Publications by authors named "Ryan K Zeidan"

6 Publications

  • Page 1 of 1

Nanoscale organization of thiol and arylsulfonic acid on silica leads to a highly active and selective bifunctional, heterogeneous catalyst.

J Am Chem Soc 2008 Oct 13;130(40):13442-9. Epub 2008 Sep 13.

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.

Ordered mesoporous silicas functionalized with alkylsulfonic acid and thiol group pairs have been shown to catalyze the synthesis of bisphenols from the condensation of phenol and various ketones, with activity and selectivity highly dependent on the distance between the acid and thiol. Here, a new route to thiol/sulfonic acid paired catalysts is reported. A bis-silane precursor molecule containing both a disulfide and a sulfonate ester bond is grafted onto the surface of ordered mesoporous silica, SBA-15, followed by simultaneous disulfide reduction and sulfonate ester hydrolysis. The resulting catalyst, containing organized pairs of arylsulfonic acid and thiol groups, is significantly more active than the alkylsulfonic acid/thiol paired catalyst in the synthesis of bisphenol A and Z, and this increase in activity does not lead to a loss of regioselectivity. The paired catalyst has activity similar to that of a randomly bifunctionalized arylsulfonic acid/thiol catalyst in the bisphenol A reaction but exhibits greater activity and selectivity than the randomly bifunctionalized catalyst in the bisphenol Z reaction.
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http://dx.doi.org/10.1021/ja804082mDOI Listing
October 2008

Cooperative catalysis by silica-supported organic functional groups.

Chem Soc Rev 2008 Jun 17;37(6):1118-26. Epub 2008 Mar 17.

Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.

Hybrid inorganic-organic materials comprising organic functional groups tethered from silica surfaces are versatile, heterogeneous catalysts. Recent advances have led to the preparation of silica materials containing multiple, different functional groups that can show cooperative catalysis; that is, these functional groups can act together to provide catalytic activity and selectivity superior to what can be obtained from either monofunctional materials or homogeneous catalysts. This tutorial review discusses cooperative catalysis of silica-based catalytic materials, focusing on the cooperative action of acid-base, acid-thiol, amine-urea, and imidazole-alcohol-carboxylate groups. Particular attention is given to the effect of the spatial arrangement of these organic groups and recent developments in the spatial organization of multiple groups on the silica surface.
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http://dx.doi.org/10.1039/b710334bDOI Listing
June 2008

Organized surface functional groups: cooperative catalysis via thiol/sulfonic acid pairing.

J Am Chem Soc 2007 Nov 12;129(44):13691-7. Epub 2007 Oct 12.

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.

The synthesis and characterization of heterogeneous catalysts containing surfaces functionalized with discrete pairs of sulfonic acid and thiol groups are reported. A catalyst having acid and thiol groups separated by three carbon atoms is ca. 3 times more active than a material containing randomly distributed acid and thiol groups in the condensation of acetone and phenol to bisphenol A and 14 times more active in the condensation of cyclohexanone and phenol to bisphenol Z. Increasing the acid/thiol distance in the paired materials decreases both the activity and selectivity. This work clearly reveals the importance of nanoscale organization of two disparate functional groups on the surface of heterogeneous catalysts.
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http://dx.doi.org/10.1021/ja074761eDOI Listing
November 2007

Administration in non-human primates of escalating intravenous doses of targeted nanoparticles containing ribonucleotide reductase subunit M2 siRNA.

Proc Natl Acad Sci U S A 2007 Apr 22;104(14):5715-21. Epub 2007 Mar 22.

Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 210-41, Pasadena, CA 91125, USA.

The results of administering escalating, i.v. doses of targeted nanoparticles containing a siRNA targeting the M2 subunit of ribonucleotide reductase to non-human primates are reported. The nanoparticles consist of a synthetic delivery system that uses a linear, cyclodextrin-containing polycation, transferrin (Tf) protein targeting ligand, and siRNA. When administered to cynomolgus monkeys at doses of 3 and 9 mg siRNA/kg, the nanoparticles are well tolerated. At 27 mg siRNA/kg, elevated levels of blood urea nitrogen and creatinine are observed that are indicative of kidney toxicity. Mild elevations in alanine amino transferase and aspartate transaminase at this dose level indicate that the liver is also affected to some extent. Analysis of complement factors does not reveal any changes that are clearly attributable to dosing with the nanoparticle formulation. Detection of increased IL-6 levels in all animals at 27 mg siRNA/kg and increased IFN-gamma in one animal indicate that this high dose level produces a mild immune response. Overall, no clinical signs of toxicity clearly attributable to treatment are observed. The multiple administrations spanning a period of 17-18 days enable assessment of antibody formation against the human Tf component of the formulation. Low titers of anti-Tf antibodies are detected, but this response is not associated with any manifestations of a hypersensitivity reaction upon readministration of the targeted nanoparticle. Taken together, the data presented show that multiple, systemic doses of targeted nanoparticles containing nonchemically modified siRNA can safely be administered to non-human primates.
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http://dx.doi.org/10.1073/pnas.0701458104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1829492PMC
April 2007

A solvent-free method for isotopically or radioactively labeling cyclodextrins and cyclodextrin-containing polymers.

Bioconjug Chem 2006 Nov-Dec;17(6):1624-6

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena California 91125, USA.

A method for installing a distinguishable label onto cyclodextrins or cyclodextrin-containing polymers is reported. Cyclodextrins (CD) and cyclodextrin-containing polymers are exposed to labeled (2H or 14C) ethylene oxide (EO) vapor and the alcohol groups on the CD ring open the EO to give ether-linked labeled methylenes and a terminal alcohol. This method provides for the incorporation of an easily tracked and quantified label without the use of solvents or purification steps. The method can be generalized for use with materials that contain nucleophiles other than alcohols, e.g., amines.
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http://dx.doi.org/10.1021/bc060211eDOI Listing
January 2007

Multifunctional heterogeneous catalysts: SBA-15-containing primary amines and sulfonic acids.

Angew Chem Int Ed Engl 2006 Sep;45(38):6332-5

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.

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http://dx.doi.org/10.1002/anie.200602243DOI Listing
September 2006