Substitutional Carbon Research Articles

Palladium-Catalyzed Benzylic Phosphorylation of Diarylmethyl Carbonates.

A palladium-catalyzed benzylic substitution of tert-butyl diarylmethyl carbonates with a pinacol-derived H-phosphonate proceeds to deliver the corresponding benzylic phosphorylated products in good yields. Moreover, the asymmetric synthesis is possible via a Pd/( Rp, R'p)-( S)-Mandyphos-catalyzed kinetic resolution-DYKAT (dynamic kinetic asymmetric transformation) sequence, and optically active α-chiral diarylmethylphosphonates are obtained with synthetically useful yields and enantiomeric ratios (up to 50% and 92:8 er).

Enhancement of the critical current density of in-situ powder-in-tube processed MgB2 wires with both xylene and SiC addition

The addition of a liquid hydrocarbon, xylene, to the starting powder of in-situ powder-in-tube (PIT) processed MgB2 wires was determined to be effective in enhancing the critical current density (Jc) in both high and low magnetic fields. Unlike the addition of SiC nanopowder, which introduces carbon substitution for boron, xylene addition reduced the amount of boron that remained unreacted after the heat treatment and the MgB2 grain size, which resulted in an almost fully-reacted MgB2 core and more flux pinning centers. The addition of both xylene and SiC powder to the starting powder provided a higher Jc than either separate addition to the wire process because both mechanisms associated with xylene and SiC additions work together. For heat treatment at 650 °C, Jc for the xylene added wire achieved 2.2 × 103 A/cm2 at 10 T, which was triple that of the pure sample. The co-added wire had a Jc of 6.3 × 103 A/cm2 at 10 T, which was higher than the SiC added wire, of which Jc was 4.1 × 103 A/cm2 at 10T.

Constructing bio-templated 3D porous microtubular C-doped g-C3N4 with tunable band structure and enhanced charge carrier separation

For the first time, the bio-templated porous microtubular C-doped (BTPMC) g-C3N4 with tunable band structure was successfully prepared by simple thermal condensation approach using urea as precursors and kapok fibre which provides a dual function as a bio-templates and in-situ carbon dopant. Prior to the thermal condensation process, the impregnation strategies (i.e. direct wet and hydrothermal impregnation) of urea on the treated kapok fibre (t-KF) were compared to obtained well-constructed bio-templated porous microtubular C-doped g-C3N4. The details on a physicochemical characteristic of the fabricated samples were comprehensively analyze using X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), N2 adsorption-desorption, Thermogravimetric (TGA), and UV–vis spectroscopy. Our finding indicated that the hydrothermal impregnation strategy resulted in well-constructed microtubular structure and more carbon substitution in sp2-hybridized nitrogen atoms of g-C3N4 as compared to the direct wet impregnation. Also, compared to pure g-C3N4, the fabricated BTPMC g-C3N4 exhibited extended photoresponse from the ultraviolet (UV) to visible and near-infrared regions and narrower bandgap. The bandgap easily tuned with the increased t-KF loading in urea precursor which responsible for in-situ carbon doping. Moreover, as compared to pristine g-C3N4, dramatic suppression of charge recombination of the BTPMC g-C3N4 was confirmed through photoluminescence, photocurrent response, and electrochemical impedance spectroscopy. The resultants BTPMC g-C3N4 possesses more stable structure, promoted charge separation, and suitable energy levels of conduction and valence bands for photocatalysis application.

Impaired mineral quality in dentin in X-linked hypophosphatemia

ABSTRACTX-linked hypophosphatemia (XLH) is a skeletal disorder arising from mutations in the PHEX gene, transmitted in most cases as an X-linked dominant trait. PHEX deficiency leads to renal phosphate wasting and hypophosphatemia, as well as impaired mineralization of bone and dentin, resulting in severe skeletal and dental complications. Dentin mineralization defects appear as characteristic, large interglobular spaces resulting from the lack of fusion of calculospherites in the circumpulpal region during the mineralization process. Here, we examined changes in the composition and structure of dentin using Raman spectroscopy on XLH human teeth, and using transmission electron microscopy on the dentin of Hyp mice (the murine model of XLH). The dentin of patients with XLH showed changes in the quality of the apatitic mineral, with greater carbonate substitution and lower crystallinity compared to the dentin of age-matched control teeth. In addition, ultrastructural analysis by transmission electron microscopy revealed a major disorganization of the peri- and intertubular structure of the dentin, with odontoblast processes residing within an unmineralized matrix sheath in the Hyp mouse. Taken together, these results indicate that like for bone and tooth cementum, there are impaired mineral quality and matrix changes in XLH dentin reflecting high sensitivity to systemic serum phosphate levels and possibly other local changes in the dentin matrix.

