Nuclear Magnetic Resonance Techniques Research Articles

Preparation, Characterization, In silico and In vitro Antimicrobial Studies of Phenothiazine-3-sulphonamide Derivatives

The antibacterial activities of phenothiazine and sulphonamide derivatives have attracted so much interest. In this study, the synthesis and characterization of phenothiazine-3-sulphonamide derivatives and evaluation of their antimicrobial activity against the following pathogenic microorganisms is reported. Two Gram-positive bacteria; (Staphylococcus aureus (ATCC: 6538) and Streptococcus pyogenes (ATCC: 27853)), two Gram-negative bacteria; (Escherichia coli(ATCC: 3008), and Salmonella typhi (ATCC: 25175)) as well as one fungus (Aspergillus fumigatus (ATCC: 10231)) were used while ciprofloxacin, gentamycin and ketoconazole served as standard drugs. The synthesis of the derivatives was achieved through a base catalyzed the reaction of 4-chloroaniline with 1-naphthylamine to form 1-(naphthalen-1-yl)benzene-1,4-diamine. This intermediate was then treated with sulphur and iodine to yield the phenothiazine derivative while subsequent treatment of the phenothiazine compound with sulphonyl chlorides gave the final products. The synthesized compounds were characterized via proton nuclear magnetic resonance (1H-NMR), carbon-13 nuclear magnetic resonance (13C-NMR) and Fourier-transform infrared (FTIR) spectroscopic techniques. The minimum inhibitory concentration (MIC) of each compound was then determined using the agar well diffusion method. To predict the binding energies and patterns of the synthesized compounds with target proteins of the above-mentioned microorganisms, molecular docking simulations were run using Autodock Vina software (version 4.2). The spectra data of the compounds for FTIR, 1H-NMR and 13C-NMR spectral data were consistent with the assigned structures of the synthesized compounds. The binding energies (kcal/mol) for in silico antimicrobial studies were in the range -5.1 to -7.6 kcal/mol. The MIC values were in the range 3.5 to 1.0 mg/L. The results of the in vitro test revealed that the synthesized compounds exhibit promising antimicrobial activity and showed excellent bactericidal and fungicidal activities. The results obtained showed that the synthesized compounds possess drug-like properties and are good starting materials for drug production.

New Schiff bases and their vanadium complexes: Synthesis, characterization, and biological assessment for antibacterial and antiviral action

From the perspective of possible antiviral and antibacterial activity of vanadium‐based complexes, we report the synthesis of new Schiff base ligand (L4) and a new Schiff‐base‐vanadium complex (C2). Both the ligand and the complex were characterized by Fourier transform infrared spectroscopy and Nuclear magnetic resonance techniques. Single‐crystal X‐ray Diffraction analysis has been used to confirm the structure of ligand L4 and complex C2. In addition, L1–4 and C1–3 were tested for their antibacterial effects against Escherichia coli and Staphylococcus aureus. Among the compounds, L2 demonstrated the most potent inhibition of both bacteria, exhibiting the lowest values for minimum inhibitory concentration (CMI) and minimum bactericidal concentration (CMB) (CMI = 0.16, CMB = 0.31 against E. coli, and CMI = CMB = 0.16 against S. aureus). Additionally, L2 produced the largest inhibition zones with diameters of 15.5 ± 0.15 against E. coli and 14.5 ± 0.04 against S. aureus. Furthermore, the antiviral efficacy of L1, L2, L4, C1, C2, and C3 against RNA viruses was assessed. C2 and C3 exhibited the most potent antiviral activity among the tested compounds.

