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The π-stacking interaction is one of the most important intramolecular and intermolecular noncovalent interactions in organic chemistry. It plays an important role in stabilizing some structures and transition states in certain reactions via both intramolecular and intermolecular interactions, facilitating different selectivities, such as chemo-, regio-, and stereoselectivities. This minireview focuses on the recent examples of the π-stacking interaction-controlled asymmetric synthesis, including auxiliary-induced asymmetric synthesis, kinetic resolution, asymmetric synthesis of helicenes and heterohelicenes, and multilayer 3D chiral molecules. [ABSTRACT FROM AUTHOR]

Human tankyrase-1 is an important regulator of poly(ADP-ribosyl)ation (PARylation) of Wnt/β-catenin signaling and has been recognized as a druggable target of gynecologic tumors. The active site of tankyrase-1 is rich with π-electron, which contains a number of aromatic amino aid residues and can form multiple π-stacking interactions with its substrates and ligands. In this study, computational analysis revealed that aromatic residues involved in tankyrase-1’s active site are significantly responsible for the intermolecular interaction between tankyrase-1 and its inhibitor ligands. Based on the harvested information, structure-based molecular design of aromatic pentapeptide inhibitors was carried out to target tankyrase-1. The pentapeptide candidates were defined by aromatic amino acids, and their π-stacking contribution is stronger than small-molecule inhibitors. Eight pentapeptide hits were determined to have moderate or high inhibitory potency against human tankyrase-1, in which two hits FYWYH and YWFYH can inhibit the enzyme potently at sub-micromolar level. Structural analysis observed a number of face-to-face, parallel-displaced and T-shaped π-stacking interactions at tankyrase-1/pentapeptide complex interface, which co-define a complicated π-stacking network and confer both stability and specificity for the complex formation. [ABSTRACT FROM AUTHOR]

Ester hydrates, as the intermediates of the esterification between acid and alcohol, are very short-lived and challenging to be trapped. Therefore, the crystal structures of ester hydrates have rarely been characterized. Herein, we present that the mono-deprotonated ester hydrates [CH3OSO2(OH)2]−, serving as the template for the self-assembly of a π-stacked boat-shaped macrocycle (CH3OSO2(OH)2)0.67(CH3OSO3)1.33@{[ClLCoII]6}·Cl4·13CH3OH·9H2O (1) (L = tris(2-benzimidazolylmethyl) amine), can be trapped in the host by multiple NH···O hydrogen bonds. In the solution of CoCl2, L, and H2SO4 in MeOH, HSO4− reacts with MeOH, producing [CH3OSO3]− via the ester hydrate intermediate of [CH3OSO3(OH)2]−. Both the product and the intermediate serve as the template directing the self-assembly of the π-stacked macrocycle, in which the short-lived ester hydrate is firmly trapped and stabilized, as revealed by single-crystal analysis. [ABSTRACT FROM AUTHOR]

The π-stacking interaction is one of the most important intramolecular and intermolecular noncovalent interactions in organic chemistry. It plays an important role in stabilizing some structures and transition states in certain reactions via both intramolecular and intermolecular interactions, facilitating different selectivities, such as chemo-, regio-, and stereoselectivities. This minireview focuses on the recent examples of the π-stacking interaction-controlled asymmetric synthesis, including auxiliary-induced asymmetric synthesis, kinetic resolution, asymmetric synthesis of helicenes and heterohelicenes, and multilayer 3D chiral molecules.

For the estimation of the biological affinity of nitrogen-containing π-conjugated heterocyclic systems toward amino acid residues in proteins, the fragment-to-fragment approach was proposed. Two mechanisms of complexation between the heterocycle molecule with different donor/acceptor properties and the amino acid residue in the active part of the protein biomolecule were considered. One of these mechanisms is the π-stacking interaction and the other is formation of hydrogen bonds with model amino acid residues. It was found that heterocycles with a π-conjugated electron-acceptor moiety form a more stable heterocycle–biomolecule complex with protein fragments. Nitrogen-containing conjugated heterocycles with several nitrogen atoms form poly-hydrogen-bonded complexes. The stabilization energy of complexes with two pyrimidine–biomolecule hydrogen bonds increases by 4–6 kcal/mol compared to similar complexes with one hydrogen bond. Hydrophobic interactions are much more sensitive to the donor-acceptor properties of heterocycles in the formation of hydrogen-bonded complexes than in the formation of π-stacked complexes. The hydrophobic effect in the fragment-to-fragment approach allows us to see the values of the stabilization energies of the heterocycle–biomolecule complexes as close as possible to the experimentally studied biological systems. [ABSTRACT FROM AUTHOR]

