Aromatic Diazonium Ions Research Articles

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.

A Chemoselective Rapid Azo-Coupling Reaction (CRACR) for Unclickable Bioconjugation.

Chemoselective modification of complex biomolecules has become a cornerstone of chemical biology. Despite the exciting developments of the past two decades, the demand for new chemoselective reactions with unique abilities, and those compatible with existing chemistries for concurrent multisite-directed labeling, remains high. Here we show that 5-hydroxyindoles exhibit remarkably high reactivity toward aromatic diazonium ions and this reaction can be used to chemoselectively label proteins. We have previously genetically encoded the noncanonical amino acid 5-hydroxytryptophan in both E. coli and eukaryotes, enabling efficient site-specific incorporation of 5-hydroxyindole into virtually any protein. The 5-hydroxytryptophan residue was shown to allow rapid, chemoselective protein modification using the azo-coupling reaction, and the utility of this bioconjugation strategy was further illustrated by generating a functional antibody-fluorophore conjugate. Although the resulting azo-linkage is otherwise stable, we show that it can be efficiently cleaved upon treatment with dithionite. Our work establishes a unique chemoselective "unclickable" bioconjugation strategy to site-specifically modify proteins expressed in both bacteria and eukaryotes.

Horseradish peroxidase-mediated oxidation of carcinogenic non-aminoazo dyes

Fifteen non-aminoazo, dyes were oxidized when catalyzed by horseradish peroxidase (HRP) in the presence of H2O2. Aromaticdiazonium ions, the ultimate carcinogen, were detected in the reaction with all of azo compounds as the substrates for HRP. The rates of oxidative cleavage fairly depended on pH. Relative enzymatic activities were compared among 15 non-aminoazo, dyes, and the structural requirements of the substrates for HRP were discussed in detail.

Selective Chemical Modification of Graphene Surfaces: Distinction Between Single‐ and Bilayer Graphene

Graphene modifications with oxygen or hydrogen are well known in contrast to carbon attachment to the graphene lattice. The chemical modification of graphene sheets with aromatic diazonium ions (carbon attachment) is analyzed by confocal Raman spectroscopy. The temporal and spatial evolution of surface-adsorbed species allows accurate tracking of the chemical reaction and identification of intermediates. The controlled transformation of sp(2) to sp(3) carbon proceeds in two separate steps. The presented derivatization is faster for single-layer graphene and allows controlled transformation of adsorbed diazonium reagents into covalently bound surface derivatives with enhanced reactivity at the edge of single-layer graphene. On bilayer graphene the derivatization proceeds to an adsorbed intermediate, which reacts slower to a covalently attached species on the carbon surface.

Encapsulation and Stabilization of Reactive Aromatic Diazonium Ions and the Tropylium Ion Within a Supramolecular Host

AbstractSupramolecular assemblies with internal cavities are being developed as nanoscale reaction vessels to protect or modify the reactivity of guest species through encapsulation. Diazonium cations and the tropylium cation were examined for their ability to encapsulate in the tetrahedral [Ga4L6]12− supramolecular assembly. The 4‐(diethylamino)benzenediazonium cation 1 readily formed a 1:1 host−guest complex with this assembly, and this encapsulation prevented 1 from reacting with 2,4‐pentanedione in D2O. The tropylium cation also formed a 1:1 host−guest complex with the [Ga4L6]12− assembly, greatly slowing its decomposition in D2O. Encapsulation in the protected environment of this host cavity alters the reactivity of these guest molecules, giving them greater stability. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Stabilization of Aliphatic and Aromatic Diazonium Ions by Coordination: An Experimental and Theoretical Study

The reaction of [Ru(bpy)2(NO)Cl]2+ and [Fe(CN)5NO]2- with n-butylamine has been studied as a plausible route for obtaining aliphatic diazonium ions stabilized by coordination. These reactions yield a variety of products originating mainly by direct attack of nucleophiles on the intermediate carbocation (or diazonium ion) and by rearrangement of the carbocation or the diazonium ion. The ratio of unrearranged to rearranged products can be taken as an experimental measurement of the stabilization of the diazonium ions. DFT-computed results suggest that the stabilization by complexation of the diazonium ions is larger in the ironpentacyano complex, in agreement with the fact that no rearrangement products are observed in the reaction of this species with n-butylamine.

