Discrimination between FRET and non-FRET quenching in a photochromic CdSe quantum dot/dithienylethene dye system

A photochromic Förster resonance energy transfer (FRET) system was employed to disentangle the fluorescence quenching mechanisms in quantum dot/photochromic dye hybrids. In the off-state of the dye the main quenching mechanism is FRET whereas the moderate quenching in the on-state is due to non-FRET pathways opened up upon assembly

Cyano-tryptophans as dual infrared and fluorescence spectroscopic labels to assess structural dynamics in proteins

The steady state and time-resolved fluorescence and infrared (IR) properties of 4- and 5-cyanotryptophan (CNTrp) are investigated and compared, and the tryptophan (Trp) analogs are found to be very attractive to study structural and dynamic properties of proteins. The position of the nitrile substitution as well as the solvent environment influences the spectroscopic properties (solvatochromism). Similar to native Trp, electronic (nanosecond) lifetime and emission spectra are modulated by the environment, making CNTrps attractive fluorescent probes to study the structural dynamics of proteins in complex media. The nitrile absorption in the IR region can provide local structural information as it responds sensitively to changes in electrostatics and hydrogen bond (HB) interactions. Importantly, we find that 4CNTrp exhibits a single absorption in the nitrile stretch region, while the model compound 4CN-indole (4CNI) shows two. Even though the spectrum of the model compound is perturbed by a Fermi resonance, we find that 4CNTrp itself is a useful IR label. Moreover, if the nitrile group is substituted at the 5 position, the Trp analog predominantly reports on its HB status. Because the current literature on similar compounds is too limited for a detailed solvatochromic analysis, we extend the available data significantly. Only now are microscopic details such as the mentioned sensitivity to electrostatics coming to light. The vibrational lifetime of the CN moiety (acting on a picosecond time scale in contrast to the nanosecond time scale for fluorescent emission) allows for its application in 2D-IR spectroscopy in the low picosecond range. Taken together, the benefits of CNTrps are that they absorb and emit separately from the naturally occurring Trp and that in these dual fluorescence/vibrational labels, observables of IR and fluorescence spectroscopy are modulated differently by their surroundings. Because IR absorption and fluorescence operate on different time and length scales, they thus provide complementary structural information.</p

Ultrafast coherent oscillations reveal a reactive mode in the ring-opening reaction of fulgides

The ultrafast ring-opening reaction of photochromic fulgides proceeds via conical intersections to the ground state isomers involving activation barriers in the excited state. The coherent oscillations observed in the femtosecond transient absorption signal of a methyl-substituted indolylfulgide were analysed in the framework of vibrational wavepackets to expose a dominant low-frequency mode at similar to 80 cm(-1). The quantum chemical calculations in the relaxed excited state geometry of this fulgide revealed that the experimentally observed vibrational normal mode has a dominant contribution to the relevant ring-opening reactive coordinate

Energetics of the primary electron transfer reaction revealed by ultrafast spectroscopy on modified bacterial reaction centers

The modification of reaction centers from Rhodobacter sphaeroides by the introduction of pheophytins instead of bacteriopheophytins leads to interesting changes in the primary photosynthetic reaction: long-living populations of the excited electronic state of the special pair P* and the bacteriochlorophyll anion B−A show up. The data allow the determination of the energetics in the reaction center. The free energy of the first intermediate P+B−A, where the electron has reached the accessory bacteriochlorophyll BA lies ≈ 450 cm−1 below the initially excited special pair P*

C-13 MAS NMR evidence for structural similarity of L162YL mutant and Rhodobacter sphaeroides R26 RC, despite widely different cytochrome c(2)-mediated re-reduction kinetics of the oxidized primary donor

