Determination of Percent Crystallinity of Side-Chain Crystallized Alkylated-Dextran Derivatives with Raman Spectroscopy and Multivariate Curve Resolution.

We demonstrate a methodology to estimate the percent crystallinity of polymers directly with Raman spectroscopy and multivariate curve resolution (MCR) by alternating least-squares (ALS). In this methodology, the Raman spectrum of semicrystalline polymer is separated into two constituent components (crystalline and molten) and their corresponding concentrations. The percent crystallinity can be estimated as the change in area intensity of the molten spectral-component when polymer cools from a temperature above melting point to room temperature. The number of carbons in the crystalline lattice has also been estimated from the position of longitudinal acoustic (LA) Raman bands with the correlation established by Mizushima and Simanouti [ Mizushima, S.; Simanouti, T. J. Am. Chem. Soc. 1949 , 71 , 1320 ]. The new method allows direct Raman estimation of absolute percent crystallinity of polymers. Until now, Raman spectroscopic estimation of percent crystallinity was possible only in conjunction with other techniques or by using internal standards.

Magnetic Biocomposites for Remote Melting.

A new approach toward the fabrication of biocompatible composites suitable for remote melting is presented. It is shown that magnetite nanoparticles (MNP) can be embedded into a matrix of biocompatible thermoplastic dextran esters. For that purpose, fatty acid esters of dextran with adjustable melting points in the range of 30-140 °C were synthesized. Esterification of the polysaccharide by activation of the acid as iminium chlorides guaranteed mild reaction conditions leading to high quality products as confirmed by FTIR- and NMR spectroscopy as well as by gel permeation chromatography (GPC). A method for the preparation of magnetically responsive bionanocomposites was developed consisting of combined dissolution/suspension of the dextran ester and hydrophobized MNPs in an organic solvent followed by homogenization with ultrasonication, casting of the solution, drying and melting of the composite for a defined shaping. This process leads to a uniform distribution of MNPs in nanocomposite as revealed by scanning electron microscope. Samples of different geometries were exposed to high frequency alternating magnetic field. It could be shown that defined remote melting of such biocompatible nanocomposites is possible for the first time. This may lead to a new class of magnetic remote control systems, which are suitable for controlled release applications or self-healing materials.

Acetone-based cellulose solvent.

Acetone containing tetraalkylammonium chloride is found to be an efficient solvent for cellulose. The addition of an amount of 10 mol% (based on acetone) of well-soluble salt triethyloctylammonium chloride (Et3 OctN Cl) adjusts the solvent's properties (increases the polarity) to promote cellulose dissolution. Cellulose solutions in acetone/Et3 OctN Cl have the lowest viscosity reported for comparable aprotic solutions making it a promising system for shaping processes and homogeneous chemical modification of the biopolymer. Recovery of the polymer and recycling of the solvent components can be easily achieved.

Efficient cellulose solvent: quaternary ammonium chlorides.

Pure quaternary tetraalkylammonium chlorides with one long alkyl chain dissolved in various organic solvents constitute a new class of cellulose solvents. The electrolytes are prepared in high yields and purity by Menshutkin quaternization, an inexpensive and easy synthesis route. The pure molten tetraalkylammonium chlorides dissolve up to 15 wt% of cellulose. Cosolvents, including N,N-dimethylacetamide (DMA), may be added in large excess, leading to a system of decreased viscosity. Contrary to the well-established solvent DMA/LiCl, cellulose dissolves in DMA/quaternary ammonium chlorides without any pretreatment. Thus, the use of the new solvent avoids some disadvantages of DMA/LiCl and ionic liquids, the most extensively employed solvents for homogeneous cellulose chemistry.

Meltable dextran esters as biocompatible and functional coating materials.

The conversion of dextran with in situ synthesized iminium chlorides of long chain carboxylic acids was used to obtain pure and defined melting dextran esters in an efficient one-pot synthesis. The melting point of these esters can be tailored by the degree of substitutions (DS), the molecular weight of the starting polymer, and the chain length of the ester moiety. The dextran esters give homogeneous and completely transparent melts, which form stable films on a broad variety of materials. Even complex geometries, such as implants, can be evenly coated by multiple melting steps. The films do not display any inhomogeneity and have a very low surface roughness. Therefore, no unspecific protein binding is observed. Moreover, the dextran esters are biocompatible as demonstrated for the interaction with three types of cells namely human brain microvascular endothelial cell, primary human fibroblasts, and mouse myoblast cells.

