Major Fragments Research Articles

Contribution of agroforestry systems to sustaining biodiversity in fragmented forest landscapes

Agroforestry systems maintain intermediate levels of biodiversity between natural forests and purely agricultural land-uses and may therefore increase connectivity or sustain biodiversity in fragmented forest landscapes. This hypothesis is tested by comparing the species richness and similarity in species composition between forest fragments and agroforestry systems in two landscapes in Guatemala. Connectivity indices were calculated based on the similarity of biodiversity held between forest and agroforestry. Tree and ant species richness was significantly higher for forest than agroforestry land-uses. Conversely, species richness of leaf hoppers (Cicadellidae) was lower in forests compared to agroforests. Chao-Sorensen estimates indicated a high proportion of ant species were shared (0.78–0.99) between different agroforestry land-uses and forest fragments, but lower proportions of tree (0.39–0.55) and leaf hopper species (0.42–0.65). Including the contribution of agroforestry systems in estimates of forest connectivity, based on their biodiversity relative to forest, substantially increased the land area rated with high connectivity (by 100–300%) and forest edge connectivity (by 70–170%), but had negligible impact on land area rated as dense forest. The major forest fragments in the two landscapes were linked by land rated as medium connectivity for forest biodiversity. Thus, agroforestry contributes to the capacity of the landscape to support biodiversity, but only partially increases connectivity between forest fragments in the two landscapes studied. If these benefits are to be sustained, consideration needs to be given to the incentives for land-owners to maintain agroforestry systems.

Computational modeling of novel inhibitory peptides targeting proteoglycan like region of carbonic anhydrase IX and in vitro validation in HeLa cells

Carbonic anhydrase IX (CAIX) is a tumour-associated, hypoxia-induced, membrane-bound metallo-enzyme which catalyzes the reversible hydration of carbon dioxide (CO2) to bicarbonate (HCO3−) and proton (H+) ions. Over expression of CAIX is observed in cancers of colon, lung, kidney, breast, etc. CAIX plays a vital role in maintaining favourable intracellular pH for tumour cell growth and extracellular acidification which in-turn leads to drug resistance and spread of factors influencing tumour invasion. The N-terminal proteoglycan (PG) – like fragment of CAIX is unique to this isoform and is considered as potential druggable hotspot. Recently, M75 monoclonal antibody targeting the LPGEEDLPG epitope of PG like region has been proposed to reduce cellular adhesion in cancer cells. LPGEEDLPG fragment in complex with M75 has been crystallized and it serves as a strong base for development of peptide inhibitors based on interacting interfaces. Thus, in this study, an in-depth analysis of intermolecular interactions in LPGEEDLPG-M75 complex was carried out by implementing extensive molecular dynamics simulations, binding free energy calculations so as to infer the major determinant fragments of M75 that can be used as peptide inhibitors targeting PG region. Based on these analyses, 3 peptides (Pep1, Pep2 and Pep3) were synthesized and validated by in vitro assays involving cytotoxicity assessment, CAIX inhibition analysis through Direct and Indirect functional assays, and inhibition of Cell adhesion in HeLa cells. The results reveal Pep1 to be a promising inhibitor as it could efficiently modulate CAIX mediated pH homeostasis and cell adhesion in cancer cells.Communicated by Ramaswamy H. Sarma

Molecular-Level Understanding of the Major Fragmentation Mechanisms of Cellulose Fast Pyrolysis: An Experimental Approach Based on Isotopically Labeled Model Compounds.

