排序方式: 共有17条查询结果,搜索用时 0 毫秒
1.
Margarita A. Deneva Pepa I. Uzunova Marin N. Nenchev 《Optical and Quantum Electronics》2007,39(3):193-212
We report (theory, experimental check) an improved approach for generation of a tunable, subnanosecond pulse (0.1–0.4 ns),
based on a single pulsation (“spike”) separation from the transient oscillations in a dye laser with active mirror (AMIR).
A pumping by 20–50 ns pulses from Q-switched Nd:YAG laser is considered. The separation is in original, two-spectral selective
channels cavity, where the forced by AMIR quenched generation at one of the wavelength stops initially started spiking generation
at the other wavelength after the first spike development. The AMIR quickly starts the quenching generation at a precisely
controlled moment and with necessary intensity thus assuring the desired separation. An advantage is a high reproducibility
of the separation for high (~250%) pump power fluctuations combined with tuning in large range (~20 nm). To obtain such an
operation we form ~1 ns leading front pump pulse by electrooptical temporal cutting of the input pump pulse and use an optical
delay line. This increases also a few times the power in the separated spike (to be ~100 kW). Our approach widens the combinations
of lasers for effective applications of spike separation technique (dye lasers excited by Q-switched solid-state or Cu-vapor
lasers). 相似文献
2.
3.
The interaction between particle-like sources of the
nematic director distortions (e.g., colloids, point
defects, macromolecules in nematic emulsions) allows for a useful
analogy with the electrostatic multipole interaction between
charged bodies. In this paper we develop this analogy to the level
corresponding to the charge density and consider the general
status of the pairwise approach to the nematic emulsions with
finite-size colloids. It is shown that the elastic analog of the
surface electric charge density is represented by the two
transverse director components on the surface imposing the
director distortions. The elastic multipoles of a particle are
expressed as integrals over the charge density distribution on
this surface. Because of the difference between the scalar
electrostatics and vector nematostatics, the number of elastic
multipoles of each order is doubled compared to that in the
electrostatics: there are two elastic charges, two vectors of
dipole moments, two quadrupolar tensors, and so on. The
two-component elastic charge is expressed via the vector of
external mechanical torque applied on the particle. As a result,
the elastic Coulomb-like coupling between two particles is found
to be proportional to the scalar product of the two external
torques and does not directly depend on the particles' form and
anchoring. The real-space Green function method is used to develop
the pairwise approach to nematic emulsions and determine its form
and restrictions. The pairwise potentials are obtained in the
familiar form, but, in contrast to the electrostatics, they
describe the interaction between pairs (dyads) of the elastic
multipole moments. The multipole moments are shown to be uniquely
determined by the single-particle director field, unperturbed by
other particles. The pairwise approximation is applicable only in
the leading order in the small ratio particle
size-to-interparticle distance as the next order contains
irreducible three-body terms. 相似文献
4.
Triple Emission from p‐Dimethylaminobenzonitrile–Cucurbit[8]uril Triggers the Elusive Excimer Emission
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Mhejabeen Sayed Dr. Frank Biedermann Dr. Vanya D. Uzunova Khaleel I. Assaf Dr. Achikanath C. Bhasikuttan Dr. Haridas Pal Prof. Werner M. Nau Dr. Jyotirmayee Mohanty 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):691-696
The intriguing dual‐emission behavior of p‐ dimethylaminobenzonitrile (DMABN) and the identity of the associated excited states is, arguably, the most extensively investigated and also controversially discussed molecule‐ specific phenomenon of modern photochemistry. We have now found a new, third fluorescence band when DMABN is encapsulated within the water‐soluble molecular container cucurbit[8]uril (CB8). It is centered between the previously observed emissions and assigned to the elusive excimer emission from DMABN through 1:2 CB8:DMABN complex formation. Heating of the CB8 ? (DMABN)2 complex from 0 to 100 °C results in the dissociation of the ternary complex and restoration of the dual‐emission properties of the monomer. Alternatively, monomer emission can be obtained by selecting cucurbit[7]uril (CB7), a host homologue that is too small to accommodate two DMABN molecules, or by introducing ethyl instead of methyl groups at the amino terminus of the aminobenzonitrile guest. 相似文献
5.
