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De novo metalloprotein design involves the construction of proteins guided by specific repeat patterns of polar and apolar residues, which, upon self‐assembly, provide a suitable environment to bind metals and produce artificial metalloenzymes. While a wide range of functionalities have been realized in de novo designed metalloproteins, the functional repertoire of such constructs towards alternative energy‐relevant catalysis is currently limited. Here we show the application of de novo approach to design a functional H2 evolving protein. The design involved the assembly of an amphiphilic peptide featuring cysteines at tandem a/d sites of each helix. Intriguingly, upon NiII addition, the oligomers shift from a major trimeric assembly to a mix of dimers and trimers. The metalloprotein produced H2 photocatalytically with a bell‐shape pH dependence, having a maximum activity at pH 5.5. Transient absorption spectroscopy is used to determine the timescales of electron transfer as a function of pH. Selective outer sphere mutations are made to probe how the local environment tunes activity. A preferential enhancement of activity is observed via steric modulation above the NiII site, towards the N‐termini, compared to below the NiII site towards the C‐termini. [ABSTRACT FROM AUTHOR]

Irradiation at 460 nm of [Mo 3 (μ 3 -S)(μ 2 -S 2 ) 3 (S 2 CNR 2 ) 3 ]I ([ 2a ]I, R = Me; [ 2b ]I, R = Et; [ 2c ]I, R = i Bu; [ 2d ]I, R = CH 2 C 6 H 5 ) in a mixed aqueous-polar organic medium with [Ru(bipy) 3 ] 2+ as photosensitizer and Et 3 N as electron donor leads to H 2 evolution. Maximum activity (300 turnovers, 3 h) is found with R = i Bu in 1:9 H 2 O:MeCN; diminished activity is attributed to deterioration of [Ru(bipy) 3 ] 2+ . Monitoring of the photolysis mixture by mass spectrometry suggests transformation of [Mo 3 (μ 3 -S)(μ 2 -S 2 ) 3 (S 2 CNR 2 ) 3 ] + to [Mo 3 (μ 3 -S)(μ 2 -S) 3 (S 2 CNR 2 ) 3 ] + via extrusion of sulfur on a time scale of minutes without accumulation of the intermediate [Mo 3 S 6 (S 2 CNR 2 ) 3 ] + or [Mo 3 S 5 (S 2 CNR 2 ) 3 ] + species. Deliberate preparation of [Mo 3 S 4 (S 2 CNEt 2 ) 3 ] + ([ 3 ] + ) and treatment with Et 2 NCS 2 1- yields [Mo 3 S 4 (S 2 CNEt 2 ) 4 ] ( 4 ), where the fourth dithiocarbamate ligand bridges one edge of the Mo 3 triangle. Photolysis of 4 leads to H 2 evolution but at ∼25% the level observed for [Mo 3 S 7 (S 2 CNEt 2 ) 3 ] + . Early time monitoring of the photolyses shows that [Mo 3 S 4 (S 2 CNEt 2 ) 4 ] evolves H 2 immediately and at constant rate, while [Mo 3 S 7 (S 2 CNEt 2 ) 3 ] + shows a distinctive incubation prior to a more rapid H 2 evolution rate. This observation implies the operation of catalysts of different identity in the two cases. Photolysis solutions of [Mo 3 S 7 (S 2 CN i Bu 2 ) 3 ] + left undisturbed over 24 h deposit the asymmetric Mo 6 cluster [( i Bu 2 NCS 2 ) 3 (μ 2 -S 2 ) 2 (μ 3 -S)Mo 3 ](μ 3 -S)(μ 3 -η 2 ,η 1 -S',η 1 -S″-S 2 )[Mo 3 (μ 2 -S) 3 (μ 3 -S)(S 2 CN i Bu 2 ) 2 (μ 2 -S 2 CN i Bu 2 )] in crystalline form, suggesting that species with this hexametallic composition and core topology are the probable H 2 -evolving catalysts in photolyses beginning with [Mo 3 S 7 (S 2 CNR 2 ) 3 ] + . When used as solvent, N , N -dimethylformamide (DMF) suppresses H 2 -evolution but to a greater degree for [Mo 3 S 4 (S 2 CNEt 2 ) 4 ] than for [Mo 3 S 7 (S 2 CNEt 2 ) 3 ] + . Recrystallization of [Mo 3 S 4 (S 2 CNEt 2 ) 4 ] from DMF affords [Mo 3 S 4 (S 2 CNEt 2 ) 4 (η 1 ,κ O -DMF)] ( 5 ), implying that inhibition by DMF arises from competition for a Mo coordination site that is requisite for H 2 evolution. Computational assessment of [Mo 3 S 4 (S 2 CNMe 2 ) 3 ] + following addition of 2H + and 2e - suggests a Mo(H)-μ 2 (SH) intermediate as the lowest energy species for H 2 elimination. An analogous pathway may be available to the Mo 6 cluster via dissociation of one end of the μ 2 -S 2 CNR 2 ligand, a known hemilabile ligand type, in the [Mo 3 S 4 ] 4+ fragment.

A series of four ullazine-donor based donor-π bridge-acceptor (D-π-A) dyes have been synthesized and compared to a prior ullazine donor-acceptor (D-A) dye as well as a triphenylamine donor with an identical π-bridge and acceptor. The D-π-A ullazine series demonstrates an unusually uniform-in-intensity panchromatic UV/Vis absorption spectrum throughout the visible region. This is in part due to the introduction of strong high-energy bands through incorporation of the ullazine building block as shown by computational analysis. The dyes were characterized on TiO 2 films and in DSC devices. Performances of 5.6 % power conversion efficiency were obtained with IPCE onsets reaching 800 nm., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)