52 research outputs found
Determination of Peptide<b>–</b>Surface Adsorption Free Energy for Material Surfaces Not Conducive to SPR or QCM using AFM
The interactions between peptides and proteins with material
surfaces
are of primary importance in many areas of biotechnology. While surface
plasmon resonance spectroscopy (SPR) and quartz crystal microbalance
(QCM) methods have proven to be very useful in measuring fundamental
properties characterizing adsorption behavior, such as the free energy
of adsorption for peptide–surface interactions, these methods
are largely restricted to use for materials that can readily form
nanoscale-thick films over the respective sensor surfaces. Many materials
including most polymers, ceramics, and inorganic glasses, however,
are not readily suitable for use with SPR or QCM methods. To overcome
these limitations, we recently showed that desorption forces (<i>F</i><sub>des</sub>) obtained using a standardized AFM method
linearly correlate to standard-state adsorption free energy values
(Δ<i>G°</i><sup><i></i></sup><sub>ads</sub>) measured from SPR in phosphate buffered saline (PBS: phosphate
buffered 140 mM NaCl, pH 7.4). This approach thus provides a means
to determine Δ<i>G°</i><sup><i></i></sup><sub>ads</sub> for peptide adsorption using AFM that can be
applied to any flat material surface. In this present study, we investigated
the <i>F</i><sub>des</sub>–Δ<i>G°</i><sup><i></i></sup><sub>ads</sub> correlation between AFM
and SPR data in PBS for a much broader range of systems including
eight different types of peptides on a set of eight different alkanethiol
self-assembled monolayer (SAM) surfaces. The resulting correlation
was then used to estimate Δ<i>G°</i><sup><i></i></sup><sub>ads</sub> from <i>F</i><sub>des</sub> determined by AFM for selected bulk polymer and glass/ceramic materials
such as polyÂ(methyl methacrylate) (PMMA), high-density polyethylene
(HDPE), fused silica glass, and a quartz (100) surface. The results
of these studies support our previous findings regarding the strong
correlation between <i>F</i><sub>des</sub> measured by AFM
and Δ<i>G°</i><sup><i></i></sup><sub>ads</sub> determined by SPR, and provides a means to estimate Δ<i>G°</i><sup><i></i></sup><sub>ads</sub> for peptide
adsorption on macroscopically thick samples of materials that are
not conducive for use with SPR or QCM
A Display Module Implemented by the Fast High-Temperatue Response of Carbon Nanotube Thin Yarns
Suspending superaligned multiwalled carbon nanotube (MWCNT)
films
were processed into CNT thin yarns, about 1 μm in diameter,
by laser cutting and an ethanol atomization bath treatment. The fast
high-temperature response under a vacuum was revealed by monitoring
the incandescent light with a photo diode. The thin yarns can be electrically
heated up to 2170 K in 0.79 mS, and the succeeding cool-down time
is 0.36 mS. The fast response is attributed to the ultrasmall mass
of the independent single yarn, large radiation coefficient, and improved
thermal conductance through the two cool ends. The millisecond response
time makes it possible to use the visible hot thin yarns as light-emitting
elements of an incandescent display. A fully sealed display with 16
× 16 matrix was successfully fabricated using screen-printed
thick electrodes and CNT thin yarns. It can display rolling characters
with a low power consumption. More applications can be further developed
based on the addressable CNT thermal arrays
A Display Module Implemented by the Fast High-Temperatue Response of Carbon Nanotube Thin Yarns
Suspending superaligned multiwalled carbon nanotube (MWCNT)
films
were processed into CNT thin yarns, about 1 μm in diameter,
by laser cutting and an ethanol atomization bath treatment. The fast
high-temperature response under a vacuum was revealed by monitoring
the incandescent light with a photo diode. The thin yarns can be electrically
heated up to 2170 K in 0.79 mS, and the succeeding cool-down time
is 0.36 mS. The fast response is attributed to the ultrasmall mass
