A Study on Bilirubin Radical Cation Generated by One-Electron Oxidation

Introduction Bilirubin (BR) is generally regarded as a toxic compound when accumulated at an abnormally high concentration in biological tissues, and in fact a normal adult man produces about 300 mg of BR a day. However, it was proposed that the bile pigments BR and biliverdin(BV), which is the precursor of BR, may protect vitamin A and linoleie acid from oxidative destruction in the intestinal tract Further stud

ESR Studies on N-Alkylphenothiazine Radical Cation Salts

he stable radical cation salts of phenothiazine and N-alkyl-phenothiazine(alkyl =methyl , ethyl , isohutyl , isopentyl and benzyl) hexachloroantimonate ,per-chlorate , and iodide were prepared by means of one-electron oxidation with 2 ,2 , 6 ,6-tetramethyl- 4-acetoxypiperidine oxoammonium hexachloroantimonate , perchloricacid, hydrogen peroxide, and molecular iodine, respectively. The radical cationswere characterized using ESR spectroscopy. Conformational analysis based on theESR parameters suggests that the radical cations adopt a planar configuration withthe nitrogen radical as the center.

N-ALKYLPHENOTHIAZINE RADICAL CATIONS GENERATED IN THE CAVITY OF β-CYCLODEXTRINS IN A(?)UEOUS SOLUTION

Phenothiazine and i^+s derivatives were oxidized by l_2 and 2,2,6,6-tetrametbyl-4- acetyloxypiperidine oxoammonium hexachloroantimonate to the corresponding radical cations in the cavity of β-cyclodextrins in aqueous solution.The mechanism of electron transfer between substrates and oxidants is discussed in terms of association of β-CDs.

EPR and DFT Study of the Polycyclic Aromatic Radical Cations from Friedel-Crafts Alkylation Reactions

Electron paramagnetic resonance and electron-nuclear double resonance methods were used to study the polycyclic aromatic radical cations produced in a Friedel-Crafts alkylating sys- tem, with m-xylene, or p-xylene and alkyl chloride. The results indicate that the observed electron paramagnetic resonance spectra are due to polycyclic aromatic radicals formed from the parent hydrocarbons. It is suggested that benzyl halides produced in the Friedel-Crafts alkylation reactions undergo Scholl self-condensation to give polycyclic aromatic hydrocar- bons, which are converted into corresponding polycyclic aromatic radical cations in the presence of AlCl3. The identification of observed two radicals 2,6-dimethylanthracene and 1,4,5,8-tetramethylanthraeene were supported by density functional theory calculations using the B3LYP/6-31G（d,p）//B3LYP/6-31G（d） approach. The theoretical coupling constants support the experimental assignment of the observed radicals.

Recent advances in electrocatalytic generation of indole-derived radical cations and their applications in organic synthesis

Indole-derived radical cations, open-shell reactive species, display distinctive dual reactivity due to the carbon-centered radical and more electrophilic carbocation, which frequently appear in a variety of single electron oxidation reactions for synthesizing structurally diverse functionalized indoles and indolines. Electrocatalysis is considered as a synthetically attractive and environmentally friendly alternative for driving the single electron oxidation of indoles. Remarkable achievements in electrocatalytic indolederived radical cation-mediated indole functionalization have been realized so far. This review comprehensively summarizes the recent progresses in the applications of electrocatalytic indole radical cations,including C(sp~2)–H functionalization, dearomative 2,3-difunctionalization, and ring-opening reaction, emphasizing the vital single electron oxidation steps of indoles, the substrates scope and limitations, and the reaction mechanisms.

