Monopalmitin, also known as 1-monopalmitoyl-rac-glycerol or glycerol monopalmitate (C₁₉H₃₈O₄, MW 330.50 g/mol), is a long-chain saturated monoacylglycerol (MAG) formed by esterification of palmitic acid (hexadecanoic acid, C16:0) at the sn-1 position of glycerol. This compound represents the final entry in the monoacylglycerol series and complements broader lipid discussions presented in prior entries.
Chemical Structure
Monopalmitin consists of a glycerol backbone esterified with a 16-carbon saturated fatty acyl chain (-CO(CH₂)₁₄CH₃) at the primary sn-1 hydroxyl position, leaving free hydroxyl groups at sn-2 and sn-3. Its IUPAC name is 2,3-dihydroxypropyl hexadecanoate, with the condensed structural formula CH₂(OCOC₁₅H₃₁)-CH(OH)-CH₂OH. The compound typically appears as a white to light yellow powder, block, or viscous solid. Structural confirmation is supported by the InChI string: InChI=1S/C19H38O4/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-19(22)23-17-18(21)16-20/h18,20-21H,2-17H2,1H3. Monopalmitin is odorless and tasteless.
Physicochemical Properties
Monopalmitin exhibits a melting point in the range of 73–77 °C (literature value ~75 °C) and a predicted boiling point of approximately 451 °C. Its density is about 0.969 g/cm³, with a pKa near 13.16. A LogP value of ~5.4 reflects strong lipophilicity. The molecule is amphiphilic and functions as a water-in-oil emulsifier with a hydrophilic–lipophilic balance (HLB) of approximately 3.8. It disperses in hot water to form emulsions, dissolves readily in ethanol and hot oils, and is insoluble in cold water. The compound is stable under frozen storage conditions (−20 °C) and exhibits dielectric properties. In pharmaceutical contexts, it has been reported to support P-glycoprotein inhibition, contributing to enhanced drug delivery performance.
Synthesis and Stability
Monopalmitin is commonly synthesized via enzymatic glycerolysis of tripalmitin or through lipase-mediated transesterification of ethyl palmitate with glycerol, achieving purities greater than 95 % as determined by gas chromatography following distillation. The C16 ester bond demonstrates resistance to rapid hydrolysis, enabling controlled release of palmitic acid in biological systems. This property provides improved stability and bioavailability relative to free fatty acids, making monopalmitin suitable for applications requiring sustained lipid delivery.
