Staudinger ligation towards cyclodextrin dimers in aqueous/organic media. Synthesis, conformations and guest-encapsulation ability

• Malamatenia D. Manouilidou,
• Yannis G. Lazarou,
• Irene M. Mavridis and
• Konstantina Yannakopoulou

Beilstein J. Org. Chem. 2014, 10, 774–783, doi:10.3762/bjoc.10.73

• of photoactive ligands [16][17], enzyme mimics [18][19], among others, although the synthesis was frequently challenging and elaborate. On another approach, the increased molecular size of oligomers may be advantageous for drug formulations due to foreseen increased circulation time and EPR (Enhanced

Thermodynamically stable [4 + 2] cycloadducts of lanthanum-encapsulated endohedral metallofullerenes

• Yuta Takano,
• Yuki Nagashima,
• M. Ángeles Herranz,
• Nazario Martín and
• Takeshi Akasaka

Beilstein J. Org. Chem. 2014, 10, 714–721, doi:10.3762/bjoc.10.65

• spectroscopic methods such as MALDI–TOF mass, optical absorption, and NMR spectroscopy. The [4 + 2] adducts of La2@C80 (3a,b, and 4a,b) and La@C82 (5b), respectively, retain diamagnetic and paramagnetic properties, as confirmed by EPR spectroscopy. Dynamic NMR measurements of 4a at various temperatures

Polyglycerol-functionalized nanodiamond as a platform for gene delivery: Derivatization, characterization, and hybridization with DNA

• Li Zhao,
• Yuki Nakae,
• Hongmei Qin,
• Tadamasa Ito,
• Takahide Kimura,
• Hideto Kojima,
• Lawrence Chan and
• Naoki Komatsu

Beilstein J. Org. Chem. 2014, 10, 707–713, doi:10.3762/bjoc.10.64

• , Lys8 and His8) through click chemistry followed by hybridization with plasmid DNA (pDNA) and its characterization by electrophoresis is reported. Results and Discussion Preparation and characterization of ND50-PG In view of actual cancer therapy utilizing the enhanced permeation and retention (EPR

Tuning the interactions between electron spins in fullerene-based triad systems

• Maria A. Lebedeva,
• Thomas W. Chamberlain,
• E. Stephen Davies,
• Bradley E. Thomas,
• Martin Schröder and
• Andrei N. Khlobystov

Beilstein J. Org. Chem. 2014, 10, 332–343, doi:10.3762/bjoc.10.31

• interactions in the electrochemically generated dianions of these triads, with one electron per fullerene cage were studied by EPR spectroscopy. The nature of electron–electron coupling observed at 77 K can be described as an equilibrium between doublet and triplet state biradicals which depends on the inter

• -fullerene spacing. The shorter oxalate-bridged triads exhibit stronger spin–spin coupling with triplet character, while in the longer terephthalate-bridged triads the intramolecular spin–spin coupling is significantly reduced. Keywords: carbon nanomaterials; electrochemistry; EPR; fullerene dimers

• systematically varied, and we explore their spin-carrying and spin-tuning capacity in reduced states using electrochemical techniques and electron paramagnetic resonance (EPR) spectroscopy. Results and Discussion Synthesis of the fullerene triads This study aimed to vary the fullerene–fullerene separation and

3-Pyridinols and 5-pyrimidinols: Tailor-made for use in synergistic radical-trapping co-antioxidant systems

• Luca Valgimigli,
• Daniele Bartolomei,
• Riccardo Amorati,
• Evan Haidasz,
• Jason J. Hanthorn,
• Susheel J. Nara,
• Johan Brinkhorst and
• Derek A. Pratt

Beilstein J. Org. Chem. 2013, 9, 2781–2792, doi:10.3762/bjoc.9.313

• and related compounds [19][33][34][35]. The results of these calculations are given in Table 1 alongside the limited experimental data obtained using the radical equilibration EPR (REqEPR) technique [12][13][22]. The calculated BDEs are in very good agreement with the experimental values, with

Recent advances in transition metal-catalyzed Csp²-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation

• Grégory Landelle,
• Armen Panossian,
• Sergiy Pazenok,
• Jean-Pierre Vors and
• Frédéric R. Leroux

Beilstein J. Org. Chem. 2013, 9, 2476–2536, doi:10.3762/bjoc.9.287

• -tert-butylnitrone (PBN) resulted respectively in no reaction and observation of the adduct of the CF3 radical on PBN by Electron Paramagnetic Resonance (EPR). These findings suggest a radical pathway for the mechanism of this reaction, as proposed by the authors and depicted in Figure 6. As

• materials; for instance, anisole and chloro- or iodobenzene gave an ortho > para ≈ meta preferential order of substitution, while toluene, acetophenone, N,N-dimethylaniline or nitrobenzene afforded the para-substituted compound as the major product. The reaction could be monitored by EPR, which showed an

• induction period and demonstrated the involvement of radical species in the reaction. The authors proposed a mechanism accounting for the EPR profile of the reaction and for the results of kinetic isotope effect experiments (Figure 21). In this mechanism, rhenium intervenes in the initiation step. It acts

