Electron transfer in biological systems.

Examples of how metalloproteins feature in electron transfer processes in biological systems are reviewed. Attention is focused on the electron transport chains of cellular respiration and photosynthesis, and on metalloproteins that directly couple electron transfer to a chemical reaction. Brief mention is also made of extracellular electron transport.

Methylammonium Tetrel Halide Perovskite Ion Pairs and Their Dimers: The Interplay between the Hydrogen-, Pnictogen- and Tetrel-Bonding Interactions.

The structural stability of the extensively studied organic-inorganic hybrid methylammonium tetrel halide perovskite semiconductors, MATtX (MA = CHNH; Tt = Ge, Sn, Pb; X = Cl, Br, I), arises as a result of non-covalent interactions between an organic cation (CHNH) and an inorganic anion (TtX). However, the basic understanding of the underlying chemical bonding interactions in these systems that link the ionic moieties together in complex configurations is still limited. In this study, ion pair models constituting the organic and inorganic ions were regarded as the repeating units of periodic crystal systems and density functional theory simulations were performed to elucidate the nature of the non-covalent interactions between them.

The Tetrel Bond and Tetrel Halide Perovskite Semiconductors.

The ion pairs [Cs•TtX] (Tt = Pb, Sn, Ge; X = I, Br, Cl) are the building blocks of all-inorganic cesium tetrel halide perovskites in 3D, CsTtX, that are widely regarded as blockbuster materials for optoelectronic applications such as in solar cells. The 3D structures consist of an anionic inorganic tetrel halide framework stabilized by the cesium cations (Cs). We use computational methods to show that the geometrical connectivity between the inorganic monoanions, [TtX], that leads to the formation of the TtX octahedra and the 3D inorganic perovskite architecture is the result of the joint effect of polarization and coulombic forces driven by alkali and tetrel bonds.

The inorganic chemistry of the cobalt corrinoids - an update.

The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed.

The Pnictogen Bond, Together with Other Non-Covalent Interactions, in the Rational Design of One-, Two- and Three-Dimensional Organic-Inorganic Hybrid Metal Halide Perovskite Semiconducting Materials, and Beyond.

The pnictogen bond, a somewhat overlooked supramolecular chemical synthon known since the middle of the last century, is one of the promising types of non-covalent interactions yet to be fully understood by recognizing and exploiting its properties for the rational design of novel functional materials. Its bonding modes, energy profiles, vibrational structures and charge density topologies, among others, have yet to be comprehensively delineated, both theoretically and experimentally. In this overview, attention is largely centered on the nature of nitrogen-centered pnictogen bonds found in organic-inorganic hybrid metal halide perovskites and closely related structures deposited in the Cambridge Structural Database (CSD) and the Inorganic Chemistry Structural Database (ICSD).

The Pnictogen Bond: The Covalently Bound Arsenic Atom in Molecular Entities in Crystals as a Pnictogen Bond Donor.

In chemical systems, the arsenic-centered pnictogen bond, or simply the arsenic bond, occurs when there is evidence of a net attractive interaction between the electrophilic region associated with a covalently or coordinately bound arsenic atom in a molecular entity and a nucleophile in another or the same molecular entity. It is the third member of the family of pnictogen bonds formed by the third atom of the pnictogen family, Group 15 of the periodic table, and is an inter- or intramolecular noncovalent interaction. In this overview, we present several illustrative crystal structures deposited into the Cambridge Structure Database (CSD) and the Inorganic Chemistry Structural Database (ICSD) during the last and current centuries to demonstrate that the arsenic atom in molecular entities has a significant ability to act as an electrophilic agent to make an attractive engagement with nucleophiles when in close vicinity, thereby forming σ-hole or π-hole interactions, and hence driving (in part, at least) the overall stability of the system's crystalline phase.

The Stibium Bond or the Antimony-Centered Pnictogen Bond: The Covalently Bound Antimony Atom in Molecular Entities in Crystal Lattices as a Pnictogen Bond Donor.

A stibium bond, i.e., a non-covalent interaction formed by covalently or coordinately bound antimony, occurs in chemical systems when there is evidence of a net attractive interaction between the electrophilic region associated with an antimony atom and a nucleophile in another, or the same molecular entity.

