23 research outputs found
Inversion using a new low-dimensional representation of complex binary geological media based on a deep neural network
Efficient and high-fidelity prior sampling and inversion for complex
geological media is still a largely unsolved challenge. Here, we use a deep
neural network of the variational autoencoder type to construct a parametric
low-dimensional base model parameterization of complex binary geological media.
For inversion purposes, it has the attractive feature that random draws from an
uncorrelated standard normal distribution yield model realizations with spatial
characteristics that are in agreement with the training set. In comparison with
the most commonly used parametric representations in probabilistic inversion,
we find that our dimensionality reduction (DR) approach outperforms principle
component analysis (PCA), optimization-PCA (OPCA) and discrete cosine transform
(DCT) DR techniques for unconditional geostatistical simulation of a
channelized prior model. For the considered examples, important compression
ratios (200 - 500) are achieved. Given that the construction of our
parameterization requires a training set of several tens of thousands of prior
model realizations, our DR approach is more suited for probabilistic (or
deterministic) inversion than for unconditional (or point-conditioned)
geostatistical simulation. Probabilistic inversions of 2D steady-state and 3D
transient hydraulic tomography data are used to demonstrate the DR-based
inversion. For the 2D case study, the performance is superior compared to
current state-of-the-art multiple-point statistics inversion by sequential
geostatistical resampling (SGR). Inversion results for the 3D application are
also encouraging
Highly <i>Cis</i>-1,4-Selective Living Polymerization of 3‑Methylenehepta-1,6-diene and Its Subsequent Thiol–Ene Reaction: An Efficient Approach to Functionalized Diene-Based Elastomer
Living polymerization of 3-methylenehepta-1,6-diene
(MHD) catalyzed
by bis(phosphino)carbazoleide-ligated yttrium alkyl complex
afforded a new product bearing pendant terminal vinyl groups with
high stereotacticity (<i>cis</i>-1,4-selectivity up to 98.5%),
proved by the NMR (<sup>1</sup>H, <sup>13</sup>C, and 1D ROESY) spectroscopic
analyses, which demonstrates overwhelmingly favorable chemoselectivity
toward conjugated diene over α-olefin moieties. High <i>cis</i>-1,4 random copolymers of MHD and isoprene could also
be obtained with pendant vinyl groups ranging from 10% to 90%. These
vinyl groups in every chain unit can be cleanly and quantitatively
converted into various functionalities via light-mediated thiol–ene
reaction, resulting in homo- and copolymers of various functional
butadiene derivatives, which display versatile thermal properties
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Binuclear Rare-Earth-Metal Alkyl Complexes Ligated by Phenylene-Bridged β‑Diketiminate Ligands: Synthesis, Characterization, and Catalysis toward Isoprene Polymerization
Deprotonation
of <i>m</i>-phenylene-bridged bis(β-diketiminate)
ligands (PBDI<sup><i>i</i>Pr</sup>-H<sub>2</sub> = [2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>NHC(Me)C(H)C(Me)N]<sub>2</sub>-(<i>m</i>-phenylene); PBDI<sup>Et</sup>-H<sub>2</sub> = [2,6-Et<sub>2</sub>C<sub>6</sub>H<sub>3</sub>NHC(Me)C(H)C(Me)N]<sub>2</sub>-(<i>m</i>-phenylene); PBDI<sup>Me</sup>-H<sub>2</sub> = [2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>NHC(Me)C(H)C(Me)N]<sub>2</sub>-(<i>m</i>-phenylene)) by rare-earth-metal tris(alkyls)
Ln(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(THF)<sub>2</sub> (Ln
= Y, Lu, Sc) gave a series of rare-earth-metal bis(alkyl) complexes:
PBDI<sup><i>i</i>Pr</sup>-[Y(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(THF)<sub>2</sub> (<b>1</b>), PBDI<sup>Et</sup>-[Ln(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(THF)<sub><i>n</i></sub> (<b>2a</b>, Ln = Y, <i>n</i> = 2; <b>2b</b>, Ln = Lu, <i>n</i> = 2; <b>2c</b>, Ln = Sc, <i>n</i> = 1), and PBDI<sup>Me</sup>-[Y(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(THF)<sub>2</sub> (<b>3</b>). All these complexes were fully characterized
by NMR spectroscopy, X-ray diffraction, and elemental analyses, adopting
binuclear structures with the two rare-earth-metal ions taking <i>trans</i> positions versus the phenyl ring. Complexes <b>1</b>, <b>2a</b>,<b>b</b>, and <b>3</b> coordinate
two solvated THF molecules, while the scandium complex <b>2c</b> incorporates only one THF molecule, owing to the steric crowding.
