Chain donor

Natural a-amino acids provide a moderately effective N,OJ chelating donor set derived from carboxylate and amino groups, respectively. Several side-chain donor atoms may also be involved in metal ion coordination, especially those of Cys (thiol sulfur) and His (imidazole nitrogen(s)). (Abbreviations for amino acid residues are those recommended by IUPAC-IUB.1702)... 

In addition to the backbone donor system the amino acid residues can contain a variety of donor centers (679E). The most important of these are the imidazole N atoms of His, the S atom of Cys, and to some extent the, 3-carboxylate O atom of Asp. Other side chain donors like the O atoms of Ser and phenolic O atoms of Tyr or amino N atoms of Lys are of minor importance for coordination of Ni11 ions. Also, thioether S-donors of Met play only a minor role in the interactions with Ni11 ions.1730... 

Pd"(mida)] chelate (mida2 = methyliminodiacetate) is used to approximate the distorted tetragonal Cun-IMAC sites in order to identify which amino acid groups or their side-chain donors of SPHHGG and HHHHHH become attached to the metal site.214... 

Intramolecular stabilization via side-chain donor ligands has also been employed in the nitrogen-stabilized... 

The enzymatic synthesis of P-lactam antibiotics from P-lactam nuclei 6-aminope-nicillanic acid (APA) and 7-aminodeacetoxycephalosporanic acid (ADCA) and appropriate side chain donors has been largely studied [75, 76]. 

An efficient synthesis of P-lactam with D-phenylglycine or its derivatives as a side chain can be accomplished only by using a kinetically controlled approach via acyl group transfer from an activated side chain donor, and D-phenylglycine can be used as ester, usually methyl (PGM) or ethyl (PGE), or as amide (PGA). As a... 

L-Prolinamides (71) with a pendant alcohol act as recoverable bifunctional catalysts of direct nitro-Michael addition of ketones to -nitrostyrenes, giving syn-de s up to 94% and ees up to 80%.204 The pyrrolidine provides enamine catalysis, and the side-chain donors can hydrogen-bond the nitro oxygens. 

F. van Rantwijk, and R. A. Sheldon, Enzymatic coupling using a mixture of side chain donors affords a greener process for ampicillin, Green Chem. 2001, 3, 316-319. 

The enzyme (YerE) involved in the biosynthesis of yersiniose A has been isolated and characterized as a flavoenzyme that catalyzes the attachment of the branched chain to a 3,6-dideoxy-4-hexulose precursor, using pyruvate as the side-chain donor.228 Substrate analogues were prepared as potential inhibitors of the biosynthesis.229... 

Similarly to monomeric donors, side-chain donor polymers can afford formation of partially stacking donor moieties, which is necessary for high conductivity, if they achieve a smectic phase. A thiophene derivative con-... 

Local side-chain to main-chain hydrogen bonds are not evenly distributed. If the geometry of these interactions is analyzed in more detail (Thble 19.3), it becomes clear that the contacts between the side-chain donor in position (n) are preferentially to the main-chain acceptor C=0 in positions (n-3) and (n-4) toward the N-terminus whereas the main-chain donor N-H is more preferred if it is 2 to 3 residues (n+2, n+3) toward the C-terminus of the main-chain. There is no case of an interaction between side-chain (n) and main-chain residue (n-1), and folding back of side-chain (n) on its own peptide is mainly with Asx, Glx hydrogen bonding to N-H (n) and with Asn, Gin, Arg binding to C=0 (n). 

Two compounds common in plant metabolism are believed to be precursors of isoprenoid cytokinins in plants adenosine-5 -monophosphate (AMP) and A -isopentenylpyrophos-phate (iPP). As a final product of the mevalonate pathway, the latter substance serves also as a precursor for a wide spectrum of metabolites including some other plant hormones, as abscisic acid, gibberellins and brassinosteroids. The hypothetical scheme of reactions resulting in the formation of iPA, Z and DHZ is given in Fig. 2. The enzyme of entry into isoprenoid cytokinin formation is A -isopentenylpyrophosphate 5 -AMP-A -iso-pentenyltransferase (EC 2.5.1.8, trivially named cytokinin synthetase ). This enzyme activity was first detected in a cell-free preparation from the slime mould Dictyostelium discoideum [7,8]. Later the enzyme from higher plants (cytokinin-independent tobacco callus [9,10] and immature Zea mays kernels [11]) was described and the data were recently summarised in [12], The enzyme is very specific as far as the substrate is concerned [13,14] only the nucleotide AMP can be converted and only iPP (with a double bond in A position) may function as a side chain donor. 

Complexes of a-Amino Acids with Chelatable Side Chain Donor Atoms... 

A rod-rod-type fully conjugated D-A BCP, where acceptor main chain donor blocks are directly connected to acceptor blocks (without insulating... 

Maltotriose is effective as a side-chain donor and acceptor in the presence of a Pseudomonas isoamylase and gives a set of 6- -a-malto-... 

CHA 11] Chang D.W., Ko S.-J., Kim J.Y. et al., Multifunctional conjugated polymers with main-chain donors and side-chain acceptors for dye sensitized solar cells (DSSCs) and organic photovoltaic cells (OPVs) , Macromolecular Rapid Communications, vol. 32, no. 22, pp. 1809-1814, 2011. 

TAN 13a] Tan H., Pan C., Wang G. et ai, Synthesis and characterization of conjugated polymers with main-chain donors and pendent acceptors for dye-sensitized solar cells , RSC Advances, vol. 3, no. 37, pp. 16612-16618, 2013. 

Brauer, D.J. Fischer, J. Kucken, S. Langhans, K.P. Stelzer, O. Weferling, N. (1994) Water-soluble phosphanes. 3. Water-soluble primary phosphanes with ammonium groups NR2R in the side-chain donor-functionalized amphiphiles, Z Naturforsch. B, 49, 1511-24. 

The presence of side chain donor atoms generally influences the thermodynamic stability and coordination geometry of peptide complexes significantly. The most important findings in this field have already been reviewed by several authors [63-66]. It is evident from these compilations that the effects of various donor atoms largely depend on the number and location of the extra donor atoms and also on the nature of the metal ions. Most of the data were published for the copper(II) complexes, but nickel(II) and paUadium(II) are also widely studied. 

The synthesis and studies of multihistidine peptides is a rapidly increasing field in metallopeptide chemistry because these hgands are the most promising models for biological conditions. The exclusive coordination of the imidazole-N side chain donor atoms of these ligands results in the formation of various macrochelates built... 

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