Noncovalent Intermolecular Interactions Research Articles

Fully physically crosslinked organohydrogel with ultrastretchability, transparency, freezing-tolerant, self-healing, and adhesion properties for strain sensor

Recently, conductive hydrogels have gained great attention in intelligent wearable devices, but the simultaneous realization of stretchability, transparency, anti-freezing, self-healing, and adhesion properties by an easy method is still a big challenge. Herein, a novel multifunctional organohydrogel based on noncovalent intermolecular interactions was developed by simply polymerization hydroxyethyl acrylamide (HEAA) in LiCl cryoprotectant/water (Cryo/water) solution via one-pot photo-polymerization method. Hydrogen bonding interactions of PHEAA-PHEAA and PHEAA-Cryo were the main driving force for gel formation. The LiCl and cryoprotectant gave PHEAA-Cryo-LiCl organohydrogel good conductivity and anti-freezing properties, respectively. The effects of the gel composition on the mechanical, transparency, anti-freezing, and conductivity properties of PHEAA-Cryo-LiCl organohydrogels were researched in detail. Moreover, poly(hydroxyethyl acrylamide)-glycerin-lithium chloride (PHEAA-Gl-LiCl) organohydrogel displayed good self-healing and adhesion properties owing to the reversible hydrogen bonding. Based on PHEAA-Gl-LiCl organohydrogel, a strain sensor was prepared for detecting human movements within a wide temperature range (−40 °C–25 °C), and the result showed various human motions could be detected stably, including joint movement, making a fist, swallowing or pronouncing, suggesting the potential application for the next generation of intelligent wearable sensors.

Biomedical Applications of Thermosensitive Hydrogels for Controlled/Modulated Piroxicam Delivery.

The objectives of this study are the synthesis of thermosensitive poly(N-isopropylacrylamide-co-2-hydroxypropyl methacrylate), p(NiPAm-HPMet), hydrogels and the analysis of a drug-delivery system based on piroxicam, as a model drug, and synthesized hydrogels. A high pressure liquid chromatography method has been used in order to determine both qualitative and quantitative amounts of unreacted monomers and crosslinkers from polymerized hydrogels. Swelling kinetics and the order of a swelling process of the hydrogels have been analyzed at 10 and 40 °C. The copolymers' thermal properties have been monitored by the differential scanning calorimetry (DSC) method. DSC termograms have shown that melting occurs in two temperature intervals (142.36-150.72 °C and 153.14-156.49 °C). A matrix system with incorporated piroxicam has been analyzed by using FTIR and SEM methods. Structural analysis has demonstrated that intermolecular non-covalent interactions have been built between side-groups of copolymer and loaded piroxicam. Morphology of p(NiPAm-HPMet) after drug incorporation indicates the piroxicam presence into the copolymer pores. Kinetic parameters of the piroxicam release from hydrogels at 37 °C and pH 7.4 indicate that the fluid transport mechanism corresponds to Fickian diffusion. As a result, formulation of thermosensitive p(NiPAm-HPMet) hydrogels with incorporated piroxicam could be of interest for further testing as a drug carrier for modulated and prolonged release, especially for topical administration.

Unraveling the Nature of Hydrogen Bonds of "Proton Sponges" Based on Car-Parrinello and Metadynamics Approaches.

