Analysis Of NMR Spectra Research Articles

Syndiospecific Copolymerization of Styrene with para-Methoxystyrene Catalyzed by Functionalized Fluorenyl-Ligated Rare-Earth Metal Complexes.

The development of efficient catalysts for the copolymerization of nonpolar monomers with polar monomers remains a great challenging task in polymer synthesis. A one-pot reaction of anhydrous LnCl3 with pyridyl-methylene-functionalized octamethylfluorenyl lithium OctFlu-CH2PyLi in a 1:1 molar ratio, followed by alkylation with 2 equiv of LiCH2SiMe3 in THF afforded the fluorenyl-ligated rare-earth metal bis(alkyl) complexes (OctFlu-CH2Py)Ln(CH2SiMe3)2(THF) [Ln = Sc (1), Y (2)]. Both complexes were isolated as neutral species and were characterized by NMR spectrum and elemental analysis. Complex 2 was subjected to single-crystal X-ray diffraction, which showed that the whole modified fluorenyl ligand was coordinated to Y3+ in the η5/κ1 mode to form a constrained geometry configuration. In the presence of excess AliBu3, and on activation with 1 equiv of [Ph3C][B(C6F5)4] in toluene, complexes 1 and 2 became active for both styrene (St) and para-methoxystyrene (pMOS) polymerization, giving polymers with high syndiotacticity (rrrr > 99%) without solvent extraction. Moreover, the ternary catalyst system composed of complex 2/AliBu3/[Ph3C][B(C6F5)4] was highly effective for the syndiospecific copolymerization of styrene with pMOS, producing random copolymers with high molecular weights and narrow molecular weight distributions. The contents of pMOS in the copolymers could be easily tuned in a wide range (11-93 mol %) by simply changing the pMOS-to-St feed ratios.

Optimization of conditions for the synthesis of calyx[4]resorcinol conformers containing 4-dimethylammoniophenyl fragments on the lower rim of the molecule based on the response surface methodology using three-level box-behnken plans

The response surface methodology using three-level Box-Behnken plans was applied in order to optimize the yield of the cone and chair conformers in the synthesis of calix[4]resorcinol functionalized with 4-dimethylammoniophenyl group along the lower rim. We used data from one-factor experiments in which the temperature, reaction time, and molar ratio of HCl to the reactants of the reaction mixture were varied to plot the response surfaces. The ratio of conformers was calculated based on the analysis of 1H NMR spectra of the products isolated from the reaction mixture. The adequacy of the proposed mathematical models for determining the yields of chair and cone conformations is confirmed by a high correlation coefficient ( R 0.99979). Optimal conditions were found for the maximum yield of the chair conformation (50°C, 2 h, molar ratio of HCl to reagents in the reaction mixture is 1-1.5, yield 100%). The optimal conditions for obtaining the cone conformation are: temperature 68.6°С, stirring time in the range of 2.24-6.44 h and the molar ratio of HCl to reagents in the reaction mixture is 2. Carrying out the synthesis under these conditions leads to the yield of the cone conformation in the range of 57.70-58.07%.

Investigation of the extraction ability and mechanism of environmentally friendly ionic liquids for phenol in the model oil

The large number of phenolic compounds contained in coal tar and coal-converted oil seriously increased their cost of processing and transportation difficulties, so methods for efficient separation of phenolic compounds is of great industrial significance. Based on the flexible designability of ionic liquids, hydroxyl functional group that can interact with phenol were introduced into ionic liquid’s cations, eight ionic liquids were synthesized and their separation properties of phenol in model oil (methylbenzene) were studied. Cations of these ionic liquids have a significant influence the phenol extraction efficiency, which follows the order: [Ch]+ > [HEMIM]+. But the anions show a relatively small influence, and the order is: [Pro]- > [Lac]- > [Gly]- > [Ac]-. Other effects such as extraction temperature, molar ratio of phenol to ILs, extraction time and other factors on the extraction efficiency and distribution coefficient were investigated, also the optimum parameters were obtained. Hydroxyl modified ionic liquids showed good extraction performance for phenol, and the choline propionate ionic liquids showed the best separating capacity and were selected as the best extractant. The extraction performance was analyzed by 1H NMR and FT-IR spectra analysis. Hydrogen bond was confirmed to be one of the extraction mechanisms and we found that there was an optimal distance between the cation and anion of ionic liquids to form hydrogen bonds with phenol, also the π-π interaction between imidazole ring and benzene ring in phenol contributed to the extraction. In addition, the ionic liquid showed good recyclability and the regenerated ionic liquids could be reused five times with highly extraction efficiency.

