Solid-state 13C Research Articles

Hydrothermal carbonization of two-phase olive mill waste (alperujo): Effect of aqueous phase recycling

Hydrothermal carbonization (HTC) is a promising technique for the conversion of lignocellulosic biomass, such as two-phase olive mill waste (TPOMW). However, the resulting generated aqueous phase (AP) rich in organic compounds is harmful if directly discharged in the environment. In this work, the use of recycled aqueous phase from the HTC process of TPOMW is evaluated as a reactive medium. The evolution of products yields, quality, morphology chemical structure, and composition with AP recycling runs are investigated by different analytical methods (Nuclear Magnetic Spectroscopy 1H and solid state 13C, Scanning Electron Microscopy, Elemental analysis, Proximate analysis, Fourier Infrared Transform spectroscopy, Total organic carbon, and total nitrogen). The results revealed significant improvement in the hydrochar yield and energy yield that increase 47.4 wt% to 53.0 wt% and 72.8%–81.3%, respectively. The increase in the number of recycling experiments promotes the lignin condensation as well as the polymerization of AP intermediates into microspheres. These phenomena lead to the increase in hydrochar yield as well as the modification of its micro-surface into a smooth porous surface through the recycling runs. Additionally, FT-IR and the solid state 13C NMR analysis demonstrated that AP recycling has no noticeable effect on the chemical structure of the produced hydrochars. Further analysis of the AP demonstrated that the total organic carbon and total nitrogen increase significantly after the first recycling run from 17.3 to 26.5 g/L and 0.4–0.6 g/L, respectively. The 1H NMR analysis revealed that AP is mainly formed by aliphatic and aromatic compounds.

Construction of a food waste biochar model and determination of contaminant adsorption sites: Combining experimental characterisation with quantum chemical calculations

Increasing urbanization has made it a serious challenge to deal with food waste (FW) from people and wastewater with pollutants from industry. Biochar from FW pyrolysis(FWB) can be used as an adsorbent to adsorb pollutants from wastewater, but its molecular structure is still unknown, limiting the understanding of its adsorption mechanism and its application in industry. In this paper, a series of combined methods of experimental characterization and quantum chemical calculations, such as solid-state 13C nuclear magnetic resonance spectroscopy (13C NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to investigate and successfully construct a model of the molecular structural features of FWB under the optimal contaminant adsorption preparation conditions. Based on the electrostatic potential distribution and adsorption experiments, the adsorption sites of the pollutants were elucidated. The results showed that the FWB prepared at different temperatures, 450 °C had a variety of oxygen-containing functional groups and polarity favorable for adsorption. In the molecular structure of FWB with the molecular formula C60H49N7O8, oxygen is present in the form of carboxyl, carbonyl, ether, alcohol hydroxyl, and phenol hydroxyl groups with numbers 1, 1, 1, 1, 2, 1, 2. Nitrogen is present in the form of pyridinyl nitrogen, pyrrolidinyl nitrogen, and primary amines with numbers 1, 1, and 5, respectively. In addition, nitrogen-containing and oxygen-containing functional groups are possible adsorption sites for pollutants on FWB, and alcohol hydroxyl and amino groups can bind better to Cu2+, which provides scientific guidance for improving the adsorption performance of biochar. This provides a solid foundation for the study of the microscopic adsorption mechanism of FWB and a method for the modeling of biochar from other biomasses.

