Guidelines for NMR measurements for determination of high and low pKa values (IUPAC Technical Report)

Abstract

Factors affecting the NMR titration procedures for the determination of pKa values in strongly basic and strongly acidic aqueous solutions (2 > pH > 0 and 14 > pH > 12) are analyzed. Guidelines for experimental procedure and publication protocols are formulated. These include: calculation of the equilibrium H+ concentration in a sample; avoidance of measurement with glass electrode in highly acidic (basic) solutions; exclusion of D2O as a solvent; use of an individual sample isolated from air for each pH value; use of external reference and lock compounds; use of a medium of constant ionic strength with clear indication of the supporting electrolyte and of the way the contribution of any ligand to the ionic strength of the medium is accounted for; use of the NMR technique in a way that eliminates sample heating to facilitate better sample temperature control (e.g., 1H-coupled NMR for nuclei other than protons, GD-mode, CPD-mode, etc.); use of Me4NCl/Me4NOH or KCl/KOH as a supporting electrolyte in basic solution rather than sodium salts in order to eliminate errors arising from NaOH association; verification of the independence of the NMR chemical shift from background electrolyte composition and concentration; use of extrapolation procedures.

Tetrahedral CoII Complexes with CoI2O2 and CoO2S2 Cores – Crystal Structures of [Co{HN(OPPh2)(SPPh2)‐O}2I2] and [Co{N(OPPh2)(SPPh2)‐O,S}2]

“…The pK a values of the HL (OS) and HL (SS) ligands were determined by NMR spectroscopic measurements according to the guidelines reported in the IUPAC Technical Report. [23] The 31 Supporting Information, section S3). Visible absorption spectra were measured with a Nicolet Evolution 300 spectrophotometer.…”

Aminoalkylbis(phosphonates): Their Complexation Properties in Solution and in the Solid State

“…The highest dissociation constants were determined by NMR titration following the procedure described recently in the literature. [17] The ligands H 4 pam, H 4 ale, H 4 meth and H 4 prop exhibit similar acid-base behaviour, with five protonation constants spread over the whole pH range ( Table 2). The first two pK a 's lie in the strongly acidic region and correspond to the first deprotonation of each phosphonic acid group.…”

Synthesis and Activity of Biomimetic Biofilm Disruptors

“…Cumulative association constants were calculated by HypNMR 14,15 (Figures S2–S11), and values for p K a (D 2 O) were finally converted to p K a (H 2 O). 16 The p K a values for the compounds are given in Table 2. For comparison, similar p K a values have been reported previously for spermidine (p K a1 = 10.90, p K a2 = 9.71, and p K a3 = 8.25).…”