Molecular Sites Research Articles

A comprehensive molecular dynamics simulation of plastic and liquid succinonitrile: Structural, dynamic, and dielectric properties.

Molecular dynamics simulations at constant temperature and pressure were carried out to investigate the structural, dynamical, and dielectric properties of succinonitrile in its plastic and liquid phases at several thermodynamic states. A six-site united atom model was employed with a force field incorporating an intramolecular torsional term that accurately describes gauche and trans conformers. Analysis of the radial distribution function showed that succinonitrile adopts a body-centered cubic arrangement below its melting point, transitioning to a less ordered state in the liquid phase. In addition, examination of alignments between methylene bonds and the diagonals of the simulating cubic box revealed pronounced directional preferences in the plastic phase. The study of conformational states suggested that succinonitrile molecules predominantly adopt gauche conformations, which exhibit longer lifetimes than trans conformers. Spectral density analysis highlighted distinct peaks for different molecular sites, revealing significant differences between gauche and trans conformers. The correlation functions of bending and torsional angles, as well as vectors joining different atoms, illustrated a sensitivity to internal motions, which were notably faster for trans conformers. Differences in decay rates between trans and gauche conformers underscored the influence of gauche-trans transitions. The static dielectric constant, which has been derived from the total dipole moment, was primarily influenced by the contribution of the gauche conformers. In addition, the distance-dependent Kirkwood factor was computed, revealing antiparallel alignment at short distances. Finally, the dielectric relaxation time and the static dielectric constant values were compared with experimental data.

Continuous Electrosynthesis of Pure H2O2 Solution with Medical-Grade Concentration by a Conductive Ni-Phthalocyanine-Based Covalent Organic Framework.

Electrosynthesis of H2O2 provides an environmentally friendly alternative to the traditional anthraquinone method employed in industry, but suffers from impurities and restricted yield rate and concentration of H2O2. Herein, we demonstrated a Ni-phthalocyanine-based covalent-organic framework (COF, denoted as BBL-PcNi) with a higher inherent conductivity of 1.14 × 10-5 S m-1, which exhibited an ultrahigh current density of 530 mA cm-2 with a Faradaic efficiency (H2O2) of ∼100% at a low cell voltage of 3.5 V. Notably, this high level of performance is maintained over a continuous operation of 200 h without noticeable degradation. When integrated into a scale-up membrane electrode assembly electrolyzer and operated at ∼3300 mA at a very low cell voltage of 2 V, BBL-PcNi continuously yielded a pure H2O2 solution with medical-grade concentration (3.5 wt %), which is at least 3.5 times higher than previously reported catalysts and 1.5 times the output of the traditional anthraquinone process. A mechanistic study revealed that enhancing the π-conjugation to reduce the band gap of the molecular catalytic sites integrated into a COF is more effective to enhance its inherent electron transport ability, thereby significantly improving the electrocatalytic performance for H2O2 generation.

Acacetin alleviates rheumatoid arthritis by targeting HSP90 ATPase domain to promote COX-2 degradation

BackgroundInflammation plays a significant role in initiating and sustaining rheumatoid arthritis (RA). Acacetin, a natural flavonoid compound, exhibits excellent anti-inflammatory effects specifically for RA. However, its relevant targets and molecular mechanisms remain to be elucidated. PurposeThis study aims to investigate the mechanism of acacetin in the therapeutic efficacy of acacetin in RA and search for new therapeutic options for RA treatment. MethodsA collagen-induced RA mouse model was established to evaluate the therapeutic effect of acacetin. Acacetin functional probes were synthesized to capture potential target proteins in RAW264.7 cells. Various small molecule-protein interaction methods were conducted to verify the binding of acacetin to target protein. Molecular docking and site directed mutagenesis tests were performed to analyze the specific binding sites. Co-immunoprecipitation, immunofluorescence assay and western blot were engineered to explore the effect of acacetin on COX-2 degradation by targeting HSP90. ResultsAcacetin specifically binds to the ATP domain of HSP90, to facilitate the dissociation between HSP90 and COX-2, inducing the ubiquitin-degradation of COX-2 in macrophages. Acacetin suppressed the production of pro-inflammatory cytokines, as well as inflammatory related pathways, exerting excellent anti-inflammatory effects in RA. ConclusionsThis research proved that acacetin, a novel HSP90 ATPase inhibitor, inhibits the functional folding of the client protein COX-2, promoting its ubiquitin degradation for anti-inflammation. Targeting HSP90 is a viable strategy to inhibit inflammation, affording a distinct way to managing joint inflammation and pains associated with RA.

