Interrelationship between water film thicknesses and contact angles and a model for CO2 adhesion

Thermodynamics of contact angle phenomena is strongly affected by the presence of thin liquid films. However, at present, studies for CO₂/brine/mineral systems only consider the films apart from contact angles. In this paper, molecular dynamics (MD) simulations have been performed to simultaneously investigate the interrelationship between water film thicknesses and water contact angles. Two types of contact angles were considered namely Young’s contact angle (no water film is present) and contact angle with film (a stable film is present). The results showed that as Young’s contact angle increased, film thickness decreased which leading to increasing of contact angle with film. The effects of CO₂-mineral pre-contact have also been investigated and it has been found that on mediate hydrophilic surfaces (Q³), water films were present when CO₂ droplets were placed above the surfaces, however, water films were absent when CO₂ droplets directly contact with the surfaces. This phenomenon implies that water films on mineral surfaces have a possibility to rupture and a film rupture mechanism for CO₂ adhesion on hydrated mineral surfaces was proposed. These results may provide new information on interactions among CO₂, water/brine and mineral to better understand the behaviour of CO₂ during geologic sequestration.     

Deciphering the role of charge,hydration, and hydrophobicity for cytotoxic activities and membrane interactions of bile acid based facial amphiphiles

We synthesized four cationic bile acid based facial amphiphiles featuring trimethyl ammonium head groups. We evaluated the role of these amphiphiles for cytotoxic activities against colon cancer cells and their membrane interactions by varying charge, hydration and hydrophobicity. The singly charged cationic Lithocholic acid based amphiphile (LCA-TMA₁) is most cytotoxic, whereas the triply charged cationic Cholic acid based amphiphile (CA-TMA₃) is least cytotoxic. Light microscopy and Annexin-FITC assay revealed that these facial amphiphiles caused late apoptosis. In addition, we studied the interactions of these amphiphiles with model membrane systems by Prodan-based hydration, DPH-based anisotropy, and differential scanning calorimetry. LCA-TMA₁ is most hydrophobic with a hard charge causing efficient dehydration and maximum perturbations of membranes thereby facilitating translocation and high cytotoxicity against colon cancer cells. In contrast, the highly hydrated and multiple charged CA-TMA₃ caused least membrane perturbations leading to low translocation and less cytotoxicity. As expected, Chenodeoxycholic acid and Deoxycholic acid based amphiphiles (CDCA-TMA₂, DCA-TMA₂) featuring two charged head groups showed intermediate behavior. Thus, we deciphered that charge, hydration, and hydrophobicity of these amphiphiles govern membrane interactions, translocation, and resulting cytoxicity against colon cancer cells.     

Molecular simulation of swelling and structure for Na-Wyoming montmorillonite in supercritical CO2

Gibbs ensemble Monte Carlo (GEMC) simulations were used to study the swelling stability and interlayer structures of Na-montmorillonite clay in supercritical CO₂ (scCO₂). From the GEMC simulation, it was found that there exist several stable mechanical spacings for Na-Wyoming montmorillonite immersed in scCO₂, which are larger than the stable spacing in vacuum condition. The swelling behaviour of Na-montmorillonite clay in scCO₂ fluid is thermodynamically favourable. However, it was also observed that the clay swelling is inhibited when in contact with CO₂ gas at atmospheric pressure. The interlayer structures were applied to investigate the mechanism of swelling. In the case of stable spacings, the interlayer sodium cations are not only well solvated with the surrounding CO₂ molecules but also show stronger tendency to adhere to the clay surface.     