Chilensosides E, F, and G—New Tetrasulfated Triterpene Glycosides from the Sea Cucumber Paracaudina chilensis (Caudinidae, Molpadida): Structures, Activity, and Biogenesis

Three new tetrasulfated triterpene glycosides, chilensosides E (1), F (2), and G (3), have been isolated from the Far-Eastern sea cucumber Paracaudina chilensis (Caudinidae, Molpadida). The structures were established based on extensive analysis of 1D and 2D NMR spectra and confirmed by HR-ESI-MS data. The compounds differ in their carbohydrate chains, namely in the number of monosaccharide residues (five or six) and in the positions of sulfate groups. Chilensosides E (1) and F (2) are tetrasulfated pentaosides with the position of one of the sulfate groups at C-3 Glc3, and chilensoside G (3) is a tetrasulfated hexaoside. The biogenetic analysis of the glycosides of P. chilensis has revealed that the structures form a network due to the attachment of sulfate groups to almost all possible positions. The upper semi-chain is sulfated earlier in the biosynthetic process than the lower one. Noticeably, the presence of a sulfate group at C-3 Glc3-a terminal monosaccharide residue in the bottom semi-chain of compounds 1 and 2-excludes the possibility of this sugar chain's further elongation. Presumably, the processes of glycosylation and sulfation are concurrent biosynthetic stages. They can be shifted in time in relation to each other, which is a characteristic feature of the mosaic type of biosynthesis. The hemolytic action of compounds 1-3 against human erythrocytes and cytotoxic activities against five human cancer cell lines were tested. The compounds showed moderate hemolytic activity but were inactive against cancer cells, probably because of their structural peculiarities, such as the combination of positions of four sulfate groups.

NMRtist: an online platform for automated biomolecular NMR spectra analysis.

We present NMRtist, an online platform that combines deep learning, large-scale optimization and cloud computing to automate protein NMR spectra analysis. Our website provides virtual storage for NMR spectra deposition together with a set of applications designed for automated peak picking, chemical shift assignment and protein structure determination. The system can be used by non-experts and allows protein assignments and structures to be determined within hours after the measurements, strictly without any human intervention. NMRtist is freely available to non-commercial users at https://nmrtist.org. Supplementary data are available at Bioinformatics online.

Alkaloids and Iridoids From the Aerial Parts of Rauvolfia cambodiana Pierre ex Pit. and Their Acetylcholinesterase Inhibitory Activity

Objective: Rauvolfia cambodiana has been used as a Vietnamese folk medicine to treat high blood pressure and for sedation and memory loss diseases. However, to date, there have been few studies on the chemical constituents and biological activity of this medicinal plant. This study aimed to find the chemical constituents of R cambodiana and evaluate their enhancement memory properties. Methods: The aerial parts of R cambodiana were powdered and ultrasonically extracted with methanol. The methanol extract was suspended in water and successively partitioned with dichloromethane and ethyl acetate to give dichloromethane, ethyl acetate, and water-soluble extracts. Each extract was fractionated and purified by column and HPLC chromatographic methods. The chemical structures of the isolated compounds were elucidated by analysis of HRESIMS, 1D and 2D NMR spectra, and experimental and TD-DFT calculated ECD spectra. The enhancement memory property of the compounds was evaluated by their in vitro acetylcholinesterase inhibitory activity. Results: Five alkaloids (1-5) and 2 iridoids (6 and 7), including one new one named rauvolcambonine (1), and 6 known compounds, perakine (2), ajmaline (3), 10-hydroxy-16- epi-affinine (4), sitsirikine (5), loganic acid (6), and secoxyloganin (7) were isolated and identified from the aerial parts of R cambodiana. Compounds 4 and 5 significantly showed acetylcholinesterase inhibitory effects in vitro with IC50 values of 30.1 ± 1.4 µM and 65.5 ± 3.3 µM, respectively. The other compounds inhibited acetylcholinesterase with IC50 values ranging from 111.0 ± 6.0 µM to 197.6 ± 19.8 µM. Conclusion: One new (1) and 3 other compounds (2, 4-7) were recorded from R cambodiana for the first time. The NMR spectroscopic data of compound 4 are reported herein for the first time. Our study preliminarily revealed that the vobasenal framework type alkaloids could be active ingredients of Rauvolfia species and responsibility for the enhancement memory property of these plants.

