Tryptophan to Tryptophan Hole Hopping in an Azurin Construct.

Electron transfer (ET) between neutral and cationic tryptophan residues in the azurin construct [Re(H126)(CO)(dmp)](W124)(W122)Cu (dmp = 4,7-Me-1,10-phenanthroline) was investigated by Born-Oppenheimer quantum-mechanics/molecular mechanics/molecular dynamics (QM/MM/MD) simulations. We focused on W124 ← W122 ET, which is the middle step of the photochemical hole-hopping process *Re(CO)(dmp) ← W124 ← W122 ← Cu, where sequential hopping amounts to nearly 10,000-fold acceleration over single-step tunneling (. , , 192-200).

Nonadiabatic excited-state dynamics of ReCl(CO)(bpy) in two different solvents.

We present a study of excited-states relaxation of the complex ReCl(CO)(bpy) (bpy = 2,2-bipyridine) using a nonadiabatic TD-DFT dynamics on spin-mixed potential energy surfaces in explicit acetonitrile (ACN) and dimethylsulfoxide (DMSO) solutions up to 800 fs. ReCl(CO)(bpy) belongs to a group of important photosensitizers which show ultrafast biexponential subpicosecond fluorescence decay kinetics. The choice of solvents was motivated by the different excited-state relaxation dynamics observed in subpicosecond time-resolved IR (TRIR) experiments.

Excitation-Wavelength-Dependent Photophysics of dd Di-isocyanide Complexes.

Binuclear Rh(I) and Ir(I) TMB (2,5-dimethyl-2,5-diisocyanohexane) and dimen (1,8-diisocyanomenthane) complexes possess dσ*pσ and dπpσ singlet and triplet excited states that can be selectively excited in the visible and UV spectral regions. Using perturbational spin-orbit TDDFT, we unraveled the detailed character and spin mixing of these electronic transitions and found that delocalization of pσ and dπ orbitals over C≡N- groups makes C≡N stretching vibrations sensitive reporters of electron density and structural changes upon electronic excitation. Picosecond time-resolved infrared spectra measured after visible light, 375 nm, and 316 nm excitation revealed excitation-wavelength-dependent deactivation cascades.

Photoinduced hole hopping through tryptophans in proteins.

Hole hopping through tryptophan/tyrosine chains enables rapid unidirectional charge transport over long distances. We have elucidated structural and dynamical factors controlling hopping speed and efficiency in two modified azurin constructs that include a rhenium(I) sensitizer, Re(His)(CO)(dmp), and one or two tryptophans (W, W). Experimental kinetics investigations showed that the two closely spaced (3 to 4 Å) intervening tryptophans dramatically accelerated long-range electron transfer (ET) from Cu to the photoexcited sensitizer.

Variable electronic structure and spin distribution in bis(2,2'-bipyridine)-metal complexes (M = Ru or Os) of 4,5-dioxido- and 4,5-diimido-pyrene.

The odd-electron compounds [M(bpy)(L)](ClO) M = Ru ([1](ClO)) or Os ([2](ClO)), and the even-electron species [M(bpy)(HL)](ClO), M = Ru ([3](ClO)) or Os ([4](ClO)) were obtained from pyrene-4,5-dione, L, or 4,5-diaminopyrene, HL, and were characterised structurally, electrochemically and spectroscopically. Experimental and computational analysis (TD-DFT) revealed rather different electronic structures and spin distributions of the paramagnetic monocations 1-4. EPR investigations and electronic absorption studies exhibit increasing metal contributions to the singly occupied MO along the series 1 < 3 < 4 < 2, illustrated by g value and long-wavelength absorbance.

Optical and Infrared Spectroelectrochemical Studies of CN-Substituted Bipyridyl Complexes of Ruthenium(II).

