The phrase "a pka of" is not correct in standard written English.
It seems to be an incomplete expression, possibly referring to "a pKa of" which is used in scientific contexts, particularly chemistry, to describe the acidity of a substance.
Example: "The compound has a pKa of 4.75, indicating its strength as an acid."
Alternatives: "a dissociation constant of" or "an acidity constant of".
Sulfinic acids are weaker (having a pKa of roughly 2.2) and less stable than sulfonic acids.
These nucleophiles have a pKa of ≥50, more than 25 orders of magnitude more basic than the nucleophiles that are typically used in such transformations.
The fluorescence ratio at 339/351 nm as a function of pH shows a sigmoidal relationship between monomer and dimer populations, with a pKa of dimerization at pH 6.5 (ref. 33).
Predictions for the acidic function of DONA compare well with PFOA's, with a pKa of 0.8 1.5 and a E0 of 2.07 2.15 V.
Inhibitor binding depends on a pKa of ∼6.5 in the free enzyme and on a pKa<3.0 when the inhibitor is bound to subtilisin.
The major features of the novel probe include two well-resolved (>100 nm) emission peaks, strong fluorescence under acidic conditions, a pKa of 4.69, low cytotoxicity and good cell membrane permeability; features which render the probe useful for monitoring pH variations from neutral to acidic conditions in living cells.
The sensors show large (ca. 300 fold) pH dependent luminescence enhancements for the Eu III) lanthanide emission, i.e. it is 'switched on' in highly acidic media, between pH ca. 1.5 and 3.5 with a pKa of 2.4 (±0.1) when excited at 350 nm.
Interestingly, we observed an pKa of 7.79 for the catalytic H199, which implies that this residue is protonated only in acidic conditions.
The EP4 receptor generates intracellular cyclic AMP (cAMP) via coupling to Gs proteins leading to activation of protein kinase A (PKA), phosphorylation of cAMP-response element binding protein (CREB) and PKA-dependent activation of extracellular signal-related kinase (ERK)[ 32].
RP1 was fluorescent in the pH range of 1.1 3.1 and has a pKa value of 2.08 (±0.07).
The substitution of N354D influenced the pH profile by weakening the bondage with the side chain of D353, which caused a pKa shift of the catalytic centre.