The molecular dynamics between reactive oxygen species (ROS), reactive nitrogen species (RNS) and phytohormones in plant's response to biotic stress.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are critical for plant development as well as for its stress response. They can function as signaling molecules to orchestrate a well-defined response of plants to biotic stress. These responses are further fine-tuned by phytohormones, such as salicylic acid, jasmonic acid, and ethylene, to modulate immune response. In the past decades, the intricacies of redox and phytohormonal signaling have been uncovered during plant-pathogen interactions. This review explores the dynamic interplay of these components, elucidating their roles in perceiving biotic threats and shaping the plant's defense strategy. Molecular regulators and sites of oxidative burst have been explored during pathogen perception. Further, the interplay between various components of redox and phytohormonal signaling has been explored during bacterial, fungal, viral, and nematode infections as well as during insect pest infestation. Understanding these interactions highlights gaps in the current knowledge and provides insights into engineering crop varieties with enhanced resistance to pathogens and pests. This review also highlights potential applications of manipulating regulators of redox signaling to bolster plant immunity and ensure global food security. Future research should explore regulators of these signaling pathways as potential target to develop biotic stress-tolerant crops. Further insights are also needed into roles of endophytes and host microbiome modulating host ROS and RNS pool for exploiting them as biocontrol agents imparting resistance against pathogens in plants.

Stabilization of High-Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis.

Heterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH-/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high-valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH- ions coupling at an open circuit condition. With excluding the Co2+ sites, the as-derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

New Approaches to Herbicide and Bioherbicide Discovery

Abstract During the past 30 yr an impasse has developed in the discovery and commercialization of synthetic herbicides with new molecular targets and novel chemistries. Similarly, there has been little success with bioherbicides, both microbial and chemical. These bioherbicides are needed to combat fast-growing herbicide resistance and to fulfill the need for more environmentally and toxicologically safe herbicides. In response to this substantial and growing opportunity, numerous start-up companies are utilizing novel approaches to provide new tools for weed management. These diverse new tools broaden the scope of discovery, encompassing advanced computational, bioinformatic, and imaging platforms; plant genome–editing and targeted protein degradation technologies; and machine learning and artificial intelligence (AI)-based strategies. This review contains summaries of the presentations of 10 such companies that took part in a symposium held at the WSSA annual meeting in 2024. Four of the companies are developing microbial bioherbicides or natural product–based herbicides, and the other six are using advanced technologies, such as AI, to accelerate the discovery of herbicides with novel molecular target sites or to develop non-GMO, herbicide-resistant crops.

Synthesis of Multivalent Glycoside-Immobilized Carboxymethyl Cellulose Nanohydrogel Particles with Superadsorption Ability for Lectins.

