Publications by authors named "David L Hughes"

154 Publications

Coordination chemistry of [2 + 2] Schiff-base macrocycles derived from the dianilines [(2-NHCH)X] (X = CHCH, O): structural studies and ROP capability towards cyclic esters.

Dalton Trans 2021 Jun;50(23):8057-8069

Plastics Collaboratory, Department of Chemistry, University of Hull, HU6 7RX, UK.

Reaction of the [2 + 2] Schiff-base macrocycles {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][CH2CH2(2-C6H4N)2]}2 (R = Me, L1H2; tBu, L2H2) with FeBr2 afforded the complexes [FeBr(L1H2)]2[(FeBr3)2O]·2MeCN (1·2MeCN), [FeBr(L2H2)][X] (X = 0.5(FeBr3)2O, 2·0.5MeCN, X = Br, 3·5.5MeCN), respectively. Reaction of L2H2 with [KFe(OtBu)3(THF)] (formed in situ from FeBr2 and KOtBu), following work-up, led to the isolation of the complex [Fe(L2)(L2H)]·3MeCN (4·3MeCN), whilst with [CuBr2] afforded [CuBr(L2H2)][CuBr2]·2MeCN (5·2MeCN). Attempts to form mixed Co/Ti species by reaction of [CoBrL2][CoBr3(NCMe)] with TiCl4 resulted in [L2H4][CoBr4]·2MeCN (6·2MeCN). Use of the related oxy-bridged Schiff-base macrocycles {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][O(2-C6H4N)2]}2 (R = Me, L3H2; tBu, L4H2) with CoBr2 led to the isolation of the complexes [(CoBr)2(L3)]·2C3H6O (7·2C3H6O), [Co(NCMe)2(L4H2)][CoBr4]·5MeCN (8·5MeCN), [Co(NCMe)6][CoBr3(MeCN)]2·2MeCN (9·2MeCN). For comparative structural/polymerisation studies, the complexes {CoBr(NCMe)L5}2·2MeCN (10·2MeCN) and [Co(NCMe)2L5]2[CoBr3(NCMe)]2 (11), [FeBr(NCMe)L5]2·2MeCN (12·2MeCN) where L5H = 2,6-(CHO)2-4-tBu-C6H2OH, as well as the chelate-free salt [Fe(NCMe)6][FeBr3OFeBr3] (13) have been isolated and structurally characterized. The ability of these complexes to act as catalysts for the ring opening polymerisation (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) was investigated, as well as co-polymerisation of ε-CL with rac-lactide (r-LA) and vice versa.
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http://dx.doi.org/10.1039/d1dt00711dDOI Listing
June 2021

Stability in solution and chemoprotection by octadecavanadates(IV/V) in E. coli cultures.

J Inorg Biochem 2021 Jun 26;219:111438. Epub 2021 Mar 26.

Departamento de Química, Universidade Federal do Paraná, Curitiba, PR, Brazil. Electronic address:

Two mixed-valence octadecavanadates, (NH)(MeN)[VVOI]·MeNI·5HO (VI) and [{K(OH)VVO(PO)·4HO}] (VP), were synthesized and characterized by single-crystal X-ray diffraction analysis and FTIR, Raman, V NMR, EPR and UV/Vis/NIR spectroscopies. The chemoprotective activity of VI and VP towards the alkylating agent diethyl sulfate was assessed in E. coli cultures. The complex VI was nontoxic in concentrations up to 5.0 mmol L, while VP presented moderate toxicity in the concentration range 0.10 - 10 mmol L. Conversely, a ca. 35% enhancement in culture growth as compared to cells treated only with diethyl sulfate was observed upon addition of VI (0.10 to 2.5 mmol L), while the combination of diethyl sulfate with VP increased the cytotoxicity presented by diethyl sulfate alone. V NMR and EPR speciation studies showed that VI is stable in solution, while VP suffers partial breakage to give low nuclearity oxidometalates of vanadium(V) and (IV). According to the results, the chemoprotective effect depends strongly on the direct reactivity of the polyoxidovanadates (POV) towards the alkylating agent. The reaction of diethyl sulfate with VI apparently produces a new, rearranged POV instead of poorly-reactive breakage products, while VP shows the formation and subsequent consumption of low-nuclearity species. The correlation of this chemistry with that of other mixed-valence polyoxidovanadates, [HVVOPO] (V) and [VVOCl] (V), suggests a relationship between stability in solution and chemoprotective performance.
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http://dx.doi.org/10.1016/j.jinorgbio.2021.111438DOI Listing
June 2021

Complementary Syntheses Giving Access to a Full Suite of Differentially Substituted Phthalocyanine-Porphyrin Hybrids.

Angew Chem Int Ed Engl 2021 03 1;60(14):7632-7636. Epub 2021 Mar 1.

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.

Phthalocyanines and porphyrins are often the scaffolds of choice for use in widespread applications. Synthetic advances allow bespoke derivatives to be made, tailoring their properties. The selective synthesis of unsymmetrical systems, particularly phthalocyanines, has remained a significant unmet challenge. Porphyrin-phthalocyanine hybrids offer the potential to combine the favorable features of both parent structures, but again synthetic strategies are poorly developed. Here we demonstrate strategies that give straightforward, controlled access to differentially substituted meso-aryl-tetrabenzotriazaporphyrins by reaction between an aryl-aminoisoindolene (A) initiator and a complementary phthalonitrile (B). The choice of precursors and reaction conditions allows selective preparation of 1:3 Ar-ABBB and, uniquely, 2:2 Ar-ABBA functionalized hybrids.
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http://dx.doi.org/10.1002/anie.202016596DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8048519PMC
March 2021

Seven-Coordinate Tb Complexes with 90% Quantum Yields: High-Performance Examples of Combined Singlet- and Triplet-to-Tb Energy-Transfer Pathways.

