Solid-state 13C NMR Spectra Research Articles

Structural, Hirshfeld surface and spectroscopic studies of the noncentrosymmetric 1-ethylpiperazinediium pentachloroantimonate (III) monohydrate

1-Ethylpiperazinediium pentachloroantimonate (III) monohydrate, C6H16N2SbCl5·H2O, has been synthesized by the reaction of antimony trioxide (Sb2O3) and 1-ethylpiperazine in an aqueous solution of hydrochloric acid. The structure crystallizes in orthorhombic system, in the non-centrosymmetric space group Pca21 and consists of isolated [C6H16N2]2+ cations, square pyramidal [SbCl5]2− anions and lattice water molecules. OH⋯Cl hydrogen bonds link the [SbCl5]2− anions and water molecules to form double chains stretching along the [101] direction. The chains in turn are linked to the organic cations via NH⋯Cl, CH⋯Cl, CH⋯O and NH⋯O hydrogen bonds to form a three-dimensional network. This structure presents an example of a general square pyramidal complex ion containing a stereo-chemically active lone pair of electrons. Solid state 13C and 15N CP-MAS NMR spectra are in agreement with the X-ray structure, and vibrational absorption bands were identified by infrared spectroscopy. DFT calculations allowed the attribution of the NMR peaks and IR absorption bands. The interactions variability of the two independent cations and ten chloride atoms is analyzed via Hirshfeld surface analysis.

Solid state structure of (pentamethylcyclopentadienyl)(2,4-dimethylpentadienyl)iron, Fe(C5Me5)(2,4-C7H11), and its incorporation into silica aerogels

The structure of Fe(C5Me5)(2,4-C7H11) has been determined (C7H11=dimethylpentadienyl), and found to be isomorphous with its ruthenium analogue. The Fe–C bond distances for the open pentadienyl ligand have been found to be about 0.02Å shorter than those for the aromatic pentamethylcyclopentadienyl ligand, whereas for the simple cyclopentadienyl analogue, the Fe–C bond distances for the two ligand types were nearly identical. While the structural data support proposals that the pentadienyl ligand is more strongly bound, the complex reacts readily with silica aerogel, during which it is the nonaromatic pentadienyl ligand which is removed via protonation. Solid state 13C NMR spectra are consistent with incorporation of the metal into one major environment, with lesser degrees of incorporation into alternative environments.

A Polymer-Coated Rhodium/Diamine-Functionalized Silica for Controllable Reaction Switching in Enantioselective Tandem Reduction–Lactonization of Ethyl 2-Acylarylcarboxylates

The design of a smart heterogeneous catalyst for controllable reaction switching is highly desirable in asymmetric catalysis. In this work, by taking advantage of the thermoresponsive behavior of a water-soluble polymer coating and the confined feature of silica nanoparticles, we have constructed a silica material with chiral rhodium/diamine functionality on SiO2 nanospheres coated with a water-soluble thermoresponsive polymer. The solid-state 13C NMR spectrum of the product demonstrated well-defined single-site chiral rhodium active centers within the thermoresponsive polymer, and scanning electron microscopy and transmission electron microscopy revealed its uniformly dispersed morphology. As a smart heterogeneous catalyst, it enables catalyst-based temperature-controlled reaction switching in the enantioselective tandem reduction–lactonization of ethyl 2-acylarylcarboxylates in water. At 40 °C, the catalyst promotes highly enantioselective tandem reduction–lactonization by adopting the extended form of the thermoresponsive polymer coating, whereas at 15 °C the reaction is terminated and the heterogeneous catalyst can be recycled because of its closed form. This feature endows this catalyst with high efficiency and recyclability for the synthesis of chiral phthalides in an environmentally friendly medium.

