Spectral Study of 1,4-bis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzene (PPB): UV-VIS Absorption Spectra Investigation in Single and Binary Solvents and Spectrophotometric Determination of the Dissociation Constant (pK_b)

Abstract

The effect of solvents of different polarity and hydrogen bonding ability on electronic absorption spectra of PPB was investigated. UV absorption spectra (200-400 nm) were recorded in five single solvents and one binary solvent (DCM-EtOH). PPB has two absorption maxima (250 and 280 nm) due to pyridyl pyrazole and benzene systems. The spectral shifts and absorption maxima in various solvents were correlated with the Kamlet and Taft parameters (α, β and π*) using linear solvation energy relationships. The multiparametric analysis indicates that hydrogen bond donor ability of the solvent (for band I) and non-specific dipolar interactions of the solvents (for band II) play an important role in absorption maxima of PPB in pure solvents. Index of preferential solvation was calculated as a function of solvent composition. Preferential solvation by ethanol (band I) and by dichloromethane (band II) was detected in DCM-EtOH solvent mixture. The pKb of PPB in two solvent mixtures; EtOH -H2O & THF -H2O, were determined using UV-Vis spectrophotometry. Two graphical methods were used to estimate the base dissociation constant (pKb) using absorbance measurements. The resulting average of pKb values in the two solvent mixtures using the two methods were 10.77 and 11.14 with a standard deviation of 0.03 & 0.33, respectively.

Recent Advancements in Spectrophotometric pKa Determinations: A Review

“…In the first study, the pKa of PPB (1,4-bis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzene) in the solvent mixtures: EtOH -H 2 O and THF -H 2 O, was considerded to be: 10.77 and 11.14 respectively. 15 In the latter, the pKa(s) of Nilutamide: approximately 10 and 14 were determined ( Figure 1B). 16 Retention time and electrophoresis mobility are depended on the pKa of the analyte and the pH of the mobile phase or analytical medium.…”

Determination of Stoichiometry and Stability Constant of Cd(II) and Zn(II) Complexes with Pyrazole Based Ligands in Mixed Solvent (EtOH-H2O)

“…There are already a number of articles accessible in the literature on pyrazole-containing ligands and their complexes [11][12][13][14][15][16][17][18]. Several methods for determining stability constants have been developed, including potentiometric titration, spectrophotometry, capillary electrophoresis, and many others [19][20][21][22]. Spectrophotometric methods are often quite sensitive, making them ideal for investigating chemical equilibria in solution.…”

“…The chemistry of nitrogen-containing heterocycle-based ligands is of particular interest since they represent a significant class of natural and synthesized compounds, many of which have beneficial biological effects [1][2][3][4][5]. F. Blau [6] pioneered the coordination chemistry of transition metals and nitrogen-containing heterocyclic ligand 2,2'bipyridine.…”

Two Different Strategies Based on Three‐Way Analysis Models of UV Spectroscopic and Spectrochromatographic Measurements to Quantify the Acidity Constant of Acetylsalicylic Acid

“…The conventional method, potentiometry, requires a chemical titration procedure with a large amount of reactant and analyte for the estimation pKa values. In other techniques, namely spectrophotometry, voltammetry, HPLC and CE, the determination of acidity constants have been performed by graphic estimations based on the relationship between pH and measured response, [13][14] or calculations based on hard [6,[15][16] or soft model equations. [17][18][19] These mentioned conventional approaches may fail to quantify acid-base equilibrium constants due to complexity of experimental conditions, variations from the established experimental procedure and multiple pKa measurements.…”