Penetration Of Glycerol Research Articles

Ex vivo confocal Raman microspectroscopy of porcine dura mater supported by optical clearing.

The effect of tissue optical clearing (TOC) to increase the probing depth and observe in-depth structure of the ex vivo porcine dura mater was studied by confocal Raman microspectroscopy (CRM). Raman intensities were significantly increased at the depth of 250 μm for all collagen bands after treatment with glycerol. The influence of glycerol on collagen hydration was also investigated. The results indicate that the process of TOC can be divided into three main steps. The first one is a fast process of tissue dehydration accompanied by collagen shrinkage while the second relatively slow process is related to the glycerol penetration into the interfibrillar space of collagen combined with swelling of tissue. The third step is collagen dissociation caused by the high concentration of glycerol. To the best of our knowledge, this study is the first example to introduce the TOC technique in assisting CRM of ex vivo dura mater in-depth probing.

Understanding the glycerol market

As a result of the booming biodiesel and oleochemicals manufacturing taking place worldwide since more than a decade, 2 million tonnes of glycerol consistently reach the market every year, even though after a decade of growth the total glycerol supply is expected to slightly decrease in 2014. Today the supply of glycerol is entirely independent of its demand, as there is as much glycerol as the amount of vegetable oils and animal fats are hydrolyzed to make oleochemicals, or transesterified to produce biodiesel. This unique situation has led to consistently low glycerol prices, which initiated both the market penetration of glycerol in countries where it was not used due to traditional high price, as well as new uses of glycerol as raw material for the production of value added chemicals. This article sheds light on the market of this uniquely versatile chemical whose number of applications is unique amid all existing chemicals.About 2 million tonnes of glycerol consistently reach the market every year, even though after a decade of growth the total glycerol supply is expected to slightly decrease in 2014. Today the supply of glycerol is entirely independent of its demand, as there is as much glycerol as the amount of vegetable oils and animal fats are hydrolyzed to make oleochemicals, or transesterified to produce biodiesel. This article sheds light on the market of this uniquely versatile chemical whose number of applications is unique amid all existing chemicals.

Study on reflection of human skin with liquid paraffin as the penetration enhancer by spectroscopy

Optical clearing agents can improve tissue optical transmittance by reducing the diffuse reflection. The reflection on in vivo human skin before and after applying anhydrous glycerol and 30 to 50% liquid paraffin glycerol mixed solution are investigated in this paper. From their visible and near-infrared reflection spectroscopy, all of their diffuse reflections are reduced after applying the agents. It is found that the three mixed solutions show stronger effect than that of anhydrous glycerol. These results further prove liquid paraffin can enhance the percutaneous penetration of glycerol and take synergistically optical clearing effect with glycerol over visible and near-infrared wave bands.

Activity Comparison of Different Solid Acid Catalysts in Etherification of Glycerol with tert-Butyl Alcohol in Flow and Batch Reactors

In the presented work, etherification of glycerol with TBA was investigated in a continuous flow and also in a batch reactor using nine different commercial solid acid catalysts, namely Amberlyst-15, Amberlyst-36, Amberlyst-35, Amberlyst-16, Relite EXC8D, Lewatit K2629, H-Beta, H-Mordenite and Nafion SAC-13. Results proved the advantages of flow reactor to achieve quite high glycerol conversion values in very short residence times, due to efficient contact of reactants with the solid catalyst, which was caused by higher catalyst to reactant ratio within the reactor. Results of batch reactor experiments obtained in the temperature range of 80–200 °C proved the importance of operating temperature on the catalytic performance of these materials. Amberlyst-15, which has the highest Bronsted acidity, gave the highest glycerol conversion at 90–100 °C. However, this material is unstable at temperatures higher than 110 °C. Performances of Amberlyst-36 and Relite EXC8D were the best in the range of 110–150 °C, which started to become unstable at 150 °C. Although the catalytic performance of Nafion-SAC-13 was not as good as Amberlyst type resins at temperatures up to 150 °C, its thermal stability was higher and could be used up to 200 °C. Although Bronsted acidity was the most important property of these materials in the etherification reaction of glycerol, results also proved the importance of diffusion resistance on the observed conversion values, which limited the penetration of glycerol to the active acid sites, especially in the catalysts with smaller pore diameters and at lower temperatures. Increased significance of swelling at higher temperatures, especially with Amberlyst-36 which had lower cross-linking in its structure and less rigidity, contributed to the penetration of the reactants to the active sites. Water produced during the etherification reaction was also shown to cause deactivation of the catalysts by reversible adsorption on the acid sites.

