Metal-organic frameworks offer tremendous potential for efficient separation of molecular mixtures. Different pore sizes and suitable functionalizations of the framework allow for an adjustment of the static selectivity. Here we report membranes which offer dynamic control of the selectivity by remote signals, thus enabling a continuous adjustment of the permeate flux. This is realized by assembling linkers containing photoresponsive azobenzene-side-groups into monolithic, crystalline membranes of metal-organic frameworks. The azobenzene moieties can be switched from the trans to the cis configuration and vice versa by irradiation with ultraviolet or visible light, resulting in a substantial modification of the membrane permeability and separation factor. The precise control of the cis:trans azobenzene ratio, for example, by controlled irradiation times or by simultaneous irradiation with ultraviolet and visible light, enables the continuous tuning of the separation. For hydrogen:carbon-dioxide, the separation factor of this smart membrane can be steplessly adjusted between 3 and 8.
Photoconductivity is ac haracteristic property of semi-conductors.H erein, we present ap hoto-conducting crystalline metal-organic framework (MOF) thin film with an on-off photocurrent ratio of two orders of magnitude.These oriented, surface-mounted MOF thin films (SURMOFs), contain porphyrin in the framework backbone and C 60 guests,l oaded in the pores using al ayer-by-layer process.B y comparison with results obtained for reference MOF structures and based on DFT calculations,w ec onclude that donoracceptor interactions between the porphyrin of the host MOF and the C 60 guests give rise to ar apid charge separation. Subsequently,h oles and electrons are transported through separate channels formed by porphyrin and by C 60 ,r espectively.The ability to tune the properties and energy levels of the porphyrin and fullerene,a long with the controlled organization of donor-acceptor pairs in this regular framework offers potential to increase the photoconduction on-off ratio.
Sulfonamide antibiotics undergo transformation in the aquatic environment through biodegradation, photolysis, or hydrolysis. In this study, the residual antibacterial activity of 11 transformation products (TPs) of sulfamethoxazole (SMX) was investigated with regard to their in vitro growth and luminescence inhibition on Vibrio fischeri (30 min and 24 h exposure). Two transformation products, 4-hydroxy-SMX and N(4)-hydroxy-acetyl-SMX, were synthesized in-house and confirmed by nuclear magnetic resonance and high-resolution mass spectrometry. Results of individual compound experiments showed that TPs modified at the para amino group still exhibit clear antibacterial effects, whereas TPs resulting from breakdown of the SMX structure lost this mechanism of action. 4-NO2- and 4-OH-SMX were found to inhibit growth to a clearly greater extent than the parent compound, SMX. In contrast, the N(4)-acetyl- and N(4)-hydroxy-acetyl-derivatives retain less than 10 and 5% of the effect of SMX on growth and luminescence inhibition, respectively. The effect of a mixture of para-modified TPs was observed to be additive. Considering the homologous series of sulfa drugs widely prescribed and their common mechanism of action, the potential environmental impact must consider the total amount of sulfonamide antibiotics and their derivative TPs, which might end up in a water body. Extrapolating the results obtained here for the para TPs of SMX to other sulfa drugs and determining the persistence and occurrence of these compounds in the aquatic environment is required for improved risk assessment.
Development of surface coatings with high antimicrobial activity is urgently required to fight bacteria and other microorganisms on technical and hygiene relevant surfaces. Control over structure and topology of the surface coatings, combined with the ability to include functional molecules within the structure, is crucial for optimizing their performance. Herein, we describe a novel strategy to synthesize structurally well-defined porphyrin polymer thin films via a template approach. In this approach, bisazido-functionalized porphyrin molecules are preorganized within a metal-organic framework (MOF) structure. Afterward, porphyrin units within the MOF are covalently connected via a secondary linker. Removal of the metal ions of the MOF results in water-stable porphyrin polymer thin films that demonstrate high antibacterial activity against pathogens via visible-light-promoted generation of reactive oxygen species. In addition, this approach offers the inherent possibility to incorporate guest molecules within the structures, to functionalize the surface with biomolecules, and to create hierarchically structured materials.
Metal-organic frameworks, MOFs,a re ac lass of crystalline porous metal-organic hybrid materials which have originally been developed for applications in gas storage and separation. Here, we demonstrate that due to the enormous chemical flexibility of these molecular materials, they also provide an excellent basis for the development of photoresist materials. In particular, we used an epitaxialp rocess with automated systems to grow either homogeneous or patterned SURMOFs (surface-anchored MOFs)o ft he type [Zn 2 (N 3 BPDC) 2 (Dabco)] on different solid substrates. The huge flexibility of the MOF chemistry allowed for different variants of photolithography based on the post-synthesis modification( PSM) of the MOF materials. Here, two particu-lar and popular PSM-strategies were employed, the azidealkyne click reaction and thiol-yne click chemistry.T he azide-alkyne click reactionw as initiated by the photoreduction of Cu II to the active Cu I catalyst, whereas the thiol-yne click chemistry was induced directly by UV light. Furthermore,h eteroepitaxial growth of multilayer systems (Cu-N 3 BPDC + Cu-BPDC + Cu-N 3 BPDC + Cu-BPDC + Cu-N 3 BPDC + Cu-BPDC) was also used to control the localizationo fs ubsequent PSM. The resultsd emonstrated that the patterned functionalization of MOF thin film is not limited to the two dimensions of the mounting surface buti si ndeed possible in 3D.
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