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201.
Sivanandam VN Jayaraman M Hoop CL Kodali R Wetzel R van der Wel PC 《Journal of the American Chemical Society》2011,133(12):4558-4566
The 17-residue N-terminus (htt(NT)) directly flanking the polyQ sequence in huntingtin (htt) N-terminal fragments plays a crucial role in initiating and accelerating the aggregation process that is associated with Huntington's disease pathogenesis. Here we report on magic-angle-spinning solid-state NMR studies of the amyloid-like aggregates of an htt N-terminal fragment. We find that the polyQ portion of this peptide exists in a rigid, dehydrated amyloid core that is structurally similar to simpler polyQ fibrils and may contain antiparallel β-sheets. In contrast, the htt(NT) sequence in the aggregates is composed in part of a well-defined helix, which likely also exists in early oligomeric aggregates. Further NMR experiments demonstrate that the N-terminal helical segment displays increased dynamics and water exposure. Given its specific contribution to the initiation, rate, and mechanism of fibril formation, the helical nature of htt(NT) and its apparent lack of effect on the polyQ fibril core structure seem surprising. The results provide new details about these disease-associated aggregates and also provide a clear example of an amino acid sequence that greatly enhances the rate of amyloid formation while itself not taking part in the amyloid structure. There is an interesting mechanistic analogy to recent reports pointing out the early-stage contributions of transient intermolecular helix-helix interactions in the aggregation behavior of various other amyloid fibrils. 相似文献
202.
In efforts to produce polymeric materials with tailored physical properties, significant interest has grown around the ability to control the spatial organization of nanoparticles in polymer nanocomposites. One way to achieve controlled particle arrangement is by grafting the nanoparticle surface with polymers that are compatible with the matrix, thus manipulating the interfacial interactions between the nanoparticles and the polymer matrix. Previous work has shown that the molecular weight of the grafted polymer, both at high grafting density and low grafting density, plays a key role in dictating the effective inter-particle interactions in a polymer matrix. At high grafting density nanoparticles disperse (aggregate) if the graft molecular weight is higher (lower) than the matrix molecular weight. At low grafting density the longer grafts can better shield the nanoparticle surface from direct particle-particle contacts than the shorter grafts and lead to the dispersion of the grafted particles in the matrix. Despite the importance of graft molecular weight, and evidence of non-trivial effects of polydispersity of chains grafted on flat surfaces, most theoretical work on polymer grafted nanoparticles has only focused on monodisperse grafted chains. In this paper, we focus on how bidispersity in grafted chain lengths affects the grafted chain conformations and inter-particle interactions in an implicit solvent and in a dense homopolymer polymer matrix. We first present the effects of bidispersity on grafted chain conformations in a single polymer grafted particle using purely Monte Carlo (MC) simulations. This is followed by calculations of the potential of mean force (PMF) between two grafted particles in a polymer matrix using a self-consistent Polymer Reference Interaction Site Model theory-Monte Carlo simulation approach. Monte Carlo simulations of a single polymer grafted particle in an implicit solvent show that in the bidisperse polymer grafted particles with an equal number of short and long grafts at low to medium grafting density, the short grafts are in a more coiled up conformation (lower radius of gyration) than their monodisperse counterparts to provide a larger free volume to the longer grafts so they can gain conformational entropy. The longer grafts do not show much difference in conformation from their monodisperse counterparts at low grafting density, but at medium grafting density the longer grafts exhibit less stretched conformations (lower radius of gyration) as compared to their monodisperse counterparts. In the presence of an explicit homopolymer matrix, the longer grafts are more compressed by the matrix homopolymer chains than the short grafts. We observe that the potential of mean force between bidisperse grafted particles has features of the PMF of monodisperse grafted particles with short grafts and monodisperse grafted particles with long grafts. The value of the PMF at contact is governed by the short grafts and values at large inter-particle distances are governed by the longer grafts. Further comparison of the PMF for bidisperse and monodisperse polymer grafted particles in a homopolymer matrix at varying parameters shows that the effects of matrix chain length, matrix packing fraction, grafting density, and particle curvature on the PMF between bidisperse polymer grafted particles are similar to those seen between monodisperse polymer grafted particles. 相似文献
203.
The mutual interaction of imidazole derivative (PIPP) with bovine serum albumin (BSA) was investigated using photoluminescent
studies. The fluorescence quenching mechanism of BSA by PIPP was analyzed and the binding constant was calculated. The binding
distance between PIPP and BSA was obtained based on the theory of Forester’s non-radiation energy transfer. Displacement experiments
were performed by using ibuprofen to identify PIPP binding site in BSA. The effect of some common ions on the binding constant
between PIPP and BSA was also examined. 相似文献
204.