Cubic phases of ternary amphiphile–water systems

The reversed cubic phases (Q_II) are a class of self-assembled amphiphile–water structures that are rich in diversity and structural complexity. These nanostructured liquid crystalline materials are generating much interest owing to their unique surface morphology, biological relevance and potential technological and medical applications. The structure of Q_II phases in binary amphiphile–water systems is affected by the molecular structure of surfactant, water content, temperature and pressure. The presence of additives also plays an important role. The structure and phase behaviour of ternary Q_II phases, which are comprised of two miscible amphiphiles and water, significantly differ from the binary system alone. The modulation of the phase behaviour through the addition of a second amphiphile offers an opportunity to control the size and shape of the nanostructures using a ‘bottom-up’ approach. In this mini-review, we discuss the structure of reversed cubic phases of amphiphile–water systems and highlight the modulation of cubic-phase structure in ternary-phase systems. We also extend this review to bulk cubic phases and the corresponding nanoscale dispersions, cubic-phase nanoparticles.     

Metabolically active microbial communities in marine sediment under high-CO2 and low-pH extremes

Sediment-hosting hydrothermal systems in the Okinawa Trough maintain a large amount of liquid, supercritical and hydrate phases of CO₂ in the seabed. The emission of CO₂ may critically impact the geochemical, geophysical and ecological characteristics of the deep-sea sedimentary environment. So far it remains unclear whether microbial communities that have been detected in such high-CO₂ and low-pH habitats are metabolically active, and if so, what the biogeochemical and ecological consequences for the environment are. In this study, RNA-based molecular approaches and radioactive tracer-based respiration rate assays were combined to study the density, diversity and metabolic activity of microbial communities in CO₂-seep sediment at the Yonaguni Knoll IV hydrothermal field of the southern Okinawa Trough. In general, the number of microbes decreased sharply with increasing sediment depth and CO₂ concentration. Phylogenetic analyses of community structure using reverse-transcribed 16S ribosomal RNA showed that the active microbial community became less diverse with increasing sediment depth and CO₂ concentration, indicating that microbial activity and community structure are sensitive to CO₂ venting. Analyses of RNA-based pyrosequences and catalyzed reporter deposition-fluorescence in situ hybridization data revealed that members of the SEEP-SRB2 group within the Deltaproteobacteria and anaerobic methanotrophic archaea (ANME-2a and -2c) were confined to the top seafloor, and active archaea were not detected in deeper sediments (13–30 cm in depth) characterized by high CO₂. Measurement of the potential sulfate reduction rate at pH conditions of 3–9 with and without methane in the headspace indicated that acidophilic sulfate reduction possibly occurs in the presence of methane, even at very low pH of 3. These results suggest that some members of the anaerobic methanotrophs and sulfate reducers can adapt to the CO₂-seep sedimentary environment; however, CO₂ and pH in the deep-sea sediment were found to severely impact the activity and structure of the microbial community.     

Effects of Hexane in Supercritical Fluid Chromatography for the Separation of Enantiomers

Supercritical fluid chromatography (SFC), operated in conventional mode, is normally recognized as normal phase chromatography, and uses a solvent combination of supercritical CO₂ and alcohols to separate compounds. Hexane, a commonly used solvent in normal phase liquid chromatography (NP‐LC), is rarely used in SFC and, in some cases, is added to the organic modifiers to increase liquid content in order to achieve better efficiency in preparative SFC for poorly retained compounds. Although hexane is believed to have similar solvent strength to that of supercritical CO₂, its effects on the enantioseparation in SFC is largely unknown. To understand the chromatographic effects of an apolar solvent, such as hexane in SFC, we compared the chromatographic behaviors of 35 chiral compounds using a parallel SFC method under traditional SFC mode of only “pure” alcohol‐CO₂ to that of hexane‐assisted SFC (HA‐SFC), which uses mixtures of alcohol and hexane (as cosolvents) and CO₂. We observed that, in some cases, hexane behaves just like supercritical CO₂, where replacement of a portion of CO₂ with hexane does not significantly change retention times or resolution of the peaks. In many cases, however, addition of hexane in mobile phases does affect chromatographic behavior of one or both enantiomers. Such effects might provide opportunities for separation of some enantiomers. Chirality 28:192–198, 2016. © 2016 Wiley Periodicals, Inc.     

