Photoinduced Electron Transfer between Triphenylpyrylium Ion (TPP+) and Certain Phenols

The photoinduced interaction between triphenylpyrylium ion (TPP+) and certain phenols were studied in acetonitrile medium by using absorption, steady state and time resolved fluorescence spectroscopic methods. The quenchers used were phenol, o-aminophenol, o-cresol, o-hydroxyphenol, o-chlorophenol, salicylic acid and salicylaldehyde. Linear Stern-Volmer plots were obtained from both steady state and time resolved measurements and also the calculated values of bimolecular quenching rate constants (k q) were matched well. The free energy change (ΔG et) has been evaluated by using Rehm-Weller equation for the confirmation of electron transfer from phenols to TPP+ ion.

A Study on the Fluorescence Quenching of Eosin by certain Organic Dyes

The fluorescence quenching of Eosin by certain dyes has been investigated using steady state technique. The dyes used are Uniblue-A, Acid blue 129, Alizarin, Alizarin red S, Erichrome Black T, Tartrazine, Methyl orange, Methyl red, Acid orange 63, Congo red. The quenching was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear in the range of quencher concentration used [0−5×10− 5] M. The quenching rate constant (k q ) is in the range of 0.85–26.65×1012 M− 1s− 1. The quenching mechanism is discussed on the basis of the quenching rate constants as well as the reduction potential of the dyes. Rehm-Weller equation is applied for the calculation of free energy change (ΔGet).

Fluorescence Quenching of Xanthene Dyes by TiO2

The fluorescence quenching of xanthene dyes by TiO2 has been investigated using steady state technique. The dyes used are eosin, rhodamine B, rhodamine 6G. The quenching was found to obey Stern-Volmer equation and the corresponding Stern-Volmer plots were linear in the range of quencher concentration used [0–5 × 10--5] M. The quenching rate constant (k q) is in the range of 0.77–8.30 × 1012 M-1 s-1. This study reveals effective quenching of xanthene dyes with TiO2. The quenching of xanthene dyes followed electron transfer mechanism.

Fluorescence Quenching of Meso-Tetrakis(p-Sulfonatophenyl)Porphyrin (TSPP) by certain Organic Dyes

The fluorescence quenching of meso-tetrakis (p-sulfonatophenyl) porphyrin (TSPP) by certain anthraquinone and azo dyes has been investigated using steady state fluorescence technique. The dyes used were Uniblue-A, Acid blue 129, Alizarin, Alizarin red S, Erichrome Black T, Tartrazine, Methyl orange, Methyl red, Acid orange 63 and Congo red. The quenching was found to obey Stern-Volmer equation and the corresponding Stern-Volmer plots were linear. The quenching rate constant (k q ) is in the order of 0.19–6.08×1012 M− 1s− 1. This study reveals effective quenching of TSPP by organic dyes.

Photosensitization of Colloidal TiO2 with ZnTPP and Pyrene

The interaction of Zinc(II) tetraphenyl porphyrin (ZnTPP) and pyrene with colloidal TiO2 was studied by absorption and fluorescence spectroscopy. Upon excitation of its absorption band, the fluorescence emission of ZnTPP and pyrene was quenched by colloidal TiO2. The bimolecular quenching rate constant (kq ) is 4.09 × 1011 M−1s−1 for ZnTPP and 2.09 × 109 M−1s−1 for pyrene. ZnTPP and pyrene adsorbed on colloidal TiO2 can participate in the sensitization process by injecting electrons from their excited states into the conduction band of TiO2. The mechanism is discussed on the basis of free energy change (ΔGet) obtained from Rehm-Weller equation considering quenching rate constants and conduction band potential of colloidal TiO2.

Photoinduced Electron Transfer from Meso-Tetrakis (N-methylpyridyl)porphyrin (TMPyP) to Colloidal CdS

A stable colloidal CdS nanoparticles were prepared. The dynamics of photoinduced interaction between meso-tetrakis(N-methylpyridyl)porphyrin (TMPyP) and colloidal CdS were studied using absorption, steady state, time resolved fluorescence and FT-IR spectral measurements. The apparent association constant (K app) of TMPyP-CdS obtained from absorption spectral changes is 1.07×103 M−1. The K app value of TMPyP-CdS as determined from fluorescence spectra is 1.34×103 M−1, which matches well with that determined from the absorption spectra changes. These data indicate that there is an interaction between TMPyP and colloidal CdS nanoparticle surface. The dynamics of photoinduced electron transfer from TMPyP to the conduction band of colloidal CdS nanoparticle has been observed and the mechanism of electron transfer has been confirmed by the calculation of free energy change (ΔG et) by applying Rehm-Weller equation as well as energy level diagram. Lifetime measurements gave the rate constant (k et) for electron injection from the excited state TMPyP into the conduction band of CdS is 3.21×108 s–1.

Photoinduced electron transfer from phycoerythrin to colloidal metal semiconductor nanoparticles

Phycoerythrin is a water soluble pigment which absorbs in the visible region at 563 nm. The interaction of phycoerythrin with colloidal metal semiconductors was studied by absorption, FT-IR and fluorescence spectroscopy. Phycoerythrin adsorbed strongly on the surface of TiO(2) nanoparticles, the apparent association constant for the association between colloidal metal-TiO(2) nanoparticles and phycoerythrin was determined from fluorescence quenching data. The free energy change (DeltaG(et)) for electron transfer process has been calculated by applying Rehm-Weller equation.

