Methyl Resonances Research Articles

Quinoline- and pyrimidine-based allosteric modulators of the sarco/endoplasmic reticulum calcium ATPase.

Small-molecule allosteric activators of the enzyme sarco/endoplasmic reticulum calcium ATPase (SERCA) hold promise as novel experimental tools to manipulate intracellular calcium concentrations and as therapeutic agents to treat medical conditions associated with elevated cytosolic calcium levels. Here, we synthesized and characterized 20 analogs of the known allosteric SERCA activator CDN1163 and tested their ability to stimulate SERCA activity. The structures of the compounds varied in the alkyl group of the parent scaffold's ether moiety as well as in the composition of the nitrogenous aromatic ring system. The most active compounds exhibited potencies in the sub-micromolar range while increasing enzyme activity by more than 25%. The observed structure-activity relationships indicated that bulky alkyl groups in the ether moiety along with a quinoline ring methyl substituent were beneficial for activity. Replacement of the quinoline by a pyrimidine ring system reduced activity. To conceive a potential mechanism of action, we generated a molecular model of the transition state of SERCA when undergoing the rate-limiting step of its catalytic cycle. Subsequent blind docking with CDN1163 identified a high-affinity binding site close to the enzyme's ATP binding pocket, suggesting that the activators may accelerate SERCA's catalytic cycle by aiding in ATP binding and positioning.

Aromatic Difluoroboron β-Ketoiminate Complexes: Effect of Substituents on Mechanofluorochromism and Polymorphic Behavior.

Aromatic difluoroboron β-ketoiminate complexes (ketimBF2) are structural nitrogen-containing analogues of aromatic difluoroboron β-diketonates (diketBF2). Aggregation-induced emission (AIE) and polymorphic behavior allow ketimBF2 to exhibit mechanofluorochromic (MFC) properties. A detailed comparative study of the luminescence of a wide range of ketimBF2 with H- and CH3-substituents of nitrogen atom and diketBF2 with various substituents of the chelate ring (methyl, phenyl, toluoyl, anisoyl, biphenyl, naphthyl, anthracyl) in the solid state was carried out. As a result, regularities of the influence of substituents on the luminescent and MFC properties for 21 dyes have been established. Replacing one oxygen atom in diketBF2 with nitrogen atom in the chelate ring (H-substituted ketimBF2) changes the nature of the molecular stacking in crystals, which is manifested in different MFC properties. The introduction of a methyl group into the chelate ring (CH3-substituted ketimBF2) induces steric hindrance, which prevents the efficient formation of supramolecular structures and, consequently, leads to the shortest-wavelength monomeric emission in the solid state in comparison with oxygen and H-substituted nitrogen analogues. Methoxy derivative of H-substituted ketimBF2 exhibits non-reversible fluorochromic switching after annealing and can be used as temperature indicator to control unauthorized heating of temperature-sensitive substances during transportation and storage.

A molecular dynamics simulation study of EthylChlorophyllide A molecules confined in a SiO2 nanoslit.

This paper investigates the dynamic behavior of EthylChlorophyllide A (EChlideA) molecules in a methanol solution confined within a 4nm silica nanoslit, using molecular dynamics simulations over a duration of 1ms. Three systems, containing 1, 2, and 4 solutes, were studied at 298K. The results demonstrate that EChlideA molecules predominantly adsorb onto the silica surfaces, driven by specific interactions between chlorin ring's methyl group and the hydroxyl groups of the silica. This adsorption leads to stable binding, particularly in less crowded environments, as indicated by the potential of mean force analysis. Higher molecular concentrations, such as those with four EChlideA molecules, introduce variation in binding strength due to molecular aggregation and complex interactions. The orientation analysis reveals that the chlorin ring tends to align parallel to the surface, requiring rotational adjustments during surface diffusion. In addition, solvent coordination around the Mg ion remains consistent under bulk conditions, although with some variation in higher concentrations. This study also highlights a decrease in linear diffusion and an increase in rotational relaxation times for EChlideA molecules within the confined nanoslit, reflecting the influence of molecular concentration and arrangement on their dynamics. These findings provide valuable insights into the role of surface interactions, molecular orientation, and solvent coordination in confined environments, offering implications for the design of nanoscale systems.

