Binding and Fluorescence Resonance Energy Transfer (FRET) of Ruthenium(II)-Bipyridine-Calixarene System with Proteins—Experimental and Docking Studies

The investigation of the interaction of ruthenium(II)-bipyridine-tert-butylcalix[4]arene complexes (Rubc2 and Rubc3) with proteins (BSA and ovalbumin) using absorption, emission, excited state lifetime and circular dichroism techniques and by docking studies show that luminophore-receptor system bind strongly with proteins. An enhancement of absorption as well as emission intensity of Ru(II)-calixarene complexes in the presence of proteins, but the quenching of the emission intensity of proteins in the presence of Ru(II)-calixarene complexes are the interesting observations. The enhancement of emission intensity of Ru(II)-calixarene complex, in the presence of proteins, is due to the fluorescence resonance energy transfer (FRET) from protein to Ru(II)-calixarene complex. Among the two Ru(II)-calixarene complexes synthesized Rubc3 has more efficient binding and energy transfer than Rubc2 and BSA, with a large cavity size, has the advantage for binding over ovalbumin. Docking studies reveal that the presence of tert-butylcalix[4]arene moiety in Ru(II)-calixarene complexes facilitates binding with proteins. After the binding of Rubc2 and Rubc3 with proteins, the nearby fluorophores present in proteins are in optimal distance from the ruthenium centre for efficient FRET process to occur.     

A novel colorimetric receptor responding AcO anions based on an azo derivative in DMSO and DMSO/water solution

A novel and efficient receptor based on the phenylhydrazone derivatives is successfully developed and applied to the acetate anion recognition, indicating that the origin of special preference for acetate (AcO⁻) anion maybe the structure well matching between the host and the guest. The sensor changes its color so obviously on addition of the acetate ions and that may make the naked-eye recognition in DMSO and even in DMSO/H₂O (95/5) solution come true. Also, the anion binding ability determinations were performed by UV-vis titration and ¹H NMR titration experiments with different anions in the solutions mentioned. The fluorescence enhancement can also be observed after the host is coordinated with the AcO⁻ anion and excited by light wavelength at 280 nm.     

Singlet excited states of anions with higher main group elements

Previous studies have shown that dipole-bound excited states exist for certain small anions. However, valence excited states have been reported for some closed-shell anions, but those with singlet valence excited states have, thus far, contained a single silicon atom. This work uses high-level coupled cluster theory previously shown to reproduce excited state energies to better than 0.1 eV compared with experiment in order to examine the electronic excited state properties of anions containing silicon and other higher main group atoms as well as their first row analogues. Of the 14 anions involved in this study, 9 possess bound excited states of some kind: CH₂SN^?, C₃H^?, CCSiH^?, CCSH^?, CCNH^?₂, CCPH^?₂, BH₃PH^?₂, AlH₃NH^?₂ and AlH₃PH^?₂. Two possess clear valence states: CCSiH^? and its first row analogue C₃H^?. Substantial mixing appears to be present in the valence and dipole-bound characters for the first excited state wavefunctions of many of the systems reporting excited states, but the mixing is most pronounced with the ammonia borane-like AlH₃NH^?₂, and AlH₃PH^?₂ anions. Inclusion of second row atoms in anions whose corresponding radical is strongly dipolar increases the likelihood for the existence of excited states of any kind, but among the systems considered to date with this methodology, only the nature of group 14 atoms in small, closed-shell anions has yet been shown to allow valence singlet excited states.     

含酚羟基席夫碱的合成及其阴离子识别

设计和合成一个基于3,5-二叔丁基水杨醛-p-硝基苯腙含酚羟基的新型阴离子受体1. 在加入AcO^-和F^-后,受体1发生从深黄色到紫色的颜色变化. 然而,在加入其它阴离子(H₂PO₄^-, Cl^-, Br^-, I^-)没有明显的颜色变化. 通过紫外和荧光滴定研究了受体与AcO^-和F^-结合的性质.     