Ruthenium(II) polypyridyl complexes [Ru(CN-Me-bpy)(bpy)] (CN-Me-bpy = 4,4'-dicyano-5,5'-dimethyl-2,2'-bipyridine, bpy = 2,2'-bipyridine, and = 1-3, abbreviated as , , and ) undergo four () or five ( and ) successive one-electron reduction steps between -1.3 and -2.75 V versus ferrocenium/ferrocene (Fc/Fc) in tetrahydrofuran.

Time-Resolved Femtosecond Stimulated Raman Spectra and DFT Anharmonic Vibrational Analysis of an Electronically Excited Rhenium Photosensitizer.

Time-resolved femtosecond stimulated Raman spectra (FSRS) of a prototypical organometallic photosensitizer/photocatalyst ReCl(CO)(2,2'-bipyridine) were measured in a broad spectral range ∼40-2000 (4000) cm at time delays from 40 fs to 4 ns after 400 nm excitation of the lowest allowed electronic transition. Theoretical ground- and excited-state Raman spectra were obtained by anharmonic vibrational analysis using second-order vibrational perturbation theory on vibrations calculated by harmonic approximation at density functional theory-optimized structures. A good match with anharmonically calculated vibrational frequencies allowed for assigning experimental Raman features to particular vibrations.

Two Tryptophans Are Better Than One in Accelerating Electron Flow through a Protein.

We have constructed and structurally characterized a azurin mutant , where two adjacent tryptophan residues (W124 and W122, indole separation 3.6-4.1 Å) are inserted between the Cu center and a Re photosensitizer coordinated to the imidazole of H126 (Re(H126)(CO)(4,7-dimethyl-1,10-phenanthroline)).

Hole Hopping Across a Protein-Protein Interface.

We have investigated photoinduced hole hopping in a Pseudomonas aeruginosa azurin mutant Re126WWCu, where two adjacent tryptophan residues (W124 and W122) are inserted between the Cu center and a Re photosensitizer coordinated to a H126 imidazole (Re = Re(H126)(CO)(dmp), dmp = 4,7-dimethyl-1,10-phenanthroline). Optical excitation of this mutant in aqueous media (≤40 μM) triggers 70 ns electron transport over 23 Å, yielding a long-lived (120 μs) Re(H126)(CO)(dmp)WWCu product. The Re126FWCu mutant (F124, W122) is not redox-active under these conditions.

Photophysical Heavy-Atom Effect in Iodinated Metallocorroles: Spin-Orbit Coupling and Density of States.

Excited-state dynamics and electronic structures of Al and Ga corrole complexes were studied as a function of the number of β-pyrrole iodine substituents. Using spectrally broad-band femtosecond-resolved fluorescence upconversion, we determined the kinetics of the Soret fluorescence decay, the concomitant rise and subsequent decay of the Q-band fluorescence, as well as of the accompanying vibrational relaxation. Iodination was found to accelerate all involved processes.

At the Borderline between Metal-Metal Mixed Valency and a Radical Bridge Situation: Four Charge States of a Diruthenium Complex with a Redox-Active Bis( mer-tridentate) Ligand.

The complex ions [LRu(μ,η:η-BL)RuL] (1 , L = 4,4',4″-tri- tert-butyl-2,6,2',6″-terpyridine and HBL = 1,2-bis(salicyloyl)hydrazide(2-)) were isolated with PF or ClO counterions ( n = 1) and as bis(hexafluorophosphate) ( n = 2). Structural, electrochemical, and spectroscopic characterization reveals the monocation as intermediate ( K = 10) in the three-step reversible redox system 1. The 1 ion has the molecule-bridged (Ru- - -Ru 4.

Ultrafast Wiggling and Jiggling: Ir(1,8-diisocyanomenthane).

Binuclear complexes of d metals (Pt, Ir, Rh,) exhibit diverse photonic behavior, including dual emission from relatively long-lived singlet and triplet excited states, as well as photochemical energy, electron, and atom transfer. Time-resolved optical spectroscopic and X-ray studies have revealed the behavior of the dimetallic core, confirming that M-M bonding is strengthened upon dσ* → pσ excitation. We report the bridging ligand dynamics of Ir(1,8-diisocyanomenthane) (Ir(dimen)), investigated by fs-ns time-resolved IR spectroscopy (TRIR) in the region of C≡N stretching vibrations, ν(C≡N), 2000-2300 cm.

