Intramolecular Hydrogen Bond Research Articles

Cycloaddition reaction of methylidyne radical with dipyrromethanol: quantum chemical insights into the formation of di(pyridin-2-yl)methanol

Density functional theory was employed to investigate methylidyne radical reaction on to the unsaturation of dipyrromethanol moiety through cycloaddition forming a six membered di(pyridin-2-yl)methanol followed by H-elimination via ring expansion. Time-dependent density functional theory (TD-DFT) simulations were performed to figure out the ultraviolet–visible spectrum of dipyrromethanol and di(pyridin-2-yl)methanol. Ultraviolet–visible spectrum of dipyrromethanol and di(pyridin-2-yl)methanol shows that two sharp absorption peaks were obtained at λ max = 161 nm and 206 nm for the reactant dipyrromethanol while a sharp peak was observed for the product di(pyridin-2-yl)methanol at shorter wavelength (λ max = 170 nm). The theoretical IR spectrum of dipyrromethanol and di(pyridin-2-yl)methanol shows that a significant red shift of 129 cm−1 was observed in the case of di(pyridin-2-yl)methanol due to presence of two strong intra-molecular hydrogen bonds, which indicates its higher stability than the dipyrromethanol. HOMO–LUMO energy gap calculations and natural bond orbital (NBO) analysis endorse the type of electronic transition for the desired product di(pyridin-2-yl)methanol is π–π*. The global reactivity analysis shows the electron donor and acceptor nature of dipyrromethanol and methylidyne radical, respectively. A potential energy surface is constructed via methylidyne radical addition, ring expansion, and hydrogen elimination transition states. Thermodynamics study and potential energy surface of the title reaction indicates its highly exothermicity and spontaneous in nature.

Regulating intramolecular hydrogen bonds of p-phenylenediimidazole-based small-molecule compounds towards the enhanced lithium storage capacity

The use of redox-active organic electrode materials in energy storage is restricted due to their inferior solvent resistance, abysmal conductivity, and the resultant low practical capacity. To address these issues, a class of bipolar p-phenylenediimidazole-based small-molecule compounds are designed and fabricated. The π-conjugated backbone of these small molecules allows for electron delocalization on a big conjugation plane, endowing them with good conductivity and reaction reversibility. Furthermore, when the para-positions of phenylene are occupied by hydroxyl groups, as-formed intramolecular hydrogen bonds (N–H…O) between phenolic hydroxyl groups and the –NH groups of imidazole rings further enhance the structural planarity, resulting in higher π-conjugation degree and better conductivity, and thus higher utilization of active sites and electrode capacity, proved by both experimental results and theoretical calculations. The optimized composite electrode DBNQ@rGO-45 shows a high specific capacity (∼308 mA h g−1 at 100 mA g−1) and a long cycling stability (112.9 mA h g−1 after 6000 cycles at 2000 mA g−1). The significantly better electrochemical properties for hydroxyl group-containing compounds than those without hydroxyl groups attributed to intramolecular hydrogen bond-induced conjugation enhancement will inspire the structure design of organic electrodes for better energy storage.

Nonclassical Zwitterions as a Design Principle to Reduce Lipophilicity without Impacting Permeability.

The ionization of bioactive molecules impacts many ADME-relevant physicochemical properties, in particular, solubility, lipophilicity, and permeability. Ampholytes contain both acidic and basic groups and are distinguished as ordinary ampholytes and zwitterions. An influential review states that zwitterions only exist if the acidic pKa is significantly lower than the basic pKa. Through concordance of measured and calculated pKa and log P, we show that the zwitterionic behavior of several marketed drugs and natural products occurs despite a low or negative ΔpKa. These nonclassical zwitterions are characterized by a weak acidic and basic pKa and conjugation through an extended aromatic system, often including pseudorings via intramolecular hydrogen bonds. In contrast to most classical zwitterions, nonclassical zwitterions can exhibit excellent permeability. As permeability and lipophilicity are typically correlated, the combination of low lipophilicity and high permeability makes nonclassical zwitterions an attractive design principle in medicinal chemistry.

Theoretical Insights into the Effect of Different Numbers of Thiophene Groups on Hydrogen Bond Interaction and Excited-State Intramolecular Proton-Transfer Process for Flavonoid Derivatives.