The Phosphorus Bond, or the Phosphorus-Centered Pnictogen Bond: The Covalently Bound Phosphorus Atom in Molecular Entities and Crystals as a Pnictogen Bond Donor.

The phosphorus bond in chemical systems, which is an inter- or intramolecular noncovalent interaction, occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a covalently or coordinately bonded phosphorus atom in a molecular entity and a nucleophile in another, or the same, molecular entity. It is the second member of the family of pnictogen bonds, formed by the second member of the pnictogen family of the periodic table. In this overview, we provide the reader with a snapshot of the nature, and possible occurrences, of phosphorus-centered pnictogen bonding in illustrative chemical crystal systems drawn from the ICSD (Inorganic Crystal Structure Database) and CSD (Cambridge Structural Database) databases, some of which date back to the latter part of the last century.

Chalcogen Bonding in the Molecular Dimers of WCh (Ch = S, Se, Te): On the Basic Understanding of the Local Interfacial and Interlayer Bonding Environment in 2D Layered Tungsten Dichalcogenides.

Layered two-dimensional transition metal dichalcogenides and their heterostructures are of current interest, owing to the diversity of their applications in many areas of materials nanoscience and technologies. With this in mind, we have examined the three molecular dimers of the tungsten dichalcogenide series, (WCh) (Ch = S, Se, Te), using density functional theory to provide insight into which interactions, and their specific characteristics, are responsible for the interfacial/interlayer region in the room temperature 2H phase of WCh crystals. Our calculations at various levels of theory suggested that the Te···Te chalcogen bonding in (WTe) is weak, whereas the Se···Se and S···S bonding interactions in (WSe) and (WS), respectively, are of the van der Waals type.

The CsAgRhCl Halide Double Perovskite: A Dynamically Stable Lead-Free Transition-Metal Driven Semiconducting Material for Optoelectronics.

-Site doping with alkali ions, and/or metal substitution at the B and B'-sites, are among the key strategies in the innovative development of BB'X halide double perovskite semiconducting materials for application in energy and device technologies. To this end, we have investigated an intriguing series of five halide-based non-toxic systems, AgRhCl ( = Li, Na, K, Rb, and Cs), using density functional theory at the SCAN-10 level. The lattice stability and bonding properties emanating from this study of AgRhCl matched well with those that have already been synthesized, characterized and discussed [viz.

The chalcogen bond: can it be formed by oxygen?

Several recent studies have shown that chalcogen bonds originate from the σ-holes localized on the electron-deficient surface of the Group 16 atoms (sulfur, selenium and tellurium) in molecules; however, the oxygen atom in molecules does not appear to form such a bond. In this study, we have considered oxygen difluoride (OF2) as a prototypical Lewis acid, and 11 Lewis bases as partner interacting species (CH3F, CH3Cl, CH3Br, H2CO, HFCO, HF, SO, CH3CN, PN, HSCN and HCN). Their complexes are examined using DFT-M06-2X and ab initio first-principles calculations at the MP2 level of theory, in conjunction with Dunning's all-electron correlated basis set aug-cc-pVTZ.

C Fullerene Cage as a Novel Catalyst for Efficient Proton Transfer Reactions between Small Molecules: A Theoretical study.

When acids are supplied with an excess electron (or placed in an Ar or the more polarizable N matrix) in the presence of species such as NH, the formation of ion-pairs is a likely outcome. Using density functional theory and first-principles calculations, however, we show that, without supplying an external electron or an electric field, or introducing photo-excitation and -ionization, a single molecule of HCl or HBr in the presence of a single molecule of water inside a C fullerene cage is susceptible to cleavage of the σ-bond of the Brønsted-Lowry acid into X and H ions, with concomitant transfer of the proton along the reaction coordinate. This leads to the formation of an X···HOH (X = Cl, Br) conjugate acid-base ion-pair, similar to the structure in water of a Zundel ion.

Nature of halogen-centered intermolecular interactions in crystal growth and design: Fluorine-centered interactions in dimers in crystalline hexafluoropropylene as a prototype.

