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The resulting sample TPDB-BP-TEA could be used as the highly efficient heterogeneous catalyst for the synthesis of cyclic carbonates from cycloaddition of CO 2 and epoxides under metal-free and solvent-free conditions. Relative high yields and selectivity are obtained over various substrates, and the catalyst can be facilely separated and reused with very steady activity. The approach in this work triggers an ideal pathway for an easy access to a series of porous, functionalizable polymers, which not only can be applied for chemical fixation of CO 2 into fine chemicals, but is also promising for a myriad of potential catalytic applications.

Appl Catal A Gen — Chem Soc Rev — Chem Rev — Chaturvedi D Recent developments on task specific ionic liquids.

1. Introduction

Curr Org Chem — Angew Chem Int Ed — ACS Catal — Catal Commun — Sekine K, Yamada T Silver-catalyzed carboxylation. Dalton Trans — Green Chem — Organometallics — J Mater Chem A — Chem Commun — J Am Chem Soc — Nano Lett — Chem Eur J — Chem Sci — Yang Y, Zhang Q, Zhang S, Li S Synthesis and characterization of triphenylamine-containing microporous organic copolymers for carbon dioxide uptake.

Polymer — Catal Sci Technol — Phys Chem Chem Phys — Chem Mater — Download references. SW is the first author. SW and SC carried out the experiments and characterizations. All authors read and approved the final manuscript. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Figure S2. Figure S3.


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Figure S4. Figure S5. Reprints and Permissions. Search all SpringerOpen articles Search. Experimental Materials and methods All the chemicals were of chemical grade and used as purchased. Scheme 1. Full size image. Conclusions A porous organic polymer with large surface area, high density of ionic sites, and functional —OH groups is developed by Friedel—Crafts alkylation and post modification reaction. References 1. Chem Rev — Article Google Scholar 4. Catal Commun — Article Google Scholar 8. Dalton Trans — Article Google Scholar Green Chem — Article Google Scholar Organometallics — Article Google Scholar Chem Commun — Chem Commun — Article Google Scholar Nano Lett — Article Google Scholar Chem Sci — Article Google Scholar The active site features that delineate the catalytic role of the zinc site have not yet been completely defined for any zinc metalloenzymes, although CA has been studied in the greatest detail Christianson and Fierke The de novo design of zinc sites using solely the geometry of structurally characterized sites Hellinga , Hellinga et al.

CA is a ubiquitous zinc metalloenzyme that catalyzes the reversible hydration of carbon dioxide. In mammals, more than seven isozymes have been identified, and the isozyme CA II has the highest specific activity Silverman and Lindskog , Silverman and Vincent Although additional CA isozymes and families have been discovered in recent years, the main features of the catalytic mechanism of the mammalian enzyme are retained Lindskog In the first step, zinc-bound hydroxide attacks the carbonyl carbon of CO 2 to form zinc-bound bicarbonate; bicarbonate is subsequently displaced with water by a ligand-exchange step.

This hydrophobic region is probably the substrate CO 2 binding site, as indicated by the structure of the complex of the enzyme with bicarbonate and formate Hakansson et al. Based on the crystal structure of the enzyme complexed with bisulfite, a catalytic mechanism has been proposed, involving a transient pentacoordinate zinc ion Fig.

The zinc-liganding side chains H 94 , H 96 and H are shown as ball-and-stick models. Although the CAs from the seven known isozymes and across a wide variety of species show a high degree of homology, two CAs have been discovered that differ significantly from mammalian CA II: a CA from the archaeon Methanosarcina thermophila Kisker et al. Although there is little primary sequence similarity between the three families, many of the important active site residues are conserved, and all three CA families contain zinc at the active site Bracey et al. The CA from M. The zinc-binding site is made up of His 81 and His from one monomer and His from the neighboring monomer along with a coordinated water.

However, because sulfonamides inhibit plant-type CAs Pocker and Ng as they do in mammalian CAs, it is presumed that the zinc bound to the plant enzyme is also catalytic. The determinants of metal affinity and catalysis in the zinc-binding site of CA have been investigated using the complementary techniques of molecular biology, enzymology and structural biology.

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These studies highlight the functional importance of the nature of the zinc ligands, the structure of the active site hydrogen bond networks and the hydrophobic residues surrounding the zinc site Huang et al. In CA II, and probably in all catalytic zinc sites, the protein scaffolding modulates the chemical properties of the zinc ion and zinc-bound solvent.

