10 research outputs found
Supplemental Material - Analyzing tourism productivity changes with complex configurations
Supplemental Material for Analyzing tourism productivity changes with complex configurations by Hai Dong, Qi Bin Liang and Nicolas Peypoch in Tourism Economics.</p
Straightforward <i>S</i>–<i>S</i> Bond Formation via the Oxidation of <i>S</i>‑Acetyl by Iodine in the Presence of <i>N</i>‑Iodosuccinimide
Straightforward <i>S</i>–<i>S</i> bond
formation via the oxidation of <i>S</i>-acetyl group by
iodine was reported here. The reaction was further applied in the
synthesis of per-<i>O</i>-acetylated glycosyl disulfides.
These studies demonstrated great improvement in reaction rate, yield,
and general convenience in the presence of <i>N</i>-iodosuccinimide.
Furthermore, selectively deacetylated glycosyl thiols were obtained
in high yields when these per-<i>O</i>-acetylated glycosyl
disulfides were reduced with trisÂ(2-carboxyethyl)-phosphine (TCEP).
Our method supplied an efficient way to obtain both per-<i>O</i>-acetylated glycosyl disulfides and per-<i>O</i>-acetylated
glycosyl thiols in which the sulfur group was located at any position
Regioselective Acetylation of Diols and Polyols by Acetate Catalysis: Mechanism and Application
We propose a principle for H-bonding
activation in acylation of
hydroxyl groups, where the acylation is activated by the formation
of hydrogen bonds between hydroxyl groups and anions. With the guidance
of this principle, we demonstrate a method for the selective acylation
of carbohydrates. By this method, diols and polyols are regioselectively
acetylated in high yields under mild conditions using catalytic amounts
of acetate. In comparison to other methods involving reagents such
as organotin, organoboron, organosilicon, organobase, and metal salts,
this method is more environmentally friendly, convenient, and efficient
and is also associated with higher regioselectivity. We have performed
a thorough quantum chemical study to decipher the mechanism, which
suggests that acetate first forms a dual H-bond complex with a diol,
which enables subsequent monoacylation by acetic anhydride under mild
conditions. The regioselectivity appears to originate from the inherent
structure of the diols and polyols and their specific interactions
with the coordinating acetate catalyst
H‑Bonding Activation in Highly Regioselective Acetylation of Diols
H-bonding
activation in the regioselective acetylation of vicinal
and 1,3-diols is presented. Herein, the acetylation of the hydroxyl
group with acetic anhydride can be activated by the formation of H-bonds
between the hydroxyl group and anions. The reaction exhibits high
regioselectivity when a catalytic amount of tetrabutylammonium acetate
is employed. Mechanistic studies indicated that acetate anion forms
dual H-bonding complexes with the diol, which facilitates the subsequent
regioselective monoacetylation
Stereoelectronic Control in Regioselective Carbohydrate Protection
Organotin-mediated regioselective protection has been
extensively
used in organic synthesis for many years. However, the mechanistic
origin of the resulting regioselectivity is still not clear. By the
comparison of the steric and stereoelectronic effects controlling
the geometry of five-membered rings formed from neighboring group
participation, from intramolecular acyl group migration, or from orthoester
transesterification on pyranoside rings, a theory on the pattern resulting
from the reaction with dibutyltin oxide is presented. It is thus suggested
that the regioselectivity of organotin-mediated protection is controlled
by analogous steric and stereoelectronic effects as in neighboring
group participation and acyl group migration, mainly dependent on
the stereoelectronic effects of the pyranoside itself, and not related
to complex stannylene structures. An organotin protection mechanism
is also suggested, emanating from steric and stereoelectronic effects,
nucleophilicity, and organotin acyl migration
Photoguided Shape Deformation of Azobenzene-Containing Polymer Microparticles
Here
we present the generation of uniform microparticles with tunable
diameters from azobenzene-based homopolymer by combining the microfluidics
technique and emulsion-solvent evaporation route. In addition, the
photoinduced deformation behavior of these microspheres, irradiated
by a linearly polarized beam with different irradiation time and direction,
