Search Results (1,235)

Hydrogen-bond-like M···H–C interactions in square-planar d⁸ metal complexes have recently gained attention as structure-directing elements and design motifs in asymmetric catalysis. In this study, we explore these weak interactions not as static features, but as key modulators of molecular motion. We synthesized four cis-[N,N′-pentamethylenebis(iminomethylazolato)]M(II) (M = Pt, Pd), including iminomethyl-2-imidazole, iminomethyl-5-imidazole, and iminomethylpyrrolato Pt(II) complexes and an iminomethylpyrrolato Pd(II) analog. All complexes display reversible flipping of the alkylene bridge across the coordination plane, with the M···H–C interaction alternately engaging from above or below. This dynamic motion was characterized by variable-temperature ¹H NMR spectroscopy, revealing activation parameters for the flipping process. X-ray crystallography confirmed geometries consistent with hydrogen-bond-like interactions, while NBO analysis based on DFT calculations provided insight into their electronic nature. Interestingly, although Pt and Pd display comparable M···H–C distances, solvent effects dominate the flipping kinetics over metal identity. These findings highlight the role of hydrogen-bond-like M···H–C interactions not only in structural stabilization, but also in regulating conformational dynamics. Full article

Moisture in coal seams significantly impacts methane adsorption/desorption, yet its microscopic mechanism in intact coal remains poorly characterized due to methodological limitations. This study introduces a novel approach that integrates low-field nuclear magnetic resonance (LF-NMR) with volumetric analysis to quantify, in real-time, the effect of moisture on methane dynamics in intact coal samples. The results quantitatively demonstrate that micropores (relative specific surface area > 700 m²/cm³) are the primary adsorption sites, accounting for over 95% of the stored gas. Moisture drastically reduces the adsorption capacity (by ~72% at 0.29 MPa and ~57% at 1.83 MPa) and inhibits the desorption process, evidenced by a strong linear decrease in desorption ratio (DR) (R² = 0.906) and a sharp exponential drop in the initial desorption rate (R² = 0.999) with increasing moisture content. The findings provide a mechanistic understanding that is crucial for optimizing coalbed methane (CBM) recovery and enhancing strategies for outburst prevention and methane emission mitigation. The results reveal distinct adsorption and desorption features of intact coal compared with coal powder, which can be useful in total methane utilization and mining safety enhancement. Full article

Prostate stem cell antigen (PSCA) is a Ly6/uPAR protein that targets neuronal nicotinic acetylcholine receptors (nAChRs). It exists in membrane-tethered and soluble forms, with the latter upregulated in Alzheimer’s disease. We hypothesize that PSCA may be linked to a wider spectrum of neurological diseases and could induce neuroinflammation. Indeed, PSCA expression is significantly upregulated in the brain of patients with multiple sclerosis, Huntington’s disease, Down syndrome, bipolar disorder, and HIV-associated dementia. To investigate PSCA’s structure, pharmacology, and inflammatory function, we produced a correctly folded water-soluble recombinant analog (ws-PSCA). In primary hippocampal neurons and astrocytes, ws-PSCA differently regulates secretion of inflammatory factors and adhesion molecules and induces pro-inflammatory responses by increasing TNFβ secretion. Heteronuclear NMR and ¹⁵N relaxation measurements reveal a classical β-structural three-finger fold with conformationally disordered loops II and III. Positive charge clustering on the molecular surface suggests the functional importance of ionic interactions by these loops. Electrophysiological studies in Xenopus oocytes point on ws-PSCA inhibition of α3β2-, high-, and low-sensitive variants of α4β2- (IC₅₀ ~50, 27, and 15 μM, respectively) but not α4β4-nAChRs, suggesting targeting of the β2 subunit. Ensemble docking and molecular dynamics simulations predict PSCA binding to high-sensitive α4β2-nAChR at α4/β2 and β2/β2 interfaces. Complexes are stabilized by ionic and hydrogen bonds between PSCA’s loops II and III and the primary and complementary receptor subunits, including glycosyl groups. This study gives new structural and functional insights into PSCA’s interaction with molecular targets and provides clues to understand its role in the brain function and mental disorders. Full article