Evaluation of the feasibility of various mechanisms possibly involved in cellulose fast pyrolysis is challenging. Therefore, selectively 13C-labeled cellotriose, 18O-labeled cellobiose, and 13C- and 18O-doubly-labeled cellobiose were synthesized and subjected to fast pyrolysis in an atmospheric pressure chemical ionization source of a linear quadrupole ion trap/orbitrap mass spectrometer. The initial products were immediately quenched, ionized using ammonium cations, and subsequently analyzed using the mass spectrometer. The loss or retention of isotope labels upon pyrolysis unambiguously revealed three major competing mechanisms-sequential losses of glycolaldehyde/ethenediol molecules from the reducing end (the reducing-end unraveling mechanism), hydroxymethylene-assisted glycosidic bond cleavage (HAGBC mechanism), and Maccoll elimination. Important discoveries include the following: (1) Reducing-end unraveling is the predominant mechanism occurring at the reducing end; (2) Maccoll elimination facilitates the cleaving of aglyconic bonds, and it is the mechanism leading to formation of reducing carbohydrates; 3) HAGBC occurs for glycosides but not at the reducing end of cellodextrins; 4) HAGBC and water loss are the predominant reactions for fast pyrolysis of 1,6-anhydrocellodextrins; and 5) HAGBC can proceed after reducing-end unraveling but unraveling does not occur once the HAGBC reaction pathway is initiated. Moreover, hydrolysis was conclusively ruled out for fast pyrolysis of cellobiose, cellotriose, and 1,6-anhydrocellodextrins up to cellotetraosan. No radical reactions were observed.

Molecular and bioinformatics analyses reveal two differentially expressed intracellular GH1 β-glucosidases from the rare alkalophilic fungus Stachybotrys microspora

The present study reports the isolation and analysis of two novel GH1 β-glucosidases from the alkalophilic fungus Stachybotrys microspora, using PCR and Nested-PCR. Three major gene fragments were obtained by PCR: the first two are very similar and constitute a novel gene, which was named Smbgl1A, and the third PCR fragment is part of a different gene, named Smbgl1B. The truncated gene sequences were completely filled using the recent partial whole genome sequencing data of S. microspora (data not yet published).Moreover, we investigated the relative effects of glucose in comparison to cellulose rather than evaluate their absolute effects.In fact, RT-PCR analysis showed that while Smbgl1A was expressed when the fungus was grown in the presence of cellulose but not when grown with glucose, Smbgl1B was equally expressed under both conditions.The putative catalytic residues and the conserved glycone binding sites were identified. Zymogram analysis showed the intracellular production of β-glucosidases in S. microspora. The predicted secondary structure exhibited a classical (β/α)8 barrel fold, showing that both SmBGL1A and SmBGL1B belong to the GH1 family.Phylogenetic studies showed that SmBGL1A and SmBGL1B belong to the same branch as β-glucosidases from Stachybotrys chlorohalonata and Stachybotrys chartarum. However, SmBGL1A and SmBGL1B form two distinct clades.

Understanding the Fragmentation Pathways of Carbocyclic Derivatives of Amino Acids by Using Electrospray Ionization Tandem Mass Spectrometry

Aminoacyl derivatives of aminoadamantanes amantadine and rimantadine have been investigated in regard to their antiviral properties. So far, few studies on the mass spectrometric fragmentation pathway of these compounds have been reported using high-resolution mass spectrometry (HRMS). Two major fragmentation pathways have been observed. For the rimantadine derivatives, losses of rimantadine and N-(1-adamantyl) ethylformamide were described. Similarly, in case of amantadine derivatives, there were losses of amantadine and N-(1-adamantyl) formamide. The loss of the aminoacyl group was common to all of the studied compounds. Understanding the fragmentation mechanism can bring new insight into the characterization of these compounds.

Simultaneous Spatial Mapping of Emtricitabine, Tenofovir, and Efavirenz in Mouse Tissue Using MALDI Mass Spectrometry Imaging