are systemically studied. The deformation process through real time
optical microscope observation can be investigated, benefiting from
the uniform and microscaled size of the polymer particles. These results
indicate that the deformation degree characterized by relative variation
of the long axial for the particles can be controlled by the irradiation
time. Moreover, elongated particles with tunable aspect ratio or tilted
shape can be generated by manipulating the irradiation direction and/or
time. Interestingly, the shape transformation kinetics displays a
significant dependence on initial size of the polymer particle. In
addition, the shape transformation of the polymer particle can lead
to the variation of the orientation and distribution of the encapsulated
anisotropic gold nanorods
Surface Roughness Modulates Diffusion and Fibrillation of Amyloid‑β Peptide
The presence of surfaces influences
the kinetics of amyloid-β
(Aβ) peptide fibrillation. Although it has been generally recognized
that the fibrillation process can be assisted or accelerated by surface
chemistry, the impact of surface topography, i.e., roughness, on peptide
fibrillation is relatively little understood. Here we study the role
of surface roughness on surface-mediated fibrillation using polymer
coatings of varying roughness as well as polymer microparticles. Using
single-molecule tracking, atomic force microscopy, and the thioflavin
T fluorescence technique, we show that a rough surface decelerates
the two-dimensional (2D) diffusion of peptides and retards the surface-mediated
fibrillation. A higher degree of roughness that presents an obstacle
to peptide diffusion is found to inhibit the fibrillation process
Surface Roughness Modulates Diffusion and Fibrillation of Amyloid‑β Peptide
The presence of surfaces influences
the kinetics of amyloid-β
(Aβ) peptide fibrillation. Although it has been generally recognized
that the fibrillation process can be assisted or accelerated by surface
chemistry, the impact of surface topography, i.e., roughness, on peptide
fibrillation is relatively little understood. Here we study the role
of surface roughness on surface-mediated fibrillation using polymer
coatings of varying roughness as well as polymer microparticles. Using
single-molecule tracking, atomic force microscopy, and the thioflavin
T fluorescence technique, we show that a rough surface decelerates
the two-dimensional (2D) diffusion of peptides and retards the surface-mediated
fibrillation. A higher degree of roughness that presents an obstacle
to peptide diffusion is found to inhibit the fibrillation process
Surface Roughness Modulates Diffusion and Fibrillation of Amyloid‑β Peptide
The presence of surfaces influences
the kinetics of amyloid-β
(Aβ) peptide fibrillation. Although it has been generally recognized
that the fibrillation process can be assisted or accelerated by surface
chemistry, the impact of surface topography, i.e., roughness, on peptide
fibrillation is relatively little understood. Here we study the role
of surface roughness on surface-mediated fibrillation using polymer
coatings of varying roughness as well as polymer microparticles. Using
single-molecule tracking, atomic force microscopy, and the thioflavin
T fluorescence technique, we show that a rough surface decelerates
the two-dimensional (2D) diffusion of peptides and retards the surface-mediated
fibrillation. A higher degree of roughness that presents an obstacle
to peptide diffusion is found to inhibit the fibrillation process
Surface Roughness Modulates Diffusion and Fibrillation of Amyloid‑β Peptide
The presence of surfaces influences
the kinetics of amyloid-β
(Aβ) peptide fibrillation. Although it has been generally recognized
that the fibrillation process can be assisted or accelerated by surface
chemistry, the impact of surface topography, i.e., roughness, on peptide
fibrillation is relatively little understood. Here we study the role
of surface roughness on surface-mediated fibrillation using polymer
coatings of varying roughness as well as polymer microparticles. Using
single-molecule tracking, atomic force microscopy, and the thioflavin
T fluorescence technique, we show that a rough surface decelerates
the two-dimensional (2D) diffusion of peptides and retards the surface-mediated
fibrillation. A higher degree of roughness that presents an obstacle
to peptide diffusion is found to inhibit the fibrillation process