Intramolecular Hydrogen Bond Research Articles

Nitrogen-Embedding Strategy for Short-Range Charge Transfer Excited States and Efficient Narrowband Deep-Blue Organic Light Emitting Diodes.

The development of deep-blue organic light-emitting diodes (OLEDs) featuring high efficiency and narrowband emission is of great importance for ultrahigh-definition displays with wide color gamut. Herein, based on the nitrogen-embedding strategy for modifying the short range charge transfer excited state energies of multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters, we introduce one or two nitrogen atoms into the central benzene ring of a versatile boron-embedded 1,3-bis(carbazol-9-yl)benzene skeleton. This approach resulted in the stabilization of the highest occupied molecular orbital energy levels and the formation of intramolecular hydrogen bonds, and thus systematic hypsochromic shifts and narrowing spectra. In toluene solution, two heterocyclic-based MR-TADF molecules, Py-BN and Pm-BN, exhibit deep-blue emissions with high photoluminescence quantum yields of 93 % and 94 %, and narrow full width at half maximum of 14 and 13 nm, respectively. A deep-blue hyperfluorescent OLED based on Py-BN exhibited a maximum external quantum efficiency of 27.7 % and desired color purity with Commission Internationale de L'Eclairage (CIE) coordinates of (0.150, 0.052). These results demonstrate the significant potential for the development of deep blue narrowband MR-TADF emitters.

Nitrogen‐Embedding Strategy for Short‐Range Charge Transfer Excited States and Efficient Narrowband Deep‐Blue Organic Light Emitting Diodes

AbstractThe development of deep‐blue organic light‐emitting diodes (OLEDs) featuring high efficiency and narrowband emission is of great importance for ultrahigh‐definition displays with wide color gamut. Herein, based on the nitrogen‐embedding strategy for modifying the short range charge transfer excited state energies of multi‐resonance (MR) thermally activated delayed fluorescence (TADF) emitters, we introduce one or two nitrogen atoms into the central benzene ring of a versatile boron‐embedded 1,3‐bis(carbazol‐9‐yl)benzene skeleton. This approach resulted in the stabilization of the highest occupied molecular orbital energy levels and the formation of intramolecular hydrogen bonds, and thus systematic hypsochromic shifts and narrowing spectra. In toluene solution, two heterocyclic‐based MR‐TADF molecules, Py‐BN and Pm‐BN, exhibit deep‐blue emissions with high photoluminescence quantum yields of 93 % and 94 %, and narrow full width at half maximum of 14 and 13 nm, respectively. A deep‐blue hyperfluorescent OLED based on Py‐BN exhibited a maximum external quantum efficiency of 27.7 % and desired color purity with Commission Internationale de L'Eclairage (CIE) coordinates of (0.150, 0.052). These results demonstrate the significant potential for the development of deep blue narrowband MR‐TADF emitters.

Photochemical Synthesis and Characterization of a Uranyl Peroxide Triethylamine N‐OxideDimer

A µ‐peroxido‐bis[di‐triethylamine N‐oxide‐dichloro‐dioxouranium] complex with the formula [(UO2)2O2(ON(CH2CH3)3)4Cl2] (complex 1) was synthesized photochemically from a reaction containing uranyl chloride, triethylamine, and H2O2. The photochemical breakdown of H2O2 yielded •OH radicals that reacted with triethylamine to form triethylamine N‐oxide (TEAO) in situ, which subsequently coordinated to UO22+ cations in a monodentate fashion via the N‐oxide functional groups. Structure determination using single crystal X‐ray diffraction revealed that TEAO ligands also formed intermolecular and intramolecular hydrogen bonds with UO22+ and peroxide moieties, and the intermolecular H‐bonding interactions displayed a temperature dependence with Oyl ‐ ‐ H – C and Oper ‐ ‐ H – C distances shortening at 100(2) K by ca. 0.1 Å. Raman spectroscopy data were collected on single crystals of 1 and peak fitting of these results allowed for assignments of peaks including C‐N stretches for TEAO ligands bound to UO22+ cations at 696.8 cm‐1, 717.8 cm‐1, and 776.5 cm‐1, which are redshifted by approximately 30 cm‐1 when compared to free triethylamine. UO22+ν1 and O22‐ν1 stretches, U‐Oper stretches, and notably, U‐Cl stretches were all identified as well, with U‐Cl modes at 198.9 cm‐1 and 212.1 cm‐1 substantially redshifted compared to the uranyl chloride starting material.

