Syntheses and crystal structures of trimethyltin(IV) coordination polymers based on mixed ligands of 5-nitroisophthalate and 2,2′(4,4′)-bipy or phen

The trimethyltin(IV) polymer [(Me₃Sn)₂(nip) · EtOH]_n (1) of 5-nitroisophthalic acid (H₂nip) and its three derivatives with mixed organic N-donor ligands 2,2′-bipy [(Me₃Sn)₂(nip) · 2H₂O] · [(Me₃Sn)₂(nip) · H₂O] · 2(2,2′-bipy) (2) 4,4′-bipy {[(Me₃Sn)₂(nip)]₂(4,4′-bipy)}_n (3) or phen [(Me₃Sn)₂(nip) · H₂O] · (phen) (4) have been synthesized by the reaction of trimethyltin(IV) chloride and H₂nip when sodium ethoxide was added in the presence of 2,2′-bipy 4,4′-bipy or phen. All complexes 1–4 were characterized by elemental, IR, ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy and X-ray crystallography analyses. Crystal, data collection and structure refinement parameters for complexes 1, 2, 3 and 4 are shown in Table 1, Table 2, respectively. The X-ray data showed the geometries of all the tin atoms in complexes 1–4 are trigonal bipyramidal. The X-ray analysis of 1 showed that the structure was a polymeric infinite chain with neighboring triorganotin centers being linked by dicarboxylate ligands and hydrogen bonds were found between adjacent chains. For 2, two different monomers were found, in one monomer, Me₃Sn were coordinated to both carboxyl groups of the ligand and water molecules were coordinated to the two Sn(IV) centers. In the other monomer, water molecules were coordinated to only one Sn center. Co-crystallized2,2′-bipy was found in 2 and a 2D supermolecular structure was formed via O–H⋯O and O–H⋯N (N atoms derived from 2,2′-bipy) hydrogen bonds. In 3 however, a 2D polymeric block was formed due to the inversion center of the 4,4′-bipy. For 4, due to the O–H⋯O and O–H⋯N (N atoms derived from phen) hydrogen bonds and intermolecular Sn⋯O bonds, a 2D polymeric structure was formed.     

Acetato complexes of molybdenum(V): A novel tetranuclear core based on the metal–metal bonded {Mo2O4}2+ units

A series of acetato complexes of molybdenum(V), based on the singly metal–metal bonded {Mo₂O₄}²⁺ structural fragment, has been prepared. A dinuclear (PyH)₃[Mo₂O₄Cl₄(OOCCH₃)] · CH₃CN (1) (PyH⁺ = pyridinium cation, C₅H₅NH⁺) was obtained upon the reaction of (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ with the equimolar solution of pyridine and acetic acid in acetonitrile at ambient conditions. The acetato ligand in 1 is coordinated to a pair of molybdenum atoms in a syn–syn bidentate bridging manner. (PyH)_n[MoOBr₄]_n afforded in an analogous synthetic procedure a tetranuclear cluster, [Mo₄O₈(OOCCH₃)₃(OH)Py₄] · 1/2CH ₃CN · 1/2H₂O (3), with a novel core which may be envisioned as the acetate- and hydroxide-assisted assembly of {Mo₂O₄}²⁺ building blocks. Its structure is presented in terms of known tetranuclear clusters which are also composed of two {Mo₂O₄}²⁺ units. The acetato ligands in 3 adopted apart from bidentate bridging binding modes also a monodentate one. Partial substitution of chlorido ligands in (PyH)₃[Mo₂O₄Cl₄(OOCCH₃)] · CH₃CN (1) with pyridine resulted in a neutral [Mo₂O₄Cl(OOCCH₃)Py₃] · PrⁱOH · Py (2) which retained the original acetate coordination. The title compounds were fully characterized by X-ray diffraction studies and infrared vibrational spectroscopy.     

