Effect of reaction conditions on the properties and behavior of wood cellulose nanocrystal suspensions

Sulfuric acid hydrolysis of native cellulose fibers produces stable suspensions of cellulose nanocrystals. Above a critical concentration, the suspensions spontaneously form an anisotropic chiral nematic liquid crystal phase. We have examined the effect of reaction time and acid-to-pulp ratio on nanocrystal and suspension properties for hydrolyzed black spruce acid sulfite pulp. Longer hydrolysis times produced shorter, less polydisperse black spruce cellulose nanocrystals and slightly increased the critical concentration for anisotropic phase formation. Increased acid-to-pulp ratio reduced the dimensions of the nanocrystals thus produced; the critical concentration was increased and the biphasic range became narrower. A suspension made from a bleached kraft eucalyptus pulp gave very similar properties to the softwood nanocrystal suspension when prepared under similar hydrolysis conditions.     

Chiral nematic ordering of polysaccharides

In this paper, evidence for the chiral nematic (cholesteric) self-ordering of cellulose-derived materials is reviewed. A wide range of cellulose derivatives, and some other polysaccharides, form chiral nematic phases, both in concentrated solution and in the melt. Solid films and gels retaining the chiral nematic ordering of the polymer chains may be prepared from these liquid crystalline phases. Optical and electron microscopic techniques may be used to elucidate the helicoidal structure of chiral nematic cellulosics in the liquid crystalline phase, and of the films, gels and solids prepared from such phases. Remarkably, dilute aqueous suspensions of cellulose crystallites prepared by acid degradation also show chiral nematic order; the order is preserved in dry films prepared from the suspensions. The structure of some of these samples prepared in vitro shows a marked resemblance to structures observed in vivo.     

Controlling the reflection wavelength of iridescent solid films of nanocrystalline cellulose

Nanocrystalline cellulose (NCC) self-assembles in suspension to form iridescent chiral nematic films upon drying that can reflect circularly polarized light at specific wavelengths. Ultrasound treatment has now been found to increase the chiral nematic pitch in suspension and red-shift the reflection wavelength of NCC films as the applied energy increases. Sonication and electrolyte addition combined allow the reflective properties of the film to be predictably tuned. The effects of sonicating an NCC suspension are cumulative and permanent. Suspensions sonicated with different energy inputs may be mixed to give an NCC film having a reflection band intermediate between those obtained from the individual suspensions. The data suggest that the ultrasound-induced red-shift is electrostatic in nature.     

In vitro chiral nematic ordering of chitin crystallites

Microfibrillar fragments of purified crab and shrimp chitin were prepared by hydrolysis in 3 HCl at its boiling point (104°C). After removal of the acid by centrifugal washing and dialysis, an ultrasound treatment converts the residual product to a colloidal suspension stabilized by NH₃⁺ charges. When dewatered to a critical concentration, spontaneous formation of a two-phase equilibrium system occurs. The upper phase (lower concentration) is isotropic and the lower phase is anisotropic. The latter displays chiral nematic order and dries to a solid film which mimics the helicoid organization characteristic of the chitin microfibrils in the cuticle of arthropods.     

Helicoidal self-ordering of cellulose microfibrils in aqueous suspension.

In many skeletal support systems of plants and animals, cellulose, chitin, and collagen occur in the form of microfibrils ordered in a chiral nematic fashion (helicoids). However, these structures remain poorly understood due to the many constituents present in biological tissues. Here we report an in vitro system that attracts by its simplicity. Only one chemical component, cellulose, is present in the form of fibrillar fragments dispersed in water. Above a critical concentration the colloidal dispersion separates spontaneously into a chiral nematic liquid crystalline phase. On drying this phase solidifies into regularly twisted fibrillar layers that mimic the structural organization of helicoids in nature.     

Microgermination of Bacillus cereus spores

The biphasic nature of germination curves of individual Bacillus cereus T spores was further characterized by assessing the effects of temperature, concentration of germinants, and some inorganic cations on microgermination. Temperature was shown to affect both phases of microgermination as well as the microlag period, whereas the concentration of l-alanine and supplementation with adenosine exerted a significant effect only on the microlag period. The germination curves of individual spores induced by inosine were also biphasic and resembled those of spores induced by l-alanine. High concentrations (0.1 m or higher) of calcium and other inorganic cations prolonged both phases of microgermination, particularly the second phase, and had a less pronounced effect on the microlag period. The second phase of microgermination was completely inhibited when spores were germinated either in the presence of 0.3 m CaCl(2) or at a temperature of 43 C; this inhibition was reversible. Observations on the germination of spore suspensions (kinetics of the release of dipicolinic acid and mucopeptides, loss of heat resistance, increase in stainability, decrease in turbidity and refractility) were interpreted on the basis of the biphasic nature of microgermination. Dye uptake by individual spores during germination appeared also to be a biphasic process.     

