Equivalent Chain Research Articles

Spectra of conjugated polymer aggregates: Symmetry of the interchain dressed states

Here we consider an interchain interaction model to understand the spectral properties of aggregate of a class of conjugated polymers. The dressed eigenstates are calculated for the equivalent and inequivalent chain dimers and are symmetry classified. We have provided the Wigner function matrix to describe the quantum interference due to nonadiabaticity in the excitonic states, the energy distribution between the chains as well as the phase relation between the vibrational modes. The various disorder-induced effects on the spectra can be explained by the dimeric chains that are generally inequivalent.

Coiled-Coil Hydrogels. Effect of Grafted Copolymer Composition and Cyclization on Gelation.

A mean-field theoretical approach was developed to model gelation of solutions of hydrophilic polymers with grafted peptide motifs capable of forming associates of coiled-coil type. The model addresses the competition between associates engaged in branching and cyclization. It results in relative concentrations of intra- and intermolecular associates in dependence on associate strength and motif concentration. The cyclization probability is derived from the model of equivalent Gaussian chain and takes into account all possible paths connecting the interacting motifs. Examination of the association-dissociation equilibria, controlled by the equilibrium constant for association taken as input information, determines the fractions of inter- and intramolecularly associated motifs. The gelation model is based on the statistical theory of branching processes and in combination with the cyclization model predicts the critical concentration delimiting the regions of gelled and liquid states of the system. A comparison between predictions of the model and experimental data available for aqueous solutions of poly[N-(2-hydroxypropyl)methacrylamide] grafted with oppositely charged pentaheptad peptides, CCE and CCK, indicates that the association constant of grafted motifs by four orders of magnitude lower than that of free motifs. It is predicted that at the critical concentration of each motif of about 6×10(-7) mol/cm(3), about half of motifs in associated state is engaged in intramolecular bonds.

Fluorine-labeling as a diagnostic for thiol-ligand and gold nanocluster self-assembly

An omega-fluorine-labeled oxyethylene thiol ligand, F(CH2CH2O)2CH2CH2SH, was synthesized, characterized and incorporated into mixed self-assembled monolayers with CH3(OCH2CH2)3SH onto a planar gold substrate and onto 2 nm gold nanoclusters. The fluorine-labeled nanocluster was self-assembled onto gold substrates using alkane dithiol (HS(CH2)nSH; n = 5, 8, 11) and oxyethylene dithiol (HS(CH2CH2O)nCH2CH2SH; n = 1, 2, 3) linking agents with equivalent chain lengths for comparative purposes. X-ray photoelectron spectroscopy (XPS) was used to track the fluorine-label in the self-assembly operations and to evaluate the effectiveness of the dithiols. For adequate XPS sensitivity at least 10% of the monolayer-forming molecules should be functionalized with this fluorine-label. In the comparative self-assembly of the fluorine-labeled gold nanoclusters in chloroform solution, the alkane dithiols were observed to be the more effective linking agents. This effectiveness correlates with the XPS analysis of alkane dithiols self-assembling onto the gold substrates with a higher packing density and with a larger fraction of molecules having one thiol group as opposed to two bonded to the gold surface. The oxyethylene dithiols self-assemble with a smaller packing density and a smaller fraction of molecules with an unbonded thiol group available for self-assembly.

Syntheses, structures and catalytic properties of one-dimensional lanthanide-dotp compounds [dotpH 8 = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis-(methylenephosphonic acid)

Based on 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis-(methylenephosphonic acid) (dotpH 8), compounds [Ln(dotpH 7)(H 2O) 2]Cl 2 · xH 2O ( 1 · Ln) (Ln = La, Nd, Sm, Eu, Gd, Tb) and [Ln(dotpH 7)(H 2O) 2](ClO 4) 2 · xH 2O ( 2 · Ln) (Ln = Nd, Sm, Eu, Gd, Tb) are synthesized in aqueous solutions at low pH. Compounds within each kind are isostructural. Both show chain structures where the neighboring {LnO 8} polyhedra are doubly bridged by {CPO 3} tetrahedra through corner-sharing. The packing of chains, however, are different in the two cases. In 1 · Ln, each chain is surrounded by six equivalent chains, with the Cl − counterions and the lattice water molecules locating between the chains. In 2 · Ln, neighboring chains are connected via strong hydrogen bond interactions to form a supramolecular layer in the ab plane. The ClO 4 - counterions fill in the inter-layer spaces. The catalytic and luminescent properties are investigated.

