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BY 4.0 license Open Access Published by De Gruyter Open Access December 31, 2019

Cyclodextrin potentiometric sensors based on selective recognition sites for procainamide: Comparative and theoretical study

  • Haitham AlRabiah , Atef Homoda , Ahmed Bakheit and Gamal AE Mostafa EMAIL logo
From the journal Open Chemistry

Abstract

Polyvinyl chloride (PVC) membrane sensors were constructed and developed for the determination of procainamide HCl (PR). Three membrane sensors incorporating α-, β- and γ- cyclodextrin (CD) as ionophores with potassium tetrakis (4-chlorophenyl) borate (KTpClPB) as the ion additive, o-nitro phenyl ether (o-NPOE) as the plasticizer and a PVC matrix. The reaction mechanisms were based on inclusion complexes. The developed α- and β- CD sensors exhibited near-Nernstian profile, whereas γ- CD showed a non-Nernstian response. At pH 4 -8, the sensors exhibited a calibration range for PR of 10-3 to 10−6, and the detection limits were 2.40 × 10-6, 2.12 × 10-6, 2.40 × 10-6 for α-, β- and γ- CD sensors, respectively. Interference was investigated by studying the selectivity coefficient values of the test sensors, which indicated that the methods were free from interference from investigated species. The determination of PR exhibited high recovery and favorable relative standard deviation using the investigated sensors. The sensors were subsequently used for the quantification of PR in a pharmaceutical formulation and the potentiometric results agreed with those of a spectrophotometric method. A molecular docking (MD) study was used to predict the structure of the inclusion complexes of PR (guest) and α- or β- or γ-CD (host). The study results indicated that the formed complexes were stable with sufficient binding energy.

1 Introduction

Procainamide is anti-arrhythmic drug indicated for the treatment of cardiac arrhythmias. It belongs to class IA and has been widely used for more than 60 years [1, 2]. Its chemical structure is p-Amino-N-[2-(diethylamino) ethyl] benzamide monohydrochloride (Figure 1). Procainamide blocks the flow of sodium into the cell (sodium channel blocker) thus inhibiting nerve signals by preventing the flow of ions necessary to initiate and connect pulses. Therefore, it also acts as a local anesthesia. PR has additional therapeutic effects, including anti-inflammatory effects and decreasing the effects of toxins on the liver and kidneys [3, 4].

Figure 1 Chemical structure of procainamide HCl.
Figure 1

Chemical structure of procainamide HCl.

Different analytical methods have been published for the determination of PR, including spectrophotometry [5, 6] spectrofluorometry [7, 8] voltammetry [9], high performance liquid chromatography [10], capillary electrophoresis [11] and gas chromatography [12]. Only one potentiometric method was developed for the determination of procainamide [13]. The published method [13] was based on using of sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl) phenyborate as the ion exchanger and 2-fluoro-2`-nitrodiphenyl ether as the membrane solvent in a PVC membrane matrix. Ionophore-based ion selective electrodes have greatly improved the response, selectivity, and detection limit of sensors compared with ion-pair or ion-exchange based sensors, in addition to the major advantage of long-term stability [14]. The detection limit using the proposed method was 0.6 mg/ml compared with reported method (1.5 mg/ml) [13]. Potentiometric sensors based on PVC membranes have numerous advantages; they are rapid, simple, sensitive, accurate, precise, economical, portable and have a wide range of applications relevant to different fields of analysis [15, 16, 17].

Cyclodextrins (CD) are neutral cyclic oligosaccharides that contain 6-, 7-, or 8-glucose units. CDs have various applications in pharmaceutical analysis and have been used increasingly in determining dissolution rates, chemical stability of drugs, and absorption efficiency, as well as their application in increasing the stability of pharmaceutical compounds compared with non-complexed drugs [16, 17, 18, 19]. CD molecules and related groups are characterized by a hydrophobic inner cavity and a hydrophilic outer surface, which allow them to easily form an inclusion complex [20, 21] with a large number of molecules, and these formulations have been approved for marketing in Japan, Europe, and the US.

