Nuclear Magnetic Resonance Spectroscopy Analysis Research Articles

Disentangle the drivers of soil organic carbon mineralization and their temperature sensitivity in both topsoil and subsoil: Implication of thermal stability and chemical composition

Information about the temperature dependence of soil organic carbon (SOC) mineralization is important to predict the possible carbon (C) release from the terrestrial ecosystem facing global warming. However, the way in which SOC quality and mineral protection of SOC affects mineralization rates and their response to increasing temperature remains poorly understood. Here, we focused on investigating thermal stability and chemical composition of soils which differed greatly with the type and extent of organo-mineral associations, and revealing their implications for SOC mineralization. Chemical composition and thermal stability of SOC were analyzed with 13C nuclear magnetic resonance spectroscopy (13C NMR) and simultaneous thermogravimeteric analysis and differential scanning calorimetry (TG-DSC), respectively. Soil mineralization and its temperature sensitivity (Q10) were assessed by incubating soils at 15 and 25 °C for 90 days.Our results showed that SOC of subsoil was more biologically stable, but exhibited higher temperature sensitivity than those of topsoil. Significant differences in chemical composition and thermal stability of SOC were detected across soils developed from four parent materials but not between two soil layers, and indicators obtained from the two techniques showed apparent associations with depth-specific SOC mineralization rates. Increase in SOC mineralization rates at two incubation temperatures and two soil layers were observed when the soils were characterized by higher percentage of labile SOC fractions (i.e., O-alkyl C and organic carbon oxidized during exothermic reactions). The Q10 values of topsoil were positively and mostly related to the percentage of Alkyl C. In addition to notable relationships with chemical composition, the Q10 values of subsoil were positively correlated with Exo1/Exo2 ratios and Energy density values, and negatively correlated with TG-50. It was interesting to note that thermal stability was possibly as a function of soil texture and total oxides. Results from VPA analysis further revealed that SOC mineralization rates at two soil layers and Q10 of topsoil were mainly driven by SOC quality, while it was related to both SOC quality and chemical protection for subsoil, implying that factors controlling the temperature sensitivity of SOC mineralization were depth-specific. Altogether, substrate accessibility as a function of chemical composition and chemical protection would play vital role in determining the feedbacks of the subsoil SOC pool to the future climate warming.

Synthesis and Antiproliferative Potential of Thiazole and 4-Thiazolidinone Containing Motifs as Dual Inhibitors of EGFR and BRAFV600E.

Thiazole and thiazolidinone recur in a wide range of biologically active compounds that reach different targets within the context of tumors and represent a promising starting point to access potential candidates for treating metastatic cancer. Therefore, searching for new lead compounds that show the highest anticancer potency with the fewest adverse effects is a major drug-discovery challenge. Because the thiazole ring is present in dasatinib, which is currently used in anticancer therapy, it is important to highlight the ring. In this study, cycloalkylidenehydrazinecarbothioamides (cyclopentyl, cyclohexyl, cyclooctyl, dihydronapthalenylidene, flurine-9-ylidene, and indolinonyl) reacted with 2-bromoacetophenone and diethylacetylenedicarboxylate to yield thiazole and 4-thiazolidinone derivatives. The structure of the products was confirmed by using infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and single-crystal X-ray analyses. The antiproliferative activity of the newly synthesized compounds was evaluated. The most effective inhibitory compounds were further tested in vitro against both epidermal growth factor receptor (EGFR) and B-Raf proto-oncogene, serine/threonine kinase (BRAFV600E) targets. Additionally, molecular docking analysis examined how these molecules bind to the active sites of EGFR and BRAFV600E.

Phyllostachys nigra (Lodd. ex Lindl.) derived polysaccharide with enhanced glycolipid metabolism regulation and mice gut microbiome

This study focuses on the characterization and regulation of glycolipid metabolism of polysaccharides derived from biomass of Phyllostachys nigra (Lodd. ex Lindl.) root (PNr). The extracts from dilute hydrochloric acid, hot water, and 2 % sodium hydroxide solution were characterized through molecular weight, gel permeation chromatography, monosaccharides, Fourier transform infrared, and nuclear magnetic resonance spectroscopy analyses. Polysaccharide from alkali extraction and molecular sieve purification (named as: PNS2A) exhibited optimal inhibitory of 3T3-L1 cellular differentiation and lowered insulin resistance. The PNS2A is made of a hemicellulose-like main chain of →4)-β-D-Xylp-(1→ that was connected by branches of 4-O-Me-α-GlcAp-(1→, T-α-D-Galp-(1→, T-α-L-Araf-(1→, →2)-α-L-Araf-(1→, as well as β-D-Glcp-(1→4-β-D-Glcp-(1→ fragments. Oral delivery of PNS2A in diabetes mice brought down blood glucose and cholesterol levels and regulated glucose and lipid metabolism. PNS2A alleviated diabetes symptoms and body weight and protected liver and kidney function in model animals by altering the gut microbiome. Polysaccharides can be a new approach to develop bamboo resources.

