1H NMR Signals Research Articles

Synthesis, Characterization and Electron Beam Curing of Poly(Glycerol Sebacate Methacrylate)

Poly (glycerol sebacate) pre-polymer was synthesized and methacrylated to different degrees (PGSm-0.1, PGSm-0.2, PGSm-0.4) to impart processability using radiation technology. Spectroscopic analyses (FTIR and 1H NMR) confirmed the presence of ester linkage in the poly (glycerol sebacate) chain and the methacrylate group in the derivatives. The degree of methacrylation (DM) computed from the 1H NMR signal integration ranged from 0.1 to 0.4. The molecular weight and polydispersity increased with an increase in DM. The DSC thermograms suggested better elastomeric properties at ambient temperature, while the TGA showed no significant shift in the degradation parameters of PGS upon methacrylation. Electron beam curing of the PGSm samples was employed, and the resulting films were characterized for gel content, surface topography, and wettability. The crosslinked PGSm-0.2 and PGSm-0.4 samples exhibited high gelation at doses 5-50 kGy. However, no gelation above 15 kGy occurred in PGSm-0.1, suggesting that main chain scission reactions prevailed. The surface properties of the films obtained from the AFM and contact angle measurements revealed high surface roughness and wettability.

Phytochemical and antiplasmodial evaluation of five Colombian plants with ethnopharmacological background of antimalarial use

Background: The study of medicinal plants has made it possible to develop products and drugs for the treatment of different diseases. Several plants in Colombia have a history of popular use for the treatment of malaria. The objective of this work was to provide information on the antiplasmodic and phytochemical activity of five neotropical native plants with a folk use for the treatment of malarial.Methods: The ethanolic extract of each species was obtained by percolation method and characterized by TLC, HPLC, and 1H-NMR. The in vitro antiplasmodial activity was evaluated against Plasmodium falciparum (strain FCR-3, chloroquine-resistant).Results: Ethanolic extracts of Ambelania duckey, Cecropia metensis, Cecropia membranacea, and Verbena littoralis showed no activity. However, Curarea toxicofera extract exhibited an IC50 of 7.6 ± 3.9 μg/mL and was classified as moderately active. Furthermore, hemolytic activity was assayed, none of the extracts were tested positive. A preliminary phytochemical study was carried out using tube analysis, thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and hydrogen nuclear magnetic resonance (1H-NMR). Steroids or triterpenes, and phenolic compounds were detected by TLC in all extracts. These findings were confirmed by characteristic aliphatic and aromatic signals in 1H-NMR spectra, corresponding to triterpenes and phenolics, respectively. Additionally, alkaloids were extracted from C. toxicofera and detected by aromatic signals in 1H-NMR spectra.Conclusion: ethanolic extract of C. toxicofera showed antiplasmodial activity (IC50 of 7.6 ± 3.9 μg/mL); this activity may be due to the bisbenzylisoquinoline alkaloids. The ethanol extracts of A. duckey, C. membranacea, C. metensis, and V. littoralis did not present antiplasmodial activity.

The heterospin cobalt complexes: peculiarities of high-resolution NMR spectra

The high-resolution 1H and 13C NMR spectra (CHCl3 solution) of sterically non-rigid heterospin complexes CoL2, CoL2-dipy, and CoL2-phen (where L is 4-(3′,3′,3′-trifluoro-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidine-1-oxyl) have been studied. The specific of the NMR phenomenon in paramagnetic systems is briefly analyzed. It is shown that the NMR spectra modified by hyperfine coupling can be successfully employed for investigation of the complexation processes. In accordance with the common protocols, the 1H and 13C NMR signals are assigned using the information on 13С – 1Н spin-spin coupling. In addition, the preliminarily recorded 1H and 13C NMR spectra of radical L are also used in the work.The temperature dependences of 1H and 13C paramagnetic shifts in the complexes under study have been obtained. A fundamental feature of these dependences is that they obey to the Curie law in a fairly wide temperature range (up to 100 °C). This observation can be used to control intramolecular processes of sterically nonrigid heterosystems in solutions.

