Publications by authors named "Alexey Popov"

229 Publications

Magnetic Hysteresis at 10 K in Single Molecule Magnet Self-Assembled on Gold.

Adv Sci (Weinh) 2021 Mar 21;8(5):2000777. Epub 2021 Jan 21.

Leibniz Institute for Solid State and Materials Research Helmholtzstraße 20 Dresden 01069 Germany.

Tremendous progress in the development of single molecule magnets (SMMs) raises the question of their device integration. On this route, understanding the properties of low-dimensional assemblies of SMMs, in particular in contact with electrodes, is a necessary but difficult step. Here, it is shown that fullerene SMM self-assembled on metal substrate from solution retains magnetic hysteresis up to 10 K. Fullerene-SMM DyScN@C and DyScN@C are derivatized to introduce a thioacetate group, which is used to graft SMMs on gold. Magnetic properties of grafted SMMs are studied by X-ray magnetic circular dichroism and compared to the films of nonderivatized fullerenes prepared by sublimation. In self-assembled films, the magnetic moments of the Dy ions are preferentially aligned parallel to the surface, which is different from the disordered orientation of endohedral clusters in nonfunctionalized fullerenes. Whereas chemical derivatization reduces the blocking temperature of magnetization and narrows the hysteresis of DyScN@C, for DyScN@C equally broad hysteresis is observed as in the fullerene multilayer. Magnetic bistability in the DyScN@C grafted on gold is sustained up to 10 K. This study demonstrates that self-assembly of fullerene-SMM derivatives offers a facile solution-based procedure for the preparation of functional magnetic sub-monolayers with excellent SMM performance.
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http://dx.doi.org/10.1002/advs.202000777DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7927621PMC
March 2021

Magnetic hysteresis and strong ferromagnetic coupling of sulfur-bridged Dy ions in clusterfullerene DyS@C.

Inorg Chem Front 2020 Oct 29;7(19):3521-3532. Epub 2020 Jul 29.

Leibniz Institute for Solid State and Materials Research, Helmholtzstraße 20, 01069 Dresden, Germany.

Two isomers of metallofullerene DyS@C with sulfur-bridged Dy ions exhibit broad magnetic hysteresis with sharp steps at sub-Kelvin temperature. Analysis of the level crossing events for different orientations of a magnetic field showed that even in powder samples, the hysteresis steps caused by quantum tunneling of magnetization can provide precise information on the strength of intramolecular Dy⋯Dy inter-actions. A comparison of different methods to determine the energy difference between ferromagnetic and antiferromagnetic states showed that sub-Kelvin hysteresis gives the most robust and reliable values. The ground state in DyS@C has ferromagnetic coupling of Dy magnetic moments, whereas the state with antiferromagnetic coupling in and cage isomers is 10.7 and 5.1 cm higher, respectively. The value for the isomer is among the highest found in metallofullerenes and is considerably larger than that reported in non-fullerene dinuclear molecular magnets. Magnetization relaxation times measured in zero magnetic field at sub-Kelvin temperatures tend to level off near 900 and 3200 s in and isomers. These times correspond to the quantum tunneling relaxation mechanism, in which the whole magnetic moment of the DyS@C molecule flips at once as a single entity.
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http://dx.doi.org/10.1039/D0QI00771DDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116581PMC
October 2020

Shape-adaptive single-molecule magnetism and hysteresis up to 14 K in oxide clusterfullerenes DyO@C and DyO@C with fused pentagon pairs and flexible Dy-(μ-O)-Dy angle.

Chem Sci 2020 May 20;11(18):4766-4772. Epub 2020 Apr 20.

Leibniz Institute for Solid State and Materials Research Helmholtzstraße 20, 01069 Dresden, Germany.

Dysprosium oxide clusterfullerenes DyO@C(10528)-C and DyO@C(13333)-C are synthesized and characterized by single-crystal X-ray diffraction. Carbon cages of both molecules feature two adjacent pentagon pairs. These pentalene units determine positions of endohedral Dy ions hence the shape of the DyO cluster, which is bent in DyO@C but linear in DyO@C. Both compounds show slow relaxation of magnetization and magnetic hysteresis. Nearly complete cancelation of ferromagnetic dipolar and antiferromagnetic exchange Dy…Dy interactions leads to unusual magnetic properties. DyO@C exhibits zero-field quantum tunneling of magnetization and magnetic hysteresis up to 14 K, the highest temperature among Dy-clusterfullerenes.
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http://dx.doi.org/10.1039/D0SC00624FDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116574PMC
May 2020

Skin Complications of Diabetes Mellitus Revealed by Polarized Hyperspectral Imaging and Machine Learning.

IEEE Trans Med Imaging 2021 Apr 1;40(4):1207-1216. Epub 2021 Apr 1.

