Silver (I)-N-heterocyclic carbene complexes: Synthesis and characterization, biological evaluation of Anti-Cholinesterase, anti-alpha-amylase, anti-lipase, and antibacterial activities, and molecular docking study

Article abstract of DOI:10.1016/j.ica.2021.120486

A series of novel silver(I)-N-heterocyclic carbene complexes have been prepared and fully characterized by spectroscopic methods and X-ray crystallographic analyses. The biological capacity of the synthesized compounds was evaluated in vitro for their anti-microbial, anti-cholinesterase, anti-lipase, anti-diabetic activities in search of potent inhibitors compound. All compounds were tested against two types of fungi and three bacterias. The results proved that most compounds indicated moderate to excellent activity against all types of bacteria and fungi except compound 2f that didn't show any antibacterial activity. The synthesized compound's capacity to inhibit the enzymes AChE, BChE, Lipase, and α-amylase were evaluated. The results showed that silver(I)–NHC complexes 3a-f are effective against all types of enzymes. The highest activity was reported toward AChE, BChE, and α-amylase enzymes, and at a lower rate against Lipase enzyme compared to the references drug. In contrast, benzimidazolium salts 2a-f, which showed significant inhibitory activity against AChE and BChE enzymes, while all salts were not active against both Lipase and α-amylase enzymes. Molecular docking simulations using AutoDock, have been performed of the new compounds as a representative set of our molecules into AChE and BChE enzymes for lead optimization of the binding interaction template of the most active inhibitors docked into the active site of their relevant AChE and BChE enzymes inhibitors.

Full text of DOI:10.1016/j.ica.2021.120486

Inorganica Chimica Acta 525 (2021) 120486
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Silver (I)-N-heterocyclic carbene complexes: Synthesis and
characterization, biological evaluation of Anti-Cholinesterase,
anti-alpha-amylase, anti-lipase, and antibacterial activities, and molecular
docking study
,
,
,c
Abd El-Krim Sandelia c, Naima Khiri-Meribouta *, Saida Benzerkaa, Nevin Gürbüzb
,
Muhammed Dündard, Hüseyin Karcıe, Chawki Bensouicif, El Hassen Mokranig,
b
h
i
a
b,c,*
¨
¨
¨
˙
˙
Ilknur Ozdemir , Ahmet Koç , Namık Ozdemir , Abdelmadjid Debache , Ismail Ozdemir
a Laboratory of Synthesis of Molecules with Biological Interest, Faculty of Exact Sciences, Brother’s Mentouri Constantine 1 University, 25000 Constantine, Algeria
b
c
˙
¨
Faculty of Science and Art, Department of Chemistry, Inonü University, Malatya, Turkey
˙
¨
Catalysis Research and Application Center, Inonü University, 44280 Malatya, Turkey
d
e
˙
¨
Faculty of Medicine, Department of the Medical Biology and Genetics, Inonü University, Malatya, Turkey
˙
¨
Medical School, Department of Medical Biology and Genetics, Inonü University, Battalgazi, Malatya, Turkey
f National Center for Biotechnologie Research (CRBt), Ali Mendjli New Town, Constantine, Algeria
g Laboratory of Applied Biochemistry, Department of Biochemistry and Cellular and Molecular Biology, Faculty of Natural and Life Sciences, Brother’s Mentouri
Constantine 1 University, Constantine, Algeria
h Inonu University, Medical School, Department Genetics, Battalgazi, Malatya, Turkey
i Department of Mathematics and Science Education, Faculty of Education, Ondokuz Mayıs University, 55139 Samsun, Turkey
A R T I C L E I N F O
A B S T R A C T
A series of novel silver(I)-N-heterocyclic carbene complexes have been prepared and fully characterized by
spectroscopic methods and X-ray crystallographic analyses. The biological capacity of the synthesized com-
pounds was evaluated in vitro for their anti-microbial, anti-cholinesterase, anti-lipase, anti-diabetic activities in
search of potent inhibitors compound. All compounds were tested against two types of fungi and three bacterias.
The results proved that most compounds indicated moderate to excellent activity against all types of bacteria and
fungi except compound 2f that didn’t show any antibacterial activity. The synthesized compound’s capacity to
Dedicated to Professor Christian Bruneau
Keywords:
Silver(I)–NHC complexes
Antimicrobial
Anticholinesterase activity (anti-Alzheimer)
Anti-lipase activity
Anti-diabetic activity
X-Ray
inhibit the enzymes AChE, BChE, Lipase, and
complexes 3a-f are effective against all types of enzymes. The highest activity was reported toward AChE, BChE,
and -amylase enzymes, and at a lower rate against Lipase enzyme compared to the references drug. In contrast,
benzimidazolium salts 2a-f, which showed significant inhibitory activity against AChE and BChE enzymes, while
α-amylase were evaluated. The results showed that silver(I)–NHC
α
Molecular docking
all salts were not active against both Lipase and
α-amylase enzymes. Molecular docking simulations using
AutoDock, have been performed of the new compounds as a representative set of our molecules into AChE and
BChE enzymes for lead optimization of the binding interaction template of the most active inhibitors docked into
the active site of their relevant AChE and BChE enzymes inhibitors.
1. Introduction
compounds[1]. It has limited to metal coordination compounds derived
from benzimidazolium precursors. Recently, N-Heterocyclic Carbenes’
The chemistry of N-heterocyclic carbenes (NHCs) has appeared as
use in organometallic chemistry as ligands pulled insignificant consid-
eration and became a rapidly growing field with a broad range of
flexible building blocks for the ligation of a large variety of coordination
Abbreviations: NHC, N-Heterocyclic carbine; NMR, Nucleare Magnetic Resonance; IR, Infrared spectra; DMSO, Dimethyl sulfoxide; Ag2O, Silver oxide; AChE,
Acetylcholinesterase; BChE, Butyrylcholinesterase; p-NPP, p-Nitrophenol Palmitate; MIC, Minimum Inhibitory Concentration; CAS, Catalytic anionic site; PAS,
Peripheral anionic site.
˙
˙
¨
¨
* Corresponding authors at: Faculty of Science and Art, Department of Chemistry, Inonü University, Malatya, Turkey (I. Ozdemir). Laboratory of Synthesis of
Molecules with Biological Interest, Faculty of Exact Sciences, Brother’s Mentouri Constantine 1 University, 25000 CONSTANTINE, ALGERIA (N. Khiri-Meribout).
https://doi.org/10.1016/j.ica.2021.120486
Received 23 March 2021; Received in revised form 9 May 2021; Accepted 29 May 2021
Available online 2 June 2021
0020-1693/© 2021 Elsevier B.V. All rights reserved.

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
medicinal applications [2]. Currently, as a new emerging field of
chemistry and medicinal research, metal-N-heterocycle carbenes (M-
NHC) complexes have strongly appeared, where NHC complexes with
different metals as (Cu, Au and Ag) proved to be active against several
types of diseases as anticancer agents[3-7]. Among different transition
metal-N-heterocyclic carbene complexes, the use of NHC with silver
metal is the more important M-NHCꢀ complexes, it has extraordinary
consideration because of their structures, now has been broadly used as
sources of different metal complexes in organic chemistry as transfer
agents in the reaction of transmetalation due to the effective carbene,
that allowed to form other NHC-metal complexes. Besides, the low silver
toxicity for humans has attracted the researcher’s attention to explore
their biological activity and their medical applications, specifically
antimicrobial and anticancer [1,8,9]. The synthesis of silver(I) com-
plexes is generally done according to a straightforward procedure listed
in the literature, starting from benzimidazolium salts or using directly
commercial N-heterocycle carbenes [10-14]. In general, the N-hetero-
cyclic carbenes (NHCs) could be generated by deprotonation of the
related benzimidazolium salts. Our experience led us directly to adopt
these types of complexes using 3,5-dimethylbenzimidazolium salts,
which consider as very reactive ligands. However, most literature
methods showed that the preparation of the silver(I)–NHC complexes
have generally based on N-alkylation reactions to synthesis benzimida-
zolium salts as a precursor to nucleophilic carbenes. This type of ligands’
2.1.2. General procedure for the preparation of benzimidazolium salts (2a-
f)
The benzimidazolium salts can be prepared in analogy to published
procedures according to a slightly modified procedure from the litera-
ture methods [19]. A mixture of 1-benzyl-5,6-dimethylbenzimidazole
(1 mmol) and an equivalent amount of alkyl halide derivative (1
mmol), in degassed dimethylformamide, was heated and stirred at 80 ◦C
for 48 h under argon. The obtained mixture was cooled at room tem-
perature. After 45 mL of ether were added and stirred for 1 h, then the
product filtered and washed with diethyl ether to remove the impurities,
and the product was left precipitated with high purity. After, the crude
products were recrystallized in dichloromethane/diethyl ether and
dried under vacuum to provide pure products for experimental analysis.
