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The photooxidation of caffeine in presence of peroxydiphosphate (PDP) in aqueous solution at natural pH (∼7.5) has been carried
out in a quantum yield reactor using a high-pressure mercury lamp. The reactions were followed spectrophotometrically by measuring
the absorbance of caffeine at λmax (272 nm). The rates of reaction were calculated under different experimental conditions. The quantum yields were calculated
from the rates of oxidation of caffeine and the intensity of light at 254 nm which was measured by using peroxydisulphate
solution as a standard chemical actinometer. The reaction rates of oxidation of caffeine by PDP increase with increase in
[PDP] as well as with increase in light intensity, while they are independent of [caffeine]. The quantum yields of oxidation
of caffeine by PDP are independent of [PDP] as well as light intensity. However, quantum yields of oxidation of caffeine by
PDP increase with increase in caffeine concentration. On the basis of these experimental results and product analysis, a probable
mechanism has been suggested in which PDP is activated to phosphate radical anions (PO4
·2−) by direct photolysis of PDP and also by the sensitizing effect of caffeine. The phosphate radical anions thus produced react
with caffeine by electron transfer reaction, resulting in the formation of caffeine radical cation, which deprotonates in
a fast step to produce C8-OH adduct radicals. These radicals might react with PDP to give final product 1,3,7-trimethyluric
acid and PO4
·2− radicals, the latter propagates the chain reaction. 相似文献
34.
The photooxidation of adenosine in presence of peroxydisulphate (PDS) has been studied by spectrophotometrically measuring
the absorbance of adenosine at 260 nm. The rates of oxidation of adenosine by sulphate radical anion have been determined
in the presence of different concentrations of caffeic acid. Increase in [caffeic acid] is found to decrease the rate of oxidation
of adenosine suggesting that caffeic acid acts as an efficient scavenger of SO
4
•
and protects adenosine from it. Sulphate radical anion competes for adenosine as well as for caffeic acid. The quantum yields
of photooxidation of adenosine have been calculated from the rates of oxidation of adenosine and the light intensity absorbed
by PDS at 254 nm, the wavelength at which PDS is activated to sulphate radical anion. From the results of experimentally determined
quantum yields (Φexpt1) and the quantum yields calculated (Φcal) assuming caffeic acid acting only as a scavenger of SO
4
•
show that Φexpt1 values are lower than Φexpt1 values. The ǵf values, which are experimentally found quantum yield values at each caffeic acid concentration and corrected
for
4
•
scavenging by caffeic acid, are also found to be greater than Φexpt1 values. These observations suggest that the transient adenosine radicals are repaired by caffeic acid in addition to scavenging
of sulphate radical anions. 相似文献
35.
Swetha Yagnam Adinarayana Murthy Akondi Balaji Rathod Reddy Shetty Prakasham B. Sridhar 《合成通讯》2018,48(3):255-266
We describe here a one-pot synthesis of 13 spirooxindole-fused pyrazolo pyridine derivatives using NiO–SiO2 catalyst via three-component reaction of isatin, 5-amino-3-methylpyrazole, and malononitrile. This multicomponent one-pot protocol also features shorter reaction time, good yield, and simple work-up using a recoverable and reusable solid acid heterogeneous catalyst. The NiO–SiO2 catalyst was characterized using different instrumental techniques such as X-ray diffraction study, surface area analysis, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-DRS (diffuse reflectance spectroscopy), and energy dispersive X-ray analysis (EDX). The new compounds were tested for in-vitro anti-microbial activity. 相似文献
36.
S. Adinarayana Reddy K. Janardhan Reddy S. Lakshmi Narayana Y. Sarala A. Varada Reddy 《中国化学会会志》2008,55(2):326-334
New synthesized reagent 2,6‐diacetylpyridine bis‐4‐phenyl‐3‐thiosemicarbazone (2,6‐DAPBPTSC) is proposed as a sensitive and selective analytical reagent for the extractive spectrophotometric determination of cobalt(II). Cobalt(II) forms a reddish brown colored complex with 2,6‐DAPBPTSC, which is extracted into isoamylalcohol, under optimum conditions. The maximum absorption of the isoamylalcohol extract is measured at 400 nm. Beer's law is applied in the range 0.6‐6.0 ppm of cobalt(II). The molar absorptivity and Sandell's sensitivity of the complex is calculated as 2.2 × 104 L mol?1 cm?1 and 2.68 × 10?3 μg cm?2, respectively. An adequate linearity with a correlation coefficient value of 0.969 is obtained for the Co(II)‐2,6‐DAPBPTSC complex. The instability constant of the complex, calculated from Asmus' method is 3.75 × 10?4 The precision and accuracy of the method is checked with calculation of relative standard deviation (n = 5), 0.388 and the detection limit a value is 0.0028 μg mL?1. The method is successfully employed for the determination of cobalt(II) in real samples, such as vegetables, soil, water samples, standard alloy samples, and the performance of the present method was evaluated in terms of Student ‘t’ test and Variance ‘f’ test, which indicates the significance of the present method is an inter comparison of the experimental values, using atomic absorption spectrometer (AAS). 相似文献
37.