Emtricitabine (FTC), tenofovir (TFV; prescribed as the tenofovir disoproxil fumarate prodrug) and efavirenz (EFV) inhibit human immunodeficiency virus (HIV) replication and are currently used in combination for HIV treatment. FTC and TFV are nucleotide analog reverse transcriptase inhibitors whereas EFV is a non‐nucleoside analog. Despite the clinical importance of these drugs as commonly used antiretrovirals, their spatial distributions within tissues including those susceptible to HIV infection are poorly understood. Therefore, in this study, we employed a Matrix‐Assisted Laser Desorption/Ionization Mass Spectrometry Imaging (MALDI MSI) method to detect, identify and localize FTC, TFV and EFV in mouse tissues following in vivo dosing. For this study, brain and liver were obtained from mice (n=3) 24 h following oral administration of FTC‐TFV‐EFV. Tissue samples were embedded with OCT medium and 20‐micron tissue sections were utilized for tissue imaging experiments. MALDI matrix α‐cyano‐4‐hydroxycinnamic acid was employed to facilitate the ionization and detection of all three compounds, FTC, TFV and EFV. FTC and EFV were detected as their sodium adducts, [M+Na]+ at m/z 270.0319 ± 5 ppm and 338.0166 ± 5 ppm, respectively; while, TFV yielded its protonated molecular ion, [M+H]+ at m/z 288.0856 ± 5 ppm. When collision‐induced dissociation fragmentation experiments were performed using an FTC‐TFV‐EFV mixture, FTC, TFV and EFV exhibited major fragment ions at m/z 130.0409, 270.0746, and 272.0430 corresponding to C4H5FN3O+, C9H13N5O3P+, and C13H10ClF3N+ structural moieties, respectively. Tissue spatial distribution profiles of FTC, TFV and EFV generated using their corresponding ions (sodium adducts and molecular ions) exhibited differences in their distribution across tissue sections. Interestingly, ion intensity of TFV was greater in liver tissue sections than FTC and EFV. In addition, relative homogeneity in distribution of an endogenous lipid species, PC (16:0/OH) indicated that the distribution patterns observed for above molecules were distinct. In order to correlate the tissue distributions of FTC, TFV, and EFV with their lipophilicities, Log P values were calculated. In conclusion, the above results demonstrate the differential spatial distribution of FTC, TFV and EFV in mouse brain and liver following in vivo dosing. Further, results from this study provide important insights into the disposition of FTC, TFV and EFV.Support or Funding InformationThis work was funded by NIH grants U19AI113127, UM1 AI068613 and R01AI128781This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

In-Situ Analysis of Essential Fragrant Oils Using a Portable Mass Spectrometer

A portable mass spectrometer was coupled to a direct inlet membrane (DIM) probe and applied to the direct analysis of active fragrant compounds (3-methylbutyl acetate, 2-methyl-3-furanthiol, methyl butanoate, and ethyl methyl sulfide) in real time. These fragrant active compounds are commonly used in the formulation of flavours and fragrances. Results obtained show that the portable mass spectrometer with a direct membrane inlet can be used to detect traces of the active fragrant compounds in complex mixtures such as essential fragrant oils and this represents a novel in-situ analysis methodology. Limits of detection (LOD) in the sub-ppb range (< 2.5 pg) are demonstrated. Standard samples in the gaseous phase presented very good linearity with RSD % at 5 to 7 for the selected active fragrant compounds (i.e., isoamyl acetate, 2-methyl-3-furanthiol, methyl butanoate, and methyl ethyl sulphide). The rise and fall times of the DIM probe are in the ranges from 15 to 31 seconds and 23 to 41 seconds, respectively, for the standard model compounds analysed. The identities of the fragrance active compounds in essential oil samples (i.e., banana, tangerine, papaya, and blueberry muffin) were first identified by comparison with a standard fragrance compounds mixture using their major fragment peaks, the NIST standard reference library, and gas chromatography mass spectrometry (GC-MS) analysis. No sample preparation is required for analysis using a portable mass spectrometer coupled to a DIM probe, so the cycle time from ambient air sampling to the acquisition of the results is at least 65 seconds.

Design, Synthesis, and Evaluation of CF3AuCNR Precursors for Focused Electron Beam-Induced Deposition of Gold.

The Au(I) complexes CF3AuCNMe (1a) and CF3AuCN tBu (1b) were investigated as Au(I) precursors for focused electron beam-induced deposition (FEBID) of metallic gold. Both 1a and 1b are sufficiently volatile for sublimation at 125 ± 1 mTorr in the temperature range of roughly 40-50 °C. Electron impact mass spectra of 1a-b show gold-containing ions resulting from fragmenting the CF3 group and the CNR ligand, whereas in negative chemical ionization of 1a-b, the major fragment results from dealkylation of the CNR ligand. Steady-state depositions from 1a in an Auger spectrometer produce deposits with a similar gold content to the commercial precursor Me2Au(acac) (3) deposited under the same conditions, while the gold content from 1b is less. These results enable us to suggest the likely fate of the CF3 and CNR ligands during FEBID.

