Academic literature on the topic 'Oxo fatty acid'

Building on the foundation of a one-year introductory course in organic chemistry, Bioorganic Synthesis: An Introduction focuses on organic reactions involved in the biosynthesis of naturally-occurring organic compounds with special emphasis on natural products of pharmacological interest. The book is designed specifically for undergraduate students, rather than as an exhaustive reference work for graduate students or professional researchers and is intended to support undergraduate courses for students majoring in chemistry, biochemistry, biology, pre-medicine, and bioengineering programs who

Grape leaves are thin and flat. As is common among leaves in general, they are composed of different sets of specialized cells. Today, on average, sunlight reaching their surface is about 4% ultraviolet (UV) (<400 nm), 52% infrared (IR) (>750 nm) and 44% visible (VIS) radiation. Little of the UV and IR are used by plants. As with other leaves that are green, only the red and blue ends of the visible part of the electromagnetic spectrum are absorbed, thus leaving green available by reflection and transmission. On the surface of the leaf (Figure 8.1), the cells of the outermost layer (the epidermis) are designed to protect the inner cells where the workings needed for gathering the sunlight used for photosynthesis and other chemistry necessary to the life of the plant are found. That is, the more delicate cells, beneath the epidermis, are involved in production of carbohydrates as well as the movement of nutrients in and products out of the leaf. The epidermis, exposed to the atmosphere, has cells that are usually thicker and are covered by a waxy layer made up of long- chain carboxylic acids that have hydroxyl groups (–OH) at or near their termini. These so-called omega hydroxy acids can then form esters using the hydroxyl group of one and the carboxylic acid of the next. This yields long-chain polyester polymers called “cutin.” As indicated in the earlier discussion of cells and, in particular, regarding the fatty acids of cell walls, the fatty acids found in the epidermis generally consist of an even number of carbon atoms, and for cutin, the sixteen carbon (palmitic acid) family (Figure 8.2) and the eighteen carbon family (oleic acid bearing a double bond or the saturated analogue stearic acid) are common. While one terminal hydroxyl group is usual (e.g., 16-hydroxypalmitic acid, 18-hydroxyoleic acid, or its saturated analogue 18-hydroxystearic acid) more than one (allowing for cross-linking) is not uncommon (e.g., 10,16-dihydroxypalmitic and 9,10,18-trihydroxystearic acid).

The maintenance of life requires a constant supply of substrate for the generation of energy and preservation of the structure of cells and tissues. The process in principle is simple, yet the individual metabolic pathways and the regulation of substrate fluxes through these pathways can be complex. Energy is derived when fuel substrates are oxidized to carbon dioxide and water in the presence of oxygen, generating adenosine triphosphate (ATP). A portion of the ingested foodstuff is also utilized, either directly or after transformation into other substrates, to repair and replace cell membranes, structural proteins, and organelles. The remainder is stored as potential energy in the form of glycogen or fat. Under normal circumstances, each individual remains in a near-steady state where weight and appearance are stable over prolonged periods. In the short term, fuel metabolism changes dramatically several times a day during alternating periods of feeding and fasting. An anabolic phase begins with food ingestion and lasts for several hours. Energy storage occurs during this period when caloric intake exceeds caloric demands. The catabolic phase usually begins 4 to 6 hours after a meal and lasts until the person eats once again. During this phase, utilization shifts from exogenous to endogenous fuels, a change heralded by the mobilization of substrate stored in liver, muscle, and adipose tissue. Both anabolic and catabolic phases are characterized by specific biochemical processes regulated by distinct hormonal profiles. In the anabolic phase that follows ingestion of a mixed meal, substrate flux is directed from the intestine through the liver to storage and utilization sites. Glucose, triglyceride, and amino acid concentrations increase in plasma, whereas those of fatty acids, ketones (acetoacetic and β -hydroxy-butyric acids), and glycerol decrease. Both glycogen and protein synthesis begin in liver and muscle, while fatty acid synthesis and triglyceride esterification are stimulated in hepatocytes and adipose tissue. In the catabolic phase, the biochemical activities are reversed and the flux of fuel is directed from storage depots to liver and other utilization sites.