Structural analyses of supernatant fractions in TEMPO-oxidized pulp/water reaction mixtures separated by centrifugation and dialysis

Side reactions occurring on cellulose during 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TMEPO)-catalyzed oxidation have not been considered to be significant. Then, TEMPO-oxidized hardwood and softwood bleached kraft pulps (HBKP and SBKP) were prepared with an excess NaOCl·5H2O. Supernatant fractions (SFs) were obtained in the aqueous reaction mixtures of TEMPO-oxidized pulps by centrifugation and dialysis. The SFs with carboxyl contents of 5.0 and 4.2 mmol/g were obtained in the yields of 19 % and 30 % from HBKP and SBKP, respectively. These carboxy contents are much higher than those (2.6–2.7 mmol/g) of the precipitate fractions in the TEMPO-oxidized pulps. Solid-state 13C NMR spectra and other analyses revealed that the water-soluble β-(1 → 4)-polyglucuronic acids were predominantly present in the SFs. In addition, water-insoluble TEMPO-oxidized cellulose nanocrystals were present in the SFs, but they constituted less than ~10 % of the SFs. The mass-average degrees of polymerization (DPw) of the SFs obtained from HBKP and SBKP were 166 and 155, respectively, whereas the original HBKP and SBKP had DPw values of 1990 and 2140, respectively. These substantial depolymerization and formation of the water-soluble β-(1 → 4)-polyglucuronic acids occur on cellulose and oxidized cellulose molecules as side reactions during TEMPO-catalyzed oxidation, which should be considered for structural analyses of TEMPO-oxidized products.

Analysis of natural organic matter chemistry in bentonite clay under compaction using different dry densities and duration

The Nuclear Waste Management Organization of Canada has adopted an adaptive phased management plan for the long-term storage of used nuclear fuel in a Deep Geological Repository (DGR). The DGR barrier system employs copper-coated used fuel containers (UFCs) surrounded by buffer material which is composed of highly compacted bentonite clay. The natural organic matter (NOM) composition of the compacted bentonite is of practical importance for the safety assessment as it regulates the biogeochemical processes at the interface between the UFCs and the buffer layer. However, insufficient investigations on NOM constituents limits the understanding of biogeochemical dynamics in bentonites compacted under different dry densities. This study analyzed the carbon content and NOM composition using targeted compound analysis and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy with bentonites compacted at 1.1, 1.4 or 1.6 g/cm3 dry density for 1, 3, 6, 12 or 18 months. Organic carbon contents were similar across bentonites with different compaction densities at various durations as compared to the reference clay (powdered bentonite sample before compaction). The overall NOM composition measured by solid-state 13C NMR suggested a predominance of alkyl and aromatic carbon in bentonite samples. No marked variations were observed for the NOM components (i.e., alkyl, O-alkyl and aromatic carbon) between the compacted bentonites and the reference clay. Targeted compound analysis revealed that the extractable lipid concentrations in the compacted clays did not significantly vary from the reference bentonite with only some compounds exhibiting nano-gram level differences. Bentonites with relatively lower dry densities (1.1 and 1.4 g/cm3) demonstrated slightly higher extractable compound concentrations, but these differences were not statistically significant. In contrast, the compound concentrations of bentonites compacted to 1.6 g/cm3 were similar or slightly lower compared with the reference bentonite, likely associated with limited microbial growth under high dry compaction density. Taken together, these results suggested that NOM composition and quantity did not significantly alter in bentonites under various pressures nor with longer experimental durations. These findings highlight that compacted bentonite exhibited geochemical stability under the simulated repository environments, which provides critical insight for design and performance of engineered barrier system in a DGR concept.

Single-Step Synthesis and Characterization of Non-Linear Tough and Strong Segmented Polyurethane Elastomer Consisting of Very Short Hard and Soft Segments and Hierarchical Side-Reacted Networks and Single-Step Synthesis of Hierarchical Hyper-Branched Polyurethane.