Aging and diabetes lead to protein glycation and cause dysfunction of collagen-containing tissues. The accompanying structural and functional changes of collagen significantly contribute to the development of various pathological malformations affecting the skin, blood vessels, and nerves, causing a number of complications, increasing disability risks and threat to life. In fact, no methods of non-invasive assessment of glycation and associated metabolic processes in biotissues or prediction of possible skin complications, e.g., ulcers, currently exist for endocrinologists and clinical diagnosis. In this publication, utilizing emerging photonics-based technology, innovative solutions in machine learning, and definitive physiological characteristics, we introduce a diagnostic approach capable of evaluating the skin complications of diabetes mellitus at the very earlier stage. The results of the feasibility studies, as well as the actual tests on patients with diabetes and healthy volunteers, clearly show the ability of the approach to differentiate diabetic and control groups. Furthermore, the developed in-house polarization-based hyperspectral imaging technique accomplished with the implementation of the artificial neural network provides new horizons in the study and diagnosis of age-related diseases.
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http://dx.doi.org/10.1109/TMI.2021.3049591DOI Listing
April 2021

Caught in Phase Transition: Snapshot of the Metallofullerene ScN@C Rotation in the Crystal.

J Am Chem Soc 2021 Jan 31;143(2):612-616. Epub 2020 Dec 31.

Leibniz Institute for Solid State and Materials Research (IFW Dresden), Helmholtzstrasse 20, 01069 Dresden, Germany.

The molecular structure of ScN@(7854)-C was determined by single-crystal X-ray diffraction. Variable-temperature X-ray diffraction analysis unraveled the details of the phase transition caused by the temperature-driven jumplike rotation of the fullerene cage between two orientations. Whereas in the lower-temperature 2/ phase the fullerene predominantly occupies one orientation, two orientations become equally occupied in the higher-temperature 2/ phase. This work provides a rare example of the well-defined order-disorder transition in metallofullerene crystals and thus gives important insight into the problem of disorder impeding metallofullerene crystallography.
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http://dx.doi.org/10.1021/jacs.0c10758DOI Listing
January 2021

In vivo nano-biosensing element of red blood cell-mediated delivery.

Biosens Bioelectron 2021 Mar 24;175:112845. Epub 2020 Nov 24.

Optoelectronics and Measurement Techniques Laboratory, University of Oulu, 90570, Oulu, Finland; Interdisciplinary Laboratory of Biophotonics, National Research Tomsk State University, 634050, Tomsk, Russia; Institute of Engineering Physics for Biomedicine (PhysBio), National Research Nuclear University (MEPhI), 115409, Moscow, Russia; Department of Histology, Cytology and Embryology, Institute of Clinical Medicine N.V. Sklifosovsky, I.M. Sechenov First Moscow State Medical University, Moscow, Russia; College of Engineering and Physical Sciences, Aston University, Birmingham, B4 7ET, UK. Electronic address:

Biosensors based on nanotechnology are developing rapidly and are widely applied in many fields including biomedicine, environmental monitoring, national defense and analytical chemistry, and have achieved vital positions in these fields. Novel nano-materials are intensively developed and manufactured for potential biosensing and theranostic applications while lacking comprehensive assessment of their potential health risks. The integration of diagnostic in vivo biosensors and the DDSs for delivery of therapeutic drugs holds an enormous potential in next-generation theranostic platforms. Controllable, precise, and safe delivery of diagnostic biosensing devices and therapeutic agents to the target tissues, organs, or cells is an important determinant in developing advanced nanobiosensor-based theranostic platforms. Particularly, inspired by the comprehensive biological investigations on the red blood cells (RBCs), advanced strategies of RBC-mediated in vivo delivery have been developed rapidly and are currently in different stages of transforming from research and design to pre-clinical and clinical investigations. In this review, the RBC-mediated delivery of in vivo nanobiosensors for applications of bio-imaging at the single-cell level, advanced medical diagnostics, and analytical detection of biomolecules and cellular activities are presented. A comprehensive perspective of the technical framework of the state-of-the-art RBC-mediated delivery systems is explained in detail to inspire the design and implementation of advanced nanobiosensor-based theranostic platforms taking advantage of RBC-delivery modalities.
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http://dx.doi.org/10.1016/j.bios.2020.112845DOI Listing
March 2021

Evolution of raw meat polarization-based properties by means of Mueller matrix imaging.

J Biophotonics 2021 May 28;14(5):e202000376. Epub 2020 Dec 28.

Opto-Electronic and Measurement Techniques research unit, University of Oulu, Oulu, Finland.

The possibilities of using Mueller matrix (MM) imaging polarimetry to assess meat quality have not yet been sufficiently explored. In the current study, the fresh porcine muscles are imaged at room temperature with a wide-field MM imaging polarimeter over 26 hours to visualize dynamics of tissue optical properties through applying Lu-Chipman decomposition. The frequency distribution histograms (FDHs) and statistical analysis of the MM elements show prominent changes over time. The wavelength spectra of both total depolarization and scalar retardance have dips at 550 nm whereas their values continuously increase with time; the former is referred to the increase of number of scattering events and decrease of myoglobin absorption in the red part of visible spectra related to meat color and freshness, while the latter is associated with the increase in birefringence and meat tenderness. The obtained results are promising to develop a novel fast noncontact optical technique for monitoring of meat quality.
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http://dx.doi.org/10.1002/jbio.202000376DOI Listing
May 2021

Furan-containing double tetraoxa[7]helicene and its radical cation.