The Use of Spectroscopic Methods to Study Organic Matter in Virgin and Arable Soils: A Scoping Review

The use of modern spectroscopic methods of analysis, which provide extensive information on the chemical nature of substances, significantly expands our understanding of the molecular composition and properties of soil organic matter (SOM) and its transformation and stabilization processes in various ecosystems and geochemical conditions. The aim of this review is to identify and analyze studies related to the application of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy techniques to study the molecular composition and transformation of organic matter in virgin and arable soils. This article is mainly based on three research questions: (1) Which NMR spectroscopy techniques are used to study SOM, and what are their disadvantages and advantages? (2) How is the NMR spectroscopy technique used to study the molecular structure of different pools of SOM? (3) How is ESR spectroscopy used in SOM chemistry, and what are its advantages and limitations? Relevant studies published between 1996 and 2024 were searched in four databases: eLIBRARY, MDPI, ScienceDirect and Springer. We excluded non-English-language articles, review articles, non-peer-reviewed articles and other non-article publications, as well as publications that were not available according to the search protocols. Exclusion criteria for articles were studies that used NMR and EPR techniques to study non-SOM and where these techniques were not the primary methods. Our scoping review found that both solid-state and solution-state NMR spectroscopy are commonly used to study the structure of soil organic matter (SOM). Solution-phase NMR is particularly useful for studying soluble SOM components of a low molecular weight, whereas solid-phase NMR offers advantages such as higher 13C atom concentration for stronger signals and faster analysis time. However, solution-phase NMR has limitations including sample insolubility, potential signal aggregation and reduced sensitivity and resolution. Solid-state NMR is better at detecting non-protonated carbon atoms and identifying heterogeneous regions within structures. EPR spectroscopy, on the other hand, offers significant advantages in experimental biochemistry due to its high sensitivity and ability to provide detailed information about substances containing free radicals (FRs), aiding in the assessment of their reactivity and transformations. Understanding the FR structure in biopolymers can help to study the formation and transformation of SOM. The integration of two- and three-dimensional NMR spectroscopy with other analytical methods, such as chromatography, mass spectrometry, etc., provides a more comprehensive approach to deciphering the complex composition of SOM than one-dimensional techniques alone.

NOE analysis using dual injection DNP‐NMR for studies of solvent–solute interactions at low concentrations

AbstractDynamic nuclear polarization (DNP) offers significant signal enhancement compared to conventional nuclear magnetic resonance (NMR) in measuring the nuclear Overhauser effect. Owing to this enhancement, DNP enables the quantitative analysis of solvent–solute interactions, which are typically challenging to assess using standard NMR techniques. However, current experimental setups generally require the use of samples with relatively high solute concentrations because of large dilution factors. This limits the studies on solvent–solute interactions for bio‐related molecules, particularly those with low solubility. In such cases, the concentration of solute post‐dilution often falls below the detection limits. Herein, we introduce a novel dual injection system designed to considerably increase the dilution factor, thereby enabling the use of samples with lower solute concentrations while maintaining detectable signal levels. The effectiveness of this system was demonstrated in experiments using trifluoroacetic acid at concentrations 50 times lower than those used in the conventional method.

Effects of polyols at low concentration on the release of sweet aroma compounds in model soda beverages

This study investigated the effect of polyols erythritol, d-mannitol, and maltitol on the volatility of aroma compounds γ-butyrolactone, 3-methyl-1-butanol, and 2-phenylethanol in aqueous solution. Headspace solid-phase microextraction/gas chromatography and diffusion-ordered nuclear magnetic resonance techniques were used to obtain information on aroma–food matrix interaction. Results demonstrated that adding polyols at final low concentrations of 5% or 10% (w/w) to an aqueous solution of 2-phenylethanol reduced the release of vapor-phase aromas, except in the case of 3-methyl-1-butanol, which was not affected by the presence of polyols in the liquid matrix. Polyols also reduced the diffusion coefficients of all three aroma compounds, probably due to friction between the molecules. At low polyol concentrations, aroma compound volatility and diffusion coefficient values were altered compared to those of aromas released from pure water. This observation is related to the physicochemical properties of the aroma compounds. These insights may help guide the use of the combination of aroma compounds and polyols in the formulation of sugar-free and reduced-sugar beverages. Chemical compoundsγ-butyrolactone (PubChem CID: 7302), 3-methyl-1-butanol (PubChem CID: 31260), 2-phenylethanol (PubChem CID: 6054), erythritol (PubChem CID: 222285), d-mannitol (PubChem CID: 6251), maltitol (PubChem CID: 493591).