Fully automated analysis of NMR data with Bayesian nonparametric statistical learning.

The characterization of individual peaks in NMR spectra is an important but challenging step in the investigation of complex biomolecular systems. The major challenge arises due to peak identification which, conventionally, occurs prior to peak characterization. Unluckily, the identification of uncharacterized peaks is highly problematic because of noise and, most importantly, substantial overlap with nearby peaks. For this reason, often the analysis of NMR spectra proceeds by first relying on experts’ opinion to identify peaks and subsequent parameter fitting. Mathematically, peak identification is a problem of model selection and, within a nonparametric analysis framework, can be avoided altogether, this way eliminating the need for experts’ input. In this study, we apply Bayesian nonparametric statistics to develop a comprehensive mathematical framework for automated peak identification and characterization. Our approach relies on advanced statistical representations of FIDs and allows for: simultaneous identification and characterization of individual peaks in an NMR spectrum, accurate noise deconvolution, and extensions to multidimensional NMR or incorporation of specialized protocols. We show that our methods can correctly identify and characterize overlapping peaks without user input. We benchmark our analyses against ground truth peak characteristics using synthetic as well as experimental datasets.

Analysis on the caged structure of polyhedral oligomeric dodecaphenyl silsesquioxane and its condensation mechanism

Polyhedral oligomeric dodecaphenyl silsesquioxane (DPS) and octaphenyl silsesquioxane (OPS) are two kinds of caged inorganic-organic hybrids and high thermal stable compounds. Concerning the caged structure of DPS, there remain some inconformity among researchers’ conclusions. Some researchers hold that the structure is in the shape of a gem containing 4 tetragons and 4 pentagons, while other articles consider the structure to be a cyclic ladder with 6 tetragons and 2 hexagons. In this paper, the correct structure of DPS is found to be gem‑like, deduced by detailed NMR spectra analysis and Euler's formula calculation, and proved by a single crystal diffraction pattern. A simulation calculation by Materials Studio (MS) proves that the gem‑like structure (Etotal=41.57 kcal·mol-1) is more stable than the cyclic ladder-like one (Etotal=43.37 kcal·mol-1). For the DPS and OPS, the distances between adjacent phenyl groups are considered to influence the chemical shifts of H, C and Si atoms in NMR due to shielding effects, deshielding effects and electron densities. The cyclic tetramer with Etotal=20.40kcal·mol-1 is proved to be the stable cyclic oligomeric phenyl silsesquioxanes with the smallest polymerization degree by the simulations. The linear dimer with Etotal=14.49 kcal·mol-1 is proved to be the stable linear oligomeric silsesquioxanes with the smallest polymerization degree. A condensation mechanism of DPS and OPS is proposed based on the simulation results.

Anticancer potential of Cu(II)prolinedithiocarbamate complex: design, synthesis, spectroscopy, molecular docking, molecular dynamic, ADMET, and in-vitro studies

Breast cancer continues to be a major health issue for women all over the world. Cancer medications like cisplatin, which are widely used, still have negative side effects. The novel complex was created as a potential anticancer medication candidate that is both effective and safe, with few side effects. The Cu(II) complex using the prolinedithiocarbamate ligands was synthesized in situ. The Cu(II) complexes Characterization by UV-Vis, FT-IR spectroscopy and melting point determination, conductivity, and HOMO-LUMO were studied. Computational NMR spectrum analysis was performed. The interaction of Cu(II)prolineditiocarbamate complex with cancer cell target protein (MCF-7) was confirmed by molecular docking and molecular dynamic. The pharmacokinetic/ADMET properties were also performed on the complex. Results of the cytotoxic complex test against cancer cells (MCF-7) undergoing apoptosis with an IC50 value of 13.64 µg/mL showed high anticancer activity in MCF-7 cancer cells. The in-vivo data for Cu(II)prolineditiocarbamate complex was predicted using the Protox online tool with an LD50 value of 2500 mg/kg and belonging to the GHS toxicity class 5, which means the compound has a low acute toxicity effect. The Cu(II) prolineitiocarbamate complex may pave the way for the development of essential metal-based chemotherapy for the treatment of breast cancer. Communicated by Ramaswamy H. Sarma

