Search Results (63)

Background/Objectives: The growing threat of antibiotic resistance necessitates the development of novel antimicrobial agents that effectively target pathogenic microorganisms while minimizing toxicity. Methods: Two series DABCO-based cationic homopolymers (D-subs 1kDa, D-subs 5kDa, D-subs 15kDa) and DABCO–pyridinium-based copolymers (PyH-subs 5kDa_Dsubs 5kDa, PyH-subs 7kDa_Dsubs 3kDa, PyH-subs 3kDa_Dsubs 7kDa) were synthesized to mimic to host-defense cationic peptides via ring-opening metathesis polymerization (ROMP). The antimicrobial activities of these polymers were determined by their minimum inhibitory concentrations (MICs) against E. coli (Gram-negative bacteria), P. aeruginosa (Gram-negative bacteria), S. aureus (Gram-positive bacteria), and C. albicans (fungus). In vitro cytotoxicity assays revealed selective toxicity towards bacterial cells, with high selectivity indices for several copolymers. To gain insight into the mechanism of action, morphological changes in S. aureus upon exposure to D-subs 1kDa were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results: The D-subs 15kDa homopolymer demonstrated the highest overall antimicrobial activity, particularly against S. aureus (MIC: 8 µg/mL), with all polymers exhibiting minimal hemolytic activity (HC₅₀ ≥ 1024 µg/mL). SEM and TEM results revealed membrane disruption indicative of polymer–bacteria interactions. Additionally, stability studies confirmed polymer integrity under physiological conditions for at least 28 days. Conclusions: These results support the potential of DABCO-based cationic polymers as a promising platform for next-generation antimicrobial therapeutics. Full article

Structural rearrangements in metal–organic supramolecules constructed from the coordination of Cu(II) with m-xpt (m-xylylenebis(pyridyltriazole)) are investigated upon their interaction with 1,4-diazabicyclo[2.2.2]octane (dabco) and carbon dioxide-enriched air. The binuclear [Cu₂(m-xpt)₂]⁴⁺ complexes react with dabco to produce a carbonate-bridged trinuclear complex, [Cu₃(m-xpt)₃(µ-CO₃)]⁴⁺, and an oxalate-bridged binuclear complex, [Cu₂(m-xpt)₂(µ-C₂O₄)]²⁺, where carbonate and oxalate likely originate from CO₂ and dabco, respectively. The trinuclear complex reassembles the original dimer upon the removal of the carbonate ion. Similarly, polymeric [Cu(o-xpt)(PF₆)]_n, formed from Cu(I) and o-xpt (o-xylylenebis(pyridyltriazole)) coordination, undergoes oxidation in CO₂-enriched air to yield a tetranuclear Cu(II) complex, Cu₄(o-xpt)₃(μ₄-CO₃)(μ₂-OH)(μ₂-OCOCH₃)⁴⁺. The reaction progress is monitored by UV-Vis spectroscopy, and the major products are characterized by single-crystal X-ray diffraction. Full article

The one-pot multicomponent aza-Morita–Baylis–Hillman (MBH) reaction was performed under green conditions using 1,4-diazabicyclo[2.2.2]octane (DABCO) and Amberlyst^® 15 as a co-catalyst, at ambient temperature and under negligible amounts of non-hazardous solvent. A number of α-methylene-β-amino acid derivatives were produced in good to excellent yields from different arylaldehydes, p-toluenesulfonamide and α,β-unsaturated carbonyl compounds. The environmental benignity of the process is accounted by the low E-factor (0.7) and high atom economy (95%) values obtained. Full article

