Coordination Behavior of the Tellurium Incorporated Mercuraazametallamacrocycle and Investigation of d10 ⋠⋠⋠d10 Interactions between Closed Shell (Ag+ Hg2+ ) 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. of AgOTf (OTf=trifluoromethansulfonate) and AgBF4 , which afforded greenish-yellow bimetallic silver complexes. The isolated silver complexes displayed intramolecular Hg⋅⋅⋅Ag, Te⋅⋅⋅Ag interactions as well as intermolecular Hg⋅⋅⋅Hg interactions and formed an extended 1D molecular chain by directing six atoms to interact as TeII ⋅⋅⋅AgI ⋅⋅⋅HgII ⋅⋅⋅HgII ⋅⋅⋅AgI ⋅⋅⋅TeII in a non linear fashion. The Hg⋅⋅⋅Ag, Te⋅⋅⋅Ag interactions have also been studied in solution by 199 Hg, 125 Te NMR spectroscopy, absorption, and emission spectroscopy. In DFT calculations, the Atom in Molecule (AIM) analysis, non-covalent interactions (NCI), natural bonding orbital (NBO) analysis strongly supported for experimental evidences and revealed that the intermolecular Hg⋅⋅⋅Hg interaction is stronger than the intramolecular Hg⋅⋅⋅Ag interactions.

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. The reaction of bis[2-((dimethylamino)methyl)phenyl] ditelluride, 1 and 8,8'diquinolinyl ditelluride, 2 with Ln0 metals (Ln=Eu, Yb) resulted in the formation of monomeric complexes [LnII (TeR)2 (Solv)2 ] [R=C6 H4 -2-CH2 NMe2 ] [3: Ln=Eu, Solv=tetrahydrofuran; 4: Ln=Eu, Solv=acetonitrile; 5: Ln=Yb, Solv=tetrahydrofuran; 6: Ln=Yb, Solv=pyridine] and [EuII (TeNC9 H6 )2 (Solv)n ] (7: Solv=tetrahydrofuran, n=3; 8: Solv=1,2-dimethoxyethane, n=2), respectively. Complexes 3-4 and 7-8 represent the first sets of examples of monomeric europium tellurolate complexes. The molecular structures of complexes 3-8 are validated by single-crystal X-ray diffraction studies. The electronic structures of these complexes were investigated using Density Functional Theory (DFT) calculations, which revealed appreciable covalency between the tellurolate ligands and lanthanoids.

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 (1H, 13C, 77Se) and 2D (1H-1H COSY and 1H-13C TOCSY) NMR spectroscopy, ESI-MS spectrometry, and RP-HPLC. The GPx-like enzyme mimicking activity of the SeC-bioconjugates 1 and 2 has been investigated through the coupled reductase assay method for the catalytic reductions of hydrogen peroxide into water. A significant enhancement in GPx-like enzymatic activity was observed for both novel bioconjugates SeC-Biotin (1) and SeC-Lipoic acid (2) as compared to diphenyl diselenide (Ph2Se2), L-selenocystine (SeC), biotin, lipoic acid, and ebselen.

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).

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.

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. Hydrogen peroxide was used as an oxidant and it was treated with 5 and 6 in excess in acidic and basic media. Compound 5, upon oxidation, afforded SeIV and SeVI products. Selenocysteic acid [HO3 SeCH2 CH(NH2 )COOH] 9, a novel SeVI compound, was isolated and characterised by single-crystal X-ray diffraction studies. In contrast, l-tellurocystine, upon oxidation with H2 O2 , afforded TeII and TeIV products. Zwitterionic organotellurolate(IV), [TeCl3 CH2 CH(NH3 )COOH] 13, was isolated and characterised by NMR and IR spectroscopy, mass spectrometry and elemental analysis. Compound 13 crystallizes in an orthorhombic space group. l-Tellurocystine, when reduced with NaBH4 , produced the desired tellurolate intermediate, which was trapped with bromoacetic acid. Furthermore, l- and d-tellurocysteine derivatives, [(RTeCH2 CH(NH2 )COOH) R=phenyl, substituted phenyl and naphthyl (24-39)] were synthesised and evaluated for their glutathione peroxidase (GPx)-like activities. The results show that l-tellurocysteine derivatives have higher activity than their D-tellurocysteine analogues. DFT calculations for l-tellurocysteine derivatives provided information about the bond lengths and bond angles. This study reveals that the introduction of naphthyl substituents (35-38) leads to twisted conformation of the amino acid derivatives.