Structural and Catalytic Properties of the Binary Systems Alumina – Amorphous Aluminosilicate

The amorphous aluminosilicate – alumina systems were examined using various physicochemical methods, including the analysis of 27Al NMR spectra of solid samples, estimation of the catalyst acidity by temperature-programmed desorption of ammonia, investigation of the sample structure by X-ray diffraction analysis, and thermogravimetric analysis of the samples. A study on the catalytic properties of the samples upon cracking on the model feedstock n-dodecane in a mixture with 2-methylthiophene revealed that conversion of the feedstock increases in the series: 100 % Al2O3 (AH) > 70 % Al-Si + 30 % Al2O3 (AH) > 30 % Al-Si + 70 % Al2O3 (AH) > 100 % Al-Si (AH – aluminum hydroxide obtained by sulfate method; Al-Si – amorphous aluminosilicate). An increase in the calcination temperature of the samples from 500 to 700 °C decreases the conversion of the feedstock. The growing contribution of hydrogen transfer reactions leads to an increase in the formation selectivity of hydrogen sulfide and a decrease in the content of sulfur compounds in the liquid products.

New Monoterpenoid Indole Alkaloids from Tabernaemontana crassa Inhibit β-Amyloid42 Production and Phospho-Tau (Thr217).

Eleven monoterpenoid indole alkaloids, including three new ones, tabercrassines A-C (1-3), were isolated from the seeds of Tabernaemontana crassa. Tabercrassine A (1) is an ibogan-ibogan-type bisindole alkaloid which is formed by the polymerization of two classic ibogan-type monomers through a C3 unit aliphatic chain. Their structures were established by extensive analysis of HRESIMS, NMR, and ECD spectra. Cellular assays showed that alkaloids 1-3 all reduce Aβ42 production and inhibit phospho-tau (Thr217), a new biomarker of Alzheimer's disease [AD] associated with BACE1-, NCSTN-, GSK3β-, and CDK5-mediated pathways, suggesting these alkaloids' potential against AD.

Isolation and Spatial Structure of 5,7-Dihydroxy-6,3′,4′-Trimethoxyflavone

The article presents the results of a chemical study of semi-dry wormwood (Artemisia semiarida), an endemic plant of Kazakhstan. The amount of extractive substances was obtained by extraction with chloroform from air-dried crushed above-ground part of the plant collected in the vegetative phase. The compound was isolated using a column chromatography method. Silica gel of the KSK brand was used with the ratio of the sum of substances – carrier = 1:10. When the column was eluted with a 13:7 petroleum ether – ethyl acetate mixture, a yellow crystalline substance of the composition C18H16O7 with m.p. 234–237° C was obtained (recrystallization from ethyl acetate). The structure of the obtained compound (5,7-dihydroxy-6,3′,4′-trimethoxyflavone or eupatilin) was established by analysis of IR and NMR spectra. The spatial structure of eupatilin was determined by X-ray diffraction. In the crystal structure of 5,7-dihydroxy-6,3′,4′-trimethoxyflavone the rotation of the phenyl ring relative to the main framework (chromene ring) was found to be only 4.1°. Four conformers with different rotations of the phenyl ring (the torsional angles of O1C2C1′C2′ are 30°, 140°, 210° and 320°, respectively) and small energy barriers (about 8.4 kJ/mol) can be realized in the free state of the molecule.