In this study, we systematically explored the impact of varying the number of thiophene groups on the hydrogen bond interaction and excited-state intramolecular proton-transfer (ESIPT) processes in flavonoid derivatives (STF, DTF, and TTF) using the density functional theory and time-dependent density functional theory methods. Initially, a thorough analysis of the optimized geometric structures revealed that the intramolecular hydrogen bond in the S1 state is enhanced and gradually weakened as the number of thiophene groups increases. To gain a deeper understanding of the hydrogen bond interaction, topological analysis, interaction region indicator scatter plots, and isosurface plots were employed. These images provide further insights that align with the structural analysis. Additionally, we observed a red-shift in the electronic spectra (absorption and fluorescence spectra), which is primarily attributed to the narrowing of the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, as elucidated by the frontier molecular orbitals. Furthermore, a combined analysis between the hole-electron distribution and the transition density matrix heat map shows that electron excitation involves the unidirectional charge-transfer mechanism. In the end, by conducting relaxed potential energy curve scans, we found that an increase in the number of thiophene groups elevates the energy barrier for ESIPT, making it more challenging for the reaction. In summary, our study underscores the vital effect of thiophene-substituted numbers in modulating the ESIPT process, which is able to provide valuable insights for the design and synthesis of desired organic fluorescent probes in the future.

Structural characterization and comparative analysis of polymorphic forms of psilocin (4-hydroxy-N,N-dimethyltryptamine)

The title compound, C12H16N2O, is a hydroxy-substituted monoamine alkaloid, and the primary metabolite of the naturally occurring psychedelic compound psilocybin. Crystalline forms of psilocin are known, but their characterization by single-crystal structure analysis is limited. Herein, two anhydrous polymorphic forms (I and II) of psilocin are described. The crystal structure of polymorphic Form I, in space group P21/c, was first reported in 1974. Along with the redetermination to modern standards and unambiguous location of the acidic H atom and variable-temperature single-crystal unit-cell determinations for Form I, the Form II polymorph of the title compound, which crystallizes in the monoclinic space group P21/n, is described for the first time. The psilocin molecules are present in both forms in their phenol–amine tautomeric forms (not resolved in the 1974 report). The molecules in Forms I and II, however, feature different conformations of their N,N-dimethyl ethylene substituent, with the N—C—C—C link in Form I being trans and in Form II being gauche, allowing the latter to bend back to the hydroxyl group of the same molecule, leading to the formation of a strong intramolecular O—H...N hydrogen bond between the hydroxyl moiety and ethylamino-nitrogen group. In the extended structure of Form II, the molecules form one-dimensional strands through N—H...O hydrogen bonds from the indole group to the oxygen atom of the hydroxyl moiety of an adjacent molecule. Form II exhibits whole-molecule disorder due to a pseudo-mirror operation, with an occupancy ratio of 0.689 (5):0.311 (5) for the two components. In contrast, Form I does not feature intramolecular hydrogen bonds but forms a layered structure through intermolecular N—H...O and O—H...N hydrogen bonds.

Concerning for the solvent-polarity-dependent conformational equilibrium and ESIPT mechanism in Pz3HC system: A novel insight

In this report, we propose a new insight into the interaction between the solvent-polarity-dependent conformational equilibrium and excited state intramolecular proton transfer (ESIPT) behavior of Pz3HC system in four different polar solvents (polarity order: ACN > THF > TOL > CYC). Using quantum chemistry method, we first announce a coexistence mechanism between Pz3HC-1 and Pz3HC-3 in the ground state in four solvents based on the Boltzmann distribution. In particular, Pz3HC-1 is the principal configuration in non-polar solvent, but Pz3HC-3 is the principal configuration in polar solvent. In addition, the simulated fluorescence spectra interprets the negative solvatochromism effect of Pz3HC-1 and Pz3HC-3 in four solvents. The evidence from intramolecular hydrogen bonding (IHB) parameters and electronic perspective collectively confirms the light-induced IHB enhancement and intramolecular charge transfer (ICT) properties in Pz3HC-1 and Pz3HC-3, which raises the likelihood of the ESIPT process. Combining the calculation of potential energy curve (PEC) and intrinsic reaction coordinate (IRC), we demonstrate that the ESIPT ease of Pz3HC-1 in different polar solvents obeys the order of CYC > TOL > THF > ACN, while the order of ESIPT ease in Pz3HC-3 is opposite. Notably, the ESIPT process of Pz3HC-3 in CYC solvent is accompanied by the twisted intramolecular charge transfer (TICT) process. In addition, we also reveal that the enol* and keto* fluorescence peaks of Pz3HC-3 in CYC solvent are quenched by ISC and TICT process, respectively. Our work not only provides a satisfactory explanation of the novel dynamics mechanism for Pz3HC system, but also brings light to the design and application of new sensing molecules in the future.

