Biological liquid crystal elastomers

Liquid crystal elastomers (LCEs) have recently been described as a new class of matter. Here we review the evidence for the novel conclusion that the fibrillar collagens and the dragline silks of orb web spiders belong to this remarkable class of materials. Unlike conventional rubbers, LCEs are ordered, rather than disordered, at rest. The identification of these biopolymers as LCEs may have a predictive value. It may explain how collagens and spider dragline silks are assembled. It may provide a detailed explanation for their mechanical properties, accounting for the variation between different members of the collagen family and between the draglines in different spider species. It may provide a basis for the design of biomimetic collagen and dragline silk analogues by genetic engineering, peptide- or classical polymer synthesis. Biological LCEs may exhibit a range of exotic properties already identified in other members of this remarkable class of materials. In this paper, the possibility that other transversely banded fibrillar proteins are also LCEs is discussed.     

Age changes in the crystallinity of bone mineral and in the disorder of its crystal

The crystallinity of bone mineral and disorder of the crystal at different ages were measured by the X-ray diffraction method of Ruland. Measurements were made on femoral mid-diaphyses of Wistar rat from 2 weeks to 1 year of age. For a given animal age, the crystallinity of bone mineral increases with age, while the overall disorder of the crystal does not vary within experimental accuracy. The increase in the crystallinity with age is attributed to an increase in crystallite size, a decrease in lattice imperfections, or a combination of both effects. It is suggested that lattice imperfections of the first kind more largely contributes to the disorder of bone mineral crystals than those of the second kind.     

Synthesis of superabsorbent from carbohydrate waste

A mixture of acrylamide (AM) and acrylic acid (AA) monomers were grafted on germinated gelatinized wheat starch using potassium persulfate (KPS) as an initiator to yield superabsorbent. The effects of different parameters such as time, temperature, monomer feed (AM:AA), starch: monomers ratio and initiator concentration on graft add-on were studied, and the optimized values were found to be 2 h, 60 °C, 1:1 (w/w), 1:1(w/w) & 1% (with respect to starch powder), respectively. The product so formed was saponified with 0.1N NaOH, dried and finely powdered sample was characterized using FT-IR, TGA. Product showed maximum absorbency of 150 g/g.     

Synthesis and antiangiogenic activity of new carbohydrate derivatives

Carbohydrate based analogues of the natural product (−)-Ovalicin have been synthesized, and shown to be potent inhibitors of angiogenesis.     

Synthesis of low-molecular-weight carbohydrate mimetics of heparin

Natural glycosaminoglycan heparin remains the most commonly prescribed anticoagulant for hospitalized patients in modern medical practice. Unfortunately, its administration can be accompanied by a series of clinical side effects, including thrombocytopenia and bleeding. This determines the urgency of the development of alternative anticoagulant drugs based on modified heparin and polyanionic oligo- and polysaccharide derivatives, such as sulfated glucans, phosphomannans, and fucoidans. Here we review work on the synthesis of oligosaccharides corresponding to low-molecular-weight heparin fragments and their derivatives, as well as oligosaccharides imitating parts of heparin chains that are responsible for biological activity. The reviewed works were aimed at developing pharmaceutical preparations lacking the aforementioned disadvantages of heparin.     

Synthesis of deoxyfluoro sugars from carbohydrate precursors

Results obtained over the past decade concerning the introduction of the fluorine atom into carbohydrate molecules, either by nucleophilic substitution or electrophilic addition reactions, are summarised. The first section mainly deals with the triflate/fluoride tandem sequence and the DAST-reaction. In the discussion, emphasis is given to the dependency of the reaction course on the stereochemical and protecting group features. Possible reaction pathways are direct substitution (with inversion or retention of configuration), rearrangement (combined with substitution and inversion of configuration at both of the centres involved) and elimination. Based on the assumption of cyclic transition states or transient intermediates (formed through participation of neighbouring groups), far-reaching mechanistic generalisations were made. On this basis, isolated examples from the literature, which are not in accordance with these generalisations, are specifically brought to attention. Results from the recently introduced reaction of safe and easy to handle N-F fluorinating agents with glycals are also reported. This approach allows the simple and stereoselective access to a series of 2-deoxy-2-fluoro aldopyranoses, as well as the synthesis of various C-1-substituted derivatives by an easy one-pot reaction. However, the same method applied to furanoid glycals is rather poor with respect to stereoselectivity. Finally, considerations on the importance of fluorine-specific reactions of the S(N)-type in related fields of organic synthesis are made.     

