Determination of lignin by size exclusion chromatography using multi angle laser light scattering

A method was developed using high-performance size exclusion liquid chromatography (HPSEC) with multi-angle laser light scattering (MALLS), quasi-elastic light scattering (QELS), interferometric refractometry (RI) and UV detection to characterize and monitor lignin. The combination proved very effective at tracking changes in molecular conformation of lignin molecules over time; i.e. changes in molecular weight distribution, radius of gyration, and hydrodynamic radius. Until this study, UV detection (280 nm) had been the primary lignin determination method for chromatography. Three different HPLC columns were used to study the effects of pH, flow conditions, and mobile phase compositions (dimethyl sulphoxide, water, 0.1M NaOH, and lithium bromide) on the chromatography of lignin. Since light scattering accuracy is highly dependent on solute concentration, both the UV and RI detectors were calibrated for use as concentration detectors. Shodex Asahipak GS-320 HQ column with 0.1M NaOH (pH 12.0) run at 0.5 ml/min was found to give the highest separation and most consistent recovery. The study also revealed that the lignin aggregated at pH below 8.5. This aggregation was detected only by MALLS and was not observed on UV or RI detectors. It is very important to take this loss in apparent concentration due to aggregation into consideration before collecting reliable depolymerization data.     

Cloning and expression of full-lengthTrichoderma reesi cellobiohydrolase I cDNAs inEscherichia coli

The process of converting lignocellulosic biomass to ethanol via fermentation depends on developing economic sources of cellulases.Trichoderma reesei cellobiohydrolase (CBH) I is a key enzyme in the fungal cellulase system; however, specific process application requirements make modification of the enzyme by site-directed mutagenesis (SDM) an attractive goal. To undertake SDM investigations, an efficient, cellulase-free host is required. To test the potential ofEscherichia coli as a host, T.reesei CBH I cDNA was expressed inE. coli strain GI 724 as a C-terminal fusion to thermostable thioredoxin protein. Full-length expression of CBH I was subsequently verified by molecular weight, Western blot analysis, and activity on soluble substrates.

     

Dilute-acid pretreatment of two short-rotation herbaceous crops

Applied Biochemistry and Biotechnology -     

Spectroscopic evidence for a dinitrogen complex of gallium and estimation of the Ga-N2 bond strength

Matrix-isolation experiments were performed to study the interaction between Ga atoms and N2 by using Raman and UV/Vis spectroscopies for detection and analysis. It was revealed that a weak complex is formed, for which resonance Raman spectra were obtained. Several overtones were sighted, allowing a rough estimate of the Ga-N2 fragmentation energy to be made (approximately 19 kJ mol(-1)). The excitation profile obtained from the spectra at different laser wavelengths agrees with the UV/Vis spectrum and shows that the complex exhibits an electronic transition at around 410 nm. At the Ga atom, this transition can be described as a 2S<--2P or 2D<--2P excitation, which is red-shifted from its position for free Ga atoms (approximately 340 nm and 270 nm for 2S<--2P and 2D<--2P, respectively) as a result of N2 complexation. The effect of complexation involves, therefore, only slight stabilization of the 2P ground state but relatively strong stabilization of the excited (2)S state. Accordingly, for the Ga atom in its excited 2S state, the Ga-N2 bond energy can be estimated to be around 79 kJ mol(-1).     

Direct imaging of surface-enhanced Raman scattering in the near field

By using near-field scanning microscopy/spectroscopy, we show that surface-enhanced Raman scattering (SERS) of rhodamine 6G deposited on self-affine silver colloidal film is localized to small, down to less than 200 nm, portions of the film. The locus of the SERS signals ("hot spots") does not necessarily reside in special topographic elements such as interstices and between nanoparticles. The local SERS enhancement is estimated to be over 3 orders of magnitude higher compared to the far-field measurements. Near-field imaging of SERS directly validates the theory of the optical response of self-affine fractal objects.     

Efficacy of hydrolytic enzyme augmentation and thermochemical pretreatments for increased secondary anaerobic digestion of treated municipal sewage sludges

Rising costs for landfill disposal of municipal sewage residues have prompted evaluation of alternative methods for reducing the bulk of the final waste. Representative samples of municipal sewage sludge residues were obtained from three major treatment plants in the United States, including Los Angeles (Hyperion), Denver (North Metro), and Chicago (Stickney). The majority of the treated, dewatered sewage sludge solids was found to be volatile (50–60%) and, presumably, biodegradable. Additionally, much of the volatile content was solubilized by both acid detergent fiber and neutral detergent fiber treatments, and was presumed to be proteineous microbial biomass in nature. Both low- and high-solids anaerobic digester systems, as well as the standard biochemical methane potential (BMP) assay, were utilized to evaluate the anaerobic digestibility of these sewage sludge residues. The low methane yields and, thus, the poor organic waste conversion indicated the need for treatment prior to bioconversion. The effectivenesss of various pretreatments based on assessment of increased soluble protein or organics and anaerobic digestibility as determined by the BMP assay was evaluated.     

The high-frequency stark effect in the balmer lineD-alpha

The calculation of the emission lineD _α under the influence of a linearly polarizedrf-field (the oscillation frequency is equal to 34.8 GHz, the electric field amplitude is of the order 200 kV/m) delivers satellites on both sides of the main peak. Deviations from symmetry with respect to the average wavelength of the central line originate from the fine structure: the entire satellite structure is slightly shifted (～ 1 pm) to the red and the intensity of the blue satellite is about 15% higher than that of the red one. The numerical analysis has incorporated also the Zeeman effect by a static magnetic field (140 mT) parallel to therf-electric field as well as Doppler broadening on account of the temperature of the deuterium atoms which amounts to 1000 K. The comparison of measured and calculated line shapes allows to determine therf-electric field strength with an accuracy of about 5%.