Improved mass spectrometric detection of acidic peptides by variations in the functional group pK_a values of reverse micelle extraction agents

Abstract

Polymeric reverse micelles can be used to selectively extract peptides from complex mixtures via a two-phase extraction approach. In previous work, we have shown that the charge polarity of the hydrophilic functional group that is in the interior of the reverse micelle dictates the extraction selectivity. To investigate how the extraction is influenced by the inherent pK of the functional group, we designed and tested a series of polymeric reverse micelles with variations in the hydrophilic functional group. From this series of polymers, we find that the extraction capability of the reverse micelles in an apolar phase is directly related to the aqueous phase pK of the interior functional group, suggesting that the functional groups maintain their inherent chemistry even in the confined environment of the reverse micelle interior. Because these functional groups maintain their inherent pK in the reverse micelle interior, they provide predictable extraction selectivity upon changes in aqueous phase pH. We exploit this finding to demonstrate that sulfonate-containing polymers can be used to remove basic peptides from complex mixtures, thereby allowing the improved detection of acidic peptides. Using these new materials, we also demonstrate a new means of isoelectric point (pI) bracketing that allows the mass spectrometric detection of peptides with a defined and narrow range of pI values.

ATR FTIR Study of the Interaction of TiO2 Nanoparticle Films with β-Lactoglobulin and Bile Salts

“…The point of zero charge of P25 titanium dioxide is likely to be close to pH 6, based on the values published for anatase (which makes up 90% of the P25 sample) . Meanwhile, the sulfonate group on taurocholic acid has a p K a between 0.5 and 2 and glycine-conjugated bile acids have a p K a of approximately 3.9 in water …”

Synergistic Interplay of Covalent and Non‐Covalent Interactions in Reactive Polymer Nanoassembly Facilitates Intracellular Delivery of Antibodies

“…To test this possibility, we synthesized a random copolymer consisting three different monomeric units, bearing PFP carbonate ester, PEG and 3‐sulfopropyl functionalities with a compositional ratio of 2:6:2 ( P Ab , Figure 4 a, see Supporting Information). Sulfonate moiety, having p K a ≈−0.5, [20] would remain as negatively charged at the conjugation pH 8.5, for interactions with positively charged groups on protein surface. To verify the effect of mere electrostatic interactions in protein conjugation, we also synthesized a control polymer consisting PEG and sulfopropyl moieties (SO3‐polymer, Figure 4 a, also see Supporting Information).…”

Synergistic Interplay of Covalent and Non‐Covalent Interactions in Reactive Polymer Nanoassembly Facilitates Intracellular Delivery of Antibodies

“…[18,19] We hypothesized that once electrostatically drawn to polymer,t he proximity-induced reactivity between lysine functionalities from the protein and the activated carbonate esters on polymer backbone should increase.T o test this possibility,w es ynthesized ar andom copolymer consisting three different monomeric units,b earing PFP carbonate ester,P EG and 3-sulfopropyl functionalities with acompositional ratio of 2:6:2(P Ab ,F igure 4a,see Supporting Information). Sulfonate moiety,h aving pK a %À0.5, [20] would remain as negatively charged at the conjugation pH 8.5, for interactions with positively charged groups on protein surface.T overify the effect of mere electrostatic interactions in protein conjugation, we also synthesized ac ontrol polymer consisting PEG and sulfopropyl moieties (SO3-polymer, Figure 4a,a lso see Supporting Information).…”