Chem Commun (Camb) 2020 Dec;56(96):15181-15184

College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083, P. R. China.

An unprecedented furan-based double oxa[7]helicene 1 was achieved, featuring a stable twisted conformation with π-overlap at both helical ends. The excellent conformational stability allowed for optical resolution of 1, which provided a pair of enantiomers exhibiting pronounced mirror-imaged circular dichroism and circularly polarized luminescence activity. The radical cation of 1 was obtained by chemical oxidation as evidenced by UV-Vis-NIR absorption, electron paramagnetic resonance spectroscopy and in situ spectroelectrochemistry. The present work is the starting point for the investigation of open-shell oxahelicenes.
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http://dx.doi.org/10.1039/d0cc06970aDOI Listing
December 2020

Development of oral cancer tissue-mimicking phantom based on polyvinyl chloride plastisol and graphite for terahertz frequencies.

J Biomed Opt 2020 11;25(12)

ITMO Univ., Russian Federation.

Significance: A new concept of a biotissue phantom for terahertz (THz) biomedical applications is needed for reliable and long-term usage.

Aim: We aimed to develop a new type of biotissue phantom without water content and with controllable THz optical properties by applying graphite powders into a polyvinyl chloride plastisol (PVCP) matrix and to give a numerical description to the THz optical properties of the phantoms using the Bruggeman model (BM) of the effective medium theory (EMT).

Approach: The THz optical properties of graphite and the PVCP matrix were measured using THz time-domain spectroscopy, which works in the frequency range from 0.1 to 1 THz. Two phantoms with 10% and 12.5% graphite were fabricated to evaluate the feasibility of describing phantoms using the EMT. The EMT then was used to determine the concentration of graphite required to mimic the THz optical properties of human cancerous and healthy oral tissue.

Results: The phantom with 16.7% of graphite has the similar THz optical properties as human cancerous oral tissue in the frequency range of 0.2 to 0.7 THz. The THz optical properties of the phantom with 21.9% of graphite are close to those of human healthy oral tissue in the bandwidth from 0.6 to 0.8 THz. Both the refractive index and absorption coefficient of the samples increase with an increase of graphite concentration. The BM of the EMT was used as the numerical model to describe the THz optical properties of the phantoms. The relative error of the BM for the refractive index estimation and the absorption coefficient is up to 4% and 8%, respectively.

Conclusions: A water-free biotissue phantom that mimics the THz optical properties of human cancerous oral tissue was developed. With 21.9% of graphite, the phantom also mimics human healthy oral tissue in a narrow frequency range. The BM proved to be a suitable numerical model of the phantom.
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http://dx.doi.org/10.1117/1.JBO.25.12.123002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7670095PMC
November 2020

A Curved Graphene Nanoribbon with Multi-Edge Structure and High Intrinsic Charge Carrier Mobility.

J Am Chem Soc 2020 Oct 20;142(43):18293-18298. Epub 2020 Oct 20.

School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Ageing, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.

Structurally well-defined graphene nanoribbons (GNRs) have emerged as highly promising materials for the next-generation nanoelectronics. The electronic properties of GNRs critically depend on their edge topologies. Here, we demonstrate the efficient synthesis of a curved GNR () with a combined cove, zigzag, and armchair edge structure, through bottom-up synthesis. The curvature of the is elucidated by the corresponding model compounds tetrabenzo[]perylene () and diphenanthrene-fused tetrabenzo[]perylene (), the structures of which are unambiguously confirmed by the X-ray single-crystal analysis. The resultant multi-edged exhibits a well-resolved absorption at the near-infrared (NIR) region with a maximum peak at 850 nm, corresponding to a narrow optical energy gap of ∼1.22 eV. Employing THz spectroscopy, we disclose a long scattering time of ∼60 fs, corresponding to a record intrinsic charge carrier mobility of ∼600 cm V s for photogenerated charge carriers in .
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http://dx.doi.org/10.1021/jacs.0c07013DOI Listing
October 2020

Unusually large hyperfine structure of the electron spin levels in an endohedral dimetallofullerene and its spin coherent properties.

Nanoscale 2020 Oct;12(39):20513-20521

Leibniz IFW Dresden, D-01069, Dresden, Germany.

