Effect of top soil wettability on water evaporation and plant growth.

In general, agricultural soil surfaces being hydrophilic in nature get easily wetted by water. The water beneath the soil moves through capillary effect and comes to the surface of the soil and thereafter evaporates into the surrounding air due to atmospheric conditions such as sunlight, wind current, temperature and relative humidity. To lower the water loss from soil, an experiment was designed in which a layer of hydrophobic soil was laid on the surface of ordinary hydrophilic soil. This technique strikingly decreased loss of water from the soil. The results indicated that the evaporation rate significantly decreased and 90% of water was retained in the soil in 83 h by the hydrophobic layer of 2 cm thickness. A theoretical calculation based on diffusion of water vapour (gas phase) through hydrophobic capillaries provide a meaningful explanation of experimental results. A greater retention of water in the soil by this approach can promote the growth of plants, which was confirmed by growing chick pea (Cicer arietinum) plants and it was found that the length of roots, height of shoot, number of branches, number of leaves, number of secondary roots, biomass etc. were significantly increased upon covering the surface with hydrophobic soil in comparison to uncovered ordinary hydrophilic soil of identical depth. Such approach can also decrease the water consumption by the plants particularly grown indoors in residential premises, green houses and poly-houses etc. and also can be very useful to prevent water loss and enhance growth of vegetation in semi-arid regions.

Self-assembled Gemini surfactant film-mediated dispersion stability.

The force-distance curves of 12-2-12 and 12-4-12 Gemini quaternary ammonium bromide surfactants on mica and silica surfaces obtained by atomic force microscopy (AFM) were correlated with the structure of the adsorption layer. The critical micelle concentration was measured in the presence or absence of electrolyte. The electrolyte effect (the decrease of CMC) is significantly more pronounced for Gemini than for single-chain surfactants. The maximum compressive force, F(max), of the adsorbed surfactant aggregates was determined. On the mica surface in the presence of 0.1 M NaCl, the Gemini micelles and strong repulsive barrier appear at surfactant concentrations 0.02-0.05 mM, which is significantly lower than that for the single C(12)TAB (5-10 mM). This difference between single and Gemini surfactants can be explained by a stronger adsorption energy of Gemini surfactants. The low concentration of Gemini at which this surfactant forms the strong micellar layer on the solid/solution interface proves that Gemini aggregates (micelles) potentially act as dispersing agent in processes such as chemical mechanical polishing or collector in flotation. The AFM force-distance results obtained for the Gemini surfactants were used along with turbidity measurements to determine how adsorption of Gemini surfactants affects dispersion stability. It has been shown that Gemini (or two-chain) surfactants are more effective dispersing agents, and that in the presence of electrolyte, the silica dispersion stability at pH 4.0 can also be achieved at very low surfactant concentrations ( approximately 0.02 mM).

Improved drug delivery using microemulsions: rationale, recent progress, and new horizons.

Microemulsions are excellent candidates as potential drug delivery systems because of their improved drug solubilization, long shelf life, and ease of preparation and administration. The formulation of microemulsions for pharmaceutical use requires a thorough understanding of the properties, uses, and limitations of microemulsions. Three distinct microemulsions--oil external, water external, and middle phase--can be used for drug delivery, depending upon the type of drug and the site of action. In this article, we present an examination of microemulsions as drug carrier systems, starting with general information and moving to a thorough review of the microemulsion literature, with a special section devoted to microemulsion-based gels.

Evaluation of local anesthesia provided by transdermal patches containing different formulations of tetracaine.

Topical formulations of tetracaine in vehicles of propylene glycol and saline are tested on human volunteers with standard occlusive, adhesive, transdermal patches. The effects of formulation composition, dose, and onset time are investigated. Dose-response studies indicate that the optimum formulation for the diffusion of tetracaine in vivo is 60% free base and 40% acid salt (w/w) in 40% propylene glycol and 60% saline (v/v). A concentration of 0.3 M [8.3% (w/v)] tetracaine is sufficient to reach the dose plateau. Time-response studies indicate that high concentrations of tetracaine in the optimum formulation [1.1 and 1.8 M, 30 and 50% (w/v), respectively] can produce statistically significant analgesia relative to a placebo after 45 min. Comparison of these in vivo data with earlier in vitro data indicate that the optimum formulation with regard to clinical studies is identical to that for in vitro diffusion through hairless mouse skin [60% free base and 40% acid salt (w/w) in 40% propylene glycol and 60% saline].

A method for attachment of peptides to a solid surface with enhanced immunoreactivity.

Another method has been developed to attach synthetic peptides to solid supports for use in enzyme immunoassays. The method is based on passively adsorbing a synthetic peptide to a solid-phase support, then further attaching more of the same peptide by means of cross-linking to the previously adsorbed peptide. This method results in highly enhanced peptide immunoreactivity compared with that obtained with standard methodologies.

A large-scale magnetic separator for selective cell separations with paramagnetic microbeads.