Synthesis and photooxygenation of 3-(p-substituted phenyl)-3a,8a-dihydro-4H-cyclohepta[d]isoxazoles: facial selectivity.

Two 3-(p-substituted phenyl)-3a,8a-dihydro-4H-cyclohepta[d]isoxazoles were synthesized by 1,3-dipolar cycloaddition of the corresponding nitrile oxides with cycloheptatriene. Two endoperoxides were synthesized as facially selective and single products in high yields (93%-95%) from the reactions of isoxazole derivatives with singlet oxygen. The exact configurations of the endoperoxide with a methyl group in the phenyl ring and the diol synthesized from it were confirmed by X-ray analysis. To elucidate the mechanism, the formation energy of the endoperoxide was investigated by simulations using the software package Gaussian 09 and density functional theory calculations via the M06-2X/6-311+G(d,p) level method in dichloromethane. The results were consistent with experimental findings showing the formation of isoxazole products.

Effect of ether chain and isomerism on surface and antimicrobial activity of mono- and dicationic imidazolium-based surface-active ionic liquids

A series of 16 imidazolium-based surface-active ionic liquids (SAILs) were synthesized. The designed SAILs, consisted of either one amphiphilic center, 3-alkoxymethyl-1-benzylimidazolium or 3-alkoxymethyl-1-benzyl-2-methylimidazolium, and two amphiphilic centers, 3,3′-[α,ω-(dioxaalkane)]bis(1-benzylimidazolium) or 3,3′-[α,ω-(dioxaalkane)]bis(1-benzyl-2-methylimidazolium). These compounds were investigated in terms of thermal analysis, ability to self-organize to micelles, and antimicrobial activity. The insertion of an ether moiety in the alkyl side or spacer chain favored adsorption at the air–water interface and micellization in the bulk solution when compared to commercial chloride surfactants. The results showed that attachment of a methyl group to the imidazolium ring led to lower the critical micelle concentration (CMC) than lengthening the alkyl chain or spacer in the imidazolium cation. Additionally, biological activity increased with increasing hydrophobicity of the compounds. The methylation of the imidazole ring at positions 2 and 2′ yielded in a notable increase in bacteriostatic activity, especially against Gram-positive bacteria, notably the Staphylococcus aureus strains. It has been demonstrated that minor structural modifications, specifically substituting the imidazole ring instead of elongating the alkyl chain or spacer, can modify the micellization and aggregation behavior, leading to differences in both the efficacy and variety of antimicrobial activity of amphiphilic SAILs.

New Hydroxylactones and Chloro-Hydroxylactones Obtained by Biotransformation of Bicyclic Halolactones and Their Antibacterial Activity.

The aim of this study was to obtain new halolactones with a gem-dimethyl group in the cyclohexane ring (at the C-3 or C-5 carbon) and a methyl group in the lactone ring and then subject them to biotransformations using filamentous fungi. Halolactones in the form of mixtures of two diasteroisomers were subjected to screening biotransformations, which showed that only compounds with a gem-dimethyl group located at the C-5 carbon were transformed. Strains from the genus Fusarium carried out hydrolytic dehalogenation, while strains from the genus Absidia carried out hydroxylation of the C-7 carbon. Both substrates and biotransformation products were then tested for antimicrobial activity against multidrug-resistant strains of both bacteria and yeast-like fungi. The highest antifungal activity against C. dubliniensis and C. albicans strains was obtained for compound 5b, while antimicrobial activity against S. aureus MRSA was obtained for compound 4a.