Enantioselective potential of polysaccharide‐based chiral stationary phases in supercritical fluid chromatography

The enantioselective potential of two polysaccharide‐based chiral stationary phases for analysis of chiral structurally diverse biologically active compounds was evaluated in supercritical fluid chromatography using a set of 52 analytes. The chiral selectors immobilized on 2.5 μm silica particles were tris‐(3,5‐dimethylphenylcarmabate) derivatives of cellulose or amylose. The influence of the polysaccharide backbone, different organic modifiers, and different mobile phase additives on retention and enantioseparation was monitored. Conditions for fast baseline enantioseparation were found for the majority of the compounds. The success rate of baseline and partial enantioseparation with cellulose‐based chiral stationary phase was 51.9% and 15.4%, respectively. Using amylose‐based chiral stationary phase we obtained 76.9% of baseline enantioseparations and 9.6% of partial enantioseparations of the tested compounds. The best results on cellulose‐based chiral stationary phase were achieved particularly with propane‐2‐ol and a mixture of isopropylamine and trifluoroacetic acid as organic modifier and additive to CO₂, respectively. Methanol and basic additive isopropylamine were preferred on amylose‐based chiral stationary phase. The complementary enantioselectivity of the cellulose‐ and amylose‐based chiral stationary phases allows separation of the majority of the tested structurally different compounds. Separation systems were found to be directly applicable for analyses of biologically active compounds of interest.     

The development of biphasic chiral recognition in chiral separation

In chiral separation, enantioseparation factor is an important parameter which influences the resolution of enantiomers. In this current overview, a biphasic chiral recognition method is introduced to the readers. This method can significantly improve the enantioseparation factor in two‐phase solvent through adding lipophilic and hydrophilic chiral selectors which have opposite chiral recognition ability to organic and aqueous phases, respectively. This overview presents the development and applications of biphasic chiral recognition in liquid‐liquid extraction and counter current chromatography. It mainly focuses on the topics of mechanism, advantages and limitations, applications, and key factors of biphasic chiral recognition. In addition, the future outlook on development of biphasic chiral recognition also has been discussed in this overview.     

Isotropic-nematic phase equilibrium and phase separation of kappa-carrageenan in aqueous salt solution: experimental and theoretical approaches

The behavior of chiral-nematic and isotropic phases of helical kappa-carrageenan in aqueous solution of sodium iodide was compared with that of the anisotropic biphasic phase that contains both these phases. On the basis of birefringence, rheology, chemical analysis, average molecular weight, and polydispersity index measurements, we derived a number of characteristic differences as well as similarities between these phases, over a range of polysaccharide concentrations obtained by the dilution of each phase. For example, we assessed the critical concentration of an isotropic-anisotropic transition (C(i)), the temperature of the anisotropic-isotropic phase shift during thermal heating-cooling cycles, and the viscosity changes due to the phase shift and due to the diminishing of the helical conformation. We also demonstrated how the different phases and their dilutions behave under the effect of shear and frequency of oscillation and how the viscoelastic properties vary in each phase and discussed the isotropic and anisotropic liquid crystal controlling behavior mechanisms. From a theoretical point of view, we propose to combine the wormlike chain model for semiflexible polyelectrolytes interacting via both hard-core and electrostatic repulsion to assess the concentration of isotropic-nematic transition, to assess the coexistence concentration range, and to determine the effects of charge by applying the effective diameter and a twisting effect.     

A Permanent Cell Viability Assay Using Alcian Blue

The alcian blue dye exclusion method for glutaraldehyde-fixed cells has been utilized with “centrifugal cytology” to prepare permanent records of the viability of individual cells present in suspensions. The viability of spleen cell suspensions separated by linear bovine serum albumin density gradient centrifugation has been measured with this method. Combined light and scanning electron microscopy of nonviable and viable cells demonstrated membrane alterations in alcian blue-stained nonviable cells, while viable cells were spherical and displayed uniform surface features.     

Reversed-phase liquid chromatographic enantioseparation by cycloalkylcarboxylates of cellulose and amylose

Three novel cycloalkylcarboxylates, cyclopentyl, cyclohexyl, and 1-adamantylcarboxylates of cellulose and amylose were prepared and their chiral recognition abilities as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) were evaluated using a methanol-water mobile phase. Among these esters, cellulose tris(cyclohexylcarboxylate) showed a relatively high chiral recognition ability. The 1-adamantylcarboxylates of cellulose and amylose showed dissimilar chiral recognition abilities from the other two, probably due to the low degree of substitution and the high hydrophobicity of this group.     

