High-resolution 13C Nuclear Magnetic Resonance Research Articles

Complete 1H and 13C NMR assignment of cellulose oligomer in LiCl/DMSO

High-resolution solution-state 1H, 13C, and various 2D nuclear magnetic resonance (NMR) spectra of cellulose were obtained using cellulose oligomer dissolved in LiCl/dimethyl sulfoxide, which enabled the assignment of all 1H and 13C resonances. The observed resonances were classified into four groups of glucose rings, corresponding to internal residue, non-reducing end, and reducing ends with α- and β-anomeric configurations. This assignment included the OH protons, which are difficult to assign in cellulose using other solvent systems. NMR measurements and assignments were performed using different LiCl concentrations because information on the hydroxy protons is important for understanding the interaction between cellulose and the solvent. The resonances from the OH protons shifted downfield with increasing LiCl concentration, suggesting that LiCl was attracted to the hydroxy groups of cellulose in solution. Moreover, the magnitude of the shifts varied depending on the positions of the hydroxy groups, which indicated the regioselectivity of the interaction between LiCl and the cellulose hydroxy groups.Graphical abstract

Molecular structure and evolution mechanism of shale kerogen: Insights from thermal simulation and spectroscopic analysis

During thermal evolution, the kerogen in shale formation undergoes significant chemical, structural and compositional changes, continuously influencing the shale storage capacity, hydrocarbon generation potential, and gas occurrence state. This study systematically examines the chemical structural changes during the thermal evolution of Longmaxi shale kerogen using hydrothermal laboratory experiments from 420 to 850 °C. Additionally, a range of characterization techniques, including Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, High-Resolution Transmission Electron Microscopy (HRTEM), X-ray Diffraction (XRD), and Solid-state 13C Nuclear Magnetic Resonance (13C NMR), were employed to systematically investigate the kerogen structure and its evolution patterns. Results indicate that Longmaxi Formation kerogen comprises a large molecular carbon framework with aromatic structures, long-chain aliphatic components, and oxygen-containing functional groups. As thermal maturity reaches 2.6 %, the alignment of aromatic fringes gradually increased, with over 60 % aligning in the main direction. Throughout thermal evolution (1.9–3.2 %), fringes in the 5–10 Å range within aromatic structures peak at over 20.45 %, with fringes over 50 Å rapidly increasing from 3 % to over 15 %. Early in the thermal evolution, the long-chain aliphatic component of the kerogen decreases rapidly and part of the structure forms small aromatic rings through aromatisation. The mature to over-mature stage can be divided into three phases: 1) 1.7–2.4 % (loss of oxygen-containing functional groups), 2) 2.4–3.5 % (formation of larger aromatic structures via condensation reactions), 3) over 3.5 % (continued aggregation of aromatic rings, resulting in an increase in the length of aromatic fringes). At a macroscopic level, this induces changes in kerogen pore structure and carbonization features. This study thus provides new insights into the thermal evolution of shale kerogen, which in turn improve understanding of shale reservoirs for hydrocarbon exploitation.

An electrochemical cell for in operando 13C nuclear magnetic resonance investigations of carbon dioxide/carbonate processes in aqueous solution.

In operando nuclear magnetic resonance (NMR) spectroscopy is one method for the online investigation of electrochemical systems and reactions. It allows for real-time observations of the formation of products and intermediates, and it grants insights into the interactions of substrates and catalysts. An in operando NMR setup for the investigation of the electrolytic reduction of at silver electrodes has been developed. The electrolysis cell consists of a three-electrode setup using a working electrode of pristine silver, a chlorinated silver wire as the reference electrode, and a graphite counter electrode. The setup can be adjusted for the use of different electrode materials and fits inside a 5 mm NMR tube. Additionally, a shielding setup was employed to minimize noise caused by interference of external radio frequency (RF) waves with the conductive components of the setup. The electrochemical performance of the in operando electrolysis setup is compared with a standard electrolysis cell. The small cell geometry impedes the release of gaseous products, and thus it is primarily suited for current densities below 1 mA cm. The effect of conductive components on CNMR experiments was studied using a -saturated solution of aqueous bicarbonate electrolyte. Despite the field distortions caused by the electrodes, a proper shimming could be attained, and line widths of ca. 1 Hz were achieved. This enables investigations in the sub-Hertz range by NMR spectroscopy. High-resolution CNMR and relaxation time measurements proved to be sensitive to changes in the sample. It was found that the dynamics of the bicarbonate electrolyte varies not only due to interactions with the silver electrode, which leads to the formation of an electrical double layer and catalyzes the exchange reaction between and , but also due to interactions with the electrochemical setup. This highlights the necessity of a step-by-step experiment design for a mechanistic understanding of processes occurring during electrochemical reduction.

