10 research outputs found
Ballistic energy transport in PEG oligomers
Energy transport between the terminal groups of the azido-PEG-succinimide ester compounds with a number of repeating PEG units of 0, 4, 8, and 12 was studied using relaxation-assisted two-dimensional infrared spectroscopy. The through-bond energy transport time, evaluated as the waiting time at which the cross peak maximum is reached, Tmax, was found to be linearly dependent on the chain length for chain lengths up to 60 Å suggesting a ballistic energy transport regime. The through-bond energy transport speed is found to be ca. 500 m/s. The cross-peak amplitude at the maximum decays exponentially with the chain length with a characteristic decay distance of 15.7 ± 1 Å. Substantial mode delocalization across the PEG bridge is found, which can support the energy propagation as a wavepacket
Ballistic Energy Transport in Oligomers
ConspectusThe development of nanocomposite materials with desired heat management
properties, including nanowires, layered semiconductor structures,
and self-assembled monolayer (SAM) junctions, attracts broad interest.
Such materials often involve polymeric/oligomeric components and can
feature high or low thermal conductivity, depending on their design.
For example, in SAM junctions made of alkane chains sandwiched between
metal layers, the thermal conductivity can be very low, whereas the
fibers of ordered polyethylene chains feature high thermal conductivity,
exceeding that of many pure metals. The thermal conductivity of nanostructured
materials is determined by the energy transport between and within
each component of the material, which all need to be understood for
optimizing the properties. For example, in the SAM junctions, the
energy transport across the metal-chain interface as well as the transport
through the chains both determine the overall heat conductivity, however,
to separate these contributions is difficult. Recently developed
relaxation-assisted two-dimensional infrared
(RA 2DIR) spectroscopy is capable of studying energy transport in
individual molecules in the time domain. The transport in a molecule
is initiated by exciting an IR-active group (a tag); the method records
the influence of the excess energy on another mode in the molecule
(a reporter). The energy transport time can be measured for different
reporters, and the transport speed through the molecule is evaluated.
Various molecules were interrogated by RA 2DIR: in molecules without
repeating units (disordered), the transport mechanism was expected
and found to be diffusive. The transport via an oligomer backbone
can potentially be ballistic, as the chain offers delocalized vibrational
states. Indeed, the transport regime via three tested types of oligomers,
alkanes, polyethyleneglycols, and perfluoroalkanes was found to be
ballistic, whereas the transport within the end groups was diffusive.
Interestingly, the transport speeds via these chains were different.
Moreover, the transport speed was found to be dependent on the vibrational
mode initiating the transport. For the difference in the transport
speeds to be explained, the chain bands involved in the wavepacket
formation were analyzed, and specific optical bands of the chain were
identified as the energy transporters. For example, the transport
initiated in alkanes by the stretching mode of the azido end group
(2100 cm<sup>–1</sup>) occurs predominantly via the CH<sub>2</sub> twisting and wagging chain bands, but the transport initiated
by the C=O stretching modes of the carboxylic acid or succinimide
ester end groups occurs via C–C stretching and CH<sub>2</sub> rocking bands of the alkane chain. Direct formation of the wavepacket
within the CH<sub>2</sub> twisting and wagging chain bands occurs
when the transport is initiated by the Nî—»N stretching mode
(1270 cm-1) of the azido end-group. The transport via optical chain
bands in oligomers involves rather large vibrational quanta (700–1400
cm<sup>–1</sup>), resulting in efficient energy delivery to
substantial distances. Achieved quantitative description of various
energy transport steps in oligomers, including the specific contributions
of different chain bands, can result in a better understanding of
the transport steps in nanocomposite materials, including SAM junctions,
and lead towards designing systems for molecular electronics with
a controllable energy transport speed
Nonprotecting Group Synthesis of a Phospholipase C Activatable Probe with an Azo-Free Quencher
The
near-infrared fluorescent activatable smart probe Pyro-phosphatidylethanolamine
(PtdEtn)-QSY was synthesized and observed to selectively fluoresce
in the presence of phosphatidylcholine-specific phospholipase C (PC-PLC).
