Phase Transformations Undergone by Triton X-100 Probed by Differential Scanning Calorimetry and Dielectric Relaxation Spectroscopy

Abstract

The phase transformations of the surfactant Triton X-100 were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and dielectric relaxation spectroscopy (DRS). In particular, crystallization was induced at different cooling rates comprised between 13 and 0.5 K min(-1). Vitrification was detected by both DSC and DRS techniques with a glass transition temperature of ∼212 K (measured on heating by DSC) allowing classifying Triton X-100 as a glass former. A fully amorphous material was obtained by cooling at a rate ≥10 K min(-1), while crystallization was observed for lower cooling rates. The temperature of the onset of melt-crystallization was found to be dependent on the cooling scan rate, being higher the lower was the scan rate. In subsequent heating scans, the material undergoes cold-crystallization except if cooled previously at a rate ≤1 K min(-1). None of the different thermal histories led to a 100% crystalline material because always the jump typical of the glass transformation in both heat flux (DSC) and real permittivity (DRS) is observed. It was also observed that the extent/morphology of the crystalline phase depends on the degree of undercooling, with higher spherulites developing for lower undercooling degree (24 K ≤ T(m) - T(cr) ≤ 44 K) in melt-crystallization and a grain-like morphology emerging for T(m) - T(cr) ≈ 57 K either in melt- or cold-crystallization. The isothermal cold- and melt-crystallizations were monitored near above the calorimetric glass transition temperature by POM (221 K) and real-time DRS (T(cr) = 219, 220, and 221 K) to evaluate the phase transformation from an amorphous to a semicrystalline material. By DRS, the α-relaxation associated with the dynamic glass transition was followed, with the observation that it depletes upon both type of crystallizations with no significant changes either in shape or in location. Kinetic parameters were obtained from the time evolution of the normalized permittivity according to a modified Avrami model taking in account the induction time. The reason the isothermal crystallization occurs to a great extent in the vicinity of the glass transition was rationalized as the simultaneous effect of (i) a high dynamic fragile behavior and (ii) the occurrence of catastrophic nucleation/crystal growth probably enabled by a preordering tendency of the surfactant molecules. This is compatible with the estimated low Avrami exponent (1.12 ≤ n ≤ 1.6), suggesting that relative short length scale motions govern the crystal growth in Triton X-100 coherent with the observation of a grainy crystallization by POM.

IKMTSL-PTE, a Phospholipid-Based EPR Probe for Surface Electrostatic Potential of Biological Interfaces at Neutral pH: Effects of Temperature and Effective Dielectric Constant of the Solvent

“…The polarity-induced p K a shift was determined from EPR titration of IKMTSL-PTE at 17 and 48 °C in micelles composed of a nonionic detergent Triton X-100. The reasons for choosing the Triton X-100 micelles as a nonpolar electrically neutral reference interface (Ψ = 0, Δp K a el = 0; eqs and ) formed between aqueous and lipidlike phases have been discussed by us previously. , Furthermore, according to recent differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy studies, Triton X-100 micelles do not exhibit any phase transitions between 17 and 48 °C, thus making such detergent micelles a suitable model for a noncharged lipid bilayer interface over this reasonably broad temperature range.…”

A Stable Amorphous Statin: Solid-State NMR and Dielectric Studies on Dynamic Heterogeneity of Simvastatin

“…At a given temperature, the measured dielectric permittivity, ε*( f ) = ε′( f ) – i ε″( f ) ( f : the frequency of the electric field), is a complex quantity whose real part (ε′) decreases as a sigmoid curve and whose imaginary part (ε″) passes through a maximum at f max , when the dipoles are no longer able to follow the electric field oscillations. DRS has been proven to be a suitable tool to study thermal transitions in low molecular weight compounds, , including pharmaceutical drugs . The complex dielectric permittivity of simvastatin was monitored in isochronal mode, ε*( T ), at five frequencies (0.1, 1, 10, 100, 1000 kHz), by carrying out a heating (run 1)/cooling (run 2) cycle allowing simvastatin to be obtained in the supercooled and glassy states (similar thermal protocol used in the DSC experiments).…”

“…Figure 6 shows C T 1ρ measured from 293 till 333 K for several carbon nuclei with the following chemical shifts (carbon numbers within parentheses): 77 (5), 69 (14), 62 (3), 33 (6,15,20), and 24 ppm (7,22,23). Single-exponential decays were used to fit the experimental data recorded at each temperature.…”

“…Dielectric measurements were carried out using an Alpha-N impedance analyzer from Novocontrol Technologies GmbH. More details about the used equipment and methodology to analyze dielectric data can be found elsewhere . It should be noted that during all dielectric measurements samples are kept under a constant nitrogen gas flux allowing a dried atmosphere to be maintained.…”

“…More details about the used equipment and methodology to analyze dielectric data can be found elsewhere. 14 It should be noted that during all dielectric measurements samples are kept under a constant nitrogen gas flux allowing a dried atmosphere to be maintained. A crystalline sample was placed in parallel plate geometry between two gold-coated electrodes with a diameter of 10 mm.…”