Upon activation with 2 equiv of organoborate, the yttrium systems
showed higher catalytic activity toward isoprene polymerization in
comparison to those based on lutetium, and the scandium system was
less active. Addition of aluminum alkyls to the above binary systems
accelerated dramatically the polymerization rate irrespective of the
central metal type through scavenging impurities in the systems and
abstracting the solvated THF molecules in the precursors. The resultant
polyisoprene had higher 3,4-regularity (20% vs 5%) as well as higher
molecular weights in comparison with the mononuclear systems, which
might be attributed to the steric bulky effect of the binuclear systems
Isoprene Polymerization with Iminophosphonamide Rare-Earth-Metal Alkyl Complexes: Influence of Metal Size on the Regio- and Stereoselectivity
The protonolysis reaction of β-iminophosphonamine
ligand
(NPN<sup>dipp</sup> = Ph<sub>2</sub>P(NC<sub>6</sub>H<sub>3</sub><sup><i>i</i></sup>Pr<sub>2</sub>-2,6)<sub>2</sub>) with one
equivalent of rare-earth-metal tris(alkyl)s afforded the corresponding
bis(alkyl) complexes NPN<sup>dipp</sup>Ln(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(THF) (Ln = Sc (<b>1</b>), Lu (<b>2</b>),
Y (<b>3</b>), Er (<b>4</b>)). The bis(4-methylbenzyl)
complexes NPN<sup>dipp</sup>Ln(CH<sub>2</sub>Ph-4-Me)<sub>2</sub>(THF)
(Ln = Nd (<b>5</b>), La (<b>6</b>)) were prepared by treatment
of the tris(4-methylbenzyl) compounds Ln(CH<sub>2</sub>Ph-4-Me)<sub>3</sub>(THF)<sub>3</sub> with β-iminophosphonamine ligand.
The small-size rare-earth-metal-based complexes <b>1</b>–<b>4</b> upon activation with Al<sup><i>i</i></sup>Bu<sub>3</sub> and [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] showed high 3,4-selectivities up to 98.1% for isoprene polymerization.
When the larger size rare-earth-metal-based 4-methylbenzyl complexes <b>5</b> and <b>6</b> were employed instead, moderate 3,4-selectivities
were obtained since the opening coordination environment facilitated
the 1,4-enchainment (Nd<sup>3+</sup>: 76.1%; La<sup>3+</sup>: 62.9%).
Replacing Al<sup><i>i</i></sup>Bu<sub>3</sub> by AlEt<sub>3</sub>, the <b>5</b> and <b>6</b> systems exhibited
high activity and excellent <i>trans</i>-1,4 selectivity
for both isoprene (96.5%, 0 °C) and butadiene (92.8%, 20 °C)
polymerizations
Polymerization of Affinity Ligands on a Surface for Enhanced Ligand Display and Cell Binding
Surfaces
functionalized with affinity ligands have been widely
studied for applications such as biological separations and cell regulation.
While individual ligands can be directly conjugated onto a surface,
it is often important to conjugate polyvalent ligands onto the surface
to enhance ligand display. This study was aimed at exploring a method
for surface functionalization via polymerization of affinity ligands,
which was achieved through ligand hybridization with DNA polymers
protruding from the surface. The surface with polyvalent ligands was
evaluated via aptamer-mediated cell binding. The results show that
this surface bound target cells more effectively than a surface directly
functionalized with individual ligands in situations with either equal
amounts of ligand display or equal amounts of surface reaction sites.
Therefore, this study has demonstrated a new strategy for surface
functionalization to enhance ligand display and cell binding. This
strategy may find broad applications in settings where surface area
is limited or the surface of a material does not possess sufficient
reaction sites
Copolymerization of ε‑Caprolactone and l‑Lactide Catalyzed by Multinuclear Aluminum Complexes: An Immortal Approach
A series of aluminum complexes L<sup>a</sup>Al<sub>2</sub>Me<sub>4</sub> (<b>1</b>), L<sup>b</sup><sub>2</sub>Al<sub>4</sub>Me<sub>4</sub> (<b>2</b>), and L<sup>c</sup>Al<sub>2</sub>Me<sub>4</sub> (<b>3</b>) have been prepared
from the reaction of
AlMe<sub>3</sub> with Salan- and Salen-type ligands (L<sup>a</sup>H<sub>2</sub> = [2-OH-3,5-<i><sup>t</sup></i>Bu<sub>2</sub>-C<sub>6</sub>H<sub>2</sub>CH<sub>2</sub>N(CH<sub>3</sub>)]<sub>2</sub>-(<i>m</i>-phenylene); L<sup>b</sup>H<sub>4</sub> = [2-OH-3,5-<i><sup>t</sup></i>Bu<sub>2</sub>-C<sub>6</sub>H<sub>2</sub>CH<sub>2</sub>NH]<sub>2</sub>-(<i>m</i>-phenylene); L<sup>c</sup>H<sub>2</sub> = [2-OH-3,5-<i><sup>t</sup></i>Bu<sub>2</sub>-C<sub>6</sub>H<sub>2</sub>CHN]<sub>2</sub>-(<i>m</i>-phenylene)), respectively. All these complexes were characterized
by NMR spectroscopy, X-ray diffraction, and elemental analyses, with
complexes <b>1</b> and <b>3</b> adopting binuclear structures,
while complex <b>2</b> being tetranuclear. In the presence of
alcohol, the binuclear complexes <b>1</b> and <b>3</b> catalyzed controlled ring-opening homopolymerizations of both ε-CL
and l-LA. In the copolymerization experiments, complexes <b>1</b> and <b>2</b> produced tapered copolymers of ε-CL
and l-LA, while complex <b>3</b> was able to provide
ε-CL-<i>co</i>-l-LA with tendentially random
structure indicated by the average lengths of the caproyl and lactidyl
sequences (<i>L</i><sub>CL</sub> = 1.4; <i>L</i><sub>LA</sub> = 2.6). Particularly, addition of excess alcohol into
the catalytic system of complex <b>3</b> established the first
“immortal” copolymerization of ε-CL/l-LA, which accelerated the polymerization rates of both monomers
and, thus, afforded random copolymers with predictable molecular weights
and narrow molecular weight distributions
Programmable Hydrogels for Controlled Cell Catch and Release Using Hybridized Aptamers and Complementary Sequences
The ability to regulate cell–material interactions
is important
in various applications such as regenerative medicine and cell separation.