Stability of 1-naphthalenediazonium ion in solution. Complexation and decomposition of 1-naphthalene- diazonium tetrafluoroborate in the presence of crown ethers and acyclic polyethers in 1,2-dichloroethane and the gas phase under fast atom bombardment conditions

The effects of solvent, temperature and pH on the rate of decomposition of uncomplexed 1-naphthalenediazonium tetrafluoroborate were studied by UV spectrometry. The complexation of the 1-naphthalenediazonium ion with crown ethers containing 4–10 oxygen atoms and some acyclic polyethers was detected and characterized in the gas phase by fast atom bombardment mass spectrometry (FAB-MS). In addition, the host–guest complexation and the kinetics of the thermal dediazoniation of 1-naphthalenediazonium ion in the presence of four crown ethers and two acyclic polyethers were studied in 1,2-dichloroethane (DCE) solution at 40 °C by UV spectrometry. All hosts, except 12-crown-4, formed 1:1 complexes under FAB conditions. The values of the thermodynamic stability K and the stabilizing ability of the complexation (k2/k1) in DCE were calculated from the kinetic data. The thermodynamic and kinetic stabilities were observed to be greater for the inclusion complex of the­1-naphthalenediazonium ion formed with crown ethers containing at least six oxygen atoms than for the non-spesific adduct formation formed with 15-crown-5. This was also true for tetraglyme, whose chain is too short to be capable of being fully wrapped around the diazonium group as in the complex of PEG 1000. Crown ethers with seven oxygen atoms are the strongest complexing agents for all the aromatic diazonium ions studied, for the 1-naphthal-enediazonium ion investigated here and for arenediazonium ions examined earlier. The values of the activation enthalpy ΔH≠ for the thermal dediazoniation of the uncomplexed salt in both the acidic aqueous solution and DCE were observed to be high, and the corresponding values of activation entropy ΔS ≠ were clearly positive. The results are consistent with a heterolytic SN1-like mechanism involving the decomposition of the uncomplexed and complexed 1-naphthalenediazonium ion into a highly reactive naphthyl cation, followed by fast product-determining reactions with nucleophiles to give the products. Copyright © 2000 John Wiley & Sons, Ltd.

Characterization of azo coupling adducts of benzenediazonium ions with aromatic amino acids in peptides and proteins.

A synthetic peptide, VLSPADKTNWGHEYRMF(cmC)QIG, was reacted with 4-chlorobenzenediazonium hexafluorophosphate as a model for reactions of aromatic diazonium ions with proteins. At a ratio of diazonium ion to peptide of 0.8:1, three products could be seen by reversed-phase HPLC. Electrospray mass spectrometric analysis of the isolated products revealed that two of the products had the same mass of 2648 Da, being 138 Da higher than the parent peptide and corresponding to the addition of a 4-chlorobenzenediazo group. The third isolated product had a mass of 2787 Da which corresponded to the addition of two 4-chlorobenzenediazo groups (276 Da). Digestion of the monoadducted intact peptides with trypsin or endoproteinase Glu-C and HPLC separation of adduct oligopeptides followed by sequencing with electrospray ionization tandem mass spectrometry showed unambiguously that histidine and tyrosine residues were the major sites of modification. Incubation of human serum albumin with 4-chlorobenzenediazonium hexafluorophosphate at molar ratios of 1:1, 1:2, and 1:10 resulted in adduct formation as detected by shifts in the HPLC retention time of the protein and also by an increase in mass as determined by electrospray mass spectrometry.

A study of the effect of chain length on nearest neighbour interactions of immobilized species

The effect of varying the length and hydrophobicity of the molecular tether that binds an indicator to a substrate was studied. The length or hydrophobicity of the tether may affect the characteristics of the immobilized indicator in several ways. Of primary interest in this study was the extent to which the tether characteristics control interactions between adjacent immobilized species. We investigated two straight-chain tethers of variable length and two branched-chained tethers of different hydrophobicities. For each of these systems, we investigated nearest neighbour interactions as a function of surface coverage. The extent of this interaction was determined by measuring the degree of coupling between adjacent immobilized aromatic diazonium ions. Our results suggest that nearest neighbour interactions between immobilized species in an aqueous environment are controlled primarily by the hydrophobicity of the tether.