Ester hydrates, as the intermediates of the esterification between acid and alcohol, are very short-lived and challenging to be trapped. Therefore, the crystal structures of ester hydrates have rarely been characterized. Herein, we present that the mono-deprotonated ester hydrates [CH3OSO2(OH)2]−, serving as the template for the self-assembly of a π-stacked boat-shaped macrocycle (CH3OSO2(OH)2)0.67(CH3OSO3)1.33@{[ClLCoII]6}·Cl4·13CH3OH·9H2O (1) (L = tris(2-benzimidazolylmethyl) amine), can be trapped in the host by multiple NH···O hydrogen bonds. In the solution of CoCl2, L, and H2SO4 in MeOH, HSO4− reacts with MeOH, producing [CH3OSO3]− via the ester hydrate intermediate of [CH3OSO3(OH)2]−. Both the product and the intermediate serve as the template directing the self-assembly of the π-stacked macrocycle, in which the short-lived ester hydrate is firmly trapped and stabilized, as revealed by single-crystal analysis.

Human poly(ADP‐ribose) polymerase 1 (PARP‐1) is involved in DNA strand break repair and has been recognized as a promising druggable target for ovarian cancer. The active site of PARP‐1 is π electron‐rich, which contains at least 12 aromatic amino aid residues in its first‐ and second‐shell regions, and can form effective π‐stacking interactions with its natural substrates and inhibitor ligands. In this study, the intermolecular interactions between the 12 PARP‐1 aromatic residues and 16 approved/clinical/preclinical small‐molecule inhibitors were systematically profiled using quantum mechanics/molecular mechanics (QM/MM) analyses and dispersion‐corrected density functional theory (DFT) calculations. It was found that the aromatic residues contribute ~50% affinity to the global binding energy of PARP‐1/inhibitor complexes, in which the four residues (His862, Tyr889, Tyr896 and Tyr907) play a primary role in π‐stacking interactions with most inhibitor ligands. Based on the harvested knowledge, we attempted to perform the rational design of aromatic amino acid‐rich (AAAr) peptides to target PARP‐1 active site by using peptide docking, affinity scoring, and QM/MM analyses. These peptides are only composed of four aromatic amino acids, namely phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp) and histidine (His), and their π‐stacking contribution is improved to ~60% from the ~50% of small‐molecule inhibitors, although their global binding energy is moderately lower than these inhibitors. Three designed AAAr peptides (WYHY, WYYH and WFYY) with high‐affinity scores were determined as potent PARP‐1 targeted agents; they exhibited high inhibitory activities and are roughly comparable with that of the sophisticated PARP‐1 inhibitor drug Olaparib, suggesting that these designed peptides, as expected, can effectively target PARP‐1 with a satisfactory inhibitory profile. Molecular modeling revealed a number of face‐to‐face, parallel‐displaced, and T‐shaped π‐stacking interactions at PARP‐1/peptide complex interface, which co‐define an intense π‐stacking network and confer both stability and specificity for the complex recognition and association. [ABSTRACT FROM AUTHOR]

The title compound, C11H11NO4S, possesses weak analgesic properties and is a source compound for the synthesis of highly active analgesic and anti-inflammatory compounds. The benzothiazine ring adopts a conformation intermediate between twist-boat and sofa. The ester substituent is turned towards the endocyclic double bond because of steric repulsion. In the crystal, the molecules form columns along the [001] direction, bound by N—H...O hydrogen bonds and stacking interactions.

Chiral acrylic esters derived from biomass were developed as models to have a better insight in the aryl–vinyl π-stacking interactions. Quantum chemical calculations, NMR studies and experimental evidences demonstrated the presence of equilibriums of at least four different conformations: π-stacked and face-to-edge, each of them in an s-cis/s-trans conformation. The results show that the stabilization produced by the π–π interaction makes the π-stacked conformation predominant in solution and this stabilization is slightly affected by the electron density of the aromatic counterpart.

