Formation of Enantiomerically Pure Luminescent Triple-Stranded Dimetallic Europium Helicates and Their Corresponding Hierarchical Self-Assembly Formation in Protic Polar Solutions.

Ditopic helicate ligands 1 and 2 were synthesized for the formation of dinuclear EuIII luminescent chiral helical assemblies (Eu2·L3) in competitive organic and protic solvent media. Spectroscopic analysis revealed formation of the 2:3 (Eu2·L3) and 2:2 (Eu2·L2) species in methanolic solutions. Circular dichroism and circularly polarized luminescence (CPL) spectroscopy confirmed the chiral purity of the helical systems, while scanning electron microscopy imaging demonstrated the formation of hierarchical self-assemblies with spherical morphologies.

Chiroptical Probing of Lanthanide-Directed Self-Assembly Formation Using btp Ligands Formed in One-Pot Diazo-Transfer/Deprotection Click Reaction from Chiral Amines.

A series of enantiomeric 2,6-bis(1,2,3-triazol-4-yl)pyridines (btp)-containing ligands was synthesized by a one-pot two-step copper-catalyzed amine/alkyne click reaction. The Eu(III) - and Tb(III) -directed self-assembly formation of these ligands was studied in CH3 CN by monitoring their various photophysical properties, including their emerging circular dichroism and circularly polarized luminescence. The global analysis of the former enabled the determination of both the stoichiometry and the stability constants of the various chiral supramolecular species in solution.

Exploring the Effect of Ligand Structural Isomerism in Langmuir-Blodgett Films of Chiral Luminescent Eu(III) Self-Assemblies.

Here we have investigated the influence of the antenna group position on both the formation of chiral amphiphilic Eu(III) -based self-assemblies in CH3 CN solution and, on the ability to form monolayers on the surface of quartz substrates using the Langmuir-Blodgett technique, by changing from the 1-naphthyl (2(R), 2(S)) to the 2-naphthyl (1(R), 1(S)) position. The evaluation of binding constants of the self- assemblies in CH3 CN solution was achieved using conventional techniques such as UV/Visible and luminescence spectroscopies along with more specific circular dichroism (CD) spectroscopy. The binding constants obtained for EuL, EuL2 and EuL3 species in the case of 2-naphthyl derivatives were comparable to those obtained for 1-naphthyl derivatives. The analysis of the changes in the CD spectra of 1(R) and 1(S) upon addition of Eu(III) not only allowed us to evaluate the values of the binding constants but the resulting recalculated spectra may also be used as fingerprints for assignment of the chiral self-assembly species formed in solution. The obtained monolayers were predominantly formed from EuL3 (≈85 %) with the minor species present in ≈15 % EuL2 .

Circularly Polarized Luminescence from Helically Chiral N,N,O,O-Boron-Chelated Dipyrromethenes.

Helically chiral N,N,O,O-boron chelated dipyrromethenes showed solution-phase circularly polarized luminescence (CPL) in the red region of the visible spectrum (λem (max) from 621 to 663 nm). The parent dipyrromethene is desymmetrised through O chelation of boron by the 3,5-ortho-phenolic substituents, inducing a helical chirality in the fluorophore. The combination of high luminescence dissymmetry factors (|glum | up to 4.7 ×10(-3) ) and fluorescence quantum yields (ΦF up to 0.73) gave exceptionally efficient circularly polarized red emission from these simple small organic fluorophores, enabling future application in CPL-based bioimaging.

Quantifying the formation of chiral luminescent lanthanide assemblies in an aqueous medium through chiroptical spectroscopy and generation of luminescent hydrogels.

