Crystallization Kinetics of Concentrated α,α‐Trehalose and α,α‐Trehalose/Salt Solutions Studied by Low‐resolution ¹H‐Pulsed NMR

Abstract

Crystallization kinetics of concentrated trehalose and trehalose/salt solutions were followed by proton ( 1 H) pulsed nuclear magnetic resonance ( 1 H p-NMR). Three concentrations (66, 70, and 72.5%) of trehalose and with the addition of ZnCl 2 .2H 2 O, CaCl 2 .2H 2 O, and MgCl 2 .2H 2 O were crystallized at 5, 10, 15, 20, and 25 8C. Supercooling and molecular diffusion determined the crystallization rates. The highest rate of crystallization of 66, 70, and 72.5% trehalose occurred at 20 8C, whereas the lowest rate occurred at 25 8C. The maximum solid content was higher at lower temperatures, as expected based on the higher supercooling values. Crystallization was delayed by the addition of salts and especially of CaCl 2 .2H 2 O.

Isothermal Desiccation and Vitrification Kinetics of Trehalose−Dextran Solutions

“…In all probability, the initial concentration of the stock solution and the temperature at which the trehalose samples were dried were crucial in determining the final state of the sample because, given sufficient mobility, trehalose molecules have the tendency to form crystals. 31 This hypothesis was later confirmed by low-temperature isothermal drying of samples of similar compositions. It was observed under a stereo microscope that, after 12-24 h of drying of trehalose solutions at 4 °C, with a very light touch on the surface of the droplet, crystallization could be started.…”

“…According to NMR data presented by Gallo et al, 16% of the 72.5% (w/w) supersaturated trehalose solution crystallizes after only 400 min at 25 °C. Crystallization of this magnitude is expected to produce significant dehydration and melting endotherms, which clearly are missing in our samples.…”

“…Crystallization. In all probability, the initial concentration of the stock solution and the temperature at which the trehalose samples were dried were crucial in determining the final state of the sample because, given sufficient mobility, trehalose molecules have the tendency to form crystals . This hypothesis was later confirmed by low-temperature isothermal drying of samples of similar compositions.…”

“…As a result of an excess free energy or a nucleation in some subregion, at some point in time, crystallization reaction is bound to start. Compartmentalization of supersaturated glucose/trehalose mixtures 36 and crystallization of supersaturated trehalose solutions are documented in the literature. , The crystallizing region would reject water while it advances. If the rejected water does not evaporate locally and immediately, it plasticizes the neighboring regions depressing their glass transition temperatures (Figure ).…”

“…Compartmentalization of supersaturated glucose/trehalose mixtures 36 and crystallization of supersaturated trehalose solutions are documented in the literature. 31,36 The crystallizing region would reject water while it advances.…”