Several studies have reported on the progress and application of potentiometric sensors for the quantification of a wide variety of drugs based on selective host-guest inclusion complexes using CD as electroactive materials (ionophores) for the assay of different drugs [22, 23, 24]. The development of inclusion complexes between CD (host) and drugs (guest) is established based on non-covalent interactions, which include hydrogen bonding, electrostatic interactions, van der Waals forces and dipole-dipole interactions, which may be involved in host-guest binding [25].

This study aimed to develop novel selective CD-modified sensors for the quantification of PR. The three sensors were constructed using CD as the electroactive materials (ionophores) in a PVC matrix with potassium tetrakis (4-chlorophenyl) borate as an ionic additive. These new PR sensors were constructed using α-CD, β-CD and γ-CD and labeled as Sensor 1, 2 and 3, respectively. The developed sensors are reported for the first time for the determination of PR in bulk and in its dosage form. Finally, molecular modelling was conducted to elucidate the characteristics of the host-guest interactions.

2 Experimental

2.1 Reagents and materials

All reagents were of analytical grade. Double distilled water was used in all experiments, as required. High molecular weight PVC powder, dioctyl phthalate (DOP), o-nitrophenyl octylether (NPOE), and tetrahydrofuran (THF) (all of >99% purity) and PR were acquired from Aldrich (Steinheim, Germany). Potassium tetrakis (4-chlorophenyl) borate, α-CD, β-CD and γ-CD were purchased from BDH (Poole, England). Procainamide injection (500 mg/ml) was the product of Nexus Pharmaceuticals Inc., Vernon Hills, IL, USA. A standard stock solution of PR (1×10-2 M) was prepared in water, and then five working solutions (1×10−2 -1×10−6 M) were further arranged by serial dilution.

2.2 Instruments

Potentiometric measurements were performed using a Wissenschaftlich-Technische Werkstaetten pH/mV meter (model 523; Weilheim, Germany) and an Orion double junction (Ag/AgCl reference electrode; model 90-02). The pH of the test solution was recorded using a glass pH electrode (Orion 81-02).2.3.

2.3 Preparation of the procainamide PVC membrane sensors

The ionophore PVC sensors were prepared according previously reported methods [15]. Briefly, the required amount of α-CD, β-CD or γ-CD (ionophores) was mixed with KTpClPB (ionic additive) and PVC powder. The plasticizer DOP or NPOE was added to the mixture and thoroughly mixed, followed by the addition of 5 ml of THF to 5 cm diameter Petri dishes and all the components were thoroughly mixed again. The mixed constituents were left overnight to enable the sensor membrane to form. The PVC membranes were then segmented and pasted on polyethylene tubes using THF. The electrode bodies were connected to a plastic tube that was pasted on the PVC membrane and the electrodes were filled with a mixture of 1×10−2 M PR and KCl [16, 17]. The working electrode was conditioned by insertion into 0.01 M aqueous PR solution for approximately 2 h before use. After completing the experiments, the indicator electrode was kept in the PR solution.

2.4 Calibration procedure

The PR PVC sensors were calibrated by inserting the electrodes (indicator and reference) into the electrochemical cell containing sodium acetate (9 ml). Subsequently, 1 ml PR (1×10-5-1×10-2 M) was added to obtain final PR concentrations of between 10−3 and 10−6 M. After each addition, the solution was continuously stirred, and the potential of the electrode (E, mV) was noted when the potential was constant. A calibration curve was constructed by plotting the potential readings against -log [PR] and the obtained graph was used to quantify unknown PR concentrations.

2.5 Dose determination

Three PR injection ampules were mixed with a suitable amount of water in a 25 ml measuring flask, shaken thoroughly and the volume was made up with water. An appropriate volume of the resulting solution was diluted in another 50 ml measuring flask and the pH was adjusted using 0.05 M sodium acetate and completed with distilled water up to the mark. An appropriate volume of the previous solution was inserted into the electrochemical cell. The (E, mV) of the proposed sensors of the test solution was determined using the investigated PR- PVC sensors. The concentration was estimated from the previously constructed calibration curve.