Controlled micelle conjugation via charged peptide amphiphiles

Abstract We report the first demonstration of nonionic detergent micelle conjugation and phase separation using purpose‐synthesized, peptide amphiphiles, C₁₀‐(Asp)₅ and C₁₀‐(Lys)₅. Clustering is achieved in two different ways. Micelles containing the negatively charged peptide amphiphile C₁₀‐(Asp)₅ are conjugated (a) via a water‐soluble, penta‐Lys mediator or (b) to micelles containing the C₁₀‐(Lys)₅ peptide amphiphile. Both routes lead to phase separation in the form of oil‐rich globules visible in the light microscope. The hydrophobic nature of these regions leads to spontaneous partitioning of hydrophobic dyes into globules that were found to be stable for weeks to months. Extension of the conjugation mechanism to micelles containing a recently discovered, light‐driven proton pump King Sejong 1‐2 (KS1‐2) demonstrates that a membrane protein may be concentrated using peptide amphiphiles while preserving its native conformation as determined by characteristic UV absorption. The potential utility of these peptide amphiphiles for biophysical and biomedical applications is discussed.     

Solubility of amphiphiles in membranes: influence of phase properties and amphiphile head group

The solubilities of two fluorescent lipid amphiphiles with comparable apolar structures and different polar head groups, NBD-hexadecylamine and RG-tetradecylamine (or -octadecylamine), were compared in lipid bilayers at a molar ratio of 1/50 at 23 degrees C. Bilayers examined were in the solid, liquid-disordered, or liquid-ordered phases. While NBD-hexadecylamine was soluble in all the examined bilayer membrane phases, RG-tetradecylamine was stably soluble only in the liquid-disordered phase. RG-tetradecylamine insolubility in solid and liquid-ordered phases manifests itself as an aggregation of the amphiphile over a period of several days and the kinetics of aggregation were studied. Solubility of these amphiphiles in the different phases examined seems to be related to the dipole moment of the amphiphile (in particular, of the polar fluorophore) and its orientation relative to the dipolar potential of the membrane. We propose that amphiphilic molecules inserted into membranes (including lipid-attached proteins) partition into different coexisting membrane phases based upon: (1) nature of the apolar structure (chain length, degree of saturation, and chain branching as has been proposed in the literature); (2) magnitude and orientation of the dipole moment of the polar portion of the molecules relative to the membrane dipolar potential; and (3) hydration forces that are a consequence of ordering of water dipoles at the membrane surface.     

Application of Supercritical Fluid Extraction in Biotechnology

ABSTRACT

In the present paper recent investigations on the applications of supercritical fluid extraction (SCE) from post fermentation biomass or in situ extraction of inhibitory fermentation products as a promising method for increasing the yield of extraction have been reviewed. Although supercritical CO₂ (SC-CO₂) is unfriendly, or even toxic, for some living cells and precludes direct fermentation in dense CO₂, it does not rule out other useful applications for in situ extraction of inhibitory fermentation products and fractional extraction of biomass constituents. This technique is a highly desirable method for fractional extraction of biomass constituents, and intracellular metabolites due to the potential of system modification by physical parameters and addition of co-solvents to selectively extract compounds of different polarity, volatility and hydrophilicity without any contamination.     

Amphiphile diffusion in model membrane systems studied by pulsed NMR

The translational diffusion of the amphiphilic molecules in a number of lyotropic liquid crystalline phases has been measured with the pulsed NMR pulsed magnetic field gradient method. The amphiphiles studied were soaps, monoglycerids and lecithins. Measurements were performed both for oriented lamellar and for cubic phases. The order of magnitude of the diffusion coefficients was found to be the same as in neat liquids of analogous compounds. It was also found that the difussion coefficient depend markedly on the amphiphile end group in a way that parallels the area per polar head group as determined in X-ray studies. When corrections for geometrical factors has been made the diffusion rate is approximately equal in cubic and lamellar phases containing the same amphiphile.     

