(INVITED) Energy transfer processes in Sr3Tb(PO4)3 eulytite-type materials singly doped with Nd3+ and Sm3+

In this study the optical spectroscopy, the excited state dynamics and in particular the energy transfer Tb3+→Ln3+ (Ln = Nd or Sm), have been investigated in detail in eulytite double phosphate hosts of the type Sr3Tb(PO4)3 doped with 1 mol% Ln3+. It has been found that for Ln=Nd and Sm, the energy transfer efficiency (ηT) is 0.76 and 0.73, respectively, thanks to the assistance of fast migration in the Tb3+ 5D4 level. The pathway responsible for the transfer of excitation has been unambiguously identified in the case of Sr3Tb0.99Nd0.01(PO4)3, whilst the situation is more complex for Sr3Tb0.99Sm0.01(PO4)3, due to high density of the final Sm3+ states that could be involved. The Tb3+→Nd3+ energy transfer has been tentatively attributed to the exchange interaction on the basis of the short transfer distance and multipolar selection rules

Vanadium(v) oxoanions in basic water solution: A simple oxidative system for the one pot selective conversion of l-proline to pyrroline-2-carboxylate

The unprecedented, direct chemical oxidation of l-proline to pyrroline-2-carboxylate was achieved in water (pH 9-10) by means of NH4VO3/NH3or V2O5/MOH (K = Na, K), and the anion was fully characterized as ammonium or alkaline metal salts. Quantitative yield and higher atom economy performance were achieved with the latter system, the alkaline salts being more stable than the ammonium one. Different mixed valence V(iv)/V(v) compounds precipitated from the reaction mixtures depending on the nature of the employed base. A possible reaction mechanism is proposed according to DFT calculations. The analogous reaction of trans-4-hydroxy-l-proline with NH4VO3/NH3afforded pyrrole-2-carboxylic acid in 81% yield, while sarcosine underwent prevalent decomposition under similar experimental conditions. Instead, no reaction was observed with primary (glycine, l-alanine, l-phenylalanine) and tertiary α-amino acids (N,N-dimethyl-l-phenylalanine, N,N-dimethylglycine)

The effect of cation substitution on the local coordination of protons in Ba2In1.85M0.15O6H2 (M = In, Ga, Sc and Y)

We report on an investigation of the local structure and vibrational dynamics in the brownmillerite-based proton conductors Ba2In1.85M0.15O6H2 with M = In, Ga, Sc and Y. The aim is to determine the effect of the cation (M) substitution on the local coordination environment of the protons. The techniques used are infrared spectroscopy and inelastic neutron scattering. The materials are characterized by two main types of proton sites, denoted as H (1) and H(2), which are featured by different local structures. We establish that the relative population of these two proton sites varies as a function of M. Specifically, it is found that, with respect to Ba2In2O6H2, the relative population of H(1) protons increases upon the substitution of In with any of the three different cations. The strongest effect is observed for M = Ga and Sc, whereas the effect observed for M = Y is minor. This new insight motivates efforts to unravel the mobility of the two types of protons, since then cation modification would offer a rational route for improving the proton conductivity of these types of materials

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

Eu(iii) and Tb(iii) complexes of 6-fold coordinating ligands showing high affinity for the hydrogen carbonate ion: A spectroscopic and thermodynamic study

In the present contribution, four classes of Ln(iii) complexes (Ln = Eu and Tb) have been synthesized and characterized in aqueous solution. They differ by charge, Ln(bpcd)+ [bpcd2- = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate] and Ln(bQcd)+ (bQcd2- = N,N'-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate) being positively charged and Ln(PyC3A) (PyC3A3- = N-picolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) and Ln(QC3A) (QC3A3- = N-quinolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) being neutral. Combined DFT, spectrophotometric and potentiometric studies reveal the presence, under physiological conditions (pH 7.4), of a couple of equally and highly stable isomers differing by the stereochemistry of the ligands (trans-N,N and trans-O,O for bpcd2- and bQcd2-; trans-O,O and trans-N,O for PyC3A3- and QC3A3-). Their high log\u2009\u3b2 values (9.97 < log\u2009\u3b2 < 15.68), the presence of an efficient antenna effect and the strong increase of the Ln(iii) luminescence intensity as a function of the hydrogen carbonate concentration in physiological solution, render these complexes as very promising optical probes for a selective detection of HCO3-in cellulo or in extracellular fluid. This particularly applies to the cationic Eu(bpcd)+, Tb(bpcd)+ and Eu(bQcd)+ complexes, which are capable of guesting up to two hydrogen carbonate anions in the inner coordination sphere of the metal ion, so that they show an unprecedented affinity towards HCO3- (log\u2009K for the formation of the adduct in the 4.6-5.9 range)

Phase transition, radio- and photoluminescence of K3Lu(PO4)2 doped with Pr3+ ions