Inorg Chem 2021 Jan 4;60(2):892-907. Epub 2021 Jan 4.

Department of Chemistry, Federal University of Paraná, 81530-900 - Curitiba-PR, Brazil.

Seven-coordinate, pentagonal-bipyramidal (PBP) complexes [Ln(bbpen)Cl] and [Ln(bbppn)Cl], in which Ln = Tb (products and ), Eu ( and ), and Gd ( and ), with bbpen = ,'-bis(2-oxidobenzyl)-,'-bis(pyridin-2-ylmethyl)ethylenediamine and bbppn = ,'-bis(2-oxidobenzyl)-,'-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by single-crystal X-ray diffraction analysis, alternating-current magnetic susceptibility measurements, and photoluminescence (steady-state and time-resolved) spectroscopy. Under a static magnetic field of 0.1 T, the Tb complexes and revealed single-ion-magnet behavior. Also, upon excitation at 320 nm at 300 K, and presented very high absolute emission quantum yields (0.90 ± 0.09 and 0.92 ± 0.09, respectively), while the corresponding Eu complexes and showed no photoluminescence. Detailed theoretical calculations on the intramolecular energy-transfer rates for the Tb products indicated that both singlet and triplet ligand excited states contribute efficiently to the overall emission performance. The expressive quantum yields, , measured for and in the solid state and a dichloromethane solution depend on the excitation wavelength, being higher at 320 nm. Such a dependence was rationalized by computing the intersystem crossing rates () and singlet fluorescence lifetimes (τ) related to the population dynamics of the S and T levels. Thin films of product showed high air stability and photostability upon continuous UV illumination, which allowed their use as downshifting layers in a green light-emitting device (LED). The prototypes presented a luminous efficacy comparable with those found in commercial LED coatings, without requiring encapsulation or dispersion of in host matrixes. The results indicate that the PBP environment determined by the ethylenediamine (en)-based ligands investigated in this work favors the outstanding optical properties in Tb complexes. This work presents a comprehensive structural, chemical, and spectroscopic characterization of two Tb complexes of mixed-donor, en-based ligands, focusing on their outstanding optical properties. They constitute good molecular examples in which both triplet and singlet excited states provide energy to the Tb ion and lead to high values of .
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http://dx.doi.org/10.1021/acs.inorgchem.0c03020DOI Listing
January 2021

First COVID-19 molecular docking with a chalcone-based compound: synthesis, single-crystal structure and Hirshfeld surface analysis study.

Acta Crystallogr C Struct Chem 2020 12 5;76(Pt 12):1043-1050. Epub 2020 Nov 5.

Chemistry Department, College of Science, Taibah University, PO Box 30002, Al-Madinah Al Munawarah, Code 1417, Saudi Arabia.

The first example of molecular docking of the SARS-CoV-2 main protease for COVID-19 [M, Protein Data Bank (PDB) code 7BQY] by a chalcone-based ligand, namely, (E)-1-(2,4-dichlorophenyl)-3-[4-(morpholin-4-yl)phenyl]prop-2-en-1-one, CHClNO, I, is presented. Two-dimensional (2D) LIGPLOT representations calculated for the inhibitor N3, viz. N-{[(5-methylisoxazol-3-yl)carbonyl]alanyl}-L-valyl-N-((1R,2Z)-4-(benzyloxy)-4-oxo-1-{[(3R)-2-oxopyrrolidin-3-yl]methyl}but-2-enyl)-L-leucinamide, and 7BQY are included for comparison with our chalcone-based complexes. The binding affinity of our chalcone ligand with 7BQY is -7.0 kcal mol, a high value which was attributed to the presence of a hydrogen bond, together with many hydrophobic interactions between the drug and the active amino acid residues of the receptor. Docking studies were also performed, employing rigid and flexible binding modes for the ligand. The superposition of N3 and the chalcone docked into the binding pocket of 7BQY is also presented. The synthesis, single-crystal structure, Hirshfeld surface analysis (HSA) and spectral characterization of heterocyclic chalcone-based compound I, are also presented. The molecules are stacked, with normal π-π interactions, in the crystal.
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http://dx.doi.org/10.1107/S2053229620014217DOI Listing
December 2020

Planar chiral palladacycle precatalysts for asymmetric synthesis.

Org Biomol Chem 2020 07;18(28):5466-5472

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TU, UK.

Chiral non-racemic palladacycles were employed as precatalysts for Pd(0) mediated asymmetric synthesis. Addition of HPAr2/base to a ferrocenyloxazoline planar chiral palladacycle resulted in ligand synthesis and palladium capture to give a bidentate Phosferrox/Pd(0) complex. A series of these complexes were generated in situ and applied successfully as catalysts for asymmetric allylic alkylation.
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http://dx.doi.org/10.1039/d0ob01331eDOI Listing
July 2020

Straightforward and Controlled Synthesis of Porphyrin-Phthalocyanine-Porphyrin Heteroleptic Triple-Decker Assemblies.

Chemistry 2020 Aug 27;26(47):10724-10728. Epub 2020 Jul 27.

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom.