Solvents Influence 1H NMR Chemical Shifts and Complete 1H and 13C NMR Spectral Assignments for Florfenicol

Florfenicol (FFC) is an important and widely used veterinary drug, and its structure has been characterized by nuclear magnetic resonance (NMR) spectroscopy. The study aimed to investigate the influences of solvent type, solvent concentration, and temperature on the chemical shifts of the 1H NMR of FFC. The results showed that different types of solvents significantly affected the chemical shifts, especially the chemical shifts of 2-H, 3-H, 5-H, and the active protons. When DMSO-d 6 is used as the solvent, there is no significant difference in the chemical shifts of FFC with a concentration ranging from 20 to 250 mmol/L; however, as the temperature increases, the chemical shifts of the active protons move to a higher field. Besides, the NMR spectroscopic data and structural analysis of FFC were refined by 1H, 13C, distortionless enhancement by polarization transfer-135 (DEPT-135), 1H–1H correlation spectroscopy (1H–1H COSY), phase-sensitive gradient heteronuclear singular quantum correlation (gHSQC), and heteronuclear multiple bond correlation (gHMBC) NMR spectroscopy using DMSO-d 6 as a solvent. The study will help with qualitative and quantitative analysis of FFC in the future.

Synthesis and Antibacterial Activity of Novel Triazolo[4,3-a]pyrazine Derivatives

Infectious diseases pose a major challenge to human health, and there is an urgent need to develop new antimicrobial agents with excellent antibacterial activity. A series of novel triazolo[4,3-a]pyrazine derivatives were synthesized and their structures were characterized using various techniques, such as melting point, 1H and 13C nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis. All the synthesized compounds were evaluated for in vitro antibacterial activity using the microbroth dilution method. Among all the tested compounds, some showed moderate to good antibacterial activities against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli strains. In particular, compound 2e exhibited superior antibacterial activities (MICs: 32 μg/mL against Staphylococcus aureus and 16 μg/mL against Escherichia coli), which was comparable to the first-line antibacterial agent ampicillin. In addition, the structure–activity relationship of the triazolo[4,3-a]pyrazine derivatives was preliminarily investigated.

Characterization of Equilibrium Catalysts from the Fluid Catalytic Cracking Process of Atmospheric Residue

In the FCC conversion of heavy petroleum fractions as atmospheric residues, the main challenge for refiners to achieve the quantity and quality of various commercial products depends essentially on the catalyst used in the process. A deep characterization of the catalyst at different steps of the process (fresh, regenerated, and spent catalyst) was investigated to study the catalyst’s behavior including the physicochemical evolution, the deactivation factor, and kinetic–thermodynamic parameters. All samples were characterized using various spectroscopy methods such as N2 adsorption–desorption, UV-visible spectroscopy, Raman spectroscopy, LECO carbon analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), nuclear magnetic resonance spectroscopy (NMR13C) analysis, and thermogravimetric analysis. The results of the N2 adsorption–desorption, UV-vis, Raman, LECO carbon, and SEM imaging showed that the main causes of catalyst deactivation and coking were the deposition of carbon species that covered the active sites and clogged the pores, and the attrition factor due to thermal conditions and poisonous metals. The XRD and XRF results showed the catalyst’s physicochemical evolution during the process and the different interlinks between catalyst and feedstock (Nickel, Vanadium, Sulfur, and Iron) elements which should be responsible for the coking and catalyst attrition factor. It has been found that, in addition to the temperature, the residence time of the catalyst in the process also influences catalyst structure transformation. NMR13C analysis revealed that polyaromatic hydrocarbon is the main component in the deposited coke of the spent catalyst. The pyridine-FTIR indicates that the catalyst thermal treatment has an influence on its Brønsted and Lewis acid sites and the distribution of the products. Thermogravimetric analysis showed that the order of catalyst mass loss was fresh > regenerated > spent catalyst due to the progressive losses of the hydroxyl bonds (OH) and the structure change along the catalyst thermal treatment. Moreover, the kinetic and thermodynamic parameters showed that all zones are non-spontaneous endothermic reactions.