Monte Carlo Simulation Study of Adsorption Characteristics in Slit-Like Micropores Under Supercritical Conditions

Abstract

Adsorption characteristics of a solute diluted in supercritical fluids has been investigated by using the Monte Carlo simulation techniques. The Lennard-Jones potential function is used for describing interactions for a model system of CO₂ + benzene in slit-like micropores with infinite graphitic carbon walls. A modified μVT ensemble method with particle exchange proposed by Cracknell, Nicholson and Quirke (1993) is found to be much superior to the conventional μVT ensemble method especially for dense mixtures in a pore. Adsorption isotherms of CO₂ and benzene, in equilibrium with a dilute benzene mixture in CO₂ (mole fraction of benzene = 0.001), are computed by varying pressure, temperature, the benzene–surface interaction potential, and the slitwidth. Adsorption isotherm curve of CO₂ increases with an increase in pressure while that of benzene shows a maximum at a pressure far below the critical pressure of CO₂ and then it decreases with increasing pressure. The decrease in benzene adsorption with increasing pressure is attributable to both the enhanced solubility in supercritical CO₂ and the competitive adsorption of CO₂. The isotherm curves of each component at two temperatures, 313.2 K and 323.2 K, show to cross at a pressure near the critical pressure due to the “density effect” on the chemical potentials of a solute at supercritical fluid conditions. When the interaction between a solute and a surface increases, the adsorption isotherm increases. Narrowing the slitwidth results in the increase in the adsorption of solute since the external potential from two walls becomes deeper.     

Calcium-induced fusion of didodecylphosphate vesicles: The lamellar to hexagonal II (HII) phase transition

Summary Electron microscopic techniques have been employed to investigate the ability of didodecylphosphate vesicles (diameter approx. 900 Å) to fuse in the presence of Ca²⁺. As revealed by negative staining, Ca²⁺ induces extensive fusion and large vesicles with diameters up to 7000 Å are formed. In a processsecondary to fusion, the fused vesicles display a tendency to flatten and are subsequently transformed into extended tubular structures. Freeze-fracture electron microscopy, in conjunction with³¹P NMR and selected area electron diffraction measurements indicate that the tubes are packed in a hexagonal (H_II) array and that the amphiphiles are converted from the lamellar to the hexagonal H_II phase.The relationship between membrane fusion and the lamellar-to-hexagonal phase transition is discussed in terms of formation and abundance of transiently stable inverted micellar intermediates at contact regions between two interacting membranes. A model for the conversion of the (vesicular) lamellar into the (tubular) hexagonal H_II phase is presented, taking into account the molecular shape of the amphiphile. The relevance of using simple synthetic amphiphiles as models for phospholipid bilayers and complex biomembrane behavior is briefly discussed.     

A model of photosynthetic CO2 assimilation and carbon-isotope discrimination in leaves of certain C3−C4 intermediates

A model of leaf, photosynthesis has been developed for C₃–C₄ intermediate species found in the generaPanicum, Moricandia, Parthenium andMollugo where no functional C₄ pathway has been identified. Model assumptions are a functional C₃ cycle in both mesophyll and bundle-sheath cells and that glycine formed in the mesophyll, as a consequence of the oxygenase activity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39), diffuses to the bundle sheath, where most of the photorespiratory CO₂ is released. The model describes the observed gas-exchange characteristics of these C₃–C₄ intermediates, such as low CO₂-compensation points () at an O₂ pressure of 200 mbar, a curvilinear response of to changing O₂ pressures, and typical responses of CO₂-assimilation rate to intercellular CO₂ pressure. The model predicts that bundle-sheath CO₂ concentration is highest at low mesophyll CO₂ pressures and decreases as mesophyll CO₂ pressure increases. A partitioning of 5–15% of the total leaf Rubisco into the bundle-sheath cells and a bundlesheath conductance similar to that proposed for C₄ species best mimics the gas-exchange results. The model predicts C₃-like carbon-isotope discrimination for photosynthesis at atmospheric levels of CO₂, but at low CO₂ pressures it predicts a higher discrimination than is typically found during C₃ photosynthesis at lower CO₂ pressures.Abbreviations and symbols PEP phosphoenolpyruvate - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) - RuBP ribulose-1,5-bisphosphate - p(CO₂) partial pressure of CO₂ - p(O₂) partial pressure of O₂. See also p. 471     

