Dharma R. Kodali

Acyl migration in 1,2-dipalmitoyl-sn-glycerol

The acyl migration of 1,2-dipalmitoyl-sn-glycerol (1,2-DPG) to 1,3-dipalmitoylglycerol (1,3-DPG) in different states, neat, in the presence of egg yolk lecithin (sonicated and unsonicated) and on silica gel was studied. The isomerization was quantitated by scanning densitometry of charred TLC plates, at different temperatures and for varying periods of time. At equilibrium the amount of 1,3-DPG was found to be 56%. The rates of initial isomerization, and the time required to isomerize to half the equilibrium quantity (i.e., t1/2 eq. = 1,3-DPG 28%) under the above conditions was estimated. In the case of neat melt at 74 degrees C and in an organic solvent the time required to t1/2 eq. is 18 h and a few days, respectively. However, at 62 degrees C in the presence of a polar solvent (sodium phosphate buffer at pH 7.0) the t1/2 eq. is 1-2 h. On dry silica gel (TLC plate) at 24 degrees C the t1/2 eq. is reached in less than 1 h.

High performance ester lubricants from natural oils

Lubricants impact on the environment at all stages of production, usage and disposal. The awareness and concern over the usage of petroleum‐based products and their impact on the environment have created an opportunity to produce environmentally acceptable lubricants from agricultural feedstocks. A new class of bio‐based esters derived from vegetable oils that exhibit excellent low temperature flow properties and oxidation stability are discussed. One of the major advantages of bio‐based synthetic esters in better performance at a lower cost compared to synthetic esters. This is possible due to recent advances in the biotechnology of vegetable oils and the chemical modifications that could be applied to convert these natural esters into high performance biolubricants.

SYNTHESIS AND POLYMORPHISM OF 1,2-DIPALMITOYL-3-ACYL-sn-GLYCEROLS.

Stereospecific 1,2-dipalmitoyl-sn-glycerol and 1,2-dipalmitoyl-3-acyl-sn-glycerols with even-carbon saturated fatty acyl chains of 2–16 carbons in length were synthesized. The polymorphic behavior and packing arrangements of the most stable crystal form obtained, from the solvent of crystallization, were studied by differential scanning calorimetry and powder X-ray diffraction. Three different layered packing modes were identified: (a) double-layer diglyceride-type; (b) triple-layer triglyceride-type; (c) double-layer triglyceride-type. The first type of packing was represented by 1,2-dipalmitoyl-3-unsubstituted, 3-acetyl and 3-butyryl-sn-glycerols packed in a bilayer with their long hydrocarbon chains in a parallel arrangement. In the second type of packing, shown by 1,2-dipalmitoyl 3-hexanoyl and 3-octanoyl-sn-glycerols, the shorter acyl chains formed a middle layer interposed between 2 layers of the 1,2-palmitoyl chains ofsn-glycerol. The third type of crystal packing was exhibited by 1,2-dipalmitoyl-3-dodecanoyl and 3-tetradecanoyl-sn-glycerols and tripalmitin, was analogous to trilaurin in which the acyl chains at the 1 and 2 positions of glycerol formed an extended, nearly straight line and the 3-acyl chain was folded to lie parallel and alongside the acyl chain at the 1 position. The intermediate member of the series, 1,2-dipalmitoyl-3-decanoyl-sn-glycerol, exhibited both the second and the third type of chain packings when obtained from different solvents of crystallization.

