62 research outputs found
Influence of C–H···O Hydrogen Bonds on Macroscopic Properties of Supramolecular Assembly
For CH···O hydrogen
bonds in assembled structures and the applications, one of the critical
issues is how molecular spatial structures affect their interaction
modes as well as how to translate the different modes into the macroscopic
properties of materials. Herein, coumarin-derived isomeric hydrogelators
with different spatial structures are synthesized, where only nitrogen
atoms locate at the <i>ortho</i>, <i>meso</i>,
or <i>para</i> position in the pyridine ring. The gelators
can self-assemble into single crystals and nanofibrous networks through
CH···O interactions, which are greatly influenced by
nitrogen spatial positions in the pyridine ring, leading to the different
self-assembly mechanisms, packing modes, and properties of the nanofibrous
networks. Typically, different cell proliferation rates are obtained
on the different CH···O bonds driving nanofibrous structures,
implying that tiny variation of the stereo-position of nitrogen atoms
can be sensitively detected by cells. The study paves a novel way
to investigate the influence of isomeric molecular assembly on macroscopic
properties and functions of materials
Chiral Metal–Organic Framework Decorated with TEMPO Radicals for Sequential Oxidation/Asymmetric Cyanation Catalysis
A chiral
porous metal–organic framework (MOF) decorated with radicals
has been successfully constructed by cocrystallizing achiral (2,2,6,6-tetramethylpiperidin-1-yl)oxyl
(TEMPO)-substituted tricarboxylate and enantiopure VO(salen)-derived
dipyridine ligands. The chiral MOF can function as an efficient heterogeneous catalyst for the
sequential alcohol oxidation/asymmetric cyanation of aldehyde reactions
with enhanced activity and enantioselectivity compared to the homogeneous
counterpart
Supramolecular Engineering of Discrete Pt(II)···Pt(II) Interactions for Visible-Light Photocatalysis
Visible-light photosensitizers
have emerged as a sustainable and
environmentally friendly medium for organic transformation. Herein,
we have developed a supramolecular strategy for manipulating visible-light
photosensitization and photocatalytic efficiencies. With the elaborate
manipulation of aggregated Pt(II)···Pt(II) interactions,
the discrete tetranuclear Pt complexes not only show high binding
affinity (<i>K</i><sub>a</sub> ∼ 10<sup>6</sup> M<sup>–1</sup>) but also feature bathochromic-shifted metal–metal-to-ligand
charge transfer transitions. Both factors are crucial for their <sup>1</sup>O<sub>2</sub> generation capability upon low-energy visible-light
irradiation (λ ≥ 590 nm). More interestingly, when a
terpyridine moiety is embedded in the structure of a supramolecular
photosensitizer, breakup of tetranuclear Pt(II)···Pt(II)
complexation can be realized upon addition of Zn(OTf)<sub>2</sub>.
As a consequence, photo-oxidation of a secondary amine to the corresponding
imine can be deactivated and reactivated, via the sequential addition
of Zn(OTf)<sub>2</sub> and unsubstituted terpyridine as the competitive
ligand. Hence, the current study proves that intelligent visible-light
photocatalysts can be achieved via rational supramolecular design
Supramolecular Cross-Linking and Gelation of Conjugated Polycarbazoles via Hydrogen Bond Assisted Molecular Tweezer/Guest Complexation
Supramolecular cross-linking and
gelation represent a fascinating
approach to improve the performance of π-conjugated polymers.
