Carboxy-derived (tpy)2Ru complexes as sub-units in supramolecular architectures: The solubilized ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy and its homoleptic Ru(II) complex

We herein describe the synthesis and characterization of a series of homoleptic, Ru(II) complexes bearing peripheral carboxylic acid functionality based upon the novel ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy (L₁), as well as 4′-(4-carboxyphenyl)tpy (L₂) and 4′-(carboxy)tpy (L₃) (where tpy = 2,2′: 6′,2″-terpyridine). Inspection of the metal-based oxidations (E_1/2 = 1.22-1.42 V) indicates an anodic shift (∼0.2 V) for (L₃)₂Ru²⁺ (3b) (E_1/2 = 1.40 V) relative to (L₂)₂Ru²⁺ (2b) (E_1/2 = 1.22 V). The metal-based oxidation (E_1/2 = 1.22 V) and ligand-based reductions (E_1/2 = −1.25 to −1.52 V) of (L₁)₂Ru²⁺ (1) are essentially invariant relative to those of the structural analogue 2b (PF₆)₂, which suggests no significant electronic effect caused by the tert-butyl groups. This is supported by invariance in the metal-to-ligand charge transfer bands in both the electronic absorption (494-489 nm) and emission spectra (654-652 nm). However, contrary to 2b, complex 1 is both very soluble and exhibits a highly porous solid-state structure with internal cavity dimensions of 15 Å × 14 Å due to the preclusion of inter-annular interactions by the bulky tert-butyl substituents.     

Synthesis, structures and in vitro cytotoxicity of some cationic cis-platinum(II) complexes containing chelating thiocarbamates

The thiocarbamates 4-RC₆H₄NHC(S)NR₂′ (R = H, Cl; R′ = Me, Et), 4-ClC₆H₄NHC(S)NR (NR = 2-pyridylpiperazine) react with cis-[PtCl₂(PTA)₂] (PTA = 1,3,5-triaza-7-phosphaadamantane) in the presence of base to afford the monocationic platinum(II) complexes cis-[Pt{SC(NR₂′) = NC₆H₄R}(PTA)₂]⁺ (R = H, Cl; R′ = Me, Et), cis-[Pt{SC(NR) = NC₆H₄Cl}(PTA)₂]⁺ (NR = 2-pyridylpiperazine), which were isolated as their PF₆ salts in high yields. The complexes were fully characterised spectroscopically and also by X-ray crystallography. Cytotoxicity of these complexes was studied in vitro in three human cancer cell lines (CH1, A549 and SW480) using the MTT assay.     

H NMR spectroscopy as a tool to determine accurate photoisomerization quantum yields of stilbene-like ligands coordinated to rhenium(I) polypyridyl complexes

In this work, the use of proton nuclear magnetic resonance, ¹H NMR, was fully described as a powerful tool to follow a photoreaction and to determine accurate quantum yields, so called true quantum yields (Φ_true), when a reactant and photoproduct absorption overlap. For this, Φ_true for the trans-cis photoisomerization process were determined for rhenium(I) polypyridyl complexes, fac-[Re(CO)₃(NN)(trans-L)]⁺ (NN = 1,10-phenanthroline, phen, or 4,7-diphenyl-1,10-phenanthroline, ph₂phen, and L = 1,2-bis(4-pyridyl)ethylene, bpe, or 4-styrylpyridine, stpy). The true values determined at 365 nm irradiation (e.g. Φ_NMR = 0.80 for fac-[Re(CO)₃(phen)(trans-bpe)]⁺) were much higher than those determined by absorption spectral changes (Φ_UV-Vis = 0.39 for fac-[Re(CO)₃(phen)(trans-bpe)]⁺). Φ_NMR are more accurate in these cases due to the distinct proton signals of trans and cis-isomers, which allow the actual determination of each component concentration under given irradiation time. Nevertheless when the photoproduct or reactant contribution at the probe wavelength is negligible, one can determine Φ_true by regular absorption spectral changes. For instance, Φ_313 nm for free ligand photoisomerization determined both by absorption and ¹H NMR variation are equal within the experimental error (bpe: Φ_UV-Vis = 0.27, Φ_NMR = 0.26; stpy: Φ_UV-Vis = 0.49, Φ_NMR = 0.49). Moreover, ¹H NMR data combined with electronic spectra allowed molar absorptivity determination of difficult to isolate cis-complexes.     