CP/MAS NMR data collected from L162YL mutant [4'-C-13]Tyr-enriched Rhodobacter sphaeroides RCs reveal that Tyr L162 is in a slightly heterogeneous and probably rigid section of the protein complex. The differences in chemical shifts of the individual components relative to those of the [4'-C-13]Tyr Rhodobacter sphaeroides R26 response are 0.2 ppm or less. This is small compared to the total dispersion of [4'-C-13] isotropic shifts, similar to 5 ppm, which measures the shift range due to variations in the microscopic environment between the various tyrosines in the protein complex. The structural changes in the mutant with respect to Rhodobacter sphaeroides R26, as probed by the labels, are thus minimal on the scale of the NMR. This suggests that the dramatic decrease of re-reduction rate of the oxidized primary donor P upon mutation (Farchaus et al., Biochemistry 32 (1993) 10885-10893) cannot be attributed to significant structural changes in the protein. Hence the NMR is in line with the current view that the decrease of the re-reduction rate in the mutant originates from slow reorientation of the docked cytochrome. (C) 1997 Elsevier Science B.V.Solid state NMR/Biophysical Organic ChemistryBiological and Soft Matter PhysicsBio-organic Synthesi

Structure guided fluorescence labeling reveals a two-step binding mechanism of neomycin to its RNA aptamer

Publisher's version (útgefin grein)The ability of the cytidine analog Ç m f to act as a position specific reporter of RNA-dynamics was spectroscopically evaluated. Ç m f-labeled single-and double-stranded RNAs differ in their fluorescence lifetimes, quantum yields and anisotropies. These observables were also influenced by the nucleobases flanking Ç m f. This conformation and position specificity allowed to investigate the binding dynamics and mechanism of neomycin to its aptamer N1 by independently incorporating Ç m f at four different positions within the aptamer. Remarkably fast binding kinetics of neomycin binding was observed with stopped-flow measurements, which could be satisfactorily explained with a two-step binding. Conformational selection was identified as the dominant mechanism.Deutsche Forschungsgemeinschaft (DFG) through the Collaborative Research Center (CRC) 902; ‘Molecular Principles of RNA-based Regulation’ sub-projects A7, B14 and Mercator Fellowship. Funding for open access charge: DFG (CRC902); sub-projects A7, B14 and Mercator Fellowship.Peer Reviewe

Early and Late Postnatal Myocardial and Vascular Changes in a Protein Restriction Rat Model of Intrauterine Growth Restriction

Intrauterine growth restriction (IUGR) is a risk factor for cardiovascular disease in later life. Early structural and functional changes in the cardiovascular system after IUGR may contribute to its pathogenesis. We tested the hypothesis that IUGR leads to primary myocardial and vascular alterations before the onset of hypertension. A rat IUGR model of maternal protein restriction during gestation was used. Dams were fed low protein (LP; casein 8.4%) or isocaloric normal protein diet (NP; casein 17.2%). The offspring was reduced to six males per litter. Immunohistochemical and real-time PCR analyses were performed in myocardial and vascular tissue of neonates and animals at day 70 of life. In the aortas of newborn IUGR rats expression of connective tissue growth factor (CTGF) was induced 3.2-fold. At day 70 of life, the expression of collagen I was increased 5.6-fold in aortas of IUGR rats. In the hearts of neonate IUGR rats, cell proliferation was more prominent compared to controls. At day 70 the expression of osteopontin was induced 7.2-fold. A 3- to 7-fold increase in the expression of the profibrotic cytokines TGF-β and CTGF as well as of microfibrillar matrix molecules was observed. The myocardial expression and deposition of collagens was more prominent in IUGR animals compared to controls at day 70. In the low-protein diet model, IUGR leads to changes in the expression patterns of profibrotic genes and discrete structural abnormalities of vessels and hearts in adolescence, but, with the exception of CTGF, not as early as at the time of birth. Invasive and non-invasive blood pressure measurements confirmed that IUGR rats were normotensive at the time point investigated and that the changes observed occurred independently of an increased blood pressure. Hence, altered matrix composition of the vascular wall and the myocardium may predispose IUGR animals to cardiovascular disease later in life