Glycerol penetration profile in phospholipid bilayers measured by ESEEM of spin-labelled lipids

Electron spin echo envelope modulation (ESEEM) spectroscopy of phospholipids systematically spin-labelled along the sn-2 chain was used to detect the penetration of a deuterium-substituted water–glycerol mixture H2O/C3D5(OH)3 (1:1 v/v) into dipalmitoyl phosphatidylcholine (DPPC) bilayer membranes. The results provide a detailed profile of the penetration of glycerol across the membrane. The ESEEM amplitude induced by the hyperfine interaction with the deuterium nuclei drops substantially beyond the 10th label position. Beyond the 12th label position, the amplitude was nearly constant. A quantitative assessment of the glycerol concentration in the middle of the bilayer resulted in a value of ∼0.4 M (∼3% v/v). For comparison, analogous measurements were performed for the penetration of pure deuterium water D2O. In both cases, the ESEEM amplitudes varied similarly across the bilayer, except for the terminal 16th position. At this position, the amplitude for pure water was small and close in magnitude to the noise level.

Elucidation of the mechanisms of optical clearing in collagen tissue with multiphoton imaging

Optical clearing (OC) is a promising method to overcome limitations in biomedical depth-resolved optical studies. Mechanisms of OC in purified bovine Achilles tendon, chicken skin, and chicken tendon were studied using time-lapsed, three-dimensional second harmonic generation (SHG) and two-photon fluorescence microscopic imaging. Quantified nonlinear optical measurements allowed temporal separation of two processes in collagen OC with glycerol. The first one is a fast process of tissue dehydration accompanied with collagen shrinkage and the second relatively slow process is glycerol penetration into the interfibrillar space of collagen alongside with CF swelling. The use of 50% glycerol induced less-expressed OC via partial substitution of water molecules with glycerol molecules. We also found that phosphate-buffered saline- and glycerol-treatments were reversible, and fiber morphology and SHG signal intensity were recovered after the removal of immersion agents. It was shown that tissue OC was a dynamic process and elucidation of its physical mechanisms may help choose optimal diagnostic, treatment, and modification regimes for collagen-based as well as other types of biomaterials.

Glycerol in comparison with ethanol in alcohol-assisted dyeing

Abstract The dyeing processes can be reformulated to reduce the environmental pollution with economic advantages by the substitution of most auxiliary products with low cost, non-toxic and biodegradable products derived from natural sources. In a previous work a chemical substitution study was carried out with ethanol and the results showed a favorable effect of ethanol addition, at about 1–3% v/v, on the dye uptake, with some differences depending on fiber nature and dye class. In the present study glycerol was considered as alternative to ethanol due to the very low volatility and high boiling point which make safer its use in industry. The effect of glycerol introduction without other additives in isothermal dyeing of various fiber yarns (wool, cotton, polyester, nylon 6 and acrylic) was experimented and compared with that of ethanol. Moreover the equilibrium data obtained were correlated with contact angle measurements of water–glycerol solutions on the yarns. Glycerol, like ethanol, is able to improve the dye uptake. In the case of synthetic fibers the wetting effect was confirmed by a minimum of interfacial tension in the range 1–3% v/v of glycerol in water. However in the case of wool and cotton other effects should be considered, involving the glycerol penetration into the fiber structure favored by hydrogen bonds formation. Finally environmental benefits and cost savings arising from substitution of auxiliary agents with glycerol were considered and some advantages of glycerol in comparison with ethanol were highlighted.

