Diganta Kumar Das

The role of heme propionate in controlling the redox potential of heme: Square wave voltammetry of protoporphyrinato IX iron(III) in aqueous surfactant micelles

The proton equilibrium in aqueous surfactant solutions of hemin, (PPIX)Fe(H2O)+2, involving the propionic acid groups is reported (PPIX = protoporphyrinato IX). The surfactant used are sodium dodecyl sulphate (SDS), triton X-100 (TX-100) and hexadecyl trimethylammonium bromide (CTAB). The pKa values, determined spectroscopically from the pH variations of the Soret absorption, are found at ca. 3.5 in SDS and TX-100 micelles. In the cationic surfactant (CTAB) the absorbance of hemin is independent of the hydrogen ion concentration in solution and this surfactant form a salt-link with the heme propionate group. The dependence of mid-point potential on pH indicates that the heme propionate undergoes a redox-linked changed in pKa from 3.2-3.5 in the ferric form to 4.4-4.5 in the ferrous form (27 degrees C, mu = 0.2 M). The change in the mid-point potential per unit change in pH. delta E/delta pH, is ca. -59 mV. Replacement of the water molecules in hemin by tetrahydrofuran, (PPIX)Fe(thf)+2, induces a considerable shift of pKa of the heme propionate: 6.2-6.8 in the ferric form and 7.5-7.8 in the ferrous form. The lower value of pKa in diaquo hemin is attributed to stabilisation of the propionate by a hydrogen bond with coordinated water molecules. All these results may be interpreted in terms of the involvement of a heme propionate group in redox linked uptake of protons and the influence of hydrogen bonding and salt-link formation on the pKa of the proton equilibrium.

A new fluorescent and electrochemical Zn2+ ion sensor based on Schiff base derived from benzil and L-tryptophan.

Single molecule acting as both fluorescent and electrochemical sensor for Zn(2+) ion is rare. The product (L) obtained on condensation between benzil and L-tryptophan has been characterized by H NMR, ESI-MS and FT-IR spectroscopy. L in 1:1 (v/v) CH3OH:H2O solution shows fluorescence emission in the range 300 nm to 600 nm with λmax at 350 nm when is excited with 295 nm photon. Zn(2+) ion could induce a 10-fold enhancement in fluorescent intensity of L. Fluorescence and UV/Visible spectral data analysis shows that the binding ratio between Zn(2+) ion and L is 1:1 with log β=4.55. Binding of Zn(2+) ion disrupts the photoinduced electron transfer (PET) process in L and causes the fluorescence intensity enhancement. When cyclic voltammogram is recorded for L in 1:1 (v/v) CH3OH:H2O using glassy carbon (GC) electrode, two quasi reversible redox couples at redox potential values -0.630±0.005 V and -1.007±0.005 V are obtained (Ag-AgCl as reference, scan rate 0.1 V s(-1)). Interaction with Zn(2+) ion makes the first redox couple irreversible while the second couple undergoes a 0.089 V positive shift in redox potential. Metal ions - Cd(2+), Cu(2+), Co(2+), Hg(2+), Ag(+), Ni(2+), Fe(2+), Mn(2+), Mg(2+), Ca(2+)and Pb(2+), individually or all together, has no effect on the fluorescent as well as electrochemical property of L. DFT calculations showed that Zn(2+) ion binds to L to form a stable complex. The detection limit for both fluorescence as well as electrochemical detection was 10(-6) M.

Salicylaldehyde phenylhydrazone: a new highly selective fluorescent lead (II) probe.

The fluorescence intensity of salicylaldehyde phenylhydrazone (L), in 1:1 (v/v) CH3OH:H2O was enhanced by ca. 100 times with a blue shift in emission maximum, on interaction with Pb2+ ion. No enhancement in fluorescent intensity of L was observed on interaction with metal ions - Na+, K+, Ca2+, Cu2+, Ni2+, Zn2+, Cd2+ and Hg2+. This signal transduction was found to occur via photoinduced electron transfer (PET) mechanism. A 1:1 complexation between Pb2+ and L with log β = 7.86 has been proved from fluorescent and UV/Visible spectroscopic data. The detection limit of Pb2+ was calculated to be 6.3 × 10−7 M.

Condensation Product of Phenylalanine and Salicylaldehyde: Fluorescent Sensor for Zn(2.).

The condensation product of phenylalanine and salicylaldehyde (L) was synthesised and characterised which was found to be selective fluorescent “off-on” sensor for Zn2+ ion with the detection limit 10−5 M. The sensor is free of interferences from metal ions - Na+, K+, Al3+, Mn2+, Co2+, Ni2+, Cu2+, Pb2+, Cd2+ and Hg2+. The Fluorescence and the UV/visible spectral data reveals a 1:1 interaction between the sensor and Zn2+ ion with binding constant 108. The DFT and TDDFT calculations confirm the structures of the sensor and the sensor-Zn2+ complex.

