Two new isostructural microporous coordination frameworks Mn3(Hpdc)2(pdc)2 (1) and Mg3(Hpdc)2(pdc)2 (2) (pdc2– = pyridine-2,4-dicarboxylate) showing primitive cubic (pcu) topology have been ...prepared and characterized. The pore aperture of the channels is too narrow for the efficient adsorption of N2; however, both compounds demonstrate substantially higher uptake of CO2 (119.9 mL·g–1 for 1 and 102.5 mL·g–1 for 2 at 195 K, 1 bar). Despite of their structural similarities, 2 shows a typical reversible type I isotherm for adsorption/desorption of CO2, while 1 features a two-step adsorption process with a very broad hysteresis between the adsorption and desorption curves. This behavior can be explained by a combination of density functional theory calculations, sorption, and X-ray diffraction analysis and gives insights into the further development of new sorbents showing adsorption/desorption hysteresis.
Fluorescence resonance energy transfer (FRET) enables photosynthetic light harvesting, wavelength downconversion in light-emitting diodes (LEDs), and optical biosensing schemes. The rate and ...efficiency of this donor to acceptor transfer of excitation between chromophores dictates the utility of FRET and can unlock new device operation motifs including quantum-funnel solar cells, non-contact chromophore pumping from a proximal LED, and markedly reduced gain thresholds. However, the fastest reported FRET time constants involving spherical quantum dots (0.12-1 ns; refs 7-9) do not outpace biexciton Auger recombination (0.01-0.1 ns; ref. 10), which impedes multiexciton-driven applications including electrically pumped lasers and carrier-multiplication-enhanced photovoltaics. Few-monolayer-thick semiconductor nanoplatelets (NPLs) with tens-of-nanometre lateral dimensions exhibit intense optical transitions and hundreds-of-picosecond Auger recombination, but heretofore lack FRET characterizations. We examine binary CdSe NPL solids and show that interplate FRET (∼6-23 ps, presumably for co-facial arrangements) can occur 15-50 times faster than Auger recombination and demonstrate multiexcitonic FRET, making such materials ideal candidates for advanced technologies.
Precise nanoscale distance measurements by pulsed electron paramagnetic resonance (EPR) spectroscopy play a crucial role in structural studies of biomolecules. The properties of the spin labels used ...in this approach determine the sensitivity limits, attainable distances, and proximity to biological conditions. Herein, we propose and validate the use of photoexcited fullerenes as spin labels for pulsed dipolar (PD) EPR distance measurements. Hyperpolarization and the narrower spectrum of fullerenes compared to other triplets (e.g., porphyrins) boost the sensitivity, and superior relaxation properties allow PD EPR measurements up to a near‐room temperature. This approach is demonstrated using fullerene–nitroxide and fullerene–triarylmethyl pairs, as well as a supramolecular complex of fullerene with nitroxide‐labeled protein. Photoexcited triplet fullerenes can be considered as new spin labels with outstanding spectroscopic properties for future structural studies of biomolecules.
Excited and exciting: Photoexcited triplet fullerenes can be successfully used for nanoscale distance measurements in biomolecules by pulsed dipolar electron paramagnetic resonance spectroscopy. They feature outstanding spectroscopic properties as spin labels, provide drastic signal enhancement compared to all known alternatives, and are applicable up to near room temperatures.
Triplet states of photoexcited organic molecules are promising spin labels with advanced spectroscopic properties for pulsed dipolar electron paramagnetic resonance (PD EPR) spectroscopy. Recently ...proposed triplet fullerene labels have shown great potential for double electron-electron resonance (DEER) distance measurements as "observer spins" due to a high quantum yield of the triplet state, hyperpolarization and relatively narrow EPR spectra. Here, we demonstrate the applicability of fullerene labels to other PD EPR techniques, such as relaxation induced dipolar modulation enhancement (RIDME) and laser induced magnetic dipolar spectroscopy (LaserIMD). In particular, a specific contaminating signal in LaserIMD experiments was observed, explained and mitigated. Comparative analyses of the signal-to-noise (SNR) ratios were performed for all employed methods. DEER on the fullerene-triarylmethyl pair shows the best performance, which allows state-of-the-art DEER acquisition at 100 nM with a SNR of ∼35 within reasonable 42 hours.
Recently, a new type of spin labels based on photoexcited triplet molecules was proposed for nanometer scale distance measurements by pulsed dipolar electron paramagnetic resonance (PD EPR). However, ...such molecules are also actively used within biological complexes as photosensitizers for photodynamic therapy (PDT) of cancer. Up to date, the idea of using the photoexcited triplets simultaneously as PDT agents and as spin labels for PD EPR has never been employed. In this work, we demonstrate that PD EPR in conjunction with other methods provides valuable information on the structure and function of PDT candidate complexes, exemplified here with porphyrins bound to human serum albumin (HSA). Two distinct porphyrins with different properties were used: amphiphilic meso-tetrakis(4-hydroxyphenyl)porphyrin (mTHPP) and water soluble cationic meso-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4); HSA was singly nitroxide-labeled to provide a second tag for PD EPR measurements. We found that TMPyP4 locates in a cavity at the center of the four-helix bundle of HSA subdomain IB, close to the interface with solvent, thus being readily accessible to oxygen. As a result, the photolysis of the complex leads to photooxidation of HSA by generated singlet oxygen and causes structural perturbation of the protein. Contrary, in case of mTHPP porphyrin, the binding occurs at the proton-rich pocket of HSA subdomain IIIA, where the access of oxygen to a photosensitizer is hindered. Structural data of PD EPR were supported by other EPR techniques, laser flash photolysis and protein photocleavage studies. Therefore, pulsed EPR on complexes of proteins with photoexcited triplets is a promising approach for gaining structural and functional insights into such PDT agents.