Global conformation analysis of irradiated xyloglucans

Xyloglucan isolated and purified from tamarind seed was subjected to various degrees of γ-irradiation treatments, from 10 to 70 kGy, monitored for radiation damage and then studied using a new combined hydrodynamic approach with regards to conformation and flexibility. Radiation products were analysed with regard to molecular weight (weight average) M w from size exclusion chromatography coupled to multi-angle laser light scattering (SEC–MALLs), intrinsic viscosity [ η] and sedimentation coefficient s o 20,w. Sedimentation coefficient distributions and elution profiles from SEC–MALLs confirmed the unimodal nature of the molecular weight distribution for each sample in solution. The chain flexibility was then investigated in terms of the persistence length, L p of the equivalent worm-like chain model. The traditional Bushin–Bohdanecky (intrinsic viscosity) and Yamakawa–Fujii (sedimentation coefficient) relations were used separately then combined together by minimisation of a target function according to a recently published procedure [Ortega, A., & García de la Torre, J. (2007). Equivalent radii and ratios of radii from solution properties as indicators of macromolecular conformation, shape, and flexibility. Biomacromolecules, 8, 2464–2475 [see also Ortega, A. Metodologías computacionales para propiedades en disolución de macromoléculas rígidas y flexibles. Ph.D. Dissertation, Universidad de Murcia, 2005]] and yielded an estimate for L p in the range 4–9 nm using floated and fixed mass per unit length analysis protocols and “point” global analysis: irradiated xyloglucans behave as flexible structures in common with pressure/heat treated materials.

Optimization of the selectivity of a cyanopropyl stationary phase for the gas chromatographic analysis of trans fatty acids

The quantification of monounsaturated and polyunsaturated trans fatty acids in partially hydrogenated fats by gas–liquid chromatography on a CP-Select CB-FAME capillary column was optimized using equivalent chain length values of fatty acids methyl esters that could coelute in the temperature range from 155 to 200 °C. The most appropriate temperature for the simultaneous determination of these trans isomers is around 197 °C. It is proposed a system to discriminate trans from cis octadecenoic fatty acid methyl esters based on the angular coefficient values of the equivalent chain length curves. The limits of detection and quantification were 0.28 and 0.93 mg g −1. Quantification was performed in the range from 0.93 to 280 mg g −1. Quantification accuracy was estimated by spike recovery of elaidic and trans-13-octadecenoic acids in hydrogenated fat samples. The obtained levels were from 97.60 to 103.28% for elaidic acid and from 98.12 to 99.27% for trans-13-octadecenoic acid. These results indicate that the accuracy of the methodology proposed for the quantification of monounsaturated and polyunsaturated trans fatty acids in hydrogenated fats is adequate.

Unusual Fatty Acids in the Fat Body of the Early Nesting Bumblebee, Bombus pratorum

Unusual fatty acids with 24, 26, and 28 carbon atoms were found in triacylglycerols (TAGs) isolated from fat body tissue of bumblebee Bombus pratorum. The most abundant one was (Z,Z)-9,19-hexacosadienoic acid. Its structure was determined by mass spectrometry after derivatization with dimethyl disulfide and by infrared spectroscopy. ECL (equivalent chain length) values of its methyl ester were determined on both DB-1 and DB-WAX capillary columns. (Z,Z)-9,19-Hexacosadienoic acid is quite rare in nature. So far it has been identified only in marine sponges, and this work is the first evidence of its occurrence in a terrestrial organism. HPLC/MS analysis of the bumblebee TAGs showed that (Z,Z)-9,19-hexacosadienoic acid is present in one third of all TAG molecular species. As it was found in all sn-TAG positions, it is likely that (Z,Z)-9,19-hexacosadienoic acid is transported to tissues. Interestingly, labial gland secretion of B. pratorum was found to contain (Z,Z)-7,17-pentacosadiene, a hydrocarbon with markedly similar double bond positions and geometry. Possible biosynthetic relationships between these two compounds are discussed.

