Nanomolar scale

Labeling of iodinated aromatics with radioactive or has proved to be a valuable approach to measure GFR in nuclear medicine. Prominent among these is sodium iothalamate, which is specifically marketed in the US for GFR measurement by the name Glofil . Studies have shown that the clearance of this marker by the glomeruli is reproducible, simple, reliable and accurate, especially in children and those with advanced renal diseases [234]. This marker can also be administered by subcutaneous infusion to obtain GFR values without the need for urine collection [235]. Since very low doses (nanomolar scale) of radioactive aromatics are administered, monitoring of renal function may be achieved without disruption of normal physiologic functions. Concerns over radioactivity and associated handling costs may prevent the use of these compounds for routine GFR measurements. 

H.H. McAdams and A. Arkin. It s a noisy business genetic regulation at the nanomolar scale. Trends Genet., 15 65-69, 1999. 

Chemoenzymatic synthesis. As for other indole positions, enzymatic prenylation appears to become competitive. Li employed the 4-dimethylallyltryptophan synthase FgaPT2 [211] and the 7-dimethylallyltryptophan synthase DM ATS [212] (both from Aspergillus fumigatus) to prenylate tryptophan derivatives (286) on the 100 nanomolar scale. In all cases shown in Scheme 54, yields >90% were obtained overnight, based on recovered starting material. As coupling partner, ammonium prenylpyrophosphate (8) was used as always. 

Carbohydrate microarrays consist of surfaces to which sugars are coupled in a nanomolar scale. To fabricate the microarray slides, carbohydrate compounds bearing a functionalized linker are, usually, chemically synthesized. Subsequently, the sugar compounds are printed onto glass slides coated with reactive surfaces using automated arraying robots. 

Tetra-substituted carboxyl iron phthalocyanine entrapped silica (TCFePc-Si02) nanoparticles have been shown to analyse the concentration of vitamin Bi (Zou and Chen 2007) at nanomolar scale. In this procedure, TCFePc-Si02 nanoparticles were used to catalyze the oxidation reaction of thiamine by hydrogen peroxide to form the highly fluorescent species, thiochrome. It produces a strong emission at 440 nm upon excitation at a wavelength of 370 nm. The fluorescence emission intensity and concentration of vitamin Bj were linearly related. The method was applied to determine the vitamin Bi content in tablets and a vitamin B complex. 

The SPOT synthesizer mentioned earlier avoids the clogging problem because the filtration support becomes the synthetic substrate (36). The size of the individual spots on which the synthesis is performed determines the scale and throughput of the synthesis. Usually, only nanomolar amounts of peptides are... 

The reactions controlling the lifetime of ozone at the surface depend on the chemical composition of the aqueous film. If this is not specified, it is therefore not possible to estimate the steady-state concentration for this photooxidant in the aqueous phase. However, the chemical effect of ozone in films or atmospheric droplets can be estimated by assuming that the steady-state concentration of ozone is still in equilibrium with the concentration of the ozone in the atmosphere. An atmospheric concentration of ozone of 1012 molecules per cubic centimeter would result in an aqueous equilibrium concentration of about 1 nanomolar (20°C) as the environmental factor to be considered in the aqueous film. Figure 7 gives examples for the rate constants for different types of compounds and a scale for the corresponding half-lives of these compounds exposed to the estimated concentration of ozone. (For further rate constants see Ncta et al., 1988 or Hoigne and Bader, 1983 and Hoigne et al., 1985). 

Certain tetravalent sLe -glycans are extremely potent inhibitors of L-selectin-depen-dent lymphocyte traffic to sites of inflammation with IC values in the nanomolar range. Large-scale synthesis of the lead compounds is needed for in vivo experiments in models if acute inflammation such as reperfusion injury and rejection of organ transplants. 

Nakanishi s method is based on the splitting of CD waves when two chromopho-res on a chiral molecule are close in space (the dibenzoate rule). Such is the case with dibromobenzoates of sugars which have a 1,2 or 1,3 relationship. In the first version of the method, saponins were permethylated, methanolyzed with acid and the liberated OH positions were p-bromobenzoylated (44). As terminal sugars are fully methylated and UV transparent, they need not be considered. Branched sugars (two substitutions at least) 3deld di-or tri-benzoates with exciton-split CD curves. The difference in Ae values of the two extrema of split CD curves is directly related to the respective positions of the benzoates (1, 2 eq-eq = 1, 2 eq-ax = 62 1, 2 ax-ax = 6 1, 3 eq-eq = 0 1, 3 eq-ax = 16). The sensitivity of circular dichroism makes the method suitable for microassays. Typical analyses are performed on a 100 pg scale (nanomolar levels). 

Just like units of weight and volume, the scale of molar concentration goes down in metric factors of 1000, and in biochemistry substances are generally in the mil-limolar (mM), micromolar ( xm) or even nanomolar (nM) ranges of concentration. 

Non-competitive inhibition was induced by metal ions (Mondal et al. 2000). The inhibition constant for Cu and Hg are in the micromolar and that for Ag is in the nanomolar range. pH dependence studies of the inhibition indicated that at least two ionisable groups of xanthine oxidase are involved in the binding of these metal ions. Xanthine oxidase formed optically observable complexes with Cu ion (Sau et al. 2001). The pH dependence studies of the formation of Cu -xanthine oxidase by optical spectroscopy and circular dichro-ism showed that at least one ionizable group may be responsible for the formation of the complex. EPR studies showed that Cu ion binds to xanthine oxidase with sulphur and nitrogenous ligands. A transient kinetic study of the interaction of Cu with xanthine oxidase showed the existence of two Cu bound xanthine oxidase complexes formed at two different time scales of the interaction, one at <5 ms and the other one at around 20 s. The complex formed at longer time scale may be responsible for the inhibition of the enzyme activity. 

Figure 11 Ultra-trace level analysis of an amino acid standard using the automated, capillary-scale amino acid analyzer. A 2 pL, low nanomolar amino acid standard (top trace) and blank (bottom trace) is derivatized and preconcentrated using the automated amino acid analyzer. The samples were contained in a polypropylene, 384-weU microtiter plate. The reagents were added, mixed, and siphoned for injection using the fused silica needle of the autosampler (Figure 14). The time axis is truncated to highlight the elution window of the amino acid derivatives. All separation and detection parameters are as described in Figure 9.

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