Successive Fragmentation Research Articles

Analysis of Fullerite C60 Electron Induced Modification in Terms of Effective Destruction Cross-section

Effective cross-sections σD(E) of fullerite C60 modification by electrons in the energy range E = 0.25–3000 eV were obtained using electron energy loss spectroscopy. Comparison of σD(E) with cross-section σF(E), describing fragmentation of individual fullerenes C60 in the gas state and known from literature, revealed several orders of magnitude difference between the absolute values of these cross-sections and the inverse behavior of their energy dependencies. This fact evidences that the mechanism of electron-induced destruction of fullerite C60 drastically differs from the one implied by the model of successive fragmentation of separate fullerenes and that condensed fullerenes C60 are radically more stable than it was considered earlier.

Molecular phylogeography of Thymus herba-barona (Lamiaceae): Insight into the evolutionary history of the flora of the western Mediterranean islands

AbstractThymus herba‐barona is endemic to Majorca, Corsica, and Sardinia. In order to gain insight into its evolutionary history, we examined the genetic diversity and phylogeography of the species using sequences of the trnT‐trnL intergenic spacer from 106 individuals belonging to 15 populations. We detected high within‐species genetic diversity and strong among‐population differentiation, but no evidence for phylogeographic structure. A haplotype network supported the occurrence of three main clades, the ancestral one being geographically restricted to the Gennargentu massif in Sardinia, while the two derived ones were relatively widespread. Coalescent‐based analyses indicated deep divergence times and limited ongoing gene flow between major clades. The inferred evolutionary history of the species involved an early range expansion followed by successive fragmentation episodes, probably related to progressive climatic aridification since the Pliocene (3.2 Ma). Our data suggest that long‐distance dispersal events played a minor role in the evolutionary history of the species. The exact origin of the species remains unclear. The highly structured pattern of genetic variability detected suggests that random genetic drift played a major role in structuring genetic variation in this endemic plant. The cytogenetic evidence does not support the proposed recognition of three taxonomic entities within T. herba‐barona based on morphological discontinuities associated with different ploidy levels.

Magnetic Reconnection Under Solar Coronal Conditions with the 2.5D AMR Resistive MHD Model

The evolutionary process of magnetic reconnection under solar coronal conditions is investigated with our recently developed 2.5D adaptive mesh refinement (AMR) resistive magneto hydrodynamics (MHD) model. We reveal the successive fragmentation and merging of plasmoids in a long-thin current sheet with Lundquist number Rm = 5.0 × 104. It is found that several big magnetic islands are formed eventually, with many slow-mode shocks bounding around the outflow regions. The multi-scale hierarchical-like structures of the magnetic reconnection are well resolved by the model and the AMR technique of the model can capture many fine pictures (e.g., the near-singular diffusion regions) of the development and simultaneously it can save a great deal of computing resources.

Freshwater crab origins—Laying Gondwana to rest

We review the available data on the phylogeny, palaeontology and divergence time estimation of primary freshwater crabs in relation to a hypothesized Gondwanan origin of these brachyurans, as postulated by some workers in recent decades. Known phylogenetic relationships within the Old World freshwater crabs do not correspond to the successive fragmentation of the Gondwana continent. This is strong evidence against an ancestral Gondwanan distribution of Afrotropical Potamonautidae and Asian-Australian Gecarcinucidae. The fossil record of freshwater crabs (no older than the Oligocene) and heterotreme brachyurans also postdate the initial break up of Gondwana. Molecular-clock based time estimates for the most common recent ancestor of freshwater crab families differ profoundly, depending on the method of calibration used, and whether freshwater or marine brachyuran fossils are used as calibration points. As such, molecular clock estimates calibrated on freshwater crab fossils favour a post-Gondwanan evolution of freshwater crabs whereas calibration based on marine brachyuran fossils date their last common ancestor before the fragmentation of Gondwana.

