Syntheses, crystal structures and photo physical aspects of azido-bridged tetranuclear cadmium (II) complexes: DFT/TD-DFT, thermal, antibacterial and anti-biofilm properties

Supramolecular clumps of μ2-1,3-acetate bridges of Cd(II)-Salen complex: Synthesis, spectroscopic characterization, crystal structure, DFT quantization's, and antifungal photodynamic therapy

The article divulges the crystal growth, synthesis, and X-ray structure characterization of one centrosymmetric cadmium complex, [Cd{CdL(μ2-1,3-acetate)}2] using Salen ligand (SL). The complex is further characterized using spectroscopic and analytical techniques, including DRS, SEM-EDX, PXRD, and ICP-MS. The crystallographic study showed that the complex has a monoclinic space P21/c. Addison parameters (Ʈ) show the hexagonal geometry of the central Cd(II) metal ion. Hirshfeld surface and 2-D fingerprint confirm supramolecular contacts despite weak C-H⋯O and C-H···π interactions. Energy frameworks, FMOs, global reactivity parameters, MEP, and energy bandgap explain the complex reactivity outlook. The complex inter- and intramolecular bonding interactions were explored through natural bond orbital (NBO), QTAIM, NCI-RDG, Electron Location Function (ELF), and Localized Orbital Locator (LOL) quantization methods. In addition, the complex and its synthetic components in vitro antibacterial efficacy were investigated using Gram-positive and Gram-negative microbial strains. SAR (structure-activity relationship) correlates with biological potency. Molecular docking assessed antimicrobial potency with proteins S. aureus (PDB ID: 1JIJ), C. albicans (PDB ID: 1M7A), E. coli (PDB ID: 1T9U), P. aeruginosa (PDB ID: 2UV0), and A. Niger (PDB ID: 3K4P). The findings are backed by the Protein-Ligand Interaction Profiler (PLIP). The antifungal potency and cell viability test of C. albicans were conducted using photodynamic therapy (APDT).

Diverse crystalline protein scaffolds through metal-dependent polymorphism

As protein crystals are increasingly finding diverse applications as scaffolds, controlled crystal polymorphism presents a facile strategy to form crystalline assemblies with controllable porosity with minimal to no protein engineering. Polymorphs of consensus tetratricopeptide repeat proteins with varying porosity were obtained through co-crystallization with metal salts, exploiting the innate metal ion geometric requirements. A single structurally exposed negative amino acid cluster was responsible for metal coordination, despite the abundance of negatively charged residues. Density functional theory calculations showed that while most of the crystals were the most thermodynamically stable assemblies, some were kinetically trapped states. Thus, crystalline porosity diversity is achieved and controlled with metal coordination, opening a new scope in the application of proteins as biocompatible protein-metal-organic frameworks (POFs). In addition, metal-dependent polymorphic crystals allow direct comparison of metal coordination preferences.

Experimental and Theoretical Survey of Intramolecular Spodium Bonds/σ/π-Holes and Noncovalent Interactions in Trinuclear Zn(II)-Salen Type Complex with OCN- Ions: A Holistic View in Crystal Engineering

In this work, one new centrosymmetric trinuclear Zn(II) complex 1, [{(OCN)Zn(L)}2Zn], using a salen-type ligand (H2L) in the presence of OCN- was synthesized and characterized via elemental, spectral, SEM-EDX, and single-crystal X-ray diffraction (SCXRD) study. In 1, SCXRD reveals two different stereochemical environments of zinc metal ions; one terminal Zn(II) center adopts square pyramidal geometries with the Addison parameter (τ) 0.095, and the central Zn(II) is tetracoordinated tetrahedral geometry. This article provides evidence of the significance and presence of spodium bonds (SpBs) in solid-state crystal structures involving a pseudotetrahedral environment of the central Zn-atom. X-ray structures reveal intramolecular Zn···O SpBs caused by the methoxy (-OCH3) substituent O-atom adjacent to the coordinated phenoxy O-atom. These noncovalent interactions have been thoroughly studied using density functional theory calculations at the RI-BP86[2]-D3[3]/def2-TZVP level of theory that characterizes the nature of SpBs, including the Baders quantum theory of atoms-in-molecules "QTAIM", molecular electrostatic potential (MEP) surface, and noncovalent index plot (NCI). In addition, a unique complex-isomer-based theoretical model has been vividly employed to estimate the SpBs energy in the complex. Natural bond orbital (NBO) analysis also tries to establish the differentiation between σ-hole and π-hole SpBs' natures more authentically. The complex energy frameworks were used to investigate noncovalent interactions. To better understand the different intermolecular interactions, we conducted a Hirshfeld surface, which revealed N···H (15.4%) and O···H (9.1%) contacts and Zn···O (5.1%) (SpBs).