Structural variation in the linkage region of pharmaceutical heparin arising from oxidative treatments during manufacture

During the manufacture of pharmaceutical heparin, a range of treatments are applied to sanitize, decolourise and reduce the pyrogenic properties of the samples. The structural effects of bleaching, an oxidative process, are examined. Among 1H and 13C NMR signals ascribable to the tetrasaccharide linkage region of heparin, samples of porcine mucosal heparin frequently display characteristic signals at chemical shift values of 4.5 and 106 ppm respectively, which have not been explained previously. Fractions enriched with material reporting this signal were isolated from heparinase digested porcine mucosal heparin samples and subjected to analysis using mass spectrometry and NMR spectroscopy. A novel structure, ΔU-Gal-Gal-Xyl–CH2–CONH2, was identified by mass fragmentation experiments and further interesting structural motifs emerged following evaluation by mass spectrometry of longer oligosaccharide chains biosynthesized away from the linker tetrasaccharide, GlcA-Gal-Gal-Xyl. The carbohydrate-protein linkage region is thus affected by the bleaching step involved in the manufacturing process of heparin. The discovery of specific modifications that reflect the extent of the oxidation treatment adopted is relevant to the monitoring of inadvertent damage to the heparin structure during manufacture that contributes to sample variation and which could also lead to reduced drug quality.

Method Improving for Isolation and Characterization of Allergy-Inducing Polymer Impurities in Cefotaxime Sodium Medicines Available From Pharmaceutical Industry.

Objective: To prepare and validate the chemical structure of the cefotaxime dimer and cefotaxime trimer impurities available from pharmaceutical industry. Methods: A polymer stock solution of cefotaxime sodium was obtained using a concentrated solution degradation method. The cefotaxime dimer and trimer impurities were separated and purified by preparative reversed-high-performance liquid chromatograph (RP-HPLC), and the pure cefotaxime dimer and trimer were obtained by a freeze-drying method. The two impurities were characterized by infrared (IR) spectroscopy, ultraviolet (UV) spectroscopy, mass spectroscopy, and nuclear magnetic resonance (NMR, including one-dimensional and two-dimensional NMR). The groups corresponding to the characteristic absorption peaks in the UV and IR spectra were analyzed, and the 1H and 13C NMR signals were assigned. Results: The cefotaxime dimer was isolated and purified from the actual sample of industrial medicines, and chemical structure of the dimer is the same as in the dimers investigated earlier. The polymerization sites and stereoscopic configuration of trimer impurity was validated for the first time. Conclusion: This study is of great significance for the study of the structures and quality control of polymer impurities in cephalosporin drugs. Promoting the polymerization sites study and providing a technical basis for allergic study of polymer impurities.

Deep regression with ensembles enables fast, first-order shimming in low-field NMR

Shimming in the context of nuclear magnetic resonance aims to achieve a uniform magnetic field distribution, as perfect as possible, and is crucial for useful spectroscopy and imaging. Currently, shimming precedes most acquisition procedures in the laboratory, and this mostly semi-automatic procedure often needs to be repeated, which can be cumbersome and time-consuming. The paper investigates the feasibility of completely automating and accelerating the shimming procedure by applying deep learning (DL). We show that DL can relate measured spectral shape to shim current specifications and thus rapidly predict three shim currents simultaneously, given only four input spectra. Due to the lack of accessible data for developing shimming algorithms, we also introduce a database that served as our DL training set, and allows inference of changes to 1H NMR signals depending on shim offsets. In situ experiments of deep regression with ensembles demonstrate a high success rate in spectral quality improvement for random shim distortions over different neural architectures and chemical substances. This paper presents a proof-of-concept that machine learning can simplify and accelerate the shimming problem, either as a stand-alone method, or in combination with traditional shimming methods. Our database and code are publicly available.

