Energies of charge transfer and formation equilibria of the complexes of [70]fullerene with some interesting polyaromatic molecules

We have investigated electron donor-acceptor complexes of [70]fullerene with various polyaromatic molecules (PAM) with different vertical ionization potentials (I(D)(v)). Well defined charge transfer (CT) absorption bands have been located in the visible region. We extract degrees of charge transfer, oscillator and transition dipole strengths by analyzing the transition energy of the CT band as a function of I(D)(v) of the donors studied. The experimental results were explained using a theoretical model that takes into account the interaction between electronic subsystems of PAM with [70]fullerene. Trends in the formation constant for the [70]fullerene/PAM complexes were discussed in terms of enthalpies and entropies of formation.     

Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction of organoboronic acids with N-protected 4-iodophenyl alanine linked isoxazoles

Suzuki-Miyaura coupling reaction of N-protected 4-iodopheyl alanine isoxazoles with arylboronic acids, catalyzed by palladium, efficiently produce benzyl-N-(4-bipheyl)-2-(3-methyl-5(E)-2-aryl-1-ethenyl-4- isoxazolyl)-amino-2-oxoethyl) carba-mates in good yields. This process is first of its kind to construct carbon-carbon bond formation having biaryl motif on amino acid linked isoxazole moiety.     

Kinetics and mechanism of oxidation of l-Cysteine by Corey’s reagent

The kinetics of oxidation of l-Cysteine by pyridinium chlorochromate (PCC) was studied at 0.1–0.3 mol dm⁻³ HClO₄ in the range 25–40 °C. The reaction exhibits first order dependence with respect to PCC and fractional order in cysteine. The increase in the oxidation rate with acidity suggests the involvement of a protonated chromium(VI) species in the rate-determining step. Cysteic acid is identified as the product of oxidation. A suitable mechanism involving the formation of a complex is proposed. The activation parameters of the rate-determining step are computed using the linear least squares method and the values of E _a and ΔS ^# are found to be 46.0 ± 2.0 KJ mol⁻¹ and −38.0 ± 3.2 JK⁻¹ mol⁻¹ respectively.     

Electrocatalytic reduction of oxygen at electrodes coated with a bimetallic cobalt(II)/platinum(II) porphyrin

Edge plane pyrolytic graphite (EPG) electrodes coated with 5-(4-pyridyl)-10,15,20-tris(3-methoxy-4-hydroxyphenyl)porphyrin and its Pt(II) and Co(II)/Pt(II) analogs undergo an electrochemical-chemical-electrochemical (ECE) reaction when anodically scanned in 1.0 M HClO4. The new redox couple formed from this anodic conditioning of the coated electrode is dependent on the pH of the solution. Roughened EPG electrodes coated with the Co(II)/Pt(II) bimetallic porphyrin show a catalytic shift of 500 mV for the reduction of O2 when compared to the reduction of O2 at a bare EPG electrode. An additional catalytic shift of ca. 100 mV is observed for O2 reduction at an EPG electrode coated with the Co(II)/Pt(II) porphyrin which has been oxidized in 1.0 M HClO4. In addition to the added electrocatalysis a significant percentage of O2 reduced at the oxidized Co(II)/Pt(II) EPG electrode is converted to H2O as determined by rotating disk electrode measurements.     

Characterization of the particulate methane monooxygenase metal centers in multiple redox states by X-ray absorption spectroscopy

The integral membrane enzyme particulate methane monooxygenase (pMMO) converts methane, the most inert hydrocarbon, to methanol under ambient conditions. The 2.8-A resolution pMMO crystal structure revealed three metal sites: a mononuclear copper center, a dinuclear copper center, and a nonphysiological mononuclear zinc center. Although not found in the crystal structure, solution samples of pMMO also contain iron. We have used X-ray absorption spectroscopy to analyze the oxidation states and coordination environments of the pMMO metal centers in as-isolated (pMMO(iso)), chemically reduced (pMMO(red)), and chemically oxidized (pMMO(ox)) samples. X-ray absorption near-edge spectra (XANES) indicate that pMMO(iso) contains both Cu(I) and Cu(II) and that the pMMO Cu centers can undergo redox chemistry. Extended X-ray absorption fine structure (EXAFS) analysis reveals a Cu-Cu interaction in all redox forms of the enzyme. The Cu-Cu distance increases from 2.51 to 2.65 A upon reduction, concomitant with an increase in the average Cu-O/N bond lengths. Appropriate Cu2 model complexes were used to refine and validate the EXAFS fitting protocols for pMMO(iso). Analysis of Fe EXAFS data combined with electron paramagnetic resonance (EPR) spectra indicates that Fe, present as Fe(III), is consistent with heme impurities. These findings are complementary to the crystallographic data and provide new insight into the oxidation states and possible electronic structures of the pMMO Cu ions.     

