Thio-iso-phthalamide pincer ligand-driven oxidative addition of a C-Br bond to gold(I): synthesis and studies of SCS-gold(III) pincer complexes.

The chelating effect of thio-iso-phthalamides was utilized to facilitate the oxidative addition of an aryl Csp-Br bond into the SMeAu(I)Cl salt, leading to the isolation of stable SCS·Au(III)X (X = Br and Cl) complexes. The subsequent displacement of bromide with silver triflate, followed by the addition of phosphine/phosphite ligands, afforded a series of neutral, highly stable organogold(III) complexes. The thioamide pincer ligand acts as a trianionic species due to iminothiolate formation.

The Role of Chalcogen Bonding in Organic Dichalcogenides of Biological Interest.

Dichalcogenides are important intermediates in the catalytic cycle of the Glutathione peroxidase (GPx), the enzyme regulating the level of reactive oxygen species (ROS). Due to their redox sensitivity, dichalcogenides are also employed in anticancer systems. The biological activity of these compounds can be related to the electrophilic behaviour of the chalcogen atoms, namely their ability to form Chalcogen Bonds (ChBs) with nucleophilic species.

Synthesis and glutathione peroxidase (GPx)-like activity of selenocystine (SeC) bioconjugates of biotin and lipoic acid.

The conjugation of active biomolecules provides insight into their bioreactivity, leading to many applications in biotechnology and materials science. Herein, we report L-selenocystine (SeC) bioconjugates of lipoic acid (universal antioxidant) and biotin (Vitamin-H). The SeC-bioconjugates, SeC-Biotin (1) and SeC-Lipoic acid (2) were synthesized using solid phase peptide synthesis (SPPS) method and were characterized by multinuclear 1D (H, C, Se) and 2D (H-H COSY and H-C TOCSY) NMR spectroscopy, ESI-MS spectrometry, and RP-HPLC.

Coordination Behavior of the Tellurium Incorporated Mercuraazametallamacrocycle and Investigation of d ⋅⋅⋅d Interactions between Closed Shell (Ag Hg ) Metal Ions.

Herein, a new tellurium and mercury containing mercuraazametallamacrocycle has been prepared via (2+2) condensation of bis(o-aminophenyl)telluride and bis(o-formylphenyl)mercury(II). The isolated bright yellow solid of mercuraazametallamacrocycle has adopted unsymmetrical figure-of-eight conformation in the crystal structure. To study the metallophilic interactions between closed shell metal ions, the macrocyclic ligand has been treated with two equiv.

Pushing the Boundary of Covalency in Lanthanoid-Tellurium Bonds: Insights from the Synthesis, Molecular and Electronic Structures of Low-Coordinate, Monomeric Europium(II) and Ytterbium(II) Tellurolates.

Owing to the strict hard/soft dichotomy between the lanthanoids and tellurium atoms, and the strong affinity of lanthanoid ions for high coordination numbers, low-coordinate, monomeric lanthanoid tellurolate complexes have remained elusive as compared to the lanthanoid complexes with lighter group 16 elements (O, S, and Se). This makes the development of suitable ligand systems for low-coordinate, monomeric lanthanoid tellurolate complexes an appealing endeavor. In a first report, a series of low-coordinate, monomeric lanthanoid (Yb, Eu) tellurolate complexes were synthesized by utilizing hybrid organotellurolate ligands containing N-donor pendant arms.

Self-Assembly of Nicotinic Acid-Conjugated Selenopeptides into Mesotubes.

The study of controlling the morphology for designing advanced supramolecular architectures by tuning the molecular motif at the elemental level has been rarely carried out. Here, we report the synthesis of a nicotinic acid-conjugated selenopeptide, which induced the formation of an unbranched mesoscale elongated tubular morphology. We rationally designed two additional peptides to find out the decisive role played by the nitrogen atom (in nicotinic acid) and selenium (in the peptide backbone) toward the formation of the mesotube.

Chalcogen Bonds in Selenocysteine Seleninic Acid, a Functional GPx Constituent, and in Other Seleninic or Sulfinic Acid Derivatives.

