Folds concentric

As stated above, calcium is an extremely important cellular ion for several cellular functions. The concentration of calcium in human extracellular fluid is about 2.5 mM, while the intracellular concentration is only 100-200 nM depending on the cell type. Thus, there is 10 000-20 000 fold concentration difference between the cell interior and exterior that has to be maintained by cellular pumping mechanisms. This requires a large amount of energy. " ... 

Intracellular Ca2+-levels are controlled by release into, and removal from, the cytoplasm (Fig. 1). Ca2+-pumps in the plasma membrane and endoplasmic reticulum (ER the Ca2+-store in a cell) keep cytoplasmic Ca2+-levels low (about 0.1 pmol/L in resting cells) and generate a 10,000-fold concentration gradient across membranes (because extracellular Ca2+ is in the millimolar range). Upon stimulation, Ca2+ enters the cytosol of the cell via Ca2+-channels (plasma membrane) or via Ca2+-channels in the ER, leading to the activation of a great variety of Ca2+-dependent processes in the cell. 

These results are plausible since according to Sand a two-fold concentration of a component yields a four-fold transition time. Now, these features show, in contrast to the net separation and pure additivity of polarographic waves and their diffusion-limited currents as concentration functions, that in chrono-potentiometry the transition times of components in mixtures are considerably increased by the preceding transition times of any other more reactive component, which complicates considerably the concentration evaluation of chronopotentiograms. 

These observations were noted over a two-fold concentration (.7 to 1.4 wt.%) change in montmorillonite. 

Wen et al. [950] used 8-hydroxyquinoline immobilised on a polyarylonitrile hollow fibre membrane to achieve a 300-fold concentration factor for rare earth elements in seawater. 

When dopa was oxidized using the PIPo-Cu catalyst, the distinguished acceleration was observed as compared with the PVIm-Cu or imidazole-Cu catalysts (Fig. 6). An increase in content of the N-vinylpyrrolidone residue in the PIPo copolymer caused higher activity of the Cu complex for the dopa oxidation. The similar acceleration was also produced when N-methyl-pyrrolidone was added to the system of PVIm-Cu. However, nearly 103 fold concentration of the pyrrolidone residue was necessary as compared with the PIPo copolymer. Addition of homopolymer of N-vinyl-pyrrolidone to PVIm-Cu caused no acceleration. 

The individual inhibitors are made as stock solutions, mosdy 1000-fold concentrated with respect to final dilution. Add the stock solutions immediately before starting homogenization. 

The second-order rate constant for the reaction between sarin and either 2-PAM I or II was found to be 170 L/mol per minute. If a phosphorylated or phosphonylated oxime that does not enter rapidly into the second step above is formed, that product may be an Inhibitor of cholinesterase. 7,88 Hydrolysis of sarin in the presence of 200-fold concentrations of V and II took place more rapidly in plasma from rats with the former oxime than with the... 

At slightly acidic pH values weak dibasic acids H2L give on dissociation anions HL , forming ion pairs MHL with metal ions. These ion pairs are neutral for M(l), which is the case of Na(I), K(I) and ammonium ions, and electrophoretically mobile for M(ll), such as Ca(II) and Mg(II). A chromophore BH/B consisting of a weak base B, which at slightly acidic pH values is in equilibrium with its conjugate acid BH, also has electrophoretic mobility due to the latter ion and may serve for indirect UVD of the M(ll) ions. These principles have been applied as a CE method for determination of trace concentrations of Ca(II) and Mg(II) in aqueous solutions containing more than 5000-fold concentrations... 

Therefore, an additional cleaning and quality assurance step was used. Columns of 100 mL of resin were prepared and eluted with 200 mL of ether. The ether was then concentrated to 1 mL by Kudema-Danish evaporation and analyzed by a capillary GC with an FID. This analysis showed that many peaks were not removed after 200-fold concentration, and additional resin cleaning steps were needed. Alternate elution of the resin with successive single bed volumes of... 

Another adsorption system evaluated was a high-volume, high-pressure, macroporous-resin-based concentrator system designed to provide a 10,000-fold concentrate. This system used four stainless steel columns in series. Columns one through four were filled with AG MP-1 (Bio-Rad), AG MP-50 (Bio-Rad), XAD-2 (Rohm and Haas), and XAD-7 (Rohm and Haas), respectively. Unlike the other adsorption processes, a pump system was employed for both the adsorption and desorption phases of the evaluation. The use of acetonitrile as the elution solvent permitted UV monitoring of the eluant. 

The method chosen to provide an aqueous concentrate was RO. The RO procedure provided 50-fold aqueous concentrates containing almost all of the organic carbon (4). However, the removal of salt that was required to achieve a 400-fold concentrate without precipitation and without forming a hypertonic solution resulted in substantial losses of organic carbon (13). 