The nature of intra- and intermolecular non-covalent interactions was studied in four naphthalene derivatives commonly referred to as "proton sponges". Special attention was paid to an intramolecular hydrogen bond present in the protonated form of the compounds. The unsubstituted "proton sponge" served as a reference structure to study the substituent influence on the hydrogen bond (HB) properties. We selected three compounds substituted by methoxy, amino, and nitro groups. The presence of the substituents either retained the parent symmetry or rendered the compounds asymmetric. In order to reveal the non-covalent interaction properties, the Hirshfeld surface (HS) was computed for the crystal structures of the studied compounds. Next, quantum-chemical simulations were performed in vacuo and in the crystalline phase. Car-Parrinello molecular dynamics (CPMD), Path Integral Molecular Dynamics (PIMD), and metadynamics were employed to investigate the time-evolution changes of metric parameters and free energy profile in both phases. Additionally, for selected snapshots obtained from the CPMD trajectories, non-covalent interactions and electronic structure were studied. Quantum theory of atoms in molecules (QTAIM) and the Density Overlap Regions Indicator (DORI) were applied for this purpose. It was found based on Hirshfeld surfaces that, besides intramolecular hydrogen bonds, other non-covalent interactions are present and have a strong impact on the crystal structure organization. The CPMD results obtained in both phases showed frequent proton transfer phenomena. The proton was strongly delocalized in the applied time-scale and temperature, especially in the PIMD framework. The use of metadynamics allowed for tracing the free energy profiles and confirming that the hydrogen bonds present in "proton sponges" are Low-Barrier Hydrogen Bonds (LBHBs). The electronic and topological analysis quantitatively described the temperature dependence and time-evolution changes of the electronic structure. The covalency of the hydrogen bonds was estimated based on QTAIM analysis. It was found that strong hydrogen bonds show greater covalency, which is additionally determined by the proton position in the hydrogen bridge.

Differentiating the effects of hydrophobic interaction and disulfide bond on the myofibrillar protein emulsion gels at the high temperature and the protein interfacial properties

The study presented the effects of modulating the hydrophobic interaction and disulfide bond on the properties of myofibrillar protein (MP) emulsion gels at high temperature (95 °C) and the differentiation on the contribution of non-covalent (hydrophobic interaction) and covalent intermolecular interactions (disulfide bond) to the properties of interfacial protein films were also determined. The hydrophobic interactions among MP were modulated by the addition of octenyl succinic anhydride (OSA), and the disulfide bonds were modulated by the SH/SS exchange reactions mediated by GSH. The results showed that the MP emulsion gel properties at 95 °C were improved by modulating the hydrophobic interaction or disulfide bonds, and the dynamic interfacial adsorption of MP and dissipation quartz crystal microbalance experiments showed the interfacial adsorption pattens of protein were also changed. In addition, the hydrophobic interactions putted emphasis on improving the gel matrix, whereas the disulfide bonds focused on increasing the stiffness of interfacial protein films.

New Ni(II) and Cu(II) Schiff base coordination complexes derived from 5-Bromo-salicylaldehyde and 3-picoyl amine/ethylenediamine: Synthesis, structure, Hirshfeld surface and molecular docking study with SARS-CoV-2 7EFP-main protease

Two co-ordination compounds, one nickel(II) complex [Ni(L1)(Phen)2]ClO4(1) and one copper(II) complex [Cu(L2)] (2), were synthesized using Schiff base ligands derived from the condensation reaction of 5-Bromo-salicylaldehyde with 3-picoyl amine (L1H)(L1H = (E)-4-Bromo-2-(((pyridin-3-ylmethylene)amino) methyl) phenol) and ethylenediamine (L2H2), respectively(L2H2 = 2,2′-((1E,1′E)-(ethane-1,2-diylbis(azaneylylidene))bis(methanelylidene))bis (4-bromophenol)). The newly synthesized complexes were fully characterized, including X-ray crystallography. The crystal structure of both the complexes was determined using Single Crystal structure analysis. The electrochemical properties of (1) were studied using cyclic voltammetry. DFT calculations were done for the newly synthesized co-ordination complexes to have a relevant and reasonably accurate calculation of their molecular and electronic behavior. The Hirshfeld surface (HS) analysis was also performed using the crystallographic data for investigating the nature and quantitative contribution of all possible non-covalent intermolecular interactions within the crystal lattice. To explore potential SARS-CoV-2 drug candidates, both the co-ordination compounds were subjected to molecular docking calculations with the SARS-CoV-2 virus (PDB ID: 7EFP). The molecular docking calculations of Ni(II) complex (1) into the 7EFP-main protease of SARS-CoV-2 virus revealed the binding energy of −11.5 kcal/mol, while Cu(II) complex (2) exhibited the binding energy of −8.5 kcal/mol at the inhibition binding site of the receptor protein.

