Biomimetic oxidation of pyrene and related aromatic hydrocarbons. Unexpected electron accepting abilities of pyrenequinones

Article abstract of DOI:10.1039/c4cc04026k

We present a mild catalytic method to oxidize PAHs and, in particular, pyrene. The pyrenediones are much better electron acceptors than benzoquinone in the gas phase and present similar accepting abilities in solution.

Full text of DOI:10.1039/c4cc04026k

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Biomimetic oxidation of pyrene and related
aromatic hydrocarbons. Unexpected electron
accepting abilities of pyrenequinones†
Cite this: Chem. Commun., 2014,
50, 9372
Received 4th June 2014,
Accepted 27th June 2014
Alejandro Lopez-Moreno,a David Clemente-Tejeda,b Joaquın Calbo,c
´
´
Atena Naeimi,ad Francisco A. Bermejo,b Enrique Ortı*c and Emilio M. Perez*a
´
´
DOI: 10.1039/c4cc04026k
www.rsc.org/chemcomm
Table 1 Non-heme iron catalyzed oxidation of pyrene
We present a mild catalytic method to oxidize PAHs and, in particular,
pyrene. The pyrenediones are much better electron acceptors than
benzoquinone in the gas phase and present similar accepting abilities
in solution.
Polycyclic aromatic hydrocarbons (PAHs) have attracted a great deal
of attention in areas of research as diverse as biochemistry,1
astrochemistry,2 and materials science.3 In this last field, PAHs have
received part of the shock wave from the recent explosion of research
on graphene,4,5 due to their structural similarities.6 Among PAHs,
pyrene is probably one of the best-known organic chromophores. Its
unique absorption and, in particular, its monomer/excimer emis-
sion properties have made it the fluorophore of choice for applica-
tions ranging from molecular recognition7 to structural biology.8
Due to its extended aromatic surface, it has also been utilized in the
supramolecular association of carbon nanotubes9 and graphene.10
Yielda (%)
Entry
Catalyst (mol%)
Oxidant (eq.)
1
2
3
1
2
3
4
5
6
[Fe(pymcy)2(OTf)2] (15%)
[Fe(bpycen)(OTf)2] (15%)
[Fe(bpmen)(OTf)2] (5%)
[Fe(bpmen)(OTf)2] (10%)
[Fe(bpmen)(OTf)2] (15%)
[Fe(bpmen)(OTf)2] (20%)
H2O2 (3 eq.)
H2O2 (3 eq.)
H2O2 (3 eq.)
H2O2 (3 eq.)
H2O2 (3 eq.)
H2O2 (3 eq.)
—
—
14
17
29
15
—
—
8
9
16
9
—
—
—
—
5
—
a
Isolated yields, after column chromatography.
Therefore, synthetic methodologies for the structural variation of several microorganisms under aerobic conditions.17 In a synthetic
pyrene are in high demand.11 Given their intrinsic stability, the laboratory setting, a similar outcome can be obtained using extreme
chemical modification of pristine PAHs often relies on harsh conditions, namely K2Cr2O7 in 4M H2SO4 under reflux for 3 hours,
conditions, like the utilization of strong oxidizing agents and/or which yields a modest 40% of the mixture of both diones.18
acids. For instance, pyrene can be nitrated with HNO3/CH3COOH,12 Alternatively, Na2Cr2O7ꢀ2H2O in acetic anhydride and acetic acid
brominated with Br213 or sulfonylated with SO3.14
can also be utilized to oxidize pyrene at room temperature. This last
In Nature, PAHs are metabolized by cytochrome P450 enzymes method requires 24 hours of reaction time and extensive purifica-
(CYPs) to form oxygen-containing electrophilic species, which are tion to yield 31% and 18% of 1 and 2, respectively.19
known to be carcinogenic.15 Taking pyrene as an example, it is
Here, we present a mild and fast method to oxidize pyrene to the
considered to be a priority environmental pollutant by the United corresponding quinoid 1,6- and 1,8-diketones with hydrogen per-
States Environment Protection Agency, and its oxidation is an oxide, utilizing a non-heme iron complex as the catalyst. This type of
