Diazonium Ion Research Articles

Determination of paracetamol in pharmaceutical samples by spectrophotometric method

It is described the use of 1,3 dinitrobenzene or 2,4 dinitrophenyl hydrazine is used as coupling agent for the spectrophotometric determination of paracetamol. This method is easy and simple based on the reaction of acid hydrolysis of paracetamol to produce p-aminophenol, which in turn reacts with nitrite in acidic standard to form diazonium ion, which is coupled with coupling agent in basic standard to produce azo dyes. The formed dyes follow Beer’s law in the range of 0.8-20.5 mg mL-1 of paracetamol with 1, 3 dinitrobenzene or 0.5-18.4 mg mL-1 of paracetamol with 2,4 dinitrophenyl hydrazine with absorption maxima at 429 nm or 430 nm. The molar absorptivity and Sandell’s sensitivity of paracetamol with 1,3 dinitrobenzene or paracetamol with 2,4 dinitrophenyl hydrazine azo dyes were 1.965×104 L mol-1 cm-1 or 2.776×104 L mol-1 cm-1, and 7.692×10-3 mg cm-2 or 5.698×10-3 mg cm-3 respectively. The dyes formed are stable for more than 12 h. The optimal reaction circumstances and other analytical parameters are evaluated. Interference due to foreign organic compounds have been studied. The method has been effectively applied to the determination of paracetamol in pharmaceutical samples.

Protonation of CH3 N3 and CF3 N3 in Superacids: Isolation and Structural Characterization of Long-Lived Methyl- and Trifluoromethylamino Diazonium Ions.

The methylamino diazonium cations [CH3 N(H)N2 ]+ and [CF3 N(H)N2 ]+ were prepared as their low-temperature stable [AsF6 ]- salts by protonation of azidomethane and azidotrifluoromethane in superacidic systems. They were characterized by NMR and Raman spectroscopy. Unequivocal proof of the protonation site was obtained by the crystal structures of both salts, confirming the formation of alkylamino diazonium ions. The Lewis adducts CH3 N3 ⋅AsF5 and CF3 N3 ⋅AsF5 were also prepared and characterized by low-temperature NMR and Raman spectroscopy, and also by X-ray structure determination for CH3 N3 ⋅AsF5 . Electronic structure calculations were performed to provide additional insights. Attempted electrophilic amination of aromatics such as benzene and toluene with methyl- and trifluoromethylamino diazonium ions were unsuccessful.

Thermodynamic and Kinetic Study of Adsorption of Azo Dyes Derived for 4-amino Anti pyrene by Activated Carbon

A commercial activated carbon was used for the study of adsorption of two di- azo dyes from aqueous solution employing batch method. These dyes were synthesized in our laboratory from the reaction of 4-amino-antipyrene 4-AAP and β-Naphthol with p-amino phenol and p-amino benzaldehyde via diazonium ions. The effect of pH, temperature, and contact time on dye removal was investigated. The apparent thermodynamic parameters were estimated and the obtained results concluded that, the dyes adsorbed onto activated carbon are driven by entropy effect, exothermic and spontaneous processes. The kinetic study of adsorption of the considered dyes was conducted by applying four models the pseudo-first order, pseudo-second order ,Elovich and intra particules diffusion kinetic models. The results showed that, the second order equation fit better the experimental data. The intra particule diffusion model indicates that, there are more than mechanism controlling the adsorption process.the adsorption process occurs through more than one mechanical and that the intra particule diffusion model is not the only mechanical that controls the adsorption of systems Studied.

Using Diazotization Reaction to Develop Portable Liquid-Crystal-Based Sensors for Nitrite Detection.

