RESUMEN
An m-phthalic diamide-linked bisporphyrin with a benzylamide substituent has been designed and synthesized. It has two types of carbonyl groups. In the solution of this zinc bisporphyrinate, these carbonyl groups are involved in the formation of two different Zn-O coordination interactions: one is formed between neighboring zinc bisporphyrinates; another is formed within zinc bisporphyrinate. The chirality sensing abilities of this zinc porphyrinate to a number of chiral monoamines have been examined. When zinc bisporphyrinate was mixed with a series of chiral monoamines, the signs of the circular dichroism spectra for the chiral monoamines of the same handedness with an aryl group as the substituent are just opposite to those with an alkyl group as the substituent. NMR studies reveal that stepwise coordinations lead to 1:1 and 1:2 host-guest complexes. The structure of the 1:1 host-guest complex was confirmed by crystallography, it is the first time that a 1:1 host-guest complex formed between zinc bisporphyrinate and a chiral monoamine has been crystallographically characterized. The structure reveals that there is an intramolecular hydrogen bond between the amide oxygen and the coordinated NH2. We further investigated the chirality transfer mechanism by density functional theory calculations. Our studies suggest that the interactions between the linker and guests in this bisporphyrin system are crucial in the chirality transfer process, and the nature of the bulkiest substituent of chiral monoamines makes a difference. For R-type guests, with an alkyl group, the steric repulsion makes the conformer A more energetically favorable, which leads to the anticlockwise twist and negative Cotton effect. However, with an aryl group, the π-π interaction makes the conformer B more energetically favorable, which leads to the clockwise twist and positive Cotton effect.
RESUMEN
A zinc trisporphyrinate has been developed as a chirality sensor for chiral mono-alcohols. In its structure, there are two "spaces" surrounded by three porphyrin moieties, which allow guests to fill in. It has shown extremely high CD sensitivity for a chiral mono-alcohol with a naphthyl substituent, 1-(1-naphthyl)ethanol, at µM level, which is at least three orders of magnitude lower concentration than previous reports. A crystallographic study of the host-guest complex reveals the binding of 1-(1-naphthyl)ethanol to the zinc trisporphyrinate is greatly enhanced by multipoint interactions, such as coordination interactions, hydrogen bonding, π-π and CH···π interactions etc. Spectroscopic studies suggest the corresponding binding constant K1 is over 105 M-1, which is two or three orders of magnitude larger than other mono-alcohols. Among porphyrin systems, this trisporphyrin have the strongest binding affinity for 1-(1-naphthyl)ethanol, which leads to the highest CD sensitivity.
RESUMEN
Although the sophisticated Langmuir and Langmuir-Blodgett (LB) techniques facilitate the fabrication of uniform ultrathin monolayer and films, they are also revealed as powerful tools for the bottom-up construction of the nanostructures through the air/water interface. In this paper, unique nanoflowers or nanospheres were constructed based on the synthesized m-phthalic diamide-linked zinc bisporphyrinate tweezers using the Langmuir and LB techniques. It was found that the two tweezer-type zinc bisporphyrinates could form stable two-dimensional spreading films at the air/water interface, which could be subsequently transferred onto solid substrates using the vertical lifting method. Atomic force microscopy (AFM) revealed that at the initial spreading stage, the compound formed flat disklike domains and then hierarchically evolved into nanoflowers or nanospheres upon compressing the floating film. Such nanostructures have not been reported before and cannot be fabricated using the other self-assembly methods.