Bombyx mori silk fibroin liquid crystallinity and crystallization at aqueous fibroin-organic solvent interfaces.

A banded morphology has been observed for Bombyx mori silk fibroin films obtained from an aqueous hexane interface; the period of the banding is approximately 1 microm. Morphology and diffraction from different regions of the banded structure suggest that it is a free surface formed by a cholesteric liquid crystal. Truncated hexagonal lamellar crystallites of B. mori silk fibroin have been observed in films formed in the surface excess layer of fibroin at the interface between aqueous fibroin and hexane or chloroform. Based on initial crystallographic evidence, a three-fold helical conformation has been ascribed to the fibroin chains within the crystals. The chain conformation and crystalline habit appear to be similar to the silk III structure previously observed at the air-water interface (Valluzzi R, Gido SP. Biopolymers 1997;42:705-717; Valluzzi R, Gido S, Zhang W, Muller W, Kaplan D. Macromolecules 1996;29:8606-8614) but the crystalline packing is different. Diffraction data obtained for the crystallites are similar to diffraction behavior for a collagen-like model peptide. Diffraction patterns obtained from crystallized regions of the banded morphology can be indexed using the same unit cell as the hexagonal lamellar crystallites. Surfactancy of fibroin and subsequent aggregation and mesophase formation may help to explain the liquid crystallinity reported for silk, which is long suspected to play a role in the biological silk spinning process (Valluzzi R, Gido SP. Biopolymers 1997;42:705-717; Willcox, P. J.; Gido, SP, Muller W, Kaplan DL. Macromolecules 1996:29:5106-5110; Magoshi J, Magoshi Y, Nakamura S. In: Kaplan D, Adams W, Farmer B, Viney C, editors, Mechanism of Fiber Formation of Silkworm. Washington, DC: American Chemical Society 1994:292-310; Magoshi J, Magoshi Y, Nakamura S. J Appl Polym Sci Appl Polym Symp 1985;41:187-204; Magoshi J, Magoshi Y, Nakamura S. Polym Commun 1985;26:309.).     

Microbial steroidconversion in lyotropic liquid crystal

Summary The activity and stability of the 1(2)-dehydrogenation system ofPimellobacter simplex in an organic solvent/liquid crystalline phase environment has been studied.     

Synthesis and possible role of carbohydrate moieties of yeast glycoproteins

The pathways for protein N- and O-glycosylation in yeast cells are summarized. Evidence is presented that the terminal glucosyl residues of the dolichyl-PP-oligosaccharide intermediate are responsible for decreasing the Km for the peptide to be N-glycosylated. A liposomal model system is introduced that allows the study of a dolichyl phosphate (Dol-P) dependent transmembrane transport of mannosyl residues. The results obtained so far suggest that the mannosylation of Dol-P and the transmembrane translocation of Dol-P-Man are catalysed by the enzyme more or less simultaneously. However, only about 8-10% of the enzyme molecules incorporated into the liposomes seem to carry out the 'coupled' reaction. The glycosylation of carboxypeptidase Y is not required for this protein to reach the vacuole, its target organelle. In the presence of low concentrations of tunicamycin, however, yeast cells do stop growth. This does not seem to be due to the inhibition of secretion of glycoproteins like external invertase. It is postulated that protein glycosylation is crucial for a cell cycle event during the G1 phase.     

