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     

Composite Silica Particles Using a Mixture of Organosilane Monomers

Composite silica particles were synthesized by a two-step (acid-base) process in an aqueous solution with a mixture of organoalkoxysilane monomers. The two-step process separates the hydrolysis and condensation procedures to easily control condensation rate. In this study, the silane monomers used were phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), methyltrimethoxysilane (MTMS), and tetraethyl-orthosilicate (TEOS). The physical properties of the resultant composite particles were investigated with the change in the molar ratio of monomers. The size of the particles increased with increasing the molar ratio of R_aSi(OR)₃/R_bSi(OR)₃ or R_aSi(OR)₃/TEOS (R_a: phenyl; R_b: vinyl, methyl).     

The convex hull property and topology of hypersurfaces with nonnegative curvature

We prove that, in Euclidean space, any nonnegatively curved, compact, smoothly immersed hypersurface lies outside the convex hull of its boundary, provided the boundary satisfies certain required conditions. This gives a convex hull property, dual to the classical one for surfaces with nonpositive curvature. A version of this result in the nonsmooth category is obtained as well. We show that our boundary conditions determine the topology of the surface up to at most two choices. The proof is based on uniform estimates for radii of convexity of these surfaces under a clipping procedure, a noncollapsing convergence theorem, and a gluing procedure.     

Effects of hysteretic and aerodynamic damping on supersonic panel flutter of composite plates

The governing equation for the finite element analysis of the panel flutter of composite plates including structural damping is derived from Hamilton's principle. The first order shear deformable plate theory has been applied to structural modelling so as to obtain the finite element eigenvalue equation. The unsteady aerodynamic load in a supersonic flow is computed by using the linear piston theory. The critical dynamic pressures for composite plates have been calculated to investigate the effects of structural damping on flutter boundaries. The effects are dependent on fiber orientation because flutter mode can be weak or strong in the fiber orientation of composite plates. Structural damping plays an important role in flutter stability with low aerodynamic damping but would not affect the flutter boundary with high aerodynamic damping.     

Homo-dinuclear σ-alkynyl complexes: past, present and opportunities

Homo-dinuclear alkynyl complexes with a distinct metal–metal bond constitute a rapidly growing field, where the focus is placed on compounds based on ruthenium, molybdenum, tungsten or rhodium. Interesting characteristics of these complexes include paramagnetism, intense charge-transfer absorptions, tunable bridging ligands, which may not be easily accessible in mononuclear acetylide systems. These complexes have significant potential for use in both molecular electronics and supramolecular chemistry. In this short account, previous work in this area is assessed, and each of the major groups of complexes is discussed in terms of both the synthetic strategies and structural motifs.     

Effect of added alpha-lactalbumin protein on the phase behavior of AOT-brine-isooctane systems

We have found that the presence of <1 wt% of the globular protein alpha-lactalbumin has a significant impact on the equilibrium phase behavior of dilute sodium bis(ethylhexyl) sulfosuccinate (AOT)/brine/isooctane systems. Nuclear magnetic resonance (NMR), Karl Fischer titration, and ultraviolet spectroscopy were used to determine the surfactant, oil, water, and protein content of the organic and aqueous phases as a function of the total surfactant and protein present. As a small amount of alpha-lactalbumin is added to the mixture, there is a substantial increase (up to 80%) in the maximum water solubility in the water-in-oil microemulsion phase. Dynamic light scattering measurements indicate that this increase is due to a decrease in the magnitude of the (negative) spontaneous curvature of the surfactant monolayer, as droplets swell in size. As the molar ratio of alpha-lactalbumin to AOT surpasses approximately 1:300, the partitioning of water, protein, and surfactant shifts to the excess aqueous phase, where soluble assemblies with positive curvature are detected by dynamic light scattering. Significant amounts of isooctane are solubilized in these aggregates, consistent with the formation of oil-in-water microemulsion droplets. Circular dichroism studies showed that the tertiary structure of the protein in the microemulsion is disrupted while the secondary structure is increased. In light of these findings, the protein most likely expands to a molten-globule type conformation in the AOT interfacial environment, but does not substantially unfold to become an extended chain.     

Hydrogen analysis in solid samples by utilizing He metastable atoms induced by TEA CO2 laser plasma in He gas at 1 atm

A TEA CO₂ laser (350 mJ–1.5 J, 10.6 μm, 200 ns, 10 Hz) was focused onto a metal sub-target under He as host gas at 1 atmospheric pressure with a small amount of impurity gas, such as water and ethanol vapors. It was found that the TEA CO₂ laser with the help of the metal sub-target is favorable for generating a strong, large volume helium gas breakdown plasma at 1 atmospheric pressure, in which the helium metastable-excited state was then produced overwhelmingly. While the metal sub-target itself was never ablated. The helium metastable-excited state produced after the strong helium gas breakdown plasma was considered to play an important role in exciting the atoms. This was confirmed by the specific characteristics of the detected H emission, namely the strong intensity with low background, narrow spectral width, and the long lifetime. This technique can be used for gas and solid samples analysis. For nonmetal solid analysis, a metal mesh was introduced in front of the nonmetal sample surface to help initiation of the helium gas breakdown plasma. For metal sample, analysis can be carried out by combining the TEA CO₂ laser and an Nd–YAG laser where the Nd–YAG laser is used to ablate the metal sample. The ablated atoms from the metal sample are then sent into the region of helium gas breakdown plasma induced by the TEA CO₂ laser to be excited through the helium metastable-excited state. This technique can be extended to the analysis of other elements, not limited only to hydrogen, such as halogens.     