Early Diagnosis of Diabetes through the Eye

Diabetes mellitus is a metabolic disorder characterized by high blood sugar levels which give rise to complications in the eye, kidneys and the brain. Diabetes triggers the development of ocular diseases like diabetic retinopathy and cataracts which are the leading cause of blindness around the world. The most common method for the diagnosis of diabetes involves measuring the blood sugar levels in the body. One major disadvantage of this method is the fluctuating blood sugar levels which contribute to false negative results. This leads to delay in treatment, eventually causing permanent damage to the organs. Therefore, diagnosis of diabetes at an early stage is very crucial. One biomarker for diabetes related diseases is the formation of Advanced Glycation End‐products (AGEs) that result from the Maillard reaction of proteins with glucose. α‐crystallin in the ocular lens is a small heat shock protein with no protein turnover and hence acts as a record for post‐translational modifications especially glycation which forms AGEs. We have used steady state and time resolved fluorescence measurements to study the spectroscopic changes in α‐crystallin with increase in time of glycation and the intact lenses from diabetic and nondiabetic donors. Overall, this study was focused on developing a noninvasive diagnostic tool for early detection of diabetes mellitus.     

Kinetics and mechanism of the oxidation of glycolaldehyde by tetrachloroaurate(III)

The kinetics of the reaction between glycolaldehyde (GA) and tetrachloroaurate(III) in acetic acid-sodium acetate buffer has been studied. The reaction is first-order with respect to [Au^III] as well as [GA]. Both H⁺ and Cl⁻ ions retard the rate of reaction. AuCl₄⁻, AuCl₃(OH₂), and AuCl₃(OH)⁻ are the reactive species of gold(III) with gradually increasing reactivity. A reaction mechanism involving two-electron transfer rate determining steps has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 613–619, 1998     

Relaxation of the folding of globulin around heme of hemoglobin of Homo sapiens by the food-grade additive molecule chlorophyllin

Abstract  

Binding of chlorophyllin (Chln), a food-grade additive molecule with hemoglobin (Hb), has been studied by photophysical and photochemical methods with a view to unravel the biochemical transport pathway of it. The binding affinity constant and binding sites between Chln and Hb are determined and found to be 3.3 × 10⁵ M⁻¹ and 15 (on tryptophan basis), respectively. Fluorimetric quenching experiments entail that Chln is bound in the vicinity of the tryptophan residue of Hb. Circular dichroism studies suggest that Chln induces a change in the α-helical content of Hb. Chlorophyllin is bound in the vicinity of the tryptophan residue of hemoglobin, which has been confirmed from spectrofluorimetric studies, when a quenching in the tryptophan fluorescence occurs because of the chlorophyllin-induced exposure of the tryptophan residue to hydrophillic zone. The cyclic voltammetric studies indicate that the redox reaction of Fe^II of Hb is inhibited shielding of it by the Chln molecule.     

Cryptand derived fluorescence signaling systems for sensing Hg(II) ion: A comparative study

Two laterally non-symmetric aza-oxa cryptands have been derivatized with the electron-withdrawing fluorophore, 7-nitrobenz-2-oxa-1,3-diazole to obtain the corresponding mono-, bis- and tris-products. In each case, no appreciable emission is observed when the fluorophore is excited due to an efficient photoinduced intramolecular electron transfer (PET) from the lone pair on nitrogen present in the bridges. In the presence of a number of transition and heavy metal ions, their emission characteristics change. The electron-withdrawing ability of the fluorophore drastically alters the binding ability of the cryptand such that Hg(ii) affords largest enhancement of fluorescence. In contrast, mono-, bis- and tris-anthryl (electron-donating) derivatives of these cryptands do not exhibit any selectivity towards Hg(ii) and affords low fluorescence enhancement. Also, the difference in cavity dimension of the o-cryptand and m-cryptand plays a crucial role in terms of selectivity.