Influence of ammonium sulphate feeding time on fed-batch Arthrospira (Spirulina) platensis cultivation and biomass composition with and without pH control

Previous work demonstrated that a mixture of NH₄Cl and KNO₃ as nitrogen source was beneficial to fed-batch Arthrospira (Spirulina) platensis cultivation, in terms of either lower costs or higher cell concentration. On the basis of those results, this study focused on the use of a cheaper nitrogen source mixture, namely (NH₄)₂SO₄ plus NaNO₃, varying the ammonium feeding time (T = 7-15 days), either controlling the pH by CO₂ addition or not. A. platensis was cultivated in mini-tanks at 30 °C, 156 μmol photons m⁻² s⁻¹, and starting cell concentration of 400 mg L⁻¹, on a modified Schlösser medium. T = 13 days under pH control were selected as optimum conditions, ensuring the best results in terms of biomass production (maximum cell concentration of 2911 mg L⁻¹, cell productivity of 179 mg L⁻¹ d⁻¹ and specific growth rate of 0.77 d⁻¹) and satisfactory protein and lipid contents (around 30% each).     

Cu(II) complexes with labile apical coordination: Synthesis, crystal structure, H NMR investigation, and oxidation properties of mononuclear [Cu(dien)(2-PhIm)(ClO4)] (1), [Cu(dien)(2-MeBzIm)] (2), complexes

The compounds [Cu(dien)(2-PhIm)(ClO₄)](ClO₄) (1); [Cu(dien)(2-MeBzIm)](ClO₄)₂ (2); where dien = diethylenetriamine, 2-PhIm = 2-phenylimidazole and 2-MeBzIm = 2-methylbenzimidazole, were synthesized and characterized. The complexes possessing [Cu(II)dien] moiety as common, the former containing 2-phenylimidazole, yielded square pyramidal geometry with apical perchlorate coordination [Cu1-O(5) = 2.449 Å], while the latter with 2-methylbenzimidazole formed square planar geometry with weak perchlorate contact [Cu1-O(8) = 2.596 Å] in its apical position. The effect of solvent and the variable temperature ¹H NMR investigation combinedly explore the geometrical rearrangement towards five coordination around Cu(II) metal center by accommodating the solvent molecule in its fifth coordination. Possessing easily labile perchlorate anion, both these complexes were investigated for their oxidation capability using 3,5-di-tert-butyl catechol (DTBC). The rate constant determined for the oxidation of DTBC to corresponding quinone indicates that they are catalytically quite similar and the k_cat of 1 ≈ 2. The crystal structure and the NMR investigations are discussed in detail.     

Spontaneous, intervesicular transfer rates of fluorescent, acyl chain-labeled phosphatidylcholine analogs

