Kinetics of cellulose regeneration from cellulose--NaOH--water gels and comparison with cellulose--N-methylmorpholine-N-oxide--water solutions

The regeneration kinetics of cellulose from cellulose--NaOH--water gels immersed in a nonsolvent bath is studied in detail. Cellulose concentration, bath type, and temperature were varied, and diffusion coefficients were determined. The results were compared with data measured and taken from the literature on the regeneration kinetics of cellulose from cellulose--N-methylmorpholine-N-oxide (NMMO) monohydrate solutions. Different theories developed for the transport behavior of solutes in hydrogels or in porous media were tested on the systems studied. While the diffusion of NaOH from cellulose--NaOH--water gels into water has to be described with "porous media" approaches, the interpretation of NMMO diffusion is complicated because of the change of NMMO's state during regeneration (from solid crystalline to liquid) and the high concentration of NMMO in the sample. The activation energies were calculated from diffusion coefficient dependence on temperature for both systems and compared with the ones obtained from the rheological measurements. The activation energy of cellulose--NaOH--water systems does not depend on cellulose concentration or the way of measurement. This result shows that whatever the system is, pure NaOH--water solution, cellulose--NaOH--water solution, or cellulose--NaOH--water gel, it is NaOH hydrate with or without cellulose in solution, which is moving in the system. The swelling of cellulose in different nonsolvent liquids such as water or different alcohols during regeneration was investigated and interpreted using the Hildebrand parameter.     

Ice adhesions in relation to freeze stress

In freezing, competitive interaction between ice and hydrophilic plant substances causes an energy of adhesion to develop through the interstitial liquid. The thermodynamic basis for the adhesion energy is discussed, with estimates of the energies involved. In this research, effects of adhesion energy were observed microscopically in conjunction with energies of crystallization and frost desiccation. The complex character of ice in intact crown tissue of winter barley (Hordeum vulgare L.) and the problems of sectioning frozen tissue without producing artifacts led to an alternative study of single barley cells in a mesh of ice and cell wall polymers. Adhesions between ice, cell wall polymers, and the plasmalemma form a complexly interacting system in which the pattern of crystallization is a major factor in determination of stress and injury.     

Membrane hydraulic permeability changes during cooling of mammalian cells

In order to predict optimal cooling rates for cryopreservation of cells, the cell-specific membrane hydraulic permeability and corresponding activation energy for water transport need to be experimentally determined. These parameters should preferably be determined at subzero temperatures in the presence of ice. There is, however, a lack of methods to study membrane properties of cells in the presence of ice. We have used Fourier transform infrared spectroscopy to study freezing-induced membrane dehydration of mouse embryonic fibroblast (3T3) cells and derived the subzero membrane hydraulic permeability and the activation energy for water transport from these data. Coulter counter measurements were used to determine the suprazero membrane hydraulic permeability parameters from cellular volume changes of cells exposed to osmotic stress. The activation energy for water transport in the ice phase is about three fold greater compared to that at suprazero temperatures. The membrane hydraulic permeability at 0 °C that was extrapolated from suprazero measurements is about five fold greater compared to that extrapolated from subzero measurements. This difference is likely due to a freezing-induced dehydration of the bound water around the phospholipid head groups. Using Fourier transform infrared spectroscopy, two distinct water transport processes, that of free and membrane bound water, can be identified during freezing with distinct activation energies. Dimethylsulfoxide, a widely used cryoprotective agent, did not prevent freezing-induced membrane dehydration but decreased the activation energy for water transport.     

The permeability of liposomes to nonelectrolytes. I. Activation energies for permeation.

The effect of temperature on the permeability of nonelectrolytes across liposomal membranes above and below their transition temperature has been studied by using an osmotic method. Below their transition temperature, liposomes are osmotically insensitive structures but, on addition of gramicidin A, the water permeability so increased that the permeability of solutes could be studied. The measured activation energies for permeation of a variety of nonelectrolytes has been found to increase when a) there is an increase in the capability of the solutes to form hydrogen bonds in water, b) the cholesterol concentration in the membranes increases and c) the membranes pass from a liquid-crystalline to a solid-crystalline state. The change in the activation energy for permeation per hydrogen bond is about 1.8 kcal/mole for all the different liposome systems investigated; the only solute tested that deviated from this correlation was urea, whose activation energy for permeation across a gramicidin-containing system was much lower than expected from its hydrogen-bonding capacity. This finding suggests that urea is permeating across the gramicidin pore. Although the literature contains only incomplete data relating the activation energies for permeation of nonelectrolytes across biological membranes to their hydrogen-bonding capacity, the available evidence suggests that there is a similar correlation to that found in liposomes. Thus, the average increase in the activation energy per hydrogen bond for permeation across ox red cell membranes (Jacobs, Glassman & Parpart, J. Cell. Comp. Physiol. 7:197, 1935) is 2.2 plus or minus 0.4 kcal/mole, a value that is similar to that obtained in liposomes. However, the activation energies for water and urea are - in such a system - very much lower than expected, suggesting that they, too, are permeating by some parallel route such as an aqueous pore.     