The title compound, C11H11NO4S, possesses weak analgesic properties and is a source compound for the synthesis of highly active analgesic and antiinflammatory compounds. The benzothiazine ring adopts a conformation intermediate between twist-boat and sofa. The ester substituent is turned towards the endocyclic double bond because of steric repulsion. In the crystal, the molecules form columns along the [001] direction, bound by N--H...O hydrogen bonds and stacking interactions. [ABSTRACT FROM AUTHOR]

To date, fabricating high sensitive, stable and facile sensing strategy for detection of nitrophenol still remains a challenge in practical applications. This article demonstrates for the first time a facile and stable colorimetric sensor based on three-dimensional graphene/mesoporous Fe 3 O 4 (3D GF/m-Fe 3 O 4 ) heterogeneous nanozyme. Using a simple hydrothermal procedure, mesoporous Fe 3 O 4 nanoparticles were in situ synthesized on 3D GF. The 3D GF/m-Fe 3 O 4 nanohybrid possesses high peroxidase mimicking activity due to the synergistic effect of 3D GF and m-Fe 3 O 4 . Based on the peroxidase-like activity and p-nitrophenol-mediated inhibition controllability, the nanohybrid was successfully adopted in the sensitive and selective sensing detections of p-nitrophenol (PNP) with a low detection limit of 45 nM. Moreover, 3D GF/m-Fe 3 O 4 nanohybrid shows to be extremely robust, as it still retains its original response to PNP after being reused for 10 times. The method was applied to the determination of PNP in spiked lake water and gave good recoveries. With the merits of high sensitivity and selectivity, simplification, recyclability, and excellent stability, this sensing platform not only expands the application of 3D GF and Fe 3 O 4 , but also provides an alternative technique to construct robust nanozyme with multiple functionalities for various biological and environmental applications. [ABSTRACT FROM AUTHOR]

Novel pseudopolymorphic Hdabco compounds with an Fe(III) complex anion, (Hdabco)[Fe(aznp) 2 ]·CH 2 Cl 2 1 and (Hdabco)[Fe(aznp) 2 ]·0.5H 2 O 2 [dabco = 1,4-diazabicyclo[2.2.2]octane, H 2 aznp = (2′-hydroxyphenylazo)-2-hydroxynaphthalene], were prepared and characterized. The magnetic susceptibility for 1 and 2 revealed that both complexes were in a high-spin (HS) state in the whole temperature range and exhibited weak ferromagnetic interactions below 40 K. The crystal structural analyses suggested that strong N–H⋯O hydrogen bonding interactions between the Hdabco cation and [Fe(aznp) 2 ] anion may induce the distortion of a coordination structure resulting in the HS complexes, whereas π-stacking interactions between the π-ligands in the [Fe(aznp) 2 ] anion and additional C–H⋯N hydrogen bonding interactions between the Hdabco cation and [Fe(aznp) 2 ] anion constructed a intermolecular interaction framework structure with one-dimensional channels. The thermogravimetry analysis for compound 1 indicated the adsorption of a water molecule took place after the desorption of a dichloromethane molecule. This transformation of 1 into 2 proved to proceed in a single-crystal-to-single-crystal way by powder X-ray diffractions and single crystal X-ray structural analysis. [ABSTRACT FROM AUTHOR]

To develop a new spin-crossover functional material, a magnetic hybrid compound [Fe(qsal)2][Ni(mnt)2] was designed and synthesized (Hqsal = N-(8-quinolyl)salicylaldimine, mnt = maleonitriledithiolate). The temperature dependence of magnetic susceptibility suggested the coexistence of the high-spin (HS) Fe(III) cation and π-radical anion at room temperature and a magnetic transition below 100 K. The thermal variation of crystal structures revealed that strong π-stacking interaction between the π-ligand in the [Fe(qsal)2] cation and [Ni(mnt)2] anion induced the distortion of an Fe(III) coordination structure and the suppression of a dimerization of the [Ni(mnt)2] anion. Transfer integral calculations indicated that the magnetic transition below 100 K originated from a spin-singlet formation transformation in the [Ni(mnt)2] dimer. The magnetic relaxation of Mössbauer spectra and large thermal variation of a g-value in electron paramagnetic resonance spectra below the magnetic transition temperature implied the existence of a magnetic correlation between d-spin and π-spin. [ABSTRACT FROM AUTHOR]

