Simple Bond Research Articles

Steering sovereign debt restructurings through the CDS quicksand

A central policy concern since the onset of the Greek debt crisis in 2010 has been whether sovereign debt restructurings trigger credit default swaps (CDS). For the first time since AIG threatened to default on its CDS in 2008, the Greek debt crisis returned CDS to the global spotlight. The question of whether sovereign debt restructurings trigger CDS matters not only for the buyers and sellers of CDS, but for financial stability more generally. Although there was universal agreement that a failure to pay when due would trigger a failure to pay credit event under CDS, whether formally voluntary/restructurings also trigger a restructuring credit event was uncertain before the Greek debt restructuring in March 2012. On the basis of the experience with the Greek restructuring, this article assesses how likely five restructuring techniques, ranging from simple bond exchanges to the use of collective action clauses, trigger CDS.

Water clusters to nanodrops: a tight-binding density functional study

We predict structures and energies of water clusters containing up to 100 waters with tight-binding density functional theory (DFTB). A per-hydrogen-bond energy correction is found to correct for systematic errors in the DFTB cluster energies. We compare the DFTB structures and energies to density functional theory (DFT) calculations and to the most accurate wave function theoretical (WFT) values available (ranging from coupled-cluster theory to second-order perturbation theory). After including the simple hydrogen bond correction, we achieve a root-mean-square difference of less than one kcal mol(-1) with the best estimates. As DFTB optimizations are orders of magnitude faster than DFT or canonical MP2, it is apparent that DFTB is a very practical method for calculating large water cluster structures and, with the hydrogen bond correction, also energies.

Becoming Latino: Mexican and Puerto Rican Community Formation in Grand Rapids, Michigan, 1926–1964

THE MICHIGAN HISTORICAL REVIEW 39:1 (Spring 2013): 71-100.©2013 by Central Michigan University. ISSN 0890-1686 All Rights Reserved. 2012 Student Essay Prize Winner Becoming Latino: Mexican and Puerto Rican Community Formation in Grand Rapids, Michigan, 1926-1964 by Delia Fernández Introduction Nilda and Virginia Fernández are still not sure which one of them is pictured in Image 1. Virginia says she is to the left in the foreground, but Nilda also recalls being at the photo site that September day in 1968, so it could be her instead. If it is Virginia, then Nilda says that maybe she was behind her sister, and that is why Nilda is not visible in the photograph. Even if they cannot remember the particulars, they both remember participating in festivals like this every year. The Mexican Independence Day celebration was a tradition in cities around the United States, much like it was in Grand Rapids, Michigan, a typical city on the west side of the state that was once dubbed the “Furniture City.”1 A unique aspect of this particular parade, however, is that the Fernández 1 For more information on Grand Rapids’ history, see Christian G. Carron, Grand Rapids Furniture: The Story of America’s Furniture City (Grand Rapids, Mich.: Public Museum of Grand Rapids, 1998); Thomas R. Dilley, Grand Rapids: Community and Industry (Charleston, S.C.: Arcadia, 2006); Richard H. Harms and Robert W. Viol, Grand Rapids Goes to War: The 1940s Homefront (Grand Rapids, Mich.: Grand Rapids Historical Society, 1993); Randal Maurice Jelks, African Americans in the Furniture City: The Struggle for Civil Rights in Grand Rapids (Urbana: University of Illinois Press, 2006); Jeff Kleiman, Strike! How the Furniture Workers Strike of 1911 Changed Grand Rapids (Grand Rapids, Mich.: Grand Rapids Historical Commission, 2006); Norma Lewis, Grand Rapids: Furniture City (Charleston, S.C.: Arcadia, 2008); Z. Z. Lydens, ed., The Story of Grand Rapids (Grand Rapids, Mich.: Kregal, 1966); Gordon L. Olson, Flight to Freedom: The Story of the Vietnamese of West Michigan (Grand Rapids, Mich.: Grand Rapids Historical Commission, 2004); idem and Susan Lovell, Grand Rapids, a City Renewed: A History since World War II (Grand Rapids, Mich.: Grand Rapids Historical Commission, 1996); Gordon L. Olson, A Grand Rapids Sampler (Grand Rapids, Mich.: Grand Rapids Historical Commission, 1992); Linda Samuelson and Andrew Schrier, Heart & Soul : The Story of Grand Rapids Neighborhoods (Grand Rapids, Mich.: William B. Eerdmans, 2003); Reinder Van Til and Gordon L. Olson, Thin Ice: Coming of Age in Grand Rapids (Grand Rapids, Mich.: William B. Eerdmans, 2007). 72 The Michigan Historical Review sisters are not actually Mexican, but Puerto Rican. Although Puerto Ricans have no historical connection to Mexican Independence Day, the sisters felt that their participation at this festival was welcomed and encouraged. The presence of both Mexican/Mexican Americans and Puerto Ricans at this Mexican celebration is significant.2 Both populations recognized similarities and differences shared by each, but many of the migrants and immigrants referred to themselves collectively as “Spanish-Speaking” people. However, this article will show that the two groups’ relationship depended on more than a simple linguistic bond. They shared work experiences, culture, a common Catholic faith, and similar opportunities for jobs and leisure, which together fostered the formation of a single Latino identity. In addition, both groups faced discrimination. As the Latino population in the United States continues to grow, it is important to understand the historical roots of this panethnic identity. Mexicans and Puerto Ricans in Grand Rapids, Michigan, provide a compelling case study of Latino identity formation. Historians like George Sanchez and David Gutiérrez have thoroughly researched Mexican American identity and community formation, while a host of others have also looked at Mexican community formation in Chicago, Detroit, and Los Angeles, as well as in smaller cities like Corona, California.3 Puerto Rican historians such as Carmen Teresa Whalen have similarly studied the Puerto Rican diaspora 2 I use “Mexican American” to refer to ethnically Mexican, but nationally American people. I use “Mexican national” to refer to an immigrant who is both ethnically and nationally Mexican. I use “Mexican” to refer to both groups. The majority of the ethnically Mexican population in Grand...