Catalytic co-aromatization of methane and heptane as an alkane model compound over Zn-Ga/ZSM-5: A mechanistic study

The joint conversion of methane and heptane, a model compound of paraffin-rich raffinate oil, over a Zn-Ga modified zeolite catalyst has been investigated at various reaction times. In comparison with the performance from a N2 environment, the introduction of methane highly promotes the formation of light aromatic compounds with a single phenyl ring, and increased carbon number and substitution index of chemical constituents formed are indicative of methane incorporation into the liquid product. In addition, with prolonged time, the interaction between catalyst and methane molecules is enhanced. Through cleavage of methane molecules, the formed moieties likely participate in the aromatization reaction, which results in the growth of larger aromatic components through further condensation. According to the NMR spectra, witnessing methane engagement into the phenyl carbon and alkyl carbon sites of the formed liquid aromatics along with increasing reaction time is evidenced 13C-methane incorporation into aromatics. The excellent catalytic performance of Zn-Ga/ZSM-5 might be ascribed to the greatly dispersed metal species on the catalyst surface as well as a certain amount of medium and weak acid sites. With regards to the spent catalyst, the presence of methane could inhibit the aggregation of loaded active metals and coke formation during the co-aromatization process. The elucidation on the co-conversion of methane and high alkane provides great potential for the utilization of natural gas resources and intermediates formed from petrochemical industries.

Determination of the Self-Compensation Ratio of Carbon in AlGaN for HEMTs

Epitaxial AlGaN/GaN/AlGaN-on-Si high-electron mobility structures with and without carbon doping have been studied. By considering the donor density required to suppress a 2D hole gas in the undoped structure, we demonstrate that the $2 \times 10^{19}$ cm−3 substitutional carbon incorporated during metal-organic chemical vapor deposition must be a source of donors as well as acceptors, with a donor to acceptor ratio of at least 0.4. This compensation ratio was determined based on the comparison of substrate bias experiments with TCAD simulations. This value, which was previously unknown, is a key parameter in GaN power switching high- electron- mobility transistors, since it determines the resistivity of the layer used to suppress leakage and increase breakdown voltage.

Co-aromatization of methane with olefins: The role of inner pore and external surface catalytic sites

The co-aromatization of methane with olefins is investigated using Ag-Ga/HZSM-5 as the catalyst at 400 °C. The presence of methane has a pronounced effect on the product distribution in terms of increased average carbon number and substitution index and decreased aromatic carbon fraction compared with its N2 environment counterpart. The participation of methane during the co-aromatization over the Ag-Ga/HZSM-5 catalyst diminishes as the co-fed olefin feedstock molecule becomes larger, from 1-hexene to 1-octene and 1-decene, in diameter. The effect of suppressed methane participation with larger olefinic molecules is not as significant when Ag-Ga/HY is employed as the catalyst, which might be attributed to the larger pore size of HY that gives more room to hold olefin and methane molecules within the inner pores and reduces the diffusion limitation of olefin molecules. The effect of olefin feedstock on the methane participation during the co-aromatization over Ag-Ga/HZSM-5 is experimentally evidenced by 13C and 2D NMR. The incorporation of the methane carbon atoms into the phenyl ring of product molecules is reduced significantly with larger co-fed olefins, whereas its incorporation into the substitution groups of the formed aromatic molecules is not notably affected, suggesting that the methane participation in the phenyl ring formation might preferably occur within inner pores, while its incorporation into substitution groups may mainly take place on external catalytic sites. This hypothesis is well supported by the product selectivity obtained over Ag-Ga/HZSM-5 catalysts prepared using conventional ZSM-5, ZSM-5 with the external catalytic sites deactivated, nanosize ZSM-5, ZSM-5 with a micro/meso pore structure and ZSM-5 with the inner pores blocked, and further confirmed by the isotopic labeling studies.

GeC film with high substitutional carbon concentration formed by ion implantation and solid phase epitaxy for strained Ge n-MOSFETs

GeC film with high substitutional carbon concentration formed by ion implantation and solid phase epitaxy for strained Ge n-MOSFETs

Towards graphite-free hot zone for directional solidification of silicon

The reduction of SiC, Si3N4 and transition metals impurities in directionally solidified Si ingots poses one of the crucial challenges in the solar cells production. Particularly strong contamination comes from the graphite parts in the hot zone. Therefore, we selected three massive ceramic materials to replace graphite, developed the novel design of the crucible support and cover and compared the crystals grown in them with ingots from the standard graphite design. The experiments were performed for phosphorus n-doped silicon of G0 size. The ingots were compared with respect to O- and C-content, metal impurities, resistivity and lifetime. The superior performance of TiC relative to other ceramics was observed, particularly due to the lower concentration of substitutional carbon in Si ingot (up to 2.6 times) and the higher minority carrier lifetime of (up to 4.4 times) with narrow red zones.