Evaluation of anisole hydrodeoxygenation reaction pathways over a Ni/Al2O3 catalyst

Anisole is a model molecule for studying hydrodeoxygenation (HDO) of lignin-derived oxygenates. Here we elucidate its HDO pathway over 10 % Ni/Al2O3 catalyst. Adsorption experiments showed that anisole is adsorbed on the acidic sites of the Al2O3. Anisole adsorption at 200–300 °C is reactive in nature, and results in its demethylation. The catalyst was tested at 100–300 °C, 5–40 bar H2 pressure. Conversion of 78 % was obtained at 5 bar and 300 °C, restricted by hydrogenation-dehydrogenation equilibrium. HDO mainly starts through the ring-hydrogenation pathway. This is followed by demethoxylation beyond 180 °C. At 5–12 bar, cyclohexane dehydrogenates to benzene. This was confirmed by conducting an HDO experiment with methoxycyclohexane. At lower pressure deoxygenation is favored; and demethylation is accompanied with methylation of the aromatic ring, for temperature >260 °C. Investigation of the initial reaction stages showed that anisole HDO on Ni/Al2O3 catalyst proceeds via two independent pathways i.e., reactive adsorption/(de)methylation and aromatic ring hydrogenation.

An Effective Method for the Evaluation of the Enantiomeric Purity of 1,2-Diacyl-sn-glycero-3-phosphocholine-Based Lipids by NMR Analysis

In this article, we report a very efficient method for the determination of the enantiopurity of 1,2-diacyl-sn-glycero-3-phosphocholine by 1H NMR analysis using a readily available chiral derivatizing boronic acid (CDA), (R)-(2-(((1-phenylethyl)amino)methyl)phenyl)boronic acid. After the removal of the acyl groups of 1,2-diacyl-sn-glycero-3-phosphocholine via methanolysis and washing fatty acid byproducts with CHCl3, the obtained sn-glycero-3-phosphocholine (GPC) with the free diol moiety is derivatized by the chiral boronic acid and analyzed by 1H NMR analysis. The choline methyl resonance of each diastereomer is observed at distinctive chemical shifts in the 1H NMR spectrum. Integration of the respective resonances allows direct determination of the enantiomeric purity. The procedure was tested successfully using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) with different enantiomeric purities and with commercially available 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC).

1H, 13C, and 15N backbone and methyl group resonance assignments of ricin toxin A subunit

Ricin is a potent plant toxin that targets the eukaryotic ribosome by depurinating an adenine from the sarcin-ricin loop (SRL), a highly conserved stem-loop of the rRNA. As a category-B agent for bioterrorism it is a prime target for therapeutic intervention with antibodies and enzyme blocking inhibitors since no effective therapy exists for ricin. Ricin toxin A subunit (RTA) depurinates the SRL by binding to the P-stalk proteins at a remote site. Stimulation of the N-glycosidase activity of RTA by the P-stalk proteins has been studied extensively by biochemical methods and by X-ray crystallography. The current understanding of RTA’s depurination mechanism relies exclusively on X-ray structures of the enzyme in the free state and complexed with transition state analogues. To date we have sparse evidence of conformational dynamics and allosteric regulation of RTA activity that can be exploited in the rational design of inhibitors. Thus, our primary goal here is to apply solution NMR techniques to probe the residue specific structural and dynamic coupling active in RTA as a prerequisite to understand the functional implications of an allosteric network. In this report we present de novo sequence specific amide and sidechain methyl chemical shift assignments of the 267 residue RTA in the free state and in complex with an 11-residue peptide (P11) representing the identical C-terminal sequence of the ribosomal P-stalk proteins. These assignments will facilitate future studies detailing the propagation of binding induced conformational changes in RTA complexed with inhibitors, antibodies, and biologically relevant targets.

