Design and preparation of nanoarchitectonics of LDH/polymer composite with particular morphology as catalyst for green synthesis of imidazole derivatives

This paper was designed and prepared a new nanoarchitectonics of LDH/polymer composite with specific morphology. For this purpose, CTAB surfactant was used to control the morphology of layered double hydroxide (LDH) and to prepare LDH/polymer nanocomposites (LDH–APS–PEI–DTPA). The polymer was synthesized using diethylenetriaminepentaacetic acid (DTPA), polyethylenimine and used with LDH to form a nanocomposite with high thermal stability. Subsequently, the prepared nanocomposite was identified using FTIR, EDX, TGA, XRD, FESEM, and BET techniques. In addition, the prepared LDH–APS–PEI–DTPA nanocomposite was used as a heterogeneous and recyclable catalyst for the synthesis of imidazole derivatives under green conditions. The results showed that the LDH–APS–PEI–DTPA nanocomposite benefit from suitable morphology, simple preparation, high catalytic activity, and high surface area. Also, the proposed LDH–APS–PEI–DTPA heterogeneous catalyst showed high stability and reusability for five consecutive runs which was consistent with the principles of green chemistry.

www.nature.com/scientificreports/ and antifungals. Imidazole compounds are used as a medicinal nucleus in some drugs such as cimetidine, ketoconazole, daclatasvir 36 and nitroimidazole, which is an antibiotic for the treatment of gastrointestinal infections. In the recent decades, the synthesis of imidazole derivatives in the presence of various catalysts has been reported. Homogeneous or heterogeneous catalysts reported for the synthesis of imidazole derivatives include molecular iodine 37 , molecularly imprinted polymer 38 , p-toluenesulfonic acid 39 , graphene oxide-chitosan composite 40 , etc. Imidazole derivatives despite their advantages have disadvantages due to the use of toxic solvents, high loading of the catalyst, low production efficiency, and the cost of metal catalysts. There have been numerous reports of the use of LDHs in multicomponent reactions (MCRs) 30,41,42 . In several cases it was found that a change in the calcination process conditions leading to the formation of mixed oxides or a change in the ratio of metal cations is a useful parameter for a highly selective reaction 43,44 . Examples of these reactions include Biginelli reaction 45 , Hantzsch reaction 46 , choromen reaction 47 , and so on. The LDH-APS-PEI-DTPA (1) nanocomposite prepared here has many advantages over previously reported work such as short reaction time, high efficiency, easy separation in multi-component reactions.
In this study, a new nanoarchitectonics of LDH-APS-PEI-DTPA (1) composite designing and prepared using Mg-Al LDH with a new morphology and a new polymer was prepared. Also, the prepared LDH-APS-PEI-DTPA nanocomposite (1) was used as a highly efficient and recoverable heterogeneous catalyst for facile one-pot green synthesis of imidazole derivatives via three-component addition of benzoin (2), aldehydes (3a-k), and ammonium acetate (4) (Fig. 1).  In addition, the absorption band at 1370 cm −1 is related to nitrate anions. The absorption band at 882-584 cm −1 corresponds to the Al-OH and M-O bonds, where M can be Mg or Al. Therefore, the observed absorption bands confirm that the change in morphology of Mg-Al LDH did not lead to a change in its chemical structure. Figure 2b shows the FTIR spectra of LDH-APS-PEI-DTPA nanocomposite (1). The absorption band at 3466 cm −1 is related to N-H groups. Also, the absorption band at around 2970 cm −1 corresponds to C-H aliphatic. Furthermore, the absorption bands at 1710 cm −1 and 1654 cm −1 belong to the stretching vibrations of C=O bond of carboxylic acid and amide groups, respectively. In addition, the adsorption band at 1402 cm −1 is attributed to the stretching vibrations of nitrate anions. The absorption bands at 1234 cm −1 , 1138 cm −1 , and 800-500 cm −1 are related to Si-O-Si, C-O and M-O, respectively, where M can be Mg or Al. Figure 3 shows XRD patterns of Mg-Al LDH (2a) and LDH-APS-PEI-DTPA nanocomposite (1, 3b). The XRD pattern of Mg-Al LDH shows sharp and symmetrical reflections at 2θ of 26.11°, 30.93°, 34.88°, 40.61°, 43.40°, 53.32°, 63.09°and 66.31°, respectively, which are characteristic of the Mg-Al LDH structure. Thus, the peaks seen in the XRD pattern show that the morphological change of Mg-Al LDH did not lead to a change in its chemical structure (Fig. 3a). Also, Fig. 3b shows the XRD pattern of the LDH-APS-PEI-DTPA nanocomposite   TGA analysis was also performed to evaluate the thermal stability of LDH-APS-PEI-DTPA nanocomposite (1) in the range of 50-800 °C. The TGA curve of LDH-APS-PEI-DTPA nanocomposite (1) in Fig. 6 shows three weight losses. The first weight loss at 50-100 °C is caused by the evaporation of surface water molecules and solvent adsorbed on the LDH-APS-PEI-DTPA nanocomposite (1), while and the second weight loss at 160-270 °C is attributed to the thermal decomposition of organic component in LDH-APS-PEI-DTPA nanocomposite (1). The third weight loss occurred in the range of 280-500 °C, which can be associated with the condensation of LDH. Therefore, the obtained results confirm the successful preparation of LDH-APS-PEI-DTPA nanocomposite (1).  Optimization of the reaction conditions using LDH-APS-PEI-DTPA nanocomposite (1) catalyst. In the following, LDH-APS-PEI-DTPA nanocomposite (1) was used for the synthesis of imidazole derivatives. Hence, the condensation was evaluated between benzoin (2, 1 mmol), aldehyde (3, 1 mmol), and ammonium acetate (4, 2.5 mmol) as the model reaction. First, the model reaction was investigated in the absence of catalyst using different solvents at different temperatures ( Table 1, Entries 1-6). As shown in Table 2, in the absence of the catalyst, the desired product was not produced after 3 h. however, in the presence of 5 mg of  . According to the obtained results, EtOH solvent under reflux conditions was used as the optimal synthesis condition for the subsequent experiments. Also, to determine the optimal catalyst value, the model reaction was performed in EtOH solvent under reflux conditions in the presence of 3, 5, 7 and 10 mg of the synthesized catalyst (Table 1, entry 10-12). Therefore, 5 mg of the LDH-APS-PEI-DTPA nanocomposite (1) catalyst and EtOH solvent under reflux conditions were determined as the optimal conditions for the reaction. In order to extend the catalytic application of LDH-APS-PEI-DTPA nanocomposite (1), three-component condensation of benzoin (2), aldehyde derivatives (3a-k), and ammonium acetate (4) were performed under optimal conditions for the synthesis of imidazole derivatives. The results are summarized in Table 2.

