Controlling the water content of never dried and reswollen bacterial cellulose by the addition of water-soluble polymers to the culture medium

For the modification of medically useful biomaterials from bacterially synthesized cellulose, fleeces of Acetobacter xylinum have been produced in the presence of 0.5, 1.0, and 2.0% (m/v) carboxymethylcellulose (CMC), methylcellulose (MC), and poly(vinyl alcohol) (PVA), respectively, in the Hestrin-Schramm culture medium. The incorporation of the water-soluble polymers into cellulose and their influence on the structure, crystal modifications, and material properties are described. With IR and solid-state ¹³C NMR spectroscopy of the fleeces, the presence of the cellulose ethers and an increase in the amorphous parts of the cellulose modifications (NMR results) have been detected. The incorporation is represented by a higher product yield, too. As demonstrated by scanning electron microscopy, a porelike cellulose network structure forms in the presence of CMC and MC. This modified structure increases the water retention ability (expressed as the water content), the ion absorption capacity, and the remaining nitrogen-containing residues from the culture medium or bacteria cells. The water content of bacterial cellulose (BC) in the never dried state and the freeze-dried, reswollen state can be controlled by the CMC concentration in the culture solution. The freeze-dried, reswollen BC-CMC (2.0%) contains 96% water after centrifugation, whereas standard BC has only 73%. About 98% water is included in a BC-MC composite in the wet state, and about 93% is included in the reswollen state synthesized in the presence of 0.5, 1.0, or 2.0% MC. These biomaterial composites can be stored in the dried state and reswollen before use, reaching a higher water absorption than pure, never dried BC. The copper ion capacity of BC-CMC composites increases proportionally with the added amount of CMC. BC-CMC (0.5%) can absorb 3 times more copper ions than original BC. In the case of 0.5 and 1.0% PVA additions to the culture solution, this polymer cannot be detected in the cellulose fleeces after they are washed. Nevertheless the presence of PVA in the culture medium effects a decreased product yield, a retention of nitrogen-containing residues in the material during purification, a reduced water absorption ability, and a slightly higher copper ion capacity in comparison with original BC. The water content of freeze-dried, reswollen BC-PVA (0.5%) is only 62%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 463–470, 2004     

Book reviews

Please forward books for review to the book review editor: Magdolna Hargittai, Structural Chemistry Research Group of the Hungarian Academy of Sciences, Eötvös University, H-1431 Budapest, Pf. 117, Hungary     

Stereoselective preparation of spirane bridged, sandwiched bisarenes

Preparation of α-oxo derivatives of spiro[4.4]nonane, spiro[4.5]decane and spiro[5.5]undecane derivatives is described. An efficient method for spiroannulation by Rh(I)-catalysed intramolecular hydroacylation provides α,α′-difunctionalised spiro[4.5]decanes. The α,α′-dioxo groups have been converted into vinyl triflates for arylation by Pd-catalysed cross-coupling reactions under Stille, Negishi or Suzuki conditions depending on relative reactivities. Stereoselective saturation of the conjugated aryl olefinic bonds by catalytic hydrogenation over Pd-carbon provides methodology for stereoselective preparation of α-aryl- and α,α′-cis,cis-diaryl spiranes, the latter with a sandwich like structure. Single crystal X-ray analyses have been used in the structural assignments.     

Limiting the Number of Potential Binding Modes by Introducing Symmetry into Ligands: Structure‐Based Design of Inhibitors for Trypsin‐Like Serine Proteases

In the absence of X‐ray data, the exploration of compound binding modes continues to be a challenging task. For structure‐based design, specific features of active sites in different targets play a major role in rationalizing ligand binding characteristics. For example, dibasic compounds have been reported as potent inhibitors of various trypsin‐like serine proteases, the active sites of which contain several binding pockets that can be targeted by cationic moieties. This results in several possible orientations within the active site, complicating the binding mode prediction of such compounds by docking tools. Therefore, we introduced symmetry in bi‐ and tribasic compounds to reduce conformational space in docking calculations and to simplify binding mode selection by limiting the number of possible pocket occupations. Asymmetric bisbenzamidines were used as starting points for a multistage and structure‐guided optimization. A series of 24 final compounds with either two or three benzamidine substructures was ultimately synthesized and evaluated as inhibitors of five serine proteases, leading to potent symmetric inhibitors for the pharmaceutical drug targets matriptase, matriptase‐2, thrombin and factor Xa. This study underlines the relevance of ligand symmetry for chemical biology.     