We report the synthesis, ESR spectroscopic and spin coherent properties of the dimetallofullerene Sc2@C80(CH2Ph). The single-electron metal-metal bond of the Sc2 dimer inside the fullerene's cage is stabilized with the electron spin density being fully localized at the metal bond. This results in an extraordinary strong hyperfine interaction of the electron spin with the 45Sc nuclear spins with a coupling constant a = 18.2 mT (∼510 MHz) and yields a fully resolved hyperfine-split ESR spectrum comprising 64 lines. The splitting is present even at low temperatures where the molecular dynamics are completely frozen. The large extent and the robustness of the hyperfine-split spectra enable us to identify and control the well-defined transitions between specific electron-nuclear quantum states. This made it possible to demonstrate in our pulse ESR study the remarkable spin coherent dynamics of Sc2@C80(CH2Ph), such as the generation of arbitrary superpositions of the spin states in a nutation experiment and the spin dephasing times above 10 μs at temperatures T < 80 K reaching the value of 17 μs at T ≤ 20 K. These observations suggest Sc2@C80(CH2Ph) as an interesting qubit candidate and motivate further synthetic efforts to obtain fullerene-based systems with superior spin properties.
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http://dx.doi.org/10.1039/d0nr06114jDOI Listing
October 2020

A highly efficient and safe gene delivery platform based on polyelectrolyte core-shell nanoparticles for hard-to-transfect clinically relevant cell types.

J Mater Chem B 2020 10;8(41):9576-9588

11 Center of Photonics & Quantum Materials, Skolkovo Institute of Science and Technology, Moscow, 143026, Russia and Educational Research Institute of Nanostructures and Biosystems, Saratov State University, Saratov, 410012, Russia.

While DNA and messenger RNA (mRNA) based therapies are currently changing the biomedical field, the delivery of genetic materials remains the key problem preventing the wide introduction of these methods into clinical practice. Therefore, the creation of new methods for intracellular gene delivery, particularly to hard-to-transfect, clinically relevant cell populations is a pressing issue. Here, we report on the design of a novel approach to format 50-150 nm calcium carbonate particles in the vaterite state and using them as a template for polymeric core-shell nanoparticles. We apply such core-shell nanoparticles as safe and efficient carriers for mRNA and pDNA. We prove that such nanocarriers are actively internalized by up to 99% of primary T-lymphocytes and exert minimal toxicity with the viability of >90%. We demonstrate that these nanocarriers mediate more efficient transfection compared with the standard electroporation method (90% vs. 51% for mRNA and 62% vs. 39% for plasmid DNA) in primary human T-lymphocytes as a model of the hard to transfect type that is widely used in gene and cell therapy approaches. Importantly, these polymeric nanocarriers can be used in serum containing basic culture medium without special conditions and equipment, thus having potential for being introduced in clinical development. As a result, we have provided proof-of-principle that our nanosized containers represent a promising universal non-viral platform for efficient and safe gene delivery.
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http://dx.doi.org/10.1039/d0tb01359eDOI Listing
October 2020

Between Aromatic and Quinoid Structure: A Symmetrical UV to Vis/NIR Benzothiadiazole Redox Switch.

Chemistry 2020 Dec 23;26(72):17361-17365. Epub 2020 Nov 23.

Institute of Chemistry and Biochemistry, Freie Universität Berlin, Takustraße 3, 14195, Berlin, Germany.

Reversibly switching the light absorption of organic molecules by redox processes is of interest for applications in sensors, light harvesting, smart materials, and medical diagnostics. This work presents a symmetrical benzothiadiazole (BTD) derivative with a high fluorescence quantum yield in solution and in the crystalline state and shows by spectroelectrochemical analysis that reversible switching of UV absorption in the neutral state, to broadband Vis/NIR absorption in the 1st oxidized state, to sharp band Vis absorption in the 2nd oxidized state, is possible. For the one-electron oxidized species, formation of a delocalized radical is confirmed by electron paramagnetic resonance spectroelectrochemistry. Furthermore, our results reveal an increasing quinoidal distortion upon the 1st and 2nd oxidation, which can be used as the leitmotif for the development of BTD based redox switches.
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http://dx.doi.org/10.1002/chem.202004009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7839704PMC
December 2020

Evaluating β-amyloidosis progression in Alzheimer's disease with Mueller polarimetry.

Biomed Opt Express 2020 Aug 21;11(8):4509-4519. Epub 2020 Jul 21.

Optoelectronics and Measurement Techniques, University of Oulu, 90570 Oulu, Finland.

We applied the wide-field Mueller imaging polarimetry for the screening of formalin-fixed paraffin-embedded samples of mouse brain tissue at different stages of brain β-amyloidosis in Alzheimer's disease (AD). The accumulation of amyloid-beta (Aβ) deposits throughout the brain tissue is one of the key pathological hallmarks observed with the AD progression. We demonstrate that the presence of Aβ plaques influences the properties of backscattered polarized light, in particular, its degree of depolarization. By means of statistical analysis, we demonstrate that the high-order statistical moments of depolarization distributions, acquired with the multi-spectral Mueller imaging polarimetry, can be used as sensitive markers of the growing presence of Aβ plaques. The introduced label-free polarimetric approach has a potential to facilitate the current practice of the histopathology screening in terms of diagnosis accuracy, time and cost efficiency.
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http://dx.doi.org/10.1364/BOE.396294DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7449745PMC
August 2020

Photoinduced Charge Accumulation and Prolonged Multielectron Storage for the Separation of Light and Dark Reaction.