Biodiversity studies through public-private partnership (PPP): The case of Fazenda São Nicolau in the northwest of Mato Grosso.

Peugeot-ONF Forest Carbon Sink Project, located at Fazenda São Nicolau (FSN) in Cotriguaçu Municipality, is a public-private initiative and has been supported by several French and Brazilian institutions. Its Research Program includes studies aiming Biodiversity Conservation, Ecology, Carbon Dynamics, Silvicultural Techniques. FSN comprises a high richness of species with more than 20 new species of beetles (Histeridae, Scarabaeidae e Melolonthidae) described among them one endemic genus. A quick overview of the SuperFamily Scarabaeoidea within the FSN area registered 260 species which nearly 100 species might be new to Science. One new species of fish as well as research with amphibian toxins as tools to treat cancer and malaria are also done with material collected at the FSN. Ecology of the decomposer´s fauna at reforestation sites showed that after 10 years, such places were more similar to native forest sites than pastures or abandoned pastures. Finally large mammals studies indicated that many large mammals use FSN as a refuge. We stress the importance to keep the FSN natural habitats linked with the Juruena National Park. The FSN contour is under heavy deforestation which will increase the species loss and turn FSN in one of the few major natural vegetation fragments.

Evaluating the supercritical extraction effects on the chemical compositions of the extracted oil using GC/TOF MS

Gas chromatography time of flight mass spectrometry (GCTOFMS) is becoming an attractive and alternative full-spectrum technique against others traditional instruments. In this study, the GCTOFMS was used to evaluate the effect of supercritical temperature and pressure on the chemical composition of the extraction yields. A total of 12 samples obtained from 3x4 general factorial design were analyzed for it chemical components using GCTOFMS. A list of compounds was identified and matched to the NIST library with a hit over 80 % on the basis of the specific mass determination of their molecular ions and their major fragments. All the overlaps peaks were separated. All the extracted oils possess similar chemical components but varied in each compound concentration. Moreover, the aromatic ethers group was identified as the main group in the supercritical extracts with the presence of Myristicin as the highest peak, whereas, in the soxhlet extraction this group concentration was found lower. This result reveals the great effect of the extraction condition and the used method on the chemical compositions of the extraction yield and the concentration of each compound. This finding indicates and confirms the potential use of supercritical extraction in producing richer extract and fractions.

Aspartic and Glutamic Acid Templated Peptides Conjugation on Plasma Modified Nanofibers for Osteogenic Differentiation of Human Mesenchymal Stem Cells: A Comparative Study

Optimization of nanofiber (NF) surface properties is critical to achieve an adequate cellular response. Here, the impact of conjugation of biomimetic aspartic acid (ASP) and glutamic acid (GLU) templated peptides with poly(lactic-co-glycolic acid) (PLGA) electrospun NF on osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs) was evaluated. Cold atmospheric plasma (CAP) was used to functionalize the NF surface and thus to mediate the conjugation. The influence of the CAP treatment following with peptide conjugation to the NF surface was assessed using water contact angle measurements, Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). The effect of CAP treatment on morphology of NF was also checked using Scanning Electron Microscopy (SEM). Both the hydrophilicity of NF and the number of the carboxyl (-COOH) groups on the surface increased with respect to CAP treatment. Results demonstrated that CAP treatment significantly enhanced peptide conjugation on the surface of NF. Osteogenic differentiation results indicated that conjugating of biomimetic ASP templated peptides sharply increased alkaline phosphatase (ALP) activity, calcium content, and expression of key osteogenic markers of collagen type I (Col-I), osteocalcin (OC), and osteopontin (OP) compared to GLU conjugated (GLU-pNF) and CAP treated NF (pNF). It was further depicted that ASP sequences are the major fragments that influence the mineralization and osteogenic differentiation in non-collagenous proteins of bone extracellular matrix.