2.6 Molecular docking (MD)

A MD study for PR with α-, β- and γ-CD complexes was performed using Molecular Operating Environment 2015.10 (Chemical Computing Group, Montreal, QC, Canada) [26]. The three dimensional (3D) structure of CD was extracted from the protein complex of SusE with α-CD (PDB code: 4FEM) [27], amylose helices with β-CD (PDB code: 3CK8) and Escherichia coli branching enzyme with γ-CD (PDB code: 5E70)[28]. The MOE Quick Prep protocol was used to add hydrogen atoms and minimize the structure of PR, which was built using the MOE Builder. Its potential energy was minimized by applying the proper force field AMBER10 (University of California, San Francisco, CA, USA) [29]. The default docking protocol implemented in MOE was used [30].

2.7 Molecular dynamic simulation (MDS)

MDS was performed using MOE 20015-10 software [26] and was followed by the selection of force field AMBER12 using the specific calculation for solvation energy with Bornimplisit solvation. The energy of the system was decreased to the relative mean standard deviation, gradient 0.1 and the partial charge option in MOE 2015-10 was utilized to adjust the total charge of the protein. All the parameters were adjusted to default values for the number of atoms/volume/temperature (N/V/T) and algorithm at Nose Poincare-Anderson (NPA) for creating the ensemble trajectory. After each 0.5 picoseconds (ps), the velocity, position and acceleration were saved. Water Soak option with soak mode BOX and layer width 5 prior were used to add water molecules to the MDS. In twenty ps, the system was heated from 0 to 300 K up to production time 1300 ps, followed by cooling back to 0 K in twenty ps.

3 Results and Discussion

3.1 Reaction mechanism

The response of the investigated CDs used as ionophores in the PVC membrane matrix was based on the molecular recognition between host and guest. The interactions between the host (CD) and guest (PR) were mainly facilitated by the hydrophobic interactions between the PR and the hydrophobic cavity of the CD receptors [31]. The formation of inclusion complexes between α-CD, β-CD and γ-CD (six, seven, and eight α-D-glucose units), respectively, with truncated cylindrical molecular shapes providing a hydrophobic cavity [30]. Numerous organic and inorganic compounds can form inclusion complexes with CD [20, 21]. The most well-known substances to forms inclusion-complexes with CD are pharmaceutical compounds [20, 21]. The inclusion complexes between CD (host) and drugs (guest) are based on different types of interactions, which include hydrogen bonding, van der Waals forces and dipole-dipole interactions [25].

The addition of the additives to the membrane composition plays an important role by increasing the ionic site of the membrane and enhancing the selectivity of the membrane sensors [33, 35]. Therefore, the selectivity and sensitivity of the sensors were increased using the ionic additive KTpClPB, which was added to the membrane composition at a ratio of 1: 1 to the ionophore (CD).

3.2 Effect of the plasticizer

The PR PVC sensors based on CD with different plasticizers, DOP and NPOE, were assessed to investigate the performance of the plasticizer. It is well recognized that the plasticizer is an important constituent of the PVC membrane sensor [15] and the structure of PVC-based sensors essentially requires the use of a plasticizer, which is a fluidizer that allows homogenous dissolution and diffusion mobility of the ionophores. These effects lower the detection limit and improve both the selectivity and sensitivity of membrane sensors. The solubility of the membranes developed using both plasticizers was approximately the same. NPOE has a high polarity (ε = 24) and provided a good potentiometric response compared with the low polarity DOP (ε = 7); 54 to 55 mV compared with ~50 mV. Therefore, NPOE was used for all the subsequent investigations.

