Mesoporous structures in never-dried softwood cellulose fibers investigated by nitrogen adsorption

Nitrogen adsorption was used to characterize mesoporous structures in never-dried softwood cellulose fibers. Distinct inflections in desorption isotherms were observed over the relative vapor pressure (P/P₀) range of 0.5–0.42 for never-dried cellulose fibers and partially delignified softwood powders. The reduction in N₂ adsorption volume was attributed to cavitation of condensed N₂ present in mesopores formed via lignin removal from wood cell walls during delignification. The specific surface areas of significantly delignified softwood powders were ~150 m² g^?1, indicating that in wood cell walls 16 individual cellulose microfibrils, each 3–4 nm in width, form one cellulose fibril bundle surrounded with a thin layer of lignin and hemicelluloses. Analysis of N₂ adsorption isotherms indicates that mesopores in the softwood cellulose fibers and partially delignified softwood powders had peaks ranging from 4 to 20 nm in diameter.     

Origin of hydrophilicity of cellulose hydrogel from aqueous LiOH/urea solvent coagulated with alkyl alcohols

Surface and structural properties of cellulose hydrogel prepared from LiOH/urea solvent with alcoholic coagulation were examined. As coagulants, alcohols from methanol to butanol were employed. Alcohol with high water miscibility (MeOH, EtOH, 1-PrOH, 2-PrOH, and t-BuOH) gave a nano-porous structure consisting of a fibrous network of cellulose, while alcohol with low water miscibility (1-BuOH, 2-BuOH, i-BuOH) showed aggregation of a fibrous structure because of large shrinkage during the coagulation process. Congo red adsorption measurement showed that an increase in the carbon number of alcohol brought about a less hydrophobic surface. This is likely to occur because the alkali/urea/cellulose complex was formed during the coagulation process in the case of ethanol, propanol, and butanol, leading to a higher crystalline content of cellulose II, the surface of which is thought to be highly hydrophilic.     

Physicochemical Studies of Demetalation of Light-harvesting Bacteriochlorophyll Isomers Purified from Green Sulfur Photosynthetic Bacteria

Demetalation kinetics of bacteriochlorophylls (BChls) c, d and e from green sulfur photosynthetic bacteria were studied under weakly acidic conditions. Demetalation rate constants of BChl e possessing a formyl group at the 7-position were significantly smaller than those of BChls c and d , which had a methyl group at this position. The activation energy of demetalation of 3¹ R -8,12-diethyl([E,E])-BChl e was 1.5-times larger than that of 3¹ R -[E,E]-BChl c . ¹⁵N-labeled 3¹ R -[E,E]-BChls c and e were purified from cells of green sulfur bacteria grown in a medium containing ¹⁵NH₄Cl, and their ¹⁵N NMR spectra were measured. The chemical shifts of N₂₁, N₂₂ and N₂₃ atoms of 3¹ R -[E,E]-BChl e were lower-field shifted than those of 3¹ R -[E,E]-BChl c , respectively, and especially the difference in chemical shifts of N₂₂ was significantly large. These results suggest that the electron-withdrawing formyl group at the 7-position of BChl e affected an electronic state of the chlorin macrocycle and caused BChl e to be more tolerant for removal of the central magnesium compared with BChls c and d .     

Derivation of extremely slow dynamics of protein motion based on entropy invariance

It is a mysterious fact that protein systems often show an extremely slow dynamics of their molecular motions with time scales much longer than nanosecond order, although their characteristic frequencies obtained by the normal mode analysis fall in much shorter temporal regions. This Letter provides a heuristic account for why and how such extremely slow modes of protein motions naturally emerge from fast molecular modes on the basis of an idea of entropy invariance in the principal component analysis.     