Simultaneous Determination of Interfacial Molarities of Amide Bonds, Carboxylate Groups, and Water by Chemical Trapping in Micelles of Amphiphiles Containing Peptide Bond Models

Chemical trapping is a powerful approach for obtaining experimental estimates of interfacial molarities of weakly basic nucleophiles in the interfacial regions of amphiphile aggregates. Here, we demonstrate that the chemical probe 4-hexadecyl-2,6-dimethylbenzenediazonium ion (16-ArN(2)(+)) reacts competitively with interfacial water, with the amide carbonyl followed by cleavage of the headgroups from the tail at the amide oxygen, and with the terminal carboxylate groups in micelles of two N-acyl amino-acid amphiphiles, sodium N-lauroylsarcosinate (SLS) and sodium N-lauroylglycinate (SLG), simple peptide bond model amphiphiles. Interfacial molarities (in moles per liter of interfacial volume) of these three groups were obtained from product yields, assuming that selectivity toward a particular nucleophile compared to water is the same in an aqueous reference solution and in the interfacial region. Interfacial carboxylate group molarities are ~1.5 M in both SLS and SLG micelles, but the concentration of the amide carbonyl for SLS micelles is ~4.6-5 times less (ca. 0.7 M) than that of SLG micelles (~3 M). The proton on the secondary N of SLG helps solubilize the amide bond in the aqueous region, but the methyl on the tertiary N of SLS helps solubilize the amide bond in the micellar core, reducing its reaction with 16-ArN(2)(+). Application of chemical trapping to proteins in membrane mimetic interfaces should provide insight into the topology of the protein within the interface because trapping of the amide carbonyl and cleavage at the C-N bond occurs only within the interface, and fragment characterization marks those peptide bonds located within the interface.

Manipulation of organic polyradicals in a single-molecule transistor

Inspired by cotunneling spectroscopy of spin-states in a single OPE5-based molecule, we investigate the prospects for electric control of magnetism in purely organic molecules contacted in a three-terminal geometry. Using the gate electrode, the molecule is reversibly switched between three different redox states, with magnetic spectra revealing both ferromagnetic and antiferromagnetic exchange couplings on the molecule. These observations are shown to be captured by an effective low-energy Heisenberg model, which we substantiate microscopically by a simple valence bond description of the molecule. These preliminary findings suggest an interesting route towards functionalized all-organic molecular magnetism.

