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This is a peer reviewed version of the paper published in ACS Applied Polymer Materials - https://dx.doi.org/10.1021/acsapm.0c00337
Supporting information for
Computationally designed perrhenate ion imprinted polymers for selective trapping of rhenium ions
Samuel Kassahun Mamo, Mathieu Ellie, Mark G. Baron and Jose Gonzalez-Rodriguez*
School of Chemistry, University of Lincoln, United Kingdom, Joseph Banks Laboratories, Green Lane, Lincoln LN6 7DL. United Kingdom. Email: [email protected]. Phone: +441522886878
Table of Contents
1. Experimental…………………………………………………………………………………………………………….......1
1.1. Chemicals and reagents………………………………………………………………………………….…..1
1.2. Materials and software packages…………………………………………………………….........…..1
1.3. Computational methods………………………………………………………………………………….…..2
1.3.1. Functional monomer screening………………………………………………………………..…..2
1.3.2. Optimisation of pre-polymerisation mixture composition………………………...…..2
1.4. Combinatorial screening of porogen composition………………………………………….......3
1.5. Synthetic procedures for perrhenate ion imprinted polymers………………………..…..3
1.6. Optimisation of template removal solution pH……………………………………………… …..4
1.7. Perrhenate ion rebinding and stripping………………………………………………………….…..4
1.8. Optimisation of imprinted polymer particle size……………………………………………. …..5
1.9. Physico-chemical characterisation and selectivity study……………………………………..5
2. Supplementary materials………………………………………………………………………………………….. …..6
3. References………………………………………………………………………………………………………………….…13
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1. Experimental
1.1. Chemicals and reagents
Functional monomers such as 95% pure 4-vinylpyridine, 97% pure 2-vinylpyridine, 99% pure
1-vinylimidazole, and aniline ≥ 99.5% pure ACS reagent were all purchased from Sigma-Aldrich (UK).
Cross-linker 98% pure ethylene glycol dimethylacrylate (EGDMA) and
98% Azobisisobutyronitrile (AIBN) radical initiator both purchased from Sigma-Aldrich (UK) were also
used in the molecular imprinting procedure. Ammonium perrhenate (APR) ≥99% pure (metal basis)
powder purchased from Alfa Aesar (USA) was used to prepare template solution for molecular
imprinting and to prepare standard solutions in the optimisation of the IIP separations. Solvents such
as chloroform, acetonitrile, ethanol, and methanol all HPLC grade purchased from Fisher Scientific
(UK) were employed as pure or mixture porogens. For preparation of alkaline pH template removal
solution, a reagent grade anhydrous sodium hydroxide pellet of ≥98% purity was purchased from
Sigma-Aldrich (UK).
Aqua-regia leach solutions were prepared using laboratory reagent grade S.G 1.18
(~37%) hydrochloric acid, and laboratory reagent grade nitric acid S.G 1.42 (70%) both acids were
purchased from Fisher Scientific (UK), and used as leaching solution for CMSX-4 superalloy scrap. For
precipitation separation of the superalloy component metals from the leach solution 50% caustic
solution, sodium hydroxide 50% (w/w) was purchased from Fisher Scientific (UK).
1.2. Instruments and computational software
Computational modelling studies have been conducted on ASUS® Windows®10 Pro computer
running on Intel®Core™i7-6700K with dual CPU each having processor speed of 4.00 GHZ and
has 16.0 GB of installed RAM. HyperChem™ 8.0.10 Molecular Modelling System for Windows
(Hypercube Inc., USA) computational software running on 64-bit operating system has been used for
molecular dynamics simulations. Density functional theory (DFT) calculations have been carried out
using Spartan ’14™ version 1.1.4 for Windows (Wavefunction Inc., USA).