3.3 Effect of pH

The behavioral response of the PR sensors were examined in different pH media. The effect of pH is graphically presented in Figure 2. The pH value of the PR solution was controlled using HCl or NaOH (very dilute solutions). The E, mV of the electrode response of the test solution was recorded against the pH change and the values were plotted. Figure 2 illustrates that the slope (E, mV) of the investigated sensors (per 10-fold concentration change) was constant ~ 55, ~54, or 30.5 mV for α-CD, β-CD, or γ-CD, respectively, at pH 4-8. In an alkaline medium of pH more than 8 (pKa 9.2) [30], the potential decreased because of the increase in the concentration of un-protonated PR species.

Figure 2 The effect of pH on the potential response of the PR sensors.
Figure 2

The effect of pH on the potential response of the PR sensors.

Response time [36], the time required for the electrode to reach a stable reading, is an important factor for electrode characterization. After inserting the electrode in different concentrations (tenfold) of PR, the response time either increases or decreases. At higher PR concentrations, the response time was short compared with low concentrations. We observed that the average response time was 20 s for the PR sensors. The lifetime of the membranes is defined as the time interval from the construction of the electrode until one parameter of the characteristic response is changed. The lifelimit of the sensors was more than 40 days, during which the analytical characterization of the electrodes was unchanged.

3.4 Effect of interference

The selectivity coefficients were estimated according to IUPAC guidelines using separate or mixed solution methods [36, 37]. Different inorganic ions and organic species were examined as interfering substances to study the selectivity of the developed sensors. The selectivity coefficients based on separate solution method was calculated using the following equation:

logKA,Bpot=EBEAS+[1ZAZB]logaA

where logKA,Bpotis the selectivity coefficient, EA and EB are the potentials of the investigated sensors when inserted in a solution of procainamide and the interfering species (equal concentration), respectively. While aA is the activity of procainamide, and ZA and ZB are the charges of PR and the interfering species, respectively.

On the other hand, the selectivity coefficient measured by mixed-solution method was calculated from the equation:

KA,Bpot=(a`AaA)aB

where a`Ais the known concentration of PR added to an unknown concentration aA. The change in potential (ᐃE) was recorded. Another test experiment used a solution with a known concentration of interfering ion (AB) added to a fixed concentration of PR until the same potential is reached. The results were recorded in Table 1. The low values of selectivity coefficient indicate that the investigated method is free from interference. The effect of different ions are presented in Figure 3

Figure 3 The effect of interference ions on the procainamide sensors.
Figure 3

The effect of interference ions on the procainamide sensors.

Table 1

Selectivity coefficients of the PR- PVC sensors.

Interferent, JKRP,BpotSensor 1KRP,BpotSensor 2KRP,BpotSensor 3
Na+9.3×10-35.7×10-35×10-3
K+9.1×10-35.1×10-35.1×10-3
Ca2+9.4×10-35.3×10-35.2×10-3
Fe2+9.3×10-35.4×10-34.9×10-3
Phosphate9.1×10-33×10-33.2×10-3
Acetate9.2×10-33.1×10-32.3×10-3
Benzoate9.4×10-33.1×10-32.4×10-3
Citrate9.1×10-33.1×10-32.5×10-3
Magnesium stearate9.0×10-35.6×10-35.1×10-3
Caffeine*9.2×10-35.7×10-35.01×10-3
Glucose*9.4×10-35.4×10-34.9×10-3
Lactose monohydrate*9.3×10-35.4×10-34.8×10-3
Starch*9.1×10-35.6×10-34.8×10-3
Microcrystalline cellulose*9.5×10-35.7×10-34.7×10-3
  1. *The selectivity coefficient was calculated by mixed solution method.

3.5 Sensors characteristics

The analytical classification of the PR-PVC sensors based on the use of the α-CD, β-CD, or γ-CD (as sensing materials), DOP (as a plasticizer) and PVC (as matrix) were assessed according to IUPAC guidelines [37]. The data shown in Table 2 present the analytical characteristics of the proposed methods. The least squares equations of the standardization curves were presented as follows:

Table 2

Analytical characteristics of the procainamide sensors.