Transformations of lead 1,3-propylenediaminetetraacetate to its MOF products for the selective adsorption of methanol

Water soluble coordination polymer of potassium lead 1,3-propylenediaminetetraacetate {K4[Pb2(1,3-pdta)2]·6H2O}n (1) and its insoluble products {[Pb(1,3-H2pdta)(H2O)]·2H2O}n (2), {[Pb2(1,3-pdta)(H2O)4]·4H2O}n (3) and [Pb2(1,3-pdta)(H2O)2]n (4) were obtained from the direct reactions of lead nitrate with 1,3-propylenediaminetetraacetic acid in different conditions (1,3-H4pdta=1,3-propylenediaminetetraacetic acid). The former 1 could be converted to the insoluble products of {[Pb2(1,3-pdta)(H2O)4]·4H2O}n (3) and [Pb2(1,3-pdta)(H2O)2]n (4) in weak acidic solution. The complexes have been full characterized by EA, FT-IR, solution and solid state 13C NMR spectra, thermogravimetric and structural analyses. Interestingly, 3 contains a unique (H2O)26 cluster and a 5.2Å pore after eliminating the guest water molecules, which exhibits reversible adsorption for methanol. This is confirmed by PXRD and solid state 13C NMR analyses. Nano-confined methanol in microporous structure has been observed based on the large downfield shift of 13C NMR signal (Δδ 9.72ppm), attributing to the methyl group in methanol.

Hydrophobic silica aerogels by silylation

In this work, silica gel networks were modified with a silylating agent dimethoxy-methyl (3,3,3-trifluoropropyl) silane (SiF3) to obtain hydrophobic aerogels of various surface energy values. The baseline aerogels were synthesized from tetraethoxy silane (TEOS) using a two-step sol–gel process followed by supercritical drying in liquid carbon dioxide. The resultant aerogels were characterized using scanning electron microscopy, Instron tensile tester, contact angle goniometry, and nitrogen adsorption–desorption isotherms. Three modification methods were studied. In method 1, TEOS and SiF3 were combined before gelation; in method 2, SiF3 was added after TEOS was hydrolyzed and before its condensation, and in method 3, SiF3 was added after the gels were produced from TEOS. It was found that method 3 produced the best results in terms of achieving high values of hydrophobicity and compressive properties. The data on solid state 13C and 29Si NMR spectra revealed chemical reactions between the silylating agents and the silanol groups on silica surface. The bulk density and the fractal dimensions of silica networks gleaned from small angle X-ray scattering (SAXS) data showed weak dependence on the degree of silylation. The silylation process rendered the aerogels strongly hydrophobic and also doubled its compressive modulus.

Correlating the role of hydrophilic/hydrophobic nature of Rh(I) and Ru(II) supported organosilica/silica catalysts in organotransformation reactions

Highly reactive and hydrophobic triphenyl phosphine based rhodium(I) and ruthenium(II) organometallic complexes over benzene containing periodic mesoporous organosilica (PMOB) have been synthesized. This has been achieved by the immobilization of neat metal complexes like RhCl(PPh3)3 [Wilkinson catalyst], RuHCl(CO)(PPh3)3 and RuCl2(PPh3)3 over aminofunctionalized PMOB to get RhCl(PPh3)2-PrNH2PMOB, RuHCl(CO)(PPh3)2-PrNH2PMOB and RuCl2(PPh3)3-PrNH2PMOB, respectively. The physico-chemical properties of the functionalized catalysts were analyzed by elemental analysis, ICP-OES, XRD, N2 sorption analyses, FT-IR, solid state 13C and 29Si NMR spectra, XPS, SEM, TEM and contact angle measurements. The XRD and N2 sorption analyses showed excellent textural properties with ordered mesoporous channel structure of all synthesized catalysts. The organic moieties anchored in PMOB were confirmed by 13C CPMAS NMR and FT-IR spectroscopy with 29Si CPMAS NMR spectroscopy providing the information about the degree of functionalization of surface silanol groups with organic moiety. The Rh(I) and Ru(II) complexes supported on MCM-41/SBA-15/PMOE (ethane–PMO) were synthesized, and their catalytic activities in hydrogenation and sulfoxidation reactions were compared with Rh(I) and Ru(II) complexes supported on PMOB. The results show that PMOB based catalysts exhibit higher activities and selectivities than MCM-41/SBA-15/PMOE supported catalysts, neat homogeneous complexes and without catalyst. The better catalytic performance of PMOB based catalyst is attributed to the hydrophobic nature and high surface area of the PMOB support. The recycling studies of anchored catalysts show no major deactivation of the catalyst.