J Am Chem Soc 2020 Sep 3;142(37):15722-15728. Epub 2020 Sep 3.

Institute of Physical Chemistry, Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany.

The utilization of solar energy is restricted by the intermittent nature of solar influx. We present novel noble-metal free complexes that can be photochemically charged in the presence of sacrificial electron donors and remain stable in its charged form for over 14 h. This allows the doubly reduced Cu(I) 4-imidazolate complex to be stored after photochemical charging and used as a reagent in dark reactions, such as the reduction of methyl viologen or oxygen. Combined UV-vis/EPR spectroelectrochemistry indicates that a two-electron reduction is induced by introducing sacrificial electron donors that facilitate proton-coupled electron transfer. Repeated photochemical reduction and chemical oxidation reveals that the complex retained a charging capacity of 72% after four cycles. We demonstrate a chemical system that can decouple photochemical processes from the day-night cycle, which has been a barrier to realizing utilization of solar energy in photochemical processes on a global scale.
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http://dx.doi.org/10.1021/jacs.0c03779DOI Listing
September 2020

Mucus-Penetrating Particles and the Role of Ocular Mucus as a Barrier to Micro- and Nanosuspensions.

Authors:
Alexey Popov

J Ocul Pharmacol Ther 2020 Jul/Aug;36(6):366-375. Epub 2020 Jul 13.

Kala Pharmaceuticals, Inc., Watertown, Massachusetts, USA.

The ocular surface is naturally covered with a layer of mucus. Along with other functions, this mucus layer serves to trap and eliminate foreign substances, such as allergens, pathogens, and debris. In playing this pivotal role, mucus can also hinder topical delivery of therapeutics to the eye. Recent studies provide evidence that drugs formulated as traditional micro- or nanoparticles are susceptible to entrapment and rapid clearance by ocular mucus. Mucus-penetrating particles (MPPs) is a nanoparticle technology that emerged over the past decade. With a muco-inert surface and a particle size smaller than the mucus mesh size, MPPs can diffuse in mucus essentially freely. Preclinical studies have shown that, compared with particles lacking the mucus-penetrating attributes, MPPs can improve the uniformity of drug particle distribution on mucosal surfaces and enhance drug delivery to ocular tissues.
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http://dx.doi.org/10.1089/jop.2020.0022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7405105PMC
July 2020

Addition of CF group to endohedral fullerene ScN@I-C.

Dalton Trans 2020 Jul 24;49(26):9137-9147. Epub 2020 Jun 24.

Chemistry Department, Lomonosov Moscow State University, Leninskie Gory, 1-3, 119991, Moscow, Russia.

We report the first successful synthesis of a CF derivative of the stable endohedral fullerene ScN@I-C. Reaction with CFClCOONa yields a single C-symmetric ScN@C(CF) adduct where the CF group is inserted into a [6,6]-bond and opens it to 2.3 Å between the bridgehead carbon atoms. As evidenced by absorption and fluorescence spectroscopy as well as cyclic voltammetry, both the HOMO and the LUMO level of ScN@C(CF) are slightly (ca. 0.1 eV) downshifted with respect to the parent ScN@I-C, so the HOMO-LUMO gap remains essentially unchanged. The DFT calculations suggest that the reaction mechanism is not the previously assumed [2 + 1]-cycloaddition of :CF carbene but rather nucleophilic addition of CFCl anion followed by elimination of Cl and closing of the CF bridge via intramolecular nucleophilic substitution. Selective formation of the [6,6]-ScN@C(CF) turns out to be kinetically controlled and promoted by a particular orientation of the endohedral ScN cluster with respect to the CFCl addition site. In its turn, the CF addend partly hampers the rotation of ScN the endohedral cluster compared to its quasi-free reorientations in the parent ScN@I-C.
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http://dx.doi.org/10.1039/d0dt01513jDOI Listing
July 2020

Role of scattering and birefringence in phase retardation revealed by locus of Stokes vector on Poincaré sphere.

J Biomed Opt 2020 05;25(5):1-13

University of Oulu, Optoelectronics and Measurement Techniques Research Unit, Oulu, Finland.

Significance: Biological tissues are typically characterized by high anisotropic scattering and may also exhibit linear form birefringence. Both scattering and birefringence bias the phase shift between transverse electric field components of polarized light. These phase alterations are associated with particular structural malformations in the tissue. In fact, the majority of polarization-based techniques are unable to distinguish the nature of the phase shift induced by birefringence or scattering of light.