Remotely controllable supramolecular rotor mounted inside a porphyrinic cage

Remotely controllable supramolecular rotor mounted inside a porphyrinic cage

Quantitative 1H NMR method for analyzing primaquine diphosphate in active pharmaceutical ingredients

Thermal analysis, Fourier Transform IR, the isotropic chemical shift of 1H NMR in different solvents, their temperature dependence and spin-lattice relaxation time constant (T1), solution 1D and 2D NMR, and solid-state 13C and 31P NMR (magic angle spinning NMR) were employed to obtain full information and elucidate the structures of primaquine diphosphate (PQD) samples used for quality controlling malaria medicines. Additionally, a simple, rapid, specific, and reliable quantitative method (qNMR) was developed to determine the PQD level in the raw material of active pharmaceutical ingredients (APIs). The method was developed using ethylene carbonate (EC) as the internal standard and dimethylsulfoxide-d6 (DMSO-d6) as the NMR solvent. For the API qNMR, 1H NMR signals at 3.82 and 1.22 ppm were used. The qNMR methodology, through the linearity, range, LOD and LOQ, stability, precision, robustness, and accuracy, was validated within the requirements of guidelines. The accuracy of the qNMR was evaluated by comparing it to a pharmacopeial HPLC technique and there were no statistical differences (p > 0.05). The proposed qNMR method authentically supports and endorses the current pharmacopoeial methods used for determining the PQD content.

Stable and inert macrocyclic cobalt(II) and nickel(II) complexes with paraCEST response.

We report the synthesis of the macrocyclic ligands 3,9-PC2AMH (2,2'-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,9-diyl)diacetamide) and 3,9-PC2AMtBu (2,2'-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,9-diyl)bis(N-tert-butyl)acetamide) which contain a pyclen platform functionalized with acetamide or tert-butylacetamide pendant arms at positions 3 and 9 of the macrocyclic unit. The corresponding Co(II) and Ni(II) complexes were prepared, isolated and characterised as potential paramagnetic chemical exchange saturation transfer (paraCEST) agents. The X-ray structures of the Ni(II) complexes reveal six-coordination of the ligands to the metal ion. The Co(II) complex with 3,9-PC2AMtBu shows a similar six-coordinate structure in the solid state, while the Co(II) complex with 3,9-PC2AMH contains a seven-coordinate metal ion, seventh coordination being completed by the presence of an inner-sphere water molecule. The structure of the Co(II) complexes was investigated using 1H NMR spectroscopy and computational methods. The complexes present a seven-coordinate structure in solution, as demonstrated by the analysis of the paramagnetic shifts using density functional theory. Ligand protonation constants and stability constants of the complexes with 3,9-PC2AMH were determined using potentiometric titrations (I = 0,15 M NaCl). The Co(II) complex was found to be more stable than the Ni(II) analogue (log KCoL = 14.46(5) and log KNiL = 13.15(3)). However, the Ni(II) and Co(II) complexes display similar rate constants characterizing the proton-assisted dissociation mechanism. The presence of highly shifted 1H NMR signals due to the amide protons in slow exchange with bulk water results in sizeable CEST signals, which are observed at +67 and +15 ppm for the Co(II) complex with 3,9-PC2AMH and +42 and +7 ppm for the Ni(II) analogue at 25 °C.

A one-shot double-slice selection NMR method for biphasic systems.

We propose a new and robust one-shot double-slice selection experiment to detect 1H NMR signals of biphasic systems simultaneously. The resultant spectrum contains opposite-phased peaks representing the chemical species from the two phases, respectively.

Concentration-Dependent Association of Flavylium Chloride with Differential Hydroxy Moieties in Ethanol

Flavylium ions (6a–6e) were synthesized using Aldol condensation to compare the spectroscopic properties caused by the different numbers and locations of hydroxy groups on the flavylium cations (AH+). Without the addition of acid, increasing the concentration of flavylium ions to 10 mM in ethanol led to the following observation. The flavylium ions with the least number of OH groups (6a and 6b) showed a change in peak at higher concentrations, whereas 6c and 6d did not show the same degree of change in their 1H-NMR signals. This suggests an equilibrium that shifts the isomers B, CE, and Cz more towards the flavylium ion with more OH groups even at low concentrations. One possibility for the cause of this shift is that the flavylium ions become more stable through aggregation. In addition to the NMR results, the UV measurements confirmed that isomers with fewer OH groups showed a more dramatic shift towards the flavylium ion at higher concentrations. Using modeling data at DFT//B3LYP/6311**G(d) level, the self-association was investigated to show that the hydrogen bonding of OH groups is the main player but cannot stabilize entirely without the presence of the chloride ion in the complex.

