Low power upconversion using MLCT sensitizers

Selective low energy excitation of the metal-to-ligand charge transfer (MLCT) transition in [Ru(dmb)(3)](2+)(dmb = 4,4'-dimethyl-2,2'-bipyridine) in the presence of anthracene or 9,10-diphenylanthracene yields easily visualized upconverted singlet fluorescence resulting from triplet-triplet annihilation at low excitation power.     

Aporphines 24. The synthesis of N-alkylderivatives of bulbocapnine and isoeorydine

The synthesis of three new racemic aporphine alkaloids ( 1b, 1c and 2 ) is reported and these alkaloids are fully characterized. The method of synthesis involved either a Bischler-Napieralski-Psehorr sequence or a Reissert alkylation-Pschorr cyclization route. The Pschorr cyclization also gave the morphinandienones 7a and 7b , respectively.     

Synthesis of pyrene and benzo[a]pyrene adducts at the exocyclic amino groups of 2'-deoxyadenosine and 2'-deoxyguanosine by a palladium-mediated C-N bond-formation strategy

Single-electron oxidation of the carcinogenic hydrocarbon benzo[a]pyrene (BaP) is thought to result in a radical cation intermediate and this species has been proposed to cause alkylation at the nitrogens of the purine nucleobases. Although several different nucleoside adducts have been isolated as arising from this mode of metabolic activation, there are no selective, total syntheses of the stable exocyclic amino group adducts formed by the single-electron oxidation of any hydrocarbon with the purine 2'-deoxynucleosides to date. In this paper we disclose the synthesis of the model adducts N(6)-(1-pyrenyl)-2'-deoxyadenosine and N(2)-(1-pyrenyl)-2'-deoxyguanosine as well as the first synthesis of the carcinogen-linked nucleoside derivatives N(6)-(6-benzo[a]pyrenyl)-2'-deoxyadenosine and N(2)-(6-benzo[a]pyrenyl)-2'-deoxyguanosine via a palladium-mediated C-N bond formation. Two different coupling strategies were attempted: coupling of an aryl bromide with a suitably protected nucleoside and the coupling of an arylamine with a suitable halonucleoside. The former had somewhat limited applicability in that only N(6)-(1-pyrenyl)-2'-deoxyadenosine was prepared by this method; on the other hand, the latter was more general. However, there are noteworthy differences in the amination reactions at the C-6 and C-2 positions. Reactions at the C-6 resulted in the competing formation of a 1:2 amine-nucleoside adduct in addition to the desired monoaryl nucleoside. Such a dimer formation was not observed at the C-2. The C-2 adducts, however, displayed an interesting conformational behavior.     

Photobiological characteristics and photosynthetic UV responses in two Ulva species (Chlorophyta) from southern Spain

The effect of different wavebands of artificial UV (UVB and UVA) and photosynthetically active radiation (PAR) was assessed in two species of the genus Ulva, U. olivascens and U. rotundata, from southern Spain in order to test for possible differences in acclimation of photosynthesis. Both species share similar morphology but are subject to different light environments: U. rotundata is an estuarine alga, inhabiting subtidal locations, while U. olivascens is an intertidal, sun-adapted organism. Algae were exposed to three different UV conditions, PAR+UVA+UVB, PAR+UVA and PAR for 7 d. Short-term exposure (6 h) was also carried out, using two PAR levels, 150 and 700 micromolm(-2)s(-1). Pigment contents and photosynthesis vs. irradiance curves from oxygen evolution were used to contrast sun- and shade adaptation between these species. O2-based net photosynthesis (Pmax) and PAM-chlorophyll fluorescence (optimal quantum yield, Fv/Fm) were used as parameters to evaluate photoinhibition of photosynthesis in the experiments. The results underline different photobiological characteristics among species: the subtidal U. rotundata had higher contents of pigments (Chl a, Chl b and carotenoids) than the sun-adapted U. olivascens, which resulted in higher thallus absorptance and P-I parameters characterized by higher photosynthetic efficiency at limiting irradiances (alpha) and lower saturating points for photosynthesis (Ek). After 7 d exposure, photoinhibition of Fv/Fm was close to 40-45% in both species. Differences between UV treatments were seen in U. rotundata after 5 d and after 7 d in U. olivascens, in which PAR+UVA impaired strongly photosynthesis (80%). Such patterns were correlated with a progressive decrease in pigment contents, specially chlorophylls. In short-term (6 h) exposures, combinations of UVA+UVB and high PAR level resulted in high rates of photoinhibition of chlorophyll fluorescence (68-92%) in U. rotundata, whereas in U. olivascens photoinhibition ranged between 42% and 53%. Photoinhibition under low PAR combined to UV radiation was lower than observed under high PAR. Net O2-Pmax revealed similar response among the species, with maximal photoinhibition rates close to 60% in algae incubated under high PAR+UVA+UVB. In the case of UV exposure in combination with low PAR, the highest photoinhibition rates were measured in U. rotundata.     