Aim: We explore the distinct contributions of scattering and birefringence in the phase retardation of circularly polarized light propagated in turbid tissue-like scattering medium.

Approach: The circularly polarized light in frame of Stokes polarimetry approach is used for the screening of biotissue phantoms and chicken skin samples. The change of optical properties in chicken skin is accomplished by optical clearing, which reduces scattering, and mechanical stretch, which induces birefringence. The change of optical properties of skin tissue is confirmed by spectrophotometric measurements and second-harmonic generation imaging.

Results: The contributions of scattering and birefringence in the phase retardation of circularly polarized light propagated in biological tissues are distinguished by the locus of the Stokes vector mapped on the Poincaré sphere. The phase retardation of circularly polarized light due to scattering alterations is assessed. The value of birefringence in chicken skin is estimated as 0.3  ×  10, which agrees with alternative studies. The change of birefringence of skin tissue due to mechanical stretch in the order of 10 is detected.

Conclusions: While the polarimetric parameters on their own do not allow distinguishing the contributions of scattering and birefringence, the resultant Stokes vector trajectory on the Poincaré sphere reveals the role of scattering and birefringence in the total phase retardation. The described approach, applied independently or in combination with Mueller polarimetry, can be beneficial for the advanced characterization of various types of malformations within biological tissues.
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http://dx.doi.org/10.1117/1.JBO.25.5.057001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7238295PMC
May 2020

Colon cancer detection by using Poincaré sphere and 2D polarimetric mapping of ex vivo colon samples.

J Biophotonics 2020 08 28;13(8):e202000082. Epub 2020 May 28.

Optoelectronics and Measurement Techniques Unit, University of Oulu, Oulu, Finland.

This work is dedicated to the diagnosis and grading of colon cancer by a combined use of Poincaré sphere and 2D Stokes vector polarimetry mapping approaches. The major challenge consists in exploring the applicability of polarized light for noninvasive screening of the histological abnormalities within the samples of biological tissues. Experimental studies were conducted in ex vivo colon sample, excised after surgical procedure for colon tumor removal of G2-adenocarcinoma lesion. Polarimetric measurements in linear and circular regime were carried via personally developed polarimetric, optical set-up, using supercontinuous fiber laser with irradiation fixed at 635 nm. We apply the Poincaré sphere and two-dimensional Stokes vector scanning approach for screening the corresponding tissue samples. A comparison between linear and circular polarization states is made both for quantitative and qualitative evaluations. It is shown that circular polarization has better diagnostic capabilities than linear polarization, with higher dynamic ranges of the polarimetric parameters and better values of the diagnostic quantities. In addition to the standard polarimetry parameters, utilized as essential diagnostic markers, we apply statistical analysis to obtain more detailed information in frame of the applied diagnostic approach.
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http://dx.doi.org/10.1002/jbio.202000082DOI Listing
August 2020

(Electrochemical) Properties and Computational Investigations of Ferrocenyl-substituted Fe(μ-PFc)(CO) and Co(μ-PFc)(CO) Clusters and Their Reduced Species.

Inorg Chem 2020 May 23;59(9):6147-6160. Epub 2020 Apr 23.

Faculty of Natural Sciences, Institute of Chemistry, Inorganic Chemistry, Technische Universität Chemnitz, D-09107 Chemnitz, Germany.

The formation of ferrocenyl-functionalized iron and cobalt carbonyl clusters is reported, based on a reaction of FcPCl () (Fc = Fe(η-CH)(η-CH)) with Fe(CO) and Co(CO), respectively. Therein, Fe(CO)(μ-PFc) () and Co(CO)(μ-PFc) () clusters were obtained as the first diferrocenyl-substituted carbonyl clusters with a symmetrical cluster core. Cluster shows two reversible one-electron processes within the anodic region, based on Fc/Fc redox events, as well as two processes in the cathodic region. In situ IR and electron paramagnetic resonance (EPR) measurements of all electronic states confirmed an Fc-based oxidation and a core-based reduction. On the basis of the results of a single-crystal X-ray analysis of structures of and , computational studies of the highest occupied molecular orbital-lowest unoccupied molecular orbital energies, the spin density, quantum theory of atom-in-molecule delocalization indices, and the atomic charges were performed to explain the experimental results. The latter revealed a reorganization of the cluster core upon reduction and the existence of weak P···P interactions in and . Ferrocenyl-related redox processes, occurring reversibly in case of , were absent for , due to a different distribution of the HOMO energies. EPR measurements furthermore confirmed the core-based radical anion and the formation of a decomposition product at potentials lower than [M] (M = Fe, Co).
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http://dx.doi.org/10.1021/acs.inorgchem.0c00276DOI Listing
May 2020

Tailoring Magnetic Features in Zigzag-Edged Nanographenes by Controlled Diels-Alder Reactions.

Chemistry 2020 Jun 12;26(33):7497-7503. Epub 2020 May 12.