established method for its detoxification.16 Pyrene can be oxidized complexes have been successfully utilized as catalysts in the C–H
to form mixtures of 1,6 and 1,8 pyrenediones (1 and 2 in Table 1) by oxidation of a variety of substrates,20 including alkanes,21 alkenes22
and a few arenes23 under relatively mild, environmentally friendly
conditions, typically utilizing H2O2 as an oxidant. Considering these
precedents, we decided to investigate the oxidation of pyrene
utilizing the following non-heme iron catalysts: [Fe(bpmen)(OTf)2],
[Fe(bpycen)(OTf)2], and [Fe(pymcy)2(OTf)2], where bpmen = N,N0-bis-
(2-pyridylmethyl)-N,N0-dimethyl-1,2-ethylenediamine, bpycen =
a IMDEA Nanoscience, C/Faraday 9, Ciudad Universitaria de Cantoblanco, 28049,
Madrid, Spain. E-mail: emilio.perez@imdea.org; Fax: +34 91 2998730
b
´
´
´
Departamento de Quımica Organica, Facultad de Ciencias Quımicas. Pza. de los
´
Caıdos 1-5, Salamanca, 37008, Spain
c Instituto de Ciencia Molecular, Universidad de Valencia, E-46980 Paterna, Spain.
E-mail: enrique.orti@uv.es
N,N0-bis(pyridin-2-ylmethylene)ethane-1,2-diimine, pymcy
=
d University of Jiroft, Department of Chemistry, Jiroft, Iran
† Electronic supplementary information (ESI) available: Experimental and com-
putational details. See DOI: 10.1039/c4cc04026k
N-(pyridin-2-ylmethylene)cyclohexanamine, and OTf = trifluoro-
methanesulfonate (see Fig. S1 in the ESI† for the structures).
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Table 1 summarizes the reaction conditions we have tested in
this work. In all cases, pyrene was dissolved in a 0.33 M CH3COOH
solution in CH3CN, to which three separate additions containing
one third of the total catalyst and H2O2 in CH3CN were added at
10 min intervals. After the last addition, the solution was allowed
to stir at room temperature for 10 more minutes and quenched
with a saturated NaHCO3 aqueous solution.24 No oxidation
products were observed in the presence of the imine-based
catalysts [Fe(pymcy)2(OTf)2] or [Fe(bpycen)(OTf)2] (entries 1 and 2
in Table 1). However, the reaction was immediately apparent when
utilizing [Fe(bpmen)(OTf)2] (entries 3–6 in Table 1). In analogy with
the biooxidation by CYPs, the main products detected by HPLC
analysis were 1,6 and 1,8 pyrenediones (1 and 2 in Table 1) with
some residual 4,5-pyrenedione (3 in Table 1) detectable in some
of the runs. All products showed spectroscopic and analytical
properties (1H NMR, 13C NMR, and MALDI-TOF) consistent with
their structure and the data reported in the literature (see the
ESI†). Under optimized conditions (entry 5 in Table 1), 29%, 16%
and 5% isolated yields for 1, 2, and 3 were obtained, respectively.
Adding more catalyst (entry 6 in Table 1) resulted in complex
mixtures of oxidation and decreased yields for 1 and 2. Although
the isolated yields were relatively modest, the mild method
proposed here compares well to the much stronger oxidation
conditions reported earlier.18,19
Other small PAHs, like naphthalene and anthracene also produce
the corresponding 1,4-naphtoquinone (NQ) and 9,10-anthraquinone
(AQ), in modest to good yields (32% and 85%, respectively,
entries 2 and 3 in Table 2). In both cases conversion was
completed by TLC, but naphthalene yielded a mixture of oxida-
tion products where 1,4-naphthoquinone was the main compo-
nent. Unsurprisingly, the oxidation of anthracene proceeded
cleanly to yield 9,10-anthraquinone. However, other substrates,
such as benzene and phenanthrene (entries 1 and 4 in Table 2),
did not show signs of reaction by TLC analysis.