A liquid-crystal (LC)-based sensor for detecting nitrite in aqueous solutions was developed using a diazotization reaction as the sensing mechanism. First, tetradecyl 4-aminobenzoate (14CBA) was synthesized and doped into a nematic LC, i.e., 4-cyano-4′-pentylbiphenyl (5CB). When the LC mixture was cast on a glass substrate and then immersed into an aqueous solution without nitrite, the orientation of LC was planar and the LC image was bright. In the presence of nitrite, it reacted with alkylanilines to give corresponding diazonium ions with a positive charge, which aligned at the LC/aqueous interface to cause homeotropic orientation of LC. As a result, a bright-to-dark transition of the LC image was observed. The limit of detection (LOD) of this system for nitrite is 25 μM with high selectivity. In addition, this system can work in environmental water samples such as tap water and pond water. Finally, we demonstrated that the optical signals of LC can be measured and recorded using a built-in digital camera of a smartphone, suggesting the portability of this system for on-site applications.

A computational investigation of cytosine and 5-methyl cytosine reactivity by means of ionization potentials and one specific methylation pathway

Results from DFT/ωB97X-D/6-311+G**/C-PCM calculations show that the aqueous vertical IP of 5-methylcytosine is lower than that of cytosine by 0.25 eV. Using the HSAB concept, the HOMO-LUMO gap for 5-methylcytosine is smaller than that of cytosine, making it soft and opt to form covalent bonds and more reactive. Carcinogenic methane diazonium ion can methylate cytosine at the N3 site and mutate it via an SN2 mechanism and the activation energy is approximately 5.05 kcal/mol in water.

Indirect determination of dopamine and paracetamol by electrochemical impedance spectroscopy using azo coupling reaction with oxidized 2,4-dinitrophenylhydrazine (DNPH): Application in commercial tablets

A new method for the determination of dopamine (DA) and paracetamol (PCT), based on the azo “coupling reaction with oxidized 2,4-dinitrophenylhydrazine (DNPH), has been established. This method was based on the fact that in the HCl buffer solution, potassium ioadate oxidized 2,4-dinitrophenylhydrazine to form the diazonium chloride at 0–5 °C and then the diazonium ion reacted with the phenolic compounds to form azo-compounds. The products of the azo coupling reaction were characterized by UV/Vis spectrophotometry, infrared spectroscopy and square wave voltammetry. Using a MeOH/Water buffer solution (pH 9.0) and electrochemical impedance spectroscopy, DA and PCT were determined in the concentration range of 0.1–1000 μmol L −1 , with limits of detection of 0.47 and 0.25 μmol L −1 , respectively. The proposed method was successfully applied to the individual determination of DA and PCT in various pharmaceutical formulas, showing the practical feasibility of the proposed method as a novel platform for the sensitive determination of these phenolic compounds. • Indirect determination of dopamine and paracetamol using electrochemical impedance spectroscopy. • Dopamine and paracetamol were changed to azo dye by coupling reaction with diazonium ion. • Various factors that influence oxidative and coupling reaction were investigated. • Determination of DA and PCT concentration in pharmaceutical samples.

Large Capacity Enhancement of Carbon Electrodes by Solution Processing for High Density Energy Storage.

An inexpensive, solution phase modification of flat carbon electrodes by electrochemical reactions of a 1,8-diaminonaphthalene derivative results in a 120- to 700-fold increase in capacity by formation of a 15-22 nm thick organic film. Modification of high surface area carbon electrodes with the same protocol resulted in a 12- to 82-fold increase in capacity. The modification layer contains 9-15% nitrogen present as -NH- redox centers that result in a large Faradaic component involving one H+ ion for each electron. The electrodes showed no capacity loss after prolonged cycling in 0.1 M H2SO4 and exhibited significantly higher charge density than similar reported electrodes based on graphene and polyaniline. Investigation of the deposition conditions revealed that N-doped oligomeric ribbons are formed both by diazonium ion reduction and diaminonaphthalene oxidation, and the 1,8 isomer is essential for the large capacity increases. The capacity increase has at least three contributions: increased microscopic surface area from ribbon formation, Faradaic reactions of nitrogen-containing redox centers, and changes in ribbon conductivity resulting from polaron formation. An aqueous fabrication process was developed which both increased capacity and improved stability and was amenable to industrial production. The high charge density, low-cost fabrication, and <25 nm thickness of the diaminonaphthalene-derived films should prove attractive toward practical application on both flat surfaces and in high surface area carbon electrodes.

