Determination of Thiol Protonation States by Sulfur X-ray Spectroscopy in Biological Systems.

Cysteine is one of the most functionally diverse of the proteinogenic amino acids, owing to its reactive thiol side chain that can undergo deprotonation to form a strongly nucleophilic thiolate. However, few techniques can directly interrogate sulfur charge and covalency in cysteine, particularly in proteins. X-ray spectroscopies provide an element specific probe of sulfur.

Strain-affected ferroelastic domain walls in RbMnFe charge-transfer materials undergoing collective Jahn-Teller distortion.

Many rubidium manganese hexacyanoferrate materials, with the general formula Rb Mn[Fe(CN)]·HO, exhibit diverse charge-transfer-based functionalities due to the bistability between a high temperature Mn( = 5/2)Fe( = 1/2) cubic phase and a low-temperature Mn( = 2)Fe( = 0) tetragonal phase. The collective Jahn-Teller distortion on the Mn sites is responsible for the cubic-to-tetragonal ferroelastic phase transition, which is associated with the appearance of ferroelastic domains. In this study, we use X-ray diffraction to reveal the coexistence of 3 types of ferroelastic tetragonal domains and estimate the spatial extension of the strain around the domain walls, which represents about 30% of the volume of the crystal.

Ligand Control of Dinitrosyl Iron Complexes for Selective Superoxide-Mediated Nitric Oxide Monooxygenation and Superoxide-Dioxygen Interconversion.

Through nitrosylation of [Fe-S] proteins, or the chelatable iron pool, a dinitrosyl iron unit (DNIU) [Fe(NO)] embedded in the form of low-molecular-weight/protein-bound dinitrosyl iron complexes (DNICs) was discovered as a metallocofactor assembled under inflammatory conditions with elevated levels of nitric oxide (NO) and superoxide (O). In an attempt to gain biomimetic insights into the unexplored transformations of the DNIU under inflammation, we investigated the reactivity toward O by a series of DNICs [(NO)Fe(μ-Pyr)Fe(NO)] () and [(NO)Fe(μ-SEt)Fe(NO)] (). During the superoxide-induced conversion of DNIC into DNIC [(K-18-crown-6-ether)(NO)][Fe(μ-Pyr)(μ-O)(Fe(NO))] () and a [Fe(Pyr)(NO)(O)] adduct, stoichiometric NO monooxygenation yielding NO occurs without the transient formation of peroxynitrite-derived OH/NO species.

Controlling Singlet Fission with Coordination Chemistry-Induced Assembly of Dipyridyl Pyrrole Bipentacenes.

Singlet fission has the potential to surpass current efficiency limits in next-generation photovoltaics and to find use in quantum information science. Despite the demonstration of singlet fission in various materials, there is still a great need for fundamental design principles that allow for tuning of photophysical parameters, including the rate of fission and triplet lifetimes. Here, we describe the synthesis and photophysical characterization of a novel bipentacene dipyridyl pyrrole (HDPP-Pent) and its Li- and K-coordinated derivatives.

Understanding Covalent versus Spin-Orbit Coupling Contributions to Temperature-Dependent Electron Spin Relaxation in Cupric and Vanadyl Phthalocyanines.

Recent interest in transition-metal complexes as potential quantum bits (qubits) has reinvigorated the investigation of fundamental contributions to electron spin relaxation in various ligand scaffolds. From quantum computers to chemical and biological sensors, interest in leveraging the quantum properties of these molecules has opened a discussion of the requirements to maintain coherence over a large temperature range, including near room temperature. Here we compare temperature-, magnetic field position-, and concentration-dependent electron spin relaxation in copper(II) phthalocyanine (CuPc) and vanadyl phthalocyanine (VOPc) doped into diamagnetic hosts.

Quantifying Entatic States in Photophysical Processes: Applications to Copper Photosensitizers.

The entatic or rack-induced state is a core concept in bioinorganic chemistry. In its simplest form, it is present when a protein scaffold places a transition metal ion and its first coordination sphere into an energized geometric and electronic structure that differs significantly from that of the relaxed form. This energized complex can exhibit special properties.

Stoichiometric Reactions of Acylnickel(II) Complexes with Electrophiles and the Catalytic Synthesis of Ketones.

Acylnickel(II) complexes feature prominently in cross-electrophile coupling (XEC) reactions that form ketones, yet their reactivity has not been systematically investigated. We present here our studies on the reactivity of acylnickel(II) complexes with a series of carbon electrophiles. Bromobenzene, α-chloroethylbenzene, bromooctane, and iodooctane were reacted with (dtbbpy)Ni(C(O)CH)(Br) () and (dtbbpy)Ni(C(O)tolyl)(Br) () to form a variety of organic products.