The lowest metal-to-bipyridine charge-transfer excited state of [Cr(2,2′-bipyridine)(CO)4]

The DV-Xα molecular-orbital calculations have been carried out on [Crbpy(CO)₄](bpy,2,2′-bipyridine) and its electron attachment and detachment products. The one-electron attachment of [Crbpy(CO)₄] yields a complex of bipyridine anion radical, while the one-electron detachment results in ionization of the central metal atom. The lowest excited state of [Crbpy(CO)₄] is the metal-to-ligand charge-transfer (MLCT) excited state which consists of the bipyridine anion radical and the central metal ionized. The transition-state calculation predicts the lowest MLCT excited states at around 23～30×10³ cm^?1 and the lowest bipyridine (π,π^*) excitations at 36×10³ cm^?1 and 42～45×10³ cm^?1. The calculation also concludes that the MLCT excitation induces a counter migration of the other electrons not directly involved in the charge-transfer excitation. The configuration-interaction calculations predict the lowest MLCT excited singlet states at around 21～35×10³ cm^?1 and the lowest bipyridine (π, π^*) excited singlet states at 42～62×10³ cm^?1, while the emissive lowest MLCT triplet state is at 17×10³ cm^?1. The transition moments evaluated with the transition-state wavefunctions can reproduce qualitatively the observed absorption spectral profile. The intensity of the MLCT transitions is obtained from the allowed (π, π^*) transitions of coordinated bipyridine but is not due to the intrinsic transition moments of MLCT excitations.     

Optical, spectroscopic, and electrochemical properties of cyclometalated complexes of platinum metals based on 2-tolylpyridine and benzo[h]quinoline in ethylenediamine

Cyclometalated [M(C∧N)En]PF₆ (M = Pd(II), Pt(II)) and [M(C∧N)₂En]PF₆ (M = Rh(III), Ir(III)) complexes ((C∧N)^? corresponds to the deprotonated forms of 2-tolylpyridine and benzo[h]quinoline, and En is ethylenediamine) are studied by ¹H NMR spectroscopy, electronic absorption and emission spectroscopy, and voltammetry. Metalation of heterocyclic ligands leads to the formation of five-membered {M(C∧N)} cycles in the composition of square planar and octahedral complexes of the cis-C,C structure. Correlation of the energy positions of the long-wavelength metal-to-ligand charge-transfer absorption bands with the difference between the potentials of one-electron waves of metal-centered oxidation and ligand-centered reduction of complexes is shown. The phosphorescence of the complexes in the visible region of 469–524 nm is attributed to the radiative transition from the metal-modified intraligand excited state. The temperature quenching of the phosphorescence of complexes is attributed to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.     

Tuning Photophysical and Electrochemical Properties of Phosphorescent Heteroleptic Iridium Complex Salts–as Chemosensors

Photophysical and electrochemical studies of cyclometalated cationic heteroleptic iridium(III) complex salts have been carried out. For these complex salts the intense absorption bands appeared around 263 nm and are assigned to spin-allowed π-π* transitions of phenanthroline ligands. Moderately intense and weak absorption bands observed around 341 and 440 nm, respectively. These bands are assigned to spin-allowed metal to ligand charge transfer ¹MLCT and ³MLCT transitions, respectively. The influence of anions and proton on the photophysical and electrochemical studies were also carried out. The emission wavelength was red shifted and emission color changed from yellow to red by the addition of CF₃CO₂H. The solution color changed from green to brown and the emission was quenched by the addition anions such as of F^?, CH₃COO^? and H₂PO₄ ^?.     

Energy transfer between Ln(III) ions in aqueous solutions upon formation of labile binuclear fluoride and nitrate complexes of these ions

