152 research outputs found
Lower critical solution temperature (LCST) phase behaviour of an ionic liquid and its control by supramolecular hostâguest interactions
Lower critical solution temperature (LCST) phase behaviour of an imidazolium-
based ionic liquid is reported, which can be controlled by concentration, the
choice of cation, anion and solvent, and by supramolecular hostâguest complex
formation. Molecular dynamics simulations provide insight into the molecular
basis of this LCST phenomenon. This thermo-responsive system has potential
applications in cloud point extraction processes
The Use of Cohort Facebook Pages in MFT Training Programs
The current study explores how private cohort Facebook pages impact a MFT studentsâ training experience. Limited research has been conducted regarding social media and clinical training programs. Students from national MFT masterâs and doctoral programs will be interviewed about their experience with private cohort Facebook pages. Students will participate in focus groups lead by student-researchers in order to increase participation and anonymity. Data will be analyzed using Strauss and Corbinâ s (1990) grounded theory. This research is essential because of the increase of usage of Social Media in todayâs society. Graduate programs are implementing the use of Facebook pages for the dissemination of program information and networking between current and former students. However, the impact of social media usage in Clinical Program Training settings among students has not been fully researched
Photoinduced hole hopping through tryptophans in proteins
Hole hopping through tryptophan/tyrosine chains enables rapid unidirectional charge transport over long distances. We have elucidated structural and dynamical factors controlling hopping speed and efficiency in two modified azurin constructs that include a rhenium(I) sensitizer, Re(His)(CO)3(dmp)+, and one or two tryptophans (W1, W2). Experimental kinetics investigations showed that the two closely spaced (3 to 4 Ă
) intervening tryptophans dramatically accelerated long-range electron transfer (ET) from CuI to the photoexcited sensitizer. In our theoretical work, we found that time-dependent density-functional theory (TDDFT) quantum mechanics/molecular mechanics/molecular dynamics (QM/MM/MD) trajectories of low-lying triplet excited states of ReI(His)(CO)3(dmp)+âW1(âW2) exhibited crossings between sensitizer-localized (*Re) and charge-separated [ReI(His)(CO)3(dmpâąâ)/(W1âą+ or W2âą+)] (CS1 or CS2) states. Our analysis revealed that the distances, angles, and mutual orientations of ET-active cofactors fluctuate in a relatively narrow range in which the cofactors are strongly coupled, enabling adiabatic ET. Water-dominated electrostatic field fluctuations bring *Re and CS1 states to a crossing where *Re(CO)3(dmp)+âW1 ET occurs, and CS1 becomes the lowest triplet state. ET is promoted by solvation dynamics around *Re(CO)3(dmp)+(W1); and CS1 is stabilized by Re(dmpâąâ)/W1âą+ electron/hole interaction and enhanced W1âą+ solvation. The second hop, W1âą+âW2, is facilitated by water fluctuations near the W1/W2 unit, taking place when the electrostatic potential at W2 drops well below that at W1âą+. Insufficient solvation and reorganization around W2 make W1âą+âW2 ET endergonic, shifting the equilibrium toward W1âą+ and decreasing the charge-separation yield. We suggest that multiscale TDDFT/MM/MD is a suitable technique to model the simultaneous evolution of photogenerated excited-state manifolds
Tryptophan to Tryptophan Hole Hopping in an Azurin Construct.
Electron transfer (ET) between neutral and cationic tryptophan residues in the azurin construct [ReI(H126)(CO)3(dmp)](W124)(W122)CuI (dmp = 4,7-Me2-1,10-phenanthroline) was investigated by Born-Oppenheimer quantum-mechanics/molecular mechanics/molecular dynamics (QM/MM/MD) simulations. We focused on W124âą+ â W122 ET, which is the middle step of the photochemical hole-hopping process *ReII(CO)3(dmpâą-) â W124 â W122 â CuI, where sequential hopping amounts to nearly 10,000-fold acceleration over single-step tunneling (ACS Cent. Sci. 2019, 5, 192-200). In accordance with experiments, UKS-DFT QM/MM/MD simulations identified forward and reverse steps of W124âą+ â W122 ET equilibrium, as well as back ET ReI(CO)3(dmpâą-) â W124âą+ that restores *ReII(CO)3(dmpâą-). Strong electronic coupling between the two indoles (â„40 meV in the crossing region) makes the productive W124âą+ â W122 ET adiabatic. Energies of the two redox states are driven to degeneracy by fluctuations of the electrostatic potential at the two indoles, mainly caused by water solvation, with contributions from the protein dynamics in the W122 vicinity. ET probability depends on the orientation of Re(CO)3(dmp) relative to W124 and its rotation diminishes the hopping yield. Comparison with hole hopping in natural systems reveals structural and dynamics factors that are important for designing efficient hole-hopping processes
Hole Hopping Across a Protein-Protein Interface.