Expanding the 4,4′-bipyridine ligand: Structural variation in {M(pytpy)2}2+ complexes (pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine,M = Fe,Ni, Ru) and assembly of the hydrogen-bonded,one-dimensional polymer {[Ru(pytpy)(Hpytpy)]}n3n+

The solid state structures of [Ni(1)₂][NO₃]₂ · 2MeOH · 2H₂O, [Fe(1)₂][ClO₄]₂ · 2MeOH · 0.5H₂O, [Ru(1)₂][PF₆]₂ and [Ru(1)₂][PF₆][NO₃] (1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) are presented and the structural variation observed for the {M(1)₂}²⁺ unit is discussed. Protonation of the pendant pyridine group in [Ru(1)₂]²⁺ leads to the formation of a hydrogen-bonded, one-dimensional polymer [{Ru(1)(H1)}_n]³ⁿ⁺ exemplifed by the solid-state structure of [{Ru(1)(H1)}{Fe(NCS)₆} · 1.25H₂O]_n.     

Syntheses, characterization and crystal structure of diorganotin and triorganotin heterocyclicdicarboxylates with monomeric, 2D network and 3D framework structures

A series of new diorganotin and triorganotin(IV) heterocyclicdicarboxylates [(ⁿBu₃Sn)₂(2,5-pdc)]_∞ (1), {[(2-FC₆H₄CH₂)₃Sn]₂(2,5-pdc)}_∞ (2), {[(2-ClC₆H₄CH₂)₃Sn]₂(2,5-pdc)}_∞ (3), {[(4-CNC₆H₄CH₂)₃Sn]₂(2,5-pdc)}_∞ (4), {[(4-ClC₆H₄CH₂)₃Sn]₂(2,5-pdc)}_∞ (5), [(Ph)₂Sn(2,6-pdc)(H₂O)]_∞ (6), {[ⁿBu₃Sn(2,6-pdc)SnⁿBu₃]₂(H₂O)₂} · C₂H₃N (7) and {[Ph₃Sn(2,3-pdz)SnPh₃]₂(H₂O)} (8) have been obtained by reactions of diorganotin(IV) and triorganotin (IV) oxide with 2,6 or 2,5-H₂pdc (pdc = pyridinedicarboxylate) or 2,3-H₂pdz (pdz = pyrazinedicarboxylate). Complexes 1-8 were characterized by elemental, IR and NMR spectra analyses. The crystal and molecular structures of compounds 1, 6, 7 and 8 have been determined by X-ray single crystal diffraction. Compound 1 has 2D network structures. Compound 6 has 1D polymeric chain and 3D framework supramolecular structures due to the coordinated water molecules. Compound 7 has a monomeric structure, but the supramolecular structures are network.     

Synthesis,crystal structures and properties of three rare earth substituted germanotungstates: M/[α-GeW11O39] (M = Nd,Eu, and Tb)

Three new polyoxometalate compounds based on the lacunary Keggin anion [α-GeW₁₁O₃₉]^8? and the rare earth cations (Ln = Nd^III, Eu^III, Tb^III), [(CH₃)₄N]_2.5H_7.5[Eu(GeW₁₁O₃₉)(H₂O)₂]₂ · 4.5H₂O (1), [(CH₃)₄N]₂H₈[Tb(GeW₁₁O₃₉)(H₂O)₂]₂ · 2.5H₂O (2) and [Nd_0.5(H₂O)₂]H_0.5[Nd₂(GeW₁₁O₃₉)(DMSO)₂(H₂O)₈] · 5.5H₂O (3), have been synthesized and characterized by elemental analysis, inductively coupled plasmas (ICP) analysis, IR spectroscopy, single-crystal X-ray diffraction. The solid-state structures of compounds 1 and 2 consist of one-dimensional linear wires built of [α-GeW₁₁O₃₉]^8? anions connected by Eu³⁺/Tb³⁺ cations, while in compound 3, the introduction of the organic molecules DMSO (DMSO = dimethyl sulphoxide) leads to a double-parallel chainlike structure constructed by two linear wires {[Nd(1)(GeW₁₁O₃₉)(DMSO)(H₂O)₂]^5?}_n linked by Nd³⁺ coordination cation. Furthermore, the luminescent property of compound 1 and the thermal stability of compound 3 were also studied.     

