NMR Spectroscopy Experiments Research Articles

Recycled PLA for 3D Printing: A Comparison of Recycled PLA Filaments from Waste of Different Origins after Repeated Cycles of Extrusion.

The objective of this work is to evaluate the reprocessing of PLA 3D printing waste from different origins, into filaments and films, and without the addition of any additive. Two types of waste were considered: a blend of different printing wastes (masks, visors, other components) of personal protective equipment coming from an association of Spanish coronamakers, and PLA waste from a single known commercial source. Both types of materials were subjected to repeated extrusion cycles and processed into films by compression molding. Samples were characterized after each cycle and their mechanical and viscosity properties evaluated. Diffusion-ordered NMR spectroscopy (DOSY) experiments were also carried out to estimate molecular weights. The results show a better performance for the PLA waste from the known origin, capable of withstanding up to three re-extrusion cycles per two for the waste blending, without significant degradation. Additionally, a model to address collection and mechanical recycling cycles under two different scenarios (full traceability and not full traceability) was proposed.

A fast and reliable method to quantify neral and geranial (citral) in essential oils using 1H NMR spectroscopy

AbstractCitral (3,7‐dimethyl‐2,6‐octadienal), a mixture of geranial and neral (two stereoisomeric monoterpene aldehydes), is considered an important raw material in the fields of fragrance, pharmaceutical, food and cosmetic industries. It is a well‐known biologically active compound present in various essential oils. A fast and reliable experimental method was developed and validated in order to quantify citral in essential oils using 1H NMR spectroscopy (experiment time at the minute level). The quantitative procedure, using anisole as internal standard, showed a perfect linearity of measurements (R2 = 0.9999), a very good accuracy (relative errors comprised between −1.9% and 0.3%) and an excellent precision (reproducibility 17.8 mg ± 1.0%). The procedure was also checked with three mixtures of weighted monoterpenes and the contents of citral, measured by GC and 1H NMR, were absolutely comparable. Then, the method was successfully applied to measure the contents of citral in 10 commercially available essential oils. Among the investigated samples, citral varied from 2.9% (Zingiber officinalis) to 90.6% (Bakhousia citriodora).

Targeted and Logical Discovery of Piperazic Acid-Bearing Natural Products Based on Genomic and Spectroscopic Signatures.

A targeted and logical discovery method was devised for natural products containing piperazic acid (Piz), which is biosynthesized from ornithine by l-ornithine N-hydroxylase (KtzI) and N-N bond formation enzyme (KtzT). Genomic signature-based screening of a bacterial DNA library (2020 strains) using polymerase chain reaction (PCR) primers targeting ktzT identified 62 strains (3.1%). The PCR amplicons of KtzT-encoding genes were phylogenetically analyzed to classify the 23 clades into two monophyletic groups, I and II. Cultivating hit strains in media supplemented with 15NH4Cl and applying 1H-15N heteronuclear multiple bond correlation (HMBC) along with 1H-15N heteronuclear single quantum coherence (HSQC) and 1H-15N HSQC-total correlation spectroscopy (HSQC-TOCSY) NMR experiments detected the spectroscopic signatures of Piz and modified Piz. Chemical investigation of the hit strains prioritized by genomic and spectroscopic signatures led to the identification of a new azinothricin congener, polyoxyperuin B seco acid (1), previously reported chloptosin (2) in group I, depsidomycin D (3) incorporating two dehydropiperazic acids (Dpz), and lenziamides A and B (4 and 5), structurally novel 31-membered cyclic decapeptides in group II. By consolidating the phylogenetic and chemical analyses, clade-structure relationships were elucidated for 19 of the 23 clades. Lenziamide A (4) inhibited STAT3 activation and induced G2/M cell cycle arrest, apoptotic cell death, and tumor growth suppression in human colorectal cancer cells. Moreover, lenziamide A (4) resensitized 5-fluorouracil (5-FU) activity in both in vitro cell cultures and the in vivo 5-FU-resistant tumor xenograft mouse model. This work demonstrates that the genomic and spectroscopic signature-based searches provide an efficient and general strategy for new bioactive natural products containing specific structural motifs.