Effects of extended π-conjugated bridge on the ESIPT process and electronic spectra of 1,8-dihydroxynaphthalene substitute

The effect of extended π-conjugated bridge on the excited state intramolecular proton transfer (ESIPT) process and photophysical property of (E)-1-(1-hydroxynaphthalen-2-yl)-3-(2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1ij]quinolin-9yl)prop-2-en-1-one (NHP) was investigated using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Theoretical analyses demonstrate that the intramolecular hydrogen bonds (IHBs) with the studied molecules are strengthened to varying extents in the excited state. Specifically, as the π-conjugated bridge is extended, the ESIPT process becomes increasingly challenging due to the elevated energy barrier. Meanwhile, the fluorescence peak prominently intensifies and red-shifts to 720 nm. The study is expected to provide new insights into ESIPT-type red-emitting materials.

Structural Characterization of Pyruvic Acid Dimers Formed inside Helium Nanodroplets by Infrared Spectroscopy and Ab Initio Study.

The structural arrangements of α-keto acid complexes hold significant interest across various fields of chemistry such as enzyme modeling, drug design, or polymer blending. Herein, we report mass-selective infrared (IR) spectra of pyruvic acid monomers and dimers in the range 1720-1820 cm-1 recorded in helium nanodroplets at 0.37 K. The monomer features IR bands at 1807.1 and 1734.5 cm-1, which are assigned to the carboxylic and ketonic C═O stretching vibrations, respectively. Furthermore, the pyruvic acid dimers generated inside the helium nanodroplets are characterized by carboxylic and ketonic C═O stretch vibrations appearing at 1799.2 and 1737.0 cm-1, respectively. This frequency shift of ±7 cm-1 for both C═O stretching bands from the monomer to the dimer demonstrates that the structural motif of the monomer is maintained upon dimer aggregation in helium nanodroplets. The structural assignments were supported by a comparison of the MP2/aug-cc-pVDZ-predicted harmonic vibrational spectra at the C═O stretching region with the experiments. The global minimum monomer structure with an intramolecular hydrogen bond and its dimer stabilized by both inter- and intramolecular hydrogen bonding interactions reproduce the experimental spectra from the monomer and dimer. This assigned dimer structure lies ca.11 kJ/mol above the corresponding global minimum and is favored in helium nanodroplets due to the long-range realignment of molecules via dipole-dipole interaction, followed by short-range stabilization upon intermolecular hydrogen bond formation. The barrier for reconfiguration of the precooled monomer conformer leading to the formation of the most stable dimer structure is around 58 kJ/mol, which is infeasible at 0.37 K.

Hydrogen bond regulation to promote the direct production of diosgenin from Dioscorea zingiberensis rhizomes

Herein, a renewable system consisted of tartaric acid and isopropanol was developed to produce diosgenin efficiently from Dioscorea zingiberensis rhizomes. The yield of diosgenin reached 4.15% comparable to the highest value reported in previous researches. The combination of experiment and DFT calculation revealed that the acid-alcohol system could regulate the hydrogen bond interaction of each component in the rhizomes to disassemble the connection network and promote the release of saponin. Meanwhile, the intramolecular hydrogen bond of tartaric acid and the steric hindrance effect of isopropanol could prevent the esterification reaction and maintain the strong acidity of the system for the high yield of diosgenin. The scale-up experiment with a 100-fold feeding capacity was also conducted successfully. Furthermore, the technological process integrated with purification of diosgenin, recovery of organic acid and solvent and upgrading of residual solid to porous carbon materials has been established systematically to verify the prospective of industrialization.

Crystal structures of four thio-glycosides involving carbamimido-thio-ate groups.