Deciphering the Self-Catalytic Mechanisms of Polymerization and Transesterification in Polybenzoxazine Vitrimers.

The use of internal catalysts has emerged as a pivotal design principle to facilitate dynamic exchanges within covalent adaptable networks (CANs). Polybenzoxazines, specifically, have shown considerable potential in generating vitrimers through thermally induced transesterification reactions catalyzed internally by tertiary amines. This study aims to investigate the chemical complexities of transesterification reactions within benzoxazine vitrimers. To achieve this, model molecules using various phenolic acids and amino-alcohol derivatives were synthesized as precursors. The structure of these model molecules was fully elucidated by using nuclear magnetic resonance (NMR). Differential scanning calorimetry (DSC) and rheology experiments evidenced the accelerated network formation of the precursors due to the presence of aliphatic -OH groups. Thermogravimetric analysis coupled with microcomputed gas chromatography (TGA-μGC) was used to provide evidence of transesterification reactions. The results showed that the spatial proximity between tertiary amine and hydroxyl groups significantly enhances the rate exchange, attributed to a neighboring group participation (NGP) effect. Interestingly, kinetic experiments using complementary NMR techniques revealed the thermal latency of the tertiary amine of benzoxazine toward transesterification reactions as its opening is needed to trigger the dynamic exchange. The study highlights the crucial role of steric hindrance and tertiary amine basicity in promoting the dynamic exchange in an internally catalyzed system.

Evolution of pore structure and analysis of freeze damage in granite during cyclic freeze-thaw using NMR technique

Understanding the changes in a rock's pore structure and unfrozen water content during the freeze-thaw (F-T) process is crucial for unraveling the F-T damage mechanism of rock masses. This study employs nuclear magnetic resonance (NMR) tests to resolve the pore structure characteristics of granite specimens subjected to varying numbers of F-T cycles (0, 50, 100, and 200 cycles). Throughout the F-T process, unfrozen water (comprising bound water and free water) is quantified through T2 distribution curves, and the freeze-induced strain at different subzero temperatures is investigated. The results reveal that F-T cycles lead to the expansion of pore sizes from small to large, reducing the complexity of the pore structure. Moreover, an increased proportion of meso- and macro-pores accelerates the rate of water-ice phase transition in granite specimens, resulting in intensified freeze damage and greater maximum freeze-induced strain. Additionally, when previously damaged granite is refrozen, the presence of free water induces higher levels of freeze-induced strain. This research comprehensively analyzes the F-T damage process in granite, laying a crucial theoretical foundation for understanding freeze damage mechanisms in rock engineering.

Assessment of the strength of grignard reagent for the synthesis of secondary and tertiary alcohols of terpenes using metal plate flow reactor

The secondary and tertiary alcohols of terpenes were synthesized from aldehydes, and ketones using allyl magnesium chloride by the continuous metal flow reactor method. The flow process was conducted using metal plate reactors of 10 ml capacity in the presence of solvent mixtures, instead of large amounts of pure solvent like tetrahydrofuran. The products were isolated, and confirmed using gas chromatography and Nuclear magnetic resonance techniques respectively. Subsequently, the optimization studies were conducted to obtain mild, and economical reaction conditions, by varying the amount of allyl magnesium chloride, temperature, pressure, retention time, and flow rates. A comparison between batch processes and flow processes proved the advantages of the flow process in terms of reproducibility and product yield without the requirement of excess reagents compared to the batch process. The product yield was found to be excellent (60–97 %) and reproducible at (1–50) gram scale through flow process. The scope of the reaction was studied by synthesizing terpene alcohols using different carbonyl compounds at optimized reaction conditions, which resulted in high product yield. This research addresses a crucial gap in terpene alcohol synthesis, offering a scalable and environmentally friendly approach with broad applicability.

