Ring Atoms Research Articles

Structure-mutagenicity relationships on quinoline and indole analogues in the Ames test.

Although the in silico predictive ability of the Ames test results has recently made remarkable progress, there are still some chemical classes for which the predictive ability is not yet sufficient due to a lack of Ames test data. These classes include simple heterocyclic compounds. This study aimed to investigate the mutagenicity and structure-mutagenicity relationships for some heterocycles in the Ames test. In the present study, we selected 12 quinoline analogues containing one or two nitrogen atoms in the naphthalene ring and 12 indole analogues containing one to three nitrogen atoms in the indole ring, without any side moiety. The Ames test was performed with five standard bacterial strains (TA100, TA1535, TA98, TA1537, and WP2uvrA) using the pre-incubation method with and without rat liver S9. Five quinoline and two indole analogues were mutagenic. Among the five quinoline analogues, four were mutagenic in the presence of S9 mix with TA100, whereas cinnoline was mutagenic in the absence of S9 mix with TA1537. Among the two indole analogues, indazole was mutagenic in the presence and absence of S9 mix with WP2uvrA and 4-azaindole was mutagenic in the absence of S9 mix with TA1537. The mechanisms underlying the induction of mutagenesis appear to differ between quinoline and indole analogues. In addition, we performed in silico analysis of the mutagenicity of all these analogues using DEREK Nexus 6.1.1 (Lhasa Limited) and GT_EXPERT from CASE Ultra 1.8.0.5 (MultiCASE Inc.) as knowledge-based models and GT1_BMUT from CASE Ultra 1.8.0.5 (MultiCASE Inc.) as a statistical-based model. The knowledge-based model showed low sensitivity for both the quinoline and indole analogues (DEREK Nexus and GT_EXPERT: 20% for quinolines and 0% for indoles). Conversely, the statistical model showed high sensitivity (100% for both quinolines and indoles) and low specificity (43% for quinolines and 10% for indoles). Based on the Ames test results, we proposed structural alerts noting that quinoline analogues were mutagenic when they had nitrogens in any of the positions 2, 5, 7, or 8 in addition to 1, and indole analogues were mutagenic when they had nitrogens at positions 2 or 4 in addition to 1.

Complexity‐Building Exhaustive Dearomatization of Benzenoid Aromatics within an ESIPT‐Initiated Three‐Step Photochemical Cascade.

AbstractDearomative cycloadditions offer rapid access to complex 3D molecular architectures, commonly via a sp2‐to‐sp3 rehybridization of two atoms of an aromatic ring. Here we report that the 6e π‐system of a benzenoid aromatic pendant could be exhaustively depleted within a single photochemical cascade. An implementation of this approach involves the initial dearomative [4+2] cycloaddition of the Excited State Intramolecular Proton Transfer (ESIPT)‐generated azaxylylene, followed by two consecutive [2+2] cycloadditions of auxiliary π moieties strategically positioned in the photoprecursor. Such photochemical cascade fully dearomatizes the benzenoid aromatic ring, saturating all six sp2 atoms to yield a complex sp3‐rich scaffold with high control of its 3D molecular shape, rendering it a robust platform for rapid systematic mapping of underexplored chemical space. Significant growth of molecular complexity—starting with a modular synthesis of photoprecursors from readily available building blocks—is quantified by Böttcher score calculations.

Can OPAH ions be a source of CO and HCO in the interstellar medium? Lessons learned from the unimolecular dissociation of dibenzofuran and dibenz[b,f]oxepin radical cations

