Search Results (129)

Pyridines are one of the most important and promising classes of N-heterocycles actively studied in modern organic and medicinal chemistry; in particular, pyridine is a privileged structural motif in drug design. From a synthetic organic chemistry perspective, nitropyridines can be considered as convenient and readily available precursors for a wide range of mono- and polynuclear heterocyclic systems demonstrating diverse activities, such as antitumor, antiviral, anti-neurodegenerative, etc. This review is an analysis of the literature on the use of nitropyridines for the synthesis of biologically active compounds, covering the period from 2015 to the present. Full article

This study is dedicated to the design of multiple redox-active oligonuclear manganese complexes supported with a bis(tetradentate) ligand (TPDP = 1,3-bis(bis(2-pyridinylmethyl)amino)-2-propanol) for high-contrast electrochromism based on the reversible redox process between Mn(II) (colorless) and Mn(III) (dark brown). Pentanuclear Mn₅ complex 1 (colorless) was synthesized via a one-pot reaction of Mn²⁺ and TPDP, while tetranuclear Mn₄ complex 2 (brown) was obtained through aerial oxidation of complex 1. Mn₅ complex 1 features a central MnCl₆ unit connected to two Mn₂(μ-TPDP) fragments through μ₃-Cl⁻ and μ-Cl⁻, whereas Mn₄ complex 2 adopts a symmetric tetranuclear structure with two mixed-valence Mn₂^II,III(μ-TPDP)(μ-Cl) fragments that are further linked by μ-oxo. Electrochemical studies revealed multi-step reversible redox properties for both complexes, attributed to Mn^II/Mn^III processes with significant electronic coupling (ΔE_1/2 = 0.27–0.37 V) between Mn centers. Spectroelectrochemical analysis revealed dynamic optical modulation through the tunable d-d transition and ligand-to-metal charge transfer (LMCT) state through reversible multiple redox processes based on Mn(II) ⇆ Mn(III) interconversion. The fabricated electrochromic device (ECD) exhibited reversible and high optical contrast between the colored state (dark brown) and the bleaching state (colorless). The results highlight the potential of polynuclear manganese complexes as high-contrast electrochromic materials for next-generation smart windows and adaptive optical technologies. Full article

Background/Objectives: Corona virus disease 2019 (COVID-19) poses a threat to global public health. The early identification of critical cases is crucial to providing timely treatment to patients. Here, we investigated whether the neutrophil levels could predict COVID-19 complications. Methods: We performed a retrospective study of patients with COVID-19, admitted to the Cheikh Khalifa International University Hospital, Casablanca, Morocco. Laboratory test results collected upon admission and during hospitalization were analyzed based on clinical information. Results: Our study revealed that a rise in neutrophil “PNN” levels was associated with respiratory deterioration and intubation. They were positively correlated with the procalcitonin and C-reactive protein levels. Interestingly, PNN (polynuclear neutrophil) levels on day 5 proved to be a better predictor of intubation, acute respiratory distress syndrome (ARDS), and mortality than the initial PNN counts, C-reactive protein, or procalcitonin. Moreover, binary logistic regression with stratified PNN-day 5 data revealed that a PNN level on day 5 > 7.7 (109/L) was an independent risk factor for mortality and ARDS. Finally, the PNN levels on day 5 and proinflammatory cytokine IL-6 were positively correlated. Conclusions: Our data showed that neutrophilia proved to be an excellent predictor of complications and mortality during hospitalization and could be used to improve the management of patients with COVID-19. Full article