The compounds 2',3',4',6'-tetra-O-acetyl-β-d-gluco-pyranosyl N'-cyano-N-phenyl-carbamimido-thio-ate (C22H25N3O9S, 5a), 2',3',4',6'-tetra-O-acetyl-β-d-galacto-pyranosyl N'-cyano-N-phenyl-carbamimido-thio-ate, (C22H25N3O9S, 5b), 2',3',4',6'-tetra-O-acetyl-β-d-galacto-pyranosyl N'-cyano-N-methyl-carbamimido-thio-ate (C17H23N3O9S, 5c), and 2',3',4',6'-tetra-O-acetyl-β-d-galacto-pyranosyl N'-cyano-N-p-tolyl-carbamimido-thio-ate (C23H27N3O9S, 5d) all crystallize in P212121 with Z = 4. For all four structures, the configuration across the central (formal) C=N(CN) double bond of the carbamimido-thio-ate group is Z. The torsion angles C5-O1-C1-S (standard sugar numbering) are all close to 180°, confirming the β position of the substituent. Compound 5b involves an intra-molecular hydrogen bond N-H⋯O1; in 5c this contact is the weaker branch of a three-centre inter-action, whereas in 5a and 5d the H⋯O distances are much longer and do not represent significant inter-actions. The C-N bond lengths at the central carbon atom of the carbamimido-thio-ate group are almost equal. All C-O-C=O torsion angles of the acetyl groups correspond to a synperiplanar geometry, but otherwise all four mol-ecules display a high degree of conformational flexibility, with many widely differing torsion angles for equivalent groups. In the crystal packing, 5a, 5c and 5d form layer structures involving the classical hydrogen bond N-H⋯Ncyano and a variety of 'weak' hydrogen bonds C-H⋯O or C-H⋯S. The packing of 5b is almost featureless and involves a large number of borderline 'weak' hydrogen bonds. In an appendix, a potted history of wavelength preferences for structure determination is presented and it is recommended that, even for small organic crystals in non-centrosymmetric space groups, the use of Mo radiation should be considered.

LNMR analysis of the retention of different guar gum structure in sandstone: Based on a new characterization method

The adsorption and retention damage of guar gum to reservoirs are important factors affecting the effectiveness of hydraulic fracturing. Accurately understanding and evaluating the adsorption and retention of guar gum can better support the research of low-damage fracturing fluid. However, previous indoor evaluation methods have some limitations in studying the adsorption and retention characteristics of guar gum. The analysis object of low-field nuclear magnetic resonance (LNMR) is water rather than guar gum, which cannot achieve visualization of guar gum retention. In addition, Ordinary guar gum (GG), hydroxypropyl guar gum (HPG), and carboxymethyl guar gum (CMG) are commonly used in the hydraulic fracturing of sandstone gas reservoirs, but there are very few studies that focus on the differences in the adsorption and retention damage of the three guar gums from a microscopic perspective. In this study, a new characterization method for evaluating the retention of polymer in fracturing fluid based on the principles and properties of LNMR was proposed. This method can quantitatively evaluate the amount of guar gum adsorption retention and achieve a visual evaluation of the adsorption and retention of guar gum in cores. The aggregation characteristics of guar gum in porous media can be reflected. The dynamic retention process of GG, HPG, and CMG in sandstone cores was directly characterized through this method. The aggregation and entanglement characteristics of the three types of guar gum in sandstone were analyzed from the structure of guar gum. The experimental results show that the difference in molecular weight and modified groups of guar gum has an impact on its adsorption and retention. The molecular chain after the gel-breaking of GG was longer due to the large molecular weight. Long chains and intramolecular hydrogen bonds caused a larger curling degree of GG molecules. The entanglement degree of guar gum increased due to the introduction of non-ionic long-chain hydroxypropyl. The introduction of anionic carboxymethyl made CMG molecules more stretched due to electrostatic repulsion. The median particle size of the gel breaking liquid of GG was 10.65 μm, HPG was 8.8 μm, and CMG was 5.88 μm. A larger molecular particle size after guar gum gel breaking would aggravate the retention in sandstone porous media. After 150 min of displacement, the adsorption and retention amount of GG in the core was 4.59 mg/g, HPG was 4.17 mg/g, and CMG was 3.86 mg/g. The compactness of aggregates formed by guar gum in the core was HPG > GG > CMG. The gas flooding can relieve the adsorption and retention of guar gum. The higher the degree of entanglement of guar gum molecules, the more difficult to remove them from the core. The flowback degree of gas flooding of GG was 10.2%, HPG was 6.8%, and CMG was 21.9%. This research provides an experimental strategy for the microscopic evaluation of polymer adsorption and retention in rock porous media. The research results provide a deep understanding of the microscopic characteristics of guar gum adsorption and retention from the perspective of guar gum structure, which has some significance for guiding the optimization of fracturing fluid and the study of low-damage fracturing fluid.