[Display omitted] • π-interaction of curcumin with aromatic rings of three different amino-acids were studied by quantum mechanical methods. • Curcumin in diketo form has a greater π-interaction with aromatic rings of amino-acids. • Curcumin in keto-enol form is a better antioxidant than in diketo form. • Sum of electron densities at bond critical points and ring critical points are good descriptors for prediction of π-stacking interactions. • Tendency of curcumin to form intramolecular hydrogen bonds increases after π-stacking interaction. The aggregation of amyloid-β peptides into amyloid fibrils is considered as one of the possible causes of Alzheimer's disease. Curcumin is a well-known inhibitor for aggregation of Aβ 1-42 peptides and has the ability to disintegrate preformed Aβ fibrils and amyloid plaques. This study provides an insight on the magnitude of π-stacking interactions between the aromatic AAs of Aβ and curcumin via quantum mechanical methods in gas phase and in water solvent. The results showed stacking interaction energies for CurK and amino acids are greater. The calculated charges on carbon atoms showed that B ring in CurE is more susceptible to π-stacking interaction. HOMO-LUMO energy gap showed that CurE is a better antioxidant than CurK. It was shown that the sum of electron densities, Ʃρ/n, calculated at BCPs and RCPs can be useful as descriptors for prediction of π-stacking interaction in the complexes. [ABSTRACT FROM AUTHOR]

To investigate the π-extension effect on an unusual negative-charged spin crossover (SCO) FeIII complex with a weak N2O4 first coordination sphere, we designed and synthesized a series of anionic FeIII complexes from a π-extended naphthalene derivative ligand. Acetonitrile-solvate tetramethylammonium (TMA) salt 1 exhibited an SCO conversion, while acetone-solvate TMA salt 2 was in a high-spin state. The crystal structural analysis for 2 revealed that two-leg ladder-like cation-anion arrays derived from π-stacking interactions between π-ligands of the FeIII complex anion and Coulomb interactions were found and the solvated acetone molecules were in one-dimensional channels between the cation-anion arrays. A desolvation-induced single-crystal-to-single-crystal transformation to desolvate compound 2' may be driven by Coulomb energy gain. Furthermore, the structural comparison between quasi-polymorphic compounds 1 and 2 revealed that the synergy between Coulomb and π-stacking interactions induces a significant distortion of coordination structure of 2. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs) have received significant environmental concern because of their potential toxicity to humans and wildlife worldwide. The photodegradation debromination of deca-BDE (BDE209) in the tetrahydrofuran (THF) solvent in the presence of furan is explored using the time-dependent density functional theory combined with the polarizable continuum model. Our calculations reveal that the lone pair–π interaction between BDE209, and THF has a significant effect on the low-lying excitation and reduces the binding energies of C–Br bonds to some extent, which accounts for the photodegradation via the πBDE209σ* excited state and explains experiment successfully. We find that the addition of a small quantity of furan can promote the photodegradation of BDE209 in THF effectively and this is attributed to the π-stacking interaction between BDE209 and furan, which plays an important role in the low-lying π → σ* transitions in the sunlight region. [ABSTRACT FROM AUTHOR]