Inductively coupled plasma-optical emission spectrometer Thermo Scientific™ iCAP™ 7000 ICP-OES
Analyser (Thermo Scientific, UK) in radial mode is used for quantitative determination of rhenium
and component metals of superalloy CMSX-4. PerkinElmer Spectrum 100 ATR-FT-IR spectrometer
(PerkinElmer, USA) is employed to characterise the chemical structure of the imprinted polymer
resins. NITON XL3t XRF analyser (Thermo Scientific, UK) is used for semi-quantitative and qualitative
investigation of the amount of trapped rhenium in IIPs.
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1.3. Computational Methods
1.3.1 Functional monomer screening
Density functional theory (DFT) calculations employed B3LYP hybrid functional with LANL2DZ basis
sets to calculate the binding energies, thermodynamic energy values, orbitals and energies, and
bond order and charges for the complexes formed in vacuum. Functional monomer 3D structures
were obtained from PubChem and ZINC database to ensure the correct geometries are employed for
DFT screening. In addition to the 3D structure of the neutral functional monomers their protonated
3D structures are also screened to evaluate their performance for acidic stripping and rebinding
from the aqueous perrhenate solutions.
1.3.2. Optimisation of the pre-polymerisation mixture
Molecular dynamics (MD) simulations in periodic boundary conditions are employed for 1 ns
followed by conjugate gradient geometry optimisation to determine the ratio of functional
monomer used in the perrhenate ion imprinting as described in the protocol reported by Karim et
al. 1. To optimise the ratio of cross-linker with respect to the functional monomer and template, a
periodic box containing saturated (by adding hydrogen to the polymerising double bonds) pre-
optimised 3D structures of the functional monomer and cross-linker with the perrhenate ion
templates. As reported by previous authors, the saturation step is employed to approximate the
formation of single C-C bonds during polymerisation 2–4. To optimise the total composition of the
pre-polymerisation mixture, periodic boxes with a uniform density of ~0.6 g cm–3 are prepared by
saturating the space around the template with the monomer selected from DFT screening, cross-
linker, and porogen molecules.
NVT-MD simulations are employed on the aforementioned periodic boxes to optimise the ratio of
functional monomer, cross-linker, and porogen to perrhenate ion template. The MD simulation
periodic boxes are initially energy minimised though geometry optimisations using MM+ force-field
conjugate gradient algorithm at RMS gradient of 0.001 kcal (Å mol)–1 to remove bad steric
interactions at the periodic boundary conditions. MD simulations are performed at 343 K, initially by
raising the temperature of the system from 298 K at a temperature step of 2 K for 20 ps of heating
time. At the end of the simulation time, simulated annealing was employed for 20 ps to cool the
system down to the starting temperature at a temperature step of 10 K. Time step size of
0.001 ps has been taken to be constant for all the MD simulations and the system evolves in periodic
boundary conditions at constant temperature with bath relaxation time of 10 ps. The electrostatic
conditions were set up based on bond dipoles and the spherical cut-offs were switched to outer
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radius of 14.35 Å and inner radius of 10.35 Å. The single point energies were calculated based on
bonded, non-bonded, hydrogen-bonded, and electrostatic interactions in addition to the bond angle
and torsion energies.
1.4. Combinatorial screening of porogen
To screen the type and composition of porogen, combinatorial screening approach is employed
using the rhenium trapping capacity of the imprinted polymer as parameter. A porogen and a
mixture of porogen in various proportions are prepared as imprinting media to achieve the highest
perrhenate ion trapping while improving the porosity of the polymer. Seven types of IIPs were
prepared by varying the type and composition of porogen while maintaining all other polymerisation
conditions and amount of porogen, and molar ratios 4-vinyl pyridine, EGDMA, and AIBN constant.
The amount of perrhenate template trapped in the imprinted polymer is quantified using XRF
analysis as the amount of rhenium per kg of the polymer.