Fig. 1 Cyclic voltammograms of 1 (black) and 2 (red) in CH3CN at room
temperature. Glassy carbon was employed as the working electrode,
Ag/AgNO3 as the reference electrode, and 0.1 M TBAPF6 as the electrolyte.
photodynamic therapy.27 Surprisingly, the electron-accepting pro-
perties of pyrenequinones have hardly been investigated.28
Fig. 1 displays the cyclic voltammograms of 1 and 2 in CH3CN.
Both quinones show two reversible reduction waves at half-wave
1
2
1
potentials E1/2 = ꢁ0.82 V and E1/2 = ꢁ1.12 V for 1 and E1/2
=
2
ꢁ0.84 V and E1/2 = ꢁ1.19 V for 2, with respect to ferrocene/
1
ferricenium. For comparison, BQ undergoes reduction at E1/2
=
=
2
1
2
ꢁ0.88 V and E1/2 = ꢁ1.47 V, NQ at E1/2 = ꢁ1.06 V and E1/2
1
2
ꢁ1.63 V and AQ at E1/2 = ꢁ1.31 V and E1/2 = ꢁ1.89 V under
identical experimental conditions (see the ESI†).
The cathodic shift of the first reduction potential along the BQ,
NQ, and AQ series can be easily rationalized in terms of the energy
and topology calculated for the LUMO (Fig. 2). The LUMO is mainly
localized on the quinoid ring and suffers a destabilization along the
BQ, NQ, and AQ series due to the additional antibonding inter-
actions arising from the inclusion of lateral benzene rings. In
contrast, the LUMOs of 1 and 2 stand close in energy with respect to
the LUMO of BQ because they resemble two BQ LUMOs with no
additional destabilizing interactions. This explains, to a first approxi-
mation, the similar values obtained for the first reduction potential
of 1, 2, and BQ.
Quinones are key electron acceptors in both biology and indus-
try. For instance, coenzyme Q10, which features a p-benzoquinone
(BQ) core as a redox unit, is involved in the electron transport chain
in aerobic respiration, and doubles as an antioxidant inhibiting
both the initiation and the propagation of lipid and protein oxida-
tions.25 From an industrial point of view, 2-alkylanthraquinones
have been utilized to produce hydrogen peroxide since the 1940s,
and indeed the anthraquinone method still monopolises the large
scale production of H2O2.26 Despite these facts, research on pyrene-
quinones has focused on their environmental interest and their
use as photosensitizers in the production of singlet oxygen for
Although the measurement of reduction potentials is usually
considered to be a valid method to evaluate the electron acceptor
ability of molecules, their electron affinity (EA) is a direct
Table 2 [Fe(bpmen)(OTf)2] catalyzed oxidation of other PAHsa
Conversion Yieldb
Entry Reagent
Product
—
(%)
(%)
1
2
3
4
Benzene
—
—
32
85
—
Naphthalene
Anthracene
Phenanthrene
1,4-Naphthoquinone 100
9,10-Anthraquinone
—
100
—
a
Fig. 2 Topology and energy (in eV) calculated for the lowest-unoccupied
All reactions were run under the conditions described in entry 5 of
b
Table 1 and the main text. Isolated yields, after column chromatography. molecular orbital (LUMO).
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Table 3 Thermochemical (in eV) and electrochemical (in V) data calcu-
lated for the one-electron attachment A + eꢁ - Aꢁ reaction. Experimental
first half-wave reduction potentials are also included
good agreement with the experimental data. Accurate values are
also predicted for NQ and AQ (Table 3). Calculations therefore
support the electron-acceptor capabilities measured in solution for
pyrenediones 1 and 2, and ascribe E1/2 values similar to BQ due to
the cancellation of two competing terms: (i) the larger EAs
computed for 1 and 2 in gas phase and (ii) the less stabilizing
solvation term (DDGsol) in the pyrenediones. This result contrasts
with the empirical linear-regression procedure usually employed to
relate E1/2 and EA (E1/2 = EA ꢁ DDGsolv. + Eref), where DDGsolv is
considered to be constant for a given family of structurally similar
compounds.31
In conclusion, we have described a mild oxidation method for
pyrene and other small PAHs, based on the use of a non-heme iron
catalyst, [Fe(bpmen)(OTf)2], with H2O2 as the oxidant. Our method
affords mainly 1,6- and 1,8-pyrenediones, in analogy with the
oxidation of pyrene by natural CYPs. Although modest, the isolated
yields of pyrenequinones are synthetically useful, and comparable
to those recently reported for the catalytic oxidation of smaller
PAHs.35 To the best of our knowledge, this constitutes the first
example of Fe-catalyzed C–H oxidation of PAHs.