Urban forest fragmentation impoverishes native mammalian biodiversity in the tropics.

Urban expansion has caused major deforestation and forest fragmentation in the tropics. The impacts of habitat fragmentation on biodiversity are understudied in urban forest patches, especially in the tropics and little is known on the conservation value of the patches for maintaining mammalian biodiversity. In this study, camera trapping was used to determine the species composition and species richness of medium‐ and large‐sized mammals in three urban forest patches and a contiguous forest in Peninsular Malaysia. We identified the key vegetation attributes that predicted mammal species richness and occurrence of herbivores and omnivores in urban forest patches. A total number of 19 mammal species from 120 sampling points were recorded. Contiguous forest had the highest number of species compared to the urban forest patches. Sunda Pangolin and Asian Tapir were the only conservation priority species recorded in the urban forest patches and contiguous forest, respectively. Top predators such as Malayan Tiger and Melanistic Leopard were completely absent from the forest patches as well as the contiguous forest. This was reflected by the abundance of wild boars. We found that mammal species richness increased with the number of trees with DBH less than 5 cm, trees with DBH more than 50 cm, and dead standing trees. In the future, the remaining mammal species in the urban forest patches are expected to be locally extinct as connecting the urban forest patches may be infeasible due to land scarcity. Hence, to maintain the ecological integrity of urban forest patches, we recommend that stakeholders take intervention measures such as reintroduction of selected species and restocking of wild populations in the urban forest patches to regenerate the forest ecosystems.

Electron correlation in double photoexcitation of H2S as studied by H( 2p ) formation: Comparison with H2O

Superexcited states of ${\mathrm{H}}_{2}\mathrm{S}$ have been investigated with determining the cross sections for emission of dispersed and nondispersed atomic fluorescence against the incident photon energy in the range 11--40 eV to address the ionization and excitation of the valence electrons. This method enables us to extract the discrete electronic state from the superposition with continuous electronic states. The cross sections for H($2p$) formation have been put on an absolute scale. Ten superexcited states have been found, two in the range 13--15 eV are singly excited $2{b}_{2}^{\ensuremath{-}1}$(mo) states with a single configuration and the other eight states in the range 16--25 eV are doubly excited states with multiple configurations. State-resolved dipole oscillator strengths for H($2p$) formation in the photoexcitation of ${\mathrm{H}}_{2}\mathrm{S}$ have been determined. Similar experiments have been performed for ${\mathrm{H}}_{2}\mathrm{O}$. The state-resolved dipole oscillator strengths for H($2p$) formation in the photoexcitation of ${\mathrm{H}}_{2}\mathrm{S}$ are $\ensuremath{\sim}{10}^{\ensuremath{-}3}$, whereas those in the photoexcitation of ${\mathrm{H}}_{2}\mathrm{O}$ range from $\ensuremath{\sim}{10}^{\ensuremath{-}3}$ to $\ensuremath{\sim}{10}^{\ensuremath{-}2}$. It is found that major fragment atoms are H($2p$) atoms in the photoexcitation of ${\mathrm{H}}_{2}\mathrm{O}$ and ${\mathrm{S}}^{*}$ in the photoexcitation of ${\mathrm{H}}_{2}\mathrm{S}$. The superexcited states of ${\mathrm{H}}_{2}\mathrm{O}$ and ${\mathrm{H}}_{2}\mathrm{S}$ are compared based on the similarity and difference of the electronic structures. It turns out from the comparison that (i) the smaller values of the dipole oscillator strengths for H($2p$) formation in the photoexcitation of ${\mathrm{H}}_{2}\mathrm{S}$ are related to the change of the major fragment atoms and (ii) the energy splitting of the doubly excited ``$4{a}_{1}^{\ensuremath{-}1}({\text{mo}}^{\ensuremath{'}})$'' states of ${\mathrm{H}}_{2}\mathrm{S}$ is enhanced in comparison with that of the doubly excited ``$2{a}_{1}^{\ensuremath{-}1}({\text{mo}}^{\ensuremath{'}})$'' states of ${\mathrm{H}}_{2}\mathrm{O}$. This enhancement is caused by the stronger electron correlation in ${\mathrm{H}}_{2}\mathrm{S}$ than in ${\mathrm{H}}_{2}\mathrm{O}$. The similarity in shape is indicated between the inner valence band and inner shell band in the fluorescence cross sections against the incident photon energy for ${\mathrm{H}}_{2}\mathrm{S}$ and ${\mathrm{H}}_{2}\mathrm{O}$.

