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Special Issue "Radical Chemistry"

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A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: closed (31 August 2011)

Special Issue Editor

Guest Editor
Prof. Dr. Rebecca Braslau

Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA
Website | E-Mail
Interests: synthetic organic chemistry; organic free radicals; nitroxides; nitroxide-mediated free radical polymerization; development of tailored materials for applications in nanotechnology; nitroxide-based sensors

Special Issue Information

Dear Colleagues,

The use of free radical intermediates in applications ranging from synthetic methodology, controlled polymerization, biomedical probes and applications in nanotechnology has flourished, growing upon the well-grounded foundation of physical measurements pioneered during the previous century.  The famed “high reactivity” of most free radical intermediates has opened doors to reactions under very mild conditions, while the “lack of selectivity” often associated with free radical species can either be circumvented by astute choreography of reaction conditions, on in some cases is simply not true: some free radical reactions are exquisitely selective. For example, carbon free radical intermediates are often highly chemoselective, adding to activated olefins while remaining inert to protic alcohol, amine and carboxylic acid functionalities as well as polar groups such as carbonyls. This allows many radical reactions to be carried out without the necessity for protecting groups required under ionic reaction conditions. The chain nature of the majority of free radical processes provides an extremely efficient vehicle for transformations that evoke the elegance of catalytic processes.  The use of paramagnetic persistent radicals, such as nitroxides, provides sensitive tools for probing dynamic systems using EPR, the opportunity to design new materials, and an entry to novel sensors.  This is an exciting time in the field of free radical chemistry.  It is my hope that this Special Edition on Free Radicals will present a forum that will reflect the creativity and diversity of advances in free radical chemistry 110 years after Moses Gomberg first demonstrated the existence of a free radical species.

Dr. Rebecca Braslau
Guest Editor

Keywords

  • chain reaction
  • photochemistry
  • rearrangement
  • cyclization
  • fragmentation
  • radical cascade
  • electron transfer
  • antioxidant
  • radical living polymerization
  • persistent radical

Published Papers (6 papers)

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Research

Open AccessArticle Mn(III)-Initiated Facile Oxygenation of Heterocyclic 1,3-Dicarbonyl Compounds
Molecules 2011, 16(11), 9562-9581; doi:10.3390/molecules16119562
Received: 27 September 2011 / Revised: 7 November 2011 / Accepted: 9 November 2011 / Published: 16 November 2011
Cited by 9 | PDF Full-text (434 KB) | Supplementary Files
Abstract
The Mn(III)-initiated aerobic oxidation of heterocyclic 1,3-dicarbonyl compounds, such as 4-alkyl-1,2-diphenylpyrazolidine-3,5-diones, 1,3-dialkylpyrrolidine-2,4-diones, 3-alkyl-1,5-dimethylbarbituric acids, and 3-butyl-4-hydroxy-2-quinolinone gave excellent to good yields of the corresponding hydroperoxides, which were gradually degraded by exposure to the metal initiator after the reaction to afford the corresponding alcohols.
[...] Read more.
The Mn(III)-initiated aerobic oxidation of heterocyclic 1,3-dicarbonyl compounds, such as 4-alkyl-1,2-diphenylpyrazolidine-3,5-diones, 1,3-dialkylpyrrolidine-2,4-diones, 3-alkyl-1,5-dimethylbarbituric acids, and 3-butyl-4-hydroxy-2-quinolinone gave excellent to good yields of the corresponding hydroperoxides, which were gradually degraded by exposure to the metal initiator after the reaction to afford the corresponding alcohols. The synthesis of 30 heterocyclic 1,3-dicarbonyl compounds, the corresponding hydroperoxides and the 10 alcohols, their characterization, and the limitations of the procedure are described. In addition, the mechanism of the hydroperoxidation and the redox decomposition of the hydroperoxides are discussed. Full article
(This article belongs to the Special Issue Radical Chemistry)
Open AccessArticle Simplified Synthesis of Isotopically Labeled 5,5-Dimethyl-pyrroline N-Oxide
Molecules 2011, 16(10), 8428-8436; doi:10.3390/molecules16108428
Received: 25 July 2011 / Revised: 14 September 2011 / Accepted: 21 September 2011 / Published: 10 October 2011
PDF Full-text (265 KB)
Abstract 5,5-Dimethylpyrroline N-oxide (15N) and 5,5-di(trideuteromethyl)pyrroline N-oxide were synthesized from the respective isotopically labeled 2-nitropropane analogs obtained from the reaction of sodium nitrate with 2-halopropanes. This facile, straightforward process allows synthesizing isotopically labeled DMPO analogs in a 4-step reaction without special equipment. Full article
(This article belongs to the Special Issue Radical Chemistry)
Figures