Structural, spectroscopic, quantum chemical, and molecular docking investigation of (E)-N'-(2,5-dimethoxybenzylidene)picolinohydrazide

Schiff bases and hydrazides are groups of compounds with important biological activities. In this contribution, (E)-N'-(2,5-dimethoxybenzylidene)picolinohydrazide (DBP) was synthesized and characterized by X-ray crystallography, IR, Raman, UV–vis and NMR spectroscopies. The Hirshfeld surface analysis was performed to investigate the interactions within the crystal package. The structure of DBP was optimized by several functionals (B3LYP, CAM-B3LYP, B3PW91, M05-2X, and M06-2X) in conjunction with the 6-311++G(d,p) basis set. The suitable level of theory was determined based on the comparison between experimental and theoretical bond lengths and angles (M06-2X/6-311++G(d,p)). The Natural Bond Orbital (NBO) and Quantum Theory of Atoms in Molecules (QTAIM) approaches were used for the quantification of the interaction strengths within a structure. The experimental IR and Raman peaks were assigned based on the calculated one, with the aid of the Potential Energy Distribution (PED) analysis. The 1H and 13C NMR signals were also assigned when compared to the calculated ones. The reproducibility of the experimental results proved that a suitable level of theory was obtained. The experimental UV–vis spectra consisted of a wide peak between 200 and 450 nm, while the most prominent theoretical transitions were located at 324, 231, and 213 nm. The nonlinear optical (NLO) studies Z-scan experiment allowed the determination of the nonlinear absorption coefficient and nonlinear refractive index, thus proving that DBP can be used as NLO material. Various reactivity descriptors of DBP and its analogs were computed and the reactivity was checked towards Cyclin-Dependent Kinase 2 protein, with the influence of structural parameters explained.

Multinuclear NMR screening of pharmaceuticals using standardization by 2H integral of a deuterated solvent

NMR standardization approach that uses the 2H integral of deuterated solvent for quantitative multinuclear analysis of pharmaceuticals is described. As a proof of principle, the existing NMR procedure for the analysis of heparin products according to US Pharmacopeia monograph is extended to the determination of Na+ and Cl- content in this matrix. Quantification is performed based on the ratio of a 23Na (35Cl) NMR integral and 2H NMR signal of deuterated solvent, D2O, acquired using the specific spectrometer hardware. As an alternative, the possibility of 133Cs standardization using the addition of Cs2CO3 stock solution is shown. Validation characteristics (linearity, repeatability, sensitivity) are evaluated. A holistic NMR profiling of heparin products can now also be used for the quantitative determination of inorganic compounds in a single analytical run using a single sample. In general, the new standardization methodology provides an appealing alternative for the NMR screening of inorganic and organic components in pharmaceutical products.

Pd on Nanodiamond/Graphene in Hydrogenation of Propyne with Parahydrogen

The catalytic behavior of Pd catalysts supported on a defective nanodiamond/graphene material (ND@G) was studied in propyne hydrogenation with parahydrogen, taking advantage of the possibility to control the character of metal distribution by changing metal loading. Two different catalysts were studied in this work: Pd1/ND@G with a monoatomic Pd distribution (0.11 wt %) and Pdn/ND@G comprising supported metal clusters (0.87 wt %). The monoatomic distribution of Pd in Pd1/ND@G was confirmed by XPS and HAADF-STEM methods. This catalyst demonstrated an outstanding selectivity to propene (up to 100%) in propyne hydrogenation. The activity of the two Pd catalysts in pairwise H2 addition to propyne was compared under the same experimental conditions by observing 1H NMR signal enhancements provided by the parahydrogen-induced polarization (PHIP) effect. The enhancements produced by the Pd1/ND@G catalyst were found to be ca. 6-fold larger than those observed with Pdn/ND@G, indicating that the character of metal distribution has important consequences for the performance of a catalyst and its efficiency in terms of PHIP effects.