Center for Advancing Electronics Dresden (cfaed) &, Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, 01062, Dresden, Germany.

Nanographenes (NGs) with tunable electronic and magnetic properties have attracted enormous attention in the realm of carbon-based nanoelectronics. In particular, NGs with biradical character at the ground state are promising building units for molecular spintronics. However, most of the biradicaloids are susceptible to oxidation under ambient conditions and photolytic degradation, which hamper their further applications. Herein, we demonstrated the feasibility of tuning the magnetic properties of zigzag-edged NGs in order to enhance their stability via the controlled Diels-Alder reactions of peri-tetracene (4-PA). The unstable 4-PA (y =0.72; half-life, t =3 h) was transformed into the unprecedented benzo-peri-tetracenes (BPTs) by a one-side Diels-Alder reaction, which featured a biradical character at the ground state (y =0.60) and exhibited remarkable stability under ambient conditions for several months. In addition, the fully zigzag-edged circumanthracenes (CAs) were achieved by two-fold or stepwise Diels-Alder reactions of 4-PA, in which the magnetic properties could be controlled by employing the corresponding dienophiles. Our work reported herein opens avenues for the synthesis of novel zigzag-edged NGs with tailor-made magnetic properties.
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http://dx.doi.org/10.1002/chem.202001130DOI Listing
June 2020

Quinoidal Azaacenes: 99 % Diradical Character.

Angew Chem Int Ed Engl 2020 Jul 28;59(30):12396-12401. Epub 2020 Apr 28.

Organisch-Chemisches Institut, Ruprecht-Karls-Universität, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany.

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low-energy gap ΔE of 0.58 to 1.0 kcal mol . The species are persistent in solution (half-life≈14-21 h) and in the solid state they are stable for weeks.
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http://dx.doi.org/10.1002/anie.201915977DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7384067PMC
July 2020

Optical Tweezers in Studies of Red Blood Cells.

Cells 2020 02 26;9(3). Epub 2020 Feb 26.

Optoelectronics and Measurement Techniques Laboratory, University of Oulu, 90570 Oulu, Finland.

Optical tweezers (OTs) are innovative instruments utilized for the manipulation of microscopic biological objects of interest. Rapid improvements in precision and degree of freedom of multichannel and multifunctional OTs have ushered in a new era of studies in basic physical and chemical properties of living tissues and unknown biomechanics in biological processes. Nowadays, OTs are used extensively for studying living cells and have initiated far-reaching influence in various fundamental studies in life sciences. There is also a high potential for using OTs in haemorheology, investigations of blood microcirculation and the mutual interplay of blood cells. In fact, in spite of their great promise in the application of OTs-based approaches for the study of blood, cell formation and maturation in erythropoiesis have not been fully explored. In this review, the background of OTs, their state-of-the-art applications in exploring single-cell level characteristics and bio-rheological properties of mature red blood cells (RBCs) as well as the OTs-assisted studies on erythropoiesis are summarized and presented. The advance developments and future perspectives of the OTs' application in haemorheology both for fundamental and practical in-depth studies of RBCs formation, functional diagnostics and therapeutic needs are highlighted.
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http://dx.doi.org/10.3390/cells9030545DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7140472PMC
February 2020

Polycyclic Aromatic Hydrocarbons Containing A Pyrrolopyridazine Core.

Chempluschem 2019 06 28;84(6):613-618. Epub 2019 Feb 28.

Dresden University of Technology, Center for Advancing Electronics Dresden (cfaed), Faculty of Chemistry and Food Chemistry, Institute for Molecular Functional Materials, Mommsenstraße 4, 01069, Dresden, Germany.

Polycyclic aromatic azomethine ylides (PAMYs) are versatile building blocks for the bottom-up construction of unprecedented nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs). Here, we demonstrate the 1,3-dipolar cycloaddition between PAMY and 1,4-diphenylbut-2-yne-1,4-dione and the subsequent condensation reaction with hydrazine, which led to unique N-PAHs with a phenyl-substituted pyrrolopyridazine core (PP-1 and PP-2). The molecular structures of pristine PP-1 and tert-butyl-substituted PP-2 were verified by NMR spectroscopy and mass spectrometry. Moreover, the structure of PP-2 was unambiguously elucidated by X-ray single crystal analysis. The optoelectronic properties were investigated by solvent-dependent UV-Vis absorption and fluorescence emission spectroscopy as well as cyclic voltammetry. Additionally, density functional theory (DFT) calculations showed that PP-1 and PP-2 exhibit push-pull behavior. Furthermore, in situ EPR/UV-Vis-NIR spectroelectrochemistry allowed the detailed insight into the spectroscopic properties and spin distribution of radical cation species of PP-2.
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http://dx.doi.org/10.1002/cplu.201900031DOI Listing
June 2019

Impact of Nanocapsules on Red Blood Cells Interplay Jointly Assessed by Optical Tweezers and Microscopy.

