Visible Channeled Spectra of a Multilayer Wood Filter

The transmission factor of multilayer Wood filters containing quartz and rutile layers was simulated in order to avoid the experimental trials for obtaining optical filters with predicted transmission. The main refractive indices of uniaxial crystals—quartz and rutile—were interferometrically determined and Cauchy constants were obtained by simulation. The transmission factor of optical devices consisting of quartz and rutile layers was simulated using the Maple Program.     

Chiral Aggregates of Triphenylamine‐Based Dyes for Depleting the Production of Hydrogen Peroxide in the Photochemical Water‐Splitting Process

Recent studies on water‐splitting photoelectrochemical cells (PECs) have demonstrated the intriguing possibility of controlling the spin state in this chemical reaction to form H₂ and O₂ by exploiting the chirality of organic π‐conjugated supramolecular polymers. Although this fascinating phenomenon has been disclosed, the chiral supramolecular materials reported thus far are not optimized for acting as efficient photosensitizer for dye‐sensitized PECs. In this work we report on the design, synthesis, and characterization of chiral supramolecular aggregates based on C₃‐symmetric triphenylamine‐based dyes that are able to both absorb visible light and control the spin state of the process. Variable temperature‐dependent spectroscopic measurements reveal the assembly process of the dyes and confirm the formation of chiral aggregates, both in solution as well as on solid supports. Photoelectrochemical measurements on TiO₂‐based anodes validate the advantage of using chiral supramolecular aggregates as photosensitizer displaying higher photocurrent compared to achiral analogues. Moreover, fluorimetric tests for the quantification of the hydrogen peroxide produced, confirm the possibility of controlling the spin of the reaction exerting spin‐selection with chiral supramolecular polymers. These results represent a further step towards the next‐generation of organic‐based water‐splitting solar cells.     

Trapping Aluminum Hydroxide Clusters with Trisilanols during Speciation in Aluminum(III)–Water Systems: Reproducible,Large Scale Access to Molecular Aluminate Models

To gain molecular level insights into the properties of certain functions and units of extended oxides/hydroxides, suitable molecular model compounds are needed. As an attractive route to access such compounds the trapping of early intermediates during the hydrolysis of suitable precursor compounds with the aid of stabilizing ligands is conceivable, which was tested for the aluminum(III)/water system. Indeed, trisilanols proved suitable trapping reagents: their presence during the hydrolysis of AlⁱBu₂H in dependence on the amount of water used allowed for the isolation of tri‐ and octanuclear aluminum hydroxide cluster complexes [Al₃(μ₂‐OH)₃(THF)₃(PhSi(OSiPh₂O)₃)₂] ( 1 ) and [Al₈(μ₃‐OH)₂(μ₂‐OH)₁₀(THF)₃(p‐anisylSi(OSiPh₂O)₃)₄] ( 2 ). 1 can be regarded as the Al(OH)₃ cyclic trimer, where six protons have been replaced by silyl residues. While 2 features a unique [Al₈(μ₃‐OH)₂(μ₂‐OH)₁₀]¹²⁺ core. In contrast to most other known aggregates of this type, 1 and 2 can be readily prepared at reasonable scales, dissolve in common solvents, and retain an intact framework even in the presence of excessive amounts of water. This finding paves the way to future research addressing the reactivity of the individual functional groups.     

A New Thiolate-Bound Dimanganese Cluster as a Structural and Functional Model for Class Ib Ribonucleotide Reductases

In class Ib ribonucleotide reductases (RNRs) a dimanganese(II) cluster activates superoxide (O₂⋅⁻) rather than dioxygen (O₂), to access a high valent Mn^III−O₂−Mn^IV species, responsible for the oxidation of tyrosine to tyrosyl radical. In a biomimetic approach, we report the synthesis of a thiolate-bound dimanganese complex [Mn^II₂(BPMT)(OAc)₂](ClO)₄ (BPMT=(2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-methylthiophenolate) ( 1 ) and its reaction with O₂⋅⁻ to form a [(BPMT)MnO₂Mn]²⁺ complex 2 . Resonance Raman investigation revealed the presence of an O−O bond in 2 , while EPR analysis displayed a 16-line S_t=1/2 signal at g=2 typically associated with a Mn^IIIMn^IV core, as detected in class Ib RNRs. Unlike all other previously reported Mn−O₂−Mn complexes, generated by O₂⋅⁻ activation at Mn₂ centers, 2 proved to be a capable electrophilic oxidant in aldehyde deformylation and phenol oxidation reactions, rendering it one of the best structural and functional models for class Ib RNRs.     

Site selectivity in the protonation of a phosphinito bridged Pt(I)-Pt(I) complex: a combined NMR and density-functional theory mechanistic study

