Self-assembly of organocatalysts: fine-tuning organocatalytic reactions.
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Journal Article↗
Biomedical subjects
Matthew L Clarke
Publications and source records attributed to Matthew L Clarke.
Highly regioselective rhodium-catalysed hydroformylation of unsaturated esters: the first practical method for quaternary selective carbonylation.
Highly regioselective hydroformylation of unsaturated esters can be achieved when a highly reactive, ligand-modified, rhodium catalyst is employed near ambient temperatures (15-50 degrees C) and pressures over 30 bar. The use of 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantane shows distinct advantages over other commonly applied phosphanes in terms of reaction rate, and regio- and chemoselectivity. Hydroformylation of a range 1,1-di- and 1,1,2-trisubstituted unsaturated esters yields quaternary aldehydes that are forbidden products according to Keulemans Rule. The aldehydes can be reductively aminated with molecular hydrogen to give beta-amino acid esters in high yield. The overall green chemical process involves converting terminal alkynes into unusual beta-amino acid esters with only water generated as an essential byproduct. This catalytic system has also been applied to the hydroformylation of simple 1,2-disubstitued unsaturated esters, which have been hydroformylated with excellent alpha-selectivity and good chemoselectivity for the first time.
Journal Article↗
Polymer surface reorientation after protein adsorption.
Surface side-chain orientation changes of two polymers have been observed upon protein adsorption using sum frequency generation vibrational spectroscopy. Side-chain-deuterated poly(ethyl methacrylate) and poly(n-butyl methacrylate) were contacted with five protein solutions: albumin, fibrinogen, ubiquitin, cytochrome c, and lysozyme. The CD(3)/CD(2) symmetric stretch ratios of the surface polymer side chains in contact with these different media were compared to each other and to that of the polymer contacting air or phosphate buffered saline. The adsorption of different proteins to the surfaces resulted in polymer side-chain orientations slightly different from each other, with orientations between the air and buffer cases.
Adsorption↗
Molecular level structures of poly(n-alkyl methacrylate)s with different side chain lengths at the polymer/air and polymer/water interfaces.
Sum frequency generation (SFG) vibrational spectroscopy has been successfully applied to study molecular structures of several poly(n-alkyl methacrylate)s (PAMAs) with different side chain lengths at the PAMA/air and PAMA/water interfaces. We have observed that the ester side chains from all PAMAs always dominate the interface, but the orientation information of the methyl end group on the side chains varies, depending on the length of the side chain. The contributions from methylene groups on the side chains have been evaluated, and the surface structures have been related to the surface tension of these polymers. Different water restructuring behaviors have been observed for different PAMAs. This phenomenon and its reversibility are strongly dependent on the glass transition temperature of each polymer, which is influenced by the side chain length. Detailed data fitting and analysis has been discussed.
Air↗
Vibrational spectroscopic studies on fibrinogen adsorption at polystyrene/protein solution interfaces: hydrophobic side chain and secondary structure changes.
Structural changes of fibrinogen after adsorption to polystyrene (PS) were examined at the PS/protein solution interface in situ using sum frequency generation (SFG) vibrational spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Different behaviors of hydrophobic side chains and secondary structures of adsorbed fibrinogen molecules have been observed. Our results indicate that upon adsorption, the hydrophobic PS surface induces fast structural changes of fibrinogen molecules by aligning some hydrophobic side chains in fibrinogen so that they face to the surface. Such structural changes of fibrinogen hydrophobic side chains are local changes and do not immediately induce significant changes of the protein secondary structures. Our research also shows that the interactions between adsorbed fibrinogen and the PS surface can induce significant changes of protein secondary structures or global conformations which occur on a much longer time scale.
Adsorption↗
Conformational changes of fibrinogen after adsorption.
The adsorption behavior of fibrinogen to two biomedical polyurethanes and a perfluorinated polymer has been investigated. Changes in the secondary structure of adsorbed fibrinogen were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and sum frequency generation vibrational spectroscopy (SFG). SFG measurements were performed in the amide I range as well as in the C-H/N-H stretching range. Amide I signals from SFG demonstrate that fibrinogen has post-adsorption conformational changes that are dependent upon the polymer surface properties. For example, strong attenuation of the amide I and N-H stretching signals with increasing residence time was observed for fibrinogen adsorbed to poly(ether urethane) but not for the other two polymers. This change is not readily observed by ATR-FTIR. Differences in the observed spectral changes for fibrinogen adsorbed to each polymer are explained by different initial binding mechanisms and post-adsorption conformational changes.
Adsorption↗
Detection of chiral sum frequency generation vibrational spectra of proteins and peptides at interfaces in situ.
In this work, we demonstrate the feasibility to collect off-electronic resonance chiral sum frequency generation (SFG) vibrational spectra from interfacial proteins and peptides at the solid/liquid interface in situ. It is difficult to directly detect a chiral SFG vibrational spectrum from interfacial fibrinogen molecules. By adopting an interference enhancement method, such a chiral SFG vibrational spectrum can be deduced from interference spectra between the normal achiral spectrum and the chiral spectrum. We found that the chiral SFG vibrational spectrum of interfacial fibrinogen was mainly contributed by the beta-sheet structure. For a beta-sheet peptide tachyplesin I, which may be quite ordered at the solid/liquid interface, chiral SFG vibrational spectra can be collected directly. We believe that these chiral signals are mainly contributed by electric dipole contributions, which can dominate the chiroptical responses of uniaxial systems. For the first time, to our knowledge, this work indicates that the off-electronic resonance SFG technique is sensitive enough to collect chiral SFG vibrational spectra of interfacial proteins and peptides, providing more structural information to elucidate interfacial protein and peptide structures.