Unlike polycyclic aromatic hydrocarbons (PAHs), which are recognized to be key players in interstellar and astrochemistry, less is known about the astrochemical relevance of oxygen-containing PAHs (OPAHs). Small O-containing molecules such as CO and HCO are ubiquitous in the interstellar medium and understanding how OPAHs may be a source for these critical small molecules is important. To this end, we have studied the unimolecular reactions of two ionized OPAHs, dibenzofuran (1+•) and dibenz[b,f]oxepin (2+•) with tandem mass spectrometry (collision-energy resolved dissociation) and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). Collision-induced dissociation (CID) results show the competition between the loss of carbon monoxide (CO) and loss of 29 Da (either the formyl radical (HCO) or sequential H loss), with the latter being the dominant reaction. Rice–Ramsperger–Kassel–Marcus (RRKM) modeling of the iPEPICO data, on the other hand, is consistent with the loss of CO from the parent ion at the dissociative ionization onset, and, in the case of 2+•, sequential H-atom loss from this product. There is significant difference between the two structurally similar systems. In 1+•, dissociation requires around 4 eV of ion internal energy, while only 2.5 eV internal energy is required for 2+• to fragment. Calculations at the CAM-B3LYP/6–311++G(d,p) level of theory were used to examine the reaction pathways. For CO loss in 1+•, the reaction is initiated by a ring expansion followed by contraction of the central ring forming an ion–molecule complex between protonated cyclopenta[3,4]cyclobuta[1,2]benzene and CO. HCO loss is preceded by H migration to a bridging carbon vicinal to the oxygen atom and subsequent ring re-organization to form a low energy cyclopenta[c][1]benzopyran cation. This channel is higher enough in energy to preclude its participation near threshold, but not at higher internal energies reached in the CID experiment, which could therefore involve both sequential H loss and HCO loss. In 2+•, the reaction starts with an opening of the central O-containing ring, lowering the energy demand relative to 1+•.

Disilicon‐Mediated Carbon Monoxide Activation: From a 1,2,3‐Trisila‐ to 1,3‐Disilacyclopentadienes with Hypercoordinate λ4Si‐λ3C Double Bonds

AbstractThe facile reaction of the SiPh2‐bridged bis‐silylene (LSi:)2SiPh2 (L=PhC(NBut)2) with diphenylacetylene affords the unprecedented 1,2,3‐trisilacyclopentadiene (LSi)2(PhC)2SiPh2 1 with a hypercoordinate λ4Si−λ3Si double bond. Compound 1 is very oxophilic and consumes three molar equivalents of inert N2O to form the bicyclic oxygenation product 2 through O‐atom insertion in the Si=Si and Si−Si bonds. Strikingly, 1 can completely split the C≡O bonds of carbon monoxide under ambient conditions (1 atm, room temperature), yielding the 1,3‐disilacyclopentadiene 3, representing the first hypercoordinate example of a cyclosilene with a λ4Si‐λ3C double bond. Likewise, reaction of Xyl‐NC (Xyl=2,6‐dimethylphenyl), an isocyanide isoelectronic with CO, with 1 furnishes the related 1,3‐disilacyclopentadiene 4 but with an amidinato silylene pendent attached to the Si=C carbon ring atom.

Disilicon-Mediated Carbon Monoxide Activation: From a 1,2,3-Trisila- to 1,3-Disilacyclopentadienes with Hypercoordinate λ4Si-λ3C Double Bonds.

The facile reaction of the SiPh2-bridged bis-silylene (LSi:)2SiPh2 (L=PhC(NBut)2) with diphenylacetylene affords the unprecedented 1,2,3-trisilacyclopentadiene (LSi)2(PhC)2SiPh2 1 with a hypercoordinate λ4Si-λ3Si double bond. Compound 1 is very oxophilic and consumes three molar equivalents of inert N2O to form the bicyclic oxygenation product 2 through O-atom insertion in the Si=Si and Si-Si bonds. Strikingly, 1 can completely split the C≡O bonds of carbon monoxide under ambient conditions (1 atm, room temperature), yielding the 1,3-disilacyclopentadiene 3, representing the first hypercoordinate example of a cyclosilene with a λ4Si-λ3C double bond. Likewise, reaction of Xyl-NC (Xyl=2,6-dimethylphenyl), an isocyanide isoelectronic with CO, with 1 furnishes the related 1,3-disilacyclopentadiene 4 but with an amidinato silylene pendent attached to the Si=C carbon ring atom.

Thermal Responsiveness of 1,2,4-Triazolium-Based Poly(ionic liquid)s and Their Applications in Dye Extraction and Smart Switch.

