Enabling Visible Light Sensitization of Yb, Nd and Er in Dimeric Ln/Ga Metallacrowns through Functionalization with Ru Complexes for NIR-II Multiplex Imaging.

Multiplex imaging in the second near-infrared window (NIR-II, 1000-1700 nm) provides exciting opportunities for more precise understanding of biological processes and more accurate diagnosis of diseases by enabling real-time acquisition of images with improved contrast and spatial resolution in deeper tissues. Today, the number of imaging agents suitable for this modality remains very scarce. In this work, we have synthesized and fully characterized, including theoretical calculations, a series of dimeric Ln/Ga metallacrowns bearing Ru polypyridyl complexes, LnRu-3 (Ln=Y, Yb, Nd, Er).

Revving up a Designed Copper Nitrite Reductase Using Non-Coded Active Site Ligands.

Herein, we report a three stranded coiled-coil (3SCC) protein containing a type II copper center (CuT2) composed of 6-membered ring N-heterocycles. This design yields the most active homogenous copper nitrite reductase (CuNiR) mimic in water. We achieved this result by controlling three factors.

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

White 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.

Insights on the Structure in Solution of Paramagnetic Ln/Ga 12-Metallacrown-4 Complexes Using 1D H NMR and Model Structures.

The solution structure of LnNa(OBz)[12-MC-4] complexes was studied through paramagnetic H NMR and DFT models. Although isostructural in the solid state, their H NMR spectra in DMSO- are extremely different from one another due to the magnetic anisotropy of the lanthanide(III) ions. NMR data were analyzed by the "all-lanthanide" method that were compared to X-ray structures and model structures, allowing to establish the extent of the structural changes that occur from the solid state to the solution phase.

Lower Energy Excitation of Water Soluble Near-Infrared Emitting Mixed-Ligand Metallacrowns.

By combining advantages of two series of lanthanide(III)/zinc(II) metallacrowns (MCs) assembled using pyrazine- (pyzHA ) and quinoxaline- (quinoHA ) hydroximate building blocks ligands, we created here water-soluble mixed-ligand MCs with extended absorption to the visible range. The Yb analogue demonstrated improved photophysical properties in the near-infrared (NIR) range in cell culture media, facilitating its application for NIR optical imaging in living HeLa cells.

Incorporation of a molybdenum atom in a Rubredoxin-type Centre of a de novo-designed αDIV-L21C three-helical bundle peptide.

The rational design and functionalization of small, simple, and stable peptides scaffolds is an attractive avenue to mimic catalytic metal-centres of complex proteins, relevant for the design of metalloenzymes with environmental, biotechnological and health impacts. The de novo designed αDIV-L21C framework has a rubredoxin-like metal binding site and was used in this work to incorporate a Mo-atom. Thermostability studies using differential scanning calorimetry showed an increase of 4 °C in the melting temperature of the Mo-αDIV-L21C when compared to the apo-αDIV-L21C.

Molecular Rotational Correlation Times and Nanoviscosity Determined by Cd Perturbed Angular Correlation (PAC) of γ-rays Spectroscopy.

The nanoviscosity experienced by molecules in solution may be determined through measurement of the molecular rotational correlation time, τ , for example, by fluorescence and NMR spectroscopy. With this work, we apply PAC spectroscopy to determine the rate of rotational diffusion, λ=1/τ , of a de novo designed protein, TRIL12AL16C, in solutions with viscosities, ξ, from 1.7 to 88 mPa⋅s.

Tunable Optical Molecular Thermometers Based on Metallacrowns.

The effect of ligands' energy levels on thermal dependence of lanthanide emission was examined to create new molecular nanothermometers. A series of LnGaLL metallacrowns (shorthand LnL), where Ln = Gd, Tb, or Sm (HL' = salicylhydroxamic acid (Hshi), 5-methylsalicylhydroxamic acid (Hmshi), 5-methoxysalicylhydroxamic acid (Hmoshi), and 3-hydroxy-2-naphthohydroxamic acid (Hnha)) and HL″ = isophthalic acid (Hiph), was synthesized and characterized. Within the series, ligand-centered singlet state (S) energy levels ranged from 23,300 to 27,800 cm, while triplet (T) energy levels ranged from 18,150 to 21,980 cm.

Catalysis and Electron Transfer in Designed Metalloproteins.