Novel perfluorocyclobutyl aryl ether‐based well‐defined amphiphilic block copolymer

AbstractA series of fluorine‐containing amphiphilic diblock copolymers comprising hydrophobic poly(p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate) (PTPFCBPMA) and hydrophilic poly(2‐(diethylamino)ethyl methacrylate) (PDEAEMA) segments were synthesized via successive reversible addition fragmentation chain transfer (RAFT) polymerizations. RAFT homopolymerization of p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate was first initiated by 2,2′‐azobisisobutyronitrile using cumyl dithiobenzoate as chain transfer agent, and the results show that the procedure was conducted in a controlled way as confirmed by the fact that the number‐average molecular weights increased linearly with the conversions of the monomer while the polydispersity indices kept below 1.30. Dithiobenzoate‐capped PTPFCHPMA homopolymer was then used as macro‐RAFT agent to mediate RAFT polymerization of 2‐(diethylamino)ethyl methacrylate, which afforded PTPFCBPMA‐b‐PDEAEMA amphiphilic diblock copolymers with different block lengths and narrow molecular weight distributions (Mw/Mn ≤ 1.28). The critical micelle concentrations of the obtained amphiphilic diblock copolymers were determined by fluorescence spectroscopy technique using N‐phenyl‐1‐naphthylamine as probe. The morphology and size of the formed micelles were investigated by transmission electron microscopy and dynamic light scattering, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

MODELING OF THE INITIAL MASS FUNCTION USING THE METROPOLIS−HASTINGS ALGORITHM

A stochastic model has been developed for the hierarchical fragmentation of a molecular cloud. Here, the number of fragments, time between successive fragmentation steps, and mass of a fragment are considered as random variables, and fragment masses are generated using the Metropolis-Hastings algorithm. The resulting mass spectra, computed at different projected distances and taking opacity into consideration, show a signature of mass segregation. The critical mass, mass spectrum, and mass segregation are consistent with the observations of young massive clusters in our Galaxy as well as in external galaxies.

Synthesis of amphiphilic tri-block copolymer poly(vinylpyrrolidone)-b-poly(methyl methacrylate)-b-poly(vinylpyrrolidone) for the modification of polyethersulfone membrane

Abstract Well-defined amphiphilic tri-block copolymer PVP-b-PMMA-b-PVP was prepared for the first time via successive reversible addition fragmentation chain transfer (RAFT) polymerization using carboxyl-terminated trithiocarbonate as the RAFT agent. The structure of the copolymer was characterized using FTIR, GPC and 1H NMR. The block copolymer could be directly blended with polyethersulfone (PES) as a macromolecule additive using N-methyl-2-pyrrolidone (NMP) as the solvent to prepare membranes. The water contact angles for the modified membranes decreased obviously, and therefore, the protein adsorption amount on the membrane surface decreased.

New polyphenolic compounds in commercial deodistillate and rapeseed oils

Different phenolic compounds were identified in commercial rapeseed oils, as well as in a commercial by-product of oil refining, the deodistillate. Reversed-phase HPLC analysis and the successive fragmentation procedure by ESI-MS n (electrospray ionisation mass spectrometry) showed a significant fragmentation pattern for new compounds, the cis- and trans-diastereomers of 4-vinylsyringol dimer [ cis-4,6-dimethoxy-5-hydroxy-1-methyl-3-(3′,5′-dimethoxy-4′-hydroxyphenyl)indane and trans-4,6-dimethoxy-5-hydroxy-1-methyl-3-(3′,5′-dimethoxy-4′-hydroxyphenyl)indane] and the vinylsyringol trimer in trace amounts. The phenylindane were isolated by preparative HPLC and was clearly identified by nuclear magnetic resonance spectroscopy. Besides sinapic acid and its decarboxylated derivative, 4-vinylsyringol, this newly identified 4-vinylsyringol dimer was present in the deodistillate of processed rapeseed oil in significant amounts (sinapic acid, approx. 500 mg/kg, 4-vinylsyringol, approx. 200 mg/kg and 4-vinylsyringol dimer, approx. 3.50 g/kg). Additionally, the phenylindane was also detected in small amounts (6.4–63.0 mg/kg or trace amounts, respectively) in commercial rapeseed oils. The newly identified phenylindane compound had a high antioxidative potential (3.9 trolox-eq.) and might be an important phenolic compound in commercial deodistillate and rapeseed oils.

Dissolution mechanisms of wood cellulose fibres in NaOH–water

Four wood pulps and a microcrystalline cellulose were dissolved in a NaOH 8%–water solution. Insoluble fractions and clear solution fractions were isolated by centrifugation and were observed by optical microscopy and transmission electron microscopy. Molecular weight distribution, carbohydrate composition and cellulose II content were measured. The dissolution of wood cellulose fibres in NaOH 8%–water solutions occurs by successive dismantlement and fragmentation steps governed by the swelling and the shearing of the original structure. The cellulose from insoluble and clear solution fractions is in both case converted in cellulose II and the insoluble fractions contain embedded mannans. Besides, the molecular weight distributions of cellulose from insoluble and clear solution fractions reveal the existence of heterogeneities in dissolution capacity of the cellulose chains, independent to the degree of polymerization, which are related to the chemical environment of the chains in the fibre structure.

