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Biomedical subjects

N Garti

Publications and source records attributed to N Garti.

At least 19 recordsLinked to original sources
PubMed2001

Water Solubilization in Nonionic Microemulsions Stabilized by Grafted Siliconic Emulsifiers.

Microemulsions containing octanol, decanol, or dodecanol as the oil phase and oligomeric, grafted nonionic amphiphiles based on ethoxylated polymethylsiloxanes (Silwets) have been studied. It was demonstrated that significant amounts of water can be solubilized only when the hydrophobic siliconic backbone is very short (trimers). The water solubilization was evaluated using SAXS, DSC, and conductivity measurements. It was found that up to 40 wt% of water can be solubilized in dodecanol and Silwet L-7607 (MW 1000 and 75 wt% ethylene oxide (EO)). Surprisingly, no free water was detected in the aggregate core. All the solubilized water was confined in the vicinity of the interphasal region and froze at -10 degrees C and below. Up to three molecules of water can be associated with each EO headgroup. Based on SAXS measurements, the structural units of the microemulsions were interpreted to be lamellar-like, a form previously found for the related monomeric microemulsions. Copyright 2001 Academic Press.

Journal Article↗
PubMed2000

Solubilization of Hydrophilic Compounds in Copolymer Aggregates.

The solubilization of five hydrophilic water-soluble aroma compounds in self-aggregating triblock amphiphilic copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO), with similar percentages of PEO and different molecular weights, was studied. The five hydrophilic compounds (diacetyl, 2-methylpyrazine, pyrrole, furfural, guaiacol) were carefully selected to represent hydrophilic molecules with a similar molecular weight and molecular volume, but with different abilities to interact with the micellar core of PPO moieties and with the PEO palisade side chains. It was found that the solubilized solute mole fraction increased and the aggregate-water partition coefficients of the solutes decreased with increasing free solute concentration in the aqueous phase. The partition coefficients were smaller than those obtained for hydrophobic compounds and equilibrium was reached at lower solubilization values. Guaiacol was the least hydrophilic molecule and had the highest partition coefficient. Diacetyl was the most water-soluble compound and exhibited the smallest partition coefficient. The data reveal that the higher molecular weight polymers solubilized more solute than the low-molecular-weight polymers. Moreover it is supposed that at low solute concentrations, guaiacol (containing a hydroxyl electron acceptor group) penetrates the core of the micelle and displaces water while at more elevated concentrations it seems to be solubilized in the micelle corona. Diacetyl, the most hydrophilic solute investigated (consisting of electron donor groups), prefers mainly the corona since its affinity for the polymeric core is very weak. The solubilization occurs in the palisade layer and the partition coefficient is independent of the free solute concentration. Selective site (palisade vs core) solubilization of hydrophilic compounds in polymeric micelles can be a powerful tool to protect sensitive materials from reactants present in the continuous water phase and to conduct surface-sensitive organic reactions. Furthermore, selective release properties of reactants and products can be designed. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Structured fluids as microreactors for flavor formation by the Maillard reaction.

Thermal reactions of cysteine/furfural and cysteine/ribose mixtures were studied in model systems to gain more insight into the influence of structured fluids such as L(2) microemulsions and cubic phases on the generation of aroma compounds. Formation of 2-furfurylthiol from cysteine/furfural was particularly efficient in L(2) microemulsions and cubic phases compared to aqueous systems. The reaction led to the formation of two new sulfur compounds, which were identified as 2-(2-furyl)thiazolidine and, tentatively, N-(2-mercaptovinyl)-2-(2-furyl)thiazolidine. Similarly, generation of 2-furfurylthiol and 2-methyl-3-furanthiol from cysteine/ribose mixtures was strongly enhanced in structured fluids. The cubic phase was shown to be even more efficient in flavor generation than the L(2) microemulsion. It was denoted "cubic catalyst" or "cubic selective microreactor". The obtained results are interpreted in terms of a surface and curvature control of the reactions defined by the structural properties of the formed surfactant associates.

Cysteine↗
PubMed2000

Some characteristics of sugar ester nonionic microemulsions in view of possible food applications.