Synthesis, Structure, and Bonding of 1-Oxa-6,6aλ(4)- chalcogenopentalenes and Related Derivatives; The Role of Intramolecular Coordination.

The synthesis and characterization of a series of alicyclic organochalcogen compounds derived from 2-chloro-1-formyl-3-hydroxymethylenecyclohexene (16) are described. The reaction of 16 with disodium disulfide afforded an unexpected 1-oxa-6,6aλ(4)-dithiapentalene 33, whereas the reaction of disodium diselenide afforded 1-oxa-6,6aλ(4)-diselenapentalene 34, along with 1,6-dioxa-6a-selenapentalene 35. In contrast, when 16 was treated with Na2Te2, it resulted in the formation of 1-oxa-6,6aλ(4)-ditellurapentalene 36 along with 1,6-dioxa-6a-tellurapentalene 37 and cyclic monotelluride 38. The oxidation of 1-oxa-6,6aλ(4)-diselenapentalene 34 with m-CPBA provided the corresponding 1-oxa-6,6aλ(4)-diselenapentalene-6,6aλ(4)-dioxide 39 in which both of the selenium atoms were found to be oxidized. The 1-oxa-6,6aλ(4)-dichalcogenopentalenes 33, 34, and 36 are stabilized by 3c-4e bond resulting from intramolecular E···O interaction. The donor oxygen donates a lone pair of electrons to the σ* orbital of acceptor E-E bond (E = S, Se, and Te) whose σ bond already has its bond pair electrons. The existence of intramolecular E···O interactions was established by multinuclear NMR spectroscopy, single crystal X-ray analysis, and computational studies. The single crystal X-ray structures of compounds 33, 34, and 36 reveal that the molecules are almost planar. Nucleus-independent chemical shifts were calculated to compare the aromaticity in both the five-membered rings of 33, 34, 36 and 1,6-dioxa-6a-chalcopentalenes (35 and 37). The isotropic shift values of the covalently fused five-membered heterocyclic rings are more negative than the five-membered heterocyclic rings formed by intramolecular coordination.

Synthesis, Structure and Antioxidant Activity of Cyclohexene-Fused Selenuranes and Related Derivatives.

Synthesis, structure and antioxidant activity of new cyclohexene-fused spiroselenuranes and a spirotellurane is reported. Oxidation reactions of bis(o-formylcyclohex- 1-ene)selenide/bis(2-hydroxymethylcyclohex-1-ene)selenide provide the corresponding spiroselenuranes. The glutathione peroxidase-like activity of the newly synthesized compounds has been evaluated.

Crystal structure of (N (1)-benzyl-N (1),N (2),N (2)-tri-methyl-ethane-1,2-di-amine-κ(2) N,N')di-chloridomercury(II).

In the structure of the title compound, [HgCl2(C12H20N2)], the Hg(II) atom has a distorted tetra-hedral coordination sphere defined by two tertiary amine N-atom donors, as well as two Cl(-) anions [the dihedral angle between the N-Hg-N and Cl-Hg-Cl planes is 82.80 (9)°]. The five-membered chelate ring adopts an envelope conformation, with puckering parameters of Q(2) = 0.446 (6) Šand ϕ(2) = 88.8 (6)°, with the two amine CH3 substituents on opposite sides of the ring. In the crystal, the mol-ecules are linked by C-H⋯Cl inter-actions into a zigzag chain parallel to [101].

Crystal structure of N (1)-benzyl-N (1),N (2),N (2)-tri-methyl-ethane-1,2-diaminium dichloride.