A New Fluorescent "Off-On" Sensor for Al(3+) Derived from L-alanine and Salicylaldehyde.

The condensation product of L-alanine and salicylaldehyde was synthesised and characterised which was found to be selective fluorescent “on” sensor for Al3+ ion with the detection limit 10−6 M. The sensor is free of interferences from metal ions - Na+, K+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Pb2+, Cd2+, Hg2+ and Fe3+. The Fluorescence and the UV/visible spectral data reveals a 1:1 interaction between the sensor and Al3+ ion with binding constant 104.5. The DFT and TDDFT calculations confirm the structures of the sensor and the sensor-Al3+ complex.

Surfactant Dependent pH Controlled “off-on”, “off-on-off” and “on-off” Fluorescent Switches Exhibited by N-Benzylidenenaphthalen-1-Amine

N-benzylidenenaphthalen-1-amine (L) acts as pH dependent “off-on”, “off-on-off” and “on-off” fluorescent switch in 1:1 (v/v) CH3CN:H2O depending on the presence of anionic sodiumdocdecyl sulphate (SDS), neutral triton X-100 (TX-100) and cationic cetyltrimethylammonium bromide (CTAB) surfactants respectively. DFT calculation shows the possibility of formation of L.H+ due to protonation at immine N and L.OH− due to introduction of OH− group at immine C. The relative stability of these two cationic and anionic species depends on the charge environment provided by surfactants. This influences the photoinduced electron transfer (PET) processes involved and results in different switch behaviour.

N-benzoate-N′ salicylaldehyde ethynelediamine: A new fluorescent sensor for Zn2+ ion by “off-on” mode

Imbalance of zinc ion (Zn2+) in human body causes diseases like Alzheimer’s and Parkinson’s and therefore Zn2+ estimation in biological fluids has diagnostic values. Fluorescence “off-on” sensors have advantages of high sensitivity and in situ application over other sensors. A new fluorescent “off-on” Zn2+ sensor, N-benzoate-N′ salicylaldehyde ethynelediamine (L), has been synthesisied. In 1:1(v/v) CH3OH:PBS (PBS = phosphate buffer solution), L shows ca. 20 times enhancement in fluorescence intensity on interaction with Zn2+, due to snapping of photoinduced electron transfer (PET) process, which is selective over metal ions - Na+, K+, Ca2+, Ni2+, Cu2+, Cd2+, Hg2+ and Pb2+. These metal ions either individually or all together does not interfere the sensing ability of L towards Zn2+. A 1:1 interaction between L and Zn2+ ion with binding constant 104.25 has been established from spectroscopic data.

Influence of charged microenvironment on redox potential and diffusion coefficient of [Fe4S4(SPh)4](NBu4)2 in DMF and inside CTAB film on electrode surface

Redox potential of [Fe4S4(SPh)4]2−/13—, a model of the active centre of ferredoxin, in DMF solution shows a 90-mV positive shift, when the charged microenvironment provided by the surfactant is changed from negative to positive. Inside the positive surfactant film on GC electrode there is a 235-mV positive shift in redox potential compared to that in neutral DMF solution. Diffusion coefficient of the reduced cluster onto the electrode surface is also found to be 102times greater in the presence of negative surfactant compared to that in positive surfactant.

Synthesis, characterization and superoxide dismutase activity of bi-copper(II)-bisacetato- μ− phthalicacid[bis(benzyloxy)ethyl]ester

AbstractA new binuclear copper(II) complex, bridged by the ligand phthalicacid[bis(benzyloxy)ethyl]ester, where each copper(II) is coordinated to one carboxylate (from ligand) and one acetate in square planar mode is reported. The ligand synthesized by the reaction of phthalic anhydride and ethylene glycol, has been characterized by FT-IR, 1HNMR and LCMS. The binuclear Copper(II) complex has been characterized by UV/visible spectra, FTIR spectra, EPR spectra, ESI-MS spectra, magnetic moment measurement and thermogravimetric analysis. DFT calculation has shown a Z type structure for the complex. Excellent superoxide dismutase activity with IC50 value 8.6 ×10−6 M for the complex has been observed. Graphical AbstractA new binuclear copper(II) complex, bridged by the ligand phthalicacid[bis (benzyloxy)ethyl]ester, where each copper(II) is coordinated to one carboxylate (from ligand) and one acetate in square planar mode is reported.

Structurally Simple Ferrocene Derivatives for Selective Cadmium Sensing

Three new ferrocene based Schiff bases 4-{[(E)-ferrocenylmethylidene] amino}benzenethiol (1b), 3-{[(E)-ferrocenylmethylidene]amino} benzenethiol (1c), 2-{[(E)-ferrocenylmethylidene]amino} benzenethiol (1d) have been synthesized to study their sensor property to various metal ions. It has been observed that 1b is highly fluorescent and its fluorescence changes in presence of metal ions. It was further observed that compound 1b is highly selective towards Cd2+ ion in solution.