Fluorination effects probed in 4-fluoroacetophenone and its monohydrate.

Rotational spectra of the 4-fluoroacetophenone monomer and its monohydrate were investigated by Fourier transform microwave spectroscopy complemented with quantum chemical calculations. One conformer of 4-fluoroacetophenone and two isomers of 4-fluoroacetophenone-H2O have been observed in the pulsed jets. The observation of all mono-substituted 13C isotopologues in natural abundance allows an accurate structural determination of the 4-fluoroacetophenone monomer. Both detected isomers of 4-fluoroacetophenone-H2O are stabilized by a dominant O-H⋯O and a secondary C-H⋯O hydrogen bond. The fluorination effects on the geometries, intermolecular non-covalent interactions and V3 barrier of the methyl internal rotation were analysed. The relative population ratio of the two observed isomers for 4-fluoroacetophenone-H2O was also estimated to be NI/NII ≈ 7/1.

Mutual-DTI: A mutual interaction feature-based neural network for drug-target protein interaction prediction.

The prediction of drug-target protein interaction (DTI) is a crucial task in the development of new drugs in modern medicine. Accurately identifying DTI through computer simulations can significantly reduce development time and costs. In recent years, many sequence-based DTI prediction methods have been proposed, and introducing attention mechanisms has improved their forecasting performance. However, these methods have some shortcomings. For example, inappropriate dataset partitioning during data preprocessing can lead to overly optimistic prediction results. Additionally, only single non-covalent intermolecular interactions are considered in the DTI simulation, ignoring the complex interactions between their internal atoms and amino acids. In this paper, we propose a network model called Mutual-DTI that predicts DTI based on the interaction properties of sequences and a Transformer model. We use multi-head attention to extract the long-distance interdependent features of the sequence and introduce a module to extract the sequence's mutual interaction features in mining complex reaction processes of atoms and amino acids. We evaluate the experiments on two benchmark datasets, and the results show that Mutual-DTI outperforms the latest baseline significantly. In addition, we conduct ablation experiments on a label-inversion dataset that is split more rigorously. The results show that there is a significant improvement in the evaluation metrics after introducing the extracted sequence interaction feature module. This suggests that Mutual-DTI may contribute to modern medical drug development research. The experimental results show the effectiveness of our approach. The code for Mutual-DTI can be downloaded from https://github.com/a610lab/Mutual-DTI.

Influence of crystal structure and composition on optical and electronic properties of pyridinium-based bismuth iodide complexes.

This study investigates the impacts of structure and composition on the optical and electronic properties of a series of pyridinium-based bismuth iodide complexes. Organic substrates with various functional groups, such as 4-aminopyridine (4-Ampy), 4-methylpyridine (4-Mepy), 4-dimethylaminopyridine (4-Dmapy), and 4-pyridinecarbonitrile (4-CNpy) with different electron-donating and electron-withdrawing groups at the para position of the pyridine ring were employed. Crystallographic analysis reveals various bismuth iodide structures, including 1D chains and discrete 0D motifs. The optical band gap of these materials, identified via diffuse reflectance spectroscopy (DRS) and verified with density functional theory (DFT) calculations, is influenced by the crystal packing and stabilising interactions. Through a comprehensive analysis, including Hirshfeld surface (HS) and void assessment, the study underscores the influence of noncovalent intermolecular interactions on crystal packing. Spectroscopic evaluations provide insights into electronic interactions, elucidating the role of electron donor and acceptor substituents within the lattice. Thermogravimetric differential thermal analysis (TG-DTA) indicates structural stability up to 250 °C. Linear sweep voltammetry (LSV) reveals significant conductivity in the range of 10-20 mS per pixel at 298.15 K. X-ray absorption spectroscopy (XAS) at the Bi L3 edge indicates a similar oxidation state and electronic environment across all samples, underscoring the role of bismuth centres surrounded by iodides.

Correlating structure and photophysical properties in thiazolo[5,4-d]thiazole crystal derivatives for use in solid-state photonic and fluorescence-based optical devices.