Two new Co(II) coordination compounds viz. [Co(H₂O)(bz)₂(μ-3-Ampy)₂]_n (1) and [Co(4-Mebz)₂(2-Ampy)₂] (2) (wherebz = benzoate, 4-Mebz = 4-Methylbenzoate and Ampy = Aminopyridine) were synthesized and characterized via elemental (CHN), electronic spectroscopy, FT-IR spectroscopy, and thermogravimetric analysis (TGA). The molecular structures were determined by single-crystal X-ray diffraction analysis, inferring that compound 1 crystallizes as a 3-Ampy bridged Co(II) coordination polymer, whereas compound 2 crystallizes as a mononuclear Co(II) compound. Compound 1 unfolds the presence of N–H⋯O, C–H⋯O, O–H⋯O, C–H⋯N and aromatic π⋯π interactions, while for compound 2, N–H⋯O, C–H⋯O, C–H⋯C and C–H⋯π interactions are observed. Both the compounds showcase scarcely reported chelate ring interactions involving the benzoate moiety (chelate ring⋯π in 1 and N–H⋯chelate ring in 2). We also conducted theoretical evaluations comprising of combined QTAIM/NCI plot analysis, DFT energy calculation and MEP surface analysis to analyze the supramolecular interactions present in the crystal structures. As per QTAIM parameters, the predominance of π-stacking interactions over hydrogen bonds in stabilizing the assembly in compound 1 is affirmed. Likewise, in compound 2, both hydrogen bonding (HBs) and C–H⋯π interactions are deemed pivotal in stabilizing the dimeric assemblies. The in vitro antiproliferative activities of compounds 1 and 2 were performed against Dalton’s lymphoma (DL) cancer cell lines through cytotoxicity and apoptosis assays, showcasing higher cytotoxicity of compound 1 (IC₅₀ = 28 μM) over compound 2 (IC₅₀ = 34 μM). Additionally, a molecular docking study investigated the structure–activity relationship of these compounds and allowed an understanding of the molecular behaviour after treatment. Full article

Hericene is an unusual hexaolefin consisting of three 1,3-diene units located on a rigid bicyclo [2.2.2]octane framework that restricts the geometrical relationships of metal atoms bonded to these olefinic units. In order to explore possible effects of this rigidity limiting metal–metal interaction in polynuclear derivatives possibly stabilizing coordinatively unsaturated species, the structures and energetics of the hericene iron carbonyl complexes (hericene)Fe_m(CO)_n (m = 1, n = 3; m = 2, n = 6, 5; m = 3, n = 9, 8) have been investigated by density functional theory. The lowest-energy (hericene)Fe_m(CO)_3m (m = 1, 2, 3) structures have the cavities of the hericene ligand filled with a single Fe(CO)₃ moiety bonded to a 1,3-diolefin unit. Such species have been synthesized by the reaction of Fe₂(CO)₉ with hericene. For the (hericene)Fe₂(CO)₅ system, the lowest energy structures are singlet structures with an Fe(CO)₃ unit bonded to a 1,3-diene unit in one hericene cavity and an Fe(CO)₂ unit in another hericene cavity bonded to three C=C double bonds from two 1,3-diene units. Higher energy (hericene)Fe₂(CO)₅ structures include a structure in which a single hericene cavity contains a Fe₂(CO)₄(µ-CO) moiety with each iron atom bonded to a 1,3-diene unit. In addition, both singlet and triplet (hericene)Fe₂(CO)₅ structures are found in which an Fe(CO)₃ moiety and an Fe(CO)₂ moiety located in separate hericene cavities are each bonded to a 1,3-diene unit. The lowest-energy (hericene)Fe₃(CO)₈ structures have two hericene cavities containing Fe(CO)₃ moieties fully bonded to 1,3-diene units and a third hericene cavity containing an Fe(CO)₂ moiety fully bonded to a 1,3-diene unit. Full article

We report the research results of polynuclear complexes consisting of 3d-4f mixed-metal cores that are maintained by acetate ligands and multidentate Schiff base ligands with structurally exposed thioether groups. The presence of the latter at the periphery of these neutral compounds enables their anchoring onto substrate surfaces. Specifically, we investigated the electronic and magnetic properties as well as the structural arrangement in {Mn^II₃Mn^IVLn^III₃} with Ln = Dy, Yb coordination complexes using various complementary methods. We studied the electronic and atomic structure of the target compounds using the XAS and XES techniques. The molecular structures of the compounds were determined using density functional theory, and the magnetic data were obtained as a function of the magnetic field. Using the XMCD method, we followed the changes in the electronic and magnetic properties of adsorbed magnetic compounds induced by the reaction of ligands through interaction with the substrate. The complexes show antiferromagnetic exchange interactions between Mn and Ln ions. The spectroscopic analyses confirmed the structural and electronic integrity of complexes in organic solution. This study provides important input for a full understanding of the dependence of the magnetic properties and the molecule–substrate interaction of single adsorbed molecules on the type of ligands. It highlights the importance of chemical synthesis for controlling and tailoring the magnetic properties of metalorganic molecules for their use as optimized building blocks of future molecular spin electronics. Full article