Synthesis and biological evaluation of nucleosides containing 8-amino-imidazo[1,2-α]pyrazine as an isosteric replacement for adenine

A number of novel C-nucleosides related to purine derivatives are described in which the purine moiety has been replaced by the isosteric heterocycle, 8-aminoimidazo[1,2-α]pyrazine. The nucleosides prepared include the ribo, 3′-deoxy, 2′,3′-dideoxy, and 2′,3′-unsaturated derivatives. These C-nucleosides represent derivatives containing acid stable glycosyl bonds and they can be considered as analogs of adenine- or 3-deazaade-nine-containing nucleosides. Preparation of the parent ribonucleoside was accomplished by reaction of the C-l functionalized sugar, (2ξ)-1-amino-3,6-anhydro-l-deoxy-4,5-O-isopropylidene-7-O-trityl-D-allo-heptitol with 2,3-dichloropyrazine, followed by ring closure to the 8-chloroimidazo[1,2-α]pyrazine nucleoside, conversion to the 8-amino derivative and deblocking. A single crystal X-ray structure of the parent 8-amino-3-(β-D-ribofuranosyl)imidazo[1,2-α]pyrazine is described and the conformation compared to that of formycin. The sugar-modified analogs were prepared by subsequent functional group manipulations on the sugar moiety. Biological evaluation against HIV in H9 T-lymphoid cell culture showed the nucleosides to be devoid of significant antiviral activity compared to DDA. The 3-deazaadenosine analog also demonstrated weak suppression of mouse splenic NK activity toward YAC cells (mouse lymphoma cell targets). The imidazo[1,2-α]pyrazine analog of 3-deazaadenosine showed antiinflammatory activity in vivo in the rat pleurisy carrageenan model in the same range with 3-deazaadenosine.     

Poly(decyl methacrylate)-based fluorescent PEBBLE swarm nanosensors for measuring dissolved oxygen in biosamples

150-250 nm Poly(decyl methacrylate)(PDMA) fluorescent ratiometric nanosensors for dissolved oxygen have been developed. Platinum octaethylporphine ketone (PtOEPK), the oxygen-sensitive dye, and octaethylporphyrin (OEP), the oxygen-insensitive dye, have been incorporated into PDMA nanoparticles to make the sensors ratiometric. Based on the corresponding Stern-Volmer plot, these nanosensors exhibit almost complete linearity over the whole range of dissolved molecular oxygen from 0 to 42.5 ppm (deoxygenated to pure oxygen-bubbled water). The overall quenching response is up to 97.5%, the best so far for all dissolved oxygen optical sensors. These PEBBLE nanosensors also show very good reversibility and stability to leaching and photobleaching, as well as very short response times and no perturbation by proteins. In human plasma they demonstrate a robust oxygen sensing capability, little affected by light scattering and autofluorescence. Potential applications include intracellular oxygen imaging and microresolved pressure profiles in biological and other heterogenous environments.     

Reversible pressure deformation of a thermophilic cytochrome P450 enzyme (CYP119) and its active-site mutants

The pressure stability of the thermophilic CYP119 from Sulfolobus solfataricus and its active-site Thr213 and Thr214 mutants was investigated. At 20 degrees C and pH 6.5, the protein undergoes a reversible P450-to-P420 inactivation with a midpoint at 380 MPa and a reaction volume change of -28 mL/mol. The volume of activation of the process was -9.5 mL/mol. The inactivation transition was retarded, and the absolute reaction volume was decreased by increasing temperature or by mutations that decrease the size of the active-site cavity. High pressure affected the tryptophan fluorescence yield, which decreased by about 37% at 480 MPa. The effect was reversible and suggested considerable contraction of the protein. Aerobic decomposition of iron-aryl complexes of the CYP119 T213A mutant under increasing hydrostatic pressure resulted in variation of the N-arylprotoporphyrin-IX regioisomer (N(B):N(A):N(C):N(D)) adduct pattern from 39:47:07:07 at 0.1 MPa to 23:36:14:27 at 400 MPa. Preincubation of the protein at 400 MPa followed by complex formation and decomposition gave the same regioisomer distribution as untreated protein. The results indicate that the protein is reversibly inactivated by pressure, in contrast to the irreversible inactivation of P450(cam) and other P450 enzymes, and that this inactivation process is modulated by changes in the active-site cavity dimensions.