Partition Experiments Research Articles

A new method to estimate the partition of corrosion inhibitors

Abstract The partitioning coefficient of the R12Na corrosion inhibitor is determined by relating its concentration in the water phase (C W) to the expected theoretical concentration (C i,T) due to a re-concentration phenomenon after the mixing stage. Partition experiments were performed by varying the water cut in brine-kerosene mixtures, temperature, and the inhibitor concentration using NACE 1D182 brine as a water phase and ultraviolet-visible spectrophotometry. The partition results varied from 37.81 to 43.75 %, 36.68 to 61.23 %, and 40.29 to 56.47 % at 40 °C, 60 °C, and 80 °C, respectively, indicating that R12Na is a water soluble inhibitor and dispersible in the organic phase. Likewise, the partition results varied from 41.69 to 44.04 % in the presence of 20, 50, and 100 mg L−1 of the inhibitor, using a ratio of 80–20 vol% WP–OP and 60 °C. Furthermore, making the same considerations, the partition of different corrosion inhibitors reported in the literature was evaluated, supporting its determination, the latter is of great importance for dosing corrosion inhibitors in the oilfield industry.

Customizable cholinium-based aqueous biphasic systems as ecofriendly extraction platform for removal of pesticide from wastewaters

This study explores the use of a series of cholinium ionic liquids (ILs) or salts in combination with polypropylene glycol 400 to form aqueous biphasic systems (ABS) for extracting various polarity pesticides (dicamba, clomazone, pyraclostrobin, and deltamethrin) from water. We assessed five cholinium-based salting-out agents ([Ch][DHP], [Ch]Cl, [Ch][Ac], [Ch][Lac], and [Ch][Nic]), chosen for their structural diversity and unique properties, such as high salting-out potential and different ability to undergo specific interactions. Liquid-liquid equilibrium phase diagrams were established, and partition experiments were conducted to evaluate extraction efficiency. Different partition patterns were obtained for studied pesticides, with [Ch][DHP] demonstrating the highest efficiency exceeding 90 % for each target pesticide due to its strong salting-out ability. On the other hand, more diverse partition trends due to specific interactions were obtained for low-melting cholinium-ILs ABS. The effect of pH and temperature on the partitioning behavior in [Ch][Ac]-based ABS highlighted the cholinium ILs extraction system's customizable nature. Focusing on [Ch]Cl for its eco-friendly aspects, widespread availability and excellent extraction performance, we optimized parameters for the removal of pesticides from real samples, applying the technology to spiked agricultural wastewater with an extraction efficiency of over 99 %. Our findings demonstrate the potential of cholinium-based IL-ABS in reducing environmental pollution through efficient pesticide extraction.

Effect of the interaction of nisin Z with various polysaccharides on its antibacterial activity

The effect of various polysaccharides commonly used as thickening or gelling agents in foods on the antibacterial activity of nisin Z was investigated. Addition of 1 g.L−1 sodium alginate in tryptic soy broth resulted in a four-fold increase of minimal inhibitory (MIC) and bactericidal (MBC) concentrations of nisin Z against Listeria innocua ATCC 33090 and Kocuria rhizophila ATCC 9341, while the addition of citrus pectin or various exopolysaccharides (Leuconostoc mesenteroides P35 exopolysaccharides, low (9–11 kDa) or medium (60–76 kDa) molecular weight dextran from Ln. mesenteroides and 2 kefirans (extracted from kefir grains provided by Crokfun or Kefiralia)) did not increase MIC and MBC of nisin Z against these bacteria. Zeta potential determination at pH 7 of the nisin Z, bacteria and polysaccharides allowed us to observe that only nisin Z had a slightly positive zeta potential, while the bacteria, sodium alginate and highly methoxylated citrus pectin zeta potentials were lower than −20 mV and zeta potentials of all exopolysaccharides were between 0 and - 10 mV. It was thus proposed that anionic sodium alginate, which is the only polysaccharide having a lower zeta potential than both bacteria, forms complexes stabilized by electrostatic interactions with oppositely charged nisin Z, thereby limiting the quantity of “free” nisin Z interacting with nisin-susceptible bacteria. This hypothesis was substantiated by the observation of nisin Z - sodium alginate aggregation at pH 7 and the estimation of the apparent affinity of sodium alginate for “free” nisin Z and immobilized nisin Z by partition experiments and by surface plasmon resonance analysis, respectively. This study thus provides useful information for food formulation regarding the effect of different polysaccharides on nisin Z antibacterial activity and some understanding of how interactions between nisin Z, polysaccharides, and nisin Z - sensitive bacteria are explanatory.