Pure, transparent-melting starch esters: synthesis and characterization.

Long chain starch esters were prepared by a new method using molten imidazole as solvent for the biopolymer. The advantage is the simplicity of the reaction mixture. Imidazole is acting not only as solvent, but also as reagent and base. The reaction succeeds via the imidazolide, which is formed in situ with an acid chloride. It yields highly pure derivatives, as could be shown by NMR spectroscopy and elemental analysis. No hints for desoxychloro substituents or other impurities could be found. The high quality of the products prepared is responsible for the occurrence of colorless melts. Although DSC measurements show a variety of thermal transitions, the formation of melts in the range of 40 to 255 °C could be observed with a hot stage microscope. The melting behavior can be adjusted by the type of ester moiety and the amount of ester functions introduced. In case of starch palmitates completely transparent melts are obtained within two distinct DS regions namely around 1.5 and 2.2 to 3.0. Upon cooling the melts form homogeneous films on different supports including glass. They show good adhesion and should therefore be a suitable basic material for the preparation of composites like laminated glass.

Polyelectrolyte synthesis and in situ complex formation in ionic liquids.

For the first time, polyelectrolyte complex (PEC) capsules were prepared from a water insoluble polyanion, namely cellulose sulfates (CSs) with a degree of substitution (DS) below 0.2 in ionic liquids (IL). Capsules prepared via interaction with the polycation poly(dimethyldiallyammonium chloride) were free of residual IL and possessed an outer shell and a hollow inner core that made them ideal containers for enzyme mediated reactions. Due to the reestablished hydrogen bond system of the low substituted CS, the capsules showed increased stability, compared to the products obtained by application of the common aqueous preparation. Encapsulation of glucose oxidase demonstrated that the steps of CS preparation, PEC capsule formation, and encapsulation could be combined in a single pot, with the elimination of time and cost consuming isolation and purification steps.

Rheological properties of cellulose/ionic liquid solutions: from dilute to concentrated states.

Steady state shear flow of different types of cellulose (microcrystalline, spruce sulfite and bacterial) dissolved in 1-ethyl-3-methylimidazolium acetate was studied in a large range of concentrations (0-15%) and temperatures (0-100 degrees C). Newtonian flow was recorded for all experimental conditions; these viscosity values were used for detailed viscosity-concentration and viscosity-temperature analysis. The exponent in the viscosity-concentration power law was found to be around 4 for temperatures from 0 to 40 degrees C, which is comparable with cellulose dissolved in other solvents, and around 2.5-3 for 60-100 degrees C. Intrinsic viscosities of all celluloses decreased with temperature, indicating a drop in solvent thermodynamic quality with heating. The data obtained can be reduced to a master plot of viscosity versus (concentration x intrinsic viscosity) for all celluloses studied in the whole temperature range. Mark-Houwink exponents were determined: they were lower than that for cellulose dissolved in LiCl/N,N-dimethylacetamide at 30 degrees C and close to theta-value. Viscosity-inverse temperature plots showed a concave shape that is dictated by solvent temperature dependence. The values of the activation energies calculated within Arrhenius approximation are in-line with those obtained for cellulose of comparable molecular weights in other solvents.

Evaluation of fluorescent polysaccharide nanoparticles for pH-sensing.

The comprehensive characterization of novel dextran nanoparticles with regard to their suitability as pH-sensors for analytical applications (e.g. in physiology) is described. The nanoparticles are labeled with both a pH-indicator dye (fluorescein isothiocyanate, FITC) and a reference dye (sulforhodamine B acid chloride) as an internal standard. The fluorescence intensity of FITC increases with increasing pH, whereas the signal of the reference dye remains constant. Plotting the ratio of both signals against the pH gives a pK(a) of 6.45, which is appropriate for most of the measurement purposes. Furthermore, the influence of temperature, ionic strength and oxidizing substances on the performance of the fluorophores inside the dextran nanoparticles is examined. These results are compared to the dissolved dyes in order to evaluate if the dextran matrix affects the fluorescence properties of the sensor and the reference dye, and whether or not these nanosensors are suitable for pH-sensing in biological samples.

Biocompatible fluorescent nanoparticles for pH-sensoring.

