Selective removal of isoquinoline and quinoline from simulated fuel using 1,1′-binaphthyl-2,2′-diol (BINOL): Crystal structure and evaluation of the adduct electronic properties

Article abstract of DOI:10.1039/c6ra03854a

1,1′-Binaphthyl-2,2′-diol/quinoline (BINOL/QUN) and 1,1′-binaphthyl-2,2′-diol/isoquinoline (BINOL/ISOQUN) adducts were successfully synthesized. X-ray single crystals of BINOL/QUN and BINOL/ISOQUN were grown and analysed. The crystal packing of the molecules in both adducts confirmed that they are held in aggregates by strong hydrogen bonds (O2-H2?O3), (O3-H3?N1), (O2-H2?O1), (O1-H1?N1), (O2-H2?O1) and weak hydrogen C-H?π bonds. The patterns of the hydrogen bonding network as well as the conformation of BINOL contribute to the formation of the shape of the voids that entrap quinoline and isoquinoline. Molecular modelling which was employed to investigate the electronic properties of BINOL/QUN and BINOL/ISOQUN shows that the HOMO positions of the adducts are localized around the 1,1′-binaphthyl-2,2′-diol (BINOL), while the LUMO is positioned on isoquinoline and quinoline. Thermodynamic parameters obtained from isothermal titration calorimetry (ITC) revealed a stronger isoquinoline/BINOL interaction compared to quinoline/BINOL. 6-Vinyl-1,1′-binaphthyl-2,2′-diol was co-polymerized with styrene to form [DBN-co-STY]. Electrospun [DBN-co-STY] exhibited selectivity for quinoline and isoquinoline in a model simulated fuel presenting an adsorption capacity of 2.2 and 2.4 mg g^-1 respectively. The adsorption study showed a higher adsorption capacity for isoquinoline compared to quinoline. This may be attributed to the more favourable electronic properties (HOMO-LUMO properties) of isoquinoline. This concept demonstrates the possibility of extracting/separating isoquinoline and quinoline from fuel.

Full text of DOI:10.1039/c6ra03854a

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Selective removal of isoquinoline and quinoline
0
0
from simulated fuel using 1,1 -binaphthyl-2,2 -diol
BINOL): crystal structure and evaluation of the
Cite this: RSC Adv., 2016, 6, 39024
(
adduct electronic properties†
Adeniyi S. Ogunlaja,* Eric Hosten, Richard Betz and Zenixole R. Tshentu*
0 0 0 0
,1 -Binaphthyl-2,2 -diol/quinoline (BINOL/QUN) and 1,1 -binaphthyl-2,2 -diol/isoquinoline (BINOL/
1
ISOQUN) adducts were successfully synthesized. X-ray single crystals of BINOL/QUN and BINOL/
ISOQUN were grown and analysed. The crystal packing of the molecules in both adducts confirmed that
they are held in aggregates by strong hydrogen bonds (O2–H2/O3), (O3–H3/N1), (O2–H2/O1), (O1–
H1/N1), (O2–H2/O1) and weak hydrogen C–H/p bonds. The patterns of the hydrogen bonding
network as well as the conformation of BINOL contribute to the formation of the shape of the voids that
entrap quinoline and isoquinoline. Molecular modelling which was employed to investigate the
electronic properties of BINOL/QUN and BINOL/ISOQUN shows that the HOMO positions of the
0
0
adducts are localized around the 1,1 -binaphthyl-2,2 -diol (BINOL), while the LUMO is positioned on
isoquinoline and quinoline. Thermodynamic parameters obtained from isothermal titration calorimetry
0
(
ITC) revealed a stronger isoquinoline/BINOL interaction compared to quinoline/BINOL. 6-Vinyl-1,1 -
0
binaphthyl-2,2 -diol was co-polymerized with styrene to form [DBN-co-STY]. Electrospun [DBN-co-STY]
exhibited selectivity for quinoline and isoquinoline in a model simulated fuel presenting an adsorption
Received 11th February 2016
Accepted 12th April 2016
ꢀ1
capacity of 2.2 and 2.4 mg g respectively. The adsorption study showed a higher adsorption capacity
for isoquinoline compared to quinoline. This may be attributed to the more favourable electronic
properties (HOMO–LUMO properties) of isoquinoline. This concept demonstrates the possibility of
extracting/separating isoquinoline and quinoline from fuel.
DOI: 10.1039/c6ra03854a
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well as tetrapentylammonium bromide (TPAB) and BNP adduct
Introduction
(TPAB/BNP). This approach is based on the concept of molecular
0 0
,1 -Binaphthyl-2,2 -diol (BINOL) is considered to be one of the similarity that is oen used for the design of substrates for
14
1
privileged ligands employed in metal-based catalysis and biological/molecular targets. The ndings reported by Owusu
1
–4
13
0
0
frameworks in asymmetric organocatalysis. BINOLs are also et al. proved that interactions between 1,1 -binaphthyl-2,2 -diol
5–7
known to be employed as hydrogen bonding catalysts. Recent (BINOL) and organic molecules play an important role in sepa-
work indicates an interest in the use of racemic 1,1 -binaphthyl- ration science and technology due to their aggregation properties.
0
0
2
,2 -diol (BINOL) for the construction of superstructures with
Selective interaction of molecules can be tailored for use in
guest molecules such as tetra-n-alkylammonium halides, mor- cleaning of contaminated organic streams via selective adsorption
0
15
pholine, dimethylsulfoxide, acetone, tetrahydrofuran, 2,2 - and molecular recognition. It has also been demonstrated to be
8
–12
16,17
bipyridine and aromatic hydrocarbons.
viable for removal of organosulfur compounds in fuel.
Owusu et al., investigated a similar aggregation system genated compounds (NCCs) such as carbazole, indole, quinoline,
between tetrabutylammonium bromide (TBAB) and 2,3,6 ,7 -tet- isoquinoline are common in coal-derived liquids, fossil fuels and
rahydro-1,1 -binaphthyl-2,2 -diol (BNP) adduct (TBAB/BNP), as shale oil, however, their presence is most problematic in synthetic
feed stocks and heavier petroleum fractions, where its concen-
Nitro-
13
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0
0
0
trations are higher due to their prevalence and aromatic
stability. Nitrogen removal is also required to maintain NOx
emissions below regulatory levels as hydrodenitrogenation (HDN)
process that is currently being employed for the removal of
Department of Chemistry, Nelson Mandela Metropolitan University, P.O. Box 77000,
Port-Elizabeth 6031, South Africa. E-mail: slaja1@yahoo.com; zenixole.tshentu@
nmmu.ac.za; Fax: +27 41 504 4236; Tel: +27 41 504 2074
18
†
1
1
Electronic supplementary information (ESI) available. CCDC 1417759 and
0
0
nitrogenated compounds suffers limitations in achieving the
450690
for
1,1 -binaphthyl-2,2 -diol/quinoline
(BINOL/QUN)
and
0
0
18
,1 -binaphthyl-2,2 -diol/isoquinoline (BINOL/ISOQUN) adduct. For ESI and nitrogen content requirement. The major deleterious effects of
crystallographic data in CIF or other electronic format see DOI:
0.1039/c6ra03854a
NCCs in fuel are the deactivation of rening catalyst which
1
39024 | RSC Adv., 2016, 6, 39024–39038
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18
inhibits deep desulfurization among others. Science research in lm of gold to prevent surface charging and also to protect the
fuel denitrogenation is devoted to removing these nitrogen material surface from thermal damage by the electron beam. No
compounds without altering the fuel specications.