ParameterSensor 1( α-CD)Sensor 2 (β-CD)Sensor 3 (γ-CD)
Slope, (mV/ decade)*55.0 ± 0.554.0 ± 0.530.5 ± 0.5
Intercept (E0), mV *222.3± 0.5222.0 ± 0.596.5 ± 0.5
Calibration range, M1×10-3- 8×10-61×10-3- 7×10-61×10-3 - 8×10-6
Correlation Coefficient, (r2)0.9990.9990.997
LOQ, M8.0×10-67.0×10-68×10-6
LOD, M2.4×10-62.12×10-62.4×10-6
Response time of 1×10-3 M solution, (s )20 ± 0.520 ± 0.520 ± 0.5
Working pH range4-84- 84- 8
  1. *± RSD (Relative standard deviation), n (number of replicates) = 5

E(mV)=slog[PR]+intercept

where E is the potential of the sensor (mV), S is the slope (55 ± 0.5, 54 ± 0.5 and 30.5± 0.5 mV/decade, respectively) and the intercept (222.3 ± 0.5, 222.0 ± 0.5 and 96.5 ± 0.5 for α-CD, or β-CD or γ-CD, respectively).

3.6 Validity of the PR-Sensors

3.6.1 The limit of quantification (LOQ) and detection (LOD)

The potential of the electrodes (n = 5) was plotted against PR concentration. The relationship between the concentration (M) and the potential (E, mV) was logarithmic as presented in the next equation:

x=slog[RP]+y

where x is the potential (E, mV), S is the slope, and Y is the intercept. At pH 4-8, the sensors showed a calibration range of 1×10−3 to 8.0×10−6, 1×10−3 to 7×10−6 , and 1×10−3 to 8×10−6 M for α-CD, or β-CD or γ-CD, respectively. According to IUPAC recommendations [37], LOD of procainamide was assessed according to the concentration of procainamide related the intersect of extrapolated lines of the calibration graph, whereas LOQ = 3.3 LOD. LOD was 2.4×10-6, 2.12×10-6 and 2.4×10-6 whereas LOQ was 8.0×10-6, 7.0×10-6 and 8.0×10-6 for sensor 1, 2 and 3, respectively (Table 2).

3.6.2 Accuracy and precision

The accuracy and precision of the proposed method were investigated [38] by assaying PR at 2.72 μg/ml during a single day and over a 3 day period. The intrα- and inter-day precision of five replicates was estimated. The calibration graphs for the examined sensors were used to calculate the known concentration of PR. The closeness of the added concentration to measured values was expressed as recovery %, whereas the repeatability (precision) was expressed as RSD%. The accuracy of the developed sensors was > 99% while the RSD% values were < 3.32% as presented in Table 3.

Table 3

Accuracy and precision of the PR-PVC sensors.

ParametersPR (2.72μg/ml ) intra-dayPR (2.72μg/ml ) inter-day
Sensor1Sensor 2Sensor 3Sensor 1Sensor 2Sensor 3
R, %99.099.510099.0102.599.5
SD0.570.090.820.550.1300.112
RSD, %1.03.323.1771.14.6624.138
Slope55.554.030.555.555.030.0
Correlation coefficient0.9980.9990.9970.9980.9980.997
  1. n=5 ± RSD.

    R %: added /found × 100%

    RSD: (SD/mean) × 100%

3.6.3 Recovery

The recovery of PR in the recommended acetate buffer was calculated. The recovery% of the determination was calculated according the following equation.

Recovery,%=(measuredconcentraion/addedconcentration)×100

The recovery % of procainamide (2.72 µg/ml) using the proposed sensors was found to be 99%, 99.5% and 100% for the developed sensors (1, 2 and 3, respectively) (Table 3).

3.6.4 Ruggedness

The ruggedness of the investigated methods was investigated [38] through the analysis of PR using two operators and two different devices on different days. The results indicated that the investigated sensors performed the analysis with very similar results; RSD < 3.2% was obtained for the assay on the same day and on different days.