Herein we present the synthesis and the photophysical evaluation of water-soluble chiral ligands (2·(R,R) and 2·(S,S)) and their application in the formation of lanthanide directed self-assembled structures. These pyridine-2,6-dicarboxylic amide based ligands, possessing two naphthalene moieties as sensitising antennae, that can be used to populate the excited state of lanthanide ions, were structurally modified using 3-propanesultone and caesium carbonate, allowing for the incorporation of a water-solubilising sulfonate motif. We show, using microwave synthesis, that Eu(III) forms chiral complexes in 1 : 3 (M : L) stoichiometries (Eu·[2·(R,R)]3 and Eu·[2·(S,S)]3) with these ligands, and that the red Eu(III)-centred emission arising from these complexes has quantum yields (Φtot) of 12% in water. Both circular dichroism (CD) and circular polarised luminescence (CPL) analysis show that the complexes are chiral; giving rise to characteristic CD and CPL signatures for both the Λ and the Δ complexes, which both possess characteristic luminescence dissymmetry factors (g(lum)), describing the structure in solution. The self-assembly process was also monitored in situ by observing the changes in the ligand absorption and fluorescence emission, as well as in the Eu(III) luminescence. The change, fitted using non-linear regression analysis, demonstrated high binding affinity for Eu(III) which in part can be assigned to being driven by additional hydrophobic effects. Moreover, using CD spectroscopy, the changes in the chiroptical properties of both (2·(R,R) and 2·(S,S)) were monitored in real time. Fitting the changes in the CD spectra allowed for the step-wise binding constants to be determined for these assemblies; these matched well with those determined from both the ground and the excited state changes. Both the ligands and the Eu(III) complexes were then used in the formation of hydrogels; the Eu(III)-metallogels were luminescent to the naked-eye.

Lanthanide directed self-assembly of highly luminescent supramolecular "peptide" bundles from α-amino acid functionalized 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligands.

Ligands containing the [2,6-bis(1,2,3-triazol-4-yl)pyridine] (btp) motif have recently shown promise in coordination chemistry. The motif is synthesized via the Cu(I)-catalyzed "click" reaction and can be conveniently functionalized when compared to other terdentate chelating motifs. Ligand 1 was synthesized and shown to sensitize Eu(III) and Tb(III) excited states effectively. The use of these ions to synthesize self-assembly structures in solution was investigated by carrying out both (1)H NMR and photophysical titrations. The latter were used to determine high binding constants from changes in the absorption, ligand emission (fluorescence), and lanthanide-centered emission. A small library of amino acid derivatives of 1, ligands 3, were prepared upon coupling reactions with Gly, Ala, Phe, and Trp methyl esters, with a view to introducing biologically relevant and chiral moieties into such ligands. All of these derivatives were shown to form stable, emissive Ln(III) self-assemblies, emitting in the millisecond time range, which were studied by means of probing their photophysical properties in organic solutions using lanthanide ion titrations. All the Tb(III) complexes, with the exception of Trp based derivatives, gave rise to highly luminescent and bright complexes, with quantum yields of Tb(III) emission of 46-70% in CH3CN solution. In contrast, the Eu(III) complexes gave rise to more modest quantum yields of 0.3-3%, reflecting better energy match for the Tb(III) complexes, and hence, more efficient sensitization, as demonstrated by using low temperature measurements to determine the triplet state of 1.

Dyspnea and Palliative Care in Advanced Chronic Obstructive Pulmonary Disease: A Rapid Review.

Dyspnea is the most common and activity-limiting symptom for those with chronic obstructive pulmonary disease (COPD). Treatment is complex, palliative care (PC) dyspnea relief interventions are poorly understood, and PC remains underutilized in COPD despite national guidelines and recommendations. The purpose of this rapid review was to explore the concept of dyspnea and role of PC through the lens of providers, caregivers, and patients with COPD. A systematic approach for synthesis was used to identify 13 articles published between January 2018 and October 2023. Team members compared data via visualization and theme clustering to identify key conclusions describing operationalization of dyspnea, management, and PC implications. Dyspnea operationalization was challenging, with inconsistent measurement and terminology. Dyspnea was a significant burden in COPD and contributed to complexity of treatment. Opioids were used most often to treat dyspnea, but provider perspectives and biases can influence treatment decisions and perceptions of opioid therapy by the patient and caregiver. Evidence-based clinical practice guidelines and policies are needed to clarify the use of opioid therapy for dyspnea management to reduce stigmatization and barriers to treatment. Provider education should emphasize a multipronged approach to treatment of dyspnea in COPD with integration of PC early in the care continuum.

Ligand Chirality Transfer from Solution State to the Crystalline Self-Assemblies in Circularly Polarized Luminescence (CPL) Active Lanthanide Systems.

