Interpretation of the dissolution of insoluble peptide sequences based on the acid‐base properties of the solvent

Abstract

The dissolution process of model insoluble peptide sequences was investigated in view of the electron acceptor (AN) and electron donor (DN) solvent properties. The Alzheimer's disease-inducing (1-42) Ab-amyloid peptide and its (1-21) fragment, the (66-97) transmembrane bradykinin B2 receptor sequence, and the strongly aggregated VVLGAAIV were selected as models of insoluble peptides. Solvents presenting similar AN and DN values failed, despite their polarities, to dissociate peptide chains (free in solution or bound to a polymer). The maximum solubility of these aggregated sequences was attained in solvents presenting the highest possible (AN-DN) values (in positive or negative mode). The AN-DN values ranged from approximately ÿ20 to +80 and, notably, the lowest dissociation power was ascribed to solvents presenting values of approximately +40. The strong hydrogen bond donor water is located in this region, indicating that, for dissociation of specific insoluble segments, the solvent should appropriately combine its acid/base strength with the potential for van der Waals interactions. We also observed a sequence-dependent pH effect on peptide solubility confirmed through circular dichroism spectroscopy. This approach also revealed a complex but, in many cases, consistent influence of peptide conformation on its solubility degree, even when structure-inducing solvents were added. In conclusion, the random method of selecting solvents to dissolve insoluble and intractable peptide sequences, still in use by some, could be partially supplanted by the strategy described herein, which may be also applicable to other solute dissociation processes.

Solvent-free MALDI-MS for the analysis of β-amyloid peptides via the mini-ball mill approach: Qualitative and quantitative advances

“…2 (10% of 4) and Mix. 3 (50% of 4), in 99.9% ACN 0.1% TFA makes peptide 4 modestly accessible°only°in°Mix.°3° (Figure°3,°Inset°4A).°Although according°to°study° [16],°4 is°not°soluble°in°ACN;°this solvent nevertheless improved the detection. However, before dissolving 4, it was homogenized with matrix to give a representative MBM sample as is evident by the successful solvent-free MALDI analysis.…”

“…For example, ␤-amyloid peptide (1-42) has very low solubility and, thus, is only soluble in solvents with low MS compatibility such as 1,1,1,3,3,3-hexafluoro-2-propanal (HFIP) and sonication (10 min) to°a°concentration°of°1°mg°mL Ϫ1° [ 15].°A°very°recent paper° [16]°evaluated°the°solubility°degree°of°(1-42)°to°be 95% in HFIP and 83% in dimethyl sulfoxide compared with MS compatible solvents with 6% in water (pH 7.4), 0% in ACN, 29% in 50% ACN:water, and 20% TFA. The solubility degree was determined by dissolving 10 mg of purified 4 in 1 mL of the respective solvent followed by centrifugation, supernatant removal, and repetition till constant weight was achieved.…”

ThT 101: a primer on the use of thioflavin T to investigate amyloid formation

“…Cleavage and purification of synthetic peptides typically involves trifluoroacetic acid (TFA), leading to TFA salts of the peptide. These are often present in lyophilized peptide preparations, along with chemical scavengers (chemical compounds added to the reaction in order to remove or de-activate impurities and unwanted reaction products) and can complicate the solubility and preparation of peptide stock solutions in physiological buffers [57][58][59].…”

Application of Electron Paramagnetic Resonance Spectroscopy for Validation of the Novel (AN+DN) Solvent Polarity Scale

“…The experiments detailed in a number of studies depict several examples of self-neutralizing effects occurring, for instance, when strong electrophilic trifluoroethanol, hexafluoroisopropanol or water are mixed with strong nucleophilic solvents such as dimethylsulfoxide [3,4,13,14]. In such cases, one component trends to interact with its amphoteric counterpart and does not solvate the aggregated solute molecules, inducing their dissociation.…”

“…In addition, the acquisition of specific knowledge regarding this type of solute-solvent interaction process has been of great value for the development of advantageous experimental approaches in the field [10][11][12]. Furthermore, the combination of the antagonic AN and DN concepts has also been extremely useful for understanding certain rules that govern solubilization of intractable and strong aggregate solutes [13,14], including peptides responsible for the development of neurodegenerative disorders such as Alzheimer's disease [15,16].…”