Effect of Moisture on the Crystalline Structure of Pure Monoglycerides

Introduction:

Monoglycerides, such as glyceryl monolaurate (GML) and glyceryl monostearate (GMS), are self-assembling amphiphilic molecules that form a variety of crystalline structures with useful mechanical properties of special interest in drug delivery. Lipid matrices containing mixtures of GML and GMS have been evaluated for their potential application as magnetically induced thermo-responsive local drug delivery systems. The presence of excess moisture is reported to influence their phase behavior. 

Objectives:

The aim of this study was to investigate the effect of moisture on the crystalline structure of GML and GMS.

Study Design:

Analytic, observational study.

Methods:

Samples containing GML and GMS were stored at various relative humidity (RH) levels. Various saturated salt solutions were used to create 12%, 33%, 44%, 75% and 97% RH, respectively. The gain or loss of weight as well as the melting points, relaxation temperature and heat of fusion were determined.  The thermal properties were evaluated using differential scanning calorimetry (DSC) and the surface morphologies were evaluated using scanning electron microscopy (SEM).

Results:

The results of the study indicate that the weight of GMS was increased by 2.5 (±0.2) wt %  at 97% RH, whereas GML gained only 0.1 wt % at the same RH level. GML stored at 75% RH showed a loss of weight (0.19 wt %). The DSC thermogram of GMS showed an endothermic melting point peak at 74.71°C. Upon exposure to 97% RH for 1 week, the melting point was shifted to 73.3 (±0.58) °C, which is in agreement with the 2.5% water gain. GML samples stored at RH of 75% showed an increase in melting point to 66.0 (±0.2) °C. The melting point of GML was 64.88 °C. 

Conclusions:

The crystalline structure of GML and GMS was not significantly affected by moisture, making them potential matrices for use in specialized drug delivery systems.