Cyanobacterial chlorophyll as a sensitizer for colloidal TiO2

Chlorophyll has been extracted from cyanobacteria. The adsorption of chlorophyll on the surface of colloidal TiO(2) through electrostatic interaction was observed. The apparent association constant (K(app)) of chlorophyll-TiO(2) obtained from absorption spectra is 3.78x10(4)M(-1). The K(app) value of chlorophyll-TiO(2) as determined from fluorescence spectra is 1.81x10(4)M(-1), which matches well with that determined from the absorption spectra changes. These data indicate that there is an interaction between chlorophyll and colloidal TiO(2) nanoparticle surface. The dynamics of photoinduced electron transfer from chlorophyll to the conduction band of colloidal TiO(2) nanoparticle has been observed and the mechanism of electron transfer has been confirmed by the calculation of free energy change (DeltaG(et)) by applying Rehm-Weller equation as well as energy level diagram. Lifetime measurements gave the rate constant (k(et)) for electron injection from the excited state chlorophyll into the conduction band of TiO(2) is 4.2x10(8)s(-1).

How to work up a patient with polyneuropathy?

Undiagnosed and untreated neuropathy may lead to disability and poor quality of life. Ordering every possible test to find the cause of polyneuropathy can waste time and resources. In this study, we investigated what could be used as a routine neuropathy screen. A retrospective audit of all charts of patients diagnosed to have polyneuropathy by nerve conduction studies from November 2001 to November 2002 were carried out. Demographics, background history, type of neuropathy and investigations done were documented. The charts of 61 patients were audited. 12 patients had a background history of diabetes mellitus. 2 patients had history of alcohol abuse. 23 patients presented with paraesthesia and 33 with weakness of limbs. We found a cause of polyneuropathy in 79% of cases. In most patients with polyneuropathy where a cause can be identified, this can be achieved by the medical history, neurological examination, nerve conduction studies and the baseline blood tests. We suggest a 3-step approach to the diagnostic workup of polyneuropathy.

Interaction between certain porphyrins and CdS colloids: a steady state and time resolved fluorescence quenching study

The interaction between porphyrins namely, meso-tetrakis (4-methoxyphenyl)porphyrin (TMeOPP), protoporphyrin IX (PPIX) and Zinc(II) meso-tetraphenylporphyrin (ZnTPP) with colloidal CdS has been studied by using steady state and time resolved fluorescence quenching measurements. The porphyrins adsorbed on the surface of colloidal CdS due to electrostatic interaction. This adsorption leads to changes in the absorption spectra related to the complex formation. The apparent association constant (Kapp) was in the order of 4.34-5.58 x 10(5) M(-1) from the effect of colloidal CdS on the absorption spectra and 0.64-1.6 x 10(5) M(-1) from fluorescence quenching data. Quenching is attributable mainly to static mechanism through ground state complex formation as confirmed by lifetime measurements.

Effect of anchoring group on the photosensitization of colloidal TiO2 nanoparticles with porphyrins

The interaction of porphyrins (TCPP, TSPP, TMeOPP and TPP) with colloidal TiO(2) nanoparticles was studied by infra-red, UV-visible absorption, steady state and time resolved fluorescence spectroscopy. The porphyrins (TCPP, TSPP and TMeOPP) adsorbed on the surface of colloidal TiO(2) nanoparticles through electrostatic interaction. According to absorption and fluorescence changes the apparent association constants (K(app)) were calculated. However, TPP did not interact with surface of colloidal TiO(2) nanoparticles due to the absence of anchoring group. The fluorescence quenching is attributable mainly to electron transfer from the excited state porphyrins to the conduction band of colloidal TiO(2). The rate of electron transfer process (k(et)) was calculated using lifetime measurement. The electron transfer mechanism has been proved by the calculation of free energy change (DeltaG(et)) by applying Rehm-Weller equation. Using all the spectroscopic measurements we confirmed that the presence of anchoring group plays major role in the adsorption as well as the electron transfer processes.

An investigation on electron transfer quenching of zinc(II) meso-tetraphenylporphyrin (ZnTPP) by colloidal TiO(2)

The interaction of zinc(II) meso-tetraphenylporphyrin (ZnTPP) with colloidal TiO(2) was studied by absorption, steady state and time-resolved fluorescence spectroscopy. The quenching was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear in the range of quencher concentration used 0-5 x 10(-4)M. The bimolecular quenching rate constants (k(q)) were 20.5 x 10(10)M(-1)s(-1) (steady-state) and 2.85 x 10(10)M(-1)s(-1) (time resolved). The quenching process is suggested to involve electron transfer from the ZnTPP to TiO(2) considering the experimental evidences obtained.

Photoinduced interaction between riboflavin and TiO(2) colloid

The adsorption of riboflavin on the surface of TiO(2) colloidal particles and the electron transfer process from its singlet excited state to the conduction band of TiO(2) were examined by absorption and fluorescence quenching measurements. The apparent association constants (K(app)) were determined. The quenching mechanism is discussed involving electron transfer from riboflavin to TiO(2).

Fluorescence quenching of meso-tetrakis (4-sulfonatophenyl) porphyrin by colloidal TiO(2)

A stable colloidal TiO(2) has been prepared. The interaction of meso-tetrakis (4-sulfonatophenyl) porphyrin (TSPP) with colloidal TiO(2) was studied by absorption and fluorescence spectroscopy. Upon excitation of its absorption band, the fluorescence emission of TSPP was quenched by colloidal TiO(2). The bimolecular quenching rate constant (k(q)) is 1.78 x 10(11)M(-1)s(-1). The porphyrin can participate in the quenching process by injecting electrons from its excited states into the conduction band of TiO(2). The quenching mechanism is discussed on the basis of the quenching rate constant as well as the reduction potential of the colloidal TiO(2). Rehm-Weller equation was applied for the calculation of free energy change (DeltaG(et)).