Abundant Production of Reactive Water Radical Cations under Ambient Conditions

Water radical cations,the crucial intermediates in many aqueous reactions and biochemical processes,are difficult to investigate experimentally due to their short lifetime andlowabundance.Herein,ahomemade device based on energy-tunable discharge was employed to deposit suitable amounts of energy to atmospheric pressure pure water vapor for abundant production of water radical cations,stabilized as(H_(2)O)n^(+·)(n=2-5)with a maximal abundance of≥8.3×10^(6) cps for(H_(2)O)_(2)^(+·),characterized by mass spectrometry(MS).The abundance of water radical cations was optimized by adjusting the experimental parameters such as the discharge voltage(2.5 kV),temperature of the MS inlet(140℃),carrier gas flow(20mL/min),and the distance between the discharge tip and MS inlet(12 mm).The ambient formation of water radical cationswas further confirmedby thehigh reactivity of as-prepared water radical cations,which reacted with benzene,ethyl acetate,and dimethyl disulfide instantly,showing rich chemistry with ionic and radical characteristics.Moreover,the computations usingCCSD(T)//MP2 method and density functional theory confirmed that the O-O single-electron bound dimer(B),as well as the hydronium hydroxyl radical complex(A),accounted for the unusual chemistry of the water radical cations,providing a facile approach to access the high reactivity ofwater radical cations under the ambient conditions.

Fast repair of purine deoxynucleotide radical cations by rutin and quercetin

Repair effects of rutin and quercetin on purine deoxynucleotide radical cations were studied using pulse radiolysis technique. On electron pulse irradiation of N2 saturated deoxynucleotide aqueous solution containing 20 mmol/L K2S2O8, 200 mmol/L f-BuOH and rutin or quercetin, the transient absorption spectra of the deoxynucleotide radical cations decayed quickly. At the same time, the spectra of flavonoid phenoxyl radicals formed within several dozen microseconds. The results indicated that deoxynucleotide radical cations can be repaired by flavonoids. The rate constants of the repair reactions were 3.8 × 108-4.4×108 mol-1 · L · s-1 and 1.3×108-1.8×108 mol-1 · L · s-1 for dAMP and dGMP radical cations, respectively.

Conjugated radical cation dimerization-driven generation of supramolecular architectures

This paper summarizes the recent advance in utilizing conjugated radical cation dimerization （CRCD） for constructing new unimolecular, such as foldamers, and supramolecular ordered structures, such as three-dimensional supramolecular polymers and two-dimensional supramolecular organic framework. Particularly, the stacking or dimerization of tetrathiafulvalene and 4,4＇-dipyridium subunits has been highlighted, and the approaches for enhancing the stability of their radical cation dimers have been discussed.

Pleated polymeric foldamers driven by donor–acceptor interaction and conjugated radical cation dimerization

Two naphthalene（NP） and bipyridinium（BIPY^2＋） alternately incorporated polymers P1 and P2 have been prepared through the formation of dynamic hydrazone bonds. The polymers formed NP–BIPY^2＋donor–acceptor interaction-induced pleated secondary structure. Upon reducing the BIPY^2＋units to radical cation BIPY＋, intramolecular dimerization of the BIPY＋units induced the backbones to afford another pleated secondary structure. Adding electron-rich macrocyclic polyether bis-1,5-dinaphtho[38]crown-10 or electron-deficient cyclobis（paraquat-p-phenylene） cyclophane did not break the first foldamer by complexing the BIPY^2＋or NP units of the polymers, whereas the di（radical cationic）ring of the second cyclophane could break the second foldamer by forming threading complexes with the BIPY＋units of the polymers.

Radical cation salts induced domino reaction of anilines with enol ethers:Synthesis of 1,2,3,4-tetrahydroquinoline derivatives

A domino reaction of anilines with cyclic and acyclic enol ethers induced by catalytic amounts of TBPA^（·＋）（5 mol%） was investigated and a series of 2,4-disubstituted-1,2,3,4-tetrahydroquinolines were synthesized.Different from cyclic enol ethers, when acyclic enol ethers were used in the reaction,they serve as surrogates of acetaldehyde,producing a series of 2-methyl-4- anilino-1,2,3,4-tetrahydroquinolines.A single electron transfer mechanism was proposed to rationalize the products formation.