3.6.5 Robustness

The robustness of the methods was investigated [38] by studying the optimum conditions of the potentiometric method, e.g. response time and pH, which affect the electrode response. The data acquired under optimum conditions suggest that the methods were fairly robust. The pH value of the measurement medium was in the range of 4-8 and the optimum pH value was 7 using 0.05 M sodium acetate.

3.6.6 Thermal stability

Effect of temperature on the response behavior of the sensors were examined by measuring the potential against the change of temperature in the range of 25°C-40°C using two concentrations of procainamide (1×10-3 M and 1×10-4 M). It was observed that with increase in the temperature the potential increased, however, the sensor behavior (slope, response time, detection limit) was not affected by the change of temperature, indicating that a good thermal stability of the proposed sensors (Figure 4).

Figure 4 Effect of temperature on the developed sensors.
Figure 4

Effect of temperature on the developed sensors.

3.7 Application of PR-PVC sensors

The developed sensors were used to determine PR in pure solutions and pharmaceutical formulations. The pure PR (2.17-272 µg/ml) was determined in five preparations using the developed sensors and the average recovery was 98.5%, 99.12%, and 98.58% with RSD (%) values of 1.4%, 3.075%, and 2.825% for α-CD, β-CD, and γ-CD sensors, respectively (Table 4). The quantification of PR in its dosage form used a typical recovery of 99%, 98%, and 98.3% with RSD values of 1.1%, 2.3%, and 2.5% for α-CD, β-CD, and γ-CD, respectively (Table 5). The assay of PR in its pharmaceutical form was compared with that obtained by a spectrophotometric method [6] as presented in Table 5. The spectrophotometric method was based on the reaction between PR and 7,7,8,8-tetracyanoquinodimethane in 0.15 M sodium carbonate, which produced a yellow color that was measured at 473 nm [6].

Table 4

Determinations of PR using the PR-PVC sensors.

Added (μg/ml)Recovery %*± RSD
Sensor1Sensor 2Sensor 3
2.1798.0 ± 1.697.0 ± 3.297.7 ± 3.3
2.7298.5 ± 1.5100.6 ±3.198.0 ± 3.2
27.298.5 ± 1.399.07 ± 2.999.23 ± 2.9
272.099.0 ± 1.299.8 ± 2.899.4 ± 2.9
  1. * n= 5 ± RSD.

    *R %, recovery percentage: added /found × 100%

    -RSD: expressed as % RSD = (SD/mean) × 100%

Table 5

Determination of procainamide in its pharmaceutical formulation using the procainamide sensors.

PreparationProcainamide (nominal, value)Proposed method* R, % (RSD, %)Spectrophotometry [ 6] R, % (RSD, %)
Sensor 1sensor 2sensor 3
500 mg500 mg99.0 (1. 1)98.0 (2.3)98.3(2.5)98.0 (2.5)
T test (3.36 )0.840.000.19
F test (6.38)0.20.840.99
  1. *n=5

    *R %, added concentration /found concentration × 100%

    -RSD Expressed as % RSD = (SD/mean) × 100%

Statistical evaluation of the assay of PR by the developed sensors and the published spectrophotometric method revealed no significant difference between the developed sensors and the published method in terms of accuracy and precision using null hypothesis method for p cutoff of 0.05 and n = 5 (Table 5). T = 0.75, 0.00, 0.02, which is less than the tabulated value (3.36) [37]. In addition, F = 0.2, 0.84 and 0.99 which is less than the tabulated value (6.38) [37].

