Chemicals found in nature

For thousands of years, humans have devised practical uses for chemicals found in nature. Egyptian priests depended on natural oils and resins as antibiotics in mummifying human and animal remains. South American Indians prepared plant extracts to tip their arrows with fast-acting poison. The ancient Chinese discovered the secret of silk, magically converting an insect s cocoon into an elegant textile. 

The systematic use of gas chromatography coupled with olfactometry [27, 28] in the last 20 years has resulted in a number of new high-impact aroma chemicals found in natural extracts, food products and reaction flavours. In general, sulphur-containing odorants play a particularly important role in food products and savoury flavours [30]. Some of them are shown in Fig. 5.54. Usually, the odour threshold is one key attribute showing the potential impact of the odorant. This may be as low as 0.00002 pg/L water reported for bis-(2-methyl-3-furyl)disulphide (BMFD) (Fig. 5.55) found in cooked meat with a typical meaty, sulphury note. 

The public s perception of toxicity and risk often differs from that found by scientific testing.16 The idea that natural 17 is better than chemical is overly simplistic. Many chemicals found in nature are extremely potent biologically. Mycotoxins are among these.18 Aflatoxins (1.4) were discovered when turkeys fed moldy ground nut (peanut) meal became ill and died. They are among the most potent carcinogens known. 

With less carbon dioxide than required for type 3 (let alone type 4), the water will be supersaturated with calcium carbonate, and a slight increase in pH (at the local cathodes) will tend to cause its precipitation or scaling. If the deposit is continuous and adherent, the metal surface may become isolated from the water and hence protected from corrosion. If type 4 carbon dioxide is present, there can be no deposition of calcium carbonate and existing deposits will be dissolved there cannot therefore be any protection by calcium carbonate scale. Please refer to Sec. 2.2.3 for detailed coverage of the indices and equilibria-associated precipitation and scaling associated with common chemicals found in natural waters. 

AH cephalosporins found in nature (Tables 1 and 2) have the D-a-aminoadipic acid 7-acyl side chain (21). AH of these compounds can be classified as having rather low specific activity. A substantial amount of the early work in the cephalosporin area was unsuccessfiiHy directed toward replacing the aminoadipic acid side chain or modifying it appropriately by fermentation or enzymatic processes (6,22). A milestone ia the development of cephalosporins occurred in 1960 with the discovery of a practical chemical process to remove the side chain to afford 7-ACA (1) (1). Several related processes were subsequendy developed (22,23). The ready avaHabHity of 7-ACA opened the way to thousands of new semisynthetic cephalosporins. The cephalosporin stmcture offers more opportunities for chemical modification than does that of penicillins There are two side chains that especiaHy lend themselves to chemical manipulation the 7-acylamino and 3-acetoxymethyl substituents. 

Metallic Materials Pure metals and their alloys tend to enter into chemical union with the elements of a corrosive medium to form stable compounds similar to those found in nature. When metal loss occurs in this way, the compound formed is referred to as the corrosion product and the metal surface is spoken of as being corroded. 

Proteins are the indispensable agents of biological function, and amino acids are the building blocks of proteins. The stunning diversity of the thousands of proteins found in nature arises from the intrinsic properties of only 20 commonly occurring amino acids. These features include (1) the capacity to polymerize, (2) novel acid-base properties, (3) varied structure and chemical functionality in the amino acid side chains, and (4) chirality. This chapter describes each of these properties, laying a foundation for discussions of protein structure (Chapters 5 and 6), enzyme function (Chapters 14-16), and many other subjects in later chapters. 

Niobium is always found in nature associated with tantalum and it closely resembles tantalum in its chemical and mechanical properties. It is a soft ductile metal which, like tantalum, work hardens more slowly than most metals. It will in fact absorb over 90% cold work before annealing becomes necessary, and it is easily formed at room temperature. In addition, welds of high quality can be produced in the metal. In appearance the metal is somewhat similar to stainless steel it has a density slightly higher than stainless steel and a thermal conductivity similar to 1% carbon steel. 

All of the isotopes of the element with atomic number 87 are radioactive. Hence, it is not found in nature. Yet, prior to its preparation by nuclear bombardment, chemists were confident they knew the chemical reactions this element would show. Explain. What predictions about this element would you make ... 

Although sodium carbonate is needed in the manufacture of glass, very little is found in nature. It is made using two very abundant chemicals, calcium carbonate (marble) and sodium chloride (salt). The process involves many steps, but the overall reaction is... 

In drug discovery, a chemist usually begins by investigating compounds that have already shown medicinal value. A fruitful path is to find a natural product, an organic compound found in nature, that has been shown to have healing characteristics. Nature is the best of all synthetic chemists, with billions of chemicals that fulfill as many different needs. The challenge is to find compounds that have curative powers. These substances are found in different ways random or blind collection of samples that are then tested, or collection of specific samples identified by native healers as medically effective. 

The process (chemical reaction) by which a chemical product is made, as depicted by an equation, is called synthesis. Working in laboratories, chemists devise new ways to synthesize known chemicals or new chemicals never made before and not found in nature. Synthesis chemists working in industrial laboratories also must find or develop uses for the new chemicals that they synthesize while considering the costs of eventual manufacture. 