The synthesis of a family of chiral and enantiomerically pure pyridyl-diamide (pda) ligands that upon complexation with europium [Eu(CF3SO3)3] result in chiral complexes with metal centered luminescence is reported; the sets of enantiomers giving rise to both circular dichroism (CD) and circularly polarized luminescence (CPL) signatures. The solid-state structures of these chiral metallosupramolecular systems are determined using X-ray diffraction showing that the ligand chirality is transferred from solution to the solid state. This optically favorable helical packing arrangement is confirmed by recording the CPL spectra from the crystalline assembly by using steady state and enantioselective differential chiral contrast (EDCC) CPL Laser Scanning Confocal Microscopy (CPL-LSCM) where the two enantiomers can be clearly distinguished.

Probing the effects of ligand isomerism in chiral luminescent lanthanide supramolecular self-assemblies: a europium "Trinity Sliotar" study.

"Trinity Sliotar" family: Chiral ligands containing pyridyl and naphthalene moieties were synthesized and characterized. These ligands were successfully used for the synthesis of Eu(III) bundles where chirality of the ligand is successfully transferred onto the lanthanide centre resulting in circularly polarized red luminescence.

Synthesis of luminescent homo-dinuclear cationic lanthanide cyclen complexes bearing amide pendant arms through the use of copper catalysed (1,3-Huisgen, CuAAC) click chemistry.

The design and synthesis of dinuclear-lanthanide complexes possessing triazole-based bridges, formed by using copper catalysed 1,3-cycloaddition reactions between heptadentate alkyne functionalised cyclen europium or terbium complexes and di-azides (CuAAC reactions), are described. While this click reaction worked well for the formation of the homo-Eu(III) and Tb(III) bis-tri-arm cyclen N,N-dimethyl acetamide complexes, 2Eu and 2Tb, and for the homo-Eu(III) chiral N-methylnaphthalene based complexes 3Eu (S,S,S) and 4Eu (R,R,R), the formation of the Eu(III) complex of the primary amide analogue of 2, namely 1Eu, was not successful, clearly demonstrating the effect that the nature of the pendant arms has on this reaction. Furthermore, the click reactions between the free alkyne cyclen bis-derivatives (5-8) and the di-azide were unsuccessful, most likely due to the high affinity of the cyclen macrocycles for Cu(II). The Eu(III) complexes of 2-4 and 2Tb all gave rise to sensitised metal ion centred emission upon excitation of the triazole or the naphthalene antennae in methanol solution, and their hydration states were determined, which showed that while the Eu(III) mono-nuclear complexes had q ∼ 2, the click products all had q ∼ 1. In the case of 3Eu (S,S,S) and 4Eu (R,R,R), the circular polarised emission (CPL) was also observed for both, demonstrating the chiral environment of the lanthanide centres.

Metal-directed synthesis of enantiomerially pure dimetallic lanthanide luminescent triple-stranded helicates.

The synthesis and photophysical evaluation of two enatiomerially pure dimetallic lanthanide luminescent triple-stranded helicates is described. The two systems, formed from the chiral (R,R) ligand 1 and (S,S) ligand 2, were produced as single species in solution, where the excitation of either the naphthalene antennae or the pyridiyl units gave rise to Eu(III) emission in a variety of solvents. Excitation of the antennae also gave rise to circularly polarized Eu(III) luminescence emissions for Eu(2):1(3) and Eu(2):2(3) that were of equal intensity and opposite sign, confirming their enantiomeric nature in solution providing a basis upon which we were able to assign the absolute configurations of Eu(2):1(3) and Eu(2):2(3).

Chiral luminescent lanthanide complexes possessing strong (samarium, SmIII) circularly polarised luminescence (CPL), and their self-assembly into Langmuir-Blodgett films.

The lanthanide directed self-assembly of chiral amphiphilic 2,6-pyridinedicarboxylic acid based ligands 1 and 2 with various Ln(CF3SO3)3 (Ln = TbIII, SmIII, LuIII, DyIII) salts was studied in CH3CN and evaluated with the expected 1 : 3 and 1 : 1 Ln : Ligand species forming in solution. Ligand chirality was retained and transferred, as depicted by circular dichroism (CD) and circularly polarised luminescence (CPL) measurements (for TbIII and SmIII), to the lanthanide centre upon complexation with high dissymmetry factor values for the SmIII complexes obtained (glum = -0.44 and 0.29 and 0.45 and -0.23 for the 4G5/2→6H5/2 and the 4G5/2→6H7/2 transitions of Sm·13 and Sm·23, respectively). The ability of the complexes to form stable Langmuir monolayers at the air-water interface was also established while Langmuir-Blodgett films of Tb·L3 and Sm·L3 exhibited lanthanide luminescent emission.