The controlled oxidation reaction of L-selenocystine under neutral pH conditions affords selenocysteine seleninic acid (3-selenino-L-alanine) which is characterized also by means of single-crystal X-ray diffraction. This technique shows that selenium forms three chalcogen bonds (ChBs), one of them being outstandingly short. A survey of seleninic acid derivatives in the Cambridge Structural Database (CSD) confirms that the C-Se(=O)O- functionality tends to act as a ChB donor robust enough to systematically influence the interactional landscape in the solid.

Bis(2-nitrophenyl) selenide, bis(2-aminophenyl) selenide and bis(2-aminophenyl) telluride: structural and theoretical analysis.

Three organoselenium and organotellurium compounds containing ortho substitutents, namely, bis(2-nitrophenyl) selenide, CHNOSe, 2, bis(2-aminophenyl) selenide, CHNSe, 3, and bis(2-aminophenyl) telluride, CHNTe, 7, have been investigated by both structural and theoretical methods. In the structures of all three compounds, there are intramolecular contacts between both Se and Te with the ortho substituents. In the case of 2, this is achieved by rotation of the nitro group from the arene plane.

Structure of a diorganotelluroxonium(IV) cation, {[2,6-(CHNMe)CHTe(μ-O)]}, with the tri-chlorido-(dimethyl sulfoxide)-platinum(II) anion.

In the title salt, di-μ-oxido-bis-{2,6-bis-[(di-methyl-amino)-meth-yl]phenyl-κ }tellurium(-IV) bis[tri-chlorido-(dimethyl sulfoxide-κ)platinate(II)], (CHNOTe)[PdCl(CHOS)], which crystallizes in the triclinic space group , each Te atom is in a distorted five-coordinated TeONC square-pyramidal geometry (τ values of 0.026 and 0.001) with the C atoms of the phenyl rings occupying the apical positions.

Structural characterization of the derivatives of bis{[2,6-(dimethylamino)methyl]phenyl} selenide with palladium(II) and mercury(II).

The intramolecularly coordinated homoleptic diorgano selenide bis{2,6-bis[(dimethylamino)methyl]phenyl} selenide, CHNSe or RSe, where R is 2,6-(MeNCH)CH, 14, was synthesized and its ligation reactions with Pd and Hg precursors were explored. The reaction of 14 with SOCl and KPdCl resulted in the formation of the meta C-H-activated dipalladated complex {μ-2,2'-bis[(dimethylamino)methyl]-4,4'-bis[(dimethylazaniumyl)methyl]-3,3'-selanediyldiphenyl-κC,N:C,N}bis[dichloridopalladium(II)], [PdCl(CHNSe)] or [{R(H)PdCl}Se], 15. On the other hand, when ligand 14 was reacted with HgCl, the reaction afforded a dimercurated selenolate complex, {μ-bis{2,6-bis[(dimethylamino)methyl]benzeneselanolato-κN,Se:Se,N}-μ-chlorido-bis[chloridomercury(II)], [Hg(CHNSe)Cl] or RSeHgCl, 16, where two Hg ions are bridged by selenolate and chloride ligands.

Metallophilic interactions: observations of the shortest metallophilicinteractions between closed shell (dd, dd, dd) metal ions [MM' M = Hg(ii) and Pd(ii) and M' = Cu(i), Ag(i), Au(i), and Pd(ii)].

The salt metathesis reaction of two equivalents of 8-lithioquinoline (CHNLi) with HgBr afforded bis(quinoline-8-yl)mercury, [(CHN)Hg]. Bis(quinoline-8-yl)mercury has been used for the synthesis of a series of heteronuclear complexes of the type [(CHN)M·M']·X [M = Hg; {M' = Cu, X = ClO; X = I; X = CFSO}, {M' = Ag, X = ClO; X = CFSO; X = BF}, {M' = Au, X = CFSO}; {M' = Pd, X = CFCO}], [M = Pd; M' = Pd, X = CFCO; n = 2]. All the complexes were well characterized by multinuclear NMR (H, C, F, B, Hg) spectroscopic analysis.

Isolation of the novel example of a monomeric organotellurinic acid.