The wide occurrence of halogen-centered noncovalent interactions in crystal growth and design prompted this study, which includes a mini review of recent advances in the field. Particular emphasis is placed on providing compelling theoretical evidence of the formation of these interactions between sites of positive electrostatic potential, as well as between sites of negative electrostatic potential, localized on the electrostatic surfaces of the bound fluorine atoms in a prototypical system, hexafluoropropylene (C F ), upon its interaction with another same molecule to form (C F ) dimers. The existence of σ- and π-hole interactions is shown for the stable dimers.

Is the Fluorine in Molecules Dispersive? Is Molecular Electrostatic Potential a Valid Property to Explore Fluorine-Centered Non-Covalent Interactions?

Can two sites of positive electrostatic potential localized on the outer surfaces of two halogen atoms (and especially fluorine) in different molecular domains attract each other to form a non-covalent engagement? The answer, perhaps counterintuitive, is as shown here using the electronic structures and binding energies of the interactions for a series of 22 binary complexes formed between identical or different atomic domains in similar or related halogen-substituted molecules containing fluorine. These were obtained using various computational approaches, including density functional and first-principles theories with M06-2X, RHF, MP2 and CCSD(T). The physical chemistry of non-covalent bonding interactions in these complexes was explored using both Quantum Theory of Atoms in Molecules and Symmetry Adapted Perturbation Theories.

Significance of hydrogen bonding and other noncovalent interactions in determining octahedral tilting in the CHNHPbI hybrid organic-inorganic halide perovskite solar cell semiconductor.

The CHNHPbI (methylammonium lead triiodide) perovskite semiconductor system has been viewed as a blockbuster research material during the last five years. Because of its complicated architecture, several of its technological, physical and geometrical issues have been examined many times. Yet this has not assisted in overcoming a number of problems in the field nor in enabling the material to be marketed.

Halogen in materials design: Chloroammonium lead triiodide perovskite (ClNH PbI ) a dynamical bandgap semiconductor in 3D for photovoltaics.

Methylammonium lead trihalides and their derivatives are photovoltaic materials. CH NH PbI is the most efficient light harvester among all the known halide perovskites (PSCs). It is regarded as unsuitable for long-term stable solar cells, thus it is necessary to develop other types of PSC materials to achieve stable PSCs (Wang et al.

A DFT assessment of some physical properties of iodine-centered halogen bonding and other non-covalent interactions in some experimentally reported crystal geometries.

A set of six binary complexes that feature iodine-centered halogen bonding, extracted from structures deposited in the Cambridge Structure Database, has been examined computationally using density functional theory calculations with the M06-2X global hybrid, and dispersion corrected B3LYP-D3 and B97-D3, to determine their equilibrium geometries, binding energies and electronic properties. The results show that gas phase calculations are very informative in evaluating what occurs in the solid state, even though these calculations ignore the importance of lattice packing and counter ion effects. The calculated binding energies for the non-covalent interactions responsible for these complexes lie between -4.

Revealing Factors Influencing the Fluorine-Centered Non-Covalent Interactions in Some Fluorine-Substituted Molecular Complexes: Insights from First-Principles Studies.

We examine the equilibrium structure and properties of six fully or partially fluorinated hydrocarbons and several of their binary complexes using computational methods. In the monomers, the electrostatic surface of the fluorine is predicted to be either entirely negative or weakly positive. However, its lateral sites are always negative.

Synthesis of copper and zinc 2-(pyridin-2-yl)imidazo[1,2-a]pyridine complexes and their potential anticancer activity.

A small library of novel copper and zinc imidazo[1,2-a]pyridine complexes have been synthesized. Their structures were confirmed by X-ray diffraction crystallography and a selection of these compounds was tested against five cancer cell lines originating from breast cancer (MCF-7 and MDA-MB-231), leukemia (K562 and HL-60) and colorectal cancer (HT-29). The imidazo[1,2-a]pyridines and their zinc complexes showed poor anticancer activity, while the copper complexes were active against the cancer cell lines with IC values comparable to and lower than camptothecin.

The synthesis of a corrole analogue of aquacobalamin (vitamin B12a) and its ligand substitution reactions.