Coarse-Grained Simulations of Protein Backbone Dynamics. 1. Local Sterics Define the Dihedral Angles.

Here, we present a coarse-grained model targeted for implicit solvent simulations of unfolded or intrinsically disordered proteins. The hierarchical model with its nonspherical building blocks allows one to reproduce the local dynamics of the backbone with simple harmonic bonds and steric collisions between a small number of atoms at the correct off-center positions on the building blocks. Here in part 1, we also describe the implementation of the global shape of the protein chain and the extended local interactions that add a first secondary structure bias, which will subsequently be augmented by additional hydrophobic interactions, hydrogen bonds, and dipole dipole couplings along the backbone. Due to its hierarchical setup, the model has a near-atomistic resolution on the local scale and the overall numerical efficiency of a coarse-grained model such that even long protein chains can be simulated efficiently.

Fratura coronorradicular: uma abordagem multidisciplinar

INTRODUÇÃO: Uma fratura coronorradicular envolve esmalte, dentina e cemento, podendo ou não haver comprometimento pulpar. Vários tratamentos são propostos na literatura, desde a colagem do fragmento dental até a extrusão cirúrgica do fragmento remanescente. O presente trabalho descreve um caso de fratura coronorradicular com envolvimento pulpar e a abordagem multidisciplinar dada ao caso. DESCRIÇÃO DO CASO CLÍNICO: Paciente procurou tratamento odontológico por causa de um "dente quebrado". O tratamento realizado consistiu em um retalho mucoperiosteal para remoção dos fragmentos dentais, tratamento endodôntico, restauração provisória, extrusão ortodôntica, uma nova restauração e a proservação do caso. CONCLUSÃO: Em pacientes jovens, na região anterior, a extrusão ortodôntica acompanhada do tratamento restaurador é uma opção de tratamento conservador e estético.

Photofragmentation of Isoleucine by Vacuum Ultraviolet Photoionization

Vacuum ultraviolet photon-induced ionization and dissociation of isoleucine are investigated with synchrotron radiation photoionization mass spectroscopy and theoretical calculations. The main fragment ions at m/z=86, 75, 74, 69, 57, 46, 45, 44, 41, 30, 28, and 18 from isoleucine are observed in the mass spectrum at the photon energy of 13 eV. From the photoionization efficiency curves, appearance energies for the principal fragment ions C5H12N+ (m/z=86), C2H5NO2+ (m/z=75), C5H9+ (m/z=69), C4H9+ (m/z=57), and CH4N+ (m/z=30) are determined to be 8.84±0.07, 9.25±0.06, 10.20±0.12, 9.25±0.10, and 11.05±0.07 eV, respectively, and possible formation pathways are established in detail by the calculations at the B3LYP/6-31++G(d, p) levels. These proposed channels include simple bond cleavage reactions as well as reactions involving intermediates and transition structures. The experimental and computational appearance energies or barriers are in good agreement.

Correlation between native bonds in a polymeric material and molecular emissions from the laser-induced plasma observed with space and time resolved imaging

Emissions from C2 molecules and CN radicals in laser-induced plasmas on polymeric materials were observed with time-resolved spectroscopic imaging. More precisely, differential imaging with a pair of narrowband filters (one centered on the emission line and another out of the line) was used to extract emission images of interested molecules or radicals. The correlation between the molecular emission image of the plasma and the molecular structure of the polymer to be analyzed was studied for four different types of materials: polyamide (PA) with native CN bonds, polyethylene (PE) with simple CC bonds, polystyrene (PS) with delocalized double CC bonds, and polyoxymethylene (POM) which neither contains CC nor CN bonds. A clear correlation is demonstrated between emission and molecular structure of the material, allowing the identification of several organic compounds by differential spectroscopic imaging.