Griseofulvin analogues from the fungus Penicillium griseofulvum and their anti-inflammatory activity

Six griseofulvin analogues named penigriseofulvins A − F (1–6), including three undescribed compounds and three undescribed natural products, were isolated from the fungus Penicillium griseofulvum. Their structures and absolute configurations were determined by NMR spectroscopic analyses, HRESIMS, and X-ray diffraction experiments. All compounds were evaluated for their anti-inflammatory activity, of which compounds 1 and 4 showed potential anti-inflammatory effects in RAW264.7 macrophages and ulcerative colitis mice.

Structural Investigation on How Guest Loading of Poly(2-oxazoline)-Based Micelles Affects the Interaction with Simulated Intestinal Fluids.

Drug loading of polymer micelles can have a profound effect on their particle size and morphology as well as their physicochemical properties. In turn, this influences performance in biological environments. For oral delivery of drugs, the intestinal environment is key, and consequently, a thorough structural understanding of what happens at this material-biology interface is required to understand in vivo performance and tailor improved delivery vehicles. In this study, we address this interface in vitro through a detailed structural characterization of the colloidal assemblies of polymeric micelles based on poly(2-oxazolines) with three different guest loadings with the natural product curcumin (17-52 wt %) in fed-state simulated intestinal fluids (FeSSIF). For this, we employ NMR spectroscopy, in particular, 1H NMR, 1H-1H-NOESY, and 1H DOSY experiments complemented by quantum chemical calculations and cryo-TEM measurements. Through this mixture of methods, we identified curcumin-taurocholate interactions as central interaction patterns alongside interactions with the polymer and lipids. Furthermore, curcumin molecules can be exchanged between polymer micelles and bile colloids, an important prerequisite for their uptake. Finally, increased loading of the polymer micelles with curcumin resulted in a larger number of vesicles as taurocholate─through coordination with Cur─is less available to form nanoparticles with the lipids. The loading-dependent behavior found in this study deviates from previous work on a different drug substance highlighting the need for further studies including different drug molecules and polymer types to improve the understanding of events on the molecular level.

Binaphthyl-Based Chiral Macrocyclic Hosts for the Selective Recognition of Iodide Anions.

In this study, we explorethe synthesis of binaphthyl-based chiral macrocyclic hosts for the first time. They exhibited the selective recognition abilities of iodide anions which can be favored over those of other anions (AcO-, NO3-, ClO4-, HSO4-, Br-, PF6-, H2PO4-, BF4-, and CO3F3S-), as confirmed by UV-vis, HRMS, and 1H NMR spectroscopy experiments, as well as DFT calculations. Neutral aryl C-H···anion interactions play an important role in the formation complexes. The recognition process can be observed by the naked eye.

DIABETES INDUCED LIPID PANEL PARTICULARITIES IN HYPERTENSIVE PATIENTS: A PILOT NMR SPECTROSCOPY STUDY

Objective: Cardiovascular diseases are the leading cause of death globally, despite significant advances in diagnosis and treatment. Among the multiple already well-known cardiovascular risk factors, hypertension, diabetes mellitus type II and dyslipidaemia are the most frequent and show the best correlations with the risk of further developing a major cardiovascular event. The main objective consists in identifying the potential particularities that diabetes could have on the lipid profile in hypertensive patients, while also discovering bio-markers with a higher potential accuracy of predicting further major cardiovascular events, using NMR spectroscopy. Design and method: We have selected a group of 30 hypertensive patients and a control group of 17 otherwise healthy individuals in order to assess the influence of diabetes on the lipid panel in hypertensive patients. A blood sample of 6 mL was collected before and after meals and 5 types of NMR spectroscopy experiments were performed for each sample. Results: It was noted that the fasten triglycerides levels, VLDL and IDL particle number, apolipoprotein A1, A2, B100 levels, as well as the ratio apolipoprotein B100/apolipoprotein A1 are all potentially useful markers that could be successfully used to differentiate between the strictly hypertensive patients and the ones that associate type II diabetes mellitus. The study also confirmed once more our previous reports that the fasting status upon sampling has little influence on the lipid panel final values. Conclusions: We have evaluated the lipid panel differences induced by diabetes mellitus type II in hypertensive patients and we have compared the results with an otherwise healthy control group. We have identified the NMR spectroscopy markers that could be able to spot subtle differences in the lipid profiles of the two study groups (two hypertensive groups, one consisting in strictly hypertensive patients, the other one including hypertensive patients with already known type II diabetes mellitus), even when LDL levels have been lowered to normal levels due to statin treatment. We have once more concluded that the patient's fasting status has no influence on the final analysis.