A versatile and straightforward protocol is disclosed for controlled synthesis of complex lanthanide-bridged heteroleptic porphyrin-phthalocyanine triple-decker assemblies. Two porphyrins, linked by a flexible spacer chain of intermediate length, sequentially capture lanthanide ions and a phthalocyanine to efficiently form the triple-decker complex. The bridge directs assembly, but also controls the mobility of the central macrocycle and further imparts a fully eclipsed arrangement of all three rings.
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http://dx.doi.org/10.1002/chem.202002500DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7497087PMC
August 2020

An Oxalate-Bridged Copper(II) Complex Combining Monodentate Benzoate, 2,2'-bipyridine and Aqua Ligands: Synthesis, Crystal Structure and Investigation of Magnetic Properties.

Molecules 2020 Apr 20;25(8). Epub 2020 Apr 20.

Departamento de Química e Biologia, Universidade Tecnológica Federal do Paraná, Cidade Industrial, Curitiba 81280-340, Brazil.

A dinuclear copper(II) complex of formula [{Cu()()(OH)}(μ-)] () (where = 2,2'-bipyridine, = benzoate and = oxalate) was synthesised and characterised by diffractometric (powder and single-crystal XRD) and thermogravimetric (TG/DTG) analyses, spectroscopic techniques (IR, Raman, electron paramagnetic resonance spectroscopy (EPR) and electronic spectroscopy), magnetic measurements and density functional theory (DFT) calculations. The analysis of the crystal structure revealed that the oxalate ligand is in bis(bidentate) coordination mode between two copper(II) centres. The other four positions of the coordination environment of the copper(II) ion are occupied by one water molecule, a bidentate and a monodentate ligand. An inversion centre located on the ox ligand generates the other half of the dinuclear complex. Intermolecular hydrogen bonds and π-π interactions are responsible for the organisation of the molecules in the solid state. Molar magnetic susceptibility and field dependence magnetisation studies evidenced a weak intramolecular-ferromagnetic interaction ( = +2.9 cm) between the metal ions. The sign and magnitude of the calculated value by density functional theory (DFT) are in agreement with the experimental data.
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http://dx.doi.org/10.3390/molecules25081898DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7221668PMC
April 2020

Allene-derived gold and platinum complexes: synthesis and first applications in catalysis.

Dalton Trans 2020 Apr;49(13):4034-4038

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.

We report here the synthesis, full characterisation and first application in catalysis of novel Au(i), Au(iii) and Pt(ii) carbene-type complexes formed from bis(pyridyl)allenes. The catalytic activity of the new Au(i)-complexes in the cyclisation of 1,6-enynes, a benchmark reaction for new Au and Pt complexes, was comparable to Au(i)-state-of-the-art catalysts used in these reactions. Reactions with the new Au(iii)- and Pt(ii)-complexes occurred under milder conditions than those reported with AuCl3 and PtCl2.
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http://dx.doi.org/10.1039/d0dt00665cDOI Listing
April 2020

Stereoselective Synthesis of All Possible Phosferrox Ligand Diastereoisomers Displaying Three Elements of Chirality: Stereochemical Optimization for Asymmetric Catalysis.

J Org Chem 2020 04 13;85(7):4838-4847. Epub 2020 Mar 13.

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.

All four possible diastereoisomers of phosphinoferrocenyloxazoline (Phosferrox type) ligands containing three elements of chirality were synthesized as single enantiomers. The configured oxazoline moiety (R = Me, -Pr) was used to control the generation of planar chirality by lithiation, with the alternative diastereoisomer formed by use of a deuterium blocking group. In each case subsequent addition of PhPCl followed by -TolMgBr resulted in a single -stereogenic diastereoisomer (,, and ,,, respectively). The alternative diastereoisomers were formed selectively by addition of -TolPCl followed by PhMgBr ((,, and ,,, respectively). Preliminary application of these four ligand diastereoisomers, together with (,) and (,) Phosferrox (PPh), to palladium catalyzed allylic alkylation of -1,3-diphenylallyl acetate revealed a stepwise increase/decrease in ee, with the configuration of the matched/matched diastereoisomer as ,, (97% ee).
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http://dx.doi.org/10.1021/acs.joc.9b03342DOI Listing
April 2020

Hydride Transfer to Gold: Yes or No? Exploring the Unexpected Versatility of Au⋅⋅⋅H-M Bonding in Heterobimetallic Dihydrides.

Chemistry 2020 Jul 11;26(37):8267-8280. Epub 2020 Jun 11.

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR47TJ, UK.

The potential for coordination and H-transfer from Cp MH (M=Zr, W) to gold(I) and gold(III) complexes was explored in a combined experimental and computational study. [(L)Au] cations react with Cp WH giving [(L)Au(κ -H WCp )] (L=IPr (1), cyclic (alkyl)(amino)carbene (2), PPh (3) and Dalphos-Me (4) [IPr=1,3-bis(diisopropylphenyl)imidazolylidene; Dalphos-Me=di(1-adamantyl)-2-(dimethylamino)phenyl-phosphine], while [Au(DMAP) ] (DMAP=p-dimethylaminopyridine) affords the C -symmetric [Au(κ-H WCp ) ] (5). The Dalphos complex 4 can be protonated to give the bicationic adduct 4 H, showing Au ⋅⋅⋅H -N hydrogen bonding. The gold(III) Lewis acid [(C^N-CH)Au(C F )(OEt )] binds Cp WH to give an Au-H-W σ-complex. By contrast, the pincer species [(C^N^C)Au] adds Cp WH by a purely dative W→Au bond, without Au⋅⋅⋅H interaction. The biphenylyl-based chelate [(C^C)Au] forms [(C^C)Au(μ-H) WCp ] , with two 2-electron-3-centre W-H⋅⋅⋅Au interactions and practically no Au-W donor acceptor contribution. In all these complexes, strong but polarized W-H bonds are maintained, without H-transfer to gold. On the other hand, the reactions of Cp ZrH with gold complexes led in all cases to rapid H-transfer and formation of gold hydrides. Relativistic DFT calculations were used to rationalize the striking reactivity and bonding differences in these heterobimetallic hydride complexes along with an analysis of their characteristic NMR parameters and UV/Vis absorption properties.
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http://dx.doi.org/10.1002/chem.202000016DOI Listing
July 2020

H activation by zirconaziridinium ions: σ-bond metathesis versus frustrated Lewis pair reactivity.