Extraction of Oils from Wheat Germ with Supercritical Carbon Dioxide

The separation of oil from wheat germ by extracting with supercritical carbon dioxide (C0₂) is described. The solubility of wheat germ oil in supercritical C0₂ at 200 atm and 40°C was about 0.35 weight%. The effect of pressure on the extraction process with liquid or supercritical C0₂ was of great significance. On the other hand, the effect of temperature on the extraction process was small. Oil extracted with supercritical C0₂ was lighter in color and contained less phosphorus than that extracted with hexane. The contents of α- and β-tocopherol in the oil extracted with supercritical CO₂. were comparable to those in the hexane-extracted oil     

Elevated CO2 and the magnitude and seasonal dynamics of root production and loss in t Betula papyrifera

The impact of elevated atmospheric CO₂ on belowground plant growth is poorly understood relative to its effects on aboveground growth. We carried out a study of the seasonal dynamics of gross root production and death to determine how elevated CO₂ affected the dynamics of net and gross root production through a full growing season. We quantified gross root production and root loss from sequential, in situ images of fine roots of t Betula papyrifera in ambient (375 ppm.) and elevated (700 ppm) CO₂ atmospheres from 2 weeks following germination through leaf senescence. We found that elevated CO₂ led to increases in the magnitude of cumulative gross production (P) and cumulative gross loss (L) of roots. However, the effect of elevated CO₂ on these processes was seasonally dependent. Elevated CO₂ led to greater levels of enhancement in P early in the growing season, prior to maximum standing root length (NP). In contrast, elevated CO₂ led to greater levels of enhancement in L in the last half of the growing season, after maximum NP had been reached. This difference in the timing of when elevated CO₂ affects P and L led to a transitory, early enhancement in NP. By the end of the growing season, there was no significant effect of elevated CO₂ on NP, and P was 87% greater than NP for ambient CO₂ and 117% greater in elevated CO₂. We conclude that static assessments of belowground productivity may greatly underestimate gross fine root productivity and turnover and this bias can be exaggerated with elevated CO₂.     

Production of biomass and recombinant human-like collagen in <Emphasis Type="Italic">Escherichia coli</Emphasis> processes with different CO<Subscript>2</Subscript> pulses

The evolution of CO₂ in a fed-batch culture of recombinant Escherichia coli containing human-like collagen (HLC) cDNA was determined with an O₂-enriched air supply (40%, v/v) in a 12.8 l fermentor; a maximum CO₂ concentration of 12.7% in the effluent gas was detected. The CO₂ pulse injection experiments showed that: (1) a 20% CO₂ pulse introduced in the batch cultivation phases inhibited cell growth but if introduced in the fed-batch cultivation phases slightly stimulated growth; and (2) CO₂ inhibited HLC expression only in the expression phase, where the final HLC concentration decreased by 34% under a 3 h 20% CO₂ pulse. The higher the CO₂ concentration and/or the longer the duration of the CO₂ pulse, the stronger the stimulatory or inhibitory effects. An erratum to this article can be found at     

Effects of temperature at constant air dew point on leaf carboxylation efficiency and CO2 compensation point of different leaf types