Carboxymethyl cellulose (CMC) is a water-soluble cellulose derivative that is nontoxic, biocompatible, biodegradable, and nonallergenic. As developing an adsorbent material for carbohydrate-binding proteins is challenging, we aimed to synthesize CMC nanohydrogel particles (CMCGPs) with an extremely high lectin adsorption tendency in this study. CMCGPs were used as the backbone of an adsorption carrier that was synthesized by cross-linking CMC with ethylene glycol diglycidyl ether. A series of glycoside-immobilized CMCGPs were synthesized by binding two types of glycans (LacNAc and lactose) to the polyvalent carboxymethyl groups that are present on the CMCGP surface and act as reaction sites. These immobilized glycosides function as molecular recognition sites. Glycan moieties were incorporated into the CMCGP backbone at degrees of immobilization (DI) ranging from 8.7 to 21.0% by altering the reaction composition. LacNAc-CMCGP (3b) showed a 19.9% DI of LacNAc glycoside to the CMCGP carboxymethyl group; on average, its particle size swelled to 418 nm in phosphate-buffered saline, which is approximately 1.4 times its dry-state size. Analyzing the adsorbent properties of glyco-CMCGPs using a lectin-binding assay showed the high structural specificity of glyco-CMCGPs to lectins. The equilibrium isotherm data was explained by the Langmuir adsorption model. Notably, compound 3b adsorbed 1.95 ± 0.05 μg of wheat germ agglutinin (WGA) lectin per 1.0 μg-dry of 3b particles at an adsorption equilibrium time of a few minutes. Furthermore, solid-state 13C nuclear magnetic resonance analysis showed that WGA lectin retained its natural structure without denaturation after binding to LacNAc-CMCGP. These results were also supported by affinity purification experiments of WGA from raw wheat germ extract using LacNAc-CMCGP, demonstrating that glyco-CMCGP is capable of adsorbing and desorbing lectin while maintaining its biological activity. Thus, multivalent glycoside-immobilized CMCGPs that use woody biomass derivatives as the backbone are expected to be applied as biorefinery materials, which specifically and abundantly adsorb not just plant lectins but also pathogenic viruses and toxin proteins.

The genomic and transcriptomic landscape of metastastic urothelial cancer

Metastatic urothelial carcinoma (mUC) is a lethal cancer, with limited therapeutic options. Large-scale studies in early settings provided critical insights into the genomic and transcriptomic characteristics of non-metastatic UC. The genomic landscape of mUC remains however unclear. Using Whole Exome (WES) and mRNA sequencing (RNA-seq) performed on metastatic biopsies from 111 patients, we show that driver genomic alterations from mUC were comparable to primary UC (TCGA data). APOBEC, platin, and HRD mutational signatures are the most prevalent in mUC, identified in 56%, 14%, and 9% of mUC samples, respectively. Molecular subtyping using consensus transcriptomic classification in mUC shows enrichment in neuroendocrine subtype. Paired samples analysis reveals subtype heterogeneity and temporal evolution. We identify potential therapeutic targets in 73% of mUC patients, of which FGFR3 (26%), ERBB2 (7%), TSC1 (7%), and PIK3CA (13%) are the most common. NECTIN4 and TACSTD2 are highly expressed regardless of molecular subtypes, FGFR3 alterations and sites of metastases.

Probing the aggregation behavior of collagen molecules regulated by dibenzaldehyde-terminated-PEG with varying molecular weights in solution.

Rigid and fragile nature of collagen-based materials cross-linked with biocompatible aldehyde-functionalized polysaccharides remains a challenge. Drawing inspiration from the pangolins' protective barrier, we introduce a novel cross-linker with a flexible chain to impart a "rigid-flexible coupled structure" to the collagen-based matrix. Successful integration of dibenzaldehyde-terminated-PEG (DF-PEG) into collagen molecules was confirmed by XRD and FTIR analyses. CD measurements demonstrated that the intact triple-helical structure was preserved in all samples. Distinct effects of DF-PEG with varying molecular weights on the aggregation behavior of collagen molecules were evaluated using multiple quantitative analysis techniques. Specifically, when the molecular weight of DF-PEG was below 20,000, multipoint hydrogen bonds and Schiff-base linkages were produced as the molecular weight of DF-PEG increased, which synergistically enhanced the aggregation behavior of collagen molecules. While the aggregation behavior of collagen molecules was slightly diminished upon the molecular weight of DF-PEG reached 20,000. This reduction can be attributed to the limited accessibility of the molecular reactive sites in the extended DF-PEG chains. Finally, a computational test of the binding interactions between collagen molecules and DF-PEG was conducted to validate the experimental results. Our biomimetic design strategy offers a new approach for the preparation of collagen-based materials with exceptional physicochemical properties.