The chemistry of some foliar litters and their sequential proximate analysis fractions

Proximate analysis (PA) is widely used to assess foliar, litter, and wood quality. The acid-unhydrolyzable residue (AUR) of PA, originally known as Klason lignin from wood analysis, is often assumed to be entirely lignin-derived, but the AUR of much plant material also includes contributions from condensed tannins (CT) and cutin or suberin. To improve understanding of chemical changes throughout the PA procedure, we characterized seven foliar litters and their sequential PA fractions (nonpolar and hot-water extracted, AUR). Changes in total C and N, extractable and insoluble CT (as detected by butanol/HCl hydrolysis), δ13C values and solid-state 13C NMR spectra were consistent with loss of carbohydrates and protein after acid hydrolysis, and support previous studies that the AUR residue includes lignin, cutin and CT, all of which are depleted in δ13C. Hot-water extraction removed the bulk of extractable plus insoluble CT. Only trace levels were detected in the AUR, although 13C NMR shows that these are likely underestimates. The assumption of lignin-AUR equivalence still causes misinterpretation of PA results for many sample categories. It is time for the scientific community to limit use of “lignin” to chemically meaningful contexts?

The chemistry of death – Adipocere degradation in modern graveyards

The formation of adipocere slows further decomposition and preserves corpses for decades or even centuries. This resistance to degradation is a serious problem, especially with regard to the reuse of graves after regular resting times.We present results from an exhumation series in modern graveyards where coffins from water-saturated earth graves contained adipocere embedded in black humic material after resting times of about 30 years. Based on the assumption that this humic material resulted from in situ degradation of adipocere, its presence contradicts the commonly held opinion that adipocere decomposition only occurs under aerobic conditions.To test our hypothesis, we collected black humic material, adipocere as well as soil samples above and below coffins from representative graves (n=7). A comprehensive chemical analysis of the samples substantiated our in situ degradation theory. Element compositions and fatty acid mass spectra confirmed that the humic black material originated from the corpses. A van Krevelen diagram classified the excavated adipocere material as lipid, whereas the black humic material was closer to the carbohydrate region. Mass fragmentograms of the humic material revealed the presence of large amounts of saturated vs. unsaturated nC16 and nC18 fatty acids, which is typical for adipocere. In addition, the soil samples exhibited a lipid signature deriving primarily from plant waxes and root components (C20C32). Solid-state 13C NMR spectra of adipocere displayed well-resolved signals of saturated aliphatic chains and a signal that corresponded to carboxylic acid groups. The NMR spectra of the black humic material revealed signals characteristic of long aliphatic chains. The intensities varied in relation to the state of degradation of the sample, as did the signals of oxidized aliphatic chains, acetals and ketals, aromatic structures, esters and amids. The analyses confirmed that the black humic material was indeed derived from adipocere, so the assumption is that the components detected must have developed from aliphatic fatty acids via a number of oxidation and condensation processes.We therefore propose the existence of chemical pathway(s) for the degradation of adipocere under poikiloaerobic conditions. Possible (biogeo)chemical reaction chains include (1) the autoxidation of fatty acids enhanced by haemoglobin, methaemoglobin and haemin, (2) the use of alternative electron acceptors, which leads to the formation of H2S that then reacts abiotically with iron (from haemoglobin), rendering iron sulphide, and (3) the Maillard reaction. These findings are another step forward in understanding the chemistry of buried corpses.

Nano-Confined Synthesis of Fullerene Mesoporous Carbon (C60-FMC) with Bimodal Pores: XRD, TEM, Structural Properties, NMR, and Protein Immobilization

Nanoconfined synthesized crystalline fullerene mesoporous carbon (C60-FMC) with bimodal pore architectures of 4.95 nm and 10-15 nm pore sizes characterized by XRD, TEM, nitrogen adsorption/ desorption isotherm and solid-state NMR, and the material was used for protein immobilization. The solid-state 13C NMR spectrum of C60-FMC along with XRD, BET and TEM confirms the formation of fullerene mesoporous carbon structure C60-FMC. The immobilization of albumin (from bovine serum, BSA) protein biomolecule in a buffer solution at pH 4.7 was used to determine the adsorption properties of the C60-FMC material and its structural changes investigated by FT-IR. We demonstrated that the C60-FMC with high surface area and pore volumes have excellent adsorption capacity towards BSA protein molecule. Protein adsorption experiments clearly showed that the C60-FMC with bimodal pore architectures (4.95 nm and 10-15 nm) are suitable material to be used for protein adsorption.