Spectral properties of chlorophyll a in liquid crystal

Solution of chlorophyll a in liquid crystals mixture (MBBA + EBBA) was investigated. Chl molecules are in LC in low electric field oriented. They can be divided into two groups: one strongly interacting with LC and subjected to reorientation by the electric field, and another weakly interacting with the solvent and insensitive to the voltage applied. The emission spectrum of the first type of chlorophyll is strongly perturbed. At higher voltages, the pigment molecules orientation in the plane of the electrode is another. Pigment absorption and emission anisotropy provides information about the reorientation of LC molecules. Even at high (10^?3M) Chl concentration and regular pigment array, the interaction between the pigment and solvent exceeds pigment-pigment interaction because the solvent appears to have a stronger influence on the Chl spectrum.     

Analysis of the carbohydrate composition of glycoproteins by high-performance liquid chromatography

A procedure for rapid and sensitive analysis of carbohydrate in glycoproteins is described. After methanolysis and benzoylation of the monosaccharides and carbohydrates of a glycoprotein, the derivatized sugars were analyzed by reverse-phase high-performance chromatography using a Vydac C₁₈ stationary phase and a mobile phase composed of a water/acetonitrile gradient. The advantages of this procedure over previously described methods are (1) the simple binary solvent system which is used requires no buffering salts and (2) separate sets of peaks from individual sugars obviate the usual need to reacetylate sugar amino groups.     

Synthesis of glycolipopeptidic building blocks for carbohydrate receptor discovery

A class of glycolipopeptides for use as building blocks for a new type of dynamic combinatorial library is reported. The members of the library consist of a variable carbohydrate moiety, coded amino acids, and lipoamino acids in order to convert them into amphiphiles. Glycolipopeptidic amphiphiles interact through non-covalent bonding when mixed together in aqueous phase and form micelles in dynamic close-packed fluid mosaic arrays. The head groups of amphiphiles are exposed on the micelle surface, providing entities which could be screened in biological assays to find the most potent combination of building blocks in order to identify new bioactive carbohydrate ligands.     

Synthesis and biodegradation of nanogels as delivery carriers for carbohydrate drugs

Biodegradable nanogels loaded with rhodamine B isothiocyanate-dextran (RITC-Dx) as a model for water-soluble biomacromolecular drugs were prepared using atom-transfer radical polymerization (ATRP) in a cyclohexane inverse miniemulsion in the presence of a disulfide-functionalized dimethacrylate cross linker. UV-vis spectroscopy was used to characterize the extent of incorporation of RITC-Dx into the nanogels. The loading efficiency of RITC-Dx into the nanogels exceeded 80%. These nanogels were degraded into polymeric sols in a reducing environment to release the encapsulated carbohydrate drugs. The released carbohydrate biomolecules specifically interacted with concanavalin A in water, suggesting that the biodegradable nanogels could be used as carriers to deliver carbohydrate drugs that can be released upon degradation to bind to pathogens based on lectins.     

Synthesis of Haemophilus influenzae carbohydrate surface antigens

The pathogenic bacteria Haemophilus influenzae, causing, i.a., meningitis and otitis, contain both capsular and lipopolysaccharide surface antigens. The syntheses of several oligosaccharides corresponding to native H. influenzae polysaccharide structures is outlined with an emphasis on synthetically challenging features. Hence, the synthesis of a branched inner core lipopolysaccharide tetrasaccharide structure, α- , -Hepp-(13)-[β- -Glcp-(14)]-α- , -Hepp-(15)-αKdo, containing the unusual higher carbon sugars -glycero- -manno-heptose and Kdo is described, as well as the assembly of di- and trimers of the repeating unit of the capsular polysaccharides of serotype c,[−4)-3-OAc-β- -GlcpNAc-(13)-α- -Galp-(1-PO⁻₃−] and serotype f[−3)-β- -GalpNAc-(14)-3-OAc-α- -GalpNAc-(1-PO⁻₃], both linked via anomeric phospodiester linkages. Also efforts towards the synthesis of the repeating unit of the capsular polysaccharide of serotype e,3)-β- -GlcpNAc-(14)-[β- -Fruf-(23)]-β- -ManpNAcA-(1, containing a β-fructofuranosidic residue, is discussed. All synthetic derivates are spacer-equipped to allow formation of glycoconjugates for biological applications.     

