Spin-labeled Crown Ethers Research Articles

Ion Complexation Induced High-Spin Associations of Spin-Labeled Crown Ethers: A Reevaluation

Abstract Between 1978 and 1989, Mukai and coworkers demonstrated that a series of spin-labeled benzo-15-crown-5 derivatives gave triplet ESR spectra in ethanol glasses in the presence of diamagnetic alkali and alkaline earth ions. They proposed that the high-spin coupling resulted from a pair of radicals being brought into close contact by a 1:2 complexation of metal ions with the crown ether moieties. The work of Mukai and his colleagues represents an early example of high-spin coupling induced in radical pairs that assemble around diamagnetic metal ions. Herein, we describe ion binding experiments with simple stable free radicals such as TEMPO and galvinoxyl that lack the crown moiety. The triplet state species that we observe require the possibility of unforeseen mechanisms for previously reported high-spin associations in spin labeled crown ethers.

Synthesis of novel spin-labeled crown ethers

Diazonium salts obtained from aminophenyl-substituted crown ethers react with paramagnetic imidazolinium salt to yield arylazoenamines, containing spin-labeled crown ethers. An alternative approach to the synthesis of related compounds, spin-labeled ureas, consists of the reaction of aminophenyl-substituted crown ethers with paramagnetic isocyanates.

Synthesis of a Dihydroxy-Substituted Aminoxyl Spin Label and its Crown Ether and Cyclic Diester Derivatives

A novel dihydroxy-substituted aminoxyl spin label, 4-hydroxy-3-(3'-hydroxypropyl)-2,2,6,6-tetramethylpiperidine-1-oxy (5), has been prepared. From this aminoxyl radical, a spin-labeled crown ether, 16,16,18,18-tetramethyl-2,5,8,11-tetraoxa-17-azabicyclo[ 13,4,0]-nonadecane-17-oxy (12), and a spin-labeled cyclic diester, 16,16,18,18-tetramethyl-3,10-dioxo-2,5,8,11-tetraoxa-17-azabicyclo[13,4,o]nonadecane-17-oxy (13), have been acquired. Other four new stable aminoxyl radicals 8,9,10, and 11 have also been obtained within the synthetic approach. It has been demonstrated that the cyclic ether compound (7) is generated by the reduction of its corresponding lactone which is sidely derived from the oxo-reduced species of 3 by intramolecular cyclization.

ENDOR Studies of the Complexation Reaction between Spin-Labeled Crown Ether and Alkali Metal Salts

Abstract A new crown ether spin-labeled by the phenoxyl radical moiety was prepared. Intramolecular odd-π electron delocalization was investigated by means of ENDOR spectroscopy. On the basis of ENDOR spectrometric titration, the equilibrium constant for Na+-labeled crown-ether-complex formation was evaluated to be pKNa+=3.5 in 2-propanol at −30 °C.

Synthesis and electron paramagnetic resonance studies of chiral spin-labeled crown ethers

The synthesis of syn and anti chiral dinitroxide [18]-crown-6 ethers and of a tetranitroxide crown ether is described. The existence of a spin–spin interaction for the syn isomer makes this spin-labeled crown ether probe particularly useful to follow by epr the effects of K+ ion binding, pH, solvent, and temperature. These observations are discussed in terms of a global dynamical fluctuation of the substituted crown ether.

Azethoxyl nitroxide spin-labeled crown ethers and cryptands with the N-O.bul. group positioned near the cavity

Azethoxyl nitroxide spin-labeled crown ethers and cryptands with the N-O.bul. group positioned near the cavity

ChemInform Abstract: THREE NOVEL SPIN‐LABELED CROWN ETHERS

Chemischer InformationsdienstVolume 13, Issue 35 Physical Organic Chemistry ChemInform Abstract: THREE NOVEL SPIN-LABELED CROWN ETHERS M. P. EASTMAN, M. P. EASTMANSearch for more papers by this authorD. E. PATTERSON, D. E. PATTERSONSearch for more papers by this authorR. A. BARTSCH, R. A. BARTSCHSearch for more papers by this authorY. LIU, Y. LIUSearch for more papers by this authorP. G. ELLER, P. G. ELLERSearch for more papers by this author M. P. EASTMAN, M. P. EASTMANSearch for more papers by this authorD. E. PATTERSON, D. E. PATTERSONSearch for more papers by this authorR. A. BARTSCH, R. A. BARTSCHSearch for more papers by this authorY. LIU, Y. LIUSearch for more papers by this authorP. G. ELLER, P. G. ELLERSearch for more papers by this author First published: August 31, 1982 https://doi.org/10.1002/chin.198235068AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue35August 31, 1982 RelatedInformation