Catalytic oxidative coupling of diols by Ru3(CO)12

Ru₃(CO)₁₂ acts as a homogeneous catalyst precursor for the transformation of αω-diols to polyesters and lactones.     

Need for food reference material in Latin America

Summary Even if some Latin American countries still need to extend their capacity for food quality control, many do have good control laboratories and high quality research institutions. That makes the need for reference material in Latin America similar to that of other parts of the world.The region has special problems related to mail and shipment delays, and to the lack of information on available reference material. It is recommended that additional reference material being made available for vitamins in food, for polar and non-polar organophosphorus pesticides in vegetables, for organophosphorus pesticide and veterinary drugs in meat etc.Reference material should simulate real samples as closely as possible; reference samples for water should contain phthalates which in environmental samples interfere with organochlorines and reference material for organophosphates in vegetables should contain metabolites and degradation products.It is also recommended that commercial standards for trace metals should have the production date and the guaranteed stability printed on the label. Information on reference material should be included in the methods published by AOAC, AOCS and similar publications.     

Formation of tricyclo[6.3.0.02,5]undecane derivatives during attempts to make the rumphellatin A–C oxacarbon skeleton

The results of several approaches to make the 4,4,8-trimethyl-12-oxatricyclo[7.2.1.0^2,5]dodecane motif present in rumphellatins A–C are reported. The strategy adopted involved (9E)-12,12-dimethyl-5-oxatricyclo[8.2.0.0^4,6]dodec-9-en-11-ol as an intermediate, but when attempts were made to connect the third methyl group to the carbon skeleton by reacting the epoxide with MeLi under boron-trifluoride catalysis, an unprecedented transannular reaction occurred. The desired product was not formed; instead, compounds containing a tricyclo[6.3.0.0^2,5]undecane moiety were obtained, in one case in better than 70% yield.     

Water structure and dynamics at a silica surface: Pake doublets in 1H NMR spectra

Detailed knowledge about the dynamics and structure of liquids in the vicinity of a solid surface is important in several fields of research. In this study a homogeneous model system of colloidal and nonporous silica particles with a narrow particle size distribution was used to examine such properties of adsorbed water and 1-heptanol. Doublet (1)H water resonances ("Pake doublets") indicate a preferred spatial orientation for the water molecules, as well as a lower molecular density in the surface-induced water structures compared to bulk water. These surface-induced structures are found to extend at least 8 nm from the silica surface. T(1) relaxation measurements at several temperatures indicate weaker H-bonding in the adsorbed water compared to bulk water. T(2) relaxation measurements at several temperatures reveal the presence of two water phases and give quantitative information on the mobility of water molecules and proton exchange processes. The presence of 1-heptanol changes the water characteristics, primarily in the water phase closer to the surface, where water molecules experience decreased translational and increased rotational freedom. In the absence of water, adsorbed 1-heptanol forms surface aggregates encompassing several molecular layers, where the first adsorbed layer shows severe restrictions in mobility and subsequent layers are more mobile.     

Bonding properties of bicyclopropylidene: gas phase electron diffraction study and X-ray crystal structure analysis

The C=C double bond length in bicyclopropylidene (1) was found to be 131.4(1) and 130.4(8) pm by electron diffraction at 20° and X-ray diffraction at −40°C respectively. This value is in remarkable agreement with that obtained by molecular mechanics calculations; it is significantly shorter than the double bond in normal olefins.