Proton transfer during the reaction between fully reduced cytochrome c oxidase and dioxygen: pH and deuterium isotope effects.

The pH dependence of proton uptake and electron transfers during the reaction between fully reduced cytochrome c oxidase and oxygen has been studied using the flow-flash method. Proton uptake was monitored using different pH indicators. We have also investigated the effect of D2O on the electron-transfer reactions. Proton uptake was biphasic throughout the pH range studied (6.3-9.3), and the decrease of the observed rate constants at increasing pH could be described by titration curves with pKa values of 8-8.5. Of the four phases resolved in the redox reaction, the rate constants for the first two were independent of pH, whereas that of the third decreased at increasing pH with a pKa of 7.9. All phases except the first were slower in D2O than in H2O. The values obtained for kH/kD were 1.0 for the first phase, 1.4 for the second and third phases, and 2.5 for the fourth phase. We suggest from these results that the fast phase of proton uptake is initiated by the second phase of the redox reaction and that this step includes a partially rate-limiting internal proton transfer. The third and fourth phases of the redox reaction are suggested to be rate limited by proton uptake from the medium. The pH dependencies of the proton uptake reactions are consistent with the participation of a titrable group in the protein in proton transfer from the medium to the oxygen-binding site.     

Intrinsic chiral domains enantioselectively segregated from twisted nematic cells of bent-core mesogens

Enantioselective segregation has been attained in the Bx phase of a novel substituted oxadiazole achiral banana-shaped liquid crystal (LC) without introducing any chiral species. This bent-core molecule exhibits LC polymorphism; the higher temperature nematic (N) phase and the lower temperature banana smectic phase (Bx phase), in which spontaneous chiral segregation with (+) and (-) chiral domains occurs with equal probabilities. In twisted cell geometries, extrinsically induced twisted N structures are formed and result in intrinsically chiral conglomerate when the temperature is decreased from N to Bx. The observed optical activity in homochiral Bx phase is comparable to those theoretically predicted and is proportional to the cell thickness.     

Investigation of viability of plant tissue in the environmental scanning electron microscopy

The advantages of environmental scanning electron microscopy (ESEM) make it a suitable technique for studying plant tissue in its native state. There have been few studies on the effects of ESEM environment and beam damage on the viability of plant tissue. A simple plant tissue, Allium cepa (onion) upper epidermal tissue was taken as the model for study. The change of moisture content of samples was studied at different relative humidities. Working with the electron beam on, viability tests were conducted for samples after exposure in the ESEM under different operating conditions to investigate the effect of electron beam dose on the viability of samples. The results suggested that without the electron beam, the ESEM chamber itself can prevent the loss of initial moisture if its relative humidity is maintained above 90%. With the electron beam on, the viability of Allium cepa (onion) cells depends both on the beam accelerating voltage and the electron dose/unit area hitting the sample. The dose can be controlled by several of the ESEM instrumental parameters. The detailed process of beam damage on cuticle-down and cuticle-up samples was investigated and compared. The results indicate that cuticular adhesion to the cell wall is relatively weak, but highly resistant to electron beam damage. Systematic study on the effect of ESEM operation parameters has been done. Results qualitatively support the intuitive expectations, but demonstrate quantitatively that Allium cepa epidermal cells are able to be kept in a hydrated and viable state under relevant operation condition inside ESEM, providing a basis for further in situ experiments on plant tissues.     

Chromatographic properties of composite chiral stationary phases based on cellulose derivatives

Chiral stationary phases (CSPs) prepared by mixing together two different cellulose derivatives, before or after being coated on macroporous silica gel, were developed in order to determine the mutual influence of two different polymers on global chiral recognition capacity. The chromatographic properties of these CSPs were evaluated using a wide range of racemic test solutes. The mixing method does not significantly affect the enantioselectivities. The composite CSPs obtained by cocoating of two different cellulose derivatives on silica generally exhibit chiral recognition capacities intermediate between those of the two individual phases, and thus broadening the application range of a single column. These results indicate that the simultaneous coating of two different cellulose derivatives does not significantly alter the optical resolution power of each chiral material and are discussed in relationship with the supramolecular structure of the polymeric stationary phases. © 1995 Wiley-Liss, Inc.     

