Modifying the Steric Properties in the Second Coordination Sphere of Designed Peptides Leads to Enhancement of Nitrite Reductase Activity

Protein design is a useful strategy to interrogate the protein structureâ function relationship. We demonstrate using a highly modular 3â stranded coiled coil (TRIâ peptide system) that a functional typeâ 2 copper center exhibiting copper nitrite reductase (NiR) activity exhibits the highest homogeneous catalytic efficiency under aqueous conditions for the reduction of nitrite to NO and H2O. Modification of the amino acids in the second coordination sphere of the copper center increases the nitrite reductase activity up to 75â fold compared to previously reported systems. We find also that steric bulk can be used to enforce a threeâ coordinate CuI in a site, which tends toward twoâ coordination with decreased steric bulk. This study demonstrates the importance of the second coordination sphere environment both for controlling metalâ center ligation and enhancing the catalytic efficiency of metalloenzymes and their analogues.Second is best: A significant increase in nitrite reductase activity is achieved by modification of the steric properties of the second coordination sphere of a typeâ 2 copper center. The steric properties can be harnessed to control metal coordination and reactivity in a 3â stranded coiled coil TRI peptide scaffold (TRIWâ H).Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142897/1/anie201712757.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142897/2/anie201712757-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142897/3/anie201712757_am.pd

Modifying the Steric Properties in the Second Coordination Sphere of Designed Peptides Leads to Enhancement of Nitrite Reductase Activity

Protein design is a useful strategy to interrogate the protein structureâ function relationship. We demonstrate using a highly modular 3â stranded coiled coil (TRIâ peptide system) that a functional typeâ 2 copper center exhibiting copper nitrite reductase (NiR) activity exhibits the highest homogeneous catalytic efficiency under aqueous conditions for the reduction of nitrite to NO and H2O. Modification of the amino acids in the second coordination sphere of the copper center increases the nitrite reductase activity up to 75â fold compared to previously reported systems. We find also that steric bulk can be used to enforce a threeâ coordinate CuI in a site, which tends toward twoâ coordination with decreased steric bulk. This study demonstrates the importance of the second coordination sphere environment both for controlling metalâ center ligation and enhancing the catalytic efficiency of metalloenzymes and their analogues.Erstklassiges aus der zweiten Reihe: Die Aktivität der Nitritreduktase kann durch Modifikation der sterischen Eigenschaften in der zweiten Koordinationssphäre eines Typâ 2â Kupferzentrums deutlich erhöht werden. à ber die Sterik lassen sich die Koordination und Reaktivität des Metalls in einem dreisträngigen â Coiledâ coilâ â TRIâ Peptidgerüst (TRIWâ H) vorgeben.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142882/1/ange201712757_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142882/2/ange201712757-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142882/3/ange201712757.pd

Synthetic and Spectroscopic Investigations of Ligand Field Effects in Molecular Lanthanide Ion Complexes

This thesis focuses on defining the electronic structure of molecular lanthanide complexes. Dy(III)/Ga(III) metallacrowns in three general coordination geometries (C4v, D4d, and C1) were isolated to examine the effects on Dy(III) emission. The ligand energy levels were tuned by making chemical substitutions onto the salicylhydroxamate or isophthalate backbone ligands. The spectral profile corresponded with the geometry in each case, despite ligand singlet and triplet energy levels ranging in the series from 25870-28860 cm-1 and 21550-22680 cm-1, respectively. Blue ligand fluorescence was also found to modify the compounds’ emission profile because variation in ligand energy levels led to shifts in the peak of blue ligand emissions (ranging 360-403 nm), as well as different ligand-Dy(III) interactions leading to a variety of ligand/Dy(III) quantum emission ratios (ranging 0.0035-0.455). Incorporation of ligand emissions leads to a wide tunability of Commission Internationale de l'éclairage coordinates ranging from x=0.29-0.40 and y=0.28-0.43, with coordination geometry and ligand emission contribution being the most important effects. The effect of shifting ligand energy levels on the thermal dependence of lanthanide emissions was examined to develop new molecular nanothermometers. Working with Ga8Ln2L8L’4 compounds (where Ln=Sm(III) or Tb(III), L’=isophthalate, L=salicylhydroxamate, 5-methylsalicylhydroxamate, 5-methoxysalicylhydroxamate, or 3-hydroxy-2-naphthohydroxamate), ligand-centric singlet energy levels ranged from 23300-27800, while triplet levels ranged from 18150-21980 cm-1. Comparison with relevant excited Sm(III)* and Tb(III)* energy levels (17800 and 20400 cm-1, respectively), showed that the excited Ln(III)*-ligand triplet gap was most important in dictating thermal dependence of emission intensity via back energy transfer, however, when the singlet-triplet ligand energy gap was especially small (3760 cm-1), energy transfer across this gap is also important. This also applies to designing imaging probes, with room-temperature, visible emission quantum yields ranging 2.07(6)-31.2(2)% for Tb(III) and 0.0267(7)-2.27(5)% for Sm(III). Maximal thermal dependence occurred over a wide thermal range (ca. 150-350 K), based on the ligand-lanthanide energy gaps. By mixing two of the Sm(III) and Tb(III) compounds, an optical thermometer was created based on the emission ratio of these two ions. For (1:1 Sm2L8:Tb2L8, [L=5-methoxysalicylhydroxamate]) in the solid state, peak temperature sensitivity greater than 3 %/K at 225 K was found. When (1:1 Sm2L8:Tb2L8, [L=salicylhydroxamate acid]) was placed in polystyrene nanobeads and examined as an aqueous suspension, maximum sensitivity of 1.9 %/K was found at 328 K, thus these materials may be useful in biological applications such as cellular thermal imaging. Finally, magnetic field-dependent luminescence was used to extract g-factors from Zeeman splitting patterns for ground and excited states of Yb(III). Extraction of the relevant parameters was performed by fitting the Zeeman response of resonant energies via luminescence. For the four states of the ground manifold for the crystal in the B/parallel/C3 orientation it was found g/par/1=4.47(0.27), g/par/2=3.69(0.39), g/par/3=2.97(0.43), and g/par/4 = 0.98(0.28). In the B/perpendicular/C3 orientation it was found g/perp/1=2.50(0.19) and g/perp/2=1.33(0.23). Meanwhile the emitting state’s g-factor could also be extracted, with g/par/E=2.70(0.27) and g/perp/E=0.52(0.19). These properties are difficult to measure by other experimental techniques and provide direct experimental insight into wavefunction mixing in the complex. In summary, this thesis used synthesis and spectroscopy to evaluate the impact of the ligand field on lanthanide physical properties while also developing technologies to probe the electronic structure more fully. These studies should assist in the design of future lanthanide based materials that exploit ligand field effects.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169607/1/esalerno_1.pd