Adsorption of Respiratory Syncytial Virus, Rhinovirus, SARS-CoV-2, and F+ Bacteriophage MS2 RNA onto Wastewater Solids from Raw Wastewater.

Despite the widespread adoption of wastewater surveillance, more research is needed to understand the fate and transport of viral genetic markers in wastewater. This information is essential for optimizing monitoring strategies and interpreting wastewater surveillance data. In this study, we examined the solid-liquid partitioning behavior of four viruses in wastewater: SARS-CoV-2, respiratory syncytial virus (RSV), rhinovirus (RV), and F+ coliphage/MS2. We used two approaches: (1) laboratory partitioning experiments using lab-grown viruses and (2) distribution experiments using endogenous viruses in raw wastewater. Partition experiments were conducted at 4 and 22 °C. Wastewater samples were spiked with varying concentrations of each virus, solids and liquids were separated via centrifugation, and viral RNA concentrations were quantified using reverse-transcription-digital droplet PCR (RT-ddPCR). For the distribution experiments, wastewater samples were collected from six wastewater treatment plants and processed without spiking exogenous viruses; viral RNA concentrations were measured in wastewater solids and liquids. In both experiments, RNA concentrations were higher in the solid fraction than the liquid fraction by approximately 3-4 orders of magnitude. Partition coefficients (KF) ranged from 2000-270,000 mL·g-1 across viruses and temperature conditions. Distribution coefficients (Kd) were consistent with results from partitioning experiments. Further research is needed to understand how virus and wastewater characteristics might influence the partitioning of viral genetic markers in wastewater.

Solvent extraction in non-ideal eutectic solvents – Application towards lanthanide separation

Hydrophobic eutectic solvents (HES) emerged as promising substitutes to the conventional organic phase used in the solvent extraction (SX) of metal ions due to the avoidance of diluents and the suppression of third-phase manifestation. However, HES present a highly structured liquid phase defined by hydrogen-bonded interactions such that intercomponent interactions are expected to play a greater role in SX using HES compared to a diluted extractant solution. In this work, the extraction of lanthanides from nitrate media by the non-ideal solvent composed of decanoic acid (C10OOH) and trioctylphosphine oxide (TOPO) was determined as a function of the lanthanide cation selection, HES molar fraction, HNO3 concentration, and temperature. Through the systematic variation of these parameters, the delicate balance between complexation and solvent reorganisation and its influence on the extraction and metal selectivity is determined by metal partition experiments, time resolved fluorescence and Raman spectroscopy, and small-angle X-ray scattering (SAXS). A compromise between maximum Ln3+ loading and selectivity was observed, driven by the variation in the quantity of weakly H-bonded TOPO and the change in the configurational entropy of the mixture. All results point towards the need to explicitly consider the HES phase structuration and its compositional changes with solute co-extraction on the Ln3+ extraction as no change in the extracted complex speciation was observed across all tested conditions. The C10OOH + TOPO was used as a model system due as lanthanide extraction using TOPO and carboxylic extractants is well described whilst the phase diagram and properties of the eutectic are reported. Nevertheless, the derived conclusions are translatable to other systems and can help guide the design and application of possible HES combinations for SX.

Particle formation in thermally initiated radical‐mediated thiol‐ene emulsion polymerizations

AbstractRadical‐mediated thiol‐ene polymerizations (RMTEPs) conducted under typical emulsion polymerization conditions were studied with the aim of determining how various experimental parameters impact particle nucleation and growth. These colloids are unusual since they are made by step‐growth polymerizations, which can be thermally initiated in an aqueous emulsion system. Four pairs of thiol‐ene monomers were used to probe how composition impacts the nucleation loci. Kinetic studies were carried out to understand how monomer conversion, molecular weight, and particle size change throughout the reaction. Additionally, the number of particles formed as a function of surfactant and initiator concentrations were studied and this data, along with information from dye partition experiments, were used to determine polymer colloid nucleation mechanisms and how monomer/polymer structure impacts nucleation processes. Within the four pairs of monomers studied, three proceeded via homogeneous nucleation (via chain collapse in the aqueous phase), while one pair, which gave the highest degree of crosslinking, underwent heterogeneous nucleation (nucleation occurs in the micellar phase). Possible factors that impact which nucleation mechanism dominates a given set of monomers, such as crosslink density, water solubility, and thiol/ene reactivity, is discussed, although no clear set of delineating guidelines can be offered with this current set of data.