Triazoliums are a family of five-membered heterocyclic cations that contain three nitrogen and two carbon atoms. In contrast to the widely studied imidazolium cations, triazoliums are less explored. In terms of the chemical structure, triazolium replaces a carbon atom in the imidazolium cation ring with an electron-withdrawing nitrogen atom, which makes the triazolium more polarized. Among the many physical properties, the thermal responsiveness of triazoliums is of particular interest to us but has been rarely investigated. In this contribution, we prepared a series of 1,2,4-triazolium-based poly(ionic liquid)s (PILs) with varying alkyl substituents and counteranions and studied their thermal-responsive behavior. We found that 1,2,4-triazolim-based PILs with a polymeric backbone structure similar to that of polyimidazoliums exhibited opposite thermal phase transition processes in solvents. For example, methyl-substituted 1,2,4-triazolium-based PILs exhibited an upper-critical-solution-temperature (UCST)-type phase transition in methanol when the counterion was I- and a lower-critical-solution-temperature (LCST)-type phase transition in acetone when the counterion was PF6 -. The thermal responsiveness was reversible and concentration-dependent. Interestingly, the thermal response of 1,2,4-triazolim-based PILs could be retained in the organogel form, which was applied in the pretreatment of anion-containing organic waste liquids and temperature-controlled "smart" switches.

Mechanism of TMB Discoloration Catalyzed by Layered CoNi@CN Nanozymes: Application Based on Smart Phone for Resorcinol Detection

Comprehensive SummaryReal‐time on‐site monitoring of resorcinol (RS) concentrations is crucial for detecting hazardous levels, enabling prompt response measures to mitigate potential environmental and health risks. In this study, we developed an innovative method using CoNi@CN‐2 nanozymes to activate peroxymonosulfate (PMS) for oxidizing 3,3',5,5'‐tetramethylbenzidine (TMB). Our results show that the formation of Ni2+ through the oxidation of Ni0 on the CoNi@CN‐2 surface significantly enhances the electron‐donating capacity of Co0. The catalytic reaction of TMB is mediated by redox active species (SO4•−, •O2−, •OH and 1O2). RS drives colorimetry by transferring electrons to the benzene ring and specific nitrogen atoms in ox‐TMB, reducing ox‐TMB to TMB. Furthermore, the colorimetric assay shows a robust linear correlation between RS concentration and absorbance (Abs), described by Abs = –0.44[RS] + 0.886 (0—200 μmol/L, R2 = 0.983). Also, we introduce a novel smartphone‐integrated autonomous detection software that can analyze RS concentration and grayscale values (GSV), yielding GSV = 0.327[RS] + 63.601 (0—200 μmol/L, R2 = 0.990) with a detection limit of 5.29 μmol/L. Additionally, excess PMS leads to ROS attacking specific sites in ox‐TMB, forming secondary oxidation products. This study has enabled rapid and accurate detection of RS, making a significant contribution to environmental safety and protection.

Experimental and theoretical investigation of benzothiazole oxidation by OH in air and the role of O2.

Benzothiazole (BTH) and its derivatives are amongst a group of emerging contaminants that are widely distributed in the environment due to their extensive use in many different consumer products. In air, reaction with the hydroxyl radical (OH) is expected to be a major loss process for BTH in the gas phase, but the kinetics and mechanisms are unknown. Here, we report a combination of experiments and theory to determine both the rate constant and products of the reaction of OH with the smallest member of the series, benzothiazole, in the gas phase. The mechanism first involves an attack by OH on BTH to produce several OHBTH intermediates. This is followed by O2 reactions with OHBTH, leading to several stable products successfully predicted by theory. Relative rate studies at 1 atm in air and 298 K using benzene as a reference gave a rate constant for the BTH + OH reaction of 2.1 ± 0.1 × 10-12 (1σ) cm3 per molecule per s, which translates to a lifetime in air of 5.5 days at 1 × 106 OH cm-3. Four hydroxybenzothiazole products reflecting attack on different carbon atoms of the benzene ring were measured (n-OHBTH, where n = 4, 5, 6, 7), with the relative product yields well predicted by the calculated formation energies of the pre-reaction OH⋯BTH complex. Attack of OH on the -CH of the thiazole ring leads to the formation of 2-OHBTH, representing a smaller fraction of the overall reaction, and is shown to proceed through a more complex mechanism than attack on the benzene ring. A theoretical approach to predicting chromatographic retention times of the products based on solvation free energies (ΔGsolv) was successful for most of the products. These studies illustrate how the powerful combination of experiment and theory can be used to predict products of atmospheric oxidation of emerging contaminants and ultimately used to assess their impacts on the environment.