Identifying the Unknown Content of an Ancient Egyptian Sealed Alabaster Vase from Kha and Merit’s Tomb Using Multiple Techniques and Multicomponent Sample Analysis in an Interdisciplinary Applied Chemistry Course

This article highlights the multianalytical study of exuded liquid from an ancient Egyptian sealed alabaster vase by Master’s students in an applied chemistry for cultural heritage course. Master students are introduced to the field of Archaeometry that see the collaboration of experts in different areas of research such as conservators, curators of museums, physicists, chemists, etc. The sample is a residue exuded on the linen strip sealing an ancient Egyptian alabaster vase (inventory number S.8448) from the collection of the Museo Egizio in Turin (Italy). The students start to plan the noninvasive investigation by X-ray fluorescence (XRF), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) for the inorganic compounds characterization, followed by the extraction of the organic components (such as oils, fats, and waxes) to be analyzed by high-resolution 1H and 13C nuclear magnetic resonance (NMR) spectroscopy and 2D NMR correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), and long-range heteronuclear correlation (HMBC) techniques and by gas chromatography coupled with mass spectrometry (GC/MS). Reference standards, spectral databases, and published data on similar artifacts served as the basis for the interpretation of the instrumental results. The approach was introduced in the course of Applied Chemistry for Cultural Heritage for Master students in Archaeology (University of Palermo, Italy), where the need is to know how to approach the scientific investigation together with the conservation scientists and how to manage with a very low amount of sample. Pedagogically, the approach introduces students to the main techniques currently used in the field of Archaeometry while reinforcing fundamental concepts in sample collecting and multicomponent microsample analysis. This interdisciplinary approach provides a unique experience that demonstrates chemistry’s broad applicability outside of the traditional laboratory. Students are guided to identify the inorganic and organic components of the exudate liquid: the first one is ascribable to clay minerals iron oxides, which could impart the brown color to the sample; the second one is ascribed to triglycerides of various kinds, which probably comes from vegetable oil.

Qualitative and Quantitative Analysis of Heavy Crude Oil Samples and Their SARA Fractions with 13C Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) approaches have unique advantages in the analysis of crude oil because they are non-destructive and provide information on chemical functional groups. Nevertheless, the correctness and effectiveness of NMR techniques for determining saturates, aromatics, resins, and asphaltenes (SARA analysis) without oil fractioning are still not clear. In this work we compared the measurements and analysis of high-resolution 13C NMR spectra in B0 ≈ 16.5 T (NMR frequency of 175 MHz) with the results of SARA fractioning for four various heavy oil samples with viscosities ranging from 100 to 50,000 mPa·s. The presence of all major hydrocarbon components both in crude oil and in each of its fractions was established quantitatively using NMR spectroscopy. Contribution of SARA fractions in the aliphatic (10–60 ppm) and aromatic (110–160 ppm) areas of the 13C NMR spectra were identified. Quantitative fractions of aromatic molecules and oil functional groups were determined. Aromaticity factor and the mean length of the hydrocarbon chain were estimated. The obtained results show the feasibility of 13C NMR spectroscopy for the express analysis of oil from physical properties to the composition of functional groups to follow oil treatment processes.

