Combining Lanthanides with PyBox Ligands: A Simple Route to Circularly Polarized Light Emitters**

AbstractWe report the facile synthesis of TbIII and EuIII adducts able to elicit circularly polarized luminescence. Both the sensitization of the lanthanide‐ion‐centered luminescence (i. e. the antenna effect) and the chiral environment around the metal ions are brought about by commercially available enantiopure 2,6‐bis(oxazolinyl)pyridine ligands (PyBox). This strategy is promising for the development of a wide range of new and simple circularly polarized luminescence (CPL) active LnIII adducts, thanks to the fine tunability of the chemical structure of the PyBox ligands

Taking advantage of Co(ii) induced enhanced VCD for the fast and sensitive determination of enantiomeric excess

Co(II) induces a large VCD signal enhancement, which overcomes the low sensitivity of VCD and opens new perspectives in quantitative VCD. We used a stereodynamic system, where the analyte determines the chirality of the Co(II) coordination sphere. The strong VCD signals stand out the baseline, which allows for their rapid and accurate quantitation. This lends itself to the first general method for the ee determination of α-amino acids based on vibrational circular dichroism and constitutes a model for the design of sensitive quantitative assays based on VCD

Chiroptical methods in a wide wavelength range for obtaining Ln3+complexes with circularly polarized luminescence of practical interest

We studied enantiopure chiral trivalent lanthanide (Ln3+= La3+, Sm3+, Eu3+, Gd3+, Tm3+, and Yb3+) complexes with two fluorinated achiral tris(β-diketonate) ligands (HFA = hexafluoroacetylacetonate and TTA = 2-thenoyltrifluoroacetonate), incorporating a chiral bis(oxazolinyl)pyridine (PyBox) unit as a neutral ancillary ligand, by the combined use of optical and chiroptical methods, ranging from UV to IR both in absorption and circular dichroism (CD), and including circularly polarized luminescence (CPL). Ultimately, all the spectroscopic information is integrated into a total and a chiroptical super-spectrum, which allows one to characterize a multidimensional chemical space, spanned by the different Ln3+ions, the acidity and steric demand of the diketone and the chirality of the PyBox ligand. In all cases, the Ln3+ions endow the systems with peculiar chiroptical properties, either allied to f-f transitions or induced by the metal onto the ligand. In more detail, we found that Sm3+complexes display interesting CPL features, which partly superimpose and partly integrate the more common Eu3+properties. Especially, in the context of security tags, the pair Sm/Eu may be a winning choice for chiroptical barcoding

Circularly Polarised Luminescence in Enantiopure Samarium and Europium Cryptates

Circularly polarised luminescence (CPL) is a chiroptical phenomenon gaining more and more attention, as the availability of the necessary spectrometers is getting better and first applications in bioimaging or for the preparation of OLEDs (organic light emitting diodes) are coming within range. Until now most examples of distinctly CPL-active compounds were europium and terbium complexes though theoretically the electronic structure of samarium should be as suitable as the one of terbium. This discrepancy can be accounted for by the high susceptibility of samarium to non-radiative deactivation processes. The aim of this study was to strategically circumvent this difficulty by the use of a ligand scaffold which has already proven to efficiently suppress these processes, namely the cryptates. The prepared partly deuterated samarium and europium complexes exhibit distinct circularly polarised luminescence with dissymmetry factors up to glum=+0.13 (SmIII) or glum=−0.19 (EuIII)

Effect of the Counterion on Circularly Polarized Luminescence of Europium(III) and Samarium(III) Complexes

Each enantiopure europium(III) and samarium(III) nitrate and triflate complex of the ligand L, with L = N,N'-bis(2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine ([LnL(tta)2]·NO3 and [LnL(tta)2(H2O)]·CF3SO3, where tta = 2-thenoyltrifluoroacetylacetonate) has been synthesized and characterized from a spectroscopic point of view, using a chiroptical technique such as electronic circular dichroism (ECD) and circularly polarized luminescence (CPL). In all cases, both ligands are capable of sensitizing the luminescence of both metal ions upon absorption of light around 280 and 350 nm. Despite small differences in the total luminescence (TL) and ECD spectra, the CPL activity of the complexes is strongly influenced by a concurrent effect of the solvent and counterion. This particularly applies to europium(III) complexes where the CPL spectra in acetonitrile can be described as a weighed linear combination of the CPL spectra in dichloromethane and methanol, which show nearly opposite signatures when their ligand stereochemistries are the same. This phenomenon could be related to the presence of equilibria interconverting solvated, anion-coordinated complexes and isomers differing by the relative orientation of the tta ligands. The difference between some bond lengths (M-N bonds, in particular) in the different species could be at the basis of such an unusual CPL activity

Piezoelectric nanocomposite bioink and ultrasound stimulation modulate early skeletal myogenesis