Gas Chromatography-Mass Spectrometry (GC-MS) and Gas Chromatography-Infrared (GC-IR) Analyses of the Chloro-1- n-pentyl-3-(1-naphthoyl)-Indoles: Regioisomeric Cannabinoids.

The analytical differentiation of the indole ring regioisomeric chloro-1- n-pentyl-3-(1-naphthoyl)-indoles is described in this report. The regioisomeric chloroindole precursor compounds, N- n-pentyl chloroindole synthetic intermediates, and the target chloro-substituted naphthoylindoles showed the equivalent gas chromatographic elution order based on the position of chlorine substitution on the indole ring. The regioisomeric chloro-1- n-pentyl-3-(1-naphthoyl)-indoles yield electron ionization mass spectra having equivalent major fragments resulting from cleavage of the groups attached to the central indole nucleus. Fragment ions occur at m/z 127 and 155 for the naphthyl and naphthoyl cations common to all indoles having the naphthoyl group substituted at the indole-3 position. Fragments resulting from the loss of the naphthoyl and/or n-pentyl groups from the molecular radical cation yield the cations at m/z 318, 304, 248, and 178. The characteristic (M-17)+ fragment ion at m/z 358 resulting from the loss of OH radical is significant in the mass spectra of all these compounds with 1-naphthoyl groups substituted at the indole-3 position. The vapor phase infrared spectra provide a number of characteristic absorption bands to identify the individual isomers.

Studying the fragmentation mechanism of selected components present in crude oil by collision-induced dissociation mass spectrometry.

Structural characterization of individual compounds in very complex mixtures is difficult to achieve. One important step in structural elucidation is understanding the mass spectrometric fragmentation mechanisms of the compounds present in such mixtures. Here, different individual compounds presumed to be present in a complex crude oil mixture have been synthesized and structurally characterized by tandem mass spectrometry (MS/MS) studies. Model compounds with different aromatic cores and various substitutents were synthesized. Major effort has been put into producing isomerically pure compounds to better understand the fragmentation pattern. Each synthesized compound has been subjected to MSn studies using either a triple quadrupole or a linear ion trap mass spectrometer with electrospray or atmospheric pressure photoionization. The results are used to analyze individual compounds from a complex vacuum gas oil (VGO). The synthesized compounds and a chromatographically simplified vacuum gas oil were used for structural analysis. The major fragmentation mechanism is the benzylic cleavage of the aliphatic side chain. Each side chain can be separately removed from the aromatic core by using MSn methods. At the end of a series of fragmentations, the base aromatic core structure remains and can be chararcterized. By defining the fragmentation mechanism in complex oil samples it was possible to structurally characterize individual compounds present in a chromatographically simplified VGO. The compounds consist of an aromatic core with aliphatic side chains. Cleavage of all side chains can be achieved by MSn measurements, allowing characterization of the remaining core structure.

Evaluating and supporting conservation action in agricultural landscapes of the Usumacinta River Basin

