18 research outputs found
Protein-Mediated Efficient Synergistic “Antenna Effect” in a Ternary System in D<sub>2</sub>O Medium
A ternary system consisting of a protein, catechin (either
+ or
– epimer), and Tb(III) in suitable aqueous buffer medium at
physiological pH (= 6.8) has been shown to exhibit highly efficient
“antenna effect”. Steady state and time-resolved emission
studies of each component in the binary complexes (protein with Tb(III)
and (+)- or (−)-catechin with Tb(III)) and the ternary systems
along with the molecular docking studies reveal that the efficient
sensitization could be ascribed to the effective shielding of microenvironment
of Tb(III) from O–H oscillator and increased Tb–C (+/−)
interaction in the ternary systems in aqueous medium. The ternary
system exhibits protein-mediated efficient antenna effect in D<sub>2</sub>O medium due to synergistic ET from both the lowest ππ*
triplet state of Trp residue in protein and that of catechin apart
from protection of the Tb(III) environment from matrix vibration.
The simple system consisting of (+)- or (−)-catechin and Tb(III)
in D<sub>2</sub>O buffer at pH 6.8 has been prescribed to be a useful
biosensor
Pentanuclear 3d–4f Heterometal Complexes of M<sup>II</sup><sub>3</sub>Ln<sup>III</sup><sub>2</sub> (M = Ni, Cu, Zn and Ln = Nd, Gd, Tb) Combinations: Syntheses, Structures, Magnetism, and Photoluminescence Properties
A new family of pentanuclear 3d–4f
heterometal complexes of general composition [Ln<sup>III</sup><sub>2</sub>(M<sup>II</sup>L)<sub>3</sub>(μ<sub>3</sub>-O)<sub>3</sub>H](ClO<sub>4</sub>)·<i>x</i>H<sub>2</sub>O (<b>1</b>–<b>5</b>) [Ln = Nd, M = Zn, <b>1</b>;
Nd, Ni, <b>2</b>; Nd, Cu, <b>3</b>; Gd, Cu, <b>4</b>; Tb, Cu, <b>5</b>] have been synthesized in moderate yields
(50–60%) following a self-assembly reaction involving the hexadentate
phenol-based ligand, viz., <i>N</i>,<i>N</i>-bis(2-hydroxy-3-methoxy-5-methylbenzyl)-<i>N</i><sup>′</sup>,<i>N</i><sup>′</sup>-diethylethylenediamine (H<sub>2</sub>L). Single-crystal X-ray diffraction
analyses have been used to characterize these complexes. The compounds
are all isostructural, having a 3-fold axis of symmetry that passes
through the 4f metal centers. The [M<sup>II</sup>L] units in these
complexes are acting as bis-bidentate metalloligands and, together
with μ<sub>3</sub>-oxido bridging ligands, complete the slightly
distorted monocapped square antiprismatic nine-coordination environment
around the 4f metal centers. The cationic complexes also contain a
H<sup>+</sup> ion that occupies the central position at the 3-fold
axis. Magnetic properties of the copper(II) complexes (<b>3</b>–<b>5</b>) show a changeover from antiferromagnetic
in <b>3</b> to ferromagnetic 3d–4f interactions in <b>4</b> and <b>5</b>. For the isotropic Cu<sup>II</sup>–Gd<sup>III</sup> compound <b>4</b>, the simulation of magnetic data
provides very weak Cu–Gd (<i>J</i><sub>1</sub> =
0.57 cm<sup>–1</sup>) and Gd–Gd exchange constants (<i>J</i><sub>2</sub> = 0.14 cm<sup>–1</sup>). Compound <b>4</b> is the only member of this triad, showing a tail of an out-of-phase
signal in the ac susceptibility measurement. A large-spin ground state
(<i>S</i> = 17/2) and a negative value of <i>D</i> (−0.12 cm<sup>–1</sup>) result in a very small barrier
(8 cm<sup>–1</sup>) for this compound. Among the three Nd<sup>III</sup><sub>2</sub>M<sup>II</sup><sub>3</sub> (M = Zn<sup>II</sup>, Ni<sup>II</sup>, and Cu<sup>II</sup>) complexes, only the Zn<sup>II</sup> analogue (<b>1</b>) displays an NIR luminescence due
to the <sup>4</sup>F<sub>3/2</sub> → <sup>4</sup>I<sub>11/2</sub> transition in Nd<sup>III</sup> when excited at 290 nm. The rest
of the compounds do not show such Nd<sup>III</sup>/Tb<sup>III</sup>-based emission. The paramagnetic Cu<sup>II</sup> and Ni<sup>II</sup> ions quench the fluorescence in <b>2</b>–<b>5</b> and thereby lower the population of the triplet state
Steady State and Time Resolved Emission of TC in Various Solvents.