Tuning white light emission using single-component tetrachroic Dy 3+ metallacrowns: the role of chromophoric building blocks

International audienceWhite light production is of major importance for ambient lighting and technological displays. White light can be obtained by several types of materials and their combinations, but single component emitters remain rare and desirable towards thinner devices that are, therefore, easier to control and that require fewer manufacturing steps. We have designed a series of dysprosium(iii)-based luminescent metallacrowns (MCs) to achieve this goal. The synthesized MCs possess three main structural types LnGa(4)(L ')(4)(L '')(4) (type A), Ln(2)Ga(8)(L ')(8)(L ''')(4) (type B) and LnGa(8)(L ')(8)(OH)(4) (type C) (H3L ', HL '' and H2L ''' derivatives of salicylhydroxamic, benzoic and isophthalic acids, respectively). The advantage of these MCs is that, within each structural type, the nature of the organic building blocks does not affect the symmetry around Dy3+. By detailed studies of the photophysical properties of these Dy3+-based MCs, we have demonstrated that CIE coordinates can be tuned from warm to neutral to cold white by (i) defining the symmetry about Dy3+, and (ii) choosing appropriate chromophoric building blocks. These organic building blocks, without altering the coordination geometry around Dy3+, influence the total emission profile through changing the probability of different energy transfer processes including the T-3(1) <- Dy3+* energy back transfer and/or by generating ligand-centered fluorescence in the blue range. This work opens new perspectives for the creation of white light emitting devices using single component tetrachroic molecular compounds

Dy 3+ White Light Emission Can Be Finely Controlled by Tuning the First Coordination Sphere of Ga 3+ /Dy 3+ Metallacrown Complexes

International audienceSingle lanthanide(III) ion white light emission is in high demand since it provides the advantage of requiring only one chromophore for the control of the color. Herein, a series of Ga3+/Dy3+ metallacrowns (MCs) is presented, demonstrating outstanding white light colorimetric properties with CIE chromaticity coordinates of (0.309, 0.334) and correlated color temperature (CCT) equal to 6670 K for the MC emitting the closest to the standard white color. Experimental data reveal that the CIE coordinates within the studied series of MCs are controlled mainly by the Dy3+-centered emission rather than by the ligand-centered bands, implying that Dy3+ can be tuned as a single ionic white light emitter by a simple modification of the coordination environment

Visible, Near-Infrared, and Dual-Range Luminescence Spanning the 4f Series Sensitized by a Gallium(III)/Lanthanide(III) Metallacrown Structure

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Visible, Near-Infrared, and Dual-Range Luminescence Spanning the 4f Series Sensitized by a Gallium(III)/Lanthanide(III) Metallacrown Structure

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Luminescent lanthanide(III)-based metallacrowns: from design to applications.

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Lanthanide(III)-based metallacrowns: unique molecules for fundamental research and optical imaging applications.

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[Ga3+8Sm3+2, Ga3+8Tb3+2] Metallacrowns are Highly Promising Ratiometric Luminescent Molecular Nanothermometers Operating at Physiologically Relevant Temperatures

Nanothermometry is the study of temperature at the submicron scale with a broad range of potential applications, such as cellular studies or electronics. Molecular luminescent- based nanothermometers offer a non- contact means to record these temperatures with high spatial resolution and thermal sensitivity. A luminescent- based molecular thermometer comprised of visible- emitting Ga3+/Tb3+ and Ga3+/Sm3+ metallacrowns (MCs) achieved remarkable relative thermal sensitivity associated with very low temperature uncertainty of Sr=1.9- %- K- 1 and δT<0.045- K, respectively, at 328- K, as an aqueous suspension of polystyrene nanobeads loaded with the corresponding MCs. To date, they are the ratiometric molecular nanothermometers offering the highest level of sensitivity in the physiologically relevant temperature range.Metallacrown- based thermometry: Mixtures of luminescent Ga3+/Tb3+ and Ga3+/Sm3+ metallacrowns proved to be highly sensitive luminescent molecular thermometers. These were placed in polystyrene nanobeads for aqueous stabilization and demonstrate the promise of a molecular approach to nanothermometry.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163582/3/chem202003239.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163582/2/chem202003239-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163582/1/chem202003239_am.pd