Syntheses,characterization and redox properties of di- and poly-phosphine linked oligomeric complexes of oxo-centered triruthenium clusters

A series of phosphine-linked oligomers of oxo-centered triruthenium-acetate clusters have been prepared by the reaction of [Ru₃O(OAc)₆(py)₂(CH₃OH)](PF₆) (1) with di- or poly-phosphine. They have been characterized by elemental analysis, ESI-MS spectrometry, UV–Vis, IR, and ³¹P NMR spectroscopy, and cyclic and differential pulse voltammetry. The structures of diphosphine-linked dimeric compounds 4 and 7 were determined by X-ray crystallography. As revealed by redox wave splitting, weak to moderate electronic communication is operative between triruthenium clusters across bridging di- or poly-phosphine. With increase of the methylene number in Ph₂P(CH₂)_nPPh₂, electronic communication decreases rapidly in diphosphine-linked dimeric complexes [{Ru₃O(OAc)₆(py)₂}₂{μ-Ph₂P(CH₂)_nPPh₂}]²⁺ (n = 1–5).     

Two new N-heterocyclic carbene silver(I) complexes with the π–π stacking interactions

The precursors bis[N-(alkyl)benzimidazoliumylmethyl]durene halide (1a: alkyl = C₂H₅, halide = Br^?; 1b: alkyl = n-C₄H₉, halide = Cl^?; durene = 1,2,4,5-tetramethylbenzene) and their two new NHC silver(I) complexes [Durene(CH₂BimyEtAgBr)₂] (2a) and [Durene(CH₂BimyⁿBuAgCl)₂] (2b) (Bimy = benzimidazol-2-ylidene) have been prepared and characterized. In the crystal structures of 2a and 2b the aromatic π–π stacking interactions are observed.     

Influence of ligands on the fac⇌Δhνmer isomerization in [RuCl3(NO)(P–P)] complexes, [P–P = R2P(CH2)nPR2 (n = 1–3) and R2P(CH2)POR2, PR2–CHCH–PR2, R = Ph and (C6H11)2P-(CH2)2-P(C6H11)2]

[RuCl₃(NO)(P–P)], [P–P = R₂P(CH₂)_nPR₂ (n = 1–3) and R₂P(CH₂)POR₂, PR₂–CHCH–PR₂, R = Ph and (C₆H₁₁)₂P-(CH₂)₂-P(C₆H₁₁)₂] were obtained and characterized by ³¹P {¹H} NMR, IR spectroscopies and cyclic voltammetry. The structures of fac-[RuCl₃(NO)(P–P)], P–P = dppm (1), dppe (2), c-dppen (3) and dppp (4), mer-[RuCl₃(NO)(dcpe)] (6a) and mer-[RuCl₃(NO)(dppmO)] (7) have been determined by X-ray diffraction. Photochemical isomerization of fac- to mer-[RuCl₃(NO)(P–P)] was observed under white light in a CH₂Cl₂ solution and in solid state. The isomerization processes were followed by IR and ³¹P {¹H} spectra. The mer-[RuCl₃(¹⁵NO)(dppb)] isomer was used for the definition of the phosphorus atoms in the structure of the complex in solution. The electrochemical study shows that the oxidation/reduction processes observed in these complexes are dependent on both the isomer (fac or mer) and the solvent. In CH₂Cl₂, the NO⁺ reduction potentials are less negative for the mer-isomers than for the fac ones, while in CH₃CN solvent these potentials are, in general, very close for both isomers.     