Study on the HPLC‐based separation of some ezetimibe stereoisomers and the underlying stereorecognition process

The enantioseparation of ezetimibe stereoisomers by high‐performance liquid chromatography on different chiral stationary phases, ie, 3 polysaccharide‐based chiral columns, was studied. It was observed that cellulose‐based Chiralpak IC column exhibited the best resolving ability. After the optimization of mobile phase compositions in both normal and reversed phase modes, satisfactory separation could be obtained on Chiralpak IC column, especially in normal phase mode. The use of prohibited solvents as nonstandard mobile phase gave rise to better resolution than that of standard mobile phases (n‐hexane/alcohol system). In addition, the presence of ethanol in nonstandard mobile phase has played an important role in enhancing chromatographic efficiency and resolution between ezetimibe stereoisomers. Various attempts were made to comprehensively compare the chiral recognition capabilities of immobilized versus coated polysaccharide‐based chiral columns, amylose‐based versus cellulose‐based chiral stationary phases, reversed versus normal phase modes, and standard versus nonstandard mobile phases. Moreover, possible solute‐mobile phase‐stationary phase interactions were derived to explain how stationary and mobile phases affected the separation. Then the method validation with respect to selectivity, linearity, precision, accuracy, and robustness was carried out, which was demonstrated to be suitable and accurate for the quantitative determination of (RRS)‐ezetimibe impurity in ezetimibe bulk drug.     

Analysis of Vero cell growth behavior on microcarrier by means of environmental scanning electron microscopy

By using environmental scanning electron microscopy, the morphological changes of Vero cells attached to and grown on the microcarrier Cytodex-3 were observed, and their behavior of adhesion, spreading and proliferation was analyzed. The effect of exogenous fibronectin/ laminin on adhesion and spreading of MCC/Vero cell was studied. The images of ESEM showed that expansion of cell growth was directed toward vacancy space. The growth curve and cell concentration change during the whole culture process were obtained from the statistical counting method based on ESEM images and the crystal violet method. The growth rate of Vero cells increases with increasing the concentration of cell inoculation, that is, the specific growth rate increases quickly with increasing the concentration of cell inoculation. When serum concentration in medium #199 ranged from 5% to 10%, experimental results indicated that serum concentration is one of the important factors influencing cell growth, particularly in the cell adhesion and spreading stage.     

Environmental scanning electron microscopy offers real-time morphological analysis of liposomes and niosomes

Liposomes have been imaged using a plethora of techniques. However, few of these methods offer the ability to study these systems in their natural hydrated state without the requirement of drying, staining, and fixation of the vesicles. However, the ability to image a liposome in its hydrated state is the ideal scenario for visualization of these dynamic lipid structures and environmental scanning electron microscopy (ESEM), with its ability to image wet systems without prior sample preparation, offers potential advantages to the above methods. In our studies, we have used ESEM to not only investigate the morphology of liposomes and niosomes but also to dynamically follow the changes in structure of lipid films and liposome suspensions as water condenses on to or evaporates from the sample. In particular, changes in liposome morphology were studied using ESEM in real time to investigate the resistance of liposomes to coalescence during dehydration thereby providing an alternative assay of liposome formulation and stability. Based on this protocol, we have also studied niosome-based systems and cationic liposome/DNA complexes.     

Analysis of Vero cell growth behavior on microcarrier by means of environmental scanning electron microscopy

By using environmental scanning electron microscopy, the morphological changes of Vero cells attached to and grown on the microcarrier Cytodex-3 were observed, and their behavior of adhesion, spreading and proliferation was analyzed. The effect of exogenous fibronectin/ laminin on adhesion and spreading of MCC/Vero cell was studied. The images of ESEM showed that expansion of cell growth was directed toward vacancy space. The growth curve and cell concentration change during the whole culture process were obtained from the statistical counting method based on ESEM images and the crystal violet method. The growth rate of Vero cells increases with increasing the concentration of cell inoculation, that is, the specific growth rate increases quickly with increasing the concentration of cell inoculation. When serum concentration in medium #199 ranged from 5% to 10%, experimental results indicated that serum concentration is one of the important factors influencing cell growth, particularly in the cell adhesio     

Spermidine-induced aggregation of nucleosome core particles: evidence for multiple liquid crystalline phases.

We investigate the effect of the addition of a trivalent cation, spermidine, to dilute solutions of nucleosome core particles (NCP). In the presence of spermidine, part of the NCP segregates from the initial homogeneous solution, forming dense aggregates. We follow this precipitation process over a wide range of spermidine and NaCl concentrations and determine the conditions of aggregation of the particles. The structure of the dense phases is analyzed by means of polarizing light microscopy and cryo-electron microscopy. We report the existence of multiple supramolecular organizations. According to the relative concentrations of spermidine, monovalent salt and NCP, the particles may aggregate into amorphous phases, stack into randomly oriented columns, or form liquid crystalline phases. Two discotic liquid crystalline phases are identified and analyzed: a columnar nematic corresponding to columns of NCP simply aligned in parallel, and a columnar hexagonal phase in which the columns order into a transversal 2D hexagonal array. We discuss the nature and origin of the interactions possibly involved in the formation and maintenance of these different types of order.