Isolation of embelin from embeliaribes berries for the development of topical anti–inflammatory preparation

Purpose: Embelin is a natural benzoquinone compound, isolated from Embeliaribes berries, known extensively for its anti-inflammatory properties. Due to its hydrophobic nature, it was less explored for topical preparation. Therefore, the purpose of this study was to explore the potential of embelin as an anti-inflammatory agent for topical preparations as well as assess its potential to replace synthetic drugs, which can be resistant to bacterial strains. A topical preparation with embelin would be potentially more effective as well as safer than synthetic drugs. Method: Embelin has been converted into its potassium salt, and a cream was developed, which was then subjected to physiochemical evaluation. The isolated Embelin and Embelin Potassium salts were characterised by various spectral analysis. The in vitro anti-inflammatory activity was determined by the heat-induced hemolysis and albumin denaturation. Docking scores of embelin and diclofenac were compared and the drug content per gram of cream was estimated. Result: The UV spectral absorption peak of Embelin was determined to be at 274 nm, while that of the potassium salt of Embelin was at 515 nm.. The IR bands were found at 1328.951cm-1,361.74 cm-1, 1616.35 cm -1,1616.35 cm -1 ,1452.4 cm -1, 748.28 cm -1 and 2947.23 cm -1 respectively due to phenolic OH bending, C=O stretching, aromatic ring bending, methylene bending and methyl stretching . The IR spectra of Embelin potassium salt exhibited similar pattern as that of Embelin but with shifted band due to presence of potassium salt. Heat-induced hemolysis using diclofenac as standard and embelin potassium salt as test showed 98.01% inhibition and 92% inhibition, respectively, at50µg/ml. The binding affinity of diclofenac was determined to be -4.9, while the binding affinity of embelin was -5.7, indicating a higher affinity for embelin. Lastly, the drug content per gram of cream was found to be 95%, indicating the amount of active drug (embelin or embelin potassium salt) present in the cream formulation. Conclusion: Embelin was isolated from Embeliaribes berries and formulated into a herbal cream. The in-vitro studies conducted on the cream showed that it has a significant effect on inflammation . However, in–vivo studies are required for the prepared topical cream to confirm its effectiveness.

Synergistic anti‐bacterial activity of imidazole‐based azo dyes with polyvinylpyrrolidone‐coated silver nanoparticles

AbstractThe high demand for novel antimicrobial textiles by the medical, healthcare, hygiene, sportswear, personal protective equipment and filtration sectors has promoted the growth of functional textiles. However, the efficacy of antimicrobial agents against different pathogens is a considerable challenge because of the distinctive mechanisms of action and resistance. The development of novel synergistic antimicrobial dyes may offer numerous opportunities to enhance antimicrobial effectiveness. In this work, a novel imidazole‐based azo dye with a p‐methoxyphenyl group in the N‐1 substituent of the imidazole ring (AzoIz‐a), and corresponding amidrazone precursor (AmIz‐a), were combined with polyvinylpyrrolidone‐coated silver nanoparticles (AgNPs). The molecules, alone and combined with the AgNPs, were characterised by ultraviolet‐visible spectrophotometry and zeta potential. Their synergistic effect was assessed against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. The results were compared with a previously reported imidazole‐based azo dye and precursor containing a methyl group in the imidazole ring (AmIz‐b and AzoIz‐b). The results showed interesting antimicrobial properties of the novel AzoIz‐a molecules when combined with a very small concentration of AgNPs. The combination showed an additive effect for S. aureus and a synergistic effect for E. coli and P. aeruginosa. Considering the synergistic results, the effective concentration of the AzoIz‐a decreased from more than 128 to 16‐32 μg.mL−1 by the addition of a small concentration of AgNPs (0.6‐1.3 μg.mL−1), which displayed comparable results with the AzoIz‐b molecule. Thus, the application of these conjugates in textiles may lead to highly coloured materials with remarkable anti‐bacterial properties, which warrant further exploration.