A fluorescent receptor for alkylammonium ions based on an anthryl-linked triazole-modified hexahomotrioxacalix[3]arene

A novel C3-symmetrical anthracene-functionalized hexahomotrioxacalix[3]arene L was synthesized via Click chemistry and its chemosensing properties with alkylammonium ions were investigated. The significant fluorescence enhancements were observed with addition of alkylammonium ions (including primary and tertiary ones), indicating a high selectivity for alkylammonium ions. Our studies demonstrated that the detection limit on fluorescence response of the sensor to is in the 10–6 M range. The mechanism of the interaction between the L and alkylammonium ions has been investigated in detail by 1H NMR spectroscopic titration experiments. Density functional theory (DFT) quantum chemical calculations were conducted to estimate the electronic interaction energies (ΔIE) between the chemosensor L and alkylammonium ions.

The first example of synthesis of a new class of spiroboracarbocycles <i>via</i> cycloboration of methylenecycloalkanes with PhBCl<sub>2</sub> catalyzed by Cp<sub>2</sub>TiCl<sub><sub>2 </sub></sub>

Cp2TiCl2-catalyzed cycloboration of methylenecycloalkanes with PhBCl2 in the presence of metallic Mg to obtain a novel spiroboracarbocycles in good yields (70-80%) is reported for the first time. The structure and properties of spiro-fused boriranes were studied using 11B, 1H, 13C NMR spectroscopy and DOSY experiments. 1-Phenyl-substituted boraspiranes are stable in solution at room temperature for a day.

1H DOSY analysis of high molecular weight acrylamide-based copolymer electrolytes using an inverse-geometry diffusion probe

Copolymers of [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETAC) and acrylamide (AAm) (AETAC-co-AAm) are polyelectrolytes used as flocculants in wastewater purification. Diffusion-ordered two-dimensional NMR spectroscopy (DOSY) experiments for AETAC-co-AAm samples with Mw ranging from 1.9 to 3.9 million and a polyacrylamide sample with Mw of 1.3 million were carried out in pure D2O and in D2O containing 0.1 or 1 M NaCl using an inverse-geometry diffusion probe system. Projections of the DOSY contour plots onto the diffusion coefficient (D) dimension gave distributions of D for the AETAC and AAm units in the samples. The D values at the maximum point of the distribution (Dp) agreed fairly well with those determined by dynamic light scattering.

Type-I Hemins and Free Porphyrins from a Western Australian Sponge Isabela sp.

Two novel free porphyrins, isabellins A and B, as well as the known compounds corallistin D and deuteroporphyrin IX were isolated from a marine sponge Isabela sp. LC-MS analysis of the crude extract revealed that the natural products were present both as free porphyrins and iron(III) coordinated hemins, designated isabellihemin A, isabellihemin B, corallistihemin D and deuterohemin IX, respectively. Structures were determined via high-resolution mass spectrometry, UV-Vis spectroscopy and extensive NOESY NMR spectroscopic experiments. The type-I alkyl substitution pattern of isabellin A and isabellihemin A was assigned unambiguously by single crystal X-ray diffraction. Biological evaluation of the metabolites revealed potent cytotoxicity for isabellin A against the NS-1 murine myeloma cell line.

Conformational flexibility of the disaccharide β-L-Fucp-(1→4)-α-D-Glcp-OMe as deduced from NMR spectroscopy experiments and computer simulations.