ESR Investigation of Alkali Metal Complexes of Galvinoxyl-labeled Benzo-15-crown-5 in Frozen Solution

Abstract A stable galvinoxyl derivative (1) of benzo-15-crown-5 was prepared and the complex formation between the spin labeled crown ether 1 and the alkali metal and ammonium salts was studied by the ESR technique. Existence of the (2:1) complex of 1 with potassium, rubidium, and ammonium salts was confirmed by the observation of the triplet ESR spectra in ethanol rigid matrix at 77 K. Essentially the same g- and D-tensor values are observed for all the (2:1) complexes, indicating similar conformation of the ligand molecule 1. The zero-field splitting parameters (D and E) are calculated on the basis of the spin distribution of 1 and the assumed molecular structures for the (2:1) complex. By comparing the observed D and E parameters with the calculated ones, the structure of the (2:1) complex in ethanol rigid matrix is discussed. On the other hand, the sodium complexes of 1 show a slightly asymmetric single line, suggesting the (1:1) complex formation between 1 and the sodium salts. No anions (SCN−, Br−, and I−) have any appreciable effect on the ESR spectra of both the (2:1) and (1:1) complexes.

Three novel spin-labeled crown ethers

The following nitroxide spin-labeled crown ethers have been synthesized: 2,2-(sym-dibenzo-16-crown-5)-4,4-dimethyloxazolidinyl-N-oxyl (1), 2,2-(sym-dibenzo-16-crown-5)-4,4,5,5-tetramethylimidazolinyl-N-oxyl (2), and 3-carboxy-2,2,5,5-tetramethyl-3-pyrrolinyl-l-oxy hydroxy-sym-dibenzo-16-crown-5 ester (3). 1 and 2 are characterized by having the nitroxide near the crown cavity and rigidly bound to a ring carbon atom of the crown. 1-3 have been studied by EPR, and the proton hyperfine splittings have been determined by second harmonic out-of-phase detection. The values obtained for the proton hyperfine splittings of 1 were compared to those determined by ENDOR and found to agree within experimental error. EPR studies of hyperfine splitting constants and Heisenberg spin exchange suggest that these spin-labeled crowns are poor complexing agents for alkali metal cations. The structure of 1 has been determined by x-ray diffraction, and the poor complexing ability of the crown is attributed to an unprecedented structural feature in which the hydrogen atoms of one methylene group of the propylene bridging linkage have turned inward with respect to the cavity of the crown. The proton hyperfine splitting observed for 1 is attributed to protons located at approximately van der Waals distances from the NO group.

ESR studies of the alkali metal complexes of verdazyl-labeled benzo-15-crown-5

A verdazyl derivative of benzo-15-crown-5 ( 1 ) has been prepared, and the complex formation between the spin labeled crown ether ( 1 ) and the alkali metal salts has been studied by ESR spectroscopy.

ESR STUDIES OP THE ALKALI METAL COMPLEXES OF GALVINOXYL-LABELED-BENZO-15-CROWN-5

Abstract A galvinoxyl derivative of benzo-15-crown-5 (1) has been synthesized, and the complex formation between the spin labeled crown ether (1) and the alkali metal thiocyanate has been studied by ESR measurement. A typical triplet ESR spectrum was observed for the potassium complex in ethanol rigid matrix at 77 K, clearly indicating the (1:2) complex formation between the KNCS salt and the 1. On the other hand, the sodium complex showed a symmetrical single line, suggesting the (1:1) complex formation between the NaNCS salt and the 1.

A SPIN LABELED CROWN ETHER (I). ESR STUDIES ON THE ALKALI METAL COMPLEXES OF TANOL DERIVATIVE OF BENZO-15-CROWN-5

Abstract A TANOL derivative of benzo-15-crown-5 shown in the Fig. 1, was synthesized, and the complex formation between the spin labeled crown ether and the alkali metal isocyanate was studied by ESR technique. The potassium complex revealed a strong spin–spin interaction due to formation of the sandwiched dimer and the structure was investigated on the basis of the ESR parameters of the triplet cluster.