Real-time hyperpolarized 13C magnetic resonance detects increased pyruvate oxidation in pyruvate dehydrogenase kinase 2/4\u2013double knockout mouse livers

The pyruvate dehydrogenase complex (PDH) critically regulates carbohydrate metabolism. Phosphorylation of PDH by one of the pyruvate dehydrogenase kinases 1–4 (PDK1–4) decreases the flux of carbohydrates into the TCA cycle. Inhibition of PDKs increases oxidative metabolism of carbohydrates, so targeting PDKs has emerged as an important therapeutic approach to manage various metabolic diseases. Therefore, it is highly desirable to begin to establish imaging tools for noninvasive measurements of PDH flux in rodent models. In this study, we used hyperpolarized (HP) 13C-magnetic resonance spectroscopy to study the impact of a PDK2/PDK4 double knockout (DKO) on pyruvate metabolism in perfused livers from lean and diet-induced obese (DIO) mice and validated the HP observations with high-resolution 13C-nuclear magnetic resonance (NMR) spectroscopy of tissue extracts and steady-state isotopomer analyses. We observed that PDK-deficient livers produce more HP-bicarbonate from HP-[1-13C]pyruvate than age-matched control livers. A steady-state 13C-NMR isotopomer analysis of tissue extracts confirmed that flux rates through PDH, as well as pyruvate carboxylase and pyruvate cycling activities, are significantly higher in PDK-deficient livers. Immunoblotting experiments confirmed that HP-bicarbonate production from HP-[1-13C]pyruvate parallels decreased phosphorylation of the PDH E1α subunit (pE1α) in liver tissue. Our findings indicate that combining real-time hyperpolarized 13C NMR spectroscopy and 13C isotopomer analysis provides quantitative insights into intermediary metabolism in PDK-knockout mice. We propose that this method will be useful in assessing metabolic disease states and developing therapies to improve PDH flux.

Molecular and Segmental Orientational Order in a Smectic Mesophase of a Thermotropic Ionic Liquid Crystal

We investigate conformational dynamics in the smectic A phase formed by the mesogenic ionic liquid 1-tetradecyl-3-methylimidazolium nitrate. Solid-state high-resolution 13C nuclear magnetic resonance (NMR) spectra are recorded in the sample with the mesophase director aligned in the magnetic field of the NMR spectrometer. The applied NMR method, proton encoded local field spectroscopy, delivers heteronuclear dipolar couplings of each 13C spin to its 1H neighbours. From the analysis of the dipolar couplings, orientational order parameters of the C–H bonds along the hydrocarbon chain were determined. The estimated value of the molecular order parameter S is significantly lower compared to that in smectic phases of conventional non-ionic liquid crystals.

Temperature Dependence of Phase Structure for Highly Drawn Ultrahigh Molecular Weight Polyethylene Using Solid-State High-Resolution 13C Nuclear Magnetic Resonance

Temperature Dependence of Phase Structure for Highly Drawn Ultrahigh Molecular Weight Polyethylene Using Solid-State High-Resolution 13C Nuclear Magnetic Resonance

Isolation of Secondary Metabolites with Antimicrobial Activities from Bacillus amyloliquefaciens LWYZ003

The strain LWYZ003, which can restrain multiple pathogens, was screened from the sediment of the ocean and identified as Bacillus amyloliquefaciens. Large-scale fermentation and modern chromatographic separation technologies (macroporous resin column chromatography, silica gel column chromatography, thin-layer chromatography and high-performance liquid chromatography) were used to separate antimicrobial products from the fermentation broth of marine-derived Bacillus amyloliquefaciens LWYZ003. Bioactive-guided separation was used in the term of seeking antimicrobial products from the secondary metabolites of Bacillus amyloliquefaciens LWYZ003. As a result, two natural products cycloheximide (1) and trehalose (2) were obtained. Their structures were elucidated by Fourier transform infrared spectroscopy, high-resolution mass spectrometry, 1H and 13C nuclear magnetic resonance analysis. In the cylinder plate method, compound 1 exhibited stronger antimicrobial activities than compound 2 against Micrococcus luteus, and also exhibited wider antimicrobial spectrum than compound 2. In conclusion, isolation of bioactive secondary metabolites from marine Bacillus sp. has enormous potentials in finding suitable antibiotics to inhibit multiple pathogens.