(Gd3+) Complexation with oligopeptide (SFVG) and amyloid peptide (Aβ13–23) in aqueous solution by NMR spectroscopy

Gadolinium (III) ion, which belongs to the subgroup of transition metal ions, has practical importance for magnetic resonance imaging (MRI) with contrast. The accumulation of complexes of transition metal ions with amyloid peptides in the human body leads to the formation of insoluble plaques, which are presumably-one of the causes of Alzheimer's disease. This paper presents the results of studying the interaction of the gadolinium (III) ion with a fragment of amyloid protein Aβ40 in aqueous solutions using nuclear magnetic resonance spectroscopy. Tetrapeptide (SFVG) was used as the simplified model of metal-peptide interaction research. Beta-amyloid peptide (Aβ13-23) was chosen as the amyloid protein Aβ40 fragment model. Analysis of 1H NMR spectra revealed that the interaction exists for both types of molecules. It was also suggested the possible location of gadolinium (III) ion in the studied molecules.

Singlet oxygen production analysis of reduced berberine analogs via NMR spectroscopy

Berberine is a natural product isoquinoline alkaloid derived from plants of the genus Berberis. When exposed to photoirradiation, it produces singlet oxygen through photosensitization of triplet oxygen. The production of singlet oxygen grants Berberine its biological activity, as singlet oxygen forms an activated complex with DNA, oxidizing its guanine residues, halting cell replication and leading to cell death, which can be applied in photodynamic therapy of cancer. Through qNMR analysis of 1H NMR spectra gathered through kinetic experiments, we were able to track the generation of a product between singlet oxygen and alpha terpinene, allowing us to quantitatively measure the photosensitizing properties of our scaffolds. Moreover, we implemented 7,8-dihydroberberine and tetrahydroberberine, the reduced and over-reduced forms of berberine, respectively, in the studies to test the effect of the reduction of a compound on its singlet oxygen production.

Pyrrole-type compounds from the flowers of Calotropis gigantea

Calotropis gigantea, a large shrub, has been used in traditional folk medicines for the treatment of fever, cough, swellings, bronchitis or dyspepsia. Previous studies on C. gigantea reported that its main constituents, specifically cardenolides and pregnanes, had cytotoxic activity against A549 human lung, Hela human cervical cancer cell lines and K562 human chronic myelogenous leukemia. This paper presents the isolation of chemical constituents from the flowers of C. gigantea (Apocynaceae) in order to provide more information about its chemical compounds to the database on medical plants in Vietnam. By using silica gel column chromatography, preparative TLC and eluting with organic solvents of different polarity, results showed that five pyrroles, including pollenopyrroside B (1), epi-acortatarin A (2), shensongine A (3), 5-methoxymethyl-1H-pyrrole-2-carbaldehyde (4), 1-[2-(furan-2-yl)-2-oxoethyl]pyrrolidin-2-one (5), were isolated from the CHCl3 extract of the flowers of C. gigantea (Apocynaceae), collected at Binh Thuan province in March, 2020. Their chemical structures were elucidated by HR-MS and 1D, 2D NMR spectra analysis and comparison with published data. All compounds were the first reported from C. gigantea.

Antioxidant Activity-Guided Isolation of Phenolic Compounds from Leaves of Vitex pinnata (Lamiaceae)

The aim of this study is to isolate phenolic compounds from the ethyl acetate fraction of the leaves of V. pinnata Linn, which have antioxidant properties, guided by a TLC-Bioautography (Thin-layer chromatography) with a reagent of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH). The TLC-antioxidant bioautography technique has several advantages. It does not require a long time in testing, the sample used is small, and it can potentially obtain promising antioxidant-positive compounds.The isolation process led to obtaining two phenolic compounds. The UV-Vis, FTIR, and NMR spectrum analysis showed that the compounds were (1) p-hydroxybenzoate and (2) luteolin. Further antioxidant evaluation by DPPH assay showed a potential radical scavenging DPPH of luteolin (2) with an IC50 of 1.56±0.18 µg/mL.