Carbohydrates in biological systems are referred to as glycans and modification of their structures is a hallmark indicator of disease. Analysis of the three-dimensional structure forms the basis for further insight into how they function and comparison of crystal structure with solution-state conformation(s) is particularly relevant, which has been performed for the disaccharide β-L-Fucp-(1→4)-α-D-Glcp-OMe. In water solution the conformational space at the glycosidic linkage between the two sugar residues is identified from molecular dynamics (MD) simulations as having a low-energy exo-syn conformation, deviating somewhat from the solid-state conformation, and two anti-conformational states, i.e., anti-ϕ and anti-ψ, indicating flexibility at the glycosidic linkage. NMR data were obtained from 1D 1H,1H-NOESY and STEP-NOESY experiments, measurement of transglycosidic 3JCH coupling constants and NMR spin-simulation. The free energy profile of the ω torsion angle computed from MD simulation was in excellent agreement with the rotamer distribution from NMR experiment being for gt:gg:tg 38 : 53 : 9, respectively, with a proposed inter-residue O5'⋯HO6 hydrogen bond being predominant in the gg rotamer. Quantum mechanics methodology was used to calculate transglycosidic NMR 3JCH coupling constants, averaged over a conformational ensemble of structures representing various rotamers of exocyclic groups, in good to excellent agreement with Karplus-type relationships previously developed. Furthermore, 1H and 13C NMR chemical shifts were calculated using the same methodology and were found to be in excellent agreement with experimental data.

Visualizing metabolomics data with R.

In communicating scientific results, convincing data visualization is of utmost importance. Especially in metabolomics, results based on large numbers of dimensions and variables necessitate particular attention in order to convey their message unambiguously to the reader; also, in the era of open science, traceability and reproducibility are becoming increasingly important. This article describes the use of the R programming language to visualize published metabolomics data resulting from ex vivo NMR spectroscopy and mass spectrometry experiments with a special focus on reproducibility, including example figures as well as associated R code for ease of reuse. Examples include various types of plots (bar plots, swarm plots, and violin plots; volcano plots, heatmaps, Euler diagrams, Kaplan-Meier survival plots) and annotations (groupings, intragroup line connections, significance brackets, text annotations). Advantages of code-generated plots as well as advanced techniques and best practices are discussed.

Bioassay-guided isolation of Fenghuang Dancong tea constituents with α-glucosidase inhibition activities.

An α-glucosidase inhibition assay showed the ethanolic extract of Fenghuang Dancong tea had potential α-glucosidase inhibitory activity. The most bioactive fraction, which was obtained via bioassay-guided isolation of the extract, was further purified to create five compounds, including three novel compounds (1-3). These compounds were analyzed and identified in detail using high-resolution-mass spectrometry and extensive one-dimensional and two-dimensional NMR spectroscopy experiments. Among the compounds, compound 1 contained cis double bonds and showed the strongest α-glucosidase inhibitory activity with an IC50 value of 7.51 μM, which is significantly lower than that of compound 2 with trans double bonds. Enzyme kinetic experiments showed that 1 was a reversible non-competitive α-glucosidase inhibitor.

Lavender (Lavandula angustifolia Mill.) industrial by-products as a source of polysaccharides

Apart from the main aroma products, the lavender essential oil industry generates huge quantities of undervalorized biomass, which was discarded nearby to the distilleries or used as a fertilizer. Therefore, the current study was performed to explore the hypothesis that the lavender waste biomass could be additionally utilized as a source of polysaccharides . An industrial residue from supercritical CO 2 -extraction (CO2-L) and steam-distilled lavender (SD-L) were used as source material after preparing the alcohol-insoluble material. Acid-soluble polysaccharides (ASPs) were obtained from CO2-L (6.97 ± 0.14%) and SD-L (5.95 ± 0.23%). The monosaccharide composition revealed that polysaccharides were composed mainly of galacturonic acid 672.44 ± 4.89 µg mg −1 (CO2-L) and 619.17 ± 5.23 µg mg −1 (SD-L). The ASPs were characterized by a medium degree of methyl-esterification (50%) and a low degree of acetylation (<3%). The pectin nature of lavender ASPs was confirmed by infrared and NMR spectroscopy experiments. ASPs’ gelling behavior was investigated by examination of high sucrose (1.25% polysaccharide and 60% sugar (w/w)) and Ca 2+ (1.25% polysaccharide (w/w) and 6 mmol/L Ca 2+ ) gel systems and compared with the gelation of two commercial citrus pectins. Both CO2-L and SD-L ASP were able to produce Ca 2+ gels, while in the presence of sucrose only the CO2-L polysaccharide yielded gel. ASPs were included in the hand cream formulation. It was found that both polysaccharides increased the apparent viscosity compared to the control hand cream. This might lead to the conclusion that lavender wastes could be regarded as a natural source of polysaccharides having valuable properties to enable incorporation into cosmetic products. • Lavender by-products from CO 2 extraction (CO2-L) and distillation (SD-L) were studied. • CO2-L and SD-L yielded 6.97 ± 0.14% and 5.95 ± 0.23% polysaccharides, respectively. • Monosaccharide composition and NMR studies suggested pectic type structure. • CO2-L and SD-L polysaccharides yielded relatively strong gels in presence of Ca 2+ . • CO2-L and SD-L polysaccharides increased the apparent viscosity of hand creams.

