Strong 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.

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.

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.

Promoting Ruddlesden-Popper Perovskite Formation by Tailoring Spacer Intramolecular Interaction for Efficient and Stable Solar Cells.

Low-dimensional Ruddlesden-Popper phase (LDRP) perovskites are widely studied in the field of photovoltaics due to their tunable energy-band properties, enhanced photostability, and improved environmental stability compared to the 3D perovskites. However, the insulating spacers with weak intramolecular interaction used in LDRP materials limit the out-of-plane charge transport, leading to poor device performance of LDRP perovskite solar cells (PSCs). Here, a functional ligand, 3-guanidinopropanoic acid (GPA), which is capable of forming strong intramolecular hydrogen bonds through the carboxylic acid group, is employed as an organic spacer for LDRP PSCs. Owing to the strong interaction between GPA molecules, high-quality LDRP (GPA)2(MA)n-1PbnI3n+1 film with promoted formation of n = 5 phase, improved crystallinity, preferential vertical growth orientations, reduced trap-state density, and prolonged carrier lifetime is achieved using GPAI as the dimensionality regulator compared to butylamine hydroiodide (BAI). As a result, GPA-based LDRP PSC exhibits a champion power conversion efficiency of 18.16% that is much superior to the BA-based LDRP PSC (15.43%). Importantly, the optimized GPA-based LDRP PSCs without encapsulation show enhanced illumination, thermal, storage, and humidity stability compared to BA-based ones. This work provides new insights into producing high n value LDRP films and their efficient and stable PSCs.

Crown ether-like octanuclear molybdenum(V) clusters for cation binding and gas adsorption.

Octanuclear polyoxomolybdenum-based porous materials, Na8[Mo8O8(μ2-O)8(μ2-OH)8(3-apz)4]2·26H2O (1, 3-Hapz = 3-aminopyrazole), K8[Mo8O8(μ2-O)8(μ2-OH)8(3-apz)4]2·7H2O (2) and (NH4)4[Mo8O8(μ2-O)8(μ2-OH)4(3-apz)8]·20.5H2O (3), have been successfully synthesized by a hydrothermal method and fully characterized. X-ray structural analyses show that microporous materials 1-3 contain round pores formed by octanuclear molybdenum-oxygen groups connected sequentially with pore sizes of 4.0, 4.0, and 4.8 Å, respectively. Both 1 and 2 are composed of two {Mo8} rings, which are connected by strong intramolecular hydrogen bonds between bridging hydroxy groups and oxygen atoms to form dimeric structures. The central pores in 1 and 2 are occupied by Na+ and K+, respectively, while they are empty in 3. This reflects the structural expansion and contraction effects induced by different cations. Through intermolecular stacking, 1-3 also exhibit channels with sizes of 14.0 × 6.4, 4.6 × 2.6, and 5.4 × 5.4 Å, respectively, which were used for the studies of gas adsorption. The results show that 1-3 can selectively adsorb CO2 and O2, including the empty hole in 3, while they show little or no affinity for gases H2, N2, and CH4. Moreover, an additional polyoxomolybdenum-based species (Mo8O26)n·4n(3-H2apz) (4) has been obtained with protonated 3-aminopyrazole in the absence of a reducing agent, which can serve as an intermediate for the polyoxomolybdenum-based porous products.

Highly efficient circularly polarized phosphorescent electroluminescence from iridium(iii) complexes with chiral ligands

CP-OLEDs based on new phosphors exhibited an EQEmax of 31.9% and a |gEL| of up to 3.0 × 10−3.

