We utilize a peptide-based methodology to prepare a diverse collection of double-helical gold nanoparticle superstructures having controllable handedness and structural metrics. These materials exhibit well-defined circular dichroism signatures at visible wavelengths owing to the collective dipole–dipole interactions between the nanoparticles. We couple theory and experiment to show how tuning the metrics and structure of the helices results in predictable and tailorable chirooptical properties. Finally, we experimentally and theoretically demonstrate that the intensity, position, and nature of the chirooptical activity can be carefully adjusted via silver overgrowth. These studies illustrate the utility of peptide-based nanoparticle assembly platforms for designing and preparing complex plasmonic materials with tailorable optical properties.

Employing a strongly electron-donating tripodal tetradentate ligand along with a reaction strategy designed to suppress binuclear peroxo complex formation, an end-on bound superoxo−copper(II) complex [CuII(NMe2−TMPA)(O2 -)]+ (1) has been generated in solution [UV−vis (THF, −85 °C):  λmax = 418 nm (ε, 4300 M-1 cm-1), 615 nm (ε, 1100), 767 nm (ε, 840)]. Resonance Raman spectroscopy employing isotopically substituted dioxygen (including mixed isotope 16/18O2) proves the end-on superoxo CuII(O2 -) structural formulation, ν(O−O) = 1121 cm-1; ν(Cu−O) = 472 cm-1. The first demonstration of CuII(O2 -) oxidative reactivity with exogenous substrates, likely involving H-atom abstraction chemistry, comes with the finding that 1 effects the oxygenation and hydroperoxylation of substituted phenols.

The observation and fast time-scale kinetic determination of a primary dioxygen-copper interaction have been studied. The ability to photorelease carbon monoxide from [Cu(I)(tmpa)(CO)](+) in mixtures of CO and O(2) in tetrahydrofuran (THF) between 188 and 218 K results in the observable formation of a copper-superoxide species, [Cu(II)(tmpa)(O(2)(-))](+) lambda(max) = 425 nm. Via this "flash-and-trap" technique, temperature-dependent kinetic studies on the forward reaction between dioxygen and [Cu(I)(tmpa)(thf)](+) afford activation parameters DeltaH = 7.62 kJ/mol and DeltaS = -45.1 J/mol K. The corresponding reverse reaction proceeds with DeltaH = 58.0 kJ/mol and DeltaS = 105 J/mol K. Overall thermodynamic parameters are DeltaH degrees = -48.5 kJ/mol and DeltaS degrees = -140 J/mol K. The temperature-dependent data allowed us to determine the room-temperature second-order rate constant, k(O2) = 1.3 x 10(9) M(-1) s(-1). Comparisons to copper and heme proteins and synthetic complexes are discussed.

Long fibers assembled from peptide amphiphiles capable of binding the metalloporphyrin zinc protoporphyrin IX ((PPIX)Zn) have been synthesized. Rational peptide design was employed to generate a peptide, c16-AHL(3)K(3)-CO(2)H, capable of forming a β-sheet structure that propagates into larger fibrous structures. A porphyrin-binding site, a single histidine, was engineered into the peptide sequence in order to bind (PPIX)Zn to provide photophysical functionality. The resulting system indicates control from the molecular level to the macromolecular level with a high order of porphyrin organization. UV/visible and circular dichroism spectroscopies were employed to detail molecular organization, whereas electron microscopy and atomic force microscopy aided in macromolecular characterization. Preliminary picosecond transient absorption data are also reported. Reduced hemin, (PPIX)Fe(II), was also employed to highlight the material's versatility and tunability.

Raman scattering enhancement was observed in systems where different metal oxide semiconductors (TiO 2 , Fe 2 O 3 , ZrO 2 , and CeO 2 ) were modified with enediol ligands. The intensity of Raman scattering was dependent on laser frequency and correlated with the extinction coefficient of the CT complex of the enediol ligands and nanoparticles. The mechanism of Raman enhancement was studied by varying both the chemical composition of the enediol ligand and the chemical composition (and crystal structure) of the nanoparticles. We found that the intensity of the Raman signal depends on the number of surface binding sites, electron density of the ligands, and their dipole moment. Changes in chemical composition caused variations in the intensity, frequency, and number of Raman bands observed. We also showed that Raman scattering is observed for the bioconjugated system, where a peptide is linked to the surface of the particle through a catechol linker, and further investigated the potential for such a system in the development of Raman-based in vivo and in vitro biodetection, cell labeling and imaging, and nanotherapeutic strategies.