1.5. Synthesis of perrhenate ion imprinted polymers
The perrhenate ion template solution (6.0 x 104 mg L–1) is prepared by dissolving ammonium
perrhenate standard in deionized water. The polymerization mixtures are prepared using a range of
porogens, ammonium perrhenate template, EGDMA cross-linker, and the functional monomers
selected from DFT screening. The pre-polymerisation mixture composition is prepared such that the
functional monomer is in a 1:10 and 4:2 molar ratios with the cross-linker EGDMA and the template,
respectively. The porogen amount is kept at 1:1 and the radical initiator at 1:40 molar ratios to the
cross-linker. Bulk polymerisation of the mixture is performed using AIBN radical initiator, as it only
produces one kind of free radical with less side reactions and also demonstrate better stability. The
polymerisation mixtures are mixed in 20 mL Fisherbrand® DIN Crimp Neck, flat bottom clear glass
head-space vials (Fisher Scientific, UK) and vortexed for 1 minute using VWR® Vortex mixer (VWR
international, Belgium), purged with nitrogen gas for 5 minutes using NitroFLow Lab (Parker
filtration and separation, The Netherlands), and finally kept in furnace (Carbolite, UK) at temperature
of 343.15 K for 48 hours. The final bulk polymer resins were ground to the desired particle size using
RETSCH® PM100 planetary oscillating ball mill (Retsch GmbH, Germany), and the ground resins are
separated based on their particle size using RETSCH® AS200 vibratory sieve shaker (Retsch GmbH,
Germany). The ground perrhenate imprinted polymer resins are packed in Oasis® HLB extraction
cartridges (Waters , Ireland), and plugged into 12 port SUPELCO® Visiprep™ SPE Vacuum Manifold
(Sigma-Aldrich, UK) attached to 80 mbar Vacuubrand® vacuum pump (Vacuubrand GmbH,
Germany).
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1.6. Optimisation of template removal solution
To optimise the pH of the template removal solution, the imprinted polymer type, particle size of the
imprinted polymers, and flow rate of template removal solution were kept constant .
The aqueous HCl template removal solutions were prepared at concentrations of 0.1, 1.0, 8.0,
and 10.0 mol L–1, and a 10.0 mL portion of each of these solutions is eluted through the cartridges
packed with the imprinted polymers. The template removal solutions are also prepared in the
alkaline pH range using 0.1 and 1.0 mol L–1 NaOH solution, and the same volume of the template
removal solution have been used in the same fashion as the acidic solutions. The removal cycles
were repeated until the rhenium amount in the imprinted polymer reaches the lowest detectable
amount.
1.7. Rebinding and stripping
The binding capacity of the imprinted polymers prepared in two porogen compositions (1:1 mixtures
of ethanol and methanol with chloroform) have been compared using the rhenium recovery values
obtained after the rebinding step of the separation procedure. Six types of the imprinted polymers
are prepared from three different types of functional monomers in two types
of porogen composition as listed in Table S1.
Table S1. Composition of the imprinting mixture for the synthesis of selected IIPs.Functional Monomer Porogen Cross-linker Template
IIP 1A 4-vinyl pyridine Methanol, Chloroform EGDMA APR
IIP 1B 4-vinyl pyridine Ethanol, Chloroform EGDMA APR
IIP 2A 2-vinyl pyridine Methanol, Chloroform EGDMA APR
IIP 2B 2-vinyl pyridine Ethanol, Chloroform EGDMA APR
IIP 3A 1-vinyl imidazole Methanol, Chloroform EGDMA APR
IIP 3B 1-vinyl imidazole Ethanol, Chloroform EGDMA APR
After successful template removal, 20.0 mL portions of 2.0 × 103 mg L–1 ammonium perrhenate
standard solution are eluted through the imprinted polymer resin packed cartridges until the
maximum binding capacity is achieved. The imprinted polymers are then stripped off the trapped
perrhenate ions, using the previously optimised template removal solution, after each stripping cycle
20.0 mL portions of the eluate are collected and analysed using ICP-OES.
