43 research outputs found
Mapping of functionalized regions on carbon nanotubes by scanning tunneling microscopy
Scanning tunneling microscopy (STM) gives us the opportunity to map the
surface of functionalized carbon nanotubes in an energy resolved manner and
with atomic precision. But this potential is largely untapped, mainly due to
sample stability issues which inhibit reliable measurements. Here we present a
simple and straightforward solution that makes away with this difficulty, by
incorporating the functionalized multiwalled carbon nanotubes (MWCNT) into a
few layer graphene - nanotube composite. This enabled us to measure energy
resolved tunneling conductance maps on the nanotubes, which shed light on the
level of doping, charge transfer between tube and functional groups and the
dependence of defect creation or functionalization on crystallographic
orientation.Comment: Keywords: functionalization, carbon nanotubes, few layer graphene,
STM, CITS, ST
Temperamentum- és karaktertípusok összefüggése a szubklinikus depressziós tünetegyüttessel, diszfunkcionális attitűdökkel és megküzdési stratégiákkal
Single Molecule Conformational Memory Extraction: P5ab RNA Hairpin
Extracting kinetic models from single
molecule data is an important
route to mechanistic insight in biophysics, chemistry, and biology.
Data collected from force spectroscopy can probe discrete hops of
a single molecule between different conformational states. Model extraction
from such data is a challenging inverse problem because single molecule
data are noisy and rich in structure. Standard modeling methods normally
assume (i) a prespecified number of discrete states and (ii) that
transitions between states are Markovian. The data set is then fit
to this predetermined model to find a handful of rates describing
the transitions between states. We show that it is unnecessary to
assume either (i) or (ii) and focus our analysis on the zipping/unzipping
transitions of an RNA hairpin. The key is in starting with a very
broad class of non-Markov models in order to let the data guide us
toward the best model from this very broad class. Our method suggests
that there exists a folding intermediate for the P5ab RNA hairpin
whose zipping/unzipping is monitored by force spectroscopy experiments.
This intermediate would not have been resolved if a Markov model had
been assumed from the onset. We compare the merits of our method with
those of others
Linear dichroism and circular dichroism in photosynthesis research
The efficiency of photosynthetic light energy conversion depends largely on the molecular architecture of the photosynthetic membranes. Linear- and circular-dichroism (LD and CD) studies have contributed significantly to our knowledge of the molecular organization of pigment systems at different levels of complexity, in pigment–protein complexes, supercomplexes, and their macroassemblies, as well as in entire membranes and membrane systems. Many examples show that LD and CD data are in good agreement with structural data; hence, these spectroscopic tools serve as the basis for linking the structure of photosynthetic pigment–protein complexes to steady-state and time-resolved spectroscopy. They are also indispensable for identifying conformations and interactions in native environments, and for monitoring reorganizations during photosynthetic functions, and are important in characterizing reconstituted and artificially constructed systems. This educational review explains, in simple terms, the basic physical principles, and theory and practice of LD and CD spectroscopies and of some related quantities in the areas of differential polarization spectroscopy and microscopy
Analgetikum nefropátiában szenvedők pszichés jellemzőinek vizsgálata. Egy hazai multicentrikus kutatás előzetes eredményei
Coupling of cytochrome and quinone turnovers in the photocycle of reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides.
A minimal kinetic model of the photocycle, including both quinone (Q-6) reduction at the secondary quinone-binding site and (mammalian) cytochrome c oxidation at the cytochrome docking site of isolated reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides, was elaborated and tested by cytochrome photooxidation under strong continuous illumination. The typical rate of photochemical excitation by a laser diode at 810 nm was 2.200 s-1, and the rates of stationary turnover of the reaction center (one-half of that of cytochrome photooxidation) were 600 +/- 70 s-1 at pH 6 and 400 +/- 50 s-1 at pH 8. The rate of turnover showed strong pH dependence, indicating the contribution of different rate-limiting processes. The kinetic limitation of the photocycle was attributed to the turnover of the cytochrome c binding site (pH < 6), light intensity and quinone/quinol exchange (6 < pH < 8), and proton-coupled second electron transfer in the quinone acceptor complex (pH > 8). The analysis of the double-reciprocal plot of the rate of turnover versus light intensity has proved useful in determining the light-independent (maximum) turnover rate of the reaction center (445 +/- 50 s-1 at pH 7.8)