Unstirred Water Research Articles

Comparisons of in Vitro Models to Evaluate the Membrane Permeability of Amorphous Drug Nanoparticles.

The spontaneous formation of amorphous drug nanoparticles following the release of a drug from a supersaturating formulation is gaining increasing attention due to their potential contribution to increased oral bioavailability. The formation of nanosized drug particles also has considerable implications for the interpretation of in vitro and in vivo data. However, the membrane transport properties of these drug particles remain less well understood. Herein, the membrane permeation of nanosized amorphous drug particles of a model drug atazanavir was evaluated using different artificial membrane-based, cell-based, and animal tissue-based models. Results showed that flux enhancement by particles was different for the various systems used. Generally, good agreement was obtained among experiments performed using the same apparatus with different model membranes, with the exception of the Madin-Darby canine kidney cell monolayer and the Long-Evans rat intestine tissue, which showed lower flux enhancements. Franz cell-based models showed slightly higher flux enhancements by particles compared to Transwell and intestinal tissue sac models. Mass transport analysis suggested that the extent of flux enhancement by particles is dependent on the geometry of the apparatus as well as the properties of the membrane and buffer used, whereas the flux plateau concentration is dependent on the unstirred water later (UWL) asymmetry. These results highlight the complexity in characterizing the permeability advantage of these nonmembrane permeable drug particles and suggest that caution should be used in selecting the appropriate in vitro model to evaluate the overall permeability of colloidal drug particles.

Nonstationary Absorption of Methane by a Quiescent Aqueous Phase

Nonequilibrium dissolution of methane in unstirred water was investigated. The experiments were carried out in the ranges of temperatures, pressures, and concentrations corresponding to the existence of methane hydrate in an equilibrium state. The experimental data were satisfactorily described by a model taking into account the methane transfer both through the gas–liquid interface layer and in the liquid phase. Calculations using the model and the experimental data showed that the methane diffusivity in water is lower than in the interface layer. This can be associated with the formation of methane hydrate in the aqueous phase, since methane hydrate molecules are larger than methane molecules.

The interaction of water flow and nutrients on aquatic plant growth

A long-term experiment was conducted to compare the effects of flowing and still water on growth, and the relationship between water flow and nutrients, in Aponogeton elongatus, a submerged aquatic macrophyte. A. elongatus plants were grown for 23 weeks with three levels of nutrition (0, 0.5 and 1g Osmocote Plus® fertiliser pot−1) in aquaria containing stirred or unstirred water. Fertilized plants grew much better than non-fertilized. The highest fertilizer level produced 29% wider leaves and 58% higher total dry weight in stirred water. Stirred water increased leaf area by 40% and tuber size by 81%, but only with the highest level of nutrition. These results suggest that this plant depends on its roots for mineral uptake, rather than from the open water, and the major limitation to growth in still water is the supply of dissolved inorganic carbon. It was the combined effects of nutrient availability and stirring that produced the strongest response in plant growth, morphology and composition. This study provides some explanation for the observations of others that these plants grow best in creeks or river systems with permanently flowing water.

Adapting Constant-volume Manometry for Studying Gas Exchange by Bulky Plant Organs

Constant-pressure manometry, previously designed to study O2 and CO2 gas exchange in small pieces of tissue, cells, and organelles, was adapted to study bulky organs. According to this new procedure, a near-zero-volume Devaux chamber connects a manometer to the internal atmosphere volume (VG) of a plant organ covered by a layer of epoxy, submerged in unstirred water, kept at constant temperature, and kept at the same VG pressure. Equations, based on CO2 and O2 solubility at equilibrium with VG, were used to follow O2 consumption as a function of reduced internal O2 pressure over time [for organs with VG < 0.1 (v/v) and respiratory quotient (RQ) of 0.7 to 1.3] to observe the transition between aerobiosis and anaerobiosis and to measure CO2 evolution during the anaerobic phase. For those measurements, bulky-organ manometry performed consistently in tomato [VG = 6.41% (v/v)], sweetpotato [VG = 8.57% (v/v)], and potato [VG = 0.34% (v/v)]. The results indicate that constant-volume manometry is sufficiently precise to detect differences in respiratory metabolism as a function of intercellular O2 concentration in intact plant organs.