It was recently shown that the structure of the fluorophore attached to the acyl chain of phosphatidylcholine analogs determines their mechanism of transport across the plasma membrane of yeast cells (Elvington et al., J. Biol Chem. 280:40957, 2005). In order to gain further insight into the physical properties of these fluorescent phosphatidylcholine (PC) analogs, the rate and mechanism of their intervesicular transport was determined. The rate of spontaneous exchange was measured for PC analogs containing either NBD (7-nitrobenz-2-oxa-1,3-diazol-4-yl), Bodipy FL (4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene), Bodipy 530 (4,4-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene), or Bodipy 581 (4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene) attached to a five or six carbon acyl chain in the sn-2 position. The rate of transfer between phospholipid vesicles was measured by monitoring the increase in fluorescence as the analogs transferred from donor vesicles containing self-quenching concentrations to unlabeled acceptor vesicles. Kinetic analysis indicated that the transfer of each analog occurred by diffusion through the water phase as opposed to transfer during vesicle collisions. The vesicle-to-monomer dissociation rate constants differed by over four orders of magnitude: NBD-PC (k_dis = 0.115 s^− 1; t_1/2 = 6.03 s); Bodipy FL-PC (k_dis = 5.2 × 10^− 4; t_1/2 = 22.2 min); Bodipy 530-PC (k_dis = 1.52 × 10^− 5; t_1/2 = 12.6 h); and Bodipy 581-PC (k_dis = 5.9 × 10^− 6; t_1/2 = 32.6 h). The large differences in spontaneous rates of transfer through the water measured for these four fluorescent PC analogs reflect their hydrophobicity and may account for their recognition by different mechanisms of transport across the plasma membrane of yeast.     

Synthesis and characterization of platinum(II) complexes of 2N1O-donor ligands with a pendent indole ring

The Pt(II) complexes of 2N1O-donor ligands containing a pendent indole, 3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-iepp), and 1-methyl-3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-miepp) (H denotes an ionizable hydrogen), were synthesized, and the structure of [Pt(tbu-iepp)Cl] (1) was determined by X-ray analysis. Complex 1 prepared in CH₃CN was revealed to have the C2 atom of the indole ring bound to Pt(II) with the Pt(II)-C2 distance of 1.981(3) Å. On the other hand, [Pt(tbu-miepp)Cl] (2) was concluded to have a phenolate coordination instead of the C2 atom of the indole ring by ¹H NMR spectra. Reaction of 1 with 1 equiv. of Ce(IV) in DMF gave the corresponding one-electron oxidized species, which exhibited an ESR signal at g = 2.004 and an absorption peak at 567 nm, indicating the formation of the Pt(II)-indole-π-cation radical species. The half-life, t_1/2, of the radical species at −60 °C was calculated to be 43 s (k_obs = 1.6 × 10⁻² s⁻¹).     

Synthesis, characterization, and reactivity of (π-allyl)palladium(II) wrap-around complexes with 1,3-dienes

Synthesis of a series of cationic “wrap-around” complexes, η³-, η²- (CH₂-CH-CHR-CH₂-CH₂-CHCHX) Pd(II)L⁺ (R = H, CH₃; X = H, Cl, CO₂Me; L = PPh₃, P(C₄H₄N)₃), is described. These chelate complexes were prepared by exposure of π-allyl chloride dimers, (η³-(CH₂-CX-CH₂)PdCl)₂, to either 1,3-butadiene or isoprene to yield π-allyl chloride dimers of the type (η³-CH₂CHCRCH₂CH₂CH = CH(X)PdCl)₂ which result from insertion of the diene into each π-allyl unit. Abstraction of chloride with either AgSbF₆ or NaB(Ar_F)₄ in the presence of L gives the cationic wrap-around complexes in high yields. Single crystal X-ray diffraction studies of 8a (R = -CH₃, X = -Cl, L = PPh₃) and 9a (R = -H, X = -Cl, L = PPh₃) show that Pd(II) adopts essentially a square planar geometry and the chelate arm occupies a syn orientation with respect to the allyl unit. Exposure of these wrap-around complexes to nitriles of differing basicities displaces the chelated alkene to varying extents and allows assessment of the relative strengths of chelation as a function of substituents, X and R. Initial rapid displacement of the chelated alkene yields a syn-π-allyl isomer which equilibrates with the anti-π-allyl isomer which cannot close to form a chelate. Treatment of 8b with 1,3-butadiene gives not polybutadiene but 2-chloro-4-methyl-1,E-4,6-heptatriene and 2-chloro-4-methyl-1,Z-4,6-heptatriene. Formation of these trienes is first-order in butadiene. This reaction serves as a model for chain-transfer in the polymerization of butadiene.     