Two novel erbium (III) coordination polymers with 5-nitroisophthalic acid: Syntheses and crystal structures and thermal stabilities

Two new coordination polymers, {[Er(5-nip)_1.5(2,2′-bipy)](H₂O)₂}_n (1) and {[Er(5-nip)₂] (4,4′-H₂bipy)_0.5}_n (2) (5-nip = 5-nitroisophthalic acid, 2,2′-bipy = 2,2′-bipyridyl, 4,4′-bipy = 4,4′-bipyridyl), have been synthesized by the hydrothermal reactions of erbium nitrate, 5-nitroisophthalic acid (5-H₂nip) and 2,2′-bipyridyl (for 1), and erbium nitrate, 5-nitroisophthalic acid and 4,4′-bipyridyl (for 2). X-ray diffraction analysis indicates that complex 1 exhibits a two-dimensional layer structure, while complex 2 displays a 3D architecture sustained by the strong hydrogen-bond interactions between the protonated 4,4′-bipyridyl and the carboxyl oxygen atom from [Er₂(5-nip)₄]²⁻ with 2D layer structure, and 4,4′-bipyridyl as the guest molecules exist in bilayer channel. They are characterized by the elemental analysis and IR spectroscopy. The studies for the thermal stabilities of the two complexes show that complex 2 is more stable than complex 1.     

Solvatomorphs of dimeric transition metal complexes based on the V4O12 cyclic anion as building block: Crystalline packing and magnetic properties

Dinuclear [{M(phen)₂}₂V₄O₁₂] · C₆H₁₂O · H₂O (M = Co^II 1, Mn^II 2, Ni^II 3 and Cu^II 4) and [{Cu(phen)₂}₂V₄O₁₂] · 3.5H₂O 5 has been prepared by biphasic and hydrothermal syntheses, respectively. All five structures exhibit the {V₄O₁₂}^4? cluster in a chair-like configuration, covalently bonded to two [M(phen)₂]²⁺ fragments, producing a super-exchange magnetic phenomenon. The magnetic study of complexes 1–5 shows that they are very weak antiferromagnetically coupled systems, with J values of ?0.14, 2; ?0.64, 3 and ?0.23, 4 cm^?1. Complexes 1 to 3 correspond to isostructural compounds in which the cyclovanadate group acts as a bidentate bridged ligand. In the copper complexes (4 and 5) the {V₄O₁₂}^4? anion presents the novel monodentate bridging mode, and therefore a more significant distortion from the chair-like configuration. The mentioned complexes, together with that reported in the literature, permit to conclude that it is quite common for a single molecular species to exist in more than one crystalline arrangement. A detailed analysis of the structures of 1–4 shows that the crystal symmetry cannot be strictly centrosymmetric, due to the presence of the cyclohexanol molecule with a single –OH group in the lattice.     

Dimerisation versus polymerisation: Affects of donor position in isomeric dilithium diamine-bis(phenolate) complexes

The synthesis and structures of isomeric lithium diamine-bis(phenolate) complexes are reported. Deprotonation of the ligands, H₂O₂NN′^tBu [Me₂NCH₂CH₂N(CH₂ArOH)₂, Ar = 3,5-C₆H₂-^tBu₂] and H₂O₂N₂^tBu [HOArCH₂NMeCH₂CH₂NMeCH₂ArOH, Ar = 3,5-C₆H₂-^tBu₂], in diethyl ether affords base-free lithium complexes Li₂O₂NN′^tBu (1) and Li₂O₂N₂^tBu (2) upon solvent removal. The dioxane adduct of (1) exhibits a polymeric structure in the solid-state, whereas the dioxane adduct of (2) possesses a dimeric structure. The syntheses of K₂O₂NN′^tBu (3), K₂O₂N₂^tBu (4), Zr(O₂NN′^tBu)Cl₂ (5) and Y(O₂NN′^tBu)Cl(THF), (6), are also reported. The transition metal complexes were isolated in good yields via salt metathesis reactions using 1 or 3.     