In vitro and in vivo evaluation of hydrophilic dendronized linear polymers

Rigid-rod dendronized linear polymers consisting of a poly(4-hydroxystyrene) backbone and fourth-generation polyester dendrons were evaluated in vitro and in vivo to determine their suitability as drug delivery vectors. Cytotoxicity assays indicated that the polymers were well tolerated by cells in vitro. Biodistribution studies of the polymers in both nontumored and tumored mice revealed that as for random coil linear polymers, renal clearance was a function of polymer size, with significant urinary excretion observed for a 67 kDa dendronized polymer. High accumulation in organs of the reticuloendothelial system was exhibited by a dendronized polymer with a very high molecular weight (M(n) = 1740 kDa), but was not as significant for smaller polymers with M(n) = 67 kDa and M(n) = 251 kDa. The rank order for tumor accumulation of the polymers on a percent injected dose per gram tumor basis was 251 kDa approximately 1740 kDa > 67 kDa. These data will help guide the selection of highly functionalizable rigid-rod dendronized polymers with pharmacokinetic properties appropriate for use as drug carriers.     

Analysis by high-performance liquid chromatography of radioactively labeled carbohydrate components of proteoglycans

Methods were developed for the separation of radioactively labeled carbohydrate components of proteoglycans by isocratic ion-moderated partition HPLC. Neutral sugars were separated after hydrolysis in trifluoroacetic acid with baseline separation between glucose, xylose, galactose, fucose, and mannose. N-Acetylneuraminic acid, N-acetylated hexosamines, glucose, galactose, and xylitol were likewise well separated from each other under isocratic elution conditions. Glucuronic acid, iduronic acid, and their lactones were separated after hydrolysis in formic acid and sulfuric acid. Glucosamine, galactosamine, galactosaminitol, and glucosaminitol were separated by HPLC on a cation exchanger with neutral buffer after hydrolysis in hydrochloric acid. The separation techniques also proved useful in fractionation of exoglycosidase digests of O- and N-linked oligosaccharides. Separations of aldoses, hexosamines, and uronic acids were adapted to sensitive photometric detection.     

Charge structure and counterion distribution in hexagonal DNA liquid crystal

A hexagonal liquid crystal of DNA fragments (double-stranded, 150 basepairs) with tetramethylammonium (TMA) counterions was investigated with small angle neutron scattering (SANS). We obtained the structure factors pertaining to the DNA and counterion density correlations with contrast matching in the water. Molecular dynamics (MD) computer simulation of a hexagonal assembly of nine DNA molecules showed that the inter-DNA distance fluctuates with a correlation time around 2 ns and a standard deviation of 8.5% of the interaxial spacing. The MD simulation also showed a minimal effect of the fluctuations in inter-DNA distance on the radial counterion density profile and significant penetration of the grooves by TMA. The radial density profile of the counterions was also obtained from a Monte Carlo (MC) computer simulation of a hexagonal array of charged rods with fixed interaxial spacing. Strong ordering of the counterions between the DNA molecules and the absence of charge fluctuations at longer wavelengths was shown by the SANS number and charge structure factors. The DNA-counterion and counterion structure factors are interpreted with the correlation functions derived from the Poisson-Boltzmann equation, MD, and MC simulation. Best agreement is observed between the experimental structure factors and the prediction based on the Poisson-Boltzmann equation and/or MC simulation. The SANS results show that TMA is too large to penetrate the grooves to a significant extent, in contrast to what is shown by MD simulation.