The mixture of hexamethylene diisocyanate (HDI) and butanol (BuOH) with the intercalation compound of 1,4-diazabicyclo[2.2.2]octane (DABCO) with α-zirconium phosphate (α-ZrP) has been evaluated as a latent thermal catalyst at varying temperatures. α-ZrP·DABCO did not show activity at 25 °C, but showed a high level of activity at a higher temperature of 80 °C. To clarify the reaction behavior of HDI-BuOH with α-ZrP·DABCO, a viscosity value of 1200 mPa·s·g/cm² was reached at 80 °C for 30 min. To investigate the deintercalation behavior of DABCO from the α-ZrP interlayer, it was investigated in BuOH and in HDI, respectively, under heated conditions. Interestingly, XRD patterns showed a reduction in α-ZrP·DABCO for the interlayer distance due to the deintercalation of DABCO in BuOH, while no changes associated with the deintercalation of DABCO were observed in HDI. Butanol was found to be important for the deintercalation of DABCO. To examine the reactivity of bifunctional monomers, the reaction of 1,4-butanediol (1,4-BDO) and HDI with α-ZrP·DABCO were investigated to show good reactivity at 80 °C and stability at 40 °C. Full article

Metal–organic frameworks (MOFs) are promising materials for processes such as carbon dioxide (CO₂) capture or its storage. In this work, the adsorption of CO₂ and nitrogen (N₂) in Co₃(ndc)₃(dabco) MOF (ndc: 2,6-naphthalenedicarboxylate; dabco: 1,4-diazabicyclo[2.2.2]octane) is reported for the first time over the temperature range of 273–323 K and up to 35 bar. The adsorption isotherms are successfully described using the Langmuir isotherm model. The heats of adsorption for CO₂ and N₂, determined through the Clausius–Clapeyron equation, are 20–27 kJ/mol and 10–11 kJ/mol, respectively. The impact of using pressure and/or temperature swings on the CO₂ working capacity is evaluated. If a flue gas with 15% CO₂ is fed at 6 bar and 303 K and regenerated at 1 bar and 373 K, 1.58 moles of CO₂ can be captured per kg of MOF. The analysis of the multicomponent adsorption of typical flue gas streams (15% CO₂ balanced with N₂), using the ideal adsorbed solution theory (IAST), shows that at 1 bar and 303 K, the CO₂/N₂ selectivity is 11.5. In summary, this work reports essential data for the design of adsorption-based processes for CO₂ capture using a Co₃(ndc)₃(dabco) MOF, such as pressure swing adsorption (PSA). Full article

A promising solution for efficient methane (CH₄) storage and transport is a metal–organic framework (MOF)-based sorbent. Hence, searching for potential MOFs like M₂(BDC)₂(DABCO) to enhance the CH₄ storage capacity in both gravimetric and volumetric uptakes is essential. Herein, we systematically elucidate the adsorption of CH₄ in M₂(BDC)₂(DABCO) or M(DABCO) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn) MOFs using multiscale simulations that combined grand canonical Monte Carlo simulation with van der Waals density functional (vdW-DF) calculation. We find that, in the M(DABCO) series, Mg(DABCO) has the highest total CH₄ adsorption capacities, with $m_{tot}=$ 231.39 mg/g at 298 K, for gravimetric uptake, and $V_{tot}=$ 231.43 cc(STP)/cc, for volumetric uptake. The effects of temperature, pressure, and metal substitution on enhancing CH₄ storage are evaluated, and we predict that the volumetric CH₄ storage capacity on M(DABCO) could meet the DOE target at temperatures of ca. 238 K–268 K and pressures of 35–100 bar. The interactions between CH₄ and M(DABCO) are dominated by the vdW interactions, as shown by the vdW-DF calculations. The Mg, Mn, Fe, Co, and Ni substitutions in M(DABCO) result in a stronger interaction and thus, a higher CH₄ storage capacity, at higher pressures for Mg, Mn, Ni, and Co and at lower pressures for Fe. This work may provide guidance for the rational design of CH₄ storage in M₂(BDC)₂(DABCO) MOFs. Full article