Novel Nanoprobe with Combined Ultrasonography/Chemical Exchange Saturation Transfer Magnetic Resonance Imaging for Precise Diagnosis of Tumors.

Given that cancer mortality is usually due to a late diagnosis, early detection is crucial to improve the patient's results and prevent cancer-related death. Imaging technology based on novel nanomaterials has attracted much attention for early-stage cancer diagnosis. In this study, a new block copolymer, poly(ethylene glycol)-poly(l-lactide) diblock copolymer (PEG-PLLA), was synthesized by the ring-opening polymerization method and thoroughly characterized using Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (H-NMR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The obtained PEG-PLLA was used to prepare nanoparticles encapsulated with perfluoropentane and salicylic acid by the emulsion-solvent evaporation method, resulting in a new dual-mode nano-image probe (PEG-PLLA@SA·PFP). The zeta potential and mean diameter of the obtained nanoparticles were measured using dynamic light scattering (DLS) with a Malvern Zetersizer Nano. The in vitro biocompatibility of the PEG-PLLA nanoparticles was evaluated with cell migration, hemolysis, and cytotoxicity assays. Ultrasonic imaging was performed using an ultrasonic imaging apparatus, and chemical exchange saturation transfer (CEST) MRI was conducted on a 7.0 T animal scanner. The results of IR and NMR confirmed that the PEG-PLLA was successfully synthesized. The particle size and negative charge of the nanoparticles were 223.8 ± 2.5 nm and -39.6 ± 1.9 mV, respectively. The polydispersity of the diameter was 0.153 ± 0.020. These nanoparticles possessed good stability at 4 °C for about one month. The results of cytotoxicity, cell migration, and hemolysis assays showed that the carrier material was biocompatible. Finally, PEG-PLLA nanoparticles were able to significantly enhance the imaging effect of tumors by the irradiation of ultrasound and saturation by a radiofrequency pulse, respectively. In conclusion, these nanoparticles exhibit promising dual-mode capabilities for US/CEST MR imaging.

The nature of insoluble organic matter in Sutter's Mill and Murchison carbonaceous chondrites: Testing the effect of x‐ray computed tomography and exploring parent body organic molecular evolution

AbstractThis study analyzed samples of the Murchison and Sutter's Mill carbonaceous chondrite meteorites in support of the future analysis of samples returned from the asteroid (10155) Bennu by the OSIRIS‐REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission. Focusing specifically on the insoluble organic matter (IOM), this study establishes that a total of 1.3 g of bulk sample from a single chondritic meteorite are sufficient to obtain a wide range of cosmochemical information, including light element analysis (H, C, and N), isotopic analysis (D/H, 13C/12C, and 15N/14N), and x‐ray fluorescence spectroscopy for major elemental abundances. IOM isolated from the bulk meteorite samples was analyzed by light element and isotopic analysis as described above, 1H and 13C solid‐state nuclear magnetic resonance spectroscopy, Raman spectroscopy, and complete noble gas analyses (abundances and isotopes). The samples studied included a pair from Murchison (CM2), one of which had been irradiated with high‐energy x‐rays in the course of computed tomographic imaging. No differences between the irradiated and non‐irradiated Murchison samples were observed in the many different chemical and spectroscopic analyses, indicating that any x‐ray–derived sample damage is below levels of detection. Elemental, isotopic, and molecular spectroscopic data derived from IOM isolated from the Sutter's Mill sample reveals evidence that this meteorite falls into the class of heated CM chondrites.

1H NMR Metabolomics on Pigs' Liver Exposed to Antibiotics Administration: An Explorative Study.

An untargeted Nuclear Magnetic Resonance (NMR) spectroscopy-based metabolomics approach was applied as a first attempt to explore the metabolome of pigs treated with antibiotics. The final goal was to investigate the possibility of discriminating between antibiotic-treated (TX group) and untreated pigs (CTRL group), with the further perspective of identifying the authentication tools for antibiotic-free pork supply chains. In particular, 41 samples of pig liver were subjected to a biphasic extraction to recover both the polar and the non-polar metabolites, and the 1H NMR spectroscopy analysis was performed on the two separate extracts. Unsupervised (principal component analysis) and supervised (orthogonal partial least squares discriminant analysis) multivariate statistical analysis of 1H NMR spectra data in the range 0-9 ppm provided metabolomic fingerprinting useful for the discrimination of pig livers based on the antibiotic treatment to which they were exposed. Moreover, within the signature patterns, significant discriminating metabolites were identified among carbohydrates, choline and derivatives, amino acids and some lipid-class molecules. The encouraging findings of this exploratory study showed the feasibility of the untargeted metabolomic approach as a novel strategy in the authentication framework of pork supply chains and open a new horizon for a more in-depth investigation.

