Photolysis Of Azide Research Articles

Synthesis of 5H-naphtho[2,3-c]phenothiazine-8,13-diones from 1-arylthio-2-azidoanthraquinones

Thermolysis of 1-arylthio-2-azidoanthraquinones in DMSO at 150 °C afforded substituted 5H-naphtho[2,3-c]phenothiazine-8,13-diones. These compounds were also formed upon photolysis of azides at 77 K and were prepared in quantitative yields by the reactions of 1-arylthio-2-azidoanthraquinones with KOH in DMSO at 20 °C.

A new caged Ca 2+, azid-1, is far more photosensitive than nitrobenzyl-based chelators

Background: Photolabile chelators that release Ca 2+ upon illumination have been used extensively to dissect the role of this important second messenger in cellular processes such as muscle contraction and synaptic transmission. The caged calcium chelators that are presently available are often limited by their inadequate changes in Ca 2+ affinity, selectivity for Ca 2+ over Mg 2+ and sensitivity to light. As these chelators are all based on nitrobenzyl photochemistry, we explored the use of other photosensitive moieties to generate a new caged calcium with improved properties. Results: Azid-1 is a novel caged calcium in which a fluorescent Ca 2+ indicator, fura-2, has been modified with an azide substituent on the benzofuran 3-position. Azid-1 binds Ca 2+ with a dissociation constant (K d) of ∼230 nM, which changes to 120 μM after photolysis with ultraviolet light (330–380 nm). Mg 2+ binding is weak (8–9 mM K d) before or after photolysis. Azid-1 photolyzes with unit quantum efficiency, making it 40–170-fold more sensitive to light than caged calciums used previously. The photolysis of azid-1 probably releases N 2 to form a nitrenium ion that adds water to yield an amidoxime cation; the electron-with-drawing ability of the amidoxime cation reduces the chelator's Ca 2+ affinity within at most 2 ms following a light flash. The ability of azid-1 to function as a caged calcium in living cells was demonstrated in cerebellar Purkinje cells, in which Ca 2+ photolytically released from azid-1 could replace the normal depolarization-induced Ca 2+ transient in triggering synaptic plasticity. Conclusions: Azid-1 promises to be a useful tool for generating highly controlled spatial and temporal increases of Ca 2+ in studies of the many Ca 2+-dependent biological processes. Unlike other caged calciums, azid-1 has a substantial cross section or shows a high susceptibility for two-photon photolysis, the only technique that confines the photochemistry to a focal spot that is localized in three dimensions. Azide photolysis could be a useful and more photosensitive alternative to nitrobenzyl photochemistry.

Effect of diphenylamine on photodissociation of aryl azides

The charge-transfer complexes of aromatic azides with diphenylamine (DPA) were studied. Irradiation of 4-nitrophenyl azide in the presence of DPA was found not to give rise to the dissociation of the azido group in the azide radical anionvia intracomplex electron transfer. The photodissociation slows down due to both the static (the formation of a photostable complex with diphenylamine) and dynamic quenching. When 4-azidoacetophenone is irradiated in the presence of DPA, the amine-sensitized decomposition of azide and the photodecomposition of the azide—DPA complex occur along with the direct photolysis of azide, which results in acceleration of the photodissociation due to an increase in the efficiency of the light absorption by the reaction system. A possible sensitization of photodecomposition of aromatic azidesvia an electron transfer mechanism by irradiation of the azide-donor complex is shown.

A synthetic approach to azepin-4-ones exploiting azide photolysis in low-temperature matrices

Photolysis of 2,6-dichloro-4-azidophenol and 2,6-dibromo-4-azidophenol in N2 or Ar matrices at 12–14 K results in ring expansion, yielding in each case either the corresponding hydroxydidehydroazepine or, in more concentrated matrices, the tautomeric azepin-4-one.

Chlorinated phenyl azides as photolabeling reagents. Synthesis of an ortho,ortho'-dichlorinated arylazido PCP receptor ligand.