The influence of anions on nonradiative electronic energy transfer between lanthanide ions in aqueous solutions is studied. The rate constant k _t of energy transfer was found to increase by three orders of magnitude upon addition of salts of hydrofluoric acid to the solution. This effect is caused by the formation of bridge labile binuclear complexes, an excited energy donor-fluorine anion-acceptor, which increase the encounter time between a donor and an acceptor, resulting in the increase in the probability of energy transfer. The independence of k _t of the Förster overlap integral in the bridge complex containing F^? was explained by the fact that energy transfer occurs in each event of the binuclear complex formation, the maximum rate constant of energy transfer being equal to the rate constant of the binuclear complex association. Bridge complexes formed via the NO ₃ ^? anion are also considered. These binuclear complexes are unstable, and k _t for them is proportional to the Förster overlap integral. In this case, energy transfer occurs not during each event of the complex formation. This allows us to estimate the lower limit of the dissociation constant of the binuclear complex and its stability constant. Thus, the study of influence of various anions on energy transfer represents a new efficient luminescent method for analysis of properties of labile binuclear complexes in solutions.     

Ferrihydrite modification by boron doping

Application of the electrostatic ion storage ring ELISA to studies of clusters and biomolecules is discussed. Ions injected from a plasma source or a sputter source are hot, and at short times the yield of neutrals is usually dominated by decay of metastable ions. We have demonstrated that the decay function is close to a 1/t dependence when the internal energy of the ions is conserved, i.e., when photon emission can be ignored. Deviations from a 1/t distribution therefore gives information about the radiative lifetime or, for larger systems, about the intensity of the emitted radiation. Systematic measurements have been carried out for fullerene anions C _N ^?, for even values of N from 36 to 96, to test a classical dielectric model. Recently we have installed an electrospray ion source with a Paul trap for bunching, which can be used to inject biomolecular ions from solution, and the first experiments on laser spectroscopy of biomolecules have been carried out. Also lifetimes of excited states have been measured for stored biomolecular ions excited by a laser pulse.

     

Influence of ligand-bridged substitution on the exchange coupling constant of chromium-wheels host complexes: a density functional theory study

Designing and introducing novel wheel-shaped supramolecular as host complexes with new magnetic properties is the theme of the day. So in this study, new eight binuclear chromium (III) complexes, as models of real chromium-wheel host complexes, were designed based on changing of bridged-ligands and exchange coupling constants (J) of them were calculated using the broken symmetry density functional theory approach. Substitution of fluorine ligand in fluoro-bridged model [Cr₂F(tBuCO₂)₂(H₂O)₂(OH)₄]^?1 by halogen anions (Cl^?, Br^? and I^? ) decreased the antiferromagnetic exchange coupling between Cr(III) centres such that by going from F^? to I^? the J values became more positive. In the case of hydroxo-bridged model [Cr₂OH(tBuCO₂)₂(H₂O)₂(OH)₄]^?1, replacement of hydroxyl by methoxy anion (OMe^?) strengthened the antiferromagnetic property of the complex but substitution by sulfanide (SH^?) and amide (NH₂^?) anions weakened it and changed the nature of complexes to ferromagnetic. Because of their different magnetic properties, these new investigated complexes can be suggested as interesting synthetic targets. Also, the J value changes due to ligand substitution were evaluated and it was found that the Cr–X bond strength and partial charges of involved atoms were the most effective factors on it.     

Optical and spectroscopic properties of substituted oxa- and thiazole luminophores metalated with platinum metals

The cyclometalated [M(pbo)En]PF₆(M = Pd(II), Pt(II)), [M(pbo)₂En]PF₆ (M = Rh(III), Ir(III)), and [Rh(C∧N)₂En]PF₆ ((C∧N)^? are the deprotonated forms of 2-phenylbenzoxazole (pbo), 2,5-diphenyloxazole (dpo), 2-phenylbenzothiazole (pbt), 2-biphenyl-4-yl-5-phenyloxazole (bpo), and 2-biphenyl-4-yl-6-phenylbenzoxazole (bpbo) and En is ethylenediamine) complexes are studied by ¹H NMR spectroscopy, IR spectroscopy, and electronic absorption and emission spectroscopy. Metalation of luminophores leads to the formation of five-membered {M(C∧N)} cycles in the composition of plane-square and octahedral complexes of the cis-C,C structure. In addition to the intraligand (IL) π-π* optical transitions in the UV region, the complexes are characterized by long-wavelength metal-to-ligand charge-transfer (MLCT) absorption bands in the region of 366–416 nm. The phosphorescence of the complexes in the visible region (482–531 nm) is attributed to radiative transition from the mixed IL/MLCT electronically excited state. The temperature quenching of the phosphorescence of complexes is attributed to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.     

