39 research outputs found
Simulations of absorption spectra of conjugated oligomers: role of planar conformation and aggregation in condensed phase
<p>This Review highlights the structure/property relationship underlying the morphology modulation through various factors towards the exploration of light-absorbing materials for efficient utilisation of solar power. Theoretical study using a combination of molecular dynamics imulations and the time-dependent density functional theory demonstrated that the planarity plays an important role in tuning spectral properties of oligomer aggregates. The aggregation-induced blue-shift in absorption spectra of oligothiophenes and the red-shift for oligofluorenols were rationalised in a unified way from the reduced (and increased) content of planar conformations in molecular aggregates. The planarity versus non-planarity of oligomers can be modulated by introduction of alkyl side chain or steric bulky substituents. The substitution with various groups in the ortho-position of azobenzene leads to the distorted backbone, breaking symmetry, and hence the red-shift in spectra, expanding the application in biological systems with visible light absorption. The donor–acceptor substituent groups in conjugated oligomers can increase the degree of planarity, electron delocalisation and polarisation, and charge separation, giving rise to the red-shift in spectra and enhancement in polarisability and charge mobility for device applications. The solvent dependent and pH-sensitive properties and intramolecular hydrogen bonds also caused the shift of absorption spectra with the appearance of planar conformers.</p
Unconventional O–H···C Hydrogen Bonding and Effects of Conformational Changes on Infrared Spectroscopy of <i>o</i>‑Cresol in Solutions
The unconventional
O–H···C intramolecular
hydrogen bonding and the effect of conformational changes on IR spectra
of <i>o</i>-cresol in aqueous solutions were investigated
by using molecular dynamics (MD) simulations, density functional theory
(DFT), and experiments. A facial rotational isomerization between
global minimum with <i>trans</i> conformation and the <i>cis</i> isomer is predicted to take place in gas phase with
a low barrier of about 3.7 kcal/mol through a <i>vertical</i>-like transition state. Upon solvation in aqueous solution, the contents
of energetically high–lying <i>vertical</i> and <i>cis</i> conformations of neutral <i>o</i>-cresol are
increased to 19% and 57%, respectively, in comparison with those (<i>vertical</i>, 0%; <i>cis</i>, 27%) in vacuum. The
IR spectra of aqueous solution are closely related to the relative
population of the different conformations, especially for the <i>cis</i> conformation with hydroxyl group facing to alkyl group.
The appearance of <i>cis</i> conformations and unconventional
O–H···C intramolecular hydrogen bond (HB) caused
the low-frequency shift in OH stretching vibration of the IR spectra,
which was also correlated with cation-like charge distribution and
the decrease in <i>s</i>-component of oxygen hybridization
orbital. However, the intermolecular HB between the <i>o</i>-cresol and surrounding water (<i>o</i>-cresol) molecules
gave rise to more evident shifts in IR spectra than that caused by
the intramolecular HB contributions in <i>cis</i> isomer.
Further identification of intramolecular HB effect is performed through
the comparison of spectrum changes that occurs on passing from aqueous
solution to less interacting (carbon tetrachloride and cyclohexane)
solvents. The absence of the intermolecular HB interaction between <i>o</i>-cresol and carbon tetrachloride (and cyclohexane) solvents
leads to the weaker intensity and narrower width of OH stretching
vibration region (around 3407 cm<sup>–1</sup>) in the IR spectra
than that in aqueous solution
Spectroscopic Compositional Analysis of Electrolyte during Initial SEI Layer Formation
The energy density of an electrochemical
capacitor can be significantly
improved by utilizing a lithiated negative electrode and a high surface
area positive electrode. During lithiation of the negative carbon
electrode, the electrolyte reacts with the electrode surface and undergoes
decomposition to form a solid electrolyte interphase (SEI) layer that
passivates the surface of the carbon electrode from further reactions
between Li and the electrolyte. The reduction reactions that the solvent
undergoes not only form insoluble and gaseous byproducts but also
electrolyte-soluble products. In this work, those liquid-phase products
generated by reductive decomposition of a carbonate-based electrolyte,
1.2 M LiPF<sub>6</sub> in EC/PC/DEC (3:1:4), were analyzed at different
stages during the lithiation process of an amorphous carbon electrode.