Steering Greece's Debt Restructuring Through the CDS Quicksand

A central policy concern since the onset of the Greek debt crisis in 2010 has been whether sovereign debt restructurings trigger credit default swaps (CDS). For the first time since AIG threatened to default on its CDS in 2008, the Greek debt crisis returned CDS to the global spotlight. The question of whether sovereign debt restructurings trigger CDS matters not only for buyers and sellers of CDS, but for financial stability more generally. While there was universal agreement that a failure to pay when due would trigger a failure to pay credit event under CDS, whether formally ‘voluntary’ restructurings also trigger a credit restructuring event was uncertain prior to the Greek debt restructuring in March 2012. With the benefit of the experience on the Greek restructuring February/March 2012, this article assesses how likely five types of restructuring, ranging from a simple bond exchange over the use of CACs to exit consent are to trigger CDS. The paper is structured into five parts. Part I outlines techniques for restructuring sovereign debt; Part II describes how CDS work and the challenges they raise in debt restructurings. Part III examines the most important credit event in the context of sovereign debt restructurings, the restructuring credit event. Part IV analyses whether five different types of sovereign debt restructurings techniques trigger CDS. Finally, Part V examines the central role of ISDA determinations committees.

Simple model for the simulation of peptide folding and aggregation with different sequences

We present a coarse-grained interaction potential that, using just one single interaction bead per amino acid and only realistic interactions, can reproduce the most representative features of peptide folding. We combine a simple hydrogen bond potential, recently developed in our group, with a reduced alphabet for the amino acid sequence, which takes into account hydrophobic interactions. The sequence does not pose any additional influence in the torsional properties of the chain, as it often appears in previously published work. Our model is studied in equilibrium simulations at different temperatures and concentrations. At low concentrations the effect of hydrophobic interactions is determinant, as α-helices (isolated or in bundles) or β-sheets are the most populated conformations, depending on the simulated sequence. On the other hand, an increase in concentration translates into a higher influence of the hydrogen bond interactions, which mostly favor the formation of β-type aggregates, in agreement with experimental observations. These aggregates, however, still keep some distinct characteristics for different sequences.

Nature of the Ga-Ga bonding in Na2[Arx*GaGaArx*] (Arx* = C6H3-2,6-(C6H5)2): Electron localization function analysis

The nature of the Ga-Ga bonding in Na2[Arx*GaGaArx*] (Arx* = C6H3-2,6-(C6H5)2) has been investigated and compared with that of in H2[Arx*GaGaArx*] using electron localization function (ELF) and orbital analysis. The calculation results show that in Na2[Arx*GaGaArx*], the Ga-Ga interaction is a non-classical triple bond, the heart of Na2[Arx*GaGaArx*] is the Ga2Na2 cluster rather than a simple Ga-Ga bond, and the contribution of the sodium atoms to the short Ga-Ga bond length is considerable. As the two sodium atoms are substituted by two hydrogen atoms, the Ga-Ga bond is replaced by two 3-center, 2-electron (3c-2e) Ga-H-Ga covalent bridged bonding.

XAS analysis of a nanostructured iron polysaccharide produced anaerobically by a strain of Klebsiella oxytoca

A strain of Klebsiella oxytoca, isolated from acid pyrite-mine drainage, characteristically produces a ferric hydrogel, consisting of branched heptasaccharide repeating units exopolysaccharide (EPS), with metal content of 36 wt%. The high content of iron in the EPS matrix cannot be explained by a simple ferric ion bond to the sugar skeleton. The bio-generated Fe-EPS is investigated by X-ray absorption spectroscopy. Fe K-edge XANES analysis shows that iron is mostly in trivalent form, with a non-negligible amount of Fe(2+) in the structure. The Fe EXAFS results indicate that iron in the sample is in a mineralized form, prevalently in the form of nano-sized particles of iron oxides/hydroxides, most probably a mixture of different nano-crystalline forms. TEM shows that these nanoparticles are located in the interior of the EPS matrix, as in ferritin. The strain produces Fe-EPS to modulate Fe-ions uptake from the cytoplasm to avoid iron toxicity under anaerobic conditions. This microbial material is potentially applicable as iron regulator.