Effect of hydration on the structure of non aqueous ethyl cellulose/propylene glycol dicaprylate gels

Changes in the structural properties of ethyl cellulose/propylene glycol dicaprylate systems (EC/PGD), intended for topical drug delivery, upon addition of water were investigated. Although designed to be a non-aqueous vehicle for moisture sensitive drugs, these systems are expected to experience an aqueous environment during production, storage and application on the skin. Hence, the interaction of water molecules with the non aqueous gel system and their distribution within the gel network is of interest and critical to its application. Experimental techniques of this study were small-deformation dynamic oscillation in shear, modulated differential scanning calorimetry (MDSC), (2)H NMR spectroscopy, ATR-infrared spectroscopy, wide-angle X-ray diffraction patterns and light microscopy. Rheological profiles of the gels containing moisture from 0.1 to 40.0% (w/w) deviated considerably from that of the non aqueous system at levels of water above 10.0% in preparations. Gradual replacement of the EC/PGD dipole interactions with stronger hydrogen bonding between ethyl cellulose chains, as the level of hydration increased, contributed to these observations. Formation of clusters of ethyl cellulose, observed under a light microscope, was thus ensued. X-ray diffraction patterns showed that the rearrangement of the polymer chains led to the loss of liquid crystal structures found in the anhydrous gel. MDSC and (2)H NMR were used to further shed light on the thermodynamic state of added water molecules in the gels. Plots of enthalpy obtained calorimetrically and a good correlation between MDSC and (2)H NMR data indicate that gels with less than two percent hydration contain water in a non-freezable bound state, whereas freezable moieties are obtained at levels of hydration above five percent in composite (EC/PGD/water) gels.     

The Arrhenius Equation as a Model for Explaining Plant Responses to Temperature and Water Stresses

The Arrhenius equation describes the response of biologicalprocesses to temperature. This study was conducted to examinethe applicability of the Arrhenius equation to whole plant processesand to explore the application of the Arrhenius equation asa basis for characterizing plant responses to water stress.Rates of growth of leaf area and shoot dry mass of spring wheatseedlings were measured at combinations of five soil water potentials(–0.03, –0.06, –0.10, –0.17 and –0.25MPa) and seven root temperatures (12, 14, 17, 22, 27, 29 and32 C). A non-linear least square procedure was used to fitthe modified Arrhenius equation to experimental observations.Adequate distribution of experimental observations with respectto temperature reduces the uncertainties in parameter evaluations.The standard error of the estimate of optimum temperature forleaf area growth increased from 1.4 C to 6.3 C when one ofthe data points was omitted. The optimum temperature and theenthalpy of denaturalization of enzyme systems were independentof soil water potential. A linear relation was found betweenthe rate constant and the activation energy: The Arrhenius equation was modified using this linear relation,leaving the activation energy as the only parameter affectedby water stress. The activation energy increased linearly assoil water potential decreased, with slopes of –27.18 10₃ and –28.09 10₂ K MPa^–1 for the rates ofgrowth of leaf area and shoot dry mass, respectively. Theseslopes could be used as indicators of the sensitivity of plantprocesses to water stress. Temperature, water, plants, Arrhenius equation     

Comparative freezing patterns of bark and xylem of “Siberian C” and “Redhaven” peach twigs

An electrophoretic mobility technique was used to study freezing patterns in excised peach twigs. Moisture content was the only qualitative difference in initial freezing patterns of similar tissues of Redhaven and Siberian C. Siberian C contained up to 18% less moisture than Redhaven. Major differences in the shape of the transition pattern were detected between bark and xylem. Even though bark tissues had twice the water content of xylem, the bark exhibited equilibrium freezing while the xylem underwent nonequilibrium freezing. Bark water must be intimately associated with the living protoplast, while xylem water is less closely associated with cellular components. Comparison of bark and xylem freezing curves with sucrose and cellulose model systems suggested that bark freezing was similar to the sucrose model while xylem freezing was similar to the cellulose model.     