Enantioselective regulation of a metal complex in reversible binding to serum albumin: dynamic helicity inversion signalled by circularly polarised luminescence.

The helicity of the (SSS)-Delta enantiomer of a terbium and europium(III) complex is inverted on reversible binding to 'drug site II' of serum albumin, signalled by a switch in its circularly polarised emission; no such behaviour occurs with the (RRR)-Lambda complexes, thereby defining a unique chiroptical probe of albumin binding.

Cobalt(II) citrate cubane single-molecule magnet.

An investigation of the magnetic properties of the cobalt(II) citrate cubane [C(NH 2) 3] 8{Co 4(cit) 4}.4H 2O reveals that the cluster is a new cobalt(II) single-molecule magnet, with an energy barrier to reorientation of the magnetization, Delta E/ k B = 21 K, and tau 0 = 8 x 10 (-7) s. The compound displays distinct, frequency-dependent peaks in the out-of-phase (chi'') component of the ac magnetic susceptibility and magnetization versus field hysteresis loops that are temperature and sweep rate dependent. The hysteresis loops collapse at zero field due to very fast quantum tunneling of the magnetization (QTM).

The effect of the linker size in C2-symmetrical chiral ligands on the self-assembly formation of luminescent triple-stranded di-metallic Eu(iii) helicates in solution.

Chiral lanthanide-based supramolecular structures have gained significant importance in view of their application in imaging, sensing and other functional purposes. We have designed chiral C2-symmetrical ligands (L) based on the use of two 2,6-pyridine-dicarboxylic-amide moieties (pda), that differ from one another by the nature of the diamine spacer groups (from 1,3-phenylenedimethanamine (1(S,S), 2(R,R)) and benzene-1,3-diamine (3(S,S), 4(R,R)) to much bulkier 4,4'-(cyclohexane-1,1-diyl)bis(2,6-dimethylaniline) (5(S,S), 6(R,R))) between these two pda units. The self-assembly between L and Eu(iii) ions were investigated in CH3CN solution at low concentration whereby the changes in the absorbance, fluorescence and Eu(iii)-centred emission spectra allowed us to model the binding equilibria occurring in the solution to the presence of [Eu:L2], [Eu2:L2], [Eu2:L3] assemblies and reveal their high binding constant values. The self-assembly in solution were also studied at higher concentration by following the changes in the 1H NMR spectra of the ligands upon Eu(iii) addition, as well as by using MALDI-MS of the isolated solid state complexes. The chiroptical properties of the ligands were used in order to study the structural changes upon self-assembly between the ligands and Eu(iii) ions using circular dichroism (CD) and circularly polarised luminescence (CPL) spectroscopies. The photophysical properties of [Eu2:L3] complexes were evaluated in solution and showed a decrease of luminescence quantum yield when going from the ligand with smaller (1(S,S)) to bulkier (5(S,S)) linker from ∼5.8% to ∼2.6%. While mass-spectrometry revealed the possible formation of trinucler assemblies such as [Eu3:L3] and [Eu3:L2].

The application of chiroptical spectroscopy (circular dichroism) in quantifying binding events in lanthanide directed synthesis of chiral luminescent self-assembly structures.

The binding of asymmetrical and optically pure tridentate ligands (L = 1(S) and 1(R)) containing one carboxylic group and 2-naphthyl as an antenna to lanthanide ions (M = La(iii) and Eu(iii)) was studied in CH3CN, showing the successive formation of M:L, M:L2 and M:L3 stoichiometric species in solution. The europium complexes EuL3 were also synthesised, structurally characterised and their photophysical properties probed in CH3OH and CH3CN. The changes in the chiroptical properties of both 1(S) and 1(R) were used (by circular dichroism (CD) spectroscopy) to monitor the formation of these chiral self-assemblies in solution. While circularly polarised luminescence (CPL) showed the formation of Eu(1(S))3 and Eu(1(R))3 as enantiomers, with high luminescence dissymmetry factors (glum), fitting the CD changes allowed for binding constants to be determined that were comparable to those seen in the analyses of absorbance and luminescence changes.