Theoretical insights of 2D Fe3GeTe2/In2Se3 multiferroic vdW heterostructure based gas sensors for high-performance NO detecting

The impact of the harmful gas NO on the atmospheric environment cannot be ignored, so it is necessary to develop efficient gas sensors to detect and absorb NO at room temperature. In this work, we systematically explored the electron transport properties and gas sensing properties of Fe3GeTe2, In2Se3 monolayers and its multiferroic van der Waals (vdW) heterostructures of Fe3GeTe2/In2Se3 for detecting NO by using density functional theory and nonequilibrium Green's function methods. The calculated adsorption energies, electron localisation functions, band structures and density of states indicate that its a chemisorption for the adsorption of NO on Fe3GeTe2 and a physisorption on In2Se3, while the specific adsorption style is highly dependent on the stacking and molecular adsorption sites of different Fe3GeTe2/In2Se3 structures. In addition, the pristine Fe3GeTe2 monolayer and Fe3GeTe2/In2Se3 based nanodevices realized a significant anisotropy for electron transport along the zigzag and armchair directions, and their anisotropic maximum current ratios in the zigzag to armchair directions were 1.90 and 1.89. Meanwhile, the NO sensitivity ratio of Fe3GeTe2 and Fe3GeTe2/In2Se3 based gas sensors can be up to 79 % and 107 %, respectively. This highlights a notably superior gas-sensitive performance of the Fe3GeTe2/In2Se3 heterostructure compared to the Fe3GeTe2 monolayer gas devices. These findings provide valuable references for the application of multiferroic heterostructures in the field of gas sensors.

Supramolecular Spin Chains via Radical-Radical Contacts Stabilizing Ferromagnetic Interactions Between Heisenberg or Ising-Like Spins.

A new paramagnetic ligand, 4-(2'-4-(2''-furyl)-pyrimidyl)-1,2,3,5-dithiadiazolyl (furylpymDTDA) and three transition metal coordination complexes, M(hfac)2(furylpymDTDA) M=Mn, Co, Ni; hfac=1,1,1,5,5,5-hexafluoroacetylacetonato-), are reported. The solid-state structures are influenced by the geometry of the coordination sphere of the M(II) centers: trigonal (Mn) vs. octahedral (Co and Ni). While the hs-Mn(II) complex exhibits pairwise multi-centre 2-electron bonds (i. e., pancake bonds) between the planar π radical DTDA moieties, the hs-Co(II) and Ni(II) complexes crystallize with close contacts between coordinated furylpymDTDA radical ligands that define linear 1D arrays of molecular units. The magnetic data for the hs-Co(II) and Ni(II) complexes indicate ferromagnetic (FM) interactions between molecular units, apparently mediated by radical-radical contacts along the supramolecular chains. Computational analysis suggests proximity between regions of large α- and β-spin density on neighbouring molecular sites enabling FM exchange, in accordance with the McConnell I mechanism. The magnetic data for the Ni(II) complex are consistent with a Heisenberg spin chain, whereas the hs-Co(II) complex exhibits Ising-like spin chain behaviour and a magnetic phase transition to an FM ordered state at 4.6 K.

N318L Blocks the Interaction of Fluralaner but Not Broflanilide or Fipronil with the Insect GABA Receptor In Vivo.

Fluralaner is a novel insecticide targeting the ionotropic GABA receptor (GABAR) subunit, RDL. A recent study revealed that N316L, a substitution of asparagine (N) with leucine (L), in the second transmembrane (M2)-spanning region reduced the antagonist action of fluralaner on the housefly Musca domestica RDL (MdRDL) in vitro. To verify the impact of N316L in vivo, the corresponding mutation (N318L) in the fruitfly Drosophila melanogaster RDL (DmRDL) was constructed using CRISPR/Cas9 genome editing. The homozygous DmRDLN318L mutant showed a 9.87-fold resistance to fluralaner compared with w1118 while still being highly sensitive to broflanilide and fipronil, which is consistent with those findings observed in the electrophysiology assays of the homomeric DmRDLWT or DmRDLN318L channel. Moreover, DmRDLN318L led to malformed ovaries, stunted eggs, and sterility in homozygous females. These results highlighted N318 as a molecular site for fluralaner in vivo and in vitro and might elucidate the resistance mechanisms of insects against fluralaner.