Polyurethane elastomers are among the most versatile classes of industrial polymers-typically achieved through a two-step synthesis of segmented block copolymers, comprising very long and soft segments that provide elasticity and significantly long and hard segments that provide strength. The present research focused on the design of a single-step synthesis of a new segmented polyurethane consisting of very short soft and hard segments, crosslinked by preferentially side-reacted hierarchical tertiary oligo-uret network structures, thus exhibiting significant strength, elasticity, and toughness. Despite the theoretically linear structure, both FTIR and solid-state 13C NMR spectroscopy analyses indicated the quasi-equal presence of urethane groups and tertiary oligo-uret structures in the resulting polymer, indicating a preferential consecutive side reaction mechanism. Thermal analysis indicated the significant crystallization of soft segments consisting of only four ethylene oxide units, which was, hereby, demonstrated to occur via an extended chain mechanism. Tensile mechanical properties included significant strength, elasticity, and toughness. Increasing the soft segment length led to a decreased tertiary oligo-uret secondary crosslinking efficacy. The preferential hierarchical side reaction mechanism was, hereby, further confirmed through the synthesis of a completely new type of hyper-branched polymer via diisocyanate and a mono-hydroxy-terminated reagent. The structure-property relations and reaction mechanisms demonstrated in the present research can facilitate the design of new polyurethanes of enhanced performance and processing efficacy for a variety of novel applications.

Biomass derived cellulose nanofiber loaded PVA-nanocurcumin coating for extending the shelf life of Mandarin oranges (Citrus reticulata)

The concern over agricultural waste disposal can be resolved by converting them into value-added products. Here, sustainable fruit coatings and films have been developed via. wealth from waste concept. The cellulose nanofibers (CNF) have been extracted from the waste onion skin. The isolated CNF has been characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical microscopy (OM), dynamic light scattering (DLS) and solid-state 13C NMR spectroscopy. A combination of cellulose nanofiber (CNF) and nanocurcumin in polyvinyl alcohol (PVA) matrix has been used for the fabrication of coating over fresh mandarin oranges. The effect of nanocurcumin in PVA-CNF nanocomposite on the post-harvest maintenance of mandarin oranges has been investigated. The morphology of the prepared films is studied by SEM and atomic force microscopy (AFM). The quality of the orange fruits coated using the above formulation by dip coating method was analysed via. weight loss analysis, total soluble solid (TSS), pH, titrable acidity (TA) and antioxidant activities. It was found that the nanocurcumin incorporated PVA-CNF coating was effective in reducing mass loss and maintaining the physiochemical properties of oranges in comparison with other formulations. The developed method could be extended to use as food packaging films, which would be a sustainable solution for agricultural waste valorisation and plastic pollution. Through this research work, we propose an environment friendly approach for the preservation of fruits and vegetables.

Research on Strengthening Fragile Paper with Polyvinylamine.

Paper documents are an important carrier of information related to human civilization, with the reinforcement and protection of fragile paper documents being a key aspect of their protection. This research utilized amphoteric polyvinylamine polymer as a paper reinforcement agent, strengthening the Xuan paper commonly used in paper documents. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), solid-state 13C NMR, and other analytical methods were employed to compare the physical properties, micro-morphology, crystallinity, and aging resistance of the paper before and after reinforcement. Research was conducted on the effects of reinforcement, the aging resistance, and the effects on the fiber structure. The results indicate that polyethylenimine has a filling and bridging effect between the paper fibers. After treatment with polyethylenimine, there was a significant improvement in the folding endurance and tensile strength of the paper. Additionally, the paper maintains a good mechanical strength even after undergoing dry heat and humid aging.

Enhancing the Crystallinity of Keto-enamine-Linked Covalent Organic Frameworks through an in situ Protection-Deprotection Strategy.