The electron accepting properties of both pyrenequinones were
investigated experimentally through cyclic voltammetry, which
showed that 1 and 2 are slightly better acceptors than BQ in
solution. A detailed theoretical investigation revealed that the
pyrenequinones show much higher EAs than BQ, approximately
by 0.4 eV. By calculating the theoretical reduction potentials in
solution, we showed that the difference in EA is cancelled out by a
significantly decreased DDGsolv in the case of 1 and 2 with respect to
BQ. Our results suggest that the commonly accepted practice of
assuming that DDGsolv remains constant for a family of structurally
related compounds,31 such as the quinones under study, can
sometimes lead to significant errors.
BQ
1.92
1.91
ꢁ2.07
ꢁ2.02
ꢁ4.09
ꢁ0.90
ꢁ0.88
NQ
1.83
1.81
ꢁ1.97
ꢁ1.91
ꢁ3.88
ꢁ1.11
ꢁ1.06
AQ
1.66
1.59
ꢁ1.80
ꢁ1.81
ꢁ3.61
ꢁ1.37
ꢁ1.31
1
2
a
EA298K,theor
2.32
2.34
b
EA298K,exp
—
—
c
DGg,298K
ꢁ2.48
ꢁ1.62
ꢁ4.09
ꢁ0.89
ꢁ0.82
ꢁ2.49
ꢁ1.62
ꢁ4.12
ꢁ0.87
ꢁ0.84
DDGsolv
DGred
1 d
E1/2,theor
1
E1/2,exp
a
b
Zero-point energy and thermal corrections are included. Experi-
c
mental values extracted from reference 29. Corrected values taking
into account the free electron as an ideal monoatomic gas, 5/2 RT,32
and the correction for the change in the standard state from 1 atm to 1
mol Lꢁ1 33 d
.
Eref = ꢁ4.99 V (reduction potential of Fc+/Fc).34
measurement of it. Table 3 gives the adiabatic EA values
computed at room temperature using the G3(MP2) procedure
(see the ESI† for full computational details). The G3(MP2)
method provides an EA of 1.92 eV for BQ in very good agreement
with the experimental value of 1.91 eV.29 Likewise, the EA values
calculated for NQ (1.83 eV) and AQ (1.66 eV) reproduce accurately
the experimental values of 1.81 and 1.59 eV, respectively.29
Therefore, the electron-accepting ability decreases with the size
of the system along the BQ, NQ, and AQ series. In contrast, the
EA values calculated for 1 (2.32 eV) and 2 (2.34 eV) indicate that
the pyrenediones are remarkably stronger electron acceptors
than BQ. To rationalize the apparent mismatch between the
theoretical EAs, calculated in gas phase, and the experimental
E1/2 values, measured in CH3CN, the first half-wave reduction
potentials were estimated theoretically using the expression30
E1/2 = DGred/(ꢁnF) + Eref
This work was supported by the European Research Council
where DGred is the free energy difference for the one-electron Starting Independent Research Grant MINT (ERC-2012-StG Proposal
attachment reaction in solution (i.e. DGred = DGg + DDGsolv.), n is No. 307609), the Spanish MINECO (CTQ2011-25714 and CTQ2012-
the number of electrons transferred (n = 1 in this case), F is the 31914), the Generalitat Valenciana (PROMETEO/2012/053), and
Faraday constant and Eref is the potential of the reference electrode. European FEDER funds (CTQ2012-31914). D.C-T acknowledges
´
The free energy difference in gas phase (DGg) and the free the F.S.E and the Junta de Castilla y Leon for a predoctoral grant.