surface coating was needed for EDS analysis. The synthesized
Complexing agents with more environmentally acceptable ligands were conrmed using an Agilent 7890A gas
properties could open possibilities for effective removal of N- chromatograph-mass chromatography (GC-MS). Polymer molec-
compounds, such as quinoline and its derivatives, from fuel. ular weight distribution was carried-out by using the Waters GPC
0
0
Herein, we developed a co-polymer, 6-vinyl-1,1 -binaphthyl-2,2 - Instrument connected to (i) Waters 2487 dual wavelength
diol-co-styrene [DBN-co-STY] for the adsorption of quinoline absorbance UV/vis detector equipped with a ultraviolet (UV)
and isoquinoline in model fuel. Isothermal titration calorimetry detector, and (ii) Waters 2414 differential refractometer (set at 30
ꢁ
(
ITC) was employed to measure the binding affinity as well as
C). The GPC analysis method had the following parameters:
0
0
the thermodynamic properties of 1,1 -binaphthyl-2,2 -diol/ columns: two PLgel 5 Mixed-C (300 ꢂ 7.5 mm) columns with pre-
quinoline and/isoquinoline interactions in solution. Crystal column (PLgel 5 Guard, 50 ꢂ 7.5 mm), column oven tempera-
ꢁ
structures of the various adducts were grown and analysed. A ture: 30 C, injection volume: 100 mL, eluent: THF, wavelength:
ꢀ
1
comparison of both co-crystals bond lengths and angles with 325 and 330 nm, ow rate: 1.0 mL min and calibrant: narrow
6
ꢀ1
modelled structures is also considered to understand the polystyrene standards ranging from 580 to 2 ꢂ 10 g mol
.
molecular assembly phenomenon. Electronic properties Adsorption studies were monitored by employing an Agilent
contributing to the formation of adducts were explained by 7890A gas chromatograph tted with ame ionization detector
employing molecular modelling.
(GC-FID). GC conditions were optimised to efficiently separate
the products from the reactants in the Zebron Phenomenex ZB-
5
MSi capillary column (30 m ꢂ 0.25 mm ꢂ 0.25 mm) on the
Experimental
Materials and methods
GC-FID/GC-MS. Helium was used as carrier gas at a ow rate of
1.63 mL min with an average velocity of 30.16 cm s and
a pressure of 63.73 kPa. The analysis run was started with an oven
ꢀ1
ꢀ1
3 2
2-Napthanol (99%, Merck Chemicals), FeCl $6H O (90%, Sigma-
ꢁ
ꢁ
ꢁ
ꢀ1
temperature of 50 C ramping to 250 C @ 15 C min
.
Aldrich), bromine (Sigma-Aldrich), ammonia solution (25%,
Merck Chemicals), 3,5-di-tert-butylcatechol (Sigma-Aldrich),
styrene (Sigma-Aldrich), palladium tetrakis(triphenylphosphine)
Isothermal titration calorimetry (ITC)
(Sigma-Aldrich), tributyl(vinyl)tin (Sigma-Aldrich) and benzoyl Isothermal titration calorimetry (ITC) which is based on the
chloride (Merck Chemicals) were employed for the ligand detection of the heat released or consumed upon titration of an
synthesis. Azobisisobutyronitrile (AIBN) with 99% purity was analyte with (sub)microliter aliquots of a titrant, has become
purchased from Sigma-Aldrich. The initiator, AIBN, was recrys- the criterion for label-free affinity measurements and the
tallized using methanol. Nitrogen containing compounds such as comprehensive thermodynamic characterization of interactions
19
quinoline and isoquinoline as well as naphthalene were in solution. This technique has found widespread application
purchased from Sigma-Aldrich (Germany). Solvents such as across many different research elds, particularly in the quan-
20
absolute ethanol, toluene, dimethylformamide (DMF), tetrahy- tication of host–guest and supramolecular assemblies, metal
21
22–27
drofuran (THF) and diethyl ether were obtained from Merck ion as well as biomolecular interactions.
The schematic
Chemical (South Africa).
diagram of ITC is presented in Fig. 1, the two lollipop shaped
cells are contained within an adiabatic jacket. A small contin-
uous power is applied by the heater on the reference cell.
Thermocouple detectors sense temperature differences between
the reference and sample cells. The heat per unit time supplied
to the sample cell is the observable signal in an ITC experiment
Instrumentations
ꢀ1
FT-IR spectra (4000–400 cm ) were run on Bruker, Tensor 27
platinum ATR-FTIR spectrometer. The solid reectance spectra
of the adducts were recorded on a Shimadzu UV-VIS-NIR Spec-
trophotometer UV-3100 with a MPCF-3100 sample compartment
with samples mounted between two quartz discs which t into
a sample holder coated with barium sulfate. The spectra were
recorded over the wavelength range of 2000–250 nm, and the
scans were conducted at a medium speed using a 20 nm slit
28
and a direct measure of the heat evolved upon binding.
For the purpose of this experiment, high-sensitivity ITC
ꢁ
experiments were carried out at 25 C. Isoquinoline–BINOL
titration was performed on a modular titration nanocalorimeter
TAM III with an injection volume of 5 mL, a time spacing of 15
min between injections and a stirrer speed of 50 rpm. The
quinoline–BINOL titration was performed with an injection
volume of 10 mL, a time spacing of 10 min between injections
and a stirrer speed of 50 rpm. The reference cell contains
water : EtOH (4 : 1). The ligand (quinoline and isoquinoline)-
molecule (BINOL) binding equation is presented below (1) as:
1
width. The H NMR spectra of the ligands were recorded on
3 6
a Bruker 400 MHz spectrometer in CDCl and DMSO-d . Ther-
mogravimetric analysis (TGA and DSC) were performed using
Perkin-Elmer TGA 7 thermogravimetric analyser. Typically the
samples were heated at a rate of 10 C min under a constant
stream of nitrogen gas. [DBN-co-STY] nanobers images and
chemical characterization were carried out by using TESCAN
Vega TS 5136LM scanning electron microscope (SEM) and
ꢁ
ꢀ1
M + nL # ML
n
(1)
energy-dispersive spectroscopy (EDS) respectively. Before images M ¼ molecule (BINOL), L ¼ ligand (quinoline and isoquino-
were taken for SEM analysis, nanobers were coated with a thin line), n ¼ stoichiometry of interaction.