In the title mol-ecular salt, C12H22N2 (2+)·2Cl(-), which was obtained as a by-product in the attempted synthesis of a mercury derivative, the conformation of the N-C-C-N bond in the cation is anti [torsion angle = 175.1 (10)°]. In the crystal, the cations are linked to the anions by N-H⋯Cl hydrogen bonds, generating ion-triplets. These are linked by numerous weak C-H⋯Cl inter-actions, generating a three-dimensional network. The structure was refined as an inversion twin.

Crystal structure of 4-bromo-N-(2-bromo-3-nitro-benz-yl)-2-nitro-naphthalen-1-amine.

In the title compound, C17H11Br2N3O4, the dihedral angle between the planes of the naphthalene system and the benzene ring is 52.86 (8)°. The nitro substituent and the attached naphthalene system are almost coplanar [dihedral angle = 5.6 (4)°], probably as a consequence of an intra-molecular N-H⋯O hydrogen bond with the amine group. The nitro substituent attached to the benzene ring is disordered over two sets of sites with occupancies of 0.694 (3) and 0.306 (3). The major component deviates significantly from the ring plane [dihedral angle = 53.6 (2)°]. In the crystal, the mol-ecules are linked into a three-dimensional array by extensive π-π inter-actions involving both the naphthalene and benzene rings [range of centroid-centroid distances = 3.5295 (16)-3.9629 (18) Å] and C-H⋯O inter-actions involving the methyl-ene H atoms and the phenyl-attached nitro group.

2-Bromo-5-tert-butyl-N-methyl-N-[2-(methyl-amino)-phen-yl]-3-(1-methyl-1H-benzimidazol-2-yl)benzamide.

In the title compound, C27H29BrN4O, benzimidazole ring system and the amide moiety are planar [r.m.s. deviations = 0.016 (2) and 0.017 (1) Å, respectively]. The mol-ecule adopts a conformation in which the amide linkage is almost perpendicular to the central ring [dihedral angle = 85.79 (8)°], while the benzimidazole ring system makes a dihedral angle of 70.26 (11)° with the central ring. In the crystal, the mol-ecules form dimers through N-H⋯O hydrogen bonds and C-H⋯O interactions. These dimers are further linked into zigzag ribbons along [201] by weak C-H⋯Br inter-actions. As a result of the bulky nature of the mol-ecule, as evidenced by the large dihedral angles between rings, there is little evidence for any π-π inter-actions.

Synthesis of anionic hypervalent cyclic selenenate esters: relevance to the hypervalent intermediates in nucleophilic substitution reactions at the selenium(II) center.

The synthesis of a diaryl diselenide that contains 2,6-dicarboxylic acid groups, 2,2'-diselanediylbis(5-tert-butylisophthalic acid) (10), is described. Diselenide 10 undergoes intramolecular cyclization in methanol to form a cyclic selenenate ester, 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylic acid (11). The cyclization reaction proceeds more rapidly in the presence of organic bases, such as pyridine, adenine, and 4,4'-bipyridine, to form pyridinium 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate (14), adeninium 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate (15), and 4,4'-bipyridiniumbis(5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate) (16), respectively. However, 2,2'-diselanediyldibenzoic acid (22) does not undergo cyclization under similar conditions. Structural studies on cyclic selenenate esters 14-16 revealed that the Se···O (COO(-)) secondary distances (2.170, 2.075, and 2.176 Å) were significantly shorter than the corresponding Se···O distances (2.465, 2.472, and 2.435 Å) observed for the selenenate esters stabilized by the neutral donors (CHO, COOH, and COOEt). (1)H, (13)C, and (77)Se NMR spectroscopy of compounds 11 and 14-16 reveal that the aryl protons of compound 11 and the organic cations of compounds 14-16 exchange between the two carboxylate groups via a hypercoordinate intermediate. The corresponding hypercoordinate intermediate (14b, pyridinium selenuranide) for compound 14 was detected at low temperatures using (77)Se NMR spectroscopy. The presumed hypercoordinate intermediates in the carboxylate-exchange reactions at the selenium(II) center for a set of model reactions were optimized using DFT-B3LYP/6-311+g(d) calculations and their structural features compared with the X-ray structure of anionic selenenate esters 14-16.

Selenadiazolopyridine: a synthon for supramolecular assembly and complexes with metallophilic interactions.