SYNTHESIS AND STUDY OF SOME NOVEL β-ARYLAMINO-2-OXY-5- METHYLPROPIOPHENONES AS POLYETHYLENE STABILIZERS

The number of -arylamino-2-oxy-5-methylpropiophenones has been synthesized by reacting of - dimethylamino-2-oxy-5-methylpropiophenone hydrochloric acid salt with aniline derivatives in order to use these compounds as stabilizers for polyethylene. It was shown that the thermal stability of the compounds, depending on the nature of the substituent in the aniline fragment of the molecule was observed in a temperature range between 165 and 213°C. All studied compounds, introduced into polyethylene, increased its resistance to temperature effects. It was revealed that -arylamino-2-oxy-5-methylpropiophenones had a stabilizing effect due to the suppression of thermo-oxidative degradation of polyethylene. They multiplied the oxidation induction period of polyethylene and reduced the rate of oxidation. Among the compounds studied -phenoxybenzylamino-2-oxy-5-methylpropiophenone showed the highest stabilizing effect. All studied compounds had sufficient light-stabilizing activity, substantially due the presence in their molecules of a strong intramolecular hydrogen bond IHB (OH ... O = C) of the chelate type between the phenolic hydroxyl proton and the carbonyl oxygen of the acyl group.

Enhanced iodine capture by the hydrogen bond reconstruction strategy

The strong intramolecular hydrogen-bond of curcumin was broken by ionization, and curcumin anions form a weaker intermolecular hydrogen bond which is easily disrupted, making it easy to react with iodine and form a new strong halogen bond.

Macrocyclization-induce emission enhancement characteristics of benzothiadiazole-based macrocycles: A theoretical study

We present a comprehensive investigation into the molecular structures in the ground state and the first singlet excited state, intramolecular and intermolecular interactions, as well as the emission properties of monomers, dimers and macrocycles using density functional theory and time-dependent density functional theory. Our study aims to unveil the macrocyclization-induce emission enhancement principle for benzothiadiazole-based macrocycles. Compared with the typical π-π stacking of monomers, macrocycles exhibit the tighter stacking arrangement due to the presence of strong intramolecular and intermolecular hydrogen bond interactions and the rigid triangular geometry of macrocycle, which is conducive to the enhancement of emissions efficiency. The calculated oscillator strength of macrocycles in the first excited state is much higher than that of dimers composed of two monomers. Meanwhile, the large transition electric dipole moment is beneficial for enhancing the emission efficiency. Additionally, our study reveals an emission wavelength red-shift for macrocycles after “CH”/N substitution in the acceptor moiety, and the transition mode from LUMO to HOMO can be mainly attributed to intramolecular charge transition characters from acceptor to donor fragments. Our theoretical study might provide valuable insights for the design of innovative luminescent macrocycles with high emission efficiency.

Anisotropy in Antimicrobial Bottle Brush Copolymers and Its Influence on Biological Activity

AbstractAntimicrobial polymers are a promising alternative to conventional antibiotics in the fight against antimicrobial resistance. Cationic bottle brush copolymers have shown to be superior to linear topologies in previous studies. Herein, the aspect ratio of such polymers is varied creating differently shaped confined unimolecular structures with varying degrees of side chain mobility. Using reversible addition‐fragmentation chain‐transfer (RAFT) polymerization, bottle brushes are produced in a one‐pot procedure. The morphology is confirmed by atomic force microscopy. The hydrophobicity, as determined via high performance‐liquid chromatography (HPLC) analysis, is drastically influenced by the topology. Using Fourier‐transform infrared (FTIR) spectroscopy, it is found that polymers with a high side chain mobility and increased global hydrophilicity, are less hydrated, and have stronger intramolecular hydrogen bonds. A phase segregated morphology leading to unimolecular micellization is assumed. Biological tests reveal increased antimicrobial activity for such segregated polymers. Their excellent hemocompatibility results in highly selective antimicrobial polymers whose adaptability seems to be a key feature in their excellent performance. This study highlights the tremendous importance of structural control in antimicrobial polymers.

