Lipscomb structure

Two stable bicarbonato complexes of bis(l,10-phenanthroline) copper(II) were reported for the first time by Mao et al. (44). These are akin to the Lipscomb and Lindskog structures of human carbonic anhydrase (HCA) (45). In the Lipscomb structure the bicarbonate acts as a bidentate ligand while in the Lindskog structure it is essentially coordinated to the metal center in unidentate fashion (Fig. 2). 

Fig. 2. [Cu(phen)2(0C02H)]+ N-N = 1,10-phenanthroline. 5 - Lipscomb structure 6 - Lindskog structure.

Stevens, R. C., J. E. Gouaux, and W. N. Lipscomb, Structural consequences of effector binding to the T state of aspartate carbamoyltransferase Crystal structures of the unligated and ATP- and CTP-complexed enzymes at 2.6 A resolution. Biochem. 29 7691, 1990. 

M) for the [12]aneN3 and [12]aneN4 complexes, respectively. The relatively higher stability of [[12]aneN3-Zn-0C02H] (for which chelation of the Zn center by the coordinated bicarbonate is possible Lipscomb structure) was attributed to its reduced reactivity. 

Dulmage W J and Lipscomb W N 1951 The crystal structures of hydrogen cyanide, HON Acta Crystallogr. 4 330... 

Figure 2.11 Beta sheets are usuaiiy represented simply by arrows in topology diagrams that show both the direction of each (3 strand and the way the strands are connected to each other along the polypeptide chain. Such topology diagrams are here compared with more elaborate schematic diagrams for different types of (3 sheets, (a) Four strands. Antiparallel (3 sheet in one domain of the enzyme aspartate transcarbamoylase. The structure of this enzyme has been determined to 2.8 A resolution in the laboratory of William Lipscomb, Harvard University, (b) Five strands. Parallel (3 sheet in the redox protein flavodoxin, the structure of which has been determined to 1.8 A resolution in the laboratory of Martha Ludwig, University of Michigan, (c) Eight strands. Antiparallel barrel in the electron carrier plastocyanln. This Is a closed barrel where the sheet is folded such that (3 strands 2 and 8 are adjacent. The structure has been determined to 1.6 A resolution in the laboratory of Hans Freeman in Sydney, Australia. (Adapted from J. Richardson.)...

Gouaux, J.E., Lipscomb, W.N. Crystal structures of phosphonoacetamide ligated T and phosphono-acetamide and malonate ligated R states of aspartate carbamoyltransferase at 2.8 A resolution and neutral pH. Biochemistry 29 389-402, 1990. 

Carboxypeptidases are zinc-containing enzymes that catalyze the hydrolysis of polypeptides at the C-terminal peptide bond. The bovine enzyme form A is a monomeric protein comprising 307 amino acid residues. The structure was determined in the laboratory of William Lipscomb, Harvard University, in 1970 and later refined to 1.5 A resolution. Biochemical and x-ray studies have shown that the zinc atom is essential for catalysis by binding to the carbonyl oxygen of the substrate. This binding weakens the C =0 bond by... 

C = 12 internationally adopted as the unified atomic weight standard by both chemi.sts and physicists. 6-coordinate carbon established in various carboranes by W. N. Lipscomb and others. (Nobel Prize 1976 for structure and bonding of boranes). 

Many attempts have been made to rationalize the structures and inechanir-mb of formation of pcilynsevillatcs. Lipscomb observed th t no individual MOn octahedral unit ever has more than twii unshared, i.c. tcrmiacil oxygens (exceptions jppi to be scible only in the solid state) and this has been explained on the basis of T-bondi e between the metal and terminal oxygen Moms awire thnn two of thc,sc... 

W. N. Lipscomb (Harvard) studies on the structure of boranes illuminating problems of chemical bonding. 

Fig. 12-9. Stereochemical structure of the decahydrodecaborate dianion (B10H o, 12.164 after Dobrott and Lipscomb, 1962).

Kleier, D. A., and W. N. Lipscomb. 1977. Molecular Orbital Study of Polypeptides. Conformational and Electronic Structure of Polyglycine. Int. J. Quantum Chem. Quantum Biol. Symp. 4, 73-86. 

One group of structures is characterized by the presence of a reasonable match of the metal ion for the radius of the cavity in the crown. An example of this type is given by the structure of the 1 1 complex between dibenzo-14-crown-4 and LiSCN (Shoham, Lipscomb Olsher, 1983a). In this species, the Li+ is five-coordinate, being bound to the four ether... 

D. Erion, S- J- Pilkis, M. R. El-Maghrabi, and W. N. Lipscomb, The allosteric site of human liver fructose 1,6-bisphosphatase. Analysis of six AMP site mutants based on the crystal structure, J. Biol. Chem. 269 27732 (1994). 

Solving the simultaneous equations (2a) and (2b) leads to y = 3 and t = n — 2, implying the presence of three B-B bonds and n — 2 B-B-B bonds in the boron skeleton. Since a deltahedron with n vertices has In — 4 faces, the n — 2 B-B-B bonds cover exactly half of the faces. In this sense a Kekule-type structure for the deltahedral boranes B H 2- has exactly half of the faces covered by B-B-B bonds just as a Kekule structure for benzene has half of its edges covered by C=C double bonds. In 1977 Lipscomb and co-workers [29] reported a variety of such Kekule-type localized bonding structures with the lowest energies for deltahedral boranes. These structures were computed using wave functions in the differential overlap approximation. 

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