energy of solvation (DDGsolv) were computed at the G3(MP2) level J.C. acknowledges the Spanish Ministry of Education, Culture and
and using a continuum solvation model (PCM with acetonitrile), Sport (MECD) for an FPU grant.
respectively (see the ESI†). DGg follows the same trend as the EA
Notes and references
1 D. W. Nebert, T. P. Dalton, A. B. Okey and F. J. Gonzalez, J. Biol.
values (Table 3) because entropy effects are computed to be as
small as 0.5 cal molꢁ1 Kꢁ1. The origin of the larger EAs calculated
´
for 1 and 2 compared to BQ stems from the larger p-electron
delocalization in the LUMO of the formers at nearly the same
molecular orbital energy (Fig. 2). On the other hand, the DDGsolv
stabilization term is computed to be 0.4 eV larger for BQ than for
1 and 2. The decrease (in absolute value) of the DDGsolv term along
the BQ 4 NQ 4 AQ 4 1 = 2 series (Table 3) is mainly due to the
fact that solvation effects stabilize to a larger extent the anion
of BQ (ꢁ2.25 eV) than the anions of NQ (ꢁ2.13 eV), AQ (ꢁ2.03 eV),
1 (ꢁ1.94 eV) and 2 (ꢁ1.95 eV) (Table S1, ESI†). EA and solvation
stability differences between BQ and the two pyrenediones cancel
each other and result in similar DGred values for the three systems
(Table 3). The final theoretical E1/2 values are computed to be
ꢁ0.90, ꢁ0.89 and ꢁ0.87 V for BQ, 1 and 2, respectively, in very
Chem., 2004, 279, 23847–23850.
2 A. G. G. M. Tielens, Annu. Rev. Astron. Astrophys., 2008, 46, 289–337.
3 (a) J. Wu, W. Pisula and K. Mu¨llen, Chem. Rev., 2007, 107, 718–747;
(b) M. D. Watson, A. Fechtenkoetter and K. Mu¨llen, Chem. Rev., 2001,
101, 1267–1300.
4 See Acc. Chem. Res., 2013, 46, 1–189, special issue on graphene, and
references cited therein.
5 (a) J. K. Wassei and R. B. Kaner, Acc. Chem. Res., 2013, 46, 2244–2253;
´
´
´
(b) L. Rodrıguez-Perez, M. A. Herranz and N. Martın, Chem. Commun.,
2013, 49, 3721–3735; (c) E. V. Iski, E. N. Yitamben, L. Gao and
N. P. Guisinger, Adv. Funct. Mater., 2013, 23, 2554–2564; (d) C. K.
Chua and M. Pumera, Chem. Soc. Rev., 2013, 42, 3222–3233; (e) K. S.
Novoselov, V. I. Fal’ko, L. Colombo, P. R. Gellert, M. G. Schwab and
K. Kim, Nature, 2012, 490, 192–200; ( f ) Y. Zhu, S. Murali, W. Cai,
X. Li, J. W. Suk, J. R. Potts and R. S. Ruoff, Adv. Mater., 2010, 22,
3906–3924; (g) M. J. Allen, V. C. Tung and R. B. Kaner, Chem. Rev.,
2010, 110, 132–145.
9374 | Chem. Commun., 2014, 50, 9372--9375
This journal is ©The Royal Society of Chemistry 2014

View Article Online
Communication
ChemComm
6 (a) A. Konishi, Y. Hirao, K. Matsumoto, H. Kurata, R. Kishi, 19 H. Cho and R. G. Harvey, J. Chem. Soc., Perkin Trans. 1, 1976, 836–839.
Y. Shigeta, M. Nakano, K. Tokunaga, K. Kamada and T. Kubo, 20 E. P. Talsi and K. P. Bryliakov, Coord. Chem. Rev., 2012, 256, 1418–1434.