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2
2.5 h, while warming to room temperature, the excess Br was
destroyed by addition of 50 mL of 10% aqueous solution of
sodium bisulte. The layers were separated, and the organic
layer was washed with saturated NaCl solution and dried. This
was further puried on a silica gel column with ethyl acetate
and ethanol (ratio 1 : 1), and it was then concentrated using
rotavap to give a dark greenish semi-solid product (2.1 g), 55%
ꢀ
1
yield. FT-IR (cm ): 3483, 3405 n(O–H), 3005 n(C–H aromatic),
1
1
337–1617 n(C]C–C aromatic), n(C–Br aromatic), 661. H NMR
(
(
400 MHz, CDCl ): d 6.90 (d, 2H), 7.10–7.30 (m, 6H), 7.85–7.90
3
0
m, 3H), 8.20 (s, OH, 2H). The molecular mass of 6-bromo-1,1 -
0
binaphthyl-2,2 -diol was also conrmed using
(
various products observed in the green product prior to puri-
cation is presented in Fig. S3.†
a GC-MS
ꢀ
1
Fig. S2†) (m/z ¼ 366 g mol ). The GC chromatogram of the
0
0
Synthesis of 6-bromo-1,1 -binaphthyl-2,2 -diyl dibenzoate
0
0
(
III). 6-Bromo-1,1 -binaphthyl-2,2 -diol (1.33 g, 0.003 mol) was
dissolved in 30 mL THF and triethylamine (0.61 g, 0.006 mol) was
added followed by benzoyl chloride (0.98 g, 0.007 mol). The
mixture was stirred overnight resulting in the formation of
precipitate within the solution, and the precipitate was ltered off
while the ltrate was concentrated to give a brown sticky liquid
which was washed with ethanol to give 1.60 g (82% yield) of 6-
0
0
bromo-1,1 -binaphthyl-2,2 -diyl dibenzoate (Scheme 1). FT-IR
Fig. 1 Schematic diagram of an ITC instrument.
ꢀ1
(
cm ): 1732 n(C]O aromatic), 1009–1357 n(C]C–C aromatic),
n(C–Br aromatic), 674. H NMR (400 MHz, CDCl ): d 8.08 (d, 1H),
1
3
7
.98 (s, 1H), 7.92 (d, 1H), 7.80 (t, 2H), 7.62–7.56 (dd, 4H), 7.49–7.45
Computational studies
(m, 2H), 7.39–7.27 (m, 4H), 7.26–7.07 (m, 6H).
Density functional theory was employed to explore the electronic
properties and vibrational analyses of the adducts. The full
geometry optimization of the chemical structures was carried out
at the DFT level of theory using Becke's three-parameter hybrid
exchange functional in combination with the gradient-corrected
0
0
Synthesis of 6-vinyl-1,1 -binaphthyl-2,2 -diyl dibenzoate (IV).
0
0
To a solution of 6-bromo-1,1 -binaphthyl-2,2 -diyl dibenzoate
1.22 g, 2.24 mmol) dissolved in dichloromethane, palladium
(
tetrakis(triphenylphosphine) (0.052 g, 0.045 mmol), tribu-
tyl(vinyl)tin (0.65 mL, 2.24 mmol) and trace amount of 3,5-di-
tert-butylcatechol were added (Scheme 1). The resulting mixture
was heated to reux under nitrogen environment for 5 h. Upon
cooling, the resulting solution was ltered and then concen-
trated to give a green viscous liquid. The resulting oil was dis-
solved into 30 mL acetonitrile and washed with 20 mL hexane.
29,30
correlation functional of Lee, Yang and Parr (B3LYP)
and
a basis set 6-311 G using the Gaussian program (calculated at
98 K).
31
2
Synthesis protocol
0
0
0
Synthesis of 1,1 -binaphthyl-2,2 -diol [BINOL] (I). 1,1 - The lower of the two immiscible liquid was run into a beaker,
Binaphthyl-2,2 -diol preparation was adopted from the concentrated to give 6-vinyl-1,1 -binaphthyl-2,2 -diyl dibenzoate
synthetic route reported by Brussee et al. with a few modi- (1.60 g, 82% yield). FT-IR (cm ): 1737 n(C]O aromatic), 1024–
3 2 3
cations which are noted below. A solution of FeCl $6H
O (56.0 1263 n(C]C–C aromatic). H NMR (400 MHz, CDCl ): d 8.16 (d,
0
0
0
32
ꢀ1
1
mmol, 15.14 g) and 2-napthanol (28.0 mmol, 4.03 g) in water 3H), 7.92 (s, 2H), 7.73 (d, 3H), 7.56–7.62 (m, 5H), 7.51–7.41 (m,
ꢁ
(
200 mL) was stirred for 1 h at 50 C (Scheme 1). Aer cooling to 5H), 7.32 (t, 2H), 6.39 (dd, 1H), 6.07 (d, 1H), 5.58 (d, 1H).
0 0
Synthesis of 6-vinyl-1,1 -binaphthyl-2,2 -diol (V). 0.45 g of 6-
room temperature, the precipitate was ltered, washed with
H O and dried in vacuo. Recrystallization was carried-out in vinyl-1,1 -binaphthyl-2,2 -diyl dibenzoate was dissolved in 10
0
0
2
0
absolute ethanol (40 mL). Yield ¼ 3.80 g, 96.3% of 1,1 - mL of ethanol. Sodium ethoxide was prepared separately by
0
ꢁ
ꢀ1
binaphthyl-2,2 -diol. Melting pt ¼ 212–214 C. FT-IR (cm ): adding 50 mg of sodium in dry ethanol (50 mL). The sodium
3
490, 3426 n(O–H), 3065 n(C–H aromatic), 1362–1598 n(C]C–C ethoxide was then added to the product solution drop wise until
1
aromatic) (Fig. 1). H NMR (400 MHz, DMSO): d 9.22 (s, 2H), the mixture became yellow it was then concentrated and dis-
7
2
.89–7.81 (m, 4H), 7.32 (d, 2H), 7.23 (t, 2H), 7.17 (d, 2H), 6.94 (d, solved in 50 mL of 0.20 M NaOH (Scheme 1). The pH was
H) (Fig. S1†).
adjusted to 6 by adding 0.1 mol HCl until the solution becomes
Synthesis of 6-bromo-1,1 -binaphthyl-2,2 -diol (II). In 40 mL cloudy, the precipitate was ltered and centrifuged and then
0
0
0
0
of CH Cl , 2.10 g (7.34 mmol) of 1,1 -binaphthyl-2,2 -diol was washed with ice cold methanol followed by cold diethyl ether
2
2
ꢁ
ꢀ1
dissolved and the system cooled to ꢀ75 C. Bromine (0.5 mL, giving a pure cream solid (Scheme 1). FT-IR (cm ): 3566, 3198
9
.8 mmol) was added drop wise over 20–30 min with constant n(O–H), 2988 n(C–H aromatic), 1024–1263 n(C]C–C aromatic).
ꢁ
33
1
stirring at ꢀ75 C (Scheme 1). Aer stirring for an additional
3
H NMR (400 MHz, CDCl ): d 7.82 (s, 2H), 7.47–7.33 (m, 5H),
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0
Scheme 1 The synthesis scheme for 6-vinyl-1,1 -binaphthyl-2,2 -diol.
0
0
Scheme 2 Co-polymerisation of 6-vinyl-1,1 -binaphthyl-2,2 -diol with styrene to form [DBN-co-STY].