Bailey DM Hennig A Uzunova VD Nau WM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(20):6069-6077
The coupling of an enzymatic transformation with dynamic host-guest exchange allows the unselective binding of macrocycles to be used for highly selective analyte sensing. The resulting supramolecular tandem enzyme assays require the enzymatic substrate and its corresponding product to differ significantly in their affinity for macrocycles, for example, cation receptors, and to show a differential propensity to displace a fluorescent dye from its host-guest complex. The enzymatic transformation results in a concomitant dye displacement that can be accurately followed by optical spectroscopy, specifically fluorescence. By exploiting this label-free continuous enzyme assay principle with the fluorescent dye Dapoxyl and the macrocyclic host cucurbit[7]uril, a multiparameter sensor array has been designed, which is capable of detecting the presence of amino acids (e.g. histidine, arginine, lysine, and tyrosine) and their decarboxylases. Only in the presence of both, the particular amino acid and the corresponding decarboxylase, is the amine or diamine product formed. These products are more highly positively charged than the substrate, have a higher affinity for the macrocycle and, therefore, displace the dye from the complex. The extension of the high selectivity and muM sensitivity of the tandem assay principle has also allowed for the accurate measurement of D-lysine enantiomeric excesses of up to 99.98 %, as only the L-enantiomer is accepted by the enzyme as a substrate and is converted to the product that is responsible for the observed fluorescence signal. 相似文献
6.
Dong-Sheng Guo Vanya D. Uzunova Khaleel I. Assaf Alexandra I. Lazar Yu Liu 《Supramolecular chemistry》2016,28(5-6):384-395
AbstractThe driving forces of association between three different families of macrocycles as hosts, namely cyclodextrins (α-, β-, and γ-), p-sulfonatocalix[n]arenes (n = 4–6) as well as cucurbit[n]urils (n = 6–8), and three different bicyclic azoalkane homologues as guests, namely 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH), 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as well as 2,3-diazabicyclo[2.2.3]non-2-ene (DBN), were examined by means of calorimetric titrations, NMR spectroscopy and molecular dynamics simulation, all in aqueous solution. The small, spherical and uncharged guests preferably bind inside the cavities of the medium sized hosts. The inclusion complexation by β-cyclodextrin and p-sulfonatocalix[4]arene shows medium binding affinities (millimolar), while cucurbit[7]uril macrocycle shows very strong binding (micromolar). For all types of macrocycles, the complex formation is enthalpically driven (ΔH° < 0), accompanied by slightly unfavourable entropy changes (ΔS° < 0). The results are discussed in terms of the flexibility of the hosts, the hydrophobic character of their cavities and the release of high-energy water upon binding, and generalised by including two additional guests, the ketones cyclopentanone and (+)-camphor. 相似文献
7.
Aneliya Ivanova Aleksandar Atemin Sonya Uzunova Georgi Danovski Radoslav Aleksandrov Stoyno Stoynov Marina Nedelcheva-Veleva 《Molecules (Basel, Switzerland)》2022,27(1)
Cells have evolved elaborate mechanisms to regulate DNA replication machinery and cell cycles in response to DNA damage and replication stress in order to prevent genomic instability and cancer. The E3 ubiquitin ligase SCFDia2 in S. cerevisiae is involved in the DNA replication and DNA damage stress response, but its effect on cell growth is still unclear. Here, we demonstrate that the absence of Dia2 prolongs the cell cycle by extending both S- and G2/M-phases while, at the same time, activating the S-phase checkpoint. In these conditions, Ctf4—an essential DNA replication protein and substrate of Dia2—prolongs its binding to the chromatin during the extended S- and G2/M-phases. Notably, the prolonged cell cycle when Dia2 is absent is accompanied by a marked increase in cell size. We found that while both DNA replication inhibition and an absence of Dia2 exerts effects on cell cycle duration and cell size, Dia2 deficiency leads to a much more profound increase in cell size and a substantially lesser effect on cell cycle duration compared to DNA replication inhibition. Our results suggest that the increased cell size in dia2∆ involves a complex mechanism in which the prolonged cell cycle is one of the driving forces. 相似文献
8.
