Characterization of nanocellulose production by strains of Komagataeibacter sp. isolated from organic waste and Kombucha.

Bacterial nanocellulose production is gaining popularity owing to its applications in food, cosmetics and medical industry. Three Acetobacter strains isolated from organic waste and fermented tea were identified using 16S rDNA sequencing and their ability to produce nanocellulose was studied. Strain isolated from Kombucha has 99% homology with Komagataeibacter rhaeticus DSM 16663 T. This is the first report where nanocellulose productivity of this strain with different carbon sources such as glucose, glycerol, fructose and sucrose has been studied. 1% glycerol was found to be optimal concentration, with up to 69% of the utilized carbon converted to nanocellulose. Maximum productivity of 4.5 g/L of bacterial nanocellulose was obtained. Average nitrogen and phosphorus consumption rate was 45 mg/L/day each. Physical properties such as crystallinity, fibril dimensions, and glass transition temperature were studied. Bacterial cellulose was 80% crystalline when glycerol and glucose were used as carbon source and 73% for fructose and sucrose. Renewable materials such as bacterial cellulose with their unique properties are the future for applications in the field of cosmetics, composite and wound care.

NMR investigation of exchange dynamics and binding of phenol and phenolate in DODAC vesicular dispersions.

The interaction between phenol molecules, both in their undissociated and dissociated states, and cationic dioctadecyl dimethylammonium chloride (DODAC) vesicles were thoroughly investigated using NMR techniques. In particular, diffusion and relaxation measurements, combined with the two sites Kärger model, were used to evaluate the exchange dynamics and the binding of the aromatic molecules to the vesicles. The results reveal that, besides concentration and vesicle preparation method, pH conditions have the biggest impact on the phenol sorption behavior. Although the dissociated form of phenol formed at high pH is more hydrophilic, the results indicated that phenol-DODAC interactions were largely favored in basic conditions as a consequence of the strong electrostatic interaction between the phenolate anions and the cationic surfactant headgroup.

Single-walled aluminosilicate nanotube/poly(vinyl alcohol) nanocomposite membranes.

The fabrication, detailed characterization, and molecular transport properties of nanocomposite membranes containing high fractions (up to 40 vol %) of individually-dispersed aluminosilicate single-walled nanotubes (SWNTs) in poly(vinyl alcohol) (PVA), are reported. The microstructure, SWNT dispersion, SWNT dimensions, and intertubular distances within the composite membranes are characterized by scanning and transmission electron microscopy (SEM and TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), XRD rocking curve analysis, small-angle X-ray scattering (SAXS), and solid-state NMR. PVA/SWNT nanocomposite membranes prepared from SWNT gels allow uniform dispersion of individual SWNTs in the PVA matrix with a random distribution of orientations. SAXS analysis reveals the length (∼500 nm) and outer diameter (~2.2 nm) of the dispersed SWNTs. Electron microscopy indicates good adhesion between the SWNTs and the PVA matrix without the occurrence of defects such as voids and pinholes. The transport properties of the PVA/SWNT membranes are investigated experimentally by ethanol/water mixture pervaporation measurements, computationally by grand canonical Monte Carlo and molecular dynamics, and by a macroscopic transport model for anisotropic permeation through nanotube-polymer composite membranes. The nanocomposite membranes substantially enhance the water throughput with increasing SWNT volume fraction, which leads to a moderate reduction of the water/ethanol selectivity. The model is parameterized purely from molecular simulation data with no fitted parameters, and shows reasonably good agreement with the experimental water permeability data.

Formation of single-walled aluminosilicate nanotubes from molecular precursors and curved nanoscale intermediates.

We report the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature in the formation of single-walled aluminosilicate nanotubes. We characterize the structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm by electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy ((27)Al liquid-state, (27)Al and (29)Si solid-state MAS), and dynamic light scattering. Together with structural optimization of key experimentally identified species by solvated density functional theory calculations, this study reveals the existence of intermediates with bonding environments, as well as intrinsic curvature, similar to the structure of the final nanotube product. We show that "proto-nanotube-like" intermediates with inherent curvature form in aqueous synthesis solutions immediately after initial hydrolysis of reactants, disappear from the solution upon heating to 95 °C due to condensation accompanied by an abrupt pH decrease, and finally form ordered single-walled aluminosilicate nanotubes. Detailed quantitative analysis of NMR and ESI-MS spectra from the relevant aluminosilicate, aluminate, and silicate solutions reveals the presence of a variety of monomeric and polymeric aluminate and aluminosilicate species (Al(1)Si(x)-Al(13)Si(x)), such as Keggin ions [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+) and polynuclear species with a six-membered Al oxide ring unit. Our study also directly reveals the complexation of aluminate and aluminosilicate species with perchlorate species that most likely inhibit the formation of larger condensates or nontubular structures. Integration of all of our results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles.