Study on adsorption behaviors of different cresols: First-principles calculation

Removal of organic pollutants is an important issue of wastewater treatment. The adsorption effects of different types and numbers of O-cresol(ortho-cresol), M−cresol(meta-cresol) and P-cresol(para-cresol) on Au(111) surface were studied by first-principles calculation based on density functional theory(DFT). Results show that Au(111) surface has different adsorption activities for different cresols. When adsorption occurs, the aromatic ring, hydroxyl group and methyl group in the aromatic ring of cresol molecules in different systems showed different tilt angles. When a single cresol molecule is adsorbed, the aromatic ring plane consists of carbon and hydrogen atoms is basically parallel to the outermost layer plane of Au(111). With increasing number of same cresol molecules, the tilt degree between the aromatic ring of two M−cresol molecules and Au(111) surface is greater. However, when the number of cresol molecules is 3, C–H bond in methyl group and H-O bond of cresol molecules that close to each other in M−cresol adsorption system are significantly elongated. At the same time, the angle between the aromatic ring plane and Au(111) surface changes greatly. For the adsorption of three types of cresol molecules, the tilt angle order of aromatic ring in cresol molecules is P-cresol > O-cresol > M−cresol. From the comprehensive analyses of adsorption configuration, adsorption energy, adsorption distance and charge transfer, it can be seen that the adsorption priority of same cresol molecule on Au(111) surface is O-cresol > P-cresol > M−cresol. For the co-adsorption of cresol molecules, the adsorption process of 1O-1 M−1P system tends to preferentially occur on Au(111) surface. This study provides theoretical guide for the design of adsorbent materials for efficient removal of organic pollutants from wastewater.

Occurrence of antibiotics in reclaimed water, and their uptake dynamics, phytotoxicity, and metabolic fate in Lolium perenne L.

Reclaimed water (RW) has been extensively used for irrigation in agriculture, yet the occurrence of antibiotics in real RW, and their toxicity, uptake dynamics and metabolic fate still needs comprehensive exploration. In this study, we investigated the residual concentrations of nineteen antibiotics in the RW from four wastewater treatment plants, and determined their toxicity on plant at environment-relevant concentration. Total found concentrations of these antibiotics ranged from 623.66 ng L−1 to 1536.96 ng L−1, which decreased 10.3 and 19.4 % of roots' length and weight. Uptake dynamics analysis of the most hazardous antibiotic, norfloxacin (NFX) showed increasing amounts in the roots and leaves up to 3087.71 μg g−1. Ryegrass also can remove >80 % of 100 μg L−1 NFX being achieved by biodegradation through ring cleavage, decarboxylation, defluorination, hydrogenation, methylation and oxidation. Toxicity assessment of the identified byproducts showed their more toxic effect on fish, daphnia and algae. This study extended our understanding of the fate of antibiotics in plants during irrigation with reclaimed water, and emphasized its safety and pollutants' biomagnification concerns.

N-benzyl-2-methoxy-5-propargyloxybenzoamides, a new type of bleaching herbicides targeting the biosynthesis pathway of plastoquinone.

Previously, the herbicidal activity of N-benzyl-2-methoxybenzamides was discovered during a random screening program in our laboratory. The chemicals resulted in bleaching effect of newly grown leaves by interfering with the biosynthesis of β-carotene in plant. A total of 28 benzamides were synthesized and subjected for the evaluation of herbicidal activity. Structure-activity relationship (SAR) showed that introducing propargyloxy group at 5-position of benzoyl-benzene ring and fluorine or methyl group at 3- or 4-position of benzyl-benzene ring is beneficial for the activity. Post-emergence herbicidal activities of compounds 406 and 412 were comparable to those of mesotrione and diflufenican. Studies on MOA showed that 406 decreased the level of both β-carotene and plastoquinone (PQ) in treated plants. The bleaching effect in green alga caused by 406 could be reversed by supplying exogenous homogentisic acid (HGA), the precursor of plastoquinone. N-benzyl-2-methoxy-5-propargyloxybenzoamides were discovered as new candidates for bleaching herbicides. Preliminary investigation on mechanism of action (MOA) showed that the title compounds might indirectly interfere with carotenoid biosynthesis by blocking the production of PQ. © 2023 Society of Chemical Industry.

Structural Analysis and Characterization of 4-F-α-PVP Analog 4-F-3-Methyl-α- PVP Hydrochloride.