Evaluation of optical clearing with the combined liquid paraffin and glycerol mixture

By scanning biological tissues in vivo and in vitro with optical coherence tomography, it is found that liquid paraffin can enhance the percutaneous penetration of glycerol in deep layers of tissue and take synergistically optical clearing effect with glycerol. It is shown from experimental results that 30% - 50% liquid paraffin glycerol solutions have the best enhancement effect. Considering the refractive index of liquid paraffin and its medicinal value, we think liquid paraffin will play an important role in optical clearing as the penetration enhancer of glycerol in future clinical research.

Green Nanocomposites from Renewable Resources: Effect of Plasticizer on the Structure and Material Properties of Clay-filled Starch

Nanocomposites of starch were prepared via different addition sequences of plasticizer and clay by the solution method. The extent of dispersion of the filler was evaluated by wide angle X-ray diffractometry (WAXD) in the resulting composites. Thermal stability, mechanical properties and water absorption studies were conducted to measure the material properties whereas FT-IR spectroscopy was used to study the microdomain structure of composites. The sequence of addition of components (starch /plasticizer (glycerol) / clay) had a significant effect on the nature of composites formed and accordingly properties were altered. Glycerol and starch both have the tendency to penetrate into the silicate layers but penetration of glycerol is favored owing to its smaller molecule size. The filler dispersion becomes highly heterogeneous and the product becomes more brittle when starch was plasticized before filling with clay due to the formation of a bulky structure resulting from electrostatic attractions between starch and plasticizer. It was concluded that best mechanical properties can be obtained if plasticizer is added after mixing of clay in the starch matrix.

Physiology of Gluconobacter oxydans during dihydroxyacetone production from glycerol

Investigations into physiological aspects of glycerol conversion to dihydroxyacetone (DHA) by Gluconobacter oxydans ATCC 621 were made. The activity levels of the enzymes involved in the three catabolic pathways previously known and the effects of specific inhibitors and uncoupling agents on cellular development, DHA synthesis, and cellular respiratory activity were determined. It was established that only two catabolic pathways are involved in glycerol dissimilation by this micro-organism. The only enzyme responsible for DHA production is membrane-bound glycerol dehydrogenase, which employs oxygen as the final acceptor of reduced equivalents without NADH mediation. The ketone is directly released into the culture broth. As the glycolytic and carboxylic acid pathways are absent, the pathway provided by the membrane-bound enzyme is indispensable for the energy requirements of G. oxydans. The cytoplasmic pathway, which begins by phosphorylation of glycerol followed by a dehydrogenation to dihydroxyacetone phosphate, allows growth of the bacterium. At the same time, the substrate transport mode was characterized as facilitated diffusion using radioactive [1(3)-3H]-glycerol. Concerning the DHA inhibition of microbial activity, the enzymatic study of the membrane-bound glycerol dehydrogenase showed the enzymatic origin of this phenomenon: a 50% decrease of the enzyme activity was observed in the presence of 576 mm DHA. The decrease in the rate of penetration of glycerol into cells in the presence of DHA indicates that growth inhibition is essentially due to the high inhibition exerted by the ketone on the substrate transport system.

Temporary reversal of serum to cerebrospinal fluid glycerol concentration gradient after intravenous infusion of glycerol.

