Biochemical Functionalization

The chemical modification of CNTs can be endohedral (inside the cavity of the tube) or exohedral [42]. There are some examples in the literature that have demonstrated the filling of CNTs with fullerenes, biomolecules (proteins, DNA), metals and oxides that have been driven inside by capillary pressure [39, 42, 72-78], However, in this section we will focus on exohedral functionalization, taking place just at the external walls of the tubes. Both covalent (chemical-bond formation) and noncovalent (physiadsorption) functionlizations can be carried out. In the following 

For electrochemical devices, such functionalization schemes can be performed either before or after the CNTs are assembled on the electrodes. 

On the other hand, and as discussed before, the chemical reactivity of CNT sidewalls increases with the tube curvature (i.e. decrease of the tube diameter), due to the increase of the pyramidalization angle and greater strain energy per atom [37, 38]. Such pyramidalization of the CNT atoms causes the exohedral lobes of the orbitals to be larger than their endohedral counterparts. The reactivity of the surface is thus enhanced by the pronounced exposure of the hybrid orbitals from the exterior, which favors the orbital overlap with incoming reactants [38]. 

Accordingly, many reactions can be performed on the sidewalls of the CNTs, such as halogenation, hydrogenation, radical, electrophilic and nucleophilic additions, and so on [25, 37, 39, 42-44]. Exhaustively explored examples are the nitrene cycloaddition, the 1,3-dipolar cycloaddition reaction (with azomethinylides), radical additions using diazonium salts or radical addition of aromatic/phenyl primary amines. The aryl diazonium reduction can be performed by electrochemical means by forming a phenyl radical (by the extrusion of N2) that couples to a double bond [44]. Similarly, electrochemical oxidation of aromatic or aliphatic primary amines yields an amine radical that can be added to the double bond on the carbon surface. The direct covalent attachment of functional moieties to the sidewalls strongly enhances the solubility of the nanotubes in solvents and can also be tailored for different 

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Identification, isolation, and removal of (polyhydroxy)benzenes from the environment have received increased attention throughout the 1980s and 1990s. The biochemical activity of the benzenepolyols is at least in part based on thek oxidation—reduction potential. Many biochemical studies of these compounds have been made, eg, of enzymic glycoside formation, enzymic hydroxylation and oxidation, biological interactions with biochemically important compounds such as the catecholamines, and humic acid formation. The range of biochemical function of these compounds and thek derivatives is not yet fully understood. 

Naturally occurring quaternary ammonium compounds have been reviewed (179). Many types of aliphatic, heterocycHc, and aromatic derived quaternary ammonium compounds are produced both in plants and invertebrates. Examples include thiamine (vitamin B ) (4) (see Vitamins) choline (qv) [62-49-7] (5) and acetylcholine (6). These have numerous biochemical functions. Several quaternaries are precursors for active metaboUtes. 

Biochemical Functions. Ascorbic acid has various biochemical functions, involving, for example, coUagen synthesis, immune function, dmg metabohsm, folate metaboHsm, cholesterol cataboHsm, iron metaboHsm, and carnitine biosynthesis. Clear-cut evidence for its biochemical role is available only with respect to coUagen biosynthesis (hydroxylation of prolin and lysine). In addition, ascorbic acid can act as a reducing agent and as an effective antioxidant. Ascorbic acid also interferes with nitrosamine formation by reacting direcdy with nitrites, and consequently may potentially reduce cancer risk. 

L-Tyrosine metabohsm and catecholamine biosynthesis occur largely in the brain, central nervous tissue, and endocrine system, which have large pools of L-ascorbic acid (128). Catecholamine, a neurotransmitter, is the precursor in the formation of dopamine, which is converted to noradrenaline and adrenaline. The precise role of ascorbic acid has not been completely understood. Ascorbic acid has important biochemical functions with various hydroxylase enzymes in steroid, dmg, andhpid metabohsm. The cytochrome P-450 oxidase catalyzes the conversion of cholesterol to bUe acids and the detoxification process of aromatic dmgs and other xenobiotics, eg, carcinogens, poUutants, and pesticides, in the body (129). The effects of L-ascorbic acid on histamine metabohsm related to scurvy and anaphylactic shock have been investigated (130). Another ceUular reaction involving ascorbic acid is the conversion of folate to tetrahydrofolate. Ascorbic acid has many biochemical functions which affect the immune system of the body (131). 

Physical Chemical Characterization. Thiamine, its derivatives, and its degradation products have been fully characterized by spectroscopic methods (9,10). The ultraviolet spectmm of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole yUd (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the piC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the patent cation and its major fragmentation ion, the pyrimidinylmethyl cation (16). 