Open AccessArticle Antioxidant Capacity of Ocimum basilicum L. and Origanum vulgare L. Extracts
Molecules 2011, 16(9), 7401-7414; doi:10.3390/molecules16097401
Received: 9 August 2011 / Revised: 25 August 2011 / Accepted: 26 August 2011 / Published: 30 August 2011
Cited by 26 | PDF Full-text (503 KB)
Abstract
The antioxidant properties of five different extracts (Et2O, CHCl3, EtOAc, n-BuOH, and H2O) of Ocimum basilicum L. and Origanum vulgare L. were studied. Antioxidant activity was assessed in six different model systems. Free radical scavenging capacity
[...] Read more.
The antioxidant properties of five different extracts (Et2O, CHCl3, EtOAc, n-BuOH, and H2O) of Ocimum basilicum L. and Origanum vulgare L. were studied. Antioxidant activity was assessed in six different model systems. Free radical scavenging capacity (RSC) was evaluated by measuring the scavenging capacity of extracts on DPPH, NO, O2·- and OH radical, as well as on hydrogen peroxide (H2O2). In addition, the protective effects on lipid peroxidation in liposomes (LPx) were evaluated by TBA-assay using the Fe2+/ascorbate induction system. The amount of total phenolic compounds and content of total flavonoids was also determined. EtOAc, n-BuOH and H2O extracts of O. basilicum and O. vulgare expressed very strong scavenger activity. Furthermore, the mentioned extracts showed notable inhibition of LPx. On the other hand, Et2O and CHCl3 extracts showed much weaker effect in the neutralization of DPPH, NO and O2·- radicals and the neutralization of H2O2. When examining the production of OH radicals and inhibition of LPx, the Et2O and CHCl3 extracts showed weak prooxidative properties. The observed differences in antioxidant activity could be partially explained by the levels of phenolics and flavonoids in the investigated O. basilicum and O. vulgare extracts. Full article
(This article belongs to the Special Issue Radical Chemistry)
Open AccessArticle Synthesis and Biological Evaluation of Novel 99mTc-Labelled Bisphosphonates as Superior Bone Imaging Agents
Molecules 2011, 16(8), 6165-6178; doi:10.3390/molecules16086165
Received: 10 June 2011 / Revised: 15 July 2011 / Accepted: 19 July 2011 / Published: 25 July 2011
Cited by 15 | PDF Full-text (651 KB)
Abstract
A series of novel zoledronic acid (ZL) derivatives 1-hydroxy-3-(2-methyl-1H-imidazol-1-yl)propane-1,1-diyldiphosphonic acid (MIPrDP), 1-hydroxy-4-(2-methyl-1H-imidazol-1-yl)butane-1,1-diyldiphosphonic acid (MIBDP), and 1-hydroxy-5-(2-methyl-1H-imidazol-1-yl)pentane-1,1-diyldiphosphonic acid (MIPeDP) were prepared and successfully labeled with 99mTc in high labeling yields. The in vitro stability and in vivo
[...] Read more.
A series of novel zoledronic acid (ZL) derivatives 1-hydroxy-3-(2-methyl-1H-imidazol-1-yl)propane-1,1-diyldiphosphonic acid (MIPrDP), 1-hydroxy-4-(2-methyl-1H-imidazol-1-yl)butane-1,1-diyldiphosphonic acid (MIBDP), and 1-hydroxy-5-(2-methyl-1H-imidazol-1-yl)pentane-1,1-diyldiphosphonic acid (MIPeDP) were prepared and successfully labeled with 99mTc in high labeling yields. The in vitro stability and in vivo biodistribution of 99mTc-MIPrDP, 99mTc-MIBDP and 99mTc-MIPeDP were investigated and compared. The biodistribution studies indicate that the radiotracer 99mTc-MIPrDP has highly selective uptake in the skeletal system and rapid clearance from soft tissues. The present findings indicate that 99mTc-MIPrDP holds great potential for use in bone imaging. Full article