Electronic Structures of Reduced and Superreduced Ir(1,8-diisocyanomenthane) Complexes.

Molecular and electronic structures of Ir(1,8-diisocyanomenthane) (Ir(dimen)) complexes have been investigated by DFT for n = 2, 1, 0 (abbreviated 2+, 1+, 0). Calculations reproduced the experimental structure of 2+, ν(C≡N) IR, and visible absorption spectra of all three oxidation states, as well as the EPR spectrum of 1+. We have shown that the two reduction steps correspond to successive filling of the Ir-Ir pσ orbital.

Different manifestations of enhanced π-acceptor ligation at every redox level of [Os(9-OP)L], n = 2+, +, 0, - (9-OP = 9-oxidophenalenone and L = bpy or pap).

The title complexes were isolated as structurally characterised compounds [Os(9-OP)L]ClO, L = 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap), and were compared with ruthenium analogues. A reversible one-electron oxidation and up to three reduction processes were observed by voltammetry (CV, DPV) and spectroelectrochemistry (UV-vis-NIR, partially EPR). Supporting calculations (DFT, TD-DFT) were used to assess the oxidation state combinations of the different redox active ligands and of the metal, revealing the effects of Os versus Ru exchange and of bpy versus pap acceptor ligation.

Extreme Basicity of Biguanide Drugs in Aqueous Solutions: Ion Transfer Voltammetry and DFT Calculations.

Ion transfer voltammetry is used to estimate the acid dissociation constants Ka1 and Ka2 of the mono- and diprotonated forms of the biguanide drugs metformin (MF), phenformin (PF), and 1-phenylbiguanide (PB) in an aqueous solution. Measurements gave the pKa1 values for MFH(+), PFH(+), and PBH(+) characterizing the basicity of MF, PF, and PB, which are significantly higher than those reported in the literature. As a result, the monoprotonated forms of these biguanides should prevail in a considerably broader range of pH 1-15 (MFH(+), PFH(+)) and 2-13 (PBH(+)).

Reduced and Superreduced Diplatinum Complexes.

A d(8)-d(8) complex [Pt2(μ-P2O5(BF2)4](4-) (abbreviated Pt(pop-BF2)(4-)) undergoes two 1e(-) reductions at E1/2 = -1.68 and Ep = -2.46 V (vs Fc(+)/Fc) producing reduced Pt(pop-BF2)(5-) and superreduced Pt(pop-BF2)(6-) species, respectively.

Thermally Tunable Dual Emission of the d(8)-d(8) Dimer [Pt2(μ-P2O5(BF2)2)4](4).

High-resolution fluorescence, phosphorescence, as well as related excitation spectra, and, in particular, the emission decay behavior of solid [Bu4N]4[Pt2(μ-P2O5(BF2)2)4], abbreviated Pt(pop-BF2), have been investigated over a wide temperature range, 1.3-310 K. We focus on the lowest excited states that result from dσ*pσ (5dz(2)-6pz) excitations, i.

Metal-Induced Thiophene Ring Opening and C-C Bond Formation To Produce Unique Hexa-1,3,5-trienediyl-Coupled Non-Innocent Ligand Chelates.

Ring opening of thiophenes containing an azo function in 2-position and subsequent dimerization through C-C coupling were observed on reaction with [Ru(acac)2 (CH3 CN)2 ] (acac=acetylacetonate) to produce two 1,3,5-hexatriene-linked redox-active azothiocarbonyl chelate systems. Interaction of the non-innocent chelate ligands and of the metals at a nanoscale distance of 1.45 nm via the conjugated hexatriene bridge was studied by magnetic and electron spectroscopic measurements in conjunction with DFT calculations, revealing four-center magnetic interactions of this unique setting and weak intervalence coupling after reduction.