There is increasing recognition that ecosystems and their services need to be managed at landscape scale and greater. The development of landscape-scale conservation strategies need to incorporate information from multiple sources. In this study, we combine various research tools to link landscape patterns with production units and systems in the Usumacinta River Basin, and inform the discussion of key questions around decision-making related to conservation action and policy in Southern Mexico. A typology based on policy-relevant farmer characteristics (land tenure, farm size, source of income, farming system) differentiated between farmers (traditional vs. cattle ranching) with different motivations that determine how management affects landscape configuration. Five main types of traditional farming systems were identified that combine different forms of land use and vary in their degree of land intensification. Major fragmentation and decrease in connectivity coincided spatially with floodplains dominated by large-scale commercial farms that specialize in livestock production. Traditional practices within large units with low-sloped high quality land were also seen to be intensive; however the presence of trees was notable throughout these units. Policies that promote livestock farming are among the principle causes motivating deforestation. Land intensification by traditional farmers decreased as the landscape became increasingly rugged. Traditional farmers are the focus of initiatives developed by the Biological Corridor project which seeks to increase forest cover and landscape connectivity. These initiatives have shown high levels of rural participation (10,010 farmers benefited from 27,778 projects involving 95,374 ha of land) and acceptance (producers carried out more than one project and several types of projects during the first eight years of work). Strong action is still required to take on the segment of large-scale ranchers. Changes in the structure of land tenure over the past decade are highlighted that could have a profound impact on conservation policies and programs.

The effect of molten FLiNaK salt infiltration on the strength of graphite

Graphite has been identified as a structural and neutron-moderator material in the molten salt reactor (MSR). In order to support the structural material development for MSR, the influence of molten salt infiltration on the mechanical strength of graphite was studied. The high-temperature mechanical strength of graphite grades IG-110 and NG-CT-10 decrease with the increasing of weight gain ratio during the molten FLiNaK salt infiltration. It shows a noticeable high-temperature mechanical strength degradation, which can be evidenced by the softening coefficients. The smaller softening coefficient of compressive strength compared with that of tensile strength at the same infiltration pressure indicates the compressive strength is more vulnerable to the molten salt infiltration than the tensile strength. The major fragments analysis of the samples after compressive strength tests shows that the molten FLiNaK salt infiltrated graphite samples experience are longitudinal splitting fracture rather than the shear fracture of virgin graphite. The increase of thermal strain after molten salt infiltration indicates an extra stress in infiltrated graphite, which may be one of the reasons for the failure mechanism change.

Dissociative protonation and long-range proton migration: The chemistry of singly- and doubly-protonated tigecycline

Tigecycline is an antibacterial drug in the tetracycline class. In electrospray mass spectrometry both singly-protonated (MH+) and doubly-protonated molecules (MH22+) are formed in abundance. The major fragmentation reactions of the molecular ions in both charge states take place around the amido group at the C2-position on the A-ring and the t-butylamino group of the side chain at the C9-position on the D-ring. Deuterium labeling reveals that losses of ammonia from C2 and isobutene from C9 from both MH+ and MH22+ take place in a consecutive fashion, and elimination of the constitutive t-butylamine as a distinct neutral species does not occur as suggested intuitively. In addition, it is found that the elimination of isobutene from MH22+ is more than 10-fold as much as that from MH+ relative to the ammonia loss. This suggests that in the “double engine” molecular ion (MH22+), the first protonation occurs on the N,N-dimethylamino substituent on the A-ring, responsible for the loss of ammonia from the adjacent C2-amido group, and the second protonation occurs on the t-butylamino moiety on the D-ring to initiate the removal of isobutene. Since these two reactions are also observed with the “single engine” molecular ion (MH+), it is clear that upon the first neutral loss (either ammonia or isobutene), a proton is required to travel across the tetracycline core to trigger the second neutral loss. Multistage mass spectrometry confirms that the structure of the final product ion is the same regardless of the order in which the two neutral species are eliminated, supporting the requirement for a long-range proton migration.

Classifications in Brief: The Russell-Taylor Classification of Subtrochanteric Hip Fracture.

Classifications in Brief: The Russell-Taylor Classification of Subtrochanteric Hip Fracture.

Scalable Synthesis of (-)-Rasfonin Enabled by a Convergent Enantioselective α-Hydroxymethylation Strategy.

A scalable synthesis of the potent antitumor agent, (-)-rasfonin, has been achieved. The synthetic strategy features a highly convergent approach based on a single protocol construction of both major fragments via catalytic enantioselective α-hydroxymethylation of simple aliphatic aldehydes. The route described has been successful in the generation of gram quantities of the natural product and serves as the first synthetic strategy to provide sufficient material to continue studies related to its mechanism of action and potential as a cancer therapeutic.