J. Am. Chem. Soc., 2013, 135, 1430–1437; (b) C.-N. Feng, M.-Y. Kuo 21 (a) Y. Hitomi, K. Arakawa, T. Funabiki and M. Kodera, Angew. Chem., Int.
´
and Y.-T. Wu, Angew. Chem., Int. Ed., 2013, 52, 7791–7794;
(c) R. Yamaguchi, S. Hiroto and H. Shinokubo, Org. Lett., 2012, 14,
2472–2475; (d) D. J. Jones, B. Purushothaman, S. Ji, A. B. Holmes
and W. W. H. Wong, Chem. Commun., 2012, 48, 8066–8068; (e) L. Chen,
Y. Hernandez, X. Feng and K. Mu¨llen, Angew. Chem., Int. Ed., 2012, 51,
Ed., 2012, 51, 3448–3452; (b) L. Gomez, I. Garcia-Bosch, A. Company,
J. Benet-Buchholz, A. Polo, X. Sala, X. Ribas and M. Costas, Angew. Chem.,
Int. Ed., 2009, 48, 5720–5723; (c) P. E. Gormisky and M. C. White, J. Am.
Chem. Soc., 2013, 135, 14052–14055; (d) M. S. Chen and M. C. White,
Science, 2007, 318, 783–787.
´
´
´
7640–7654; ( f ) J. M. Alonso, A. E. Dıaz-Alvarez, A. Criado, D. Perez, 22 (a) P. Spannring, V. Yazerski, P. C. A. Bruijnincx, B. M. Weckhuysen
˜
´
D. Pena and E. Guitian, Angew. Chem., Int. Ed., 2012, 51, 173–177;
(g) X. Yang, X. Dou, A. Rouhanipour, L. Zhi, H. J. Raeder and K. Mu¨llen,
J. Am. Chem. Soc., 2008, 130, 4216–4217; (h) Z. Liu and R. C. Larock,
Angew. Chem., Int. Ed., 2007, 46, 2535–2538; (i) X. Feng, J. Wu, M. Ai,
W. Pisula, L. Zhi, J. P. Rabe and K. Mu¨llen, Angew. Chem., Int. Ed., 2007,
46, 3033–3036; ( j) M. Kastler, J. Schmidt, W. Pisula, D. Sebastiani and
K. Mu¨llen, J. Am. Chem. Soc., 2006, 128, 9526–9534; (k) X. Feng, J. Wu,
V. Enkelmann and K. Mu¨llen, Org. Lett., 2006, 8, 1145–1148;
(l) M. C. Bonifacio, C. R. Robertson, J.-Y. Jung and B. T. King, J. Org.
and R. J. M. Klein Gebbink, Chem. – Eur. J., 2013, 19, 15012–15018;
(b) B. F. Perandones, E. del Rio Nieto, C. Godard, S. Castillon, P. De
Frutos and C. Claver, ChemCatChem, 2013, 5, 1092–1095; (c) D. Clemente-
´
Tejeda, A. Lopez-Moreno and F. A. Bermejo, Tetrahedron, 2013, 69,
2977–2986; (d) I. Garcia-Bosch, Z. Codola, I. Prat, X. Ribas, J. Lloret-
Fillol and M. Costas, Chem. – Eur. J., 2012, 18, 13269–13273; (e) S. M.
Barry, H. Mueller-Bunz and P. J. Rutledge, Org. Biomol. Chem., 2012,
10, 7372–7381; ( f ) M. S. Chen and M. C. White, Science, 2010, 327,
566–571.
Chem., 2005, 70, 8522–8526; (m) Z. Wang, Z. Tomovic, M. Kastler, 23 (a) P. Liu, Y. Liu, E. L.-M. Wong, S. Xiang and C.-M. Che, Chem. Sci.,
R. Pretsch, F. Negri, V. Enkelmann and K. Mu¨llen, J. Am. Chem. Soc.,
2004, 126, 7794–7795.
7 S. Karuppannan and J.-C. Chambron, Chem. – Asian J., 2011, 6,
964–984.