1-Benzhydryl ꢀ 5,6-dimethyl-(2,3,5,6-tetramethylbenzyl)benzimi-
dazolium chloride (2a)
Yield 85% (421 mg, white solid); m.p = 152–153 ◦C; FT-IR ν(CN)
=
1549 cmꢀ 1 .1H NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 10.45 (s,
1H, NCHN); 7.62 (s, 1H, N-C6H2(CH3)2-N); 7.38–7.36 (m, 6H, CH-Ar);
7.34–7.30 (m, 4H, CH-Ar); 7.01 (s, 1H, N-C6H2(CH3)2-N); 6.93 (s, 1H,
Ph-CH-Ph); 5.90 (s, 2H, CH2N); 2.23 (s, 3H, CH3); 2.21 (s, 6H, CH3); 2.19
(s, 9H, CH3). 13C NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 142.3
(NCHN,C1); 137.0 (C4); 136.9 (C6); 135.7 (C22,28); 134.9 (C14,17); 134.0
(C12,19); 133.3 (C11); 130.6 (C2); 130.0 (C9); 129.3 (4CH, C24,26,30,32);
129.2 (2CH, C25,31); 128.4 (4CH, C23,27,29,33); 128.1 (CH, C16); 114.6
(CH, C3); 113.6 (CH, C8); 66.1 (CH, C21); 47.9 (N-CH2, C10); 20.8 (2CH3,
characteristic was considered a strong σ donor property, which confirms
that benzimidazolium salts are stronger than alkyl phosphines ligand
and even the steric properties are also different than phosphines. In
many cases, these properties and advantages frequently lead to greater
stability of the catalysts[15-17]. On the other hand, benzimidazole salts
are an important class that attracted considerable attention in various
chemical, biological and industrial areas [18]. Further, the family of N-
heterocyclic carbenes (NHCs) possessing a wide range of biological ac-
tivities [3]. The coupling of these two types of compounds generates a
pharmaceutically enhanced class of compounds known as M-NHC
complexes.
C15,18); 20.7 (CH3, C7); 20.5 (CH3, C5); 16.1 (2CH3, C13,20). Elemental
analysis calcd. (%) for C33H36ClN2 (M.w. = 496.11 g/mol): C 79.89, H
7.31, N 5.65; found (%): C 79.83, H 6.78, N 5.35
1-Benzhydryl ꢀ 5,6-dimethyl-(4-methylbenzyl)benzimidazolium
chloride (2b)
Yield 71% (322 mg, white solid); m.p = 159–160 ◦C; FT-IR ν(CN)
=
1548 cmꢀ 1. 1H NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 11.27 (s,
1H, NCHN); 7.37 (d, J = 5.7 Hz, 6H, CH-Ar); 7.34 (s, 3H, CH-Ar); 7.32 (s,
2H, CH-Ar); 7.29 (s, 2H, CH-Ar); 7.11 (d, J = 7.2 Hz, 2H, CH-Ar); 6.97 (s,
1H, Ph-CH-Ph); 5.84 (s, 2H, CH2N); 2.28 (s, 3H, CH3); 2.27 (S, 3H, CH3);
2.20 (s, 3H, CH3). 13C NMR(400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) =
142.6 (NCHN,C1). 138.9 (C14); 137.2 (C6); 137.1 (C4); 135.5 (C19,25);
130.3 (C2); 130.2 (C9); 129.9 (2CH,C12,17); 129.8 (C11); 129.4 (4CH,
As part of our ongoing research into novel functionalized NHC li-
gands as supporting a favorable environment for the development and
application of metal complexes, Herein, we report the preparation of a
new series of silver(I)–NHC complexes that contain 5,6-dimethylbenzi-
midazole. All the new products are tested against different biological
activities such as anti-microbial, anti-Alzheimer, anti-lipase, and anti-
diabetic. Also, to recognize and validate the inhibition mechanisms, a
molecular docking analysis was carried out.
C
C
C
21,23,27,29); 129.3 (2CH, C22,28); 128.4 (4CH, C20,24,26,30); 128.1 (2CH,
13,16); 114.5 (CH, C3); 113.4 (CH, C8); 66.4 (CH, C18); 51.2 (N-CH2,
10); 21.1 (CH3, C15); 20.7 (CH3, C7); 20.6 (CH3, C5). Elemental analysis
calcd. (%) for C30H29ClN2 (M.w. = 453.02 g/mol): C 79.54, H 6.45, N
6.18; found (%): C 79.28, H 6.73, N 5.35
1-Benzhydryl ꢀ 5,6-dimethyl-3-(2,4,6-trimethylbenzyl)benzimida-
zolium chloride (2c)
2. Experimental
Yield 81% (390 mg, white solid); m.p = 155–156 ◦C; FT-IR ν(CN)
=
2.1. Chemistry
1546 cmꢀ 1. 1H NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 10.88 (s,
1H, NCHN), 7.50 (s, 1H, N-C6H2(CH3)2-N), 7.36 (dd, J = 5.3 Hz, 1.6 Hz,
6H, CH-Ar); 7.31 (dd, J = 7.0 Hz, 2.5 Hz, 4H,CH-Ar); 6.94 (s, 1H, CH-
Ar); 6.92 (s, 1H, Ph-CH-Ph); 6.86 (s, 2H, CH-Ar); 5.88 (s, 2H, CH2N);
2.26 (s, 6H, CH3); 2.24 (s, 3H, CH3); 2.20 (s, 3H, CH3); 2.17 (s, 3H, CH3).
13C NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 142.8 (NCHN,C1);
139.4 (C15); 137.8 (C12,18); 137.0 (C4); 136.9 (C6); 135.6 (C21,27); 130.4
(C2); 130.0 (2CH, C14,17); 129.9 (C9); 129.3 (4CH C23,25,29,31); 129.2
(2CH, C24,30); 128.3 (4CH, C22,26,28,32); 125.5 (C11); 114.5 (CH, C3);
113.6 (CH, C8); 66.2 (CH, C20); 47.4 (N-CH2, C10); 21.0 (CH3, C16); 20.7
(CH3, C7); 20.6 (CH3, C5); 20.2 (2CH3, C13,19). Elemental analysis calcd.
(%) for C32H33ClN2 (M.w. = 481.08 g/mol): C 79.89, H 6.91, N 5.82;
found (%): C 79.71, H 6.86, N 6.38
2.1.1. Materials and methods
All reactions for the preparation of the benzimidazolium salts and
their complexes Ag(I)–NHC were carried out under argon in flame-dried
glassware using standard Schlenk techniques. All reagents were pur-
1
chased from Sigma-Aldrich, Merck, and Fluka. H NMR and 13C NMR
spectra were recorded with a Varian As 400 Merkur spectrometer
operating at 400 MHz (1H), 100 MHz (13C) in CDCl3 with tetrame-
thylsilane as an internal reference. Coupling constants (J values) are
given in Hertz. NMR multiplicities are abbreviated as follows: s =
singlet, d = doublet, t = triplet, sept = septet, q = quartet and m =
multiplet signal. FT-IR spectra were recorded on the ATR unit in the
range 400–4000 cmꢀ 1 on Perkin Elmer Spectrum 100. Melting points
were measured in open capillary tubes with Stuart SMP 40 melting point
apparatus and uncorrected. Elemental analyses were performed at the
1-Benzhydryl ꢀ 5,6-dimethyl-(2-methylbenzyl)benzimidazolium
chloride (2d)
Yield 82% (372 mg, white solid); m.p = 151–152 ◦C; FT-IR ν(CN)
=
Inonü University research center.
1541 cmꢀ 1. 1H NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 11.06 (s,
1H, NCHN), 7.39–7.33 (m, 11H, CH-Ar), 7.33 (s, 1H, CH-Ar); 7.21–7.13
(m, 3H, C6H4); 7.08 (d, J = 7.2 Hz, 1H, CH-Ar); 6.98 (s, 1H, Ph-CH-Ph);
5.92 (s, 1H, CH2N); 2.27 (s, 6H, CH3); 2.20 (s, 3H, CH3). 13C NMR (400
˙
¨
2

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
◦
MHz, CDCl3, TMS, 25 C): δ (ppm) = 142.5 (NCHN,C1); 139.1 (C12);
137.3 (C4); 137.1 (C6); 135.5 (C19 25); 133.1 (C11); 130.3 (C2); 129.8
Chloro[1-benzhydryl-3-(4-methylbenzyl)-5,6-dimethylbenzimidazole-2-yli-
dene]silver(I) (3b). Yield 80% (0.450 g, white solid); m.p = 144–145 ◦C;
FT-IR ν(CN) = 1542 cm-1. 1H NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ
(ppm) = 7.39 (m, 7H, CH-Ar); 7.22 (m, 4H, CH-Ar); 7.14 (s, 1H, N-
C6H2(CH3)2-N); 7.12 (sl, 4H, C6H4); 7.09 (s, 1H, N-C6H2(CH3)2-N); 6.92
(s, 1H, Ph-CH-Ph); 5.52 (s, 2H, CH2N); 2.31 (s, 3H, CH3); 2.26 (s, 3H,
CH3); 2.20 (s, 3H, CH3). 13C NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ
,
(C9); 129,7 (CH, C17); 129.4 (4CH, C21,23,27,29); 129.3 (2CH, C22,28);
129.1 (CH, C15); 128.5 (CH, C16); 128.4 (4CH, C20,24,26,30); 125.0 (C14);
114.4 (CH, C3); 113.4 (CH, C8); 66.4 (CH, C18); 51.3 (N-CH2, C10); 21.3
(CH3, C13); 20.7 (CH3, C7); 20.6 (CH3, C5). Elemental analysis calcd. (%)
for C30H29ClN2 (M.w. = 453.02 g/mol): C 79.54, H 6.45, N 6.18; found
(%): C 79.74, H 6.36, N 6.13
(ppm) = 138.2 (C14); 137.3 (C19,25); 133.9 (C6); 133.6 (C4); 132.9 (C2);
1-Benzhydryl ꢀ 5,6-dimethyl-(4-tert-butylbenzyl)benzimidazolium
bromide (2e)
132.5 (C9); 132.0 (C11); 129.7 (2CH, C13,15); 129.2 (4CH, C21,23,27,29);
128.7 (2CH, C22,28); 128.3 (4CH, C20,24,26,30); 126.9 (2CH, C12,17); 112.9
(CH, C3); 112.3 (CH, C8); 66.9 (CH, C18); 53.8 (CH2, C10); 21.1 (CH3,
Yield 71% (384 mg, white solid); m.p = 179–180 ◦C; FT-IR ν(CN)
=
1542 cmꢀ 1. 1H NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 10.73 (s,
1H, NCHN), 7.42–7.37 (m, 11H, CH-Ar); 7.34 (sl, 5H, CH); 7.00 (s, 1H,
Ph-CH-Ph); 5.84 (s, 2H, CH2N); 2.31 (s, 3H, CH3); 2.22 (s, 3H, CH3); 1.25
(s, 9H, CH3). 13C NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 152.1
(C14); 141.6 (NCHN,C1); 137.3 (C4); 137.2 (C6); 135.3 (C22,28); 130.4
(C11); 129.9 (C2); 129.8 (C9); 129.4 (4CH, C24,26,30,32); 129.3 (2CH,
C
15); 20.4 (CH3, C7); 20.3 (CH3, C5). Elemental analysis calcd. (%) for
C
30H28AgClN2 (M.w. = 559.88 g/mol): C 64.36, H 5.04, N 5.00; found
(%): C 64.64, H 5.19, N 5.12
Chloro[1-benzhydryl-3-(2,4,6-trimethylbenzyl)-5,6-dimethylbenzimida-
zole-2-ylidene]silver(I) (3c). Yield 74% (0.435 g, white solid); m.p =
200–201 ◦C; FT-IR ν(CN) = 1542 cm-1. 1H NMR (400 MHz, CDCl3, TMS,
C
C
C
25,31); 128.4 (4CH, C23,27,29,33); 127.8 (2CH, C12,20); 126.2 (2CH,
13,19); 114.4 (CH, C3); 113.4 (CH, C8); 66.4 (CH, C21); 51.1 (N-CH2,
10); 34.6 (C15); 31.1 (3CH3, C16,17,18); 20.7 (CH3, C7); 20.6 (CH3, C5).