<p>(<b>A</b>) Fluorescence spectra of TC (25 µM) at 298 K in (1) water, (2) ethanol (EtOH), (3) isopropanol (iPrOH), (4) ethylene glycol (EG), (5) dimethylformamide (DMF), (6) dimethyl sulphoxide (DMSO); λ<sub>exc</sub> = 370 nm; excitation and emission band pass = 10 nm and 5 nm respectively. (<b>B</b>) Fluorescence decay of TC (25 µM) at 298 K in (B) EtOH, iPr-OH, EG, DMF, DMSO; λexc = 370 nm; excitation and emission bandpass = 10 nm each.</p
Plot of φ (A) and <τ> (B) against (I) dielectric constant (ε), (II) solvent polarizability parameter (π*), (III) Hydrogen bond donating ability (α) of different solvents, (1) DMSO, (2) DMF, (3) EG, (4) EtOH, (5) i-PrOH.
<p>Plot of φ (A) and <τ> (B) against (I) dielectric constant (ε), (II) solvent polarizability parameter (π*), (III) Hydrogen bond donating ability (α) of different solvents, (1) DMSO, (2) DMF, (3) EG, (4) EtOH, (5) i-PrOH.</p
The Changes in Accessible Surface Area (ΔASA)<sup>a</sup> of the Residues of Serum Albumins after Complexed with Tetracycline.
a<p>ΔASA<sub>i</sub> = ASA<sup>i</sup><sub>HSA/BSA</sub> – ASA<sup>i</sup><sub>HSA/BSA – TC complex.</sub></p
Fluorescence anisotropy decays of TC (25 µM) at 298 K in pure EG.
<p>I<sub>VV</sub> and I<sub>VH</sub> represent decays of emission of TC with excitation polarizer at vertical position and emission polarizer at vertical and horizontal position, respectively. λ<sub>exc</sub> = 370 nm; excitation and emission band pass = 10 nm each.</p
Variation of (I) fluorescence quantum yield (φ).
<p>(II) fluorescence anisotropy (r); (III) singlet state average lifetime (τ) of TC (25 µM) in aqueous buffer with increasing concentration of serum albumins. (A) for BSA, (B) for HSA.</p
The plot of (A) (I) [F<sub>∞</sub> − F<sub>0</sub>]/[F<sub>x</sub> − F<sub>0</sub>] against [BSA]<sup>−1</sup>(II) (r−r<sub>f</sub>)/R(r<sub>b</sub>−r) against [BSA]; (B) (I) and (II) similar plot for HSA.
<p>The plot of (A) (I) [F<sub>∞</sub> − F<sub>0</sub>]/[F<sub>x</sub> − F<sub>0</sub>] against [BSA]<sup>−1</sup>(II) (r−r<sub>f</sub>)/R(r<sub>b</sub>−r) against [BSA]; (B) (I) and (II) similar plot for HSA.</p
The Energy Transfer Efficiency and The Rate Constant of Protein-TC Complexes at 298 K.
a<p>Ref <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060940#pone.0060940-Anand1" target="_blank">[66]</a>.</p>b<p>Considering the distance from indole N of Trp to O attached with 10-C of TC.</p
Distances and of Tryptophan Residues of Different Proteins from TC Changes in Accessible Surface Area (ΔASA) of Tryptophan Obtained by the Docking Studies.
<p>Distances and of Tryptophan Residues of Different Proteins from TC Changes in Accessible Surface Area (ΔASA) of Tryptophan Obtained by the Docking Studies.</p