Design and synthesis of fluorescent shell functionalized polymer micelles for biomedical application
Selen R. Ismail Rayna G. Bryaskova Nikolai I. Georgiev Nikoleta D. Philipova Ventsislav V. Bakov Veselina P. Uzunova Rumiana D. Tzoneva Vladimir B. Bojinov 《先进技术聚合物》2020,31(6):1365-1376
pH‐sensitive polymers can be defined as polyelectrolytes that include in their structure weak acidic or basic groups that either accept or release protons in response to a change in the environmental pH. This work summarizes the design, synthesis, and potential applications of pH‐responsive fluorescent copolymers in the biomedical field. This was achieved using atom transfer radical polymerization (ATRP) of tert‐butyl acrylate using a CuBr/N,N,N′,N″N″‐pentamethyldiethylenetriamine catalyst system in conjunction with an alkyl bromide as the initiator. Well‐defined macroinitiators based on poly(tert‐butyl acrylate) with narrow molecular weight distributions were obtained by the addition of an appropriate solvent system in order to create a homogeneous catalytic system. The addition of n‐butyl acrylate as a second building block in order to create well‐defined poly(tert‐butyl acrylate)‐b‐poly(n‐butyl acrylate) block copolymers (PtBA‐b‐PnBA) followed by chemical modification of the block copolymers and functionalization with an appropriate fluorescent compound are the basis for the preparation of well‐defined fluorescent pH‐sensitive micelles. Thus, prepared water soluble nanosized pH‐sensitive micelles consisting of hydrophobic poly(n‐butyl acrylate) core and hydrophilic polyacrylic acid shell decorated with an appropriate fluorescent compound determined their potential applications of these systems in the field of biomedicine as biosensors, controlled drug delivery systems, and so on. In this respect, the cell viability and internalization of the polymer micelles were studied. 相似文献
9.
Dr. Aleksander Czogalla Dominik J. Kauert Dr. Henri G. Franquelim Dr. Veselina Uzunova Dr. Yixin Zhang Prof. Ralf Seidel Prof. Petra Schwille 《Angewandte Chemie (International ed. in English)》2015,54(22):6501-6505
We report a synthetic biology‐inspired approach for the engineering of amphipathic DNA origami structures as membrane‐scaffolding tools. The structures have a flat membrane‐binding interface decorated with cholesterol‐derived anchors. Sticky oligonucleotide overhangs on their side facets enable lateral interactions leading to the formation of ordered arrays on the membrane. Such a tight and regular arrangement makes our DNA origami capable of deforming free‐standing lipid membranes, mimicking the biological activity of coat‐forming proteins, for example, from the I‐/F‐BAR family. 相似文献
10.
The 3d-element transition metal dioxide MO(2), peroxide M(O(2)), and superoxide MOO clusters (M=Sc-Zn), are studied by density functional theory with the B1LYP functional. The reliability of the methods and basis sets employed was tested by a reinvestigation of the monoxides, for which a database of experimental data is available. The global minima on the M+O(2) potential energy surfaces correspond to dioxide structure, the only exception being CuOO, with a superoxide structure. All Zn dioxygen clusters are thermodynamically unstable-their ground states lie higher than the dissociation limit to Zn+O(2). Our calculations are in favor of the high-spin configurations for the FeO(2), CoO(2), and NiO(2) ground states, which are still a subject of extensive theoretical and experimental studies. These assignments are confirmed by the coupled-cluster method, CCSD(T), except for NiO(2). Based on the existence of a stable NiO(2) monoanion in a (4)B(1) state, however, it can be concluded that NiO(2) in its (5)A(1) state should also be stable. The vibrational frequencies are calculated for clusters entrapped in the cubic cell of solid Ar matrix and compared with those obtained for gas-phase clusters. The matrix has no influence on the vibrations of the monoxides and most of the dioxides; however, Co and Ni-dioxoclusters interact strongly with the atoms from the noble gas matrix. The most intense frequencies in the IR spectra are shifted to lower energies and the ordering of the low-lying electronic states by stability is also reversed. According to the electrostatic potential maps, the oxygen atoms in the peroxides are more nucleophilic than those in the dioxides and superoxides. The terminal oxygen atom in superoxides is more nucleophilic than its M-bonded oxygen atom, though charge distribution analysis predicts a smaller negative charge on the terminal oxygen. TiO(2) is the only dioxide in which nucleophilic character in the vicinity of the metal cation is induced. 相似文献