◦
25 C): δ (ppm) = 7.36 (m, 7H, CH); 7.19 (m, 5H, CH); 6.94 (s, 2H,
C6H2); 6.92 (s, 1H, N-C6H2(CH3)2-N); 6.84 (s, 1H, Ph-CH-Ph); 5.51 (s,
2H, CH2N); 2.32 (s, 3H, CH3); 2.23 (s, 9H, CH3); 2.18 (s, 3H, CH3). 13
C
Elemental analysis calcd. (%) for C33H35BrN2 (M.w. = 539.56 g/mol): C
73.46, H 6.54, N 5.19; found (%):C 73.15, H 6.28, N 5.20
1-Benzhydryl-5,6-dimethyl-3-(3,4,5-trimethoxybenzyl)benzimi-
dazolium bromide (2f)
NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 139.2 (C15); 137.4
(C21,27); 137.4 (C12,18); 133.5 (C6); 133.4 (C4); 130.1 (C14,17); 129.0
(4CH, C23,25,29,31); 128.6 (2CH, C24,30); 128.3 (4CH, C22,26,28,32); 126.9
(C11); 113.3 (CH, C3); 112.0 (CH, C8); 68.0 (CH, C20); 48.7 (N-CH2, C10);
21.1 (CH3, C16); 20.5 (2CH3, C13,19); 20.4 (CH3, C7); 20.4 (CH3, C5).
Elemental analysis calcd. (%) for C32H32AgClN2 (M.w. = 559.88 g/mol):
C 64.37, H 5.49, N 4.76; found (%): C 64.74, H 5.65, N 4.78
Yield 70% (373 mg, white solid); m.p = 157–158 ◦C; FT-IR ν(CN)
=
1552 cmꢀ 1. 1H NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 11.25 (s,
1H, NCHN); 7.42–7.32 (m, 12H, CH-Ar), 6.98 (s, 1H, Ph-CH-Ph); 6.76 (s,
2H, C6H2), 5.81 (s, 2H, CH2N); 3.79 (s, 6H, OCH3); 3.78 (s, 6H, OCH3);
2.33 (s, 3H, CH3); 2.23 (s, 3H, CH3). 13C NMR (400 MHz, CDCl3, TMS,
◦
25 C): δ (ppm) = 153.72 (C13,17); 142.70 (NCHN, C1); 138.38 (C15);
Chloro[1-benzhydryl-3-(2-methylbenzyl)-5,6-dimethylbenzimidazole-2-yli-
dene]silver(I) (3d). Yield 90% (0.532 g, white solid); m.p = 222–223 ◦C;
137.30 (C4); 137.21 (C6); 135.50 (C21,27); 130.28 (C2); 129.77 (C2);
128.78 (C11); 129.41 (4CH, C23,25,29,31); 129.38 (2CH, C24,30); 128.40
(4CH, C22,26,28,32); 114.41 (CH, C3); 113.4 (CH, C8); 105.69 (2CH,
1
1
◦
FT-IR ν(CN) = 1542 cm- . H NMR (400 MHz, CDCl3, TMS, 25 C) : δ
(ppm) = 7.39 (s, 7H, CH-Ar); 7.23 (m, 4H, CH-Ar); 7.20 (s, 1H, CH-Ar);
7.16 (s, 1H, N-C6H2(CH3)2-N); 7.10 (s, 1H, CH-Ar); 7.08 (s, 1H, CH-Ar);
7.00 (m, 2H, CH-Ar);0.6.94 (s, 1H, Ph-CH-Ph); 5.53 (s, 2H, CH2N); 2.31
(s, 3H, CH3); 2.26 (s, 3H, CH3); 2.21 (s, 3H, CH3). 13C NMR (400 MHz,
C
12,19); 66.46 (CH, C20); 60.84 (OCH3, C16); 56.53 (2OCH3, C14,18);
51.43 (N-CH2, C10); 20.8 (2CH3, C5,7). Elemental analysis calcd. (%) for
C
32H33ClN2O3 (M.w. = 529.07 g/mol): C 72.65, H 6.29, N 5.29; found
CDCl3, TMS, 25 ◦C): δ (ppm) = 138.8 (C12); 137.3 (C19 25
, ); 134.9 (C11);
(%): C 72.47, H 6.51, N 5.32
133.9 (CH, C4); 133.3 (CH, C6); 132.9 (CH, C2); 132.5 (CH, C9); 129.2
(4CH, C21,23,27,29); 129.1 (CH, C15); 128.9 (CH, C16); 128.8 (2CH,
C22,28); 128.3 (4CH, C20,24,26,30); 123.9 (C17); 112.9 (CH, C3); 112.2 (CH,
C8); 66.9 (CH, C18); 53.9 (N-CH2, C10); 21.4 (CH3, C13); 20.4 (CH3, C7);
20.3 (CH3, C5). Elemental analysis calcd. (%) for C32H32AgClN2 (M.w. =
559.88 g/mol): C 64.36, H 5.04, N 5.00; found (%): C 64.96, H 5.31, N
4.95.
2.1.3. General procedure for preparation of Ag(I)–NHC complexes (3a-f)
The complexes of silver(I)–NHC were prepared with the method of
Organ [20]. According to the use of benzimidazolium salts (1 mmol)
with Ag2O (1.5 mmol) in dry chloroform at 50 ◦C for 48 h, in dark
conditions, under argon and covered with aluminum foil. The reaction
mixture was filtered through celite, and the solvent was removed under
vacuum to afford the product. The salts were converted to silver(I)–NHC
complexes automatically by the reaction, which allowed us to obtain a
solution mixture, that affords a white solid as silver(I)–NHC. The
resulting white solid was isolated by filtration then dried in a vacuum,
and recrystallized in CHCl3/Et2O.
Bromo[1-benzhydryl-3-(4-tert-butylbenzyl)-5,6-dimethylbenzimidazole-2-
ylidene]silver(I) (3e). Yield 70% (0.433 g, white solid); m.p
=
219–220 ◦C; FT-IR ν(CN) = 1542 cm-1. 1H NMR (400 MHz, CDCl3, TMS,
25 ◦C): δ (ppm) = 7.39 (m, 7H, CH-Ar); 7.34 (s, 1H, CH-Ar); 7.32 (s, 1H,
C6H4); 7.22 (m, 4H, CH-Ar); 7.17 (s, 1H, N-C6H2(CH3)2-N); 7.15 (s, 2H,
C6H4); 7.12 (s, 1H, N-C6H2(CH3)2-N); 6.93 (s, 1H, Ph-CH-Ph); 5.54 (s,
2H, CH2N); 2.27 (s, 3H, CH3); 2.21 (s, 3H, CH3); 1.28 (s, 9H, CH3 (t-Bu)).
13C NMR (400 MHz, CDCl3, TMS, 25 ◦C): δ (ppm) = 151.3 (C14); 137.3
(C22,28); 133.9 (C4); 133.5 (C6); 132.9 (C9); 132.6 (C2); 132.0 (C11);
129.4 (C); 129.2 (4CH, C24,26,30,32); 128.7 (2CH, C25,31); 128.4 (C);
128.3 (4CH, C23,27,29,33); 126.6 (2CH, C13,19); 125.9 (2CH, C12,20); 114.4
(CH, C3); 113.5 (CH, C8); 66.9 (CH, C21); 53.6 (N-CH2, C10); 34.5 (C15);
31.2 (3CH3, C16,17,18); 20.4 (CH3, C7); 20.3 (CH3, C5). Elemental analysis
calcd. (%) for C33H34AgClN2 (M.w. = 601.96 g/mol): C 65.84, H 5.69, N
4.65; found (%): C 65.94, H 5.92, N 4.43.