Modulation of trans-to-cis photoisomerization and photoluminescence of 1,2-bis(4-pyridyl)ethylene or 4-styrylpyridine coordinated to fac-tricarbonyl(5-chloro-1,10-phenathroline)rhenium(I)

Photochemical and photophysical properties of fac-[Re(CO)₃(Clphen)(trans-L)]⁺ complexes, Clphen = 5-chloro-1,10-phenathroline and L = 1,2-bis(4-pyridyl)ethylene, bpe, or 4-styrylpyridine, stpy, were investigated to complement the understanding of intramolecular energy transfer process in tricarbonyl rhenium(I) complexes having an electron withdrawing group attached to polypyridyl ligands. These new compounds were synthesized, characterized and the photoisomerization quantum yields were accurately determined by ¹H NMR spectroscopy. The true quantum yields for fac-[Re(CO)₃(Clphen)(trans-bpe)]⁺ were constant (Φ = 0.55) at all investigated irradiation wavelengths. However, for fac-[Re(CO)₃(Clphen)(trans-stpy)]⁺, similar true quantum yields were observed only at higher energy irradiation (Φ_{313 nm} = 0.53 and Φ_{365 nm} = 0.57), but it decreased significantly at 404 nm (Φ = 0.41). These results indicated different deactivation pathways for the trans-stpy complex photoisomerization. Quantum yields decreased as the ³IL_trans-L and ³MLCT_Re→NN excited states become closer and the behavior was discussed in terms of the excited state energy gaps. Additionally, luminescence properties of photoproducts, fac-[Re(CO)₃(Clphen)(cis-L)]⁺, were also investigated in different environments to analyze the relative energy of the ³MLCT_Re→Clphen excited state for each compound.     

Chemical implantation of Group 4 cations on silica via cyclopentadienyl- and N,N-dialkylcarbamato derivatives

Chemical implantation of Group 4 cations [Ti(III), Ti(IV), Zr(IV), Hf(IV)] has been carried out under mild conditions by the reaction of polycyclopentadienyl- (MCp_n; M = Ti, n = 3, 4; M = Zr, Hf, n = 4), mixed cyclopentadienyl/N,N-dialkylcarbamato (ML_x(O₂CNEt₂)_y; M = Ti, L = Cp, C₅Me₅ (Cp*), x = 2, y = 1; M = Hf, L = Cp, x = 1, y = 3), and N,N-dialkylcarbamato (M(O₂CNR₂)_n, M = Ti, n = 3, R = ⁱPr; M = Ti, Hf, n = 4, R = Et; M = Zr, n = 4, R = ⁱPr) derivatives, with the silanol groups of amorphous silica. Cyclopentadiene/pentamethylcyclopentadiene and/or carbon dioxide and the secondary amine are released in the process. The amount of implanted cations depends on the metal and on the ligands, the pentamethylcyclopentadienyl complex being less reactive than the unsubstituted congener. The starting complexes and the final products have been characterized by EPR or by ¹³C CP-MAS NMR spectroscopy.     

Repellent activity of catmint, Nepeta cataria, and iridoid nepetalactone isomers against Afro-tropical mosquitoes, ixodid ticks and red poultry mites