Permeability of hydrated poly(vinyl alcohol): Effect of relaxation behaviors and hydrogen bonds in supramolecular structure

The particular permeability of hydrated poly(vinyl alcohol) (PVA) was investigated from the point of polymeric relaxation behavior, and the more essential effect of hydrogen bonds in supramolecular structure was further analyzed as well. The permeability measurement showed that various hydrated PVA samples all had lower permeability to non-polar solvents, and the permeability was affected by relaxation state, which can be controlled by water content. Dynamic mechanical analysis measurements indicated that, in PVA with lower water content the relaxation motion benefiting permeation almost became frozen in glassy amorphous region, due to high activation energy of conformation transition, which then induced the slower permeation to occur. Solid-state 1H and 13C NMR spectra of hydrated PVA samples allowed to analyze the effect of hydrogen bonds. It was found that in PVA with lower water content conformation transition in amorphous region was restricted by more intermolecular and intramolecular hydrogen bonds, especially by the former. Also relatively added crystalline regions, which can affect permeability as physical cross-linking points, were mainly constructed by chain segments with no intramolecular hydrogen bonds. Above results suggest that intermolecular and intramolecular hydrogen bonds via conformation transition control relaxation behavior. Consequently, the relaxation behavior affects the permeability of hydrated PVA, in which water play an important role.

Physicochemical characteristics of epichlorohydrin, pyridine and trimethylamine functionalized cotton stalk and its adsorption/desorption properties for perchlorate

Amine-impregnated cotton stalk (AICS) prepared by the reaction of cotton stalk with epichlorohydrin, pyridine and trimethylamine was used as the effective adsorbent for perchlorate removal. Solid-state 13C NMR spectra, FT-IR, BET principle and element analysis provided evidence that amine groups have been successfully introduced onto the surface of AICS. The adsorption capacity of perchlorate by AICS was about 83.8mgg−1 at 20°C. It was decreased to 80.6mgg−1 as the temperature was increased to 40°C, which implied an exothermic nature for this adsorption process. Perchlorate adsorption capacity in fixed-bed column was optimum at neutral condition (pH: 6.0, 70.8mgg−1) with bed depth of 2.7cm and flow rate of 5mlmin−1. In addition, chemical regeneration by HCl or NaOH (0.1molL−1) achieved more than 95% of regeneration efficiency. Biological regeneration of the saturated AICS with mixed bacteria has shown its merit with regeneration and biological perchlorate destruction simultaneously although its regeneration efficiency was only 56.8–74.8%.

Chemical quality of aboveground litter inputs for jack pine and black spruce stands along the Canadian Boreal Forest Transect Case Study

In the Canadian boreal forest, jack pine stands generally have a thin forest floor and occupy sites with coarsetextured soils and good drainage. Black spruce occurs more often on poorly drained sites and develops a thick mossdominated forest floor, but the common attribution of this development to poor quality of black spruce foliar litter has not been tested. We determined needle, twig, cone, and bark litter inputs during 10 y for black spruce and jack pine along the Boreal Forest Transect Case Study in northern Saskatchewan and Manitoba. Analysis of C, N, total phenolics, condensed tannins, and solid-state 13C NMR spectra from years 1–3 showed only small differences between species, notably higher tannins in black spruce cones. There was similarly little difference between area-based inputs, including classes of C structures determined by NMR. Condensed tannin input for black spruce was approximately twice that for jack pine, but both were in the very low range of reported values. Similar analyses showed that black spruce forest floor was less decomposed than that of jack pine, and for both species, aromatic litter C inputs appear to be poorly conserved, with a large influence of mosses and lichen. It is unlikely, however, that these large differences are mainly due to the small differences in aboveground litter inputs.