To investigate the flow characteristics of movable water in coal under the influence of micro-nano pore fractures with multiple fractal structures, this study employed nuclear magnetic resonance (NMR) and multifractal theory to analyze gas–water seepage under different injection pressures. Then, the scale threshold for mobile water entering coal pores and fractures was determined by clarifying the relationship among “injection pressure-T₂ dynamic multiple fractal parameter seepage resistance-critical pore scale”. The results indicate that coal samples from Yiwu (YW) and Wuxiang (WX) enter the nanoscale pore size range at an injection pressure of 8 MPa, while the coal sample from Malan (ML) enters the nanoscale pore size range at an injection pressure of 9 MPa. During the water injection process, there is a significant linear relationship between the multiple fractal parameters log X(q, ε) and log(ε) of the sample. The generalized fractal dimension D(q) decreases monotonically with increasing q in an inverse S-shape. This decrease occurs in two distinct stages: D(q) decreases rapidly in the low probability interval q < 0; D(q) decreases slowly in the high probability interval q > 0. The multiple fractal singularity spectrum function f(α) has an asymmetric upward parabolic convex function relationship with α, which is divided into a rapidly increasing left branch curve and a slowly decreasing right branch curve with α₀ as the boundary. Supporting evidence indicates the feasibility of a methodology for identifying the variation in multiple fractal parameters of gas–water NMR seepage and the critical scale transition conditions. This investigation establishes a methodological foundation for analyzing gas–water transport pathways within porous media materials. Full article

Nowadays, most of the heavy oil fields around the world have entered difficult exploiting stages, with problems regarding high viscosity and poor fluidity. However, there has been little previous research on the accurate identification and distribution of remaining oil with different levels of steam dryness. Therefore, this paper proposes a new nuclear magnetic resonance (NMR) interpretation method, as well as a new samples analysis method for remaining oil in the core. We conducted core displacement experiments using different methods. The nuclear magnetic resonance (NMR) tests and analysis of core thin sections after steam flooding were used to study the effect of different steam dryness levels on the migration and sedimentation mechanisms of heavy oil components. The results showed that the viscosity of crude oil and the permeability of rock cores are both sensitive to steam dryness; therefore, the improvement of steam dryness is beneficial for improving oil recovery. Heavy oil is mainly distributed in the medium pores of 10–50 μm and the small pores of 1–10 μm. However, with the decrease in steam dryness, the dynamic amount of crude oil in both medium and small pores decreases, and the bitumen in crude oil stays in the pores in the form of stars, patches, and envelopes, which leads to a decline in oil displacement efficiency. Thus, our study provides a micro-level understanding of remaining oil which lays the foundation for the further enhancement of oil recovery in heavy oilfields. Full article

The retrogradation of starch strongly influences the texture and stability of starchy foods. This study applied low-field nuclear magnetic resonance (LF NMR) to examine the effect of buckwheat hull (BH) fiber and green barley (GB) on water dynamics in normal (NPS) and waxy (WPS) potato starch gels. Relaxation times (T₁, T₂) and mean correlation times (τ_c) were monitored during 15 days of storage to evaluate changes in water mobility and starch–polymer interactions. Results showed that WPS, with its high amylopectin content, retrograded earlier than NPS. The addition of BH inhibited conformational changes associated with water binding in WPS gels, indicating that insoluble fiber entrapped water within the amylopectin network. Conversely, GB promoted higher τ_c values in WPS, reflecting enhanced ordering and reduced water mobility, while its impact on NPS was minor. In NPS systems, BH decreased τ_c, suggesting disruption of amylose-driven structural reorganization. These findings demonstrate that BH and GB exert opposite effects on starch retrogradation and highlight their potential as functional additives for tailoring texture and stability in starch-based food systems. Full article