Effect of initial water saturation and water film on imbibition behavior in tight reservoirs using nuclear magnetic resonance technique

Initial water saturation has a significant influence on spontaneous imbibition, and it impacts the imbibition rate and imbibed liquid dynamic distribution among pore networks. At present, the effect of initial water saturation on spontaneous imbibition is still unclear, especially the water film effect caused by initial water saturation varies during imbibition. To address these issues, we prepared the samples with varied initial water saturation through vapor adsorption and then conducted spontaneous imbibitions on these samples, which were monitored by nuclear magnetic resonance (NMR). Samples were selected from tight sandstone reservoirs in the eastern Ordos Basin. From the NMR spectrum corresponding to different imbibition duration, the left wing of the left peak at the initial water saturation is usually higher than the ones after imbibition, mainly caused by the water film effect. When the water film on the surface of large pores is too thin, it is prone to be interpreted as water in small pores because the water film has a quick relaxation time than the water in the center part of pores. The water film effect disappears when the whole pores are filled with water, and the inversed small pores decrease. The relaxation time of the water film is shorter than 0.51 ms in the tested samples. This study is conducive to understanding the effect of initial water saturation on liquid dynamic distribution during imbibition, especially the water film effect variation during imbibition and the T2 value of the water film.

Efficient synthesis of dihydropyranochromene derivatives via nanocopper immobilized on Zn/Cr-LDH functionalized with poly(p-phenylenediamine)

A new catalyst, poly(p-phenylenediamine) functionalized with copper nanoparticles stabilized on layered double hydroxide (LDH@poly(p-phenylenediamine)@CuI), was prepared. The structure of the new catalyst was identified and confirmed using different analyzes such as FESEM, EDX, XRD, TGA and elemental mapping. The efficiency of the mentioned catalyst was confirmed in the three-component one-pot synthesis of various derivatives of dihydropyrano[3,2-c]chromene in aqueous ethanol solvent. The structure of the synthesized products was confirmed using infrared spectrometry (FT-IR), nuclear magnetic resonance (1H NMR and 13C NMR) and Mass techniques. High yield of products, short reaction time, easy purification, reuse of catalyst, and the use of a soft reaction method can be considered as the main advantages of this method. Additionally, this catalyst was recycled four times without a significant loss of catalytic power.

Efficient and Selective Construction of 412 Metalla‐links Using Weak C−H⋅⋅⋅Halogen Interactions

AbstractThrough a coordination‐driven self‐assembly method, four metalla‐links and one tetranuclear monocycle were constructed with high selectivity and yield by adjusting the substituent species of the building blocks, as evidenced using X‐ray crystallographic analysis, electrospray ionization‐time‐of‐flight/mass spectrometry (ESI‐TOF/MS), elemental analysis and detailed solution‐state nuclear magnetic resonance (NMR) spectroscopy. Based on X‐ray crystallographic analysis and independent gradient model analysis, a significant factor leading to the formation of metalla‐links was the introduction of F, Cl, Br and I atoms, which generated additional weak C−H⋅⋅⋅X (X=F, Cl, Br and I) interactions. Furthermore, the dynamic conversion of metalla‐links to monocyclic rings in methanol solution was systematically investigated using quantitative 1H NMR techniques.

Efficient and Selective Construction of 41 2 Metalla-links Using Weak C-H⋅⋅⋅Halogen Interactions.

Through a coordination-driven self-assembly method, four metalla-links and one tetranuclear monocycle were constructed with high selectivity and yield by adjusting the substituent species of the building blocks, as evidenced using X-ray crystallographic analysis, electrospray ionization-time-of-flight/mass spectrometry (ESI-TOF/MS), elemental analysis and detailed solution-state nuclear magnetic resonance (NMR) spectroscopy. Based on X-ray crystallographic analysis and independent gradient model analysis, a significant factor leading to the formation of metalla-links was the introduction of F, Cl, Br and I atoms, which generated additional weak C-H⋅⋅⋅X (X=F, Cl, Br and I) interactions. Furthermore, the dynamic conversion of metalla-links to monocyclic rings in methanol solution was systematically investigated using quantitative 1H NMR techniques.