A New Clerodane from the Leaves of Croton krabas and Its Cholinesterase Inhibitory Activities.

Chromatographic separation of the leaves of Croton krabas resulted in the isolation of one new clerodane, crotoeurin D (1), along with two known compounds, 6S-crotoeurin C (2) and blumenol A (3). Their structures were determined based on extensive nuclear magnetic resonance spectroscopic data analysis and mass spectrometry. The absolute configuration of the new clerodane was assigned by nuclear overhauser effect spectroscopy correlations and electronic circular dichroism calculations. Compound 1 exhibited significant acetylcholinesterase and butyrylcholinesterase inhibitory activities. Moreover, the binding modes of 1 revealed that its structure formed strong hydrogen bonds and hydrophobic interactions with the active sites of both enzymes.

Incorporation of exemestane into ternary nanosponge system for enhanced anti-tumor potential in breast cancer

The present investigation reports the potential of exemestane loaded cyclodextrin based nanosponges for the treatment of breast cancer. Fourier transform infrared, and nuclear magnetic resonance (NMR) spectroscopic analysis confirmed the encapsulation of ring B, C, and D of exemestane in the nanosponge cavity. In vitro studies demonstrated a 6.58-folds increase in the aqueous solubility and a 1.76-folds increase in the dissolution of exemestane in the optimized nanosponge formulation EF2. It also exhibited enhanced cytotoxicity in MCF-7 cell line. Pharmacokinetic studies revealed a 1.37-fold increase in C max and a 2.10-fold increase in oral bioavailability of EF2, as compared to its marketed product Aromasin®. Concomitantly, this nano-formulation reduced the tumor burden to 45.71% in a DMBA-induced breast cancer rat model. This EF2-treatment also improved the hematological parameters of the animals. Histopathology of breast tissue also presented reduction in characteristic cytoarchitectural features of breast tumor. In vivo toxicity studies demonstrated reduced hepatotoxicity of the nanosponge formulation when compared with Aromasin®. These results were further supported by histological studies of excised liver tissues, where the size of hepatocytes in EF2-treated animals was like the normal hepatocyte size. In conclusion, the encapsulation of exemestane in β-cyclodextrin nanosponge along-with HPMC E5 improved its aqueous solubility, bioavailability, and ultimately therapeutic efficacy for the treatment of breast cancer.

Pyripyropene U, a new alkaloid from the sponge-derived fungus Aspergillus sp. SCSIO41420

One new alkaloid, named pyripyropene U (1), and six known natural products (2–7) were obtained from the marine sponge-derived fungus Aspergillus sp. SCSIO41420. Their structures were determined by detailed nuclear magnetic resonance (NMR) and mass spectroscopic (MS) analyses, while the absolute configurations of the new compound were unambiguously confirmed by theoretical electronic circular dichroism (ECD) calculation. Those natural products were evaluated in the antimicrobial tests against various fungi and bacteria, and 7 possessed obvious inhibitory activity against Staphylococcus aureus ATCC 29213.

Pathway selection in the self-assembly of Rh4L4 coordination squares under kinetic control

Pathway selection principles in reversible reaction networks such as molecular self-assembly have not been established yet, because achieving kinetic control in reversible reaction networks is more complicated than in irreversible ones. In this study, we discovered that coordination squares consisting of cis-protected dinuclear rhodium(II) corner complexes and linear ditopic ligands are assembled under kinetic control, perfectly preventing the corresponding triangles, by modulating their energy landscapes with a weak monotopic carboxylate ligand (2,6-dichlorobenzoate: dcb–) as the leaving ligand. Experimental and numerical approaches revealed the self-assembly pathway where the cyclization step to form the triangular complex is blocked by dcb–. It was also found that one of the molecular squares assembled into a dimeric structure owing to the solvophobic effect, which was characterized by nuclear magnetic resonance spectroscopy and single-crystal X-ray analysis.