The repellent activity of the essential oil of the catmint plant, Nepeta cataria (Lamiaceae), and the main iridoid compounds (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone, was assessed against (i) major Afro-tropical pathogen vector mosquitoes, i.e. the malaria mosquito, Anopheles gambiae s.s. and the Southern house mosquito, Culex quinquefasciatus, using a World Health Organisation (WHO)-approved topical application bioassay (ii) the brown ear tick, Rhipicephalus appendiculatus, using a climbing repellency assay, and (iii) the red poultry mite, Dermanyssus gallinae, using field trapping experiments. Gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS) analysis of two N. cataria chemotypes (A and B) used in the repellency assays showed that (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone were present in different proportions, with one of the oils (from chemotype A) being dominated by the (4aS,7S,7aR) isomer (91.95% by GC), and the other oil (from chemotype B) containing the two (4aS,7S,7aR) and (4aS,7S,7aS) isomers in 16.98% and 69.83% (by GC), respectively. The sesquiterpene hydrocarbon (E)-(1R,9S)-caryophyllene was identified as the only other major component in the oils (8.05% and 13.19% by GC, respectively). Using the topical application bioassay, the oils showed high repellent activity (chemotype A RD₅₀ = 0.081 mg cm⁻² and chemotype B RD₅₀ = 0.091 mg cm⁻²) for An. gambiae comparable with the synthetic repellent DEET (RD₅₀ = 0.12 mg cm⁻²), whilst for Cx. quinquefasciatus, lower repellent activity was recorded (chemotype A RD₅₀ = 0.34 mg cm⁻² and chemotype B RD₅₀ = 0.074 mg cm⁻²). Further repellency testing against An. gambiae using the purified (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone isomers revealed overall lower repellent activity, compared to the chemotype A and B oils. Testing of binary mixtures of the (4aS,7S,7aR) and (4aS,7S,7aS) isomers across a range of ratios, but all at the same overall dose (0.1 mg), revealed not only a synergistic effect between the two, but also a surprising ratio-dependent effect, with lower activity for the pure isomers and equivalent or near-equivalent mixtures, but higher activity for non-equivalent ratios. Furthermore, a binary mixture of (4aS,7S,7aR) and (4aS,7S,7aS) isomers, in a ratio equivalent to that found in chemotype B oil, was less repellent than the oil itself, when tested at two doses equivalent to 0.1 and 0.01 mg chemotype B oil. The three-component blend including (E)-(1R,9S)-caryophyllene at the level found in chemotype B oil had the same activity as chemotype B oil. In a tick climbing repellency assay using R. appendiculatus, the oils showed high repellent activity comparable with data for other repellent essential oils (chemotype A RD₅₀ = 0.005 mg and chemotype B RD₅₀ = 0.0012 mg). In field trapping assays with D. gallinae, addition of the chemotype A and B oils, and a combination of the two, to traps pre-conditioned with D. gallinae, all resulted in a significant reduction of D. gallinae trap capture. In summary, these data suggest that although the nepetalactone isomers have the potential to be used in human and livestock protection against major pathogen vectors, intact, i.e. unfractionated, Nepeta spp. oils offer potentially greater protection, due to the presence of both nepetalactone isomers and other components such as (E)-(1R,9S)-caryophyllene.     

Interfacial electron transfer on TiO2 sensitized with an axially anchored trans tetradentate Ru(II) compound

The ruthenium complexes, trans-[Ru(phen-NH-phen)(eina)₂](PF₆)₂ and trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ where phen-NH-phen = N,N-bis(1,10-phenanthroline-2-yl)amine, ina = isonicotinic acid and eina = ethyl isonicotinate, have been synthesized and characterized by ¹H NMR, elemental analysis, and IR spectroscopy. The compounds were non-emissive at room temperature, but displayed intense photoluminescence in 4:1 ethanol/methanol glasses at 77 K with corrected emission maximum at 570-580 nm. A quasi-reversible wave observed in cyclic voltammetry experiments was assigned to the Ru^III/II couple, E° (trans-[Ru(phen-NH-phen)(eina)₂)^3+/2+ = +1.22 V versus Ag/AgCl. The trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ compound was found to bind to nanocrystalline TiO₂ thin films from acetonitrile solution. Pulsed 532 nm excitation of trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ anchored to mesoporous nanocrystalline TiO₂ thin films resulted in an absorption difference spectra consistent with the formation of an interfacial charge separated state trans-[Ru^III (phen-NH-phen)(ina)₂]⁺/TiO₂ (e⁻). The formation of this state could not be time resolved, consistent with rapid excited state injection into the TiO₂, k_inj > 10⁸ s⁻¹. Comparative measurements with a thin film actinometer yielded an injection quantum yield (?_inj) of 0.8. Charge recombination required milliseconds for completion and followed a bi-second-order equal concentration kinetic model with k₁ = 1.0 × 10⁸ s⁻¹, and k₂ = 3.0 × 10⁵ s⁻¹. In regenerative solar cells with 0.5 M LiI and 0.005 M I₂ in acetonitrile, incident photon-to-current efficiencies were typically less than 10%.     