Influence of Oxygen Vacancies on the Luminescence Spectra of Y2O3 Thin Films

Luminescence spectra of Y₂O₃ thin films annealed in air and in vacuum are investigated. It is established that the presence of oxygen vacancies leads to a decrease in the intensity of the luminescence band with a maximum at 3.4 eV (related to emission of selflocalized Frenkel excitons describing the excited state of a molecular ion (YO₆)^9–) and of the luminescence band with a maximum at 2.9 eV (related to the anion sublattice). It is revealed that the oxygen vacancies also lead to a decrease in the luminescence intensity in the 2.60, 2.35, 2.10. 1.90, and 1.70 eV bands that are related to radiative recombination in the donor–acceptor Y³⁺–O^2– pairs. The donor–acceptor distances are calculated.     

Design of Two Pyrazole-Based Sensors with Similar Configuration and Different Fluorescent Response to Anions

Two simple fluorescent anion receptors based on 1-phenyl-3-methylpyrozole-5-one-4-one phenylhydrazone (L1) and 1-phenyl-3-methylpyrozole-5-one-4-one p-nitrophenylhydrazone (L2) were designed, synthesized and characterized with ¹H NMR, COSY spectrum, ¹³C NMR, ESI-mass and elemental analyse. Interestingly, two receptors with similar configuration exhibited different anion binding behaviors in DMSO solution. The results of Job plots and ESI-mass spectrum indicate that L1 bind anions such as F⁻, AcO⁻, H₂PO₄⁻ to form 2:1 host-guest complexation, while L2 bind anions to form 1:1 host-guest complexation in the solution.     

Hypersensitivity in the Luminescence and 4f?C4f Absorption Properties of Mono- and Dinuclear EuIII and ErIII Complexes Based on Fluorinated ??-Diketone and Diimine/ Bis-Diimine Ligands

The results of our investigation on the sensitized luminescence properties of three Eu(III) ??-diketonate complexes of the form [Eu₂(fod)₆(??-bpm)], [Eu(fod)₃(phen)] and [Eu(fod)₃(bpy)] and 4f?C4f absorption properties of their Er(III) analogues ( fod = anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2??-bipyrimidine, phen = 1,10-phenanthroline and bpy = 2,2??-bipyridyl) in a series of non-aqueous solvents are presented. The Eu(III) complexes are highly luminescent and their luminescence properties (intensity and band shape) are sensitive to the changes in the inner coordination sphere of the Eu(III) ion. The luminescence intensity of the mononuclear complexes in pyridine is drastically decreased. The coordination structure of the complexes in pyridine is transformed into a more symmetrical one which results into a slow radiative rate of the emission from the complexes. The ancillary ligands, phen and bpy are found better co-sensitizers as compared to the bpm to sensitize Eu(III)-luminescence. The 4f?C4f absorption properties (oscillator strength and band shape) of the Er(III) complexes demonstrate that ⁴G_11/2 ?? ⁴I_11/2 and ²H_11/2 ?? ⁴I_15/2 hypersensitive transitions of Er(III) are very sensitive in some coordinating solvents which reflects complex?Csolvent interaction in solution. The hypersensitive transitions of [Er(fod)₃(phen)] remain unaffected in any of the solvents and this complex retains its bulk composition in solution. The erbium complexes as well as the Er(fod)₃ chelate are invaded by DMSO. This solvent enters the inner coordination sphere by replacing heterocyclic ligand and the complexes acquire similar structure [Er(fod)₃(DMSO)₂] in this solvent. The results reveal that the luminescence and absorption properties of lanthanide complexes in solution can be controlled by tuning the coordination structure through ancillary ligands and donor solvents. This work shall prove useful in designing new biological applications with such probes.     