The Role of Matrix Composition in the Mechanical Behavior of Bone.

While thinning of the cortices or trabeculae weakens bone, age-related changes in matrix composition also lower fracture resistance. This review summarizes how the organic matrix, mineral phase, and water compartments influence the mechanical behavior of bone, thereby identifying characteristics important to fracture risk. In the synthesis of the organic matrix, tropocollagen experiences various post-translational modifications that facilitate a highly organized fibril of collagen I with a preferred orientation giving bone extensibility and several toughening mechanisms. Being a ceramic, mineral is brittle but increases the strength of bone as its content within the organic matrix increases. With time, hydroxyapatite-like crystals experience carbonate substitutions, the consequence of which remains to be understood. Water participates in hydrogen bonding with organic matrix and in electrostatic attractions with mineral phase, thereby providing stability to collagen-mineral interface and ductility to bone. Clinical tools sensitive to age- and disease-related changes in matrix composition that the affect mechanical behavior of bone could potentially improve fracture risk assessment.

Development of Egg Shell Derived Carbonated Apatite Nanocarrier System for Drug Delivery.

Carbonated apatite has a chemical composition quite similar to biological apatite found in native bone. The incorporation of carbonate (CO2-3) ions groups into the apatitic crystal structure can tailor its crystallinity, solubility and biological activity that benefit the bone repair and regeneration. In this study, we report a simple and elegant method of synthesizing carbonated calcium deficient hydroxyapatite (ECCDHA) nanoparticles from egg shell wastes and its efficacy has been compared with synthetic calcium deficient hydroxyapatite (SCDHA) nanoparticles. Egg shell contains about 94% of calcium carbonate. Fourier transform infrared (FT-IR) spectroscopy results confirmed the carbonate substitution in the apatite as B-type and CHNS/O elemental analysis showed 6 wt.% of carbonate content in ECCDHA. Energy dispersive spectroscopy (EDS) analysis confirmed the presence of biologically relevant elements such as magnesium, strontium, fluoride, potassium etc., in ECCDHA inherited from the egg shell. In vitro cell culture studies confirmed that the ECCDHA is cellular compatible and it has enhanced cell adhesion and proliferation of L6 myoblast cells as compared to SCDHA. The potential of ECCDHA suitable for bone drug applications was tested with an antibiotic drug, doxycycline. The results showed higher drug loading and releasing for ECCDHA as compared to SCDHA during the period of study. Based on these results, the ECCDHA may be considered as a potential bone substitute and drug carrier system.

Linking Ab Initio Data on Hydrogen and Carbon in Steel to Statistical and Continuum Descriptions

We present a selection of scale transfer approaches from the electronic to the continuum regime for topics relevant to hydrogen embrittlement. With a focus on grain boundary related hydrogen embrittlement, we discuss the scale transfer for the dependence of the carbon solution behavior in steel on elastic effects and the hydrogen solution in austenitic bulk regions depending on Al content. We introduce an approximative scheme to estimate grain boundary energies for varying carbon and hydrogen population. We employ this approach for a discussion of the suppressing influence of Al on the substitution of carbon with hydrogen at grain boundaries, which is an assumed mechanism for grain boundary hydrogen embrittlement. Finally, we discuss the dependence of hydride formation on the grain boundary stiffness.

Metaplastic woven bone in bone metastases: A Fourier-transform infrared analysis and imaging of bone quality (FTIR)