Antimicrobial Properties of Tris(homoleptic) Ruthenium(II) 2-Pyridyl-1,2,3-triazole "Click" Complexes against Pathogenic Bacteria, Including Methicillin-Resistant Staphylococcus aureus (MRSA).

A series of tris(homoleptic) ruthenium(II) complexes of 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine "click" ligands (R-pytri) with various aliphatic (R = butyl, hexyl, octyl, dodecyl, and hexdecyl) and aromatic (R = phenyl and benzyl) substituents was synthesized in good yields (52%-66%). The [Ru(R-pytri)3]2+(X-)2 complexes (where X- = PF6- or Cl-) were characterized by elemental analysis, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), 1H and 13C nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies, and the molecular structures of six of the compounds confirmed by X-ray crystallography. 1H NMR analysis showed that the as-synthesized materials were a statistical mixture of the mer- and fac-[Ru(R-pytri)3]2+ complexes. These diastereomers were separated using column chromatography. The electronic structures of the mer- and fac-[Ru(R-pytri)3]2+ complexes were examined using ultraviolet-visible (UV-Vis) spectroscopy and cyclic and differential pulse voltammetry. The family of R-pytri ligands and the corresponding mer- and fac-[Ru(R-pytri)3]2+ complexes were tested for antimicrobial activity in vitro against both Staphylococcus aureus and Escherichia coli bacteria. Agar-based disk diffusion assays indicated that two of the [Ru(R-pytri)3](X)2 complexes (where X = PF6- and R = hexyl or octyl) displayed good antimicrobial activity against Gram-positive S. aureus and no activity against Gram-negative E. coli at the concentrations tested. The most active [Ru(R-pytri)3]2+ complexes ([Ru(hexpytri)3]2+ and Ru(octpytri)3]2+) were converted to the water-soluble chloride salts and screened for their activity against a wider range of pathogenic bacteria. As with the preliminary screen, the complexes showed good activity against a variety of Gram-positive strains (minimum inhibitory concentration (MIC) = 1-8 μg/mL) but were less effective against Gram-negative bacteria (MIC = 16-128 μg/mL). Most interestingly, in some cases, the ruthenium(II) "click" complexes proved more active (MIC = 4-8 μg/mL) than the gentamicin control (MIC = 16 μg/mL) against two strains of methicillin-resistant S. aureus (MRSA) (MR 4393 and MR 4549). Transmission electron microscopy (TEM) experiments and propidium iodide assays suggested that the main mode of action for the ruthenium(II) R-pytri complexes was cell wall/cytoplasmic membrane disruption. Cytotoxicity experiments on human dermal keratinocyte and Vero (African green monkey kidney epithelial) cell lines suggested that the complexes were only modestly cytotoxic at concentrations well above the MIC values.

TG/DTG, FT-ICR Mass Spectrometry, and NMR Spectroscopy Study of Heavy Fuel Oil

There is an increasing interest in the comprehensive study of heavy fuel oil (HFO) due to its growing use in furnaces, boilers, marines, and recently in gas turbines. In this work, the thermal combustion characteristics and chemical composition of HFO were investigated using a range of techniques. Thermogravimetric analysis (TGA) was conducted to study the nonisothermal HFO combustion behavior. Chemical characterization of HFO was accomplished using various standard methods in addition to direct infusion atmospheric pressure chemical ionization Fourier transform ion cyclotron resonance mass spectrometry (APCI-FTICR MS), high resolution 1H nuclear magnetic resonance (NMR), 13C NMR, and two-dimensional heteronuclear multiple bond correlation (HMBC) spectroscopy. By analyzing thermogravimetry and differential thermogravimetry (TG/DTG) results, three different reaction regions were identified in the combustion of HFO with air, specifically, low temperature oxidation region (LTO), fuel deposition (FD), and hig...

Distribution ratio of carbon black in polyisobutyrene/polyisoprene rubber blends using high-resolution solid-state 13C NMR

We establish the 13C nuclear magnetic resonance (NMR) method as the best available method for the evaluation of carbon black (CB) distribution in rubber blend. We find that the line widths of NMR peaks increase as CB contents increase. Using this phenomenon it is found that, in polyisobutyrene rubber (IIR)/polyisoprene rubber (IR)/CB composites, CB more easily distributes in IR than in IIR. And we can estimate that more than 70% of CB is distributed in to the IR phase, irrespective of CB content.