Synthesis, Characterization, and Preliminary Antimicrobial Evaluation of New Schiff Bases and Mannich Bases of Isatin

Till now, isatin derivatives have received a lot of interest in organic and medicinal chemistry due to their significant biological and pharmacological activities. Schiff’s and Mannich bases of isatins are an effective group of heterocyclic derivatives that play a significant role in medicinal chemistry as antimicrobial agents. In light of these facts, new Schiff bases and Mannich bases of isatin were synthesized. The monomer Mannich bases; 3(a-e) have been synthesized by reacting isatin with different secondary amines, piperidine, morpholine, and pyrrolidine, dimethylamine, diphenylamine, separately, and formaldehyde, while the dimer (5) formed by using piperazine and formaldehyde which then react separately with Phenylhydrazine to form new Schiff bases 4(a-e), and dimer Schiff base (6) as final products. The structures of the newly synthesized compounds were identified using two spectroscopic methods; (Fourier- transform infrared) FTIR and proton nuclear magnetic resonance spectroscopy (¹H-NMR) analysis. The preliminary in vitro antibacterial and antifungal screening results of new isatin derivatives [4(a-e) and 6] reported moderate to potent antimicrobial activity, the compound 4c exhibited moderate broad-spectrum antibacterial and antifungal activities compared to other derivatives. Moreover, compounds 4c and 6 have a good inhibitory effect against B. subtilis while amoxicillin (standard drug) shows no activity. For antifungal activity compounds (4a-c and 4e) have considerable activity towards C. albicans, whereas compound 4d exhibits slight activity and 6 of no activity.

Quinolone Tethered 1,2,3-triazole Conjugates: Design, Synthesis, and Computational Docking Studies on New Heterocycles as Potent Antimicrobial Targets

Abstract: The synthesis and biological properties of molecules simultaneously comprising various heterocycles, such as fused 2-quinolones and 1,2,3-triazoles, have been evaluated as a part of our ongoing research in medicinal and organic chemistry. We were successful in developing a synthetic procedure for 1,2,3-triazole substituted quinolone derivatives. Infrared, proton, and carbon nuclear magnetic resonance, mass spectroscopy and elemental analysis were used to characterise the structures of the recently synthesised triazole derivatives. From screening results, all the compounds demonstrated increased antibacterial action against both Gram-positive and Gram-negative bacteria. Moreover, 1,2,3-triazoles linked to tert-butyl benzyl (3a), trifluoromethyl benzyl (3b), 3-chlorobenzyl (3c), 4- hydroxy-3-nitrobenzyl (6b), 4-hydroxy-4-trifluoromethylbenzyl (6d), and 4-hydroxy-2,4- difluorobenzyl (6e) compounds showed promising antibacterial and antifungal activities with MICs values of 1.07-4.33 μg/mL. The prepared ligand 4-hydroxy-2,4-difluoro benzyl-1,2,3-triazole (6e) exhibited the highest docking score of -6.34 kcal/mol and showed interacting amino acid residues ArgB:1122, MetB:1121, AspB:1083, TryB:1087, AlaB:1118, AlaB:1120, GluB:1088, GlyB:1117, SerB:1084, and AlaB:1119 within the active site of 2XCT. Final scaffolds were further evaluated for their ADMET and physicochemical properties by using ADMETlab2.0 and SwissADME web servers as good oral bioavailability drugs.

Functional characterization of a naphthalene-O-methyltransferase from Nocardia sp. CS682

Methylation plays important roles in biosynthesis, metabolism, signal transduction, detoxification, protein sorting and repair, and nucleic acid processing. Generally the methyltransferases transfer methyl groups in various natural products using S-adenosyl methionine (SAM) as a cofactor. In this study, we examined and functionally characterized ThnM3 (enzyme), by testing various substrates with different chemical structures. Among the tested substrates, 1,8-dihydroxynaphthalene was the best substrate for methylation. Whole-cell biotransformation was performed using the enzyme in engineered Escherichia coli to produce 8-methoxynaphthalene-1-ol, and 1,8-dimethoxynaphthalene derivatives of 1,8-dihydroxynaphthalene. The products were confirmed using high-performance liquid chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopic analyses. Therefore, this study is the first to amplify, express the thnM3 (gene), and functionally characterize theThnM3, which exhibits the regioselective modifications of 1,8-dihydroxynaphthalene.

Arthproliferins A-D, Four New Sesterterpenes from the Mangrove-Sediment-Derived Fungus Arthrinium sp. SCSIO41221.