Synthesis and Crystal Structure Studies of a New Complex of Co (III)-Schiff Base Derivative Derived from Isonicotinohydrazide

A new Co(III) complex prepared by the reaction of N'–(1–(pyridin–2 yl)ethylidene) isonicotinohydrazide (H2L) with Co(II) ion is reported in this paper. The H2L ligand is structurally characterized by elemental analysis, NMR, and infrared spectroscopies. The mononuclear complex [Co(HL)2]·Cl·3H2O (1), is characterized by infrared spectroscopy, elemental analysis, conductance, magnetic room temperature measurement and single X-ray diffraction. The complex crystallizes in the monoclinic system with space group P21/c. The parameters of the unit cell are a = 9.6818(3) Å; b = 25.1587(6) Å; c = 11.5481(3) Å; β = 101.797(3) °; Z = 4; Rint = 0.0313 and wR(F2) = 0.0812. The asymmetric unit of the compound contains a discrete [Co(HL)2]+ cation one free chloride anion and three uncoordinated water molecules. In the discrete cation one Co3+ ion two organic ligand molecules are present. The coordination polyhedron around the Co3+ center is best described as a distorted octahedral with CoN4O2 chromophore. The crystal structure of the complex is stabilized by intramolecular and intermolecular hydrogen bonds.

Synthesis, structure, hirshfeld surface analysis and antibacterial activities of [Cd(2-ampy)3(NCS)(μ1,5-SCN)]2 and [Cd(4-ampy)2(μ1,5-dca)2]n complexes (2-ampy = 2-aminopyridine, 4-ampy = 4-aminopyridine, NCS = thiocyanate, dca = dicyanamide)

The complexes [Cd(2-ampy)3(NCS)(μ-SCN)]2 (1) and [Cd(4-ampy)2(μ1,5-dca)2]n (2) were synthesized and characterized using single crystal XRD. Complex 1 has a dimer structure with a triclinic crystal system and space group P1¯, whereas complex 2 has a polymer structure with a monoclinic crystal system and space group P21/c. Hirshfeld surface analysis of complex 1 showed the presence of S⋯N–H and N–H–S interactions between dimer molecules and intramolecular hydrogen bonds N–H⋯N. In complex 2, the analysis showed the polymer coordination chain bonds between Cd(II) ions with N atoms from dicyanamide and intermolecular hydrogen bonds of N–H⋯N. In vitro antibacterial testing for both complexes against Escherichia coli (gram-negative) and Staphylococus aureus (gram-positive) showed a higher inhibition zone diameter than the constituent reactants, where complex 2 had the a higher antibacterial activity.

Effect of different substituted groups on excited state intramolecular proton transfer of BOHMB

AbstractThe photophysical features of 3‐(benzo[d]oxazol‐2‐yl)‐2‐hydroxy‐5‐methoxy benzaldehyde (BOHMB) were investigated through experimental (J. Phys. Chem. A 2019, 123, 10,246–10,253) and theoretical (Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2022, 266, 120,406) methods. However, the effect of substituent groups on the excited state proton transfer process has not been studied. In this work, the excited state intramolecular proton transfer (ESIPT) dynamics and photophysical properties of BOHMB with different substituent groups were investigated by density‐functional theory (DFT) and time‐dependent DFT (TDDFT) methods at CAM‐B3LYP/6‐311G(d,p) level. The primary parameters related to hydrogen bonding and infrared vibration frequency were obtained to understand the ESIPT properties of BOHMB derivatives. The results indicate that the excited‐state intramolecular hydrogen bond (ESIHB) strengthening behaviors, and the intramolecular hydrogen bond O1–H2···O3 for 1a in the S1 state is the strongest among BOHMB derivatives. From the calculated potential energy curves, it can be inferred that the substitution and position of NH2 and NO2 groups will regulate the excited‐state energy barrier and thus affect the ESIPT process. The molecular absorption peak and fluorescence peak are affected by different substituting groups and different positions.