Molecular Dynamics Investigation of the Physical Binding of the NNK Diazonium Ion to TP53 exon 5

The diazonium ion metabolite of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a strong carcinogen found in tobacco smoke. NNK diazonium ion has been shown to damage DNA through the formation of pyridyloxobutyl (POB) adducts. The current study focuses on the physical interaction of a tumor suppressor gene (TP 53, exon 5) with NNK diazonium ion. TP53 is mutated in nearly 50% of all human tumors and 40% of lung cancer cases. Our work explores the physical interactions that precede bond formation. Density functional theory was used to generate improved force field parameters for the diazonium ion. Molecular dynamics simulations were performed on two systems: NNK diazonium ion and TP53/NNK diazonium ion. Results of the MD simulations that will be presented include an analysis of the various conformations NNK diazonium ion explores and distances of its reactive carbon atoms to reactive atoms of TP53 bases. This will provide insight into the possible reaction mechanism of POB adduct formation.

Physico-chemical Properties of the Strong Tobacco Smoke Carcinogen NNK Diazonium Ion

We have explored the physico-chemical properties of the NNK diazonium ion to gain insight into its shape, bonding, charge distribution, and ro-vibrational features. This information is essential if the chemical reactivity and spectroscopic properties of this important intermediate are to be predicted. NNK diazonium ion is a well-known alkylating agent. Its enzymatic production, its reaction with DNA, and its role in mutagenesis/carcinogenesis have all received significant study. The ion itself, however, is relatively unstable and its direct observation has not yet been reported. Likewise, data on its shape, spectroscopic properties, bonding, and charge distribution are lacking. The species is sufficiently small such that its properties may be probed using sophisticated model chemistries. We present the first computational investigation of NNK diazonium ion deploying Kohn-Sham Density Functional Theory (B3LYP/6-311G∗∗) and Coupled Cluster theory (CCSD(T)/cc-pVDZ). We have obtained energies, geometries, electrostatic potential surfaces, molecular orbitals, and vibrational analyses for several energy-minimized structures. By providing detailed information on the geometry of and ro-vibrational motion in this ion, we hope to inform future, molecular dynamics, electronic structure, and/or spectroscopic work on this important reactive intermediate and on its interaction with DNA.

Use of hydroxylamines, hydroxamic acids, oximes and amines as nucleophiles in the Zbiral oxidative deamination of N-acetyl neuraminic acid. Isolation and characterization of novel mono- and disubstitution products

The oxidative deamination of N-nitroso N-acetylneuraminic acid (NeuAc) derivatives is a useful reaction for the formation of 5-desamino-5-hydroxy NeuAc derivatives and their stereoisomers. We demonstrated previously that replacement of the classical nucleophile in these reactions, acetic acid, by phenols resulted in a novel double displacement process with substitution of the acetoxy group at the 4-position taking place in addition to that of the 5-acetamido group, for which we postulated a mechanism centered on the formation of a highly reactive vinyl diazonium ion. We now extend these studies to encompass the use of hydroxylamine-based systems and weakly basic amines as nucleophile. We find that the nature of the product depends significantly on the pKa of the nucleophile, with the more acidic species typically affording only substitution at the 5-position, while the less acidic species give mixtures of elimination products and disubstitution products. The use of aniline as nucleophile is of particular note as it affords a novel aziridine spanning positions 4- and 5- of the neuraminic acid skeleton.

Robust non-covalent and covalent anchored N,N,N',N'-tetramethyl-p-phenylenediamine derivative on electrode surface via spontaneous physical immobilization and in situ generated aryldiazonium ion electro-grafting: implication for on-surface chemistry and electro-catalytic determinations.

