Radhey M. Naik

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (lambda(max) of [Fe(CN)(5)PhNHNH(2)](3-), complex) under the optimum reaction conditions at: 2.5x10(-3)M [Fe(CN)(6)](4-), 1.0x10(-3)M [PhNHNH(2)], 8.0x10(-7)M [Ag(+)], pH 2.8+/-0.02, ionic strength (mu) 0.02 M (KNO(3)) and temperature 30+/-0.1 degrees C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8-8.0x10(-8)M with a detection limit of 2x10(-9)M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst-inhibitor (K(CI)), catalyst-substrate (K(s)) and Michaelis-Menten constant (K(m)) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.

Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0x10(-6)M and the progress of reaction was followed spectrophotometrically at 525nm (lambda(max) of purple-red complex [Ru(CN)(5)NRS](3-), epsilon=3.1x10(3)M(-1)s(-1)) under the optimized reaction conditions; 8.75x10(-5)M [Ru(CN)(6)(4-)], 3.50x10(-4)M [nitroso-R-salt], pH 7.00+/-0.02, ionic strength, I=0.1M (KCl), temp 45.0+/-0.1 degrees C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times (t=15, 20 and 25min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0x10(-7)M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.

Kinetic and Mechanistic Studies of Oxidation of Amine-N-Polycarboxylates Complexes of Cobalt(II) by Periodate Ions in Aqueous Medium

The kinetics and mechanism of interaction of periodate ion with [CoIIL(H2O)]2-n [L = trimethylenediaminetetraaceticacid (TMDTA)] and ethylene glycol bis(2-aminoethyl ether) N,N,N’,N’-tetraaceticacid (EGTA) have been studied spectrophotometrically by following an increase in absorbance at λmax = 550 nm in acetate buffer medium as a function of pH, ionic strength, temperature, various concentration of periodate and [CoIIL(H2O)]2-n under pseudo-first order conditions. The experimental observations have revealed that the intermediates having sufficiently high half life are produced during the course of both the reactions which finally get converted into a corresponding [CoIIIL(H2O)]3-n complexes as a final reaction product. The reaction is found to obey the general rate law Rate = (k2 [IO4−] + k3 [IO4−]2) [CoIIL(H2O)]2-n. This rate law is consistent with a four step mechanistic scheme (vide supra) where electron transfer proceeds through an inner sphere complex formation. The value of rate constant k2 is independent of pH over the entire pH range which suggest that unprotonated form of [CoIIL(H2O)]2-n is the only predominant species. The value of k2 is invariant to ionic strength variation in both the systems. The value of k3 is also found to be almost invariant to ionic strength in case of [CoIITMDTA(H2O)]2−-[IO4]− system but it decreases considerably in case of [CoIIEGTA(H2O)]2−-[IO4]− system with the corresponding decrease in ionic strength. The activation parameters have been computed and given in support of proposed mechanistic scheme.

Epidermal growth factor receptor mutation in non-small-cell lung carcinomas: A retrospective analysis of 1036 lung cancer specimens from a network of tertiary cancer care centers in India

BACKGROUND Epidermal growth factor receptor (EGFR) mutation plays a vital role in the prognosis of patients with lung cancer. However, there is a dearth of studies on EGFR mutation in Indian population. In this retrospective study conducted at a network of tertiary cancer care centers across India, we evaluated the proportion of EGFR mutation in patients with non-small-cell lung carcinomas (NSCLC). MATERIALS AND METHODS A total of 1036 cases of non-small lung cancer were assessed for EGFR mutation status using Scorpion amplified refractory mutation system real time polymerase chain reaction method from fine needle aspiration cytology core biopsy, pleural fluid and cell blocks. For a few cases, macro dissection of tumor from H and E slides was also performed for EGFR analysis. EGFR Status was assessed for the most commonly known driver mutations in Exons 18, 19, 20 and 21, which contributes to a total of 29 somatic mutations including the resistance mutation T790M. RESULTS Around 39% of the cohort was female and 61% were male. Mutation was positive in 40.3% and negative (wild type) in 59.7%. There was 1.8% mutation in exon 18, 24.6% in exon 19, 1.6% in exon 20 and 12.8% in exon 21. 38.2% had a mutation in a single site and 1.1% had a mutation in two sites. Overall mutation was significant in females (50.5% vs. 33.9%) compared with males (χ2 = 28.3, P < 0.001). Mutation was significant in exon 21 (16.8% vs. 10.3%, χ2 = 9.44, P = 0.002) and exon 19 (30.7% vs. 20.7%, χ2 = 13.2, P < 0.001) in females compared with males. CONCLUSION EGFR is expressed differentially/mutated in patients with NSCLC. Further studies to unravel the predictors for acquired genetic alterations of EGFR are needed.