Comparing anti-HIV,antibacterial, antifungal,micellar, and cytotoxic properties of tricarboxylato dendritic amphiphiles

Three series of homologous dendritic amphiphiles—RCONHC(CH₂CH₂COOH)₃, 1(n); ROCONHC(CH₂CH₂COOH)₃, 2(n); RNHCONHC(CH₂CH₂COOH)₃, 3(n), where R = n-C_nH_2n+1 and n = 13–22 carbon atoms—were assayed for their potential to serve as antimicrobial components in a topical vaginal formulation. Comparing epithelial cytotoxicities to the ability of these homologues to inhibit HIV, Neisseria gonorrhoeae, and Candida albicans provided a measure of their prophylactic/therapeutic potential. Measurements of the ability to inhibit Lactobacillus plantarum, a beneficial bacterium in the vagina, and critical micelle concentrations (CMCs), an indicator of the potential detergency of these amphiphiles, provided additional assessments of safety. Several amphiphiles from each homologous series had modest anti-HIV activity (EC₅₀ = 110–130 μM). Amphiphile 2(18) had the best anti-Neisseria activity (MIC = 65 μM), while 1(19) and 1(21) had MICs against C. albicans of 16 and 7.7 μM, respectively. Two measures of safety showed promise as all compounds had relatively low cytotoxic activity (EC₅₀ = 210–940 μM) against epithelial cells and low activity against L. plantarum, 1(n), 2(n), and 3(n) had MICs ? 490, 1300, and 940 μM, respectively. CMCs measured in aqueous triethanolamine and in aqueous potassium hydroxide showed linear dependences on chain length. As expected, the longest chain in each series had the lowest CMC—in triethanolamine: 1(21), 1500 μM; 2(22), 320 μM; 3(22), 340 μM, and in potassium hydroxide: 1(21), 130 μM; 3(22), 40 μM. The CMC in triethanolamine adjusted to pH 7.4 was 400 μM for 1(21) and 3900 μM for 3(16). The promising antifungal activity, low activity against L. plantarum, relatively high CMCs, and modest epithelial cytotoxicity in addition to their anti-Neisseria properties warrant further design studies with dendritic amphiphiles to improve their safety indices to produce suitable candidates for antimicrobial vaginal products.     

Copper(II) and zinc(II) complexes with Schiff-base ligands derived from salicylaldehyde and 3-methoxysalicylaldehyde: Synthesis,crystal structures,magnetic and luminescence properties

The following Schiff bases were employed as ligands in synthesizing copper(II) and zinc(II) complexes: N-[(2-pyridyl)-methyl]-salicylimine (Hsalampy), N-[2-(N,N-dimethyl-amino)-ethyl]-salicylimine (Hsaldmen), and N-[(2-pyridyl)-methyl]-3-methoxy-salicylimine (Hvalampy). The first two ligands were obtained by reacting salicylaldehyde with 2-aminomethyl-pyridyne and N,N-dimethylethylene diamine, respectively, while the third one results from the condensation of 3-methoxysalicylaldehyde with 2-aminomethyl-pyridine. Four new coordination compounds were synthesized and structurally characterized: [Cu(salampy)(H₂O)(ClO₄)] 1, [Cu₂(salampy)₂(H₂trim)₂] 2 (H₂trim^? = the monoanion of the trimescic acid), [Cu₄(valampy)₄](ClO₄)₄ · 2CH₃CN 3, and [Zn₃(saldmen)₃(OH)](ClO₄)₂ · 0.25H₂O 4. The crystal structure of 1 consists of supramolecular dimers resulted from hydrogen bond interactions established between mononuclear [Cu(salampy)(H₂O)(ClO₄)] complexes. Compound 2 is a binuclear complex with the copper ions connected by two monoatomic carboxylato bridges arising from two molecules of monodeprotonated trimesic acid. The crystal structure of 3 consists of tetranuclear cations with a heterocubane {Cu₄O₄} core, and perchlorate ions. Compound 4 is a trinuclear complex with a defective heterocubane structure. The magnetic properties of complexes 1–3 have been investigated. Compound 4 exhibits solid-state photoluminescence at room temperature.     

