Single-Photon Ionization Induced New Covalent Bond Formation in Acrylonitrile(AN)–Pyrrole(Py) Clusters

The formation of nitrogen-containing organic compounds is crucial for understanding chemical evolution and the origin of life in the interstellar medium (ISM). In this study, we explore whether acrylonitrile (AN) and pyrrole (Py) can form new nitrogen-containing compounds after single-photon ionization in their gaseous clusters by vacuum ultraviolet (VUV)-infrared (IR) spectroscopy and theoretical calculations. The results show that a strong linear H-bond is formed in neutral AN-Py, while cyclic or bicyclic H-bonded networks are formed in the neutral AN-Py2 cluster. It is found that the structure containing a new C–C covalent bond between two moieties in (AN-Py)+ is formed besides the formation of H-bonded structures after AN-Py is ionized by VUV light. In (AN-Py2)+ cluster cations, new C–C or C–N covalent bonds tend to be formed between two Py, with (Py)2+ as the core in the cluster. The results reveal that new covalent bonds are more likely to be formed between two Py species when AN and Py are present in the cationic clusters. These results provide spectroscopic evidence of the formation of new nitrogen-containing organic compounds from AN and Py induced by VUV, which are helpful for our understanding of the formation of diverse prebiotic molecules in interstellar space

Laser Desorption Postionization Mass Spectrometry Imaging of Folic Acid Molecules in Tumor Tissue

Mass spectrometry imaging (MSI) is an innovative and powerful tool in biomedical research. It is well-known that folic acid (FA) has a high affinity for folic acid receptor (FR), which is overexpressing in epithelial cancer. Herein, we propose a novel method to diagnose cancer through direct mapping of the label-free FA spatial distribution in tissue sections by state-of-the-art laser desorption postionization-mass spectrometry imaging (LDPI-MSI). Compared with other tumor imaging methods, such as fluorescence imaging, photoacoustic imaging (PAI), magnetic resonance imaging (MRI), and micro-SPECT/CT, complicated synthesis and labeling processes are not required. The LDPI-MSI was performed on 30 μm thick sections from a murine model of breast cancer (inoculation of 4T1 cells) that were predosed with 20 mg/kg of FA. The image obtained from the characteristic mass spectrometric signature of FA at <i>m</i>/<i>z</i> 265 illustrated that FA was concentrated primarily in tumor tissue and displayed somewhat lower retention in adjacent normal controls. The results suggest that the proposed method could be used potentially in cancer diagnosis

Site-Selective Dissociation Processes of Cationic Ethanol Conformers: The Role of Hyperconjugation

In present report, we explored hyperconjugation effects on the site- and bond-selective dissociation processes of cationic ethanol conformers by the use of theoretical methods (including configuration optimizations, natural bond orbital (NBO) analysis, and density of states (DOS) calculations, etc.) and the tunable synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry. The dissociative mechanism of ethanol cations, in which hyperconjugative interactions and charge-transfer processes were involved, was proposed. The results reveal C_α–H and C–C bonds are selectively weakened, which arise as a result of the hyperconjugative interactions σ_Cα‑H → p in the trans-conformer and σ_C–C → p in gauche-conformer after being ionized. As a result, the selective bond cleavages would occur and different fragments were observed

Functional Characterization of Human Peptide/Histidine Transporter 1 in Stably Transfected MDCK Cells

The proton-coupled oligopeptide transporter PHT1 (SLC15A4), which facilitates cross-membrane transport of histidine and small peptides from inside the endosomes or lysosomes to cytosol, plays an important role in intracellular peptides homeostasis and innate immune responses. However, it remains a challenge to elucidate functional properties of the PHT1 transporter because of its subcellular localization. The purpose of this study was to resort hPHT1 protein from the subcellular to outer cell membrane of MDCK cells stably transfected with human PHT1 mutants, and to characterize its functional activity in these cells. Using this model, the functional activity of hPHT1 was evaluated by cellular uptake studies with d₃-l-histidine, GlySar, and the bacterial peptidoglycan products MDP and Tri-DAP. We found that the disruption of two dileucine motifs was indispensable for hPHT1 transporter being preferentially targeting to plasma membranes. hPHT1 showed high affinity for d₃-l-histidine and low affinity for GlySar, with <i>K</i>_m values of 16.3 ± 1.9 μM and 1.60 ± 0.30 mM, respectively. Moreover, the bacterial peptidoglycan components MDP and Tri-DAP were shown conclusively to be hPHT1 substrates. The uptake of MDP by hPHT1 was inhibited by di/tripeptides and peptide-like drugs, but not by glycine and acyclovir. The functional activity of hPHT1 was also pH-dependent, with an optimal cellular uptake in buffer pH 6.5. Taken together, we established a novel cell model to evaluate the function of hPHT1 <i>in vitro</i>, and confirmed that MDP and Tri-DAP were substrates of hPHT1. Our findings suggest that PHT1 may serve as a potential target for reducing the immune responses and for drug treatment of inflammatory diseases

Chemical Modulation of the Human Oligopeptide Transporter 1, hPepT1

In humans, peptides derived from dietary proteins and peptide-like drugs are transported via the proton-dependent oligopeptide transporter hPepT1 (SLC15A1). hPepT1 is located across the apical membranes of the small intestine and kidney, where it serves as a high-capacity low-affinity transporter of a broad range of di- and tripeptides. hPepT1 is also overexpressed in the colon of inflammatory bowel disease (IBD) patients, where it mediates the transport of harmful peptides of bacterial origin. Therefore, hPepT1 is a drug target for prodrug substrates interacting with intracellular proteins or inhibitors blocking the transport of toxic bacterial products. In this study, we construct multiple structural models of hPepT1 representing different conformational states that occur during transport and inhibition. We then identify and characterize five ligands of hPepT1 using computational methods, such as virtual screening and QM-polarized ligand docking (QPLD), and experimental testing with uptake kinetic measurements and electrophysiological assays. Our results improve our understanding of the substrate and inhibitor specificity of hPepT1. Furthermore, the newly discovered ligands exhibit unique chemotypes, providing a framework for developing tool compounds with optimal intestinal absorption as well as future IBD therapeutics against this emerging drug target