Micromachines (Basel) 2019 Dec 23;11(1). Epub 2019 Dec 23.

Optoelectronics and Measurement Techniques Research Unit, University of Oulu, 90014 Oulu, Finland.

In the framework of novel medical paradigm the red blood cells (RBCs) have a great potential to be used as drug delivery carriers. This approach requires an ultimate understanding of the peculiarities of mutual interaction of RBC influenced by nano-materials composed the drugs. Optical tweezers (OT) is widely used to explore mechanisms of cells' interaction with the ability to trap non-invasively, manipulate and displace living cells with a notably high accuracy. In the current study, the mutual interaction of RBC with polymeric nano-capsules (NCs) is investigated utilizing a two-channel OT system. The obtained results suggest that, in the presence of NCs, the RBC aggregation in plasma satisfies the 'cross-bridges' model. Complementarily, the allocation of NCs on the RBC membrane was observed by scanning electron microscopy (SEM), while for assessment of NCs-induced morphological changes the tests with the human mesenchymal stem cells (hMSC) was performed. The combined application of OT and advanced microscopy approaches brings new insights into the conception of direct observation of cells interaction influenced by NCs for the estimation of possible cytotoxic effects.
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http://dx.doi.org/10.3390/mi11010019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7020003PMC
December 2019

Influence of blood pulsation on diagnostic volume in pulse oximetry and photoplethysmography measurements: publisher's note.

Appl Opt 2019 Dec;58(35):9688

This publisher's note corrects several errors in Appl. Opt.58, 9398 (2019).APOPAI0003-693510.1364/AO.58.009398.
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http://dx.doi.org/10.1364/AO.58.009688DOI Listing
December 2019

Influence of blood pulsation on diagnostic volume in pulse oximetry and photoplethysmography measurements.

Appl Opt 2019 Dec;58(34):9398-9405

Recent advances in the development of ultra-compact semiconductor lasers and technology of printed flexible hybrid electronics have opened broad perspectives for the design of new pulse oximetry and photoplethysmography devices. Conceptual design of optical diagnostic devices requires careful selection of various technical parameters, including spectral range; polarization and intensity of incident light; actual size, geometry, and sensitivity of the detector; and mutual position of the source and detector on the surface of skin. In the current study utilizing a unified Monte Carlo computational tool, we explore the variations in diagnostic volume due to arterial blood pulsation for typical transmitted and back-scattered probing configurations in a human finger. The results of computational studies show that the variations in diagnostic volumes due to arterial pulse wave are notably (up to 45%) different in visible and near-infrared spectral ranges in both transmitted and back-scattered probing geometries. While these variations are acceptable for relative measurements in pulse oximetry and/or photoplethysmography, for absolute measurements, an alignment normalization of diagnostic volume is required and can be done by a computational approach utilized in the framework of the current study.
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http://dx.doi.org/10.1364/AO.58.009398DOI Listing
December 2019

Helical Nanographenes Containing an Azulene Unit: Synthesis, Crystal Structures, and Properties.

Angew Chem Int Ed Engl 2020 Mar 3;59(14):5637-5642. Epub 2020 Feb 3.

Centre for Advancing Electronics Dresden (cfaed), Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, 01062, Dresden, Germany.

Three unprecedented helical nanographenes (1, 2, and 3) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X-ray crystallographic analysis. The embedded azulene unit in 2 possesses a record-high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis-spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps (2: 1.88 eV; 3: 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in-situ EPR/Vis-NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties.
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http://dx.doi.org/10.1002/anie.201914716DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7155134PMC
March 2020

Substrate-Independent Magnetic Bistability in Monolayers of the Single-Molecule Magnet Dy ScN@C on Metals and Insulators.

Angew Chem Int Ed Engl 2020 Mar 24;59(14):5756-5764. Epub 2020 Jan 24.

Leibniz Institute for Solid State and Materials Research, Helmholtzstraße 20, 01069, Dresden, Germany.

Magnetic hysteresis is demonstrated for monolayers of the single-molecule magnet (SMM) Dy ScN@C deposited on Au(111), Ag(100), and MgO|Ag(100) surfaces by vacuum sublimation. The topography and electronic structure of Dy ScN@C adsorbed on Au(111) were studied by STM. X-ray magnetic CD studies show that the Dy ScN@C monolayers exhibit similarly broad magnetic hysteresis independent on the substrate used, but the orientation of the Dy ScN cluster depends strongly on the surface. DFT calculations show that the extent of the electronic interaction of the fullerene molecules with the surface is increasing dramatically from MgO to Au(111) and Ag(100). However, the charge redistribution at the fullerene-surface interface is fully absorbed by the carbon cage, leaving the state of the endohedral cluster intact. This Faraday cage effect of the fullerene preserves the magnetic bistability of fullerene-SMMs on conducting substrates and facilitates their application in molecular spintronics.
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http://dx.doi.org/10.1002/anie.201913955DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7155138PMC
March 2020