Most osteolytic tumors are in fact mixed and contain an osteoblastic component associated with the predominant osteolytic areas. This metaplastic woven bone is always evidenced by histological analysis even in the absence of radiological expression. Metaplastic bone formation reflects the activation of new osteoblasts coming from the stimulation of the dormant lining cells. Twelve patients with secondary metastases of the iliac crest evidenced by hot spots on a 99Tc-MBP san were diagnosed by histomorphometry on bone biopsies. Fourier Transformed InfraRed analysis and Imaging (FTIRI) was used on 4μm thick sections of undecalcified bone. The mineralization degree, carbonate substitution, crystallinity and the cross-links ratio of collagen (1660/1690cm-1 bands) were determined. The matrix characteristics were analyzed and imaged in the pre-existing residual bone and in the metaplastic woven bone in the vicinity of the tumor cells. FTIRI provided images of the phosphate, amide and combination of peak ratio after having selected the peaks of interest. In addition, the matrix properties can be measured and compared between the old and newly-formed bones. Woven bone appeared poorly calcified with a low phosphate/amide ratio (P=0.03) crystallinity (P<0.0001) and carbonate substitution (P=0.003). Collagen was less mature as evidenced by lower cross-links (P=0.01). Woven bone associated with bone metastasis appears poorly mineralized and rapidly elaborated by osteoblasts. The collagenous phase of the bone matrix has a low level of reticulation. FTIRI is a powerful tool to measure and visualize the various components of the bone matrix in human diseases.

Irradiation-Induced Compositional Effects on Human Bone After Extracorporeal Therapy for Bone Sarcoma.

The present study investigates Raman scattering of human bone irradiated with 50Gy single dose during therapeutic treatment of Ewing and Osteosarcoma. Bone quality was evaluated via mineral-to-matrix ratio, degree of crystallinity, change in amount of calcium, and carbonate substitution. Alteration in collagen and its cross-links was quantified through second-derivative deconvolution of Amide I peak. A dose of 50Gy radiation leads to almost 50% loss of mineral content, while maintaining mineral crystallinity, and small changes in carbonate substitution. Deconvolution of Amide I suggested modifications in collagen structure via increase in amount of enzymatic trivalent cross-linking (p < 0.05). Overall irradiation led to detrimental effect on bone quality via changes in its composition, consequently reducing its elastic modulus with increased plasticity. The study thus quantifies effect of single-dose 50Gy radiation on human bone, which in turn is necessary for designing improved radiation dosage during ECRT and for better understanding post-operative care.

Rich interfacial chemistry and properties of carbon-doped hexagonal boron nitride nanosheets revealed by electronic structure calculations

The effect of C doping to hexagonal boron nitride (h-BN) to its electronic structure is examined by first principles calculations using the association from π-electron systems of organic molecules embedded in a two-dimensional insulator. In a monolayered carbon-doped structure, odd-number doping with carbon atoms confers metallic properties with different work functions. Various electronic interactions occur between two layers with odd-number carbon substitution. A direct sp3 covalent chemical bond is formed when C replaces adjacent B and N in different layers. A charge transfer complex between layers is found when C replaces B and N in the next-neighboring region, which results in narrower band gaps (e.g., 0.37 eV). Direct bonding between C and B atoms is found when two C atoms in different layers are at a certain distance.

Quantification of Carbon Reduction Effects of Domestic Wood Products for Valuation of Public Benefit

This study was carried out to quantify degree of contribution of harvested wood product (HWP) on mitigation of climate change by valuation of public benefits, environmentally and economically. The potential carbon dioxide emission reduction of HWP was estimated by accounting carbon storage effect and substitution effect. Based on 2014 statistics of Korea Forest Service, domestic HWPs were sorted by two categories, such as wood products produced domestically from domestic and imported roundwood. The wood products were divided into seven items; sawnwood, plywood, particle board, fiberboard (MDF), paper (including pulp), biomass (wood pellet) and other products. The carbon stock of wood products and substitution effects during manufacturing process was evaluated by items. Based on the relevant carbon emission factor and life cycle analysis, the amount of carbon dioxide emission per unit volume on HWP was quantified. The amounts of carbon stock of HWP produced from domestic and from imported roundwood were 3.8 million tCO2eq., and 2.6 million tCO2eq., respectively. Also, each reduction of carbon emission by substitution effect of HWP produced from domestic and imported roundwood was 3.1 million tCO2eq. and 2.1 million tCO2eq., respectively. The results of this study, the amount of carbon emission reduction of HWP, can be effectively used as a basic data for promotion of wood utilization to revise and establish new wood utilization promotion policy such as ‘forest carbon offset scheme’, and ‘carbon storage labeling system of HWP’.

