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921.
Namieśnik J 《Talanta》1988,35(7):567-587
Three basic methods of preconcentration of organic atmospheric pollutants, viz. by cold trap, absorption in solutions and adsorption on solids at ambient temperature, and methods of liberating the trapped components, are discussed. Adsorption on solids is becoming more widely employed because of its advantages, and selection of the most appropriate sorbent for a given group of pollutants is of major importance. The characteristics of individual types of sorbents are presented, as well as the basic methods of determination of sorption capacity. 相似文献
922.
Gruszecki WI Gagoś M Hereć M 《Journal of photochemistry and photobiology. B, Biology》2003,69(1):49-57
Fluorescence emission from amphotericin B dissolved in 2-propanol-water was recorded in the spectral region 500-650 nm. The fluorescence excitation spectrum corresponds to the absorption spectrum of the monomeric drug. The large energy shift between the excitation and emission bands indicates that emission takes place from an energy level different than that responsible for absorption. These levels were attributed to the 2(1)A(g) and 1(1)B(u) states, respectively. Excitation of the same sample with short wavelength radiation (below 350 nm) yields light emission between 400 and 550 nm. The fluorescence excitation spectrum corresponding to this emission band displays distinct maxima at 350, 334 and 318 nm. This band was analyzed in terms of the exciton splitting theory and assigned to amphotericin B in a dimeric form, in which chromophores are spaced by 4.9 A. The binding energy of the dimers, determined to be 4.9 kJ/mol, indicates that the structures are stabilized by van der Waals interactions. The same type of molecular structures was also detected in the lipid membranes formed with dipalmitoylphosphatidylcholine. Linear dichroism of amphotericin B embedded in lipid multibilayers indicates that molecules are distributed between two fractions: parallel (38%) and perpendicular (62%) with respect to the membrane. The biological importance of such membrane organization is discussed. 相似文献
923.
Andrew ER Głowinkowski S Radomski J Szcześniak E 《Solid state nuclear magnetic resonance》2000,15(4):227-230
Spin-lattice relaxation times T1 in solid pregnenolone have been studied over a wide range of temperatures, from 77 up to 417 K. The dynamic processes arising from C3 motion of the three methyl substituents are separated, and their activation parameters are determined. 相似文献
924.
Dr. Witold Andrałojć Julia Wieruszewska Dr. Karol Pasternak Prof. Dr. Zofia Gdaniec 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(66):e202202114
In this contribution we report the high-resolution NMR structure of a recently identified lanthanide-binding aptamer (LnA). We demonstrate that the rigid lanthanide binding by LnA allows for the measurement of anisotropic paramagnetic NMR restraints which to date remain largely inaccessible for nucleic acids. One type of such restraints - pseudocontact shifts (PCS) induced by four different paramagnetic lanthanides - was extensively used throughout the current structure determination study and the measured PCS turned out to be exceptionally well reproduced by the final aptamer structure. This finding opens the perspective for a broader application of paramagnetic effects in NMR studies of nucleic acids through the transplantation of the binding site found in LnA into other DNA/RNA systems. 相似文献
925.
Ewelina Maślak Wojciech Kupczyk Viorica Railean Paweł Pomastowski Marek Jackowski Bogusław Buszewski 《Electrophoresis》2022,43(20):2005-2013
One of the challenges medicine faces is the constantly growing resistance of pathogens to various classes of antibiotics. In this study, we investigated the use of capillary electrophoresis (CE) to characterize and assess the physiological states of three clinical bacterial strains—methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA), and Escherichia coli extended-spectrum β-lactamases (ESβL)—exposed to different antibiotics. All chosen bacteria are the leading causes of healthcare-associated and hospital-acquired invasive infections in adults. In the first part of the research, it was determined the optimal incubation time of the tested strains with antibiotics, represented as an optimal time of 24 h. In the second part, we have compared two approaches: flow cytometry (FC) as a standard method and CE as a proposed alternative approach. The viability of clinical strains treated with different class antibiotics calculated in CE measurements was strongly correlated (>0.83 for MSSA, >0.92 for ESβL and MRSA) with the viability obtained on the basis of FC measurements. As a result, CE has a chance to become a modern diagnostic method used in clinical practice. The CE cutoff was found to be 50%; above this value, the strain shows resistance to the action of the antibiotic. 相似文献
926.