Discovery of a Series of 4-Amide-thiophene-2-carboxyl Derivatives as Highly Potent P2Y14 Receptor Antagonists for Inflammatory Bowel Disease Treatment.

The P2Y14 receptor has been proven to be a potential target for IBD. Herein, we designed and synthesized a series of 4-amide-thiophene-2-carboxyl derivatives as novel potent P2Y14 receptor antagonists based on the scaffold hopping strategy. The optimized compound 39 (5-((5-fluoropyridin-2-yl)oxy)-4-(4-methylbenzamido)thiophene-2-carboxylic acid) exhibited subnanomolar antagonistic activity (IC50: 0.40 nM). Moreover, compound 39 demonstrated notably improved solubility, liver microsomal stability, and oral bioavailability. Fluorescent ligand binding assay confirmed that 39 has the binding ability to the P2Y14 receptor, and molecular dynamics (MD) simulations revealed the formation of a unique intramolecular hydrogen bond (IMHB) in the binding conformation. In the experimental colitis mouse model, compound 39 showed a remarkable anti-IBD effect even at low doses. Compound 39, with a potent anti-IBD effect and favorable druggability, can be a promising candidate for further research. In addition, this work lays a strong foundation for the development of P2Y14 receptor antagonists and the therapeutic strategy for IBD.

Effect of glycerol plasticizer on the structure and characteristics of bacterial cellulose-based biocomposite films

Abstract Biocomposite film was successfully produced by combining bacterial cellulose (BC) and sodium alginate (ratio of 80:20) with the addition of glycerol as conventional plasticizer at varied concentration (2, 4, 6% w/w, based on total sample weight) through solution casting method. The influence of glycerol content on structure (by FTIR), mechanical properties, optical properties (by colorimeter and spectrophotometer) and water vapor permeability (WVP, gravimetric method) of BC biocomposite film was investigated. The addition of glycerol disrupts the inter- and intramolecular hydrogen bonds in the cellulose chains, replaced by weaker BC-alginate-glycerol bonds. This resulted a decrease in film density, causing lower tensile strength, lightness, opacity and WVP of BC biocomposite film. An increase in glycerol concentration led to an increase in elongation percentage due to the effect of glycerol plasticization. Film with 4% glycerol exhibited the lowest WVP (5.08x10-13 g/m.s.Pa), highest lightness (L = 73.49), lowest opacity (3.24 Abs/mm) with tensile strength of 19.57 MPa and elongation 8.38%. The addition of glycerol significantly affects the BC biocomposite film properties. The resulting biofilm shows performance equivalent to commercial bioplastic TeloRoll.

Theoretical study on the atomic substitution effect on the aromaticity and ESIPT behavior of a novel chalcone-based fluorophore

Recently, a new ESIPT-based fluorophore (E)-2-(4-(dimethylamino) benzylidene)-7-hydroxy-1-indanone (7HIN) was designed and obtained experimentally. We investigated the excited state intramolecular proton transfer (ESIPT) behavior and photophysical properties of 7HIN based on density functional theory (DFT) and time-dependent DFT. Two derivatives of 7HIN (4HID and 4HBF) were obtained by replacing the CH2 group in the five-membered ring with NH group and O atom to study the atomic substitution effect on the proton transfer reactions and fluorescent features of 7HIN. All data from structural parameters, infrared frequencies and electron density showed that the intramolecular hydrogen bonds (IHB) in 7HIN and its derivatives were strengthened in the excited state (S1), which will accelerate the ESIPT process. The potential energy curves (PECs) indicated that the proton transfer can easily occur in the S1 state because of the lower energy barrier. The electron-hole analysis revealed that the S0 → S1 transition is an intramolecular charge transfer transition. The NH- and O-substitution led to a weakening of IHB, increased the ESIPT barrier and red-shifted the absorption/emission wavelength of 7HIN. The PBE38 functional in this work is very reliable since the experimental absorption/fluorescence wavelength of 7HIN was reproduced well.

