Mild Organosolv Delignification of Residual Aspen Bark after Extractives Isolation as a Step in Biorefinery Processing Schemes

European aspen (Populus tremula (L.) (Salicaceae)) bark is a promising raw material in multi-step biorefinery schemes due to its wide availability and higher content of secondary metabolites in comparison to stem wood biomass. The main objective of this study was to investigate the major cell wall component-enriched fractions that were obtained from aspen bark residue after extractives isolation, primarily focusing on integration of separated lignin fractions and cellulose-enriched bark residue into complex valorization pathways. The “lignin first” biorefinery approach was applied using mild organosolv delignification. The varying solvent systems and process conditions for optimal delignification of residual aspen bark biomass were studied using a response surface methodology approach. The conditions for maximum process desirability at which the highest amount of lignin-enriched fraction was separated were as follows: 20-h treatment time at 117 °C, butanol/water 4:1 (v/v) solvent system with solid to liquid ratio of 1 to 10. At optimal separation conditions, lignin-enriched fraction exhibited a higher content of β–O–4 linkages vs. C–C linkages content in its structure as well as a high amount of hydroxyl groups, being attractive for its further valorization. At the same time, the content of glucose in products of cellulose-enriched residue hydrolysis was 52.1%, increased from 10.3% in untreated aspen bark. This indicates that this fraction is a promising raw material for obtaining cellulose and fermentable glucose. These results show that mild organosolv delignification of extracted tree bark can be proposed as a novel biorefinery approach for isolation of renewable value-added products with various application potentials.     

Ultrafast anisotropy dynamics of water molecules dissolved in acetonitrile

Infrared pump-probe experiments are performed on isolated H(2)O molecules diluted in acetonitrile in the spectral region of the OH stretching vibration. The large separation between water molecules excludes intermolecular interactions, while acetonitrile as a solvent provides substantial hydrogen bonding. Intramolecular coupling between symmetric and asymmetric modes results in the anisotropy decay to the frequency-dependent values of approximately 0-0.2 with a 0.2 ps time constant. The experimental data are consistent with a theoretical model that includes intramolecular coupling, anharmonicity, and environmental fluctuations. Our results demonstrate that intramolecular processes are essential for the H(2)O stretching mode relaxation and therefore can compete with the intermolecular energy transfer in bulk water.     

Dielectric profile of interfacial water and its effect on double-layer capacitance

The framework for deriving tensorial interfacial dielectric profiles from bound charge distributions is established and applied to molecular dynamics simulations of water at hydrophobic and hydrophilic surfaces. In conjunction with a modified Poisson-Boltzmann equation, the trend of experimental double-layer capacitances is well reproduced. We show that the apparent Stern layer can be understood in terms of the dielectric profile of pure water.     

Morphology and Fine Structure of Membranes upon Osmotic Upshifts

Lipid bilayers are impermeable to most polar molecules. Osmoregulated transporters are responsible for controlling the intracellular osmolarity and protecting the cell against changes in osmolality in the environment. The mechanisms by which membranes regulate the activity of these transporters are still largely unknown. In this paper we investigate the response to hyperosmotic stress in artificial, chemically well-defined membrane models called Giant Unilamellar Vesicles (GUV). The lipid compositions analysed are relevant for the activity of an ABC-transport system that is controlled by the physicochemical properties of the membrane bilayer. Morphology changes are monitored by phase-contrast optical microscopy, and fine structural details related to domain formation are investigated by fluorescence confocal optical microscopy.     

Coherent spin transport through a 350 micron thick silicon wafer

We use all-electrical methods to inject, transport, and detect spin-polarized electrons vertically through a 350-micron-thick undoped single-crystal silicon wafer. Spin precession measurements in a perpendicular magnetic field at different accelerating electric fields reveal high spin coherence with at least 13pi precession angles. The magnetic-field spacing of precession extrema are used to determine the injector-to-detector electron transit time. These transit time values are associated with output magnetocurrent changes (from in-plane spin-valve measurements), which are proportional to final spin polarization. Fitting the results to a simple exponential spin-decay model yields a conduction electron spin lifetime (T1) lower bound in silicon of over 500 ns at 60 K.     

1H n.m.r. investigation on the site of hydration in the asymmetric diazanaphthalenes

The site of hydration for 1,6- and 1,7-naphthyridine has been determined by specific line broadening in the ¹H n.m.r. spectra on the addition of water. The site of hydration appears to be the same as the site of protonation (β-nitrogen atom). The site of hydration in quinazoline has been shown to be the α-nitrogen atom. This strongly indicates that the site of protonation in this compound will also be at that nitrogen.     

Photon-echo relaxation measurements with two dye-lasers application to pentacene-h14 and -d14 in p-terphenyl-h crystals at 1.5 K

Electronically controlled photon-echo relaxation measurements, using two nitrogen pumped dye-lasers, are reported for mixed crystals of pentacene-h₁₄ and -d₁₄ in p-terphenyl-h₁₄ at 1.5 K. In dilute mixed crystals (ca. 10^?8 M) the photon-echo lifetime is found to be exclusively determined by the fluorescence lifetime. Homogeneous linewidths of 7.1 and 5.9 MHz at 1.5 K are then calculated for the electronic origin of the ¹B_2u ← ¹A_1g transition of pentacene-h₁₄ and -d₁₄ respectively. The decrease in photon-echo lifetime at higher guest concentrations (ca. 10^?7 M) is ascribed to energy transfer between excited and neutral guest molecules.     

Stark shifts of the visible absorption systems of the NO−2 ion in NaNO2

Stark effect measurements on the lowest triplet and singlet transitions of the nitrite ion show that the change of dipole moment on excitation is very small (ca. 0.30 D) and of opposite sign for the two states. The dipole moment change in the triplet manifold is also found to distinctly depend on vibrational (ν₂) excitation. This is explained as a result of vibronic coupling among B₁ triplet states.     

13C n.m.r. investigation on the first and second nitrogen protonation in the diazanaphthalenes

The ¹³C chemical shifts of the diazanaphthalenes have been recorded as a function of the pH value, providing classical titration curves. From these curves the pK₁ and pK₂ values have been determined taking into account the activity coefficients. The changes in ¹³C chemical shift under the influence of nitrogen protonation (Δδ) can be described by two protonation parameter sets.