The interactions of formaldehyde (FA), glyoxal (Gly) and methylglyoxal (MGly) with hydroxylamine (HA) isolated in solid argon and nitrogen were studied using FTIR spectroscopy and ab initio methods. The spectra analysis indicates the formation of two types of hydrogen-bonded complexes between carbonyl and hydroxylamine in the studied matrices. The cyclic planar complexes are stabilized by O–H⋯O(C), and C–H⋯N interactions and the nonplanar complexes are stabilized by O–H⋯O(C) bond. Formaldehyde was found to form with hydroxylamine, the cyclic planar complex and methylglyoxal, the nonplanar one in both argon and nitrogen matrices. In turn, glyoxal forms with hydroxylamine the most stable nonplanar complex in solid argon, whereas in solid nitrogen, both types of the complex are formed. 相似文献
927.
Toward assessment of density functionals for vibronic coupling in two‐photon absorption: A case study of 4‐nitroaniline
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Robert Zaleśny Guangjun Tian Christof Hättig Wojciech Bartkowiak Hans Ågren 《Journal of computational chemistry》2015,36(15):1124-1131
In this study, we predict vibronic two‐photon absorption (TPA) spectra for 4‐nitroaniline in vacuo. The simulations are performed using density functional theory and the approximate second‐order coupled‐cluster singles and doubles model CC2. Thereby we also demonstrate the possibility of simulations of vibronic TPA spectra with ab initio wavefunction methods that include electron correlation for medium‐sized systems. A special focus is put on the geometric derivatives of the second‐order transition moment and the dipole moment difference between the charge‐transfer excited state and the ground state. The results of CC2 calculations bring new insight into the vibronic coupling mechanism in TPA spectra of 4‐nitroniline and demonstrate that the mixed term is quite large and that it also exhibits a negative interference with the Franck‐Condon contribution. © 2015 Wiley Periodicals, Inc. 相似文献
928.
Modulation of Melanogenesis and Antioxidant Status of Melanocytes in Response to Phototoxic Action of Doxycycline
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Jakub Rok Ewa Buszman Artur Beberok Marcin Delijewski Michał Otręba Dorota Wrześniok 《Photochemistry and photobiology》2015,91(6):1429-1434
Doxycycline is a commonly used tetracycline antibiotic showing the broad spectrum of antibacterial action. However, the use of this antibiotic is often connected with the risk of phototoxic reactions that lead to various skin disorders. One of the factors influencing the photosensitivity reactions is the melanin content in melanocytes. In this study, the impact of doxycycline and UVA irradiation on cell viability, melanogenesis and antioxidant defense system in cultured normal human epidermal melanocytes (HEMn‐DP) was examined. The exposure of cells to doxycycline and UVA radiation resulted in concentration‐dependent loss in melanocytes viability and induced melanin biosynthesis. Significant changes were stated in cellular antioxidant enzymes activity: SOD, CAT and GPx, which indicates alterations of antioxidant defense system. The results obtained in vitro may explain the mechanisms of phototoxic reactions that occur in normal human epidermal melanocytes in vivo after exposure of skin to doxycycline and UVA radiation. 相似文献
929.
Szymon Kapuściński Agata Wojciechowska Katarzyna Urbaniak Piotr Kaszyński 《Liquid crystals》2017,44(7):1093-1103
A series of hockey-stick shaped 6-oxoverdazyl radicals 1[n]–3[n], containing CH3 (a), CF3 (b) and CN (c) groups in the short ‘arm’, were prepared and their physical properties were investigated. Mesogenic behaviour was found only in the CN derivatives with the COO (1[n]c) and N=N (2[12]c) linking groups, which exhibited a nematic phase. Analysis of binary mixtures of selected compounds with bent-core nematic host 4[12] gave virtual nematic-isotropic transition temperatures, [TNI], which follow the order 1[12]b < 1[12]c < 1[12]a in one series and 1[12]c < 2[12]c < (3[12]c) in another. The observed effectiveness of the short-arm substituent, CF3 < CN < CH3, was related to the magnitude and orientation of the molecular dipole moment calculated with density functional theory methods. 相似文献
930.
Sesime Coffie James M. Hogg Lucie Cailler Dr. Albert Ferrer‐Ugalde Richard W. Murphy Dr. John D. Holbrey Dr. Fergal Coleman Dr. Małgorzata Swadźba‐Kwaśny 《Angewandte Chemie (International ed. in English)》2015,54(49):14970-14973
The first examples of ionic liquids based on borenium cations, [BCl2L]+, are reported. These compounds form highly Lewis acidic liquids under solvent‐free conditions. Their acidity was quantified by determining the Gutmann acceptor number (AN). Extremely high ANs were recorded (up to AN=182, δ31P=120 ppm), demonstrating that these borenium ionic liquids are the strongest Lewis superacids reported to date, with the acidity enhanced by the ionic liquid environment. 相似文献