β-Keto-enamine-linked 2D covalent organic frameworks (COFs) have emerged as highly robust materials, showing significant potential for practical applications. However, the exclusive reliance on 1,3,5-triformylphloroglucinol (Tp aldehyde) in the design of such COFs often results in the production of non-porous amorphous polymers when combined with certain amine building blocks. Attempts to adjust the crystallinity and porosity by a modulator approach are inefficient because Tp aldehyde readily forms stable β-keto-enamine-linked monomers/oligomers with various aromatic amines through an irreversible keto-enol tautomerization process. Our research employed a unique protection-deprotection strategy to enhance the crystallinity and porosity of β-keto-enamine-linked squaramide-based 2D COFs. Advanced solid-state NMR studies, including 1D 13 C CPMAS, 1 H fast MAS, 15 N CPMAS, 2D 13 C-1 H correlation, 1 H-1 H DQ-SQ, and 14 N-1 H HMQC NMR were used to establish the atomic-level connectivity within the resultant COFs. The TpOMe -Sqm COFs synthesized utilizing this strategy have a surface area of 487 m2 g-1 , significantly higher than similar COFs synthesized using Tp aldehyde. Furthermore, detailed time-dependent PXRD, solid-state 13 C CPMAS NMR, and theoretical DFT studies shed more light on the crystallization and linkage conversion processes in these 2D COFs. Ultimately, we applied this protection-deprotection method to construct novel keto-enamine-linked highly porous organic polymers with a surface area of 1018 m2 g-1 .

Controlled Sublimation Rate of Guest Drug from Polymorphic Forms of a Cyclodextrin-Based Polypseudorotaxane Complex and Its Correlation with Molecular Dynamics as Probed by Solid-State NMR.

Encapsulation of active pharmaceutical ingredients (APIs) in confined spaces has been extensively explored as it dramatically alters the molecular dynamics and physical properties of the API. Herein, we explored the effect of encapsulation on the molecular dynamics and physical stability of a guest drug, salicylic acid (SA), confined in the intermolecular spaces of γ-cyclodextrin (γ-CD) and poly(ethylene glycol) (PEG)-based polypseudorotaxane (PPRX) structure. The sublimation tendency of SA encapsulated in three polymorphic forms of the γ-CD/PEG-based PPRX complex, monoclinic columnar (MC), hexagonal columnar (HC), and tetragonal columnar (TC), was investigated. The SA sublimation rate was decreased by 3.0-6.6-fold and varied in the order of MC form > HC form > TC form complex. The 13C and 1H magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectra and 13C spin-lattice relaxation time (T1) indicated that the encapsulated SA molecules existed as the monomeric form, and its molecular mobility increased in the order of MC form > HC form > TC form complex. In the complexes, a rapid chemical exchange between two dynamic states of SA (free and bound) was suggested, with varying adsorption/desorption rates accounting for its distinct molecular mobility. This adsorption/desorption process was influenced by proton exchange at the interaction site and interaction strength of SA in the complexes, as evidenced by 1H MAS spectra and temperature dependency of the 13C carbonyl chemical shift. A positive correlation between the molecular mobility of SA and its sublimation rate was established. Moreover, the molecular mobility of γ-CD and PEG in the complexes coincided with that of SA, which can be explained by fast guest-driven dynamics. This is the first report on the stability improvement of an API through complexation in polymorphic supramolecular host structures. The relationship between the molecular dynamics and physical properties of encapsulated API will aid in the rational design of drug delivery systems.

Activity of a Recombinant Chitinase of the Atta sexdens Ant on Different Forms of Chitin and Its Fungicidal Effect against Lasiodiplodia theobromae.

This study evaluates the activity of a recombinant chitinase from the leaf-cutting ant Atta sexdens (AsChtII-C4B1) against colloidal and solid α- and β-chitin substrates. 1H NMR analyses of the reaction media showed the formation of N-acetylglucosamine (GlcNAc) as the hydrolysis product. Viscometry analyses revealed a reduction in the viscosity of chitin solutions, indicating that the enzyme decreases their molecular masses. Both solid state 13C NMR and XRD analyses showed minor differences in chitin crystallinity pre- and post-reaction, indicative of partial hydrolysis under the studied conditions, resulting in the formation of GlcNAc and a reduction in molecular mass. However, the enzyme was unable to completely degrade the chitin samples, as they retained most of their solid-state structure. It was also observed that the enzyme acts progressively and with a greater activity on α-chitin than on β-chitin. AsChtII-C4B1 significantly changed the hyphae of the phytopathogenic fungus Lasiodiplodia theobromae, hindering its growth in both solid and liquid media and reducing its dry biomass by approximately 61%. The results demonstrate that AsChtII-C4B1 could be applied as an agent for the bioproduction of chitin derivatives and as a potential antifungal agent.

