SI- Table 1. Selected Physicochemical Properties of P-Type Pharmaceutical Chemicals Used

SI- Table 1. Selected Physicochemical Properties of P-Type Pharmaceutical Chemicals Used

SI- Table 1. Selected physicochemical properties of p-type pharmaceutical chemicals used in this study*

p-type chemical / Structure / Hazardous waste number / Molecular weight / Water solubility / pKa / logKow
Nicotine / / P075 / 162.26 / Completely miscible / 8.5 / 1.2
Epinephrine / / P042 / 183.2 / 0.01g/100mL at 18C / 8.28 / 2.59
Physostigmine / / P204 / 275.34 / 1.33 g/100mL at 20C / 6.12 / 1.6

* D.V. Sweet, 1997, Registry of Toxic Effects of Chemical Substances (RTECS) - Comprehensive Guide to Their RTECS. U.S. Department of Health and Human Services, National Institute of Occupational Safety and Health, Cincinnati, Ohio 45226.

SI Computer Simulations

Combinatorial Screening of Polymer precursors for preparation of p-type chemicals imprinted polymer

To understand nature of interactions between p-type chemicals and the polymer adsorbents, Dell ™ Precision T7500 Workstation was used to run the software Gaussian 4.21 (Gaussian, Inc. Willingford CT, USA). The steps followed for prediction of binding nature in pre-polymer complex:

  1. 2-D chemical structures of the functional monomer (itaconic acid), templates (nicotine, epinephrine and physostigmine) and cross-linking monomers (EGDMA) were prepared, then using molecular builder option 2 D structures were converted to 3-D structures.
  2. The geometric optimization was carried out on the semi-empirical (SE) quantum mechanical approach (PM3 method) to obtain optimized energy structures with aid of Polak – Ribiere algorithm until the root mean square gradient was 0.01; which is the acceptable in molecules optimization.
  3. The binding energy of monomer-template complexes were computed on Haltree-Fock (HF) method with 6-31G basis set in a virtually created 18.6Ǻ solvent (water) box. The minimum binding energies between the optimized conformations of 1: 1 ratio of template–monomer complexes was computed. The interaction energy between a pair of molecules in the solvent box was calculated according to following equation:

E = E (T-F-X complex) – ∑ E(T)(F)(X)

where E, binding energy and E interaction energy are in kcal/mol; T, template (p-type chemical); F, functional monomer (itaconic acid) and X, cross linking monomer (EGDMA)

  1. This step was further extended to determine template accommodation potential of the functional monomer using confirmation optimization the most stable template–monomer complexes based on interaction energy scores.

For preparation of the imprinted polymer an appropriate functional monomer is very importance to have high affinity for the template. The functional monomer suitableto template p-type chemicals; where nicotine was selected as the model molecule and then the virtual library of functional monomers by computing the interaction energies nicotine and functional monomers. The software Gaussian 4.21 ver. was used in PM-3 semi-empirical mode, and the computed energies are given in Table SI.1.

Table SI-1: Interaction energies for functional monomer and nicotine

Functional Monomers / Interaction Energy
(E) kcal/mol
1-vinylimidazole / -0.026
2-vinylpyridine / -0.016
4-ethylstyrene / -0.036
4-vinylpyridine / -0.017
acrylamide / -0.075
acrylamido-2-methyl-1-propane- sulphonic acid / 0.046
acrylic acid / -0.088
acrylonitrile / 0.103
Itaconicacid / -0.512
Methacrylamide / 0.082
Methacrylic acid / -0.099
Methyl Methacrylic acid / -0.033
N-(2-aminethyl)-methacrylamide / -0.084
p-vinylbenzoic acid / 0.014
Styrene / -0.072
trans-3-(3-pyridyl)-acrylic acid / 0.041
Trifluoromethacrylic acid / 0.266
Urocanic ethyl ester / 0.133

Interaction energy is the measure of monomer-template stability. The monomer with high interaction energy tends to have stable pre-polymer complex of nicotine and functional monomer. Such complexes result in covalent imprinted polymers and from these polymers removal of template after rebinding will be difficult [43]. Monomers with lower interaction energies were preferred for creation of non-covalent imprint polymers. These non-covalent imprinted polymers have reasonable binding capacity and excellent molecular recognition properties. Nuclear magnetic resonance (NMR) studies on nicotine in literature have indicated that nicotine is capable of interacting with MAA [1]. Based on computer simulations carried out in this study, two monomers namely itaconic acid (IA) and methacrylic acid (MAA), were chosen based on interaction energies for preparation of nicotine MIPs. From the computationally derived best functional monomers, a suitable cross-linker was selected following similar procedure discussed above. Interaction energies between template-monomer complex and cross-linker given in the results indicated that EGDMA and TRIM could form less interaction with itaconic acid and MAA (Fig.SI.1).