Chem Commun (Camb) 2020 Feb 4;56(17):2542-2545. Epub 2020 Feb 4.

Department of Chemistry, University of Naples Federico II, Via Cintia, I-80126, Naples, Italy.

Zirconaziridinium ions [CpZr(η-CHNR)] can potentially activate H by two routes: σ-bond metathesis or FLP reactivity. We show here that Zr-C hydrogenolysis by σ-bond metathesis precedes and enables subsequent heterolytic H cleavage through FLP pathways. DFT calculations show the involvement of transition states with approximately linear NHH and bent ZrHH arrangements without any direct Zr-amine interaction.
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http://dx.doi.org/10.1039/c9cc09466kDOI Listing
February 2020

Do Gold(III) Complexes Form Hydrogen Bonds? An Exploration of Au Dicarboranyl Chemistry.

Chemistry 2020 Jan 7;26(4):939-947. Epub 2020 Jan 7.

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.

The reaction of 1,1'-Li [(2,2'-C B H ) ] with the cyclometallated gold(III) complex (C^N)AuCl afforded the first examples of gold(III) dicarboranyl complexes. The reactivity of these complexes is subject to the trans-influence exerted by the dicarboranyl ligand, which is substantially weaker than that of non-carboranyl anionic C-ligands. In line with this, displacement of coordinated pyridine by chloride is only possible under forcing conditions. While treatment of (C^N)Au{(2,2'-C B H ) } (2) with triflic acid leads to Au-C rather than Au-N bond protonolysis, aqueous HBr cleaves the Au-N bond to give the pyridinium bromo complex 7. The trans-influence of a series of ligands including dicarboranyl and bis(dicarboranyl) was assessed by means of DFT calculations. The analysis demonstrated that it was not sufficient to rely exclusively on geometric descriptors (calculated or experimental) when attempting to rank ligands for their trans influence. Complex (C^N)Au(C B H ) containing two non-chelating dicarboranyl ligands was prepared similar to 2. Its reaction with trifluoroacetic acid also leads to Au-N cleavage to give trans-(Hpy^C)Au(OAc )(C B H ) (8). In crystals of 8 the pyridinium N-H bond points towards the metal centre, while in 7 it is bent away. The possible contribution of gold(III)⋅⋅⋅H-N hydrogen bonding in these complexes was investigated by DFT calculations. The results show that, unlike the situation for platinum(II), there is no evidence for an energetically significant contribution by hydrogen bonding in the case of gold(III).
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http://dx.doi.org/10.1002/chem.201904790DOI Listing
January 2020

Unusual Nucleophilic Addition of Grignard Reagents in the Synthesis of 4-Amino-pyrimidines.

ACS Omega 2018 Aug 10;3(8):8937-8944. Epub 2018 Aug 10.

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ, U.K.

Pyrimidines have always received considerable attention because of their importance in synthesis and elucidation of biochemical roles, in particular that of vitamin B1. Herein, we describe a reaction pathway in a Grignard reagent-based synthesis of substituted pyrimidines. A general synthesis of α-keto-2-methyl-4-amino pyrimidines and their C6-substituted analogues from 4-amino-5-cyano-2-methylpyrimidine is reported. The presence of the nitrile substituent in the starting material also results in an unusual reaction pathway leading to C6-substituted 1,2-dihydropyrimidines. Grignard reagents that give normal pyrimidine products under standard reaction conditions can be switched to give dihydropyrimidines by holding the reaction at 0 °C before quenching.
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http://dx.doi.org/10.1021/acsomega.8b01137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6644423PMC
August 2018

Promoting a Significant Increase in the Photoluminescence Quantum Yield of Terbium(III) Complexes by Ligand Modification.

Inorg Chem 2019 Sep 26;58(18):12099-12111. Epub 2019 Aug 26.

Department of Chemistry , Federal University of Paraná , Centro Politécnico, Jardim das Américas, 81530-900 Curitiba , Paraná , Brazil.

Two discrete mononuclear complexes, [Tb(bbpen)(NO)] () and [Tb(bbppn)(NO)] (), for which = -bis(2-hydroxybenzyl)--bis(pyridin-2-ylmethyl)ethylenediamine and = bis(2-hydroxylbenzyl)-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates from and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of is described here for the first time, while that of complex has been redetermined in the monoclinic 2 space group in light of new diffraction data. In , selective crystallization leads to spontaneous resolution of enantiomeric molecules in different crystals. Absolute emission quantum yields (ϕ) and luminescence excited-state lifetimes (at room temperature and 11 K) were measured for both complexes. Despite their similar molecular structures, and exhibit remarkably different ϕ values of 21 ± 2% and 67 ± 7%, respectively, under UV excitation at room temperature. Results of quantum-mechanical (DFT and TD-DFT) calculations and experimental PL measurements also performed for and confirmed that both ligands are suitable to work as "antennas" for Tb. Considering the D lifetime profiles and the significantly higher absolute quantum yield of , it appears that thermally active nonradiative pathways present in are minimized in due to differences in the conformation of the ethylenediamine bridge.
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http://dx.doi.org/10.1021/acs.inorgchem.9b01397DOI Listing
September 2019

Methyl Ester Functionalized Phenalenyl Arene- and Bipyridine-Ruthenium-Based Complexes for Electroactive Langmuir-Blodgett Films.