Synthesis of (+)-disparlure from diethyl (−)-malate via opening and fragmentation of the three-membered ring in tertiary cyclopropanols

(+)-Disparlure [(7R,8S)-7,8-epoxy-2-methyloctadecane, pheromone of the gypsy moth Lymantria dispar L.] was synthesized starting from diethyl (−)-malate via cyclopropanation of the ester groups, selective protection of the 1,3-diol functionality, and successive opening and fragmentation of the three-membered rings in the corresponding tertiary cyclopropanols as key stages.

Plastid DNA variation in highly fragmented populations of Microbiota decussata Kom. (Cupressaceae), an endemic to Sikhote Alin Mountains

Microbiota decussata Kom. (Cupressaceae) is a subalpine species endemic to the Sikhote Alin Mountains with populations scattered throughout the range. We used sequence data for four noncoding regions of chloroplast DNA to characterize the genetic diversity in populations sampled from different parts of M. decussata natural range. No variation was observed in the trnT-trnF region, whereas the trnH-psbA, trnS-trnfM, and trnS-trnG regions showed polymorphisms. At the species level, we found a low nucleotide diversity (pi = 0.0009) and high haplotype diversity (h = 0.981) as well as high differentiation (Phi(ST) = 0.420). N(ST) and G(ST) values suggested the existence of a phylogeographic structure in M. decussata. The observed patterns of diversity could be explained in part by ecological features of the species and its long-term persistence throughout the range with population expansion, successive fragmentation and isolation.

Evaluation of Data-Dependent versus Targeted Shotgun Proteomic Approaches for Monitoring Transcription Factor Expression in Breast Cancer

In breast cancer, there is a significant degree of molecular diversity among tumors. Multiple perturbations in signal transduction pathways impinge on transcriptional networks that in turn dictate malignant transformation and metastatic progression. Detailed knowledge of the sequence-specific transcription factors that become activated or repressed within a tumor and comparison of their relative levels of expression in cancer versus normal tissue should therefore provide insight into disease mechanisms, improving patient stratification and facilitating personalized treatment. While high-throughput tandem mass spectrometry methods for global proteome profiling have been developed, existing approaches have limited sensitivity and are often unable to detect low-abundance transcription factors in a complex biological specimen like a biopsy or tumor cell extract. To this end, we have undertaken a systematic comparative evaluation of three MS/MS methods for the ability to detect reference transcription factors spiked in known amounts into a cell-free breast cancer nuclear extract: Data-Dependent Acquisition (DDA), wherein precursor ion intensity dictates selection for fragmentation; Targeted Peptide Monitoring (TPM), a directed approach using successive isolation and fragmentation of predefined m/ z ratios; and Multiple Reaction Monitoring (MRM), in which specific precursor ion to product ion transitions are selectively monitored. Through a series of controlled, parallel benchmarking experiments, we have determined the relative figures-of-merit of each approach, and have established that prior knowledge of signature proteotypic peptides markedly improves overall detection sensitivity, reliability, and quantification.

Confirmation of Fenthion Metabolites in Oranges by IT-MS and QqTOF-MS

Identification of degradation products of the organophophorous pesticide fenthion formed in two orange varieties, Valencia Navel and Navel Late, under field conditions has been assessed using liquid chromatography quadrupole time-of-flight mass spectrometry and ion trap mass spectrometry. The structural elucidation of the metabolites was accomplished by the accurate mass measurements provided by the quadrupole time-of-flight mass spectrometer in MS and MS/MS modes. This instrument achieved elemental composition diagnosis for the precursor and product ions with absolute mass error of <5 ppm, which unambiguously establishes the identity of the metabolites even at low concentration. The presence of these compounds was also confirmed by electrospray ionization-ion trap mass spectrometry, performing successive fragmentation steps (MS(n)). Once identified, each molecule was confirmed by comparison with its analytical standard, also used to explore the quantitative capabilities of both mass analyzers. The extraction method was evaluated because it predetermines the metabolites that can be found (e.g., according to their polarity). Recoveries ranged from 70% for fenoxon sulfoxide (the most polar) to 101% for fenthion (the most apolar), which also indicates the method's facility to extract other more polar metabolites if present. Satisfactory linear range (r > 0.99) of more than 2 orders of magnitude was obtained with both analyzers for standards prepared in methanol and in untreated orange extracts. However, the matrix-matched standards showed suppression of the mass signal due to the matrix effect, especially for fenoxon sulfoxide and sulfone. The limits of quantification ranged from 0.005 to 0.015 mg/kg. The QqTOF-MS provided better quantification limits for fenthion and its sulfoxide and sulfone than the IT-MS. The resulting fenthion degration curves in oranges indicated that it was mainly degraded by sunlight photolysis to its sulfoxide and sulfone. However, hydrolysis was also observed by the appearance of fenoxon, fenoxon sulfoxide, and fenoxon sulfone, but always in low concentrations, which can be related to the rain events.

