24 research outputs found
A comparative study of interaction of tetracycline with several proteins using time resolved anisotropy, phosphorescence, docking and FRET
A comparative study of the interaction of an antibiotic Tetracycline hydrochloride (TC) with two albumins, Human serum albumin (HSA) and Bovine serum albumin (BSA) along with Escherichia Coli Alkaline Phosphatase (AP) has been presented exploiting the enhanced emission and anisotropy of the bound drug. The association constant at 298 K is found to be two orders of magnitude lower in BSA/HSA compared to that in AP with number of binding site being one in each case. Fluorescence resonance energy transfer (FRET) and molecular docking studies have been employed for the systems containing HSA and BSA to find out the particular tryptophan (Trp) residue and the other residues in the proteins involved in the binding process. Rotational correlation time (Īøc) of the bound TC obtained from time resolved anisotropy of TC in all the protein-TC complexes has been compared to understand the binding mechanism. Low temperature (77 K) phosphorescence (LTP) spectra of Trp residues in the free proteins (HSA/BSA) and in the complexes of HSA/BSA have been used to specify the role of Trp residues in FRET and in the binding process. The results have been compared with those obtained for the complex of AP with TC. The photophysical behaviour (viz., emission maximum, quantum yield, lifetime and Īøc) of TC in various protic and aprotic polar solvents has been determined to address the nature of the microenvironment of TC in the protein-drug complexes
Protein-Mediated Efficient Synergistic āAntenna Effectā in a Ternary System in D<sub>2</sub>O Medium
A ternary system consisting of a protein, catechin (either
+ or
ā epimer), and TbĀ(III) in suitable aqueous buffer medium at
physiological pH (= 6.8) has been shown to exhibit highly efficient
āantenna effectā. Steady state and time-resolved emission
studies of each component in the binary complexes (protein with TbĀ(III)
and (+)- or (ā)-catechin with TbĀ(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 TbĀ(III) from OāH oscillator and increased TbāC (+/ā)
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 ĻĻ*
triplet state of Trp residue in protein and that of catechin apart
from protection of the TbĀ(III) environment from matrix vibration.
The simple system consisting of (+)- or (ā)-catechin and TbĀ(III)
in D<sub>2</sub>O buffer at pH 6.8 has been prescribed to be a useful
biosensor
Interaction of multitryptophan protein with drug: An insight into the binding mechanism and the binding domain by time resolved emission, anisotropy, phosphorescence and docking
The interaction of antibiotic Tetracycline hydrochloride (TC) with Alkaline Phosphatase (AP) from Escherichia coli, an important target enzyme in medicinal chemistry, having tryptophan (Trp) residues at 109, 220 and 268 has been studied using the steady state and time resolved emission of the protein and the enhanced emission of the bound drug. The association constant at 298 K (ā10<sup>6</sup> [M]<sup>ā1</sup>) and the number of binding site (= 1) were estimated using the quenched Trp emission of AP, the enhanced emission and the anisotropy of the bound drug. The values of ĪH<sup>0</sup> and ĪS<sup>0</sup> are indicative of electrostatic and H-bonding interaction. The low temperature phosphorescence of free AP and the protein- drug complex and molecular docking comprehensively prove the specific involvement of partially exposed Trp 220 in the binding process without affecting Trp 109 and Trp 268. The Fƶrster energy transfer (ET) efficiency and the rate constant from the Trp residue to TC = 0.51 and ā10<sup>8</sup> s<sup>ā1</sup> respectively. Arg 199, Glu 219, Trp 220, Lys 223, Ala 231, Arg 232 and Tyr 234 residues are involved in the binding process. The motional restriction of TC imposed by nearby residues is reflected in the observed life time and the rotational correlation time of bound TC
Pentanuclear 3d-4f heterometal complexes of MII3LnIII2 (M = Ni, Cu, Zn and Ln = Nd, Gd and Tb) combinations: syntheses, structures, magnetism and photoluminescence properties