Examining urban growth in metropolitan areas from both morphological and functional perspectives is paramount for sustainable development in developing and developed countries. As a collaborative and critical approach, polycentrism operates concurrently at local, regional, and national levels. However, the decentralized morphologies and functional attributes of polycentric urban spaces are yet to be adequately explored, despite their significant influence on sustainable urban planning and management. Colombo, the only metropolitan area in Sri Lanka, has experienced considerable yet ambiguously imbalanced spatial growth due to insufficient data. This study employed time-series satellite imagery from 1988 to 2022, in conjunction with a network model, to elucidate Colombo’s uneven urban patterns, while achieving an accuracy of over 80% throughout the period. The results revealed that the metropolis has evolved into a polynuclear city, complicating the identification of centers and their corresponding developmental stages. Nevertheless, the study successfully pinpointed the morphological and functional Grama Niladhari divisions, disclosing the morphological features of centralized dispersion and the functional traits of decentralized concentration. These insights provide significant implications for local government, guiding urban planning initiatives to achieve sustainable development goals. Full article

A curious and noticeable structural feature in Schiff bases from 2-aminoaldoses is the fact that imino tautomers arranged equatorially in the most stable ring conformation exhibit a counterintuitive reverse anomeric effect (RAE) in the mutarotational equilibrium, i.e., the most stable and abundant anomer is the equatorial one (β). As shown by our very recent research, this effect arises from the total or partial inhibition of the exo-anomeric effect due to the presence of an intramolecular hydrogen bond between the anomeric hydroxyl and the iminic nitrogen in the axial anomer (α). When the Schiff base adopts either an enamine structure or the imino group is protonated, the exo-anomeric effect is restored, and the axial α-anomer becomes the most stable species. Although the intramolecular H-bonding should appropriately be interpreted as a genuine stereoelectronic effect, the magnitude of the RAE could be affected by other structural parameters. Herein and through a comprehensive analysis of benzylidene, cinnamylidene, naphthalene, phenanthrene, and anthracene aldehydes, we show the robustness of the RAE effect, which is similar in extent to simple aldehydes screened so far, irrespective of the size and/or hydrophobicity of the substituent at the nitrogen atom. Full article

The widespread availability of Land Surface Temperature (LST) data from various sources presents a contemporary challenge for urban climate studies: how to efficiently compare these data with the results of traditional methods of temperature monitoring, which typically assume measurements at 2 m under sheltered conditions. In this line, the current study is based primarily on data extracted from a network of 31 points of hourly temperature monitoring at the 2 m level (Tair2m), in use between 2019 and 2021, in the city of Suceava in north-eastern Romania. These data allowed a detailed mapping for each hourly time step through multiple regression, adjusted by IDW, which was identified as the best interpolation method of Tair2m. These data were analyzed in parallel with LST data derived from Landsat imagery available in the analyzed period for 35 summer days with no or low cloud cover. The mapping results of both the Tair2m and LST data describe the main characteristics of the Suceava urban agglomeration (SvMA) heat island, which presents polynuclear features with intensities—as expressed by the temperature difference between the cores of the heat island and the surrounding rural areas—spanning during the summer noontime between 3.0 °C based on Tair2m and 7.1 °C on LST, respectively. The values of the Tair2m–LST differences were 0.68 °C on average, ranging from 5.33 to −19.17 °C, directly proportional to the imperviousness ratio (IMD) values, reaching the highest values in the local climate zones (LCZs) with a high built-up ratio (up to −19.17 °C) and the lowest (0.5 ÷ −0.5 °C) for those with bare soils, with isolated bushes and trees, with few or no buildings. The study results could serve as a tool to downscale the LST data to the level of Tair2m, which is useful for interpretation of the data derived from these commonly used tools in urban climate monitoring. Full article