Biodegradable Nanocomposites Based on Blends of Poly(Butylene Adipate-Co-Terephthalate) (PBAT) and Thermoplastic Starch Filled with Montmorillonite (MMT): Physico-Mechanical Properties.

Poly(butylene adipate-co-terephthalate) (PBAT) is widely used for production of biodegradable films due to its high elongation, excellent flexibility, and good processability properties. An effective way to develop more accessible PBAT-based bioplastics for wide application in packaging is blending of PBAT with thermoplastic starch (TPS) since PBAT is costly with prices approximately double or even triple the prices of traditional plastics like polyethylene. This study is focused on investigating the influence of TPS/PBAT blend ratio and montmorillonite (MMT) content on the physical and mechanical properties and molecular mobility of TPS-MMT/PBAT nanocomposites. Obtained TPS-MMT/PBAT nanocomposites through the melt blending process were characterized using tensile testing, dynamic mechanical thermal analysis (DMTA), and X-ray diffraction (XRD), as well as solid-state 1H and 13C NMR spectroscopy. Mechanical properties demonstrated that the addition of TPS to PBAT leads to a substantial decrease in the tensile strength as well as in the elongation at break, while Young's modulus is rising substantially, while the effect of the MMT addition is almost negligible on the tensile stress of the blends. DMTA results confirmed the formation of TPS domains in the PBAT matrix. With increasing TPS content, mobility of starch-rich regions of TPS domains slightly increases. However, molecular mobility in glycerol-rich regions of TPS domains in the blends was slightly restricted. Moreover, the data obtained from 13C CP/MAS NMR spectra indicated that the presence of TPS in the sample decreases the mobility of the PBAT chains, mainly those located at the TPS/PBAT interfaces.

The hidden depths of forest soil organic carbon chemistry in a pumice soil

Forest ecosystems can store massive amounts of organic carbon (OC) deep in their soils. Soil OC (SOC) is composed of several complex organic compounds of which groupings of these organic compounds can provide an insight into evaluating the formation and fate of SOC. However, there is little information available regarding the chemical composition of deep forest SOC and how they compare to upper soil depths. The objective of this study was to explore the SOC chemistry changes with increasing soil depth on a fine spatial scale in a planted forest soil derived from young volcanic erupted airfall deposits. Soil core samples to 1 m depth were collected from Puruki Experimental Forest (New Zealand) and examined for incremental depth changes in SOC functional groups, or chemical shift regions, using solid-state 13C cross polarisation magic angle spinning nuclear magnetic resonance (13C CPMAS-NMR) spectroscopy. The results showed that soil depth was a driver of change in soil chemical shift regions. The presence of a coarse-textured soil horizon, lapilli layer, at depth was a driver of significant (p < 0.05) differences between SOC functional groups. In the upper soil profile (0–10 cm), the chemical shift distribution was dominated by O-alkyl C (39%) followed by alkyl C (32%), aromatic C (23%), and carboxyl C (6%). In the deep soil layers, we found alkyl C increased below the lapilli layer (varying depth > 50 cm) compared to above the lapilli layer. In the deep soil layers the alkyl C was the dominant functional group (55%), followed by O-alkyl C (28%). Furthermore, there was a decrease at depth in aromatic (12%) and carboxyl C (5%). The A/O-A ratio increased with depth from soil above the lapilli layer compared to soils below the lapilli layer indicating a greater degree of organic matter decomposition and a corresponding decrease in the labile OC fractions. Within the lapilli layer the SOC functional groups and A/O-A ratio were highly variable. These results highlight that changes in SOC chemical composition occur with increasing soil depth, a property of deep soil that is frequently understudied, and are highly influenced by the multi layered nature of soil derived from volcanic airfall deposits.

