Sulfur Ligands. from β-Lactam Antibiotics to Contrast Agents for MRI

Abstract

NMR, IR and semi empirical Molecular Orbital PM3 studies on selected β-lactam antibiotics are reported. The role of sulfur in β-lactam antibiotics is discussed.     

Synthesis, spectroscopic characterization, X-ray structure and DFT calculations of [Re(CO)3L2Cl] (L = 1,2,4-triazolo-[1,5-a]pyrimidine)

The paper presents a combined experimental and computational study of novel tricarbonyl complex – fac-[Re(CO)₃(tp)₂Cl] (tp = 1,2,4-triazolo-[1,5-a]pyrimidine). The compound has been characterized spectroscopically and structurally (by single-crystal X-ray diffraction). The absorption and emission spectra of the complex have been discussed on the basis of DFT and time-dependent (TD)DFT calculations.     

Push-Pull Effect of Terpyridine Substituted by Triphenylamine Motive—Impact of Viscosity,Polarity and Protonation on Molecular Optical Properties

The introduction of an electron-donating triphenylamine motive into a 2,2′,6′,2′′-terpyridine (terpy) moiety, a cornerstone molecular unit in coordination chemistry, opens new ways for a rational design of photophysical properties of organic and inorganic compounds. A push-pull compound, 4′-(4-(di(4-tert-butylphenyl)amine)phenyl)-2,2′,6′,2′′-terpyridine (tBuTPAterpy), was thoroughly investigated with the use of steady-state and time-resolved spectroscopies and Density Functional Theory (DFT) calculations. Our results demonstrate that solvent parameters have an enormous influence on the optical properties of this molecule, acting as knobs for external control of its photophysics. The Intramolecular Charge Transfer (ICT) process introduces a remarkable solvent polarity effect on the emission spectra without affecting the lowest absorption band, as confirmed by DFT simulations, including solvation effects. The calculations ascribe the lowest absorption transitions to two singlet ICT excited states, S₁ and S₂, with S₁ having several orders of magnitude higher oscillator strength than the “dark” S₂ state. Temperature and viscosity investigations suggest the existence of two emitting excited states with different structural conformations. The phosphorescence emission band observed at 77 K is assigned to a localized ³terpy state. Finally, protonation studies show that tBuTPAterpy undergoes a reversible process, making it a promising probe of the pH level in the context of acidity determination.     

Tricarbonyl rhenium complexes of bis(pyrazol-1-yl)methane and bis(3,5-dimethylpyrazol-1-yl)methane – Synthesis,spectroscopic characterization,X-ray structure and DFT calculations

Two novel tricarbonyl rhenium complexes based on the bidentate heterocyclic N–N ligands [bis(pyrazol-1-yl)methane(bpzm) and bis(3,5-dimethylpyrazol-1-yl)methane(bdmpzm)] have been synthesized by heating at reflux [Re(CO)₅Cl] with the appropriate N–N ligand in toluene. The compounds have been characterized by IR and UV–Vis spectroscopy and X-ray analysis. Density functional theory (DFT) and time-dependent (TD) DFT calculations have been carried out for the [Re(CO)₃(bdmpzm)Cl] complex.     

Comparative Analysis of GPCR Crystal Structures†

The phototransduction cascade is perhaps the best understood model system for G protein‐coupled receptor (GPCR) signaling. Phototransduction links the absorption of a single photon of light to a decrease in cytosolic cGMP. Depletion of the cGMP pool induces closure of cGMP‐gated cation channels resulting in the hyperpolarization of photoreceptor cells and consequently a neuronal response. Many biochemical and both low‐ and high‐resolution structural approaches have been utilized to increase our understanding of rhodopsin, the key molecule of this signaling cascade. Rhodopsin, a member of the GPCR or seven‐transmembrane spanning receptor superfamily, is composed of a chromophore, 11‐cis‐retinal that is covalently bound by a protonated Schiff base linkage to the apo‐protein opsin at Lys²⁹⁶ (in bovine opsin). Upon absorption of a photon, isomerization of the chromophore to an all‐trans‐retinylidene conformation induces changes in the rhodopsin structure, ultimately converting it from an inactive to an activated state. This state allows it to activate the heterotrimeric G protein, transducin, by triggering nucleotide exchange. To fully understand the structural and functional aspects of rhodopsin it is necessary to critically examine crystal structures of its different photointermediates. In this review we summarize recent progress on the structure and activation of rhodopsin in the context of other GPCR structures.     

APEX Strategy Represented by Diels–Alder Cycloadditions—New Opportunities for the Syntheses of Functionalised PAHs

Diels–Alder cycloaddition of various dienophiles to the bay region of polycyclic aromatic hydrocarbons (PAHs) is a particularly effective and useful tool for the modification of the structure of PAHs and thereby their final properties. The Diels–Alder cycloaddition belongs to the single-step annulative π-extension (APEX) reactions and represents the maximum in synthetic efficiency for the constructions of π-extended PAHs including functionalised ones, nanographenes, and π-extended fused heteroarenes. Herein we report new applications of the APEX strategy for the synthesis of derivatives of 1,2-diarylbenzo[ghi]perylene, 1,2-diarylbenzo[ghi]perylenebisimide and 1,2-disubstituted-benzo[j]coronene. Namely, the so far unknown cycloaddition of 1,2-diarylacetylenes into the perylene and perylenebisimide bay regions was used. 1,2-Disubstituted-benzo[j]coronenes were obtained via cycloaddition of benzyne into 1,2-diarylbenzo[ghi]perylenes by using a new highly effective system for benzyne generation and/or high pressure conditions. Moreover, we report an unprecedented Diels–Alder cycloaddition–cycloaromatisation domino-type reaction between 1,4-(9,9-dialkylfluoren-3-yl)-1,3-butadiynes and perylene. The obtained diaryl-substituted core-extended PAHs were characterised by DFT calculation as well as electrochemical and spectroscopic measurements.     

Electronic structure and spectra of nitrosyl complexes with cobalt and manganese porphyrins

The DFT calculations for nitrosyl manganese and cobalt porphyrins were carried out with the use of several density functionals. The binding energy of nitrosyl ligand and spin state of nitrosyl-free manganese porphyrin were determined. The best values of binding energy are obtained from the OLYP functional. The NBO analysis of metal?Cnitrosyl bonding was performed. Electronic spectra of nitrosyl cobalt and manganese porphyrin were calculated with the TDDFT method. The calculated electronic transitions agree well with the experimental data except for the Soret band of (Por)Mn(NO), where they are 0.3?C0.5?eV higher in energy than the experimental ones.     

Competition between S‐oxidation and nitration in reactions of some β‐ and γ‐quinolinyl sulfides with nitrating mixture

This study was performed in order to explain different orientation in the reaction of quinolinyl sulfides with nitrating mixture, which converted on one hand quinolinyl sulfides 1 , 3 and 5 to sulfoxides 2 , 4 and 8 , respectively, on the other hand, sulfides 6 , 7 to the respective nitroderivatives 9 and 10 . Competitive experiments showed following reactivity order: thianthrene 11 ≥ thianthrene 5‐oxide 12 ≥ isothioquinanthrene 3 ≥ thioquinanthrene 1 ≥ 3,3′‐diquinolinyl sulfide 5 ≥ 3,4′‐diquinolinyl sulfide 6 ≥ 4,4′‐diquinolinyl sulfide 7 . Considering that NO₂⁺ (as reactive form of nitrating mixture) attacks the most electronodonating (sulfur or carbon) center the reactivity order well correlates with the results of HOMO as well as MEP calculations.