Near-infrared OLEDs with high radiance of ∼105 mW Sr−1 m−2 for single-wavelength oxygen saturation detection

Real-time in-home monitoring oxygen saturation (SpO2) is of great significance for early diagnosis and treatment of severe COVID-19, however, which should be based on multi-wavelength technology and complicated equipment. Herein, as a proof of concept, 740 nm is chosen as singlet light source for single-wavelength SpO2 detection, since absorbance differences between oxyhemoglobin (HbO2) and other interferences are the most rational. To controllably optimize excited-state characteristics of a near-infrared (NIR) thermally activated delayed fluorescence (TADF) emitters, an “extra conjugation” method is demonstrated by CNQP-TPA, whose 2,3-dicyanoquinoxaline phenanthroline (CNQP) acceptor forms strong intramolecular hydrogen bonds with two phenyls of triphenylamine (TPA) donors, which not only reduce excited-state relaxation-induced energy lose, but also provide more space for accurate modulation of intermolecular charge transfer (CT) interactions. As consequence, at the suitable doping concentration, CNQP-TPA endowed its device with a high radiance reaching ∼105 mW Sr−1 m−2 and desired electroluminescence peak at 744 nm. This device is further used as light source to detect SpO2 variation under single-wavelength mode. These results indicate the potential of NIR TADF materials and devices for in-home SpO2 monitoring and pre-diagnosis and prevention of severe COVID-19.

Trans-3-Benzyloxycarbonylamino-1-methyl-3-(methylcarbamoyl)azetidine-1-oxide

trans-3-Benzyloxycarbonylamino-1-methyl-3-(methylcarbamoyl)azetidine-1-oxide was prepared by stereoselective oxidation of the corresponding azetidine precursor. The stable molecule was characterized in a low-polarity solution by IR, 1H-NMR and 13C-NMR, and in the solid state as a co-crystal with water by X-Ray diffraction. The N-oxide function made a strong intramolecular 7-membered ring hydrogen bond with the methyl amide NH in solution and formed an intermolecular H-bond with the carbamate NH in a neighboring molecule in the solid state.

Synthesis, structure and Hirshfeld surface analysis of a coordination compound of cadmium acetate with 2-amino-benzoxazole.

A first coordination compound of 2-amino-benzoxazole (2AB), namely, bis-(2-amino-benzoxazole-κN 3)bis-(acetato-κ2 O,O')cadmium(II), [Cd(CH3COO)2(2AB)2], has been synthesized from ethanol solutions of Cd(CH3(COO)2 and 2AB. In the monoclinic crystals with the space group C21/c, the cadmium ions coordinate two neutral 2AB mol-ecules in a monodentate fashion through the oxazole N atom, while two acetate ligands are coordinated through the O atoms in a bidentate manner. The coordination polyhedron of the central ion is substanti-ally distorted octa-hedral. There are two relatively strong intra-molecular hydrogen bonds in the complex mol-ecule. Additionally, two inter-molecular hydrogen bonds associate complex mol-ecules into columns running in the [10] and [110] directions. The Hirshfeld surface analysis shows that 45.7% of the inter-molecular inter-actions are from H⋯H contacts, 24.7% are from O⋯H/H⋯O contacts and 18.8% are from C⋯H/H⋯C contacts, while other contributions are from N⋯H/H⋯N and O⋯O contacts.

Photo-induced synthesis, stereochemistry and antitumor activity of natural cyclopeptide Hikiamide B analogs

Peptide cyclization has been recognized as capable of overcoming the shortcomings of linear peptides such as poor stability, short half-life, low selectivity and low affinity to receptors, and the modification of cyclic peptides to achieve specific activity requirements is receiving increasing attention. Hikiamide B is a cyclic pentadepsipeptide that can induce the expression of peroxisome-proliferator-activated receptor-γ (PPAR-γ). Considering that PPAR-γ can effectively regulate the expression of genes related to tumorigenesis, and is a potential tumor target, in this paper, we have prepared several Hikiamide B analogs by intramolecular photo-induced single-electron-transfer (SET) reaction to find novel antitumor drugs The stereochemistry and the in vitro antitumor activity against HepG-2 and HeLa cells were investigated. We found that the compound with stronger intramolecular hydrogen bonds (compound 2) than other compounds showed more promising antitumor activity, and the cyclic compounds present stronger bioactivity than that of their linear precursors. In vitro studies of apoptosis mechanisms and mitochondrial membrane potential following cyclopeptide 2 treat have shown that the cyclopeptide may induce apoptosis in tumor cells. Finally, in silico ADME analysis has shown the potential of compound 2 for practical application.

