Germanium,carbon‐germanium,and silicon‐germanium triangulenes

A series of germanium‐containing triangular molecules have been studied by density functional theory (DFT) calculations. The triangulene topology of the compounds provides for their high‐spin ground states and strong sign alternation of spin density and atomic charge distributions. High values of the exchange coupling constants witness ferromagnetic ordering of electronic structures of all studied triangulenes. The compounds bearing more electronegative atoms in a‐positions of the triangular networks possess higher aromatic character and stronger ferromagnetic ordering. © 2015 Wiley Periodicals, Inc.     

Strain‐Induced Reactivity in the Dynamic Covalent Chemistry of Macrocyclic Imines

The displacement of molecular structures from their thermodynamically most stable state by imposition of various types of electronic and conformational constraints generates highly strained entities that tend to release the accumulated strain energy by undergoing either structural changes or chemical reactions. The latter case amounts to strain‐induced reactivity (SIR) that may enforce specific chemical transformations. A particular case concerns dynamic covalent chemistry which may present SIR, whereby reversible reactions are activated by coupling to a high‐energy state. We herewith describe such a dynamic covalent chemical (DCC) system involving the reversible imine formation reaction. It is based on the formation of strained macrocyclic bis‐imine metal complexes in which the macrocyclic ligand is in a high energy form enforced by the coordination of the metal cation. Subsequent demetallation generates a highly strained free macrocycle that releases its accumulated strain energy by hydrolysis and reassembly into a resting state. Specifically, the metal‐templated condensation of a dialdehyde with a linear diamine leads to a bis‐imine [1+1]‐macrocyclic complex in which the macrocyclic ligand is in a coordination‐enforced strained conformation. Removal of the metal cation by a competing ligand yields a highly reactive [1+1]‐macrocycle, which then undergoes hydrolysis to transient non‐cyclic aminoaldehyde species, which then recondense to a strain‐free [2+2]‐macrocyclic resting state. The process can be monitored by ¹H NMR spectroscopy. Energy differences between different conformational states have been evaluated by Hartree–Fock (HF) computations. One may note that the stabilisation of high‐energy molecular forms by metal ion coordination followed by removal of the latter, offers a general procedure for producing out‐of‐equilibrium molecular states, the fate of which may then be examined, in particular when coupled to dynamic covalent chemical processes.     

Conformational Flexibility in the Transmembrane Protein TSPO

The translocator protein (TSPO) is an integral membrane protein that interacts with a wide variety of endogenous ligands, such as cholesterol and porphyrins, and is also the target for several small molecules with substantial in vivo efficacy. When complexed with the TSPO‐specific radioligand (R)‐PK11195, TSPO folds into a rigid five‐helix bundle. However, little is known about the structure and dynamics of TSPO in the absence of high‐affinity ligands. By means of NMR spectroscopy, we show that TSPO exchanges between multiple conformations in the absence of (R)‐PK11195. Extensive motions on time scales from pico‐ to microseconds occur all along the primary sequence of the protein, leading to a loss of stable tertiary interactions and local unfolding of the helical structure in the vicinity of the ligand‐binding site. The flexible nature of TSPO highlights the importance of conformational plasticity in integral membrane proteins.     

Supramolecular nanostructures based on bacterial reaction center proteins and quantum dots

Design of the nanostructures based on membrane proteins (the key functional elements of biomembranes) and colloid nanoparticles is a fascinating field at the interface of biochemistry and colloids, nanotechnology and biomedicine. The review discusses the main achievements in the field of ultrathin films prepared from bacterial reaction center proteins and light-harvesting complexes, as well as these complexes tagged with quantum dots. The principles of preparation of these thin films and their structure and properties at different interfaces are described; as well as their characteristics estimated using a combination of the modern interfacial techniques (absorption and fluorescence spectroscopy, atomic force and Brewster angle microscopy, etc.) are discussed. Further approaches to develop the nanostructures based on the membrane proteins and quantum dots are suggested. These supramolecular nanostructures are promising prototypes of the materials for photovoltaic, optoelectronic and biosensing applications.     