Oxygen transport in the submerged freshwater macrophyte Egeria densa planch. II. Role of lacunar gas pressures

A pressure transducer was used to measure internal gas pressures ( p I) in the lacumar system of Egeria densa Planch. Under illumination, p I values up to 25 kPa above atmospheric developed in shoots in unstirred water. Upon circulation of the water, p I values decreased to 50–90% of the maximal values in unstirred water. Positive pressures, indicating partitioning of photosynthetic O 2 into the lacunae, were recorded in both re-circulating and open-circuit flow. When the shoot was darkened, negative internal pressures (5–10 kPa below atmospheric) developed. The pressure gradient ( Δp) required to drive O 2 transport in the lacunar system was calculated from the Hagen-Poiseuille equation. This gradient was 9.15 × 10 −4 kPa m −1. Manometric measurements of p I and pressure transfer rates showed that transient gradients of approximately 0.9 kPa m −1 developed following dark to light changes. However, pressure equilibration (mean rate = 0.02 m s −1) resulted in rapid attainment of constant p I under steady-state conditions. It is proposed that O 2 transport in Egeria is sustained by simple diffusion, assisted by advective movements under internal pressure gradients that develop following changes in external conditions.

Effects of Dissolved Oxygen Concentrations in Aero-hydroponics on the Formation and Growth of Adventitious Roots

Abstract Cuttings of Ficus benjamina L. and Chrysanthemum × morifolium(Dendranthema grandiflora tzvelev.) were rooted in aero-hydroponics to study the effect of dissolved oxygen concentrations in the range of 8 mg·liter. (ambient saturation) to 0 mg·liter−1. The results of this study indicate that dissolved oxygen is essential to root formation and root growth. Woody (Ficus) and herbaceous (Chrysanthemum) cuttings responded similarly. Lowering the dissolved oxygen concentration increased the time required to form adventitious roots, reduced rooting percentages, reduced numbers of roots formed per cutting, and reduced average root lengths. Comparisons between stirred and unstirred water suggested the development of an area of depleted oxygen concentration (boundary layer) at the stem-water interface on cuttings immersed in unstirred water. Cuttings in water stirred constantly rooted sooner and formed more roots than did those in unstirred water. Maximum rooting occurred in misted (high dissolved oxygen concentrations) sections of cuttings suspended in the aero-hydroponics chambers. Chemical name used: potassium salt of lH-indole-3-butyric acid (K-IBA).

Rinsing Part V: The Dilution of Films of Sulphuric Acid and Sodium Hydroxide during Rinsing

SummaryUsing vapour rinsing, dilution ratios were measured as functions of rinsing time for carry-over films of sulphuric acid (simulating pickle drag-out) and sodium hydroxide (cleaner drag-out). Sulphuric acid films were diluted very quickly in unstirred rinse water, and also in solutions of sodium sulphate with concentrations up to saturation. In contrast sodium hydroxide films were diluted much more slowly, and in unstirred rinse water they clung persistently to the metal surface. Agitation of the rinse accelerated the dilution of sodium hydroxide, but to a lesser extent than that observed for other residues. The dilution of sodium hydroxide films in rinses containing sodium sulphate, calcium sulphate, or sulphuric acid, was faster than in a plain water rinse.

Factors Affecting Emergence, Survival and Infectivity of Meloidogyne Naasi

Soil moisture affected larval emergence and infectivity of Meloidogyne naasi. Most larvae emerged in soil that was kept at 74% field capacity in a monthly drying cycle and least in soil that was flooded constantly. The converse was true for the larval invasion tests following exposure to these different moisture regimes. A similar phenomenon was observed in the flooding and fallowing experiments where greater larval invasion was observed following flooding of the soil than in soil that was fallowed or left to natural weed growth for up to 12 weeks. Lipid disappeared most rapidly in second stage M. naasi larvae stored under aerobic conditions. Storage in unstirred distilled water at 15° limited infectivity to 4-8 days with concurrent reduction in lipid reserves. Some larvae became quiescent under anaerobic conditions. In unstirred water many larvae became quiescent and infectivity was lost between 8-16 days, although lipid reserves were only partially depleted under these conditions.