7
(
.08–6.97 (m, 4H), 6.75 (dd, 2H), 5.73 (d, 1H), 5.19 (d, 1H), 4.61
Polymer solutions were respectively poured into a 25 mL
s, 1H). The H NMR of the various products (II–V) and the FT-IR syringe attached to a needle connected to the positive electrode of
of product (I–V) are overlaid and presented in Fig. S4 and S5† a high voltage power supply (Series EL, Glassman high voltage
1
respectively.
Inc.). A syringe pump (Model NE-1010, New Era Pump Systems
Inc. USA) was used to supply a constant ow of polymer solution
from the syringe during the electrospinning process. A voltage of
0
0
Polymerisation of 6-vinyl-1,1 -binaphthyl-2,2 -diol
1
6 kV was applied to the polymer solution which was pumped at
0
For the synthesis of [DBN-co-STY] polymer, the 6-vinyl-1,1 -
ꢀ1
a ow-rate of 0.5 mL h , with a distance between the needle tip
and aluminium collector plate placed at 17 cm. The repulsive
electrical forces between charged nanobers enable them to
spread smoothly and the solvent evaporates resulting in solidi-
cation while traveling toward the grounded collector.
0
binaphthyl-2,2 -diol [DBN] and styrene [STY] monomers were
polymerized by free radicals reaction in toluene using AIBN as
a free radical initiator (Scheme 2). 2.012 g of monomer, [DBN], 1.5
mL of styrene and 100 mg (ꢃ5 wt% of the monomer, [DBN]) of
initiator were charged in a glass test tube containing 1.5 mL of
toluene, which was bubbled with nitrogen gas for 30 min. The test
0
0
tube was then sealed under nitrogen and placed in a constant Synthesis of 1,1 -binaphthyl-2,2 -diol/quinoline (BINOL/QUN)
ꢁ
0
0
temperature (80 C) oil bath for 48 h. Aer this period, the reac- and 1,1 -binaphthyl-2,2 -diol/isoquinoline (BINOL/ISOQUN)
tion mixture was cooled to room temperature, and the polymer adducts
was isolated by precipitating the product, [DBN-co-STY], in
Similar experimental procedures were followed for the synthesis
ethanol (20 times the volume of the reaction mixture) followed by
of BINOL/QUN and BINOL/ISOQUN adducts. To a 15 mL

ltration and subsequent drying overnight.
0
0
methanolic solution of 1,1 -binaphthyl-2,2 -diol (0.3 g, 0.001
mol), quinoline (0.136 g, 0.001 mol) was added. The mixture was
stirred for 30 min, thereaer allowed to stand. Aer one night
Fabrication of [DBN-co-STY] nanobers by electrospinning
A polymer solution for electrospinning was prepared by dis- suitable brown crystals were collected. The crystals were dried
solving 2.0 g of [DBN-co-STY] polymer in 3 mL of THF : DMF under a nitrogen ow and subjected to single-crystal X-ray
ꢀ1
(
1 : 1). The mixture was gently stirred for 4 h at room temper- diffraction. FT-IR (cm ): 3490, 3426 n(O–H), 3065 n(C–H
ature to obtain a homogeneous solution for electrospinning.
aromatic), 1362–1598 n(C]C–C aromatic), 1090–1020 n(C–N).
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1
H NMR (400 MHz, DMSO): d 9.19 (s, 2H), 8.92 (s, 1H), 8.37 (s, UV studies
1
¼
H), 8.01 (d, J ¼ 10.3 Hz, 2H), 7.81 (d, J ¼ 30.3 Hz, 5H), 7.58 (d, J
Solid reectance spectra of BINOL and BINOL/QUN were
recorded on a Shimadzu UV-VIS-NIR Spectrophotometer UV-
32.1 Hz, 2H), 7.42–7.08 (m, 7H), 6.95 (s, 2H).
3100. Maximum absorption (lmax) of 344, 348 and 356 nm
attributed to p–p for BINOL BINOL/QUN and BINOL/ISOQUN
respectively was observed (Fig. 5). The observed shi in lmax
to a longer wavelength (bathochromic shi) upon formation of
BINOL/QUN and BINOL/ISOQUN are due the increase in the
conjugation of the system. The energetically favorable p–p
excitation occurs from the highest energy bonding pi-orbital
(HOMO) to the lowest energy antibonding pi-orbital (LUMO).
Results and discussion
0
Structure determination and renement of 1,1 -binaphthyl-
0
0
0
2
,2 -diol/quinoline (BINOL/QUN) and 1,1 -binaphthyl-2,2 -
diol/isoquinoline (BINOL/ISOQUN)
0
0
Single crystals of 1,1 -binaphthyl-2,2 -diol/quinoline (BINOL/
0
0
QUN) and 1,1 -binaphthyl-2,2 -diol/isoquinoline (BINOL/
ISOQUN) suitable for X-ray analysis were analysed. The molec-
ular structure of BINOL/QUN and BINOL/ISOQUN are presented
in Fig. 2 and 3 respectively. Intensity data were collected on
a Bruker APEX II CCD diffractometer with graphite mono-
Stoichiometry of the interaction-isothermal titration
calorimetry (ITC)
chromated Mo Ka radiation using the APEX 2 data collection The binding isotherms were carried out using the isothermal
34
soware. Crystal data and details for the determination of the titration calorimetry (ITC). The same titration conditions were
structures are presented in Table 1. The structure was solved by employed (i.e., concentrations, injection volumes, etc.) for
0
0
direct methods applying SHELXS-2013 and rened by least- quinoline and isoquinoline titrations with 1,1 -binaphthyl-2,2 -
35
squares procedures using SHELXL-2013. The crystal struc- diol (BINOL). The ITC interaction titrations for quinoline vs.
ture diagrams were drawn with ORTEP-3 for windows. Some of 1,1 -binaphthyl-2,2 -diol and isoquinoline vs. 1,1 -binaphthyl-
the bond distances and angles between atoms within adduct are 2,2 -diol are presented Fig. 6. The peaks displayed the progress
presented in Table 2. Hydrogen bonding geometries and short of binding of the analyte (quinoline or isoquinoline) to 1,1 -
contacts (A, ) for both BINOL/QUN and BINOL/ISOQUN are binaphthyl-2,2 -diol with time. The amount of heat released as
provided in Table 3. A schematic illustration showing the interaction progresses decrease, hence conrming a decrease in
entrapment of quinoline by BINOL in crystal packing is shown adsorption capacity (Fig. 6). The stoichiometry of interaction
36
0
0
0
0
0
ꢀ
ꢁ
0
is Fig. 4.
a b b
(n), association constant (K ), free energy (DG ), enthalpy (DH )
Fig. 2 An ORTEP view of the BINOL/QUN with ellipsoids drawn at 50% probability level.
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Fig. 3 An ORTEP view of the BINOL/ISOQUN with ellipsoids drawn at 50% probability level.
and entropy (DS ) is presented in Table 4. For the adsorption
b
Table 1 Crystal data for the structural determination of BINOL/QUN process to be spontaneous there must be a decrease in free
(I) and BINOL/ISOQUN (II)
b
energy of the system, i.e. DG of the system must have a negative
value.