3.8 Molecular docking studies

3.8.1 Molecular docking

For more insights into the binding mechanisms and parameters for PR and each CD, MD was performed between them. MDS is the optimal process to predict at the molecular level the orientation of the drug (guest), molecular fitting, and interactions with the host’s (CDs) hydrophobic cavity and hydrophilic surface [39]. Figure 5 illustrates the MD results. The binding constants calculated for PR with α-, β-, and γ-CDs complexes were -5.58, -5.36, -4.93 kcal/mol, respectively, and the binding force of PR with the CDs was in this order: γ-CD>β-CD>α-CD. The H-bonding (electrostatic interactions) between the carboxylate group of PR and the hydroxyl groups (OH) (hydrophilic rim) of α-CD (Figure 5a and c) were registered. Although the α-CD cavity was of a size insufficient to host the [2-(diethylamino)ethyl] benzamide of PR, the methyl diethyl amine was completely outside the CD cavity, and as a result, a complex with lower stability and a binding constant of -5.58 kcal/mol was obtained. The data agreed well with molecular dynamic simulation studies in which the PR melting peak appeared for PR and α-CD mixture, pointing to a physicochemical interaction.

Figure 5 The predicted orientations and binding interactions of procainamide within the cavity of three cyclodextrins (a) α-CD, (b) β-CD, and (c) γ-CD from the table view of the wide edge (a, d, and h), side view (b. e and i), and as stick molecular depiction (c, f and g). Hydrogen bonds and hydrophobic interactions are demonstrated as magenta and green dashed lines, respectively.
Figure 5

The predicted orientations and binding interactions of procainamide within the cavity of three cyclodextrins (a) α-CD, (b) β-CD, and (c) γ-CD from the table view of the wide edge (a, d, and h), side view (b. e and i), and as stick molecular depiction (c, f and g). Hydrogen bonds and hydrophobic interactions are demonstrated as magenta and green dashed lines, respectively.

Conversely, γ- and β-CDs had cavities at suitable sizes for incorporating PR in their hydrophobic cavity, and the methyldiethylamine of PR was fully integrated into γ-and β-CDs. The size of the β-CD cavity was greater than that of α-CD and it contained an extra extension from the hydroxypropyl substitution by comparison to α-CD. The three hydrogen bonds also likely contributed to a very stable complex with β-CDs with a binding energy of -5.36 kcal/mol. The cavity of γ-CD was of adequate size to host PR with a hydrogen bond and three hydrophobic interactions, which produced a relatively stable complex that had a binding energy of -4.93 kcal/mol (Figure 5g). Although the cavity size of β-CD was greater compared with α-CD, the phenyl amine ring could not be completely incorporated within it (Figure 5e) and parts of this ring were outside the cavity (Figure 5e). However, the [2-(diethylamino) ethyl] benzamide chain formed three hydrogen bonds between the two amine groups and carbonyl groups of PR as shown in Figure 5f. This led to a highly stable complex that had a binding energy of -5.36 kcal/mol.

3.8.2 Molecular dynamic simulation (MDS)

The MDS tool of MOE 2015 was used to develop and fine-tune the model [26]. Briefly, at the start, model saturation with partial charges was performed, followed by decreasing the energy 0.1 RMS with the designated force field AMBER 12 [40]. In the NVT ensemble, N stands for number of atoms, V for volume and T for temperature. The MDS was performed with these parameters kept constant [41]. To create an accurate simulation trajectories, the simulation used NPT algorithm, as a highly accurate and sensitive method that uses the NPA method to create theoretically correct NVE, NVT, NPH, and NPT ensembles; N, V, T, H, E, P indicate number of atoms, volume, temperature, enthalpy, energy, and pressure, respectively. The MDS parameters were controlled at standard conditions (nominal temperature fixed at 0 K to start the simulation and setting to 20 K for heating; the system was cooled for 20 ps to obtain stable bond energies and then the simulation was run for 1300 ps [42]). This process indicated the stability of PR with α-, β-, and γ-CD at control conditions. The MDS results can be interpreted by selection of the potential energy plot, created by graphical representation of conformations over time. The acquired conformations described the 3D structures of α-, β-, and γ-CD, which could be altered without shifting the covalent bonds. Figures 6 and 7 present potential energy plots of the α-, β-, and γ-CD conformation versus time. The motion dynamics data sheet is presented in Table 6.