There is a growing demand for new fluorescent small molecule dyes for solid state applications in the photonics and optoelectronics industry. Thiazolo[5,4-d]thiazole (TTz) is an organic heterocycle moiety which has previously shown remarkable properties as a conjugated polymer and in solution-based studies. For TTz-based small molecules to be incorporated in solid-state fluorescence-based optical devices, a thorough elucidation of their structure-photophysical properties needs to be established. Herein, we have studied four TTz-based materials functionalized with alkyl appendages of varying carbon chain lengths. We report the single crystal structures of the TTz derivatives, three of which were previously unknown. The packing modes of the crystals reveal that molecular arrangements are largely governed by a chorus of synergistic intermolecular non-covalent interactions. Three crystals packed in herringbone mode and one crystal packed in slipped stacks proving that alkyl appendages modulate structural organization in TTz-based materials. Steady state and time-resolved photophysical properties of these crystals were studied via diffuse-reflectance, micro-Raman, and photoluminescence spectroscopy. The crystals fluoresce from orange-red to blue spanning through the whole gamut of the visible spectrum. We have established that photophysical properties are a function of crystal packing in symmetrically substituted TTz-based materials. This correlation was then utilized to fabricate crystalline blends. We demonstrate, for the first time, that symmetrically substituted donor-acceptor-donor TTz-based materials can be used for phosphor-converted color-tuning and white-light emission. Given the cost effectiveness, ease of synthesis and now a structure-photophysics correlation, we present a compelling case for the adoption of TTz-based materials in solid-state photonic and fluorescence-based optical devices.

Modular metallotecton for engineering permanently porous frameworks: supernumerary role of ancillary ion.

The formation of robust supramolecular frameworks built from hetero-polytopic metal complexes and interacting with different ancillary ions remains a long-standing and underexplored desire. Herein, the secondary sphere interaction chemistry of [Ru(5-oxido-6-hydroxy-1,10-phenanthroline)a(5,6-dihydroxy-1,10-phenanthroline)(3-a)]-(a-2) (1) (a = 1, 3) coordination ion is reported, where the π-conjugated phenanthroline ligands are functionalized with catecholate groups used as H-bond donors and ligands. The deprotonation of the catechols is found to control the overall charge stoichiometry in 1, acting as a metallotecton to interact with anions of different basicity (Cl- in 1.Cl and Br- in 1.Br) as well as with Li+ cations (in 1.Li+). These interactions lead to the formation of 2D porous honeycomb networks without any significant alteration in the molecular packing. This implies that the self-assembly process is controlled by complementary intermolecular non-covalent interactions making the choice of the ancillary ion insignificant. The robust porous structure of the frameworks is established by uptake of D2O and I2 molecules within the microporous channels. This work demonstrates that supramolecular frameworks appear as flexible candidates for applications in gas sorption, separation and chemical sensing.

Crystal Structure of N‐(2‐Hydroxynapthylidene)‐L‐isoleucinyl‐4,6‐O‐ethylidene‐β‐D‐glucopyranosylamine and an Insight from Experimental and Theoretical Calculations

AbstractDimethyl sulfoxide solution of N‐(2‐hydroxynapthylidene)‐L‐isoleucinyl‐4,6‐O‐ethylidene‐β‐D‐glucopyranosylamine (L1) affords single crystals of its ketoenamine configuration. The noncovalent intermolecular interactions present in the molecules have been explored by Hirshfeld surface analysis and 2D fingerprint plots generated using crystallographic data. The structural parameters of L1 in both the tautomeric forms (ketoenamine and phenolimine) at ground states have been optimized using Hartree–Fock and density functional theory calculations in gaseous and solution phases. The Fourier transform infrared, nuclear magnetic resonance, and UV–visible spectra of this molecule have been compared with the theoretically calculated data of both the tautomeric forms. Additionally, Mulliken population analysis, molecular electrostatic potential, and natural bond order analysis provide a better understanding of charge distribution, presence of electrophilic/nucleophilic sites, and intramolecular charge transfer, respectively, in the molecule.