Triphenylamines consisting of bulky 3,5-di–tert–butyl–4-anisyl group:Synthesis, redox properties and their radical cation species

Triphenylamine(TPA) derivatives have been widely used as useful building blocks for diverse functional materials because of their excellent redox activity. Most of the molecular structures of TPA-based organic functional materials contain 4-anisyl groups, which on one hand could reduce their oxidation potential and on the other hand significantly delocalize the spin density of the resultant TPA radical cation species and enhance their stability. However, molecular-level investigation of the redox behavior of triphenylamines consisting of 4-anisyl group and the electronic structures of their radical cation species has not been reported in the literature. Herein, we design a series of triphenylamines consisting of one, two, or three 3,5-di–tert–butyl–4-anisyl groups and investigate their redox behaviors and corresponding radical cation species. We disclose that the resonance hybrid and steric protection could both contribute to the stability of triphenylamine radical cations. Moreover, further oxidation leads to an unexpected oxidative demethylation. The findings in this work may reveal new insights for the understanding of the unique redox properties of 4-anisyl substituted triphenylamines.

A study of vitamin A radical cation generated by chemical and radiolytic oxidation

Electron transfer reaction between vitamin A (1) and tris(p-bromophenyl)aminium hexachloroautimonate (2) in dichloromethane (DCM) has been investigated by means of UV-VIS absorption and ESR spectroscopy. The title radical cation formed in the reaction was characterized by a new absorption band around 600 nm and a singlet unresolved ESR spectrum with g factor of 2.0038-2.0039 and line width of 20 G. Further studies indicated that ESR pattern and parameters of the radical cation generated by 7-irradiation of 1 in CFCl3 matrix at 77 K are consistent with that resulted in the chemical oxidation in DCM at ambient temperature.

Fluphenazine hydrochloride radical cation assay:A new,rapid and precise method to determine in vitro total antioxidant capacity of fruit extracts

A new procedure based on generation and subsequent reduction of orange-colored fluphenazine hydrochloride radical （FPH^＋） is presented for the screening of total antioxidant capacity （TAC） of various fruit matrices. The FPH^＋ was obtained by mixing fluphenazine hydrochloride with persulfate （final concentration 2 mmol/L and 0.05 mmol/L, respectively） in 3 mol/L H2SO4 with constant shaking for 5 min. The solution formed showed maximum absorption as 0.8 ＋ 0.02 at 500 nm in first-order derivative spectrum. The percent inhibition of the solution increased linearly on addition of increasing amounts of standard antioxidants i.e., ascorbic acid etc. The TACs of sample citrus juices were calculated in terms of ascorbic acid equivalents （AAEs） by comparing their inhibition curves with that of ascorbic acid. Comparison of AAE values of different commercial orange juices using the newly developed FPH^＋ assay and the well-known ABTS/K2S2Os and DMPD/FeC13 assays indicated the precision and comparable sensitivity of the method. The proposed procedure is quick, economical, and more precise and gives results comparable to contemporary assays.

Putting aniline radical cations in a bottle

Salts containing aniline radical cations have been isolated and characterized by electron paramagnetic resonance(EPR)spectroscopy, UV-Vis absorption spectroscopy and single crystal X-ray diffraction. The EPR spectra and theoretical calculations indicate the unpaired electron is delocalized on phenyl rings and nitrogen atoms. Both radical cations feature a quinoidal geometry with a partially double C–N bond, but are distinct in that the C–N bond is coplanar to the phenyl plane in one cation while deviates from the plane in the other due to steric crowding. The work provides the first unequivocal examples of stable aniline radical cations.

DOPING LEVEL INCREASE OF POLY(3-METHYLTHIOPHENE)FILM DURING ELECTROCHEMICAL POLYMERIZATION PROCESS

The Raman spectra of poly(3-methylthiophene) (PMeT) films with different thicknesses, which have been electrochemically deposited on a flat stainless steel electrode surface by direct oxidation of 3-methylthiophene in boron trifluoride diethyl etherate (BFEE) at a constant applied potential of 1.38 V (versus SCE), have been investigated by excitation with a 633-nm laser beam. The spectroscopic results demonstrated that the doping level of PMeT film was increasing during film growth. This finding was also confirmed by electrochemical examination. Moreover, the Raman bands assigned to radical cations and dications in doped PMeT films were found approximately at 1420 and 1400 cm(-1), respectively. Radical cations and dications coexist on the backbone of PMeT as conductive species and their concentrations increase with the increase of doping level. Successive cyclic voltammetry was proved to be an effective approach to improving the doping level of as-grown thin compact PMeT film.

