排序方式: 共有33条查询结果,搜索用时 31 毫秒
1.
Joseph R. Lakowicz Ignacy Gryczynski Henryk Malak Zygmunt Gryczynski 《Photochemistry and photobiology》1996,64(4):632-635
Abstract— We report the observation of two-photon excitation of an organic fluorophore with two different wavelengths, a phenomenon we refer to as two-color two-photon (2C2P) excitation. Ultraviolet emission of p -Merphenyl at 340 nm was observed when the sample was illuminated with both 375 and 750 nm pulses from a picosecond dye laser. The emission of p -terphenyl was about 100-fold and more than 1000-fold less for illumination at only 375 or 750 nm, respectively. Observation of the 2C2P signal required temporal and spatial overlap of the 375 and 750 nm pulses. The amplitude of the signal depended on the polarization of each beam. 2C2P excitation can have applications in fluorescence microscopy and elsewhere when spatially localized excitation is desirable. 相似文献
2.
Malak Azmat Ali G. Murtaza Afzal Khan Eman Algrafy Asif Mahmood Shahid M. Ramay 《International journal of quantum chemistry》2020,120(19):e26357
Highly spin-polarized ferromagnetic materials are essential for efficient spintronic devices. Here, 100% spin-polarized compounds Rb2TaZ6 (Z = Cl, Br) studied via density functional theory are reported. These compounds show stability in the ferromagnetic phase with cubic symmetry and half metallic behavior, thereby exhibiting a nonzero direct band gap in the spin-down channel and zero band gap in the spin-up configuration. The Ta-d sates contribute mainly to the net magnetic moments as explained by the crystal field theory and density of states. High Curie temperatures of 960.35 and 1021.74 K for Ra2TaCl6 and Rb2TaBr6, along with maximum spin polarizability, make these compounds favorable for efficient spintronic applications. 相似文献
3.
Acidification is a common method for preserving dissolved organic matter (DOM) in natural water samples until sophisticated laboratory analyses can be performed. However, little is known about the effects of this practice on the composition and optical properties of DOM. In this study, the effects of acidification on DOM in porewater samples collected from the RL IV bog system of the Glacial Lake Agassiz Peatlands in northern Minnesota were characterized. Molecular composition was determined by ultrahigh resolution mass spectrometry and optical properties by UV absorption and three-dimensional fluorescence spectroscopy. Excitation–emission matrix fluorescence spectroscopy results indicate that the fluorescence properties of the peatland porewater DOM were sensitive to pH and that the observed changes were fluorophore dependent. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed the appearance of newly formed, oxygen-rich compounds upon acidification. The extent to which these oxygen-rich compounds were formed was also dependent on the composition of the DOM. 相似文献
4.
Henryk Malak Ignacy Gryczynski Jonathan D. Dattelbaum Joseph R. Lakowicz 《Journal of fluorescence》1997,7(2):99-106
We observed the emission of l,6-diphenyl-l,3,5-hexatriene (DPH) when excited with the fundamental output of a fs Ti:sapphire
laser at 860 nm. The emission spectra of DPH were identical to that observed for one-photon excitation at 287 nm. The dependence
of the DPH emission intensity on laser power was cubic, indicating three-photon excitation of DPH at 860 nm. At a shorter
wavelength of 810 nm, the dependence on laser power was quadratic, indicating a two-photon process. At an intermediate wavelength
of 830 nm the mode of excitation was a mixture of two- and three-photon excitation. At 830 nm the anisotropy is no longer
a molecular parameter, and the mode of excitation and anisotropy of DPH depends on laser power. Frequency-domain anisotropy
decays of DPH in triacetin revealed the same rotational correlation times for two- and three-photon excitation. However, the
time 0 anisotropy of DPH was larger for three-photon excitation than for two-photon excitation. Steady-state anisotropy data
for DPH-labeled membranes revealed the same transition temperature for one- and three-photon excitation. These anisotropy
data indicate that membrane heating was not significant with three-photon excitation and that three-photon excitation may
thus be of practical usefulness in fluorescence spectroscopy and microscopy of membranes. 相似文献
5.
Saba Hemmati Mohammad Yousefi Mirmehdi Hashemi Salehi Mahdis Amiri Malak Hekmati 《应用有机金属化学》2020,34(8):e5653
This paper develops a green method for in situ decorated of palladium nanoparticles over Fe3O4 nanoparticles, by utilizing Strawberry fruit extract and ultrasound irradiations, with no use of any toxic reducing agent. The structure's characterization is represented via diverse analytical methods such as FT-IR, FE-SEM, TEM, WDX, ICP, EDS and XXPS. Catalytic efficiency of magnetic Fe3O4@Strawberry/Pd nanocatalyst is investigated in production of different biphenyls with good turnover frequencies (TOF) and turnover numbers (TON) through Suzuki coupling reactions. Furthermore, the catalyst could be recovered and reused 7 runs without considerable palladium leaching or alteration in its performance. 相似文献
6.