Antioxidant properties of catechin and its 3′O-α-glucoside: Insights from computational chemistry calculations

Density functional theory (DFT) calculations were used to investigate the conformational landscape of catechin and one of its main glucoside derivative (catechin-3′ O- α −glucopyranoside), and to determine the corresponding antioxidant properties. These investigations were carried out in benzene and water using the SMD universal continuum solvation model. Both properties were found to be significantly affected. The structures are characterized in both solvents by strong intramolecular hydrogen bonds (IMHB). In an apolar environment, Hydrogen Atom Transfer (HAT) is by far favored whereas in water the Sequential Proton Loss Electron Transfer (SPLET) mechanism is strongly preferred. In benzene, the catechin fragment has the best antioxidant character (from 27 kJ/mole) whereas in polar surroundings, the glucoside derivative has a slightly better antiradical activity (from 5 kJ/mole). Our results confirm the key role of the 3′-OH and 4′-OH groups of the catechole ring in these properties.

Highly Stable Silicon Anode Enabled by a Water-Soluble Tannic Acid Functionalized Dual-Network Binder.

Silicon (Si), a high-capacity electrode material, is crucial for achieving high-energy-density lithium-ion batteries. However, Si suffers from poor cycling stability due to its significant volume changes during operation. In this work, a tannic acid functionalized aqueous dual-network binder with an intramolecular tannic acid functionalized network has been synthesized, which is composed of covalent-cross-linked polyamide and ionic-cross-linked alginate (Alg(Ni)-PAM-TA), and employed as an advanced binder for stabilizing Si anodes. The resultant Alg(Ni)-PAM-TA binder, incorporating diverse functional groups including amide, carboxylic acid, and dynamic hydrogen bonds, can easily interact with both Si nanoparticles and the Cu foil, thereby facilitating the formation of a highly resilient network characterized by exceptional adhesion strength. Moreover, molecular dynamics (MD) simulations indicate that the Alg(Ni)-PAM-TA network shows an increased intramolecular hydrogen bond number with increasing concentration of TA and a decreased intramolecular hydrogen bond between PAM and Alg as a result of the aggregation behavior of tannic acids themselves. Consequently, the binder significantly enhances the Si electrode's integrity throughout repeated charge/discharge cycles. At a current density of 0.84 A g-1, the Si electrode retains a capacity of 1863.4 mAh g-1 after 200 cycles. This aqueous binder functionalized with the intramolecular network via the incorporation of TA molecules holds great promise for the development of high-energy-density lithium-ion batteries.

Synergetic effects of inter- and intramolecular hydrogen bonding interactions in XC5H3HC = Y···HO···H2O2 complexes (X = N, P, As and Sb; Y = O, S and NH): the role of aromaticity and exchange interactions

ABSTRACT Intramolecular hydrogen bonding (IHB) interactions were considered in XC5H3HC = Y···HO molecules which include OH···Y unit (Y = O, S and NH) and heteroatom X (X = N, P, As and Sb). Alteration of heteroatoms X in para position causes a change of properties of electron charge densities on these molecules and influences on strength of the IHB interactions. The aromaticity of the ring A (involving IHB interaction) and ring B (involving heteroatoms X) of XC5H3HC = Y···HO molecules was calculated using para-delocalisation index (PDI). Results reveal that the change of X from N to Sb is followed by the decrease in aromaticity of the mentioned rings. However, the strength of the IHB interactions increases during the change of X. Moreover, IHB energies were estimated using some computational methods and a viewpoint based on the properties of ring critical points (RCPs). The IHB energies obtained using a viewpoint based on the properties of RCPs have a better relationship with hydrogen bonding descriptors. Also, intermolecular hydrogen bond (HB) interactions of hydrogen peroxide with the close and open forms of the XC5H3HC = Y···HO molecules were considered. Cooperative effects of the HB and IHB interactions are revealed. Moreover, energy decomposition analysis (EDA) highlights the role of exchange interactions on the stability of the XC5H3HC = Y···HO···H2O2 complexes.