Effect of gem 2,2′-disubstitution and base in the formation of spiro- and ansa-1,3-propandioxy derivatives of cyclotriphosphazenes

The gem-dialkyl effect has been investigated in the reactions of cyclotriphosphazene, N₃P₃Cl₆1, with various 2,2′-derivatives of 1,3-propandiol, CXY(CH₂OH)₂, in either THF or DCM to form spiro (6-membered) and ansa (8-membered ring) derivatives. The reactions were made with a number of symmetrically-substituted (X = Y, methyl, ethyl, n-butyl and a malonate ester) and unsymmetrically-substituted (X ≠ Y, methyl/H, phenyl/H, methyl/n-propyl, ethyl/n-butyl and Br/NO₂) 1,3-propandiols. The products were analysed by ¹H and ³¹P NMR spectroscopy and some of the spiro and ansa derivatives were also characterized by X-ray crystallography. Reactions of 1 with unsymmetrically-substituted 1,3-propandiols results in the formation of two structural isomers of ansa-substituted compounds, both isomers (endo and exo) have been structurally-characterized by X-ray crystallography for the ethyl/n-butyl derivative. It is found that the regioselectivity of the reaction is changed when the base is changed. The relative proportions of spiro and ansa compounds formed under different reaction conditions were quantified by ³¹P NMR measurements of the reaction mixtures. The results were rationalised mainly in terms of the electronic effect of the substituents, whereas the steric effect has a secondary role in the formation of both spiro and ansa compounds.     

Synthesis, structural determination and magnetic properties of a heterobimetallic CuRe complex containing a macrocyclic ligand

Reaction of the rhenium(IV) compound, [Bu₄N]₂ReCl₄ox, with the highly unsaturated tetraazabismacrocyclic copper(II) complex cation [CuCuL]⁴⁺ (L = 6,13-Bis(dodecylaminomethylidene)-1,4,8,11-tetraazacyclotetradeca-4,7,11,14-tetraene) produced a new kind of heterobimetallic compound: [CuCuL][ReCl₄ox]₂ · 2DMF in which [ReCl₄ox]²⁻ anions and [CuCuL]⁴⁺ cations are linked by electrostatic forces. The crystal structure of this compound was determined at 173(2) K. It crystallizes triclinic, space group , with a = 9.441(4), b = 11.032(5), c = 15.261(7) Å, α = 89.05(1)°, β = 88.93(1)°, γ = 77.09(1)°, Z = 1, R₁ = 0.0557, wR₂ = 0.1332. The magnetic behavior of this compound has been investigated over the temperature range 1.72-300 K. The compound behaves as a ferrimagnetic Cu^IIRe^IV bimetallic, chain with intrachain antiferromagnetic coupling.     