The kinetics and mechanism of oxidation of hexacyanoferrate(II) by periodate ion in highly alkaline aqueous medium

The oxidation of hexacyanoferrate(II) by periodate ion has been studied spectrophotometrically by registering an increase in absorbance at 420 nm (λmax of yellow colored [Fe(CN)63−] complex under pseudo first-order conditions by taking excess of [IO4−] over [Fe(CN)64−]. The reaction conditions were: pH = 9.5 ± 0.02, I = 0.1 M (NaCl) and Temp. = 25 ± 0.1 °C. The reaction exhibited first-order dependence on each [IO4−] and [Fe(CN)64−]. The effects of variations of pH, ionic strength and temperature were also studied. The experimental observations revealed that the periodate ion exists in its protonated forms viz. [H2IO6]3− and [H3IO6]2− while [Fe(CN)6]4− is present in its deprotonated form throughout the pH region selected for the present study. It has also been observed that deprotonated form of [Fe(CN)64−] and protonated forms of periodate ion are the most reactive species towards oxidation of [Fe(CN)64−]. The repetitive spectral scan is provided as an evidence to prove the conversion of [Fe(CN)64−] to [Fe(CN)63−] in the present reaction. The activation parameters have also been computed using the Eyring’s plot and found to be, ΔH‡ = 51.53 ± 0.06 kJ mol−1, ΔS‡ = −97.12 ± 1.57 J K−1 mol−1 and provided in support of a most plausible mechanistic scheme for the reaction under study.

The Removal of Nickel from Waste Water by Modified Coconut Coir Pith

In this study, Coconut Coir Pith was used to prepare a low cost bio adsorbent through chemical modification. The effect of adsorbent dosage, contact time, initial metal-ion concentration, pH and temperature on the adsorption of nickel onto chemically modified coconut coir pith was investigated. The maximum removal was observed at pH 6.0 and adsorbent dose 2.0 g/L for initial metal-ions concentration 50 mg/L. Study of temperature effect proved that the process is endothermic. Langmuir and Freundlich isotherm models were used for equilibrium adsorption data. Langmuir isotherm proved to be a better fit. Pseudo first order and pseudo second order kinetic models were applied to analyze the kinetic mechanism of adsorption. The values of Gibbs free energy ΔG°, Enthalpy ΔH° and Entropy ΔS° was calculated by the thermodynamic studies.

Prevalence of KRAS mutations in metastatic colorectal cancer: A retrospective observational study from India

BACKGROUND One of the genetic alterations implicated in tumor progression in colorectal cancers (CRCs) are abnormalities in Kristen Rat Sarcoma (KRAS) gene. Evaluation of KRAS mutation status is an important prognostic factor and has predictive value in deciding first line therapy based on monoclonal antibodies such as Cetuximab and Panitumumab in metastatic CRCs. MATERIALS AND METHODS In this retrospective study, we analyzed 7 different somatic mutations in Exon 2 of KRAS gene in 299 unselected incidental CRC patients who visited the hospital for clinical management during the period 2009-2013. Most of the tumors were primarily originating from colon and rectum; nevertheless, there were a few from rectosigmoid, sigmoid, ceacum and anal canal in the study group. Genomic DNA extracted from paraffin embedded tumor tissues was screened for 7 point mutations located in Codons 12 and 13 of KRAS gene, using Scorpions amplified refractory mutation system real time polymerase chain reaction technology. Statistical analysis was performed to assess bivariate relationship between different variables that includes: mutation status, mutation type, tumor location, tumor morphology, age and sex. RESULTS Prevalence of mutation in Codons 12 and 13 was 42.8% in the study group. Well-differentiated tumors had significantly more mutation positivity than moderately and poorly differentiated tumors (P = 0.001). 92% of the mutations were from Codon 12 and 8% in Codon 13. Glycine to Arginine was relatively more common in rectosigmoid followed by ceacum, while Glycine to Alanine mutation was relatively more prevalent in sigmoid, followed by rectum and rectosigmoid. CONCLUSION The results suggest a prevalence of KRAS mutation at 42.8% in Indian population indicating that this testing is very crucial for targeted therapy management in metastatic CRC in India. Further analysis on mutation status of other homologues such as NRAS and downstream partner, v-raf murine sarcoma viral oncogene homolog B1, would add value to understanding the role of anti-epidermal growth factor receptor therapy in CRC management.