Jayabharathi J Thanikachalam V Srinivasan N Perumal MV 《Journal of fluorescence》2011,21(4):1585-1597
The synthesis, structure and photophysical properties of series of new luminescent cyclometalated Iridium (III) complexes
are reported. The cyclometalated ligand used here is 2-aryl imidazole and the auxiliary ligand is acetyl acetone (acac). The
crystal structure of the complex (dmdpi)2Ir(acac) (5) show that the Iridium(III) ion resides in a distorted octahedral environment. All complexes exhibit bright photoluminescence
(PL) at room temperature and (fpdmdmpi)2Ir(acac) 4 has a high solution PL quantum efficiency of 0.56. The role played by electron releasing and electron withdrawing substituents
of the 2-arylimidazole ligands towards the stability of HOMO and how the substituent influences the luminescent behaviour
are discussed. Furthermore those substituents have effect on the contribution to mixing between 3(π-π*) and 3(MLCT) for the lowest excited states. 相似文献
205.
A series of novel six iridium complexes (1–6) bearing two substituted phenylimidazole and an additional acetylacetone as the third co-auxilary ligand are reported. The
lowest absorption band for all iridium complexes consist of a mixture of heavy atom Ir(III) enhanced 3MLCT and 3 π-π* transitions and the phosphorescent peak wavelength can be fine-tuned to cover the spectral range 455–518 nm with high
quantum efficiencies. The peak wavelength of the dopants can be finely tuned depending upon the electronic properties of the
substituents. On the basis of onset potentials of the oxidation and reduction, the HOMO-LUMO energies were calculated and
the reported iridium complexes emit green light with exceeding higher efficiency. 相似文献
206.
Jayabharathi J Thanikachalam V Srinivasan N Jayamorthy K Perumal MV 《Journal of fluorescence》2011,21(4):1813-1823
A series of substituted imidazoles have been synthesized in very good yield under solvent free condition by grinding 1,2-diketone,
aromatic aldehyde and ammonium acetate in the presence of molecular iodine as the catalyst. The short reaction time, good
yield and easy workup make this protocol practically and economically attractive and characterized by NMR spectra, X-ray,
mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazoles (dpip and dptip)
have been studied using emission spectroscopy and it was detected that the two distinct ground state rotamers are responsible
for the normal and the tautomer emissions. DFT calculations on energy, dipole moment, charge distribution of the rotamers
in the ground and excited states of the imidazole derivatives were performed and discussed. DFT analysis about HOMO, HOMO-1,
LUMO and LUMO + 1 were carried out and discussed. PES calculation indicates that the energy barrier for the interconversion
of two rotamers is too high in the excited state than the ground state. 相似文献
207.
Xia Ma Paul T. GiguereBalaji Jayaraman Duan Z. Zhang 《Journal of computational physics》2010,229(20):7819-7833
When using the time explicit material point method to simulate interaction of materials accompanied by large deformations and fragmentation, one often encounters a numerical instability caused by small node mass, because acceleration on a mesh node is obtained by dividing the total force on the node by the mass of the node. When the material points are in the far sides of the cells containing the node, typically happening near material interfaces, the node mass can be very small leading to artificially large acceleration and then numerical instability. For the case of small material deformations, this instability is typically avoided by placing the material points away from cell boundaries. For cases with large deformations, with the exception of initial conditions, there is no control on locations of the material points. The instability caused by small mass nodes is often encountered. To avoid this instability tiny time steps are usually required in a numerical calculation. 相似文献
208.
209.
J. Rajesh Kapil Gupta Hari Shankar Kusumakar V. K. Jayaraman B. D. Kulkarni 《Journal of Heuristics》2003,9(4):307-319
In this paper an approach based on the tabu search paradigm to tackle the bilevel programming problems is presented. The algorithm has been tested for a number of benchmark problems and the results obtained show superiority of the approach over the conventional methods in solving such problems. 相似文献
210.
Andrews Maneesha E. Murali Jayaraman Muralidharan Chellappa Madhulata Wuppalamarthy Jayakumar Rajadas 《Colloid and polymer science》2003,281(8):766-770
The molecular mechanism of the stabilization of collagen with hydrolyzable tannin, corilagin, has been investigated using techniques like centrifugation, shrinkage temperature, infrared spectroscopy, and differential scanning calorimetry. Thermodynamic measurements were also carried out for the collagen–corilagin interaction. Results of this study indicate the enthalpic nature of non-specific binding of collagen with corilagin. The shrinkage temperature increases linearly with corilagin, indicating that the helix–to–coil transition is hindered by corilagin interaction with collagen triple helix. This study suggests that ingested polyphenols (corilagin) alter the stability of the proline-rich protein in the gut. Thereby, the stability of collagen present in the serosa layer may be hindered. 相似文献