A modular ditopic crown-shielded phosphate ion-pair receptor.

The synthesis of a modular hybrid receptor containing both an aza macrocycle and crown ether is described; a complete thermodynamic characterisation of the binding properties, in water, of the zinc(II) complex of the receptor towards phosphate is presented and the parameters are compared to those of the aza macrocycle precursor.

Absorption, Circular Dichroism, and Luminescence Spectroscopy of Electrogenerated Delta-[Ru(bipy)(3)](+/0/)(-) and Delta-[Os(bipy)(3)](+/0/)(-) (bipy = 2,2'-Bipyridine).

The electronic absorption and circular dichroism (CD) spectra of the complexes produced by the one, two, and three electron reduction of Delta-[Ru(bipy)(3)](2+) and Delta-[Os(bipy)(3)](2+) are reported. The CD spectra give unequivocal proof that the added electrons are localized on individual bipiridine ligands and thus that the complexes are correctly formulated [M(bipy)(2)(bipy(-))](+), [M(bipy)(bipy(-))(2)](0), and [M(bipy(-))(3)](-). The absorption spectra of the triply reduced species [M(bipy(-))(3)](-) (M = Ru, Os) are compared to those of the Fe(II) and Ir(III) analogs. The luminescence spectra of the two triply reduced complexes [Ru(bipy(-))(3)](-) and [Os(bipy(-))(3)](-). are also presented. The MLCT luminescence found in the parent complexes is completely quenched and is replaced by a weak luminescence attributed to the pi(10) --> pi(7) transition of the (coordinated) [bipy](-) ion.

Metal Complexes of New, Chiral N(2)O(2) Tetradentate Ligands.

N,N'-Bis(2R-hydroxy-2R-phenylethyl)-N,N'-dimethyl-1R,2R-diaminocyclohexane, H(2)L1, and N,N'-bis(2S-hydroxy-2S-methylethyl)-N,N'-dimethyl-1R,2R-diaminocyclohexane, H(2)L2, have been synthesized from readily available chiral precursors. They coordinate as neutral tetradentate ligands to Ni(II) and Cu(II) ions, from which the thiocyanates [M(H(2)L)(NCS)(2)] have been isolated and the structures of the H(2)L1 complexes determined by single-crystal X-ray techniques. In the blue complex [Ni(H(2)L1)(NCS)(2)].H(2)O.2EtOH, 1, and green [Cu(H(2)L1)(NCS)(2)]. 0.5H(2)O, 2, the neutral tetradentate ligands coordinate with the cis-alpha geometry with mutually cis N-bound thiocyanate groups, though the chiral ligands adopt a different stereochemistry in the two complexes. In 2, the absolute configuration about the Cu(II) center is Delta, with the nitrogens possessing the S stereochemistry, whereas for the Ni(II) analogue, coordination gives the Lambda isomer with the R configuration at the stereogenic nitrogens. Addition of H(2)L1 or H(2)L2 to Mn(II) in basic methanol solution results in rapid aerial oxidation. Delta-cis-alpha-[Mn(L1)(OMe)(2)].MeOH, 3, was isolated as black crystals from the reaction mixture after addition of 2 mol of NaOMe. The analogous complex with (L2)(2)(-) proved extremely hygroscopic and was not obtained in pure form. Colorless crystals of Lambda-cis-alpha-[MoO(2)(L1)], 4, were precipitated from a methanolic solution of [MoO(2)(acac)(2)] and H(2)L1. The analogous reaction with H(2)L2 gave Delta-cis-alpha-[MoO(2)(L2)], 5. Structures of 3, 4, and 5 are reported. The reactions of H(2)L1 and H(2)L2 with 1 mol equiv of [Ti(OPr(i))(4)] produced the complexes Delta-cis-alpha-[Ti(L1)(OPr(i))(2)] (white solid) and Lambda-cis-alpha-[Ti(L2)(OPr(i))(2)] (colorless oil), structural assignments for which were made possible by analysis of their (1)H NOE difference spectra. Thus the coordination of these tetradentate ligands is stereospecific, but the absolute configuration of the complexes formed (Delta or Lambda) is dependent on the metal ion involved.