Tailoring the Surface Chemical Reactivity of Transition‐Metal Dichalcogenide PtTe2 Crystals

AbstractPtTe2 is a novel transition‐metal dichalcogenide hosting type‐II Dirac fermions that displays application capabilities in optoelectronics and hydrogen evolution reaction. Here it is shown, by combining surface science experiments and density functional theory, that the pristine surface of PtTe2 is chemically inert toward the most common ambient gases (oxygen and water) and even in air. It is demonstrated that the creation of Te vacancies leads to the appearance of tellurium‐oxide phases upon exposing defected PtTe2 surfaces to oxygen or ambient atmosphere, which is detrimental for the ambient stability of uncapped PtTe2‐based devices. On the contrary, in PtTe2 surfaces modified by the joint presence of Te vacancies and substitutional carbon atoms, the stable adsorption of hydroxyl groups is observed, an essential step for water splitting and the water–gas shift reaction. These results thus pave the way toward the exploitation of this class of Dirac materials in catalysis.

Investigation of composition and structure of spongy and hard bone tissue using FTIR spectroscopy, XRD and SEM

Valuable structural and chemical features can be obtained for spongy and hard bone by infrared spectroscopy and X-ray diffraction. A better understanding of chemical and structural differences between spongy and hard bone is a very important contributor to bone quality. Our data according to IR data showed that the collagen cross-links occurred to be higher in spongy bone, and crystallinity was lower in spongy bone. Deconvolution of the infrared band near 870 cm-1 reveals evidence for A2-type carbonate substitution on hydroxyapatite of spongy bone in addition to the A and B type carbonate substitution that are also found in hard bone. IR and XRD data confirmed the results of each other since full width at half maximum of 002-apatite pattern of XRD showed that the crystallinity was lower in spongy bone. The microstructure was examined by using scanning electron microscope and the result showed that the lattice of thin threads in spongy bone and is less dense than hard bone.

Estimation of the metabolic rate by assessing carbon-13 turnover in broiler tissues using the stable isotope technique

The aim of this study was to estimate the metabolic rate of broiler tissues by assessing carbon turnover in different growth phases by using the stable isotope technique and by evaluating the natural changes in Carbon-13 (13C) between C3 and C4 cycle plants. Six-hundred 1-day-old broiler chicks were divided into six groups and subjected to dietary changes containing different isotopic values at 7, 14, 21, 28, and 35 days of age. Birds of Group 1 received diets composed predominantly of C3 cycle plants shortly after accommodation, while birds of other groups remained predominantly fed with C4 diet. The diet of Group 2 was mainly replaced by C3 diet on the 7th day of age. Group 3 started to receive C3 diet on the 14th day of age, whereas the diet of Group 4 was replaced on the 21st, Group 5 on the 28th. In Group 6, the substitution occurred on the 35th day of age. Samples of the pectoral muscle, keel, tibia, legs muscle, intestinal mucosa, blood, plasma, and feathers were collected. Carbon isotope ratios were determined by mass-spectrometry of isotope ratios. To measure the speed of carbon substitution after a set interval (turnover), a time exponential function was employed and obtained by exponential equations of the first order calculated with Minitab® 16 software. The carbon half-life varied from 1.78 to 8.20 days for the pectoral muscle, from 1.91 to 12.24 days for the keel, from 2.32 to 10.71 days for the tibia, from 1.87 to 9.43 days for the leg muscle, from 0.8 to 1.58 days for the intestinal mucosa, from 0.64 to 1.71 days for the plasma, from 2.61 to 11.07 days for blood, and from 1.84 to 28.41 days for the feathers during the total growth phase. With the exception of tibia and blood, all other tissues presented a high metabolic rate in the first week of the broilers’ life. The metabolic rate of tissues is faster in younger animals, and the metabolism slows down as the broilers get older. The metabolic rates in the pectoral muscle, keel, tibia, and feathers decreased with age, whereas those of the plasma and intestinal mucosa were high in all evaluated periods; thus, these tissues can be used to study traceability of feed at all stages of the broilers’ life.

Improvement of Anion Transport Systems by Modulation of Chalcogen Interactions: The influence of solvent.

A series of potential anion transporters, dithieno[3,2-b;2',3'-d]thiophenes (DTT), involving anion-chalcogen interactions have been studied by analyzing the interaction energy, geometry, and charge transfer. It was found that gas phase calculations show very negative interaction energies with short anion-chalcogen distances, but when solvent effects are considered, the interaction energy values decreased drastically concomitantly with an elongation on the interatomic distances. To enhance the chalcogen interaction between the DTT derivatives and the anion, increasing the anion transporter capacity, bisisothioazole moiety was considered; i.e., the σ-hole of the chalcogen atom was modulated by substitution of the adjacent carbon by a nitrogen atom in the S-C axis, increasing the depth of the σ-hole and therefore the interaction between the chalcogen and anion. Finally, different anions were analyzed within the complexes, finding that F- and NO3- would be the best candidates to form complexes and possibly displace other anions such as Cl- or Br-.