Specifically, the protein plays a critical role in lowering the p K a of zinc-bound water to 6. In addition, the affinity of sulfonamide inhibitors, in which the sulfonamide anionic nitrogen displaces the zinc-water to directly coordinate zinc Vidgren et al. These data suggest that the neutral ligand field in CA is essential for high affinity coordination of anions and efficient catalysis of CO 2 hydration. To further test this hypothesis, two neutral amino acid substitutions, asparagine or glutamine, were substituted for the histidine zinc ligands.

The slight increase in the p K a of zinc-bound water and the high affinity for sulfonamide inhibitors of these carboxamide CA II variants indicate that the positive charge on the zinc ion is crucial for stabilizing bound anions at the active site of CA II Lesburg et al. Furthermore, in each case, the activity of the asparagine or glutamine substitution was higher than the respective aspartate or glutamate substitution, suggesting that the net positive charge at the active site is important for stabilizing the catalytic transition state. However, the activity of the CA II variants with carboxamide side chains coordinating zinc decreased compared with the wild-type His 3 metal polyhedron in each case.

The bulky histidine ligands especially H may play a role in disfavoring higher coordination numbers, and therefore stabilizing a low coordination number, for the active site zinc ion of native CA II. This decreased coordination number should both depress the p K a of zinc-bound solvent and increase its reactivity Bertini et al. Furthermore, the metal affinity of the variants with carboxamide ligands is significantly compromised Lesburg et al. Taken together, these data indicate that the neutral histidine ligands of the zinc-binding site optimize the electrostatic environment of the active site to maintain high catalytic activity and high zinc affinity in CA II.

This loss of zinc-binding affinity is not due to the total loss of a hydrogen bond; compensatory hydrogen bonds are formed to either water or alternative amino acid side chains Lesburg and Christianson , Xue et al. In each case, the hydrogen bond to the direct ligand is weakened, due to either the entropic cost of sequestering a solvent molecule into the hydrophobic active site Fersht or the nonoptimal hydrogen bonding stereochemistry.

The weakening of these hydrogen bonds should increase the mobility of the direct ligands, and hence the role of the indirect ligands is to preorganize the histidines for optimal zinc coordination and avidity. Not only are all three histidines preordered by a hydrogen bonding network Kiefer et al. The water-to-T hydrogen bond seems to be a high energy interaction Krebs et al.

Even in the apo-CA II structure, the water is present in a similar position as in the zinc structure Hakansson et al. The importance of preordering the catalytic water in encouraging a tetrahedral binding site is underlined by two branches of evidence; when the threonine is eliminated, by making a T A substitution, the zinc ion is found to have two solvent ligands Xue et al.

Altogether, these data indicate that the H-bonding network to zinc-water is crucial for catalytic activity and must be included in enzyme modeling or design attempts. The role of highly conserved aromatic residues near the zinc-binding site of CA II in affecting metal ion binding has also been examined. Similar changes in metal specificity are observed when wild-type CA II is partially unfolded by incubation with guanidine hydrochloride, suggesting that the changes in metal binding properties are due to increased flexibility of the protein structure in the metal binding site Hunt et al.

These data reveal one of the structural features a protein may use to optimize binding specificity for a catalytic metal ion; the high stability of the protein structure surrounding the direct ligands. Knowledge of the structural factors that lead to high metal ion specificity will aid in the design of metal ion biosensors. An understanding of naturally occurring metal ion binding sites, in particular the factors governing specificity and avidity, will also aid in creating de novo metal-binding proteins and in designing new metal sites in existing proteins.

Such metal-binding sites could be designed to act as metal-activated switches for control of activity McGrath et al. The use of modified metalloproteins as sensors has several advantages over current analytical techniques. The use of biomolecules allows high selectivity in the recognition of analytes, such as metal ions, in complex natural solutions, e. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign In. Advanced Search.

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Background

Properties of zinc. Application of knowledge. Oxford Academic. Google Scholar. Chih-chin Huang. Carol A. Cite Citation. Permissions Icon Permissions. TABLE 1. Open in new tab. TABLE 2. Open in new tab Download slide. Alexander et al Search ADS. Argos et al Similarities in active center geometries of zinc-containing enzymes, proteases and dehydrogenases. Arnold and Haymore Bertini et al Betts et al Cytidine deaminase: the 2. Bode et al Structure of astacin and implications for activation of astacins and zinc-ligation of collagenases.