Relationship of the structure of cellulose and certain model compounds to the dynamics of molecular reactions

Using the results of kinetic studies of free radical recombination in cellulose and in some model compounds, some data as to their structure were obtained. Cellulose is characterized by the distribution function of microregions with different energy of molecular interaction. The minimal value of activation energy of macromolecule movement is 37-42 kJ/mol (1.5-2 hydrogen bonds per glucopyranose ring), the maximal one is 63-105 kJ/mol corresponding to the most ordered (crystalline) regions of cellulose. After amorphization of cellulose the warming-up by stages curve points to even distribution by the forces of molecular interaction.     

Logistic distributed activation energy model--part 2: application to cellulose pyrolysis

The pyrolysis behavior of cellulose has been investigated by using thermogravimetric analysis (TGA). The non-isothermal TGA data obtained at different heating rates have been analyzed simultaneously. Pattern Search Method has been proposed for the estimation of the model parameter values. Predicted values from the logistic distributed activation energy model have been compared with the experimental data and the results have indicated that the model describes the kinetic behavior of cellulose pyrolysis very well. The mean value and standard deviation of the logistic activation energy distribution for cellulose pyrolysis are found to be 258.5718 kJ mol(-1) and 2.6601 kJ mol(-1), the reaction order is 1.1101 and the k(0) is 1.6218×10(17) s(-1).     

Leaf and stem physiological responses to summer and winter extremes of woody species across temperate ecosystems

Winter cold limits temperate plant performance, as does summer water stress in drought‐prone ecosystems. The relative impact of seasonal extremes on plant performance has received considerable attention for individual systems. An integrated study compiling the existing literature was needed to identify overall trends. First, we conducted a meta‐analysis of the impacts of summer and winter on ecophysiology for three woody plant functional types (winter deciduous angiosperms, evergreen angiosperms and conifers), including data for 210 records from 75 studies of ecosystems with and without summer drought across the temperate zone. Second, we tested predictions by conducting a case study in a drought‐prone Mediterranean ecosystem subject to winter freezing. As indicators of physiological response of leaves and xylem to seasonal stress, we focused on stomatal conductance (g_s), percent loss of stem xylem hydraulic conductivity (PLC) and photochemical efficiency of photosystem II (F_v/F_m). Our meta‐analysis showed that in ecosystems without summer drought, g_s was higher during summer than winter. By contrast, in drought‐prone ecosystems many species maintained open stomata during winter, with potential strong consequences for plant carbon gain over the year. Further, PLC tended to increase and F_v/F_m to decrease from summer to winter for most functional types and ecosystems due to low temperatures. Overall, deciduous angiosperms were most sensitive to climatic stress. Leaf gas exchange and stem xylem hydraulics showed a coordinated seasonal response at ecosystems without summer drought. In our Mediterranean site subjected to winter freezing the species showed similar responses to those typically found for ecosystems without summer drought. We conclude that winter stress is most extreme for systems without summer drought and systems with summer drought and winter freezing, and less extreme for drought‐prone systems without freezing. In all cases the evergreen species show less pronounced seasonal responses in both leaves and stems than deciduous species.     

On the mechanism of non-electrolyte permeation through lipid bilayers and through biomembranes

The temperature effects on the permeation of polyhydroxy alcohols through the lipid bilayers of liposomes with a great variety in chemical composition were studied. Although important differences in the permeability of the various lipid bilayers were observed, Arrhenius plots demonstrated that the activation energy is independent of the degree of unsaturation or the presence of cholesterol in the paraffin barriers. The activation energies found for the penetration of a bilayer with a liquid paraffin core are 14.3 kcal for glycol, 19.4 kcal for glycerol, and 20.8 kcal for erythritol. These values are in agreement with the energies that can be expected for complete dehydration of the permeant molecules. The idea that the activation energy is determined by the number of hydrogen bonds with water is supported by the finding that a series of different diols did demonstrate practically identical activation energies. Studies on a number of biological membranes demonstrated the same activation energies for the penetration of glycerol and erythritol as found in the experiments with liposomes. These facts support the view that both the lipid bilayers and the biological membranes are penetrated by single fully dehydrated molecules.     