The two-electron oxidation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) results in highly unstable TMPD2+ in aqueous solutions. Despite its low redox potential, TMPD2+/TMPD couple is not considered as a suitable charge transfer functional group to modify the electrode due to instability of TMPD2+ in aqueous solutions. The main focus of the present paper is to fabricate an efficient redox-active electrode by coupling TMPD with 4-nitroaniline to be utilized for on-surface chemistry. The nitro functional group in the coupling product N2,N2,N5,N5-tetramethyl-4'-nitro-[1,1'-biphenyl]-2,5-diamine (MNPD) was reduced electrochemically to the corresponding amino derivative (MAPD). The oxidized form of MAPD (MAPD2+) exhibited high stability as well as low reduction potential in aqueous solutions. A redox active electrode was designed via the immobilization of the electro-generated MAPD onto a nanofibrillated mesoporous carbon (IFMC) modified glassy carbon electrode (GCE). The redox signal increased several folds with the deposition of IFMC onto glassy carbon electrode compared to bare GCE. Two functionalization routes, electro-grafting and spontaneous physical immobilization, were examined for the attachment of the redox species to the electrode surface. In the first approach, electro-grafting was attained via the electrochemical reduction of MNPD in the presence of sodium nitrite to produce diazonium ions in situ. The redox centers covalently grafted to the surface showed dense deposition and appreciable stability. In the second route, spontaneous adsorption was performed by the same strategy of electro-grafting in the absence of sodium nitrite. In this case, the hydrophobic nanofiber structure of IFMC was capable of robustly trapping MAPD. The anchored MAPD shows high reactivity in Michael addition reactions in ultrafast reaction times. The post-functionalization of the electrodes was easily performed by the oxidation of the redox centers in the presence of species with nucleophilic properties at the electrode/electrolyte interface. In addition, both the constructed electrodes are introduced as suitable mediators in electro-catalytic implications because of their reversibility, stability, and low oxidation potential. The electro-catalytic activity of the electrodes was established for the indirect electrochemical oxidation of homocysteine as a typical substrate.

Use of Phenols as Nucleophiles in the Zbiral Oxidative Deamination of N-Acetyl Neuraminic Acid: Isolation and Characterization of Tricyclic 3-Keto-2-deoxy-nonulosonic Acid (KDN) Derivatives via an Intermediate Vinyl Diazonium Ion.

It is well established that the N-nitrosoamide derived from peracetylated derivatives of N-acetyl neuraminic acid on treatment with a mixture of sodium isopropoxide and trifluoroethanol, followed by the addition of acetic acid, gives an oxidative deamination product, in which the AcN(NO)-C5 bond is replaced with a AcO-C5 bond with the retention of configuration, affording a practical synthesis of 2-keto-3-deoxy-d-glycero-d-galactononulosonic acid (KDN) derivatives. Application of other strong acids, including hydrogen fluoride, thioacetic acid, trifluoromethanesulfonic acid, and hydrogen azide, functions similarly to afford KDN derivatives functionalized at the 5-position. We describe our attempts to extend the range of useful nucleophiles employed in this oxidative deamination process to include phenols and thiophenols, resulting in the discovery of a new branch of the general reaction and the formation of a series of products resulting from substitution of the 5-acetamido group and of the 4-acetoxy group from neuraminic acid. A mechanistic rationale for the formation of these products is advanced according to which, in the absence of acids of pKa ≤ 8, the intermediate diazonium ion resulting from the elimination of acetic acid and nitrogen from the nitrosoacetamide undergoes elimination of acetic acid from the 4-position to afford a highly electrophilic alkenediazonium ion. Reversible conjugate addition of the nucleophile to the 4-position then initiates the reaction cascade leading to the ultimate products.

A "Quenchergenic" Chemoselective Protein Labeling Strategy.

Dynamic changes in protein structure can be monitored by using a fluorescent probe and a dark quencher. This approach is contingent upon the ability to precisely introduce a fluorophore/quencher pair into two specific sites of a protein of interest. Despite recent advances, there is continued demand for new and convenient approaches to site-selectively label proteins with such optical probes. We have recently developed a chemoselectively rapid azo-coupling reaction (CRACR) for site-specific protein labeling; it relies on rapid coupling between a genetically encoded 5-hydroxytryptophan residue and various aromatic diazonium ions. Herein, it is reported that the product of this conjugation reaction, a highly chromophoric biarylazo group, is a potent fluorescence quencher. The absorption properties of this azo product can be tuned by systematically altering the structure of the aryldiazonium species. A particular "quenchergenic" aryldiazonium has been identified that, upon conjugation, efficiently quenches the fluorescence of green fluorescent protein, which is a widely used genetically encoded fluorescent probe that can be terminally attached to target proteins. This fluorophore/quencher pair was used to evaluate the protein-labeling kinetics of CRACR, as well as to monitor the proteolysis of a fusion protein.

