Effect of Temperature on the Interactions of Glycyl Dipeptides with Sodium Dodecyl Sulfate in Aqueous Solution: A Volumetric, Conductometric, and Fluorescence Probe Study

The interactions of glycyl dipeptides (2-[(2-aminoacetyl)amino]acetic acid (commonly known as glycylglycine), 2-[(2-aminoacetyl)amino]-3-methylbutanoic acid (commonly known as glycyl-l-valine), and (2S)-2-[(2-aminoacetyl)amino]-4-methylpentanoic acid (commonly known as glycyl-l-leucine)) with sodium dodecyl sulfate (SDS) as a function of temperature in aqueous solution have been investigated by a combination of density, conductivity, and fluorescence methods. The standard partial molar volume (V2,ϕo), standard partial molar volumes of transfer for dipeptide from water to aqueous SDS solutions (ΔtVo), partial molar expansibility (Eϕo), and Hepler's constant have been calculated from density data. Electrical conductivity was used to estimate the critical micellar concentration (cmc) and the thermodynamic parameters of micellization of SDS in aqueous peptide solutions. The change of micropolarity produced by the interaction was monitored by the measurement of emission intensity ratio between the first and the third bands (I1/I3) of pyrene fluorescence. The obtained data have been discussed in light of various interactions operating in the ternary system of peptide, water, and SDS.