The proposed mechanism for the synthesis of imidazole derivatives in the presence of LDH-APS-PEI-DTPA nanocomposite (1).
The proposed mechanism is shown in Fig. 8 One of the interesting advantages of LDH-APS-PEI-DTPA nanocomposite (1) is its recyclability and reusability in subsequent reactions. In order to evaluate the reusability of the catalyst, the LDH-APS-PEI-DTPA nanocomposite (1) was collected after filtration washed with distilled water and ethanol and then dried at 70 °C. The recycled catalyst was then reused in the model reaction. This process was repeated five times with no significant reduction in the catalytic efficiency of LDH-APS-PEI-DTPA nanocomposite (1, Fig. 9).
To demonstrate the performance of the LDH-APS-PEI-DTPA nanocomposite (1) as catalyst, a comparison was made with the previously reported catalysts for the synthesis of imidazole derivatives. As shown in Table 3, the synthesis of imidazole derivatives in the presence of LDH-APS-PEI-DTPA nanocomposite (1) Table 2. Synthesis of imidazole derivatives 5a-k from three-component condensation of benzoin (2), aldehyde derivatives 3a-k, and ammonium acetate (4)  www.nature.com/scientificreports/ advantages over other reported catalysts such as lower catalyst loading, shorter reaction time, and environmentally friendly reaction conditions. Therefore, the composite prepared here is a more efficient catalyst for the preparation of imidazole derivatives with high-efficiency and shorter time than the previously reported catalysts. General procedure for the preparation of polymer. A mixture of diethylenetriaminepentaacetic acid (DTPA, 2 g), hydroxybenzotriazole (HOBT, 1.35 g) and 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDCI, 1.56 g) were dissolved in acetonitrile (10 mL). The mixture was then stirred for 1 h at room temperature. Then, polyethylenimine (PEI, 1 g) and triethylamine (0.5 mL) were added to the mixture and stirred for 12 h at room temperature. Finally, the precipitate was filtered, washed with acetonitrile and EtOH, and dried at 80 °C for 6 h.

Preparation of LDH-APS-PEI-DTPA nanocomposite (1).
Mg-Al LDH-APS (1 g) was dissolved in acetonitrile (20 mL), to which HOBT (0.6 g) and EDCI (0.78 g) were added and stirred for 30 min. After that, the prepared polymer (1 g) and triethylamine (0.5 mL) were added dropwise and stirred at 80 °C for 24 h. Finally, the precipitate was separated from the mixture, washed with acetonitrile and EtOH, and dried at 80 °C for 6 h (Fig. 10).   (1) in EtOH solvent (5 mL) was stirred at 80 °C. The improvement of the reaction was checked out by TLC in a mixture of hexane and EtOAc (4:1 v/v). Eventually, the LDH-APS-PEI-DTPA nanocomposite (1) was filtered from the reaction mixture. Also, the LDH-APS-PEI-DTPA (1) nanocomposite was also washed with acetone for reuse in subsequent reaction periods.

Conclusions
In this study, a new nanocomposite with acidic properties was successfully prepared using LDH and polymer by a suitable method and characterized by different analysis methods. Also, the morphology of LDH was altered by changing the synthesis parameters. Due to its high thermal stability and high surface area (160 m 2 g −1 ), the new LDH-APS-PEI-DTPA nanocomposite (1) was used as a heterogeneous and efficient catalyst in the threecomponent condensation reaction of aldehyde derivatives, benzoin, and ammonium acetate for the synthesis of imidazole derivatives under mild conditions. acceptable stability and reusability with a slight reduction in activity as well as easy and fast separation of products can be considered as the main advantages of the prepared LDH-APS-PEI-DTPA nanocomposite (1).

Data availability
All data generated or analyzed during this study are included in this published article [and its supplementary information files].