Contrasting solution-state properties within a family of amyloid-binding molecular tools

Rational modification to the molecular structure of a family of amyloid-binding bifunctional molecular tools improves their hydrophilicity and aqueous solubility, yet raises questions about self-aggregation. Bifunctional organic molecules enable chemists to design and build molecules that have a wide variety of emergent functional properties. While the majority of these compounds are designed to bind to proteins, this work focuses on those that can bind to amyloid fibrils. These molecular tools can add new functional properties to the fibrils by delivering functional molecular cargo to their surfaces. Second generation tools, which have redesigned amyloid-binding and linker regions, are presented herein. Solubility measurements and partition experiments show that these changes enable the new compounds to dissolve better in pH 7.4 buffered water, which is the natural solvent in which they are most likely to find use and application. One of these compounds, however, contrasts to the others in that it self-associates in DMSO solution. This self-association can be seen experimentally by NMR broadening and fluorescence auto-quenching. An enhanced understanding of how the structural details of these compounds cause this undesired self-association will aid the subsequent development of highly useful amyloid-targeting bifunctional molecules. Herein, several molecular dynamics simulations and DFT geometry optimizations are used to evaluate multiple hypotheses about the nature of the observed self-association.

Poloxamer-based aqueous biphasic systems in designing an integrated extraction platform for the valorization of pharmaceutical waste

Unused/expired pharmaceuticals can be regarded as a source of valuable compounds. Valorization of active pharmaceutical ingredients (APIs) from pharmaceutical waste, as an alternative to widely adopted treatment by incineration, is a big challenge in terms of designing green, efficient, scalable and sustainable separation methods. Concerning these demands, this work aimed to investigate and propose new integrated extraction technology based on aqueous biphasic systems (ABS) with eco-friendly components namely, poloxamer (Pluronic PE 6200) and one of two salts (sodium citrate, cholinium dihydrogenphosphate) or ionic liquid (1-butyl-3-methylimidazolium chloride). Liquid-liquid equilibria of each ABS were determined at room temperature followed by partition experiments in the biphasic medium to evaluate the most favorable systems for APIs extraction (acetaminophen and caffeine from one commercial product, and theophylline from the other). The finely designed ABSs were then employed to separate APIs from pharmaceutical solids and fractionate them. The results show that citrate-based ABS induces the strongest salting-out effect leading to extraction of all APIs to the Pluronic-rich phase with high recovery efficiencies between 79.4 and 97.90%; insoluble compounds were removed as residues while hydrophilic excipients remained in the citrate-rich aqueous phase. Ionic liquid/PL6200-based ABS was further applied to fractionate acetaminophen and caffeine toward opposite phases. These results underpin the viability and adjustability of PL6200-based ABSs within an integrated process, by a deftly selected salting-out agent, as a sustainable and efficient alternative platform with the great potential to be implemented on a larger scale.

Rapid Ag diffusion in granitic melt: Implications for Ag mineralization and melt inclusion record