Conformational behavior of polypeptides derived through simultaneous global conservative site-directed mutagenesis of chymotrypsin inhibitor 2

The natural occurrence of conservative residue substitutions in proteins suggests that side-chain packing schemes in protein interiors can accommodate mutational replacements of residues by others of similar nature. To explore the extent to which such substitutions are tolerated, especially when introduced simultaneously and globally over the entire length of a polypeptide chain, we examined the conformational behavior of a model 65 residues-long protein, wild-type chymotrypsin inhibitor 2 (WTCI2), and two globally-mutated (GM) variants named GMCI2-1 and GMCI2-2, each incorporating 55 conservative residue substitutions. GMCI2-1, was soluble over a wide range of pH, and folded into a compact, spherical, monomer marked by (i) complete absence of surface hydrophobicity, (ii) a WTCI2-like betaII-type CD spectrum, (iii) high WTCI2-like thermal stability, and (d) 1D and 2D NMR spectra characteristic of folded protein structure. GMCI2-2 was insoluble over a wide range of pH, and could be solubilized only at pH 4.0, showing non-WTCI2-like far-UV CD spectra characterized by high helical content. These results tentatively indicate that polypeptides incorporating residues of identical nature at equivalent chain locations can show the potential to fold with similar characteristics. However, further detailed investigations would be required to determine whether indeed the structural fold of GMCI2-1 resembles that of WTCI2, and to evaluate the extent to which it does so.

The Role of (ETA) Violence in the Construction of Nationalism in Spain and the Basque Country

AbstractUsing the theoretical concepts of the discourse theory of Laclau and Mouffe, the author discusses the different ways in which three political parties in Spain ‐ PP, PSOE and PNV ‐ construct their discourse in relation to the nation and violence. It is claimed that the PP has developed a discourse based on chains of equivalence, one of which has the nation as a nodal point and the other ‐ the (ETA) violence. These chains are not just political but also ethical constructions. The PSOE bases its discourse on the logic of difference, which attempts to expand the political field to include more and more elements, but sometimes fails to renegotiate some important concepts. The PNV is in a constant fluctuation between the sovereignist position of a permanent struggle to preserve the Basque identity and to liberate the Basque Country and the autonomist position where the logic of difference is employed and only violence is left aside.

Rapid identification of fatty acid methyl esters using a multidimensional gas chromatography–mass spectrometry database

A multidimensional approach for the identification of fatty acid methyl esters (FAME) based on GC/MS analysis is described. Mass spectra and retention data of more than 130 FAME from various sources (chain lengths in the range from 4 to 24 carbon atoms) were collected in a database. Hints for the interpretation of FAME mass spectra are given and relevant diagnostic marker ions are deduced indicating specific groups of fatty acids. To verify the identity of single species and to ensure an optimized chromatographic resolution, the database was compiled with retention data libraries acquired on columns of different polarity (HP-5, DB-23, and HP-88). For a combined use of mass spectra and retention data standardized methods of measurement for each of these columns are required. Such master methods were developed and always applied under the conditions of retention time locking (RTL) which allowed an excellent reproducibility and comparability of absolute retention times. Moreover, as a relative retention index system, equivalent chain lengths (ECL) of FAME were determined by linear interpolation. To compare and to predict ECL values by means of structural features, fractional chain lengths (FCL) were calculated and fitted as well. As shown in an example, the use of retention data and mass spectral information together in a database search leads to an improved and reliable identification of FAME (including positional and geometrical isomers) without further derivatizations.

Bis(μ4-butane-1,4-dithiolato)bis[hexacarbonyldiiron(II)(Fe—Fe)

The novel title double-butterfly Fe/S cluster complex, [Fe(4)(C(4)H(8)S(2))(2)(CO)(12)], which is structurally similar to the active site of the Fe-only hydrogenases, contains two inversion-related Fe(2)S(2)(CO)(6) subcluster cores connected by two equivalent butyl chains to afford a 16-membered macrocycle. The formation of the 16-membered macrocycle has an influence on the C-S-Fe angles, while the Fe-Fe and Fe-S bond lengths remain similar to those in related complexes.