The applications of electromagnetic (EM) field treatment on water in agriculture have garnered increasing attention as a sustainable method to enhance plant growth, water-use efficiency, and metabolic performance. A growing body of evidence suggests that exposure to EM fields can affect water molecules, possibly by influencing hydrogen bonding dynamics, the structuring of water clusters, and electrokinetic properties of the water molecules. These alterations are thought to correlate with plant physiological performance. The methodology of the study was divided into two parts. The first part focused on the preparation of electromagnetically treated water. The second part involved applying this treated water to spinach plants. The present study investigates the physiological responses of Spinacia oleracea L. to irrigation with electromagnetically treated water (EMTW), focusing on elucidating the potential mechanisms that may underlie the observed effects. EMTW was generated using a solenoid-based system operating in dual-frequency ranges (100–1000 Hz and 10–100 kHz), which has been previously shown to influence both the microbiological and electrokinetic properties of aqueous systems. To evaluate the structural and functional implications of EMTW, a combined methodological approach was employed, integrating proton nuclear magnetic resonance (¹H-NMR) spectroscopy, density functional theory (DFT) modeling of water hydrogen bonds and clusters, and comprehensive plant physiological assessments. Plants were cultivated under both controlled and field conditions to assess consistency across environmental settings. Physiological measurements demonstrated that EMTW irrigation increased photosynthetic rate by ~80%, transpiration by 49–67%, stomatal conductance by 78–129%, intercellular CO₂ concentration by 42–80%, and chlorophyll content by 9.3–9.5% compared to control samples. Additionally, phenoloc and flavonoid contents were elevated by 7.4% and 7.6%, respectively, in field-grown plants. These enhancements were statistically significant (p < 0.001 or p < 0.01) under both laboratory and field conditions, confirming the robustness of the observed effects. Full article

Cyclodextrin-based nanosponges (CDNSs) are novel polymers composed of cross-linked cyclodextrin (CD) macrocyclic units, whose characteristics make them great candidates for drug delivery systems with adjustable properties for the drug release process. Examination of the molecular structure and dynamics of CDNSs is a necessary starting point in the first step toward their broad application. Spectroscopic methods are effective analytical tools for probing the structure–property relationships of polymer structures. Infrared (IR) and Raman spectroscopies provide insight into the behavior of hydrogen bond (H-bond) networks influencing the properties of CDNS polymeric networks. Scattering techniques such as inelastic neutron scattering (INS) and Brillouin light scattering (BLS) probe elastic properties, while small-angle neutron scattering (SANS) examines the structural inhomogeneities and water sorption abilities of CDNS materials. Complete evaluation is possible using nuclear magnetic resonance (NMR), which can provide data on CDNS network dynamics. This article summarizes the results of a wide examination of CDNSs with the use of spectroscopic methods and reveals the links between the microscopic behavior and macroscopic properties of CDNSs, enabling the customization of their properties for various biomedical purposes. Full article

Background: Hemiplegic cerebral palsy (HCP) is a motor dysfunction disorder resulting from perinatal developmental brain injury, predominantly impairing upper limb function in children. Nonetheless, there has been insufficient research on the brain activation patterns and inter-brain coordination mechanisms of HCP children when performing motor control tasks, especially in contrast to children with typical development(CD). Objective: This cross-sectional study employed functional near-infrared spectroscopy (fNIRS) to systematically compare the cerebral blood flow dynamics and brain network characteristics of HCP children and CD children while performing upper-limb mirror training tasks. Methods: The study ultimately included 14 HCP children and 28 CD children. fNIRS technology was utilized to record changes in oxygenated hemoglobin (HbO) signals in the bilateral prefrontal cortex (LPFC/RPFC) and motor cortex (LMC/RMC) of the subjects while they performed mirror training tasks. Generalized linear model (GLM) analysis was used to compare differences in activation intensity between HCP children and CD children in the prefrontal cortex and motor cortex. Finally, conditional Granger causality (GC) analysis was applied to construct a directed brain network model, enabling directional analysis of causal interactions between different brain regions. Results: Brain activation: HCP children showed weaker LPFC activation than CD children in the NMR task (t = −2.032, p = 0.049); enhanced LMC activation in the NML task (t = 2.202, p = 0.033); and reduced RMC activation in the MR task (t = −2.234, p = 0.031). Intragroup comparisons revealed significant differences in LMC activation between the NMR and NML tasks (M = −1.128 ± 2.764, t = −1.527, p = 0.025) and increased separation in RMC activation between the MR and ML tasks (M = −1.674 ± 2.584, t = −2.425, p = 0.031). Cortical effective connectivity: HCP group RPFC → RMC connectivity was weaker than that in CD children in the NMR/NML tasks (NMR: t = −2.491, p = 0.018; NML: t = −2.386, p = 0.023); RMC → LMC connectivity was weakened in the NMR task (t = −2.395, p = 0.022). Conclusions: This study reveals that children with HCP exhibit distinct abnormal characteristics in both cortical activation patterns and effective brain network connectivity during upper limb mirror training tasks, compared to children with CD. These characteristic alterations may reflect the neural mechanisms underlying motor control deficits in HCP children, involving deficits in prefrontal regulatory function and compensatory reorganization of the motor cortex. The identified fNIRS indicators provide new insights into understanding brain dysfunction in HCP and may offer objective evidence for research into personalized, precision-based neurorehabilitation intervention strategies. Full article

