Search results for "RESONANCE"
showing 10 items of 6625 documents
Comparative analysis of the coordinated motion of Hsp70s from different organelles observed by single-molecule three-color FRET.
2021
Cellular function depends on the correct folding of proteins inside the cell. Heat-shock proteins 70 (Hsp70s), being among the first molecular chaperones binding to nascently translated proteins, aid in protein folding and transport. They undergo large, coordinated intra- and interdomain structural rearrangements mediated by allosteric interactions. Here, we applied a three-color single-molecule Forster resonance energy transfer (FRET) combined with three-color photon distribution analysis to compare the conformational cycle of the Hsp70 chaperones DnaK, Ssc1, and BiP. By capturing three distances simultaneously, we can identify coordinated structural changes during the functional cycle. Be…
Rapid cooling experiments and use of an anionic nuclear probe to sense the spin transition of the 1D coordination polymers [Fe(NH2trz)3]SnF6n x H2O (…
2008
[Fe(NH(2)trz)(3)]SnF(6)n H(2)O (NH(2)trz=4-amino-1,2,4-triazole; n=1 (1), n=0.5 (2)) are new 1D spin-crossover coordination polymers. Compound 2 exhibits an incomplete spin transition centred at around 210 K with a thermal hysteresis loop approximately 16 K wide. The spin transition of 2 was detected by the Mossbauer resonance of the (119)Sn atom in the SnF(6) (2-) anion primarily on the basis of the evolution of its local distortion. Rapid-cooling (57)Fe Mossbauer and superconducting quantum interference device experiments allow dramatic widening of the hysteresis width of 2 from 16 K up to 82 K and also shift the spin-transition curve into the room temperature region. This unusual behavio…
Synthesis and Characterization of theO-Alkylation Products of Resorcinarene
2013
O-Substitution reactions of tetramethoxyresorcinarene with alkyl halides produced a variety of partially O-alkylated resorcinarene derivatives with terminal alkyne functionality. The degree of alkylation was affected by the reactivity of the alkylating halide used. NMR spectroscopy proved to be an ideal tool for analyzing the complex reaction mixtures and the isolated products based on the symmetry and degree of alkylation of the resorcinarene derivatives. Single-crystal X-ray diffraction studies furthermore showed diversity in the self-assembly of the various O-alkylation products that was greatly affected by the degree of alkylation, as well as the nature of the alkyne moiety.
Synthesis and characterisation of tetrazole compounds: 3 series of new ligands representing versatile building blocks for iron(II) spin-crossover com…
2005
Abstract New tetrazole compounds were synthesized and characterised by NMR and FTIR spectroscopy as well as by single crystal X-ray diffraction. We present in this paper mono- and ditetrazoles, which represent a versatile class of building blocks for the formation of mononuclear iron(II) complexes with monotetrazoles as terminal ligands as well as iron(II) coordination polymers with ditetrazoles as bridging ligands. Especially, the series of α,ω-bis[tetrazol-1-yl]-alkanes open the field of fascinating supramolecular structures with spin transition properties.
How Structure-Related Collapse Mechanisms Determine Nanoscale Inhomogeneities in Thermoresponsive Polymers
2012
Continuous wave electron paramagnetic resonance (CW EPR) spectroscopy on the amphiphilic spin probe TEMPO in solutions of selectively chosen functional, thermoresponsive poly(propylene oxide) (PPO)- and poly(ethylene oxide) (PEO)-based copolymers of both linear and branched structure is used to elucidate their host–guest interactions and inverse phase transitions. Three different fundamental types of host–guest interactions between probes and polymers could be correlated to the phase transition mechanisms (supported by MD simulations), evidencing that these proceed via nanoscale inhomogeneities of the polymers. Because of their ability to host small amphiphilic guest molecules, thermorespon…
Straightforward synthesis of bioconjugatable azo dyes. Part 1: Black Hole Quencher-1 (BHQ-1) scaffold
2014
Abstract Azo dyes are currently used to quench the fluorescence of energy donors in bioassays through Forster resonance energy transfer (FRET) phenomenon. Common examples of such dark quenchers are DABCYL and the three members of Black Hole Quencher® (BHQ) family. Yet, only carboxylic acid and phosphoramidite derivatives of such azo dyes are presently commercially available. This Letter presents a straightforward synthesis method to novel bioconjugatable quenchers derived from BHQ-1 scaffold and equipped with a reactive group being either azido, terminal alkyne, or maleimide. The potential utility of the ‘clickable’ azido and thiol-reactive derivatives was notably demonstrated through the p…
Single molecule spectroscopy of multichromophoric assemblies
2003
We have investigated multichromophoric assemblies composed of a variable number of chromophores by single molecule spectroscopy. Specific spectral signatures have allowed to distinguish at the single molecule level between molecular dimers representing strong and weak electronic dipole-dipole coupling. By using fluorescence excitation spectroscopy at low temperature, the sharp purely electronic zero-phonon lines of single chromophores within a single dendrimer containing four chromophores could be isolated in the frequency domain.
Double-quantum nutations in a two-level spin system
1986
The transient oscillatory behavior of the nonlinear response of a two-level electron-spin system is experimentally investigated in a sample of glassy silica with ${E}_{1}^{\mathcal{'}}$ centers (S=(1/2)) at microwave frequency at T=4.2 K. The transient regime, excited by an intense step-modulated radiation tuned to double-quantum (DQ) resonance, is monitored by revealing the second-harmonic (SH) wave radiated by the spins undergoing DQ transitions. Time- and frequency-domain results show that the emitted SH wave has two components: the former, which vanishes at the DQ resonance, exhibits an overdamped transient regime, the latter consists of damped oscillations at a frequency which depends …
1H,13C and17O NMR spectroscopic study of four bicyclo [3.1.1]heptenes (derivatives of α-pinene) and four bicyclo[3.1.1]heptanes (derivatives of β-pin…
1992
Four derivatives of 2, 6, 6-trimethylbicyclo[3.1.1]hept-2-ene (α-pinene) and four derivatives of 2-methylene-6, 6-dimethylbicyclo[3.1.1]heptane (β-pinene) were synthesized and their 1H, 13C and 17O NMR spectra were measured, analysed and assigned. The 1H NMR spectral parameters were obtained by computer-aided analyses of the very complex multi-spin, second-order spectra. Some of the 13C NMR chemical shift assignments of these compounds reported in the literature should be changed, based on these accurate 1H NMR spectral analyses and carbon-proton chemical shift correlated spectra (COSY). The new assignments are supported by the 1J(C, H) values, which show a strong dependence on the bond ang…
Molecular dynamics of solid polymers as revealed by deuteron NMR
1983
Pulsed deuteron NMR spectroscopy is described, which has recently been developed to become a powerful tool for studying molecular dynamics in solid polymers. It is shown that by analyzing the line shapes of2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. By applying these techniques to selectively deuterated polymers, motional mechanisms involving different segments of the monomer unit can be monitored. In addition, motional heterogeneities in glassy polymers can be detected. The information a…