To identify 1-(4-fluorophenyl)-2-(1-pyrrolidinyl) pentan-1-one (4-F-α-PVP) analog 1-(4-fluoro-3-methyl phenyl)-2-(1-pyrrolidinyl) pentan-1-one (4-F-3-Methyl-α-PVP) hydrochloride without reference substance. The direct-injection electron ionization-mass spectrometry (EI-MS), GC-MS, electrospray ionization-high resolution mass spectrometry (ESI-HRMS), ultra-high performance liquid chromatography-high resolution tandem mass spectrometry (UPLC-HRMS/MS), nuclear magnetic resonance (NMR), ion chromatography and Fourier transform infrared spectroscopy (FTIR) were integrated utilized to achieve the structural analysis and characterization of the unknown compound in the sample, and the cleavage mechanism of the fragment ions was deduced by EI-MS and UPLC-HRMS/MS. By analyzing the direct-injection EI-MS, GC-MS, ESI-HRMS and UPLC-HRMS/MS of the compound in the samples, it was concluded that the unknown compound was a structural analog of 4-F-α-PVP, possibly with one more methyl group in the benzene ring. According to the analysis results of 1H-NMR and 13C-NMR, it was further proved that the methyl group is located at the 3-position of the benzene ring. Since the actual number of hydrogen in 1H-NMR analysis was one more than 4-F-3-Methyl-α-PVP neutral molecule, it was inferred that the compound existed in the form of salt. Ion chromatography analysis results showed that the compound contained chlorine anion (content 11.14%-11.16%), with the structural analysis of main functional group information by FTIR, the unknown compound was finally determined to be 4-F-3-Methyl-α-PVP hydrochloride. A comprehensive method using EI-MS, GC-MS, ESI-HRMS, UPLC-HRMS/MS, NMR, ion chromatography and FTIR to identify 4-F-3-Methyl-α-PVP hydrochloride in samples is established, which will be helpful for the forensic science laboratory to identify this compound or other analog compounds.

Gallate Moiety of Catechin Is Essential for Inhibiting CCL2 Chemokine-Mediated Monocyte Recruitment

Leukocyte recruitment witnesses an orchestrated complex formation between the chemokines and their molecular partners. CCL2 chemokine that regulates monocyte trafficking is a worthwhile system from the pharmaceutical perspective. In the current study, four major catechins (EC/EGC/ECG/EGCG) were assessed for their inhibitory potential against CCL2-regulated monocyte/macrophage recruitment. Interestingly, catechins with the gallate moiety (ECG/EGCG) could only attenuate the CCL2-induced macrophage migration. These molecules specifically bound to CCL2 on a pocket comprising the N-terminal, β0-sheets, and β3-sheets, and the binding affinity of ECGC (Kd = 22 ± 4 μM) is ∼4 times higher than that of the ECG complex (Kd = 85 ± 6 μM). MD simulation analysis evidenced that the molecular specificity/stability of CCL2-catechin complexes is regulated by multiple factors, including stereospecificity, number of hydroxyl groups on the annular ring-B, the positioning of the carbonyl group, and the methylation of the galloyl ring. Further, a significant overlap on the binding surface of CCL2 for EGCG/ECG and receptor interactions as evidenced from NMR data provided the rationale for the observed inhibition of macrophage migration in response to EGCG/ECG binding. In summary, these galloylated epicatechins can be considered as potent protein-protein interaction (PPI) inhibitors that regulate CCL2-directed leukocyte recruitment for resolving inflammatory/immunomodulatory disorders.

Anti-inflammatory maistemonine-class alkaloids of Stemona japonica

Three hitherto undescribed Stemona alkaloids, named stemajapines A–C (1–3), along with six known alkaloids (4–9), were isolated and identified from the roots of Stemona japonica (Blume) Miq. (Stemonaceae). Their structures were established by the analysis of the mass data, NMR spectra, and computational chemistry. Stemjapines A and B were degraded maistemonines without spiro-lactone ring and skeletal methyl from maistemonine. Concurrence of alkaloids 1 and 2 revealed an undescribed way to form diverse Stemona alkaloids. Bioassay results disclosed the anti-inflammatory natural constituents stemjapines A and C with IC50 values of 19.7 and 13.8 µM, respectively, compared to positive control dexamethasone with 11.7 µM. The findings may point out a new direction of Stemona alkaloids inaddition to its traditional antitussive and insecticide activities.