Agrocinopine C, a Ti-plasmid-coded enzyme-product, is a 2-O, 6-O linked phosphodiester of D-Glucose and sucrose

Agrocinopine C is a small molecule found in crown gall tumours induced by pathogenic Agrobacterium radiobacter carrying the tumour-inducing plasmid pTi Bo542. This phosphodiester opine was isolated (at 0.02 g/100 g fresh wt.) from sunflower (Helianthus annuus L.) galls. It is structurally related to agrocinopine A and is a glucose-2-phosphodiester linked to the C6-hydroxy-methyl group of the glucose moiety of sucrose. Sugar-2-phosphates are uncommon in plant tissues, whether transformed by Agrobacterium or not. 1H and 31P NMR signal multiplicity indicates five-fold anomeric complexity of agrocinopine C in solution, implying that the permeases taking up these sucrose-phosphodiesters could recognise any one of the five anomers. Data suggests that the open chain aldehyde forms of the 2-phosphorylated opines agrocinopine C and agrocinopine A and the corresponding phosphorylated glucose-2-phosphoramidate component of the antibiotic agrocin 84 play a central role in agrocin's selective toxicity to certain strains of Agrobacterium after uptake via Ti plasmid-encoded permeases.

Sensitivity Enhancement by Progressive Saturation of the Proton Reservoir: A Solid-State NMR Analogue of Chemical Exchange Saturation Transfer.

Chemical exchange saturation transfer (CEST) enhances solution-state NMR signals of labile and otherwise invisible chemical sites, by indirectly detecting their signatures as a highly magnified saturation of an abundant resonance—for instance, the 1H resonance of water. Stimulated by this sensitivity magnification, this study presents PROgressive Saturation of the Proton Reservoir (PROSPR), a method for enhancing the NMR sensitivity of dilute heteronuclei in static solids. PROSPR aims at using these heteronuclei to progressively deplete the abundant 1H polarization found in most organic and several inorganic solids, and implements this 1H signal depletion in a manner that reflects the spectral intensities of the heteronuclei as a function of their chemical shifts or quadrupolar offsets. To achieve this, PROSPR uses a looped cross-polarization scheme that repeatedly depletes 1H–1H local dipolar order and then relays this saturation throughout the full 1H reservoir via spin-diffusion processes that act as analogues of chemical exchanges in the CEST experiment. Repeating this cross-polarization/spin-diffusion procedure multiple times results in an effective magnification of each heteronucleus’s response that, when repeated in a frequency-stepped fashion, indirectly maps their NMR spectrum as sizable attenuations of the abundant 1H NMR signal. Experimental PROSPR examples demonstrate that, in this fashion, faithful wideline NMR spectra can be obtained. These 1H-detected heteronuclear NMR spectra can have their sensitivity enhanced by orders of magnitude in comparison to optimized direct-detect experiments targeting unreceptive nuclei at low natural abundance, using modest hardware requirements and conventional NMR equipment at room temperature.

Vecuronium bromide and its advanced intermediates: A crystallographic and spectroscopic study

Vecuronium bromide (Piperidinium, 1-[(2β,3α,5α,16β,17β)-3,17-bis(acetyloxy)-2-(1-piperidinyl)androstan-16-yl]-1-methyl-, bromide; Norcuron®) has been extensively used in anesthesiology practice as neuromuscular blocking agent since its launch on the market in 1982. However, a detailed crystallographic and NMR analysis of its advanced synthetic intermediates is still lacking. Hence, with the aim of filling this literature gap, vecuronium bromide was prepared starting from the commercially available 3β-hydroxy-5α-androstan-17-one (epiandrosterone), implementing some modifications to a traditional synthetic procedure. A careful NMR study allowed the complete assignment of the 1H, 13C, and 15N NMR signals of vecuronium bromide and its synthetic intermediates. The structural and stereochemical characterization of 2β,16β-bispiperidino-5α-androstane-3α,17β-diol, the first advanced synthetic intermediate carrying all the stereocenters in the final configuration, was described by means of single-crystal X-ray diffraction and Hirshfeld surface analysis, allowing a detailed conformational investigation.