One of the hallmark advances in our understanding of metalloprotein function is showcased in our ability to design new, non-native, catalytically active protein scaffolds. This review highlights progress and milestone achievements in the field of metalloprotein design focused on reports from the past decade with special emphasis on designs couched within common subfields of bioinorganic study: heme binding proteins, monometal- and dimetal-containing catalytic sites, and metal-containing electron transfer sites. Within each subfield, we highlight several of what we have identified as significant and important contributions to either our understanding of that subfield or metalloprotein design as a discipline.

Tuning the photophysical properties of lanthanide(iii)/zinc(ii) 'encapsulated sandwich' metallacrowns emitting in the near-infrared range.

A family of ZnLn(HA) metallacrowns (MCs; Ln = Yb, Er, and Nd; HA = picoline- (picHA), pyrazine- (pyzHA), and quinaldine- (quinHA) hydroximates) with an 'encapsulated sandwich' structure possesses outstanding luminescence properties in the near-infrared (NIR) and suitability for cell imaging. Here, to decipher which parameters affect their functional and photophysical properties and how the nature of the hydroximate ligands can allow their fine tuning, we have completed this ZnLn(HA) family by synthesizing MCs with two new ligands, naphthyridine- (napHA) and quinoxaline- (quinoHA) hydroximates. ZnLn(napHA) and ZnLn(quinoHA) exhibit absorption bands extended into the visible range and efficiently sensitize the NIR emissions of Yb, Er, and Nd upon excitation up to 630 nm.

Cu(I) Binding to Designed Proteins Reveals a Putative Copper Binding Site of the Human Line1 Retrotransposon Protein ORF1p.

Long interspersed nuclear elements-1 (L1) are autonomous retrotransposons that encode two proteins in different open reading frames (ORF1 and ORF2). The ORF1p, which may be an RNA binding and chaperone protein, contains a three-stranded coiled coil (3SCC) domain that facilitates the formation of the biologically active homotrimer. This 3SCC domain is composed of seven amino acid (heptad) repeats as found in native and designed peptides and a stammer that modifies the helical structure.

Lanthanide Identity Governs Guest-Induced Dimerization in Ln [15-MC -5]) Metallacrowns.

Series of lanthanide-containing metallic coordination complexes are frequently presented as structurally analogous, due to the similar chemical and coordinative properties of the lanthanides. In the case of chiral (Ln [15-MC -5]) metallacrowns (MCs), which are well established supramolecular hosts, the formation of dimers templated by a dicarboxylate guest (muconate) in solution of neutral pH is herein shown to have a unique dependence on the identity of the MC's central lanthanide. Calorimetric data and nuclear magnetic resonance diffusion studies demonstrate that MCs containing larger or smaller lanthanides as the central metal only form monomeric host-guest complexes whereas analogues with intermediate lanthanides (for example, Eu, Gd, Dy) participate in formation of dimeric host-guest-host compartments.

Open Reading Frame 1 Protein of the Human Long Interspersed Nuclear Element 1 Retrotransposon Binds Multiple Equivalents of Lead.

The human long interspersed nuclear element 1 (LINE1) has been implicated in numerous diseases and has been suggested to play a significant role in genetic evolution. Open reading frame 1 protein (ORF1p) is one of the two proteins encoded in this self-replicating mobile genetic element, both of which are essential for retrotransposition. The structure of the three-stranded coiled-coil domain of ORF1p was recently solved and showed the presence of tris-cysteine layers in the interior of the coiled-coil that could function as metal binding sites.

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

Lanthanide(III) ions (Ln) in coordination compounds exhibit unique luminescence properties with narrow and characteristic f-f transitions throughout the visible and near-infrared (NIR) ranges. In addition, some Ln such as Pr, Sm, Dy, Ho, Er, and Tm possess an exceptional ability, although less explored, to exhibit dual-range emissions. Such remarkable features allow highly specific use in materials science and biology, for example, for the creation of sophisticated barcode modules or for the next generation of optical imaging applications.

The pH-Induced Selectivity Between Cysteine or Histidine Coordinated Heme in an Artificial α-Helical Metalloprotein.

De Novo metalloprotein design assesses the relationship between metal active site architecture and catalytic reactivity. Herein, we use an α-helical scaffold to control the iron coordination geometry when a heme cofactor is allowed to bind to either histidine or cysteine ligands, within a single artificial protein. Consequently, we uncovered a reversible pH-induced switch of the heme axial ligation within this simplified scaffold.

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

Single 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 Ga/Dy metallacrowns (MCs) is presented, demonstrating outstanding white light colorimetric properties with CIE chromaticity coordinates of (0.309, 0.