An improved magnetic separator has been developed for use in large-scale cell separations. This separation method uses paramagnetic microbeads coated with antibodies that selectively bind to target cells. The magnetic separator attracts the microbead-target cell aggregates and holds these aggregates at its surface while the suspending fluid and nontarget cells flow past. The optimum separator design was determined to be two magnetic assemblies in series along with a peristaltic pump. The assemblies consist of neodymium-iron-boron magnet bars sandwiched between steel bars (magnetic pole pieces). The size and pole spacing of the two magnetic assemblies are designed to be different, so that the first assembly, which captures greater than 99.99% of the microbeads, has good magnetic reach-out and a high magnetic holding force at its surface, while the second assembly has an even higher magnetic holding force at its surface. Studies show that the separator can remove 1 x 10(10) microbeads from a suspension of red blood cells processed at a flow rate of 9 ml/min, so that no microbeads are detected in the effluent.

Controlled release of steroids through microporous membranes with sodium dodecyl sulfate micelles.

The effect of solubilization by sodium dodecyl sulfate (SDS) micelles on the transport of steroids across synthetic microporous membranes has been studied experimentally in a diffusion cell and compared with theoretical calculations. The model used for calculations accounted for the fluxes of free and micelle-solubilized drug. Since the pores of the microporous membranes were only 10 times larger than the micelle, hindered diffusion effects for the micelles were taken into account. The compounds of interest (hydrocortisone, testosterone, and progesterone) had a wide range of aqueous solubilities and distribution coefficients between the aqueous and the micellar phases. In general, the theoretical predictions of drug diffusion agreed with the data to within approximately 10%.

Transport of micelle-solubilized steroids across microporous membranes.

The effect of solubilization by micelles on the transport of steroids across microporous membranes has been studied theoretically and experimentally. Our theoretical model requires the following parameters: micelle and drug diffusion coefficients in free solution, the distribution coefficient of the drug between the bulk and micellar phases, and micelle and membrane pore radii. The steroids used were hydrocortisone, testosterone, and progesterone. Since the model accounts for the flux of free drug as well as micelle-solubilized drug, the distribution coefficient of the drug between micelles and the aqueous phase had to be determined by solubilization experiments for each of the steroids. Membrane pore diameters, as determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), ranged from approximately 500 to 4000 A. Steroid diffusion coefficients were calculated from membrane diffusion experiments. Quasi-elastic light scattering was used to find the free-solution diffusion coefficients and hydrodynamic radii of the micelles. With these experimentally determined parameters, the model is shown to be capable of predicting the rate of transport of micelle-solubilized drugs through microporous membranes. The application of our model to the design of controlled-release devices is also discussed.

Lubrication and surface chemical properties of ophthalmic solutions.

Surface chemical and lubrication parameters such as contact angle, surface tension, and coefficient of friction, together with viscosity, were measured for commercial ophthalmic solutions. A sensitive friction-testing instrument was employed to measure the coefficient of friction between low-energy polymeric surfaces, e.g., polymethylmethacrylate (PMMA). The viscosity of ten commercial tear substitutes employed in the present study ranged from 2 to 25 cp. The results showed that there is no correlation between the coefficient of friction and viscosity, surface tension, or contact angle of these tear substitutes. The coefficient of friction of tear substitutes appears to depend upon the structure, conformation, and adsorption characteristics of polymer as well as surface characteristics of sliding surfaces. A systematic study was undertaken to evaluate the effect of speed and load on the coefficient of friction between different sliding surfaces, namely PMMA/nylon and PMMA/PMMA. The analysis of data established that our system was operating in the region of "boundary lubrication." In general, a PMMA/PMMA system exhibited a lower coefficient of friction as compared with the PMMA/nylon system.

31P and two-dimensional 31P/1H correlated NMR spectra of Duplex d(Ap[17O]Gp[18O]Cp[16O]T) and assignment of 31P signals in d(ApGpCpT)2-actinomycin D complex.

A solid-phase phosphoramidite method was used for the synthesis of unlabeled and phosphoryl-labeled d(Ap-[17O]Gp[18O]Cp[16O]T). The ability to label the phosphoryl oxygens of d(ApGpCpT) and thus assign the 31P signals, combined with a two-dimensional 31P/1H chemical shift correlated NMR spectral technique, provided a novel means for the ready assignment of the H5' and H3' protons coupled to the phosphates. Phosphoryl labeling has also allowed us to assign the 31P NMR signals in the actinomycin D-d(Ap-[17O]Gp[18O]Cp[16O]T)2 duplex complex and confirm that the drug intercalates between the GpC stacked base pairs.

A two-dimensional NMR method for assignment of deoxyribose proton NMR signals in d(ApGpCpT).

The ability to label the phosphoryl oxygens of d( ApGpCpT ) and thus assign the 31P signals, combined with a 2-D 31P/1H chemical shift correlated NMR spectral technique, provides a novel means for the ready assignment of the H5' and H3' protons coupled to the phosphates.

Proton and fluorine nuclear magnetic resonance spectroscopic observation of hemiacetal formation between N-acyl-p-fluorophenylalaninals and alpha-chymotrypsin.

