Marc R Knecht

Professor
Director of Undergraduate Studies

Phone:
(305) 284-9351
Locator Code:
0431

 
Career

Education

2004Ph.D. Vanderbilt University
Research
Research in the Knecht Group focuses on the use of biological macromolecules to construct nanomaterials for specifically targeted applications. These applications include catalysis, self-assembly, detection, and materials design. We use a wide variety of biological, chemical, and material synthetic strategies to design and engineer specific functionalities into our materials that can be exploited for desired processes. The ultimate goal of our research is to understand the relationship between the material and its function through structure-function analyses.

Publications

Merrill, N.A.; Yan, F.; Jin, H.; Mu, P.; Chen, C.-L.; Knecht, M.R. Tunable assembly of biomimetic peptoids as templates to control nanostructure catalytic activity 26 (Nanoscale. 2018). [Link]

SUMMARY: Nanostructured materials present new opportunities to achieve sustainable catalytic reactivity. Fabrication and organization of these catalytic particles for enhanced reactivity remain challenging due to limited synthetic and organization strategies. Biomimetic approaches represent new avenues to address such challenges. Here we report the tunable assembly of sequence-defined peptoids as templates to control the formation of highly reactive Pd nanostructures of different arrangements. In this regard, peptoid 2D membranes and 1D fibers were assembled and used to template Pd nanoparticles in specific orientations. Catalytic analysis of the resulting materials demonstrated enhanced reactivity from the fiber-based system due to changes in inorganic material display. These results suggest that the morphology of peptoid-based templates plays an important role in controlling material properties, which could open a new direction of using peptoid assemblies for applications in optics, plasmonics, sensing, etc.

Nguyen, M.A.; Hughes, Z.E.; Liu, Y.; Swihart, M.T.; Knecht, M.R.; Walsh, T.R. Peptide-Mediated Growth and Dispersion of Au Nanoparticles in Water via Sequence Engineering 11532–11542122 (The Journal of Physical Chemistry. 2018). [Link]


Munro, C.J.; Knecht, M.R. Solution Effects on Peptide-Mediated Reduction and Stabilization of Au Nanoparticles 13757–1376533 (48) (Langmuir. 2017). [Link]


Walsh, T.R. and Knecht, M.R. Biointerface Structural Effects on the Properties and Applications of Bioinspired Peptide-Based Nanomaterials 12641-12704117 (Chemical Reviews. 2017). [Link]

SUMMARY:

Peptide sequences are known to recognize and bind different nanomaterial surfaces, which has resulted in the screening and identification of hundreds of peptides with the ability to bind to a wide range of metallic, metal oxide, mineral, and polymer substrates. These biomolecules are able to bind to materials with relatively high affinity, resulting in the generation of a complex biointerface between the biotic and abiotic components. While the number of material-binding sequences is large, at present, quantitative materials-binding characterization of these peptides has been accomplished only for a relatively small number of sequences. Moreover, it is currently very challenging to determine the molecular-level structure(s) of these peptides in the materials adsorbed state. Despite this lack of data related to the structure and function of this remarkable biointerface, several of these peptide sequences have found extensive use in creating functional nanostructured materials for assembly, catalysis, energy, and medicine, all of which are dependent on the structure of the individual peptides and collective biointerface at the material surface. In this Review, we provide a comprehensive overview of these applications and illustrate how the versatility of this peptide-mediated approach for the growth, organization, and activation of nanomaterials could be more widely expanded via the elucidation of biointerfacial structure/property relationships. Future directions and grand challenges to realize these goals are highlighted for both experimental characterization and molecular-simulation strategies.