Bogin et al Thermoanaerobacter brockii alcohol dehydrogenase: characterization of the active site metal and its ligand amino acids. Bracey et al Spinach carbonic anhydrase: investigation of the zinc-binding ligands by site-directed mutagenesis, elemental analysis, and EXAFS. Bryce-Smith Butler Carrell et al Cedergren-Zeppezauer et al X-ray analysis of structural changes induced by reduced nicotinamide adenine dinucleotide when bound to cysteinecarboxymethylated liver alcohol dehydrogenase.

Chakrabarti Geometry of interaction of metal ions with sulfur-containing ligands in protein structures.

Akiyama-Terada Catalyst

Chakrabarti a. Geometry of interaction of metal ions with histidine residues in protein structures. Chakrabarti b. Interaction of metal ions with carboxylic and carboxamide groups in protein structures. Christianson Christianson and Cox Catalysis by metal-activated hydroxide in zinc and manganese metalloenzymes. Christianson and Fierke Carbonic anhydrase: evolution of the zinc binding site by nature and by design.


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  • Christianson and Lipscomb Coleman Zinc proteins: enzymes, storage proteins, transcription factors, and replication proteins. Google Preview. Cotton and Wilkinson Dideberg et al Eriksson et al Fersht Fierke et al Functional consequences of engineering the hydrophobic pocket of carbonic anhydrase II.

    Fuiji et al The crystal structure of zinc-containing ferredoxin from the thermoacidophilic archaeon Sulfolobus sp. Glusker Gomis-Ruth et al Refined 1. Gonzalez et al Cobalamin-independent methionine synthase from Escherichia coli : a zinc metalloenzyme. Gooley et al Secondary structure and zinc ligation of human recombinant short-form stromelysin by multidimensional heteronuclear NMR. Goulding and Matthews Cobalamin-dependent methionine synthase from Escherichia coli : involvement of zinc in homocysteine activation.

    Metal-templated chiral Brønsted base organocatalysis

    Gregory et al Hakansson et al Structure of native and apo carbonic anhydrase II and some of its anion-ligand complexes. Hakansson and Wehnert Hellinga Hellinga et al Construction of new ligand binding sites in proteins of known structure: II. Grafting of a buried transition metal binding site into Escherichia coli thioredoxin.

    Intramolecular versus Intermolecular Hydrogen Bond

    Hewett-Emmett and Tashian Hightower et al H-Ras peptide and protein substrates bind protein farnesyltransferase as an ionized thiolate. Holz et al Honzatko et al Crystal and molecular structures of native and CPP-liganded aspartate carbamoyltransferase from Escherichia coli. Hough et al High-resolution 1. Huang et al Reversal of the hydrogen bond to zinc ligand histidine dramatically diminishes catalysis and enhances metal equilibration kinetics in carbonic anhydrase II. Huheey et al Hunt et al Metal binding specificity in carbonic anhydrase is influenced by conserved hydrophobic core residues.

    Hunt and Fierke Selection of carbonic anhydrase variants displayed on phage: aromatic residues in zinc binding site enhance metal affinity and equilibration kinetics. Ippolito et al Structure-assisted redesign of a protein-zinc binding site with femtomolar affinity. Ippolito and Christianson Jackman et al Disruption of the active site solvent network in carbonic anhydrase ii decreases the efficiency of proton transfer. Jernigan et al Kiefer and Fierke Functional characterization of human carbonic anhydrase II variants with altered zinc binding sites.

    Kiefer et al a. Kiefer et al b. Engineering a cysteine ligand into the zinc binding site of human carbonic anhydrase II. Kiefer et al Hydrogen bond network in the metal binding site of carbonic anhydrase enhances zinc affinity and catalytic efficiency. Kim and Wyckoff Reaction mechanism of alkaline phosphatase based on crystal structures: two-metal ion catalysis.

    Kisker et al Klabunde et al Krebs and Fierke Determinants of catalytic activity and stability of carbonic anhydrase ii as revealed by random mutagenesis. Krebs et al a. Structural and functional importance of a conserved hydrogen bond network in human carbonic anhydrase II. Krebs et al b. Kinetic and spectroscopic studies of hydrophilic amino acid substitutions in the hydrophobic pocket of human carbonic anhydrase II.

    LeClerc and Grahame Methylcobamide:coenzyme M methyltransferase isozymes from Methanosarcina barkeri. Lesburg and Christianson X-ray crystallographic studies of engineered hydrogen bond networks in a protein-zinc binding site. Lesburg et al