Impact of Protonation Sites on Collision-Induced Dissociation-MS/MS Using CIDMD Quantum Chemistry Modeling.

Protonation is the most frequent adduct found in positive electrospray ionization collision-induced mass spectra (CID-MS/MS). In a parallel report Lee, J. J. Chem. Inf. Model. 2024, 10.1021/acs.jcim.4c00760, we developed a quantum chemistry framework to predict mass spectra by collision-induced dissociation molecular dynamics (CIDMD). As different protonation sites affect fragmentation pathways of a given molecule, the accuracy of predicting tandem mass spectra by CIDMD ultimately depends on the choice of its protomers. To investigate the impact of molecular protonation sites on MS/MS spectra, we compared CIDMD-predicted spectra to all available experimental MS/MS spectra by similarity matching. We probed 10 molecules with a total of 43 protomers, the largest study to date, including organic acids (sorbic acid, citramalic acid, itaconic acid, mesaconic acid, citraconic acid, and taurine) as well as aromatic amines including uracil, aniline, bufotenine, and psilocin. We demonstrated how different protomers can converge different fragmentation pathways to the same fragment ions but also may explain the presence of different fragment ions in experimental MS/MS spectra. For the first time, we used in silico MS/MS predictions to test the impact of solvents on proton affinities, comparing the gas phase and a mixture of acetonitrile/water (1:1). We also extended applications of in silico MS/MS predictions to investigate the impact of protonation sites on the energy barriers of isomerization between protomers via proton transfer. Despite our initial hypothesis that the thermodynamically most stable protomer should give the best match to the experiment, we found only weak inverse relationships between the calculated proton affinities and corresponding entropy similarities of experimental and CIDMD-predicted MS/MS spectra. CIDMD-predicted mechanistic details of fragmentation reaction pathways revealed a clear preference for specific protomer forms for several molecules. Overall, however, proton affinity was not a good predictor corresponding to the predicted CIDMD spectra. For example, for uracil, only one protomer predicted all experimental MS/MS fragment ions, but this protomer had neither the highest proton affinity nor the best MS/MS match score. Instead of proton affinity, the transfer of protons during the electrospray process from the initial protonation site (i.e., mobile proton model) better explains the differences between the thermodynamic rationale and experimental data. Protomers that undergo fragmentation with lower energy barriers have greater contributions to experimental MS/MS spectra than their thermodynamic Boltzmann populations would suggest. Hence, in silico predictions still need to calculate MS/MS spectra for multiple protomers, as the extent of distributions cannot be readily predicted.

Unveiling Inequality of Atoms in Ultrasmall Pt Clusters: Oxygen Adsorption Limited to the Uppermost Atomic Layer

The concept of preferential atomic and molecular adsorption site is of primary relevance in heterogeneous catalysis. In the case of ultrasmall size‐selected clusters, distinguishing the role played by each atom in a reaction is extremely challenging due to their reduced size and peculiar structures. Herein, it is revealed how the inequivalent atoms composing graphene‐supported Pt12 and Pt13 clusters behave differently in the photoinduced dissociation of O2, with only those in the uppermost layer of the clusters being involved in the reaction. In this process, the epitaxial graphene support plays a fundamental active role: its corrugation and pinning induced by the presence of the clusters are crucial for defining the preferential adsorption site on the Pt atomic agglomerates, facilitating the lateral diffusion of physisorbed oxygen at a distance that induces its selective adsorption in the topmost layer of the clusters, and inducing an inhomogeneous charge distribution within the clusters which directly affects the O2 adsorption. The inhomogeneous oxidation of the clusters is resolved by means of synchrotron‐based X‐ray photoelectron spectroscopy and supported by ab initio density functional theory calculations. The possibility to identify the active sites on Pt clusters induced by cluster–support interactions has the potential to enhance the experimentally supported design of nanocatalysts.