p-toluenesulfonic acid (pTSA) was used for the synthesis of porous silica xerogels while applying different synthesis conditions. Key parameters included acid concentration, drying temperature and the method of acid removal. The resulting organic–inorganic composites were investigated by nitrogen physisorption, X-ray powder diffraction (XRD), solid-state NMR and thermal analysis. The results demonstrated that both the drying temperature and quantity of the pTSA significantly influenced the pore structure of the xerogels. The utilization of such strong acids like pTSA yielded high surface area and pore volume, as well as narrow pore size distribution. Environmentally friendly template removal by solvent extraction produced materials with superior textural properties compared to traditional calcination, enabling the recovery and reuse of pTSA with over 95% efficiency. A selected mesoporous silica xerogel was modified by a simple two-step post-synthesis procedure with 1-(2-Hydroxyethyl) piperazine (HEP). High CO₂ adsorption capacity was determined for the HEP-modified material in dynamic conditions. The isosteric heat of adsorption revealed the stronger interaction between functional groups and CO₂ molecules. Total CO₂ desorption could be achieved at 60 °C. Leaching of the silica functional groups could not be detected even after four consecutive adsorption cycles. These findings provide valuable insights into the sustainable synthesis of tunable piperazine-modified mesoporous silica xerogels with potential applications in CO₂ capture. Full article

Hyperpolarization (HP) techniques, such as Parahydrogen-Induced Polarization (PHIP), Signal Amplification by Reversible Exchange (SABRE), and dissolution Dynamic Nuclear Polarization (d-DNP), significantly enhance the sensitivity of nuclear magnetic resonance (NMR) spectroscopy for chemical analysis and metabolic imaging. However, the high cost of equipment, ranging from tens of thousands to millions of dollars, limits accessibility of hyperpolarization for the broad scientific community. In this work, we aim to mitigate some of the challenges by developing a cost-effective solution for parahydrogen (pH₂)-based PHIP and SABRE HP methods. A custom coil-winding machine was designed to fabricate solenoid magnet coils, which were then evaluated for their magnetic field profiles, demonstrating a high degree of magnetic field homogeneity. A model ¹H SABRE experiment successfully implemented the constructed solenoid, achieving efficient hyperpolarization. Additionally, the solenoid magnet can be utilized for in situ detection of hyperpolarization when integrated with a low-field NMR spectrometer, reducing the total setup cost to a few thousand dollars. These findings suggest that our approach makes HP technology more affordable and accessible, potentially broadening its applications in chemical and biomedical research, as well as educational settings involving undergraduate student researchers. This work provides a practical pathway to lower the financial barriers associated with pH₂ HP setups. Full article