The complex isotopologue space of glucose as a framework for the study of human intermediary metabolism

The positional distributions of stable isotopes in metabolites provide specific fingerprints of the pathways and fluxes that have occurred in the organisms under study. In particular, modern nuclear magnetic resonance (NMR) spectroscopy enables the detailed assignment of isotope patterns in natural products, for example, in metabolites obtained from labelling experiments using 13C-enriched precursors, such as glucose, acetate or CO2. In this study, the transient 13C-isotopologue composition of blood glucose from an adult human volunteer after intravenous supply of [U-13C6]glucose was determined by high-resolution 13C NMR spectroscopy. The non-linear progression curves displaying the relative amounts of eight 13C-glucose isotopologues reflected the contributions of glucose metabolism by glycolytic cycling, the pentose phosphate pathway and anaplerotic reactions involving the citric acid cycle. The pilot study suggests that the experimental setting can be useful in analysing under non-invasive conditions the impact of physiological and pharmacological constraints on glucose turnover in humans.

Bound solvent in different stereoregular syndiotactic polypropylene gels

The coagulation size of the solvent in syndiotactic polypropylene (sPP)/o-dichlorobenzene gels was investigated for different stereoregular samples with racemic diads of 98% (sPP98) and 83% (sPP83) using thermal analysis, optical microscopy, and solid-state high resolution 13C nuclear magnetic resonance (NMR). For the sPP98 gel, the coagulation size of freezable bound solvent was smaller than that in the sPP83 gel. The non-crystalline region of the sPP83 gel is large due to the incomplete stereoregularity, so that a large coagulation of the solvent occurs. The weight contents of the crystalline, amorphous, and interphase components were estimated using solid-state high resolution 13C NMR. The interphase weight content was comparable with that of the non-freezable solvent estimated by thermal analysis, which implies that the non-freezable solvent is bound in the interphase. The coagulation size of the solvent in the sPP98 gel increased with gelation temperature. Large spherulites are formed at higher gelation temperatures; therefore, the non-crystalline region between lamellae is larger, which results in the large coagulation size of the solvent.

Phase Structure and Helical Jump Motion of Poly(ethylene oxide)/LiCF3SO3 Crystalline Complex: A High-Resolution Solid-State 13C NMR Approach

By employing solid-state high-resolution 13C nuclear magnetic resonance (NMR), we found that the helical jump motion of crystalline poly(ethylene oxide) (PEO) segments only exists for the PEO3/LiF3...

Reversibly meltable layered alkylsiloxanes with melting points controllable by alkyl chain lengths

Meltable layered alkylsiloxanes (CnLSiloxanes) were synthesized from tetraethoxysilane and alkyltrialkoxysilanes with carbon numbers (n) of 12, 16, and 18 via hydrolysis and polycondensation at 100 and 150 °C under basic conditions. Differential scanning calorimetric (DSC) measurements revealed that CnLSiloxanes melted reversibly at −0.8 to 51.3 °C, the melting points being dependent on n. Scanning electron microscope (SEM) images showed that thin plates were stacked. X-ray diffraction (XRD) peaks were observed at angles corresponding to distances (d) of 2.1, 2.5, and 2.8 nm for C12-, C16-, and C18LSiloxanes, respectively. High-resolution solid-state 13C nuclear magnetic resonance (NMR) measurements showed that the organic moieties were alkylsilyl groups with long alkyl chains and that an all-trans conformation was dominant. This was supported by the XRD peak corresponding to a d value of 0.41 nm. High-resolution solid-state 29Si NMR measurements demonstrated the presence of SiO4 and CSiO3 units. A structural model has been proposed for CnLSiloxanes, where siloxane sheets consisting of the SiO4 and CSiO3 units are stacked with the ordered interdigitated monolayer of the alkyl chains in between and are bonded covalently with the alkyl chains.