Determination of cis/trans fatty acid contents in edible oils by 1H NMR spectroscopy in association with multivariate calibration

In this work, cis and trans fatty acid (FA) contents in edible oils was determined using 1H nuclear magnetic resonance (1H NMR) spectroscopy. The comparison of 1H NMR spectra of edible oil and cis-trans isomerized oil showed that they were different in three regions: (1) 2.880 - 2.650 ppm caused by bis-allylic protons; (2) 2.140 - 1.900 ppm due to allylic protons; and (3) 1.030 - 0.930 ppm due to methyl protons of linolenic acyl groups. The 1H NMR signals in these regions were combined with partial least squares method to predict contents of cis/trans fatty acids in edible oils. The results showed that the predicted values were consistent with the gas chromatography-measured values and had a good linear relationship with a correlation coefficient (R2) of above 0.98. This work demonstrates that 1H NMR spectroscopy was successfully used to determine the composition of both cis and trans fatty acids in edible oils.

Molecular Assembly in Block Copolymer-Surfactant Nanoparticle Dispersions: Information on Molecular Exchange and Apparent Solubility from High-Resolution and PFG NMR.

Internally structured block copolymer-surfactant particles are formed when the complex salts of ionic-neutral block copolymers neutralized by surfactant counterions are dispersed in aqueous media. Here, we report the 1H NMR signal intensities and self-diffusion coefficients (D, from pulsed field gradient nuclear magnetic resonance, PFG NMR) of trimethyl alkylammonium surfactant ions and the poly(acrylamide)-block-poly(acrylate) (PAAm-b-PA) polyions forming such particles. The results reveal the presence of an “NMR-invisible” (slowly exchanging) fraction of aggregated surfactant ions in the particle core and an “NMR-visible” fraction consisting of surface surfactant ions in rapid exchange with the surfactant ions dissociated into the aqueous domain. They also confirm that the neutral PAAm blocks are exposed to water at the particle surface, while the PA blocks are buried in the particle core. The self-diffusion of the polyions closely agree with the self-diffusion of a hydrophobic probe molecule solubilized in the particles, showing that essentially all copolymer chains are incorporated in the aggregates. Through centrifugation, we prepared macroscopically phase-separated systems with a phase concentrated in particles separated from a clear dilute phase. D values for the surfactant and block copolymer indicated that the dilute phase contained small aggregates (ca. 5 nm) of surfactant ions and a few anionic-neutral block copolymer chains. Regardless of the overall concentration of the sample, the fraction of block copolymer found in the dilute phase was nearly constant. This indicates that the dilute fraction represented a tail of small particles created by the dispersion process rather than a true thermodynamic solubility of the complex salts.

The Exploitation of Xanthan Cryogels as Pattern for Edible Oleogel Preparation

In this study, xanthan gum was used to produce cryogel and conversion of cryogel to oleo-gels, and the structural and chemical characteristics of the produced oleo-gels was investigated. Results showed, the produced oleo-gels (COS) contained about 66% oil content and they have able to holding oil at about 60%. The pseudo-second order model can predict the oil absorption kinetics of cryogels. There was no difference between the amount of fatty acids of sunflower oil and COS. 1H NMR and 13C NMR signals, the hydro peroxide (initial oxidation product) and aldehydes (secondary product oxidation) was not revealed in COS. Also, it was observed no exothermic process in the curve in the differential thermal analysis curve (DTA) up to 350 °C. AFM the formation of a uniform, homogeneous, and stable gel network that matched the results of the mechanical properties of the COS.