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IIP 1A, IIP 1B, and IIP 3B have been selected for binding kinetics studies where 1.0 g of each type of
the imprinted polymer is weighed in 50.0 mL falcon tube, template was removed by shaking the
polymers in 8.0 mol L–1 HCl solution for 6 hours followed by washing with 50.0 mL of deionised
water. The stripped and washed polymers in each falcon tube are then mixed with 50.0 mL of the
superalloy leach solution which has rhenium concentration of 500.0 mg L–1. The falcon tubes were
then tightly sealed and clamped on to a rolling sample mixer at room temperature. The first four
samples were taken every 30 minutes, three samples were taken every 60 minutes, four samples
taken after every 120 minutes, and the last sample is taken 24 hours after the experiment was
started. During each sampling time, 0.5 mL sample was taken from each falcon tube and diluted to
50.0 mL using deionised water for ICP-OES quantitative analysis. The equilibrium binding capacities
(Qe) were calculated by subtracting the free concentration (Ce) of ReO4- from the initial
concentrations. The dissociation constant (Kd) and the kinetics of the rebinding were estimated by
fitting the results into pseudo-first order and pseudo-second order kinetics using the kinetic model
equations described elsewhere5 .
1.8. Optimisation of particle size
The perrhenate ion imprinted polymer that demonstrated highest binding capacity in the rebinding
studies is selected for particle size optimisation experiments. The bulk polymer is initially crushed to
smaller particle sizes using mortar and pestle before being further crushed down to lower particle
sizes using a planetary ball mill and sieved to separate different particle size ranges. Polymers with
particle sizes less than 350 μm, less than 600 μm, and less than 650 μm are separated, and 1.0 g of
the imprinted polymer from each particle size range is packed in SPE cartridges. The sieves used
were manufactured by Endecotts (London, UK). All were fabricated in stainless steel, 200 mm In
external diameter and compliant with ISO3310-1.
After the template removal and washing steps, 20.0 mL portion of the
standard ammonium perrhenate solution is eluted through the imprinted polymer packed
cartridges. The amount of rhenium in each eluate is quantified via ICP-OES analysis and the elution
cycles continued until the maximum binding capacity is achieved for each imprinted polymer particle
size packed column.
1.9. Selectivity study and polymer characterisation
The selectivity of the imprinted polymer resins is studied by eluting the CMSX-4 superalloy leach
solution at the rebinding stage until the maximum binding capacity is achieved. The superalloy leach
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solution at pH = 8.0 contains the chlorides, oxides, and hydroxides of all the component metals of
the superalloy CMSX-4.
FT-IR -ATR spectroscopic analysis of the perrhenate ion imprinted polymer resins are performed
to investigate the possibility of any change in their chemical structure after each template removal,
rebinding, and stripping treatments. All spectra underwent instrument base line correction and
normalisation to allow for spectra comparison
Swelling capacities of the IIP resins are determined by placing 1.0 g the polymer resin, with optimum
particle size, in a sealed 50.0 mL pre-weighed beakers containing deionised water. After 24 hours of
soaking in deionised water; the supernatant is decanted, the resins are removed from the beakers,
excess water on the resin surface is wiped using filter paper, and weighed to calculate the weight
ratio between the dry and wet resins.
To evaluate the long-term stability of the imprinted polymer resins, the rebinding–stripping
experiments were performed using 1.0 g of the selected polymer resin, with the optimum particle
size, for 5 repeated cycles. Each cycle involved rebinding with standard APR solution until the
maximum binding capacity, followed by the stripping, washing and drying of the imprinted polymer
resin.
2. Supplementary materials
Table S2. Randomised experimental runs for a 3 X 3 Latin square design for the optimisation of the
composition of the pre-polymerisation mixture 4-vinylpyridine.
ExperimentNumber of template
moleculesNumber of EGDMA
moleculesNumber of solvent
molecules1 1 20 40
2 4 20 20
3 2 20 10
4 2 40 40
5 1 10 10
6 1 40 20
7 2 10 20
8 4 10 40
9 4 40 10
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Figure S1. The total interaction energy profile for the optimisation of the pre-polymerisation mixture composition prepared using Latin square experimental design (Table S2) for 10 ns of NVT- MD simulations.