Because of their unique visual optic and electronic properties, substituted quinones are commonly used as dyes and pigments; nevertheless, a theoretic background of relationship between the structures and optical properties of such compounds seems to be still undeveloped. Two crystalline forms of 2-methoxynaphth-1-yl-naphthoquinone (MNQ) have been synthesized and characterized by means X-ray, NMR, UV-VIS, as well as, MS spectroscopy. The interpretation of intriguing optical properties of two crystalline forms of MNQ, based on detailed spectral and structural characterization, as well as, DFT and MP2 computations clearly connects the conformation of the molecules with their optical and electronic properties. Thus, flatter conformation, stabilized by crystal net force, favours the intense electron density transition from auxochrome to chromophore moiety (which corresponds excitation from HOMO to LUMO), as well as, favours the π-stacking interaction, that eventually results in colour enhancement. At the same time, small molecules of solvents included into the crystal net allow molecules of arylnaphthoquinones to adopt less rigid conformation what has a dramatic optical outcome. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The crystal structure of novel complex [LuL 3]3+·0.5{[Lu[(NO3)5(H2O)]2−·2[Lu(NO3)3(H2O)3]·4(NO3)−}6−·2(CH3NO2)·0.75(H2O) (1) (where L is napy-CMe2–P(O)Ph2, and napy is 1,8-naphthyridin-2-yl) was determined by single-crystal X-ray diffraction and discussed with respect to structures of other previously studied crystal Ln complexes of this ligand (2–4). Complex cation [LnL 3]3+ (Ln=Nd, Eu, Lu) is the main structural component of compounds 1–4. Intramolecular interligand π-stacking interaction is observed in all [LnL 3]3+ cations between three adjacent molecules of ONN coordinated ligands. π-Stacking interaction energy was estimated from Bader’s AIM theory calculations performed on DFT level. The data of ESI-MS agree well with assumption on π-stacking interaction. The lanthanide complexes [LnL 3]3+ (Ln=Nd, Eu, Lu) are the first example of mononuclear complexes with triple intramolecular π-stacking in ligand system of complex. [ABSTRACT FROM AUTHOR]

Mutations in the KV7.2 gene encoding for voltage-dependent K+ channel subunits cause neonatal epilepsies with wide phenotypic heterogeneity. Two mutations affecting the same positively charged residue in the S4 domain of KV7.2 have been found in children affected with benign familial neonatal seizures (R213W mutation) or with neonatal epileptic encephalopathy with severe pharmacoresistant seizures and neurocognitive delay, suppression-burst pattern at EEG, and distinct neuroradiological features (R213Q mutation). To examine the molecular basis for this strikingly different phenotype, we studied the functional characteristics of mutant channels by using electrophysiological techniques, computational modeling, and homology modeling. Functional studies revealed that, in homomeric or heteromeric configuration with KV7.2 and/or KV7.3 subunits, both mutations markedly destabilized the open state, causing a dramatic decrease in channel voltage sensitivity. These functional changes were (i) more pronounced for channels incorporating R213Q- than R213W-carrying KV7.2 subunits; (ii) proportional to the number of mutant subunits incorporated; and (iii) fully restored by the neuronal Kv7 activator retigabine. Homology modeling confirmed a critical role for the R213 residue in stabilizing the activated voltage sensor configuration. Modeling experiments in CA1 hippocampal pyramidal cells revealed that both mutations increased cell firing frequency, with the R213Q mutation prompting more dramatic functional changes compared with the R213W mutation. These results suggest that the clinical disease severity may be related to the extent of the mutation-induced functional K+ channel impairment, and set the preclinical basis for the potential use of Kv7 openers as a targeted anticonvulsant therapy to improve developmental outcome in neonates with KV7.2 encephalopathy. [ABSTRACT FROM AUTHOR]

Due to the different molecular stacking conformations, two kinds of intermolecular interactions, arene-arene π-stacking interaction and Cu-Cu interaction coexist in the polymorphs of [CFCu](4,4′-bipy) crystals, 3-α and 3-β. However, the relative magnitude of the two kinds of intermolecular interactions in 3-α and 3-β is different . With the help of first-principle band structure calculations, the relationship between the charge transport abilities and the intermolecular interactions in the two polymorphs was investigated for the first time. The analysis of band structures and Г point wave functions of the band-edge state in the valence band of crystal 3-α shows that the Cu-Cu interaction so-called cuprophilic interaction determines the hole transport ability, although this interaction is weaker than that in crystal 2 of CFCu(py) discussed in our previous work, which is a promising hole transport material. For polymorph crystal 3-β, the wave functions of LUMO are mainly localized on the bipyridine (bpy) groups, which are result from the arene-arene π-stacking interaction between the bpy groups. Such a π-π stacking interaction dominates the electron transport ability in the conduction band of 3-β and makes the electron main carrier for transporting. The results are also supported by the analysis of effective masses and density of states (DOS). Thus, the charge transport properties are dominated by different intermolecular interactions due to the different molecule stacking in the two polymorphs. [ABSTRACT FROM AUTHOR]