Phylogeography of Pseudacris regilla (Anura: Hylidae) in western North America, with a proposal for a new taxonomic rearrangement

The Baja California populations of Pseudacris regilla, a widespread species in Western North America ranging from British Columbia to southern Baja California, are characterized by extensive geographic fragmentation. We performed phylogeographic and historical demographic analyses on 609 bp of the cytochrome b mitochondrial gene of 110 individuals representing 28 populations to determine the relative influences of current and historical processes in shaping the present distribution of genetic diversity on the Baja California Peninsula. Haplotypes from this area were nested in a clade with three well-differentiated groups. Two of these groups are from Baja California Sur and another is from California and Baja California. The estimated date for the split of these groups, between 0.9–1 Ma, fits with previously proposed hypotheses of vicariance due to different transpeninsular seaways, although successive population fragmentation and expansion due to climatic oscillations during Pleistocene glaciations cannot be discarded. Historical demographic analyses detected signs of past population expansions, especially in the southernmost group. With respect to populations north of this region, two older clades were identified, one with haplotypes mainly distributed in central California, and the other corresponding to the northern half of the species range, in what apparently is a recurrent pattern in the Pacific coast of North America. Based on the concordance between mt-DNA and available allozyme data indicating that these species have a long independent evolutionary history, we propose to consider the three major clades as distinct species: P. regilla, P. pacifica, and P. hypochondriaca.

From population to species: morphological and molecular diversity in east African stem borer species of the genus Manga Bowden 1956 (Lepidoptera: Noctuidae)

Larvae of noctuid stem borers were collected from wild monocot plants in Eastern Africa, from Ethiopia to Mozambique, and reared to the adult stage. Three species of the African genus Manga Bowden 1956 (Lepidoptera: Noctuidae) were found, all restricted to host plants of the family Poaceae. M. melanodonta (Hampson) was collected in stems of Panicum maximum Jacquin, Setaria megaphylla (Steudel) Th. Durand & Schinz and Setaria plicatilis (Hochstetter) Engler; M. nubifera (Hampson) stat. rev., and M. fuliginosa n. sp., were both found only in stems of P. maximum. The second species was in the past sunk with M. melanodonta as a synonym, but the present study shows its validity. Descriptions are given of the new species as well as of features not yet described of known species (female habitus and male and female genitalia of M. melanodonta and M. nubifera) and of the intraspecific morphological variation observed in the male genitalia. Larval morphology and life habits are described. Pictures of the adults and genitalia of the other species of the genus are provided except for M. bisignata Laporte that is sunk with Busseola quadrata Bowden as a synonym (n. syn.). The molecular diversity of the collected species was studied using the mitochondrial gene Cytochrome b. A complex history of successive fragmentation events was revealed. The combination of three forces appeared to have shaped this diversity: the main paleo-climatic events (successive dry and humid periods), the geological barriers, particularly the Rift Valley, and specialization on new host plants. A molecular clock proved to be acceptable for all clades except for the species that first diverged, Manga fuliginosa. The dates of the major paleo-climatic events of the last 5 million years appeared to correspond to the observed divergence events when using an evolutionary rate of 1.15% per million years, with a correction for M. fuliginosa. Isolation by the Rift Valley favoured diversification in some instances, and the adaptation of Manga melanodonta to new host plants enabled the colonization of humid environments. A scenario for the evolution of the group is proposed, from its origin in Austral Africa about 5 million years ago and its northward expansion, until the recent migrations of Manga nubifera during the past million years.

Reactivity of C10H7+ and C10D7+ with H2 AND D2.