Planarity is one of the essential requirements for fluorescence in Red Fluorescent Protein chromophore analogs

Synthesis and photophysical properties of four red fluorescent protein (RFP) chromophore analogs are reported. The analogs in crystals are held by different non-covalent intermolecular interactions such as C–H....O hydrogen bonding, C–H....π, π....π, and halogen bonding interactions, stabilizing the molecular stacks. The carbonyl group in the imidazol-5(4H)-one ring generates diverse packing systems in the compound via intermolecular C–H....O hydrogen bonds. Compounds 1 and 2 adopt a non-planar geometry, while 3 and 4 are slightly bent. Compound 3 shows a donor-acceptor type of π-π interactions resulting in a lateral offset stacking that is stabilized by strong π-π stacking between the imidazolin-5-one ring and methoxy substituted benzene, along with halogen....halogen bonding interactions. Compound 4 displays a strong π-π stacking between two imidazol-5(4H)-one rings. The Hirshfeld surfaces of two-dimensional fingerprint plots were used to analyze the strength of intermolecular interactions in the structures. The photoluminescence is also tuned in these molecules by appropriate substitution. Thus, the azine compounds are completely non-fluorescent compared to the other two.

An investigation on 3-hydroxybenzaldehyde for exploring terahertz low-frequency vibration modes with quasi-harmonic approximation method

3-Hydroxybenzaldehyde (3-HBA) was investigated in the range of 0.6–2.8 THz by terahertz time-domain spectroscopy (THz-TDS) and solid-state density functional theory (ss-DFT) with first-principles calculation. Four distinct peaks were found respectively, and among them, the intensity disparity between experiment and simulation spectra at 2.04 THz was recognized as the biggest inconsistency. Considering thermal behavior can be responsible for this, quasi-harmonic approximation (QHA) method was introduced to mimic the unit cell volume expansion. According to vibrational modes analysis, it was ascertained that the biggest vibrational modes discrepancy was also located at 2.04 THz. Molecules in 0% and 4% unit cell expansion exhibit an opposite rotational direction in a-b plane compared with 2% unit cell expansion. Noncovalent intermolecular interactions were investigated with independent gradient model (IGM), and the result indicates that hydrogen bonding is the dominating noncovalent interaction of 3-HBA. While calculating systematic potential energy to the displaced bonds stretching involving hydrogen atoms, it was found the anomalous potential energy variation to the bond stretching provides a possible explanation for the rotation direction divergence, that is, the rotation direction divergence can be related to some hydrogen atoms seeking lower overall potential energy around their equilibrium positions during bond stretching in response to the variational intermolecular van der Waals force. This research combined THz-TDS with the quasi-harmonic approximation method, elucidating the principle of vibrational characteristics in different volumes, which is beneficial to the investigation of the terahertz low-frequency vibration to thermal behavior as a reference in biochemistry and other fields.

Atomic-Resolution Experimental Structural Biology and Molecular Dynamics Simulations of Hyaluronan and Its Complexes.

This review summarizes the atomic-resolution structural biology of hyaluronan and its complexes available in the Protein Data Bank, as well as published studies of atomic-resolution explicit-solvent molecular dynamics simulations on these and other hyaluronan and hyaluronan-containing systems. Advances in accurate molecular mechanics force fields, simulation methods and software, and computer hardware have supported a recent flourish in such simulations, such that the simulation publications now outnumber the structural biology publications by an order of magnitude. In addition to supplementing the experimental structural biology with computed dynamic and thermodynamic information, the molecular dynamics studies provide a wealth of atomic-resolution information on hyaluronan-containing systems for which there is no atomic-resolution structural biology either available or possible. Examples of these summarized in this review include hyaluronan pairing with other hyaluronan molecules and glycosaminoglycans, with ions, with proteins and peptides, with lipids, and with drugs and drug-like molecules. Despite limitations imposed by present-day computing resources on system size and simulation timescale, atomic-resolution explicit-solvent molecular dynamics simulations have been able to contribute significant insight into hyaluronan's flexibility and capacity for intra- and intermolecular non-covalent interactions.