We have investigated photoinduced hole hopping in a Pseudomonas aeruginosa azurin mutant Re126WWCuI, where two adjacent tryptophan residues (W124 and W122) are inserted between the CuI center and a Re photosensitizer coordinated to a H126 imidazole (Re = ReI(H126)(CO)3(dmp)+, dmp = 4,7-dimethyl-1,10-phenanthroline). Optical excitation of this mutant in aqueous media (//(CuII)' back ET that occurs over 12 Ă
, in contrast to the 23 Ă
, 120 us step in Re126WWCuI. Importantly, dimerization makes Re126FWCuI photoreactive and, in the case of {Re126WWCuI}2, channels the photoproduced "hole" to the molecule that was not initially photoexcited, thereby shortening the lifetime of ReI(H126)(CO)3(dmpâą-)//CuII. Whereas two adjacent W124 and W122 indoles dramatically enhance CuI->*Re intramolecular multistep ET, the tryptophan quadruplex in {Re126WWCuI}2 does not accelerate intermolecular electron transport; instead, it acts as a hole storage and crossover unit between inter- and intramolecular ET pathways. Irradiation of {Re126WWCuII}2 or {Re126FWCuII}2 also triggers intermolecular *Re////(W122âą+)' intermolecular charge recombination. Our findings shed light on the factors that control interfacial hole/electron hopping in protein complexes and on the role of aromatic amino acids in accelerating long-range electron transport
O co chcÄ zapytaÄ pacjenci z niskozaawansowanym rakiem stercza przed podjÄciem decyzji o leczeniu?
Two Tryptophans Are Better Than One in Accelerating Electron Flow through a Protein
We
have constructed and structurally characterized a <i>Pseudomonas
aeruginosa</i> azurin mutant <b>Re126WWCu<sup>I</sup></b>, where two adjacent tryptophan residues (W124 and W122, indole separation
3.6â4.1 Ă
) are inserted between the Cu<sup>I</sup> center
and a Re photosensitizer coordinated to the imidazole of H126 (Re<sup>I</sup>(H126)Â(CO)<sub>3</sub>(4,7-dimethyl-1,10-phenanthroline)<sup>+</sup>). Cu<sup>I</sup> oxidation by the photoexcited Re label (*Re)
22.9 Ă
away proceeds with a âŒ70 ns time constant, similar
to that of a single-tryptophan mutant (âŒ40 ns) with a 19.4
Ă
ReâCu distance. Time-resolved spectroscopy (luminescence,
visible and IR absorption) revealed two rapid reversible electron
transfer steps, W124 â *Re (400â475 ps, <i>K</i><sub>1</sub> â
3.5â4) and W122 â W124<sup>âą+</sup> (7â9 ns, <i>K</i><sub>2</sub> â
0.55â0.75),
followed by a rate-determining (70â90 ns) Cu<sup>I</sup> oxidation
by W122<sup>âą+</sup> ca. 11 Ă
away. The photocycle is
completed by 120 ÎŒs recombination. No photochemical Cu<sup>I</sup> oxidation was observed in <b>Re126FWCu<sup>I</sup></b>, whereas
in <b>Re126WFCu<sup>I</sup></b>, the photocycle is restricted
to the ReH126W124 unit and Cu<sup>I</sup> remains isolated. QM/MM/MD
simulations of <b>Re126WWCu<sup>I</sup></b> indicate that indole
solvation changes through the hopping process and W124 â *Re
electron transfer is accompanied by water fluctuations that tighten
W124 solvation. Our finding that multistep tunneling (hopping) confers
a âŒ9000-fold advantage over single-step tunneling in the double-tryptophan
protein supports the proposal that hole-hopping through tryptophan/tyrosine
chains protects enzymes from oxidative damage
Molecular dynamics simulation studies of the interactions between ionic liquids and amino acids in aqueous solution
Although the understanding of the influence of ionic liquids (ILs) on the solubility behavior of biomolecules in aqueous solutions is relevant for the design and optimization of novel biotechnological processes, the underlying molecular-level mechanisms are not yet consensual or clearly elucidated. In order to contribute to the understanding of the molecular interactions established between amino acids and ILs in aqueous media, classical molecular dynamics (MD) simulations were performed for aqueous solutions of five amino acids with different structural characteristics (glycine, alanine, valine, isoleucine, and glutamic acid) in the presence of 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide. The results from MD simulations enable to relate the properties of the amino acids, namely their hydrophobicity, to the type and strength of their interactions with ILs in aqueous solutions and provide an explanation for the direction and magnitude of the solubility phenomena observed in [IL + amino acid + water] systems by a mechanism governed by a balance between competitive interactions of the IL cation, IL anion, and water with the amino acids
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