Mechanism of thermoluminescence in Sm- and Eu-doped barium sulphate

Thermoluminescence, TL emission spectra, ESR and optically excited luminescence of BaSO₄:Sm and BaSO₄:Eu were investigated. The optically excited luminescence studies showed that samarium ions were stabilized in the trivalent state in doped samples, and a fraction of these ions was reduced to the divalent state on γ-irradiation. These reduced ions were reoxidized on thermal annealing. Europium was found to be stabilized in the divalent form in BaSO₄:Eu phosphor, both before and after γ-irradiation. These results were further confirmed from the emission spectra of different glow peaks from BaSO₄:Sm and BaSO₄:Eu samples. The ESR spectra of these samples, recorded after γ-irradiation and various post-irradiation thermal annealings, revealed that anion radicals (such as SO₄^?, SO₃^?, SO₂⁺ and O₃^?) are formed on γ-irradiation and get annihilated at temperatures which corresponds to some of the glow peaks. An attempt is made to explain the results by a mechanism, suggested earlier for other impurity-doped BaSO₄ phosphors, in which holes released on thermal activation from anion radicals recombine with the electrons trapped at certain defect centres and the energy thus released is non-radiatively transferred to the impurity ions, which give their characteristic emission.     

Theory and experiment: Anion binding property of novel phenanthroline or aromatic bridged compounds

A series of artificial compounds, phenanthroline or aromatic bridged indoline derivatives, have been designed and synthesized. The interaction of these compounds with biologically important anions fluoride (F^?), acetate (AcO^?), dihydrogen phosphate (H₂PO₄^?), chloride (Cl^?), bromide (Br^?) and iodide (I^?) was determined by UV–vis, fluorescene titration and theoretical experiments. Results indicate that compound 1 (Di((1″,2″-dihydro-indol-3″-one-2″-hydrazone-1′-hydrazyl)-2′-methylene)-1,3-did-ehydebenzo) and 2 (Di((1″,2″-dihydro-indol-3″-one-2″-hydrazone-1′-hydrazyl)-2′-methylene)-1,3-didehyde-5-nitrobenzo) containing aromatic bridge do not show binding ability for various anions, and that compound 3 (Di((1″,2″-dihydro-indol-3″-one-2″-hydrazone-1′-hydrazyl)-2′-methylene)-2,9-dial-dehyde-1,10-phenanthroline) containing phenanthroline bridge shows the strongest binding ability for F^? among various anions, the moderate binding ability for AcO^? and H₂PO₄^?, and almost no binding ability for Cl^?, Br^?, I^?. The different binding ability of aromatic and phenanthroline bridged compounds may be related to the conjugative effect. What's more, the binding ability of compound 3 with F^? is not interfered by the existence of other anions. Hence, theoretical investigations explore the reasons of different binding ability between compound 3 and anions.     

Counter anion effect on structural,opto-electronic and charge transport properties of fused π-conjugated imidazolium compound

The structure–activity relationship of fused π-conjugated imidazolium cation with three counter anion molecules, BF₄^?, CF₃SO₃^? and (CF₃SO₂)₂N^?, was studied using electronic structure calculations. The structural, opto-electronic and charge transport properties of these complexes were studied. The charge transfer from π-conjugated imidazolium(I) to counter anion was confirmed in all the studied complexes. Interaction energy varies significantly depending on the counter anion and the stability was found higher for I-BF₄ complex than both I–CF₃SO₃ and I–(CF₃SO₂)₂N complexes. The strong (C–H)⁺···F^? hydrogen bond of length 1.95 Å between fused π-conjugated imidazolium and BF^?₄ anion is the driving force for the strongest interaction energy in I–BF₄ complex. The energy decomposition analysis confirms that the interaction between imidazolium and counter anion is mainly driven by electrostatic and orbital interaction. It has been observed that the absorption spectra of the complex are independent of anion nature but the influence of anion character is observed on frontier molecular orbital pattern. The charge transport property of I–BF₄ complex was studied by using tight-binding Hamiltonian approach and found that the hole mobility in I–BF₄ is 1.13 × 10^?4 cm² V^?1 s^?1.     