This study explores some characteristics of microemulsions composed of sucrose monostearate (SMS), medium-chain triglycerides (MCT), or R-(+)-limonene, alcohols, and water. The systems are homogeneous, soft, and waxy solids at room temperature but liquefy and structure into homogeneous microemulsions when heated to >40 degrees C. The amount of solubilized water is enhanced as a function of the alcohol/oil ratio and is inversely proportional to the alcohol chain length. Over 60 wt % water can be solubilized in systems consisting of propanol/MCT/SMS at a weight ratio of 3:1:4 (initial weight ratio). These microemulsions are unique and differ from nonionic ethoxylated-based microemulsions in that their viscosity is very low and is reduced with increasing amounts of solubilized water. The electrical conductivity increases only slightly as a function of the water content and does not show typical bicontinuous or percolated behavior. The water in the core of the microemulsion strongly binds to the headgroups of the surfactant. Only at >15 wt % solubilization of water was free or bulk water detected in the core of the microemulsions. Such unique behavior of the core water might have a possible application in systems requiring monitoring of enzymatic (lipase) reactions carried out in the microemulsions as microreactors.

Cyclohexenes↗
PubMed1997

Structural Polymorphism in a Four-Component Nonionic Microemulsion

The Winsor IV microemulsion system composed of octaethylene glycol mono n-dodecylether [C12(EO)8]/1-dodecane + n-pentanol (1:1 by weight)/water has been investigated at constant temperature using small angle X-ray scattering and electrical conductivity measurements. The results obtained are interpreted in terms of structural evolution of the molecular aggregates as a function of the stepwise addition of water or (oil + alcohol). The size and shape of a variety of microstructures are described: small, spherical micelles near the water corner and hexagonal and lamellar mesophases, which are oil- and alcohol-poor. Simple multishell models of these provide some insight into how dilution with water or swelling with (oil + alcohol) influences the overall symmetry of the aggregates, pentanol and dodecane partitioning, surfactant headgroup conformation, and the contribution of pentanol to oil solubilization. The previously identified "local" lamellar structure [O. Regev et al., Langmuir 12, 668 (1996)], which is a surfactant-rich and (oil + alcohol)-rich intermediate state between the W/O and O/W regions, is characterized here as a type of ordered, but highly obstructed, bicontinuous microemulsion.

Journal Article↗
PubMed1995

Induction of crystallization of calcium oxalate dihydrate in micellar solutions of anionic surfactants.

Calcium oxalate dihydrate (CaC2O4 center dot (2+x)H2O; COD; x < or = 0.5) does not readily crystallize from electrolytic solutions but appears as a component in crystalluria. In this paper, we review in vitro studies on the factors responsible for its nucleation and growth with special attention given to the role of surfactants. The following surfactants were tested: dodecyl ammonium chloride (cationic), octaethylene mono-hexadecylether (non-ionic), sodium dodecyl sulfate (SDS, anionic), dioctyl sulphosuccinate (AOT, anionic), and sodium cholate (NaC, anionic). The cationic and some of the anionic surfactants (SDS, AOT) induced different habit modifications of growing calcium oxalate crystals by preferential adsorption at different crystal faces. In addition, the anionic surfactants effectively induced crystallization of COD at the expense of COM, the proportion of COD in the precipitates abruptly increasing above a critical surfactant concentration, close to, but not necessarily identical with the respective CMC. A mechanism is proposed, whereby crystallization of COD in the presence of surfactants is a consequence of the inhibition of COM by preferential adsorption of surfactant hemimicelles (two-dimensional surface aggregates) at the surfaces of growing crystals.

Calcium Oxalate↗
PubMed1986

The amino acid factor in stone formers' and normal urines.