The reaction of Mn(II) salts in the air with different R-salicylaldehyde oximes and the sodium or cesium salts of 9-anthracenecarboxylato (9-AC) allows for the isolation of new six polynuclear compounds: [Mn₃NaO(salox)₃(9-AC)₂(EtOH)₃H₂O]_n·2EtOH (1), [Mn₃NaO(3-Me-salox)₃(9-AC)₂(EtOH)₃H₂O]_n·EtOH (2), [Mn₆O₂(salox)₆(9-AC)₂(EtOH)₂(H₂O)₂]·3EtOH (3), [Mn₃O(3-Me-salox)₃(9-AC)(EtOH)₃(H₂O)]·1.8EtOH·3H₂O (4), [Mn₆O₂(Me-salox)₆(9-AC)₂(EtOH)₄(H₂O)₂]·0.5H₂O (5), and [Mn₆O₂(Et-salox)₆(9-AC)₂(EtOH)₄(H₂O)₂]·3EtOH (6). H₂salox is a salicylaldehyde oxime, H₂(3-Me-salox) is a 3-methyl-salicylaldehyde oxime, H₂Me-salox is a 1-(2-hydroxyphenyl)ethan-1-one oxime and a H₂-Et-salox is 1-(2-hydroxyphenyl)propan-1-one oxime. Structurally, compounds 1 and 2 consist of chains of trinuclear {Mn^III₃(μ₃-O)(salox)₃}⁺ units connected by Na⁺ ions. Compounds 3, 5, and 6 are hexanuclear units formed by two parallel trinuclear units {Mn^III₃(μ₃-O)(salox)₃}⁺ or {Mn^III₃(μ₃-O)(Me-salox)₃}⁺ planes related through an inversion center. Compound 4 consists of two isolated [Mn₃O(3-Me-salox)₃(9-AC)(EtOH)₃(H₂O)] trinuclear molecules in the unit cell showing crystallographic differences. Magnetic studies reveal a set of antiferromagnetic interactions in compounds 1 and 2 and a combination of antiferromagnetic and ferromagnetic interactions in compounds 3, 5, and 6. In all cases, the magneto-structural correlation between the intramolecular Mn^III-N-O-Mn^III torsion angle and the magnetic exchange within these units have been confirmed. For compounds 5 and 6, ac magnetic measurements reveal the slow relaxation of magnetization with moderate energy barriers of 19.9 cm⁻¹ and 31.1 cm⁻¹, respectively. Absorbance and fluorescence measurements in solution show the transitions of the 9-anthracenecarboxylate chromophore for all the compounds. Full article

Preferential oxidation of carbon monoxide (CO-PROX) in H₂-rich mixture is an effective way of hydrogen purification for fuel cells. High-performance PtCo/ZSM-5 catalysts with reduced Pt loading for this process were prepared using polynuclear platinum acetate complex known as platinum acetate blue (PAB) of the empirical formula Pt(CH₃COO)_2.5 as a novel precursor. The impregnation of HZSM-5 (Si/Al = 15 and 28) with PAB and its decomposition at 200 °C resulted in the stabilization of highly dispersed Pt⁰ and PtO_x species on the zeolite surface. The catalytic properties were improved by the addition of Co(CH₃COO)₂ followed by calcination at 450 °C. Produced materials were studied by SEM, TEM, EDX, XPS, and DRIFTS methods and tested in a CO-PROX reaction. The relationship between the synthesis conditions, structure, and catalytic behavior of composites is discussed in this paper. The synergistic effect of Pt and Co was observed when they both were located together in zeolite channels. The Pt-Co interaction provides new active catalytic sites and prevents platinum aggregation during the process. Due to this, the 100% CO conversion in the wide temperature range from 50 to 130 °C is achieved for PtCo/ZSM-5 catalysts (Si/Al = 15), which is the best result compared to low-loaded Pt catalysts prepared with traditional precursors. Full article