Ramezani-Dakhel, H.; Bedford, N.M.; Woehl, T.J.; Knecht, M.R.; Naik, R.R.; Heinz, H. Nature of Peptide Wrapping onto Metal Nanoparticle Catalysts and Driving Forces for Size Control 24 (Royal Society of Chemistry. 2017). [Link]

SUMMARY: Colloidal metal nanocrystals find many applications in catalysis, energy conversion devices, and therapeutics. However, the nature of ligand interactions and implications on shape control have remained uncertain at the atomic scale. Large differences in peptide adsorption strength and facet specificity were found on flat palladium surfaces versus surfaces of nanoparticles of 2 to 3 nm size using accurate atomistic simulations with the Interface force field. Folding of longer peptides across many facets explains the formation of near-spherical particles with local surface disorder, in contrast to the possibility of nanostructures of higher symmetry with shorter ligands. The average particle size in TEM correlates inversely with the surface coverage with a given ligand and with the strength of ligand adsorption. The role of specific amino acids and sequence mutations on the nanoparticle size and facet composition is discussed, as well as the origin of local surface disorder that leads to large differences in catalytic reactivity.

Dharmawardhana, C.; Kanhaiya, K.; Lin, T.Z. Knecht, M.R.; Miao, J.; Heinz, H. Reliable Computational Design of Biological and Inorganic Materials to the Large Nanometer Scale Using the Interface Force Field 1394-1405,43 (Molecular SiMulation. 2017). [Link]

SUMMARY:

The function of nanomaterials and biomaterials greatly depends on understanding nanoscale recognition mechanisms, crystal growth and surface reactions. The Interface Force Field (IFF) and surface model database are the first collection of transferable parameters for inorganic and organic compounds that can be universally applied to all materials. IFF uses common energy expressions and achieves best accuracy among classical force fields due to rigorous validation of structural and energetic properties of all compounds in comparison to perpetually valid experimental data. This paper summarises key aspects of parameterisation, including atomic charges and transferability of parameters and current coverage. Examples of biomolecular recognition at metal and mineral interfaces, surface reactions of alloys, as well as new models for graphitic materials and pi-conjugated molecules are described. For several metal–organic interfaces, a match in accuracy of computed binding energies between of IFF and DFT results is demonstrated at ten million times lower computational cost. Predictive simulations of biomolecular recognition of peptides on phosphate and silicate surfaces are described as a function of pH. The use of IFF for reactive molecular dynamics is illustrated for the oxidation of Mo3Si alloys at high temperature, showing the development of specific porous silica protective layers. The introduction of virtual pi electrons in graphite and pi-conjugated molecules enables improvements in property predictions by orders of magnitude. The inclusion of such molecule-internal polarity in IFF can reproduce cation–pi interactions, pi-stacking in graphite, DNA bases, organic semiconductors and the dynamics of aqueous and biological interfaces for the first time.

 


Metal oxide semiconductor nanomaterial for reductive debromination: Visible light degradation of polybrominated diphenyl ethers by Cu2O@Pd nanostructures 147-1542017 (Applied Catalysis B: Environmental. ). [Link]

SUMMARY: Polybrominated diphenyl ethers (PBDEs), which have found extensive use as flame-retarding additives to many polymer materials, are now environmentally ubiquitous and persistent pollutants that present potential health risks to humans and wildlife. Herein, we report for the first time the use of metal oxide semiconductor nanostructures for photocatalytic reductive debromination of PBDEs using visible light. Well-defined cubic Cu2O crystals, surface-decorated with Pd nanoparticles, were prepared via a hydrothermal approach. The Cu2O@Pd demonstrated light-activated tandem photocatalysis, in which Cu2O produces H2 from H2O under visible light irradiation; the evolved H2 is subsequently activated by Pd to achieve the reductive hydrodehalogenation of the PBDE. Cu2O@Pd demonstrated effective debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), one of the PBDEs of greatest environmental concern, with initial pseudo-first-order rate constant of 0.21 h−1. It is shown that the reaction proceeds via a reductive mechanism with preferential debromination at the para positions. Reaction rates for various monobromo- and dibromo-congeners were evaluated, confirming that the debromination order of preference is para > meta >> ortho, which is opposite to the order reported for direct photolysis. We conclude that Cu2O@Pd is a promising photocatalyst for reductive dehalogenation of halogenated organic compounds.