The synthesis and characterization of the complexes of Cu(I), Ag(I), Cu(II), and Co(II) ions with 1,2,5-selenadiazolopyridine (psd) is reported. The following complexes have been prepared: [Cu(2)(psd)(3)(CH(3)CN)(2)](2+)2(PF(6)(-)); [(CuCl)(2)(psd)(3)]; [Cu(2)(psd)(6)](2+)2(ClO(4))(-); [Ag(2)(psd)(2)](2+)2(NO(3))(-); [Ag(2)(psd)(2)](2+)2(CF(3)COO)(-); [Cu(psd)(2)(H(2)O)(3)](2+)2(ClO(4))(-)·(psd)(2); [Cu(psd)(4)(H(2)O)](2+)2(ClO(4))(-)·(CHCl(3)); [Cu(psd)(2)(H(2)O)(3)](2+)2(NO(3))(-)·(H(2)O)·(psd)(2), and [Co(psd)(2)(H(2)O)(4)](2+)2(ClO(4))(-)·(psd)(2). The electronic structure of ligand psd, in particular the bond order of Se-N bonds, has been probed by X-ray diffraction, (77)Se NMR, and computational studies. A detailed analysis of the crystal structures of the ligand and the complexes revealed interesting supramolecular assembly. The assembly was further facilitated by the presence of neutral ligands for some complexes (Cu(II) and Co(II)). The molecular structure of the ligand showed that it was present as a dimer in the solid state where the monomers were linked by strong secondary bonding Se···N interactions. The crystal structures of Cu(I) and Ag(I) complexes revealed the dinuclear nature with characteristic metallophilic interactions [M···M] (M = Cu, Ag), while the Cu(II) and Co(II) complexes were mononuclear. The presence of M···M interactions has been further probed by Atoms in Molecules (AIM) calculations. The paramagnetic Cu(II) and Co(II) complexes have been characterized by UV-vis, ESI spectroscopy, and room temperature magnetic measurements.

Dibromidochlorido{2-[(dimethyl-amino)-meth-yl]phenyl-κN,C}tellurium(IV).

The title compound, C(9)H(13)Br(2)ClNTe, was synthesized by reacting [2-(dimethyl-amino-meth-yl)phen-yl]tellurium(II) chlor-ide with Br(2). As a consequence, the Cl and Br atoms are not well ordered but distributed over the three possible positions such that the overall stiochiometry is two Br atoms and one Cl atom. The scrambling of the Br and Cl atoms indicates a small energy barrier for the exchange process between the apical and equatorial positions. Overall, the Te atom geometry is slightly distorted square pyramidal (τ = 0.052 for the major component). However, there is a weak secondary inter-action between the Te atoms and the disordered Br/Cl atoms of a nearby mol-ecule. The Te-Br and Te-Cl distances in both disorder components fall into two groups; a longer distance for the Br/Cl involved in this secondary inter-action [2.6945 (17) Šfor Br and 2.601 (9)Å for Cl] and shorter bond distances to the remaining halogen atoms, indicating that this inter-action has slightly weakened the Te-X bond, as is the case in the previously reported tribromido structure [Singh et al. (1990). J. Chem. Soc. Dalton Trans. pp. 907-913]. Otherwise, the metrical parameters in the two structures are not significantly different. An intermolecular C-H⋯Br interaction occurs.

Chlorido{2-[(dimethyl-amino)-meth-yl]phenyl-κN,C}tellurium.

The crystal structure of the title compound, C(9)H(12)ClNTe, contains isolated mol-ecules with no close Te⋯Cl inter-molecular contacts and has the same composition as a previously published structure [Engman et al. (2004 ▶). Phospho-rus Sulfur Silicon Relat. Elem.179, 285-292]. However, in this case, the compound has crystallized in a centrosymmetric space group, unlike the previously published structure which contained enanti-omerically pure chiral mol-ecules. In all other aspects, the metrical parameters are similar. The mol-ecules with a T-shaped coordination environment about the Te atom are linked into dimers by C-H⋯Cl inter-actions.

Bis{µ-2-[(dimethyl-amino)-meth-yl]benzene-seleno-lato}bis-[chloridopalladium(II)] dichloromethane hemisolvate.