Figure 6 Structure of procainamide and α-, β-, or γ-CD inclusion complex.
Figure 6

Structure of procainamide and α-, β-, or γ-CD inclusion complex.

Figure 7 Structure of β-CD and its oligosaccharide unit.
Figure 7

Structure of β-CD and its oligosaccharide unit.

Table 6

Motion dynamics data sheet.

InitialFinalaverageStd. Dev.
α-CDThe potential energy Ukcal/mol.-9539.84-9885.14-8151.78179.46
The kinetic energy K(v)kcal/mol.272.55101.0381371.03139.44
The instantaneous temperatureKelvin58.5521.71294.5329.95
β- CDThe potential energy Ukcal/mol.-16063.28-16818.25-13945.5299.637
The kinetic energy K(v)kcal/mol.399.38171.642261.05228.36
The instantaneous temperatureKelvin52.0722.38294.8629.403
γ- CDThe potential energy Ukcal/mol.-16948.93-17214.65-14236.7202.2489
The kinetic energy K(v)kcal/mol.306.66176.592349.43150.8703
The instantaneous temperatureKelvin38.8122.35297.412118.47183

3.8.3 Physical stability of inclusion complexes

The MDS of two types of inclusion complexes in an aqueous solution was investigated; in practice, these complexes are normally constructed in aqueous solutions. The trajectories of the host and guest molecules of inclusion complexes (two types) are shown in Supplementary Figure S1( a, b, and c) Although the atomic positions did not show any significant change for Α- and Β-type complexes during the time range of the simulation in vacuum, both complexes showed stability in aqueous solution.

In the case of the α- and γ-type dynamic inclusion structure, both the phenylene amine ring and [2-(diethylamino) ethyl] benzamide groups of PR were integrated into the CD cavity, whereas the methyldiethylamine of PR was in the periphery of the more constricted side of β-CD. This was because of the hydrogen bond interactions (between the amine and carbonyl groups of β-CD) and hydrophobic interaction (between the phenylene group and the solvent). The phenylene ring of PR in the case of the β-type inclusion structure was outside β-CD, indicating that the hydrophobic effect (between the phenylene group and the solvent) was negligible. Furthermore, the [2-(diethylamino) ethyl] benzamide of PR was close to the broader side of β-CD. In addition, the distance between the phenylamine group of PR and CD was larger in the case of the β-type compared with those in the α- and γ-type complexes. This indicates the development of hydrogen bond interaction between the phenylamine of PR and CD (in the case of the α- and γ-type complexes) and the amine and carbonyl groups of the [2-(diethylamino) ethyl] benzamide of PR (in the case of the β-type).

4 Conclusion

PVC membrane sensors for procainamide were developed based on use of α-CD, β-CD, and γ-CD as ionophores, KTpClPB as anionic additive, NPOE as a plasticizer and PVC as a polymeric matrix. The sensors appeared to exhibit high selectivity and sensitivity for procainamide. The sensors displayed a near-Nernstian response with the calibration slope for procainamide of 55 mV and 54 mV/decade in the case of α-CD and β-CD, whereas γ-CD showed a non-Nernstian response of 30.5 mV/decade. The investigated sensors exhibited good selectivity, fast response time (20 sec) and wide working pH 4-8. A broad calibration range for procainamide was achieved (8×10- 6-1 ×10-3, 7×10-6-1×10-3 and 8×10-6-1 ×10-3 M for α-CD, β-CD and γ-CD, respectively) with a life-time of >1 month. The sensors were used for determining procainamide in bulk and pharmaceutical formulation with a good accuracy and precision. The molecular docking study indicated the formation of stable inclusion complexes between procainamide (guest) and CD (host) with sufficient binding energy.



Acknowledgements

The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding the work through the research group project No. RGP-1438-045.

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Received: 2019-04-28
Accepted: 2019-08-07
Published Online: 2019-12-31

© 2019 Haitham AlRabiah et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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