Molecular Targets in Streptococcus pyogenes for the Development of Anti-Virulence Agents.

Streptococcus pyogenes, commonly known as Group A Streptococcus (GAS), is a significant human pathogen responsible for a wide range of diseases, from mild pharyngitis to severe conditions such as necrotizing fasciitis and toxic shock syndrome. The increasing antibiotic resistance, especially against macrolide antibiotics, poses a challenge to the effective treatment of these infections. This paper reviews the current state and mechanisms of antibiotic resistance in S. pyogenes. Furthermore, molecular targets for developing anti-virulence agents, which aim to attenuate virulence rather than killing it outright, are explored. This review specifically focuses on virulence regulators, proteins that coordinate the expression of multiple virulence factors in response to environmental signals, playing a crucial role in the pathogen's ability to cause disease. Key regulatory systems, such as RopB, Mga, CovRS, and the c-di-AMP signaling system, are discussed for their roles in modulating virulence gene expression. Additionally, potential molecular target sites for the development of anti-virulence agents are suggested. By concentrating on these regulatory pathways, it is proposed that anti-virulence strategies could enhance the effectiveness of existing antibiotics and reduce the selective pressure that drives the development of resistance.

Tyrosine phosphorylation and palmitoylation of TRPV2 ion channel tune microglial beta-amyloid peptide phagocytosis

Alzheimer’s disease (AD) is the leading form of dementia, characterized by the accumulation and aggregation of amyloid in brain. Transient receptor potential vanilloid 2 (TRPV2) is an ion channel involved in diverse physiopathological processes, including microglial phagocytosis. Previous studies suggested that cannabidiol (CBD), an activator of TRPV2, improves microglial amyloid-β (Aβ) phagocytosis by TRPV2 modulation. However, the molecular mechanism of TRPV2 in microglial Aβ phagocytosis remains unknown. In this study, we aimed to investigate the involvement of TRPV2 channel in microglial Aβ phagocytosis and the underlying mechanisms. Utilizing human datasets, mouse primary neuron and microglia cultures, and AD model mice, to evaluate TRPV2 expression and microglial Aβ phagocytosis in both in vivo and in vitro. TRPV2 was expressed in cortex, hippocampus, and microglia.Cannabidiol (CBD) could activate and sensitize TRPV2 channel. Short-term CBD (1 week) injection intraperitoneally (i.p.) reduced the expression of neuroinflammation and microglial phagocytic receptors, but long-term CBD (3 week) administration (i.p.) induced neuroinflammation and suppressed the expression of microglial phagocytic receptors in APP/PS1 mice. Furthermore, the hyper-sensitivity of TRPV2 channel was mediated by tyrosine phosphorylation at the molecular sites Tyr(338), Tyr(466), and Tyr(520) by protein tyrosine kinase JAK1, and these sites mutation reduced the microglial Aβ phagocytosis partially dependence on its localization. While TRPV2 was palmitoylated at Cys 277 site and blocking TRPV2 palmitoylation improved microglial Aβ phagocytosis. Moreover, it was demonstrated that TRPV2 palmitoylation was dynamically regulated by ZDHHC21. Overall, our findings elucidated the intricate interplay between TRPV2 channel regulated by tyrosine phosphorylation/dephosphorylation and cysteine palmitoylation/depalmitoylation, which had divergent effects on microglial Aβ phagocytosis. These findings provide valuable insights into the underlying mechanisms linking microglial phagocytosis and TRPV2 sensitivity, and offer potential therapeutic strategies for managing AD.