The exponential nature of the recovery response is represented graphically in Figure 1. The necessity for selecting membranes with high organic rejections is quite apparent. For example, in a 50-fold concentration, the recovery of a compound will not exceed 70% unless membrane rejection of that solute exceeds 0.9 (90 rejection). 

Sample Concentration Experiments. A CLLE quality assurance blank was run by extracting 90 L of Milli-Q water with three CLLE samplers in a parallel configuration and concentrating the composited extract to 4 mL by Kudema-Danish evaporation. The 22,500-fold concentrate was analyzed by GC-flame ionization detection (GC-FID) and GC-MS. Thirty-two peaks were observed by using GC-FID analysis, but because of their low concentrations, only four contaminants were identified by GC-MS cyclohexene, 2-cyclohexen-1-one, n-butyl phthalate, and bis(2-ethylhexyl) phthalate. Cyclohexene is a solvent preservative that has been identified in commercial high-purity methylene chloride (16), and 2-cyclohexen-l-one is its air oxidation product. The phthalates are ubiquitous laboratory contaminants and have also been identified in commercial methylene chloride (17). 

Freeze-drying. For a 7000-fold concentration, 70 L of drinking water was lyophilized in a Virtus Unitrap II. The dried residue was then divided into equal weights and packed into two columns (25 X 1.5 cm) with a sintered glass filter. The organic material was eluted consecutively with acetone, ether, and DMSO. The ether in the ether eluate was removed by rotary evaporation, and the dried residue was dissolved in DMSO. The DMSO concentrates were sterilized by filtration over a 0.2-/xm Teflon filter (Millipore). The acetone and DMSO concentrates were tested in the Ames test. 

Figure 1. Effect of resin type on the mutagenic activity of drinking water concentrates in the Ames test. The sampling, 7000-fold concentration with either XAD-2 or XAD-4/8, DMSO elution (20 mL, neutral fraction), and subsequent mutagenicity testing were as described in Materials and Methods. Similar concentrates of The Hague tap water were used as controls. Each point represents the average of four plates, and 0.50 mL of concentrate corresponds to 3.5 L of water per plate.

Figure 4. Molecular weight determination of a drinking water concentrate with Sephadex LH20. Sampling, 10 -fold concentration of drinking water before and after chlorination (L5 mg/L of CI2, Meuse River source) on XAD-4/8, elution with DMSO (neutral fraction), and subsequent gel filtration were as described in Materials and Methods. After measuring the absorbance at 263 mm, the fractions were pooled as indicated. After dilution in water, the fractions were reconcentrated on XAD-4/8, eluted with DMSO, and assayed in the Salmonella mutagenicity test (strain TA98 S9).

Figure 6. Fractionation of a mutagenic drinking water concentrate with Sephadex LH20. On a Sephadex LH20 column, 1.6 mL of a drinking water concentrate (IX 106-fold concentrated, neutral fraction) was separated by using stepwise isopropyl alcohol (ISOP) and dioxane/water (D/W) elution as described in Material and Methods. Fractions were pooled as indicated. After reconcentration the fractions were assayed for mutagenic activity in the Salmonella mutagenicity test and CHO cells (Table I).

Figure 10. Influence of a chlorine treatment on the mutagenic activity detectable with TA98NR and TA100NR strains. Sampling, 7000-fold concentration of water samples before and after a chlorine treatment (1.5 mg/L of Ch) on XAD-4/8, elution with DMSO (neutral fraction)> and subsequent testing of the DMSO concentrate in the Salmonella mutagenicity test were as described in Materials and Methods. Each value represents the average of three plates, and 0.2 mL of concentrate corresponds to 1.4 L of...

The pineal gland appears also to play a role in maintaining the mammalian circadian cycle.1081-1083 The concentration of the pineal hormone melatonin (Fig. 27-11) as well as its precursor N-acetylserotonin and the enzyme serotonin N-acetyltransferase (Eq. 30-4) all fluctuate far more than do the concentrations of other metabolites during the 24-h cycle. These metabolites increase over 10-fold concentration at night and decrease by day. During the daytime the serotonin N-acyltransferase, which forms the precursor, is rapidly... 

The term folded oils refers to concentrated oils. This typically involves a distillation process however, alcohol washing can also be used. Alcohol washing is based on the insolubility of d-limonene in 60% to 70% ethanol. These processes predominately remove terpene compounds, although aldehydes (octanal) are also reduced. Oils that are more than 20-fold concentrated are called terpeneless oils and are more stable. Distillation is predominately used by flavor houses. Flavor houses purchase cold-pressed oil, which is concentrated and fractionated. These fractionated portions are sold for flavorings or flavor precursors. 

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