Kinetic determination of trace amounts of thiosulfate based on its inhibitory effect

The sulfur containing ligand viz., thiosulfate is found to inhibit the Ag(I) catalyzed substitution of cyanide in hexacyanoferrate(II) by phenylhydrazine. The inhibitory effect of thiosulfate is attributed due to its tendency to form complexes with Ag(I), leading to the production of inhibitor-catalyst complexes. The reactions, followed spectrophotometrically in aqueous medium at 488 nm, was possible by the increase in absorbance of the cherry-red product, [Fe(CN)5PhNHNH2]3- at pH 2.8 (±0.02), at 30 (±0.1) °C, and an ionic strength (μ) of 0.02 M (KNO3). The linear calibration curves were obtained using the absorbance measured at different times (At) and thiosulfate concentrations under specified conditions. The calculated detection limit was 4.9 × 10-7 M. The Michaelis-Menten constant (Km) and equilibrium constants for the formation of complexes between catalyst and inhibitor (KCI), and the catalyst and substrate (KS) were computed from the kinetic data. A general mechanistic scheme is proposed for this reaction.

The palladium(II)-catalysed ligand exchange between hexacyanoferrate(II) and 4-cyanopyridine in aqueous acidic medium

The kinetics of the palladium(II)-catalysed ligand exchange of the hexacyanoferrate(II) complex ion with 4-Cyanopyridine (4-CNpy) in aqueous acidic medium have been investigated at 25.0 ∓ 0.1 °C, pH 3.2 ∓ 0.02 and ionic strength, I=0.1 M (KNO3). The reaction was followed spectrophotometrically by measuring the increase in absorbance of the intense cherry red complex [Fe(CN)54-CNpy] 3-, corresponding to metal-to-ligand charge transfer (MLCT) transitions, atλ.max 477 nm. The effects of pH, ionic strength, the concentrations of [Fe(CN)54-], Pd2+ and 4-CNpy on the reaction rate have been studied and analysed. The kinetic data suggest that substitution follows an interchange dissociative (Id) mechanism and occurs via formation of a solvent-bound intermediate. The effects of the dielectric constant of the medium on the reaction rate have been used to visualize the formation of a polar activated complex and an interchange dissociative mechanism for the reaction. A most probable mechanism has been proposed in order to interpret the kinetic data. Kinetic evidence is reported for the displacement of CN- by 4-CNpy in [Fe(CN)64-]. Activation parameters for the proposed reaction have been evaluated using an Eyring plot, and provided further support to the proposed mechanistic scheme.

Kinetics and mechanism of formation of [Fe(CN)5INH]3– by ligand substitution in acidic media (INH = isoniazid)

The kinetics and mechanism of formation of [Fe(CN)5INH]3- by a ligand substitution reaction between aquapentacyanoferrate(II) ion and isoniazid, (pyridine-4-carboxylic acid hydrazide) (INH) have been investigated spectrophotometrically in acidic media at 435 nm (Λmax of product), under pseudo-first order conditions, using excess of INH over [Fe(CN)5H2O]3-. The reaction was studied as a function of [Fe(CN)5H2O3-], [INH], pH, ionic strength and temperature, by varying only one of these variables while other variables were held constant. The reaction exhibited first-order kinetics in [INH] while it was independent of [Fe(CN)5H2O3-] in the chosen concentration range. The effect of temperature on the reaction rate yielded the activation parameters. The most plausible mechanism consistent with the experimental results has been proposed.