Flow Characterization in Fractured Shale Oil Matrices Using Advanced Nuclear Magnetic Resonance Techniques

The evaluation of flow dynamics in fractured shale oil reservoirs presents significant challenges due to the complex pore configurations and high organic material concentration. Conventional methods for petrophysical and fluid dynamic evaluations are insufficient in addressing these complexities. However, nuclear magnetic resonance (NMR) technology is an effective technique for quantitatively delineating fluid micro-transport properties across the reservoir core. This study presents an experimental methodology rooted in NMR technology to quantify the flow capabilities within the shale oil matrix. This approach incorporates high-pressure saturation flow experiments across seven distinct core samples to gauge the micro-transport phenomena of fluids across various pore dimensions. The results revealed that under high-pressure saturation, shale cores devoid of fractures demonstrated an average crude oil saturation rate of merely 19.44%. Cores with evident stratification exhibited a 16.18% increase in flow capacity compared to their non-stratified counterparts. The flow dynamics within these shale reservoirs exhibited a range of behaviors, from non-linear to linear. In lower-permeability zones, non-linear patterns became increasingly apparent. An NMR T2 spectrum analysis was used to identify the minimum effective pore size conducive to shale oil flow within the matrix, which was between 8 and 10 nanometers. These insights provide a foundation for a deeper understanding of the mechanisms behind oil and gas migration in fractured shale oil matrices, offering valuable insight into their extractive potential.

NMR-based pore water distribution characteristics of silty clay during the soil compaction, saturation, and drying processes

The pore water distribution (PWD) of soil provides key information about soil shear strength, hydraulic conductivity, and water-retention ability. The PWD characteristics of the soil depend on the specimen preparation conditions (i.e., the variations in initial water content or compaction degree) and drying-wetting processes, which were investigated by using the nuclear magnetic resonance (NMR) technique. The NMR T2 spectrum is mathematically transformed into the PWD curve to more accurately quantify the variations in pore water content stored with pores of different radii. The pore water in silty clay can be categorized into strongly bound water, intra-aggregate pore water, and inter-aggregate pore water, which are identified by the pore radius of <0.05 μm, 0.05-1.0 μm and >1.0 μm, respectively. The effects of compaction degree and initial water content on the PWD of the soil exhibit distinctions. For unsaturated compacted specimens, the PWDs remain unaffected by changes in compaction degree, while an increase in initial water content promotes the formation of clay aggregates, thereby increasing the maximum water-holding pore radius and the intra-aggregate pore water content. For saturated compacted specimens, the inter-aggregate and intra-aggregate pore water content increases with a decrease in the compaction degree, while the changes in the PWD shape from unimodal to bimodal with an increase in the initial water content. During the soil drying process, inter-aggregate pore water is rapidly drained, the intra-aggregate dominant pore water content increases first and then decreases, and the strongly bound water content remains constant. The relationship between the cumulative pore water distribution curve and the soil-water characteristic curve (SWCC) can be established through the Young-Laplace theory. The SWCC can be well predicted by using the envelope of the cumulative pore water distribution curves during soil drying.

Carbon capture in polymer-based electrolytes.