μ
-Dikloro-bis-{[1-benzhydryl-3-(2,3,5,6-tetramethylbenzyl)-5,6-dime-
thylbenzimidazole-2-ylidene]silver(I) (3a). Yield 70% (0.422 g, white
solid); m.p = 245–246 ◦C; FT-IR
ν
(CN) = 1542 cmꢀ 1. 1H NMR (400 MHz,
CDCl3, TMS, 25 ◦C): δ (ppm) = 7.37–7.32 (m, 7H, CH); 7.21 (s, 1H,
C6H1); 7.17 (dd, J = 6.1 Hz, 2.6 Hz, 4H, CH-Ar); 7.10 (s, 2H, N-
C6H2(CH3)2-N); 6.81 (s, 1H, Ph-CH-Ph); 5.49 (s, 2H, CH2N); 2.29 (s, 3H,
CH3); 2.28 (s, 6H, CH3); 2.19 (s, 3H, CH3); 2.14 (s, 6H, CH3). 13C NMR
◦
(400 MHz, CDCl3, TMS, 25 C): δ (ppm) = 137.4 (CH, C22,28); 135.1
(C14,17); 133.5 (C12,19); 133.4 (C4); 133.4 (C6); 133.0 (C11); 129.9 (CH,
C16); 128.9 (4CH, C24,26,30,32); 128.5 (2CH, C25,31); 128.31(4CH,
C
23,27,29,33); 113.6 (CH, C3); 111.7 (CH, C8); 68.6 (CH, C21); 48.1 (CH2,
C10); 20.7 (2CH3,C15,18); 20.4 (CH3, C7); 20.4 (CH3,C5); 16.2 (2CH3,
Chloro[1-benzhydryl-3-(3,4,5-trimethoxybenzyl)-5,6-dimethylbenzimida-
zole-2-ylidene] silver(I) (3f). Yield 80% (0.540 g, white solid); m.p =
117–118 ◦C; FT-IR ν(CN) = 1542 cm-1. 1H NMR (400 MHz, CDCl3, TMS,
25 ◦C): δ (ppm) = 7.38 (m, 7H, CH-Ar); 7.22 (m, 4H, CH-Ar); 7.15 (s, 1H,
C
13,20). Elemental analysis calcd. (%) for C64H68Ag2Cl2N4 (M.w. =
1179.90 g/mol): C 65.15, H 5.81, N 4.75; found (%): C 66.04, H 5.95, N
4.51
3

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
2.2. X-Ray crystallographic analysis study
Table 1
Crystal data and structure refinement parameters for 2c, 2f, and 3a.
The structure of 3,5-dimethylbenzimidazolium salts 2c, 2f, and Ag-
NHC complex 3a was determined by the X-ray diffraction technique,
the obtained results confirmed all the spectroscopic data. A suitable
single crystal of complex 2c, 2f, and 3a for X-ray diffraction analysis was
were grown by slow diffusion of diethyl ether in a saturated chloroform
solution at room temperature. Crystallographic data of 2c, 2f, and 3a
were gathered with an STOE IPDS II diffractometer using graphite-
Parameters
3,5-dimethylbenzimidazolium salts
Silver(I)–NHC
complex
3a
2c
2f
CCDC depository
Color/shape
2,058,369
Colorless/
prism
2,058,370
2,058,371
Colorless/plate
Colorless/plate
Chemical
(C32H33N2)+
Cl- 2H2O
517.08
(C32H33N2O3)+
Cl-CH2Cl2
613.98
[Ag2Cl2(C33H34N2)2]
formula
monochromated Mo Kα radiation by applying the ω -scan method at
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell
1203.88
296(2)
296(2)
296(2)
room temperature. X-AREA was used for data collection and cell
refinement. [21] while data reduction was applied using X-RED32 [21].
The structures were solved using the charge-flipping algorithm by
SUPERFLIP [22] and refined using the full-matrix least-squares calcu-
lations on F2 using SHELXL-2018 [23]. The H atoms were calculated
geometrically and a riding model was applied during the refinement
process. Crystal data, data collection, and structure refinement details
are collected in Table 1. Molecular graphics were generated by using
OLEX2 [24].
0.71073 Mo K
Monoclinic
α
0.71073 Mo K
Triclinic
α
0.71073 Mo K
Monoclinic
α
P21/c (No. 14)
P (No. 2)
C2/c (No. 15)
parameters
a, b, c (Å)
13.5311(12),
16.4277(17),
14.5904(13)
90, 116.407
(6), 90
10.9830(8),
12.0714
(8),12.0148(9)
85.937(6),
86.665(6),
85.163(6)
1581.1(2)
2
27.6791(19), 9.3376
(7), 22.9241(16)
α
, β, γ (◦)
90, 106.436(5), 90
Volume (Å3)
Z
2904.8(5)
4
5682.8(7)
4
2.3. Biological capacity study
D
calc. (g/cm3)
1.182
1.290
1.407
μ
(mmꢀ 1
)
0.162
0.325
0.827
All the synthesized 3.5-dimethylbenzimidazolium salts 2a-f and their
related silver(I)–NHC complexes 3a-f were tested for antimicrobial,
Anti-Cholinesterase (anti-Alzheimer), anti-Lipase, and anti-Alpha-
amylase (anti-Diabetic) activities.
Absorption
correction
Integration
Integration
Integration
T
min., Tmax.
0.9231, 0.9490
1104
0.9128, 0.9867
644
0.7750, 0.9776
2480
F000
Crystal size
0.62 × 0.37 ×
0.36
0.49 × 0.19 ×
0.06
0.55 × 0.21 × 0.02
(mm3)
2.3.1. Material
Diffractometer/
measurement
method
STOE IPDS II/
STOE IPDS II/
ω
STOE IPDS II/ω scans
ω
scans
scans
Candida albicans (ATCC MYA-2876) and Candida glabrata (ATCC
2001), which are pathogenic yeast species, were used in antifungal tests,
and Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 29213),
and Pseudomonas aeruginosa (ATCC 27853) species were used antibac-
terial tests. All types of bacteria and fungi used in the study were pro-
vided by the Molecular Genetics Laboratory of the Department of
Index ranges
ꢀ 16 ≤ h ≤ 16,
ꢀ 19 ≤ k ≤ 18,
ꢀ 16 ≤ l ≤ 16
1.680 ≤ θ ≤
25.047
ꢀ 13 ≤ h ≤ 12,
ꢀ 14 ≤ k ≤ 12,
ꢀ 14 ≤ l ≤ 14
2.322 ≤ θ ≤
25.047
ꢀ 32 ≤ h ≤ 32, ꢀ 11 ≤
k ≤ 11, ꢀ 27 ≤ l ≤ 27
θ range for data
collection (◦)
Reflections
collected
1.534 ≤ θ ≤ 25.049
24,599
15,167
14,288
˙
¨
¨
Genetics at Inonü University Turgut Ozal Medical Faculty (Battalgazi,
Malatya, Turkey).
Independent/
observed
4965/1707
5581/2845
5037/2296
The acetylthiocholine iodide, butyrylthiocholine chloride which was
employed as substrates of the reaction were obtained from Sigma
Chemical Co (Sigma-Aldrich GmbH, Stern-Heim, Germany). The AChE
from Electrophorus electricus eel-AChE (Type-VI-S, EC 3.1.1.7, 425.84
U/mg) and horse serum butyrylcholinesterase eq BChE, (EC 3.1.1.8,
11.4 U/mg), which are enzymes that were used in anticholinesterase
assay, were obtained from Sigma-Aldrich. All other chemicals and sol-
vents were of analytical grade. The measurements and calculations of
the enzymatic activity results were evaluated by using quantitative
colorimetric assay, they were carried out on a 96-well microplate reader,
(PerkinElmer Multimode Plate Reader EnSpire, USA) at the Center of
Biotechnology Research. (Ali Mendjli, Constantine, Algeria)
reflections
Rint.
0.1204
0.0781
0.1441
Refinement
method
Full-matrix
least-squares
on F2
Full-matrix least-
Full-matrix least-
squares on F2
squares on F2
Data/restraints/
parameters
4965/0/339
5581/0/378
1.030
5037/0/339
0.984
Goodness-of-fit
0.945
on F2
Final R indices [I
R1 = 0.1148,
wR2 = 0.2957
R1 = 0.2210,
wR2 = 0.3492
0.36, ꢀ 0.31
R1 = 0.0734, wR2
= 0.1244
R1 = 0.0764, wR2
0.1382
=
=
> 2σ(I)]
R indices (all
data)
R1 = 0.1565, wR2
= 0.1492
R1 = 0.1820, wR2
0.1739
Δ
ρmax., Δρmin. (e/
0.18, ꢀ 0.28
0.61, ꢀ 0.48
Å3)
2.3.2. Methods
N-C6H2-(CH3)2-N); 7.14 (s, 1H, N-C6H2-(CH3)2-N); 6.96 (s, 1H, Ph-CH-
Ph); 6.43 (S, 2H, CH-Ar), 5.50 (s, 2H, CH2N); 3.82 (s, 3H, OCH3); 3.77 (s,
6H, OCH3); 2.30 (s, 3H, CH3); 2.23 (s, 3H, CH3). 13C NMR (400 MHz,
CDCl3, TMS, 25 ◦C): δ (ppm) = 153.6 (C13,17); 137.9 (C15); 137.3
(C21,27); 134.1 (C4); 133. (C6); 130.7 (C11); 129.4 (C9); 129.2 (4CH,
C23,25,29,31); 128.8 (2CH, C24,30); 128.4 (C2); 128.3 (4CH, C22,26,28,32);
112.9 (CH, C3); 112.1 (CH, C8); 105.7 (2CH, C12,19); 66.8 (CH, C20); 60.9
(OCH3, C16); 56.2 (2OCH3, C14,18); 53.8 (N-CH2, C10); 20.4 (CH3, C7);
20.4 (CH3, C5). Elemental analysis calcd. (%) for C32H33AgClN2O3 (M.
w. = 635.12 g/mol): C 60.44, H 5.07, N 4.41; found (%): C 60.33, H
5.59, N 3.96.
