Synthesis and Light-Harvesting Functions of Ring-Shaped Re(I) Trinuclear Complexes Connected with an Emissive Ru(II) Complex.

Ring-shaped Re(I) multinuclear complexes (Re(I) rings) in which Re(I)-diimine-biscarbonyl complexes are connected to each other through bisphosphine bridging ligands exhibit very suitable photophysical and electrochemical properties as redox photosensitizers. We developed two approaches for synthesizing Re(I) rings connected with a Ru(II) complex: cyclization of a linear Re(I) trinuclear complex connected with a Ru(II) complex and Mizoroki-Heck coupling of a ring-shaped Re(I) trinuclear complex and a Ru(II) complex. Photophysical measurements of these heteromultinuclear complexes and comparisons with their model complexes indicated that they exhibit efficient light-harvesting abilities, where energy transfer from the excited ring-shaped Re(I) trinuclear complex unit to the Ru(II) complex unit proceeds efficiently.

Synthesis of Re(I) Rings Comprising Different Re(I) Units and Their Light-Harvesting Abilities.

Trimethylamine N-oxide (MeNO) could selectively remove only one CO ligand from fac-[Re(N^N)(CO)(PRR')] (N^N = diimine ligand), whereby only the CO ligand in the trans position to the phosphorus ligand was selectively removed to give cis,trans-[Re(N^N)(CO)(PRR')(L)] in good yields. This decarbonylation reaction using MeNO was found to be especially useful for synthesizing biscarbonyl Re(I) complexes with electron-withdrawing groups in the diimine ligand, which could not be synthesized or were obtained only in low yields by the photochemical method. MeNO also selectively removed the carbonyl ligands in the trans position to the phosphorus ligands from the edge Re(I) complex units, which have the fac-[Re(N^N)(CO)(PRR')] structure, in linear-shaped Re(I) multinuclear complexes.

Comparison of Complexation-Induced pK Shifts in the Ground and Excited States of Dyes as Well as Different Macrocyclic Hosts and Their Manifestation in Host-Retarded Excited-Dye Deprotonation.

1-Aminopyrene and 1-naphthylamine-5-sulfonic acid were converted to the putrescine (1,4-diaminobutane)-substituted derivatives (dyes 1 and 2). The diaminobutyl anchor serves as a common binding motive for cation-receptor macrocycles such as cucurbit[n]urils (n = 6-8) and p-sulfonatocalix[4]arene. When protonated, they are prone to undergo a rapid deprotonation in their excited state to result in fluorescence from the unprotonated form (Förster cycle).

Rhenium(i) trinuclear rings as highly efficient redox photosensitizers for photocatalytic CO reduction.

We developed new cyclic Re(i)-based trinuclear redox photosensitizers with both high oxidation power in the excited state and strong reduction power in the reduced form. These excellent properties were achieved by introducing electron-donating groups on the diimine ligand of the Re(i) metal centre and by connecting each Re(i) unit with polyphenyl-bisphosphine bridging ligands. These Re-rings were applied to homogenous visible light-driven photocatalytic CO reduction in conjunction with various mononuclear catalysts, such as Re(i), Ru(ii) and Mn(i) metal complexes, employing a relatively weak sacrificial electron donor, triethanolamine.

Photofunctional multinuclear rhenium(i) diimine carbonyl complexes.

This account looks comprehensively at the syntheses, photophysical properties and applications of structurally diverse, multinuclear coordination compounds that embed a Re(i)-diimine-carbonyl moiety. Different types of linkages in terms of configuration and proper bridging lead to several types of discrete linear or cyclic macromolecular aggregates with different sizes, which consequently have a significant effect on their properties. The Re-backbone in the multinuclear assembly may have only a structural role and mainly exhibits host-guest behaviour for encapsulation, or it may produce photofunctional properties as a direct result of the Re(i) chromophoric unit, which makes these compounds applicable in light-harvesting systems or photochemical CO reduction.

Molecular analyses reveal high species diversity of trematodes in a sub-Arctic lake.

To identify trematode diversity and life-cycles in the sub-Arctic Lake Takvatn, Norway, we characterised 120 trematode isolates from mollusc first intermediate hosts, metacercariae from second intermediate host fishes and invertebrates, and adults from fish and invertebrate definitive hosts, using molecular techniques. Phylogenies based on nuclear and/or mtDNA revealed high species richness (24 species or species-level genetic lineages) and uncovered trematode diversity (16 putative new species) from five families typical in lake ecosystems (Allocreadiidae, Diplostomidae, Plagiorchiidae, Schistosomatidae and Strigeidae). Sampling potential invertebrate hosts allowed matching of sequence data for different stages, thus achieving molecular elucidation of trematode life-cycles and exploration of host-parasite interactions.