Proton nuclear magnetic resonance (NMR) spectroscopy shows that the free aldehyde and not the hydrate of N-acetyl-DL-p-fluorophenylalaninal binds to alpha-chymotrypsin. A proton NMR cross-saturation experiment shows that the initial noncovalent complex is in equilibrium with a hemiacetal formed between the aldehyde and the active site serine residue. Fluorine NMR spectra of N-acetyl-DL- (and N-acetyl-L-) p-fluorophenylalaninal in the presence of alpha-chymotrypsin show separate signals for the hemiacetal complex, the bound aldehyde, the free aldehyde, and the free hydrate. N-Benzoyl-DL-p-fluorophenylalaninal fluorine NMR signals are also observed for all species except the bound aldehyde form in the presence of alpha-chymotrypsin. The D and L enantiomers of the hydrate of the N-acetyl aldehyde inhibitor give separate fluorine NMR signals, arising from chemical exchange between the L-aldehyde-alpha-chymotrypsin complex and the free L hydrate. The enzyme-bound inhibitor fluorine signals disappear upon proton decoupling due to a negative nuclear Overhauser effect. Upon gated decoupling of protons, the L hydrate and free aldehyde fluorine signals are reduced in intensity relative to that of the D hydrate signal in the racemate aldehyde complex. This is attributed to a saturation transfer of the heteronuclear nuclear Overhauser effect.

Effects of chaotropic and antichaotropic agents on elution of poliovirus adsorbed on membrane filters.

The association of poliovirus with membrane filters results from both electrostatic and hydrophobic interactions. At low pH, electrostatic interactions appear to dominate. However, at high pH, hydrophobic interactions appear to dominate with both Millipore and Zeta plus filters. With both filters, viral elution was prevented at high pH by the presence of antichaotropic salts, which strengthen hydrophobic associations. This effect was antagonized by detergents and by chaotropic salts, which weaken hydrophobic associations. Excellent correlation was observed between viral elution, the solubilization of adenine, and the micelle-formation process in the presence of chaotropic and antichaotropic agents. Such simple measurements of the relative ability of solvents to accommodate hydrophobic groups may be of predictive value in designing methods for concentration and purification of viruses. The hypothesis that hydrophobic interactions are the primary force involved in the stabilization of virus attachment at high pH is consistent with observations that cannot be explained by consideration of electrostatic interactions as the major stabilizing factor.

The dynamic film thickness of cushioning agents on contact lens materials.

Using an in vitro technique, a number of commercial as well as pure polymer solutions were evaluated for their ability to form thick aqueous layers on contact lens materials. It was demonstrated that the thickness of adhered pure polymer films was strictly viscosity dependent and did not depend upon the solution's wetting properties (ie, contact angle and surface tension) nor the surface upon which the solution was deposited (eg, glass, a hydrophilic surface versus Plexiglass, a relatively hydrophobic surface). The clinical implications of this study are that the desired solution properties of tear substitutes may be quite different from those of wetting and "cushioning" solutions.

The instilled fluid dynamics and surface chemistry of polymers in the preocular tear film.

Using slit lamp fluorophotometry it was demonstrated that the rate of drainage of a vehicle placed in the eye increased with increasing volume and that polymer solutions increased the thickness of the precorneal tear film (PTF). By increasing the viscosity of the delivery vehicle, (e.g., a hydroxypropylmethylcellulose polymer solutions), the PTF retention of fluorescein could be increased. The increased retention was shown to be due to an increase in the tear reservoir volume provided by the more viscous solutions. The PTF retention of fluorescein in a polyvinyl alcohol (PVA) vehicle was not as viscosity dependent, although PVA did seem to produce greater initial PTF fluorescence. This suggested that PVA initially produced a thicker PTF. The PTF retention of fluorescein by five commercial solutions did not have any relation to their wetting properties. The only good correlation with fluorescein retention in the PTF measured, seemed to be the ability of different polymer solutions to stabilize a thick layer of water as measured by the spontaneous spreading of polymer molecules at the air/liquid interface on wet glass surfaces. This model was designed to simulate tear film spreading in vivo. The results suggest that different polymer solutions may produce thicker PTF's than normal by virtue of their ability to drag water with them as they spread over the ocular surface with each blink. Mechanisms by which polymer solutions may increase the thickness of the PTF are discussed.

Venous air embolism prophylaxis with a surface-active agent.

The protective effect of a nonionic surface-active polyol agent (Pluronic F-68) against bolus injection and constant-rate IV infusion of air was studied in 21 dogs anesthetized with pentobarbital. Aortic, pulmonary artery and right ventricular pressures, cardiac output, end-tidal CO2 concentration, wasted ventilation, and blood surface tensions were measured before and after the IV administration of this surfactant. The magnitudes of change in the cardiorespiratory responses measured after venous air embolism were significant (p less than 0.05) reduced in the treated animals. This agent may be advantageous for surgical patients when an increased risk of venous air embolism exists.