Synthesis and structures of three,four, and six-coordinate monomeric tin(II) and tin(IV) compounds containing η2-ketiminate ligands

A series of Sn(II) and Sn(IV) compounds containing ketiminate ligands were synthesized. Reactions of SnCl₂ with 1 or 2 equiv. Li[OCMeCHCMeNAr] (where Ar = 2,6-diisopropylphenyl) generate [OCMeCHCMeNAr]SnCl (1) and [OCMeCHCMeNAr]₂Sn (2) in moderate yield, respectively. Similarly, reacting SnCl₄ with 2 equiv. Li[OCMeCHCMeNAr] yields a six-coordinated [OCMeCHCMeNAr]₂SnCl₂ (3). Divalent tin compound 2 can be oxidized with I₂ in diethyl ether to generate tetravalent tin compound [OCMeCHCMeNAr]₂SnI₂ (4) in moderate yield. Compounds 1–4 have been characterized by ¹H and ¹³C NMR spectroscopy and have been analyzed by X-ray crystallography. Theoretical calculation found that the bonding of ketiminate ligands and tin atom in compound 2 has a strong ionic character.     

Radiosynthesis of N-(4-chloro-3-[11C]methoxyphenyl)-2-picolinamide ([11C]ML128) as a PET radiotracer for metabotropic glutamate receptor subtype 4 (mGlu4)

N-(Chloro-3-methoxyphenyl)-2-picolinamide (3, ML128, VU0361737) is an mGlu₄ positive allosteric modulator (PAM), which is potent and centrally penetrating. 3 is also the first mGlu₄ PAM to show efficacy in a preclinical Parkinson disease model upon systemic dosing. As a noninvasive medical imaging technique and a powerful tool in neurological research, positron emission tomography (PET) offers a possibility to investigate mGlu₄ expression in vivo under physiologic and pathological conditions. We synthesized a carbon-11 labeled ML128 ([¹¹C]3) as a PET radiotracer for mGlu₄, and characterized its biological properties in Sprague Dawley rats. [¹¹C]3 was synthesized from N-(4-chloro-3-hydroxyphenyl)-2-picolinamide (2) using [¹¹C]CH₃I. Total synthesis time was 38 ± 2.2 min (n = 7) from the end of bombardment to the formulation. The radioligand [¹¹C]3 was obtained in 27.7 ± 5.3% (n = 5) decay corrected radiochemical yield based on the radioactivity of [¹¹C]CO₂. The radiochemical purity of [¹¹C]3 was >99%. Specific activity was 188.7 ± 88.8 GBq/mol (n = 4) at the end of synthesis (EOS).PET images were conducted in 20 normal male Sprague Dawley rats including 11 control studies, 6 studies blocking with an mGlu₄ modulator (4) to investigate specificity and 3 studies blocking with an mGlu₅ modulator (MTEP) to investigate selectivity. These studies showed fast accumulation of [¹¹C]3 (peak activity between 1–3 min) in several brain areas including striatum, thalamus, hippocampus, cerebellum, and olfactory bulb following with fast washout. Blocking studies with the mGlu₄ modulator 4 showed 22–28% decrease of [¹¹C]3 accumulation while studies of selectivity showed only minor decrease supporting good selectivity over mGlu₅. Biodistribution studies and blood analyses support fast metabolism. Altogether this is the first PET imaging ligand for mGlu₄, in which the labeled ML128 was used for imaging its in vivo distribution and pharmacokinetics in brain.     

