Easily prepared air- and moisture-stable Pd-NHC (NHC=N-heterocyclic carbene) complexes: a reliable, user-friendly, highly active palladium precatalyst for the Suzuki-Miyaura reaction

The synthesis of NHC-PdCl(2)-3-chloropyridine (NHC=N-heterocyclic carbene) complexes from readily available starting materials in air is described. The 2,6-diisopropylphenyl derivative was found to be highly catalytically active in alkyl-alkyl Suzuki and Negishi cross-coupling reactions. The synthesis, ease-of-use, and activity of this complex are substantial improvements over in situ catalyst generation and all current Pd-NHC complexes. The utilization of complex 4 led to the development of a reliable, easily employed Suzuki-Miyama protocol. Employing various reaction conditions allowed a large array of hindered biaryl and drug-like heteroaromatic compounds to be synthesized without difficulty.     

First observation in the gas phase of the ultrafast electronic relaxation pathways of the S(2) states of heme and hemin

The time evolution of electronically excited heme (iron II protoporphyrin IX, [Fe(II) PP]) and its associated salt hemin (iron III protoporphyrin IX chloride, [Fe(III) PP-Cl]), has been investigated for the first time in the gas phase by femtosecond pump-probe spectroscopy. The porphyrins were excited at 400 nm in the S(2) state (Soret band) and their relaxation dynamics was probed by multiphoton ionization at 800 nm. This time evolution was compared with that of the excited state of zinc protoporphyrin IX [Zn PP] whose S(2) excited state likely decays to the long lived S(1) state through a conical intersection, in less than 100 fs. Instead, for [Fe(II) PP] and [Fe(III) PP-Cl], the key relaxation step from S(2) is interpreted as an ultrafast charge transfer from the porphyrin excited orbital π* to a vacant d orbital on the iron atom (ligand to metal charge transfer, LMCT). This intermediate LMCT state then relaxes to the ground state within 250 fs. Through this work a new, serendipitous, preparation step was found for Fe(II) porphyrins, in the gas phase.     

Density Functional Theory Investigation of the Alkyl–Alkyl Negishi Cross‐Coupling Reaction Catalyzed by N‐Heterocyclic Carbene (NHC)–Pd Complexes

Why bigger is better : A “steric wall” created by the N‐(2,6‐diisopropylphenyl) substituent on the bulky NHC ligand IPr (1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) guides the reactants to and from the Pd center through weak, fleeting (IPr)H–Pd interactions that help the oxidative addition intermediate escape “the anti‐trap”. The alternative “side” approach leads to transmetalation (the rate‐limiting step) for which a novel Pd–Zn interaction was identified.

     

Synthesis,structural characterization,density functional theory calculations and biological evaluation of a new organotin(IV) complex containing N‐isonicotinyl‐N',N″‐diaryl phosphorictriamide as N‐donor ligand

A new diorganotin(IV) complex with the formula SnCl₂(CH₃)₂L₂ ( C_1a ), L = 4‐NC₅H₄CONHPO(NCH₃CH₂C₆H₅)₂, was synthesized and characterized using ¹H NMR, ¹³C NMR, ³¹P NMR, ¹¹⁹Sn NMR and infrared spectroscopies. The molecular structure of C_1a was determined using X‐ray crystallography, revealing that C_1a contains hexa‐coordinated Sn(IV) centres with trans‐configuration of donor atoms around them. Each Sn(IV) atom is positioned in the centre of inversion of an octahedron. C_1a forms one‐dimensional chains via two equal intermolecular P?O…H? N hydrogen bonds. These hydrogen bonds produce centrosymmetric rings as a supramolecular hydrogen‐bonded pattern. In order to compare the relative stability of C_1a (with N‐ligated configuration) and its possible O‐ligated isomer, C_1b , density functional theory calculations were performed, the results showing a preference of C_1a over C_1b from an energy point of view. Also, natural bond orbital analysis was carried out to obtain detailed information on the electronic features of the optimized structures. The theoretical results show that intermolecular hydrogen bonding in the crystal structure has a significant role in the stabilization of C_1a , and Sn(IV) interacts more strongly with the N_py atom than the P?O functional group. Furthermore, the free ligand and its complex were tested against three human cancer cell lines, i.e. human cervical carcinoma (HeLa), human prostate cancer (PC‐3) and human breast adenocarcinoma cancer (MCF‐7). C_1a displays moderate to good cytotoxicity towards all three cancer cell lines. Moreover, antibacterial tests were carried out using the disc‐diffusion method, in which C_1a shows high activity against selected Gram‐negative and Gram‐positive bacteria. Copyright © 2015 John Wiley & Sons, Ltd.     