Structural, spectroscopic, fluorescent, and computational studies of binuclear copper (II) and zinc (II) complexes with an asymmetric salamo‐type ligand

Salamo‐type ligand H2L was designed and synthesized and reacted with Cu (II) and Zn (II) acetate, respectively, to obtain two binuclear Cu (II) and Zn (II) complexes: [Cu2(L)2]·2CH3OH (1) and [Zn2(L)2] (2) having the same coordination number but distinct geometries. Complex 1 is a Cu (II) complex containing two crystalline ethanol molecules, where two Cu (II) atoms are surrounded by two utterly deprotonated (L)2− parts, forming slightly twisted tetragonal pyramidal configurations of pentacoordinate. In complex 2, two utterly deprotonated (L)2− parts surround two Zn (II) atoms, forming pentadentate twisted triangular bipyramidal configurations. The complexes were elucidated via IR analyses and ultraviolet spectroscopy. Using DFT theoretical calculation, MEPs, IRI, and Hirshfeld surface analysis to investigate further the molecular interactions and reaction sites. Ultimately, the fluorescence characteristics of H2L and its complexes 1 and 2 were discussed.

Cupric ion coordination-mediated molecularly imprinted electrochemical sensor for the recognition and ratiometric detection of lidocaine

Molecularly imprinted polymers (MIPs) have been widely used as artificial recognition elements in sensing applications. However, their electrochemical sensing performance is generally hampered by limited affinity and uncontrolled condition change. In this work, a novel MIP electrochemical sensor based on metal coordination interaction was prepared and used for the recognition and ratiometric detection of lidocaine (LC). The sensor was constructed by electrodepositing Cu-coordinated MIP on biomass carbon modified glassy carbon electrode. Herein, Cu2+ ions acted as anchor for the immobilization of LC during the synthesis process, enabling the orderly formation of molecular recognition sites. Reversely, the metal coordination between Cu2+ ions and LC molecules facilitated the recognition of LC. Moreover, the doped cupric ions in the polymer film could provide a reference signal for subsequent ratiometric strategy. Thus the resulting sensor exhibited high selectivity, sensitivity, satisfactory reproducibility, and anti-interference ability. Under the selected conditions, the peak current ratio of LC and cupric ion was linear to LC concentration in the range of 0.008–2.5 μmol L−1 (R2 = 0.9951), and the limit of detection was 1.9 nmol L−1 (S/N = 3). The practical feasibility of the sensor was evaluated by detecting human serum and pharmaceutical samples, and satisfactory outcomes were obtained.

Molecularly Imprinted Polymer Modified Laser-Engraved Graphene Electrode for the Ultra-Sensitive and Specific Detection of Ascorbic Acid