Inorg Chem 2019 Jul 19;58(13):8408-8418. Epub 2019 Jun 19.

Departamento de Química , Universidade Federal do Paraná , 81530-900 , Curitiba - Paraná , Brazil.

We report the synthesis of a new phenalenyl ligand, functionalized with a methyl ester electron withdrawing group, named 9-hydroxy-1-oxo-1 H-phenalen-5-methyl carboxylate (L), and the generated complexes [Ru(bpy)L]PF and [(η-CH)Ru(L)Cl]. Compounds were characterized by spectroscopic and X-ray diffraction methods, and their electrochemical behavior was investigated via cyclic voltammetry and UV-vis spectroelectrochemistry. The one-electron oxidized compounds have an unpaired electron located in the phenalenyl ring, as supported by theoretical calculations (DFT) and EPR results. Langmuir-Blodgett (LB) films deposited by [Ru(bpy)L] species mixed with stearic acid are electroactive, showing a quasi-reversible wave with E = 0.74 V and E = 0.81, which are promising systems that allow access to immobilized open-shell species in the film.
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http://dx.doi.org/10.1021/acs.inorgchem.9b00530DOI Listing
July 2019

Cyclometallated Au(iii) dithiocarbamate complexes: synthesis, anticancer evaluation and mechanistic studies.

Metallomics 2018 11;10(11):1655-1666

School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.

A series of cationic mixed cyclometallated (C^N)Au(iii) dithiocarbamate complexes has been synthesized in good yields [HC^N = 2-(p-t-butylphenyl)pyridine]. The crystal structure of [(C^N)AuS2CNEt2]PF6 (3) has been determined. The cytotoxic properties of the new complexes have been evaluated in vitro against a panel of human cancer cell lines and healthy cells and compared with a neutral mixed (C^C)Au(iii) dithiocarbamate complex (C^C = 4,4'-di-t-butylbiphenyl-2,2'-diyl). The complexes appeared to be susceptible to reduction by glutathione but were stable in the presence of N-acetyl cysteine. The potential mechanism of action of this class of compounds has been investigated by measuring the intracellular uptake of some selected complexes, by determining their interactions with higher order DNA structures, and by assessing the ability to inhibit thioredoxin reductase. The complexes proved unable to induce the formation of reactive oxygen species. The investigations add to the picture of the possible mode of action of this class of complexes.
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http://dx.doi.org/10.1039/c8mt00225hDOI Listing
November 2018

Crystal structure of sodium (1)-d-mannit-1-yl-sulfonate.

Acta Crystallogr E Crystallogr Commun 2018 Sep 24;74(Pt 9):1314-1318. Epub 2018 Aug 24.

School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.

The title salt, Na·CHOS [systematic name: sodium (1,2,3,4,5)-1,2,3,4,5,6-hexa-hydroxy-hexane-1-sulfonate], is formed by reaction of d-mannose with sodium bis-ulfite (sodium hydrogen sulfite) in water. The anion has an open-chain structure with the S atom and the C atoms of the carbohydrate chain forming an essentially planar zigzag chain in which the absolute values of the torsion angles lie between 173.6 (2) and 179.9 (3)°. The sodium cations are penta--coordinated by O atoms, with one link to a carbohydrate O atom and four to O atoms of sulfonate residues in separate anions, thus creating a three-dimensional network. The carbohydrate anions are arranged in a head (-SO) to head (-SO) arrangement, thereby forming two parallel sheets linked through coordination to sodium ions, with each sheet containing inter-molecular hydrogen bonds between the anionic residues. Unusually, the double sheets are not connected to neighbouring sets of double sheets, either by ion coordination or inter-molecular hydrogen bonding.
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http://dx.doi.org/10.1107/S2056989018011556DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6127687PMC
September 2018

Effects of Decavanadate Salts with Organic and Inorganic Cations on Escherichia coli, Giardia intestinalis, and Vero Cells.

Inorg Chem 2018 Oct 10;57(19):11930-11941. Epub 2018 Sep 10.

Fundação Osvaldo Cruz, Av. Brazil , Manguinhos , 4365 Rio de Janeiro , Brazil.

Decavanadate salts with nicotinamide (3-pyridinecarboxamide, 3-pca) and isonicotinamide (4-pyridinecarboxamide, 4-pca) in both neutral and protonated forms, (3-Hpca)[HVO]·2HO·2(3-pca) (complex I) and (4-Hpca)[HVO]·2(4-pca) (complex II), have been synthesized and characterized by vibrational spectroscopy (infrared and Raman), thermogravimetric analysis (TGA), V NMR, and single-crystal X-ray diffraction analysis. The effects of sodium decavanadate (henceforth called NaV) and compounds I and II on Escherichia coli, Giardia intestinalis, and Vero (African green monkey epithelial kidney) cells were evaluated. Enhanced growth inhibitory activity against E. coli cultures was observed upon treatment with products I and II when compared to that with NaV (GI values of 2.8, 4.0, and 11 mmol L, respectively), as well as lower cell viability as measured by the intake of propidium iodide (PI). Exposure of Giardia trophozoites to NaV and II revealed reduction in trophozoite viability (GI values of ca. 10 μmol L) and affected the parasite adherence to both polystyrene culture tubes and a monolayer of Vero cells, even at low concentrations. A lesser effect on Giardia was shown for I. Furthermore, all three compounds were significantly less toxic to Vero cells than the reference drug, albendazole, employed in the treatment of giardiasis. Toxicity reports of oxidovanadium compounds toward Giardia are unprecedented and open a path to the development of new therapeutic agents.
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http://dx.doi.org/10.1021/acs.inorgchem.8b01298DOI Listing
October 2018

A Rare Example of Four-Coordinate Nonoxido Vanadium(IV) Alkoxide in the Solid State: Structure, Spectroscopy, and Magnetization Dynamics.