Structural and Biological Studies of Bioactive Silver(I) Complexes with Coumarin Acid Derivatives.

Two new Ag(I) complexes with coumaric carboxylic acid derivatives have been synthesized. Structural studies of these noncrystalline complexes have been performed using a methodology that combines laboratory and synchrotron techniques, supported by density functional theory calculations. The arrangement of ligands around the Ag(I) cation has been refined using infrared, extended X-ray absorption fine structure, and X-ray absorption near edge structure spectroscopies. Different coordination modes of carboxylate ligands are observed for the studied compounds. Carboxylate bridges are characteristic for the Ag(I) complex with 4-oxo-4H-1-benzopyran-2-carboxylic acid (1), while a bidentate chelating motif was found for the complex with 2-oxo-2H-1-benzopyran-3-carboxylic acid (2). Additionally, the carbonyl oxygen atom of the coumarin ring coordinates to the silver cation in complex 2, while it is inactive in complex 1. Antimicrobial evaluation has been performed for both compounds. The complexes show activity against selected bacteria as well as Candida yeast. This activity is slightly lower for bacteria and the same or higher for Candida in relation to the reference substances: ciprofloxacin or fluconazole.

Different Patterns of Pd-Promoted C-H Bond Activation in (Z)-4-Hetarylidene-5(4H)-oxazolones and Consequences in Photophysical Properties

This work aims to amplify the fluorescence of (Z)-4-hetarylidene-5(4H)-oxazolones 1 by suppression of the hula-twist non-radiative deactivation pathway by C^N-orthopalladation of the 4-hetarylidene ring. Different (Z)-4-hetarylidene-2-phenyl-5(4H)-oxazolones, 1a–1c, prepared by the Erlenmeyer–Plöchl method, have been studied. The orthopalladation of (Z)-2-phenyl-4-(5-thiazolylmethylene)-5(4H)-oxazolone (1a) takes place by C-H bond activation of the H4 of the heterocycle and C^N-chelation, giving the dinuclear trifluoroacetate derivative 2a. By further metathesis of bridging ligands in 2a, complexes containing the orthometalated oxazolone and a variety of ligands 3a–5a, were prepared. The study of the photophysical properties of 1a–5a shows that the bonding of the Pd metal to the 4-hetaryliden-5(4H)-oxazolone does not promote, in these cases, an increase in fluorescence. Interestingly, the orthopalladation of (Z)-2-phenyl-4-(4-thiazolylmethylene)-5(4H)-oxazolone (1b) gives orthopalladated 2b, where the incorporation of the Pd to the oxazolone takes place by C-H bond activation of the ortho-H2 of the 2-phenyl group, ring opening of the oxazolone heterocycle and simultaneous N,N-bonding of the N atoms of the thiazole ring and the generated benzamide fragment. This N^N^C-tridentate dianionic bonding mode is obtained for the first time in oxazolones. Despite a similar lock of the hula-twist deactivation, 2b does not show fluorescence.

Intracellular Redox Environment Determines Cancer-normal Cell Selectivity of Selenium Nanoclusters.

