Solvent radiolabeled

Validation of true extraction efficiency normally requires the identification and quantitation of field-applied radiolabeled analyte(s), including resulting metabolites and all other degradation products. The manufacturer of a new pesticide has to perform such experiments and is able to determine the extraction efficiency of aged residues. Without any identification of residue components the calculation of the ratio between extracted radioactivity and total radioactivity inside the sample before extraction gives a first impression of the extraction efficiency of solvents. At best, this ratio is nearly 1 (i.e., a traceability of about 100%) and no further information is required. Such an efficient extraction solvent may serve as a reference solvent for any comparison with other extraction procedures. 

Concentrations of radiolabeled proteins, substrates, or products can be quantified by scintillation counters, which detect both emitters of weak (e. g., 3H) and high energy (e.g., 32P) by excitation of an organic solvent (e.g., toluene) which then emits fluorescence fight. In commercial systems the primary fluorescence is transformed via one or two additional fluorescent dyes in the solution into a visible emission signal which can easily be detected by conventional photomultipliers. 

Enhancement of cholesterol solubility by high molecular weight DHS in river water, where solvent extraction of the radiolabeled cholesterol was ineffective as a means of recovery unless the OM content was altered by UV radiation. 

Note (1) the liquid must be a non-solvent for the drug powder to be radiolabelled some suitable ones include water for budesonide, chlorofluorocarbon 11 for salbutamol... 

Know the physical properties of the substances with which you are working. Keep in mind that some compounds (such as acetaldehyde and tritiated water) have low boiling points. Again, keep in mind that some gloves do not offer an adequate barrier to certain chemicals. Some compounds enter the body with such facility that special care must be exercised when they are in use. One example is dimethyl sulfoxide, which as a solvent facilitates the entry of many solutes into the body. There are many known cases where radiolabeled compounds contaminated individuals who failed to consider this power of DMSO as a solute vehicle. 

Residue depletion studies with radiolabeled furazolidone have shown that the almost complete degradation of the drug in the body resulted in formation of a variety of protein-bound metabolites that were not solvent-extractable. Thus, when pigs were given radiolabeled furazolidone orally at 16.5 mg/kg bw/day for 14 days (123), total residual radioactivity in liver, kidney, muscle, and fat accounted for 41.1 ppm, 34.4 ppm, 13.2 ppm, and 6.2 ppm furazolidone equivalents, respectively, at zero withdrawal (132). Total residues were substantially lower by 21 days withdrawal, but were still in the ppm range at 45 days withdrawal. Extraction of the incurred muscle tissue at 0 and 45 days withdrawal with organic solvents led to removal of 21.8 and 13.7% of the total radioactivity, respectively. In contrast, 44 and 8.3% of the total radioactivity was extracted from liver on days 0 and 45, respectively. 

Following implantation of 200 mg of radiolabeled trenbolone acetate in calves and heifers, maximum levels of residues in tissues occurred at about 30 days postimplantation (31). The highest total drug-related residues expressed as trenbolone equivalents were approximately 50 and 3 ppb in liver and muscle, respectively. Only 25% and 10% of those residues could be extracted by ether or ethyl acetate from glucuronidase-treated liver and muscle samples, respectively. Tire majority of trenbolone residues were not extractable by organic solvents, a finding suggesting that they were covalently bound to tissues (32). 

Plants may have a role to play in enhancing microbial biodegradation of halogenated solvents, for it has recently been shown that mineralization of radiolabelled trichlorodiylene is substantially greater in vegetated rather... 

A fully concerted mechanism for reaction 299 has been eliminated as inconsistent with 14C and 15N KIEs and also with the observed inverse solvent D2O effect. The reaction path for the deamination of AMP has been formulated613 as a stepwise conversion involving the formation of tetrahedral intermediate 515 characterized by full-bonded hydroxyl and amino groups (equation 300). The TS for slow formation of 515, resulting from the attack of the hydroxyl from enzyme zinc-activated water at the C(6), is characterized by the C(6) OH bond order of 0.8 0.1 (late TS) and fully bonded NH2, that is by the nearly complete conversion to sp3 at C(6), and by nearly complete protonation of Nq), 516, The protonation of NH2 (in 515) and departure of NH3 (with TS 517) take place in the subsequent rapid steps as shown in equation 300, Zinc hydroxide is formed prior to attack514 at C(6). Enzymatic degradation of [6-14C]AMP has been carried out to prove the position of the radiolabel in 513 (equation 301). No radioactivity in the allantoin... 

A two dimensional TI/ system was developed to attempt the purification of Thy-1 glycolipid using only one plate. The radiolabeled glycolipid material (brain or lymphoma) was spotted in a small area in the corner of the plate. The plate was developed twice in one dimension in solvent 1 (C M W, 50 40 9, 0.02% CaCl2) and once in solvent 2 (C M W, NH4OH, 60 35 6 14) in the second dimension. Each plate was air dried for one hour then dried in vacuo for 45 minutes (between runs) to ensure dryness. 

A high-throughput assay for bacterial RNA polymerase has been successfully developed and validated using a 96-well, automated format [70], The reaction mixture contained a DNA template, nucleotide substrates (NTPs), supplemented with a-33P-labeled CTP in Tris-acetate buffer (pH 6.8). The polymerase reaction was carried out at 34°C for 40 min (providing linear kinetics). The effect of dimethylsulfoxide (DMSO), the usual solvent for test compounds used in a screen, was taken into consideration. The radiolabeled RNA transcripts were allowed to bind diethyl aminoethyl (DEAE) beads, which were then separated via filtration, and radioactivity associated with the wells was quantitated to measure the RNA polymerase activity. The standard deviation of the measured activity was typically < 15% of the average. Use of this assay to screen for RNA polymerase inhibitors from chemical libraries and natural products led to the identification of DNA intercalators (known to inhibit RNA polymerase activity), rifampicin (a known inhibitors of RNA polymerase), and several derivatives of rifampicin from Actinomycetes extracts. Therefore this assay can be reliably utilized to detect novel inhibitors of bacterial RNA polymerase. 

Cheng-Lee et al. (2005) demonstrated the multistep synthesis of a radiolabeled imaging probe in a PDMS microreactor, consisting of a complex array of reaction channels, with typical dimensions of 200 pm (wide) 45 pm (deep). Employing a sequence of five steps, comprising of (1) [18F] fluoride concentration (500 /iCi), (2) solvent exchange from H20 to MeCN, (3) [18F]fluoride substitution of the D-mannose triflate 252 (324 ng), to afford the labeled probe 253 (100 °C for 30 s and 120 °C for 50 s), (4) solvent exchange from MeCN to H20, and finally, (5) acid hydrolysis of 254 at 60 °C, the authors demonstrated the synthesis of 2-[18F]-FDG 254 (Scheme 72). 

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