Glycoconjugation is a well-established technology for vaccine development: linkage of the polysaccharide (PS) antigen to an appropriate carrier protein overcomes the limitations of PS T-independent antigens, making them effective in infants and providing immunological memory. Glycoconjugate vaccines have been successful in reducing the burden of different diseases globally. However, many pathogens still require a vaccine, and many of them display a variety of glycans on their surface that have been proposed as key antigens for the development of high-valency glycoconjugate vaccines. CDAP chemistry represents a generic conjugation strategy that is easily applied to PS with different structures. This chemistry utilizes common groups to a large range of PS and proteins, e.g., hydroxyl groups on the PS and amino groups on the protein. Here, new fast analytical tools to study CDAP reaction have been developed, and reaction conditions for PS activation and conjugation have been extensively investigated. Mathematical models have been built to identify reaction conditions to generate conjugates with wanted characteristics and successfully applied to a large number of bacterial PSs from different pathogens, e.g., Klebsiella pneumoniae, Salmonella Paratyphi A, Salmonella Enteritidis, Salmonella Typhimurium, Shighella sonnei and Shigella flexneri. Furthermore, using Salmonella Paratyphi A O-antigen and CRM₁₉₇ as models, a design of experiment approach has been used to study the impact of conjugation conditions and conjugate features on immunogenicity in rabbits. The approach used can be rapidly extended to other PSs and accelerate the development of high-valency glycoconjugate vaccines. Full article

The glycolysis process of flexible polyurethane foams containing styrene–acrylonitrile and calcium carbonate as fillers was explored in detail. The use of DABCO as a catalyst allowed us to reduce the catalyst concentration and the polyurethane-to-glycol mass ratio to 0.1% and 1:1, respectively. The glycolysis process allowed us to obtain a high-purity polyol (99%), which can totally replace raw polyols in the synthesis of new flexible polyurethane foams, maintaining the standard mechanical properties of the original one and modifying the ratio of isocyanates employed to correct the closed cell structure caused by the impurities present in the recovered polyol. This isocyanate mixture was also optimized, resulting in a ratio of 30 and 70% of the isocyanates TDI80 and TDI65, respectively. Additionally, the fillers incorporated in the glycolyzed foams were recovered. Both recovered fillers, styrene–acrylonitrile and calcium carbonate, were fully characterized, showing a quality very similar to that of commercial compounds. Finally, the replacement of commercial fillers by the recovered ones in the synthesis of new polyurethane foams was studied, demonstrating the feasibility of using them in the synthesis of new foams without significantly altering their properties. Full article

In the exploration of chiral solvating agents (CSAs) for nuclear magnetic resonance (NMR) spectroscopy designed for the chiral analysis of amino acid derivatives, notable advancements have been made with thiourea–CSAs. 1-TU, derived from 2-[(1R)-1-aminoethyl]phenol and benzoyl isothiocyanate, is effective in the enantiodifferentiation of N-3,5-dinitrobenzoyl (N-DNB) amino acids. In order to broaden the application of 1-TU for configurational assignment, enantiomerically enriched N-DNB amino acids were analyzed via NMR. A robust correlation was established between the relative position of specific ¹H and ¹³C NMR resonances of the enantiomers in the presence of 1-TU. 1,4-Diazabicyclo[2.2.2]octane (DABCO) was selected for the complete solubilization of amino acid substrates. Notably, the para and ortho protons of the N-DNB moiety displayed higher frequency shifts for the (R)-enantiomers as opposed to the (S)-enantiomers. This trend was consistently observed in the ¹³C NMR spectra for quaternary carbons bonded to NO₂ groups. Conversely, an inverse correlation was noted for quaternary carbon resonances of the carboxyl moiety, amide carbonyl, and methine carbon at the chiral center. This observed trend aligns with the interaction mechanism previously reported for the same chiral auxiliary. The configurational correlation can be effectively exploited under conditions of high dilution or, significantly, under sub-stoichiometric conditions. Full article