Cellular metabolism is divided into catabolism — responsible for converting nutrients into the energy sources and smaller molecules required for the chemical reactions of the body — and anabolism, which is the interconversion and synthesis of the molecules that maintain the body’s structure and function. This chapter examines the control of metabolism and the central metabolic pathways. Such control includes compartmentalization of metabolic processes and the cooperation between the metabolic activities of different organs. Metabolic control is important because metabolism must match the availability of nutrients to the demand for the products of the metabolic processes and both will vary over time. The synthesis of adenosine triphosphate (ATP), with its high-energy phosphate bond, lies at the heart of these central metabolic pathways. Most of the ATP is produced by oxidative phosphorylation in the mitochondria, but glycolysis and the tricarboxylic acid cycle (also known as the citric acid cycle or Krebs cycle) provide additional amounts. Of the nutrients entering the body from the diet, fat, glucose, and amino acids are the main fuels for cellular metabolism. The utilization of lipids, fatty acids, and ketone bodies is important in metabolism in addition to the key role played by glucose. Glucose is the fuel for energy production in glycolysis. It is also manufactured by gluconeogenesis and stored as glycogen by glycogenesis. It is important to know how different organs utilize different fuels and how energy production alters between the fed state and starvation. Amino-acid metabolism and coenzymes in amino acid oxidation are also important although some details, including the urea cycle, have not been covered here. Energy balance and the relationship between food intake and energy expenditure lead to the concept of body mass index (BMI). The BMI offers a quick method of quantifying the nutritional status of a person, and BMI values may be helpful in assessing the risk of, for example, obesity-related diseases such as type II diabetes and coronary heart disease. Cellular metabolism not only contributes to the medical sciences background to clinical reasoning, but there are also a number of identifiable, inborn errors of metabolism. While individually rare (with incidences of approx. 1–25 per 100,000 births), collectively they present a considerable number of new cases each year.

Beginning with fruit set (generally the grape berry is now between 1.5 and 3.0 mm, i.e., less than 1/ 8 of an inch in diameter) the grape berry growth is divided into three stages. Stages I and III correspond to periods of rapid growth, and the intervening slow growth phase is called Stage II. Generally the slow growth stage (Stage II) corresponds to the slowing of Stage I and the acceleration of Stage III, but it is clear that different grape cultivars have stages of different lengths even under ostensibly identical conditions. In the first stage of fruit set (also called “nouaison”) the actual development of the flower ovary into the grape berry begins. The seeds in the two seed cavities (the locules) and the flesh (the pericarp) begin to take form. The pericarp separates into the exocarp (the skin with its cuticle—a thin wax coating) and the mesocarp. The mesocarp, as it grows and divides, will eventually (by the end of Stage III) account for more than 90% of the grape’s weight. The exocarp, significantly thinner than the mesocarp, may be only five or six cells thick, and the cuticle only several layers of lipids (waxy, fatty acid esters, and compounds similar to those of cell walls and the chloroplast envelope, see pages 30 and 31). It is in this stage that the as yet undeveloped berries are green and hard (it has been sug¬gested that this is because chlorophyll is present and photosynthesis in the berry—as well as in leaves—is occurring). The berries are low in sugar (sucrose) but high in carboxylic acids, predominately malic acid and tartaric acid along with, generally, a lesser amount of ascorbic acid (vitamin C), hydroxycinnamic acid, and some acidic tannins (Figures 13.1 and 13.2). The grape berry structure is generally divided into three types of tissue: skin, flesh, and seed (Figure 13.3). The first, skin, as already mentioned is also known as exocarp.

Partially oxidized organic compounds, i.e., those containing carbon, hydrogen, and oxygen atoms, and optionally other heteroatoms, are often referred to as “oxygenates” because they contain O-atoms as well as a C-atom skeleton. These enter the atmosphere as emissions from various industrial and transportation-related operations, evaporation and release from home usage of certain products, and release from vegetation. They are also formed in the atmosphere as oxidation products of all hydrocarbon emissions that enter the atmosphere from mobile and stationary sources as well as natural emissions from plants and animals. The common oxygenates consist of the alcohols (ROH), ethers (ROR), aldehydes (RCHO), ketones [RC(O)R], esters [RC(O)OR], and acids [RC(O)OH] together with N-atom-containing oxygenates and other less abundant classes of oxygen-containing organic compounds. The use of alternative fuels is increasing and is anticipated to continue to grow in the future. Many of these alternative fuels are oxygenates: methanol, ethanol, butanol, fatty acid methyl esters, and other biofuels. Thus, the scientific community is interested in identifying the important sources and sinks for these compounds. As with the hydrocarbons, the oxygenates serve as fuel for the reactions that generate ozone and other air pollutants within the troposphere. In illustration, consider the influence of the very common and important oxygenate, formaldehyde (CH2O).

As described in other chapters of this book and elsewhere (Jessop, 1999), a wide range of catalytic reactions can be carried out in supercritical fluids, such as Fischer–Tropsch synthesis, isomerization, hydroformylation, CO2 hydrogenation, synthesis of fine chemicals, hydrogenation of fats and oils, biocatalysis, and polymerization. In this chapter, we describe experiments aimed at addressing the potential of using supercritical carbon dioxide (and carbon dioxide/propane mixtures) for applications in the hydrogenation of vegetable oils and free fatty acids. Supercritical fluids, particularly carbon dioxide, offer a number of potential advantages for chemical processing including (1) continuously tunable density, (2) high solubilities for many solids and liquids, (3) complete miscibility with gases (e.g., hydrogen, oxygen), (4) excellent heat and mass transfer, and (5) the ease of separation of product and solvent. The low viscosity and excellent thermal and mass transport properties of supercritical fluids are particularly attractive for continuous catalytic reactions (Harrod and Moller, 1996; Hutchenson and Foster, 1995; Kiran and Levelt Sengers, 1994; Perrut and Brunner, 1994; Tacke et al., 1998). There are a number of reports on hydrogenation reactions in supercritical fluids using homogenous and heterogeneous catalysts (Baiker, 1999; Harrod and Moller, 1996; Hitzler and Poliakoff, 1997; Hitzler et al., 1998; Jessop et al., 1999; Meehan et al., 2000; van den Hark et al., 1999). We have investigated the selective hydrogenation of vegetable oils and the complete hydrogenation of free fatty acids for oleochemical applications, since there are some disadvantages associated with the current industrial process and the currently used supported nickel catalyst. The hydrogenation of fats and oils is a very old technology (Veldsink et al., 1997). It was invented in 1901, by Normann, in order to increase the melting point and the oxidation stability of fats and oils through selective hydrogenation. Since the melting point increases during the hydrogenation, the reaction is also referred to as hardening. The melting behavior of the hydrogenated product is determined by the reaction conditions (temperature, hydrogen pressure, agitation, hydrogen uptake). Vegetable oils (edible oils) are hydrogenated selectively for application in the food industry; whereas free fatty acids are completely hydrogenated for oleochemical applications (e.g., detergents).