Glycerol 50 g infused i.v. over 2 to 6 h is widely used to treat cerebral oedema in patients with acute stroke. Its transit through the blood-cerebrospinal fluid barrier in subjects with uninflamed meninges has now been examined. In 7 patients with an external ventriculostomy for occlusive hydrocephalus, each of whom was given 500 ml of a 10% solution IV over 4 h, serum and CSF were repeatedly sampled during and after the infusion and glycerol was measured enzymatically. The highest serum glycerol level of 191-923 mg/l was observed at the end of the infusion. The maximum CSF glycerol of 18.7-110.8 mg/l was attained 0-1 h after the end of the infusion. Elimination both from serum and CSF approximated a single-exponential decay; the elimination half-life from serum was 0.29-0.56 h compared to 1.03-3.68 h from CSF. In six of the seven cases there was a temporary reversal of the serum/CSF concentration gradient during glycerol elimination. The ratios of the AUCs of CSF and serum, which describe the overall penetration of glycerol into CSF, ranged from 0.09-0.31. In conclusion, the serum level of glycerol produced by giving 50 g IV glycerol over 4 h may not be sufficiently high reliably dehydrate to brain tissue in many patients, and the slow elimination of glycerol from the CSF may be related to the so-called rebound phenomenon.

Mechanisms of corneal drug penetration I: In vivo and in vitro kinetics

Corneal penetration studies were conducted in unanesthetized albino rabbits using various organic compounds representing both polar and nonpolar species. Very low molecular weight compounds demonstrate rapid uptake into the aqueous humor despite the lipid-like barrier imposed by the corneal epithelium. Evidence that these compounds may have access to a diffusional channel for corneal transport is presented. In vitro permeability studies were also conducted in an effort to quantitate the corneal diffusion of compounds covering a range of molecular weights and partition coefficients; the results corresponded well with the results of in vivo experiments. Calculations of energies of activation, taken from Arrhenius plots, indicate that the diffusion of drug across the cornea may be by two different mechanisms that depend on the physicakhemical characteristics of the perfusant. One mechanism appears similar to drug movement in an aqueous environment and is characterized by an activation energy similar to that for diffusion in water. The other relates to the expected partitioning of a compound across cellular membranes represented by a relatively high activation energy for diffusion. For hyrdophilic compounds, the epithelium appears to be rate limiting to drug movement, whereas for hydrophobic compounds, the stroma is rate limiting. In the presence of calcium-chelating agents, glycerol demonstrated an increase in corneal penetration in vivo. This effect appears to be reversible at specific concentrations of chelator. In contrast, divalent cations reduced corneal penetration of glycerol. The known calcium chelator EDTA was shown to penetrate the cornea, conjunctiva, and iriskiliary body from a topically applied dose. The implications of this observation pertain to toxicity effects when EDTA is incorporated into ocular drug products for stability purposes, or novel stratagems for improving ocular bioavailability of topically applied drugs are employed. The addition of calcium-chelating agents to in vivo mounted corneas demonstrated increases in permeability of the cornea to glycerol which were directly related to the concentration of chelating agent used. These results paralleled the findings of similar in vivo studies. The results of these studies are consistent with a currently proposed ‘pore’ model for the penetration of drugs through the cornea which demonstrates both a partition coefficient and molecular weight dependency on the permeability of the cornea to transported compounds.

Hydration of the stratum corneum

Synopsis Topically applied water, occlusion and topically applied glycerol were used to investigate and characterize some of the changes which occur in the hydrated stratum corneum. The effects of these treatments were monitored using non-invasive techniques under controlled conditions. The Servomed Evaporimeter was used to determine natural water flux from the skin surface before and after treatment. The performance of the Evaporimeter in this type of study had previously been improved by attaching a paper baffle to the detector. This eliminated the variance in output caused by atmospheric movement. Experiments were carried out at temperatures below the threshold of thermal sweating and emotional sweating was minimized. Skin surface topography was characterized by means of a new type of profilometer. The instrument's design allowed a diamond stylus to traverse the living skin surface without significantly altering its structure. Changes in skin surface roughness were further elucidated using scanning electron microscopy and macrophotography. In vivo penetration of glycerol was assessed by chemical analysis of stratum corneum layers of treated skin. Samples were obtained by sequential stripping of the stratum corneum using adhesive tape. Topically applied water produced only a transient benefit because of rapid evaporation. More prolonged hydration was achieved by suppressing transepidermal water loss with polyethylene film. This occlusive hyperhydration was characterized by a significant reduction in profile roughness and by a smoother macroscopic appearance. Glycerol achieved the same effects by reducing the magnitude of the natural water flux from the skin surface and by reducing the rate of evaporation of water from applied aqueous glycerol solution or cosmetic product. Both effects were seen as the result of lowered water activity in the proximity of glycerol. Smoothing effects of glycerol on the skin surface, and improved appearance, persisted for at least 24 h. This persistence was explained by evidence for diffusion of glycerol into the stratum corneum where it formed a reservoir. Hydration of the skin is known to affect its barrier function and thereby exert a profound effect on penetration of both lipophilic and hydrophilic molecules. Clinically, this effect may be achieved using liberal applications of occlusive petroleum jelly and ointments. The results presented in this paper suggest that the use of humectants could achieve useful hydration using cosmetically acceptable materials.