Figure S2. Effect of alkaline and acidic pH template removal on perrhenate binding capacity of IIPs; a) template removal using 20.0 mL portion of each solution, and b) rebinding of the IIPs using 1.0 × 103 mg L-1 ammonium perrhenate standard solution.
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Figure S3. Efficiency of perrhenate ion (quantified as amount of Re) template removal in acidic pH range for template removal solution prepared using HCl solution.
Figure S4. Perrhenate binding capacity (quantified as amount of Re) of IIPs prepared from different types of functional monomers and porogen composition (For triplicate perrhenate ion binding capacity measurements of the IIPs with error bars calculated as ±2σ).
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Figure S5. Selectivity experiments for the different MIPs in the presence of superalloy leach solution component metals. The inset diagram shows the amount of sodium trapped with the perrhenate ions for the different IIPs investigated.
Figure S6. a) Binding kinetics of ReO4- on IIPs for 480 minutes of equilibration with superalloy leach
solution, b) pseudo-second-order and c) pseudo-first-order kinetics model fitting, and d) binding isotherms of ReO4
- on to IIPs at different equilibrium concentrations (Ce).
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Table S3. Binding kinetics parameters for IIPS for perrhenate ion in the leach solution
Polymer kinetics Qmax (mg g-1) Qe (mg g-1) Kd R2
IIP 1APseudo-first order 122.37 24.15 0.0048 min-1 0.9633
Pseudo-second order 122.37 42.37 0.0006 g mg-1 min-1 0.9988
IIP 1BPseudo-first order 112.76 19.87 0.0051 min-1 0.9324
Pseudo-second order 112.76 52.91 0.0005 g mg-1 min-1 0.9985
IIP 3BPseudo-first order 123.25 16.68 0.0048 min-1 0.9365
Pseudo-second order 123.25 62.11 0.0004 g mg-1 min-1 0.9996
Figure S7. FT-IR spectra of the IIPs (IIP 1A) after the 1. imprinting, 2. washing, 3 stripping (template removal), and 4. rebinding stages of perrhenate ion separation using IIP.
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Table S4. Swelling capacity and percentage swelling of the selected IIPs.
M(B+WP)
(g)M(B+DP)
(g)M(B)
(g)M(DP)
(g)M(WP)
(g)
Swelling Capacity(g. g1)
Percentage swelling
MIP 1A 20.59 19.67 18.61 1.00 1.98 0.98 98.0%
MIP 1B 20.42 19.61 18.61 1.00 1.81 0.81 81.0%
MIP 3B 21.06 20.14 19.14 1.00 1.92 0.92 92.0%
M(B+WP) = mass of beaker and wet polymer, M (B+DP) = mass of beaker and dry polymer, M (B) = mass of beaker, M(DP) = mass of dry polymer, and M(WP) = mass of wet polymer.
3. References
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the computational design of high affinity molecularly imprinted polymer synthetic
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methoxyphenyl) ethylamine imprinted polymer: An answer from theoretical and
experimental studies. Talanta. 2014;129:155-164. doi:10.1016/j.talanta.2014.05.029
3. Sobiech M, Zołek T, Lulinski P, Maciejewska D. A computational exploration of
imprinted polymer a ffi nity based on voriconazole metabolites. Analyst.
2014;139:1779-1788. doi:10.1039/c3an01721d
4. Cowen T, Karim K, Piletsky S. Computational approaches in the design of synthetic
receptors: A review. Anal Chim Acta. 2016;936:62-74. doi:10.1016/j.aca.2016.07.027
5. Cai X, Li J, Zhang Z, Yang F, Dong R, Chen L. Novel Pb2+ ion imprinted polymers based
on ionic interaction via synergy of dual functional monomers for selective solid-phase
extraction of Pb2+ in water samples. ACS Appl Mater Interfaces. 2014;6(1):305-313.
doi:10.1021/am4042405
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