I
II
From the obtained thermodynamic parameters (Table 4),
negative free energies were observed for both isoquinoline/
BINOL and quinoline/BINOL interactions (Table 4). During
the adsorption process, the randomness of the interacting
molecules decreases, hence giving rise to negative entropies
Formula
C
20
H
14
O
2
, C
9
H
7
N
C
20 14 2 9 7
H O , C H N
Formula weight
Crystal system
Space group
415.47
Triclinic
P 1ꢁ (no. 2)
415.47
Triclinic
P 1ꢁ (no. 2)
9.8716(5), 10.7064(5),
12.3284(6)
a, b, c [angstrom]
10.2219(4),
(
ꢀve DS
b
). Isoquinoline/BINOL presented a higher degree of
1
1
0.7838(4),
1.7729(4)
randomness as compared to the interaction obtained via
quinoline/BINOL. Enthalpy (DH
ꢀ
3
ꢀ1
ꢀ
) values of ꢀ5.6 kJ mol and
V [A ]
1067.88(7)
2
1.292
0.081
436
1052.56(10)
2
1.311
0.082
b
ꢀ1
Z
270 ꢄ 68 kJ mol was obtained for quinoline/BINOL and
ꢀ1
D (calc) [g mL
Mu (MoKa) [mm
F(000)
Crystal size [mm]
Temperature (K)
Radiation
]
isoquinoline/BINOL respectively, and this conrmed a stronger
interaction between isoquinoline and BINOL as compared to
quinoline and BINOL (Table 4).
ꢀ1
]
436
0.26 ꢂ 0.34 ꢂ 0.45
0.34 ꢂ 0.54 ꢂ 0.54
200
200
MoKa 0.71073
MoKa 0.71073
[
angstrom]
Theta min.–max.
Deg]
Thermal analysis
2.2, 28.4
1.9, 28.4
[
Thermogravimetry (TG) and differential scanning calorimetry
Dataset
ꢀ13: 13; ꢀ14: 14;
ꢀ13: 13; ꢀ14: 14; ꢀ16: (DSC) were carried out on a PerkinElmer TGA 7 thermogravi-
ꢀ15: 15
16
metric analyzer. The experiments were performed over
Tot., uniq. data,
R(int)
19 180, 5327, 0.016
28 615, 5246, 0.016
ꢁ
a temperature range of 30–350 C at a constant heating rate of
ꢁ
ꢀ1
1
0 C min , with a purge of dry nitrogen owing at 30 mL
Observed data [I >
.0sigma(I)]
4393
4486
ꢀ
1
0
0
2
min . The TG trace of 1,1 -binaphthyl-2,2 -diol/quinoline
(BINOL/QUN) shows a three-step degradation pattern (Fig. 7),
Nref, Npar
5327, 291
0.0388, 0.1121, 1.04
0.00, 0.00
5246, 291
0.0393, 0.1095, 1.05
0.00, 0.00
R, wR
2
, S
a weight loss of 31% equivalent to quinoline occurred between
30 and 198 C, followed by a further weight loss of 6% attrib-
Max. and av. shi/
error
Min. and max. resd.
dens. [e A
ꢁ
1
uted to one –OH group of BINOL at a temperature range of 207–
ꢀ0.20, 0.31
ꢀ0.20, 0.34
ꢀ
3
ꢁ
ꢀ
252 C. A rapid collapse/decomposition of the BINOL (60 wt%
]
ꢁ
loss) occurred at a temperature range of 253–327 C to give
a residue. BINOL/QUN desorbs in two distinct steps (Fig. 7),
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ꢁ
Table 2 Some bond distances (angstrom) and bond angles ( ) of BINOL/QUN and BINOL/ISOQUN (experimental and calculated values)
ꢀ
ꢁ
Bond lengths (A)
Experimental values
Calculated values
Bond angles [ ]
Experimental values
Calculated values
BINOL/QUN
O1–C2
O2–C12
N1–C21
N1–C29
O1–H1
O2–H2
—
1.3632(14)
1.3552(14)
1.3101(17)
1.3719(15)
0.8400
0.8400
—
—
1.3960
1.3990
1.3322
1.3818
0.9724
0.9728
—
O1–C2–C3
O1–C2–C1
120.83(11)
118.13(11)
121.71(9)
117.58(11)
118.55(11)
123.85(12)
121.36(11)
119.04(11)
120.37
117.79
120.13
117.92
118.31
123.50
121.77
118.84
O2–C12–C13
O2–C12–C11
C21–N1–C29
N1–C21–C22
N1–C29–C24
N1–C29–C28
—
—
BINOL/ISOQUN
O2–C20
O3–C30
N1–C11
O2–H2
O2–H3
N1–C19
—
1.3590(12)
1.3703(16)
1.3160(19)
0.8400
0.8400
1.363(2)
—
1.3975
1.3760
1.3307
0.9723
0.9721
1.3770
O2–C20–C29
O2–C20–C21
O3–C30–C31
O3–C30–C39
C11–N1–C19
N1–C11–C12
N1–C19–C18
121.14(9)
117.87(9)
119.30(10)
119.43(11)
117.61(11)
124.21(15)
123.28(13)
120.56
118.81
120.19
118.85
118.54
122.76
122.08
ꢀ
ꢁ
Table 3 Hydrogen bonding geometry and short contacts (A, ) for
BINOL/QUN and BINOL/ISOQUN
ꢀ
ꢁ
Hydrogen bonds
Bond lengths (A)
Bond angles ( )
BINOL/QUN
O1–H1/N1
O2–H2/O1
0.8400
0.8400
1.8000
1.9200
2.6317(14)
2.7580(11)
168.00
173.00
BINOL/ISOQUN
O2–H2/O3
O3–H3/N1
0.8400
0.8400
0.9500
1.9200
1.8500
2.5300
2.7576(11)
2.6809(14)
3.4199(19)
172.00
169.00
156.00
C34–H34/O2
each corresponding to the loss of a single quinoline guest. The
DSC shows two accompanying endotherms, one broad (T ¼ 164
ꢁ
ꢁ
C) for guest melt followed by the host melt at T ¼ 215 C. The
ꢁ
crystallization peak observed at 325 C conrmed the formation
Fig. 5 Solid reflectance spectra of (I) BINOL, (II) BINOL/QUN and (III)
BINOL/ISOQUN.
of crystalline residue.
Fig. 4 A schematic illustrations showing the entrapment of quinoline by BINOL.
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0
0
Fig. 6 ITC titration involving 1,1 -binaphthyl-2,2 -diol (BINOL) and (A) isoquinoline and (B) quinoline. 9.98 mM (quinoline/isoquinoline) was
0
0
titrated into 0.998 mM 1,1 -binaphthyl-2,2 -diol (BINOL).
a D
Table 4 Thermodynamic properties, association constant (K ) and dissociation constant (K ) obtained from isothermal titration calorimetry (ITC)
Free energy (DG
b
)
Stoichiometry of the
interaction (n)
Enthalpy (DH
b
)
Entropy (DS
b
)
Association constant
(K
Dissociation
D
constant (K )
ꢀ
1
ꢀ1
ꢀ1
(
kJ mol
)
(kJ mol
)
(kJ mol
)
a
)
ꢀ
ꢀ
2
2
2
2
ꢀ3
ꢀ3
BINOL/quinoline
BINOL/isoquinoline
ꢀ16.9
ꢀ16.3
1.322 ꢄ 5 ꢂ 10
1.240 ꢄ 4 ꢂ 10
ꢀ5.6
ꢀ12
9.2 ꢂ 10
7.3 ꢂ 10
1.08 ꢂ 10
1.37 ꢂ 10
ꢀ270 ꢄ 68
ꢀ835
0
0
0
0
Fig. 7 TG and DSC curves for 1,1 -binaphthyl-2,2 -diol/quinoline Fig. 8 TG and DSC curves for 1,1 -binaphthyl-2,2 -diol/isoquinoline
(
BINOL/QUN).