The reaction of ZrCl₄ or HfCl₄ with excess 2-methylpropanoic acid when boiling under reflux has been studied. The formation of polynuclear Zr and Hf complexes of the composition M₂O(i-C₃H₇CO₂)₆ during prolonged reflux of the reaction mixtures was found. The complexes are very sensitive to hydrolysis, forming hexanuclear [M₆(O)₄(OH)₄(i-C₃H₇CO₂)₁₂]. The reactions have a general character for aliphatic acids and can be used as an alternative to the known methods for the synthesis of polynuclear carboxylate clusters of Group 4 metals. The crystal and molecular structures of previously undescribed {[Hf₆(μ₃-O)₄(μ₃-OH)₄(i-C₃H₇CO₂)₁₂(H₂O)]·3i-C₃H₇COOH} have been determined. The molecular structure is a completely asymmetric hexanuclear cluster containing six Hf(IV) atoms united by a 4:4 μ₃-O/OH system of bridges, and stabilized by twelve 2-methylpropanoate ligands, eight of which are bidentate bridging, three are chelating, and one is monodentate. The crystal structure of the complex includes three independent solvating 2-methylpropanoic acid molecules. The obtained IR spectroscopy data make it possible to determine the type of complexes in the reaction mixture. The results of the study may be useful for improving the catalytic systems for ethylene oligomerization. Full article

New hetero-polynuclear coordination complexes based on a pentacoordinated Zn(II) metal center with tridentate terpyridine-based ligands and monoanionic gallates functionalized with long alkyl chains containing ferrocene units were designed, synthesized and characterized using spectroscopic and analytical methods. The complexes are mesomorphic, exhibiting columnar hexagonal mesophases. The photophysical properties in a solution and in an ordered condensed state were accurately investigated and the influence of the polarity of the solvent was evidenced. Full article

A series of polynuclear, dinuclear, and mononuclear Mo(VI) complexes were synthesized with the hydrazonato ligands derived from 5-methoxysalicylaldehyde and the corresponding hydrazides (isonicotinic hydrazide (H₂L¹), nicotinic hydrazide (H₂L²), 2-aminobenzhydrazide (H₂L³), or 4-aminobenzhydrazide (H₂L⁴)). The metallosupramolecular compounds obtained from non-coordinating solvents, [MoO₂(L^1,2)]_n (1 and 2) and [MoO₂(L^3,4)]₂ (3 and 4), formed infinite structures and metallacycles, respectively. By blocking two coordination sites with cis-dioxo ligands, the molybdenum centers have three coordination sites occupied by the ONO donor atoms from the rigid hydrazone ligands and one by the N atom of pyridyl or amine-functionalized ligand subcomponents from the neighboring Mo building units. The reaction in methanol afforded the mononuclear analogs [MoO₂(L^1-4)(MeOH)] (1a–4a) with additional monodentate MeOH ligands. All isolated complexes were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP) as an oxidant in water. The impact of the structure and ligand lability on the catalytic efficiency in homogeneous cyclooctene epoxidation was elucidated based on theoretical considerations. Thus, dinuclear assemblies exhibited better catalytic activity than mononuclear or polynuclear complexes. Full article

The olefinic dithioether (Z)-1,4-bis(pyridin-2-ylthio)but-2-ene Z-PyS(CH₂CH=CHCH₂)SPy (L) was prepared by the treatment of cis-ClCH₂CH=CHCH₂Cl with in situ generated potassium pyridine-2-thiolate Py-SK and analyzed by IR and NMR spectroscopy. To investigate the chemistry of polynuclear iodobismuthate complexes, two equivalents of BiI₃ were reacted with L in the MeOH solution to afford the anionic tetranuclear title compound (C₁₄H₁₅S₂N₂)₂(C₉H₁₀SN)₂[Bi₄I₁₁₆] with a N-protonated (Z)-1,4-bis(pyridin-2-ylthio)but-2-ene as a counterion. Compound 1 was characterized by IR and UV spectroscopy; the formation of a tetranuclear framework was ascertained by a single-crystal X-ray diffraction study performed at 100 K. Furthermore, an unusual Bi(III)-meditated cyclization of one Z-PyS(CH₂CH=CHCH₂)SPy ligand occurred, affording the bicyclic pyridinium salt 3-vinyl-2,3-dihydrothiazolo[3,2-a]pyridinium bearing a terminal vinyl group, compensating the second negative charge of the Bi₄I₁₆⁴⁻ cluster anion. The SCXRD characterization was completed by a Hirshfeld surface analysis, revealing some secondary interactions occurring in the crystal. Full article