Fast Catalysis Research Articles

Double geminal C-H activation and reversible alpha-elimination in 2-aminopyridine iridium(III) complexes: the role of hydrides and solvent in flattening the free energy surface.

[H2Ir(OCMe2)2L2]BF4 (1) (L = PPh3), a preferred catalyst for tritiation of pharmaceuticals, reacts with model substrate 2-(dimethylamino)pyridine (py-NMe2; py = 2-pyridyl) to give chelate carbene [H2Ir(py-N(Me)CH=)L2]BF4 (2a) via cyclometalation, H2 loss, and reversible alpha-elimination. Agostic intermediate [H2Ir(py-N(Me)CH2-H)L2]BF4) (4a), seen by NMR, is predicted (DFT(B3PW91) computations) to give C-H oxidative addition to form the alkyl intermediate [(H)(eta2-H2)Ir(py-N(Me)CH2-)L2]BF4. Loss of H2 leads to the fully characterized alkyl [HIr(OCMe2)(py-N(Me)CH2-)L2]BF4 (3a(Me2CO)), which loses acetone to give alkylidene hydride 2a by rapid reversible alpha-elimination. 2a rapidly reacts with excess H2 in d6-acetone to generate [H2Ir(OC(CD3)2)2L2]BF4 (1-d12), 3a((CD3)2CO), and py-NMe2 in a 1:1:1 ratio, showing reversibility and accounting for the selective isotope exchange catalyzed by 1. Reaction of 1 with py-N(CH2)4 gives the fully characterized carbene 2c. A cis-L(2) carbene intermediate, cis-2c, observed by NMR, reacts with CO via retro alpha-elimination to give the alkyl 3cCO, while the trans isomer, 2c, does not react; retro alpha-elimination thus requires the Ir-H bond to be orthogonal to the carbene plane. Consistent with experiment, computational studies show a particularly flat PE surface with activation of the agostic C-H bond giving a less stable H2 complex, then formation of a kinetic carbene complex with cis-L, only seen experimentally for py-N(CH2)4. Hydrides at key positions, together with gain or loss of solvent and H2, flatten the PE (DeltaG) surfaces to allow fast catalysis.

Aqueous biphasic hydrogenations.

In addition to the useful physical properties of biphasic systems (easy separation of products and catalyst, facile catalyst reuse) aqueous media may largely influence the chemistry of catalytic reactions. By appropriate pH manipulations, the selectivity of hydrogenation of unsaturated aldehydes with ruthenium(II) phosphine catalysts was controlled from the exclusive formation of saturated aldehydes to that of unsaturated alcohols. Phase separation of the constituents of catalytic systems eliminated substrate inhibition (hydrogenation of aldehydes) and helped formation of catalytically active species ([RhH(PPh(3))(3)] from [RhCl(PPh(3))(3)] in hydrogenation of acetophenone). The reactive nature of H(2)O was revealed by fast catalysis of H/D exchange and deuteration processes.

Downsizing proteolytic digestion and analysis using dispenser-aided sample handling and nanovial matrix-assisted laser/desorption ionization-target arrays.

An efficient technique for enzymatic digestion of proteins in nanovial arrays and identification by peptide mass fingerprinting using matrix-assisted laser desorption/ionization (MALDI-MS) is presented in this work. Through dispensing of a protein solution with simultaneous evaporation the protein (substrate) is concentrated up to 300 times in-vial. At higher substrate concentrations the catalytic turnover numbers increase according to the Michaelis-Menten kinetics. Therefore, the dispenser-aided nanodigestion is valuable for identification of low-level proteins (10 nM-500 nM) as well as for automatic high efficiency digestions performed in 0.2-10 min. As an example of low-level protein identification, a 10 nM solution of lysozyme C was unambiguously identified after 5 min of nanodigestion. Moreover, only 30 s nanodigestion was sufficient to identify hemoglobin (10 microM), exemplifying the fast catalysis of the nanodigestion technique. The developed silicon flow-through piezoelectric dispenser is adapted for low-volume and preconcentrated samples in the nL-microL range and provides fast, accurate and contact-free sample positioning into the nanovials. In this work, the properties of the nanodigestion concept regarding proteins of different characteristics are explored. Furthermore, the potential of automated protein identification using precoated proteolytic nanovial-arrays is demonstrated.

Dynamics of low-barrier proton transfer in polar solvents and protein media

Abstract Proton transfer in chemical, physical, and biological systems frequently involves low and shallow barriers. This is caused by strong donor-acceptor interaction which also imposes fully adiabatic character on the process. Low or shallow barriers are not covered straightforwardly by tunnel views otherwise central in proton transfer theory. We introduce a formalism focused on a shallow enough proton transfer mode that the proton dynamics is indistinguishable from classical behaviour, strongly coupled to stochastic environmental nuclear motion. We derive rate constants for three cases, namely fast solvent relaxation, fast proton equilibration, and proton transfer followed by fast decay of the donor-acceptor complex. These cases may constitute useful descriptions of several kinds of processes including fast intramolecular proton transfer, hydrolytic and redox enzyme catalysis, and physical or biological proton conductivity.

ChemInform Abstract: FAST CATALYSIS OF A HYDROGEN EXCHANGE REACTION AT LOW TEMPERATURES BY GOLD

Chemischer InformationsdienstVolume 6, Issue 23 Preparative Organic Chemistry ChemInform Abstract: FAST CATALYSIS OF A HYDROGEN EXCHANGE REACTION AT LOW TEMPERATURES BY GOLD D. I. BRADSHAW, D. I. BRADSHAWSearch for more papers by this authorR. B. MOYES, R. B. MOYESSearch for more papers by this authorP. B. WELLS, P. B. WELLSSearch for more papers by this author D. I. BRADSHAW, D. I. BRADSHAWSearch for more papers by this authorR. B. MOYES, R. B. MOYESSearch for more papers by this authorP. B. WELLS, P. B. WELLSSearch for more papers by this author First published: June 10, 1975 https://doi.org/10.1002/chin.197523153Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue23June 10, 1975 RelatedInformation

Fast catalysis of a hydrogen exchange reaction at low temperatures by gold

Download options Please wait... Article information DOI https://doi.org/10.1039/C39750000137 Article type Paper Download Citation J. Chem. Soc., Chem. Commun., 1975, 137-138 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Fast catalysis of a hydrogen exchange reaction at low temperatures by gold D. I. Bradshaw, R. B. Moyes and P. B. Wells, J. Chem. Soc., Chem. Commun., 1975, 137 DOI: 10.1039/C39750000137 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author David I. Bradshaw Richard B. Moyes Peter B. Wells