(This article belongs to the Special Issue Radical Chemistry)
Open AccessArticle Synthesis of Gentiooligosaccharides of Genistein and Glycitein and Their Radical Scavenging and Anti-Allergic Activity
Molecules 2011, 16(6), 4740-4747; doi:10.3390/molecules16064740
Received: 19 April 2011 / Revised: 27 May 2011 / Accepted: 2 June 2011 / Published: 7 June 2011
PDF Full-text (168 KB)
Abstract
The synthesis of gentiooligosaccharides of genistein and glycitein using cultured cells of Eucalyptus perriniana as biocatalysts was investigated. The cells of E. perriniana glycosylated genistein and glycitein to give the corresponding 4'-O-b-glucosides, 7-O-b-glucosides, and 7-
[...] Read more.
The synthesis of gentiooligosaccharides of genistein and glycitein using cultured cells of Eucalyptus perriniana as biocatalysts was investigated. The cells of E. perriniana glycosylated genistein and glycitein to give the corresponding 4'-O-b-glucosides, 7-O-b-glucosides, and 7-O-b-gentiobiosides, which were two new compounds. The b-glucosides of genistein and glycitein showed 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging activity and superoxide-radical scavenging activity. On the other hand, 7-O-b-glucosides of genistein and glycitein and the 7-O-b-gentiobioside of glycitein exerted inhibitory effects on IgE antibody production. Full article
(This article belongs to the Special Issue Radical Chemistry)
Open AccessArticle Free Radical Scavenging Activity and Characterization of Sesquiterpenoids in Four Species of Curcuma Using a TLC Bioautography Assay and GC-MS Analysis
Molecules 2010, 15(11), 7547-7557; doi:10.3390/molecules15117547
Received: 6 October 2010 / Revised: 19 October 2010 / Accepted: 25 October 2010 / Published: 27 October 2010
Cited by 34 | PDF Full-text (318 KB)
Abstract
The sesquiterpenoids are one of major groups of antioxidants in Curcuma besides curcuminoids. However, the real substances contributing to the antioxidant activity are still unknown. In this paper, the antioxidant activity of sesquiterpenoids in four species and two essential oils from Curcuma genus
[...] Read more.
The sesquiterpenoids are one of major groups of antioxidants in Curcuma besides curcuminoids. However, the real substances contributing to the antioxidant activity are still unknown. In this paper, the antioxidant activity of sesquiterpenoids in four species and two essential oils from Curcuma genus was determined and compared based on TLC separation and DPPH bioautography assay. Their antioxidant capacities were quantitatively evaluated using densitometry with detection at 530 nm (λreference = 800 nm) using vitamin C as reference. The results showed that Curcuma longa rhizomes had the highest antioxidant capacity while C. phaeocaulis presented the lowest one among the four species of Curcuma. Moreover, essential oil of C. wenyujin showed higher antioxidant potential than that of C. longa. The main TLC bands with antioxidant activity of the four species of Curcuma were collected and characterized using GC-MS, and thus curzerene, furanodiene, α-turmerone, β-turmerone and β-sesquiphellandrene were determined as major sesquiterpenoids with antioxidant activity in Curcuma. Full article
(This article belongs to the Special Issue Radical Chemistry)

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