Nanoparticle organic hybrid materials (NOHMs) have been proposed as excellent electrolytes for combined CO2 capture and electrochemical conversion due to their conductive nature and chemical tunability. However, CO2 capture behavior and transport properties of these electrolytes after CO2 capture have not yet been studied. Here, we use a variety of nuclear magnetic resonance (NMR) techniques to explore the carbon speciation and transport properties of branched polyethylenimine (PEI) and PEI-grafted silica nanoparticles (denoted as NOHM-I-PEI) after CO2 capture. Quantitative 13C NMR spectra collected at variable temperatures reveal that absorbed CO2 exists as carbamates (RHNCOO- or RR'NCOO-) and carbonate/bicarbonate (CO32-/HCO3-). The transport properties of PEI and NOHM-I-PEI studied using 1H pulsed-field-gradient NMR, combined with molecular dynamics simulations, demonstrate that coulombic interactions between negatively and positively charged chains dominate in PEI, while the self-diffusion in NOHM-I-PEI is dominated by silica nanoparticles. These results provide strategies for selecting adsorbed forms of carbon for electrochemical reduction.

Cross-Polarization Solid-State NMR Quantification of Species within Pores of Metal-Organic Frameworks: A Case Study of α-Mg3(HCOO)6.

The quantitative measurement of adsorbed guest species within Metal-organic framework (MOF) pores is of fundamental importance for evaluating the adsorption performance of MOFs. However, routine analytic techniques such as thermogravimetric analysis cannot distinguish the contribution from species adsorbed within pores, species adsorbed on the surface, and gas phase or liquid phase encapsulated in the inter-crystalline space. Herein, we developed a new quantification method based on the cross-polarization (CP) solid-state nuclear magnetic resonance (SSNMR) technique, in which only the species within MOF pores are selectively probed due to the dramatically reduced mobility. Using the commercialized MOF α-Mg3(HCOO)6 as an example, a good linear correlation between Areaguest/Areaframework (i.e., the integrated area of guest and framework 13C NMR signals, respectively) and guest loading can be observed for several representative molecules such as benzene, tetrahydrofuran (THF), and 1,4-dioxane, clearly revealing the feasibility of CP quantification approach. The effects of guest molecule and corresponding residual mobility on the CP quantification are further discussed by varying the geometry and size of guest molecules. This methodology thus provides an effective and irreplaceable route to evaluate the adsorption performance of porous materials in-depth, especially for liquid-phase adsorption and gas-phase adsorption in which the capillary condensation is not negligible.

Grey modeling study on mechanical properties and pore structure of concrete with different basalt fiber contents based on NMR

This paper investigates the correlation between strength and pore characteristics of basalt fiber-reinforced concrete (BFRC) with different fiber contents and establishes a link between meso- and macro-properties. The research focuses on BFRC with differing fiber contents, analyzing compressive strength, flexural strength, and splitting tensile strength across eight admixture levels (ranging from 0 % to 0.35 %). Using the nuclear magnetic resonance (NMR) technique, T2 spectra of BFRC with varying fiber contents are obtained, deriving curves of the pore distribution. Additionally, considering the parameters of different pore size proportions, the paper delves into analyzing the impact of pore structure on BFRC's distinct mechanical properties using grey correlation. Utilizing the optimal pore structure parameters derived from GCA to forecast different strengths, this study establishes GM(1,3) prediction models for three strengths, respectively. The results showed that basalt fibers can enhance concrete strength. And, 0.25 % basalt fibers optimize concrete's the inner structure of BFRC by decreasing harmful pores. The comprehensive correlation between pore parameters and BFRC strength ranges significantly indicating a notable relationship between strength and pore alterations. The compressive strength was most related to the total porosity and the proportion of non-harmful pores, and the splitting tensile and flexural strengths were related to the fractal dimension and porosity of the harmful pores as well as to the total and non-harmful porosity, respectively. A BFRC strength prediction model formula was developed based on the most relevant pore structure parameters derived from GCA. This calculation formula showcases a high accuracy in predicting BFRC strength, establishing a mesoscopic-to-macroscopic quantitative relationship that effectively informs the production and application of BFRC.

Exploring Crystal-Phase Molecular Dynamics of the Low-Viscous Mesogen 6CHBT: A Combined FFC and High-Field NMR Relaxometry Investigation.