Effects of amino‐ and dimethylamine‐groups on the fluorescent properties of novel flavone‐based derivatives with ESIPT behavior: A TD‐DFT study

AbstractIn this work, the effects of different functional groups on the excited‐state intramolecular proton transfer behavior and fluorescent features of 3‐hydroxy‐2‐(naphthalen‐2‐yl)‐4H‐chromen‐4‐one (HFN) are explored in detail. Three new compounds (HFN‐1, HFN‐2, and HFN‐3) are designed based on the HFN by introducing the electron‐donating groups (–NH2, –N(CH3)2). The mainly geometrical parameters of optimized configuration showed that the intramolecular hydrogen bonds of the studied compounds are enhanced in the excited (S1) state, confirming by the ground (S0) and excited states infrared spectra, electron densities and reduced density gradient isosurfaces. The S0 → S1 transitions of HFN derivatives are dominated by ππ* charge transfer transition. The introduction of electron‐donating group (–NH2, –N(CH3)2) weakens the intramolecular hydrogen bond, increases the excited‐state intramolecular proton transfer barrier and red‐shifts the absorption/fluorescence peak. The coexistence of –NH2 and –N(CH3)2 make the absorption and fluorescence wavelengths of HFN‐1/HFN‐2 red‐shift/blue‐shift.

Molecular dynamics simulations of the proline and hydroxyproline of collagen

Collagen is an important natural, bioactive, and abundant material in living systems. Developing collagen materials that resolve practical issues in tissue engineering is the focus of significant research. However, its properties and behavior are not sufficiently understood, not in the least because proteins undergo significant conformational changes while performing their function. Moreover, it is difficult to determine the solvent impact on the structure and interatomic bonding at the atomistic level. Molecular Dynamics (MD) simulation is a technique that can be used successfully to understand macromolecular structure-to-function relationships. This work investigates the influence of hydroxyproline and proline on hexamer and heptamer collagen structures using the GROMACS software. We applied the Amber99sb force field to conduct molecular dynamics simulations in triplicate of the collagen fragments over a trajectory of 200 ns. We studied the root mean square (RMS) distribution, hydrogen bonds, and solvent accessible surface area (SASA). The results showed proline and hydroxyproline helped to stabilize the 3-helix of collagen; hydroxyproline did so more extensively than proline did. Hydroxyproline is responsible for the formation of intermolecular hydrogen bonds. It increases the stability of the triple helical, while proline promotes the formation of the intramolecular hydrogen bonds and makes the overall structure less stable than hydroxyproline. The solvent-accessible surface area (SASA) indicates that collagen is a lipophilic polymer.

The influence of the conditions of applying sealing polymer materials on the deformation resistance of the sealanter to sclofibro concrete

The article deals with the features of the treatment of solid surfaces with a primer before using sealing materials. The adhesive strength of the sealant to the area of adhesion is the basis for sealing the joints. Lack of adhesion leads to the ingress of water, dirt, precipitation and other climatic effects, which eventually lead to the destruction of the seams. Therefore, it is extremely important to observe the seam treatment technology before applying the sealant. Proper treatment of seams with a primer, observing the time of application to the base, before using sealing materials will increase the durability and service lifespan of the sealed joint. To improve the adhesive strength between the adhesive and the substrate, as a rule, the hard surface (substrate) is pre-treated with a primer based on polyurethane foam or epoxy resins. These primers are used because when exposed to a hard surface, a polymer matrix is formed, which, upon further contact with the sealant, increases the adhesion strength in the contact zone. In surface defect zones with moisture content, a new surface layer is also formed due to the participation of polymer groups in forming intramolecular hydrogen bonds. The formation of a polymer layer on a solid surface containing defective zones requires a certain time. Tests were carried out to determine the resistance to deformations of a combination of sealant/primer sealing materials in combination with glass fiber reinforced concrete samples and to establish the influence of the conditions for applying a primer/sealant to the surface of a glass fiber reinforced concrete composition on resistance to a series of character cycles of equal loads and temperature changes, with a deformation of the sealing material of 25% . It has been established that the time of treatment of a solid surface with a primer should be at least 5 minutes. If this condition is not observed when sealing materials are applied to glass fiber reinforced concrete, it may cause the sealant to separate from the base.