Adaptation de la technique de congélation avec faible concentration en glycérol à des concentrés globulaires resuspendus en SAG

We describe here a freezing method with a final low concentration of 20% glycerol and storage in a aluminium flask at - 150 degrees C. This technique allows the freezing of red blood cells concentrates collected on CPD and resuspended in SAG, without having to eliminate the SAG solution. For this we used an initial solution of 60% glycerol, which we added to the red blood cell concentrate in two steps separated by a resting time. Accordingly to the final concentration of glycerol, this freezing process is similar to the method currently used in our laboratory. This consists in one step addition V/V of 40% glycerol solution to the CPD red blood cells. The two techniques have been compared after thawing, and washing in a IBM Blood Processor 2991. The following parameters have been studied mainly: --haemoglobin level --residual glycerol --leucocytes and platelets --amount of 2-3 DPG and of intra-erythrocyte ATP. The results of the two freezing techniques are similar. They show that the SAG solution does not impair the intracellular penetration of glycerol. The in vitro qualities of the erythrocytes are well preserved.

Potassium fluxes on hyperosmotic shock and the effect of phenol and bronopol (2-bromo-2-nitropropan-1,3-diol) on deplasmolysis of Pseudomonas aeruginosa.

Potassium fluxes and the effect of phenol and bronopol on deplasmolysis of Pseudomonas aeruginosa were followed in sucrose and glycerol plasmolysing systems.In sucrose, K+ uptake related to the solute concentration. Proline increased the rate and overall K+ uptake, the latter by a factor of three. It was concluded that there was no rigid maximum in the accumulation of intracellular K+ as long as intracellular neutrality in electrical charges was maintained.In glycerol, K+ uptake was parallel with glycerol penetration. The process was reversed, however, on equilibration of glycerol. This suggested that glycerol inhibited K+ retention against a concentration gradient rather than that K+ was excluded as a consequence of the osmotic established steady state. This view was enforced by the fact that the reversal of K+ uptake occurred in 20 and 30% glycerol but not in 10%.Phenol and bronopol did not affect deplasmolysis in glycerol significantly, although some effect on K+ uptake and glycerol permeability could be seen. In the sucrose system, phenol acted according to its mode of action generally accepted, i.e. inhibiting deplasmolysis at low and allowing solute penetration at higher concentrations, whereas very high concentrations caused coagulation of the cytoplasm. Bronopol inhibited deplasmolysis, except at very low concentrations. Proline did not prevent the inhibition of deplasmolysis in either of the solute systems, except at the very low bronopol concentrations where the deplasmolysis rate only was affected.

Studies on the hydrogen belts of membranes: III. Glycerol permeability of dihydrosphingomyelin-cholesterol membranes.

The permeability of an N-oleoyldihydrosphingomyelin bilayer against glycerol was similar to that of a bilayer of phosphatidylcholine with identical effective hydrophobic chain length. Cholesterol at 1:1 molar ratio reduced the permeability, and also reduced the energy of activation of glycerol penetration, an effect not found for diesterphosphatidylcholine with cholesterol. The higher level of the ground state of the entropy of activation for permeability can be interpreted in terms of a hydrogen belt model which postulates lipid-lipid hydrogen bonding in membranes and explains the effect found as a disturbance of the hydrogen belt structure. Dihydrosphingomyelin can be considered to function as an "extender" in the hydrogen belt network.