2.3.2.1. Antibacterial activity
2.3.2.1.1. Determination of the minimum inhibitory concentration
(MIC). Antifungal and antibacterial MIC (Minimal Inhibitory Concen-
tration) analysis was performed using the BMD (Broth Microdilution)
test, as described in EUCAST EDef 7.3.2 [25] for yeasts and CLSI M07-
A10 [26] for bacteria. Briefly, the broth micro-dilution technique
using a 96-wells microplate was used to determine the minimum
inhibitory concentration (MIC) (Erdemoglu et al., 2007). The selected
compounds (NHCs) were dissolved in dimethylsulfoxide (DMSO), and
serial dilutions were made in a flat-bottom sterile 96-well microplate, in
SDB (Sabouraud Dextrose Broth) medium (1% peptone, 2% glucose, pH
5.6) [27] for yeasts, and LB (Luria-Bertani) broth medium (1% tryptone,
1% NaCl, 0.5% yeast extract, pH 7.0) [28] for bacteria. In sterile water,
yeast (1-5x105 CFU/mL) and bacteria (1x106 CFU/mL) cell solutions
4

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
(inoculums) were prepared and added in equal volumes to wells con-
taining different concentrations of the compounds. After the cell solu-
tions were added, the compounds’ final concentrations were between
0.8 and 800 mg/L, and the cell concentrations were 0.5–2.5x105 CFU/
mL for yeasts and 5x105 CFU/mL for bacteria in the final step. Finally,
the microplate was covered and incubated at 37 ◦C for 24 h for yeasts
absorbances of lipase products (p-nitrophenol) were measured using a
96-well microplate reader (Perkin Elmer, Enspire) at 410 nm. The
findings were expressed as IC50 values. (µM) corresponding to the 50%
inhibition concentration. The percent inhibition I (%) of pancreatic
lipase was determined using the following equation [36].
I(%) = [(A ꢀ a) ꢀ (B ꢀ b)/(A ꢀ a) ] × 100
◦
and 16–18 h at 37 C for bacteria. The MIC was determined spectro-
photometrically at 530 nm after incubation in yeasts and by naked eyes
in bacteria. The MIC value was measured as the lowest drug concen-
tration causing at least 50% or more reduction in yeasts’ growth
compared to the control (no drug) cell group, and as the lowest drug
concentration without visible growth in bacteria. Ampicillin, Tetracy-
cline, Amphotericin B, and Voriconazole were used as the reference
drugs.
Where A: is the absorbance in the absence of the possible inhibitor,
which corresponds to the control enzyme assay; a: is the absorbance in
the absence of the sample and enzyme (blank substrate); B: is the
absorbance in the presence of the possible inhibitor with the enzyme and
substrate; b: is the absorbance in the absence of the enzyme.
c. Anti-α-amylase activity
The inhibitory activity of alpha-amylase was tested using the iodine
/potassium iodide (IKI) method according to (G. Zengin et al. 2014)
[37]. With some modifications. Briefly, in this experiment, the assay was
2.3.2.2. Enzymatic evaluation. This study evaluated the capacity of the
novel benzimidazolium salts and silver (I)–NHC complexes as inhibitors
of different enzymes. In this context, all compounds were evaluated
against a panel of important biological activities such as anticholines-
terase, anti-Lipase, and anti-diabetic activities.
conducted by mixing of 25 μL of the sample at different concentrations
in methanol with 50 μL of α amylase solution in 1U of sodium phosphate
buffer (pH = 6.9 with 6 Mm NaCl) and incubated for 10 min at 37 ◦C,
Afterwards, 50 μL of Amidon (0.1%), was added. Similarly, by adding
a. Anti-Cholinesterase assay (Anti-Alzheimer)
sample solution to all reaction reagents, a blank was prepared without
enzyme (α-amylase) solution. For 20 min, the reaction mixture was
Cholinesterase family inhibitors of acetylcholinesterase (AChE) and
butyrylcholinesterase (BChE) are the most investigated and common
strategy used for the treatment of Alzheimer’s disease [29–32].
Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibi-
tory activities of the new compound were done according to the method
described by Rhee et al. [33]. based on the spectrophotometric method
of Ellman’s [34] with slight modifications. In this experiment, a reaction
incubated at 37 ◦C. After incubation, The reaction was then stopped by
the addition of HCl 25 µL (1 M), finally, the reaction was initiated by the
addition of 100
μL of (IKI) iodine-potassium iodide solution. The
absorbance of the solution was measured at 630 nm by the use of a 96-
well microplate reader (Perkin Elmer, Enspire). The results were pre-
sented as IC50 values (µM) corresponding to 50% inhibition concentra-
tion. The acarbose was used as a reference. The percentage of inhibition
I (%) was calculated as follows in the formula:
volume of 200
mM, Ph = 8.0), 10
methanol, and 20 L of AChE or BChE solution in buffer was mixed and
left to incubate for 15 min at 37 ◦C, Afterwards, 10
L of DTNB (0.5 mM)
were added. After that, 10 L of acetylthiocholine iodide or 10 L of
μ
L consisting, 150
μL of sodium phosphate buffer (100
μ
L of the sample at different concentrations in
μ
I % = 1 ꢀ [(Ac ꢀ Ae) ꢀ (As ꢀ Ab)/(Ac ꢀ Ae) ]
μ
As = Absorbance [Extrait, Enzyme, Amidon, HCl, IKI]; Ab
=
μ
μ
Absorbance [Extrait, sodium phosphate buffer, IKI]; Ae = Absorbance
[solvant vol Extrait, Enzyme, Amidon, HCl, IKI]; Ac = Absorbance
[solvant vol Extrait, sodium phosphate buffer, Amidon, HCl, IKI]
butyrylthiocholine chloride (0.2 mM). was added to start the reaction.
The hydrolysis of these substrates was monitored spectrophotometri-
cally by the formation of yellow 5-thio-2-nitrobenzoate anion as the
result of the reaction of DTNB with thiocholine released by the enzy-
matic hydrolysis of acetylthiocholine iodide or butyrylthiocholine
chloride. The absorbance of the solution was measured at 412 nm by the
use of a 96-well microplate reader (Perkin Elmer, Enspire). The results
were given as IC50 values (µM) corresponding to the 50% inhibition
concentration. Percentage of inhibition I (%) was determined using the
following formula
2.4. Statistical analysis
All data on activity tests were the averages of triplicate analyses. The
data were recorded as means ± standard error meaning. Significant
differences between means were determined by Student’s t-test; p
values < 0.05 were regarded as significant.
Inhibition (I %) = (E ꢀ S / S ) × 100
2.5. Molecular docking study
Where E is the activity of the enzyme without a test sample, and S is
the activity of the enzyme in the presence of the test sample. The mea-
surements were carried out in triplicate and Galanthamine was used as a
reference compound.
Molecular modeling studies were accomplished to investigate the
possible binding mode of the designed compounds into BChE and AChE
active sites. Before docking, the crystal structures of human AChE (PDB
ID: 4M0E [38]) and BChE (PDB ID: 2XQF [39]) were downloaded from
the Protein Data Bank. The binding site of these enzymes was defined by
selecting all the residues with at least one heavy atom within 6 Ǻ from
the inhibitor of the crystal structure. This selection was refined by
adding every residue beyond 6 Ǻ considered essential for the continuity
of the cavity [40]. Then, AChE and BChE were prepared using the
Protein Preparation Wizard of Schrodinger [41] by removing their Chain
B, water molecules, heteroatoms, and co-factors. Hydrogen and missing
atoms were added and bond charges were computed. Finally, the intra-
molecular energy was minimized and a mol2 file was exported and used
as a starting structure for docking [42]. Meanwhile, the synthesized
compounds were drawn and prepared using the built and LigPrep
module implemented in Maestro version 11.3 of the Schrodinger suite
[43]. This preparation was carried out in order to create several struc-
tures for each molecule. (up to 32) with different enantiomers (when
b. Anti-lipase assay
The assay to determine the inhibitory capacity against pancreatic
lipase was performed according to the method of (Souza, 2009) [35]
with minor modification. Briefly, in this experiment the selected com-
pounds were prepared at the concentration of 4 mM in dimethyl sulf-
oxide (DMSO). A reaction volume of 200 μL in triplicate consisting, 50
μ
L of a sample at different concentrations in DMSO with 100 μL of
pancreatic Lipase solution in Tris-HCl buffer (pH = 8) were mixed and
incubated for 20 min at 37 ◦C, Afterwards, The reaction was then
initiated by the addition of 50 μL of p-Nitrophenol Palmitate (p-NPP)
after incubation for 2 h at 37 ◦C. A blank with DMSO instead of enzyme
solution was prepared. orlistat was used as a positive control. The
5

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
Scheme 1. Synthetic route for the preparation of benzimidazolium salts 2a-f.
undefined), protonation states at pH = 7.4 ± 1, and tautomers [44]. All
the conformations generated were minimized and exported as mol2
files. Molecular docking studies were performed using GOLD version
5.2.2 in which the target atoms are fixed and the ligands are flexible
[45]. The GoldScore scoring function was employed for the ranking of
molecules according to their score which is given as fitness. Best cluster
poses were saved and visually analyzed by PyMol version 2.2.3 [46] and
Maestro version 11.3 of the Schrodinger suite [43].
using 5,6-dimethylbenzimidazole with bromodiphenylmethane. The
second N-alkylation reaction allowed us to prepared six benzimidazo-
lium salts 2a-f by reacting N-benzhydryl-5,6-dimethylbenzimidazole 1
with different benzyl chloride in degassed DMF at 80 ◦C. All the new 3,5-
dimehylbenzimidazolium salts 2a-f were obtained with good yield, in
the solid-state.
