8 research outputs found
A Comparison of Imputation Strategies for Ordinal Missing Data on Likert Scale Variables
<div><p>This article compares a variety of imputation strategies for ordinal missing data on Likert scale variables (number of categories = 2, 3, 5, or 7) in recovering reliability coefficients, mean scale scores, and regression coefficients of predicting one scale score from another. The examined strategies include imputing using normal data models with naïve rounding/without rounding, using latent variable models, and using categorical data models such as discriminant analysis and binary logistic regression (for dichotomous data only), multinomial and proportional odds logistic regression (for polytomous data only). The result suggests that both the normal model approach without rounding and the latent variable model approach perform well for either dichotomous or polytomous data regardless of sample size, missing data proportion, and asymmetry of item distributions. The discriminant analysis approach also performs well for dichotomous data. Naïvely rounding normal imputations or using logistic regression models to impute ordinal data are not recommended as they can potentially lead to substantial bias in all or some of the parameters.</p></div
Janus Composite Nanorod from a Molecular Bottlebrush Containing a Block Copolymer
The asymmetric ABC-type
Janus polymer composite nanorods are synthesized
by the in situ preferential growth of functional materials against
the molecular bottlebrush containing a triblock copolymer of polyÂ(ethylene
oxide)-<i>b</i>-polyÂ(2-methÂacrylÂoylÂoxyÂethyl
pentynÂoate-<i>g</i>-polyÂ(acrylic acid))-<i>b</i>-polystyrene. PEO and PS single chains are terminated onto the opposite
ends of the composite nanorods. The two polymer chains are responsible
for amphiphilic performance, while the composite nanorod is responsible
for the functionality. The Janus nanorods can stand vertically at
an emulsion interface, making the interfaces easily functionalized
and manipulated. Protection of the PAA molecular bottlebrush via electrostatic
interaction is important to obtaining individual nanorods at high
solid contents. A huge family of Janus composite nanorods is expected
by changing the compositions of the two polymer chains and the nanorod
Amide Bond Formation through Iron-Catalyzed Oxidative Amidation of Tertiary Amines with Anhydrides
A general
and efficient method for amide bond synthesis has been
developed. The method allows for synthesis of tertiary amides from
readily available tertiary amines and anhydrides in the presence of
FeCl<sub>2</sub> as catalyst and <i>tert</i>-butyl hydroperoxide
in water (T-Hydro) as oxidant. Mechanistic studies indicated that
the in situ-generated α-amino peroxide of tertiary amine and
iminium ion act as key intermediates in this oxidative transformation
Three-Dimensional Phosphorus-Doped Graphitic‑C<sub>3</sub>N<sub>4</sub> Self-Assembly with NH<sub>2</sub>‑Functionalized Carbon Composite Materials for Enhanced Oxygen Reduction Reaction
Oxygen reduction reaction (ORR) is
the major reaction that occurs
at the cathodes of fuel cells and metal–air batteries. Development
of inexpensive, active, and durable heteroatom doped carbon-based
ORR catalysts can lead to significant cost reduction of these electrochemical
energy devices, which therefore has recently attracted enormous research
attentions. This work reports a three-dimensional porous composite
(P-<i>g</i>-C<sub>3</sub>N<sub>4</sub>@NH<sub>2</sub>–CB)
for the highly efficient ORR catalyst. P-<i>g</i>-C<sub>3</sub>N<sub>4</sub>@NH<sub>2</sub>–CB was prepared by mixing
phosphorus-doped graphitic carbon nitride nanosheets (P-<i>g</i>-C<sub>3</sub>N<sub>4</sub> NSs) with NH<sub>2</sub>-functionalized
carbon black (NH<sub>2</sub>–CB) via a novel self-assembly
approach. The NH<sub>2</sub>–CB was rationally chosen as the
spacer that enables the self-assembled with the P-<i>g</i>-C<sub>3</sub>N<sub>4</sub> NSs driven by the electrostatic interaction.