We have investigated, both theoretically and experimentally, the reactions of naphthylium C10H7+ and d-naphthylium C10D7+ ions with H2 and D2. Cross sections as functions of the collision energy have been measured for a variety of reaction channels. Theoretical calculations have been carried out at the density functional theory level which utilizes the hybrid functional B3LYP and the split-valence 6-31G* basis set. The key features of the potential energy surfaces and the relevant thermochemical parameters have been calculated and they provide insights on the reaction mechanisms. The bimolecular reactivity of C10H7+ with H2 is dominated by the production of naphthalene cation C10H8+. The reaction is not a direct atom-abstraction process, but instead it proceeds via the formation of a stable intermediate complex C10H9+ of sigma type geometry, with a significant mobility of hydrogen along the ring. This mobility allows the scrambling of the hydrogen atoms and causes the successive statistical fragmentation of the complex into a variety of product channels. Elimination of one H(D) atom appears to be favored over elimination of one H2 or HD molecule. Alternatively, the intermediate complex can be stabilized either by collision with a third body or by emission of a photon.

Molecular phylogeny of Haematoloechus Looss, 1899 (Digenea: Plagiorchiidae), with emphasis on North American species.

Phylogenetic hypothesis of 23 populations corresponding to 18 species of the digenean Haematoloechus from America, Europe, and Africa, based on ribosomal DNA 28S partial sequences (approximately 890 bp), is presented. Genetic divergence between the in-group and the out-groups ranged from 9.7 to 14.5% and within the in-group, from 0.9 to 12.2%. Eight most parsimonious trees 569 steps long were obtained, with a consistency index of 72%. Groups in the tree are not congruent with those in previous classification schemes of species in the genus, based on a small number of morphological characters. For this subset of Haematoloechus species, plesiomorphic hosts are species of Rana, with 2 colonizations to other amphibian groups. African species appear to have diverged after the separation of Gondwana and Laurasia. Therefore, South American species should appear as the closest relatives of African species when included in the analysis. The evidence presented suggests an ancestral wide distribution of North American representatives of the group, followed by successive contraction, amplification, and fragmentation of ranges and speciation events as a result of the intense volcanic activity in the central part of Mexico since the late Tertiary, the drying climate of western and central United States and northwestern Mexico from the early Eocene to the Pleistocene, and the glaciation during the Pleistocene.

The Successive Fragmentation of a Structurally Characterized Metalloid Cluster Anion in the Gas Phase: [Ga13(GaR)6]— → ··· → [Ga13]— + 6 GaR (R = C(SiMe3)3)

AbstractBy collisions with argon atoms in the gas phase (SORI‐CAD experiments by means of FT‐ICR mass spectrometry) the metalloid cluster ion [Ga19(C(SiMe3)3)6]— fragments in a very precise way detaching step by step neutral Ga(C(SiMe3)3) units and finally leading to the stable 40‐electron bare metal cluster [Ga13]—. In combination with quantum chemical calculations the exploration of the fragmentation process leads to an experimentally based understanding of the bond properties of many of the recently investigated metalloid gallium and aluminum clusters.

MD simulation of cluster ejection due to sputtering by polyatomic projectiles

We studied the fragmentation of sputtered clusters due to Cu-cluster impact on a Cu surface using MD simulations. The sputtered clusters become stable after the successive fragmentation of nascent sputtered clusters. Then the vibration energy spectrum of sputtered clusters is independent on the incident cluster size and energy. For sputtered clusters Cu n ( n≥5), it has a peak, whose energy corresponds to the melting temperature of Cu. The recombination is not important. Most of the monomers come from direct ejection; the clusters are produced mainly by fragmentation.

Determination of regioselectivity in ring opening of tert-butylaziridinones by a combination of (15)N labeling and electrospray ionization-ion trap mass spectrometry.

The ring opening of 1,3-di-tert-butylaziridinone by tert-butylamine and aniline was investigated by using electrospray ionization and collision-induced dissociation in an ion trap mass spectrometer in conjunction with (15)N labeling of the two amine nucleophiles. Using the MS(n) capabilities of the ion trap instrument, we were able to monitor the retention of the (15)N label through successive fragmentation steps. Both amines exhibited a remarkable degree of selectivity in that they both cleaved exclusively the 1,3-bond (the alkyl-nitrogen bond). This result is in contrast to that obtained previously with methylamine, which cleaved just the opposite bond, namely, the 1,2-bond (the acyl-nitrogen bond). These contrasting results could not have been predicted by previously published guidelines.