New arylamide- and arylthiourea-based chiral solvating agents (CSAs) were synthesized starting from commercially available isomannide and isosorbide. The two natural isohexides were transformed into the three amino derivatives, having isomannide, isosorbide, and isoidide stereochemistry, then the amino groups were derivatized with 3,5-dimethoxybenzoyl chloride or 3,5-bis(trifluoromethyl)phenyl isothiocyanate to obtain the CSAs. Bis-thiourea derivative containing the 3,5-bis(trifluoromethyl)phenyl moiety with exo–exo stereochemistry was remarkably efficient in the differentiation of NMR signals (NH and acetyl) of enantiomers of N-acetyl (N-Ac) amino acids in the presence of 1,4-diazabicyclo[2,2,2]octane (DABCO). Nonequivalences in the ranges of 0.104–0.343 ppm and 0.042–0.107 ppm for NH and acetyl groups, respectively, allowed for very accurate enantiomeric excess determination, and a reliable correlation was found between the relative positions of signals of enantiomers and their absolute configuration. Therefore, a complete stereochemical characterization could be performed. Dipolar interactions detected in the ternary mixture CSA/N-Ac-valine/DABCO led to the identification of a different interaction model for the two enantiomers, involving the formation of a one-to-one substrate/CSA complex for (S)-N-Ac-valine and a one-to-two complex for (R)-N-Ac-valine, as suggested by the complexation stoichiometry. Full article

Haloalkanes and amines are common halogen-bond (XB) donors and acceptors as well as typical reagents in nucleophilic substitution reactions. Thus, crystal engineering using these molecules requires an understanding of the interchange between these processes. Indeed, we previously reported that the interaction of quinuclidine (QN) with CHI₃ in acetonitrile yielded co-crystals showing a XB network of these two constituents. In the current work, the interactions of QN with C₂H₅I or 1,4-diazabicyclo[2.2.2]octane (DABCO) with CH₂I₂ led to nucleophilic substitution producing I⁻ anions and quaternary ammonium (QN-CH₂CH₃ or DABCO-CH₂I⁺) cations. Moreover, the reaction of QN with CHI₃ in dichloromethane afforded co-crystals containing XB networks of CHI₃ with either Cl⁻ or I⁻ anions and QN-CH₂Cl⁺ counter-ions. A similar reaction in acetone produced XB networks comprising CHI₃, I⁻ and QN-CH₂COCH₃⁺. These distinctions were rationalized through a computational analysis of XB complexes and the transition-state energies for the nucleophilic substitution. It indicated that the outcome of the reactions was determined mostly by the relative energies of the products. The co-crystals obtained in this work showed bonding between the cationic (DABCO-CH₂I⁺, QN-CH₂Cl⁺) or neutral (CHI₃) XB donors and the anionic (I⁻, Cl⁻) or neutral (CHI₃) acceptors. Their analysis showed comparable electron and energy densities at the XB bond critical points and similar XB energies regardless of the charges of the interacting species. Full article

Metal-organic frameworks (MOFs) have been investigated with regard to the oxygen evolution reaction (OER) due to their structure diversity, high specific surface area, adjustable pore size, and abundant active sites. However, the poor conductivity of most MOFs restricts this application. Herein, through a facile one-step solvothermal method, the Ni-based pillared metal-organic framework [Ni₂(BDC)₂DABCO] (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane), its bimetallic nickel-iron form [Ni(Fe)(BDC)₂DABCO], and their modified Ketjenblack (mKB) composites were synthesized and tested toward OER in an alkaline medium (KOH 1 mol L⁻¹). A synergistic effect of the bimetallic nickel-iron MOF and the conductive mKB additive enhanced the catalytic activity of the MOF/mKB composites. All MOF/mKB composite samples (7, 14, 22, and 34 wt.% mKB) indicated much higher OER performances than the MOFs and mKB alone. The Ni-MOF/mKB14 composite (14 wt.% of mKB) demonstrated an overpotential of 294 mV at a current density of 10 mA cm⁻² and a Tafel slope of 32 mV dec⁻¹, which is comparable with commercial RuO₂, commonly used as a benchmark material for OER. The catalytic performance of Ni(Fe)MOF/mKB14 (0.57 wt.% Fe) was further improved to an overpotential of 279 mV at a current density of 10 mA cm⁻². The low Tafel slope of 25 mV dec⁻¹ as well as a low reaction resistance due to the electrochemical impedance spectroscopy (EIS) measurement confirmed the excellent OER performance of the Ni(Fe)MOF/mKB14 composite. For practical applications, the Ni(Fe)MOF/mKB14 electrocatalyst was impregnated into commercial nickel foam (NF), where overpotentials of 247 and 291 mV at current densities of 10 and 50 mA cm⁻², respectively, were realized. The activity was maintained for 30 h at the applied current density of 50 mA cm⁻². More importantly, this work adds to the fundamental understanding of the in situ transformation of Ni(Fe)DMOF into OER-active α/β-Ni(OH)₂, β/γ-NiOOH, and FeOOH with residual porosity inherited from the MOF structure, as seen by powder X-ray diffractometry and N₂ sorption analysis. Benefitting from the porosity structure of the MOF precursor, the nickel-iron catalysts outperformed the solely Ni-based catalysts due to their synergistic effects and exhibited superior catalytic activity and long-term stability in OER. In addition, by introducing mKB as a conductive carbon additive in the MOF structure, a homogeneous conductive network was constructed to improve the electronic conductivity of the MOF/mKB composites. The electrocatalytic system consisting of earth-abundant Ni and Fe metals only is attractive for the development of efficient, practical, and economical energy conversion materials for efficient OER activity. Full article