An LCMS analysis of the electrolyte during the initial lithiation
process was correlated to a DRIFTS analysis of the carbon electrode
surface and the results from the EIS and gas-phase analysis previously
reported. It was concluded that the formation reactions of the electrolyte-soluble
reduction products are dependent on electrochemical processes but
are independent of those reactions that directly lead to the generation
of the decomposition gases. This is the first time that the composition
of the electrolyte during the initial stages of formation of the SEI
layer was systematically determined through the use of an <i>in situ</i> electrochemical-MS analysis. The results presented
in this work are focused on the initial analysis, elucidation of the
empirical formulas, and determining possible structures for these
compounds through a detailed analysis of the spectra from each of
these unknowns
Results of subgroups analyses of pooled ORs (95% CIs).
<p>NCC, nest case-control study; CS, cross-sectional study; CC, case-control study; NA, not available; ABL, alveolar bone loss; OHI, oral health index; PI, periodontal index; CAL, clinical attachment loss; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; GOLD criteria, Global Initiative for Chronic Obstructive Lung Disease spirometry guidelines; PFT, pulmonary function test, that means the article just mentioned but did not give what measurement have been used.</p
Study characteristics of included studies.
<p>NCC, nest case-control study; CS, cross-sectional study; CC, case-control study; NA, not available; ABL, alveolar bone loss; OHI, oral health index; PI, periodontal index; CAL, clinical attachment loss; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; GOLD criteria, Global Initiative for Chronic Obstructive Lung Disease spirometry guidelines; PFT, pulmonary function test, that means the article just mentioned but did not give what measurement have been used.</p
Flow chart from identification of studies that tested the association between PD and risk of COPD to final inclusion.
<p>PD, periodontal dsease; COPD, chronic obstructive pulmonary disease.</p
Forst plot of sensitivity analysis by removing each study in each turn.
<p>The pooled OR was represented by a diamond of standard height, with the width indicating the 95% CI. PD, periodontal dsease; COPD, chronic obstructive pulmonary disease; OR, odds ratio; CI, confidence interval; NCC, nest case-control study; CC, case-control study; CS, cross-sectional study.</p
Filled funnel plot with pseudo-95% CIs of results of 14 studies.
<p>Log of OR represents the natural logarithm of the OR of individual studies; Standard Error by Log odds ratio represents the standard error in the natural logarithm of the OR of individual studies. A circle in the figure represents a study, while a black spot represents an unpublished study that would have to exist to negate the results of the meta-analysis.</p
Direct Synthesis of Unilamellar MgAl-LDH Nanosheets and Stacking in Aqueous Solution
Two-dimensional (2D) materials, such
as graphene, inorganic oxides,
and hydroxides, are one of the most extensively studied classes of
materials due to their unilamellar crystallites or nanosheet structures.
In this study, instead of using the universal exfoliation method of
the bulky crystal precursor, 2D crystals/nanosheets of MgAl-layered
double hydroxides (LDHs) were synthesized in formamide. We propose
that the obtained crystals are unilamellar according to the XRD, TEM,
and AFM observations. The HRTEM and fast Fourier transform images
confirm that the crystal structures are the same as those of the exfoliated
MgAl-LDH nanosheets. The directly synthesized sheets can stack into
a 3D crystal structure, which is the same as that of typical LDHs
except for the disordered orientation of the <i>a</i>-/<i>b</i>- crystal axis of each sheet. This result provides not
only a novel approach to the preparation of 2D crystals but also insight
into the formation mechanism of LDHs
Colloidal Synthesis of Lettuce-like Copper Sulfide for Light-Gating Heterogeneous Nanochannels
Lettuce-like Cu<sub><i>x</i></sub>S micron particles
were successfully prepared by a colloidal hot-injection method, and
the preliminary evaluation of the light-gating artificial ionic nanochannels
designed using these particles was also demonstrated. A likely underlying
mechanism behind the formation of the lettuce architecture was tentatively
proposed <i>via</i> monitoring the evolution process. These
particles are hydrophobic and possess a high surface area that can
readily absorb the light-responsive 1,3,3-trimethylindolino-6′-nitrobenzopyrylospiran
(Spiro) molecules. Finally, the heterogeneous nanochannels were constructed
by spin-coating the preprepared Cu<sub><i>x</i></sub>S particles
loaded with Spiro onto the commercially available anodic alumina (AAO)
substrate. The AAO-Cu<sub><i>x</i></sub>S/Spiro heterogeneous
nanochannels “close” under illumination of ultraviolet
light (365 nm) and then “open” by visible light irradiation,
which exhibits a regulated ionic transport property with good responsive
switchability and stability