Oceans cover the majority of the planet and are home to a vast quantity of diverse yet interconnected ecosystems. The volume of living space provided by the sea is 168 times greater than that provided by the earth’s landscapes (Clark et al. 5). Given the wealth of creatures living in the seas, as well as those in lakes, swamps, and rivers, and given the much-touted health aspects of aquatic flesh and the environmental nightmare linked with animal agriculture, should we turn to a diet of pollock, shrimp, and salmon? In the 18th and 19th centuries, a mercury wash was used to produce felt hats. In the process workers were exposed to and absorbed bits of the substance and developed mercury poisoning. As a consequence, those who were employed in the felt hat industry often stumbled about “in a confused state with slurred speech and trembling hands” and “were sometimes mistaken for drunks” (“Mad as a Hatter”). Mercury poisoning “attacks the nervous system, causing drooling, hair loss, uncontrollable muscle twitching, a lurching gait, and difficulties in talking and thinking” (“Mad as a Hatter”). From this comes the term made famous in Lewis Carroll’s Alice in Wonderland, “mad as a hatter.” Between 1973 and 1997, fish consumption rose from 45 to 91 million metric tons (Delgado 1). The American Heart Association recommends eating fish at least twice a week for heart health (“Omega-3 Fatty Acids”). The National Healthy Mothers, Healthy Babies Coalition accepted “thousands of dollars from the fishing industry” to promote a recommendation that pregnant women eat “at least 12 ounces of fish per week” (“Fishy Recommendations” 23). Fish flesh is touted as “healthy meat” in comparison with the flesh of terrestrial animals. Omega-3 fatty acids found in fish are credited with helping everything from heart disease to diabetes, but fish flesh also contains deadly mercury (as well as “dioxins . . . and poly-chlorinated biphenyls”—PCBs) (“Omega-3 Fatty Acids”). Longer-living predator fish such as tuna, marlin, shark, mackerel, and swordfish “can have mercury concentrations that are hundreds or thousands of times, possibly even a million times, greater than concentrations in the water in which they swim” (Smith and Lourie 151).

Acyl group transfer processes are plentiful in enzymatic reactions. Examples may be found in ATP-dependent ligation in chapter 11, carbon-carbon bond formation in chapter 14, and fatty acid biosynthesis in chapter 18. In this chapter, we begin by presenting the basic chemistry of acyl group transfer. We then consider four major classes of proteases that catalyze acyl group transfer in the hydrolysis of peptide bonds. Acyl group transfer is so common in organic and biochemistry that the chemistry by which it occurs is often taken for granted. Early studies provided evidence for a mechanism initiated by nucleophilic addition of the acyl group acceptor to the carbonyl group to form a tetrahedral intermediate, analogous to the reversible addition of a nucleophilic molecule to the carbonyl group of an aldehyde or ketone. A mechanism of this type is shown in scheme 6-1 for acyl group transfer from a group :X to a nucleophile :G catalyzed by a general base. This mechanism is drawn from a larger family of possible mechanisms involving specific acid-base, general acid, general base, or concerted general acid-base catalysis of nucleophilic addition to an acyl carbonyl group to form a tetrahedral intermediate, followed by the elimination of :X–H to produce the new acyl compound. In enzymatic reactions the nucleophilic atom G in scheme 6-1 is normally nitrogen, oxygen, sulfur, or a carbanionic species. An acyl carbonyl group is less polar and correspondingly less reactive toward nucleophilic addition than an aldehyde or ketone. The reason is the effect on the heteroatom of nonbonding electrons, which reside in p orbitals that overlap the π orbital of the carbonyl group. The consequent delocalization of electrons stabilizes the carbonyl group and attenuates its reactivity with nucleophiles. Other factors being equal, the order of reactivity is thioester > ester > amide, which is the inverse of the degree of delocalization. Delocalization is least in thioesters because of the high energy of the sulfur p orbitals, which reside in the next higher principal quantum number relative to oxygen in the acyl carbonyl group.