Photochemical interconversion of phenylnitrene and the isomeric pyridylmethylenes

Chapman, O. L.; Sheridan, Robert S.; Leroux, Juliette

doi:10.1021/ja00487a054

Cited by 73 publications

(49 citation statements)

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“…Note that a benzazirine analogous to 6 was not detected upon photolysis of phenyl azide in an Ar matrix. 31,32 As seen in Fig. 1, the electronic absorption (EA) spectrum of triplet nitrene 4 is well reproduced by CASSCF/CASPT2 calculations.…”

Section: Resultssupporting

confidence: 53%

Matrix isolation and computational study of the photochemistry of p-azidoaniline

Pritchina

Gritsan

Bally

2006

Phys. Chem. Chem. Phys.

152

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The photochemistry of p-azidoaniline was studied in argon matrices in the absence and presence of oxygen. With the help of quantum chemical calculations we were able to characterize the triplet p-aminophenylnitrene as well as the cis-and trans-p-aminophenylnitroso oxides. It was found that the latter two isomers can be interconverted by selective irradiation and that they are ultimately converted into p-nitroaniline. Although restricted wavefunctions of the nitroso oxides are unstable, CASSCF calculations turned up no evidence for the claimed diradical character of these compounds. Also we found no evidence for dioxaziridines as intermediates of the conversion of the nitroso oxides to p-nitroaniline. IntroductionGreat progress has been made in understanding the photochemistry of aryl azides over the past few years. 1,2 Singlet phenylnitrene and a series of its simple derivatives have been detected directly and the effects of substituents on the spectra and the decay kinetics of singlet aryl nitrenes have been examined systematically. 2 Thereby it was found that groups which act as strong p donors dramatically accelerate the rate of intersystem crossing. This could be the reason why photolysis of p-azidoaniline (1) and p-azidodimethylaniline, unlike that of phenyl azide and most of its derivatives, gives only products of triplet nitrene reactions. 3,4 For instance, in the presence of oxygen at ambient temperature p-nitroaniline (2) and p-nitrosoaniline (3) are formed in quantitative yield upon photolysis of 1 (Scheme 1). 3,5 Since the early seventies it has been known that triplet arylnitrenes react with oxygen by formation of adducts. [5][6][7][8][9] In an early study on 1,4-diazidobenzene, two types of adducts (diamagnetic and paramagnetic) were detected in glassy matrices. 6 It was proposed that the diamagnetic adduct is an arylnitroso oxide, R-NQO 1 -O À , and the paramagnetic species is a ''spin isomer'' thereof, the triplet aryliminodioxy diradical, R-N-O -O . 6,10 Although subsequent studies did not confirm the formation of triplet adducts of arylnitrenes with oxygen, 3,5,7,8 speculations about the occurrence of aryliminodioxy diradicals in the photooxidation of aryl azides continue to surface occasionally in the literature. 11 This paper is devoted to a comprehensive experimental and computational study of the reactions of triplet arylnitrenes with oxygen in order to unambiguously identify the resulting adducts by their experimentally observed spectra, and to understand their properties. It should be noted that the earlier assignments of a strong near-UV absorption to arylnitroso oxides 3,5,7-9 were never supported by calculations. p-Azidoaniline was used in our matrix isolation study because, as noted above, it gives exclusively products of triplet nitrene reactions in solution, and we thought that this would also simplify the photochemistry in Ar matrices. In addition, the reaction of triplet p-aminophenylnitrene (4) with oxygen in solution and in glassy matrices has previously been studied. 5 2 Experim...

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Section: Resultssupporting

confidence: 53%

Matrix isolation and computational study of the photochemistry of p-azidoaniline

Pritchina

Gritsan

Bally

2006

Phys. Chem. Chem. Phys.

152

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“…This represents a 40-fold increase in efficiency on a mole-to-mole basis. Such a discrepancy between the amount of protein labeled and the amount of protein present may indicate that the reactive species of the probe is a short-lived electrophilic intermediate such as azacycloheptatetraene (11 monitor the location of the photoreactive group in a vesicle suspension. We asked the following question.…”

Section: Resultsmentioning

confidence: 99%

Photoreactive labeling of M13 coat protein in model membranes by use of a glycolipid probe.