The asymmetric unit of the title compound, [Pd(2)(C(9)H(12)NSe)(2)Cl(2)]·0.5CH(2)Cl(2), contains two half-mol-ecules, each lying on a twofold axis; each mol-ecule is chiral and of the same enanti-omer. This is only possible as the mol-ecule has a hinged cis arrangement about the Pd(2+) coordination spheres. For this hinged dimeric structure, the angles between the two coordination planes in each mol-ecule are 15.02 (5) and 14.91 (5)°. This hinged cis arragement also allows the two mol-ecules to form pairs linked by secondary inter-actions between the Pd and Se atoms [3.4307 (9) and 3.4317 (9) Å] of adjoining mol-ecules, leading to an overall tetra-meric structure. During the refinement stages, it was noticed that there were dichloromethane solvent mol-ecules present disordered about a twofold axis. After unsuccessful attempts were made to model this, they were removed using SQUEEZE.

Bis{µ-2-[(dimethyl-amino)-meth-yl]benzene-tellurolato}bis-[chlorido-palladium(II)] dichloro-methane hemisolvate.

The asymmetric unit of the title compound, [Pd(2)(C(9)H(12)NTe)(2)Cl(2)]·0.5CH(2)Cl(2), contains two half-mol-ecules, each lying on a twofold rotation axis; each mol-ecule is chiral and of the same enanti-omer. This is only possible as the mol-ecule has a hinged cis arrangement about the Pd(2+) coordination spheres. For this hinged dimeric structure, the angles between the two coordination planes in each mol-ecule are 21.59 (4) and 22.10 (4)°. This hinged cis arrangement also allows the two mol-ecules to form pairs linked by secondary inter-actions between the Pd and Te atoms of an adjoining mol-ecule, leading to a tetra-meric overall structure. C-H⋯Cl inter-actions consolidate the crystal packing.

Synthesis, structure, and glutathione peroxidase-like activity of amino acid containing ebselen analogues and diaryl diselenides.

The synthesis of some ebselen analogues and diaryl diselenides, which have amino acid functions as an intramolecularly coordinating group (Se···O) has been achieved by the DCC coupling procedure. The reaction of 2,2'-diselanediylbis(5-tert-butylisophthalic acid) or the activated ester tetrakis(2,5-dioxopyrrolidin-1-yl) 2,2'-diselanediylbis(5-tert-butylisophthalate) with different C-protected amino acids (Gly, L-Phe, L-Ala, and L-Trp) afforded the corresponding ebselen analogues. The used precursor diselenides have been found to undergo facile intramolecular cyclization during the amide bond formation reaction. In contrast, the DCC coupling of 2,2'-diselanediyldibenzoic acid with C-protected amino acids (Gly, L/D-Ala and L-Phe) affords the corresponding amide derivatives and not the ebselen analogues. Some of the representative compounds have been structurally characterized by single-crystal X-ray crystallography. The glutathione peroxidase (GPx)-like activities of the ebselen analogues and the diaryl diselenides have been evaluated by using the coupled reductase assay method. Intramolecularly stabilized ebselen analogues show slightly higher maximal velocity (V(max)) than ebselen. However, they do not show any GPx-like activity at low GSH concentrations at which ebselen and related diselenides are active. This could be attributed to the peroxide-mediated intramolecular cyclization of the corresponding selenenyl sulfide and diaryl diselenide intermediates generated during the catalytic cycle. Interestingly, the diaryl diselenides with alanine (L,L or D,D) amide moieties showed excellent catalytic efficiency (k(cat)/K(M)) with low K(M) values in comparison to the other compounds.

2-Phenoxyethanol derived diselenide and related compounds; synthesis of a seven-membered seleninate ester.

Syntheses of several diorganodiselenides and, in particular, a seven-membered cyclic seleninate ester derived from 2-phenoxyethanol are described. The seleninate ester was obtained from allyl (2-(2-hydroxyethoxy)phenyl) selenide through a series of oxidation and [2,3] sigmatropic rearrangement steps. The ester exhibits good GPx-like activity in the coupled reductase assay.