Inorg Chem 2018 Sep 30;57(18):11393-11403. Epub 2018 Aug 30.

Departamento de Química , Universidade Federal do Paraná, Centro Politécnico, Jardim das Américas , 81530-900 Curitiba , Paraná , Brazil.

The distorted tetrahedral [V(OAd)] alkoxide (OAd = 1-adamantoxide, complex 1) is the first homoleptic, mononuclear vanadium(IV) alkoxide to be characterized in the solid state by X-ray diffraction analysis. The compound crystallizes in the cubic P4̅3 n space group with two highly disordered, crystallographically independent molecules in the asymmetric unit. Spin Hamiltonian parameters extracted from low temperature X- and Q-band electron paramagnetic resonance (EPR) experiments performed for polycrystalline samples of 1, both in the concentrated (bulk) form and diluted in the diamagnetic [Ti(OAd)] analogue, reveal a fully axial system with g < g , g and A ≫ A , A . Complex 1 has also been characterized by alternate current susceptometry with varying temperature (3-30 K) and static magnetic field (up to 8.5 T), showing field-induced slow relaxation of the magnetization with relaxation times ranging from ca. 3 ms at 3 K to 0.02-0.03 ms at 30 K, in line with relevant results described recently for other potential molecular quantum bits. Pulsed EPR measurements, in turn, disclosed long coherence times of ca. 4 μs at temperatures lower than 40 K, despite the presence of the H-rich ligands. The slow spin relaxation in 1 is the first observed for a tetracoordinate nonoxido vanadium(IV) complex, and results are compared here to those generated by square-pyramidal V(O) and trigonal prismatic V with oxygen donor atom sets. Considering that the number of promising d complexes investigated in detail for slow magnetization dynamics is still small, the present work contributes to the establishment of possible structural/electronic correlations of interest to the field of quantum information processing.
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http://dx.doi.org/10.1021/acs.inorgchem.8b01117DOI Listing
September 2018

Synthesis, crystal structure, and cytotoxicity studies of titanacalix[4 and 8]arene complexes.

Dalton Trans 2018 Jul;47(27):8992-8999

Chemistry, School of Mathematics and Physical Sciences, University of Hull, Hull, HU6 7RX, UK.

Reaction of 5,11,17,23-tetra-tert-butyl-dihydroxy-26,28-bis(2-pentoxy)calix[4]arene (L(OH)2(Opentyl)2) with [TiCl4] afforded the dichlorotitanoacalix[4]arene complex [TiCl2L(O)2(Opentyl)2] (1) in good yield. Hydrolysis of 1 led to the isolation of the complex {[TiL(O)3(Opentyl)]2(μ-OH)(μ-Cl)} (2). Reaction of 5,11,17,23,29,35,41,47-p-tert-butyl-49,50,51,52,53,54,55,56-octapropoxycalix[8]arene (L'(Opropyl)8) with [TiCl4] in refluxing toluene afforded, following work-up, a 35 : 65 mixture (3) of the complex [Ti(NCMe)Cl]2[TiCl(μ-O)]2L' and the silicone grease derived complex [Ti(NCMe)Cl]2[Ti(μ-O)]2[OSi(CH3)2OSi(CH3)2O]L' in which the grease replaces two chloride ligands. The molecular structures of 1·2MeCN, 2·7¼MeCN, and 3·10MeCN have been determined. The complexes were studied using in vitro cell assays and were found to have CC50 values in the range 111-186 μM, i.e. they have low toxicity.
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http://dx.doi.org/10.1039/c8dt01992dDOI Listing
July 2018

Thermally Stable Gold(III) Alkene and Alkyne Complexes: Synthesis, Structures, and Assessment of the trans-Influence on Gold-Ligand Bond Enthalpies.

Chemistry 2018 Aug 6;24(44):11467-11474. Epub 2018 Jul 6.

School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.

The reaction of [C^C)Au(OEt ) ] with 1,5-cyclooctadiene or norbornadiene affords the corresponding olefin complexes [(C^C)Au(COD)]SbF and [(C^C)Au(NBD)]SbF , which are thermally stable in solution and the solid state (C^C=4,4'-di-tert-butylbiphenyl-2,2'-diyl). The crystal structures of these complexes have been determined. By contrast, dienones such as dibenzylideneacetone are O- rather than C=C-bonded. The reactions of (C^C)Au(OAc )(L) (L=PMe or CNxyl) with B(C F ) in the presence of bis(1-adamantyl)acetylene give the mixed-ligand alkyne complexes [(C^C)Au(AdC≡CAd)(L)] , the first complexes of their type in gold chemistry. In the presence of an excess of acetylene these compounds are thermally stable in solution and as solids. The bonding of n- and π-donor ligands to Au fragments and the effect of the trans influence exerted by N- and C-donors was explored with the aid of DFT calculations. Results show that the Au-L bond enthalpies trans to anionic C are 35-60 % of the enthalpies trans to N, with strong π-acceptors being particularly affected. In comparison with [Me Au] , the [(C^C)Au] fragment is more polar and in bond enthalpy terms resembles Me Pt.
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http://dx.doi.org/10.1002/chem.201802160DOI Listing
August 2018

Carbon-sulfur bond formation by reductive elimination of gold(iii) thiolates.