Four new sesterterpenes, arthproliferins A-D (1-4), together with four known derivatives, were isolated and characterized from the mangrove-sediment-derived fungus Arthrinium sp. SCSIO41221. Their structures were determined using detailed nuclear magnetic resonance (NMR) and mass spectroscopic (MS) analyses. Some of the isolated compounds were evaluated for their cytotoxicity in vitro. The results revealed that terpestacin (6) exhibited significant activity with an IC50 value of 20.3 μM, and compounds 2 and 5 were found to show weak inhibitory effects against U87MG-derived GSCs.

Structure elucidation and gene cluster of the O-antigen of Shewanella xiamenensis strain DCB-2-1 containing an amide of d-glucuronic acid with d-alanine and its bonding with U, Cr and V

The aim of this work was to examine the structure and gene cluster of O-OPS of S. xiamenensis strain DCB-2-1 and survey its conceivability for chelating uranyl, chromate and vanadate ions from solution. O-polysaccharide (OPS, O-antigen) was isolated from the lipopolysaccharide of Shewanella xiamenensis DCB-2-1 and studied by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy and sugar analysis. The following structure of the brunched pentasaccharide was established: [Display omitted] where d-β-GlcpA(d-Ala) is d-glucuronic acid acylated with NH group of d-Ala. The OPS structure established is unique among known bacterial polysaccharide structures. Interestingly, that dN-(d-glucuronoyl)-d-alanine derivative is not found in bacterial polysaccharides early.The O-antigen gene cluster of Shewanella xiamenensis strain DCB-2-1 has been sequenced. The gene functions were tentatively assigned by comparison with sequences in the available databases and found to be in agreement with the OPS structure. Based on the analysis of the IR spectra of the isolated polysaccharide DCB-2-1 and the products of its interaction with UO2(NO3)2 ∗ 6H2O, NH4VO3 and K2Cr2O7, a method of binding them can be proposed. Laboratory experiments show that the use of polysaccharide can be effective in removing uranyl, chromate and vanadate from solution.

Controllable Topological Transformations of 818 Molecular Metalla-knots by Oxidation of Thiazole-Based Ligands.

By exploiting coordination-driven self-assembly, high yields of two 818 molecular metalla-knots could be obtained using a thiazole-moiety-containing asymmetric dipyridyl ligand 2-(pyridin-4-yl)-5-(pyridin-4-ylethynyl)benzo[d]thiazole (L1 ), as confirmed using X-ray crystallographic analysis, electrospray ionization-time-of-flight/mass spectrometry (ESI-TOF/MS), and detailed liquid-state nuclear magnetic resonance (NMR) spectroscopy. To modulate the self-assembled structures, m-chloroperbenzoic acid (m-CPBA) was utilized to oxidize thiazole-based ligand L1 to N-thiazole-oxide-based ligand 2-(pyridin-4-yl)-5-(pyridin-4-ylethynyl)benzo[d]thiazole 3-oxide (L2 ), which enabled the selective construction of the corresponding tetranuclear macrocycles. Notably, two molecular metalla-knots could be topologically transformed from 818 knots to simple monocycles because the L1 alkyne bond was inert toward m-CPBA, as confirmed by liquid-state NMR spectroscopy, ESI-TOF/MS, and elemental analysis.

Evaluation of NMR-based strategies to differentiate fresh from frozen-thawed fish supported by multivariate data analysis

The differentiation of fresh and frozen-thawed fish is a relevant authenticity aspect as in the European Union fish holds a high statistical risk of being adulterated. Here, nuclear magnetic resonance spectroscopy (NMR) in combination with principal components analysis followed by linear discriminant analysis (PCA-LDA) was used for a non-targeted based differentiation of fresh from frozen-thawed fish. To identify the most promising NMR approach(es), six different approaches were applied to 96 fish samples (mackerel, trout, cod). These approaches included different sample preparation procedures and different NMR methods to investigate both the lipid fraction and the polar fraction of the fish samples. After cross-validation embedded in a Monte Carlo resampling design, six independent classification models were obtained. Evaluation of the multivariate data analysis revealed that the most promising approaches were the 1H NMR analysis of the lipid fraction (correct prediction of about 90.0%) and the 1H NMR based screening of minor components of the lipid fraction with a correct prediction of about 91.9%. 1H NMR analysis of the water extract of the fish samples showed a correct prediction of about 82.6%. Hence, a general differentiation of fresh from frozen-thawed fish via non-targeted NMR is feasible, even though the underlying sample batch contained different fish species. Additional fish samples need to be analyzed with the three most promising NMR approaches to further improve the developed classification models.