Photochromic Semiconductors: Bottom-Up Strategy to Construct Type II-Stacking Viologen π-Aggregates.

Semiconductor conductivities depend largely on the crystal structures and the associated electronic structures. If the electronic structures can be switched reversibly in the same crystal structure, then a drastic conductivity change may be controllable. The effect of electron transfer (ET) on semiconductor conductivity remained elusive so far. In this work, a series of two pillared inorganicorganic hybrid photochromic semiconductors (PSCs), [(CQ)Pb3X6(H2O)]·2H2O [X = Cl (1) and Br (2), CQ = N-4,4'-bipyridiniopropionate (viologen)], with II-stacking viologen π-aggregates, are constructed by a bottom-up self-assembly strategy through inorganic skeleton-directed intercalation and intermolecular noncovalent interaction. The conductivities are abnormally "invariant" after photoinduced ET, breaking the convention that the generation of radicals favors conductivity. The abnormally "invariant" conductivities are mainly derived from approximate electronic couplings before and after ET between II-stacking viologen π-aggregates.

Quantitative Analysis the Weak Non-Covalent Interactions of the Polymorphs of Donepezil.

Donepezil has polymorphism. Different crystalline forms can exhibit different physicochemical properties and biological activities. Exploration of intermolecular interactions is essential to reveal the formation mechanism and differences in properties of polymorphs. This study explores the weak non-covalent intermolecular interactions of donepezil polymorphs through fully ab initio quantum mechanical methods, semi-empirical methods, and Hirshfeld surface analysis. The results show that the Hirshfeld surface analysis method can clearly and intuitively reveal the intermolecular interactions. Theoretical calculations using the atom–atom Coulomb–London–Pauli (AA-CLP) method were also performed to understand the interaction energies toward the total lattice energy. The value of the lattice energy was in accordance with the melting points of the donepezil polymorphs and brought to light the nature of thermal stability. In the specific energy distribution, the contribution of the dispersion force is the most prominent. Further interaction energy analysis found that within a distance of 3.8 Å from the center of the donepezil molecule, different crystalline forms of donepezil molecules have different interaction energies with surrounding molecules. The different interaction energies between polymorphs may lead to polymorphs with different physical–chemical properties.

Recent Progress of Noncovalent Interaction‐Driven Self‐Assembly of Photonic Organic Micro‐/Nanostructures

AbstractModern organic photonics is heavily reliant on micro‐/nanostructured organic crystalline materials, not least because they exhibit advantageous physicochemical properties and can be easily fabricated by bottom‐up approaches such as self‐assembly driven by weak noncovalent intermolecular interactions (van der Waals forces, π–π interactions, hydrogen bonds, halogen bonds, charge transfer interactions, etc.). Herein, the effects of these interactions on organic crystal nucleation are summarized, the resulting low‐dimensional organic crystal structures and their optoelectronic applications are discussed, and future development prospects are presented to inspire the further investigation of such optofunctional structures.

Theoretical evaluation of charge transport properties and mobility of tetraphenyldipyranylidene derivatives in organic field-effect transistors

Density functional theory calculations were performed to calculate the structural, electronic, physical, and hole/electron charge transport properties of three possible pathways of Tetraphenyldipyranylidene (DPPh) derivatives including electron-acceptor atoms and electron-donor groups as the organic semiconductors in organic field-effect transistors (OFETs). Additionally, the reduced density gradient-based non-covalent interaction (RDG-NCI) analysis was performed to investigate the presence of non-covalent intermolecular interactions. The results of electronic and physical properties show that all compounds are stable in environmental conditions and intermolecular interactions between the three possible dimers of each compound are different. The maximum mobility (µ(max)) and anisotropic mobility (µφ(max)) of the hole (0.16 cm2 V−1 s−1) is greater than that of the electron in DPPh, which is in good agreement with the experiment. The mobility of the hole decreases by introducing the electron-acceptor atoms and electron-donor groups. However, µ(max) and µφ(max) values of the electron in the case of DPPh derivatives increase including C(CH3)3, Br, OCH3, CH3, Cl, and –OCH2CH3, respectively. According to different analyses, DPPh-CH3, DPPh-C(CH3)3, DPPh-Br, and DPPh-Cl semiconductors are proposed as the preferred candidates for use in the OFET devices.