Sensitive and accurate detection of small molecule targets is critical for a variety of applications, including environmental monitoring, food safety and medical diagnostics. Electrochemical sensors with the advantages of high sensitivity, accuracy, convenience and low-cost make them well suited for these applications. Moreover, the combination of electrochemical sensors with micro-and nanofabrication technology offers the possibility of integrated and intelligent sensing systems.Figure 1. (a) The SEM characterization of PPD/LEG electrode, (b) the FT-IR of LEG and PPD/LEG electrode, (c) the Nyquist plots of LEG and PPD/LEG electrode, (d) the specificity, (e) linear relationship and (f) sensitivity of integrated electrochemical microsensor.In general, the ultimate performance of an electrochemical sensor relies on the high efficiency of bio/chemical reactions as well as transport of the analytes by diffusion onto the electrode. Accordingly, the desired electrode materials should permit very fast mass transport rates and possess the capability of specific capture of target analytes. Laser-etched graphene (LEG) electrodes featured with the advantages of porous three-dimensional network structure, large specific surface area, and high conductivity, are considered as an ideal sensing element for sensitive molecules detection, but cannot recognize specific targets. Molecularly imprinted polymers (MIPs) are low-cost and easy to modify on electrochemical sensing surfaces. It can be used to form molecular recognition sites by synthesizing target templates in polymers, giving the modified electrodes the ability to specifically recognize target molecules, which is an ideal modification material for electrochemical sensor platforms.Herein, we propose an integrated electrochemical microsensor sensing ultra-low concentration of ascorbic acid (AA) molecules by using MIP modified LEG as electrode material. The main characteristics of the detection system are as follows: 1) LEG electrode enables electrochemical sensing strategy with simple preparation and high sensitivity, 2) MIP poly-o-phenylenediamine (PPD) membrane on the surface of graphene provides the desirable property for highly selective AA molecular recognition, 3) the integrated PPD/LEG electrode allows to detect AA molecules in a ultra-low concentration range which is superior than that of other electrochemical detection techniques.The surface morphology of PPD/LEG electrode is characterized by using scanning electron microscopy (SEM, shown in Figure 1a), from which LEG shows three-dimensional network porous structure and the nature of graphene. In addition, the electropolymerized PPD membrane exhibits a rough and porous surface which would provide the large surface area for the adsorption of target AA molecules at the modified electrode. The formation of PPD/LEG electrode is further examined by Fourier Transform Infrared Spectroscopy (FT-IR Spectrometer) in Figure 1b. The polymerization of PPD membrane on the surface of the LEG electrode is confirmed by the appearance of two absorption peaks at 3385 cm-1 and 3360 cm-1, which are related to the stretching vibration of the -NH2 from the PPD. As shown in the Nyquist plots (Figure 1c), the semicircle in the high-frequency region is described as an intrinsic electron-transfer resistance in the electrode materials. The identical semicircles at high-frequency region of two electrodes indicate nearly equal electron transfer resistance (Rct) of LEG and PPD/LEG. The low-frequency region of the Nyquist plot is described as surface diffusion control, and the increase in the linear slope represents an enhanced surface diffusion control process at the electrodes demonstrating the lower impedance of the PPD/LEG electrode. Figure 1d verifies the specific recognition of AA molecules by the PPD/LEG electrode in PBS mixed with 1 mM of AA, dopamine (DA), uric acid (UA) and acetaminophen (AP) molecules. It can be seen that compared with the LEG electrode, the DPV response of the PPD/LEG electrode to DA, UA and AP molecules is significantly reduced, while the response to AA molecules is significantly enhanced. Furthermore, the ability of the integrated electrochemical microsensor to detect ultra-low concentrations of AA molecules in the 10 nM to 100 nM range is shown in Figure 1e, with a LOD of 2 nM (Figure 1f).In conclusion, we present an integrated electrochemical microsensor that can specifically detect AA molecules with ultra-high sensitivity. The LEG electrode with the modification of PPD membrane can effectively realize the specific recognition and accurate detection of AA molecules in mixed solutions. This integrated electrochemical sensing method is expected to be applied to the selective detection of multiple small molecule targets in complex environments.Key words: Laser-engraved Graphene Electrodes, Molecularly Imprinted Polymers, Integrated Electrochemical Microsensor, Ultra Sensitivity Detection. Figure 1

Understanding Ligand Effects on Bielectronic Transitions: Chemo‐ and Electroreduction of Rhodium Bis(Diphosphine) Complexes to Low Oxidation States

AbstractRhodium complexes in the −I and 0 oxidation states are of great potential interest in catalytic applications. In contrast to their rhodium +I congeners, however, the structural and electronic parameters governing their access and stability are far less understood. Herein, we investigate the two‐electron reduction of a parameterized series of bis(diphosphine) Rh complexes [Rh(dxpy)2]NTf2 (x=P‐substituent, y=alkanediyl bridging P atoms). Through (electro)reductions from the RhI parents, Rh−I d10‐complexes were obtained and characterized spectroscopically, including 103Rh NMR data. The reductive steps convolute with structural rearrangements from square planar to tetrahedral coordination. We found that the extent of these reorganisations defines whether the first E0(RhI/0) and second E0(Rh0/−I) reduction potentials are normally ordered, leading to monoelectronic stepwise transitions, or inverted, giving bielectronic events. Reductionist approaches based on Hammett parameters or the P−Rh‐P bite angles provide only partial correlations with the redox potentials. However, we identified the C−O stretch of analogue diphosphine complexes as an expedient computational parameter that enables these correlations through both electronic and geometric features, even in a predictive manner. Gaining control over two‐electron reduction behaviors through rationalized ligand effects has potential impact beyond Rh complexes, for molecular and enzymatic metal sites commonly exhibiting bielectronic transitions.