Elucidating the chemical structure and intracellular action mechanisms is still the critical limit for the clinical translation of nanomedicines. Intracellular redox environments originating from cell metabolism are key factors affecting internalized drug efficacy. Herein, we engineer Se-Se/Se-S bond to assemble selenium nanoclusters with intracellular redox environment-driven selective structure. Chemical structure analysis reveals that, the bonding of sulfur atom in intermediates to the two neighboring or interposition selenium atoms in selenium rings is the key internal driving force for nanoparticle cluster formation. This nanocluster can be predominantly transformed to selenocysteine to facilitate selenoproteins synthesis in normal cells, while metabolize to cytotoxic SeO32- based on the oxidative intracellular redox environment of cancer cells. Resultantly, selenium nanoclusters exhibit significant cell proliferation inhibition ability to cancer cells and impressive safety to normal cells. Taken together, this study not only clarifies the chemical nature of the atom engineering of selenium nanocluster, but also elucidates its intracellular redox environment-oriented anticancer mechanism.

Intracellular Redox Environment Determines Cancer‐normal Cell Selectivity of Selenium Nanoclusters

Elucidating the chemical structure and intracellular action mechanisms is still the critical limit for the clinical translation of nanomedicines. Intracellular redox environments originating from cell metabolism are key factors affecting internalized drug efficacy. Herein, we engineer Se‐Se/Se‐S bond to assemble selenium nanoclusters with intracellular redox environment‐driven selective structure. Chemical structure analysis reveals that, the bonding of sulfur atom in intermediates to the two neighboring or interposition selenium atoms in selenium rings is the key internal driving force for nanoparticle cluster formation. This nanocluster can be predominantly transformed to selenocysteine to facilitate selenoproteins synthesis in normal cells, while metabolize to cytotoxic SeO32‐ based on the oxidative intracellular redox environment of cancer cells. Resultantly, selenium nanoclusters exhibit significant cell proliferation inhibition ability to cancer cells and impressive safety to normal cells. Taken together, this study not only clarifies the chemical nature of the atom engineering of selenium nanocluster, but also elucidates its intracellular redox environment‐oriented anticancer mechanism.

A Dynamic Loop in Halohydrin Dehalogenase HheG Regulates Activity and Enantioselectivity in Epoxide Ring Opening.

Halohydrin dehalogenase HheG and its homologues are remarkable enzymes for the efficient ring opening of sterically demanding internal epoxides using a variety of nucleophiles. The enantioselectivity of the respective wild-type enzymes, however, is usually insufficient for application and frequently requires improvement by protein engineering. We herein demonstrate that the highly flexible N-terminal loop of HheG, comprising residues 39 to 47, has a tremendous impact on the activity as well as enantioselectivity of this enzyme in the ring opening of structurally diverse epoxide substrates. Thus, highly active and enantioselective HheG variants could be accessed through targeted engineering of this loop. In this regard, variant M45F displayed almost 10-fold higher specific activity than wild type in the azidolysis of cyclohexene oxide, yielding the corresponding product (1S,2S)-2-azidocyclohexan-1-ol in 96%eeP (in comparison to 49%eeP for HheG wild type). Moreover, this variant was also improved regarding activity and enantioselectivity in the ring opening of cyclohexene oxide with other nucleophiles, demonstrating even inverted enantioselectivity with cyanide and cyanate. In contrast, a complete loop deletion yielded an inactive enzyme. Concomitant computational analyses of HheG M45F in comparison to wild type enzyme revealed that mutation M45F promotes the productive binding of cyclohexene oxide and azide in the active site by establishing noncovalent C-H ··π interactions between epoxide and F45. These interactions further position one of the two carbon atoms of the epoxide ring closer to the azide, resulting in higher enantioselectivity. Additionally, stable and enantioselective cross-linked enzyme crystals of HheG M45F were successfully generated after combination with mutation D114C. Overall, our study highlights that a highly flexible loop in HheG governs the enzyme's activity and selectivity in epoxide ring opening and should thus be considered in future protein engineering campaigns of HheG.