Micro‐scale (1.5 µm) sulphur isotope analysis of contemporary and early Archean pyrite

We present a method for in situ sulphur (S) isotopic analysis of significantly small areas (1.5 µm in diameter) in pyrite using secondary ion mass spectrometry (NanoSIMS) to interpret microbial sulphur metabolism in the early earth. We evaluated the precision and accuracy of S isotopic ratios obtained by this method using hydrothermal pyrite samples with homogeneous S isotopic ratios. The internal precision of the δ³⁴S value was 1.5‰ at the level of 1 sigma of standard error (named 1SE) for a single spot, while the external reproducibility was estimated to be 1.6‰ at the level of 1 sigma of standard deviation (named 1SD, n = 25). For each separate sample, the average δ³⁴S value was comparable with that measured by a conventional method, and the accuracy was better than 2.3‰. Consequently, the in situ method is sufficiently accurate and precise to detect the S isotopic variations of small sample of the pyrite (less than 20 µm) that occurs ubiquitously in ancient sedimentary rocks. This method was applied to measure the S isotopic distribution of pyrite within black chert fragments in early Archean sandstone. The pyrite had isotopic zoning with a ³⁴S‐depleted core and ³⁴S‐enriched rim, suggesting isotopic evolution of the source H₂S from ?15 to ?5‰. Production of H₂S by microbial sulphate reduction (MSR) in a closed system provides a possible explanation for both the ³⁴S‐depleted initial H₂S and the progressive increase in the δ³⁴S_H2S value. Although more extensive data are necessary to strengthen the explanation for the origin of the MSR, the results show that the S isotopic distribution within pyrite crystals may be a key tracer for MSR activity in the early earth. Copyright © 2010 John Wiley & Sons, Ltd.     

Intra- and intermolecular interactions between cyclic-AMP receptor protein and DNA: ab initio fragment molecular orbital study

The ab initio fragment molecular orbital (FMO) calculations were performed for the cAMP receptor protein (CRP) complexed with a cAMP and DNA duplex to elucidate their sequence-specific binding and the stability of the DNA duplex, as determined by analysis of their inter- and intramolecular interactions. Calculations were performed with the AMBER94 force field and at the HF and MP2 levels with several basis sets. The interfragment interaction energies (IFIEs) were analyzed for interactions of CRP-cAMP with each base pair, DNA duplex with each amino acid residue, and each base pair with each residue. In addition, base-base interactions were analyzed including hydrogen bonding and stacking of DNA. In the interaction between DNA and CRP-cAMP, there was a significant charge transfer (CT) from the DNA to CRP, and this CT interaction played an important role as well as the electrostatic interactions. It is necessary to apply a quantum mechanical approach beyond the "classical" force-field approach to describe the sequence specificity. In the DNA intramolecular interaction, the dispersion interactions dominated the stabilization of the base-pair stacking interactions. Strong, attractive 1,2-stacking interactions and weak, repulsive 1,3-stacking interactions were observed. Comparison of the intramolecular interactions of free and complexed DNA revealed that the base-pairing interactions were stronger, and the stacking interactions were weaker, in the complexed structure. Therefore, the DNA duplex stability appears to change due to both the electrostatic and the CT interactions that take place under conditions of DNA-CRP binding.     

Quantum sieving effect of modified activated carbon fibers on H2 and D2 adsorption at 20 K

Quantum sieving of activated carbon fibers (ACFs) and their fluorides was observed for H(2) and D(2) adsorption at 20 K. Fluorination reduced the slit-shaped pore width of ACFs by 0.2 nm. The activated carbon fibers can act as highly efficient quantum sieves for H(2) and D(2), because the effective size of an H(2) molecule is larger than that of a D(2) molecule due to the uncertainty principle and the molecular size difference between H(2) and D(2) is significant in the micropore space. The D(2)/H(2) selectivity of ACFs evaluated by ideal adsorption solution theory was larger than that of the fluorinated ACFs.     

Nanocopying of individual DNA strands and formation of the corresponding surface pattern of titania nanotube

Titania nanotube was prepared by nanocopying of the individual DNA double strand as template. DNA was first spread on a solid substrate, and its molecular surface was coated with an ultrathin titania layer by 3 cycles of the surface sol-gel process. Fluorescence microscopic images before and after titania coating of the DNA/YOYO-1 complex were essentially identical, showing that the titania coating did not change the chemical properties of the complex. Titania coating effectively prohibited chemical degradation of titania-coated DNA with DNase I and physically separated the DNA strand from the surrounding environment with an ultrathin titania barrier. The morphology of the DNA strand was preserved, as confirmed by microscopic and spectroscopic observations. The presence of the hollow (tubular) structure was confirmed by a silver staining experiment coupled with scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX) analysis. The present finding shows the effectiveness of nanocopying of the individual DNA strand.