Effect of buffer on heparin binding and sensing in competitive aqueous media

Abstract

Although buffer-specific effects on molecular recognition are known in biological science, they remain rare in supramolecular chemistry. The binding between a cationic dye, Mallard Blue (MalB), and polyanionic heparin in aqueous NaCl (150 mM) is studied in three commonly-used buffers (Tris-HCl, HEPES, Phosphate, each 10 mM). Although MalB has a very similar UV-Vis spectrum in each buffer, the sensory response towards heparin was different in each case. This can be ascribed to differences in the complex formed. In Tris-HCl which has the least competitive chloride counter-anions, MalB exhibits a hypsochromic shift of 25 nm, assigned to strong binding and aggregation of the dye on heparin. In more competitive HEPES, containing a sulfonate anion, there is weaker binding and less aggregation of MalB along the heparin; the hypsochromic shift is only 15 nm. In phosphate buffer, MalB can interact quite strongly with buffer phosphate anions; although heparin binding is still observed, the hypsochromic shift associated with dye aggregation is only 5 nm. As such, specific buffer interactions with the MalB-heparin complex mediate host-guest binding and sensing. Buffer choice must be made carefully in studies of molecular recognitionwe would caution against using phosphate and sulfonate containing buffers when studying electrostatic binding.

Dynamic light scattering studies of the effects of salts on the diffusivity of cationic and anionic cavitands

“…As a result, as Smith has eloquently pointed out [1], the effects of buffers and salts on dissolved organics can be quite bewildering. Why is this?…”

Specific Buffer Effects on the Intermolecular Interactions among Protein Molecules at Physiological pH

“…Kim et al reported the first pioneering work on the specific effect of buffers measuring the activity of restriction enzymes . After that, buffer specificity was observed for lipase activity, lysozyme electrophoretic mobility, antibody aggregation, , lysozyme adsorption on ordered mesoporous silica, binding of a cationic dye to heparin, and amyloid fibril formation mechanism and in other works. − Different from the specific effects of strong electrolytes, for which a myriad of experiments and different theoretical approaches are available, − for buffers there is much less experimental evidence, and moreover, no theory has been developed yet.…”

Photobleaching of Erythrosine B in Aqueous Environment Investigation Beyond pH†

“…However, the buffer role extends beyond pH and the Henderson-Hasselbalch textbook equation that considers pK a as the only parameter of importance (28). Nowadays, there are increasing evidences that highlight specific buffer effects (28)(29)(30). Indeed, buffer solutions are known to play roles in cellular mechanisms from influencing cellular growth to modifying lipid interactions (31,32).…”

“…For instance, a recent study showed that the electrophoretic mobility of lysozyme recorded at the exact same pH was vastly different depending on the buffer employed (34). Since then, specific buffer effects have been highlighted in protein-surface interactions (35)(36)(37), supramolecular recognition (30,38,39), protein diffusion (40), protein-protein interactions (40,41) and protein structural and thermal stability (42).…”