On‐Line Monitoring of Chemical Reactions by using Bench‐Top Nuclear Magnetic Resonance Spectroscopy

Real‐time nuclear magnetic resonance (NMR) spectroscopy measurements carried out with a bench‐top system installed next to the reactor inside the fume hood of the chemistry laboratory are presented. To test the system for on‐line monitoring, a transfer hydrogenation reaction was studied by continuously pumping the reaction mixture from the reactor to the magnet and back in a closed loop. In addition to improving the time resolution provided by standard sampling methods, the use of such a flow setup eliminates the need for sample preparation. Owing to the progress in terms of field homogeneity and sensitivity now available with compact NMR spectrometers, small molecules dissolved at concentrations on the order of 1 mmol L^?1 can be characterized in single‐scan measurements with 1 Hz resolution. Owing to the reduced field strength of compact low‐field systems compared to that of conventional high‐field magnets, the overlap in the spectrum of different NMR signals is a typical situation. The data processing required to obtain concentrations in the presence of signal overlap are discussed in detail, methods such as plain integration and line‐fitting approaches are compared, and the accuracy of each method is determined. The kinetic rates measured for different catalytic concentrations show good agreement with those obtained with gas chromatography as a reference analytical method. Finally, as the measurements are performed under continuous flow conditions, the experimental setup and the flow parameters are optimized to maximize time resolution and signal‐to‐noise ratio.     

Accelerated Nuclear Magnetic Resonance Spectroscopy with Deep Learning

Nuclear magnetic resonance (NMR) spectroscopy serves as an indispensable tool in chemistry and biology but often suffers from long experimental times. We present a proof‐of‐concept of the application of deep learning and neural networks for high‐quality, reliable, and very fast NMR spectra reconstruction from limited experimental data. We show that the neural network training can be achieved using solely synthetic NMR signals, which lifts the prohibiting demand for a large volume of realistic training data usually required for a deep learning approach.     

Synthesis and Spectroscopy of Novel‐α‐Pyrazolylglycine Derivatives

The synthesis of α‐pyrazolylglycine derivatives(7a‐d) with different substituents, starting from glycine have been pre pared. The spectroscopy of intermediate compounds and the final amino acids have been discussed.     

Partial‐Homogeneity‐Based Two‐Dimensional High‐Resolution Nuclear Magnetic Resonance Spectroscopy under Inhomogeneous Magnetic Fields

High‐resolution multidimensional nuclear magnetic resonance (NMR) spectroscopy serves as an irreplaceable and versatile tool in various chemical investigations. In this study, a method based on the concept of partial homogeneity is developed to offer two‐dimensional (2D) high‐resolution NMR spectra under inhomogeneous fields. Oscillating gradients are exerted to encode the high‐resolution information, and a field‐inhomogeneity correction algorithm based on pattern recognition is designed to recover high‐resolution spectra. Under fields where inhomogeneity primarily distributes along a single orientation, the proposed method will improve performances of 2D NMR spectroscopy without increasing the experimental duration or significant loss in sensitivity, and thus may open important perspectives for studies of inhomogeneous chemical systems.     

Real‐Time Monitoring of New Delhi Metallo‐β‐Lactamase Activity in Living Bacterial Cells by 1H NMR Spectroscopy

Disconnections between in vitro responses and those observed in whole cells confound many attempts to design drugs in areas of serious medical need. A method based on 1D ¹H NMR spectroscopy is reported that affords the ability to monitor the hydrolytic decomposition of the carbapenem antibiotic meropenem inside Escherichia coli cells expressing New Delhi metallo‐β‐lactamase subclass 1 (NDM‐1), an emerging antibiotic‐resistance threat. Cell‐based NMR studies demonstrated that two known NDM‐1 inhibitors, L ‐captopril and ethylenediaminetetraacetic acid (EDTA), inhibit the hydrolysis of meropenem in vivo. NDM‐1 activity in cells was also shown to be inhibited by spermine, a porin inhibitor, although in an in vitro assay, the influence of spermine on the activity of isolated NDM‐1 protein is minimal. This new approach may have generic utility for monitoring reactions involving diffusible metabolites in other complex biological matrices and whole‐cell settings, including mammalian cells.     