(BINOL/ISOQUN).
Computational studies
0
0
The TG prole of 1,1 -binaphthyl-2,2 -diol/isoquinoline
BINOL/ISOQUN) shows two-step degradation pattern
Electronic properties (UV adsorption analysis). The elec-
tronic properties of BINOL/QUN and BINOL/ISOQUN were
calculated using the TD-DFT approach. The calculations were
performed in air as carried out in the experimental studies. TD-
DFT calculations predict three transitions in the near ultra-
violet region for BINOL, BINOL/QUN and BINOL/ISOQUN with
varying intensities and energies. The transitions of BINOL,
BINOL/QUN and BINOL/ISOQUN are presented in Table 5.
(
(
a
Fig. 8), a weight loss of 32% equivalent to isoquinoline
occurred between 125 and 180 C. A rapid decomposition of the
BINOL (68 wt% loss) occurred at a temperature range of 181–
75 C. The DSC displayed two complementary endotherms,
ꢁ
ꢁ
2
ꢁ
one broad (T ¼ 180 C) for guest melt followed by the host melt
ꢁ
at T ¼ 220 C. TG prole of BINOL is provided in Fig. S6.†
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a
Table 5 UV electronic properties of BINOL/QUN and BINOL/ISOQUN
BINOL
BINOL/QUN
BINOL/ISOQUN
l (nm)
E (eV)
(f)
l (nm)
E (eV)
(f)
l (nm)
E (eV)
(f)
Assignment
3
3
3
17.83
15.97
00.43
3.9010
3.9240
4.1268
0.0330
0.0006
0.1340
320.29
316.74
309.14
3.8710
3.9144
4.0106
0.0078
0.0048
0.0038
424.51
394.65
333.61
2.9207
3.1416
3.7165
0.0045
0.0014
0.0015
p–p
p–p
p–p
a
l ¼ wavelength; f ¼ oscillator strength.
Fig. 9 The HOMO and LUMO position of (A) BINOL/QUN and (B) BINOL/ISOQUN.
Observed shi to a longer wavelength from BINOL to BINOL/
The energy difference between HOMO and LUMO orbital is
QUN and BINOL/ISOQUN further conrmed an increase in called the energy gap, and it indicates the reactivity and stability
the conjugation of the system. The maximum absorption of structures. The DFT level calculated energy gaps showed that
wavelength corresponds to the electronic transition from the the energy gaps for BINOL, BINOL/QUN and BINOL/ISOQUN
HOMO to LUMO. The calculated excitation energies, oscillator are 4.50242 eV, 4.17016 eV and 3.70919 eV respectively. BINOL
strength (f) and wavelength (k) and spectral assignments are interaction with quinoline (QUN) and isoquinoline (ISOQUN)
presented in Table 5.
caused a decrease in the HOMO–LUMO energy gap.
HOMO–LUMO and electrostatic potential analysis. The
Attractive and repulsive forces between interacting atoms
HOMO represents the ability of a molecule to donate an elec- and molecules of BINOL/QUN and BINOL/ISOQUN occur as
tron and LUMO the electron acceptor ability. The molecular a result of their electropositive and electronegative properties,
orbitals play an important role in the electric and optical explained through electrostatic potential energies. The electro-
properties of the BINOL/QUN. The plot of the HOMO and static potentials for BINOL/QUN and BINOL/ISOQUN were
LUMO orbitals of BINOL/QUN and BINOL/ISOQUN in MeOH color-mapped based on the electron density distribution of the
are shown in Fig. 9. From the computational analysis, it was various compounds (Fig. 10). The red end of the spectrum
found that the HOMO position of the adduct is localized around (Fig. 10) shows regions of highest stability for a positive test
the BINOL, while the LUMO is positioned around quinoline and charge (more favorable to interactions), magenta/blue show the
isoquinoline. Electrons are mainly populated on the oxygen regions of least stability for a positive test charge (less favorable
atoms of BINOL and the nitrogen atom of quinoline and to interactions). The negative characteristic electrostatic
isoquinoline.
potentials, represented in red color, are reactive as they are rich
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Fig. 10 Electrostatic potential mapping of (A) BINOL/QUN and (B) BINOL/ISOQUN.
in electrons. For BINOL, negative electrostatic potential are
distributed on the two oxygen atoms, while quinoline and iso-
quinoline has a higher electron density on the nitrogen atom.
Adducts (BINOL/QUN and BINOL/ISOQUN) also show evidence
of electrostatic potentials on the aromatic planes of both
BINOL/QUN and BINOL/ISOQUN which contributed to the p–p
interaction between the molecules, hence leading to adduct
formation.
[DBN-co-STY] nanober characterization. BINOL was incor-
porated into polymer and electrospun for benets of electro-
spinning. Electrospinning is a workable method for fabrication
of polymer bers with diameters in tens to hundreds of nano-
meters. It provides polymer bers with controlled pore size as
well as high surface-to-volume ratio, and it decreases adsorp-
37,38
tion time and mass transfer constraints.
According to the
characterization result obtained for the synthesized monomer,
0 0
-vinyl-1,1 -binaphthyl-2,2 -diol, the coupling of a vinyl group to
Fig. 11 FT-IR spectrum of (A) [DBN-co-STY] polymer and (B) 6-vinyl-
6
0
0
1
,1 -binaphthyl-2,2 -diol.
0
0
one end of 1,1 -binaphthyl-2,2 -diol (V) offers exibility and free
movement of the molecule upon polymerization. Energy
Dispersive Spectroscopy (EDS) of [DBN-co-STY] polymer nano-
and S12 in the ESI† shows the graph of molecular weight
distribution of DBN-co-STY as a function of time and the

bers conrmed the presence of oxygen, nitrogen and carbon
on the nanobers (Fig. S7†). The UV spectra of polymer material
DBN-co-STY] and the resulting polymer nanobers are pre-
distribution plot (dw/d(log M
w
) vs. log M
w
) respectively.
[
0
0
FT-IR. The FT-IR spectra of 6-vinyl-1,1 -binaphthyl-2,2 -diol
and [DBN-co-STY] is provided in Fig. 11. Of importance are the
visible –OH, –C–H aromatic (stretching), –C–H aromatic (in-
plane bend) and –C–C]C aromatic stretch bands at 3337
sented in the ESI (Fig. S8†). Maximum absorption (lmax) of 348
and 345 nm attributed to p–p transition was observed for
polymer material [DBN-co-STY] and the resulting polymer
nanobers respectively. This illustrates that the polymer integ-
rity is preserved aer electrospinning to form nanobers. TG
prole of [DBN-co-STY] polymer nanobers is provided in
ꢀ
1
ꢀ1
ꢀ1
cm , 2918 cm and ꢃ1440 cm respectively on [DBN-co-STY]
0
0
aer the polymerization of 6-vinyl-1,1 -binaphthyl-2,2 -diol.