Targeted drug delivery is a promising approach to overcome the limitations of classical chemotherapy. In this respect, Imatinib‐loaded chitosan‐modified magnetic nanoparticles were prepared as a pH sensitive system for targeted delivery of drug to tumor sites by applying a magnetic field. The proposed magnetic nanoparticles were prepared through modification of magnetic Fe3O4 nanoparticles with chitosan and Imatinib. The structural, morphological and physicochemical properties of the synthesized nanoparticles were determined by different analytical techniques including energy‐dispersive X‐ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), Fourier‐transform infrared (FTIR) spectroscopy, high resolution transmission electron microscopy (HR‐TEM), vibrating sample magnetometry (VSM), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). UV/visible spectrophotometry was used to measure the Imatinib contents. Thermal stability of the prepared particles was investigated and their efficiency of drug loading and release profile were evaluated. The results demonstrated that Fe3O4@CS acts as a pH responsive nanocarrier in releasing the loaded Imatinib molecules. Furthermore, the Fe3O4@CS/Imatinib nanoparticles displayed cytotoxic effect against MCF‐7 breast cancer cells. Results of this study can provide new insights in the development of pH responsive targeted drug delivery systems to overcome the side effects of conventional chemotherapy. 相似文献
7.
Lazrak Malak Toufik Hamid Bouzzine Si Mohamed Lamchouri Fatima 《Research on Chemical Intermediates》2020,46(8):3961-3978
Research on Chemical Intermediates - In this work, a series of six organic dyes-sensitized solar cells (DSSCs) combining various π-bridges with a fixed donor (triphenylamine) and a fixed... 相似文献
8.
Henryk Malak Ignacy Gryczynski Joseph R. Lakowicz Gerald J. Meyers Felix N. Castellano 《Journal of fluorescence》1997,7(2):107-112
We examined the intensity and anisotropy decays of DNA labeled with two ruthenium metalligand complexes, [Ru(bpy)2(dppz)]2+ and [Ru(phe)2(dppz)]2+. Both complexes display high emission anisotropies in the absence of rotational diffusion, making them suitable probes for
rotational motions. When bound to DNA, these complexes display decay times as long as 294 ns, providing long-lived probes
of DNA dynamics. The decay times of both complexes were rather insensitive to dissolved oxygen. We examined anisotropy decays
of these complexes bound to B-form DNA. The anisotropy decays revealed correlation times near 10, 50, and several hundred
nanoseconds, suggesting that these probes are sensitive to a wide range of DNA motions. The use of metalligand complexes should
allow resolution of both the torsional and bending motions of DNA, the latter of which has been mostly inaccessible using
shorter-lived fluorescent probes bound to DNA.
Dedicated to Professor Robert F. Steiner upon his retirement 相似文献
9.
A. Malak K. Fic G. Lota C. Vix-Guterl E. Frackowiak 《Journal of Solid State Electrochemistry》2010,14(5):811-816
In the present study, a manganese oxide obtained by the acid treatment of LiMn2O4 spinel has been used as a positive electrode of supercapacitor. Removal of lithium from a spinel allowed to obtain MnO2 compound with the pores partly distributed in atomic scale, hence, an efficient use of its pseudocapacitive properties could
be reached. On the other hand, residual lithium remaining in the structure preserved layered framework of MnO2 with pathways for ions sorption. Physical properties, morphology, and specific surface area of electrode materials were studied
by scanning and transmission electron microscopy, and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge,
and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure
electrochemical parameters. Neutral Li2SO4 aqueous solution has been selected for electrolytic medium. Extension of operating voltage for supercapacitor has been realized
through asymmetric configuration with an activated carbon as a negative electrode. The asymmetric capacitor was operating
within a voltage range up to 2.5 V (limited to 2.0 V for cycling tests) and was able to deliver a specific capacitance of
60 Fg−1 per capacitor at 100 mA g−1 current density. High specific energy of 36 Wh kg−1 was reached but with a moderate power density. 相似文献
10.
The presented program ALIGN_MTX makes alignment of two textual sequences with an opportunity to use any several characters for the designation of sequence elements and arbitrary user substitution matrices. It can be used not only for the alignment of amino acid and nucleotide sequences but also for sequence-structure alignment used in threading, amino acid sequence alignment, using preliminary known PSSM matrix, and in other cases when alignment of biological or non-biological textual sequences is required. This distinguishes it from the majority of similar alignment programs that make, as a rule, alignment only of amino acid or nucleotide sequences represented as a sequence of single alphabetic characters. ALIGN_MTX is presented as downloadable zip archive at http://www.imbbp.org/software/ALIGN_MTX/ and available for free use.As application of using the program, the results of comparison of different types of substitution matrix for alignment quality in distantly related protein pair sets were presented. Threading matrix SORDIS, based on side-chain orientation in relation to hydrophobic core centers with evolutionary change-based substitution matrix BLOSUM and using multiple sequence alignment information position-specific score matrices (PSSM) were taken for test alignment accuracy. The best performance shows PSSM matrix, but in the reduced set with lower sequence similarity threading matrix SORDIS shows the same performance and it was shown that combined potential with SORDIS and PSSM can improve alignment quality in evolutionary distantly related protein pairs. 相似文献