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• was established by trapping them with a spin trap and then analyzing using EPR. Additionally, detection of benzaldehyde by HPLC and VPC provided further evidence for their formation. In contrast, no products from the amine half (e.g., 131 and 132) were detected. Li and Wang recently applied this

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• be applied without disturbing the energetics and kinetics. NMR exchange spectroscopy [3] or EPR line broadening experiments [4] employ radiofrequency pulse schemes to generate a suitable magnetization or coherence for this purpose; however, as all such self-exchanges by necessity involve radical

• surplus D to give [24]. Except for an order-of-magnitude estimate of the exchange rate from EPR line broadening [25] and a brief remark in an earlier communication by us [26], this is the first report on direct measurements of the electron self-exchange of such sulfur-centered aliphatic radical cations

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• conditions. This hypothesis was supported by spectroscopic and analytical evidence. By simply adding NHPI to a solution of acetonitrile containing m- chloroperbenzoic acid we could observe the characteristic Electron Paramagnetic Resonance (EPR) spectrum of PINO radical, while m-chlorobenzoic acid (90%) and

• lamp promoted the selective homolysis of the O–C bond, leading to the formation of the N-oxyl radical, as documented by the strong characteristic EPR signal. The efficiency of the initiation approach was documented by measuring the dioxygen consumption during the aerobic oxidation of cumene. In the

Conformational analysis and intramolecular interactions in monosubstituted phenylboranes and phenylboronic acids

• Josué M. Silla,
• Rodrigo A. Cormanich,
• Roberto Rittner and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2013, 9, 1127–1134, doi:10.3762/bjoc.9.125

• doublet with 1hJF,H(O) of 6.0 and 3.0 Hz, respectively (Figure 5). These coupling constants are much lower than those calculated at the BHandH/EPR-III level (−18.9 and −21.9 Hz for 1a and 1b, respectively), because of the experimental acidity of these hydrogen atoms, which can be proved by the smaller

• the AIMAll program [29]. Finally, spin–spin coupling constant calculations were performed at the BHandH/EPR-III level in order to check for possible intramolecular hydrogen bonds through 1hJF,H(O) and the nF→pB interaction through 1TSJF,B in 2-fluorophenylboronic acid. 2- and 4-fluorophenylboronic

• dependence of 1hJF,H(O) and nF→σ*OH in 1a, obtained at the BHandH/EPR-III (J) and B3LYP/aug-cc-pVDZ (nF→σ*OH) levels. Molecular graphs indicating bond paths (BPs), bond critical points (BCPs; green dots), and ring critical points (RCPs; red dots) for the conformers of 2-substituted phenylboranes 3–9

Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes

• Roy T. McBurney and
• John C. Walton

Beilstein J. Org. Chem. 2013, 9, 1083–1092, doi:10.3762/bjoc.9.120

• Roy T. McBurney John C. Walton EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife, KY16 9ST, UK 10.3762/bjoc.9.120 Abstract Sensitised photolyses of ethoxycarbonyl oximes of aromatic and heteroaromatic ketones yielded iminyl radicals, which were characterised by EPR

• , benzofuro- or benzothieno-isoquinolines, formed at higher temperatures. Estimates by steady-state kinetic EPR established that iminyl radical cyclisations onto aromatics took place about an order of magnitude more slowly than prototypical C-centred radicals. The cyclisation energetics were investigated by

• DFT computations, which gave insights into factors influencing the two cyclisation modes. Keywords: cyclisation; EPR spectroscopy; free radicals; heterocycles; oxime carbonates; Introduction Radical cyclisations onto aromatic acceptors take place readily, even though disruption of the 6π-electron

High-spin intermediates of the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine

• Sergei V. Chapyshev,
• Denis V. Korchagin,
• Patrik Neuhaus and
• Wolfram Sander

Beilstein J. Org. Chem. 2013, 9, 733–742, doi:10.3762/bjoc.9.83

• Abstract In contrast to theoretical expectations, the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine in argon at 5 K gives rise to EPR peaks of just two triplet mononitrenes, two quintet dinitrenes, and a septet trinitrene. EPR spectral simulations in combination with DFT calculations show that

• associated with strong π-conjugation of these groups with the pyridine ring. On photoexcitation, such azido groups are more efficiently involved in reorganization of the molecular electronic system and more easily adopt geometries of the locally excited predissociation states. Keywords: azides; EPR

• ][6]. When aromatic polyazides contain nonequivalent azido groups, these groups can undergo selective photolysis, providing important information about the selective cleavage of chemical bonds in organic molecules with light. The direction and selectivity of such processes can be monitored with EPR

Spin state switching in iron coordination compounds

• Philipp Gütlich,
• Ana B. Gaspar and
• Yann Garcia

Beilstein J. Org. Chem. 2013, 9, 342–391, doi:10.3762/bjoc.9.39

• peak, lifetime of the ortho-positronium) in different spin states, the technique will probably not attain the status of a widely employed method in SCO research. Magnetic resonance spectroscopy (NMR, EPR). Proton NMR measurements (Evans method) have been carried out to follow a temperature-dependent ST