The composition of amino-acids in kidney stone matrices and inhibitory materials from normal urines, reported in different independent studies has been reviewed. No obvious difference was found between the composition of amino acids from healthy and pathological sources. Studies carried out in this laboratory showed a specific marked effect of glutamic acid on the crystallization of calcium oxalate while aspartic acid and alanine affected the process very slightly. It is known that aspartic acid and alanine are transformed into glutamic acid by enzyme activity. A short survey performed in this laboratory showed that the relevant enzyme activity was relatively high in healthy urine and low in stone formers' urine. The AA factor (FAA) proposed is FAA = [Glutamic acid]/[( Aspartic acid] + [Alanine]) its value in fractions of non-potent inhibitory material and in kidney stone matrices is below 0.6. In potent portions of the inhibitory material separated from healthy people and young animals urine the value is 0.8 and above.

Amino Acids↗
PubMed1985

Evaluation of the relative inhibitory potential of fractionated urinary macromolecules.

UNLABELLED: Ultrafiltration membranes of 10,000 d, 1,000 d and 500 d were used to remove urinary macromolecules from the urine of normal subjects and from the urine of stone forming patients. The filtrated urines were examined for their residual inhibitory potential for calcium-oxalate precipitation, by the discrimination method of Sarig et al. (D.I. test). The results of testing the filtrate were complementary to the information gained by analyses of retentates obtained in successive ultrafiltration. The method has an inherent advantage because the manipulation of solids retained on membranes may inadvertantly modify their inhibitory potential. At least two distinct groups of inhibitors were found in 20 normal urines. The first group has MW above 10,000 d while the second group of inhibitors has MW in the range of 500-1,000 d. The mean of the D.I. values increased dramatically from the normal range (less than 0.6) to the stone former range (greater than 1.1) (p less than 0.001) after the 500 d filtration. Some of the normal urines, even after the 500 d filtration, still had a degree of inhibitory potential. This inhibitory potential may be related to the inorganic compounds which were found in the urines. The inhibitory activity of macromolecules with MW above 10,000 d and below 500 delta was negligible in 7 stone formers (SF) urines. The relative contribution of 500-1,000 d macromolecules is the highest both in SF and normal urines. CONCLUSIONS: 1) inhibitors in human urine are of wide range in MW; 2) stone formers and normals differ in the level of inhibitor activity at all MW ranges; especially in above 10,000 d and below inhibitors.

Calcium Oxalate↗
PubMed1985

Use of the discriminant index in dynamic treatment to reduce recurrence of calcium oxalate kidney stones.

Treatment with phosphates, thiazides and allopurinol was undertaken in 54 idiopathic calcium oxalate stone formers, 38 of whom were recurrent stone formers. The patients were followed up for 1 1/2 to 4 years (mean 2.6). During the same period at the pre-treatment stage the patients formed 80 stones, but during therapy only one stone was formed. A dynamic scheme of therapy was used. Each patient was tested before the start of drug treatment by the discriminant index (DI) method, which measures the overall inhibitory potential to calcium oxalate crystallisation. About 10 days after the start of treatment the DI was tested again. If the response was positive, therapy was continued; if not, the patient was given another drug. Adjustments were made as required. The stopping of stone formation correlated well with the DI prediction but less well with the hypocalciuric effect of the drugs.

Adult↗
PubMed1985

Biological control to diminish dangers of urolithiasis.

High concentrations of phosphate, oxalate, and calcium ions in urine may cause formation of mineral deposits, i.e., urolithiasis. This is prevented in healthy individuals by substances present in trace quantities. However, there is no recognizable difference between normals and stone formers in urinary substance content. The enzymes glutamic oxaloacetic transaminase and glutamic pyruvic transaminase produce glutamic acid which retards calcium oxalate crystallization. The combined transaminase activity in 70 stone former urine samples was 12.2 +/- 4.1 IU and 31.9 +/- 10.7 IU for 47 normal controls. Incubation of stone former urine with glutamic oxaloacetic transaminase improved overall inhibitory potential, raised glutamic acid levels, and decreased aspartic acid concentrations. Correlation was established between the success of therapeutic treatment and the improvement of enzyme activity. The relative content of glutamic acid is low stone former urines and high in active inhibitory fractions of urinary materials. It is suggested that part of the mechanisms of prevention of stone formation is subjected to biological control.

Alanine Transaminase↗
PubMed1984

Determination of GOT activity on nucleation and crystal growth of calcium oxalate.