Element diffusion in silicate melts is an important process in the transport and enrichment of metals in magmatic and magmatic-hydrothermal systems, but the diffusivity of Ag, unlike other metals such as Cu, Mo, and W, is still unknown. In this study, Ag diffusion in granitic melts with up to 6.9 wt% H2O was investigated at 973–1673 K and 0.1–1 GPa in a piston cylinder apparatus and a cold seal vessel, using both a diffusion couple approach and an argentite (Ag2S) dissolution approach. Silver concentration profiles were analyzed by LA-ICP-MS on recovered samples. Silver solubility, determined by Ag concentration at melt-argentite interface, increases with increasing temperature. Silver diffusivity is found to increase with increasing temperature and water content but to decrease with pressure. At 1 GPa, Ag diffusivity in granitic melt can be described by the following expression:lnDAg,1GPa=-13.77±0.46-13341±534-700±39wTwhere D is Ag diffusivity in m2/s, w is the water content in wt%, and T is the temperature in K. The pressure effect over 0.1–1 GPa gives an activation volume of 11.3 cm3/mol for Ag diffusion. While not being on a par with the mobility of Na and Li, Ag diffusion is among the most rapid, comparable to Cu and faster than other species including H2O and Fe. This implies that Ag diffusion in melt is unlikely to be a rate-limiting step for Ag enrichment into exsolved fluid bubbles or sulfide blobs. Furthermore, melt inclusions in silicate minerals are expected to record Ag concentration in the bulk melt instead of an elevated concentration in the presence of an Ag-rich boundary layer. Our Ag diffusivity data also suggest that a few tens of hours are long enough to homogenize Ag concentration in melt in solubility or partition experiments at temperatures above 800 °C.

A simple method to estimate the mean number of lipophilic molecules on nanoparticle surfaces by fluorescence measurements

Measurements of fluorescence intensity of the hydrophobic pyridinium salt (DTPSH) remaining in the organic phase after partition experiments in the DCM/H2O system allowed an approximate method to be developed to estimate the mean number of molecules (N = 942) on the surface of 22.8 nm gold nanoparticles and the separation (1.89 nm) between these organic molecules. This protocol is based on the ability that the organic molecules possess to coat the surface of the nanoparticle, which can migrate from the organic to the aqueous phase as a result of the driving force of the strong binding of sulfur to gold. To validate our estimation, we used a projection of the results obtained by Wales and Ulker to solve the Thomson problem, a mathematicians’ challenge, used as a model to calculate the mean distance (1.82 nm) separating particles on the surface, in excellent agreement with the results obtained by our method. The quality of results, the simplicity of calculations, the low fluorescence detection limit, and the inexpensive materials, recommend this procedure for rapid estimates of the mean number of molecules on the surface of nanoparticles.

How Sugars Modify Caffeine Self-Association and Solubility: Resolving a Mechanism of Selective Hydrotropy.

The aggregation of drugs and nutraceuticals in aqueous media is an outstanding problem for their efficacy and bioavailability. A common solution is to add excipients or hydrotropes that increase solubility and limit aggregation. Here we study caffeine, a widely consumed drug that undergoes oligomerization and aggregation in aqueous solutions. Combining partition and solubility experiments with molecular dynamics simulations, we determined the effect of sugars (mono- and disaccharides) on caffeine self-association and solubility. We find that sugars selectively increase the concentration of caffeine in its monomeric state, but decrease its solubility in all oligomeric forms. Thus, we determine that, in contrast to common hydrotropes, sugars act as selective hydrotropes toward caffeine, since they differentially act on specific solvated forms of the drug. We furthermore unravel the molecular mechanism for this selectivity, and comment on the general design principles that should help develop targeted excipients for bioavailability and taste modification in drugs and foods.

Sharp 660-km discontinuity controlled by extremely narrow binary post-spinel transition

The Earth’s mantle is characterized by a sharp seismic discontinuity at a depth of 660 km that can provide insights into deep mantle processes. The discontinuity occurs over only 2 km—or a pressure difference of 0.1 GPa—and is thought to result from the post-spinel transition, that is, the decomposition of the mineral ringwoodite to bridgmanite plus ferropericlase. Existing high-pressure, high-temperature experiments have lacked the pressure control required to test whether such sharpness is the result of isochemical phase relations or chemically distinct upper and lower mantle domains. Here, we obtain the isothermal pressure interval of the Mg–Fe binary post-spinel transition by applying advanced multi-anvil techniques with in situ X-ray diffraction with the help of Mg–Fe partition experiments. It is demonstrated that the interval at mantle compositions and temperatures is only 0.01 GPa, corresponding to 250 m. This interval is indistinguishable from zero at seismic frequencies. These results can explain the discontinuity sharpness and provide new support for whole-mantle convection in a chemically homogeneous mantle. The present work suggests that distribution of adiabatic vertical flows between the upper and lower mantles can be mapped on the basis of discontinuity sharpness. The post-spinel transition in mantle composition, which occurs at 660-km depth in Earth’s mantle, takes place over a pressure range equivalent to 250 m in depth, according to multi-anvil experiments for realistic mantle compositions and temperatures.