Animals↗
The electron-poor phosphines P{C6H3(CF3)2-3,5}3 and P(C6F5)3 do not mimic phosphites as ligands for hydroformylation. A comparison of the coordination chemistry of P{C6H3(CF3)2-3,5}3 and P(C6F5)3 and the unexpectedly low hydroformylation activity of their rhodium complexes.
The fluoroaryl phosphines P{C6H3(CF3)2-3,5}3 (La) and P(C6F5)3 (Lb) form the complexes trans-[MCl2(La)2] and trans-[MCl2(Lb)2](M = Pd or Pt) which have been isolated and fully characterised. 31P NMR studies of competition experiments show that the stability of trans-[PdCl2L2] is in the order L = Lb< La <PPh3. The crystal structure of trans-[PtCl2(La)2] is reported and reveals that the Pt-P bond lengths in trans-[PtCl2L2] are in the order L = Lb< La < PPh3. The equilibria established when [Pt(norbornene)3] is treated with or are investigated by 31P and 195Pt NMR spectroscopy and the species [PtLn(norbornene)3-n](n= 1-3) identified. Ligands and appear to have similar affinities for platinum(0). The complexes trans-[MCl(CO)(La)2] and trans-[MCl(CO)(Lb)2](M = Rh or Ir) have been synthesised and fully characterised; the values of nu(CO) are comparable with those for analogous phosphite complexes. The ligands La, Lb, P(C6H2F3-3,4,5)3 (Lc), P{C6H4(CF3)-2}3 (Ld), PPh3 and P(OPh)3 have been tested in rhodium-catalysed hydroformylation of 1-hexene and La, Lb, and PPh3 have been tested in rhodium-catalysed hydroformylation of 4-methoxystyrene. Ligands La, and Lb, have been shown to be stable under the hydroformylation catalysis conditions. For the 1-hexene reaction, the activity and selectivity for and are very similar to the PPh3 catalyst (TOF ca. 400 h(-1); n : iso 2.5-3.0) but for the sterically demanding and the activity and selectivity was much lower than with PPh3 (TOF ca. 15, n : iso ratio 0.6). Thus, the yield of heptanals obtained with the catalyst derived from La is 94% while under the same conditions with Lb only 6%. The TOF for the La/Rh catalyst was 5 times lower than for the P(OPh)3/Rh catalyst despite the superficially similar ligand electronic characteristics for La and P(OPh)3.
Journal Article↗
Phenylphosphatrioxa-adamantanes: bulky, robust, electron-poor ligands that give very efficient rhodium(I) hydroformylation catalysts.
The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane (1a) and 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-phosphaadamantane (1b) have been made by the acid catalysed addition of PhPH(2) to the appropriate beta-diketones; the acid used (HCl, H(3)PO(4) or H(2)SO(4)) and its concentration affect the rate and selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl(2)(NCPh)(2)] to form complexes trans-[PdCl(2)(1a)(2)](2a) and trans-[PdCl(2)(1b)(2)](2b) as mixtures of rac and meso diastereoisomers. The platinum(II) chemistry is more complicated and when 1a or 1b is added to [PtCl(2)(cod)], equilibrium mixtures of trans-[PtCl(2)L(2)] and [Pt(2)Cl(4)L(2)](L = or ) are formed in CH(2)Cl(2) solution. Meso/rac mixtures of trans-[MCl(CO)(1a)(2)] M = Ir (6a) or Rh (7a) are formed upon treatment of MCl(3).nH(2)O with an excess of 1a and the anionic cobalt complex [NHEt(3)][CoCl(3)(1a)](9) was isolated from the product formed by CoCl(2).6H(2)O and 1a. The nu(CO) values from the IR spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C-P-C angle of ca. 94 degrees is observed; this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are similar and large (ca. 200 degrees). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any previously reported catalyst.
Journal Article↗
Polarization mapping: a method to improve sum frequency generation spectral analysis.
A "polarization mapping" method has been applied to improve the fitting quality of sum frequency generation (SFG) vibrational spectra of complicated systems and validate the data analysis of simple SFG spectra. Using such a method, two-dimensional SFG spectra can be constructed, from which more reliable spectral information can be obtained from a surface/interface. Model calculations as well as experiments have been employed to illustrate the power of the polarization mapping method for spectral analysis of SFG spectra. By using a deuterated polystyrene surface and interfacial protein molecules as examples, we demonstrate that this method is especially important for complicated molecules, such as polymers and proteins.
Journal Article↗
Sum frequency generation studies on the surface structures of plasticized and unplasticized polyurethane in air and in water.
This study characterizes the molecular surface structures of polyurethane (PU) and plasticized PU films in air, in water, and in albumin solution in situ using a nonlinear optical technique, sum frequency generation (SFG) vibrational spectroscopy. Two different plasticizers are investigated: dioctyl sebacate (DOS) and o-nitrophenyl octyl ether (NPOE). Plasticization of PU is common for biosensors to achieve better adhesion, malleability, elasticity, and permeability; however, this can adversely affect biocompatibility. Our research indicates that plasticizers can segregate to the PU surface not only in air but also in water. In addition, plasticizer content can affect protein adsorption behaviors of PU surfaces. This is the first time surface-sensitive SFG has been applied to deduce plasticizer surface behavior in situ. More specifically, we found that DOS dominates the surface of the film with DOS surface concentrations higher than DOS bulk concentrations both in air and in contact with an aqueous environment. NPOE has a reduced effect at the surface compared to DOS in both air and aqueous environments. Addition of either DOS or NPOE to PU was also found to cause a change in albumin adsorption.
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