Conversion of agricultural residues to carboxymethylcellulose and carboxymethylcellulose acetate

In view of continuing interest in the utilization of agricultural by-products, we have converted cellulose, wheat straw, barley straw, and rice hull into carboxymethylcellulose (CMC), using both conventional heat and microwave-assisted synthesis. The application of microwave technology has enabled an improved synthesis of CMC to be conducted, with similar degrees of substitution as conventional heat (3h) but reduced reactions times (30min). The CMC obtained can be acetylated to form carboxymethylcellulose acetate (CMC acetate). The FT-IR and solid state 13C NMR spectra of these materials have been characterized. With variations in the degrees of substitution of carboxymethyl and acetyl groups, a family of CMC acetate products can be made. The polymer may perhaps find applications as filtration membranes, functional fillers in polymers, and additives in commercial formulations.

Preparation and Characterization of Activated Carbons from Peanut Shell and Rice Bran and a Comparative Study for Cr(VI) Removal from Aqueous Solution

Low-cost activated carbons (AC) were prepared from peanut shell (PS) and rice bran (RB) by microwave heating with ZnCl2 as the activating agent and characterized by solid-state 13C-NMR, FT-IR, Boehm titration, and mass titration methods. The solid-state 13C-NMR spectra showed that aliphatic structures of the raw materials were almost completely transformed to condensed aromatic rings, a typical characteristic of AC. The potentials of ACs produced from peanut shell (PACs) and from rice bran (RACs) for Cr(VI) removal were examined by using iodine and methylene blue (MB) as adsorbates, respectively. The effects of solution pH, the dosage of AC, and the initial Cr(VI) concentration on Cr(VI) removal were investigated. The desorption experiments were also performed to examine the regeneration of AC. The results demonstrated that both PAC and RAC were excellent adsorbents for Cr(VI) removal. The maximum removal amounts of Cr(VI) by PAC and RAC reached to 96.27 and 76.04 mg/g, respectively. The adsorption capacity of PAC was higher than that of RAC because PAC held a larger surface area and a more microporous pore structure than RAC. The removal of Cr(VI) by PAC and RAC greatly depended on solution pH, with low pH (in a pH range of 2 to 6) being more conducive to the removal of Cr(VI). The adsorption-coupled reduction of Cr(VI) contributed to the removal of Cr(VI) by PAC and RAC.

Competing Occupation of Guest Molecules in Hydroquinone Clathrates Formed from Binary C2H4 and CH4 Gas Mixtures

When reacted with pure ethylene (C2H4) and pure methane (CH4) at 2.0 and 4.0 MPa, respectively, pure hydroquinone (HQ) was converted into β-form clathrate compounds. Experimental solid-state 13C NMR spectra and powder X-ray diffraction patterns provided direct evidence of C2H4 and CH4 enclathration in the β-form HQ clathrates. On the basis of cage occupancy from the solid-state 13C NMR spectra, C2H4 (cage occupancies of 0.81–0.88) molecules are more likely to occupy the clathrate cages than CH4 molecules (cage occupancies of 0.38–0.39). The selective occupation by C2H4 was also observed for HQ clathrates formed from C2H4 and CH4 gas mixtures of 10, 30, 50, 70, and 90 mol % concentrations of C2H4. The experimental results from this study could be applied to a clathrate-based process for separating and concentrating C2H4 from gas mixtures.

Chemical and carbon isotopic dynamics of grass organic matter during litter decompositions: A litterbag experiment

A litterbag method was used for studying the variability in chemical and carbon isotopic compositions of four grasses during litter decomposition. After the 300d degradation, >90% of litter mass was lost for three C4 species (Setaria viridis, Eleusine indica, Amaranthus retroflexus) and one C3 species (Erigeron speciosus). The solid state 13C NMR spectra showed that mean proportion of aromatic and alkyl carbon increased from ca. 10% to 15% and ca. 10% to 20%, respectively, whereas that of O-alkyl carbon substantially decreased from ca. 70% to 50%. The carbon preference index and average chain length of n-alkanes remained relatively constant, whereas the carbon isotopic compositions of long chain n-alkanes varied <2‰. Our results demonstrate that the degradation of litters alone does not significantly change the n-alkane chemical and carbon isotopic proxies. Compared to open plant–soil systems, our litterbag experiments present much less variability in chemical and carbon isotopic compositions of n-alkanes. Based on these facts, we recommend a combined measurement of chemical and carbon isotopic properties in evaluation of carbon sources, dynamics and paleoenvironments.