One-dimensional alkylate-bridged Würster's blue-based diradical dications

By using weakly coordinating anions we succeeded in the stabilization and isolation of two Wfirster＇s blue-based diradicaloid dications with saturated spacers. Their geometries and electronic structures were investigated by various experiments in conjunction with DFT calculations. Both one-dimensional alkylate-bridged dications show considerable diradical character with spacer-dependent singlet-triplet energy gaps. One of them displays a much enhanced diradical character and could basically be viewed as a pure diradical with degeneracy of singlet and triplet states.

TBPA^(+·) mediated aromatization of 1,3,5-trisubstituted pyrazolines

1,3,5-Trisubstituted pyrazolines were oxidized to the corresponding pyrazoles in high yield with tris（4-bromophenyl）aminium （TBPA＊＊） hexachloroantimonate in chloroform at room temperature.

Electrochemistry and In-situ Spectroelectrochemistry Studies of Carbazole and 9-Ethylcarbazole

Mechanisms of electron transfer of carbazole （CZ） and 9-ethylcarbazole （ECZ） were studied by electrochemistry and in-situ spectroelectrochemistry. The result indicated that the electrochemical reaction mechanism of ECZ was the same as that of CZ. Both of them undergo ECE process： the initial step is removal of one electron to generate very reactive cation radical, this species then proceeded by deprotonation-coupling reaction to form the corresponding dimer, which was oxidized continuously.

Pulse radiolysis study on gatifloxacin——A fluoroquinolone antibiotic

The reactions between gatifloxacin(GFX) and various one-electron oxidants,such as ˙OH,N3˙,Br2˙ˉ,and SO4˙ˉ,have been studied by pulse radiolysis techniques.The GFX radical anion formed in the reaction of GFX with eaqˉ could either be protonated or deprotonated,and the absorption of GFX radical anion was located at 390 nm.The transient species produced by the reaction of GFX with ˙OH radical shows a broad band in the 380?600 nm region with a shoulder,while the oxidation by N3˙,SO4˙ˉ,and Br2˙ˉ results in an absorption band with λmax = 370 nm.At neutral condition(pH 7),the rate constants of GFX reacting with ˙OH,N3˙,Br2˙ˉ,SO4˙ˉ and eaqˉ are estimated to be 1.0 × 1010,3.1 × 109,2.8 × 109,3.0 × 109,and 1.8 × 1010 dm3 mol?1 s?1,respectively.From the pH dependence on the formation of electron adducts and on the rate constant of GFX with eaqˉ,the pKa of GFX radical anion is estimated to be 5.5 and 9.3.

Cucurbit[7]uril-threaded flexible organic frameworks: Quantitative polycatenation through dynamic covalent chemistry

A three-dimensional flexible organic framework FOF-1 has been synthesized from the condensation of a tetratopic acylhydrazine and a rigid 4,4-diphenyl-4,4-bipyridinium dialdehyde in water through the quantitative formation of hydrazone bond. FOF-1 is further applied to construct a polycatenane framework FOF-pc-1 through the quantitative cucurbit[7]uril encapsulation for the diphenylbipyridinium subunits of the framework by making use of the dynamic nature of the hydrazone bond in water. The bipyridinium subunits in both frameworks can be reduced their radical cation counterparts to produce conjugated radical cation-linked dynamic organic frameworks rc-FOF-1 or rc-FOF-pc-1. Polycatenation is revealed to enhance the stability of the dynamic frameworks in water, whereas depolycatenation can be reached for both FOF-pc-1 and rc-FOF-pc-1 by using a ferrocene guest to form a more stable complex with CB[7].