Synthesis of bipyridine and terpyridine based ruthenium metallosynthons for grafting of multiple pyrene auxiliaries

The synthesis of novel ruthenium(II) bipyridine or terpyridine complexes bearing an increasing number of pyrene or toluyl moieties is described. The ruthenium complexes are constructed in a first step with ligands bearing the required bromine functions, followed in a second step by stepwise grafting of 1-ethynylpyrene or 4-ethynyltoluene promoted by Pd(0). A complex bearing a protected triethylsilylacetylene function was also prepared. In situ deprotection of this function with K₂CO₃ and cross-coupling with 1-bromopyrene afforded a soluble complex in which two pyrene moieties are linearly linked via ethynyl spacers to one of the bipyridine ligands. These highly coloured complexes exhibit well defined absorption and emission properties in solution at both rt and 77 K.     

Correlating axial and equatorial ligand field effects to the single-molecule magnet performances of a family of dysprosium bis-methanediide complexes

Treatment of the new methanediide–methanide complex [Dy(SCS)(SCSH)(THF)] (1Dy, SCS = {C(PPh₂S)₂}²⁻) with alkali metal alkyls and auxillary ethers produces the bis-methanediide complexes [Dy(SCS)₂][Dy(SCS)₂(K(DME)₂)₂] (2Dy), [Dy(SCS)₂][Na(DME)₃] (3Dy) and [Dy(SCS)₂][K(2,2,2-cryptand)] (4Dy). For further comparisons, the bis-methanediide complex [Dy(NCN)₂][K(DB18C6)(THF)(toluene)] (5Dy, NCN = {C(PPh₂NSiMe₃)₂}²⁻, DB18C6 = dibenzo-18-crown-6 ether) was prepared. Magnetic susceptibility experiments reveal slow relaxation of the magnetisation for 2Dy–5Dy, with open magnetic hysteresis up to 14, 12, 15, and 12 K, respectively (∼14 Oe s⁻¹). Fitting the alternating current magnetic susceptibility data for 2Dy–5Dy gives energy barriers to magnetic relaxation (U_eff) of 1069(129)/1160(21), 1015(32), 1109(70), and 757(39) K, respectively, thus 2Dy–4Dy join a privileged group of SMMs with U_eff values of ∼1000 K and greater with magnetic hysteresis at temperatures >10 K. These structurally similar Dy-components permit systematic correlation of the effects of axial and equatorial ligand fields on single-molecule magnet performance. For 2Dy–4Dy, the Dy-components can be grouped into 2Dy–cation/4Dy and 2Dy–anion/3Dy, where the former have almost linear C Dy C units with short average Dy C distances, and the latter have more bent C Dy C units with longer average Dy C bonds. Both U_eff and hysteresis temperature are superior for the former pair compared to the latter pair as predicted, supporting the hypothesis that a more linear axial ligand field with shorter M–L distances produces enhanced SMM properties. Comparison with 5Dy demonstrates unusually clear-cut examples of: (i) weakening the equatorial ligand field results in enhancement of the SMM performance of a monometallic system; (ii) a positive correlation between U_eff barrier and axial linearity in structurally comparable systems.

Studies on equatorial donor and C Dy C angle variation effects on energy barriers to the slow relaxation of magnetisation are reported.     

Lipophilic Diamides as Ionophores for Alkali and Alkaline Earth Metal Cations

A series of lipophilic N, N, N′,N′-tetrasubstituted diamides were prepared and their selectivity in solvent polymeric membranes was studied, cis-N, N, N′, N′-Tetraisobutylcyclohexane-1,2-dicarboxamide induces a selectivity in membranes for Li⁺over alkaline earth metal cations and other alkali metal cations by a factor of about 1000 and 100 respectively. The ionophore N, N′-diheptyl-N,N′-dimethylethylmalonamide is an attractive candidate for the use in microelectrodes for the determination of intracellular Mg²⁺-activities.     

Palladium salicylaldimine complexes containing boronate esters

Reactions of salicylaldehydes with boronate ester derivatives of aniline have been examined. Addition of these Schiff base ligands to palladium acetate or Na₂PdCl₄ afforded novel boron-containing trans-bis(N-arylsalicylaldiminato) palladium complexes.Condensation of salicylaldehyde (2-HOC₆H₄C(O)H) with H₂NC₆H₄Bpin (pin=1,2-O₂C₂Me₄) afforded the boron-containing Schiff bases, 2-HOC₆H₄C(H)=NC₆H₄Bpin (1–3a). Similar reactivity with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy-1-naphthaldehyde gave the corresponding Schiff bases (1-3b) and (1-3c), respectively. Reaction of Schiff bases (2) and (3) with palladium acetate or Na₂PdCl₄ afforded complexes of the type PdL₂ (4,5), where L=deprotonated Schiff base. The molecular structure of the nitro-salicylaldehyde 4-Bpin palladium complex (5b) was characterized by an X-ray diffraction study. All new palladium compounds have been characterized fully and tested for their antifungal activity against Aspergillus niger and Aspergillus flavus.