Crystal Structure of the Explosive Parent Benzyne Precursor: 2‐Diazoniobenzenecarboxylate Hydrate

AbstractThe structure of the highly unstable benzyne precursor 2‐diazoniobenzenecarboxylate (3) has been determined by single‐crystal X‐ray diffraction. The structure is discussed in comparison to ab initio results for several conformers of 3, related aromatic diazonium ions, and phenyl cation and also to crystal structures of simple diazonium ion salts and of benzoates. Structural features and characteristic distortions are related to the electron density distributions and to intra‐ and intermolecular interactions between the neighboring functional groups.

Preparation of Aromatic Fluorides Via Diazotization and Photochemically Induced Fluoro-Dediazoniation of Aromatic Amines in Anhydrous Hydrogen Fluoride - Organic Base Solutions

Abstract Fluoro-dediazoniation of aromatic diazonium ions, produced by the diazotization of the corresponding aromatic amines with NaNO2 in anhydrous hydrogen fluorides (AHF) - organic base solutions, was accelerated photochemically to afford Ar-F efficiently in AHF - organic base solutions in situ.

Diazo Coupling of Nortricyclene‐(Tricyclo[2.2.1.02,6]heptane)‐1‐diazonium Ions

Like aromatic diazonium ions, the title compound 1 couples with phenols to form azo compounds, e.g., 2. Compound 1 reacts with alcohols, undergoing reductive deamination. These reactions are neither possible with cyclopropane-1-diazonium ions nor with norbornane-1-diazonium ions.

Activated aromatic diazonium ions, sulfonates and halides as new initiators for the cationic polymerization of p-methoxystyrene: exceptional effectiveness of p-nitrobenzenediazonium tetrafluoroborate

Nitro-substituted aromatic diazonium ions, sulfonates, and halides initiated cationic polymerization of p-methoxystyrene in nitromethane solution. p-Nitrobenzenediazonium tetrafluoroborate was by far the most effective of five such compounds tested. The mechanism is believed to involve addition of the nucleophilic monomer to the aromatic ring to form a Meisenheimer intermediate. Elimination of the leaving group forms a carbenium ion which initiates polymerization.

Prototypes for aliphatic and aromatic diazonium ions. An ab initio study of the methane- and benzenediazonium ions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPrototypes for aliphatic and aromatic diazonium ions. An ab initio study of the methane- and benzenediazonium ionsMark A. Vincent and Leo RadomCite this: J. Am. Chem. Soc. 1978, 100, 11, 3306–3312Publication Date (Print):May 1, 1978Publication History Published online1 May 2002Published inissue 1 May 1978https://doi.org/10.1021/ja00479a009RIGHTS & PERMISSIONSArticle Views125Altmetric-Citations27LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (758 KB) Get e-Alerts Get e-Alerts

Nitrogen as Leaving Group: Dediazoniations of Aromatic Diazonium Ions

AbstractOn heating, aromatic diazonium salts eliminate nitrogen by two fundamentally different mechanistic pathways, i.e. heterolysis and homolysis. Among these pathways a series of variants are known, giving rise to a whole variety of mechanisms. This article considers the effect of specific solvation, apparently characteristic of diazonium ions, by various solvents (fluorinated alcohols, methanol, water, dimethyl sulfoxide, pyridine, and hexamethylphosphoric triamide) on the mechanism. Apart from the donor properties of the solvent, the oxidation potential and the presence of additives play a major role in determining what reaction type will predominate.

Nitrogen as Leaving Group: Aliphatic Diazonium Ions

AbstractNitrogen is one of the best known leaving groups. Decomposition of aliphatic diazonium ions has rendered carbocations (carbon cations) accessible in cases where the solvolysis of halides or sulfonic esters follows different pathways. The limits of unassisted decomposition are seen in primary diazonium ions, where the participation of external nucleophiles and of neighboring groups in the elimination of nitrogen becomes noticeable. Cyclopropanediazonium ions occupy a position intermediate between aliphatic and aromatic diazonium ions. New versatile methods of generating aliphatic diazonium ions facilitate their preparative use.