Magnesium Probes

Figltfe194S. DeiieiideiiceofFiiaseaii (9)andiiio(kilation(m)of Soditiin Onea on Na concentratioii. Excttadon was at 514 nm, arid einlaaion above 530 nm was observed. Data from Ref. 122. 

Green series all increase on Ca binding, alloanng the calcium concentration to be determined ftom the Sfe-times. One of the first calcium probes, Quin-2, also displays a 10-fold increase in lifetime when boimd to 

Fi uie19.52. chwnicalstructuies of the calcium prob Indo-1 and the magneaiuni probe Mag-Indo-I- Revised Itom Ret 152. 

Althougli the use of the calcium probes seems stnugfit-finward. calibration is difficult when such probes are located within cells. Reference 141 should be consulted fin a detailed description of the calibration procedures. When Used as iniracdlular indicalDrs, tbecalcium probes are typically calibrated in the presence of otlra intracellular ions at thdr expected concentrations, Also, it is difficult to maintain nanomolar Ca concentrations. 

For completeness, we note that Ca probes have also been developed using azacrown ethers as the chelator, rather than BAPTA. However, these probes have been studied mostly in organic solvents and used to study the effects of Cif on dectron transfer. Such probes have not found use in cell physiology. Magnesium-sensitive probes are also available (Table 19.4), and some have been characterized as lifetime probes. These probes typically have the AFTRA chdator, father than BAFTA, as can be seen for the calcium probe Indo-1 and the analogous magnesium probe Mag-Indo-1 (Hguie 19.52). 

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Szmacinski, H. Lakowicz, J. R. Fluorescence lifetime characterization of magnesium probes improvement of Mg " " dynamic range and sensitivity using phase-modulation fluorometry. J. Fluoresc. 1996, 6, 83-95. 

Calcium sensors are merely representative of a much wider class of ion sensors, albeit probably the best understood. Fluorescent probes have now been developed for a wide range of metal ions of biological interest, particularly sodium, potassium, magnesium, and zinc. 

Ion Probe Magnesium Isotopic Measurements of Allende Inclusions... 

Surface characterization studies by X-ray photoelectron spectroscopy (XPS) were conducted using DuPont 650 and Perkin Elmer 5300 instruments. Samples were prepared by placing solid material on double stick adhesive tape, or by allowing solvent to evaporate from an acetone dispersion of a suspension placed on a stainless steel probe. A magnesium anode was used as the X-ray source (hv 1253.6 eV). The temperature of samples during the analysis was approximately 30-40°C and the vacuum in the analysis chamber was about 10 torr. Potential... 

By keeping the same fluorophores, but reducing the cavity size of the ion-ophore, we obtain PCT-13 (Mag-Indol) and PCT-14 (Mag-Fura2) (Figure 10.22), which are selective for magnesium. PCT-8, PCT-9 and PCT-11 to PCT-14 are commercially available in the non-fluorescent acetoxymethylester form so that they are cell permeant and they recover their fluorescence upon hydrolysis by enzymes (Molecular Probes, Inc., Eugene, OR). 

Fig. 10.22. Chelating PCT sensors for calcium and magnesium ions (PCT-11 and PCT-12 Grynkiewicz G. et al. (1985) J. Biol. Chem. 260, 3440. PCT-13 and PCT-14 Haugland R. P., Handbook of Fluorescent Probes and Research Chemicals, 6th edn, Molecular Probes, Inc., Eugene, OR).

Desimoni and coworkers84 probed the catalytic effect of metal perchlorate salts on the rate of the Diels-Alder reactions between malonates 88 and cyclopentadiene (equation 27). They found that especially magnesium perchlorate was able to catalyze the reaction by binding two malonates in a bidentate fashion. Reaction times were shortened up to 1000 times. The endo/exo selectivity was inverted from 89/90 = 40/60 (n =4) and 17/83 (n = 5) for the thermal uncatalyzed reactions to 89/90 = 60/40 (n = 4) and 80/20 (n = 5) for the magnesium perchlorate catalyzed reactions. 

The sensor reported by Shirai(69) used a natural carboxylic polyether antibiotic (Aem = 481 nm) for the detection of magnesium and calcium. Detection limits of I0 5 and KT4 M, respectively, were reported but, interference from other metals was difficult to overcome. Ishibashi(69) used a bulkier hexadecyl-acridine orange dye (Xem = 525 nm) plasticized in a PVC membrane for the fluorescent detection of ammonium ions. Signal interference due to superfluous ions and poor detection limits of KT5 M restricted the use of the probe. 

New probe, quantum yield, and lifetime changes are expected be similar to Calcium Green and Magnesium Green. 

Hutcheon ID (1982) Ion probe magnesium isotopic measurements of Allende inclusions. Amer Chem Soc... 

In many syntheses activation is not effected by sonochemical preparation of the metal alone but rather by sonication of a mixture of the metal and an organic reagent(s). The first example was published many years ago by Renaud, who reported the beneficial role of sonication in the preparation of organo-lithium, magnesium, and mercury compounds [86]. For many years, these important findings were not followed up but nowadays this approach is very common in sonochemistry. In another early example an ultrasonic probe (25 kHz) was used to accelerate the preparation of radical anions [87]. Unusually for this synthesis of benzoquinoline sodium species (5) the metal was used in the form of a cube attached to the horn and preparation times in diethyl ether were reduced from 48 h (reflux using sodium wire) to 45 min using ultrasound. 

A metal-nucleotide complex that exhibits low rates of ligand exchange as a result of substituting higher oxidation state metal ions with ionic radii nearly equal to the naturally bound metal ion. Such compounds can be prepared with chromium(III), cobalt(III), and rhodi-um(III) in place of magnesium or calcium ion. Because these exchange-inert complexes can be resolved into their various optically active isomers, they have proven to be powerful mechanistic probes, particularly for kinases, NTPases, and nucleotidyl transferases. In the case of Cr(III) coordination complexes with the two phosphates of ATP or ADP, the second phosphate becomes chiral, and the screw sense must be specified to describe the three-dimensional configuration of atoms. 

Because muscle cells are especially rich in terms of phosphorus-containing metabolites (e.g., ATP, ADP, phos-phocreatine, and orthophosphate), nuclear magnetic resonance " has proved to be a valuable noninvasive probe of metabolic changes attending muscle activity. The spectral sensitivity of P is especially high relative to other nuclei, and one can detect cellular concentrations as low as 0.5 mM as well as utilize chemical shift data to define intracellular pH and free magnesium ion concentrations. See also Nuclear Magnetic Resonance Chemical Shift... 

B. M. Altura and B. T. Altura, Role of magnesium and calcium in alcohol-induced hypertension and strokes as probed by in-vivo television microscopy, digital image microscopy, optical spectroscopy, P-NMR spectroscopy and a unique magnesium ion-selective electrode. Alcohol. Clin. Exp. Res., 1994,18,1057-1068. 

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