Scanning electron micrograph (SEM). SEM images of [DBN-
co-STY] nanobers are presented in Fig. 12. The electrospun
nanobers displayed uniform morphology without beads
formation. A diameter range of 0.46–2.42 mm was presented by
the nanobers.
1
Fig. S9.† The H-NMR (in DMSO) of [DBN-co-STY] conrmed
polymerization via the broadening of peaks (Fig. S10†).
Molecular weight and polydispersity analysis. DBN-co-STY
presented a weight-average (M ) and number-average (M )
w
n
ꢀ
1
molecular weights of 4790 and 2635 g mol
respectively.
Quinoline and isoquinoline adsorption selectivity in simu-
lated model fuel. The adsorption assay was carried out to
evaluate the adsorption capacity and selectivity of quinoline
with [DBN-co-STY] nanobers in a simulated model fuel.
Simulated model fuel containing quinoline, isoquinoline,
Polydispersity (Đ) index of DBN-co-STY, which is the ratio of the
weight-average (M and number-average (M molecular
weights, is reported to be 1.82. The high dispersity index
w
)
n
)
39,40
conrmed a wide molecular weight distribution.
Fig. S11
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Fig. 12 Scanning electron microscopy of [DBN-co-STY] polymer nanofibers.
Fig. 13 A continuous flow set-up employed in this study. [DBN-co-STY] nanofibers are packed into a filter tip compartment, placed in the front
of a syringe containing a mixture of quinoline, isoquinoline, carbazole, 1-benzothiophene, naphthalene and dibenzothiophene.
carbazole, 1-benzothiophene, naphthalene and dibenzothio-
phene (100 ppm each) was employed for adsorption studies
under a continuous ow process. 200 mg of [DBN-co-STY]
nanobers was packed unto the tip of a syringe containing 2 mL
of simulated fuel (Fig. 13).
VðC ꢀ C Þ
o
e
Q
e
¼
(2)
W
ꢀ1
where C
o
, C
e
, W and V are the initial concentration (mg L ),
ꢀ1
equilibrium concentration (mg L ), dry weight of nanobers
(
g) and solution volume (L) respectively.
Maximum adsorption concentrations of naphthalene, 1-ben-
zothiophene, dibenzothiophene, carbazole, isoquinoline and
ꢀ
1
A ow-rate of 1 mL h was employed for the adsorption
ꢀ
1
e
process. Adsorption capacity, Q (mg g ) was calculated from
eqn (2). Conditioning of [DBN-co-STY] nanobers was carried-
out by pre-wetting adsorbents with methanol prior to adsorp-
tion studies. The nal concentration aer adsorption was
quantied using GC-FID.
quinoline aer adsorption were 94.3 ꢄ 6.9 ppm, 97.7 ꢄ 4.9 ppm,
9
(
0.1 ꢄ 3.2 ppm, 93.5 ꢄ 4.8 ppm 5.1 ꢄ 3.1 ppm and 11.0 ꢄ 2.8 ppm
e
Fig. 14). The adsorption capacities, Q , of quinoline and
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Computation study on formation carbazole/BINOL adduct.
Experimental studies could not conrm the formation of
adduct between carbazole and BINOL aer 48 h of interaction,
as both molecules remained in solution. Herein, we apply
computational modelling to understand the electronic proper-
ties between BINOL and carbazole. The DFT level calculated
HOMO and LUMO positions of the carbazole–BINOL adduct
indicated that the HOMO position centers around carbazole,
while the LUMO position is located on the BINOL. The calcu-
lated energy gap of the adduct gave a relatively small difference
when compared to BINOL band gap (4.50242 eV) as the carba-
zole–BINOL adduct gave a band gap of 4.43083 eV. Hence,
conrming the hardness of carbazole in allowing surface
interaction as compared to isoquinoline and quinoline which
gave a lower gap (Fig. 9). The HOMO–LUMO hardness further
illustrate the reasons why interaction may not be favourable,
secondly the nitrogen atom on carbazole is readily not available
for interaction (electron donation) as it is attached to hydrogen
atom (pyrrole nitrogen). Carbazole–BINOL adduct could only be
Fig. 14 Adsorption of quinoline and isoquinoline in simulated model
fuel.
0
0
formed via p–p stacking of carbazole and 1,1 -binaphthyl-2,2 -
diol (BINOL) which could translate to a weak interaction. The
electrostatic potential mapping of carbazole–BINOL adduct
presented in Fig. 15 revealed that carbazole is predominantly
dominated by the magenta/blue colour which conrmed that it
is less favorable to interactions.
ꢀ
1
isoquinoline were 2.2 and 2.4 mg g respectively. Complete
desorption of adsorbed quinoline and isoquinoline from [DBN-co-
STY] nanobers was achieved by washing [DBN-co-STY] nano-
Binding selectivity coefficient. The selectivity coefficient (k)
dened for BINOL–QUN and BINOL–ISOQUN using the poly-
mer, [DBN-co-STY], in the presence of interfering molecules is
represented by eqn (3) below. k is inversely related to
a competitive affinity binding of molecule of interest competing
with interfering molecule on the same binding site on [DBN-co-
STY]. The higher the value of k, the better is the adsorption.

bers with a mixture of excess warm water/ethanol (1 : 1).
High selectivity for quinoline and isoquinoline was observed
for the simulated model fuel adsorption study. The observation
above (Fig. 16) clearly conrmed the binding interaction data
obtained from the isothermal titration calorimetry (ITC)
0
0
between quinoline vs. 1,1 -binaphthyl-2,2 -diol and isoquinoline
0
0
vs. 1,1 -binaphthyl-2,2 -diol (Fig. 6). Low analyte adsorptions
<10%) observed for carbazole, 1-benzothiophene, naphthalene
(
K
d
ðtemplate moleculeÞ
ðinterfering moleculeÞ
k ¼ K
(3)
and dibenzothiophene were attributed to weak p–p aromatic
interactions. Further studies on carbazole vs. 1,1 -binaphthyl-
d
0
where Kd ¼ Q /C is the distribution coefficient of selected
e
e
0
2,2 -diol binding interaction titration show mostly identical
molecules employed for the simulated model fuel between
DBN-co-STY] and the simulated fuel. The binding selectivity
peaks which reect only a non-binding process (Fig. S13†),
hence conrms the reported observation in Fig. 14. Molecular
modelling was further explored to understand the electronic
properties between BINOL and carbazole.
[
coefficient (k) value of isoquinoline w.r.t naphthalene is 318, 1-
benzothiophene is 821, dibenzothiophene is 175 and carbazole
is 295. While the binding selectivity coefficient (k) value of
Fig. 15 Electrostatic potential mapping of carbazole–BINOL adduct.
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o e
Fig. 16 Breakthrough curves of (A) quinoline and (B) isoquinoline using DBN-co-STY nanofibers. C represents the initial concentration and C is
the eluted concentration.