Hu¹,

Wisnieski²

1979

Proc. Natl. Acad. Sci. U.S.A.

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Coliphage M13 coat protein in synthetic bilayer membranes was labeled by use of 12,(4-azido-2-nitrophenoxy)stearoyl[I-14Clglucosamine, a photoreactive glycolipid probe that spontaneously inserts into membranes. In this model system, the probe preferentially labeled the proteins over the lipids. Experiments designed to test the probe's restriction to integral membrane proteins revealed that extrinsic proteins as well as external peptide fragments of integral membrane proteins were not accessible to the photogenerated nitrene on the fatty acid chain. Only integral membrane peptides were labeled by the membrane-bound probe. These results indicate that protein labeling can be effected specifically from within the hydrocarbon milieu of a model membrane system. Recently, we described the synthesis of several photoreactive probes designed for the high-resolution mapping of membrane proteins (1, 2). In addition, we demonstrated the ability of one of these probes, 12-(4-azido-2-nitrophenoxy)stearoyl[1-'4C]-glucosamine, designated 12-APS-GlcN, to specifically label the envelope proteins of Newcastle disease virus (3) and to follow the transmembrane dynamics involved in cholera toxin activity (4). These studies prompted further investigation into the nature of the interaction of the probe with membrane proteins in an effort to define the region of the probe's reactivity and to verify the probe's restriction to integral membrane proteins. Toward this goal, we have constructed phospholipid vesicles containing the 5000-dalton coat protein of the coliphage M13, which orients itself unidirectionally across the membrane bilayer under appropriate conditions (5). Because the amino acid sequence as well as the hydrophobic region of this protein are known, it should be possible to determine the position of the probe in the membrane by using the hydrophobic amino acids of the protein as a gauge of membrane depth.In this report, we show that M13 coat protein incorporated into dimyristoyllecithin (DML) vesicles is indeed labeled by the photoreactive probe (12-APS-GlcN) upon irradiation. Furthermore, evidence is presented that indicates that the probe does not label externally added coat protein, nor does it label amino acid residues of the protein that are shown to be outside of the phospholipid bilayer by trypsin cleavage experiments.MATERIALS AND METHODS DML was obtained from Sigma or Calbiochem; trypsin treated with L-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK) was purchased from Worthington. Both were used without further purification.Preparation of M13 Coat Protein. M13 virus was grown and isolated as described by Wickner (6) with slight modifications. Escherichia coli strains K-37 and LA-9 were used for growing unlabeled and [3H]proline-labeled virus, respectively. The bacteria were cultured either in YT medium or in M63 minimal medium (7) to optimize the uptake of label. The M13 coat protein was extracted from whole virus by established procedures (8) and stored at either +40C or -20°C in 50 mM Tris buffer (pH...

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“…144 The assignment of the other bands was not made; however, the authors hypothesised that these bands belong to photolysis products of ketene imine. In addition, the ESR spectrum characteristic of nitrene 3 (29) (|D/hc| = 1.027 cm 71 , E = 0 cm 71 ) was observed upon irradiation (l > 216 nm) of phenyl azide in an argon matrix at 12 K. 145 Detailed study of the photolysis products of phenyl azide in organic solvents in a wide temperature range (77 ± 293 K) combined with the measurements of their electronic absorption and luminescence spectra led to the conclusion 139 that triplet nitrene 29 is the major product at 77 K.…”

Section: Photochemistry Of Phenyl Azidementioning

confidence: 94%

Study of photochemical transformations of organic azides by matrix isolation techniques and quantum chemistry

Gritsan¹

2007

Russ. Chem. Rev.

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Photochemical interconversion of phenylnitrene and the isomeric pyridylmethylenes

Cited by 73 publications

References 1 publication

Matrix isolation and computational study of the photochemistry of p-azidoaniline

Matrix isolation and computational study of the photochemistry of p-azidoaniline

Photoreactive labeling of M13 coat protein in model membranes by use of a glycolipid probe.

Study of photochemical transformations of organic azides by matrix isolation techniques and quantum chemistry

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