PC-PLC is an important biological target as it is known to be upregulated
in a variety of cancers, including triple negative breast cancer.
Pyro-PtdEtn-QSY features a QSY21 quenching moiety instead of the Black
Hole Quencher-3 (BHQ-3) used previously because the latter contains
an azo bond, which could lead to biological instability
Ballistic energy transport in PEG oligomers
Energy transport between the terminal groups of the azido-PEG-succinimide ester compounds with a number of repeating PEG units of 0, 4, 8, and 12 was studied using relaxation-assisted two-dimensional infrared spectroscopy. The through-bond energy transport time, evaluated as the waiting time at which the cross peak maximum is reached, Tmax, was found to be linearly dependent on the chain length for chain lengths up to 60 Å suggesting a ballistic energy transport regime. The through-bond energy transport speed is found to be ca. 500 m/s. The cross-peak amplitude at the maximum decays exponentially with the chain length with a characteristic decay distance of 15.7 ± 1 Å. Substantial mode delocalization across the PEG bridge is found, which can support the energy propagation as a wavepacket
Band-Selective Ballistic Energy Transport in Alkane Oligomers: Toward Controlling the Transport Speed
Intramolecular
transport of vibrational energy in two series of
oligomers featuring alkane chains of various length was studied by
relaxation-assisted two-dimensional infrared spectroscopy. The transport
was initiated by exciting various end-group modes (tags) such as different
modes of the azido (νÂ(Nî—¼N) and νÂ(Nî—»N)),
carboxylic acid (νÂ(Cî—»O)), and succinimide ester (ν<sub>as</sub>(Cî—»O)) with short mid-IR laser pulses. It is shown
that the transport via alkane chains is ballistic and the transport
speed is dependent on the type of the tag mode that initiates the
transport. The transport speed of 8.0 Ã…/ps was observed when
initiated by either νÂ(Cî—»O) or ν<sub>as</sub>(Cî—»O).
When initiated by νÂ(Nî—¼N) and νÂ(Nî—»N), the
transport speed of 14.4 ± 2 and 11 ± 4 Å/ps was observed.
Analysis of the vibrational relaxation channels of different tags,
combined with the results for the group velocity evaluation, permits
identification of the chain bands predominantly contributing to the
transport for different cases of the transport initiation. For the
transport initiated by νÂ(Nî—¼N) the CH<sub>2</sub> twisting
and wagging chain bands were identified as the major energy transport
channels. For the transport initiated by νÂ(Cî—»O), the
C–C stretching and CH<sub>2</sub> rocking chain bands served
as major energy transporters. The transport initiated by νÂ(Nî—»N)
results in direct formation of the wave packet within the CH<sub>2</sub> twisting and wagging chain bands. These developments can aid in
designing molecular systems featuring faster and more controllable
energy transport in molecules
Тerminology of rectal cancer: consensus agreement of the expert working group
Unified terminology is a necessary condition for successful interdisciplinary communication within the field of oncology. The variety of anatomical, pathomorphological, and clinical terms used in rectal cancer is often accompanied by their ambiguous interpretation both in domestic and foreign scientific literature. This not only complicates the interaction between specialists, but also complicates the comparison of the results of rectal cancer treatment obtained in different medical institutions.
Based on the analysis of recent domestic and international scientific and methodological literature on rectal cancer, the key terms used in the diagnosis and treatment planning of rectal cancer were selected, followed by a two-time online discussion of their interpretations by experts from the Russian Society of Radiologists and Therapeutic Radiation Oncologists, the Association of Oncologists of Russia, and the Russian Association of Therapeutic Radiation Oncologists until reaching consensus (≥80%) of experts on all items. Terms that fail to attain consensus were excluded in the final list.
A list of anatomical, pathomorphological, and clinical terms used in the diagnosis, staging, and treatment planning of rectal cancer has been compiled and, based on expert consensus, their interpretation has been determined.
A lexicon recommended in the description and formulation of the conclusion of diagnostic studies in patients with rectal cancer is proposed
Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)
In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field