Green Chemistry

Solar Electrochemistry: The cover-art produced for a paper published in Green Chemistry that describes the use of
sunlight-driven electrochemical reactions to recycle chemical oxidants. Kevin Moeller is researching this and other electrochemical reactions. Find out more at his group website.

Faculty, doctoral students and undergraduates talk about the department and their experiences at Washington University. From the outset, students get exposed to a broad range of expertise and fields. Interdisciplinary and collaborative research are strengths of this medium-sized department with considerable resources, instrumentation, and facilities.

The photosynthetic megacomplex from a cyanobacterium, which scientists have managed to isolate in its complete, functioning form, weighs about 6 million Daltons. Bob Blankenship and Michael Gross collaborated on the research.

The Ponder lab is researching advanced force fields for molecular dynamics simulation of water, ions, organic molecules and biopolymers. Our AMOEBA polarizable model produces "chemically accurate" interaction energetics for many systems and is being used in a variety of applications, including: proteins folding analysis, computation of free energies of binding in host-guest and protein-ligand systems, and prediction of small molecule crystal structures.

Azapentadienyl-metal complexes possess two potential sites of reactivity for electrophiles, the nitrogen atom and the basic metal center.  The Bleeke group has investigated the reactions of (1,2,3-η3)-(5-t-butylazapentadienyl)Rh(PMe3)x (x = 2 or 3) and (1,2,3-η3)-(5-t-butylazapentadienyl)Ir(PEt3)x (x = 2 or 3) with triflic acid and has shown that either the nitrogen atom or the metal center can serve as the primary reaction site (see accompanying graphic).

This class of asymmetric catalysts developed by the Birman group shows remarkable efficacy and versatility in promoting enantioselective acylation reactions and related transformations. Their ease of preparation and flexibility of the catalyst design contribute to their growing popularity in the synthetic community.

The Hayes and Conradi groups are collaborating on in situ high-pressure high-temperature NMR to monitor the reaction of CO2 as it converts to magnesium carbonate and calcium carbonate.  This work involves WU's Consortium for Clean Coal Utilization

Read more in this special issue of Environmental Science & Technology: Surface et al. Environ. Sci. Technol., 2013, 47, 119?125. DOI: 10.1021/es301287n

The image shows a "site-selective" reductive amination sequence on a microelectrode array, investigated by Kevin Moeller's group. In this experiment, Pd(II) is used at selected electrodes as an oxidant to generate a carbonyl for the reductive amination. Two reactions were conducted placing different fluorescent dyes on the array.

Two Lasers

The Michael Gross group intersects two lasers: the first is a temperature jump at 1900 cm-1(IR) to heat a flowing solution containing a protein and perturb its folding. The second at 248 nm (UV) is an FPOP probe generating OH radicals that footprint the folding state of the protein on the microsec time scale. For a description of this work, see: T-jump and Fast Photochemical Oxidation Probe Sub Millisecond Protein Folding, Jiawei Chen, Don L. Rempel, Michael L. Gross, J. Am. Chem. Soc. 132, 15502–15504 (2010).

Native Electrospray Mass Spectrometry Reveals the Nature and Stoichiometry of Pigments in the FMO Photosynthetic Antenna Protein

The FMO antenna protein from green sulfur photosynthetic bacteria has been analyzed by native mass spectrometry by Wen et al. Biochemistry (2011) 50: 3502-3511. This revealed additional pigments that function to couple this complex to the chlorosome complex that feeds energy to it. This work was a collaboration between the Blankenship and Gross research groups.

The image shows a "site-selective" Wacker oxidation on a microelectrode array, fabricated(?) by Kevin Moeller's research group. In this experiment, the Wacker oxidation is triggered by using the electrodes in the array to generate a Pd(II) oxidant.

Determining Protein:Ligand Affinities by PLIMSTEX (Protein-Ligand Interactions by Mass Spectrometry, Titration, and H/D EXchange):

Using a new approach in mass spectrometry, the Michael Gross group follows amide exchange of a protein during titration with any ligand to give protein affinities. The curve, after modeling, yields the binding constant (Κi or βi)

Read more. . .

Using a pulsed laser, the Michael Gross group photolyzes HO-OH to produce HO• for foot printing solvent-accessible side chains on proteins. The approach, coupled with MS analysis, maps protein interfaces faster than a protein can unfold.

Coupling two light absorbing pigments, a perylene and a porphyrin, into a dyad motif results in the unexpected ability to tune electronic structure of the chromophores and allows intense absorption of light spanning near-ultraviolet to near-infrared regions of the solar spectrum while maintaining a long excited-state lifetime and high fluorescence yield.

Three synthetic bacteriochlorins (mauve, gold, teal) are each attached to a native-like bacterial photosynthetic β-peptide (green), which self assembles with α-peptide (blue) and bacteriochlorophyll (purple) to form a dyad (top left) and then a cyclic oligomer with enhanced absorption (lower left).  The three constructs can be combined to give cyclic oligomers (top right) with blended bacteriochlorin absorption (lower right) and ~95% energy-transfer efficiency.

Microelectrode arrays can be used to monitor in “real-time” binding events between small molecules and proteins. The result is unique opportunity to ascertain the effectiveness of chemical probes that target a given receptor. For this reason, the Moeller group is developing the synthetic and analytical chemistry needed to take full advantage of the arrays and then employing them in biological studies. 