Luminescent characteristics of K3Lu(PO4)2:Pr3+ (1 and 5 mol.%) microcrystalline powders, a promising optical material for scintillation applications, were investigated using various experimental techniques. The material shows emission features connected with both high intensity interconfigurational 4f15d→4f2 transitions (broad UV emission bands) and intraconfigurational 4f2→4f2 transitions (weak emission lines in the visible range). The output of X-ray excited 4f15d→4f2 emission of Pr3+ increases with a temperature rise from 90 K to room tem- perature and higher depending on the Pr3+ ions concentration. The high 5% concentration of Pr3+ ions is found to be favourable for the stabilization of a monoclinic phase (P21/m space group) over a trigonal one (P3 space group) while emission properties of the material reveal that a phase transition occurs at higher temperatures. Decay kinetics of Pr3+ 4f15d→4f2 emission are recorded upon excitation with high repetition rate X-ray syn- chrotron excitation and pulse cathode ray excitation. Issues related to a non-exponential decay of luminescence and presence of slow decay components are discussed in terms of energy transfer dynamics. The presence of defects was revealed with thermoluminescence measurements and these are suggested to be the mainly responsible for delayed recombination of charge carriers on the Pr3+ 4f15d states. Some peculiarities of host-to- impurity energy transfer are discusse

Optical properties of Eu(III) and Tb(III) complexes with pyridine- and quinoline- based ligands under high hydrostatic pressure

The spectroscopy of nitrate complexes of Eu(III) and Tb(III) with chiral and racemic imine-based [L1 = (N,N'-bis (2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine) and L3 = N, N'-bis(2-quinolylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine] and amine-based [L2 = N,N'-bis(2-pyridylmethyl)-1,2-(R,R + S,S)-cyclohexanediamine) and L4 = N,N'-bis(2-quinolylmethyl)-1,2-(R,R + S,S)-cyclohexanediamine] ligands has been studied under high hydrostatic pressure (above 100 kbar). With the increasing pressure, a reduction of the Tb(III) and Eu(III) luminescence intensity is detected for all the complexes, whilst a significant reduction of the Tb(III) and Eu(III) excited state lifetimes has been observed for all Tb-based complexes [L1Tb(NO3)(3) -> L4Tb(NO3)(3)] and only for the Eu(III) complexes containing the imine-based ligands [L1Eu(NO3)(3) and L3Eu(NO3)(3)]. This behavior has been rationalized taking into account two main aspects: i) the relative position of the energy levels of the ligands and the metal ions and ii) the change of these position upon compression DFT calculations have been also performed to elucidate the nature of the orbitals involved in the UV electronic absorption transitions (NTO orbitals) upstream of the energy transfer process to the metal ion

Theoretical and Experimental Investigation of the Tb3+-Eu3+ Energy Transfer Mechanisms in Cubic A3Tb0.90Eu0.10({PO}4)3 (A = Sr, Ba) Materials

In this study the optical spectroscopy, the excited state dynamics, and in particular the Tb3+ -> Eu3+ energy transfer, have been investigated in detail both from the theoretical and experimental point of view in eulytite double phosphate hosts A(3)Tb(PO4)(3) (A = Sr, Ba) doped with Eu3+. It has been found that the energy transfer is strongly assisted by fast migration in the donor Tb3+ subset. Moreover, the transfer rates and efficiencies depend significantly on the nature of the divalent elements present in the structure and hence on the distances between Tb3+-Eu3+ nearest neighbors. It is shown that the competition between quadrupole-quadrupole and exchange interaction is crucial in accounting for the transfer rates

Effect of the Heteroaromatic Antenna on the Binding of Chiral Eu(III) Complexes to Bovine Serum Albumin

The cationic enantiopure R) and luminescent Eu(III) complex [Eu(bisoQcd)(H2O)(2)] OTf (with bisoQcd = N,N'-bis(2-isaquinolinmethyl)-trarts-1,2diaminocyclohexane N/N1 -diacetate and OTf = triflate) was synthesized and characterized. At physiological pH, the 1:1 [Eu(bisoQcd)(H2O)(2)](+) species, possessing two water molecules in the inner coordination sphere, is largely dominant. The interaction with bovine serum albumin (BSA) was studied by means of several experimental techniques, such as luminescence spectroscopy, isothermal titration calorimeti-y (ITC), molecular docking (MD), and molecular dynamics simulations M11.-.)S). In this direction, a ligand competition study was also performed by using three clinically established drugs (i.e., ibuprofen, warfarin, and digito)cin). The nature of this interaction is strongly affected by the type of the involved heteroaromatic antenna in the complexes. In fact, the presence of isoqiiinolirie rings drives the corresponding complex toward the protein superficial area containing the tryptophan residue 134 (Trp134). As the main consequence, the metal center undergoes the loss of one water molecule upon interaction with the side chain of a glutamic acid residue. On the other hand, the similar complex containing pyridine rings f[Eti(bpcd)(H2O)(2)]Cl with bpcd = N,N'-bis(2-pytidylmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate)interacts more weakly with the protein in a different superficial cavity, without losing the coordinated water molecules

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