Trinuclear and Tetranuclear Re(I) Rings Connected with Phenylene, Vinylene, and Ethynylene Chains: Synthesis, Photophysics, and Redox Properties.

A series of highly luminescent trinuclear and tetranuclear ring-shaped Re(I) complexes wherein the Re units are linked with rigid bidentate phosphine ligands, namely, bis(diphenylphosphino)-p-phenylene, -trans-vinylene, and -ethynylene, were synthesized and fully characterized. Their strong emissive properties and the long lifetimes of their triplet metal-to-ligand charge transfer excited states originate primarily from enhanced, rigidity-induced interligand interactions between the 2,2'-bipyridine (bpy) ligand and the phenyl groups of the phosphine ligands. In addition, another type of interligand interaction was also observed between the bpy ligand and the phosphine-bridging group; this interaction also strongly affected the photophysical and redox properties of the Re-rings.

Ring-shaped Re(I) multinuclear complexes with unique photofunctional properties.

We synthesized for the first time a series of emissive ring-shaped Re(I) complexes (Re-rings) with various numbers of Re(I) units and various lengths of bridge ligands. The photophysical properties of the Re-rings could be varied widely through changes in the size of the central cavity. A smaller central cavity of the Re-rings induced intramolecular π-π interactions between the ligands and consequently caused a stronger emission and a longer lifetime of the excited state.

Dansyl labeling to modulate the relative affinity of bile acids for the binding sites of human serum albumin.

Binding of natural bile acids to human serum albumin (HSA) is an important step in enterohepatic circulation and provides a measure of liver function. In this article, we report on the use of four dansyl (Dns) derivatives of cholic acid (ChA) to demonstrate a regiodifferentiation in their relative affinity for the two binding sites of HSA. Using both steady-state and time-resolved fluorescence, formation of Dns-ChA@HSA complexes was confirmed; the corresponding binding constants were determined, and their distribution between bulk solution and HSA microenvironment was estimated.

Unconjugated bile salts shuttle through hepatocyte peroxisomes for taurine conjugation.

Unlabelled: Bile acid-CoA:amino acid N-acyltransferase (BAAT) conjugates bile salts to glycine or taurine, which is the final step in bile salt biosynthesis. In addition, BAAT is required for reconjugation of bile salts in the enterohepatic circulation. Recently, we showed that BAAT is a peroxisomal protein, implying shuttling of bile salts through peroxisomes for reconjugation.

Stereodifferentiation in fluorescence quenching within cholic acid aggregates.

Two cholic acid (ChA) analogues, containing a 4-nitrobenzo-2-oxa-1,3-diazole (NBD) moiety at C-3, were incorporated into ChA aggregates and submitted to fluorescence quenching by the two enantiomers of several tryptophan derivatives. In all cases, a significant stereodifferentiation was observed; the most remarkable effect was found when comparing the 3alpha and the 3beta diastereomers.

Complexes between fluorescent cholic acid derivatives and human serum albumin. a photophysical approach to investigate the binding behavior.

Interaction between bile acids and plasma proteins has attracted considerable attention over past decades. In fact, binding of bile acids to human serum albumin (HSA) determines their level in plasma, a value that can be used as a test for liver function. However, very little is known about the role that bile acids-HSA complexes play in hepatic uptake.

Synthesis of new, UV-photoactive dansyl derivatives for flow cytometric studies on bile acid uptake.

Four new fluorescent derivatives of cholic acid have been synthesized; they incorporate a dansyl moiety at 3alpha-, 3beta-, 7alpha- or 7beta- positions. These cholic acid analogs are UV photoactive and also exhibit green fluorescence. In addition, they have been demonstrated to be suitable for studying the kinetics of bile acid transport by flow cytometry.

Fluorescent benzofurazan-cholic acid conjugates for in vitro assessment of bile acid uptake and its modulation by drugs.

One of the most common mechanisms of hepatotoxicity is drug-induced cholestasis. Hence, new approaches for screening the cholestatic potential of drug candidates are desirable. In this context, we describe herein the use of synthetic 4-nitrobenzo-2-oxa-1,3-diazole (NBD) fluorescent conjugates of cholic acid (ChA) at positions 3alpha, 3beta, 7alpha, and 7beta for in vitro assessment of bile acid uptake.

Photophysical characterization and flow cytometry applications of cholylamidofluorescein, a fluorescent bile acid scaffold.

Cholylamidofluorescein (CamF) has been selected as a fluorescent bile acid scaffold to perform a full characterization of its photophysical properties. In aqueous medium, under nitrogen, the absorption spectrum of CamF was expectedly dependent on pH. Under air, the presence of CO(2) resulted in a partial protonation of the photoactive form, reducing the absorbance of CamF.