This study successfully demonstrates that the binding states of cells
on a hydrogel surface can be programmed by using hybridized aptamers
and triggering complementary sequences (CSs). In the absence of the
triggering CSs, the aptamers exhibit a stable, hybridized state in
the hydrogel for cell-type-specific catch. In the presence of the
triggering CSs, the aptamers are transformed into a new hybridized
state that leads to the rapid dissociation of the aptamers from the
hydrogel. As a result, the cells are released from the hydrogel. The
entire procedure of cell catch and release during the transformation
of the aptamers is biocompatible and does not involve any factor destructive
to either the cells or the hydrogel. Thus, the programmable hydrogel
is regenerable and can be applied to a new round of cell catch and
release when needed
Highly 3,4-Selective Living Polymerization of Isoprene and Copolymerization with ε‑Caprolactone by an Amidino N‑Heterocyclic Carbene Ligated Lutetium Bis(alkyl) Complex
The
amidino-modified N-heterocyclic carbene ligated lutetium bis(alkyl)
complex <b>1</b>, (Am-NHC)Lu(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>, was synthesized by treatment of (AmH-NHC-H)Br ((2,6-<sup><i>i</i></sup>PrC<sub>6</sub>H<sub>3</sub>NC(C<sub>6</sub>H<sub>5</sub>)NHCH<sub>2</sub>CH<sub>2</sub>(NCHCHN(C<sub>6</sub>H<sub>2</sub>Me<sub>3</sub>-2,4,6)CH)Br) with ((trimethylsilyl)methyl)lithium
(LiCH<sub>2</sub>SiMe<sub>3</sub>) and lutetium tris(alkyls) (Lu(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(THF)<sub>2</sub>) via double-deprotonation
reactions and characterized by NMR spectroscopy and X-ray diffraction
analysis. Under activation of an organoborate, complex <b>1</b> exhibited distinguished catalytic performance for the polymerization
of isoprene with respect to high activity, 3,4-regioselectivity (99.3%),
and livingness mode. In contrast to the systems reported to date,
this system seemed not to be affected obviously by the polymerization
temperature (0–80 °C), solvents, monomer-to-initiator
ratios (500–5000), and type of organoborate. The resultant
polymers have high glass-transition temperatures (38–48 °C)
and moderate syndiotacticity (racemic enchainment triad <i>rr</i> 45%, pentad <i>rrrr</i> 20%). In addition, the living
lutetium–polyisoprene active species could further initiate
the ring-opening polymerization of ε-caprolactone to give selectively
the poly(3,4-isoprene)-<i>b</i>-polycaprolactone block copolymers
with controllable molecular weight (from 4.9 × 10<sup>4</sup> to 10.2 × 10<sup>4</sup>) and narrow polydispersity
Aptamer-Based Polyvalent Ligands for Regulated Cell Attachment on the Hydrogel Surface
Natural
biomolecules are often used to functionalize materials
to achieve desired cell-material interactions. However, their applications
can be limited owing to denaturation during the material functionalization
process. Therefore, efforts have been made to develop synthetic ligands
with polyvalence as alternatives to natural affinity biomolecules
for the synthesis of functional materials and the control of cell-material
interactions. This work was aimed at investigating the capability
of a hydrogel functionalized with a novel polyvalent aptamer in inducing
cell attachment in dynamic flow and releasing the attached cells in
physiological conditions through a hybridization reaction. The results
show that the polyvalent aptamer could induce cell attachment on the
hydrogel in dynamic flow. Moreover, cell attachment on the hydrogel
surface was significantly influenced by the value of shear stress.
The cell density on the hydrogel was increased from 40 cells/mm<sup>2</sup> to nearly 700 cells/mm<sup>2</sup> when the shear stress
was decreased from 0.05 to 0.005 Pa. After the attachment onto the
hydrogel surface, approximately 95% of the cells could be triggered
to detach within 20 min by using an oligonucleotide complementary
sequence that displaced polyvalent aptamer strands from the hydrogel
surface. While it was found that the cell activity was reduced, the
live/dead staining results show that ≥98% of the detached cells
were viable. Therefore, this work has suggested that the polyvalent
aptamer is a promising synthetic ligand for the functionalization
of materials for regulated cell attachment