Merrill, N.A.; Nitka, T.T.; McKee, E.M.; Merino, K.C.; Drummy, L.F.; Lee, S.; Reinhart, B.; Ren, Y.; Munro, C.J.; Pylypenko, S.; Frenkel, A.I.; Bedford, N.M.; Knecht, M.R. E ff ects of Metal Composition and Ratio on Peptide-Templated Multimetallic PdPt Nanomaterials 8030 − 80409 (Applied Materials and Interfaces. 2017). [Link]

SUMMARY:

It can be difficult to simultaneously control the size, composition, and morphology of metal nanomaterials under benign aqueous conditions. For this, bioinspired approaches have become increasingly popular due to their ability to stabilize a wide array of metal catalysts under ambient conditions. In this regard, we used the R5 peptide as a three-dimensional template for formation of PdPt bimetallic nanomaterials. Monometallic Pd and Pt nanomaterials have been shown to be highly reactive toward a variety of catalytic processes, but by forming bimetallic species, increased catalytic activity may be realized. The optimal metal-to-metal ratio was determined by varying the Pd:Pt ratio to obtain the largest increase in catalytic activity. To better understand the morphology and the local atomic structure of the materials, the bimetallic PdPt nanomaterials were extensively studied by transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and pair distribution function analysis. The resulting PdPt materials were determined to form multicomponent nanostructures where the Pt component demonstrated varying degrees of oxidation based upon the Pd:Pt ratio. To test the catalytic reactivity of the materials, olefin hydrogenation was conducted, which indicated a slight catalytic enhancement for the multicomponent materials. These results suggest a strong correlation between the metal ratio and the stabilizing biotemplate in controlling the final materials morphology, composition, and the interactions between the two metal species.

 


Hughes, Z.E.; Nguyen, M.A.; Li, Y.; Swihart, M.T.; Walsh, T.R.; Knecht, M.R. Elucidating the influence of materials-binding peptide sequence on Au surface interactions and colloidal stability of Au nanoparticles 7.2331 (Nanoscale. 2017). [Link]

SUMMARY: Peptide-mediated synthesis and assembly of nanostructures opens new routes to functional inorganic/organic hybrid materials. However, understanding of the many factors that influence the interaction of biomolecules, specifically peptides, with metal surfaces remains limited. Understanding of the relationship between peptide sequence and resulting binding affinity and configurations would allow predictive design of peptides to achieve desired peptide/metal interface characteristics. Here, we measured the kinetics and thermodynamics of binding on a Au surface for a series of peptide sequences designed to probe specific sequence and context effects. For example, context effects were explored by making the same mutation at different positions in the peptide and by rearranging the peptide sequence without changing the amino acid content. The degree of peptide-surface contact, predicted from advanced molecular simulations of the surface-adsorbed structures, was consistent with the measured binding constants. In simulations, the ensemble of peptide backbone conformations showed little change with point mutations of the anchor residues that dominate interaction with the surface. Peptide-capped Au nanoparticles were produced using each sequence. Comparison of simulations with nanoparticle synthesis results revealed a correlation between the colloidal stability of the Au nanoparticles and the degree of structural disorder in the surface-adsorbed peptide structures for this family of sequences. These findings suggest new directions in the optimization and design of biomolecules for in situ peptide-based nanoparticle growth, binding, and dispersion in aqueous media.

Pálmai, M.;Zahran, E.; Angamaro, S.; Bálint, Z.; Pászti, Z.; Knecht, M.R.; Bachas, L.G. Pd-decorated m-BiVO4/BiOBr ternary composite with dual heterojunction for enhanced photocatalytic activity 9.9312 (Journal of Materials Chemistry A. 2017). [Link]

SUMMARY: We introduce a unique material ensemble to boost the photocatalytic activity of m-BiVO4 by creating dual heterojunction of bismuth oxybromide nanosheets and Pd nanodomains. The m-BiVO4/BiOBr/Pd ternary composite demonstrates substantially higher photocatalytic activity compared to pure m-BiVO4. We demonstrate for the first time the use of such visible light photocatalyst in highly efficient degradation of polychlorinated biphenyls.