Anharmonicity Effects in IR Spectra of [Re(X)(CO)3(α-diimine)] (α-diimine = 2,2'-bipyridine or pyridylimidazo[1,5-a]pyridine; X = Cl or NCS) Complexes in Ground and Excited Electronic States.

Infrared spectra of [Re(X)(CO)(3)(α-diimine)] (α-diimine = 2,2'-bipyridine, X = Cl, NCS, or pyridylimidazo[1,5-a]pyridine, X = Cl) in the ground and the lowest triplet electronic states were calculated by a global hybrid density functional going beyond the harmonic level by means of second-order vibrational perturbation theory (VPT2) and including bulk solvent effects by the polarizable continuum model (PCM). The full-dimensionality (FD) VPT2 is compared with the reduced-dimensionality (RD) model, where only selected vibrational modes are calculated anharmonically. The simulated difference IR spectra (excited state minus ground state) in the ν(CO) region closely match experimental time-resolved infrared (TRIR) spectra.

Luminescent Diamond Nanoparticles: Physical, Chemical and Biological Aspects of the Phenomenon.

Biosensors based on nanodiamonds are able to penetrate through the cell membrane in a targeted manner and probe changes in real-time in the inner cellular space. In this work we performed exclusive theoretical and experimental study of nanodiamond particles adjusted for application in optically-traceable intracellular nanodiamond sensors. Theoretical and experimental study of specific optical properties of high-pressure high-temperature nanodiamonds containing NV- and NV0 centres were performed.

Electronic Excited States of Tungsten(0) Arylisocyanides.

W(CNAryl)6 complexes containing 2,6-diisopropylphenyl isocyanide (CNdipp) are powerful photoreductants with strongly emissive long-lived excited states. These properties are enhanced upon appending another aryl ring, e.g.

Metal-Chelating N,N'-Bis(4-dimethylaminophenyl)acetamidinyl Radical: A New Chromophore for the Near-Infrared Region.

A new non-innocent ligand redox system, N,N'-bis(4-dimethylaminophenyl) substituted acetamidinato/acetamidinyl, has been designed and described by example of structurally and spectroscopically characterized ruthenium complexes. The hitherto unreported ligand is responsible for rather intense and narrow absorptions in the near-infrared region of the one- and two-electron oxidized forms. The spectroscopic, computational, and first structural characterization of an amidinyl radical complex adds to the list of established N-based radical ligands.

Spin-orbit TDDFT electronic structure of diplatinum(II,II) complexes.

[Pt2(μ-P2O5H2)4](4-) (Pt(pop)) and its perfluoroborated derivative [Pt2(μ-P2O5(BF2)2)4](4-) (Pt(pop-BF2)) are d(8)-d(8) complexes whose electronic excited states can drive reductions and oxidations of relatively inert substrates. We performed spin-orbit (SO) TDDFT calculations on these complexes that account for their absorption spectra across the entire UV-vis spectral region. The complexes exhibit both fluorescence and phosphorescence attributable, respectively, to singlet and triplet excited states of dσ*pσ origin.

Vinyl ruthenium-modified biphenyl and 2,2'-bipyridines.

We report here on ruthenium alkenyl complexes 2 and 3 derived from 2,2'-bipyridine and their Re(CO)3X adducts 4a,b and 5. Detailed electrochemical studies on these complexes and spectroscopic characterization of their oxidized forms by IR, UV/vis/NIR, and electron paramagnetic resonance spectroscopies as well as quantum chemical studies reveal sizable (bridging) ligand contributions to the redox orbitals. Engagement of the free bipy functions of complexes 2 and 3 in binding to the electron-withdrawing fac-Re(CO)3X (X = Br, Cl) moiety enhances the metal-to-ligand charge-transfer character of the optical excitations, causes sizable anodic shifts of the redox potentials, and decreases the number of observable anodic redox waves by one when compared to complexes 2 and 3.