Inter- vs. Intra-Molecular Hydrogen Bond in Complexes of Nitrophthalic Acids with Pyridine.

This study covers the analysis of isomeric forms of nitrophthalic acids with pyridine. This work dwells on the complementary experimental (X-ray, IR and Raman) and theoretical (Car-Parrinello Molecular Dynamics (CPMD) and Density Functional Theory (DFT)) studies of the obtained complexes. The conducted studies showed that steric repulsion between the nitro group in ortho-position and the carboxyl group causes significant isomeric changes. Modeling of the nitrophthalic acid-pyridine complex yielded a short strong intramolecular hydrogen bond (SSHB). The transition energy from the isomeric form with an intermolecular hydrogen bond to the isomeric form with an intramolecular hydrogen bond was estimated.

Synthesis and Crystal Structure of a New Complex of Nickel(II) Nitrate and Ethoxycarbonyl-Substituted (γ-piperidono)aza-14-crown-4-ether

A new coordination compound—derivative of aza-14-crown-4-ether, containing an ethoxycarbonyl subunit, with nickel(II) nitrate, of the [Ni3(NO3)4L4]2(NO3) composition—has been obtained for the first time in the form of single crystals. The presence of nickel atoms in the complex is confirmed by X-ray fluorescence analysis. The complex structure has been studied by precise X-ray diffraction on a laboratory X-ray source. The molecule of this complex is shown to have an intricate geometry and consist of four pairwise symmetric ligand molecules, coordinated by three nickel atoms. Stabilization of the complex molecule is provided by the presence of strong intramolecular hydrogen bonds, involving a crown-ether fragment.

Protonated and deprotonated vanadyl imidazole tartrates for the mimics of the vanadium coordination in the FeV-cofactor of V-nitrogenase.

Chiral imidazole-based oxidovanadium tartrates (H2im)2[Δ,Λ-VIV2O2(R,R-H2tart)(R,R-tart)(Him)2]·Him (1, H4tart = tartaric acid, Him = imidazole) and [Λ,Λ-VIV2O2(R,R-tart)(Him)6]·4H2O (2) and their corresponding enantiomers (H2im)2[Λ,Δ-VIV2O2(S,S-H2tart)(S,S-tart)(Him)2]·Him (3) and [Δ,Δ-VIV2O2(S,S-tart)(Him)6]·4H2O (4) were obtained in alkaline solutions. Interestingly, the tartrates chelate with vanadium bidentately through α-alkoxy/α-hydroxy and α-carboxy groups and imidazole coordinates monodentately through nitrogen atom. It is worth noting that complexes 1 and 3 contain both protonated α-hydroxy and deprotonated α-alkoxy groups simultaneously, which have short V-Oα-alkoxy distances [1.976(4)av Å in 1-4] and long V-Oα-hydroxy distances [2.237(3)av Å in 1 and 2.230(2)av Å in 3]. There is an interesting strong intramolecular hydrogen bond [O(11)⋯O(1) 2.731(5) Å] between the two parts in 1 and 3. The protonated V-O distances are closer to the average bond distance in reported FeV-cofactors (FeV-cos, V-Oα-alkoxy 2.156av Å) in VFe proteins, which corresponds to the feasible protonation of coordinated α-hydroxy in R-homocitrate in V-nitrogenase, showing the homocitrate in the mechanistic model for nitrogen reduction as a secondary proton donor. Furthermore, vibrational circular dichroism (VCD) and IR spectra of 1-4 pointed out the disparity between the characteristic vibrations of the C-O and C-OH groups clearly. EPR experiment and theoretical calculations support +4 oxidation states for vanadium in 1-4. Solution 13C {1H} NMR spectra and CV analyses exhibited the solution properties for 1 and 2, respectively, which indicates that there should be a rapid exchange equilibrium between the protonated and deprotonated species in solutions.