A new family of pentanuclear 3d-4f heterometal complexes of general composition [LnIII2(MIIL)3(Ī¼3-O)3H](ClO4)Ā·xH2O (1-5) [Ln = Nd, M = Zn, 1; Nd, Ni, 2; Nd, Cu, 3; Gd, Cu, 4; Tb, Cu, 5] have been synthesized in moderate yields (50-60%) following a self-assembly reaction involving the hexadentate phenol-based ligand, viz., N,N-bis(2-hydroxy-3-methoxy-5-methylbenzyl)-Nā²,Nā²-diethylethylenediamine (H2L). 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 [MIIL] units in these complexes are acting as bis-bidentate metalloligands and, together with Ī¼3-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+ ion that occupies the central position at the 3-fold axis. Magnetic properties of the copper(II) complexes (3-5) show a changeover from antiferromagnetic in 3 to ferromagnetic 3d-4f interactions in 4 and 5. For the isotropic CuII-GdIII compound 4, the simulation of magnetic data provides very weak Cu-Gd (J1 = 0.57 cm-1) and Gd-Gd exchange constants (J2 = 0.14 cm-1). Compound 4 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 (S = 17/2) and a negative value of D (-0.12 cm-1) result in a very small barrier (8 cm-1) for this compound. Among the three NdIII2MII3 (M = ZnII, NiII, and CuII) complexes, only the ZnII analogue (1) displays an NIR luminescence due to the 4F3/2 ā 4I11/2 transition in NdIII when excited at 290 nm. The rest of the compounds do not show such NdIII/TbIII-based emission. The paramagnetic CuII and NiII ions quench the fluorescence in 2-5 and thereby lower the population of the triplet stat
Pentanuclear 3dā4f 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 3dā4f
heterometal complexes of general composition [Ln<sup>III</sup><sub>2</sub>(M<sup>II</sup>L)<sub>3</sub>(Ī¼<sub>3</sub>-O)<sub>3</sub>H]Ā(ClO<sub>4</sub>)Ā·<i>x</i>H<sub>2</sub>O (<b>1</b>ā<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
(50ā60%) following a self-assembly reaction involving the hexadentate
phenol-based ligand, viz., <i>N</i>,<i>N</i>-bisĀ(2-hydroxy-3-methoxy-5-methylbenzyl)-<i>N</i><sup>ā²</sup>,<i>N</i><sup>ā²</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 Ī¼<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 copperĀ(II) complexes (<b>3</b>ā<b>5</b>) show a changeover from antiferromagnetic
in <b>3</b> to ferromagnetic 3dā4f interactions in <b>4</b> and <b>5</b>. For the isotropic Cu<sup>II</sup>āGd<sup>III</sup> compound <b>4</b>, the simulation of magnetic data
provides very weak CuāGd (<i>J</i><sub>1</sub> =
0.57 cm<sup>ā1</sup>) and GdāGd exchange constants (<i>J</i><sub>2</sub> = 0.14 cm<sup>ā1</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> (ā0.12 cm<sup>ā1</sup>) result in a very small barrier
(8 cm<sup>ā1</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> ā <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>ā<b>5</b> and thereby lower the population of the triplet state
Plot of Ļ (A) and <Ļ> (B) against (I) dielectric constant (Īµ), (II) solvent polarizability parameter (Ļ*), (III) Hydrogen bond donating ability (Ī±) of different solvents, (1) DMSO, (2) DMF, (3) EG, (4) EtOH, (5) i-PrOH.
<p>Plot of Ļ (A) and <Ļ> (B) against (I) dielectric constant (Īµ), (II) solvent polarizability parameter (Ļ*), (III) Hydrogen bond donating ability (Ī±) of different solvents, (1) DMSO, (2) DMF, (3) EG, (4) EtOH, (5) i-PrOH.</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 (ĪASA) of Tryptophan Obtained by the Docking Studies.
<p>Distances and of Tryptophan Residues of Different Proteins from TC Changes in Accessible Surface Area (ĪASA) of Tryptophan Obtained by the Docking Studies.</p
Steady State and Time Resolved Emission of TC in Various Solvents.
<p>(<b>A</b>) Fluorescence spectra of TC (25 ĀµM) at 298 K in (1) water, (2) ethanol (EtOH), (3) isopropanol (iPrOH), (4) ethylene glycol (EG), (5) dimethylformamide (DMF), (6) dimethyl sulphoxide (DMSO); Ī»<sub>exc</sub>ā=ā370 nm; excitation and emission band passā=ā10 nm and 5 nm respectively. (<b>B</b>) Fluorescence decay of TC (25 ĀµM) at 298 K in (B) EtOH, iPr-OH, EG, DMF, DMSO; Ī»excā=ā370 nm; excitation and emission bandpassā=ā10 nm each.</p
The Changes in Accessible Surface Area (ĪASA)<sup>a</sup> of the Residues of Serum Albumins after Complexed with Tetracycline.
a<p>ĪASA<sub>i</sub>ā=āASA<sup>i</sup><sub>HSA/BSA</sub> ā ASA<sup>i</sup><sub>HSA/BSA ā TC complex.</sub></p