The first three compounds based on a {copper–thiocyanate–dabco} combination, namely, (Hdabco)[Cu₂(NCS)₃] (1), (H₂dabco)[Cu(NCS)₃] (2), and [Cu(Hdabco)₂(NCS)₄]∙2dmso (3), where dabco = 1,4-diazabicyclo[2.2.2]octane were synthesized and characterized by single-crystal XRD, elemental analysis, Raman, and partial IR spectroscopy. In copper(I) derivatives, the influence of the charge of the organic cation on the dimensionality of the crystal structure is observed. Thus, in the case of 1, monoprotonated Hdabco⁺ cations provide the template for the formation of a polymeric anionic 3D framework {[Cu₂(NCS)₃]⁻}_n, while in the case of 2, diprotonated H₂dabco²⁺ cations together with discrete [Cu(SCN)₃]²⁻ anions generate a simple ionic 0D structure with an island-like crystal lattice. The anionic {[Cu₂(SCN)₃]⁻}_n framework has infinite square channels of 10 × 10 Å size running along the 001 crystallographic direction. In 3, both the Hdabco⁺ and thiocyanato units behave as terminal monodentate ligands attached to copper(II) centers via N-donor atoms, forming neutral molecular complexes with an elongated (4+2) octahedral environment. The crystallization molecules of dmso are hydrogen bonded to the protonated parts of the coordinated dabco molecules. A series of by-products Cu(SCN)₂(dmso)₂ (4), (Hdabco)SCN (5), (H₂dabco)(SCN)₂ (6), and (H₂dabco)(SCN)₂∙H₂O (7) were identified and characterized. Full article

Allylation of N-unsubstituted isatin N,N′-cyclic azomethine imines with Morita-Baylis-Hillman carbonates in the presence of 1–10 mol% DABCO in DCM at room temperature, rapidly gave N-allylated and N, β-diallylated isatin N,N′-cyclic azomethine imine 1,3-dipoles in moderate to high yields. The reaction features mild reaction conditions, easily practical operation, and short reaction times in most cases. Furthermore, the alkylated products were transformed into novel bicyclic spiropyrrolidine oxoindole derivatives through the [3+2] or [3+3]-cycloaddition with maleimides or Knoevenagel adducts. Full article

Components for manufacturing polyurethane foams can adversely affect the human body, particularly if they are in contact with it for long periods. In applications where the foam is not placed directly into the body, the study of the product’s effects is often neglected. In the case of human skin, distinguishing the increasingly frequent problems of skin atopy, more attention should be paid to this. This paper presents the influence of the different catalytic systems on cytotoxic and thermomechanical properties in polyurethane foams. Among others, foams were produced with the most popular catalysts on the market, DABCO and a metal-organic tin catalyst. The foams were characterized by thermomechanical properties and were subjected to a cytotoxicity test against human keratinocytes. In biocompatibility tests with skin cells, the results were highly variable. VAB 2 with a catalytic system consisting of commercial Diethanolamine and Addocat^®105 performed the best. However, with such a catalytic system, the mechanical properties have worsened. Full article