Traversing the Red-Green-Blue Color Spectrum in Rationally Designed Cupredoxins.

Blue copper proteins have a constrained Cu(II) geometry that has proven difficult to recapitulate outside native cupredoxin folds. Previous work has successfully designed green copper proteins which could be tuned blue using exogenous ligands, but the question of how one can create a self-contained blue copper site within a de novo scaffold, especially one removed from a cupredoxin fold, remained. We have recently reported a red copper protein site within a three helical bundle scaffold which we later revisited and determined to be a nitrosocyanin mimic, with a CuHisCysGlu binding site.

Making or Breaking Metal-Dependent Catalytic Activity: The Role of Stammers in Designed Three-Stranded Coiled Coils.

While many life-critical reactions would be infeasibly slow without metal cofactors, a detailed understanding of how protein structure can influence catalytic activity remains elusive. Using de novo designed three-stranded coiled coils (TRI and Grand peptides formed using a heptad repeat approach), we examine how the insertion of a three residue discontinuity, known as a stammer insert, directly adjacent to a (His) metal binding site alters catalytic activity. The stammer, which locally alters the twist of the helix, significantly increases copper-catalyzed nitrite reductase activity (CuNiR).

[Ga Sm , Ga Tb ] 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 Ga /Tb and Ga /Sm metallacrowns (MCs) achieved remarkable relative thermal sensitivity associated with very low temperature uncertainty of S =1.

Heteromeric three-stranded coiled coils designed using a Pb(II)(Cys) template mediated strategy.

Three-stranded coiled coils are peptide structures constructed from amphipathic heptad repeats. Here we show that it is possible to form pure heterotrimeric three-stranded coiled coils by combining three distinct characteristics: (1) a cysteine sulfur layer for metal coordination, (2) a thiophilic, trigonal pyramidal metalloid (Pb(II)) that binds to these sulfurs and (3) an adjacent layer of reduced steric bulk generating a cavity where water can hydrogen bond to the cysteine sulfur atoms. Cysteine substitution in an a site yields Pb(II)AB heterotrimers, while d sites provide pure Pb(II)CD or Pb(II)CD scaffolds.

Iodinated Metallacrowns: Toward Combined Bimodal Near-Infrared and X-Ray Contrast Imaging Agents.

Multimodal probes capable of combining imaging modalities within a single molecule are in high demand today as they can provide information at both molecular and anatomical levels. Herein, a study was conducted on a series of gallium(III)/lanthanide(III) bis(12-MC-4) metallacrowns (MCs) with the general composition {Ln[12-MC -4]} (iph) (Ln-I , x=0, 4, 8, 12), where shi and iph are salicylhydroximate and isophthalate ligands, respectively, or their iodinated derivatives. For Yb-I , the attenuation in X-ray computed tomography (XCT) imaging and near-infrared (NIR) luminescence properties can be finely tuned by controlled structural modifications based on iodo groups.

Explaining How α-Hydroxamate Ligands Control the Formation of Cu(II)-, Ni(II)-, and Zn(II)-Containing Metallacrowns.

Four different crystal structures for quinolinehydroxamic acid () and picolinehydroxamic acid () MCs with Cu(II) and Ni(II), and solution studies on the formation of Cu(II), Ni(II), and Zn(II) MC complexes with , , and pyrazylohydroxamic acid () are described. In polynuclear complex , [Cu(-2H)(NO)(DMSO)](NO), the metallamacrocyclic cavity is formed by four Cu(II) ions and four doubly deprotonated hydroximate ligands, and the center of the cavity is occupied by the fifth Cu(II) ion coordinated by four hydroximate oxygen atoms. The complex , [Cu(-2H)(HO)(ClO)](ClO)·4HO, exhibits a dimeric structure based on two pentanuclear collapsed 12-MC-4 Cu(2H) fragments united by two chiral capping Cu(II) ions exo-coordinated to the peripheral vacant (O,O') chelating units of each tetranuclear collapsed MC moiety.

Rational De Novo Design of a Cu Metalloenzyme for Superoxide Dismutation.

Superoxide dismutases (SODs) are highly efficient enzymes for superoxide dismutation and the first line of defense against oxidative stress. These metalloproteins contain a redox-active metal ion in their active site (Mn, Cu, Fe, Ni) with a tightly controlled reduction potential found in a close range around the optimal value of 0.36 V versus the normal hydrogen electrode (NHE).