The stoichiometrically controlled alkaline hydrolysis of 4, (ppy)TeCl3, [ppy = 2-(2'-pyridyl)phenyl] afforded the partially hydrolyzed μ-oxo-bridged dinuclear telluroxane 5, [(ppyTeCl2)2(μ-O)] and a novel example of an Intramolecular Chalcogen Bonding (IChB) stabilized, monomeric organotellurinic acid 6, (ppy)Te(O)OH. The oxidation of diaryl ditelluride 7, (ppyTe)2 using H2O2 resulted in the isolation of μ-oxo-bridged dimethyl ester 8, [(ppy)Te(O)(OH)(OMe)]2(O). The molecular structures of 4-6 and 8 are unambiguously authenticated by single crystal X-ray diffraction studies.

Facile synthesis of stable selenocystine peptides and their solution state NMR studies.

A facile general route for the synthesis of various selenocystine tripeptides containing acidic, basic and neutral side chain amino acids is reported. Here, TFA labile side chain protected selenocysteine has been used as a precursor for the synthesis of selenopeptides. The peptides are highly stable in dimethyl sulphoxide, thus enabling detailed NMR studies by solution phase 1- and 2-dimensional NMR spectroscopy.

Oxidation behavior of intramolecularly coordinated unsymmetrical diorganotellurides: isolation of novel tetraorganoditelluronic acids, [RR'Te(μ-O)(OH)].

The oxidation reaction of unsymmetrical diorganotellurides, namely, bis[2-{(dimethylamino)methyl}aryl]tellurides [aryl = phenyl (6), 2-methylphenyl (7), 2,6-dimethylphenyl (8) and 2,6-diisopropylphenyl (9)] with meta-chloroperbenzoic acid afforded the first examples of tetraorganoditelluronic acids, [RR'Te(μ-O)(OH)], where R = 2-NMeCHCH, R' = CH (10), 2-MeCH (11), 2,6-MeCH (12) and 2,6-PrCH (13). The structures of tetraorganoditelluronic acids 10-13 were authenticated by single crystal X-ray diffraction studies. From the molecular structures of 10-13, it was observed that the sp N-donor atoms, which were initially involved in intramolecular TeN bonding interactions in diorganotellurides 6-9, did not interact with the tellurium atoms in tetraorganoditelluronic acids 10-13.

Isolation and structure of an 18-membered macrocycle containing two diselenide linkages and its precursor.

The structures of the 18-membered diselenide-linked macrocycle 10,27-di-tert-butyl 11,28-dioxo-2,3,19,20-tetraselena-10,12,27,29-tetraazapentacyclo[28.4.0.

Synthesis of selenopeptides: an alternative way of incorporating selenocystine.

Selenocysteine (Sec) residue cannot be directly attached to a peptide sequence unless the selenol form is protected beforehand and several problems have been reported in the preparation of Sec building blocks. In this article a series of selenocystine, the oxidized form of Sec, containing peptides has been synthesized using a new methodology, where Boc-NH-chloroalanine is coupled with methyl ester protected residues (Ala, Met, Phe) using DCC/HOBt as the coupling reagents providing di- and tripeptides. Further, the treatment of disodium diselenide with chloroalanine peptides (Boc-ClAla-Ala-OMe, Boc-ClAla-Met-OMe and Boc-ClAla-Ala-Phe-OMe) afforded the respective selenocystine-containing peptides (Boc-Sec-Ala-OMe, Boc-Sec-Met-OMe and Boc-Sec-Ala-Phe-OMe).

Hypervalent organoselenium compounds stabilized by intramolecular coordination: synthesis and crystal structures.

Two novel hypervalent selenium(IV) compounds stabilized by intramolecular interactions, namely 6-phenyl-6,7-dihydro-5H-2,3-dioxa-2aλ-selenacyclopenta[hi]indene, CHOSe, 14, and 5-phenyl-5,6-dihydro-4H-benzo[c][1,2]oxaselenole-7-carbaldehyde, CHOSe, 15, have been synthesized by the reaction of 2-chloro-1-formyl-3-(hydroxymethylene)cyclohexene with in-situ-generated disodium diselenide (NaSe). The title compounds were characterized by FT-IR spectroscopy, ESI-MS, and single-crystal X-ray diffraction studies. For 14, there is whole-molecule disorder, with occupancies of 0.

Adaptive responses of sterically confined intramolecular chalcogen bonds.

