drugs of abuse cocaine (C), heroin (H), and morphine (M) have been studied to enable understanding of the occurrence of cocaine–opioid interactions at a molecular level. Electrochemical, Raman, and NMR studies of the free drugs and their mixtures were used to study drug–drug interactions. The results were analyzed using data obtained from quantum-mechanical calculations. For the cocaine–morphine mixture (C–MH), formation of a binary complex was detected; this involved the 3-phenolic group and the heterocyclic oxygen of morphine and the carbonyl oxygen and the methyl protons of cocaine’s methyl ester group. NMR studies conducted simultaneously also revealed C–MH binding geometry consistent with theoretical predictions and with electrochemical and vibrational spectroscopy results. These results provide evidence for the occurrence of a cocaine–morphine interaction, both in the solid state and in solution, particularly for the hydrochloride form. A slight interaction, in solution, was also detected by NMR for the cocaine–heroin mixture. Figure "Schematic representation of the proposed model for cocaine:morphine salt interaction"     

Electrochemical investigations of baicalin and DNA–baicalin interactions

Baicalin is an anti-HIV drug purified from the traditional Chinese medicinal plant Scutellaria Baicalensis Georgi. Baicalin has proven to be electroactive at pyrolytic graphite (PG) electrodes. We thus studied its interaction with DNA via the electrochemical approach. We observed that the peak currents corresponding to the baicalin reduction–oxidation (redox) reaction significantly decrease upon the addition of DNA. With complementary ultraviolet/visible (UV/Vis) spectroscopic evidence, we suggest that baicalin binds to DNA through intercalation. This feature has enabled baicalin to discriminate between double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA).Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

On the effect of thermophoretic force,gravitational force,and particle–particle interactions in field-flow fractionation

The theoretical calculations confirmed that the gravitational force cannot be neglected in all field-flow fractionation techniques separating nanometer-sized colloidal particles whenever particle diameter is approximately 200?nm and larger. Particle–particle repulsive interactions, mostly electrostatic repulsions, influence substantially concentration distribution established by any effective field acting across the fractionation channel, as confirmed explicitly for thermophoretic force generated by temperature gradient in microthermal field-flow fractionation. The ionic strength of the carrier liquid causes the screening of the electrostatic double layer around the dispersed particles and thus influences the retention. The attractive particle–particle forces occur when the zeta potential of the particles approaches to 0?mV, the electrostatic repulsions are screened, and the aggregation of the particles is observed. The pH influences differently the size and zeta potential of the plain polystyrene latex particles and of the particles modified on the surface by the groups –COOH and –NH₂. The role of a detergent in carrier liquid is non-negligible, as demonstrated by its presence or absence in carrier liquid.