The synthesis of a Co(III) corrole, [10-(2-[[4-(1H-imidazol-1-ylmethyl)benzoyl]amino]phenyl)-5,15-diphenylcorrolato]cobalt(III), DPTC-Co, bearing a tail motif terminating in an imidazole ligand that coordinates Co(III), is described. The corrole therefore places Co(III) in a similar environment to that in aquacobalamin (vitamin B12a, H2OCbl(+)) but with a different equatorial ligand. In coordinating solvents, DPTC-Co is a mixture of five- and six-coordinate species, with a solvent molecule occupying the axial coordination site trans to the proximal imidazole ligand.

Outer-sphere anion recognition by a cyclen-based octadentate europium(III) complex: pH dependent recognition of ortho-phthalic acid.

An octadentate cyclen-based europium complex with amidic and hydroxyalkyl pendent moieties exhibits pH dependent ligand denticity associated with anion recognition. Unusually high hydration numbers are determined for ortho-phthalate ternary outer-sphere complexes for which modulation of lanthanide-based luminescence is observed.

The preparation of N-acetyl-Co(III)-microperoxidase-8 (NAcCoMP8) and its ligand substitution reactions: a comparison with aquacobalamin (vitamin B(12a)).

The synthesis of the Co(III) porphyrin octapeptide N-acetyl-Co(III) microperoxidase-8 (NAcCoMP8) is described. NAcCoMP8 provides a means of comparing and contrasting the chemistry of Co(III) porphyrins and corrins to assess the influence of the macrocycle. Log K values, and ΔH and ΔS, for the coordination of anionic (CN(-), N3(-), NO2(-), HSO3(-)) and neutral (pyridine, N-methylimidazole, methoxylamine and hydroxylamine) ligands by aquacobalamin (H2OCbl(+)) and NAcCoMP8 are reported.

Phenylvinylcobalamin: an alkenylcobalamin featuring a ligand with a large trans influence.

Cob(I)alamin reacts with phenylacetylene to produce two diastereomers in which the organic ligand is coordinated to the upper (β) and lower (α) face of the corrin ring, respectively. The isomers were separated chromatographically and characterised by ESI-MS and, in the case of the β isomer, by (1)H and (13)C NMR. Only the β isomer crystallised and its molecular structure, determined by X-ray diffraction, shows that the organic ligand coordinates Co(III) through the β carbon of the phenylvinyl ligand.

DFT studies of trans and cis influences in the homolysis of the Co-C bond in models of the alkylcobalamins.

Density functional theory (DFT) calculations (BP86/6-31+G(d,p)) and an analysis of the electron density using Bader's quantum theory of atoms in molecules (QTAIM) are used to explore factors that influence the bond dissociation energy (BDE) of the Co-C bond in models for the cofactor in the coenzyme B12-dependent enzymes. An increase in the basicity of L in [L-Co(III)(corrin)-CH3](n+), L = NH3, NH2(-), and NH(2-), causes an elongation of the trans Co-C bond, but this does not necessarily cause the BDE to decrease. The bond between the metal and the N-donor of L, Co-Nα, usually becomes shorter after Co-C homolysis as the resulting five-coordinate product permits the metal ion to move toward L.

Probing the nature of the Co(III) ion in corrins: comparison of reactions of aquacyanocobyrinic acid heptamethyl ester and aquacyano-stable yellow cobyrinic acid hexamethyl ester with neutral N-donor ligands.

Equilibrium constants (log K) for substitution of coordinated H(2)O in aquacyanocobyrinic acid heptamethyl ester (aquacyanocobester, ACCbs) and aquacyano-stable yellow cobyrinic acid hexamethyl ester (aquacyano-stable yellow cobester, ACSYCbs), in which oxidation of the C5 carbon of the corrin interrupts the normal delocalized system of corrins, by neutral N-donor ligands (ammonia, ethanolamine, 2-methoxyethylamine, N-methylimidazole, and 4-methylpyridine) have been determined spectrophotometrically as a function of temperature. Log K values increase with the basicity of the ligand, but a strong compensation effect between ΔH and ΔS values causes a leveling effect. The aliphatic amines with a harder donor atom produce ΔH values that are more negative in their reactions with ACSYCbs than with ACCbs, while the softer, aromatic N donors produce more negative ΔH values with ACCbs than with ACSYCbs.