Table SI-2: Interaction energies for cross-linkers

Template /Monomer / Cross-linker / Interaction Energy
(E) kcal/mol
Nicotine/ Itaconic acid / Ethylene glycol dimethacrylate (EGDMA) / -0.937
Pentaerythritoltetraacrylate (PETEA) / -0.668
Pentaerythritoltriacrylate (PETRA) / -0.805
Trimethylpropanetrimethacrylate (TRIM) / -0.914
Nicotine/Methacrylic acid / Ethylene glycol dimethacrylate (EGDMA) / -0.176
Pentaerythritoltetraacrylate / -0.005
Pentaerythritoltriacrylate (PETRA) / -0.019
Trimethylpropanetrimethacrylate (TRIM) / -0.381

Fig.SI.1. HyperChem simulated interactions between nicotine and (a) itaconic acid and (b) methacrylic acid

Thus EGDMA was selected as best cross-linker for nicotine-itaconic acid MIP while TRIM for nicotine-methacrylic acid MIP. In general, cross-linking monomer calculations are 5 times more than functional monomer and hence cross-linking monomer shows dominant role in forming 3D architecture of the binding site in imprinted polymers. Here the interaction between cross-linker and functional monomer-template is very crucial to decide binding site properties such as covalent or non-covalent type imprints and the blend of cross-linker also provides physical strength and feudality to the polymer architecture.

In non-covalent imprinting process, the formation of template-monomer complex is very important for the MIP to have better capacity and selectivity. The formation of Nic-IA and Nic-MAA complexes is the key step in preparation of MIP selective for nicotine. Solvent that interacts stronglywith nicotine leads to weaker Nic-IA or Nic-MAA complexes formation. The interaction energies (ΔE) of nicotine in different solvent were calculated to characterize the strength of their respective interaction with the solvent. The solvent of strong affinity to the template molecule have potential to hinder the formation of hydrogen bond network between the template and the monomer [133]. Nicotine interaction with monomers was optimized in various solvents and interaction energies were computed. Similarly computations were carried out on itaconic acid as well as methacrylic acid which were used as monomers. Table SI-3 represents the interaction energies of nicotine, itaconic acid and methacrylic acid studied with various solvents in virtual solvent environment of Hyperchem8.0 software.

Table SI-3: Computational selection of solvent for nicotine imprinting

Solvents / Dielectric constant / Polarity Index / Interaction energies ΔE (Kcal/mol)
Nicotine / Itaconic acid / Methacrylic acid
Acetonitrile / 37.5 / 5.8 / -1221366.65 / -2558281.96 / -2552099.28
Dichloromethane / 8.9 / 3.1 / -642229.52 / -1607760.84 / -1609089.61
Chloroform / 4.8 / 4.1 / 6955.787 / 6873.171 / 6125.551
Toluene / 2.38 / 2.4 / 52399.45 / 32798.023 / 41205.288

Based on the interaction energy criteria two of the solvents were selected for the preparation of nicotine MIPs. The amount of solvent used for synthesis also affects the imprinting process. Low volume of solvent used causes the polymer to precipitate early and would not form good MIP. A high volume of solvent would dilute the solution and cause defects in the imprinting site. The optimized volume of solvent used was 5ml. It has already been studied that MIP resulted from synthesis with a volume of solvent below 5ml, the adsorption capacity of polymers decreases with decrease in volume of solvent and at high volume above 5ml the adsorption capacity decreases with increase in volume of solvent.

Fig. SI.2: Initiation of polymerization

The termination of polymerization may take place by combination, disproportionation and chain transfer. Nitrogen purging is very important for chain termination to occur since the presence of oxygen can initiate another chain somewhere else along the length of the polymer[3].Nicotine forms hydrogen bonds with carboxyl groups in methacrylic acid and Itaconic acid. The interaction takes place between basic pyrrolidine-N and pyridine-N of nicotine and carboxyl groups in the monomers. [4], this is represented in the Fig SI-3. These interactions between nicotine and IA and MAA simulated in Gaussian 4.21 ver. were depicted in Fig SI-4.Along with nicotine MIPs, non-imprinted polymers (NIPs) were prepared to compare polymer capacity and selectivity. The nicotine MIPs formed were colored with yellow while the non-imprinted polymers were colorless.

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Fig.SI.3: Schematic representation of nicotine imprinting using methacrylic acid as functional monomer

Fig.SI.4: Schematic representation of the molecular imprinting of nicotine showing binding cavity dimensions and functional groups orientation

SI-1