Tomasz Ratajczyk

Bio: Tomasz Ratajczyk is an academic researcher from Polish Academy of Sciences. The author has contributed to research in topics: Nuclear magnetic resonance spectroscopy & Catalysis. The author has an hindex of 11, co-authored 31 publications receiving 288 citations.

Synthesis, solid-state NMR characterization, and application for hydrogenation reactions of a novel Wilkinson's-type immobilized catalyst.

Abstract: Silica nanoparticles (SiNPs) were chosen as a solid support material for the immobilization of a new Wilkinson's-type catalyst. In a first step, polymer molecules (poly(triphenylphosphine)ethylene (PTPPE); 4-diphenylphosphine styrene as monomer) were grafted onto the silica nanoparticles by surface-initiated photoinferter-mediated polymerization (SI-PIMP). The catalyst was then created by binding rhodium (Rh) to the polymer side chains, with RhCl(3)xH(2)O as a precursor. The triphenylphosphine units and rhodium as Rh-I provide an environment to form Wilkinson's catalyst-like structures. Employing multinuclear (P-31, Si-29, and C-13) solid-state NMR spectroscopy (SSNMR), the structure of the catalyst bound to the polymer and the intermediates of the grafting reaction have been characterized. Finally, first applications of this catalyst in hydrogenation reactions employing para-enriched hydrogen gas (PHIP experiments) and an assessment of its leaching properties are presented.

NMR Signal Enhancement by Effective SABRE Labeling of Oligopeptides

Abstract: Signal amplification by reversible exchange (SABRE) can enhance nuclear magnetic resonance signals by several orders of magnitude. However, until now this was limited to a small number of model target molecules. Here, a new convenient method for SABRE activation applicable to a variety of synthetic model oligopeptides is demonstrated. For the first time, a highly SABRE-active pyridine-based biocompatible molecular framework is incorporated into synthetic oligopeptides. The SABRE activity is preserved, demonstrating the importance of such earmarking. Finally, a crucial exchange process responsible for SABRE activity is identified and discussed.

Monitoring Hydrogenation Reactions using Benchtop 2D NMR with Extraordinary Sensitivity and Spectral Resolution

Abstract: Low-field benchtop nuclear magnetic resonance (BT-NMR) spectrometers with Halbach magnets are being increasingly used in science and industry as cost-efficient tools for the monitoring of chemical reactions, including hydrogenation. However, their use of low-field magnets limits both resolution and sensitivity. In this paper, we show that it is possible to alleviate these two problems through the combination of parahydrogen-induced polarization (PHIP) and fast correlation spectroscopy with time-resolved non-uniform sampling (TR-NUS). PHIP can enhance NMR signals so that substrates are easily detectable on BT-NMR spectrometers. The interleaved acquisition of one- and two-dimensional spectra with TR-NUS provides unique insight into the consecutive moments of hydrogenation reactions, with a spectral resolution unachievable in a standard approach. We illustrate the potential of the technique with two examples: the hydrogenation of ethylphenyl propiolate and the hydrogenation of a mixture of two substrates - ethylphenyl propiolate and ethyl 2-butynoate.

Application of Parahydrogen-Induced Polarization to Unprotected Dehydroamino Carboxylic Acids

Abstract: One focus of current nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) investigation is the hyperpolarization of biologically relevant substrates In this study, the application of parahydrogen-induced polarization (PHIP) to amino carboxylic acids was enabled by protonation of the amino group as well as of the carboxylic acid Due to the donor character of these functional groups, they usually act as ligands at the active catalytic sites To enable parahydrogenation, blocking of the catalytic sites by the functional groups has to be avoided In a new approach, this was realized via protonation of the starting material For the first time PHIP spectra of allylglycine, vigabatrin and γ-amino-butyric acid (GABA) were generated The feasibility of the hydrogenation of amino carboxylic acids without using a protection group supersedes the deprotection reaction usually required Hence, hydrogenation after protonation of the substrate opens the class of free dehydroamino carboxylic acids to PHIP

Image Processing

Abstract: MUCKE aims to mine a large volume of images, to structure them conceptually and to use this conceptual structuring in order to improve large-scale image retrieval. The last decade witnessed important progress concerning low-level image representations. However, there are a number problems which need to be solved in order to unleash the full potential of image mining in applications. The central problem with low-level representations is the mismatch between them and the human interpretation of image content. This problem can be instantiated, for instance, by the incapability of existing descriptors to capture spatial relationships between the concepts represented or by their incapability to convey an explanation of why two images are similar in a content-based image retrieval framework. We start by assessing existing local descriptors for image classification and by proposing to use co-occurrence matrices to better capture spatial relationships in images. The main focus in MUCKE is on cleaning large scale Web image corpora and on proposing image representations which are closer to the human interpretation of images. Consequently, we introduce methods which tackle these two problems and compare results to state of the art methods. Note: some aspects of this deliverable are withheld at this time as they are pending review. Please contact the authors for a preview.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

Abstract: The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ev...

Dynamic nuclear polarization with a rigid biradical

Abstract: A new polarizing agent with superior performance in dynamic nuclear polarization experiments is introduced, and utilizes two TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) moieties connected through a rigid spiro tether (see structure). The observed NMR signal intensities were enhanced by a factor of 1.4 compared to those of TOTAPOL, a previously described TEMPO-based biradical with a flexible tether.

Parahydrogen-Based Hyperpolarization for Biomedicine

Abstract: Magnetic resonance (MR) is one of the most versatile and useful physical effects used for human imaging, chemical analysis, and the elucidation of molecular structures. However, its full potential is rarely used, because only a small fraction of the nuclear spin ensemble is polarized, that is, aligned with the applied static magnetic field. Hyperpolarization methods seek other means to increase the polarization and thus the MR signal. A unique source of pure spin order is the entangled singlet spin state of dihydrogen, parahydrogen (pH2 ), which is inherently stable and long-lived. When brought into contact with another molecule, this "spin order on demand" allows the MR signal to be enhanced by several orders of magnitude. Considerable progress has been made in the past decade in the area of pH2 -based hyperpolarization techniques for biomedical applications. It is the goal of this Review to provide a selective overview of these developments, covering the areas of spin physics, catalysis, instrumentation, preparation of the contrast agents, and applications.