Despite the significant progress in bioprinting for skeletal muscle tissue engineering, new stimuli-responsive bioinks to boost the myogenesis process are highly desirable. In this work, we developed a printable alginate/Pluronic-based bioink including piezoelectric barium titanate nanoparticles (nominal diameter: ∼60 nm) for the 3D bioprinting of muscle cell-laden hydrogels. The aim was to investigate the effects of the combination of piezoelectric nanoparticles with ultrasound stimulation on early myogenic differentiation of the printed structures. After the characterization of nanoparticles and bioinks, viability tests were carried out to investigate three nanoparticle concentrations (100, 250, and 500 μg mL−1) within the printed structures. An excellent cytocompatibility was confirmed for nanoparticle concentrations up to 250 μg mL−1. TEM imaging demonstrated the internalization of BTNPs in intracellular vesicles. The combination of piezoelectric nanoparticles and ultrasound stimulation upregulated the expression of MYOD1, MYOG, and MYH2 and enhanced cell aggregation, which is a crucial step for myoblast fusion, and the presence of MYOG in the nuclei. These results suggest that the direct piezoelectric effect induced by ultrasound on the internalized piezoelectric nanoparticles boosts myogenesis in its early phases

A circular dichroism study of the protective role of polyphosphoesters polymer chains in polyphosphoester‐myoglobin conjugates

Protein-polymer conjugates are a blooming class of hybrid systems with high biomedical potential. Despite a plethora of papers on their biomedical properties, the physical–chemical characterization of many protein-polymer conjugates is missing. Here, we evaluated the thermal stability of a set of fully-degradable polyphosphoester-protein conjugates by variable temperature circular dichroism, a common but powerful technique. We extensively describe their thermodynamic stability in different environments (in physiological buffer or in presence of chemical denaturants, e.g., acid or urea), highlighting the protective role of the polymer in preserving the protein from denaturation. For the first time, we propose a simple but effective protocol to achieve useful information on these systems in vitro, useful to screen new samples in their early stages

Modular chiral Eu(iii) complexes for efficient circularly polarized OLEDs

Achieving both high dissymmetry factors and strong emission in circularly polarized (CP) luminescent materials and, at the same time, compatibility with manufacturing processes for organic electronic devices, is a crucial issue for reliable applications of CP emitters in many fields, such as chiral electronics and optoelectronics. In this communication, we show that the independent choice of the sensitizing and the chirality inducing ligands allows europium(III) complexes to meet the multiple requirements for solution processed efficient CP electroluminescent devices

Primers for the Adhesion of Gellan Gum-Based Hydrogels to the Cartilage: A Comparative Study

A stable adhesion to the cartilage is a crucial requisite for hydrogels used for cartilage regeneration. Indeed, a weak interface between the tissue and the implanted material may produce a premature detachment and thus the failure of the regeneration processes. Fibrin glue, cellulose nanofibers and catecholamines have been proposed in the state-of-the-art as primers to improve the adhesion. However, no studies focused on a systematic comparison of their performance. This work aims to evaluate the adhesion strength between ex vivo cartilage specimens and polysaccharide hydrogels (gellan gum and methacrylated gellan gum), by applying the mentioned primers as intermediate layer. Results show that the fibrin glue and the cellulose nanofibers improve the adhesion strength, while catecholamines do not guarantee reaching a clinically acceptable value. Stem cells embedded in gellan gum hydrogels reduce the adhesion strength when fibrin glue is used as a primer, being anyhow still sufficient for in vivo applications

A chiral lactate reporter based on total and circularly polarized Tb(iii) luminescence

The coordination features and signaling of a l-lactate ion by a [Tb(bpcd)]+(bpcd = N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N′-diacetate) complex have been investigated by means of a combination of techniques, including total luminescence, calorimetry and circularly polarized luminescence. The l-lactate/[Tb(bpcd)]+association constant, determined by both luminescence titration and isothermal titration calorimetry, indicates a weak interaction (log K = 1.3-1.45) between the analyte and both enantiomers of the complex. The theoretical DFT calculations suggest that the most likely coordination of l-lactate to the possible stereoisomers of the [Tb(S,S-bpcd)]+complex (trans-O,O or trans-Npy,Npy) is one involving a hydroxyl group. The results of [Tb(rac-bpcd)]+as a chiroptical luminescent probe of l-lactate underline the peculiar role of the chiral 1,2-diaminocyclohexane (DACH) backbone. Indeed, the target anion is capable of inducing CPL activity in the racemic mixture of Tb complexes containing DACH-based ligands. The same is not observed for the achiral analogue [Tb(bped)]+(bped = N,N′-bis(2-pyridylmethyl)ethylenediamine-N,N′-diacetate) complex, likely because of the flexibility of the ethylenic group which allows an interconversion between different isomers which produces a null net CPL activity. Thanks to the differential quantum yield of the two diastereomeric species (R,R)-l and (S,S)-l, one can use the racemic complex to reveal l-lactate by measuring the induced CPL spectrum. Interestingly, this has been demonstrated in a commercial complex solution for medical use, containing several electrolytes, namely Ringer's lactate