The intercalation of NH<sub>2</sub>–CB induces the transformation
of 2-D P-<i>g</i>-C<sub>3</sub>N<sub>4</sub> NSs into a
3-D composites material of higher surface area, thereby exposing more
ORR active sites. The P-<i>g</i>-C<sub>3</sub>N<sub>4</sub>@NH<sub>2</sub>–CB exhibited a remarkable ORR activity with
an electron transfer number of 3.83 and Tafel slope of 89 mV dec<sup>–1</sup> in alkaline electrolyte, which is comparable to the
ORR performance on Pt/Vulcan XC-72. It is found that the incorporated
P atoms as well as employing NH<sub>2</sub>–CB spacer not only
reduces the overpotential of ORR, but also enhances the ORR activity
of carbon nitride-based materials, owing to the synergistic effect
between P and N in tri-s-triazine rings of carbon nitrides and the
optimum interaction between the oppositely charged P-<i>g</i>-C<sub>3</sub>N<sub>4</sub> and NH<sub>2</sub>–CB
Direct Benzothiophene Formation via Oxygen-Triggered Intermolecular Cyclization of Thiophenols and Alkynes Assisted by Manganese/PhCOOH
An intermolecular oxidative cyclization between thiophenols and alkynes for benzothiophene formation has been established. A variety of multifunctional benzothiophenes are synthesized. In addition, we demonstrated that the obtained benzothiophenes can be used for further transformation to give diverse benzothiophene derivatives efficiently and selectively
Janus Nanoparticles of Block Copolymers by Emulsion Solvent Evaporation Induced Assembly
We present a facile approach toward
straightforward synthesis of Janus nanoparticles (NPs) of polyÂ(4-vinylpyridine)-based
block copolymers by solvent evaporation induced assembly within emulsion
droplets. Formation of the Janus NPs is arisen from the synergistic
effect between solvent selectivity and interfacial selectivity. This
method is robust without the requisites of narrow molecular weight
distribution and specific range of block fraction of the copolymers.
Janus NPs can also be achieved from mixtures of copolymers, whose
aspect size ratio and thus Janus balance are finely tunable. The Janus
NPs are capable to self-assemble into ordered superstructures either
onto substrates or in dispersions, whose morphology relies on Janus
balance
Surface-Adaptive Gold Nanoparticles with Effective Adherence and Enhanced Photothermal Ablation of Methicillin-Resistant Staphylococcus aureus Biofilm
Biofilms that contribute
to the persistent bacterial infections
pose serious threats to global public health, mainly due to their
resistance to antibiotics penetration and escaping innate immune attacks
by phagocytes. Here, we report a kind of surface-adaptive gold nanoparticles
(AuNPs) exhibiting (1) a self-adaptive target to the acidic microenvironment
of biofilm, (2) an enhanced photothermal ablation of methicillin-resistant Staphylococcus aureus (MRSA) biofilm under near-infrared
(NIR) light irradiation, and (3) no damage to the healthy tissues
around the biofilm. Originally, AuNPs were readily prepared by surface
modification with pH-responsive mixed charged zwitterionic self-assembled
monolayers consisting of weak electrolytic 11-mercaptoundecanoic acid
(HS-C<sub>10</sub>-COOH) and strong electrolytic (10-mercaptodecyl)Âtrimethylammonium
bromide (HS-C<sub>10</sub>-N<sub>4</sub>). The mixed charged zwitterion-modified
AuNPs showed fast pH-responsive transition from negative charge to
positive charge, which enabled the AuNPs to disperse well in healthy
tissues (pH ∼7.4), while quickly presenting strong adherence
to negatively charged bacteria surfaces in MRSA biofilm (pH ∼5.5).
Simultaneous AuNP aggregation within the MRSA biofilm enhanced the
photothermal ablation of MRSA biofilm under NIR light irradiation.
The surrounding healthy tissues showed no damage because the dispersed
AuNPs had no photothermal effect under NIR light. In view of the above
advantages as well as the straightforward preparation, AuNPs developed
in this work may find potential applications as a useful antibacterial
agent in the areas of healthcare