Enhancing Light-Emitting Efficiency of Blue Through-Space Charge Transfer Emitters via Fixing Configuration Induced by Intramolecular Hydrogen Bonding.

Closely aligned configuration of the donor (D) and acceptor (A) is crucial for the light-emitting efficiency of thermally activated delayed fluorescence (TADF) materials with through-space charge transfer (TSCT) characteristics. However, precisely controlling the D-A distance of blue TSCT-TADF emitters is still challenging. Herein, an extra donor (D*) located on the side of the primary donor (D) is introduced to construct the hydrogen bonding with A and thus modulate the distance of D and A units to prepare high-efficiency blue TSCT emitters. The obtained "V"-shaped TSCT emitter presents a minimal D-A distance of 2.890 Å with a highly parallel D-A configuration. As a result, a high rate of radiative decay (>107 s-1) and photoluminescence quantum yield (nearly 90%) are achieved. The corresponding blue organic light-emitting diodes show maximum external quantum efficiencies (EQEmax) of 27.9% with a Commission Internationale de L'Eclairage (CIE) coordinate of (0.16, 0.21), which is the highest device efficiency of fluorene-based blue TSCT-TADF emitters. In addition, the TSCT-TADF emitter-sensitized OLEDs also achieve a high EQEmax of 29.3% with a CIE coordinate of (0.12, 0.16) and a narrow emission.

Precise Regulation on the Bond Dissociation Energy of Exocyclic C-N Bonds in Various N-Heterocycle Electron Donors via Machine Learning.

Heterocycles with saturated N atoms (HetSNs) are widely used electron donors in organic light-emitting diode (OLED) materials. Their relatively low bond dissociation energy (BDE) of exocyclic C-N bonds has been closely related to material intrinsic stability and even device lifetime. Thus, it is imperative to realize fast prediction and precise regulation of those C-N BDEs, which demands a deep understanding of the relationship between the molecular structure and BDE. Herein, via machine learning (ML), we rapidly and accurately predicted C-N BDEs in various HetSNs and found that five-membered HetSNs (5-HetSNs) have much higher BDEs than almost all 6-HetSNs, except emerging boron-N blocks. Thorough analysis disclosed that high aromaticity is the foremost factor accounting for the high BDE of 5-HetSNs, and introducing intramolecular hydrogen-bond or electron-withdrawing moieties could also increase BDE. Importantly, the ML models performed well in various realistic OLED materials, showing great potential in characterizing material intrinsic stability for high-throughput virtual-screening and material design efforts.

Positive profile of natural small molecule organic matters on emerging antivirus pharmaceutical elimination in advance reduction process: A deep dive into the photosensitive mechanism of triplet excited state compounds

Natural small molecular organic matter (NSOM), ubiquitous in natural waters and distinct from humic acid or fulvic acid, is a special type of dissolved organic matter (DOM) which is characterized as strong photosensitivity and simple molecular structure. However, little study had been directed on the role of NSOM in eliminating emerging contaminants in advanced reduction process (ARP). This study took three small molecular isomeric organic acids (p−hydroxybenzoic acid, pHBA; salicylic acid, SA; m−hydroxybenzoic acid, mHBA) as the representative substances of NSOM to explore these mechanisms on promoting Ribavirin (RBV, an anti COVID−19 medicine) degradation in ultraviolet activated sulfite (UV/Sulfite) process. The results demonstrated that the observed degradation rate constant of RBV (kobs-RBV) was 7.56 × 10−6 s−1 in UV/Sulfite process, indicating that hydrated electron (eaq−) from UV/Sulfite process could not effectively degrade RBV, while it increased by 178 and 38 times when pHBA and SA were introduced into UV/Sulfite process respectively, suggesting that pHBA and SA strongly promoted RBV degradation while mHBA had no promotion on RBV abatement in UV/Sulfite process. Transient absorption spectra and reactive intermediates scavenging experiment indicated that the triplet excited state pHBA and SA (3pHBA* and 3SA*) contributed to the degradation of RBV through non−radical process. Notably, eaq− played the role of key initiator in transforming pHBA and SA into their triplet states. The difference of kobs-RBV in UV/Sulfite/pHBA and UV/Sulfite/SA process was attributed to different generation pathways of 3pHBA* and 3SA* (high molar absorptivity at the wavelength of 254 nm and photosensitive cycle, respectively) and their second order rate constants towards RBV (kRBV-3pHBA* = 8.60 × 108 M−1 s−1 and kRBV-3SA* = 6.81 × 107 M−1 s−1). mHBA could not degrade RBV for its lack of intramolecular hydrogen bond and low molar absorptivity at 254 nm to abundantly transform into its triplet state. kobs-RBV increased as pH increased from 5.0 to 11.0 in UV/Sulfite/SA process, due to the high yield of eaq− in alkaline condition which promoted the generation of 3SA* and the stable of the absorbance of SA at 254 nm. By contrast, kobs-RBV underwent a process of first increasing and then decreasing in UV/Sulfite/pHBA process as the increase of pH, and its highest value achieved in a neutral condition. This lied in the exposure of eaq− increased as the increase of pH which promoted the generation of 3pHBA*, while the molar absorptivity of pHBA at 254 nm decreased as the increase of pH in an alkaline condition which inhibited the yield of 3pHBA*. The RBV degradation pathways and products toxicity assessment indicated that UV/Sulfite/pHBA had better detoxification performance on RBV than UV/Sulfite/SA process. This study disclosed a novel mechanism of emerging contaminants abatement through non-radical process in NSOM mediated ARP, and provide a wide insight into positive profile of DOM in water treatment process, instead of only taking DOM as a quencher of reactive intermediates.