Two constitutionally isomeric 9,10-anthraquinonecarboxylic acids 1 and 2 are reported to yield DMSO-solvated crystals ( 1a and 2a) on the crystallization from DMSO. The molecular and crystal structures are described and comparatively discussed with reference to the effect implicated by the different position of the carboxylic group at the anthraquinone basis and the involvement of the solvent molecule. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel graphene (G) based solid-phase microextraction (SPME) fiber was firstly prepared by immobilizing the synthesized G on stainless steel wire as coating. The new fiber possessed a homogeneous, porous and wrinkled surface and showed excellent thermal (over 330°C), chemical and mechanical stability, and long lifespan (over 250 extractions). The SPME performance of the G-coated fiber was evaluated in detail through extraction of six pyrethroid pesticides. Although the thickness of G-coated fiber was only 6–8μm, its extraction efficiencies were higher than those of two commercial fibers (PDMS, 100μm; PDMS/DVB, 65μm). This high extraction efficiency may be mainly attributed to huge delocalized π-electron system of G, which shows strong π-stacking interaction with pyrethroid pesticide. The G-coated fiber was applied in the gas chromatographic determination of six pyrethroids, and their limits of detection were found to be ranged from 3.69 to 69.4ngL−1. The reproducibility for each single fiber was evaluated and the relative standard deviations (RSDs) were calculated to be in the range from 1.9% to 6.5%. The repeatability of fiber-to-fiber and batch-to-batch was 4.3–9.2% and 4.1–9.9%. The method developed was successfully applied to three pond water samples, and the recoveries were 83–110% at a spiking of 1μgL−1. [ABSTRACT FROM AUTHOR]

A new [2]pseudorotaxane from the 1,2-bis(isoquinolinium)ethane axle and the dibenzo-24-crown-8 ether wheel and its self-assembly were investigated by 1H NMR spectroscopy and single crystal X-ray diffraction technique. The results demonstrated that the supramolecular adduct was held together by three noncovalent interaction such as N+ ... O ion-dipole interactions, C-H ... O hydrogen bonding, and π-stacking between electron-poor isoquinolinium rings of the axle and electron-rich catechol rings of the wheel. They, furthermore, showed that the phenyl ring as a substituent or a fused ring on pyridinium has a similar effect on the association ability. [ABSTRACT FROM AUTHOR]

Background: The fragment-to-fragment approach for the estimation of the biological affinity of the pharmacophores with biologically active molecules has been proposed. It is the next step in the elaboration of molecular docking and using the quantum-chemical methods for the complex modeling of pharmacophores with biomolecule fragments., Methods: The parameter φ 0 was used to estimate the contribution of π-electron interactions in biological affinity. It is directly related to the position of the frontier levels and reflects the donor-acceptor properties of the pharmacophores and stabilization energy of the [Pharm꞉BioM] complex Results: By using quantum-chemical calculations, it was found that the stacking interaction of oxazoles with phenylalanine is 7-11 kcal/mol, while the energy of hydrogen bonding of oxazoles with the amino group of lysine is 5-9 kcal/mol. The fragment-to-fragment approach can be applied for the investigation of the dependence of biological affinity on the electronic structure of pharmacophores.c Conclusion: The founded quantum-chemical regularities are confirmed with the structure-activity relationships of substituted oxazoles., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