All the new 3,5-dimehylbenzimidazolium salts 2a-f depicted in
Scheme 1 were obtained with good yield. The spectroscopic data of 3,5-
dimethylbenzimidazolium salts are consistent with the data observed in
literature for other benzimidazolium salts [7,9-12]. The physical and
some spectroscopic data of 3,5-dimethylbenzimidazolium salts are
summarized in Table 2.
3. Results and discussion
3.1. Chemistry
These new 5,6-dimethylbenzimidazolium salts were characterized
by different techniques. The FT-IR data indicated that 5,6-dimethylben-
zimidazolium salts show a characteristic ν(CN) band typically for all salts
2a-f at 1549, 1548, 1546, 1541, 1542, and 1552 cmꢀ 1 respectively. In
1H NMR the important pick for all 3,5-dimethylbenzimidazolium salts is
3.1.1. Preparation of 3,5-dimethylbenzimidazolium salts 2a–f
The 3,5-dimehylbenzimidazolium salts 2a-f were synthesized via two
N-alkylation reaction processes as illustrated in scheme 1. Compound 1
as a starting material was obtained by the first N-alkylation reaction
Table 2
Physical and Spectroscopic data for 3,5-dimethylbenzimidazolium salts 2a-f.
Code
Chemical Formula
Molecular Weight (g/mol)
Melting point◦C
1H NMRCH (C2) ppm
13C NMR(C2) ppm
IRν(CN)
2a
2b
2c
2d
2e
2f
C33H36 ClN2
495.11
453.03
481.08
453.03
539.56
529.08
153
260
156
152
180
158
10.52
11.27
10.91
11.15
10.75
11.27
142.3
142.6
142.8
142.5
141.6
142.7
1549
1548
1546
1541
1542
1552
C30H29ClN2
C32H33ClN2
C30H29ClN2
C33H35BrN2
C32H33ClN2O3
6

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
Scheme 2. Synthesis of Ag(I)–NHC complexes 3a-f.
Table 3
Physical and Spectroscopic data for Ag(I)–NHC complexes.
Code
Chemical Formula
Molecular Weight (g/mol)
Melting point
◦C
1H NMRCH (C2) ppm
13C NMR
IR
(C2) ppm
ν(CN)
3a
3b
3c
3d
3e
3f
C32H34AgClN2
C30H28AgClN2
601.97
559.89
584.97
559.89
646.42
635.94
245–246
144–145
200–201
222–223
218–219
117–118
–
–
–
–
–
–
–
–
–
–
–
–
1471
1484
1496
1485
1481
1505
C
32H32AgClN2
C30H28AgClN2
C
C
33H34AgBrN2
32H33AgClN2O3
the pick of the acidic proton NCHN that confirms the formation of the
salt, this pick was detected at 10.52, 11.25, 10.91, 11.08, 10.73, and
11.25 ppm respectively for the salts 2a-f, as sharp singlets. In 13C NMR
the carbon NCHN was observed as typical singlets at 142.4, 142.7,
142.8, 142.5, 141.6, and 142.7 ppm respectively for the salts 2a-f.
as white solids in high yields, soluble in halogenated solvents. In the air,
these complexes are stable but are light-sensitive.
All the new Ag(I)–NHC complexes 3a-f depicted in Scheme 3 were
obtained with good yield. The spectroscopic data of these complexes are
consistent with the data observed in literature for other Ag(I)–NHC
complexes [9–12]. The physical and some spectroscopic data are sum-
marized in Table 3.
3.1.2. Preparation of silver(I)–NHC complexes 3a-f
The Ag(I)–NHC complexes 3a-f were synthesized via the in situ
deprotonation of 3,5-dimethylbenzimidazolium salts by Ag2O. Treat-
ment of the benzimidazolium salts with Ag2O in dichloromethane at
room temperature in the dark afforded the expected silver complexes Ag
(I)–NHC 3a-f (Scheme 2). The silver-NHC complexes 3a-f were obtained
These new six Ag(I)–NHC complexes were characterized by different
techniques. The FT-IR data indicated that Silver(I)–NHC complexes
show a characteristic ν(CN) band typically for all complexes 3a-f at 1471,
1484, 1496, 1485, 1481, and 1505 cmꢀ 1 respectively. The characteristic
proton peak NCHN of the starting benzimidazolium was not detected in
7

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
the 1H NMR spectra of novel Ag(I)–NHC complex that confirmed the
formation of the Ag(I)–NHC complexes Table 3. Similarly, in the 13C
NMR data, the characteristic signals of carbon NCHN were observed at
around 144 ppm for the starting benzimidazolium salts. However, the
formation of silver NHC complexes is checked by the disappearance of
the signal of NCHN.
3.2. X-ray crystal structures
The molecular diagrams of 2c, 2f, and 3a with the adopted atom-
labeling scheme are shown in Figs. 1-3, while important bond dis-
tances and angles are listed in Table 4.
3.2.1. Description of the structure of the salts 2c and 2f
The 3,5-dimethylbenzimidazolium salts 2c and 2f crystallize in
chloroform/diethyl ether as depicted in Figs. 1 and 2.
The compounds 2c and 2f crystallize as a salt in which the charge of
the NHC cation is neutralized by a chloride anion. Furthermore, in their
asymmetric units, 2c contains two solvent water molecules whilst 2f
contains one dichloromethane molecule. The bonding within the imid-
azole rings indicates a pattern of delocalization that extends from atom
N1 to atom N2 through atom C1, the N1─C1 and N2─C1 distances being
significantly shorter than the N1─C2 and N2─C9 distances. The
remaining bond lengths are normal within experimental uncertainty
[47].
3.2.2. The structure description of the silver complex 3a
The silver(I)NHC complex 3a crystallizes in chloroform/diethyl
ether as depicted in Fig. 3.
Fig. 1. Molecular structure of salt 2c.
The silver(I)–NHC complex 3a crystallizes as dimers via bridging
chloride atoms to form an Ag2(μ-Cl)2 quadrangular arrangement which
is frequently observed in silver complexes (Fig. 3). Because of the
inversion center, the Ag2Cl2 cluster is strictly planar at the mid-point of
i
the Ag∙∙∙Agi line [symmetry code: ꢀ x + 1/2, ꢀ y + 3/2, ꢀ z + 1],
where each silver(I) atom is tri-coordinated with one carbene carbon
atom and two chlorine atoms to adopt a distorted trigonal planar ge-
ometry. The two (NHC)AgCl moieties are present around an inversion
center with the chlorides asymmetrically bound to the silver center with
different Ag─Cl bond lengths of 2.464(2) and 2.629(2) Å. The Ag1─C1
distance of 2.111(8) Å falls in the range typical for other silver-carbene
complexes [48]. With an angle of 143.2(2)◦ the C─Ag─Cl vector de-
viates from linearity as a result of coordination from an additional
bridging Cl. The bond angles of the C1─Ag1─Cl1i, Ag1─Cl11─Ag1i, and
Cl1─Ag1─Cl1i are 124.1(2), 87.34(7), and 92.66(7)◦, respectively. The
Ag… Ag distance is 3.5186(11) Å, much greater than the sum of two van
der Waals radii for Ag (3.44 Å) [49], ruling out the presence of any
‘argentophilic’ interaction. Due to coordination of the NHC ligand, the
ring’s internal angle (N1─C1─N2) is reduced at the carbene center from
109.2(6) to 106.2(7)◦. All the aforementioned data are comparable to
those reported dinuclear Ag(I)–NHC complexes [50–54].
3.3. Evaluation of biological
3.3.1. Evaluation of antibacterial activity
Investigations have been performed for antibacterial and antifungal
activities in vitro against (E.coli, P.aeruginosa, S.aureus, C.albicans, and
C.glabrata) for all the newly 3.5-dimethylbenzimidazolium salts 2a-f
and their related silver(I)–NHC complexes 3a-f, using AmphotericinB,
Voriconazole, Ampicillin, and Tetracycline as a standard control drug.
The (MIC μg/mL) results of the antimicrobial activity of all new com-
pounds are reported in Table 5.
Globally, all benzimidazoluim salts and silver-NHC complexes tested
showed an important antifungal activity against the human pathogenic
microorganisms (Candida albicans and Candida glabrata) as are presented
in Table 4. The benzimidazolium salts 2a-f showed high antifungal ac-
tivity against Candida albicans, especially the three salts 2a, 2c, and 2e.
Fig. 2. Molecular structure of salt 2f.
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A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
Fig. 3. Molecular structure of silver-carbene complexes 3a.
3.3.2. Enzymatic inhibitory activity assay
Table 4
The inhibitory effect of all benzimidazolium salts 2a-f and their sil-
ver(I)NHC complexes 3a-f against different enzymes as AChE, BChE,
Selected geometric parameters for 2c, 2f, and 3a.
Parameters
3,5-
Silver(I)–NHC
Lipase, and α-amylase was studied in vitro at different concentrations.