Calibration parameters for the passive sampling of organic UV filters by silicone; diffusion coefficients and silicone–water partition coefficients

In recent years, organic ultraviolet filters (UVFs) received considerable attention as a group of emerging contaminants, including in Australia where the use of UVFs is particularly relevant. Passive sampling using polymers has become widely used for routine monitoring of chemicals in the aquatic environment. Application of passive samplers for monitoring chemicals in the water relies on calibration data such as chemical's polymer-water partition coefficient (Kpw) and diffusion coefficients in the sampling material (Dp), for understanding uptake and kinetic limitations. In the present study, Kpw and Dp for nine UVFs were estimated. Kpw values were determined in different water – polymer partition experiments where (1) a given mass of chemicals was dosed into the water and (2) into the polymer. Diffusion coefficients were determined using the stacking method. The estimated log Kpw and log Dp ranged from 2.9 to 6.4 L kg−1 and -11.1 to −10.5 m2s-1, respectively. The sufficient high Dp allows application of kinetic models that only consider water boundary-controlled uptake for converting silicone sampler uptake into an aqueous phase concentration using the presented Kpw.

Psd2 pea defensin shows a preference for mimetic membrane rafts enriched with glucosylceramide and ergosterol

Psd2 is a pea defensin with 47 amino acid residues that inhibits the growth of fungal species by an uncharacterized mechanism. In this work, Psd2 interactions with model membranes mimicking the lipid compositions of different organisms were evaluated. Protein-lipid overlay assays indicated that Psd2 recognizes Fusarium solani glucosylceramide (GlcCerF.solani) and ergosterol (Erg) in addition to phosphatidylcholine (POPC) and some phosphatidylinositol species, such as PtdIns (3)P, (5)P and (3,5)P2, suggesting that these lipids may play important roles as Psd2 targets. Assays using lipid vesicles were also performed to study the behaviour and dynamics that occur after peptide-membrane interactions. Surface plasmon resonance analysis showed that Psd2 has a higher affinity for pure POPC and POPC-based vesicles containing GlcCer and Erg at a 70:30 proportion than for vesicles containing cholesterol (Chol). Partition experiments by fluorescence spectroscopy showed a decrease in Trp42 quantum yield of Psd2 in the presence of GlcCerF.solani and Erg, individually or in simultaneously enriched membranes. The partition coefficient (Kp) obtained indicated a Psd2 partition preference for this vesicles, confirmed by quenching assays using acrylamide and 5/16-doxyl-stearic acid. Furthermore, we showed that the presence of C8C9 double bonds and a methyl group at position C9 of the sphingoid base backbone of GlcCer was relevant to Psd2 activity against Aspergillus nidulans. These results are consistent with the selectivity of Psd2 against fungi and its lack of toxicity in human erythrocytes. Psd2 represents a promising natural compound for the treatment of fungal infections.

Photoenhanced oxidation of nC60 in water: Exploring H2O2 and hydroxyl radical based reactions

The transformations of water-stable C60 clusters (nC60) to oxidized C60 derivatives via photoreactions and ground-state reactions have been described as critical processes in understanding the ultimate environmental fate of fullerene-based materials. However, (photo)oxidation of aqueous-based C60 (as water stable, nanoscale aggregates termed nC60) with hydrogen peroxide (H2O2) and/or hydroxyl radical (OH), common environmental oxidants, has not been fully explored. To address this, the aqueous physicochemical transformations of C60 (as nC60 aggregates) in the presence of H2O2 and/or OH in both photoexcited-state and ground-state under environmentally relevant conditions are quantitatively described. Results show that nC60 undergoes facile oxidation in the presence of H2O2 under UVA irradiation but not under dark conditions, and the oxidation reaction rates increase with effective OH concentration (via photodecomposition of H2O2), while being inversely related to solution pH. Product characterization via dynamic light scattering, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, total organic carbon, high-performance liquid chromatography, and octanol-water partition experiments collectively describe resulting C60 derivatives with new covalent oxygen functionality which are also relatively more hydrophilic. For all cases, photoirradiation was observed to significantly enhanced the rates and extent of C60 oxidation.