Adsorption of aromatic alcohols into the walls of hollow polyelectrolyte capsules.

Hollow polyelectrolyte microcapsules prepared by layer-by-layer assembly of polyelectrolytes onto colloidal particles and subsequent core removal are investigated concerning their uptake capacity and the exchange dynamics of aromatic alcohols, that is, hydroquinone and phenol. Diffusion coefficients of the alcohols in the dispersion are determined by pulsed field gradient (PFG) NMR spectroscopy. In addition, spin relaxation rates are determined, which characterize the molecular dynamics. Alcohol molecules in capsule dispersions occur as a bound fraction that is adsorbed to the wall and as a free fraction in the aqueous phase. According to a previously established procedure, from diffusion and relaxation data, population fractions and exchange times are calculated using a two-site model. The adsorbed amounts are well described by Langmuir isotherms, where for hydroquinone as compared to phenol the equilibrium constant is about a factor of 3 larger, and the maximum adsorbed amount about a factor of 3 lower. This indicates the relevance of H bonds for adsorption as well as size effects controlling the uptake capacity of the wall for small molecules.

Scaling law of poly(ethylene oxide) chain permeation through a nanoporous wall.

This paper presents a study of the permeation of poly(ethylene oxide) (PEO) chains through the nanoporous wall of hollow polymeric capsules prepared by self-assembly of polyelectrolytes. We employ the method of pulsed field gradient (PFG) NMR diffusion to distinguish chains in different sites, i.e., in the capsule interior and free chains in the dispersion, by their respective diffusion coefficient. From a variation of the observation time, the time scale of the molecular exchange between both sites and thus the permeation rate constant is extracted from a two-site exchange model. Permeation rate constants show two different regimes with a different dependence on chain length. This suggests a transition between two different mechanisms of permeation as the molecular weight is increased. In either regime, the permeation time can be described by a scaling law tau approximately N (b) , with b = (4)/ 3 for short chains and b = (1)/ 3 for long chains. We discuss these exponents, which clearly differ from the theoretical predictions for chain translocation.

Pulsed field gradient NMR study of phenol binding and exchange in dispersions of hollow polyelectrolyte capsules.

The distribution and exchange dynamics of phenol molecules in colloidal dispersions of submicron hollow polymeric capsules is investigated by pulsed field gradient NMR (PFG-NMR). The capsules are prepared by layer-by-layer assembly of polyelectrolyte multilayers on silica particles, followed by dissolution of the silica core. In capsule dispersion, (1)H PFG echo decays of phenol are single exponentials, implying fast exchange of phenol between a free site and a capsule-bound site. However, apparent diffusion coefficients extracted from the echo decays depend on the diffusion time, which is typically not the case for the fast exchange limit. We attribute this to a particular regime, where apparent diffusion coefficients are observed, which arise from the signal of free phenol only but are influenced by exchange with molecules bound to the capsule, which exhibit a very fast spin relaxation. Indeed, relaxation rates of phenol are strongly enhanced in the presence of capsules, indicating binding to the capsule wall rather than encapsulation in the interior. We present a quantitative analysis in terms of a combined diffusion-relaxation model, where exchange times can be determined from diffusion and spin relaxation experiments even in this particular regime, where the bound site acts as a relaxation sink. The result of the analysis yields exchange times between free phenol and phenol bound to the capsule wall, which are on the order of 30 ms and thus slower than the diffusion controlled limit. From bound and free fractions an adsorption isotherm of phenol to the capsule wall is extracted. The binding mechanism and the exchange mechanism are discussed. The introduction of the global analysis of diffusion as well as relaxation echo decays presented here is of large relevance for adsorption dynamics in colloidal systems or other systems, where the standard diffusion echo decay analysis is complicated by rapidly relaxing boundary conditions.