Insight into the Reversible Hydrogen Storage of Titanium-Decorated Boron-Doped C20 Fullerene: A Theoretical Prediction

Hydrogen storage has been a bottleneck factor for the application of hydrogen energy. Hydrogen storage capacity for titanium-decorated boron-doped C20 fullerenes has been investigated using the density functional theory. Different boron-doped C20 fullerene absorbents are examined to avoid titanium atom clustering. According to our research, with three carbon atoms in the pentagonal ring replaced by boron atoms, the binding interaction between the Ti atom and C20 fullerene is stronger than the cohesive energy of titanium. The calculated results revealed that one Ti atom can reversibly adsorb four H2 molecules with an average adsorption energy of −1.52 eV and an average desorption temperature of 522.5 K. The stability of the best absorbent structure with a gravimetric density of 4.68 wt% has been confirmed by ab initio molecular dynamics simulations. These findings suggest that titanium-decorated boron-doped C20 fullerenes could be considered as a potential candidate for hydrogen storage devices.

Palladium(II) complexes comprising thiazole-hydrazone Schiff base ligand: Synthesis, structure and catalytic activity in Suzuki-Miyaura coupling reactions

The reaction of PdCl2 and Pd(OAc)2 with (E)-2-(2-(pyridin-2-ylmethylene)hydrazinyl)benzo[d]thiazole (HL) in methanol resulted in the formation of two neutral mononuclear Pd(II) complexes. By using PdCl2 two kinds of crystals with general formula of [Pd(Cl)L]·0.5(C2H5OH) (1a) and [Pd(Cl)L] (1b) were obtained while Pd(OAc)2 gave one type of crystal with general formula of [Pd(OAc)L]·0.5(H2O) (2). These complexes were characterized using spectroscopic methods, and their molecular structures were determined by single crystal X-ray diffraction analysis. In these complexes, the ligand coordinates to the Pd(II) core through the nitrogen atoms of the thiazole ring, pyridine ring, and imine moiety, acting as tridentate mononegative NNN donor ligand. These palladium(II) complexes were also found to exhibit catalytic activity in Suzuki-Miyaura coupling reactions.

Synthetic Protocols, Structural Activity Relationship, and Biological Activity of Piperazine and its Derivatives.

The versatile basic structure of piperazine allows for the development and production of newer bioactive molecules that can be used to treat a wide range of diseases. Piperazine derivatives are unique and can easily be modified for the desired pharmacological activity. The two opposing nitrogen atoms in a six-membered piperazine ring offer a large polar surface area, relative structural rigidity, and more acceptors and donors of hydrogen bonds. These properties frequently result in greater water solubility, oral bioavailability, and ADME characteristics, as well as improved target affinity and specificity. Various synthetic protocols have been reported for piperazine and its derivatives. In this review, we focused on recently published synthetic protocols for the synthesis of the piperazine and its derivatives. The structure-activity relationship concerning different biological activities of various piperazine-containing drugs was also highlighted to provide a good understanding to researchers for future research on piperazines.

The infrared spectrum of the protic ionic liquid 1-methylimidazolium nitrate: An ab initio molecular dynamics simulation study

Complex features observed in the infrared (IR) spectrum of the protic ionic liquid 1-methylimidazolium nitrate, [C1im][NO3], are assigned using ab initio molecular dynamics (AIMD) simulation. AIMD is used at the same level of theory to simulate the known X-ray crystal structure of [C1im][NO3] and a cluster of ionic pairs representing the liquid phase. The calculation of several single particle and collective time correlation functions of velocity forms the basis for the AIMD simulation assignment of the infrared spectra. The AIMD simulation demonstrates that the lift of the degeneracy of the anion asymmetric stretching mode, νas(NO3), due to symmetry breaking and coupling to external modes result in multiple band splitting in the crystal spectrum in the region of the νas(NO3) mode. Owing of the intrinsic anharmonic characteristic of the AIMD simulation, the calculation accounts for the broad band in the high-frequency range of the IR spectrum caused by the cation ν(NH) stretching mode in strong cation–anion hydrogen bond. The AIMD simulation of the liquid captures spectral changes upon melting of [C1im][NO3] due to loosening of the NH···O hydrogen bond and changes in the [NO3]- interaction with other hydrogen atoms of the imidazolium ring. The AIMD simulation assigns the intermolecular stretching mode of the hydrogen bond, ν(NH…O), as the band at 183 cm−1 in the far infrared spectrum of the [C1im][NO3] crystal.