Novel and safe debranched starch-zinc complexes with endoconcave structure as zinc supplements

Zinc deficiency is a serious risk to human health and growth, especially in children. The development of zinc supplements can effectively reduce this harm. Here, a series of debranched starch‑zinc complexes (DS-Zn) were prepared, whose zinc complexation was inversely proportional to the amylopectin content in the debranched starch (DS). The physicochemical properties of DS-Zn were characterized using the conductivity, XRD, iodine staining and thermogravimetry. Combined with XPS, solid-state 13C NMR and IR, it was elucidated that the structure of DS-Zn is endoconcave structure with 2-O and 3-O of DS on the inner side and 6-O of DS on the outer side, where zinc is located. The DS-Zn exhibits good biosafety including blood, cellular and mutagenicity. In vitro simulations of digestion and zinc-deficient cellular models showed that DS-Zn was more tolerant to the gastrointestinal environment and more effective in zinc supplementation (increased by 33 %) than inorganic zinc supplements. Utilizing the compressibility of starch, DS-Zn was prepared as a more palatable oral cartoon tablet for children. This study will provide important support to advance the development and application of novel starch-based zinc nutritional supplements.

Effect of SH/SBA‐15 Molar Ratio on Pb(II) and Cd(II) Ions Adsorption from Aqueous Solution by Mercaptopropyl‐grafted SBA‐15 Mesoporous Material as Adsorbent

AbstractThe purposes of the current study were to investigate the adsorption of Pb(II) and Cd(II) from aqueous solution by thiol‐functionalized SBA‐15 materials designed by SBA‐15‐SH (x) where x is the SH/SBA‐15 molar ratio, which corresponds to the introduced moles number of Mercapto moieties to that of siliceous of the SBA‐15 materials. Furthermore, these materials were synthesized using 3‐Mercaptopropyltrimethoxysilane (MPTMS) via post‐grafting approach. SBA‐15‐SH(x) materials were characterized by XRD, N2 adsorption‐desorption and FT‐IR. The incorporation of SH fragments was proved by FT‐IR Spectroscopy, thermogravimetric analysis (TGA) and solid state 13C and 29Si NMR Spectroscopy.The removal of lead ions is more important than that of cadmium ions. Furthermore, the lead removal on SBA‐15‐SH(x) increased with the increase of SH/SBA‐15 molar ratio (removal rate of 28.5, 71.3, and 96.8 % for SH/SBA‐15 molar ratio=0.35, 0.7 and 1.4, respectively) while the removal of cadmium was not affected (around 57 % removal rate for all molar ratios).

Small organic molecules containing amorphous calcium phosphate: synthesis, characterization and transformation.

As the primary solid phase, amorphous calcium phosphate (ACP) is a pivotal precursor in cellular biomineralization. The intrinsic interplay between ACP and Howard factor underscores the significance of understanding their association for advancing biomimetic ACP development. While organic compounds play established roles in biomineralization, this study presents the synthesis of ACP with naturally occurring organic compounds (ascorbate, glutamate, and itaconate) ubiquitously found in mitochondria and vital for bone remodeling and healing. The developed ACP with organic compounds was meticulously characterized using XRD, FTIR, and solid-state 13C and 31P NMR. The morphological analysis revealed the characteristic spherical morphology with particle size close to 20nm of all synthesized ACP variants. Notably, the type of organic compound strongly influences true density, specific surface area, particle size, and transformation. The in vitro analysis was performed with MC3T3-E1 cells, indicating the highest cell viability with ACP_ASC (ascorbate), followed by ACP_ITA (itaconate). The lowest cell viability was observed with 10 %w/v of ACP_GLU (glutamate); however, 1 %w/v of ACP_GLU was cytocompatible. Further, the effect of small organic molecules on the transformation of ACP to low crystalline apatite (Ap) was examined in Milli-Q® water, PBS, and α-MEM.

