New article in The Journal of Physical Chemistry C
08 August 2024The Role of Boron Dopant in the Improvement of Electron Transfer in g-C3N4 Photocatalyst
Ewelina Wierzyńska, Klaudia Korytkowska, Krzysztof Kazimierczuk, Tomasz Łęcki, Kamila Zarębska, Krzysztof P. Korona, Marcin Pisarek, Bartosz Furtak, Magdalena Skompska
In this work, graphitic carbon nitride (g-C3N4) was doped with boron by thermal treatment with NaBH4. We have shown that the morphology of the modified polymer gradually changes from graphitic-like to amorphous, with increasing amounts of NaBH4 used for annealing. On the other hand, the boron doping has a very small influence on the band gap energy, as well as on the positions of the valence and conduction band edges of the polymer, but strongly improves the activity of g-C3N4 in the photocatalytic reduction of oxygen and degradation of methyl orange (8-fold increase of the degradation rate constant with respect to that of pure g-C3N4). The enhancement of the photocatalytic properties was explained by the increased rate of charge transport, both in the polymer plane and across the film, due to formation of N–B–N bonds between the adjacent heptazine units and the interlayer Coulomb interactions. The best photocatalytic activity was obtained for samples prepared from a mixture of g-C3N4 and NaBH4 at a moderate weight ratio (4:1), while increased amounts of NaBH4 led to significant and unfavorable changes in both the morphology and molecular structure of the polymer.
New Article in Journal of Biomolecular NMR
08 November 2021Clustered sparsity and Poisson-gap sampling
Paweł Kasprzak, Mateusz Urbańczyk, Krzysztof Kazimierczuk
Non-uniform sampling (NUS) is a popular way of reducing the amount of time taken by multidimensional NMR experiments. Among the various non-uniform sampling schemes that exist, the Poisson-gap (PG) schedules are particularly popular, especially when combined with compressed-sensing (CS) reconstruction of missing data points. However, the use of PG is based mainly on practical experience and has not, as yet, been explained in terms of CS theory. Moreover, an apparent contradiction exists between the reported effectiveness of PG and CS theory, which states that a “flat” pseudo-random generator is the best way to generate sampling schedules in order to reconstruct sparse spectra. In this paper we explain how, and in what situations, PG reveals its superior features in NMR spectroscopy. We support our theoretical considerations with simulations and analyses of experimental data from the Biological Magnetic Resonance Bank (BMRB). Our analyses reveal a previously unnoticed feature of many NMR spectra that explains the success of ”blue-noise” schedules, such as PG. We call this feature “clustered sparsity”. This refers to the fact that the peaks in NMR spectra are not just sparse but often form clusters in the indirect dimension, and PG is particularly suited to deal with such situations. Additionally, we discuss why denser sampling in the initial and final parts of the clustered signal may be useful.
New article in RSC Advances
Variable-temperature NMR spectroscopy for metabolite identification in biological materials
Ewa K. Nawrocka, Mateusz Urbańczyk, Kamil Koziński, Krzysztof Kazimierczuk
Nuclear magnetic resonance is a “workhorse technique” used in metabolomics, complementary to mass spectrometry. Unfortunately, only the most basic NMR methods are sensitive enough to allow fast medical screening. The most common of them, a simple 1H NMR, suffers from low dispersion of resonance frequencies, which often hampers the identification of metabolites. In this article we show that 1H NMR spectra contain previously overlooked parameters potentially helpful in metabolite identification, namely the rates of temperature-induced changes of chemical shifts. We prove that they are reproducible between various metabolite mixtures and can be determined quickly when Radon transform is used to process the data.
New article in Nanoscale
04 October 2021Development of a universal conductive platform for anchoring photo- and electroactive proteins using organometallic terpyridine molecular wiresResolution enhancement in NMR spectra by deconvolution with compressed sensing reconstruction
Margot Jacquet, Miriam Izzo, Silvio Osella, Sylwia Kozdra, Paweł P. Michałowski, Dariusz Gołowicz, Krzysztof Kazimierczuk, Maciej T. Gorzkowski, Adam Lewera, Marian Teodorczyk, Bartosz Trzaskowski, Rafał Jurczakowski, Daniel T. Gryko ORCID and Joanna Kargul
The construction of an efficient conductive interface between electrodes and electroactive proteins is a major challenge in the biosensor and bioelectrochemistry fields to achieve the desired nanodevice performance. Concomitantly, metallo-organic terpyridine wires have been extensively studied for their great ability to mediate electron transfer over a long-range distance. In this study, we report a novel stepwise bottom-up approach for assembling bioelectrodes based on a genetically modified model electroactive protein, cytochrome c553 (cyt c553) and an organometallic terpyridine (TPY) molecular wire self-assembled monolayer (SAM). Efficient anchoring of the TPY derivative (TPY-PO(OH)2) onto the ITO surface was achieved by optimising solvent composition. Uniform surface coverage with the electroactive protein was achieved by binding the cyt c553 molecules via the C-terminal His6-tag to the modified TPY macromolecules containing Earth abundant metallic redox centres. Photoelectrochemical characterisation demonstrates the crucial importance of the metal redox centre for the determination of the desired electron transfer properties between cyt and the ITO electrode. Even without the cyt protein, the ITO-TPY nanosystem reported here generates photocurrents whose densities are 2-fold higher that those reported earlier for ITO electrodes functionalised with the photoactive proteins such as photosystem I in the presence of an external mediator, and 30-fold higher than that of the pristine ITO. The universal chemical platform for anchoring and nanostructuring of (photo)electroactive proteins reported in this study provides a major advancement for the construction of efficient (bio)molecular systems requiring a high degree of precise supramolecular organisation as well as efficient charge transfer between (photo)redox-active molecular components and various types of electrode materials.
Special Issue of Magnetic Resonance in Chemistry
“Applications of Alternative Sampling Methods” guest-edited by Krzysztof Kazimierczuk
New Article in ChemComm
25 January 2021Resolution enhancement in NMR spectra by deconvolution with compressed sensing reconstruction
Krzysztof Kazimierczuk, Paweł Kasprzak, Panagiota S. Georgoulia, Irena Matečko-Burmann, Björn M. Burmann, Linnéa Isaksson, Emil Gustavsson, Sebastian Westenhoff and Vladislav Yu. Orekhov
NMR spectroscopy is one of the basic tools for molecular structure elucidation. Unfortunately, the resolution of the spectra is often limited by inter-nuclear couplings. The existing workarounds often alleviate the problem by trading it for another deficiency, such as spectral artefacts or difficult sample preparation and, thus, are rarely used. We suggest an approach using the coupling deconvolution in the framework of compressed sensing (CS) spectra processing that leads to a major increase in resolution, sensitivity, and overall quality of NUS reconstruction. A new mathematical description of the decoupling by deconvolution explains the effects of thermal noise and reveals a relation with the underlying assumption of the CS. The gain in resolution and sensitivity for challenging molecular systems is demonstrated for the key HNCA experiment used for protein backbone assignment applied to two large proteins: intrinsically disordered 441-residue Tau and a 509-residue globular bacteriophytochrome fragment. The approach will be valuable in a multitude of chemistry applications, where NMR experiments are compromised by the homonuclear scalar coupling.