• studies of the solid state, however, the NMR spectrum of SCO compounds has been of little value. The various different protons typically present in the ligand molecules give rise to broad lines, which are difficult or impossible to analyze. EPR spectroscopy has been more successfully employed in SCO

• research than has NMR. SCO compounds of iron(III), iron(II), and cobalt(II), which are the 3d transition metal elements most actively studied with EPR, typically reveal characteristic spectra that are sufficiently well resolved in both HS and LS states. There is no spin–orbit coupling in SCO compounds of

Efficient synthesis of phenylene-ethynylene rods and their use as rigid spacers in divalent inhibitors

• Francesca Pertici,
• Norbert Varga,
• Arnoud van Duijn,
• Matias Rey-Carrizo,
• Anna Bernardi and
• Roland J. Pieters

Beilstein J. Org. Chem. 2013, 9, 215–222, doi:10.3762/bjoc.9.25

• phenylene-ethynylene units and their incorporation into divalent ligands. For design purposes this system has the advantage that due to the high rigidity and linearity it is easy to predict their length, as was recently shown by EPR measurements [24]. The solubility of rigid hydrophobic spacers in an

Conformational analysis, stereoelectronic interactions and NMR properties of 2-fluorobicyclo[2.2.1]heptan-7-ols

• Fátima M. P. de Rezende,
• Marilua A. Moreira,
• Rodrigo A. Cormanich and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2012, 8, 1227–1232, doi:10.3762/bjoc.8.137

• F–H(O) coupling constant (1hJF,H(O)). This can be important for monitoring fluorine-based interactions in biological systems and material sciences. The angular dependence of 1hJF,H(O) as a function of the nF→σ*OH interaction was theoretically evaluated at the BHandH/EPR-III level (which has shown to

High-affinity multivalent wheat germ agglutinin ligands by one-pot click reaction

• Henning S. G. Beckmann,
• Heiko M. Möller and
• Valentin Wittmann

Beilstein J. Org. Chem. 2012, 8, 819–826, doi:10.3762/bjoc.8.91

• [36] and EPR spectroscopy [45]. Crystal structure analysis of a complex of WGA and four molecules of a divalent ligand containing two GlcNAc residues showed that each ligand bridged adjacent binding sites with a distance of approx. 13–14 Å between the anomeric oxygen atoms of the GlcNAc residues. This

EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

• Giorgio Bencivenni,
• Riccardo Cesari,
• Daniele Nanni,
• Hassane El Mkami and
• John C. Walton

Beilstein J. Org. Chem. 2010, 6, 713–725, doi:10.3762/bjoc.6.84

• of Chemistry, University of St. Andrews, EaStChem, St. Andrews, Fife KY16 9ST, UK 10.3762/bjoc.6.84 Abstract The reactions of group 13 metal trichlorides with aromatic azides were examined by CW EPR and pulsed ENDOR spectroscopies. Complex EPR spectra were obtained from reactions of aluminium

• suggested that the unpaired electrons were accommodated in extensive π-delocalised orbitals. A mechanism to account for the reductive conversion of aromatic azides to the corresponding anilines and thence to the dimers and trimers is proposed. Keywords: aluminium; aromatic azides; ENDOR; EPR; gallium

• ], and δ-azidoesters and chlorides into allylated nitrogen heterocycles [30]. To help in elucidating the mechanisms of these reductions, we used CW EPR spectroscopy and attempted to characterise the reactive intermediates in selected reactions involving gallium trichloride. Surprisingly, we found that

Mechanistic aspects of the isomerization of Z-vinylic tellurides double bonds in the synthesis of potassium Z-vinyltrifluoroborate salts

• Hélio A. Stefani,
• Rafael C. Guadagnin,
• Artur F. Keppler,
• Giancarlo V. Botteselle,
• João V. Comasseto and
• Carlos A. Suganuma

Beilstein J. Org. Chem. 2008, 4, No. 9, doi:10.1186/1860-5397-4-9

• , Universidade de São Paulo, São Paulo, Brazil 10.1186/1860-5397-4-9 Abstract Through direct transmetalation reaction of Z-vinylic tellurides with nBuLi was observed the unexpected isomerization of double bonds leading to potassium E-vinyltrifluoroborates salts in low to moderate yields. Using EPR spin trapping

• ), generates nBu•, which is responsible for the cis-trans isomerization. The butyl radical attack occurs at the boronic “ate” complex 4 (Scheme 1) [16], yielding the nBuBF3K salt as a final product. In order to verify the presence of radical species in the reaction mixture, we performed EPR spin trapping

• detected in the 15 min incubation spectrum (Figure 2B). The DBNBS/•TenBu signal maintained its intensity during the course of the EPR analysis. After the addition of the B(OiPr)3 (ii, Scheme 1), the reaction mixture produced a complex EPR spectra that can be attributed to a mixture of radical species