The enhanced photolabeling properties of chlorinated phenyl azides are demonstrated by the synthesis and photolysis of methyl 4-azido-2,3,5,6-tetrachlorobenzoate (3) and methyl 4-azido-3,5-dichlorobenzoate (4). Photolysis of azide 3 in 1 M diethylamine/cyclohexane as the trapping medium gave 34% NH-insertion product. Similar photolysis of azide 4 gave 35% NH insertion product. These results demonstrate that chlorinated phenyl azides are significantly better at undergoing NH insertion than nonhalogenated analogs and suggest that improvement of existing aryl azide-based photolabels might be achieved by introduction of chlorine atoms on either side of the azide group. As an application, 3-azido-2,4-dichloro-10,5-(iminomethano)-10,11-dihydro-5H- dibenzo[a,d]cycloheptene (19), an analog of the potent PCP receptor ligand IDDC (14), was synthesized and its affinity for the PCP receptor was determined to be 6.3 +/- 0.7 microM (IC50 against [3H]MK801).

Quantitative structure-activity relationships of mutagenic aromatic and heteroaromatic azides and amines.

Photolysis of arylazides with long-wavelength UV light in an aqueous medium produces short-lived reactive species that bind to DNA and induce mutations in Salmonella typhimurium TA98. Nitrenes are known reactive products of azide photolysis, so that the DNA-binding and mutagenic species is either a nitrene or nitrene derivative. In the present study we presupposed that the nitrenium ion is the key intermediate. The electronic properties of 19 nitrenium ions with different chemical structures were calculated by the semi-empirical method AM1 and the resulting values plotted against the logarithm of the mutagenicity (log MUT) by means of linear regression analysis. Log MUT correlates with the stability of the nitrenium ion, the energy level of the LUMO and the charges on the exocyclic nitrogen with r = -0.804, 0.865 and -0.874 respectively. Thus, the mutagenicity of the azides is directly proportional to the stability of the nitrenium ions and inversely proportional to the electrophilicity of the exocyclic nitrogen. Furthermore, the mutagenicity of the azides correlates with the mutagenicity of the corresponding arylamines with r = 0.91 (n = 13). These correlations support the key role of the nitrenium ions and demonstrate the value of their electronic structure for the prediction of the mutagenicity of arylazides and arylamines.

ChemInform Abstract: 4-Azido-2-iodo-3,5,6-trifluorophenylcarbonyl Derivatives. A New Class of Functionalized and Iodinated Perfluorophenyl Azide Photolabels.

Abstract Iodinated perfluorophenyl azide 4 and NHS ester 7 were synthesized. Photolysis of azide 4 in DEA/cyclohexane gave N-H insertion product 9 (24%). For photolabeling purposes, this constitutes a significant improvement over the behavior of non-fluorinated analogues.

ChemInform Abstract: 1,2‐Didehydroazepines from the Photolysis of Substituted Aryl Azides: Analysis of Their Chemical and Physical Properties by Time‐Resolved Spectroscopic Methods.

AbstractThe reaction mechanism of the photolysis of azides of type (I) in the presence and absence of Et2NH (IV) or iPr2NH is investigated by conventional product studies in combination with time‐resolved IR and UV spectroscopy (kinetics) and MNDO calculations on five C6H5N species such as singlet (120) and triplet nitrene (II) (99) and didehydroazepine (III) (100 kcal/mol; X: ‐H).

4-azido-2-iodo-3,5,6-trifluorophenylcarbonyl derivatives. A new class of functionalized and iodinated perfluorophenyl azide photolabels

Iodinated perfluorophenyl azide 4 and NHS ester 7 were synthesized. Photolysis of azide 4 in DEA/cyclohexane gave N-H insertion product 9 (24%). For photolabeling purposes, this constitutes a significant improvement over the behavior of non-fluorinated analogues.

Photolysis of arylazides and generation of highly electrophilic DNA-binding and mutagenic intermediates.

Photolysis of arylazides with long wavelength ultraviolet (NUV) light in an aqueous medium produces short-lived reactive chemical species which bind to DNA and deoxynucleoside 3'-phosphates and induce reversion mutations in frameshift tester strains of Salmonella typhimurium. Nitrenes are known reactive products of azide photolysis, so the DNA-binding and mutagenic species is either a nitrene or a nitrene-derivative. An N-hydroxyarylamine intermediate, potentially formed from a nitrene and water, can be excluded because the mutagenic potencies of the reactive species in TA98 and in the hydroxylamine-resistant TA98/1,8-DNP6 are of the same order, and because the life-time of this species is very short. The mutagenic potency of the arylazide photolysis products decreases in the order azido-IQ greater than 1-azidopyrene greater than azido-MeIQx greater than 6-azidochrysene greater than 2-azidofluorene greater than 4-azidobiphenyl greater than 2-azido-naphthalene greater than 1-azido-naphthalene. This potency sequence correlates with that of the corresponding arylamines. Furthermore, their DNA binding products are chromatographically identical with those obtained in cellular, metabolizing systems from nitroarenes and arylamines. Therefore, the reactive, electrophilic azide photolysis product is very likely a nitrenium ion formed by protonation of a nitrene. Nitrenium ions are also the ultimate mutagens/carcinogens formed from nitroarenes and arylamines. Arylazides can therefore be considered as stabilized forms of arylnitrenium ions. The arylazide-nitrene technique reported here is new and simple and provides ready access to presumed nitrenium ions which are otherwise difficult to obtain.