Dialysis of a mixture of fluorescein and sulforhodamine B marked dextran derivatives yields biocompatible and tuneable nanosensors that can be used for ratiometric pH measurements.

Structure design of multifunctional furoate and pyroglutamate esters of dextran by polymer-analogous reactions.

Well-defined multifunctionalized dextran esters bearing photo-crosslinkable and chiral groups as well as small alkyl moieties for the adjustment of the solubility were prepared from two dextran samples with different origin and molecular weight. The examination of side structures of the starting dextran was carried out by different one- and two-dimensional NMR techniques. The main synthesis path via in situ activation of furan-2-carboxylic- and pyroglutamic acid with CDI under mild conditions gives highly functionalized dextran derivatives possessing a degree of polymerization in the range of the starting polysaccharide. The subsequent reaction with propionic anhydride leads to completely substituted, CHCl(3) soluble derivatives useful for the determination of the particular degree of substitution. By variation of the molar ratios of polymer to reagent with photo-crosslinkable- and chiral moieties during the reaction and even by subsequent peracylation, multifunctional dextran derivatives with adjustable properties like the hydrophilic/hydrophobic balance were obtained that may form biocompatible spherical nanoparticles.

6-Deoxy-6-aminoethyleneamino cellulose: synthesis and study of hemocompatibility.

Hemocompatibility of aqueous solutions of antimicrobial 6-deoxy-6-aminoethyleneamino (AEA) cellulose with different degrees of substitution (DS, 0.54-0.92) was investigated in vitro. The AEA cellulose derivatives were synthesized by tosylation of cellulose and subsequent nucleophilic substitution with 1,2-diaminoethane. The structure was confirmed by elemental analysis as well as by FTIR and NMR spectroscopies. Markers for coagulation (thrombin generation, aPTT, PT, blood clotting, thrombocyte activation) and membrane integrity (hemolysis) were measured in human whole blood, human platelet-rich plasma, human pooled plasma, and erythrocytes suspension. AEA cellulose with a low DS of 0.54 showed the highest hemocompatibility in vitro, suggesting the possibility of biomedical applications.

Biocompatible multishell architecture for iron oxide nanoparticles.

The coating of super-paramagnetic iron oxide nanoparticles (SPIONs) with multiple shells is demonstrated by building a layer assembled from carboxymethyldextran and poly(diallydimethylammonium chloride). Three shells are produced stepwise around aggregates of SPIONs by the formation of a polyelectrolyte complex. A growing particle size from 96 to 327 nm and a zeta potential in the range of +39 to -51 mV are measured. Microscopic techniques such as TEM, SEM, and AFM exemplify the core-shell structures. Magnetic force microscopy and vibrating sample magnetometer measurements confirm the architecture of the multishell particles. Cell culture experiments show that even nanoparticles with three shells are still taken up by cells.

Studies on the tosylation of cellulose in mixtures of ionic liquids and a co-solvent.

The tosylation of cellulose in ionic liquids (ILs) was studied. Due to the beneficial effect of different co-solvents, the reaction could be performed at 25°C without the need of heating (in order to reduce viscosity) or cooling (in order to prevent side reactions). The effects of reaction parameters, such as time, molar ratio, and type of base, on the degree of substitution (DS) with tosyl- and chloro-deoxy groups as well as on the molecular weight were evaluated. Products with a DStosyl≤1.14 and DSCl≤0.16 were obtained and characterized by means of NMR- and FT-IR spectroscopy in order to evaluate their purity and distribution of functional groups within the modified anhydroglucose unit (AGU). Tosylation of cellulose in mixtures of IL and a co-solvent was found to result in predominant substitution at the primary hydroxyl group. Size exclusion chromatography (SEC) revealed only a moderate degradation of the polymer backbone at a reaction time of 4-8h. Finally, the nucleophilic displacement (SN) of tosyl- and chloro-deoxy groups by azide as well as recycling of the ILs was studied.

Stable cellulose nanospheres for cellular uptake.

Pure, perfectly spherical cellulose nanoparticles with sizes of ≈80-260 nm can be prepared by dialysis starting from trimethylsilylcellulose (TMSC). The aqueous suspensions obtained are storable for several months. Subsequent covalent labeling of the cellulose nanoparticles with FITC has no influence on particle size, shape, and stability. The particles can be sterilized and suspended in biological media without structural changes. Incorporation of FITC-labeled cellulose nanoparticles into living human fibroblasts is studied using confocal LSM. In contrast to cellulose nanocrystals, fast cellular uptake is found for the nanospheres without transfection reagents or attachment of a receptor molecule. This suggests an influence of the geometry of biocompatible nanomaterials on endocytosis.