The responsive behavior of an entity towards its immediate surrounding is referred to as an adaptive response. The adaptive responses of a noncovalent interaction at the molecular scale are reflected from its structural and functional roles. Intramolecular chalcogen bonding (IChB), an attractive interaction between a heavy chalcogen E (E = Se or Te) centered sigma hole and an -heteroatom Lewis base donor D (D = O or N), plays an adaptive role in defining the structure and reactivity of arylchalcogen compounds.

Self-assembly of penta-selenopeptides into amyloid fibrils.

Here, we report the synthesis of a penta-selenopeptide consisting of five benzyl protected selenocysteine residues. This selenopeptide was well characterized by both one- and two-dimensional (D) NMR spectroscopies. We find that the solution conformation is enriched with β-sheet structures, which have a propensity to self-assemble and form amyloid fibrils.

Reactivity of Selenocystine and Tellurocystine: Structure and Antioxidant Activity of the Derivatives.

l-Selenocystine (5) and l-tellurocystine (6) have been prepared and the reactivity of these amino acids, i.e., oxidation of 5 and 6, has been performed at various pH values.

{-[2-(Butyl-selan-yl)benz-yl]-,-di-methyl-ethane-1,2-di-amine}-dichlorido-mercury(II).

In the title compound, [HgCl(CHNSe)], the primary geometry around the Se and Hg atoms is distorted trigonal-pyramidal and distorted square-pyramidal, respectively. The distortion of the mol-ecular geometry in the complex is caused by the steric demands of the ligands attached to the Se atom. The Hg atom is coordinated through two chloride anions, an N atom and an Se atom, making up an unusual HgNSeCl coordination sphere with an additional long Hg⋯N inter-action.

Synthesis and structure of an aryl-selenenium(II) cation, [CHNSe][Hg(SeCN)], based on a 5--butyl-1,3-bis-(1-pentyl-1-benzimidazol-2-yl)benzene scaffold.

In the title salt, bis-{[5--butyl-1,3-bis-(1-pentyl-1-benzimidazol-2-yl)benzene]selenium} tetra-kis-(seleno-cyanato)-mercury, (CHNSe)[Hg(SeCN)], the aryl-selenenium cations, [CHNSe], are linked through [Hg(SeCN)] anions by C-H⋯N hydrogen bonds. In the cation, the geometry around the Se atom in the 5--butyl-1,3-bis-(1-pentyl-1-benzimidazol-2-yl)benzene scaffold is T-shaped, resulting from the coordination of Se by the C atom of the central aromatic ring and the N atoms of both of the benzimidazole moieties. The Se-N bond lengths are almost equal [2.

Synthesis and structure of arylselenium(ii) and aryltellurium(ii) cations based on rigid 5-tert-butyl-1,3-bis-(N-pentylbenzimidazol-2'-yl)benzenes.

The transmetalation reactions of a mercury precursor, [Pentyl(N^C^N)HgCl] (19), with selenium halides (SeCl4, SeBr4, and SeCl2) were attempted to obtain the corresponding organoselenium trichloride [Pentyl(N^C^N)SeCl3], tribromide [Pentyl(N^C^N)SeBr3], and monochloride [Pentyl(N^C^N)SeCl], respectively [(N^C^N) = 5-tert-butyl-1,3-bis-(N-pentyl-benzimidazol-2'-yl)phenyl]. However, in all the cases, a very facile ionization of the Se-halogen bond was observed leading to the isolation of a new class of air stable arylselenium(ii) complexes: [Pentyl(N^C^N)Se+]2[HgCl4]2- (20) and [Pentyl(N^C^N)Se+]2[HgBr4]2- (21). This is the first report on the formation of NCN pincer-based arylselenium(ii) cations via the transmetalation route.

Synthesis and structure of an aryl-tellurenium(II) cation; [4--butyl-2,6-bis-(1-pentyl-1-benz-imidazol-2-yl-κ)phenyl-κ]tellurium(II) (1,4-dioxane)tri-iodido-mercurate(II).

In the title salt, (CHNTe)[HgI(CHO)], the aryl-tellurenium [CHNTe] cations and [HgI(dioxane)] anions are linked by a short inter-action between the Te atom and one of the I-atom donors of the anion, as well as through weak C-H⋯I inter-actions. The geometry around the Te atom is T-shaped with the coordination comprising a C atom of the central aromatic ring and two N atom donors of the benzimidazolyl moiety. The Te-N bond lengths are almost equal [2.