High field solid state 13C NMR spectroscopy of cucurbituril materials

Solid state 13C NMR spectra of several cucurbituril materials, CB[n] where n = 5, 6, 7 and 8, have been analysed in detail. Where crystal structures are known the complex splitting patterns for the CO, CH and CH2 resonances can be directly related to the different site symmetries imposed on the CB molecule by the crystal. Conversely, where the structure is not known the NMR splitting patterns can be used to suggest possible symmetries for the CB, and these could conceivably aid in solving crystal structures. The fact that each structure produces a uniquely different 13C NMR splitting pattern makes it a useful fingerprinting tool which can be used to detect new phases.

A comparison of the structure and reactivity of five Jordanian oil shales from different locations

Reactions of five Jordanian oil shales, Yarmouk in the north, El-Lajjun, Sultani and Attrat Um Ghudran in the center and Ma’an in the south have been carried out at 355°C, 390°C and 425°C for 1h under N2 or H2. The shales showed significant differences in reactivity, with central and northern Jordanian oil shales being more reactive on a dmmf basis than those from the south. However, the dmmf product yields of southern (Ma’an) oil shale for 5h reactions were similar to those for 1h reactions of the other shales. The only relationship between characteristics of the oil shales and the yields of useful products was the proportion of aromatic carbon in the solid state 13C NMR spectra of the shales, the Ma’an shale with the lowest aromatic carbon value being the least reactive. The central Jordanian oil shales were less sensitive to the action of catalysts than those from the north and the south. H2 generally gave higher yields of useful products than N2. Mo-based catalysts were the most effective in all cases for both gases.The composition of the liquid products from 390°C reactions as reflected in the 1H NMR spectra and gas chromatography–mass spectroscopy did not correlate with the differences in reactivity. Similarly the C, H, N and S elemental analysis data for the products did not correlate with the reactivity nor did the sulfur content of the products correlate with that of the shale. The CO2 yields under the reaction conditions used were small.In summary, the Jordanian oil shales show unexpected structural and reactivity differences, when it is considered that they were deposited at roughly the same time in the same region.

Formation, Molecular Structure, and Morphology of Humins in Biomass Conversion: Influence of Feedstock and Processing Conditions

Neither the routes through which humin byproducts are formed, nor their molecular structure have yet been unequivocally established. A better understanding of the formation and physicochemical properties of humins, however, would aid in making biomass conversion processes more efficient. Here, an extensive multiple-technique-based study of the formation, molecular structure, and morphology of humins is presented as a function of sugar feed, the presence of additives (e.g., 1,2,4-trihydroxybenzene), and the applied processing conditions. Elemental analyses indicate that humins are formed through a dehydration pathway, with humin formation and levulinic acid yields strongly depending on the processing parameters. The addition of implied intermediates to the feedstocks showed that furan and phenol compounds formed during the acid-catalyzed dehydration of sugars are indeed included in the humin structure. IR spectra, sheared sum projections of solid-state 2DPASS (13) C NMR spectra, and pyrolysis GC-MS data indicate that humins consist of a furan-rich polymer network containing different oxygen functional groups. The structure is furthermore found to strongly depend on the type of feedstock. A model for the molecular structure of humins is proposed based on the data presented.

A silver complex with ibuprofen: Synthesis, solid state characterization, DFT calculations and antibacterial assays

The present work describes the synthesis of a silver(I) complex with the non-steroidal anti-inflammatory ibuprofen, Ag-ibu. Elemental and thermal analyses indicate a 1:1 metal/ligand composition. Thermogravimetric analysis shows that Ag-ibu decomposition starts at 180°C, and ends at 400°C (mass loss 64.6%; calcd. 65.5%). UV/Vis kinetic measurements suggest the decomposition of Ag-ibu in dimethyl sulfoxide, with the appearance of a broad band in the spectrum of the complex in the range 300–500nm. Infrared and solid state 13C NMR spectra show the coordination of ibuprofen to silver through the carboxylate group. The DFT calculations led us to propose a dimeric silver bridging structure for the complex. Biological studies show the antibacterial activity of the Ag-ibu complex against Gram-positive and Gram-negative bacterial strains, with MIC values ranging from 6.25 to 12.5μgmL−1.