Semi-synthetic polysaccharide sulfates as anticoagulant coatings for PET, 1--cellulose sulfate.

In the present study, blood-compatible PET surfaces were prepared by coating with anticoagulant cellulose sulfates that were synthesized homogeneously in ionic liquids. The adsorption behavior of polysaccharides on PET films was investigated using QCM-D. It was demonstrated that pre-coating with different amino-group-containing polysaccharides improves the affinity toward cellulose sulfate. Moreover, the effect of different degrees of sulfation on the adsorption process was evaluated. Based on these results, several layer-by-layer coated PET foils were prepared that showed significantly improved blood compatibility compared to the initial untreated material.

Studies on the boronation of methyl-beta-D-cellobioside--a cellulose model.

The conversion of phenylboronic acid (PBA) with methyl-beta-D-cellobioside (Me-beta-D-clb) and cellodextrins (DP(w) 12) was investigated to gain a basic understanding of the interactions of boric acid derivatives with oligo- and polyglucans. By means of MS and NMR experiments, it was possible to show a first stage formation of a six-membered ring at C-4 and C-6 of the non-reducing glucose occurs as in the case of monosaccharides. If the amount of reagent is increased the formation of seven-membered rings at the secondary OH moieties is observed. Even the existence of two of these large ring-systems in the direct neighborhood was found. Application of an excess of boronation reagent led to dimerization reactions of Me-beta-D-clb via the primary reducing glucose residue as confirmed by DOSY NMR studies. Preliminary (13)C NMR studies for the interaction of cellodextrins with PBA in DMSO solution confirmed a functionalization at the trans-1,2-diol moieties of these oligomers. The amount of reagent applied may either was shown to lead to soluble products or to insoluble cross-linked material.

Interaction of ionic liquids with polysaccharides, 8 - synthesis of cellulose sulfates suitable for polyelectrolyte complex formation.

Water-soluble CS with different DS were synthesized by homogeneous conversion of cellulose (microcrystalline cellulose and spruce sulfite pulp) with different sulfating agents in the ionic liquids BMIMCl, AMIMCl and EMIMAc. N,N-Dimethylformamide was used as a dipolar aprotic co-solvent in order to improve the miscibility of the reaction mixture. The CS prepared by the new homogeneous reaction pathway were studied towards the formation of PEC capsules. CS obtained from SSP formed mechanically stable PEC capsules with PolyDADMAC. Exploiting this method, the microencapsulation of glucose oxidase was studied and enzyme activity tests were performed with encapsulated GOD.

Ammonium-based cellulose solvents suitable for homogeneous etherification.

New ammonium-based cellulose solvents with triethylmethylammonium- and tributylmethylammonium cations and carboxylate anions were synthesized and investigated as potential solvents for cellulose. Triethylmethylammonium formate was found to dissolve cellulose. Small amounts of formic acid may be used to adjust the melting point of the organic salt and can increase the dissolution velocity of cellulose. Carboxymethylation as a common etherification reaction was investigated in the new ammonium-based system. The watersoluble carboxymethyl cellulose obtained, had a degree of substitution as high as 1.55. An unconventional pattern of substitution was accessible.

Determination of the surface coverage of adsorbed dextran and beta-cyclodextrin derivatives on gold by surface titration.

The self-assembly of thiophene-containing dextran and cyclodextrin derivatives on gold surfaces was investigated. Morphological studies (AFM) and the elemental characterization (XPS) of the surfaces show that the carbohydrate derivatives form either aggregates or uniform films depending on the structure and the solvent used. The real coverage of the surface, and hence the amount of unmodified free gold, was examined by a "titration" of the surface with a carboxyl-terminated SAM (11-mercaptoundecanoic acid, MUA) and with Mn-12, a manganese oxocluster. Each carboxyl group reacts with one acetate ligand of the manganese cluster, with each Mn-12 cluster capable of binding multiple MUAs, leading to defined manganese-functionalized surfaces. The weight percentage of manganese and consequently the coverage area of the carboxyl-terminated SAM is examined by XPS.