Solvent-Free Conditions as an Eco-Friendly Strategy for Synthesis of Organophosphorus Compounds

A series of diverse NH- and CH-acids are used for a one-pot synthesis of stable phosphorus ylides and 1,4-diionic organophosphorus compounds by trapping of the zwitterionic intermediate from the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates under solvent-free conditions. The structural geometry for one of the products was confirmed by single crystal X-ray diffraction analysis.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Nano- and micro-structure tin (IV) complexes bearing 4-pyridinecarbacylamidophosphate: Sonochemical synthesis,crystal structure,anti-cholinesterase activity,and docking studies

Two di- and triorganotin (IV) complexes, Sn (CH₃)₂Cl₂(4-PCAPh)₂ ( C ₁ ) and Sn(C₆H₅)₃Cl(4-PCAPh) ( C ₂ ); {4-PCAPh = 4-NC₅H₄C(O)NHP(O)(C₆H₁₂N)₂}, have been synthesized and characterized by elemental analysis, ¹H, ¹³C, ³¹P NMR and IR spectroscopy. The crystal structure of C ₁ has been confirmed by X-ray crystallography, which reveals an octahedral geometry surrounding Sn (IV). Both ligands function in an all-trans conformation, with an N-ligated mode for 4-PCAPh. Also, the complexes were prepared at nano- ( Ć ₁ ) and micro-size ( Ć ₂ ) by the sonochemical process. The role of reaction solvent and the concentration of initial reactants on the size and morphology of particles were studied and the products were characterized by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). The activities and mechanism of complexes C ₁ , C ₂ , Ć ₁ , Ć ₂ and their corresponding ligand ( L ) on cholinesterase (ChE) were evaluated using a modified Ellman's method and Lineweaver-Burk plots. Nanosheet Ć ₁ showed the best activity against AChE and BChE with the IC₅₀ values being 73.08 ± 0.12 μM and 122.48 ± 0.69 μM, respectively, and the mixed-type mechanism. Molecular modeling simulation revealed the binding interaction template for Sn (CH₃)₂Cl₂(4-PCAPh)₂ with the ChE.     

A simple graphical approach to predict local residue conformation using NMR chemical shifts and density functional theory

The dependency of amino acid chemical shifts on φ and ψ torsion angle is, independently, studied using a five‐residue fragment of ubiquitin and ONIOM(DFT:HF) approach. The variation of absolute deviation of ¹³C^α chemical shifts relative to φ dihedral angle is specifically dependent on secondary structure of protein not on amino acid type and fragment sequence. This dependency is observed neither on any of ¹³C^β, and ¹H^α chemical shifts nor on the variation of absolute deviation of ¹³C^α chemical shifts relative to ψ dihedral angle. The ¹³C^α absolute deviation chemical shifts (ADCC) plots are found as a suitable and simple tool to predict secondary structure of protein with no requirement of highly accurate calculations, priori knowledge of protein structure and structural refinement. Comparison of Full‐DFT and ONIOM(DFT:HF) approaches illustrates that the trend of ¹³C^α ADCC plots are independent of computational method but not of basis set valence shell type. © 2016 Wiley Periodicals, Inc.     

Predictive QSAR models for the anti-cancer activity of topoisomerase IIα catalytic inhibitors against breast cancer cell line HCT15: GA-MLR and LS-SVM modeling

Structural Chemistry - Structural analysis of topoisomerase IIα catalytic inhibitors exhibited anti-tumor properties to use them in cancer therapeutic procedures. In this study, a quantitative...     

Photolysis of allene and propyne in the 7-30 eV region probed by the visible fluorescence of their fragments

The photolysis of allene and propyne, two isomers of C(3)H(4), has been investigated in the excitation energy range of 7-30 eV using vacuum ultraviolet synchrotron radiation. The visible fluorescence excitation spectra of the excited neutral photofragments of both isomers were recorded within the same experimental conditions. Below the first ionization potential (IP), this fluorescence was too weak to be dispersed and possibly originated from C(2)H or CH(2) radicals. Above IP, three excited photofragments have been characterized by their dispersed emission spectra: the CH radical (A (2)Delta-X (2)Pi), the C(2) radical (d (3)Pi(g)-a (3)Pi(u), "Swan's bands"), and the H atom (4-2 and 3-2 Balmer lines). A detailed analysis of the integrated emission intensities allowed us to determine several apparition thresholds for these fragments, all of them being interpreted as rapid and barrierless dissociation processes on the excited potential energy surfaces. In the low energy range explored in this work, both isomers exhibit different intensity distributions in their fragment emission as a function of the photolysis energy, indicating that mutual allene<-->propyne isomerization is not fully completed before dissociation occurs. The effect of isomerization on the dissociation into excited fragments is present in the whole excitation energy range albeit less important in the 7-16 eV region; it gradually increases with increasing excitation energy. Above 19 eV, the fragment distribution is very similar for the two isomers.     

Characterization of gelatin/cellulose acetate nanofibrous scaffolds: Prediction and optimization by response surface methodology and artificial neural networks

Gelatin/cellulose acetate electrospun nanofibers are a good candidates for simulation of extracellular matrix (ECM). Electrospinning of the blend is controlled by many parameters such as applied voltage, gap distance, solvent composition, polymer composition and solution concentration. The individual and interactive effects of these parameters on pH, electrical conductivity (EC) and viscosity of solutions, and diameter and quality of fibers were investigated. Response surface methodology (RSM) and artificial neural networks (ANNs) were considered to model and optimize the responses. EC, pH and viscosity of solutions were dependent on the solution parameters. The solvent composition and solution concentration had an influence on the fiber diameter and quality. The optimum conditions for fabricating qualified nanofibers with minimum diameter were 16.9 kV, 15.3 cm, 77.5 wt % of gelatin, 88.9 vol % of acetic acid and solution concentration of 20 wt %/vol %. Uniform beadless nanofibers with a diameter of 284 nm were attained at this optimum condition.