Dr. B. Adinarayana Mainak Das Dr. Cherumuttathu H. Suresh Prof. A. Srinivasan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(18):4683-4687
Stable homocarbaporphyrinoids were successfully synthesized by incorporating the m-o-m and p-o-p terphenyl units into the porphyrin core. The distinct bonding modes of terphenyl in the macrocycle generated two structural isomers with two and four carbon atoms in the macrocyclic environment. The core was utilized to stabilize the RhI ion. The spectral and structural analyses revealed that the restricted (m-o-m) and allowed (p-o-p) conjugation in the macrocyclic core provide overall non-aromatic characteristics both to the free bases and their complexes. 相似文献
38.
To the determination of trace amount of Cd(II) present in food and water samples, a selective and extractive spectrophotometric method were developed with 2,6‐diacetylpyridine‐bis‐4‐phenyl‐3‐thiosemicarbazone as a complexing agent. The yellowish orange colored metal complex, Cd(II)‐2,6‐DAPBPTSC with 1:1 (M:L) composition was extracted in to cyclohexanol at pH 9.5 and was shows maximum absorbance at λmax 390 nm. This method obeys Beer's law in the range of 1.12‐11.25 ppm with 0.972 correlation coefficient of Cd(II)‐2,6‐DAPBPTSC complex, which is indicates linearity between the two variables. The molar absorptivity and sandell's sensitivity were found to be 6.088 × 104 L mol?1 cm?1 and 0.0018 μg cm?2, respectively. The instability constant calculated from Asmus' method (1.447 × 10?4)at room temperature. The precision and accuracy of the method were checked by relative standard deviation (n = 5), 0.929 and its detection limit, 0.0060 μg mL?1. The interfering effects of various cations and anions were also studied. The proposed method was successfully applied to the determination of Cd(II) in foods and water samples, and was evaluated its performance in terms of Student ‘t’ test and Variance ‘f’ test, which indicates the significance of present method. The inter comparison of the experimental values, using atomic absorption spectrometer (AAS), was also repoted. 相似文献
39.
Dr. Adinarayana Doddi Dr. Dirk Bockfeld Dr. Thomas Bannenberg Prof. Dr. Matthias Tamm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14878-14887
Chloride abstraction from the complexes [(η6-p-cymene){(IDipp)P}MCl] ( 2 a , M=Ru; 2 b , M=Os) and [(η5-C5Me5){(IDipp)P}IrCl] ( 3 b , IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF) in the presence of trimethylphosphine (PMe3), 1,3,4,5-tetramethylimidazolin-2-ylidene (MeIMe) or carbon monoxide (CO) afforded the complexes [(η6-p-cymene){(IDipp)P}M(PMe3)]BArF] ( 4 a , M=Ru; 4 b , M=Os), [(η6-p-cymene){(IDipp)P}Os(MeIMe)]BArF] ( 5 ) and [(η5-C5Me5){(IDipp)P}IrL][BArF] ( 6 , L=PMe3; 7 , L=MeIMe; 8 , L=CO). These cationic N-heterocyclic carbene-phosphinidene complexes feature very similar structural and spectroscopic properties as prototypic nucleophilic arylphosphinidene complexes such as low-field 31P NMR resonances and short metal-phosphorus double bonds. Density functional theory (DFT) calculations reveal that the metal-phosphorus bond can be described in terms of an interaction between a triplet [(IDipp)P]+ cation and a triplet metal complex fragment ligand with highly covalent σ- and π-contributions. Crystals of the C−H activated complex 9 were isolated from solutions containing the PMe3 complex, and its formation can be rationalized by PMe3 dissociation and formation of a putative 16-electron intermediate [(η5-C5Me5)Ir{P(IDipp)}I][BArF], which undergoes C−H activation at one of the Dipp isopropyl groups and addition along the iridium-phosphorus bond to afford an unusual η3-benzyl coordination mode. 相似文献
40.
The rates of photooxidation of thymine in presence of peroxydisulphate (PDS) have been determined by measuring the absorbance
of thymine at 264 nm spectrophotometrically. The rates and the quantum yields (φ) of oxidation of thymine by sulphate radical
anion have been determined in the presence of different concentrations of caffeic acid. Increase in [caffeic acid] is found
to decrease the rate of oxidation of thymine suggesting that caffeic acid acts as an efficient scavenger of SO
4
•-
and protects thymine from it. Sulphate radical anion competes for thymine as well as for caffeic acid. The rate constant
of sulphate radical anion with caffeic acid has been calculated to be 1.24 x 1010 dm3 mol-1s-1. The quantum yields of photooxidation of thymine have been calculated from the rates of oxidation of thymine and the light
intensity absorbed by PDS at 254 nm, the wavelength at which PDS is activated to sulphate radical anion. From the results
of experimentally determined quantum yields (φexpt1) and the quantum yields calculated (φcl) assuming caffeic acid acting only as a scavenger of SO
4
•-
radicals show that φexpt1 values are lower than φcl values. The φ ’ values, which are experimentally found quantum yield values at each caffeic acid concentration and corrected
for SO
4
•-
scavenging by caffeic acid, are also found to be greater than φexpt1 values. These observations suggest that the thymine radicals are repaired by caffeic acid in addition to scavenging of sulphate
radical anions. 相似文献