Dimethylbenzimidazolium
salts
complex
The benzimidazolium salts and their silver complexes demonstrated
close percentages of inhibition against AChE compering with the stan-
dard Galanamine, while against BChE, all newly compound inhibited
more effectively than the standard drug. The inhibitory effect of silver
complexes against lipase showed that all compounds 3a-f could effec-
tively inhibit lipase with a value of IC50 approximates the standard
(Orlistat). Also, this series of silver complexes exhibited strong and good
2c
2f
3a
Bond lengths
(Å)
Ag1─Cl1
–
–
2.464(2)
2.629(2)
2.111(8)
1.342(9)
1.390(9)
1.355(10)
1.391(9)
143.2(2)
124.1(2)
92.66(7)
87.34(7)
125.7(6)
127.9(6)
106.2(7)
111.4(7)
110.4(6)
Ag1─Cl1i
–
–
Ag1─C1
–
–
N1─C1
1.351(7)
1.322(4)
N1─C2
1.392(7)
1.392(5)
anti-diabetic activity against the
results, all benzimidazolium salts didn’t show any activity against both
lipase and -amylase enzymes. Enzymatic activity was reported in the
α-amylase enzyme. Contrary to these
N2─C1
1.341(7)
1.334(5)
N2─C9
1.406(8)
1.398(5)
Bond angles
(◦)
Cl1─Ag1─C1
Cl1i─Ag1─C1
Cl1─Ag1─Cl1i
Ag1─Cl1─Ag1i
Ag1─C1─N1
Ag1─C1─N2
N1─C1─N2
C1─N1─C2
C1─N2─C9
–
–
α
–
–
same manner as IC50 values presented in Table 6. Based on the IC50
values, the results were given as a concentration of 50% inhibition
(IC50). The inhibition of different enzymes was determined by
comparing the reaction rates of samples relative to the blank sample.
The capacity of the newly synthesized compound to inhibit the enzymes
–
–
–
–
–
–
–
–
109.2(6)
109.6(5)
110.1(5)
110.5(3)
108.4(3)
107.6(3)
(AChE, BChE, Lipase, and α-amylase) was evaluated according to the
spectrophotometric methods. The low IC50 values designated the high
inhibition activity.
Symmetry code: i ꢀ x + 1/2, ꢀ y + 3/2, ꢀ z + 1.
besides, the silver-NHC complex 3a-f showed high antifungal activity
against Candida albicans, and Candida glabrata, with almost the same
values. Complex 3c is the more active complex. The antibacterial ac-
tivity of all benzimidazoluim salts 2a-f and silver-NHC complexes 3a-f
tested showed an important antibacterial activity against the human
pathogenic microorganisms (Escherichia coli, Pseudomonas aeruginosa,
and Staphylococcus aureus), except the salt 2f as are presented in Table 4.
All benzimidazolium salts 2a-e showed good antibacterial activity
against Staphylococcus aureus and Escherichia coli, with almost the same
values, but they didn’t show high activity against Pseudomonas aerugi-
nosa especially for the two salts 2b, and 2d the last salt 2f didn’t show
any activity against E. coli. In contrast, the silver-NHC complexes 3a-f
showed high antimicrobial activity against Staphylococcus aureus and
Escherichia coli. The results revealed that the highest antimicrobial
activity was reported in Ag-NHC complexes 3b and 3c.
A. Evaluation of Acetylcholinesterase and Butyrylcholinesterase inhib-
itory capacity
To find out the capacity of both benzimidazolium salts 2a-f and their
silver(I)–HNC complexes 3a-f against anticholinesterase activity, all the
compounds were screened in an in vitro complementary system.
Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are the
enzymes that catalyze the hydrolyses of substrate acetylthiocholine or
butyrylthiocholine, respectively. The product thiocholine reacts with
Ellman’s reagent (DTNB) to produce 2- nitrobenzoic-5-
mercaptothiocholine and 5-thio-2-nitrobenzoate which can be detec-
ted at 412 nm. For comparison purposes, Galantamine, a medicinal
cholinesterase inhibitor used in mild Alzheimer’s disease treatment, was
used as the positive control.
As can be seen in Table 6, The obtained IC50 values revealed that all
tested compounds showed a strong inhibitory against both enzymes.
The lipophilicity of Ag(I)–NHC complexes are thought to play a
significant role in the ability of these compounds to penetrate cellular
membranes, and increased lipophilicity through modification of the
NHC wingtip substituents improved the antibacterial activity of com-
pounds [55-57].
(AChE and BChE) with IC50 values ranging from (IC50: 1.33 ± 0.3 μM to
17.97 ± 0.27
2a for salts with (IC50: 1.33 ± 0.3
plexes with (IC50: 1.60 ± 0.19 M) comparing to that of the Galantamine
(4.14 ± 0.07 M). The compound 2f is the least active AChE inhibitor
μ
M). The best AChE inhibitors between all compounds are
μ
M), and 3a for their silver(I) com-
μ
μ
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A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
Table 5
Antifungal and anti-Bacterial activities (MIC μg/mL) of benzimidazolium salts 2a-f and their silver(I)NHC complexes 3a-f.
Compounds
Anti-Fungal
Anti-Bacterial
E. colia
C.
C.
P. aeruginosaa
S. aureusa
albicansa
glabrataa
Benzimida-zolium Salts
Silver complexes
2a
2b
2c
2d
2e
2f
25
100
200
100
200
100
400
12.5
12.5
6.25
12.5
12.5
12.5
–
200
400
200
400
200
NA
25
200
800
200
800
200
NA
50
200
400
200
400
100
NA
200
25
100
12.5
200
12.5
12.5
6.25
12.5
12.5
25
3a
3b
3c
3d
3e
3f
25
25
25
6.25
6.25
12.5
12.5
25
25
25
25
50
25
25
25
50
Ampicillinb
–
–
0.05
0.4
12.5
0.8
–
400
12.5
–
3.125
0.2
Tetracyclineb
Amphotericin Bb
Voriconazoleb
–
0.1
–
–
0.4
–
–
a: Tested microorganisms.
b: Reference drugs.
NA: Not Active.
3f showed IC50 values in the same range of the standard Galantamine.
Accordingly, benzimidazolium salts and silver (I)–NHC complexes could
be considered promising acetylcholinesterase inhibitors. According to
Taylor et al [58]. The compounds that give a good inhibitory activity of
acetylcholinesterase (AChE) are more beneficial for human health.
The data obtained for inhibition of BChE by benzimidazolium salts
(2a-f) and their silver(I)–NHC complexes (3a-f) demonstrated that all
compounds had high activity toward BChE. In terms of anti-BChE ac-
tivity, the inhibitory potencies of all compounds toward BChE with IC50
Table 6
Anti-Cholinesterase, anti-Lipase, and Anti-α-Amylase activities of benzimida-
zolium salts 2a-f and their silver(I)–NHC complexes 3a-f.
Anti-
Anti-
Anti-
Cholinesterase
Lipase
Lipase
α
-Amylase
Compound
AChE
BChE
α
-amylase
IC50
SD
±
IC50
SD
±
IC50
SD
±
IC50 ± SD
(μ
M)a
(μ
M)a
(μ
M)a
(μ
M)a
NAc
NAc
NAc
NAc
NAc
NAc
NAc
NAc
NAc
NAc
NAc
NAc
values ranging from (IC50: 0.29 ± 0.04
values ranging from (IC50: 0.29 ± 0.04
μ
M to 4.29 ± 0.18
M to 4.29 ± 0.18
μM), with IC50
Benzimidazolium
salts
2a
1.33 ±
0.03
0.96 ±
0.02
μ
μM). The most
2b
5.56 ±
0.57
0.72 ±
0.04
active benzimidazolium salts were 2d with (IC50: 0.15 ± 0.02 µM). The
most active silver (I)–NHC complexes were 3e with (IC50: 0.18 ± 0.01
µM). The benzimidazolium salt 2f and their silver(I) complex 3f are the
2c
6.17 ±
0.33
0.70 ±
0.04
least active BChE inhibitor with (4.29 ± 0.18 μM) and (3.57 ± 0.15 μM)
2d
4.19 ±
0.02
0.15 ±
0.02
respectively. On the other hand, compared with galantamine standard.
All-new compounds were more potent than the standard drug galant-
amine against the BChE enzyme. Generally, the inhibition of BChE by
the benzimidazolium salt and their silver(I)–NHC complexes were more
efficient than the AChE inhibitor activity. It was also noted that all
compounds were more selective for BChE than the standard drug Gal-
antamine. The selectivity was especially pronounced for compounds 2c,
2d, 2e, 3c, 3d, and 3e. The performance for the compound 3d was
30.07-fold more selective for BChE. While for AChE inhibitors, all
compounds had less affinity than Galantamine.
2e
9.06 ±
0.26
1.08 ±
0.12
2f
17.97
± 0.27
1.60 ±
0.19
4.29 ±
0.18
Silver(I)–NHC
3a
0.88 ±
0.00
33.79
± 6.17
52.25
± 1.83
34.61
± 2.50
40.72
± 2.47
33.15
± 1.47
58.66
± 1.47
/
7.00 ±
0.87
complexes
3b
3.50 ±
0.52
0.47 ±
0.04
70.69 ±
2.69
3c
5.64 ±
0.02
0.50 ±
0.03
98.57 ±
2.18
3d
4.21 ±
0.12
0.61 ±
0.02
43.18 ±
2.60
As presented in Table 7, the compounds Ag(II)–NHC complexes 3a-f
are polar molecules, these compounds present high log P values superior
to 5 (log P > 5), which means that these compounds are too lipophilic
(poor aqueous solubility). The benzimidazolium slats 2a-f have a good
aqueous solubility because of their log P value which included between
0 and 5. The standard (Galantamine) has log P values inferior to 3 (log P
= -1.42) which has low partition coefficients. This compound is a polar
molecule whith a good aqueous solubility.
3e
4.53 ±
0.13
0.18 ±
0.01
65.87 ±
2.66
3f
4.14 ±
0.46
3.57 ±
0.15
47.55 ±
1.28
Reference
Galanamineb
Orlistat b
Acarbose b
4.14 ±
0.07
20.38
± 2.10
/
25.07
± 0.48
/
/
/
5258.02
± 46.9
B. Evaluation of Pancreatic Lipase inhibitory capacity.
a: IC50 values represent the means ± SD of three parallel measurements (p <
0.05).