Estimation of the effective hydrophobicity of protiens: Re-evaluation of methods

Summary Partition coefficients of distribution of proteins were measured in two systems: i) 3-phenoxy-2-hydroxypropyl derivatives of bead cellulose (PHPC)/water solution — coefficients P; and ii) Aqueous polyethylene glycol (PEG)/dextran (DXT) two-phase system — coefficient K. Following proteins were used for the measurements: lysozyme, trypsin, chymotrypsin, ovalbumin, bovine serum albumin and immunoglobulin G. The obtained P and K values were correlated with previous data about hydrophobicity of the above proteins available in the literature. The literary data concerned: i) the efficacy of energy transfer from tryptophan residues of proteins to cis-parinaric acid applied as hydrophobic probe, estimated by fluorescent spectroscopy; ii) the hydrophobic ratio indicating the ratio between the hydrophobic and hydrophilic parts (in volumes) of protein molecules deduced from their primary structure; and iii) the interfacial tension at 0.2% protein-water solution/corn oil interface. Significant corrlations were obtained for P and efficacy of energy transfer (r=0.964; p<0.01) and for K and interfacial tension (r=0.936; p<0.05). When P and K were fitted as exponential function of three independent variables (i.e., efficacy of energy transfer, hydrophobic ratio and interfacial tension) good agreement between the measured and computed data was obtained. The increases in efficacy of energy transfer, hydrophobic ratio and decrease in interfacial tension were found to be accompanied by increase in P. In contrary, K behaved always similarly as efficacy of energy transfer, hydrophobic ratio and interfacial tension.     

Measurement of the surface free energy of bacterial cell surfaces and its relevance for adhesion

An experimental technique is described to determine contact angles on bacterial layers deposited on cellulose triacetate filters. Measurements with water, water-n-propanol mixtures, and alpha-bromonaphthalene were employed to calculate surface free energies of various oral bacteria. Differences of 30 to 40 erg cm-2 were obtained for four different bacterial species isolated from the human oral cavity, if the concept of dispersion and polar surface free energies is applied. The free energies obtained were used to calculate interfacial free energies of adhesion of these bacteria from saliva onto tooth surfaces. Bacterial adhesion is energetically unfavorable, if the enamel surface free energy is less than 50 erg cm-2.     

Measurement of the surface free energy of bacterial cell surfaces and its relevance for adhesion.

An experimental technique is described to determine contact angles on bacterial layers deposited on cellulose triacetate filters. Measurements with water, water-n-propanol mixtures, and alpha-bromonaphthalene were employed to calculate surface free energies of various oral bacteria. Differences of 30 to 40 erg cm-2 were obtained for four different bacterial species isolated from the human oral cavity, if the concept of dispersion and polar surface free energies is applied. The free energies obtained were used to calculate interfacial free energies of adhesion of these bacteria from saliva onto tooth surfaces. Bacterial adhesion is energetically unfavorable, if the enamel surface free energy is less than 50 erg cm-2.     

Technological problems in cultivation of plant cells at high density

Using Cudrania tricuspidata cells as model plant cells which have high sensitivity to hydrodynamic stress, technology problems in the cultivation of the plant cells at high density were investigated. Using “shake” flasks on a reciprocal shaker and Erlenmeyer flasks on a rotary shaker and with a high supply of oxygen on order to obtain high cell densities in shaken cultures, particles breakdown and damage to the largest cell aggregate group (above 1981 μm in diameter) occurred and normal cell growth became impeded. The mass-transfer coefficient (K)for a model solid–liquid system (β-naphthol particles and water) in place of a system of plant cells and a liquid medium was proposed as an intensity index of hydrodynamic stress effects on plant cells in subsequent cultures under various conditions in the bioreactor systems. Normal cell growth was obtained under culture conditions for K values less than about 4.4 × 10^?3 cm/sec. The characteristics of various bioreactors used until now were investigated by considering the three main technological factors (capacity of oxygen supply, intensity of hydrodynamic stress effects on plant cells, and intensity of culture broth mixing and air-bubble desperation). The most suitable bioreactor for culturing plant cells at high density was ajar fermentor with a modified paddle-type impeller (J-M). The yield of cell mass in the 10-liter J-M (working volume 5 liter) was about 30 g dry weight per liter of medium.     

Application of the thermorheologically complex nonlinear Adam-Gibbs model for the glass transition to molecular motion in hydrated proteins

The nonlinear thermorheologically complex Adam Gibbs (extended "Scherer-Hodge") model for the glass transition is applied to enthalpy relaxation data reported by Sartor, Mayer, and Johari for hydrated methemoglobin. A sensible range in values for the average localized activation energy is obtained (100-200 kJ mol(-1)). The standard deviation in the inferred Gaussian distribution of activation energies, computed from the reported KWW beta-parameter, is approximately 30% of the average, consistent with the suggestion that some relaxation processes in hydrated proteins have exceptionally low activation energies.     