New Bicyclic Pyridine-Based Hybrids Linked to the 1,2,3-Triazole Unit: Synthesis via Click Reaction and Evaluation of Neurotropic Activity and Molecular Docking.

The synthesis of new original bicyclic pyridine-based hybrids linked to the 1,2,3-triazole unit was described via a click reaction. The anticonvulsant activity and some psychotropic properties of the new compounds were evaluated. The biological assays demonstrated that some of the studied compounds showed high anticonvulsant and psychotropic properties. The five most active compounds (7a, d, g, j, and m) contain a pyrano [3,4-c]pyridine cycle with a methyl group in the pyridine ring in their structures. Furthermore, molecular docking studies were performed, and their results are in agreement with experimental data.

BİS-(TSİKLOPENTADİENİLDİKARBONİLDӘMIR(I)) KOMPLEKSİNİN METİL HOMOLOQLARININ SİNTEZİ, İQ- VӘ 1H NMR-SPEKTROSKOPİYA ÜSULLARI İLӘ TӘDQİQİ

Three dimer complexes of iron [MenC5H5–nFe(CO)2]2 (n = 2, 3, 5) were obtained from the interaction of methyl homologues of cyclopentadiene (1,3-dimethyl-, 1,2,4-trimethyl- and 1,2,3,4,5-pentamethylcyclopentadien)with iron pentacarbonyl. The complexes were characterized by melting temperatures, infrared (IR) and proton magnetic resonance (1 H NMR) spectra. It was determined that despite the monotonous increase in the melting temperature of the complexes in the [C5H5Fe(CO)2]2  [Me2C5H3Fe(CO)2]2  [Me3C5H2Fe(CO)2]2  [Me5C5Fe(CO)2]2 sequence, the complexes with 2 and 3 methyl groups in the ring (n = 2, 3) undergo severe thermal decomposition during melting. The investigation (analysis) of the reasons for the change in the frequencies of the valence vibration of the CO bond in the indicated order allowed to associate the observed thermal behavior of the complexes with the steric and electronic interactions between the methyl and carbonyl groups. The obtained results suggest that among the four studied complexes, the complexes with two and three methyl groups in the cyclopentadienyl ring ([Me2C5H3Fe(CO)2]2,[Me3C5H2Fe(CO)2]2) are more promising as precursors in the synthesis of carbon nanotubes.

Subtle hydrogen bond preference and dual Franck-Condon activity - the interesting pairing of 2-naphthol with anisole.

The hydrogen-bonded complexes between 2-naphthol (or β-naphthol) and anisole are explored by detecting their IR absorption in the OH stretching range as well as their UV absorption by means of laser-induced fluorescence and resonance-enhanced two-photon UV ionisation. For the more stable cis and the metastable trans conformations of the OH group in 2-naphthol, hydrogen bonding to the oxygen atom of anisole is consistently detected in different supersonic jet expansions. Alternative hydrogen bonding to the aromatic ring of anisole remains elusive, although the majority of state-of-the-art hybrid DFT functionals with London dispersion correction and - less surprisingly - MP2 wavefunction theory predict it to be slightly more stable at zero-point level, unless three-body dispersion correction is added to the B3LYP-D3(BJ) approach. This changes at the CCSD(T) level, which forecasts an energy advantage of 1-3 kJ mol-1 for the classical hydrogen bond arrangement even after including (DFT) zero-point energy contributions. The UV and IR spectra of the cis complex exhibit clear evidence for intensity redistribution of the primary OH stretch oscillator to combination states with the same low-frequency intermolecular bending mode by Franck-Condon-type vertical excitation mechanisms. This rare case of dual (vibronic and vibrational) Franck-Condon activity of a low-frequency mode invites future studies of homologues where aromatic ring docking of the OH group may be further stabilised, e.g. through anisole ring methylation.