The elements are the simplest form of matter. An element contains only one type of atom and cannot be decomposed into other chemical components. Of the more than 100 known chemical elements, only a few are found in nature in their pure form. Figure J shows three of these Diamonds are pure carbon, nuggets of pure gold can be found by panning in the right stream bed, and sulfur is found in abundance in its elemental form. 

Point defects were mentioned in a prior chapter. We now need to determine how they aiffect the structure auid chemical reactivity of the solid state. We will begin by identifying the various defects which can arise in solids and later will show how they can be manipulated to obtain desirable properties not found in naturally formed solids. Since we have already defined solids as either homogeneous and heterogeneous, let us look first at the homogeneous t5 e of solid. We will first restrict our discussion to solids which are stoichiometric, and later will examine solids which can be classified as "non-stoichiometric", or having an excess of one or another of one of the building blocks of the solid. These occur in semi-conductors as well as other types of electronically or optically active solids. 

A number of carboxylic acids are found in nature and also present in metabolic pathways. Accordingly, if monobasic acids are smoothly decarboxylated, they are expected to provide us with new routes to supply useful materials for chemical industry without depending on petroleum. Actually, there are some already known examples. The representative examples are the decarboxylation of cinnamic acid derivatives (Table 8). ... 

The metallurgical extraction of the metals from their ore is the noted chemical reaction of removing the metal from its stable compound form (as normally found in nature) to become an unstable, artificial form (as used by industry to make tools, containers, equipment, etc.). That instability (of those refined metallic compounds) is the desire of... 

Liquid interfaces are widely found in nature as a substrate for chemical reactions. This is rather obvious in biology, but even in the diluted stratospheric conditions, many reactions occur at interfaces like the surface of ice crystallites. The number of techniques available to carry out these studies is, however, limited and this is particularly true in optics, since linear optical methods do not possess the ultimate molecular resolution. This resolution is inherent to nonlinear optical processes of even order. For liquid-liquid systems, optics turns out to be rather powerful owing to the possibility of nondestructive y investigating buried interfaces. Furthermore, it appears that planar interfaces are not the only config-... 

Several general characteristics of the results compiled in Table I are worthy of mention. Compared to the variety of chemicals postulated to be involved in allelopathy (1), few specific compounds have been tested for inhibition of mineral absorption. The most extensively studied compounds are the phenolic acids, probably because of their being ubiquitously found in nature (1). Also, several flavonoids are inhibitory to mineral absorption (Table I). Both of these groups of compounds are often cited as being responsible for allelopathic interactions between plants. 

There is a wide diversity of chemical structures of anthraquinone colorants. Many anthraquinone dyes are found in nature, perhaps the best known being alizarin, 1,2-dihydroxyanthraquinone, the principal constituent of madder (see Chapter 1). These natural anthraquinone dyes are no longer of significant commercial importance. Many of the current commercial range of synthetic anthraquinone dyes are simply substituted derivatives of the anthraquinone system. For example, a number of the most important red and blue disperse dyes for application to polyester fibres are simple non-ionic anthraquinone molecules, containing substituents such as amino, hydroxy and methoxy, and a number of sul-fonated derivatives are commonly used as acid dyes for wool. 

One of the most unusual carbohydrate - amino acid linkages so far found in Nature is the thio linkage between glucose or galactose and cysteine.35,40 41 This glycopeptide has not yet been isolated or synthesized. Therefore, in order to obtain 13C-n.m.r. chemical-shift data for... 

Lead (chemical symbol Pb, from the Latin name for the metal, plumbum) is a gray, soft, ductile, and very poisonous metal, although its poisonous properties were probably unknown to the ancients. The metal has been used, particularly in China and India, since very ancient times. Lead is not found in nature in the native, metallic form, although tiny particles of the metal are occasionally encrusted in rocks. It is unlikely, therefore, that the metal would... 

Mercury (chemical symbol Hg, from the Latin name of the metal, hydrar-gyrium, liquid silver), previously also known as quicksilver is, at ordinary temperatures, a silvery white liquid metal that boils at 360°C. The metal is occasionally found in nature in the native state. Most mercury has been derived, however, from the red mineral cinnabar (composed of mercuric sulfide) that was also used in the past as a red pigment known as vermilion (see Textbox 41). The Greek philosopher Aristotle, writing in the fourth... 

Polyamides are macromolecules with acidamide units —CONH—, where the chemical structure of the other parts of the monomers can be aliphatic and/or aromatic. Similar structures are found in nature, for example, polypeptides. Although in principle a large number of potential polyamide structures can be produced, only a few polyamides are produced in industrial scale. 

The word "polymer" (first proposed by Berzelius in 1833) is made of "poly" from the ancient Greek word "mlvq" meaning "many" and "pepot " meaning "part". Polymers are molecules built up from numerous identical chemical "units" spatially repeated to form a chain. From the early times and still nowadays, a distinction is often made between "natural" and "synthetic" polymers, but it is somewhat artificial as natural polymers can now sometimes be synthesized (e.g., synthetic "natural rubber") and some synthetic polymers, which are never found in nature, can be synthesized by natural ways (enzymatic syntheses). 

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