Photolysis and thermolysis of phenyl azide in acetic acid. Trapping of 1-azacyclohepta-1,2,4,6-tetraene and nucleophilic aromatic substitution

Photolysis and thermolysis of phenyl azide in acetic acid yielded 1H-azepin-2(3H)-one (4), 2-methylbenzoxazole (15), 2- and 4-acetamidophenyl acetates (16) and (12), 2- and 4-acetamidophenols (14) and (13), acetanilide, and azobenzene. Addition of ethanol to the system caused a linear decrease in the yield of (4) and a more remarkable decrease in total yield for the para-products than that for the ortho-products to give 2- and 4-acetamidophenyl ethyl ethers (9) and (8). Photolysis of the azide in ethanol in the presence of phenol afforded 2-phenoxy-3H-azepine (5) and aniline, but no 2- and 4-phenetidines. The yield of compounds (4) and (12)–(16) was independent of the presence of penta-1,3-diene (0.01 M), and somewhat decreased by an addition of bromobenzene. The rate of decomposition of azide in acetic acid was not accelerated as compared with that in 1,4-dioxan, and the activation parameters varied little in the two solvents. The results suggest that 1-azacyclohepta-1,2,4,6-tetraene (1) formed via singles phenylnitrene or via singles excited phenyl azide is trapped by acetic acid or phenol to give (4) or (5), and that a resonance-stabilized ion (3) neighbouring acetate anion is formed by an attack of the singlet nitrene on acetic acid to give aromatic nucleophilic substitution.

Photolysis of azides in glassy solutions: spectral and photochemical properties of nitrenes

The spectral and photochemical properties of nitrenes formed during the photolysis of aromatic azides in rigid solutions at 77 K were investigated. The T 1—T 0 fluorescences of 4-biphenyl nitrene and 4,4′-biphenyl dinitrene were observed. A photoreduction of the nitrenes in rigid solutions at 77 K was found. The excited nitrene was shown to react with the matrix to form a substituted amine.

Photooxidation of azides in polymer matrices

It is known that oxygen is an inhibitor of the reaction of photochemical cross-linking of polymers by bis-azides [1-5]. The action of oxygen leads to a substantial (by 2-3 orders of magnitude) decrease in the light sensitivity of photoresistors based on the polymer--bisazide system. In [4, 5] it was suggested that the inhibition by oxygen of the reaction of cross-linking of polymers by azides is due to the interaction of molecular oxygen with nitrenes, formed in the photolysis of azides. On the basis of the data of [6, 7], it was assumed that this interaction leads to the formation of the corresponding nitrocompounds. In the present work this assumption was subjected to experimental verification.

Photolysis of Azide Dissolved in Alkali Halides

Photolysis of Azide Dissolved in Alkali Halides

Acyl azide photolysis. Proximity and ring-size factors and mechanism

Photolysis of hexanoyl azide in cyclohexane gave 6-methyl-2-piperidone (13%), 5-ethyl-2-pyrrolidone (8%), and N-cyclohexylhexanamide (3%). In contrast, photosensitized decomposition of the azide with acetophenone gave hexanamide (78%), cyclohexene (11%), and dicyclohexyl (11%), but no lactams. It is concluded that the direct photolysis gives singlet acyl nitrene as the reactive species, which yields the δ-lactam preferentially. The importance of proximity in determining the γ- to δ-lactam ratio is emphasized.

The detection of free radicals in the high intensity photolysis of hydrogen azide

The absorption spectra of the radicals NH and NH 2 have been observed in the flash photo­lysis of hydrogen azide in the presence of an excess of inert gas. A new complex, but slightly diffuse, absorption has been detected around 2700 Å. This spectrum shows no shift when DN 3 is substituted for HN 3 , and it is attributed to the N 3 radical. The mechanism of the hydrogen azide photolysis is discussed briefly with reference to these observations.