The research reported herein focuses on the synthesis of two new Cu(II) complexes {[Cu 2 (2-X-4,6-bis(di-2-picolylamino)-1,3,5-triazine], with X = butane-1,4-diamine (2) or N -methylpyrenylbutane-1,4-diamine (3) }, the latter with a pyrene group as a possible DNA intercalating agent. The structure of complex (3) was determined by X-ray crystallography and shows the dinuclear {CuII(μ-OCH 3) 2 CuII} unit in which the CuII···CuII distance of 3.040 Å is similar to that of 2.97 Å previously found for 1 , which contains a {CuII(μ-OH) 2 CuII} structural unit. Complexes (2) and (3) were also characterized in spectroscopic and electrochemical studies, and catecholase-like activity were performed for both complexes. The kinetic parameters obtained for the oxidation of the model substrate 3,5-di- tert -butylcatechol revealed that the insertion of the spacer butane-1,4-diamine and the pyrene group strongly contributes to increasing the catalytic efficiency of these systems. In fact, K ass becomes significantly higher, indicating that these groups influence the interaction between the complex and the substrate. These complexes also show DNA cleavage under mild conditions with moderate reaction times. The rate of cleavage (k cat) indicated that the presence of butane-1,4-diamine and pyrene increased the activity of both complexes. The reaction mechanism seems to have oxidative and hydrolytic features and the effect of DNA groove binding compounds and circular dichroism indicate that all complexes interact with plasmid DNA through the minor groove. High-resolution DNA cleavage assays provide information on the interaction mechanism and for complex (2) a specificity for the unpaired hairpin region containing thymine bases was observed, in contrast to (3). Two new copper(II) complexes were synthetized and characterized, which presented high catalytic activity in the oxidation of the substrate 3,5-di- tert -butylcatechol. In addition, the complexes also showed significant interaction with plasmid DNA in minor groove sites, with specificity for the unpaired hairpin region containing thymine bases. Unlabelled Image • The insertion of the 1,4-butanediamine and pyrene units enhanced the catalytic efficiency. • Complexes have some specificity for the hairpin sequence containing thymine bases. • Pyrene plays a role in the oxidation of the model substrate 3,5-di- tert -butylcatechol. • Mechanism of plasmid DNA cleavage is both hydrolytic and oxidative. [ABSTRACT FROM AUTHOR]

Although the π-stacking interaction between the substituted aromatic ring of small molecule inhibitors and the cytosine nucleobase present at the active site of HIV integrase (IN) are abundantly seen, no current study systematically covers differing positional substituents. Herewith, we report a comprehensive and systematic study aimed at unraveling the nature of substituent effects on model C||X-MB-Y (|| denotes π-stacking interaction, X is CHO, CN, NO 2 , COOH, Cl, SH, SCH 3 , F, NH 2 , OH, OCH 3 , CH 3 and H; MB denotes methylbenzene and Y typifies diverse substituent positioning which includes m 1 , m 2 , o 1 , o 2 and p) based on findings from the methodical incorporation of B3LYP-D3/6-311++G(d,p) binding energy (E bind) as well as symmetry-adopted perturbation theory (SAPT) results. Energy data indicated that stability of the C||X-MB-Y complexes increased in the presence of both the electron-withdrawing substituents (EWSs) and electron-donating substituents (EDSs) relative to the unsubstituted ones (X = H). Moreso, the lack of a good correlation between E bind and σ meta confirmed that the mechanism by which the various substituents facilitated the stability of each complex is not only by electrostatic interactions. In agreement with this finding, it was observed in this study that the combination of different substituent constant terms for all positions gave excellent correlations with E bind. In addition, the results indicated that the strength of π-stacking interactions depends on the corresponding orientations of interacting rings. Also, it was observed that the most stable complexes for EWSs and EDSs corresponded to positions o 1 and o 2 , respectively. Estimations of SAPT revealed the importance of the electrostatic term (E ele) in the prediction of E bind for each position, except at position m 2 , where all energy components played important roles in the stability of the complexes. Also, comparative studies of the different positions indicated that the stability of the complexes decreases by a decreasing E ele. Image 10895525 • The mechanisms by which the various substituents facilitated the stability of each complexes is not only by electrostatic interactions. • The strength of π-stacking interactions also depends on the corresponding orientations of interacting rings. • Estimations of SAPT revealed the importance of electrostatic term (E ele) in the prediction of E bind for each position, except at position m 2. [ABSTRACT FROM AUTHOR]

Chiral acrylic esters derived from biomass were developed as models to have a better insight in the aryl-vinyl π-stacking interactions. Quantum chemical calculations, NMR studies and experimental evidences demonstrated the presence of equilibriums of at least four different conformations: π-stacked and face-to-edge, each of them in an s-cis/s-trans conformation. The results show that the stabilization produced by the π-π interaction makes the π-stacked conformation predominant in solution and this stabilization is slightly affected by the electron density of the aromatic counterpart.