Target‐Based Whole‐Cell Screening by 1H NMR Spectroscopy

An NMR‐based approach marries the two traditional screening technologies (phenotypic and target‐based screening) to find compounds inhibiting a specific enzymatic reaction in bacterial cells. Building on a previous study in which it was demonstrated that hydrolytic decomposition of meropenem in living Escherichia coli cells carrying New Delhi metallo‐β‐lactamase subclass 1 (NDM‐1) can be monitored in real time by NMR spectroscopy, we designed a cell‐based NMR screening platform. A strong NDM‐1 inhibitor was identified with cellular IC₅₀ of 0.51 μM , which is over 300‐fold more potent than captopril, a known NDM‐1 inhibitor. This new screening approach has great potential to be applied to targets in other cell types, such as mammalian cells, and to targets that are only stable or functionally competent in the cellular environment.     

Proton Nuclear Magnetic Resonance Measurements of 2′-Aminodeoxyuridylyl-3′,5′-Deoxyuridine

A dideoxyribonucleotide, 2′-amino-2′-deoxyuridylyl 3′,5′-deoxyuridine, containing an unsual base (2′-amino-2′-deoxyuridine) that isresistant to nucleases was investigated by ′H NMR. The pK_a of the protonation of the amino group (5.8) was determined by profiles of chemical shifts of protons in the vicinity of amino group versus pH. However, protonation of the amino group has little effect on the conformation of the dimer, assumed to be B-form DNA. This conclusion is drawn from the chemical shift data and coupling constants of H₁-H₂. Thus, 2′-amino-2′-deoxyuridine can be used in antisense and anticode oligonucleotides.     

Enantiodifferentiation through Frequency‐Selective Pure‐Shift 1H Nuclear Magnetic Resonance Spectroscopy

A frequency‐selective 1D ¹H nuclear magnetic resonance (NMR) experiment for the fast and sensitive determination of chemical‐shift differences between overlapped resonances is proposed. The resulting fully homodecoupled ¹H NMR resonances appear as resolved 1D singlets without their typical J(HH) coupling constant multiplet structures. The high signal dispersion that is achieved is then exploited in enantiodiscrimination studies by using chiral solvating agents.     

Nuclear Magnetic Resonance Structure Elucidation of Peptide b2 Ions

Tandem mass spectrometry (MS/MS) is powerful for chemical identification but it is still insufficient for explicit ion structure determination. A strategy is introduced to elucidate MS fragment ion structures using NMR spectroscopy for the first time. In our experiments, precursor ions are dissociated at atmospheric pressure and the resulting fragment ions are identified by mass spectrometry but collected outside the mass spectrometer, making the subsequent NMR measurements possible. This new strategy has been applied to determine the chemical structure of the characteristic b₂ fragment ion, a subject of longstanding debate in MS‐based proteomics.     

Structural Changes of β-Casein Induced by Temperature and pH Analysed by Nuclear Magnetic Resonance,Fourier-Transform Infrared Spectroscopy,and Chemometrics

This study investigated structural changes in β-casein as a function of temperature (4 and 20 °C) and pH (5.9 and 7.0). For this purpose, nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopy were used, in conjunction with chemometric analysis. Both temperature and pH had strongly affected the secondary structure of β-casein, with most affected regions involving random coils and α-helical structures. The α-helical structures showed great pH sensitivity by decreasing at 20 °C and diminishing completely at 4 °C when pH was increased from 5.9 to 7.0. The decrease in α-helix was likely related to the greater presence of random coils at pH 7.0, which was not observed at pH 5.9 at either temperature. The changes in secondary structure components were linked to decreased hydrophobic interactions at lower temperature and increasing pH. The most prominent change of the α-helix took place when the pH was adjusted to 7.0 and the temperature set at 4 °C, which confirms the disruption of the hydrogen bonds and weakening of hydrophobic interactions in the system. The findings can assist in establishing the structural behaviour of the β-casein under conditions that apply as important for solubility and production of β-casein.