Carbohydrates hydration

The basic carbohydrate molecule possesses an aldehyde or ketone group and a hydroxyl group on every carbon atom except the one involved in the carbonyl group. As a result, carbohydrates are defined as aldehyde or ketone derivatives of polyhydroxy alcohols and their reaction products. A look at the formula for glucose (C H O ) shows that it contains hydrogen and oxygen atoms in the ratio in which they are found in water. The name carbohydrate (hydrate of carbon) is derived from the fact that the basic carbohydrate molecule has the formula Ck(H20)k. 

Intersecting chains form four-connected nets, observed in carbohydrate hydrates, cyclodextrin hydrates, some hydrated nucleosides, also in some hydrochlorides ... 

The presence of two water molecules in the structure of 2-thiocytidine dihydrate [TCYTDH] results in a hydrogen-bonding pattern (Fig. 17.44) very similar to that observed in the carbohydrate hydrates. It consists of an infinite chain cross-linked to two finite chains through the four-coordinated water molecules. 

Galema, S.A., Howard, E., Engberts, J.B.F.N. and Grigera, J.R., The effect of stereochemistry upon carbohydrate hydration. A molecular dynamics simulation of beta-n-galactopyranose and (alpha,beta)-D-talopyranose, Carhohydr. Res., 1994, 265, 215-225. 

Crystallizes from water in large colourless prisms containing 2H2O. It is poisonous, causing paralysis of the nervous system m.p. 101 C (hydrate), 189°C (anhydrous), sublimes 157°C. It occurs as the free acid in beet leaves, and as potassium hydrogen oxalate in wood sorrel and rhubarb. Commercially, oxalic acid is made from sodium methanoate. This is obtained from anhydrous NaOH with CO at 150-200°C and 7-10 atm. At lower pressure sodium oxalate formed from the sodium salt the acid is readily liberated by sulphuric acid. Oxalic acid is also obtained as a by-product in the manufacture of citric acid and by the oxidation of carbohydrates with nitric acid in presence of V2O5. 

Historically carbohydrates were once considered to be hydrates of carbon because their molecular formulas m many (but not all) cases correspond to C (H20) j It IS more realistic to define a carbohydrate as a polyhydroxy aldehyde or polyhydroxy ketone a point of view closer to structural reality and more suggestive of chemical reactivity... 

Chemists and biochemists And it convenient to divide the principal organic substances present m cells into four mam groups carbohydrates proteins nucleic acids and lipids Structural differences separate carbo hydrates from proteins and both of these are structurally distinct from nucleic acids Lipids on the other hand are characterized by a physical property their solubility m nonpolar solvents rather than by their structure In this chapter we have examined lipid molecules that share a common biosynthetic origin m that all their carbons are derived from acetic acid (acetate) The form m which acetate occurs m many of these processes is a thioester called acetyl coenzyme A... 

Even if It could be shown that RNA preceded both DNA and proteins in the march toward living things that doesn t automatically make RNA the first self replicating molecule Another possibility is that a self replicating polynucleotide based on some carbo hydrate other than o ribose was a precursor to RNA Over many generations natural selection could have led to the replacement of the other carbohydrate by D ribose giving RNA Recent research on unnatural polynucleotides by Professor Albert Eschenmoser of the Swiss Federal Institute of Technology (Zurich) has shown for example that nucleic acids based on L threose possess many of the properties of RNA and DNA... 

Kohle-gehalt, m. carbon content, -hydrat, n. carbohydrate, -klemme, /. Elec.) carbon terminal, -kom, n. carbon granule, -lampe, /. carbon lamp, -lichtbogen, m. Elec.) carbon arc. 

Kohlenstoff-hydrat, n. carbohydrate, -kalium, n. potassium carbide, -kem, m. carbon nucleus. -kette,/. carbon chain, -legiening,/, carbon alloy, -metall, n. carbide, kohlenstoffrelch, a. rich in carbon. Kohlenstoff-silicium, n. carbon silicide. -ske-lett, n. carbon skeleton, -stahl, m. carbon steel, -stein, m. carbon brick, -sticlKtoff-titan, n. titanium carbonitride. -sulfid, n. 

At one stage in our project we were surprised to learn that some workers had found difficulties in preparing the tetroxide from the dioxide, until we experienced the same trouble. This problem has now been resolved (3). Ruthenium dioxide is available commercially in both anhydrous and hydrated forms, the former being obtained by direct oxidation of ruthenium metal and the latter by a precipitation process. Only the hydrated form is oxidizable under the mild conditions (2,3) that we use and this form must be specified when purchasing the dioxide. It is noteworthy that the dioxide recovered from carbohydrate oxidations is always easily re-oxidized to the tetroxide. The stoichiometry has been determined of both the oxidation of the dioxide by periodate and reduction of the tetroxide which results on oxidation of an alcohol. 

The word carbohydrate derives historically from the fact that glucose, the first simple carbohydrate to be obtained pure, has the molecular formula C6H,206 and was originally thought to be a "hydrate of carbon, C6(Tl20)6." This view was soon abandoned, but the name persisted. Today, the term carbohydrate is used to refer loosely to the broad class of polyhydroxvlated aldehydes and ketones commonly called sugars. Glucose, also known as dextrose in medical work, is the most familiar example. 

The catalyst is a mixture of copper, zinc oxide, and chromium(lll) oxide. Ethanol is produced in large quantities throughout the world by the fermentation of carbohydrates. It is also prepared by the hydration of ethene in an addition reaction ... 

Harding, S.E. Day, K. Dham, R. Lowe, P.M. 1997a. Further observations on the size, shape and hydration of kappa-carrageenan in dilute solution. Carbohydrate Polymers 32, 81-87. 

Cellulose and starch are macromolecules with empirical formulas that resemble hydrated carbon, CX (H2 0)y, where x and y are integers. The monomers from which these macromolecules are consfructed are sugars such as glucose and fructose. These monomers and macromolecules are the carbohydrates. Structurally, carbohydrates are very different from simple combinations of carbon and water. Even the smallest carbohydrates contain carbon chains with hydrogen atoms, OH groups, and occasional ether linkages. 

Carbohydrates were first analyzed in the early nineteenth century and described as compounds that were literally hydrates of carbon because they had the general formula CX(H20)X. In recent years, carbohydrate molecules are generally classified on the basis of their structures, not their formulas. Among the compounds that belong to this family are cellulose, starch, glycogen, and most sugars. 

The primary energy source in PN solutions is carbohydrate, usually as dextrose monohydrate. Available concentrations range from 5% to 70%. When oxidized, 1 g of hydrated dextrose provides 3.4 kcal. 

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