New cytotoxic steroidal saponins from Cestrum parqui

Two new steroidal saponins, 25(R)-3β [(O-β-d-glucopyranosyl-(1 → 3)-β-d-glucopyranosyl-(1 → 2)-O-[β-d-xylopyranosyl-(1 → 3)-O-β-d-glucopyranosyl-(1 → 4)-β-d-galactopyranosyl)oxy]-5α, 15β, 22R, 25R-spirostan-3,15-diol (1, named parquispiroside) and 25R-26-[(β-d-glucopyranosyl)Oxy]-(3β [(O-β-d-glucopyranosyl-(1 → 3)-β-d-glucopyranosyl-(1 → 2)-O-[β-d-xylopyranosyl-(1 → 3)-O-β-d-glucopyranosyl-(1 → 4)-β-d-galactopyranosyl)oxy], 5α, 15β, 22R, 25R)-furostane-3,15,22-triol (2, named parquifuroside), along with the known saponins, capsicoside D (3) and 22-OMe-capsicoside D (4) and the known glycoside, benzyl primeveroside (5), were isolated from the leaves of Cestrum parqui. The structures of these compounds were elucidated by careful analysis of 1D and 2D NMR spectra and ESIMS data. Parquispiroside (1) exhibited moderate inhibition of Hela, HepG2, U87, and MCF7 cell lines with IC₅₀ values in the range of 3.3–14.1 μM.     

Dicarboxylatodirhodium derivatives of polyoxotungstates

Salts of the new complexes [PW₁₁O₃₉{Rh₂(O₂CR)₂}]⁵⁻; R = Prⁿ (1), CH₂Cl (2), CH₂OH (3), o-C₆H₄OH (4), p-C₆H₄OH (5), and [XW₁₁O₃₉{Rh₂(p-O₂CC₆H₄OH)₂}]⁶⁻; X = Si (6), Ge (7) have been prepared in good yield and characterized by elemental analysis, multinuclear NMR spectroscopy, and structural crystallography of the cesium salts of anions 1 and 5 with chloride ions in axial positions of the dirhodium moiety. The incorporation of the dirhodium group into the Keggin structure significantly increases the hydrolytic kinetic stability of the polyoxotungstates at pH 7–8.5, a result that has implications for the use of such complexes for imaging and for phase determination in structural studies of large biomolecules. Based on NMR studies, the axial sites of the dirhodium moiety of the polytungstate anions are accessible to ligation by molecules such as cysteine, methionine, and isonicotinic acid.     

Voulkensin C–E,new 11-oxocassane-type diterpenoids and a steroid glycoside from Caesalpinia volkensii stem bark and their antiplasmodial activities

A bioassay guided isolation of potential antimalarial molecules from the stem bark of Caesalpinia volkensii Harms (Fabaceae) achieved three new 11-oxocassane-type diterpenoids named voulkensin C (1), D (2) and E (3) together with one steroid glycoside named 3-O-[β-glucopyranosyl(1→2)-O-β-xylopyranosyl]-stigmasterol (4) and seven other known compounds including stigmasterol (5), β-sitosterol (6), oleanolic acid (7), 3-β-acetoxyolean-12-en-28-methyl ester (8), voucap-5-ol (9), caesadekarin C (10), deoxycaesaldekarin C (11). The structures of the new compounds were determined on the basis of extensive spectroscopic data (IR, MS, ¹H and ¹³C NMR and 2D NMR) analyses. The polar extracts revealed moderate to good antiplasmodial activities against chloquine-sensitive (D6) and -resistant strains (W2) of Plasmodium falciparum. Whereas the pure isolates exhibited limited to moderate antiplasmodial activities with compound 4 showing the highest antiplasmodial activities (IC₅₀ values of 4.44 ± 0.88 and 2.74 ± 1.10 μM against D6 and W2 strains, respectively). These results suggest a possible contribution of phytochemicals from C. volkensii stem bark towards inhibition of plasmodial parasites’ growth hence potential antimalarial.     