Heparan sulfate proteoglycans serve as initial attachment sites for several viruses and bacteria. Recent studies suggest that SARS-CoV-2 similarly exploits these glycosaminoglycans, facilitating conformational changes in the spike protein that promote the interaction between the receptor-binding domain (S1-RBD) and the cellular angiotensin-converting enzyme 2 receptor (ACE2), thereby triggering the virus internalization process. The molecular details that drive this process, particularly the co-receptor role of heparan sulfate (HS), remain incompletely understood. The interaction between an HS hexasaccharide (hexa) and the N343 glycosylated S1-RBD of the wild-type (WT) and Omicron variant of SARS-CoV-2 was investigated. The conformational properties of hexa with these S1-RBDs in unbound and bound states are explored using multiple independent MD simulations; the protein binding epitope of hexa, as well as the details of its interaction with S1-RBD of the Omicron variant, are characterized by comparing experimental and theoretical ¹H STD NMR signals. This investigation identifies the role played by the glycosyl moiety at N343 in potentially affecting this interaction in both WT and Omicron S1-RBD, explaining the observed low specificity and multi-modal nature of the interaction between HS oligosaccharides and these S1-RBDs. Full article

Given the limited knowledge of the effect of post-translational modifications (PTMs) on protein structure, in this study we investigated whether introducing one-to-three RA-related PTMs into the α-fibrin (617–631) peptide influences the conformation and structure of the peptide antigen that could be responsible for the autoantibody recognition. Ten peptides containing a different number of PTMs within their primary structure were synthesized and their recognition by sera from RA patients was analyzed. The conformation of the peptides was studied by circular dichroism (CD) and the structure of the most relevant antigenic peptides was determined by nuclear magnetic resonance (NMR) and enhanced-sampling molecular dynamics (MD). Although peptides containing citrulline (Cit) showed a higher degree of binding to AMPAs than peptides containing only homocitrulline and/or acetyl-lysine, the latter were able to bind to AMPAs in sera that showed a small response to peptides with Cit, with the response being different depending on the position of each PTM. CD and NMR analyses indicated a series of half-turn conformations in the Lys620-Arg630 region. MD simulations generated a set of conformations compatible with the NMR NOEs. The effect of the PTMs was observed in intra-molecular contacts, hydrogen bonds and van der Waals interactions, generating more collapsed conformations. Differences in autoantibody reactivity between peptides bearing different PTMs within their primary structures are noted. Peptides with PTMs adopt different conformations than unmodified peptides, probably due to the lower net charge of peptides with multiple PTMs, which may explain their recognition by autoantibodies. Full article

Protein dynamics are crucial for the acyl carrier protein (ACP) acting as a cofactor, communicating with various fatty acid synthesis (FAS) enzymes. Using a combination of NMR spectroscopy and molecular dynamics (MD) simulations, we demonstrate how the conformational flexibility of Escherichia coli ACP (EcACP) modulates metal binding and facilitates its molecular switches, thereby determining the pathway for different acyl chains. Our results show that Ca²⁺ binding greatly stabilizes the protein—boosting thermal stability by over 13 °C—and modulates its dynamic properties, affecting two acidic metal binding sites and the conformation of the hydrophobic cavity. Hydrogen–deuterium exchange and chemical denaturation experiments revealed that Ile11 and Ile72 are the key residues for the global folding of EcACP, stabilizing hydrophobic cavity. Backbone dynamics and MD simulation results indicate that longer acyl chains induce conformational adjustments, increasing flexibility in α3-helix and hydrophobic motifs, including Phe28 and Ile54. Furthermore, our findings highlight the conformational plasticity of EcACP, with key molecular switches, Leu42 and Leu46, adapting to accommodate various acyl chains and directing their pathway. These insights deepen our understanding of ACP flexibility and its functional role in FAS, offering a new strategy for designing inhibitors that target the dynamic nature of bacterial FAS pathways. Full article

Conformational heterogeneity is essential for protein function, yet validating theoretical molecular dynamics (MD) ensembles remains a significant challenge. In this study, we present an approach that integrates free MD simulations, starting from an AlphaFold-generated structure, with refined experimental NMR-relaxation data to identify biologically relevant holistic time-resolved 4D conformational ensembles. Specifically, we select trajectory segments (RMSD plateaus) consistent with experimental observables. For the extracellular region of Streptococcus pneumoniae PsrSp, we found that only specific segments of the long MD trajectory aligned well with experimental data. The resulting ensembles revealed two regions with increased flexibility, both of which play important functional roles. Full article