Triterpenoid saponins from a cytotoxic root extract of Sideroxylonfoetidissimum subsp. gaumeri

Evaluation of the cytotoxicity of an ethanolic root extract of Sideroxylonfoetidissimum subsp. gaumeri (Sapotaceae) revealed activity against the murine macrophage-like cell line RAW 264.7. Systematic bioassay-guided fractionation of this extract gave an active saponin-containing fraction from which four saponins were isolated. Use of 1D (¹H, ¹³C, DEPT135) and 2D (COSY, TOCSY, HSQC, and HMBC) NMR, mass spectrometry and sugar analysis gave their structures as 3-O-(β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)[β-d-xylopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, 3-O-β-d-glucopyranosyl-28-O-(α-l-rhamnopyranosyl-(1 → 3)[β-d-xylopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, 3-O-(β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)[β-d-apiofuranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, and the known compound, 3-O-β-d-glucopyranosyl-28-O-(α-l-rhamnopyranosyl-(1 → 3)[β-d-xylopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-protobassic acid. Two further saponins were obtained from the same fraction, but as a 5:4 mixture comprising 3-O-(β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)[β-d-apiofuranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid and 3-O-(β-d-apiofuranosyl-(1 → 3)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)[β-d-xylopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, respectively. This showed greater cytotoxicity (IC₅₀ = 11.9 ± 1.5 μg/ml) towards RAW 264.7 cells than the original extract (IC₅₀ = 39.5 ± 4.1 μg/ml), and the saponin-containing fraction derived from it (IC₅₀ = 33.7 ± 6.2 μg/ml).     

Synthesis of rhodium and iridium boryl complexes via oxidative addition of haloboranes

B-Chlorocatecholborane undergoes oxidative addition to M(PR₃)₃Cl (M = Rh, R = Me; M = Ir, R = Me, Et) yielding six-coordinate complexes of general formula mer,cis-(PR₃)₃Cl₂M(BO₂C₆H₄). The same M(PR₃)₃Cl complexes also react with B-bromocatecholborane to give a mixture of metal boryl homo- and heterodihalides (PR₃)₃X¹X²M(BO₂C₆H₄) (X¹, X² = Cl, Br), and the observed disproportionation is believed to involve the formation of a heteronuclear halide-bridged intermediate. The alkene 4-vinylanisole failed to react with the six-coordinate, 18-electron (PR₃)₃Cl₂M(BO₂C₆H₄) complexes at ambient temperatures.     

Effect of substituent dtp to optical properties of heterobimetallic M/Ag/S nest-shaped clusters (M = Mo, W)

Clusters [MoS₄Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (1), [WS₄Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (2) and [WOS₃Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (3) were synthesized by the reaction of (NH₄)₂MoS₄/(NH₄)₂WS₄, (NH₄)₂WOS₃ with Ag[S₂P(OPrⁱ)₂]. Their structures have been characterized by X-ray diffraction. The clusters consist of a distorted tetrahedral MS₄ (or MOS₃) (M = Mo, W) with three Ag atoms and three sulfur atom bridges (Fig. 1), and resemble roughly that of cubane-like clusters. The nonlinear optical (NLO) properties were studied with an 8 ns pulsed laser at 532 nm. Its optical response to the incident light exhibits good optical absorptive and refractive effects, with α₂ = 1.56 × 10⁻¹⁰ m W⁻¹, n₂ = 3.87 × 10⁻¹⁷ m² W⁻¹ for cluster 1; α₂ = 1.33 × 10⁻¹⁰ m W⁻¹, n₂ = 6.52 × 10⁻¹⁷ m² W⁻¹for cluster 2; and α₂ = 2.54 × 10⁻¹⁰ m W⁻¹, n₂ = 4.07 × 10⁻¹⁷ m² W⁻¹ for cluster 3 for a 1.56 × 10⁻⁴ mol dm⁻³ CH₂Cl₂ solution.     