The protonation of the dinuclear phosphinito bridged complex [(PHCy2)Pt(mu-PCy2){kappa(2)P,O-mu-P(O)Cy2}Pt(PHCy2)] (Pt-Pt) (1) by Br?nsted acids affords hydrido bridged Pt-Pt species the structure of which depends on the nature and on the amount of the acid used. The addition of 1 equiv of HX (X = Cl, Br, I) gives products of formal protonation of the Pt-Pt bond of formula syn-[(PHCy2)(X)Pt(mu-PCy2)(mu-H)Pt(PHCy2){kappaP-P(O)Cy2}] (Pt-Pt) (5, X = Cl; 6, X = Br; 8, X = I), containing a Pt-X bond and a dangling kappa P-P(O)Cy2 ligand. Uptake of a second equivalent of HX results in the protonation of the P(O)Cy2 ligand with formation of the complexes [(PHCy2)(X)Pt(mu-PCy2)(mu-H)Pt(PHCy2){kappaP-P(OH)Cy2}]X (Pt-Pt) (3, X = Cl; 4, X = Br; 9, X = I). Each step of protonation is reversible, thus reactions of 3, 4, with NaOH give, first, the corresponding neutral complexes 5, 6, and then the parent compound 1. While the complexes 3 and 4 are indefinitely stable, the iodine analogue 9 transforms into anti-[(PHCy2)(I)Pt(mu-PCy2)(mu-H)Pt(PHCy2)(I)] (Pt-Pt) (7) deriving from substitution of an iodo group for the P(OH)Cy2 ligand. Complexes 3 and 4 are isomorphous crystallizing in the triclinic space group P1 and show an intramolecular hydrogen bond and an interaction between the halide counteranion and the POH hydrogen. The occurrence of such an interaction also in solution was ascertained for 3 by (35)Cl NMR. Multinuclear NMR spectroscopy (including (31)P-(1)H HOESY) and density-functional theory calculations indicate that the mechanism of the reaction starts with a prior protonation of the oxygen with formation of an intermediate (12) endowed with a six membered Pt(1)-X...H-O-P-Pt(2) ring that evolves into thermodynamically stable products featuring the hydride ligand bridging the Pt atoms. Energy profiles calculated for the various steps of the reaction between 1 and HCl showed very low barriers for the proton transfer and the subsequent rearrangement to 12, while a barrier of 29 kcal mol(-1) was found for the transformation of 12 into 5.     

How Ligand Geometry Affects the Reactivity of Co(II) Cyclam Complexes

Cobalt complexes are extensively studied as bioinspired models for non-heme oxygenases as they facilitate both the stabilization and characterization of metal-oxygen intermediates. As an analog to the well-known Co(cyclam) complex Co{N₄} (cyclam=1,4,8,11-tetraazacyclotetradecane), the Co^II complex Co{i-N₄} with the isomeric isocyclam ligand (isocyclam=1,4,7,11-tetraazacyclotetradecane) was synthesized and characterized. Despite the identical N₄ donor set of both complexes, Co{i-N₄} enables the 2e⁻/2H⁺ reduction of O₂ with a lower overpotential (η_eff of 385 mV vs. 540 mV for Co{N₄} ), albeit with a diminished turnover frequency. Characterization of the intermediates formed upon O₂ activation of Co{i-N₄} reveals a structurally identified stable μ-peroxo Co^III dimer as the main product. A superoxo Co^III species is also formed as a minor product, as indicated by EPR spectroscopy. In further reactivity studies, the electrophilicity of these in situ generated Co−O₂ species was demonstrated by the oxidation of the O−H bond of TEMPO−H (2,2,6,6-tetramethylpiperidin-1-ol) via a H atom abstraction process. Unlike the known Co(cyclam), Co{i-N₄} can be employed in oxygen atom transfer reactions oxidizing triphenylphosphine to the corresponding phosphine oxide highlighting the impact of geometrical modifications of the ligand while preserving the ring size and donor atom set on the reactivity of biomimetic oxygen activating complexes.     

Structure-based approach for identification of novel phenylboronic acids as serine-β-lactamase inhibitors

β-Lactamases are bacterial enzymes conferring resistance to β-lactam antibiotics in clinically-relevant pathogens, and represent relevant drug targets. Recently, the identification of new boronic acids (i.e. RPX7009) paved the way to the clinical application of these molecules as potential drugs. Here, we screened in silico a library of ~1400 boronic acids as potential AmpC β-lactamase inhibitors. Six of the most promising candidates were evaluated in biochemical assays leading to the identification of potent inhibitors of clinically-relevant β-lactamases like AmpC, KPC-2 and CTX-M-15. One of the selected compounds showed nanomolar K _i value with the clinically-relevant KPC-2 carbapenemase, while another one exhibited broad spectrum inhibition, being also active on Enterobacter AmpC and the OXA-48 class D carbapenemase.     

Creating Iron– and Rhenium–Bismuth Bonds by Reactions with Organometallic Hydrides

While addition of [Cp₂ReH] to [Bi(OtBu)₃] leads to an equilibrium containing [Cp₂Re‐Bi(OtBu)₂], [{Cp₂Re}₂Bi(OtBu)], tBuOH and [CpRe(μ‐η⁵,η¹‐C₅H₄)Bi–ReCp₂], in the presence of water [{(Cp₂Re)₂Bi}₂O] ( 1 ) is formed selectively. Also [FpH] [Fp = (η⁵‐C₅H₅)(CO)₂Fe] can be employed as a precursor to form heterometallic bismuth compounds. Synthesis of [FpBi{OCH(CF₃)₂}₂]₂ ( 5 ) can be achieved by reaction of [FpH] with [Bi{OCH(CF₃)₂}₃(thf)]₂ and carboxylates [FpBi(O₂CR)₂]₂ are generated upon treatment of [FpH] with [Bi(O₂CR)₃] (R = CH₃, tBu). While the compounds [Fp‐Bi(O₂CR)₂]₂ can also be obtained from reactions with Fp‐Fp, they are formed far more readily using [FpH] as the precursor. They typically crystallize as dimers, like the alkoxide 5 . A monomeric compound of the type [Fp‐BiX₂] ( 6 ) could be isolated for X = thd (tetramethylheptanedionate), that is, after the reaction of [FpH] with [Bi(thd)₃]. Altogether, the results demonstrate the potential of [FpH] as a precursor for [Fp‐BiX₂] compounds, which are formed in reactions with bismuth alkoxides, carboxylates and diketonates.