Intramolecular hydrogen bond-tuned thermal-responsive carbon dots and their application to abnormal body temperature imaging

A steric hindrance strategy was used to prepare intramolecular hydrogen bond–controlled thermosensitive fluorescent carbon dots (CDs) via the solvothermal treatment of o-phenylenediamine respectively with three dihydroxybenzene isomers. The CDs obtained from different isomers have very similar morphology, surfaces, and photophysical properties but exhibited different thermal sensitivities. Meanwhile, the orange-emitting CDs (p-CDs) obtained from o-phenylenediamine and p-hydroquinone exhibited an optimal thermal sensitivity of 1.1%/°C. Comprehensive experimental characterizations and theoretical calculations revealed that even a small difference in substituent locations in the phenyl ring of the precursors can considerably affect the formation of intramolecular hydrogen bonds and that the CDs with strong intramolecular hydrogen bonds exhibited poor thermosensitivity. The p-CDs were incorporated with reference CDs (B-CDs) that exhibited heating–quenching blue emission through electrostatic self-assembly to construct a dual-emission probe (p-CDs/B-CDs), which exhibited a thermal sensitivity of 2.0%/°C. Test strips based on the p-CDs/B-CDs were prepared to measure temperature fluctuations based on sensitive and instant fluorescence color evolution. Further, this fluorescent colorimetry was successfully applied to a test strip–integrated wearable wristband to measure the body temperature. This study establishes an inherent relationship between precursors and the resulting intramolecular hydrogen bonds for precisely tuning the thermal sensitivity of CDs. It also offers a visual quantitative strategy for the early warning of abnormal body temperatures.

Rational design strategies for nonconventional luminogens with efficient and tunable emission in dilute solution

The design and synthesis of organic nonconventional luminescent (NL) materials with efficient emission have attracted significant attention. However, these materials usually suffer from the fact of low photoluminescent quantum efficiency (Φ), poor tunability of emission wavelength, and non-luminescence in dilute solution, limiting their further application. Herein, rational molecular design strategies for NL compounds with efficient and tunable emission in dilute solution were presented via theoretical calculation and practical verification. Firstly, increasing the ratio of π → π* transition in the excited state to suppress the n → π* transition, inhibit intersystem crossing, and avoid the generation of triplet excitons which can be easily quenched by water or oxygen. Secondly, introducing strong intramolecular hydrogen bonds to suppress intramolecular rotation and inhibit non-radiative transitions. Besides, D-π-A structure can effectively adjust the luminescence color. Based on the proposed design strategies, two novel compounds named LJ-1 and LJ-2 were synthesized, both compounds can emit bright green fluorescence in dilute solution with Φ of up to 59.8 %, and their photophysical properties are pH-dependent. The results showed that pH had a great impact on the strength of intramolecular hydrogen bonds and the degree of conjugation. For example, the emission wavelength of LJ-1 exhibited red-shift as the increase of pH value. Furthermore, LJ-1 can be used for visual detection of Ag+ in water solution in naked eye and the precise localization of lysosomes. We believe that our work will greatly broaden the application range of nonconventional luminogenic compounds in future.

Blockade of persistent colored isomer formation in photochromic 3H-naphthopyrans by excited-state intramolecular proton transfer

In photochemistry the excited-state intramolecular proton transfer process (ESIPT) is often observed as a highly efficient singlet excited state depletion pathway, which in the presence of a strong intramolecular hydrogen bond may proceed on a subpicosecond time scale. The present work describes the suppression of unwanted transoid-trans isomer formation in photochromic 3H-naphthopyran derivatives by the introduction of a 5-hydroxy substituent. According to time-resolved spectroscopy experiments and excited-state ab initio calculations, transoid-cis → transoid-trans photoisomerization is reduced by a competitive ESIPT channel in nonpolar solvent (cyclohexane). Upon specific solute–solvent interactions (methanol, acetonitrile) the intramolecular hydrogen bond in the transoid-cis form is perturbed, favoring the internal conversion S1 → S0 process as photostabilizing channel.