Up to now, supramolecular π-conjugated polymer networks have
been mainly developed by grafting noncovalent recognition motifs onto
the side-chain of π-conjugated polymers. In comparison, much
less attention has been paid to the construction of main-chain-type
supramolecular polymer networks, in which π-conjugated polymers
themselves serve as the noncovalent linkages. Herein we have developed
a novel and efficient strategy to attain this objective. The design
principle is primarily on the basis of noncovalent molecular recognition
between bis[alkynylplatinum(II)]terpyridine molecular
tweezer receptor and <i>NH</i>-type carbazole guest, which
shows enhanced binding affinity due to the cooperative participation
of donor–acceptor and intermolecular N–H---N hydrogen-bonding
interactions. The “hydrogen-bond enhanced molecular tweezer/guest
recognition” strategy can be further applied for multivalent
complexation between π-conjugated polycarbazoles and homoditopic
molecular tweezer cross-linker, leading to the formation of main-chain-type
supramolecular polymer networks and gels with thermal and solvent
responsiveness. Hence, π-conjugated polymers can be endowed
with excellent processability via the supramolecular engineering approach,
which provides a new avenue toward flexible optoelectronic applications
Design and Assembly of Chiral Coordination Cages for Asymmetric Sequential Reactions
Supramolecular
nanoreactors featuring multiple catalytically active
sites are of great importance, especially for asymmetric catalysis,
and are yet challenging to construct. Here we report the design and
assembly of five chiral single- and mixed-linker tetrahedral coordination
cages using six dicarboxylate ligands derived-from enantiopure Mn(salen),
Cr(salen) and/or Fe(salen) as linear linkers and four Cp<sub>3</sub>Zr<sub>3</sub> clusters as three-connected vertices. The formation
of these cages was confirmed by a variety of techniques including
single-crystal and powder X-ray diffraction, inductively coupled plasma
optical emission spectrometer, quadrupole-time-of-flight mass spectrometry
and energy dispersive X-ray spectrometry. The cages feature a nanoscale
hydrophobic cavity decorated with the same or different catalytically
active sites, and the mixed-linker cage bearing Mn(salen) and Cr(salen)
species is shown to be an efficient supramolecular catalyst for sequential
asymmetric alkene epoxidation/epoxide ring-opening reactions with
up to 99.9% ee. The cage catalyst demonstrates improved activity and
enantioselectivity over the free catalysts owing to stabilization
of catalytically active metallosalen units and concentration of reactants
within the cavity. Manipulation of catalytic organic linkers in cages
can control the activities and selectivities, which may provide new
opportunities for the design and assembly of novel functional supramolecular
architectures
Receiver-operating characteristic curves to predict heart failure patients.
<p>(A), ROC curves of HSP70 for diagnosing stage B HF. (B), ROC curves of NT-proBNP for diagnosing stage B HF. HSP70 has a high sensitive cut-off value (2.72 ng/mL) in predicting stage B HF, while NT-proBNP hasn’t. (C), ROC curves of HSP70 for diagnosing stage C HF. (D), ROC curves of NT-proBNP for diagnosing stage C HF. NT-proBNP has a more sensitive cut-off value in diagnosing stage C HF (92.9%) while HSP70 has a more specific one (84.6%).</p
Mechanically Linked Poly[2]rotaxanes Constructed via the Hierarchical Self-Assembly Strategy
Mechanically linked poly[2]rotaxanes
have been successfully constructed
via the hierarchical self-assembly strategy. The integration of two
noninterfering noncovalent recognition motifs facilitates chain extension
of the B21C7-based [2]rotaxane monomer, demonstrating the capabilities
to form self-standing films with preferable transparency and softness
The expressions of HSP 70, HSP 90 and HSP 27 in the hearts from mice subjected to ISO or vehicle at 3days,7 days, 14days and 84 days.
<p>The levels of Hsp 70, Hsp 90 and Hsp 27 in hearts protein extracts were examined by Western blotting. A representative Western blot from three independent experiments is shown. EIF-5 was used as an internal control.</p
Chiral DHIP-Based Metal–Organic Frameworks for Enantioselective Recognition and Separation
Two chiral porous 2,3-dihydroimidazo[1,2-<i>a</i>]pyridine (DHIP)-based metal–organic frameworks
(MOFs) are assembled from an enantiopure dipyridyl-functionalized
DHIP bridging ligand. The Zn-DHIP MOF shows a good enantioseparation
performance toward aromatic sulfoxides, and the heterogeneous adsorbent
can be readily recovered and reused without significant degradation
of the separation performance
Multivariate Metal–Organic Frameworks as Multifunctional Heterogeneous Asymmetric Catalysts for Sequential Reactions
The search for versatile
heterogeneous catalysts with multiple
active sites for broad asymmetric transformations has long been of
great interest, but it remains a formidable synthetic challenge. Here
we demonstrate that multivariate metal–organic frameworks (MTV-MOFs)
can be used as an excellent platform to engineer heterogeneous catalysts
featuring multiple and cooperative active sites. An isostructural
series of 2-fold interpenetrated MTV-MOFs that contain up to three
different chiral metallosalen catalysts was constructed and used as
efficient and recyclable heterogeneous catalysts for a variety of
asymmetric sequential alkene epoxidation/epoxide ring-opening reactions.
Interpenetration of the frameworks brings metallosalen units adjacent
to each other, allowing cooperative activation, which results in improved
efficiency and enantioselectivity over the sum of the individual parts.
The fact that manipulation of molecular catalysts in MTV-MOFs can
control the activities and selectivities would facilitate the design
of novel multifunctional materials for enantioselective processes
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