of the independent single yarn, large radiation coefficient, and improved
thermal conductance through the two cool ends. The millisecond response
time makes it possible to use the visible hot thin yarns as light-emitting
elements of an incandescent display. A fully sealed display with 16
× 16 matrix was successfully fabricated using screen-printed
thick electrodes and CNT thin yarns. It can display rolling characters
with a low power consumption. More applications can be further developed
based on the addressable CNT thermal arrays
Duration of Chemotherapy for Small Cell Lung Cancer: A Meta-Analysis
<div><p>Background</p><p>Maintenance chemotherapy is widely provided to patients with small cell lung cancer (SCLC). However, the benefits of maintenance chemotherapy compared with observation are a subject of debate.</p><p>Methodology and Principal Findings</p><p>To identify relevant literature, we systematically searched the Medline, Embase, and Cochrane Central Register of Controlled Trials databases. Eligible trials included patients with SCLC who either received maintenance chemotherapy (administered according to a continuous or switch strategy) or underwent observation. The primary outcome was 1-year mortality, and secondary outcomes were 2-year mortality, overall survival (OS), and progression-free survival (PFS). Of the 665 studies found in our search, we identified 14 relevant trials, which together reported data on 1806 patients with SCLC. When compared with observation, maintenance chemotherapy had no effect on 1-year mortality (odds ratio [OR]: 0.88; 95% confidence interval [CI]: 0.66–1.19; P = 0.414), 2-year mortality (OR: 0.82; 95% CI: 0.57–1.19; P = 0.302), OS (hazard ratio [HR]: 0.87; 95% CI: 0.71–1.06; P = 0.172), or PFS (HR: 0.87; 95% CI: 0.62–1.22; P = 0.432). However, subgroup analyses indicated that maintenance chemotherapy was associated with significantly longer PFS than observation in patients with extensive SCLC (HR, 0.72; 95% CI: 0.58–0.89; P = 0.003). Additionally, patients who were managed using the continuous strategy of maintenance chemotherapy appeared to be at a disadvantage in terms of PFS compared with patients who only underwent observation (HR, 1.27; 95% CI: 1.04–1.54; P = 0.018).</p><p>Conclusions/Significance</p><p>Maintenance chemotherapy failed to improve survival outcomes in patients with SCLC. However, a significant advantage in terms of PFS was observed for maintenance chemotherapy in patients with extensive disease. Additionally, our results suggest that the continuous strategy is inferior to observation; its clinical value needs to be investigated in additional trials.</p></div
Conformal Fe<sub>3</sub>O<sub>4</sub> Sheath on Aligned Carbon Nanotube Scaffolds as High-Performance Anodes for Lithium Ion Batteries
A uniform Fe<sub>3</sub>O<sub>4</sub> sheath is magnetron
sputtered
onto aligned carbon nanotube (CNT) scaffolds that are directly drawn
from CNT arrays. The Fe<sub>3</sub>O<sub>4</sub>–CNT composite
electrode, with the size of Fe<sub>3</sub>O<sub>4</sub> confined to
5–7 nm, exhibits a high reversible capacity over 800 mAh g<sup>–1</sup> based on the total electrode mass, remarkable capacity
retention, as well as high rate capability. The excellent performance
is attributable to the superior electrical conductivity of CNTs, the
uniform loading of Fe<sub>3</sub>O<sub>4</sub> sheath, and the structural
retention of the composite anode on cycling. As Fe<sub>3</sub>O<sub>4</sub> is inexpensive and environmentally friendly, and the synthesis
of Fe<sub>3</sub>O<sub>4</sub>–CNT is free of chemical wastes,
this composite anode material holds considerable promise for high-performance
lithium ion batteries
Ice-Assisted Transfer of Carbon Nanotube Arrays
Decoupling the growth and the application
of nanomaterials by transfer
is an important issue in nanotechnology. Here, we developed an efficient
transfer technique for carbon nanotube (CNT) arrays by using ice as
a binder to temporarily bond the CNT array and the target substrate.