Sham dustbathing in cages by subordinate hens is increased by a partition providing isolation

Subordinate hens express less sham dustbathing in cages than higher ranked hens, their bouts often being disturbed by a higher ranked hen. However, seeing conspecifics seems to encourage this behaviour by hens. So to avoid being disturbed, a partition between hens in a cage may facilitate sham dustbathing by subordinates. Therefore, one aim of this experiment was to test the effects of two types of partition, transparent (wire) and opaque (cardboard). The other aim was to test the response of birds of different rank. Experiments began when the hens were 35 weeks of age in non-furnished experimental cages, after determination of rank in groups of four (low (two birds), ‘middle’ or high). Thirty two hens were divided into eight pairs for each of two types: low and middle or low and high ranks. These were used first in wire partition experiments, then in cardboard partition experiments. For each experiment, four pairs were tested with a partition in a cage for two days, while the other four were used as controls, then the treatments were switched so that all pairs experienced both. Subordinate hens performed fewer sham dustbathing bouts than higher ranked hens in controls for both wire and cardboard experiments. However, when there was a wire partition between a low and a middle ranked hens, total time and percentage of hens sham dustbathing increased in subordinates compared to controls (P < 0.05), while middle ranked hens did not show a difference. When there was a wire partition between a low and a high ranked hens, total time spent sham dustbathing and number of bill rakes increased in subordinates compared to controls (P < 0.05), while high ranked hens did not show a difference. With a cardboard partition, the number of hens sham dustbathing and total sham dustbathing bouts increased in subordinate hens compared to controls (P < 0.05), whereas bouts decreased in middle ranked hens. With a partition, termination of sham dustbathing by interruption from another hen decreased by half in subordinate hens. These results indicate that a partition between hens, whether subordinate hens could see the other bird or not, allowed sham dustbathing to start with little or no disturbance from higher ranked hens. However, it may be also important for some hens to see conspecifics to start and to continue this behaviour. Therefore, a partition that prevents agonistic behaviour and allows performance of other behaviours may facilitate better environment and welfare for hens.

In Vitro Characterization of the Biomimetic Properties of Poly(dimethylsiloxane) To Simulate Oral Drug Absorption

The potential use of poly(dimethylsiloxane) (PDMS) as an in vitro biomimetic analogue of the passive drug absorption process in the human gastrointestinal tract (GI) is assessed. PDMS is biomimetic because of similarities in small molecule transport, such as mechanism, ionization selectivity, lipophilicity. Nine molecular probes are used to evaluate the transport pathways and properties used to predict human oral absorption rates. The transport pathways through PDMS (bulk/pore) are analogous to transcellular (TCDT) and paracellular (PCDT) drug transport pathways. PDMS PCDT is assessed using positronium annihilation lifetime spectroscopy (PALS) and partition experiments; TCDT using diffusion and partition experiments. PALS determined that PDMS pores were uniform (D ∼ 0.85 nm), isolated, and void volume was unaffected by drug accumulation after equilibrium partitioning. Therefore, there is no PCDT or convective flow through PDMS. A strong linear correlation exists between predicted octanol-water partition coefficients and PDMS partition coefficients (LogKPDMS = 0.736 × LogPO-W - 0.971, R2 = 0.981). The pH-partition hypothesis is confirmed in PDMS using ibuprofen over pH 2-12. Diffusivity through PDMS is a function of lipophilicity and polar surface area K × DPDMS = 4.46 × 10-8 × e2.91×LogKPDMS(R2 = 0.963) and [Formula: see text] (R2 = 0.973). Varying the mass% of curing agent changed the lipophilicity and diffusivity (p < 0.02), but not practically (K × D = 2.23 × 10-5cm2s-1 vs 2.60 × 10-5cm2s-1), and does affect elastic modulus (3.2% = 0.3 MPa to 25% = 3.2 MPa).