Programming xenon diffusion in maltose-binding protein

Protein interiors contain void space that can bind small gas molecules. Determination of gas pathways and kinetics in proteins has been an intriguing and challenging task. Here, we combined computational methods and the hyperpolarized xenon-129 chemical exchange saturation transfer (hyper-CEST) NMR technique to investigate xenon (Xe) exchange kinetics in maltose-binding protein (MBP). A salt bridge ∼9 Å from the Xe-binding site formed upon maltose binding and slowed the Xe exchange rate, leading to a hyper-CEST 129Xe signal from maltose-bound MBP. Xe dissociation occurred faster than dissociation of the salt bridge, as shown by 13C NMR spectroscopy and variable-B1 hyper-CEST experiments. “Xe flooding” molecular dynamics simulations identified a surface hydrophobic site, V23, that has good Xe binding affinity. Mutations at this site confirmed its role as a secondary exchange pathway in modulating Xe diffusion. This shows the possibility for site-specifically controlling xenon protein-solvent exchange. Analysis of the available MBP structures suggests a biological role of MBP’s large hydrophobic cavity to accommodate structural changes associated with ligand binding and protein-protein interactions.

The Synthesis of Novel P,N-Ferrocenylpyrrolidine-Containing Ligands and Their Application in Pd-Catalyzed Allylic Alkylation – A Synthetic and Mechanistic Investigation

AbstractThe synthesis of a series of planar chiral P,N-ferrocenylpyrrolidine-containing ligands, with varying substituents at the phosphorus donor atom, is described. The phosphorus donor atom was introduced via a diastereoselective ortho-directed metalation of N-methylpyrrolidinyl ferrocene followed by a quench with various chlorophosphines. These P,N systems are very active in Pd-catalyzed allylic alkylation of 1,3-diphenylpropenyl acetate with dimethylmalonate (conversions of up to 100%) and demonstrated good levels of enantioselectivity (up to 85% ees). Good selectivity for the (R)-enantiomer was observed and mechanistic studies, involving X-ray crystallography and NMR spectroscopic experiments, were employed to help rationalize the observed stereochemical outcome of the reaction.

Comparative CO2 Hydrogenation Catalysis with MACHO-type Manganese Complexes

A pair of manganese complexes containing MACHO-type pincer ligands bearing a secondary amine, [HN{CH2CH2(PiPr2)}2]MnH(CO)2, which can participate in pathways involving metal–ligand cooperation (MLC), and a tertiary amine, [MeN{CH2CH2(PiPr2)}2]MnH(CO)2, which cannot participate in pathways involving MLC, are compared for the hydrogenation of CO2 to formate in the presence of a base. Lewis acid cocatalysts are crucial for increasing the activity of both catalysts, with [MeN{CH2CH2(PiPr2)}2]MnH(CO)2 reaching TONs of up to 18,300 and yields of up to 73% in the presence of lithium triflate. This productivity is far greater than for the MLC capable secondary amine MACHO-supported manganese catalyst. Preliminary mechanistic experiments indicate that CO2 insertion into the Mn–H of each catalyst affords a stable manganese formate complex. In situ NMR spectroscopy and comparative catalytic experiments are consistent with the intermediacy of these manganese formate complexes in the catalytic cycle, likely representing the catalyst resting states. Our findings suggest that the tertiary amine ligated system gives greater productivity due to a combination of longer catalyst lifetime and greater enhancement from Lewis acid additives.