The effect of temperature on photosynthesis at constant water-vapor pressure in the air was investigated using two sclerophyll species, Arbutus unedo and Quercus suber, and one mesophytic species, Spinacia oleracea. Photosynthesis and transpiration were measured over a range of temperatures, 20–39° C. The external concentration of CO₂ was varied from 340 bar to near CO₂ compensation. The initial slope (carboxylation efficiency, CE) of the photosynthetic response to intercellular CO₂ concentration, the CO₂ compensation point (), and the extrapolated rate of CO₂ released into CO₂-free air (R _i) were calculated. At an external CO₂ concentration of 320–340 bar CO₂, photosynthesis decreased with temperature in all species. The effect of temperature on was similar in all species. While CE in S. oleracea changed little with temperature, CE decreased by 50% in Q. suber as temperature increased from 25 to 34° C. Arbutus unedo also exhibited a decrease in CE at higher temperatures but not as marked as Q. suber. The absolut value of R _i increased with temperature in S. oleracea, while changing little or decreasing in the sclerophylls. Variations in and R _i of the sclerophyll species are not consistent with greater increase of respiration with temperature in the light in these species compared with S. oleracea.Abbreviations and symbols A net photosynthetic rate - C and C _i CO₂ concentration in the air and in the intercellular airspace of the leaf, respectively - CE carboxylation efficiency - E transpiration rate - R _i CO₂ release into CO₂-free air estimated from extrapolation to 0 bar CO₂ - T _i leaf temerature - VPD difference in water-vapor pressure between mesophyll and air - CO₂ compensation point     

Extraction of indole alkaloids fromCatharanthus roseus by using supercritical carbon dioxide

Summary Indole alkaloids, particularly vindoline and catharanthine, were extracted from the leaves ofCatharanthus roseus by supercritical extraction with CO₂. The contents of vindoline and catharanthine in the extracts were determined by HPLC and identified by LC/MS. About 52 %(w/w) of the initial vindoline content, 1.5 mg vindoline/g dry wt leaves, was recovered after extracting this material for 10 h with the CO₂ flow rate of 400 ml/min at 40°C and 150 bar. Vindoline concentration in the extract was 67 %(w/w).     

Cationic triple-chain amphiphiles facilitate vesicle fusion compared to double-chain or single-chain analogues

Cationic, triple-chain amphiphiles promote vesicle fusion more than structurally related double-chain or single-chain analogues. Two types of vesicle fusion experiments were conducted, mixing of oppositely charged vesicles and acid-triggered self-fusion of vesicles composed of cationic amphiphile and anionic cholesteryl hemisuccinate (CHEMS). Vesicle fusion was monitored by standard fluorescence assays for intermembrane lipid mixing, aqueous contents mixing and leakage. Differential scanning calorimetry was used to show that triple-chain amphiphiles lower the lamellar-inverse hexagonal (L_α-H_II) phase transition temperature for dipalmitoleoylphosphatidylethanolamine. The triple-chain amphiphiles may enhance vesicle fusion because they can stabilize the inversely curved membrane surfaces of the fusion intermediates, however, other factors such as extended conformation, packing defects, chain motion, or surface dehydration may also contribute. From the perspective of drug delivery, the results suggest that vesicles containing cationic, triple-chain amphiphiles (and cationic, cone-shaped amphiphiles in general) may be effective as fusogenic delivery capsules.     

Supercritical Extraction of Carotenoids from Rosa canina L. Hips and their Formulation with β-Cyclodextrin

The purpose of this research was to preliminary assess the suitability of a new method for the preparation of a solid formulation in form of powder composed by β-cyclodextrin and the supercritical extract of Rosa canina hips. The method implies the extraction of carotenoids, in particular β-carotene, from freeze dried fruits of R. canina with supercritical CO₂ at 70 °C and 300 bar, in the presence of varying quantity of ethanol as entrainer. The obtained supercritical solution is then expanded at ambient conditions into an aqueous solution of β-cyclodextrin to favour the interaction between β-cyclodextrin and the lipophilic components of the extract. β-carotene solubility (mole fraction) in supercritical CO₂ or in supercritical CO₂/ethanol mixtures were in the order of 1 10⁻⁷. The β-carotene extracted from R. canina fruits (nearly 10 μg/g of dry matrix), interacts almost quantitatively with β-cyclodextrin affording a solid phase, which presents a low apparent solubility in water. Finally the interaction with β-cyclodextrin results in a higher concentration of the β-carotene trans- form relative to the cis- form in the extracted product when collected in an aqueous solution of β-cyclodextrin with respect to the extract in n-hexane.