A 1,3,5-triazine μ3-bridged neutral Cu(I) framework with enhanced stability and CO2 capture selectivity

Compounds with 1,3,5-triazine ring such as melamine derivatives, known for their low cost and high stability, offer potential for affordable, stable metal organic framework (MOF) synthesis. However, reported such frameworks are facing issues like low stability and reduced porosity. To overcome such problems, we explored organic ligands with protonated nitrogen atoms on the 1,3,5-triazine ring, facilitated by introducing hydroxyl groups on carbon atoms of the triazine ring to construct MOFs. By using 5-azacytosine, we have successfully synthesized SXU-121, a neutral ultramicroporous MOF with eta-topology and high density of open Cu(I) sites. SXU-121 features robust structural stability and significant CO2 adsorption capacity with high selectivity over N2 under ambient conditions. We believe SXU-121's development opens new avenues for creating a class of stable and low cost metal-triazine frameworks with potential diverse functionalities.

Interaction of 6-Thioguanine with Aluminum Metal-Organic Framework Assisted by Mechano-Chemistry, In Vitro Delayed Drug Release, and Time-Dependent Toxicity to Leukemia Cells.

6-thioguanine (6-TG) is an antimetabolite drug of purine structure, approved by the FDA for the treatment of acute myeloid lesukemia, and it is of interest in treating other diseases. The interaction of drugs with matrices is of interest to achieving a delayed, sustained, and local release. The interaction of 6-TG with an aluminum metal-organic framework (Al-MOF) DUT-4 is studied using a novel experimental approach, namely, mechano-chemistry by liquid-assisted grinding (LAG). The bonding of 6-TG to the DUT-4 matrix in the composite (6-TG)(DUT-4) was studied using ATR-FTIR spectroscopy and XRD. This interaction involves amino groups and C and N atoms of the heterocyclic ring of 6-TG, as well as the carboxylate COO- and (Al)O-H groups of the matrix, indicating the formation of the complex. Next, an in vitro delayed release of 6-TG was studied from composite powder versus pure 6-TG in phosphate buffered saline (PBS) at 37 °C. Herein, an automated drug dissolution apparatus with an autosampler was utilized, and the molar concentration of the released 6-TG was determined using an HPLC-UV analysis. Pure 6-TG shows a quick (<300 min) dissolution, while the composite gives the dissolution of non-bonded 6-TG, followed by a significantly (factor 6) slower release of the bonded drug. Each step of the release follows the kinetic pseudo-first-order rate law with distinct rate constants. Then, a pharmaceutical shaped body was prepared from the composite, and it yields a significantly delayed release of 6-TG for up to 10 days; a sustained release is observed with the 6-TG concentration being within the therapeutically relevant window. Finally, the composite shows a time-dependent (up to 9 days) stronger inhibition of leukemia MV-4-11 cell colonies than 6-TG.

Simple/commercially‐available Lewis acid in anionic ring‐opening polymerization: powerful compounds with multiple applications in macromolecular engineering

Simple and commercially‐available Lewis acids (LA) are commonly used catalysts in anionic ring‐opening polymerization (AROP) reactions. In particular, for the AROP of epoxides, the addition of a Lewis acid allows the transition from a so‐called end‐chain mechanism to a monomer‐activated mechanism. The presence of the LA simultaneously leads to a decrease in the reactivity of active centers through the formation of a three‐species ate complex and to the activation of the monomer by LA coordination to the oxygen atom of the oxirane ring. These two effects result in both an increase in propagation kinetics and a decrease in transfer reactions, which has enabled the synthesis of high molecular weight polyethers. However, the impact of Lewis acids goes far beyond these classic effects. They have indeed enabled the polymerization of new functional monomers as well as the synthesis of heterotelechelic macromolecules. Also widely used as catalysts in copolymerization reactions (statistical, sequential, or alternating) Lewis acids can strongly influence the composition and sequence of monomer units in macromolecules. Finally, Lewis acids can also significantly influence the architecture of the obtained macromolecules. This review aims to list the various contributions of Lewis acids to macromolecular engineering and illustrate them with well‐chosen examples.