A Dual-Bond Crosslinking Strategy Enabling Resilient and Recyclable Electrolyte Elastomers for Solid-State Lithium Metal Batteries.

Elastomeric solid polymer electrolytes (SPEs) are highly promising to address the solid-solid-interface issues of solid-state lithium metal batteries (LMBs), but compromises have to be made to balance the intrinsic trade-offs among their conductive, resilient and recyclable properties. Here, we propose a dual-bond crosslinking strategy for SPEs to realize simultaneously high ionic conductivity, elastic resilience and recyclability. An elastomeric SPE is therefore designed with hemiaminal dynamic covalent networks and Li+-dissociation co-polymer chains, where the -C-N- bond maintains the load-bearing covalent network under stress but is chemically reversible through a non-spontaneous reaction, the weaker intramolecular hydrogen bond is mechanically reversible, and the soft chains endow the rapid ion conduction. With this delicate structure, the optimized SPE elastomer achieves high elastic resilience without loading-unloading hysteresis, outstanding ionic conductivity of 0.2 mS cm-1 (25 °C) and chemical recyclability. Then, exceptional room-temperature performances are obtained for repeated Li plating/stripping tests, and stable cycling of LMBs with either LiFePO4 or 4.3 V-class LiFe0.2Mn0.8PO4 cathode. Furthermore, the recycled and reprocessed SPEs can be circularly reused in LMBs without significant performance degradation. Our findings provide an inspiring design principle for SPEs to address the solid-solid-interface and sustainability challenges of solid-state LMBs.

In Silico Approach: Anti-Tuberculosis Activity of Caespitate in the H37Rv Strain.

Tuberculosis is a highly lethal bacterial disease worldwide caused by Mycobacterium tuberculosis (Mtb). Caespitate is a phytochemical isolated from Helichrysum caespititium, a plant used in African traditional medicine that shows anti-tubercular activity, but its mode of action remains unknown. It is suggested that there are four potential targets in Mtb, specifically in the H37Rv strain: InhA, MabA, and UGM, enzymes involved in the formation of Mtb's cell wall, and PanK, which plays a role in cell growth. Two caespitate conformational structures from DFT conformational analysis in the gas phase (GC) and in solution with DMSO (CS) were selected. Molecular docking calculations, MM/GBSA analysis, and ADME parameter evaluations were performed. The docking results suggest that CS is the preferred caespitate conformation when interacting with PanK and UGM. In both cases, the two intramolecular hydrogen bonds characteristic of caespitate's molecular structure were maintained to achieve the most stable complexes. The MM/GBSA study confirmed that PanK/caespitate and UGM/caespitate were the most stable complexes. Caespitate showed favorable pharmacokinetic characteristics, suggesting rapid absorption, permeability, and high bioavailability. Additionally, it is proposed that caespitate may exhibit antibacterial and antimonial activity. This research lays the foundation for the design of anti-tuberculosis drugs from natural sources, especially by identifying potential drug targets in Mtb.

Antioxidant Mechanism, Spectroscopic and Pharmacological Properties of Four Flavonoids: DFT, Docking and Molecular Dynamics.

Myricetin (1), Quercetin (2), Kaempferol (3) and Kaempferide (4) were flavonoids with phenolic hydroxyl groups. The antioxidant and pharmacological mechanisms of them were investigated in detail. The lowest hydroxyl dissociation enthalpies of 1, 2, 3 and 4 were calculated by DFT, respectively. The hydroxyl dissociation enthalpies of the four flavonoids at the O2 site are the highest. By analyzing the intramolecular hydrogen bonds and HOMO-LUMO orbitals of the four flavonoids, the reasons for their divergence of hydroxyl dissociation enthalpies and antioxidant mechanisms were further investigated. The UV-vis and IR spectra of four flavonoids were compared. The interactions about electrostatic attraction, p-π conjugation and hydrogen bond combined the flavonoid with the target protein closely. The root mean square deviation of peroxisome proliferator-activated receptor γ combined with 1, 2 and 3 increased, while that of PPARγ combined with 4 decreased.