A ‘meta effect’ in the fragmentation reactions of ionised alkyl phenols and alkyl anisoles

The competition between benzylic cleavage (simple bond fission [SBF]) and retro-ene rearrangement (RER) from ionised ortho, meta and para RC(6) H(4) OH and RC(6) H(4) OCH(3) (R = n-C(3) H(7) , n-C(4) H(9) , n-C(5) H(11) , n-C(7) H(15) , n-C(9) H(19) , n-C(15) H(31) ) is examined. It is observed that the SBF/RER ratio is significantly influenced by the position of the substituent on the aromatic ring. As a rule, phenols and anisoles substituted by an alkyl group in meta position lead to more abundant methylene-2,4-cyclohexadiene cations (RER fragmentation) than their ortho and para homologues. This 'meta effect' is explained on the basis of energetic and kinetic of the two reaction channels. Quantum chemistry computations have been used to provide estimate of the thermochemistry associated with these two fragmentation routes. G3B3 calculation shows that a hydroxy or a methoxy group in the meta position destabilises the SBF and stabilises the RER product ions. Modelling of the SBF/RER intensities ratio has been performed assuming two single reaction rates for both fragmentation processes and computing them within the statistical RRKM formalism in the case of ortho, meta and para butyl phenols. It is clearly demonstrated that, combining thermochemistry and kinetics, the inequality (SBF/RER)(meta) < (SBF/RER)(ortho) < (SBF/RER)(para) holds for the butyl phenols series. It is expected that the 'meta effect' described in this study enables unequivocal identification of meta isomers from ortho and para isomers not only of alkyl phenols and alkyl anisoles but also in other alkyl benzene series.

Dissociative electron attachment to the silane derivatives trichlorovinylsilane (SiCl3C2H3), tetravinylsilane (Si(C2H3)4) and trimethylvinylsilane (Si(CH3)3C2H3)

The formation of negative ions following low energy (0–12eV) electron attachment to the title compounds is studied in a crossed electron-molecular beam experiment applying mass spectrometric detection of the anions. All silane derivatives presently studied are weak electron scavengers which also holds for trichlorovinylsilane. The behaviour in the silanes is hence in strong contrast to the hydrocarbons where chlorination usually results in a strong increase of the cross section for dissociative electron attachment (DEA) yielding intense Cl− signals already at very low electron energies (near 0eV). The different behaviour can be explained by the appreciably stronger Si–Cl binding energy compared to that of C–Cl making the DEA reaction leading to Cl− endothermic for trichlorovinylsilane while the corresponding reaction is exothermic for most chlorinated hydrocarbons. Trichlorovinylsilane and tetravinylsilane undergo various further DEA reactions via different resonances at higher energy (in the range between 4 and 10eV) leading to a variety of ionic fragments. These reactions range from simple bond cleavages to considerably more complex unimolecular decompositions involving multiple bond cleavages, hydrogen transfer in the temporary negative ion and formation of new bonds. Trimethylvinylsilane yields only one single fragment due to the loss of a neutral hydrogen atom ((M−H)−).

Surface fluorination of zirconia: Adhesive bond strength comparison to commercial primers

ObjectiveThis study evaluated contact angle and shear bond strength of three commercial zirconia primers and compared them to a recently developed fluorination pre-treatment. Earlier investigations reported that plasma fluorinated zirconia modifies the chemical bonding structure creating a more reactive surface. Materials and methodsYttria-stabilized zirconia (LAVA, 3M ESPE) plates were highly polished using 3μm diamond paste (Ra ∼200nm) prior to pretreatments. After primer and fluorination treatment, contact angles were measured to quantify surface hydrophobicity before and after ethanol clean. Additionally, simple shear bond tests were performed to measure the adhesion strength to a composite resin. ResultsPlasma fluorination produced the lowest contact angle (7.8°) and the highest shear bond strength (37.3MPa) suggesting this pretreatment facilitates a more “chemically” active surface for adhesive bonding. ConclusionsIt is hypothesized that plasma fluorination increase hydroxylation at the surface, making it more reactive, thus allowing for covalent bonding between zirconia surface and resin cement. A strong correlation was observed between contact angle and adhesion strength for all specimens; a relationship which may help understand the frequency and modes of failures, clinically. It is also believed that this surface treatment can increase long-term viability of zirconia restorations over other adhesive techniques.