The inhibitor of digestive lipase that limits intestinal fat absorption
at an initial stage could prove as a proper medication for the treatment of
hyperlipidemia and holds great promise as an anti-obesity agent. To find
new pancreatic lipase (triacylglycerol lipase, EC 3.1.1.3) inhibitors from
these new compounds, all the 3,5-dimethylbenzimidazolium salts 2a-f
and the related silver(I)–NHC complexes 3a-f were tested for their anti-
b: Reference compound.
c: Not Active.
with (IC50: 17.97 ± 0.27
the least active AChE inhibitor with (IC50: 5.64 ± 0.02
silver(I) complexes. It should be noted that compounds 2d, 3d, 3e, and
μ
M) between all salts. While compound 3c is
μ
M) between the
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A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
Table 7
The selectivity index for AChE over BChE and BChE over AChE with docking score and log P of benzimidazolium salts 2a-f and their silver(I)–NHC complexes 3a-f.
Compounds
AChE
BChE
IC50 ± SD (
μ
M)a
Selectivity indexc
Docking score
IC50 ± SD (
μ
M)a
Selectivity indexd
Docking score
Log P
Benzimidazolium salts
2a
1.33 ± 0.03
5.56 ± 0.57
6.17 ± 0.33
4.19 ± 0.02
9.06 ± 0.26
0.72
0.13
0.11
0.06
0.11
0.23
0.55
0.13
0.08
0.14
0.07
0.86
4.92
59.20
54.43
51.78
56.48
52.73
51.65
59.11
58.43
53.04
56.22
56.87
57.09
57.02
0.96 ± 0.02
0.72 ± 0.04
0.70 ± 0.04
0.15 ± 0.02
1.08 ± 0.12
4.29 ± 0.18
0.88 ± 0.00
0.47 ± 0.04
0.50 ± 0.03
0.61 ± 0.02
0.18 ± 0.01
3.57 ± 0.15
1.38
7.72
74.74
76.60
76.71
77.60
70.26
68.27
74.98
77.12
76.80
76.58
77.10
70.15
53.04
5.17
5.04
4.80
4.00
5.30
3.23
8.40
7.46
8.19
7.41
8.62
6.64
ꢀ 1.42
2b
2c
8.81
2d
14.45
8.39
2e
2f
17.97 ± 0.27
1.60 ± 0.19
3.50 ± 0.52
5.64 ± 0.02
4.21 ± 0.12
4.53 ± 0.13
4.14 ± 0.46
4.14 ± 0.07
4.18
Silver complexes
3a
1.82
3b
7.44
3c
11.28
30.07
12.94
1.16
3d
3e
3f
Galantamine b
20.38 ± 2.10
0.20
c : Selectivity for AChE: IC50(BChE)/IC50(AChE).
d: Selectivity for BChE: IC50(AChE)/IC50(BChE)
Fig. 4. The positioning of galantamine (a) and, 2a (b) in the AChE active site.
Fig. 5. Binding mode prediction of galantamine (a), and compound 2a (b) into the entire AChE active pocket.
11

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
Fig. 6. The positioning of galantamine (a), and 2d (b) in BChE active site.
lipase activity using a radioactive screening method. The results shown
in Table 5 represent a significant inhibitory activity against Lipase by all
the silver complexes, especially the complexes 3a and 3e that displayed
remarkable anti-lipase activity with (IC50 = 33.79 ± 6.17 µM) and (IC50
= 33.15 ± 1.47 µM) respectively, were found to be very close to the
reference drug orlistat (IC50 = 25.07 ± 0.48 µM). Opposite of that, all
salts 2a-f were not active against the lipase enzyme. This study proved
that Ag’s presence in the compound gave the capacity for the complexes
to had anti-lipase activity.
3.4. Molecular docking study
Molecular docking studies were carried out to get a better insight
into the binding modes and amino acid interactions of the synthesized
compounds into AChE and BChE actives sites. Table 7 reveals that the
experiment data of enzyme inhibitory activity in vitro showed that the
molecular docking findings were in good agreement. Indeed, the most
potent inhibitors from in vitro assays showed the best docking scores
against both enzymes. The most promising compounds (compound 2a
for AChE and 2d for BChE) were chosen to be investigated further of
their binding mode with their target. As shown in Fig. 4, compound 2a
covers both the catalytic anionic site (CAS) and the peripheral anionic
site (PAS) of AChE, leading to an inhibitory potency 3 fold more than
that of galantamine, which binds only to the CAS. Also, The disparity in
inhibitory potency between these two compounds may be explained by
the different number of interactions between them and the protein
C. Evaluation of
α-amylase inhibitory capacity
The evaluation of 3,5-dimethylbenzimidazolium salts and their silver
(I)–NHC complexes effect were tested using -amylase inhibitory assay;
the study was investigated the anti-diabetic activity of these new com-
pounds. As shown in table 5. The -amylase inhibitor effects of silver (I)–
NHC complexes showed higher inhibitory activity than acarbose (IC50
5258.02 ± 4.9 M). The greatest –amylase inhibition activity was ob-
M). While all
–amylase. They
α
α
=
(Fig. 5). Indeed, whereas 2a is involved in eight interactions (six
stacking with Trp86, Tyr124, Tyr337, Phe338, Tyr341, and two -cation
interactions with Trp86 and Tyr341), galantamine is involved in only
four interactions (two -cation interactions with Trp86 and Phe338, a
hydrogen bond with Gly121 and a
π-π
μ
α
π
tained in the compound 3a, with (IC50 = 7.00 ± 0.87
μ
benzimidazolium salts 2a-f are not active against
didn’t show any anti-diabetic activity.
α
π
π-π stacking with Phe338).
The most plausible pose of each compound is presented as obtained
by docking with Gold. Residue Tyr341, which protects the pocket’s
ligand, is omitted for clarity. The CAS area of the cavity is shown in blue,
Fig. 7. Binding mode prediction of galantamine (a) and compound 2d (b) into the entire BChE active pocket.
12

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
Fig. 8. The positioning of complex 3a (c) in AChE, and 3e (d) in BChE active sites.
Fig. 9. Binding mode prediction of compound 3a (c) and compound 3e (d) into the entire AChE and BChE active pocket.
while the PAS is shown in red. The ligand atoms are color-coded as
follows: oxygen in red, carbon in green, and nitrogen in blue. The images
were drawn by PyMol.
Remarkably, salts are more powerful compared to complexes since
the positively charged nitrogen of the cycle engages in the formation of
π
-cation bonds with the residues of the active site of the enzyme (Trp86 in
the case of AChE and Trp82 in the case of BChE) which increases the
affinity of the salts, as for 2a and 2d compared to their silver(I)–NHC
complex analog (3a and 3d) against AChE and BChE respectively. This
increase of the inhibitory potency may be explained by the formation of
Purple arrows head from the donor to the acceptor of hydrogen
bonds, red lines represent π-cation interactions, and green lines π-π
stacking. The images were done with the Ligand Interaction Diagram
¨
script from the Schrodinger Suite.
Concerning the BChE, The inhibitory potency of compound 2d is
higher than that of galantamine. because of its rational positioning in
this enzyme’s binding site. Indeed, compound 2d binds both the CAS
and PAS of BChE in contrary to galantamine which covers only the CAS
(Fig. 6). Also, 2d establishes a higher number of interactions against
BChE active site than that of galantamine (Fig. 7). Indeed, whereas
galantamine is involved in only two interactions (hydrogen bond with
a
π
-cation interaction between the nitrogen of salts, and Trp86 for AChE
(Trp82 for BChE). As shown in (Figure 08 (c)) , the Ag(II)NHC complex
3a forms three stackings with Tyr124, Tyr341 and His447 of AChE
active site. The absence of -cation with Trp86 seems to decrease its
affinity compared to its salt analog 2a. Likewise, the absence of -cation
π-π
π
π
with Trp82 seems to decrease the affinity of silver(I)–NHC complexes
against BChE, as for 3e establishes a π-π stacking with His438 of BChE
Glu197 and
π
-cation interaction with Trp82), 2d is involved in six in-
active site (Figure 08 (d)).
teractions of which two
π-π stackings with His438. This residue was
described to play an important role in the BChE activity [39]. Fig. 8.
Fig. 9.
13

A.E.-K. Sandeli et al.
Inorganica Chimica Acta 525 (2021) 120486
heterocyclic carbene complexes, J. Organomet. Chem. 696 (5) (2011) 1066–1071,
https://doi.org/10.1016/j.jorganchem.2010.10.054.
4. Conclusion
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In this research, six benzimidazolium salts and their related silver(I)–
NHC complexes have been synthesized and identified with different
spectroscopic analysis methods. All selected compounds were tested for
their biological capacity using anti-microbial, anti-cholinesterase, anti-
¨
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α
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evidence for showing the best results comparing with the reference
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˙
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enzymes, such as AChE, BChE, α-amylase, and lipase. Contrary to this
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and the inhibition by enzymes was recorded just for AChE and BChE. A
great correlation between experimental and theoretical studies for these
new compounds was obtained by molecular docking study. Based on our
findings, the synthesis of Ag-NHC complexes allowed us to confirm that
the use of Ag as a metal with NHCs increase the biological activity,
which made silver(I)–NHC complexes considered as metal-
lopharmaceutical compound par excellence to be used in the medicine
and pharmaceutical industries, and provide promising starting points for
further research to develop new drugs for the treatment of many
diseases.
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Declaration of Competing Interest
[19] J.C. Garrison, W.J. Youngs, “Ag (I) N-Heterocyclic Carbene Complexes : Synthesis,
Structure, and Application”, I (2005) 3978–4008.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
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The authors greatly acknowledge financial support from the Inonü
University Research Fund of this work. X-ray analyses were supported
by the Scientific Research Projects Unit of Ondokuz Mayıs University
(Project No: PYO.FEN.1906.19.001).
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Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
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