Infrared Micro-imaging of Atherosclerotic Arteries

Micro-FT-IR spectroscopy is a versatile technique that enables the user to obtain high-quality spectra on small samples. This technique is employed to probe the subcellular chemical composition of atherosclerotic arterial walls and create three-dimensional images representing changes in the composition. Two different rabbit model systems that produced atherosclerosis, either due to genetic disorder or due to physical injury, are studied. The FT-IR spectra are collected from a 20- × 20-μm area of 5-μm-thick arterial section, which is smaller than a single cell. The presence of cholesterol esters and other ester-containing compounds is identified from the -O-C=O stretching (1735 cm−1) absorption, and the cis unsaturation in the acyl chains of these compounds is represented by C=C-H stretching (3005 cm−1) absorption. The protein content is indicated by the intensities of the amide I (1650 cm−1) band. The data clearly show the changes occurring in the chemical composition of an arterial wall, varying with the physiological and morphological changes within the artery and the arteries from different animal models. The power of this technique is demonstrated by excellent correlation with the hot stage polarizing microscopy technique, used to characterize the arterial lipids in situ. The three-dimensional images of the arterial walls, indicating the concentration of different chemical constituents, are very useful in understanding the mechanism of atherosclerosis development.

Debenzylation and detritylation by bromodimethylborane: synthesis of mono-acid or mixed-acid 1,2- or 2,3-diacyl-sn-glycerols.

A novel method of deprotecting primary alcohols protected with either benzyl or trityl groups by using bromodimethylborane under mild reaction conditions (dichloromethane, -20 to 5 degrees C) has been applied to the synthesis of optically pure mono-acid or mixed-acid 1,2- or 2,3-diacyl-sn-glycerols. This method was particularly useful for the synthesis of long saturated acyl (C12 to C24) as well as unsaturated diacyl-sn-glycerols since little or no acyl migration occurred during deprotection. Diacylation of 3-benzyl-sn-glycerol or 1-benzyl-sn-glycerol followed by bromodimethylborane debenzylation gave mono-acid 1,2- or 2,3-diacyl-sn-glycerols, respectively. The mixed-acid 1,2- or 2,3-diacyl-sn-glycerols were prepared from 1-acyl-sn-glycerols or 3-acyl-sn-glycerols, respectively, by tritylation, acylation with a different fatty acid, followed by detritylation with bromodimethylborane.

MOLECULAR PACKING IN TRIACYL-sn-GLYCEROLS: INFLUENCES OF ACYL CHAIN LENGTH AND UNSATURATION

Abstract The molecular packing in triacylglycerols having different acyl chains has been examined by differential scanning calorimetry, powder X-ray diffraction and vibrational spectroscopy (infrared and Raman) techniques. In the triacylglycerols examined, the acyl chain length, unsaturation or the position of substitution on the glycerol were changed systematically to observe their influence on the molecular packing in different polymorphic forms. Variation in the 3-acyl chain length of 1,2-dipalmitoyl-3-acyl-sn-glycerols (PPX) influenced the molecular packing along the long axis in the stable polymorphic forms. Three different modes of packing were observed. If X ≤ 4, the compounds packed in a bilayer structure similar to diacylglycerols, or if X ≥ 10 and ≤ 16 the compounds packed in a bilayer structure but similar to mono acid triacylglycerols. However for intermediate 3-acyl chain lengths, as in PP6 and PP8 the stable packing can occured only through chain segregation resulting in a trilayer structure...

Effects of lipid composition on the association of plasma proteins with lipid emulsions

Abstract Lipid emulsions stabilized with phospholipids provide a means for experimental study of lipid-protein interactions at the emulsion surface. The triacylglycerol-rich plasma lipoproteins can be modeled by emulsions, to determine how associations with plasma proteins may regulate the metabolism of chylomicrons and very-low-density lipoproteins. In these experiments emulsions of methyl oleate, ethyl oleate, glyceryl trioleate, and erythrityl tetraoleate were prepared. In each case the emulsion was stabilized with egg yolk phosphatidylcholine, and cholesterol was present in amounts similar to nascent triacylglycerol-rich lipoproteins. When these four emulsions were incubated with plasma or with plasma subfractions the glyceryl trioleate and erythrityl tetraoleate emulsions bound the plasma apolipoproteins AI, AIV, CII, CIII, and E plus albumin, in patterns similar to lymph chylomicrons. In contrast the methyl oleate and ethyl oleate emulsions bound less proteins overall, and the pattern was different from lymph chylomicrons. Also in comparison with the glyceryl trioleate emulsion, the commercial emulsion Intralipid bound more albumin and less apolipoproteins. The glyceryl trioleate emulsion bound bovine serum albumin in larger amounts than human serum albumin. Emulsions with cores of erythrityl tetraoleate may be useful as experimental substitutes for triacylglycerols in lipoprotein model emulsions.