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•Pulsed dipolar EPR provides valuable information on the structure and function of PDT candidate complexes.•Complexes of human serum albumin (HSA) with two porphyrins (mTHPP and TMPyP4) are investigated.•TMPyP4 locates in HSA subdomain IB, close to the interface with solvent and its photolysis causes oxidation of HSA.•mTHPP locates at the proton-rich pocket of HSA subdomain IIIA.
Catalytic properties of Fe-MIL-101 and Cr-MIL-101 metal-organic frameworks in the solvent-free oxidation of cyclohexene and alpha-pinene with molecular oxygen have been explored. Both catalysts allow ...alkene oxidation under mild conditions (1 bar O-2, 40-60 degrees C) and afford allylic oxidation products. The nature of catalysis and the product distribution strongly depend on the nature of the transition metal. Cr-MIL-101 behaves as truly heterogeneous catalyst to give predominantly alpha,beta-unsaturated ketones. Catalysis over Fe-MIL-101 has true heterogeneous nature only at 40 degrees C, producing mainly 2-cyclohexene-1-ol. At 50-60 degrees C, iron leaching into solution occurs, leading to cyclohexenyl hydroperoxide as the major product. Under optimal conditions, both catalysts can be reused several times without suffering a loss of the catalytic properties. Rate-retarding and rate-accelerating effects of inhibitors and initiators, respectively, indicate radical chain mechanism. Different pathways for transformation of hydroperoxide have been suggested to rationalize the observed differences in the reaction selectivities over Cr- and Fe-MIL-101.
The review surveys new data on the directed construction of supramolecular organic–inorganic compounds from macrocyclic cavitand cucurbit6uril (C
)and mono- and polynuclear aqua complexes. Due to the ...presence of polarized carbonyl groups, cucurbit6uril forms strong complexes with alkali, alkaline earth and rare-earth metal ions, and hydrogen-bonded supramolecular adducts with cluster and polynuclear aqua complexes of transitional metals. A wide variety of supramolecular compounds and their unique structures are described.
The features of previously unexplored labile complexes of human 40S ribosomal subunits with RNAs, whose formation is manifested in the cross-linking of aldehyde derivatives of RNAs to the ribosomal ...protein uS3 through its peptide 55-64 located outside the mRNA channel, were studied by EPR spectroscopy methods. Analysis of subatomic 40S subunit models showed that a likely site for labile RNA binding is a cluster of positively charged amino acid residues between the mRNA entry site and uS3 peptide 55-64. This is consistent with our finding that the 3'-terminal mRNA fragment hanging outside the 40S subunit prevents the cross-linking of an RNA derivative to this peptide. To detect labile complexes of 40S subunits with RNA by DEER/PELDOR spectroscopy, an undecaribonucleotide derivative with nitroxide spin labels at terminal nucleotides was utilized. We demonstrated that the 40S subunit channel occupancy with mRNA does not affect the RNA derivative binding and that uS3 peptide 55-64 is not involved in binding interactions. Replacing the RNA derivative with a DNA one revealed the importance of ribose 2'-OH groups for the complex formation. Using the single-label RNA derivatives, the distance between the mRNA entry site and the loosely bound RNA site on the 40S subunit was estimated.
Using the reactions of copper(II) acetate magnesium(II) oxide with 2-furancarboxylic acid (HFur), compounds with chemical compositions Cu
2
(Fur)
4
(MeCN)
2
(
I
) and Mg
2
(Fur)
4
(H
2
O)
5
∙ MeCN∙H
...2
O (
II
) are synthesized. According to the X-ray diffraction data (CIF files CCDC nos. 2085817 (
I
) and 2085818 (
II
)), both complexes have a binuclear structure. The metal core of
I
correspond to the tetracarboxylate bridged {Cu
2
(μ-Fur)
4
} complex, the coordination number of the copper atom in which is 5 (CuNO
4
); in
II
, the metal atoms are linked by two carboxylate groups and a water molecule, and the coordination environment of the metal centers is completed to the polyhedron (MgO
6
) by oxygen atoms of the Fur
–
anions and water molecules. According to EPR spectroscopy data, exchange-coupled copper(II) dimers with a substantial zero-field splitting are observed in
I
. For
I
and
II
, antibacterial activity against the nonpathogenic strain of
M. smegmatis
, and cytotoxicity against human ovarian adenocarcinoma cells
SCOV3
and normal human fibroblast cells of the
HDF
line have been determined.
We report herein a family of polynuclear complexes, Au@Ag4(Py3P)4X5 and Au@Cu4(Py3P)4X5 X = NO3, ClO4, OTf, BF4, SbF6, containing unprecedented Au-centered Ag4 and Cu4 tetrahedral cores supported ...by tris(2-pyridyl)phosphine (Py3P) ligands. The Au@Ag45+ clusters are synthesized via controlled substitution of the central Ag(I) ion in all-silver Ag@Ag45+ precursors by the reaction with Au(tht)Cl, while the Au@Cu45+ cluster is assembled through the treatment of a pre-organized Au(Py3P)4+ metallo-ligand with 4 equiv of a Cu(I) source. The structure of the Au@M4 clusters has been experimentally and theoretically investigated to reveal very weak intermolecular Au–M metallophilic interactions. At ambient temperature, the designed compounds emit a modest turquoise-to-yellow luminescence with microsecond lifetimes. Based on the temperature-dependent photophysical experiments and DFT/TD-DFT computations, the emission observed has been assigned to an MLCT or LLCT type depending on composition of the cluster core.
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