Conformers influence on UV-absorbance of avobenzone

Avobenzone is most commonly used FDA approved chemical UV-A filter in many sunscreen formulations. An important drawback of avobenzone is its photounstability and undergoes chemical transformation upon exposure to UV-radiation/sunlight. Eventhough single bond rotations are implicated in the radiation induced chemical modification of avobenzone, the conformers role of avobenzone on UV absorbance is yet to be addressed. Using the In silico platform working on Density Functional Theory (DFT), the communication evaluates the role of conformers on UV absorbance spectra of enol/keto forms of avobenzone. The results indicate that the conformers of enolic-form of avobenzone have broad range of absorbance from 273-389 nm and the keto-form has relatively narrow range of absorbance from 266-288 nm. The chelated conformers of enolic-avobenzone with intramolecular hydrogen bond are swingy in nature yet possessing strong bond contributing to its broad-spectrum UVA filtering activity. Among the conformers of keto-form of avobenzone, the planar conformer with the torsional angle 180° undergo facile Norrish Type-I cleavage. Mapping of the data with previous experimental results has allowed identifying 3D structures involved in the key steps of photoketonization process of avobenzone. The reported results may help to understand the molecular basis of enol-to-keto photochemical transformation of avobenzone and to develop photostabilizer to endure long-lasting photoprotection to avobenzone.

Comparing industrial and analytical kraft lignins as biobased UV-protective additives in coatings

Lignin as the second most abundant biopolymer on Earth has the potential to become the alternative to petroleum-derived materials. It exhibits excellent UV absorption ability due to its aromatic structure and the presence of numerous phenolic, ketone, and intramolecular hydrogen bonds. Due to its complex nature, it is important to investigate its properties which is a very important step towards the valorization of lignin. Revealing its structural complexity allows for a better examination of its influence on the properties of the final lignin-based materials. In our research, we used two different kraft lignins: commercial analytical kraft lignin (AL) and industrial LignoBoost kraft lignin (KL) as UV-protect additives in BPA(Bisphenol A)-free polymer coatings based on diurethane dimethacrylate (DIUR). The maximum addition of KL and AL was 2 wt%. Both lignin samples were characterized in detail (composition analysis, ash content, molar mass and polydispersity, surface morphology, thermal properties, and quantitative measurement of hydroxyl group content). We investigated the influence of lignins on the textural and thermal properties of the coatings. Finally, we studied the application of lignin as a value-added UV-protective component by UV-Vis electronic absorption spectroscopy. KL with a higher purity and lower number of aliphatic OH had a better dispersion in the polymer matrix than AL lignin which had more agglomeration in the polymer matrix. The better dispersion resulted in producing a smoother surface in the coatings made from KL. Finally, a noticeable and significant impact of KL additive on the photoprotective properties of the coating material was demonstrated. These results showed a potential application and opportunity in the valorization of available industrial lignins toward sustainable and value-added products.