4,4′-Bis(tert-butyl)-2,2′-bipyridinedichlorometal(II) - Synthesis, structure and EPR spectroscopy

Due to the better solubility of the 4,4′-substituted bipyridine ligand a series of 4,4′-bis(tert-butyl)-2,2′-bipyridinedichlorometal(II) complexes, [M(tbbpy)Cl₂], with M = Cu, Ni, Zn, Pd, Pt was synthesised and characterised. The blue copper complex 4,4′-bis(tert-butyl)-2,2′-bipyridinedichlorocopper(II) was isolated in two different polymorphic forms, as prisms 1 with a solvent inclusion and solvent-free as needles 2. Both structures were determined by X-ray structure analysis. They crystallise in the monoclinic space group P2₁/c with four molecules in the unit cell, but with different unit cells and packing motifs. Whereas in the prisms 1, with the unit cell parameters a = 12.1613(12), b = 10.6363(7), c = 16.3074(15) Å, β = 94.446(8)°, the packing is dominated by intra- and intermolecular hydrogen bonds, in the needles 2, with a = 7.738(1), b = 18. 333(2), c = 13.291(3) Å, β = 97.512(15)°, only intramolecular hydrogen bonds appear and the complex molecules are arranged in columns which are stabilised by π-π-stacking interactions. In both complexes the copper has a tetrahedrally distorted coordination sphere. These copper complexes were also studied by EPR spectroscopy in solution, as frozen glass and diamagnetically diluted powder with the analogue [Pd(tbbpy)Cl₂] as host lattice.     

The sedimentation properties of ferritins. New insights and analysis of methods of nanoparticle preparation

Background

Ferritin exhibits complex behavior in the ultracentrifuge due to variability in iron core size among molecules. A comprehensive study was undertaken to develop procedures for obtaining more uniform cores and assessing their homogeneity.

Methods

Analytical ultracentrifugation was used to measure the mineral core size distributions obtained by adding iron under high- and low-flux conditions to horse spleen (apoHoSF) and human H-chain (apoHuHF) apoferritins.

Results

More uniform core sizes are obtained with the homopolymer human H-chain ferritin than with the heteropolymer horse spleen HoSF protein in which subpopulations of HoSF molecules with varying iron content are observed. A binomial probability distribution of H- and L-subunits among protein shells qualitatively accounts for the observed subpopulations. The addition of Fe²⁺ to apoHuHF produces iron core particle size diameters from 3.8 ± 0.3 to 6.2 ± 0.3 nm. Diameters from 3.4 ± 0.6 to 6.5 ± 0.6 nm are obtained with natural HoSF after sucrose gradient fractionation. The change in the sedimentation coefficient as iron accumulates in ferritin suggests that the protein shell contracts ∼ 10% to a more compact structure, a finding consistent with published electron micrographs. The physicochemical parameters for apoHoSF (15%/85% H/L subunits) are M = 484,120 g/mol, ν? = 0.735 mL/g, s_20,w = 17.0 S and D_20,w = 3.21 × 10⁻⁷ cm²/s; and for apoHuHF M = 506,266 g/mol, ν? = 0.724 mL/g, s_20,w = 18.3 S and D_20,w = 3.18 × 10⁻⁷ cm²/s.

Significance

The methods presented here should prove useful in the synthesis of size controlled nanoparticles of other minerals.     

The human xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 (NAT1) is irreversibly inhibited by inorganic (Hg) and organic mercury (CH3Hg): Mechanism and kinetics

Human arylamine N-acetyltransferase 1 (NAT1) is a xenobiotic-metabolizing enzyme that biotransforms aromatic amine chemicals. We show here that biologically-relevant concentrations of inorganic (Hg²⁺) and organic (CH₃Hg⁺) mercury inhibit the biotransformation functions of NAT1. Both compounds react irreversibly with the active-site cysteine of NAT1 (half-maximal inhibitory concentration (IC₅₀) = 250 nM and k_inact = 1.4 × 10⁴ M⁻¹ s⁻¹ for Hg²⁺ and IC₅₀ = 1.4 μM and k_inact = 2 × 10² M⁻¹ s⁻¹ for CH₃Hg⁺). Exposure of lung epithelial cells led to the inhibition of cellular NAT1 (IC₅₀ = 3 and 20 μM for Hg²⁺ and CH₃Hg⁺, respectively). Our data suggest that exposure to mercury may affect the biotransformation of aromatic amines by NAT1.