Dalton Trans 2018 May;47(18):6333-6343

School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK.

Whereas the reaction of the gold(iii) pincer complex (C^N^C)AuCl with 1-adamantyl thiol (AdSH) in the presence of base affords (C^N^C)AuSAd, the same reaction in the absence of base leads to formation of aryl thioethers as the products of reductive elimination of the Au-C and Au-S ligands (C^N^C = dianion of 2-6-diphenylpyridine or 2-6-diphenylpyrazine). Although high chemical stability is usually taken as a characteristic of pincer complexes, results show that thiols are capable of cleaving one of the pincer Au-C bonds. This reaction is not simply a function of S-H acidity, since no cleavage takes place with other more acidic X-H compounds, such as carbazole, amides, phenols and malonates. The reductive C-S elimination follows a second-order rate law, -d[1a]/dt = k[1a][AdSH]. Reductive elimination is enabled by displacement of the N-donor by thiol; this provides the conformational flexibility necessary for C-S bond formation to occur. Alternatively, reductive C-S bond formation can be induced by reaction of pre-formed thiolates (C^N^C)AuSR with a strong Brønsted acid, followed by addition of SMe2 as base. On the other hand, treatment of (C^N^C)AuR (R = Me, aryl, alkynyl) with thiols under similar conditions leads to selective C-C rather than C-S bond formation. The reaction of (C^N^C)AuSAd with H+ in the absence of a donor ligand affords the thiolato-bridged complex [{(C^N-CH)Au(μ-SAd)}2]2+ which was crystallographically characterised.
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http://dx.doi.org/10.1039/c8dt00906fDOI Listing
May 2018

Fixing the Conformation of Calix[4]arenes: When Are Three Carbons Not Enough?

Chemistry 2018 Mar 26;24(17):4436-4444. Epub 2018 Feb 26.

Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, CO2-Glyco, UMR 5246, CNRS, Université Claude Bernard Lyon 1, 43 Boulevard du 11 Novembre 1918, 69622, Villeurbanne, France.

Calix[4]arenes are unique macrocycles that through judicious functionalisation at the lower rim can be either fixed in one of four conformations or remain conformationally flexible. Introduction of propynyl or propenyl groups unexpectedly provides a new possibility; a unidirectional conformational switch, with the 1,3-alternate and 1,2-alternate conformers switching to the partial cone conformation, whilst the cone conformation is unchanged, under standard experimental conditions. Using H NMR kinetic studies, rates of switching have been shown to be dependent on the starting conformation, upper-rim substituent, where reduction in bulk enables faster switching, solvent and temperature with 1,2-alternate conformations switching fastest. Ab initio calculations (DFT) confirmed the relative stabilities of the conformations and point towards the partial cone conformer being the most stable of the four. The potential impact on synthesis through the "click" reaction has been investigated and found not to be significant.
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http://dx.doi.org/10.1002/chem.201705955DOI Listing
March 2018

Synthesis and crystal structure of a new pyridinium bromide salt: 4-methyl-1-(3-phen-oxy-prop-yl)pyridinium bromide.

Acta Crystallogr E Crystallogr Commun 2017 Dec 3;73(Pt 12):1831-1834. Epub 2017 Nov 3.

Department of Chemistry, Taibah University, 30002, Al-Madina Al-Mounawara, Saudi Arabia.

In the cation of the title mol-ecular salt, CHNO·Br, the pyridinium and phenyl rings are inclined to one another by 11.80 (8)°. In the crystal, the Br anion is linked to the cation by a C-H⋯Br hydrogen bond. The cations stack along the -axis direction and are linked by further C-H⋯Br inter-actions, and offset π-π inter-actions [inter-centroid distances = 3.5733 (19) and 3.8457 (19) Å], forming slabs parallel to the plane. The effects of the C-H⋯ inter-action on the NMR signals of the and pyridinium protons in a series of related ionic liquids, . 4-methyl-1-(4-phen-oxy-but-yl)pyridin-1-ium salts, are reported and discussed.
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http://dx.doi.org/10.1107/S2056989017015481DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5730234PMC
December 2017

(C^N^C)Au complexes of acyclic carbene ligands: synthesis and anticancer properties.

Dalton Trans 2017 Oct;46(39):13397-13408

School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.

A series of cyclometallated gold(iii) complexes supported by pyrazine-based (C^N^C)-type pincer ligands were synthesized via two different pathways. Nucleophilic attack on the isocyanide complex [(C^N^C)Au(C[triple bond, length as m-dash]NCHMe-2,6)]SbF (2) gave [(C^N^C)Au(ACC)]SbF complexes with aniline (4·SbF), adamantylamine (5), glycine ethyl ester (6), alanine methyl ester (7), valine methyl ester (8), phenylglycine methyl ester (9) and methionine methyl ester (10) substituents (ACC = acyclic carbene). The pathway via isocyanide insertion into gold-amide bonds was also investigated; e.g. the reaction of xylyl isocyanide with (C^N^C)AuNHPh followed by protonation with HBF·OEt gave the acyclic carbene complex 4·BF. To the best of our knowledge compounds 6-10 represent the first examples of gold(iii) acyclic carbene complexes bearing amino acid functions. The compounds provide a versatile platform for the study of the anti-proliferative properties of gold(iii) complexes. Tests against human adenoma-type lung cancer cells identified 5, 6, 7 and 10 as particularly promising and demonstrate the synthetic flexibility of acyclic carbene complexes and the potential of that class of compounds for anticancer applications. Compared to cisplatin, amino ester-containing ACC complexes showed improved selectivity for MCF-7 breast cancer cells over that for healthy fibroblasts.
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http://dx.doi.org/10.1039/c7dt02804kDOI Listing
October 2017

Crystal structure of a 1,1,2,2-tetra-chloro-ethane-solvated hydrazinecarbo-thio-amide compound.

