br Acknowledgments We thank the anonymous reviewers for thei

Acknowledgments We thank the anonymous reviewers for their constructive comments on the manuscript, and also thank Dr. Hans-U. Dahms for his comments on the manuscript. This work was supported by a grant from the National Research Foundation (2009-0071218) funded to Young-Mi Lee. This work was also supported by a grant from the National Research Foundation (2012R1A1A2000970) funded to Jae-Seong Lee.
Introduction Heterocyclic chemistry with nitrogen heteroatom is emerging as one of the hottest topics in the synthetic organic chemistry arena due to its wide presence in various bioactive natural compounds, synthetic intermediates and pharmaceuticals [1]. Imidazole comprises a five-membered hetero-aromatic ring structure with two nitrogen atoms at non-adjacent position. The imidazole scaffold is ubiquitous in nature present as substructures in many natural products which possess wide spectrum of biological activities and found frequently in the main structure of some well-known components of human organisms, i.e. the amino Ezatiostat synthesis histidine, a component of DNA base structure, vitamin B12, purines, histamine and biotin [2], [3], [4]. Imidazole derivatives are currently under intensive focus due to their wide range of applications in pharmaceuticals, material and synthetic chemistry, and also plays important role in biochemical processes [5], [6]. They have been reported to possess various biological properties viz. antitumor, anti-HIV, antimicrobial, anticonvulsant, antioxidant, antihypertensive, anti-allergy, anticancer, analgesic, anti-inflammatory, FTase and p38 MAP kinase inhibitory activities [7], [8], [9], [10], [11], [12], [13], [14]. The excellent therapeutic properties of imidazole-related drugs have encouraged medicinal chemists to synthesize a large number of novel chemotherapeutic agents [15]. There are various drugs with imidazole nucleus such as Cimetidine, Omeprazole, Metronidazole, Losartan, Etomidate, and Ketoconazole are currently in clinical use. The potency and wide applicability of the imidazole pharmacophore can be attributed to its hydrogen bond donor-acceptor capability as well as its high affinity for metals. Apart from being biologically active, it is also used as potential corrosion inhibitors for transition metals [16], green solvents for organic reactions in form of ionic liquids [17], efficient ligands in coordination chemistry [18], N-heterocyclic carbenes for organometallic catalysis [19], fluorescence labelling agents [20], organic light emitting diodes (OLED) [21] and chromophores for non-linear optic (NLO) systems [22]. This versatile applicability of the imidazole derivatives highlights the importance of accessing efficient synthetic methodologies for assembling and decorating the imidazole ring with diverse functional groups. DFT methods along with their complementary experimental techniques play crucial role in studying structural and spectral properties as well as various structures based molecular properties of organic molecules. The hybrid functional, B3LYP [23], [24] is most widely used for the organic compounds as it offers low computational cost than Post Hartree-Fock methods and commonly yields comparable results. Nowadays, the dispersion corrected functional B3LYP-D3 is preferred for molecules having inter- or intra-molecular interactions where Grimme's D3 correction is employed for long range dispersion interactions [25]. Devi et al. have synthesized similar crystal structure and studied it by X-ray single crystal and FTIR techniques as well as by low level DFT calculations [26]. The asymmetric unit of crystal of present molecule has Cl⋯H-O interaction while in asymmetric unit of crystal reported by Devi et al., the Cl⋯H-N interaction is presented [26]. Present synthesis has provided different polymorph of the compound as compare with that reported in literature [26]. The different polymorphs show different physicochemical properties [27]. Therefore, the FTIR spectrum and molecular properties of asymmetric unit of crystal reported in this work are found different from the molecule reported elsewhere [26]. To the best of our knowledge, the dispersion corrected DFT/TD-DFT calculations with 6–311++G(d,p) basis set, NMR spectra, UV/Vis absorption studies, biological activities and various other theoretical molecular properties of the present molecule have not been reported so far. Herein, we have synthesized the functionalised imidazole by reacting ninhydrin with guanidinium chloride in presence of acetic acid and also explored its antioxidant and AChE inhibition property. The present studies aim to explain single crystal X-ray structure, FTIR, NMR, UV/Vis spectra and other molecular properties of synthesized compound with the help of advanced quantum chemical approach (DFT). The DFT/B3LYP-D3 calculations have been performed on asymmetric unit of crystal structure of the present compound. The molecular structure, IR, NMR spectra and various other molecular properties have been calculated at B3LYP-D3/6–311++G(d,p) level of theory. The UV/Vis absorption spectra have been simulated in the gaseous as well as solvent phase at TD-B3LYP-D3/6–311++G(d,p) level of theory. The theoretical results were compared with experimental data and are found in good agreement.