Mass Spectrometric Quantitation of Pyridyloxobutyl DNA Phosphate Adducts in Rats Chronically Treated with N'-Nitrosonornicotine.

The tobacco-specific carcinogens N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) require metabolic activation to exert their carcinogenicity. NNN and NNK are metabolized to the same reactive diazonium ions, which alkylate DNA forming pyridyloxobutyl (POB) DNA base and phosphate adducts. We have characterized the formation of both POB DNA base and phosphate adducts in NNK-treated rats and the formation of POB DNA base adducts in NNN-treated rats. However, POB DNA phosphate adducts in NNN-treated rats are still uncharacterized. In this study, we quantified the levels of POB DNA phosphate adducts in tissues of rats chronically treated with ( S)-NNN or ( R)-NNN for 10, 30, 50, and 70 weeks during a carcinogenicity study. The highest amounts of POB DNA phosphate adducts were observed in the esophagus of the ( S)-NNN-treated rats, with a maximum level of 5400 ± 317 fmol/mg DNA at 50 weeks. The abundance of POB DNA phosphate adducts in the esophagus was consistent with the results of the carcinogenicity study showing that the esophagus was the primary site of tumor formation from treatment with ( S)-NNN. Compared to the ( R)-NNN group, the levels of POB DNA phosphate adducts were higher in the oral mucosa, esophagus, and liver, while lower in the nasal mucosa of the ( S)-NNN-treated rats. Among 10 combinations of all isomers of POB DNA phosphate adducts, Ap(POB)C and combinations with thymidine predominated across all the rat tissues examined. In the primary target tissue, esophageal mucosa, Ap(POB)C accounted for ∼20% of total phosphate adducts in the ( S)-NNN treatment group throughout the 70 weeks, with levels ranging from 780 ± 194 to 1010 ± 700 fmol/mg DNA. The results of this study showed that POB DNA phosphate adducts were present in high levels and persisted in target tissues of rats chronically treated with ( S)- or ( R)-NNN. These results improve our understanding of DNA damage during NNN-induced carcinogenesis. The predominant POB DNA phosphate isomers observed, such as Ap(POB)C, may serve as biomarkers for monitoring chronic exposure of tobacco-specific nitrosamines in humans.

Molecular Dynamics Investigation of the Physical Binding of the NNK Diazonium Ion to Exon 5 of Tp53

Molecular Dynamics Investigation of the Physical Binding of the NNK Diazonium Ion to Exon 5 of Tp53

The effect of covalently bonded aryl layers on the band bending and electron density of SnO2 surfaces probed by synchrotron X-ray photoelectron spectroscopy.

Tin(iv) dioxide (SnO2) is a technologically important transparent conducting oxide with high chemical stability. In air, the SnO2 surface is terminated with hydroxyl groups which cause the electronic bands to bend downward at the surface capturing a two-dimensional surface electron accumulation layer (SEAL). The SEAL promotes adsorption at the surface, giving environmentally-sensitive electronic properties; this sensitivity is a barrier to some potential applications of the material. This work investigates surface modification of SnO2via reaction with an aryldiazonium salt as a route to controlling the surface band bending. We compare the surface layers formed by reaction at open-circuit potential and under potential control of 4-(trifluoromethyl)benzene diazonium ions with moderately- and highly-doped (101) SnO2 thin films grown by plasma-assisted molecular beam epitaxy. Atomic force microscopy and synchrotron X-ray photoelectron spectroscopy (XPS) measurements demonstrate that both reaction conditions lead to covalently-attached 4-(trifluoromethyl)phenyl groups, with grafting at open-circuit potential giving thinner layers (<2 nm) and fewer direct bonds to the surface than electrografting (layer thickness >3 nm). Valence band investigations show that for all samples the 4-(trifluoromethyl)phenyl layers decrease the surface downward band bending with the greatest effect observed for the electrografted sample. In the latter case, a +0.29 eV shift in band bending relative to that of the unmodified material indicates the success in turning the surface electron accumulation layer into a depletion layer.