The molecular dynamics study of thermotropic mesogens exhibiting the crystal phases is valuable in unraveling the complex global (collective) and local (noncollective) motions executed by liquid crystal molecules, which would further advance the existing knowledge on orientationally disordered crystalline (ODIC) phases. Toward the fulfillment of such a task, a combined nuclear magnetic resonance (NMR) relaxometry approach employing the fast field cycling (FFC) NMR (10 kHz-30 MHz) and high-field pulsed NMR (400 MHz) techniques is utilized to sample the broad frequency range offered by molecular motions in the crystal phase of 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The validity of the observed relaxation data is tested and interpreted by the Bloembergen-Purcell-Pound (BPP) model involving the superposition of four mutually independent Lorentzian spectral densities, reflecting molecular dynamical processes on different time scales. The salient feature of the detailed analysis reveals that the lengthening of temporal dynamics in the crystal phase due to molecular rotations by jumps, which are of intermolecular origin, is evident and further supports the presence of collective-like local dynamics. The analysis does permit decoupling of the molecular reorientations about their short axes (∼100 ns) as well as long axes (∼50 ns) and methyl group rotations (∼0.5 ns) on distinct time scales. The activation energies for reorientations about the short axes and methyl group rotations are found to be 27.3 ± 2.7 and 15.8 ± 1.1 kJ/mol, respectively. The fast methyl rotations in the crystal phase of 6CHBT obtained from FFC NMR are further well complemented by high-field NMR, where 1H NMR line shapes are relatively narrow when compared to those of the nematic phase.

Cell wall water induced dimensional changes of beech and pine wood

Hygroexpansion in timber construction is a phenomenon that occurs as a result of changes in the cell wall structure of wood caused by water. In this study, beech (Fagus sylvatica) and pine (Pinus taeda L.) wood were conditioned at different relative humidities with saturated salt solutions and saturated through vacuum pressure impregnation. The moisture content and dimensions of the samples were evaluated under various adsorption equilibrium states, as well as during drying from water saturation to an air-dried state. The results obtained using the two-dimensional time-domain nuclear magnetic resonance technique revealed two distinct types of cell wall water in both wood species, designated as B-water and C-water, as they displayed different mobilities. With increasing moisture content, the mobility of cell wall water increased; however, B-water maintained a constant level of mobility and formed water clusters when it accumulated in the high humidity region and at slightly above the fiber saturation point (FSP), which is evidence of the occurrence of free-bound water. The B-water, located in the amorphous region of microfibrils and their surrounding hemicellulose, exerted a predominant influence on the dimensional changes of the wood both under equilibrium and nonequilibrium conditions, in comparison to the C-water which located in the matrix of hemicellulose and lignin.

Mandarin Variety Significantly Affects the Metabolites Present in the Leaves

Late-season varieties of mandarin (Citrus reticulata Blanco) have a high economic value, so their study, characterization, and comparison among different commercial varieties is of great interest for agriculture. Detailed metabolomic analysis of mandarin leaves can provide valuable information on agronomic characteristics, vegetative development, and tree response to abiotic and biotic stresses. In this study, an analysis of the main metabolites presents in the leaves of three late-season mandarin orange varieties (‘Afourer’, ‘Orri’ and ‘Tango’), cultivated under homogeneous conditions, was carried out using nuclear magnetic resonance (1H NMR) and multivariate statistical analysis techniques. The results show that organic acids and sugars are the metabolites with the highest presence in mandarin leaves, especially malate and sucrose. Ten amino acids and other metabolites such as choline and trigonelline were also detected. Metabolites such as asparagine and isoleucine were widely implicated in the metabolic pathways of the detected compounds. The ‘Orri’ variety showed significantly more differences in metabolite concentrations compared to the other two varieties studied. Malate and sucrose were shown to be the metabolites with the greatest significant differences between the varieties compared. From an agronomic point of view, the ‘Orri’ variety differs from the other two varieties because it has concentrations of metabolites that provide good resistance to abiotic and biotic stresses and fruits of higher quality and sweetness.