Host-Guest Recognition-Mediated Supramolecular Aggregation-Induced Electrochemiluminescence of Iridium(III) Complexes for Nucleic Acid Bioassay.

Currently reported aggregation-induced electroluminescence (AIECL) is usually based on the electrostatic integration of luminous monomers, and its application is still limited by the low ECL efficiency and poor structural stability of electrostatic integration-based AIECL emitters. Herein, host-guest recognition-mediated supramolecular AIECL was creatively developed to overcome the defects of electrostatic-integration-based AIECL. Cucurbit[8]uril (CB[8]) as the host recognized tris (2-phenylpyridine) iridium(III) [Ir(ppy)3] as the guest to form a novel supramolecular complex Ir-CB[8]. CB[8] can not only provide a large hydrophobic cavity to efficiently load Ir(ppy)3 and enrich coreactant tripropylamine but also utilize its carbonyl-laced portals to form intramolecular hydrogen bonds to stabilize the supramolecular structure, so Ir-CB[8] revealed excellent AIECL performance. The AIECL emitter Ir-CB[8] coupled the efficient DNA walker to construct a sensing system for miRNA-16 detection. Au nanoparticles@norepinephrine (AuNPs@NE) trapped by single-strand S1 was developed to significantly quench the ECL emission of Ir-CB[8]. When the target microRNA-16 (miRNA-16) existed, H1 was opened and the sequential assembly from H2 to H7 was triggered, forming "windmill"-like DNA walker with six Pb2+-dependent leg DNA. The assembled DNA walker, which was centered on DNA structure, had high efficiency and biocompatibility and can cut S1 to keep the DNA fragment-carrying quencher AuNPs@NE away from the electrode surface, thus restoring the ECL emission of Ir-CB[8] and realizing ultrasensitive detection of miRNA-16. Supramolecular AIECL mediated by host-guest recognition provides a new way for constructing AIECL emitters with excellent structural stability and AIECL efficiency, and an Ir-CB[8] coupling "windmill"-like DNA walker builds a promising ECL-sensing system for bioassay.

A perspective on cellulose dissolution with deep eutectic solvents

Currently, membrane manufacturing relies heavily on fossil-based solvents and polymers, resulting in significant negative impacts on human health and the environment. Thus, there is an urgent need for eco-friendly, low-toxicity, and sustainable solvents and polymers to comply with the United Nations’ sustainable development goals. Cellulose, as a green, natural, and abundant polymer, offers a sustainable source for membrane manufacturing. However, a significant challenge exists in dissolving cellulose due to strong intermolecular and intramolecular hydrogen bonds within cellulose molecules. Deep eutectic solvents (DESs), which contain both hydrogen bond donor and acceptor groups, have received significant attention as alternative solvents for cellulose dissolution owing to their low cost, low toxicity, environmentally friendly nature, ease of synthesis, and versatility. This review examines experimental studies, and theoretical approaches, highlighting key findings and factors influencing cellulose dissolution in deep eutectic solvents.

Recognition of Amino Acid Salts by Temperature-Dependent Allosteric Binding with Stereodynamic Urea Receptors.

Positive homotropic artificial allosteric systems are important for the regulation of cooperativity, selectivity and nonlinear amplification. Stereodynamic homotropic allosteric receptors can transmit and amplify induced chirality by the first ligand binding to axial chirality between two chromophores. We herein report stereodynamic allosteric urea receptors consisting of a rotational shaft as the axial chirality unit, terphenyl units as structural transmission sites and four urea units as binding sites. NMR titration experiments revealed that the receptor can bind two carboxylate guests in a positive homotropic allosteric manner attributed to the inactivation by intramolecular hydrogen-bonding between urea units within the receptor. In addition, the VT-CD spectra observed upon binding of the urea receptor with l- or D-amino acid salts in MeCN showed interesting temperature-dependent Cotton effects, based on the differences of the receptor shaft unit and the guest structure. The successful discrimination of hydrocarbon-based side chains of amino acid salts indicated that the input of chiral and steric information for the guest was amplified as outputs of the Cotton effect and the temperature-dependence of VT-CD spectra through cooperativity of positive allosteric binding.