Polyglucuronic acids prepared from α-(1 → 3)-glucan by TEMPO-catalytic oxidation

2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-catalytic oxidation was applied to a water-insoluble α-(1 → 3)-glucan in water at pH 10 and room temperature (∼24 °C), with solid NaOCl·5H2O as the primary oxidant. Oxidation with NaOCl at 15 mmol/g gave a water-soluble TEMPO-oxidized product at a mass recovery ratio of 97 %. The carboxy content of the TEMPO-oxidized product was 5.3 mmol/g, which corresponds to a degree of C6-oxidation (DO) of 93 %. A new water-soluble α-(1 → 3)-polyglucuronic acid with a nearly homogeneous chemical structure was therefore quantitatively obtained. X-ray diffraction and solid-state 13C NMR spectroscopic analyses showed that the original α-(1 → 3)-glucan and its TEMPO-oxidized product with a carboxy content of 5.3 mmol/g had crystalline structures, whereas the oxidized products with DOs of 50 % and 66 % had almost disordered structures. The carboxy groups in the oxidized products were regioselectively methyl esterified with trimethylsilyl diazomethane, and analyzed by using size-exclusion chromatography with multi-angle laser-light scattering and refractive index detections. The results show that the original α-(1 → 3)-glucan and its oxidized products with DOs of 50 %, 66 %, and 93 % had weight-average degrees of polymerization of 671, 288, 54, and 45, respectively. Substantial depolymerization of the α-(1 → 3)-glucan molecules therefore occurred during catalytic oxidation, irrespective of the oxidation pH.

Chemical composition of soil carbon is governed by microbial diversity during understory fern removal in subtropical pine forests

Understory vegetation has an important impact on soil organic carbon (SOC) accumulation. However, little is known about how understory vegetation alters soil microbial community composition and how microbial diversity contributes to SOC chemical composition and persistence during subtropical forest restoration. In this study, removal treatments of an understory fern (Dicranopteris dichotoma) were carried out within pine (Pinus massoniana) plantations restored in different years in subtropical China. Soil microbial community composition and microbial diversity were measured using phospholipid fatty acids (PLFAs) biomarkers and high-throughput sequencing, respectively. The chemical composition of SOC was also measured via solid-state 13C nuclear magnetic resonance (13C NMR). Our results showed that fern removal decreased alkyl C by 4.2 % but increased O-alkyl C by 15.6 % on average, leading to a decline of alkyl C/O-alkyl C ratio, suggesting altered chemical composition of SOC and lowered SOC recalcitrance without fern. Fern removal significantly lowered the fungi-to-bacteria ratio, and it also reduced fungal and bacterial diversity. Partial correlation analysis revealed that soil nitrogen availability was a key factor influencing microbial diversity. Bacterial diversity showed a close relationship with the Alkyl C/O-alkyl C ratio following fern removal. Furthermore, the microbial community structure and bacterial diversity were responsible for 18 % and 55 % of the explained variance in the chemical composition of SOC, respectively. Taken together, these analyses jointly suggest that bacterial diversity exerts a greater role than microbial community structure in supporting SOC persistence during understory fern removal. Our study emphasizes the significance of understory ferns in supporting microbial abundance and diversity as a means of altering SOC persistence during subtropical forest restoration.

Effects of cage topology on ethylene adsorption mechanism in silver exchanged CHA and RHO zeolites: An Inelastic Neutron Scattering and Density Functional study