Gauge equivalence of the Gross–Pitaevskii equation and the equivalent Heisenberg spin chain

In this paper, we construct an equivalent spin chain for the Gross–Pitaevskii equation with quadratic potential and exponentially varying scattering lengths using gauge equivalence. We have then generated the soliton solutions for the spin components S3 and S−. We find that the spin solitons for S3 and S− can be compressed for exponentially growing eigenvalues while they broaden out for decaying eigenvalues.

A simple method to calculate mobility with Jacobian

Although many mobility formulae have been set in the last 150 years, unfortunately, some of them are not fit for many classical mechanisms and some are indigestible. This paper gives a simple method to calculate the mobility of all kinds of parallel mechanisms only with Jacobian matrixes. It can analyze composition of degrees-of-freedom and output speeds of moving platform in passing. Furthermore, this method can be used to determine the existence of inactive joints and equivalent serial chain of complicated parallel chain.

Electrochemical impedance spectroscopic study of perfluorovinyl ether copolymer with tetrafluoroethylene in the swollen state

The temperature and frequency dependences of the dielectric impedance of the perfluorovinyl ether copolymer with tetrafluoroethylene have been studied. The impedance spectra of the films swollen in water have been measured in the frequency range of 10−1–107 Hz at 213–278 K. The model of equivalent electric chains has been suggested for analysis of the frequency dependence of dielectric impedance. The parameters of this model have been calculated. The correlation of these parameters with effects in a polymer matrix is described. Specifically, the pure ohmic conductivity is determined for the copolymer under study.

Cluster self-organization of Li- and TR-Containing silicate systems: Suprapolyhedral precursors and self-assembly of LiY[7]SiO4 and LiTR[6]SiO4 (TR = Y, Sc, Tm) dimorphic crystal structures

The combinatorial and topologic analysis (the TOPOS 4.0 program package, the coordination sequences method) is carried out for silicates LiY[7]SiO4 (a synthetic phase (SIN), space group P21/b) and LiTR[6]SiO4 (TR = Y, Sc, Tm; the olivine structure type (OLI), space group Pnma). The framework of these silicates is built of polyhedral structural units YO7 + SiO4 and YO6(ScO6, TmO6) + SiO4, respectively. The framework structures TRTO4, built of Y,O- and Si,O-polyhedra in SIN and OLI, respectively, are represented as three-dimensional (3D) Y,Si-nets with distal oxygen atoms. The crystal-forming 2D Y,Si-net is the four-nodal net Y(1) (43333) + Y(2) (4334334) + Si(1) (434) + Si(2) (3343) for SIN and the two-nodal net Y 443333 + Si 4433 for OLI. In the 2D Y,Si, nets, equivalent chains of four-nodal precursor clusters Y-Si-Y-Si with three shared bonds are identified. In the dimorphic crystals structures of LiTRTO4, polyhedral precursor clusters Li2TR2T2 are linked into a ring with two Li atoms lying one above the other below the center of the ring, thus retaining the center of symmetry\(\bar 1\). Precursor clusters Li2TR2T2 through the matrix self-assembly mechanism control the evolution of high-level crystal-forming clusters. Cluster coordination numbers in layers are equal to six.

Ground State Structure of F1-ATPase from Bovine Heart Mitochondria at 1.9 Aå Resolution

The structure of bovine F(1)-ATPase, crystallized in the presence of AMP-PNP and ADP, but in the absence of azide, has been determined at 1.9A resolution. This structure has been compared with the previously described structure of bovine F(1)-ATPase determined at 1.95A resolution with crystals grown under the same conditions but in the presence of azide. The two structures are extremely similar, but they differ in the nucleotides that are bound to the catalytic site in the beta(DP)-subunit. In the present structure, the nucleotide binding sites in the beta(DP)- and beta(TP)-subunits are both occupied by AMP-PNP, whereas in the earlier structure, the beta(TP) site was occupied by AMP-PNP and the beta(DP) site by ADP, where its binding is enhanced by a bound azide ion. Also, the conformation of the side chain of the catalytically important residue, alphaArg-373 differs in the beta(DP)- and beta(TP)-subunits. Thus, the structure with bound azide represents the ADP inhibited state of the enzyme, and the new structure represents a ground state intermediate in the active catalytic cycle of ATP hydrolysis.