Physical Properties of Organogels Made of Rice Bran Wax and Vegetable Oils

Publisher Summary This chapter presents the physical properties of organogel made of Rice Bran Wax (RBX) and vegetable oils, examined with thermal, structural, and optical methods. The physical properties of organogels formed by RBX and liquid oils in comparison with other typical plant waxes of Candellila Wax ( CLX) and Carnauba Wax (CRX) can be summarized as follows: (a) the rate of formation of organogels was highest for RBX gels, as determined by visual observation and viscosity-temperature relationships, (b) the hardness assessed by the penetration depth measurement was highest for RBX gels, (c) thermal stability expressed as the Tm of wax crystals in organogels was highest for RBX gels. These properties may be ascribed to the high crystallinity of RBX crystals having the highest ΔHm and ΔSm, whose values are similar to those of the PPP β form. As PPP crystals are tightly packed in the T// subcell, it is reasonable to assume that the RBX crystals are also tightly packed in the O⊥ subcell structures. The differences in the subcell structure may be responsible for the molecular differences between RBX and PPP structures. Furthermore, the crystal morphology of the needle-shaped RBX crystals in organogels may indicate a greater ability to entrap the liquid oils to form organogels. Crystallization kinetics and physical properties of organogels prepared by RBX and different. Furthermore, the crystal morphology of the needle-shaped RBX crystals in organogels may indicate a greater ability to entrap the liquid oils to form organogels.

Development, properties and applications of high-performance biolubricants

Abstract: This chapter provides the fundamental understanding of how the inherent structural features of fatty acid ester derivatives make them suitable for lubrication applications. It provides sources of new triacylglycerol oils, their fatty acid composition, markets and performance compared to regular oils. Also discussed are the general functional requirements of lubricants and how the new functional fluids produced by various chemical modifications of fatty acid esters overcome the shortcomings of oxidative stability and low temperature fluidity. The cost effectiveness and high performance of biobased esters make them useful as base stocks and functional additives. A number of new technologies developed in the last two decades that have potential for commercial applications, their salient features and advantages along with future trends are presented.

Trans Fats: Health, Chemistry, Functionality, and Potential Replacement Solutions

Publisher Summary This chapter provides a comprehensive overview of trans fats, including their health effects, chemistry, sources, properties, and functionality. It also provides an in-depth analysis of fats and oils and their functionality in foods, discusses the relationship between structure, properties, and functionality of Triacylglycerols (TAG) and its constituent fatty acids and addresses how this knowledge can provide an insight into finding ideal trans fat replacement solutions. The holy grail of trans fats replacement solutions is to find an ideal trans fat replacement with an equal or better performance without an increase in saturated fat. The chapter also provides background for such solutions and suggests practical solutions of how to create trans fat replacement solutions, including the ideal designer fats with low saturates as a trans replacement solution. Trans fats, similar to saturated fats, offer desirable food functionality without being labeled as saturated fat. Therefore, Partially Hydrogenated Vegetable Oils (PHVOs) replaced saturated fats in food products. But numerous studies have showed a direct correlation between Coronary Heart Disease (CHD) risk and the consumption of trans fats. These studies have made it very clear that trans fats are responsible for higher CHD incidence and do not provide any nutritional value. There are a number of enabling technologies, such as formulation, trait- enhanced oils, tropical oils and their fractions, and interesterified fats, that are available to eliminate trans fats in food products. The substitution of saturated fat for trans fat is an easy but not healthful solution.