Physical binding of the tobacco smoke carcinogen NNK diazonium ion to the human tumor suppressor gene TP53 Exon 5.

The tobacco smoke N-nitrosamine, NNK, is an important carcinogen. It has been shown to induce lung, liver, and pancreatic cancer in animals. Its metabolites are associated with lung cancer in tobacco smokers. Our work focuses upon the physical interaction of NNK diazonium ion with DNA. This species is implicated in the formation of pyridyloxobutyl adducts, reacting with DNA bases and phosphate groups. Past research has investigated the metabolic activation of NNK by various enzymes, subsequent adduct formation with DNA, and the role of these adducts in mutagenesis. We present the first study of the physical interaction of NNK diazonium ion with TP53 (exon 5), a frequently mutated human tumor suppressor gene. We identify physical binding sites found via free energy minimization in computational docking simulations. These structures represent local potential energy minima in this system and suggest plausible sites for adduct formation.

Coumarin Triazabutadienes for Fluorescent Labeling of Proteins.

The use of small-molecule fluorophores to label proteins with minimal perturbation in response to an external stimulus is a powerful tool to probe chemical and biochemical environments. Herein, we describe the use of a coumarin-modified triazabutadiene that can deliver aryl diazonium ions to fluorescently label proteins by tyrosine-selective modification. The labeling can be triggered by low-pH-induced liberation of the diazonium species, thus making the fluorophore especially useful in labeling biochemical surroundings such as those found within the late endosome. Additionally, we show that a variety of coumarin triazabutadienes might also be prone to releasing their diazonium cargo after irradiation with UV light.

A theoretical investigation of sugar and phosphate contributions to the activation barriers of guanine methylation by carcinogenic methane diazonium ion

Feedback from electrostatic potential and local ionization potential maps provides evidence that in the gas phase electrostatic interactions cause the activation barriers of guanine methylation by methane diazonium ion at the N7 site to increase upon addition of sugar and phosphate moieties, from 24.6 kcal/mol with the 6–31 + G∗ basis set to 29.87 kcal/mol with the 6–311 + G (2df, 2p) basis set at the DFT/B3LYP-D3 level of theory. Aqueous activation barriers strongly depend on the interaction of guanine with discrete number of water molecules and, in implicit water, they lie between 4.37 for free guanine to 5.39 kcal/mol for syn-dGMP−

Spectrophotometric Determination of Sulfamethoxazole in Pure and in Pharmaceutical Preparations by Diazotization and Coupling Reaction

A highly sensitive, simple and accurate spectrophotometric method has been developed for quantitative determination of sulfamethoxazole(SMX) in both pure form and pharmaceutical preparations. In this method SMX is diazotized with equimolar of sodium nitrite(NaNO2) in acid medium of hydrochloric acid to form diazonium ion , which is reacted with 2,4,6-trihydroxybenzoic acid in alkaline medium of NaOH to form a yellow water soluble azo dye that has absorption maximum at 416 nm versus reagent blank. Beer's law is obeyed over the concentration range 0.2-16 µg. ml-1 with an excellent determination coefficient (r2= 0.9996) and molar absorptivity 1.84×104 l.mol-1.cm-1. The recoveries are obtained in the range of 97.8 - 99.8% and the relative standard deviation is better than ±0.23% . The stoichiometry of the resulting azo dye has been also worked out and it is found to be 1:1 SMX: 2,4,6-trihydroxybenzoic acid. This method has been applied successfully for the determination of SMX in pharmaceutical preparations (tablets and oral suspension).