Revealing the ESIPT process in benzoxazole fluorophores within polymeric matrices through theory and experiment.

The impact of the polymeric matrix on the photophysical characteristics of monomeric dyes responsive to excited-state intramolecular proton transfer (ESIPT) was investigated through UV-Vis absorption as well as steady-state and time-resolved emission spectroscopies. For this purpose, two benzoxazole monomers (M1 and M2) with acryloyl groups at different positions in their molecular structures were employed to facilitate covalent bonding within a styrene chain. Our findings reveal significant variations in their excited-state properties due to the proximity of the acryloyl groups, which affects the energy barrier of the ESIPT reaction, the emission wavelength, and the balance between the normal and tautomeric forms. The experimental results were corroborated through theoretical investigations at the DFT/TDDFT level, specifically using the B3LYP-D3/def2-TZVP methodology. Three notable observations emerged: donor/acceptor groups at the meta/para positions induced electron distribution changes, causing red-shifted emission for M2; in the polymer film, particularly in PM1, intramolecular hydrogen bond deactivation favored N* emission over T* emission; and the zwitterionic character of the T* species. This study underscores the advantages of functionalization in polymers, which can lead to colorless films and prevalent N* or T* emission, and contributes valuable insights into molecular design strategies for tailoring the photophysical properties of polymeric materials.

Effect of different substituent on the ESIPT process and fluorescence features of 2-(2-hydroxyphenyl)benzoxazole derivatives: A DFT/TD-DFT study

In this contribution, four derivatives of 5′-(para-R-Phenylene) vinyl-2-(2′-hydroxyphenyl) benzoxazole (PVHBO) were ingeniously designed by introducing two electron-withdrawing substituents and two electron-donating substituents, aiming to investigate the influence of different substituents on the photophysical properties of PVHBO and the excited state intramolecular proton transfer (ESIPT) process via the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. By utilizing the geometric parameters and the simulated infrared (IR) spectra, we compared the intramolecular hydrogen bonds (IHBs) strengths in the S0 and S1 states of the molecules. Via conducting the hole-electron analysis, the reduction in fluorescence intensity for the enol and keto forms of PVHBO, PVHBO-MeO, and PVHBO-NH2 were also well explicated. Besides, the potential energy curves (PECs) and corresponding transition state (TS) structures for both S0 and S1 states were also constructed to accurately obtain energy barriers of forward and reversed proton transfer processes. The calculated absorption and fluorescence spectra also show that PVHBO-NH2 has the largest Stokes shifts of 158 nm and 219 nm in both the enol and keto states, with a significant increase in fluorescence intensity observed upon the induction of electron-withdrawing groups. Through this work, it can provide the theoretical basis for the design of novel luminescent materials.

De Novo Synthesis and Structural Elucidation of CDR-H3 Loop Mimics.

The binding affinity of antibodies to specific antigens stems from a remarkably broad repertoire of hypervariable loops known as complementarity-determining regions (CDRs). While recognizing the pivotal role of the heavy-chain 3 CDRs (CDR-H3s) in maximizing antibody-antigen affinity and specificity, the key structural determinants responsible for their adaptability to diverse loop sequences, lengths, and noncanonical structures are hitherto unknown. To address this question, we achieved a de novo synthesis of bulged CDR-H3 mimics excised from their full antibody context. CD and NMR data revealed that these stable standalone β-hairpin scaffolds are well-folded and retain many of the native bulge CDR-H3 features in water. In particular, the tryptophan residue, highly conserved across CDR-H3 sequences, was found to extend the kinked base of these β-bulges through a combination of stabilizing intramolecular hydrogen bond and CH/π interaction. The structural ensemble consistent with our NMR observations exposed the dynamic nature of residues at the base of the loop, suggesting that β-bulges act as molecular hinges connecting the rigid stem to the more flexible loops of CDR-H3s. We anticipate that this deeper structural understanding of CDR-H3s will lay the foundation to inform the design of antibody drugs broadly and engineer novel CDR-H3 peptide scaffolds as therapeutics.