Spectroscopic study of thulium-activated double sodium yttrium fluoride Na<Subscript>0.4</Subscript>Y<Subscript>0.6</Subscript>F<Subscript>2.2</Subscript>:Tm<Superscript>3+</Superscript> crystals: I. Intensity of spectra and luminescence kinetics

Na_0.4Y_0.6F_2.2:Tm³⁺ crystals with a thulium content from 1 to 100 at % have been grown by the Stockbarger-Bridgman method. The optical spectra of Na_0.4Y_0.6F_2.2:Tm³⁺ crystals were investigated in detail at room and low (10 K) temperatures, and the luminescence kinetics was analyzed using different excitation methods. The structure of the Stark splitting of thulium levels as “quasi-centers,” characterized by inhomogeneous broadening of the Stark components, is determined from analysis of the absorption spectrum at 10 K. The oscillator strengths of the transitions from the ground state to excited multiplets are determined from the absorption cross-section spectra at 300 K for ten transitions in the range 5000–38 500 cm^?1 and seven transitions in the range 5000–28 500 cm^?1. The transition intensity parameters Ω _t , obtained by the Judd-Ofelt method from the spectra due to the transitions to ten and seven excited levels, were found to be, respectively, (i) Ω₂ = 1.89 × 10^?20, Ω₄ = 2.16 × 10^?20, and Ω₆ = 1.40 × 10^?20 cm² and (ii) Ω₂ = 2.04 × 10^?20, Ω₄ = 2.01 × 10^?20, and Ω₆ = 1.44 × 10^?20 cm². These values of the intensity parameters were used to calculate the radiative transition probabilities and branching ratios and to estimate the multiphonon nonradiative transition probabilities for NYF:Tm. The luminescence decay kinetics from thulium radiative levels upon their selective excitation by nanosecond laser pulses has been studied and the lifetimes of thulium radiative levels in NYF crystals have been found.     

Luminescence properties of lanthanide(III) ions in concentrated carbonate solution

Luminescence properties of lanthanide(III) ions (Ln = Nd, Sm, Eu, Gd, Tb, Dy and Tm) were investigated by measuring the excitation and emission spectra, and emission lifetimes in H₂O and D₂O solutions of 3 moll^?1 K₂CO₃, where anionic tetra-carbonate complexes, [Ln(CO₃)₄]^5- were the predominant species.

Electronic transitions of the carbonato complex corresponding to both the excitation and emission spectra were assigned from the energy level diagrams of Ln(III) and compared with those of the aqua ion. Enhancement of emission intensity of the complex was observed at particular excitation transitions of Eu(III), Gd(III) and Tb(III), and at particular emission transitions of Sm(III), Eu(III), Dy(III) and Tm(III). The enhancement at the emission transition was estimated quantitatively as a branching ratio from the lowest emitting state of Ln(III), and discussed in terms of hypersensitivity.

Emission lifetimes of the carbonato complexes were all longer than those of aqua ions in H₂O solution, while the lifetimes of the complexes for Eu(III) and Tb(III) shorter than those in D₂O solution. The difference in non-radiative decay constants for the excited complex in H₂O and D₂O solutions was found to be proportional to an exponential of the energy gap of Ln(III). The lifetime ratio between the H₂O and D₂O solutions showed the order of Sm > Dy > Eu > Tb, corresponding to the opposite order of the energy gap. These were discussed in terms of an energy gap law, i.e. a relationship between the energy gap of Ln(III) and vibration energies of the ligand or water molecules.     

Optimization of soft x-ray line emission from laser-produced carbon plasma with laser intensity

Absolute measurement for He-α resonance (1s^{2 1}S₀?1s2p¹ P ₁, at 40.2 Å) line emission from a laser-produced carbon plasma has been studied as a function of laser intensity. The optimum laser intensity is found to be ≈1.3×10¹² W/cm² for the maximum emission of 3.2 × 10¹³ photons sr^?1 pulse^?1. Since this line lies in the water window spectral region, it has potential application in x-ray microscopic imaging of biological sample in wet condition. Theoretical calculation using corona model for the emission of this line is also carried out with appropriate ionization and radiative recombination rate coefficients