Zeolite-based adsorbents have been successfully used for many challenging separations due to their tunable properties. A particularly notable application involves the separation of light olefins from paraffins, wherein the molecular sieving properties of zeolites play a pivotal role. Additionally, the selective interaction of alkenes with transition metal cations, positioned within the channels and cavities of microporous zeolites, further enhances separation capabilities.This study aims to comprehensively characterize the interactions between ethylene and Ag+ exchanged zeolites, employing a multidisciplinary approach, combining Inelastic Neutron Scattering (INS), Infrared (IR) spectroscopy, Nuclear Magnetic Resonance (NMR), UV–Vis and Density Functional Theory (DFT) calculations. CHA and RHO, zeolites largely applied in gas separation processes, were chosen due to their similar small pore sizes and pore volume, but different cavity shapes and flexibilities.The interpretation of derived DFT Electron Density Difference, experimentally supported by 13C Solid State NMR results, provide an understanding of each framework’s role during the charge transfer mechanisms between ethylene and transition metal species. Specific deformations in the flexible framework of zeolite RHO explain a blueshift of the band at 400 cm−1 in the librational region of INS spectra compared to CHA. This structural change in RHO, represented by the conic shape of the cage 8-ring side pockets, increases steric effects over the adsorbate while rendering the metallic adsorption center less exposed within the zeolite’s cavity, finally leading to a weaker adsorption energy. The redshift of C=C stretching frequencies observed by IR spectroscopy and DFT calculations, as well as C=C and C-H bond lengthening of ethylene confirm the formation of π-complexes on silver in both zeolites and allowed a further evaluation of the effects of the different frameworks cages on the aforementioned interaction.

Stoke's shift and quantum efficiency enhancement in fluorescent coumarin aldehyde (HMCA) dye-conjugated chitosan matrix for optoelectronic applications

A greenish-yellow emissive fluorescent coumarin aldehyde conjugated chitosan matrix was prepared by performing a Schiff base reaction between 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde (HMCA) and chitosan. The newly formed imine linkage was confirmed by the appearance of an absorption band at 1641 cm−1 in the IR spectrum and also supported by the solid-state 13C-NMR with cross polarisation magic angle spinning (CPMAS) method. The molecular weight of the HMCA-conjugated chitosan matrix was augmented with an increase in the HMCA concentration. The SEM images unveiled crystallite aggregates in the chitosan matrix and the improved crystallinity was witnessed in the PXRD result. The chemically conjugated chitosan film unveiled a larger Stoke's shift value of 183–224 nm which was just 50–130 nm in pure HMCA. The conjugate material could overcome the self-absorption issue associated with the coumarin aldehyde. The coumarin aldehyde exhibited dual emission at 390 nm and 440 nm but it was shifted to 520 nm with single emission upon reaction with chitosan. The observed redshift could be assigned for the formation of static excimer that resulted from the chitosan backbone containing pendant chromophore (coumarin dye) which could interact with another neighbouring chromophoric group of the same chain or different chain creating a ground-state stable dimer. The emission of conjugate material shifted from blue to greenish yellow region with a higher quantum yield of 30.21 % compared to 8.57 % of HMCA alone. The calculated indirect band gap of 2.25–2.34 and the optimum refractive index suggested the potential optoelectronic applications of HMCA-conjugated chitosan as an OLED Material.

Solid-state 1H and 13C NMR studies of new ionic plastic-crystals with branched structures: [NEtxMe(3-x)(i-Pr)][BEt(4-y)Mey] (x = 1-3, y = 0, 1).

Eight salts of [NEtxMe(3-x)(i-Pr)][BEt(4-y)Mey] (x = 1-3, y = 0, 1) were prepared to reduce Coulombic interactions in the crystals. These novel ionic plastic crystals exhibited low activation energies for isotropic rotational motion (Ea rot) and ion diffusion (Ea diff). The lattice constant a in the cubic structure indexed to a CsCl-type was larger than that of the corresponding plastic crystals of [NEtxMe(4-x)][BEt(4-y)Mey] (nonbranched sample). Solid-state 1H and 13C nuclear magnetic resonance (NMR) spectra of the salts revealed that both cations and anions undergo isotropic reorientation motions in the plastic crystalline phase. This result is consistent with the differential scanning calorimetry data, which showed that the compounds have large entropy changes at the transition temperature between the ordinal and plastic crystalline phases, except for [NEt2Me(i-Pr)][BEt3Me] and [NEt3(i-Pr)][BEt3Me]. The Ea rot and Ea diff values were estimated using 1H NMR spin-lattice relaxation time (T1) and electrical conductivity measurements, respectively.