Technological problems in cultivation of plant cells at high density. Reprinted from Biotechnology and Bioengineering, Vol. XXII, No. 6, Pages 1203-1218 (1981)

Using Cudrania tricuspidata cells as model plant cells which have high sensitivity to hydrodynamic stress, technological problems in the cultivation of the plant cells at high density were investigated. Using "shake" flasks on a reciprocal shaker and Erlenmeyer flasks on a rotary shaker and with a high supply of oxygen in order to obtain high cell densities in shaken cultures, particle breakdown and damage to the largest cell aggregate group (above 1981 microm in diameter) occurred and normal cell growth became impeded. The mass-transfer coefficient (K) for a model solid-liquid system (beta-naphthol particles and water) in place of a system of plant cells and a liquid medium was proposed as an intensity index of hydrodynamic stress effects on plant cells in suspension cultures under various conditions in the bioreactor systems. Normal cell growth was obtained under culture conditions for K values less than about 4.4 x 10(-3) cm/sec. The characteristics of various bioreactors used until now were investigated by considering the three main technological factors (capacity of oxygen supply, intensity of hydrodynamic stress effects on plant cells, and intensity of culture broth mixing and air-bubble dispersion). The most suitable bioreactor for culturing plant cells at high density was a jar fermentor with a modified paddle-type impeller (J-M). The yield of cell mass in the 10-liter J-M (working volume 5 liter) was about 30 g dry weight per liter of medium.     

Freezing behavior of water in small pores and the possible role in the freezing of plant tissues

Two model systems were used to study the freezing of water in small diameter pores. Water in pores having a diameter of less than 100 nanometers froze at lower temperatures than bulk water. Data obtained with a range of pore sizes were consistent with predicted values based on equations developed by Mazur (1965 Ann NY Acad Sci 125: 658-676), and Homshaw (1980 J Soil Sci 31: 399-414). The addition of solutes lowered the freezing point of water in small pores. We propose that the freezing behavior of water in small pores may account for some of the freezing patterns observed in plant tissues. In tissues where cells are tightly packed, share common walls, and lack intercellular spaces, the presence of water in cell wall microcapillaries would alter the freezing temperature of tissue water, impede the spread of ice, and facilitate supercooling.     

Lipid lateral diffusion in ordered and disordered phases in raft mixtures

Lipid lateral diffusion coefficients in the quarternary system of dioleoylphosphatidylcholine (DOPC), sphingomyelin, cholesterol, and water were determined by the pulsed field gradient NMR technique on macroscopically aligned bilayers. The molar ratio between dioleoylphosphatidylcholine and sphingomyelin was set to 1:1, the cholesterol content was varied between 0 and 45 mol %, the water content was 40 wt %, and the temperature was varied between 293 and 333 K. The diffusion coefficients were separated into fast and slow spectral components by using the CORE method for global analysis of correlated spectral data. A large two-phase region, tentatively assigned to the liquid disordered (l(d)) and the liquid ordered (l(o)) phases, was present in the phase diagram. The l(d) phase was enriched in dioleoylphosphatidylcholine and exhibited diffusion coefficients that were about three to five times larger than for the l(o) phase. Both the diffusion coefficients and the apparent activation energies for the quarternary systems were compatible with earlier reports on ternary phospholipid/cholesterol/water systems. However, in contrast to the latter ternary systems, the exchange of lipids between the l(o) and the l(d) phases was slow on the timescale for the diffusion experiment for the quarternary ones. This means that on the millisecond timescale fluid, ordered domains are floating around in a sea of faster diffusing lipids, assigned to consist of mainly dioleoylphosphatidylcholine.     

Mechanical properties of primary plant cell wall analogues

Mechanical effects of turgor pressure on cell walls were simulated by deforming cell wall analogues based on Acetobacter xylinus cellulose under equi-biaxial tension. This experimental set-up, with associated modelling, allowed quantitative information to be obtained on cellulose alone and in composites with pectin and/or xyloglucan. Cellulose was the main load-bearing component, pectin and xyloglucan leading to a decrease in modulus when incorporated. The cellulose-only system could be regarded as an essentially linear elastic material with a modulus ranging from 200 to 500 MPa. Pectin incorporation modified extensibility properties of the system by topology/architecture changes of cellulose fibril assemblies, but the cellulose/pectin composites could still be described as a linear elastic material with a modulus ranging from 120 to 250 MPa. The xyloglucan/cellulose composite could not be modelled as a linear elastic material. Introducing xyloglucan into a cellulose network or a cellulose/pectin composite led to very compliant materials characterised by time-dependent creep behaviour. Modulus values obtained for the composite materials were compared with mechanical data found for plant-derived systems. After comparing bi-axial and uni-axial behaviour of the different composites, structural models were proposed to explain the role of each polysaccharide in determining the mechanical properties of these plant primary cell wall analogues.