Synthesis, Covalency Sequence, and Crystal Features of Pentagonal Uranyl Acylpyrazolone Complexes along with DFT Calculation and Hirshfeld Analysis.

Three uranyl acylpyrazolone complexes [UO2(PCBPMP)2(CH3CH2OH)] (complex I), [UO2(PCBMCPMP)2(CH3CH2OH)] (complex II), and [UO2(PCBPTMP)2(CH3CH2OH)] (complex III) were synthesized from σ-donating acypyrazolone ligands to analyze their sequence of covalent characteristics, reactivity, and redox properties (PCBPMP: p-chlorobenzoyl 1-phenyl 3-methyl 5-pyrazolone; PCBMCPMP: p-chlorobenzoyl 1-(m-chlorophenyl) 3-methyl 5-pyrazolone; PCBPTMP: p-chlorobenzoyl 1-(p-tolyl) 3-methyl 5-pyrazolone). An examination of the structure, pentagonal bipyramidal geometry, and composition of these complexes was conducted mainly through their single-crystal X-ray diffraction (XRD) data, 1H nuclear magnetic resonance (NMR) δ-values, plots of thermogravimetric-differential thermal analysis (TG-DTA), significant Fourier transform infrared (FTIR) vibrations, gravimetric estimation, and molar conductivity values. The covalency order was found to be complex II > III > I, which mainly depends on values of stretching frequencies, average bond lengths of axial uranyl bonds, values of average bond lengths on the pentagonal equatorial plane, solvent coordination on the fifth site of a pentagonal plane, and the type of aryl group on the nitrogen of the pyrazolone ring. This was confirmed by FTIR spectroscopy and single-crystal spectral characterization. To verify experimental results by comparison with theoretical results, density functional theory (DFT) calculations were carried out, which further gives evidence for the covalency order through theoretical frequencies and the gap of highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energies. Theoretical bond properties were also examined by the identification of global index parameters. Intermolecular noncovalent surface interactions were studied by the Hirshfeld surface analysis. The irreversible redox behavior of uranyl species was identified through electrochemical cyclic voltammetry-differential pulse voltammetry (CV-DPV) plot analysis.

Self-assembly and label-free fluorescent aptasensor based on deoxyribonucleic acid intercalated dyes for detecting lactoferrin in milk powder.

Lactoferrin (Lf), an iron-binding glycoprotein, regulates the immune system. It has broad-spectrum antimicrobial activity and is critical for child physical growth and development. As a common additive in the dairy industry, it is crucial to quantify LF content. This study established a self-assembly and universal fluorescence aptasensor for detecting LF in milk powder based on structure-selective dyes of PicoGreen intercalated in the label-free aptamer. Herein, the aptamer functions as both a specific recognition element against targets and a fluorescent signal reporter integrated with structure-selective dyes. First, the aptamer folds into a three-dimensional spatial structure based on complementary base pairings and intermolecular weak non-covalent interactions. Then, the dye is intercalated into the minor groove structures of the aptamer and triggers its potential fluorescent property. When the target exists, the aptamer binds to it preferentially, and its space structure unfolds. This causes the freeing of the subsequent dye and decreases the corresponding fluorescence. Hence, the reflected fluorescence signals could directly determine the target concentrations. Under the optimum conditions, a good linear relationship (R2, 0.980) was obtained in the Lf range from 20 to 500 nM with a detection limit of 3 nM (2.4 mg/kg) and good specificity, as well as a reliable recovery of 95.8–105.1% in milk powder. In addition, the universality was also confirmed with a good performance by quickly changing the aptamers against other targets (chlorpyrifos, acetamiprid, bovine thyroglobulin, and human transferrin) or utilizing another fluorescence dye. Therefore, this self-assembly aptasensor provides a universal and concise strategy for effective detection.