47 research outputs found
Improving Fatigue Resistance of Dihydropyrene by Encapsulation within a Coordination Cage
Photochromic molecules undergo reversible isomerization upon irradiation with light at different wavelengths, a process that can alter their physical and chemical properties. For instance, dihydropyrene (DHP) is a deep-colored compound that isomerizes to light-brown cyclophanediene (CPD) upon irradiation with visible light. CPD can then isomerize back to DHP upon irradiation with UV light or thermally in the dark. Conversion between DHP and CPD is thought to proceed via a biradical intermediate; bimolecular events involving this unstable intermediate thus result in rapid decomposition and poor cycling performance. Here, we show that the reversible isomerization of DHP can be stabilized upon confinement within a PdII6L4 coordination cage. By protecting this reactive intermediate using the cage, each isomerization reaction proceeds to higher yield, which significantly decreases the fatigue experienced by the system upon repeated photocycling. Although molecular confinement is known to help stabilize reactive species, this effect is not typically employed to protect reactive intermediates and thus improve reaction yields. We envisage that performing reactions under confinement will not only improve the cyclic performance of photochromic molecules, but may also increase the amount of product obtainable from traditionally low-yielding organic reactions
Reticular synthesis and the design of new materials
The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62718/1/nature01650.pd
The development of CD4 binding site antibodies during HIV-1 infection.
Broadly neutralizing antibodies to the CD4 binding site (CD4bs) of gp120 are generated by some HIV-1-infected individuals, but little is known about the prevalence and evolution of this antibody response during the course of HIV-1 infection. We analyzed the sera of 113 HIV-1 seroconverters from three cohorts for binding to a panel of gp120 core proteins and their corresponding CD4bs knockout mutants. Among sera collected between 99 and 258 weeks post-HIV-1 infection, 88% contained antibodies to the CD4bs and 47% contained antibodies to resurfaced stabilized core (RSC) probes that react preferentially with broadly neutralizing CD4bs antibodies (BNCD4), such as monoclonal antibodies (MAbs) VRC01 and VRC-CH31. Analysis of longitudinal serum samples from a subset of 18 subjects revealed that CD4bs antibodies to gp120 arose within the first 4 to 16 weeks of infection, while the development of RSC-reactive antibodies was more varied, occurring between 10 and 152 weeks post-HIV-1 infection. Despite the presence of these antibodies, serum neutralization mediated by RSC-reactive antibodies was detected in sera from only a few donors infected for more than 3 years. Thus, CD4bs antibodies that bind a VRC01-like epitope are often induced during HIV-1 infection, but the level and potency required to mediate serum neutralization may take years to develop. An improved understanding of the immunological factors associated with the development and maturation of neutralizing CD4bs antibodies during HIV-1 infection may provide insights into the requirements for eliciting this response by vaccination
Crystal Engineering of “Porphyrin Sieves” Based on Coordination Polymers of Pd- and Pt-tetra(4-carboxyphenyl)porphyrin
Synthesis and characterization of new tetra-substituted porphyrins with exo-donor carboxylic groups as building blocks for supramolecular architectures: Catalytic and structural studies of their metalated derivatives
Design of Pyroelectric Mixed Crystals Having a Varying Degree of Polarity: The l‑Asparagine·H<sub>2</sub>O/l‑Aspartic Acid System
As part of an ongoing program on
the design of functional materials
with a varying degree of polarity, we investigated the processes of
conversion of a nonpolar host, l-asparagine monohydrate crystal
(space group <i>P</i>2<sub>1</sub>2<sub>1</sub>2<sub>1</sub>), into a conglomerate of mixed polar sectors when grown in the presence
of varying amounts of l-aspartic acid guest at the glass–aqueous/solution
interface. The structure, composition, and the reduction of symmetry
of the mixed crystals were confirmed with pyroelectric coefficient
measurements, X-ray diffraction, and HPLC analysis and supported by
atom–atom potential energy computations. The pyroelectricity
measured at the (010) and (01Ě…0) faces imply the formation of
hybrid crystals with top and bottom parts having opposite polarities.
Pyroelectric coefficients measured at these two faces as a function
of the occluded guest concentration increase linearly up to 8 wt %/wt
of guest, followed by an enhancement of polarity at 8–12 wt
%/wt of guest and subsequent reduction upon an increase up to 16 wt
%/wt of guest. An interpretation of the magnitude of the pyroelectric
effect on guest concentration is proposed
Supramolecular Crystal Chemistry with Porphyrin Tinkertoys. Hydrogen-Bonding and Coordination Networks with the “Chair” and “Table” Conformers of Tetra(3-carboxyphenyl)porphyrin
Disequilibrating azobenzenes by visible-light sensitization under confinement
Photoisomerization of azobenzenes from their stable E isomer to the metastable Z state is the basis of numerous applications of these molecules. However, this reaction typically requires ultraviolet light, which limits applicability. In this study, we introduce disequilibration by sensitization under confinement (DESC), a supramolecular approach to induce the E-to-Z isomerization by using light of a desired color, including red. DESC relies on a combination of a macrocyclic host and a photosensitizer, which act together to selectively bind and sensitize E-azobenzenes for isomerization. The Z isomer lacks strong affinity for and is expelled from the host, which can then convert additional E-azobenzenes to the Z state. In this way, the host–photosensitizer complex converts photon energy into chemical energy in the form of out-of-equilibrium photostationary states, including ones that cannot be accessed through direct photoexcitation