Synthesis, spectroscopic investigation, molecular docking, ADME/T toxicity predictions, and DFT study of two trendy ortho vanillin-based scaffolds

In this article, we have synthesized two contemporary ortho-vanillin-based Salen-type ligands (H₂L¹/H₂L²) characterized by modern spectroscopic tools. EDX analysis supports the elemental composition (C, N, O, and Br). SEM examined the morphology of the synthesized compounds. The molecular geometry was optimized in the gas phase using B3LYP-D3/6-311G (d, p) level. The global reactivity parameters, HOMO-LUMO energy gap (Δ), atomic properties, MESP, and ADME/T, vividly explore the chemical reactivity and toxicity of two Salen-type ligands. The DFT simulated IR/NMR characterized essential structural assignments, and UV-Visible spectra were employed to predict the optical properties. The article demonstrated in silico molecular docking against the Gm + ve Bacillus subtilis (6UF6), and Gm -ve Proteus Vulgaris establishes the ligand binding ability with essential amino acids through conventional H-bonding or other significant interactions. The docking simulation is compared for two compounds better than the control drugs and confirms the antimicrobial activity. The theoretical drug-like properties have been explored in-depth by ADME/T using the SWISSADME database. The analysis estimated the molecule's lipophilicity, the consensus P0/W, and water solubility. Thus, using various pharmaco-logical parameters, toxicity explains where the electron-withdrawing Br group plays a more toxic effect in H₂L² than in H₂L¹.

Synthesis, Molecular, and Supramolecular Structures of Two Azide-Bridged Cd(II) and Cu(II) Coordination Polymers

Two 1D coordination polymers were synthesized by reaction of two ligands, 2-amino-4-picoline (2A4Pic) and quinoline-6-carboxylic acid (Qu-6-COOH) with two metal (II) nitrate (M = Cd and Cu) in the presence of azide as a linker. The synthesized metal complexes [Cd(2A4Pic)2(N3)2]n; (1) and [Cu(Qu-6-COO)(N3)(H2O)]n; (2) were isolated in single crystals and their X-ray structures revealed a 1D polymeric structure. Due to symmetry considerations, the asymmetric formula is half a [Cd(2A4Pic)2(N3)2] unit for 1 and one [Cu(Qu-6-COO)(N3)(H2O)] unit for 2. In complex 1, the Cd(II) is hexa-coordinated with two 2A4Pic molecules and four μ(1,1) azide units. Hence, the CdN6 coordination environment has a slightly distorted octahedral geometry. In 2, the Cu(II) is hexa-coordinated with three different ligands (Qu-6-COO¯, H2O and μ(1,1) N3¯) where all are connectors between the crystallographically related Cu(II) sites. Additionally, complex 2 distorted CuN2O4 octahedral geometry. In both complexes, the polymer arrays are connected by N…H hydrogen bonds and π–π stacking interactions. Based on Hirshfeld analysis, the percentages of N…H contacts are 43.1 and 27.4% for 1 and 2, respectively, while %C...C are 5.6 and 9.3%, respectively. Analysis of Cu-N, Cu-O, and Cd-N bonds using DFT calculations showed predominantly closed-shell coordination interactions with little covalent characters. Additionally, the negatively charged ligand groups were found to compensate the positive charge of the central metal ion to a larger extent than the electrically neutral ligands.

The importance of tetrel bonding interactions with carbon in two arrestive iso-structural Cd(ii)-Salen coordination complexes: a comprehensive DFT overview in crystal engineering

In this article, we describe the serendipitous synthesis of two remarkable iso-structural Cd(ii)-Salen complexes [L2Cd4(OAc)2(NCS)2] in the presence of H2L and NaSCN {where L = L1 (N,N'-bis(3-methoxysalicylidene)-1,2-diaminopropane) and L = L2 (N,N'-bis(3-methoxysalicylidene)-ethylenediamine) in 1 and 2, respectively}. The complexes were characterized by using elemental analysis, SEM-EDX, PXRD, spectroscopy, and X-ray crystallography. The X-ray crystal structure revealed that both complexes crystallize in the orthorhombic space group Pbcn, with unit cell parameters: a = 20.758(6), b = 11.022(3), c = 21.396(6) Å, V = 4895(2) Å3, and Z = 4. The inner N2O2 and outer O4 compartments are essentially occupied by two different Cd(ii) metal ions resulting from the de-protonated form of the ligand (L2-) with the Cd(1) metal ions adopting a capped octahedral geometry. At the same time, Cd(2) assumes a distorted trigonal prismatic geometry. The solid-state crystal structure involves various non-covalent supramolecular interactions delineated by Hirshfeld Surface and 2D fingerprint plot analysis. Noteworthily, interesting S⋯H, O⋯H, and N⋯H contacts were observed, which have identical percentages in both complexes. The sparse tetrel bonding interactions in the complex, involving the CH3 group, were evaluated in a new dimension of DFT. We observed this privileged bonding landscape that leads to the formation of self-assembled dimers in the crystal complexes. DFT-based MEP, RDG surface, NBO, and QTAIM/NCI plot investigation quantified such unique tetrel bonding interactions.