Generalized vibrational perturbation theory for rotovibrational energies of linear,symmetric and asymmetric tops: Theory,approximations, and automated approaches to deal with medium‐to‐large molecular systems

Models going beyond the rigid‐rotor and the harmonic oscillator levels are mandatory for providing accurate theoretical predictions for several spectroscopic properties. Different strategies have been devised for this purpose. Among them, the treatment by perturbation theory of the molecular Hamiltonian after its expansion in power series of products of vibrational and rotational operators, also referred to as vibrational perturbation theory (VPT), is particularly appealing for its computational efficiency to treat medium‐to‐large systems. Moreover, generalized (GVPT) strategies combining the use of perturbative and variational formalisms can be adopted to further improve the accuracy of the results, with the first approach used for weakly coupled terms, and the second one to handle tightly coupled ones. In this context, the GVPT formulation for asymmetric, symmetric, and linear tops is revisited and fully generalized to both minima and first‐order saddle points of the molecular potential energy surface. The computational strategies and approximations that can be adopted in dealing with GVPT computations are pointed out, with a particular attention devoted to the treatment of symmetry and degeneracies. A number of tests and applications are discussed, to show the possibilities of the developments, as regards both the variety of treatable systems and eligible methods. © 2015 The Authors International Journal of Quantum Chemistry Published by Wiley Periodicals, Inc.     

Bridging Nonaselenium Ring in [Se9(IrBr3)2], and Three Modifications of the Mononuclear Complex [IrBr3(SeBr2)3]

The reaction of iridium powder with an excess of selenium and SeBr₄ yielded lustrous, vermillion crystals of the mononuclear iridium complex [IrBr₃(SeBr₂)₃]. The transition metal is coordinated octahedrally by three SeBr₂ and three bromide ligands with facial or meridional configuration. Three different modifications were obtained under similar conditions: a‐fac‐IrBr₃(SeBr₂)₃, space group P$\bar{1}$ , with a = 789.4(1) pm, b = 830.4(1) pm, c = 1334.4(1) pm, α = 81.634(5)°, β = 84.948(5)°, γ = 67.616(4)°; m‐fac‐IrBr₃(SeBr₂)₃, space group P2₁/n, with a = 1205.3(1) pm, b = 962.4(1) pm, c = 1383.9(1) pm, β = 91.114(3)°; mer‐IrBr₃(SeBr₂)₃, space group P2₁/n with a = 859.7(1) pm, b = 1284.3(1) pm, c = 1437.5(1) pm, β = 94.427(3)°. A lower bromine content in the starting composition resulted in shiny, deep‐red crystals of [Se₉(IrBr₃)₂]. X‐ray diffraction on a single‐crystal revealed a tetragonal lattice (space group I4₁/a) with a = 1245.4(1) pm and c = 2486.8(1) pm at 296(1) K. In the [Se₉(IrBr₃)₂] complex, a crown‐shaped uncharged Se₉ ring coordinates two iridium(III) cations as a bridging bis‐tridentate ligand. Three terminal bromide ions complete the distorted octahedral coordination of each transition metal atom.     

Four Decades of the Chemistry of Planar Hypercoordinate Compounds

The idea of planar tetracoordinate carbon (ptC) was considered implausible for a hundred years after 1874. Examples of ptC were then predicted computationally and realized experimentally. Both electronic and mechanical (e.g., small rings and cages) effects stabilize these unusual bonding arrangements. Concepts based on the bonding motifs of planar methane and the planar methane dication can be extended to give planar hypercoordinate structures of other chemical elements. Numerous planar configurations of various central atoms (main‐group and transition‐metal elements) with coordination numbers up to ten are discussed herein. The evolution of such planar configurations from small molecules to clusters, to nanospecies and to bulk solids is delineated. Some experimentally fabricated planar materials have been shown to possess unusual electrical and magnetic properties. A fundamental understanding of planar hypercoordinate chemistry and its potential will help guide its future development.     

Structure and Reactivity of an Isolable Seven‐Membered‐Ring trans‐Alkene

The isolation and characterization of a trans‐oxasilacycloheptene is reported. Single‐crystal X‐ray crystallographic studies indicate a high level of strain and deviation from ideal geometry. Reactions with several electrophiles demonstrated the nucleophilicity of the C?C double bond, affording oxasilacycloheptane and tetrahydrofuran products as single diastereomers.     

Strained Cyclooctyne as a Molecular Platform for Construction of Multimodal Imaging Probes

Small‐molecule‐based multimodal and multifunctional imaging probes play prominent roles in biomedical research and have high clinical translation ability. A novel multimodal imaging platform using base‐catalyzed double addition of thiols to a strained internal alkyne such as bicyclo[6.1.0]nonyne has been established in this study, thus allowing highly selective assembly of various functional units in a protecting‐group‐free manner. Using this molecular platform, novel dual‐modality (PET and NIRF) uPAR‐targeted imaging probe: ⁶⁴Cu‐CHS1 was prepared and evaluated in U87MG cells and tumor‐bearing mice models. The excellent PET/NIRF imaging characteristics such as good tumor uptake (3.69 %ID/g at 2 h post‐injection), high tumor contrast, and specificity were achieved in the small‐animal models. These attractive imaging properties make ⁶⁴Cu‐CHS1 a promising probe for clinical use.