The role of hydrophobicity in tuberculosis evolution and pathogenicity

The evolution of tubercle bacilli parallels a route from environmental Mycobacterium kansasii, through intermediate “Mycobacterium canettii”, to the modern Mycobacterium tuberculosis complex. Cell envelope outer membrane lipids change systematically from hydrophilic lipooligosaccharides and phenolic glycolipids to hydrophobic phthiocerol dimycocerosates, di- and pentaacyl trehaloses and sulfoglycolipids. Such lipid changes point to a hydrophobic phenotype for M. tuberculosis sensu stricto. Using Congo Red staining and hexadecane-aqueous buffer partitioning, the hydrophobicity of rough morphology M. tuberculosis and Mycobacterium bovis strains was greater than smooth “M. canettii” and M. kansasii. Killed mycobacteria maintained differential hydrophobicity but defatted cells were similar, indicating that outer membrane lipids govern overall hydrophobicity. A rough M. tuberculosis H37Rv ΔpapA1 sulfoglycolipid-deficient mutant had significantly diminished Congo Red uptake though hexadecane-aqueous buffer partitioning was similar to H37Rv. An M. kansasii, ΔMKAN27435 partially lipooligosaccharide-deficient mutant absorbed marginally more Congo Red dye than the parent strain but was comparable in partition experiments. In evolving from ancestral mycobacteria, related to “M. canettii” and M. kansasii, modern M. tuberculosis probably became more hydrophobic by increasing the proportion of less polar lipids in the outer membrane. Importantly, such a change would enhance the capability for aerosol transmission, affecting virulence and pathogenicity.

Zone I of Tear Microdesiccates Is a Lipid-Containing Structure

Morphological features of tear microdesiccates on glass surfaces have been associated with tear fluid status. Tear-film lipids play a critical role in the pathophysiology of some ocular surface disorders. Tear microdesiccates display 4 distinctive morphological domains (zones I, II, III, and transition band). In this study, we investigated the lipid location in tear microdesiccates. Tear from individual healthy eyes (assessed by symptoms, signs, and slit-lamp examination) was collected using absorbing minisponges. One-µL aliquots were allowed to dry under ambient conditions on microscope slides. Tear microdesiccates were examined by various transmitted light microscopy methods. Tear lipids were located both by partition experiments using 2 lipophilic dyes (Oil red O and Nile blue A) mixed with tear fluid under conditions preserving morphological features of microdesiccates and by assessing the effect of 2 solvents markedly differing in polarity (water and ethanol) on the morphology of particular domains of preformed microdesiccates. During desiccation, both Nile blue A and Oil red O became preferentially located in the outermost domain of tear microdesiccates (zone I) without affecting the formation of major fern-like crystalloids (zones II and III). Low volumes of water drastically affected fern-like crystalloids, whereas the gross morphology of zone I was maintained. Contrarily, ethanol, a less polar solvent, was a fixative for fern-like crystalloids, although it markedly affected the bulk of zone I by extracting liquid droplets out of microdesiccates and visibilizing some filamentous subcomponents. Zone I is a hydrophobic domain, whereas zones II and III are highly hydrophilic domains of tear microdesiccates. Zone I represents a lipid-rich structure.

Biorelevant physicochemical profiling of (E)- and (Z)-resveratrol determined from isomeric mixtures

Biorelevant, isomer-specific physicochemical parameters of resveratrol, a multifunctional component in red wines, with cardioprotective, anti-Alzheimer and several other pharmacologic activities were determined. The parameters include site-specific basicities, lipophilicities, solubilities and diffusion constants for the two geometric isomers. The protonation equilibria of (E)- and (Z)-resveratrol were monitored by 1H NMR-pH titrations. Five closely related auxiliary compounds ((E)-pinostilbene, (Z)-pinostilbene, (E)-pterostilbene, (Z)-pterostilbene and resorcinol) were also studied. Combining the datasets, the group-specific protonation constants of resveratrol isomers were determined. The results show that (Z)-resveratrol is more basic at every protonation site than the (E)-isomer. Lipophilicities are quantified in terms of logP values and were determined by octanol/water partition experiments and quantitative NMR spectroscopy: (E)-resveratrol was found to be more lipophilic. Since the molecular geometries of the isomers differ, diffusion ordered NMR spectroscopy (DOSY) experiments were also carried out to quantify the diffusion capabilities of the isomers: (Z)-resveratrol of bent shape has a slightly higher diffusion coefficient than its extended (E) counterpart. A striking 10-fold difference of water solubility was found in favor of the (Z) isomer, due obviously to the reduced water-repellent character in the more compact molecule. This is so far the greatest recorded solubility difference between geometric isomers of any compounds.