The Mirica group have used a tetradentate pyridonophane ligand containing a phenyl group to isolate several organometallic NiIII complexes and investigate their C-O bond formation reactivity. Interestingly, the NiIII-dihydroxide and NiIII-dimethoxide species can be synthesized and they undergo aryl methoxylation and hydroxylation that is favored by addition of an oxidant, which also depresses the β-hydride elimination side reaction.

A series of NiIII complexes containing aryl and alkyl ligands was shown to reductively eliminate to form new C-C or C-heteroatom bonds. The Mirica Group is investigating these NiIII complexes to better understand the role of NiIII intermediates in Ni-catlayzed coupling reactions.

Bis(hydrocarbyl)NiIII complexes have been commonly proposed in Ni-catalyzed cross-coupling reactions, however no such bis(hydrocarbyl) complexes have been reported to date. Recently, several organometallic NiIII complexes containing two trifluoromethyl ligands were recently synthesized and fully characterized in the Mirica Group.

Using electrochemical techniques, the Mirica Group has recently shown that the tetradentate pyridinophane ligand tBuN4 undergoing conformational changes that are essential for stabilizing PdIII and other uncommon oxidation states of various transition metals.

While previously the tetradentate ligand tBuN4 was shown to stabilize uncommon oxidation states such as PdIII, the Mirica group has also shown that other uncommon oxidation states (e. g., CoI, NiI, CuI, and NiIII) can be accessed using this ligand system.

The Mirica group has recently reported that an organometallic PdII complex supported by the common tridentate ligand Me3tacn exhibits a very low oxidation potential and undergoes unprecedented rapid aerobic oxidation to generate a PdIV–OH complex. Thermolysis of the PdIV complex leads to selective formation of 2-tert-butylphenol.

High-valent PdIII and PdIV species have been recently proposed as catalytically relevant intermediates in Pd-mediated C-C and C-heteroatom bond formation reactions. In this regard, the Mirica group has employed tetradentate RN4 ligands that allowed the unprecedented detection and characterization of both PdIII and PdIV intermediates in aerobically and photoinduced C-C bond formation reactions. Read more here or

The Mirica group has reported that a PdII-dimethyl complex supported by the tridentate ligand Me3tacn undergoes rapid oxidation in the presence of O2 to produce a PdIV-trimethyl species. Upon thermolysis, reductive elimination occurs to generate a quantitative amount of ethane. This communication was features on the cover of Organometallics.

The tetradentate ligand tBuN4 facilitates the aerobic oxidation of organometallic PdII complexes by lowering their oxidation potential and stabilizing PdIII and PdIV species, which undergo facile reductive elimination to generate C-C bond formation products. The study reported by the Mirica group suggests the possibility of using molecular oxygen as a green oxidant to promote the oxidative coupling of C-H bonds through transition metal catalysis.

A series of PdII and PtII complexes supported by a tetradentate ligand having both nitrogen and sulfur donor atoms displays unique d8-d8 interactions between metal centers unsupported by bridging ligands. The Mirica group is probing the role of these interactions in methyl group transfer reactions and other organometallic transformations.

The effect of Cu2+ and Zn2+ on the Aβ42 peptide aggregation and cellular toxicity has been reported by the Mirica group. A series of biochemical studies reveal that Cu2+ and Zn2+ ions can both inhibit the formation of Aβ42 fibrils. However, while the presence of Cu2+ can lead to the formation of neurotoxic soluble Aβ42 oligomers, the presence of Zn2+ leads to formation of non-toxic Aβ42 aggregates.

Two new bifunctional compouds that have metal-chelating and amyloid β (Aβ)-interacting groups were synthesized in the Mirica group. The two compounds can promote Aβ42 fibrillization, inhibit Cu2+-induced Aβ42 oligomerization, and reduce their neurotoxicity. Overall, these new bifunctional compounds could be potentially used to control metal-mediated peptide aggregation processes in Alzheimer’s disease.

The Mirica group has developed bifunctional compounds that contain both amyloid-binding and metal-chelating molecular motifs. These compounds are efficient inhibitors of the metal-mediated aggregation of the Aβ42 peptide and promote disaggregation of amyloid fibrils. Interestingly, the formation of soluble Aβ42 oligomers in the presence of metal ions and these compounds leads to an increased cellular toxicity.

Azapentadienyl-metal complexes possess two potential sites of reactivity for electrophiles, the nitrogen atom and the basic metal center.  The Bleeke group has investigated the reactions of (1,2,3-η3)-(5-t-butylazapentadienyl)Rh(PMe3)x (x = 2 or 3) and (1,2,3-η3)-(5-t-butylazapentadienyl)Ir(PEt3)x (x = 2 or 3) with triflic acid and has shown that either the nitrogen atom or the metal center can serve as the primary reaction site (see accompanying graphic).


Date Event description Operations
McMillen 311 @ 4:00 pm
ACS St. Louis Award Symposium | Doug Keszler, Oregon State University
Louderman 458 @ 1:00 pm to 5:30 pm
New Insights into Molecular Structure and Ion Solvation from Mass Spectrometry | Evan Williams, University of California, Berkeley
McMillen 311 @ 4:00 pm