Structures of crystalline and amorphous phases of the poly(ethylene oxide)/lithium trifluoromethanesulfonate complexes as studied by solid-state high-resolution 13C nuclear magnetic resonance

Solid-state high-resolution 13C NMR studies are carried out on a series of PEO/LiCF3SO3 complexes with different EO/Li molar ratios at room temperature. The obtained spectra clearly show that there are four phases, namely the crystalline PEO, the amorphous PEO, the PEO3:LiCF3SO3 crystalline complex and the PEO3:LiCF3SO3 amorphous complex, coexisting in the samples with EO/Li molar ratios larger than 3. The solid-state 13C NMR spectrum of the PEO3:LiCF3SO3 crystalline complex exhibits six peaks with high resolution at room temperature, while the previously reported 13C NMR spectra showed only one peak. These six peaks are assigned with the combination of the 13C dipolar-INADEQUATE and the two-dimensional exchange spectra. Moreover, remarkable helical jumps of PEO segments are demonstrated to exist in the crystalline complex. Our study paves the way towards a better understanding of the phase structures and subsequently the conduction mechanism of PEO-based solid polymer electrolytes.

Molecular Dynamics of a Polyaniline/β-Cyclodextrin Complex Investigated by 13C Solid-State NMR

The molecular dynamics of a polyaniline/β-cyclodextrin inclusion complex (PANI/β-CD IC) and its relation with optical properties were investigated using high-resolution solid-state (13)C nuclear magnetic resonance (NMR) and optical absorption spectroscopies. UV-vis measurements revealed a π-π* absorption peak of a PANI film that had a 10 nm blue-shift by inclusion of β-CD, indicating that π-conjugation of PANI was shortened in the IC. Temperature dependent analysis of (13)C NMR spectra and spin-lattice relaxation times (T(1C)) revealed that the inclusion induced acceleration of the twisting motion of the PANI chain. Moreover, two twisting motions attributed to different torsional angle modes were observed following Arrhenius plots of T(1C) measurements, and the twisting frequency and angle increased above -25 °C. These results suggest that the β-CD inclusion weakens the intermolecular π-π interaction and enhances the accompanying twisting motion, consequently leading to a blue-shift of UV-vis absorption.

High-resolution 13C nuclear magnetic resonance evidence of phase transition of Rb,Cs-intercalated single-walled nanotubes

We present 13 C high-resolution magic-angle-turning (MAT) and magic angle spinning nuclear magnetic resonance data of Cs and Rb intercalated single walled carbon nanotubes. We find two distinct phases at different intercalation levels. A simple charge transfer is applicable at low intercalation level. The new phase at high intercalation level is accompanied by a hybridization of alkali (s) orbitals with the carbon (sp2) orbitals of the single walled nanotubes, which indicate bundle surface sites is the most probable alkali site.

The concentration of polysaccharides and proteins in EPS of Pseudomonas putida and Aureobasidum pullulans as revealed by 13C CPMAS NMR spectroscopy

Extracellular polymeric substances were extracted from the bacterial strain Pseudomonas putida and the fungal species Aureobasidium pullulans using three different methods (formaldehyde-NaOH, ethylenediaminetetraacetic acid (EDTA) and cation-exchange-resin). The composition of the extracellular polymeric substances (EPS) was analysed by biochemical and high-resolution solid state 13C nuclear magnetic resonance (NMR) spectroscopic methods. The EPS yield was strongly dependent on the extraction method, with the formaldehyde-NaOH method showing the best extraction efficiency. The NMR method revealed that when using the EDTA extraction method, about 40% of the EDTA accumulated in the EPS and that was responsible for the apparent high extraction yields. EPS protein content determined by the NMR method was up to 30% higher than the protein content determined using the biochemical (Lowry) method for P. putida and for A. pullulans. The average protein carbon content determined by the NMR method was approximately 70% of the total carbon content. NMR results could be supported by elemental analysis, which showed a high nitrogen content (approximately 10%) in the EPS. The carbohydrate carbon content detected with both methods in the cell aggregates and the EPS was approximately 20% in each. In this study, quantitative 13C cross-polarisation magic angle spinning NMR spectroscopy was conducted on unlabeled cell strains, and EPS and could be used to quantify protein and carbohydrate of different samples.