Acta Crystallogr E Crystallogr Commun 2017 Sep 1;73(Pt 9):1271-1274. Epub 2017 Aug 1.

Chemistry Department, Taibah University, PO Box 30002, Code 14177, Al-Madinah Al-Munawarah, Kingdom of Saudi Arabia.

The title compound, [(1-{4-[2-(2,4-di-hydroxy-phen-yl)diazen-1-yl]phen-yl}ethyl-idene)amino]-thio-urea, 1,1,2,2-tetra-chloro-ethane monosolvate, CHNOS·CHCl, was prepared from 4-(4-acetyl-phenyl-diazendi-yl)resorcinol and thio-semicarbazide and recrystallized from mixed solvents of tetra-chloro-ethane and -hexane. H NMR and X-ray diffraction data are in support of the thione tautomeric form. The X-ray analysis shows the mol-ecule crystallizes as a zwitterion, with proton transfer from the nominal phenol to the azide group; the N-N bond length is 1.291 (5) Å, and an intra-molecular N-H⋯O hydrogen bond is formed. In the crystal, N-H⋯O, N-H⋯N and O-H⋯S hydrogen bonds connect the mol-ecules into a three-dimensional network. The tetra-chloro-ethane solvent mol-ecules are linked to this network through weak C-H⋯O linkages.
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http://dx.doi.org/10.1107/S2056989017010830DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5588558PMC
September 2017

Naphthoquinones of Sinningia reitzii and Anti-inflammatory/Antinociceptive Activities of 8-Hydroxydehydrodunnione.

J Nat Prod 2017 06 9;80(6):1837-1843. Epub 2017 Jun 9.

Departamento de Química, Universidade Federal do Paraná , 81530-900, Curitiba, PR, Brazil.

Chemical investigation of the tubers of Sinningia reitzii led to the isolation of five new naphthoquinones, 8-hydroxydehydrodunnione (1), 7-hydroxydehydrodunnione (2), 5-hydroxy-6,7-dimethoxy-α-dunnione (3), 5-hydroxy-6,7-dimethoxydunniol (4), and 8-hydroxy-7-methoxy-2-O-methylstreptocarpone (5). Three known naphthoquinones, 7-hydroxy-α-dunnione, 8-hydroxydunnione, and 6,8-dihydroxy-7-methoxy-2-O-methyldunniol, were also identified. When tested for anti-inflammatory activity in a mouse model, compound 1 (50-500 pg/paw) reduced the edema induced by carrageenan in a dose-dependent fashion. The highest dose showed a similar inhibition to that observed for the positive control dexamethasone. At lower doses (5-10 pg/paw), 1 also dose dependently reduced the mechanical hyperalgesia induced by carrageenan. Compound 1 (15 pg/paw) abolished the mechanical hyperalgesia induced by prostaglandin E and dopamine, but not that induced by dibutyryl cyclic AMP. Dipyrone (320 μg/paw) completely abolished the hyperalgesia induced by these algogens. Additionally, compound 1 did not alter heat-induced nociception. These results suggest that this new naphthoquinone exhibits important anti-inflammatory and antinociceptive activities, which is dissimilar to that of most known analgesics.
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http://dx.doi.org/10.1021/acs.jnatprod.6b01186DOI Listing
June 2017

Formation of Gold(III) Alkyls from Gold Alkoxide Complexes.

Organometallics 2017 Apr 27;36(7):1358-1364. Epub 2017 Mar 27.

School of Chemistry, University of East Anglia, Norwich NR4 7TJ, U.K.

The gold(III) methoxide complex (CNC)AuOMe () reacts with tris(-tolyl)phosphine in benzene at room temperature under O abstraction to give the methylgold product (CNC)AuMe () together with O=P(-tol) ((CNC) = [2,6-(CH Bu-4)pyridine]). Calculations show that this reaction is energetically favorable (Δ = -32.3 kcal mol). The side products in this reaction, the Au(II) complex [Au(CNC)] () and the phosphorane (-tol)P(OMe), suggest that at least two reaction pathways may operate, including one involving (CNC)Au radicals. Attempts to model the reaction by DFT methods showed that PPh can approach to give a near-linear Au-O-P arrangement, without phosphine coordination to gold. The analogous reaction of (CNC)AuOEt, on the other hand, gives exclusively a mixture of and (-tol)P(OEt). Whereas the reaction of (CNC)AuOR (R = Bu, -CHF) with P(-tol) proceeds over a period of hours, compounds with R = CHCF, CH(CF) react almost instantaneously, to give and O=P(-tol). In chlorinated solvents, treatment of the alkoxides (CNC)AuOR with phosphines generates [(CNC)Au(PR)]Cl, via Cl abstraction from the solvent. Attempts to extend the synthesis of gold(III) alkoxides to allyl alcohols were unsuccessful; the reaction of (CNC)AuOH with an excess of CH=CHCHOH in toluene led instead to allyl alcohol isomerization to give a mixture of gold alkyls, (CNC)AuR' (R' = -CHCHCHO (), -CHCH(CHOH)OCHCH=CH ()), while 2-methallyl alcohol affords R' = CHCH(Me)CHO (). The crystal structure of was determined. The formation of Au-C instead of the expected Au-O products is in line with the trend in metal-ligand bond dissociation energies for Au(III): M-H > M-C > M-O.
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http://dx.doi.org/10.1021/acs.organomet.7b00077DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5388904PMC
April 2017
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