Table 6 Breakthrough parameters for the adsorption of quinoline and
isoquinoline
V
R
K ¼ V ꢀ 1
(5)
M
N-Compounds
V
B
(mL)
V
R
(mL)
V
M
(mL)
N
K
n
s
r (%)
n
s
¼ V
M
KC
o
(6)
(7)
Quinoline
Isoquinoline
1.9
2.2
3.6
3.8
0.16
0.16
11.6 21.5 172 69
14.3 22.8 182 73
n
s
r ¼ C
ꢂ 100%
o
V
o
where Vo is the initial volume of the analyte, breakthrough
volume (V ), retention volume (V ) and hold-up volume (V ) of
the analyte. From Table 6, a higher amount of isoquinoline was
recovered aer continuous ow compared to quinoline.
B
R
M
quinoline w.r.t naphthalene is 135, 1-benzothiophene is 349,
dibenzothiophene is 74 and carbazole is 125.
Continuous ow breakthrough adsorption studies. Break-
through volumes were evaluated, and they represent the
evolution of the concentration of a solution as a function of
parameters such as contact time between liquid and solid
phase, solvent concentration and temperature. 200 mg of [DBN-
co-STY] nanobers were packed into a cylindrical tube attached
to the tip of a syringe containing 5 mL of 100 ppm of the
respective N-compounds (quinoline and isoquinoline).
Reusability studies. Reusability studies of [DBN-co-STY]
nanobers were carried out by using the same adsorption study
protocol described above. The [DBN-co-STY] nanobers pre-
sented a consistent but slightly variable overall adsorption for
the second (94% and 82%) and third (91% and 83%) cycle of
usage (Fig. 17) for isoquinoline and quinoline respectively,
hence conrming the integrity of the [DBN-co-STY] nanobers.
The [DBN-co-STY] nanobers were easily contained in the
tube without leaving much space and the packing was tightened
ꢀ1
by conditioning the material with solvent at 1 mL h
.
Adsorption progressed as respective N-compounds (quinoline
and isoquinoline) were pumped through the conditioned
ꢀ
1
adsorbent at a ow-rate of 1 mL h . The breakthrough curves
of the N-compounds solutions obtained are presented in
Fig. 16. From the adsorption curve, a maximum amount of N-
compounds, quinoline and isoquinoline were retained aer 2
mL (2000 mL) of the solution have been dispensed (Fig. 16). The
number of theoretical plates (N), the linear capacity of the
s
column (n ), the capacity factor of the solute (K) and percentage
37,41
recovery (r) are calculated from eqn (4)–(7)
and presented in
Table 6.
V
R
N ¼ s ðV
R
ꢀ s Þ
V
(4)
2
V
Fig. 17 Reusability of [DBN-co-STY] nanofibers showing the %
adsorption of quinoline and isoquinoline.
where 2s
V
¼ V
R
ꢀ V
B
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The initial adsorption (1 cycle) for isoquinoline and quinoline
were 95% and 85%, respectively (Fig. 14). Desorption of adsor-
bed quinoline and isoquinoline from [DBN-co-STY] nanobers
was achieved by washing [DBN-co-STY] nanobers with
a mixture of excess warm water/ethanol (1 : 1).
7 N. T. McDougal, W. L. Trevellini, S. A. Rodgen, L. T. Kliman
and S. E. Schaus, Adv. Synth. Catal., 2004, 346, 1231–1240.
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1
25, 12094–12095.
Conclusions
1
1 F. Toda, M. Senzaki and R. Kuroda, Chem. Commun., 2002,
0
0
1788–1789.
1
1
,1 -Binaphthyl-2,2 -diol/quinoline adduct (BINOL/QUN) and
0
0
12 S. G. Telfer and R. Kuroda, Coord. Chem. Rev., 2003, 242, 33–
6.
3 E. M. Owusu and A. L. Thompson, Mol. Cryst. Liq. Cryst. Sci.,
015, 607, 50–59.
,1 -binaphthyl-2,2 -diol/isoquinoline adduct (BINOL/ISOQUN)
4
are held by strong hydrogen bonds (O2–H2/O3), (O3–H3/
N1) and (O2–H2/O1), (O1–H1/N1), (O2–H2/O1) respectively.
Computationally optimized BINOL/QUN and BINOL/ISOQUN
conrmed that interaction between BINOL–quinoline and
BINOL–isoquinoline took place through electron transfer and
via hydrogen bonding. It was discovered that the HOMO posi-
tions of BINOL/QUN and BINOL/ISOQUN are localized around
BINOL, while the LUMO is positioned on quinoline and iso-
quinoline. BINOL was hosted on a polymer which was electro-
spun into nanobers. [DBN-co-STY] polymer nanobers
exhibited selectivity for quinoline and isoquinoline in a model
1
1
2
4 G. J. Kemperman, R. de Gelder, F. J. Dommerholt,
P. C. Raemakers-Franken, A. J. H. Klunder and
B. Zwanenburg, J. Chem. Soc., Perkin Trans., 2000, 2, 1425–
1
429.
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943.
1
1
2
2
ꢀ1
17 A. S. Ogunlaja, M. J. Coombes, N. Torto and Z. R. Tshentu,
React. Funct. Polym., 2014, 81, 61–76.
8 J. R. Katzer and R. Sivasubramanian, Catal. Rev.: Sci. Eng.,
simulated fuel with an adsorption capacity of 2.2 and 2.4 mg g
respectively. The adsorption study showed a higher selectivity
towards isoquinoline as compared to quinoline. A total of 95%
and 85% isoquinoline and quinoline was extracted in a model
simulated fuel containing a mixture of naphthalene, 1-benzo-
thiophene, dibenzothiophene, carbazole, isoquinoline and
quinoline (Fig. 16). The higher selectivity towards isoquinoline
as compared to quinoline was attributed to more favourable
electronic properties (HOMO–LUMO properties) of isoquino-
line. Computational analyses showed that carbazole–BINOL
adduct could only be formed via p–p stacking of carbazole and
1
1
2
2
2
2
2
1979, 20, 155–208.
9 G. Krainer, J. Broecker, C. Vargas, J. Fangh ¨a nel and S. Keller,
Anal. Chem., 2012, 84, 10715–10722.
0 A. Cooper, M. A. Nutley and P. Camilleri, Anal. Chem., 1998,
7
0, 5024–5028.
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2
2 S. Leavitt and E. Freire, Curr. Opin. Struct. Biol., 2001, 11,
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0
0
1
,1 -binaphthyl-2,2 -diol (BINOL), and this is understood to be
a weak interaction. This concept shows the ease of separating
isoquinoline and quinoline from similar compounds in fuel.
Acknowledgements
25 X. Wang, E. Matei, A. M. Gronenborn, O. Ramstrom and
M. Yan, Anal. Chem., 2012, 84, 4248–4252.
We are thankful for nancial support provided by Sasol (Pty)
Ltd. The South African National Research Foundation (NRF) is
also acknowledged for funding A. S. Ogunlaja (Green Economy
Postdoctoral Scholarship). The authors thank the Center for
High Performance Computing (CHPC), Cape Town, South
Africa for providing the platform in carrying out the molecular
modelling studies on the Gaussian09 soware.
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39038 | RSC Adv., 2016, 6, 39024–39038
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