Isomerization and Dissociation of n-Butylbenzene Radical Cation

Fragmentation mechanisms of ionized butylbenzene to give m/z 91 and m/z 92 fragment ions have been examined at the G3B3 and G3MP2B3 levels of theory. It is shown that the energetically favored pathways lead to tropylium, Tr(+), and methylene-2,4-cyclohexadiene, MCD(•+), ions. Formation of m/z 91 benzyl ions, Bz(+), by a simple bond fission (SBF) process, needs about 30 kJ/mol more energy than Tr(+). Possible formation of C(7)H(8)(•+) ions of structures different from the retro-ene rearrangement (RER) product, MCD(•+), has been also considered. Comparison with experimental data of this "thermometer" system is done through a kinetic modeling using Rice-Ramsperger-Kassel-Marcus (RRKM) and orbiting transition state (OTS) rate constant calculations on the G3MP2B3 0 K energy surface. The results agree with previous experimental observation if (i) the competitive formation of Tr(+) and Bz(+) is taken into account in the m/z 91 pathway, and (ii) the stepwise character of the RER fragmentation is introduced in the m/z 92 fragmentation route.

Spectroscopic and computational studies of matrix-isolated iso-CXBr3 (X = F, Cl, Br): Structure, properties, and photochemistry of substituted iso-tribromomethanes

Iso-polyhalomethanes are important reactive intermediates in the condensed and gas-phase chemistry of halomethanes. Building upon our recent study of iso-bromoform, in this work the substituted iso-tribromomethanes (iso-CXBr3; X=F, Cl, Br) were characterized by matrix isolation infrared and UV/Vis spectroscopy, supported by ab initio calculations, to further probe the structure, spectroscopy, properties, and photochemistry of these important intermediates. Selected wavelength laser irradiation of CXBr3 samples in an inert rare gas (typically Ar; mixing ratio 1:500) held at ∼5K yielded iso-CXBr3 (XBrC–Br–Br or Br2C–Br–X). The observed infrared and UV/Vis absorptions are in excellent agreement with computational predictions, and the energies of various stationary points on the CXBr3 Potential Energy Surfaces (PESs) were characterized computationally using DFT, MP2, and CCSD (T) methods in combination with triple-zeta quality basis sets. These calculations show that the isomers are minima on the PESs that lie ∼200kJ/mol above the global CXBr3 minimum, yet are bound by some 50–70kJ/mol in the gas-phase with respect to the CXBr2+Br asymptote. Laser irradiation of the isomers resulted in back photoisomerization to CXBr3, and intrinsic reaction coordinate (IRC) calculations confirmed the existence of a first order saddle point connecting the two isomers. Calculations of important stationary points on the CXBr3 PESs show that in the gas-phase the isomerization barrier lies energetically near the threshold for simple bond fission. The iso-CXBr3 species are significantly stabilized in the condensed phase, due to the high degree of ion-pair character, as revealed by Natural Resonance Theory analysis.

Theoretical and experimental exploration of the photochemistry of resveratrol: beyond the simple double bond isomerization

The photochemical isomerization of resveratrol has been the subject of recent studies in which contradictory results were reported. The photoproduct mixture of this reaction needs to be considered more complex than the coexistence of cis and trans isomers. An unidentified third product, at least, has been detected in various studies although its nature was unknown. In this work, we aim to provide a thorough description of the photochemical course of this reaction through experimental and computational approaches working in a synergetic association.

Rhodamine-labeled cyclodextrin derivatives

Four different rhodamine-labeled cyclodextrin-based derivatives were synthesized by coupling rhodamine B (Rho B) with β-cyclodextrin (βCD) or rhodamine B isothiocyanate (RBITC) with βCD, randomly (2-hydroxy)propylated βCD (HPβCD) and randomly methylated-βCD (RAMEβ). The introduction of a single amino unit on the primary side of the cyclodextrin scaffolds allowed the coupling of the fluorophore through either a thioureido moiety or a simple amide bond.