Facilitated diffusion in starling erythrocytes

1. 1. A densimeter was used to make a kinetic study of the permeability of starling ( Sternus vulgaris) erythrocytes to the four nonelectrolytes, urea, thiourea, ethylene glycol and glycerol. 2. 2. Exit studies with urea and thiourea gave kinetics of facilitated diffusion. 3. 3. Urea inhibited the exit of thiourea and vice versa. 4. 4. Entrance studies with glycerol did not give any evidence of saturation. The penetration of glycerol, however, was inhibited by ethylene glycol. 5. 5. It was concluded that these four nonelectrolytes cross the membrane of starling erythrocytes by facilitated diffusion.

Osmotically induced volume and turbidity changes of Escherichia coli due to salts, sucrose and glycerol, with particular reference to the rapid permeation of glycerol into the cell.

SUMMARY Increases in turbidity of Escherichia coli strain K12 due to added non-permeant salts (NaCl and MgCl2) and sucrose are strictly dependent on medium osmotic pressure, when correction is made for changes in medium refractive index. The volume of the whole cell and the fraction of the intact cell bounded by the cyto-plasmic membrane have been measured by dextran and [14C]sucrose exclusion spaces. Increases in medium osmotic pressure due to non-penetrant medium solutes cause outflow of water across the cytoplasmic membrane and contraction away from the cell wall (plasmolysis), corresponding to the increases in turbidity. In addition salts (NaCl and MgCl2) cause appreciable contraction in volume of the whole cell, presumably due to ionic interaction with the wall; sucrose causes only marginal decreases in whole cell volume. Electron micrographs of cells plasmo-lysed by NaCl or MgCl2, but not by sucrose, show numerous adhesion points between the wall and the cytoplasmic membrane. Glycerol penetrates the cell to the same extent as water, but because of its slower rate of penetration, transient decreases in volume occur which can be measured in a stopped-flow spectrophotometer due to concomitant increases in turbidity. In cells grown on glucose-containing medium the rate of glycerol penetration is non-saturating. In cells grown on glycerol an additional saturating-facilitated diffusion system is induced. Mutants deleted in the facilitator (F-) are available and do not show facilitated diffusion when grown on glycerol. Water exit and glycerol penetration in glucose-grown cells show transition points in Arrhenius plots corresponding to phase changes of the membrane lipids.

Bovine sperm cell volume at various intervals after addition of glycerol at 5 °C

Sperm cell volume measurements were made by electronic particle sizing equipment and by the determination of packed-cell volume at intervals after glycerol addition to test for glycerol penetration. In the absence of penetration by glycerol, dehydration and shrinkage of the cells through efflux of water would be expected, while if penetration occurred the cells should return to their former size at a rate reflecting the rate of glycerol penetration. No significant changes in cell volume were observed after glycerol addition at 5 °C, but changes could have occurred during the 3–7 min before the volume measurements could be completed. The average mean volumes determined electronically were 25 μ 3, vs. 26 μ 3 for sperm cells with and without glycerol, respectively. The corresponding modal volumes were 21 μ 3 and 23 μ 3, respectively. The lack of substantial differences in cell volume in media with and without glycerol, and the absence of size changes with time in the presence of glycerol, suggest that glycerol penetration of bull sperm was very rapid at 5 °C, occurring within the 3 min required for the first volume determination to be made. Packed cell volume determinations gave similar results when glycerol was added at 5 °C and 25 °C. Even when the cells were previously swollen in hyposmotic media so that they had known potential for undergoing shrinkage after glycerol addition, detectable changes in volume were not observed over time. Furthermore, the volume of cells suspended in media with and without glycerol was similar. Thus, glycerol probably penetrated these cells within the 5–7 min required to make the first volume measurement.

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.