Polymerization of Kraft lignin via ultrasonication for high-molecular-weight applications

Kraft lignin is an inexpensive and abundant byproduct of pulp mills that can be used in the synthesis of adhesives and carbon fibers along with energy production. Some of these material applications favor the utilization of high molecular weight (HMW) lignin. This study investigates the use of ultrasonics as a means to increase the degree of polymerization (DP) of highly purified Kraft lignin. Treated samples were characterized by gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, ¹³C and ³¹P nuclear magnetic resonance (NMR). After 15 min of sustained cavitation, ultrasonicated lignin generated a high molecular-weight fraction (～35%) that had a weight-average molecular weight (M_w) over 450-fold greater than the initial Kraft lignin sample. ¹³C-NMR and ³¹P-NMR analysis indicated that the highly-polymerized fraction was enriched with C5 condensed phenolic structures.     

Generation of electron beams in high-aspect-ratio magnetron guns with secondary emission cathodes

The generation of electron beams in high-aspect-ratio magnetron guns with cold metallic secondary-emission small-diameter cathodes is discussed. The parameters of the beams as functions of the electric and magnetic fields are studied for various ways of generating voltage pulses needed for the secondary emission multiplication of the electrons and the beam generation.     

Ion-pair chromatographic monitoring of photographic effluents

Ion-pair chromatographic technique was developed for the rapid and simple determination of the main contaminants (bromide, iodide, sulphite, thiosulphate, thiocyanate, iron(III)-EDTA chelate, free EDTA, hydroquinone and phenidone) in spent photographic solutions. Free EDTA was converted into stable Ni(II)-EDTA chelate prior to analysis. The optimal mobile phase conditions were established by varying the concentrations of tetrabutylammonium (TBA) phosphate and acetonitrile, pH and ionic strength. Separation of five inorganic anions, two metal chelates and two neutral compounds was accomplished in about 30 min using a mobile phase containing 7.5 mmol/L TBA-phosphate, 10 mmol/L NaCl (pH 6.5) and 20% (v/v) acetonitrile. The detection limits (UV detection at 210 nm) ranged from 0.4 μmol/L for phenidone to 8 μmol/L for sulphite with a linearity of 2–2.5 orders of magnitude. The method was applied to the rapid monitoring of spent photographic solutions before and after decomposition. The recovery tests established for two samples were within the range 95–103%.      

Determination of EDTA in used fixing solutions by capillary electrophoresis

A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm × 75 μm I.D.) filled with a borate buffer (50 mmol L^–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved is 2 × 10^–6 mol L^–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions. Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998     

Deuterium incorporation into cellulose: a mini-review of biological and chemical methods

Cellulose - Isotopic enrichment offers structural insights that are not easily accessible with natural abundance isotopic composition. Deuterated cellulose has attracted considerable attention in...     

Biology evolves to fight chemistry

A human enzyme variant, PON1-G3C9, accidentally catalyzes the hydrolysis of organophosphorus chemical weapons. In this issue of Chemistry & Biology, Goldsmith and coworkers describe a new PON1 variant with improved hydrolysis by several hundred fold; enough that it may protect animals from a toxic dose.     

Grafting of model primary amine compounds to cellulose nanowhiskers through periodate oxidation

This study demonstrates regioselective oxidation of cellulose nanowhiskers using 2.80–10.02 mmols of sodium periodate per 5 g of whiskers followed by grafting with methyl and butyl amines through a Schiff base reaction to obtain their amine derivatives in 80–90 % yield. We found a corresponding increase in carbonyl content (0.06–0.14 mmols/g) of the dialdehyde cellulose nanowhiskers with the increase in oxidant as measured by titrimetric analysis and this was further evidenced by FT-IR spectroscopy. Grafting of amine compounds to the oxidized cellulose nanowhiskers resulted in their amine derivatives, which are found to be partially soluble in DMSO. Therefore, the reduction reaction between amines and carbonyl groups was confirmed through ¹³C NMR spectra, which was also supported by copper titration, XPS, and FT-IR spectroscopy. Morphological integrity and crystallinity of the nanowhiskers was maintained after the chemical modification as studied by AFM and solid-state ¹³C NMR, respectively.     

Dipole magnet of the injection system for the SALO recirculator

A design of a dipole magnet was developed for the injection system of the SALO recirculator. The constructed prototype magnet has a C-shaped structure with rectangular sections. The pole section is 100 × 100 mm; the aperture is 25 mm. Field distributions in the magnet at a gap induction of 0.05 and 0.2 T were measured. The effective length of the magnet and multipole components of the magnetic field were calculated.     

Increased Saccharification Yields from Aspen Biomass Upon Treatment with Enzymatically Generated Peracetic Acid

The recalcitrance of lignocellulosic biomass to enzymatic release of sugars (saccharification) currently limits its use as feedstock for biofuels. Enzymatic hydrolysis of untreated aspen wood releases only 21.8% of the available sugars due primarily to the lignin barrier. Nature uses oxidative enzymes to selectively degrade lignin in lignocellulosic biomass, but thus far, natural enzymes have been too slow for industrial use. In this study, oxidative pretreatment with commercial peracetic acid (470 mM) removed 40% of the lignin (from 19.9 to 12.0 wt.% lignin) from aspen and enhanced the sugar yields in subsequent enzymatic hydrolysis to about 90%. Increasing the amount of lignin removed correlated with increasing yields of sugar release. Unfortunately, peracetic acid is expensive, and concentrated forms can be hazardous. To reduce costs and hazards associated with using commercial peracetic acid, we used a hydrolase to catalyze the perhydrolysis of ethyl acetate generating 60–70 mM peracetic acid in situ as a pretreatment to remove lignin from aspen wood. A single pretreatment was insufficient, but multiple cycles (up to eight) removed up to 61.7% of the lignin enabling release of >90% of the sugars during saccharification. This value corresponds to a predicted 581 g of fermentable sugars from 1 kg of aspen wood. Improvements in the enzyme stability are needed before the enzymatically generated peracetic acid is a commercially viable alternative.     

Focusing mutations into the P. fluorescens esterase binding site increases enantioselectivity more effectively than distant mutations

Rational design of enzymes with improved properties, such as enantioselectivity, usually focuses mutations within the substrate binding site. On the other hand, directed evolution of enzymes usually targets the entire protein and discovers beneficial mutations far from the substrate binding site. In this paper, we propose an explanation for this discrepancy and show that a combined approach--random mutagenesis within the substrate binding site--is better. To increase the enantioselectivity (E) of a Pseudomonas fluorescens esterase (PFE) toward methyl 3-bromo-2-methylpropionate, we focused mutagenesis into the substrate binding site at Trp28, Val121, Phe198, and Val225. Five of the catalytically active mutants (13%) showed better enantioselectivity than wild-type PFE. The increases in enantioselectivity were higher (up to 5-fold, reaching E = 61) than with mutants identified by random mutagenesis of the entire enzyme.