2011, 2, 2187–2195; (b) I. Prat, A. Company, V. Postils, X. Ribas,
L. Que, Jr., J. M. Luis and M. Costas, Chem. – Eur. J., 2013, 19,
6724–6738.
´
24 D. Clemente-Tejeda, A. Lopez-Moreno and F. A. Bermejo, Tetra-
8 G. Bains, A. B. Patel and V. Narayanaswami, Molecules, 2011, 16,
7909–7935.
9 F. D’Souza, A. S. D. Sandanayaka and O. Ito, J. Phys. Chem. Lett.,
2010, 1, 2586–2593.
hedron, 2012, 68, 9249–9255.
25 L. Ernster and G. Dallner, Biochim. Biophys. Acta, Mol. Basis Dis.,
1995, 1271, 195–204.
´
26 J. M. Campos-Martın, G. Blanco-Brieva and J. L. G. Fierro, Angew.
´
´
˜
10 J. A. Mann, J. Rodrıguez-Lopez, H. D. Abruna and W. R. Dichtel,
J. Am. Chem. Soc., 2011, 133, 17614–17617.
Chem., Int. Ed., 2006, 45, 6962–6984.
27 J. Arnbjerg, M. J. Paterson, C. B. Nielsen, M. Jørgensen, O. Christiansen
and P. R. Ogilby, J. Phys. Chem. A, 2007, 111, 5756–5767.
11 (a) A. Mateo-Alonso, Chem. Soc. Rev., 2014, DOI: 10.1039/c4cs00119b;
(b) S.-i. Kawano, M. Baumgarten, D. Chercka, V. Enkelmann and 28 E. J. Moriconi, B. Rakoczy and W. F. O’Connor, J. Org. Chem., 1962,
K. Mu¨llen, Chem. Commun., 2013, 49, 5058–5060. 27, 2772–2776.
12 Y. Hashimoto and K. Shudo, Chem. Pharm. Bull., 1984, 32, 1992–1997. 29 E. C. M. Chen and W. E. Wentworth, Mol. Cryst. Liq. Cryst., 1989,
13 S. Bernhardt, M. Kastler, V. Enkelmann, M. Baumgarten and K. Mu¨llen,
Chem. – Eur. J., 2006, 12, 6117–6128.
14 A. R. Katritzky, M. S. Kim, D. Fedoseyenko, K. Widyan, M. Siskin and
M. Francisco, Tetrahedron, 2009, 65, 1111–1114.
15 W. Xue and D. Warshawsky, Toxicol. Appl. Pharmacol., 2005, 206,
73–93.
171, 271–285.
30 M. Namazian and M. L. Coote, J. Phys. Chem. A, 2007, 111,
7227–7232.
31 R. S. Ruoff, K. M. Kadish, P. Boulas and E. C. M. Chen, J. Phys.
Chem., 1995, 99, 8843–8850.
32 J. E. Bartmess, J. Phys. Chem., 1994, 98, 6420–6424.
16 P. Barathi and A. Senthil Kumar, Langmuir, 2013, 29, 10617–10623. 33 M. D. Liptak, K. C. Gross, P. G. Seybold, S. Feldgus and G. C. Shields,
17 (a) L. A. Launen, L. J. Pinto and M. M. Moore, Appl. Microbiol. Biotechnol., J. Am. Chem. Soc., 2002, 124, 6421–6427.
1999, 51, 510–515; (b) T. Wunder, S. Kremer, O. Sterner and H. Anke, 34 M. Namazian, C. Y. Lin and M. L. Coote, J. Chem. Theory Comput.,
Appl. Microbiol. Biotechnol., 1994, 42, 636–641; (c) M. Lambert, S. Kremer,
O. Sterner and H. Anke, Appl. Environ. Microbiol., 1994, 60, 3597–3601.
18 A. J. Fatiadi, J. Chromatogr., 1965, 20, 319–324.
2010, 6, 2721–2725.
35 P. Kumari, R. Nagpal and S. M. S. Chauhan, Catal. Commun., 2012,
29, 15–20.
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