Crystal Size Distribution (CSD) and the yield of Calcium Oxalate Crystals in solutions with an admixture of 5 normal and 3 stone forming urines, were determined. A positive correlation was found between the median size, the number of particles and the overall inhibitory potentials of the urines toward calcium oxalate precipitation in vitro as reflected by Discriminating Index (DI) measurements. Incubation of two samples of stone formers' (SF) urines with glutamic-oxalacetic-transaminase (GOT) caused a reduction of aspartic acid concentration, an increase in glutamic acid concentration and a parallel decrease in the DI values. After 90 min of SF urine incubation with GOT the DI in three samples was improved and both the median size and number of particles reduced, by 28% and 45% respectively. These results could indicate that GOT activity changes the inhibitory power of the SF urine by transforming aspartic acid into glutamic acid, having thus most probably a part in the inhibition of CaOx stone formation.

Aspartate Aminotransferases↗
PubMed1983

Follow-up of drug therapy efficacy to prevent recurrence of calcium oxalate kidney stone formation.

Results of a prospective study of response to phosphate treatment after surgery in a group of kidney stone formers, some of them recurrent are presented. The follow-up, of 1 year duration, was carried out by periodic tests of the stone formers' urine using the Discriminating Index (DI) procedure. In a group of 32 stone formers, 30 individuals showed a remarkable change in the DI value; i.e., the inhibiting potential of their urine was similar to that of normals. Two of the patients did not respond well, and their drug treatment was adjusted accordingly. During this year no recurrency was reported.

Calcium↗
PubMed1982

Retardation of calcium oxalate precipitation by glutamic-oxalacetic-transaminase activity.

It has been found that calcium oxalate stone formers have low UGOT activity compared to healthy individuals (controls). Urine from stone formers with no GOT activity and no effect on calcium oxalate precipitation was incubated with GOT for various periods. Subsequently calcium oxalate precipitation was decreased and found to be considerably retarded i.e., the pathological urine after the incubation acted in a way similar to that of normal urine. The yield of Glutamic-Oxalacetic Transaminase (GOT) activity is glutamic acid. It was shown that glutamic acid has a significant retardation effect on the precipitation of calcium oxalate stone formation. Therefore it may be suggested that GOT activity involved in glutamic acid creation in situ, has a role in kidney stone formation.

Aspartate Aminotransferases↗
PubMed1982

May enzyme activity in urine play a role in kidney stone formation?

It has been found that calcium oxalate stone formers have low UGOT and UGPT activity compared to healthy individuals. The urine of 23 stone formers and 19 controls has been tested for combined UGOT and UGPT activity. The effect of L-aspartic acid, alanine and L-glutamic acid on calcium oxalate precipitation has been tested. Only L-glutamic acid exerted a significant retardation effect at physiological concentrations. As GPT and GOT convert alanine and aspartic acid respectively into glutamic acid, a possible mechanism of retardation of kidney stone formation involving enzyme steps via glutamic acid creation in situ is suggested.

Alanine↗
PubMed1982

A method for discrimination between calcium oxalate kidney stone formers and normals.

Calcium ion concentration versus time was measured in solutions containing admixture of 10 per cent tested urine of normals and stone-formers, during induced calcium oxalate precipitation. A Discriminating Index was formulated by statistical analysis of the data. It was found that stone-formers and normals differ significantly with respect to the measurements and the Discriminating Indices. An equation to evaluate the odds of stone-forming based on results of an individual test has been derived. The Discrimination Index may be recommended as a diagnostic tool.

Adolescent↗
PubMed1981

Correlation between crystal habit and the composition of solvated and nonsolvated cholesterol crystals.

The correlation between the crystal habit and the composition of cholesterol crystals formed in four organic solvents (methanol, acetonitrile, ethanol, and acetone) was studied. Anhydrous and monohydrate cholesterol were precipitated in anhydrous and aqueous organic solvent mixtures, respectively. The main conclusions derived from the study were that 1) the appearance of plates does not automatically guarantee the presence of hydrated cholesterol, and 2) the presence of 5% or more of water in the crystallization solvent may not results in the formation of monohydrate cholesterol.

Acetone↗