Measuring log

The superpositioning of experimental and theoretical curves to evaluate a characteristic time is reminiscent of the time-tefnperature superpositioning described in Sec. 4.10. This parallel is even more apparent if the theoretical curve is drawn on a logarithmic scale, in which case the distance by which the curve has to be shifted measures log r. Note that the limiting values of the ordinate in Fig. 6.6 correspond to the limits described in Eqs. (6.46) and (6.47). Because this method effectively averages over both the buildup and the decay phases of radical concentration, it affords an experimentally less demanding method for the determination of r than alternative methods which utilize either the buildup or the decay portions of the non-stationary-state free-radical concentration. 

As shown in Figure B2.1, double-beam spectrophotometers automatically record the true absorbance by measuring log(IR/Is), thanks to a double compartment containing two cuvettes, one filled with the solution and one filled with the solvent. Because the two cuvettes are never perfectly identical, the baseline of the instrument is first recorded (with both cuvettes filled with the solvent) and stored. Then, the solvent of the sample cuvette is replaced by the solution, and the true absorption spectrum is recorded. 

Lipophilicity appears in several Quantitative Structure-Activity Relationships (QSAR) studies [16], emphasizing its importance. Different in vitro assays have been reported to measure lipophilicity from the classical shake-flask technique that still remains the reference for lipophilicity measurements to more actual methodologies. The first procedure is time-consuming, sensitive to impurities and the measurable log Poct range restricted to -3 to 3 [17]. 

To obviate to these problems and to increase the productivity, short columns packed with small porous particles (sub-2 pm), and high flow rates that decrease the analysis time and extend the range of measurable log Poct were recently applied in HPLC and UHPLC [18-20] with a gain in terms of chromatographic performance. 

A quantitative analysis of the structure-retention relationship can be derived by using the relative solubility of solutes in water. One parameter is the partition coefficient, log P, of the analyte measured as the octanol-water partition distribution. In early work, reversed-phase liquid chromatography was used to measure log P values for drug design. Log P values were later used to predict the retention times in reversed-phase liquid chromatography.The calculation of the molecular properties can be performed with the aid of computational chemical calculations. In this chapter, examples of these quantitative structure-retention relationships are described. 

Kaliszan and Markuszewski [23] used the 20-compound Young s data set with slightly different parameters and reported several equations. In Eq. 22, they used the measured log P values given by Young and workers together with the molecular weight ... 

The enthalpy of complexation can be measured directly by reacting the metal and ligand in a calorimeter. It can also be determined indirectly by measuring log at different temperatures and applying the equation... 

SF Shake flask, referring to traditional method to measure log P or log D... 

Consequently, the SDS microemulsion system is the best model for indirect measurement of log Pow. However, this is valid only for neutral solutes. We reported that the relationship between MI and log Pow for ionic solutes is different from that for neutral solutes (49). This would be caused by the ionic interaction between ionic solutes and the ionic microemulsion as well as ionic surfactant monomer in the aqueous phase. Kibbey et al. used pH 10 buffer for neutral and weak basic compounds and pH 3 buffer for weak acidic compounds (53). Although their purpose was to avoid measuring electrophoretic mobility in the aqueous phase, this approach is also helpful for measuring log Pow indirectly. 

Two retention indices are then measured, log kgs (log k obtained with a mobile phase containing 95% of acetonitrile and 5% of buffer solution) and log ko (retention factor obtained with a pure aqueous mobile phase). The difference between these two values (log ko 9s) is correlated to the 1-octanol/water partition coefficient of the neutral form of tested compounds (Equation 5.13) ... 

What requirements must parameters fulfil in order to be suitable in the search for new drugs The type of parameter which is principally suitable depends on the respective problem, i.e. whether we are concerned with series design or with derivation of structure-activity-relationships. In the former case only parameters which can be calculated directly from the chemical structure can be used whereas in the latter case one can also (and preferably) apply measured parameters. Thus, measured log P values as well as calculated ones ( ) are suitable in structure-activity-analysis, whereas for series design lipophilicity can only be represented by the calculated values. 

Another approach to the study of proteins has been the reaction of silver ions with simpler model compounds, for example di- and tri-peptides.416 The reaction with glycylglycine was first studied in 1951 and the formation constants for 1 1 and 1 2 complexes were determined.403 Thermodynamic parameters for these reactions have since been measured (log 0i = 2.90, logp2 = 5.65, AHfo = -56.9 0.8kjmol"1, ASj32 = -80.5 3 JK"1 mol"1).416... 

Veith et al. [20] studied the correlation between Kow and (C is) reversed-phase HPLC retention time for a wide variety compounds, such as substituted benzenes, PAHs, and PCBs. Their calibration set consisted of benzene, bromobenzene, biphenyl, bibenzyl, DDE, and 2,2, 4,5,5 -pentachlorobiphenyl with measured log Kow values of 2.13, 2.99, 3.76, 4.81, 5.69, and 6.11, respectively. Similarly, Chin et al. 

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