Pterocarpans and isoflavones from the root bark of Millettia micans and of Millettia dura

From the CH₂Cl₂/CH₃OH (1:1) extract of the root bark of Millettia micans, a new pterocarpan, (6aR,11aR)-3-hydroxy-7,8,9-trimethoxypterocarpan (1), named micanspterocarpan, was isolated. Similar investigation of the CH₂Cl₂/CH₃OH (1:1) extract of the root bark of Millettia dura gave a further new pterocarpan, (6aR,11aR)-8,9-methylenedioxy-3-prenyloxypterocarpan (2), named 3-O-prenylmaackiain, along with six known isoflavones (3-8) and a chalcone (9). All purified compounds were identified by NMR and MS, whereas the absolute configurations of the new pterocarpans were established by chriptical data analyses including quantum chemical ECD calculation. Among the isolated constituents, calopogonium isoflavone B (3) and isoerythrin A-4′-(3-methylbut-2-enyl) ether (4) showed marginal activities against the 3D7 and the Dd2 strains of Plasmodium falciparum (70–90% inhibition at 40 μM). Maximaisoflavone B (5) and 7,2′-dimethoxy-4′,5′-methylenedioxyisoflavone (7) were weakly cytotoxic (IC₅₀ 153.5 and 174.1 μM, respectively) against the MDA-MB-231 human breast cancer cell line. None of the tested compounds showed in-vitro translation inhibitory activity or toxicity against the HEK-293 human embryonic kidney cell line at 40 μM.     

Magnetostructural correlations and catecholase-like activities of μ-alkoxo-μ-carboxylato double bridged dinuclear and tetranuclear copper(II) complexes

Two μ-alkoxo-μ-carboxylato bridged dinuclear copper(II) complexes, [Cu₂(L¹)(μ-HCO₂)] (1) ((H₃L¹ = 1,3-bis(5-bromosalicylideneamino)-2-propanol)), [Cu₂(L²)(μ-HCO₂)] · dmf (2) (H₃L² = 1,3-bis(3,5-chlorosalicylideneamino-2-propanol)), and two μ-alkoxo-μ-dicarboxylato doubly bridged tetranuclear copper(II) complexes, [{Cu₂(L³)}₂(μ-O₂C–C(CH₃)₂–CO₂)] · 5H₂O · 3CH₃OH (3) ((H₃L³ = 1,3-bis(salicylid-deneamino)-2-propanol)) and [{Cu₂(L³)}₂(μ- O₂CCH₂–C₆H₄–CH₂CO₂)] · 2H₂O (4) have been prepared and characterized. The single crystal X-ray analysis shows that the structures of complexes 1 and 2 are dimeric with two adjacent copper(II) atoms bridged by μ-alkoxo-μ-carboxylato ligands with the Cu⋯Cu distances and Cu–O(alkoxo)–Cu angles are 3.511 Å and 132.85° for 1, 3.517 Å and 131.7° for 2, respectively. Complexes 3 and 4 consist of μ-alkoxo-μ-dicarboxylato doubly bridged tetranuclear Cu(II) complexes with mean Cu–Cu distances and Cu–O–Cu angles of 3.158 Å and 108.05° for 3 and 3.081 Å and 104.76° for 4, respectively. Magnetic measurements reveal that 1 and 2 are strong antiferromagnetically coupled with 2J = −156 and −152 cm⁻¹, respectively, while 3 and 4 exhibit ferromagnetic coupling with 2J = 86 and 155.2 cm⁻¹, respectively. The 2J values of 1–4 are linearly correlated to the Cu–O–Cu angles. Dependence of the pH at 25 °C on the reaction rate of oxidation of 3,4-di-tert-butylcatechol (3,5-dtbc) to the corresponding quinone catalyzed by 1–4 was studied. Complexes 1–4 exhibit high catecholase-like activity at pH 9.0 and 25 °C for oxidation of 3,5-di-tert-butylcatechol.