Eortunately, a 3D model does not have to be absolutely perfect to be helpful in biology, as demonstrated by the applications listed above. However, the type of question that can be addressed with a particular model does depend on the model s accuracy. At the low end of the accuracy spectrum, there are models that are based on less than 25% sequence identity and have sometimes less than 50% of their atoms within 3.5 A of their correct positions. However, such models still have the correct fold, and even knowing only the fold of a protein is frequently sufficient to predict its approximate biochemical function. More specifically, only nine out of 80 fold families known in 1994 contained proteins (domains) that were not in the same functional class, although 32% of all protein structures belonged to one of the nine superfolds [229]. Models in this low range of accuracy combined with model evaluation can be used for confirming or rejecting a match between remotely related proteins [9,58]. 

Biochemical functions of each gene. I-V = transferase l-V. Acy - acetylases I II. Ket = ketaiase. Pol = polymerase. Exp - export... 

Structural aspects and biochemical functions of erythrocuprein. U. Weser, Struct. Bonding (Berlin), 1973,17, 1-65 (226). 

Artificial organs that perform the physical and biochemical functions of the heart, hver, pancreas, or lung are one class of organ replacements. A rather different target of opportunity is the development of biologieal materials that play a more passive role in the body for example,... 

Weser U (1985) Redox Reactions of Sulphur-Containing Amino-Acid Residues in Proteins and Metalloproteins, an XPS Study. 61 145-160 Weser U (1973) Structural Aspects and Biochemical Function of Erythrocuprein. 17 1-65 Weser U, see Abolmaali B (1998) 91 91-190... 

The R groups of amino acids determine their unique biochemical functions. Amino acids are classified as basic, acidic, aromatic, aliphatic, or sulfur-containing based on the properties of their R groups. 

Vitamins are a group of organic nutrients required in small quantities for a variety of biochemical functions and which, generally, cannot be synthesized by the body and must therefore be supphed in the diet. 

MINERALS ARE REQUIRED FOR BOTH PHYSIOLOGIC BIOCHEMICAL FUNCTIONS... 

Padh H Vitamin C newer insights into its biochemical functions. Nutr Rev 1991 49 65. 

It is generally felt that a substance is more likely to be a NT if it is unevenly distributed in the CNS although if it is widely used it will be widely distributed. Certainly the high concentration (5-10 pmol/g) of dopamine, compared with that of any other monoamine in the striatum or with dopamine in other brain areas, was indicative of its subsequently established role as a NT in that part of the CNS. This does not mean it cannot have an important function in other areas such as the mesolimbic system and parts of the cerebral cortex where it is present in much lower concentrations. In fact the concentration of the monoamines outside the striatum is very much lower than that of the amino acids but since the amino acids may have important biochemical functions that necessitate their widespread distribution, the NT component of any given level of amino acid is difficult to establish. 

Inhibitors of AR have been demonstrated to prevent a wide variety of biochemical, functional and structural alterations in animal models of diabetes. Early studies demonstrated arrest of both early cataract development and nerve conduction velocity. At least 30 clinical trials of AR inhibitors have been published involving nearly 1000 patients in total. However, there is little impressive data of their efficacy up to now but, rather than undermine the hypothesis linking excess polyol pathway activity to diabetic complications, it may reflect methodological difficulties and trial design errors. 

Biasi, F., Albano, E., Chiarpotto, E., Corongju, F.P., Pron-zato, M.A., Marinari, U. M., Parola, M., Dianzani, M.U. and Poli, G. (1991). Invivo and in vitro evidence concerning the role of lipid peroxidation in the mechanism of hepatocyte death due to carbon tetrachloride. Cell Biochem. Function 9, 111-118. 

Le Page, KN., Cheeseman, K.H., Osman, N. and Slater, T.F. (1988). Lipid peroxidation in purified plasma membrane fractions of rat liver in relation to the toxicity of carbon tetrachloride. Cell Biochem. Function 6, 87-99. 

Weser, U. Structural Aspects and Biochemical Function of Erythrocuprein. Vol. 17, pp. 1-65. 

Table 2 Biochemical Function of Nodulation Gene Products Involved in Nod Fiictor Synthesis and Transport...

H. P. Spaink, O. Geiger. D. M. Sheeley, A. A. N. Van Brussel, W. S. York, V. N. Reinhold, B. J. J. Lugtenberg, and E. P. Kennedy, The biochemical function of the Rhizobium leguminosarum proteins involved in the production of host-specific signal molecules. Advances in Molecular Genetics of Plant-Microbe Interactions. Vol. 1 (H. Hennecke and D. P. S. Verma, eds.), Kluwer Academic Publishers, Dordrecht, The Netherlands, 1991. 

Figure 7.6. Purification of protein from pooled yeast strains. Each yeast ORF was cloned as a fusion to glutathione-S-transferase in a protein expression vector to create 6144 yeast strains. The individual strains were pooled in groups of 96 to create a set of 64 pools. Each pool was grown and the 96 fusion proteins are purified in batch. Each pool was then assayed for a biochemical function (Martzen et al., 1999). Pools positive for function were then deconvoluted using smaller pools consisting of strains from rows and columns of a 96-well plate.

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