Isolation of α-mangostin from mangosteen (Garcinia mangostana L.) peels and evaluation of its inhibitory activity toward α-glucosidase and α-amylase in the combination with acarbose

Using the natural agents with inhibitory activity against digestive enzymes α-glucosidase and α-amylase capable of hydrolyzing carbohydrates into glucose to reduce blood glucose levels in the blood is one of the effective strategies to control diabetes, especially type II diabetes. α-Mangostin (AMG) was proven to have strong biological activities, such as antifungal, antibacterial, anti-inflammatory, anti-cancer. However, the evaluation of the antidiabetic activity of this substance through inhibition of starch hydrolytic enzymes activity has not been fully carried out, especially when they are combined with commercial drugs, such as acarbose. In this study, AMG was isolated from the peels of the mangosteen grown in Vietnam using a simple isolation process with two steps: i) fractionation of the material in n-hexane solvent, and ii) chromatography of n-hexane fraction on a silica gel column combined with crystallization. The α-glucosidase inhibitory activity (AGI) and α-amylase inhibitory activity (AAI) of purified AMG alone or in combination with acarbose were then determined spectrophotometrically. The obtained results indicated that AMG had a purity of > 98% by HPLC examination and its chemical structure was confirmed by NMR spectra analysis combined with the reference. The isolated AMG showed good AGI and AAI with IC50 values of 8.25 µg/mL and 24.5 µg/mL, respectively. The AGI increased to 69.4% when AMG (5.0 µg/mL) was combined with acarbose at a concentration of 2.5 µg/mL, while the AAI did not have a clear synergistic effect. Our finding suggests the possibility of using the combination formula to enhance acarbose efficacy in treatment of the disease.

Flavonols, lignans and diacetylenes from leaves of Hydrocotyle leucocephala Cham. & Schltdl. and aerial parts of H. bonariensis Comm. ex Lam

Chemical investigation of ethyl acetate and n-butanol fractions from methanol extracts from leaves of Hydrocotyle leucocephala Cham. & Schltdl. and aerial parts of H. bonariensis Comm. ex Lam. resulted in the identification of 6 compounds and a putative identification of 12 more, including thirteen glycosylated flavonols (1–13), two dibenzylbutyrolactone lignans (14 and 15) and three diacetylenes (16–18) based on UPLC-ESI-QToF-MS/MS analysis in the positive and negative ionization modes. In the case of compounds 3, 14–18, their structures were confirmed by analysis of NMR spectra. Compounds 5, 7, 10–12 or isomeric compounds of them were identified for the first time in this genus. The obtained results contribute with chemotaxonomy of Hydrocotyle since flavonoids, dibenzylbutyrolactone lignans, and diacetylenes were characterized, in consonance with other species previously investigated.

Hyrtiosins F and G, two new scalarane sesterterpenes from the South China sea sponge Hyrtios erecta

Two new scalarane sesterterpenes, hyrtiosins F and G (1 and 2), along with two known related compounds, hyrtiosin D and sesterstatin 6 (3 and 4), were isolated from the Hainan marine sponge Hyrtios erecta. The structures of new compounds 1 and 2 were determined by detailed analysis of 1D and 2D NMR spectra and by comparison of the spectroscopic data with those reported in the literatures.

Synthesis and Biological Evaluation of Novel Pyrimidine Amine Derivatives Bearing Bicyclic Monoterpene Moieties.

A series of novel pinanyl pyrimidine amine derivatives (1e~1n) and camphoryl pyrimidine amine derivatives (2b~2f) bearing bicyclic monoterpene moieties were designed and synthesized from natural and renewable nopinone and camphor. All chemical structures of target compounds were characterized by 1H NMR, 13C NMR and HRMS spectra analyses, and the antimicrobial activities were evaluated. The results indicated that most compounds showed considerable antibacterial and antifungal activities against Klebsiella pneumoniae, Streptococcus pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Methicillin-Resistant Staphylococcus aureus (MRSA), Bacillus cereus and Candida albicans. Among them, 1f showed potent antibacterial activity against all tested bacteria, 1i exhibited excellent inhibition against Streptococcus pneumoniae (1 μg/mL) and Escherichia coli (1 μg/mL), which was better than the control drug amikacin (2 μg/mL). As to antifungal activity against Candida albicans (C. albicans), compound 1l showed comparable activity (16 μg/mL) to the control drug ketoconazole. Furthermore, five active compounds with better antimicrobial activities also showed anti-inflammatory potencies against mouse mononuclear macrophages leukemia cells (RAW). Especially, 1f (IC50 = 1.37 μM) and 2f (IC50 = 1.87μM) are more potent than the control drug aspirin (IC50 = 1.91 μM).