Ice makes it an ultraclean transfer because the evaporation of ice
ensures that no contaminants are introduced. The transferred superaligned
carbon nanotube (SACNT) arrays not only keep their original appearance
and initial alignment but also inherit their spinnability, which is
the most desirable feature. The transfer-then-spin strategy can be
employed to fabricate patterned CNT arrays, which can act as 3-dimensional
electrodes in CNT thermoacoustic chips. Besides, the flip-chipped
CNTs are promising field electron emitters. Furthermore, the ice-assisted
transfer technique provides a cost-effective solution for mass production
of SACNTs, giving CNT technologies a competitive edge, and this method
may inspire new ways to transfer other nanomaterials
Flow diagram of the literature search and trials selection process.
<p>Flow diagram of the literature search and trials selection process.</p
Adsorption-Induced Changes in Ribonuclease A Structure and Enzymatic Activity on Solid Surfaces
Ribonuclease
A (RNase A) is a small globular enzyme that lyses
RNA. The remarkable solution stability of its structure and enzymatic
activity has led to its investigation to develop a new class of drugs
for cancer chemotherapeutics. However, the successful clinical application
of RNase A has been reported to be limited by insufficient stability
and loss of enzymatic activity when it was coupled with a biomaterial
carrier for drug delivery. The objective of this study was to characterize
the structural stability and enzymatic activity of RNase A when it
was adsorbed on different surface chemistries (represented by fused
silica glass, high-density polyethylene, and polyÂ(methyl-methacrylate)).
Changes in protein structure were measured by circular dichroism,
amino acid labeling with mass spectrometry, and in vitro assays of
its enzymatic activity. Our results indicated that the process of
adsorption caused RNase A to undergo a substantial degree of unfolding
with significant differences in its adsorbed structure on each material
surface. Adsorption caused RNase A to lose about 60% of its native-state
enzymatic activity independent of the material on which it was adsorbed.
These results indicate that the native-state structure of RNase A
is greatly altered when it is adsorbed on a wide range of surface
chemistries, especially at the catalytic site. Therefore, drug delivery
systems must focus on retaining the native structure of RNase A in
order to maintain a high level of enzymatic activity for applications
such as antitumor chemotherapy
Cyclopropanations via Heme Carbenes: Basic Mechanism and Effects of Carbene Substituent, Protein Axial Ligand, and Porphyrin Substitution
Catalytic carbene
transfer to olefins is a useful approach to synthesize
cyclopropanes, which are key structural motifs in many drugs and biologically
active natural products. While catalytic methods for olefin cyclopropanation
have largely relied on rare transition-metal-based catalysts, recent
studies have demonstrated the promise and synthetic value of iron-based
heme-containing proteins for promoting these reactions with excellent
catalytic activity and selectivity. Despite this progress, the mechanism
of iron-porphyrin and hemoprotein-catalyzed olefin cyclopropanation
has remained largely unknown. Using a combination of quantum chemical
calculations and experimental mechanistic analyses, the present study
shows for the first time that the increasingly useful Cî—»C functionalizations
mediated by heme carbenes feature an Fe<sup>II</sup>-based, nonradical,
concerted nonsynchronous mechanism, with early transition state character.
This mechanism differs from the Fe<sup>IV</sup>-based, radical, stepwise
mechanism of heme-dependent monooxygenases. Furthermore, the effects
of the carbene substituent, metal coordinating axial ligand, and porphyrin
substituent on the reactivity of the heme carbenes was systematically
investigated, providing a basis for explaining experimental reactivity
results and defining strategies for future catalyst development. Our
results especially suggest the potential value of electron-deficient
porphyrin ligands for increasing the electrophilicity and thus the
reactivity of the heme carbene. Metal-free reactions were also studied
to reveal temperature and carbene substituent effects on catalytic
vs noncatalytic reactions. This study sheds new light into the mechanism
of iron-porphyrin and hemoprotein-catalyzed cyclopropanation reactions
and it is expected to facilitate future efforts toward sustainable
carbene transfer catalysis using these systems
Subgroup analysis for 1-year mortality, 2-year mortality, OS, and PFS.
<p>Subgroup analysis for 1-year mortality, 2-year mortality, OS, and PFS.</p
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