Glutamic acid can crystallize in two polymorphic structures depending on the crystn. regime. The study demonstrates an efficient method to preferentially crystallize the nonstable polymorphic structure (the $\alpha$-form) in the presence of surface active agents. The rate of transformation depends on the rate of growth of $\beta$ and not on the rate of dissoln. of $\alpha$. The growth rate of $\beta$ was a function of the supersatn. of the solute in soln. The transformation could be inhibited by the addn. of surfactants. The surfactants are capable of adsorbing preferentially to the $\alpha$-growing crystals and soln. mediating (retarding) the transformation of the $\alpha$- to the $\beta$-form. Probably the surfactant nature and steric considerations were important for the inhibition of both nucleation and growth of the $\beta$-polymorph. A Langmuir approach indicated that the kinetic parameter was related to the vol. of surfactant adsorbed at the crystal surface. No changes in crystal morphol. were obsd., indicating that adsorption was not specific to any crystal face. Different mechanisms of surfactant adsorption were suggested: adsorption of single mols. at low concns. of surfactant and formation of hemimicelles at higher concns. [on SciFinder(R)]

Phospholipase A2 (PLA2) was used to hydrolyze phosphatidylcholine (PC) in microemulsions. Phase diagrams were constructed for mixt. of alcs. (C2-C6), medium chain triglycerides (tricaprylin (TC) or vegetable oils), PC and water, and areas corresponding to isotropic systems were identified. The PC hydrolysis was carried out with high yields of lysophosphatidylcholine at various PC/(TC+alc.) compns. within the areas of isotropic systems at increasing amts. of solubilized water. The initial reaction rates depended on the aggregation state of the PC (size and nature of microemulsion structures), as well as on temp. and mode of calcium addn. At low enzyme concns., hydrolysis was preceded by a lag phase followed by an abrupt increase in rate. By contrast, no latency was obsd. at higher PLA2/PC ratios and the rate was significantly higher. The easy access of the enzyme to the substrate in the curved phospholipid-contg. microemulsion particles facilitates activation of the enzyme and pushes the reaction to completion. Hence, these microemulsions can serve as microreactors for high yield enzymic hydrolysis. [on SciFinder(R)]

The Winsor IV microemulsion system composed of octaethylene glycol monododecyl ether [C12(EO)8]/dodecane + pentanol (1:1 by wt.)/water has been investigated at const. temp. using small-angle x-ray scattering and elec. cond. measurements. The results are interpreted in terms of structural evolution of the mol. aggregates as a function of the stepwise addn. of water or (oil + alc.). 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 alc.-poor. Simple multishell models provide some insight into how diln. with water or swelling with (oil + alc.) 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, which is a surfactant-rich and (oil + alc.)-rich intermediate state between the W/O and O/W regions, is characterized here as a type of ordered, but highly obstructed, bicontinuous microemulsion. [on SciFinder(R)]

A dough conditioner is described wherein the dough conditioner is soybean peroxidase or an aq. ext. of soybean hulls. [on SciFinder(R)]

A review with 170 refs. on micelles, microemulsions, emulsions, and other emulsion systems and their applications in the food industry. [on SciFinder(R)]

The transport properties near the percolation temp. threshold in the ternary H2O-in-oil microemulsion stabilized by ionic surfactant was studied by measuring the self-diffusion coeffs. of all the constituents of the microemulsion, and the cond. at 10-40°. It can be conjectured that 2 different transition mechanisms of the charge carriers in this temp. region may take place. These may be attributed to either the transfer of counterions from 1 droplet to another through H2O channels or hopping of surfactant ions from droplets within clusters. The cond. and dielec. polarization below the percolation threshold is mainly due to the motion of counterions via H2O channels within the droplet clusters and not a charge-hopping mechanism at the surfactant interface. Above the percolation threshold the latter mechanism appears, connected with migration of surfactant mols. from droplet to droplet within a percolation cluster. The 1st mechanism still dominates. [on SciFinder(R)]

Ca oxalate was crystd. in the presence of the anionic surfactant diisooctyl sulfosuccinate, AOT, and the phase compn. of the ppts. (by x-ray diffraction powder patterns and thermal anal.) and their crystal growth morphol. (by SEM and electron diffraction) were detd. In the control systems and in the presence of low concns. of AOT (below the crit. micellar concn., CMC) Ca oxalate monohydrate (CaC2O4·H2O, COM) was the dominant crystal phase. Crystals grown in the presence of C(AOT)\textgreater0.75 CMC were thinner and more elongated than in the controls, indicating preferential adsorption of the surfactant at the 1̅01 and \010\ crystal faces. When the AOT concn. exceeded the crit. micellar concn., the morphol. changes in COM crystals became more intense and the compn. of the ppts. abruptly changed to mixts. of COM and Ca oxalate dihydrate (CaC2O4·(2+x)H2O, x\textless0.5; COD) with a COM/COD ratio up to 50%. The morphol. of the COD crystals was mostly unaffected. The phase change was attributed to preferential adsorption of AOT - as surface aggregates - at the crystal faces of COM with the consequence of strong inhibition of nucleation and crystal growth of this crystal type and growth of the kinetically less favored COD crystals. [on SciFinder(R)]

The study of the relaxation properties near the percolation threshold in ternary water-in-oil microemulsion stabilized by ionic surfactant are presented as an example of the dynamics in self-assembled complex fluids. The data treatment for dynamic behavior of the microemulsions was carried out in the time domain in terms of dipole correlation functions. The correlation functions exhibit complex non-exponential relaxation behavior and must be de-convoluted into normal modes and represented as the sum of non-exponential terms; exp[-(t/$\tau$)$\beta$]. The temp. dependence of the stretched parameters shows the existence of spatial, temporal, and energetic disorder assocd. with anomalous diffusion of charge carriers in the percolation clusters. [on SciFinder(R)]

A review with 430 refs. Interfacial phenomena, emulsion formation, stability, characterization, etc., are discussed. [on SciFinder(R)]

One recently reported application of microemulsions is as a fire-resistant hydraulic fluid where efficacy and stability depend among other factors upon the water-solubilizing capacity of the microemulsion and on the relative concn. of the surfactant. A model for such a microemulsion system has been studied using cryo-transmission electron microscopy (cryo-TEM), 1H NMR self-diffusion, and small angle X-ray (SAXS) and neutron scattering (SANS). The phase behavior of the system contg. a 1p1:2 oil:alc.:surfactant wt. ratio is characterized by a single continuous microemulsion region starting from a soln. contg. no water and approaching the water corner. Along this diln. line, a structural transition sequence: oil drops → short range, noncontinuous lamellar microstructure → weakly hydrated aggregates is inferred as the water concn. is decreased. The local lamellar microstructure, i.e., stacks of surfactant sheets, oil, and water, randomly oriented in space without the long range correlations that characterize a lamellar liq. crystal is imaged for the first time. [on SciFinder(R)]