Chromophore assemblies within well-defined porous coordination polymers, such as metal−organic frameworks (MOFs), can emulate the functionality of the antenna rings of chlorophylls in light-harvesting complexes (LHCs). The chemical, electronic, and structural diversities define MOFs as a promising platform where photogenerated excitons can be displaced to redox catalysts similar to the reaction center of the LHC. The precise positioning of the pigments and complementary redox units enables us to understand the charge/ energy-transfer process within these crystalline solid compositions. In this study, we postsynthetically anchored tetraphenylporphyrinato zinc(II) (TPPZn)-derived complementary pigment within the 1D pores of 1,3,6,8-tetrakis(p-benzoicacid)pyrene (H 4 TBAPy)-derived NU-1000 MOF to form a high-density donor−acceptor system. The ground-and excited-state redox potentials of the donor and acceptor were chosen to facilitate an energy transfer (EnT) from the excited MOF (i.e., NU-1000*) to TPPZn and a charge transfer (CT) from excited porphyrin (i.e., TPPZn*). Thus, the processes depend on the excitation wavelength. The energy transfer process was spectroscopically probed by excitation−emission mapping: MOF emission was completely quenched at 460 nm, where the pyrene-centered emission was expected. Instead, the excited MOF efficiently transfers the energy to manifest a TPPZn-centered emission at 670 nm (k EnT ≈ 4.7 × 10 11 s −1 ). The excited TPPZn pigment, with a neighboring TBAPy linker, forms an artificial "special-pair"-like system driving the charge-separation process (k CT = 1.2 × 10 10 s −1 ). The findings demonstrate a synthetic MOF-based artificial LHC system where their well-defined structure will open up new possibilities as the separated charge can hop along the 1D pore channel for further mechanistic understanding and future developments.

We describe the computational design of a single-chain four-helix bundle that noncovalently selfassembles with fully synthetic non-natural porphyrin cofactors. With this strategy, both the electronic structure of the cofactor as well as its protein environment may be varied to explore and modulate the functional and photophysical properties of the assembly. Solution characterization (NMR, UV/ vis) of the protein showed that it bound with high specificity to the desired cofactors, suggesting that a uniquely structured protein and well-defined site had indeed been created. This provides a genetically expressed single-chain protein scaffold that will allow highly facile, flexible, and asymmetric variations to enable selective incorporation of different cofactors, surfaceimmobilization and introduction of spectroscopic probes.

Abstract:The de novo design of membrane proteins remains difficult despite recent advances in understanding the factors that drive membrane protein folding and association. We have designed a membrane protein PRIME (PoRphyrins In MEmbrane) that positions two non-natural iron diphenylporphyrins (Fe III DPP's) sufficiently close to provide a multicentered pathway for transmembrane electron transfer. Computational methods previously used for the design of multiporphyrin water-soluble helical proteins were extended to this membrane target. Four helices were arranged in a D 2 -symmetrical bundle to bind two Fe(II/III) diphenylporphyrins in a bis-His geometry further stabilized by secondshell hydrogen bonds. UV-vis absorbance, CD spectroscopy, analytical ultracentrifugation, redox potentiometry, and EPR demonstrate that PRIME binds the cofactor with high affinity and specificity in the expected geometry.Significant progress has been achieved in the computational design of functional water-soluble proteins.1-6 However, the de novo design of membrane proteins remains difficult despite recent advances in understanding the factors that drive membrane protein folding and association. 7 Here, we present the de novo design of a membrane protein PRIME (PoRphyrins In MEmbrane) that utilizes a non-natural iron diphenylporphyrin (Fe III DPP) with the ultimate goal of facilitating electron transfer across a bilayer. Transmembrane (TM) electron transfer lies at the heart of photosynthesis and ATP production in a variety of organisms and thus is of great fundamental interest and, potentially, of practical importance.Considerable progress has been made in the design of watersoluble multiheme proteins [8][9][10][11] and amphiphilic maquettes [12][13][14][15] that position a single heme in the membrane phase. Also, in an elegant study, Cordova et al. 16 designed a TM peptide that binds a single heme between two helices whose geometry is defined by a GXXXG motif. To be generally useful for transmembrane electron transfer, it is important to also design systems that position multiple redox-active cofactors sufficiently close to provide a multicentered pathway for electrons to rapidly pass across the bilayer.Here we extend previous computational methods used for the design of water-soluble multiheme proteins to membrane targets. The design of PRIME is based on the backbone of a water-soluble multiporphyrinbinding peptide. 17,18 Its fold appeared to be particularly well suited for a membrane environment, because it has a tight interhelical "Ala-coil" motif, which is favored in both water and membrane-soluble proteins. 19Four helices were arranged in a D 2 -symmetrical bundle to bind two Fe(II/III) diphenylporphyrins in a bis-His geometry. In the design, the His ligands are stabilized by a bifurcated second-shell hydrogen bond with a main chain carbonyl and a Thr (T18) hydroxyl from a neighboring helix (Figure 1). 20Following the optimization of the coordination sphere of the iron, the backbone was repacked to produce a final sequence. Sid...