Bis-benzimidazolium salts as bifunctional organocatalysts for the cycloaddition of CO2 with epoxides

A series of 1,2-bis(benzimidazolium)ethane dihydrohalide salts was prepared and characterized, including five structures elucidated by single-crystal X-ray diffraction. These compounds were tested as organocatalysts for the cycloaddition reaction of CO2 with epoxides to produce cyclic carbonates. Effects of counteranions, N-substituents and C-5 substituents, and how they affect solubility in the catalytic system, were evaluated. The salts containing 1,2-bis(5-methyl-benzimidazolium)ethane cation presented the best activities and the one with bromide as counteranion (2Br) was selected to carry out a study of several parameters of the catalytic system. Various epoxides could be selectively converted to the respective cyclic carbonate and, reuse experiments were conducted, showing that catalyst 2Br can be reused at least six times, with no decline in conversion and selectivity. In addition, a catalytic mechanism was carefully proposed, taking into account 1H NMR spectroscopy experiments. Simple, nontoxic and low cost synthetic route to obtain the catalysts, as well as the high conversions using low catalyst loading, make this class of catalysts promising for the use of carbon dioxide in the production of cyclic carbonates.

Illustrating the overall reaction network of the synthesis-gas-to-hydrocarbons process over iron-zeolite bifunctional catalysis

Since its discovery in the early 20 th century, Fischer-Tropsch synthesis (FTS) has opened a path, as an alternative to crude oil, to produce fuels and chemicals. When classical FTS catalysts are combined with acidic zeolites, the scope of this gas-phase polymerization can be narrowed, thus maximizing the production of value-added commodities and eliminating energy-consuming separation steps. However, from a mechanistic standpoint, even now, little is known about the role of the different reaction intermediates. Here, we present a comprehensive, in-depth, mechanistic investigation using solid-state NMR spectroscopy and well-designed control experiments on combining a classical Fe-based FTS catalyst and zeolites with different topologies to establish the impact of “co-catalytic” key organic carbon-based reaction intermediates, including carbonylated/oxygenated species (ester/ketone/alcohol/ether/epoxide/ketene). Consequently, this work provides experimental evidence supporting the “co-existence” of oxygenate (cf. surface-enol and CO-insertion) mechanisms (together with the traditional carbide-based FTS mechanism). The significance of “supramolecular reactive centers” within zeolite and host-guest chemistry has also been illuminated. • Zeolite topologies altered preferential hydrocarbon product selectivities • Mobility-based solid-state NMR identified crucial carbon-based reaction intermediates • Co-involvement of oxygenated/carbonylated species is evaluated during syngas conversion • Significance of inorganic-organic supramolecular reaction centers has been established To alleviate pressure from increased environmental regulations over carbon emissions, the direct hydrogenation of CO/CO 2 to diverse hydrocarbons over bifunctional catalysts is a priority research topic worldwide. Identifying new catalytic routes to valorize C1-feedstock is a key to combating climate change, whereby Fischer-Tropsch synthesis (FTS) over bifunctional metal-zeolite catalysts offers elegant solutions to diversify global fuel/chemical supply. However, their overall reaction network to deliver preferential final product selectivity remains elusive and controversial. Through this work, we achieve this goal by identifying key carbon-based reaction intermediates and establishing a full reaction network of the synthesis-gas-to-hydrocarbons process over Fe 2 O 3 @KO 2 /zeolite catalyst. This established structure-reactivity relationship can upgrade the current FTS process and improve the fundamental understanding of bifunctional catalysis. Identifying “descriptor”-style carbon-based reaction intermediates is significant in upgrading the current state of metal-zeolite bifunctional “cascade” catalysis. In this work, four different product selectivities (short olefins, light paraffins, long-chain hydrocarbons, and aromatics) were observed during the syngas-to-hydrocarbon process (Fischer-Tropsch type) over potassium superoxide-doped iron oxide/zeolite-based bifunctional catalysts. Here, we demonstrate that the zeolite topology and “co-catalytic” hybrid supramolecular reactive centers (i.e., organic hydrocarbons pool species trapped by the inorganic zeolite) regulate the reaction mechanism and the final product selectivity.