Syntheses, Structure, Magnetism, and Optical Properties of the Ordered Mixed‐Lanthanide Sulfides γ‐LnLn′S3 (Ln: La, Ce; Ln′: Er, Tm, Yb).

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Electrostatic and Hydrophobic Interactions Governing the Interaction and Binding of β-Lactoglobulin to Membranes

The role of electrostatic and hydrophobic interactions in the binding and penetration of beta-lactoglobulin (betaLG) to preformed lipid membranes was studied using various phospholipid micelles and vesicles. Zwitterionic lysophospholipid micelles are able to induce the beta-sheet to alpha-helix transition, as judged by circular dichroism (CD), but the degree of transition is dramatically below and the amount of lipid required above that for anionic phospholipids with equivalent hydrocarbon chains. Anionic phospholipids with short hydrocarbon chains induce only low alpha-helical content in betaLG as compared to phospholipids with the same head group but longer hydrocarbon chains. These results suggest that both electrostatic and hydrophobic interactions are indispensable in betaLG-lipid interaction. Furthermore, air-water interface monolayer surface pressure and fluorescence anisotropy studies reveal that the membrane insertion of betaLG strongly depends on the nature of phospholipids, given the identical headgroup, particularly lipid packing. These results are supported by urea denaturation and acrylamide fluorescence quenching tests and by the FTIR-ATR polarization results for betaLG in multilayers on a surface. Under the same experimental conditions, the membrane binding and insertion of betaLG as well as the stability of the betaLG-lipid complexes can be enhanced by lowering the pH. Collectively, electrostatic interactions play a crucial role in all the processes involved in the betaLG-lipid interaction, while the presence of hydrophobic interaction remains necessary. Finally, betaLG biological function in the transport of fatty acids was tested by demonstrating the release of 2-AS from a 2-AS-betaLG complex on binding to lipids.

Universality in one-dimensional orbital wave ordering in spinel and related compounds: an experimental perspective

Recent state-of-the-art crystallographic investigations of transition metal spinel compounds have revealed that the d-orbital charge carriers undergo ordering transitions with the formation of local ‘molecular bonding’ units such as dimers in MgTi2O4, octomers in CuIr2S4, and heptamers in AlV2O4. Herein, we provide a unifying scheme involving one-dimensional (1D) orbital wave (OW) ordering applicable to all of these spinels. The relative phase of the orbitals in the chains is shown to be crucial to the formation of different local units, and thus both the amplitude and phase of the OW play important roles. Examination of Horibe et al's (2006 Phys. Rev. Lett.96 086406) structure for AlV2O4 serves as the vehicle for developing the general behaviour for such orbital wave ordering. Ordered AlV2O4 will be seen to organize into three equivalent chains in 2D Kagome planes coupled so as to form units of three dimer bonds. Three additional equivalent chains manifest a more complex tetramerization with three different charge states and two different bonding schemes. The OW ordering scheme developed is extended to other spinel and related compounds with local triangular transition metal coordination and partial filling of the t2g-d orbitals.

Investigation of the ligand spectrum of human sterol carrier protein 2 using a direct mass spectrometry assay

Sterol carrier protein 2 (SCP2) has been investigated by nearly native electrospray ionisation mass spectrometry in the presence of long chain fatty acyl CoAs (LCFA-CoAs) and carnitine derivatives of equivalent fatty acid chain length (LCFA-carnitines). Four SCP2 constructs were compared to examine the influence of the N-terminal presequence and the C-terminal peroxisomal targeting signal on ligand binding. Removal of N- or C-terminal residues did not influence ligand binding. The observation that LCFA-CoAs are high affinity ligands for SCP2 was confirmed, while LCFA-carnitines were demonstrated for the first time not to interact with SCP2. LCFA-CoAs formed non-covalent complexes with SCP2 of 2:1 and 1:1 stoichiometry, which could be dissociated by elevating the energy of the ions upon entrance to the mass spectrometer. A fluorescence-competition assay using Nile Red butyric acid confirmed the mass spectrometric observations in solution. The physiological significance of the lack of LCFA-carnitine binding by SCP2 is discussed.