NOVEL FLUORESCENT NEAR-INFRARED AGENT FOR BIOMEDICAL APPLICATIONS

Squaraines represent a class of organic dyes operating in red and near-infrared regions. Due to their unique optical characteristics, such as high extinction coefficients, reduced background fluorescence and light scattering, photostability, these fluorophores attract ever-growing attention as prospective bioimaging agents. The present contribution overviews the spectral properties and some biological applications of the novel squaraine dye SQ-1. This probe was found to possess very high lipid-associating ability manifesting itself in a sharp increase of its emission. Binding of SQ-1 to the lipid bilayers containing zwitterionic and anionic lipids was found to be controlled mainly by hydrophobic interactions. Analysis of SQ-1 spectral behavior in the model membrane systems containing heme proteins revealed the dye sensitivity to the reactive oxygen species. This effect was supposed to originate from the reaction between lipid radicals and SQ-1 occuring at the squaric moiety or in its vicinity. Resonance energy transfer studies highlight the applicability of SQ-1 to structural characterization of amyloid fibrils

HEMOGLOBIN BINDING TO PHOSPHOLIPID MEMBRANES AS REVEALED BY PYRENE FLUORESCENCE STUDY

In this work hemoglobin (Hb) association with lipid bilayers was investigated using fluorescent probe pyrene. Model membranes were prepared from zwitterionic lipid phosphatidylcholine (PC), anionic lipid phosphatidylglycerol (PG) and cholesterol (Chol). Hb-lipid binding was followed by the pyrene fluorescence quenching. Hb-induced decrease of pyrene monomer fluorescence was followed by the increase of relative intensities of vibronic bands. Presumably, Hb penetration into the bilayer increases the space between neighbouring lipids and promotes water penetration into the membrane core. Pyrene excimer emission quenching was interpreted in terms of resonance energy transfer. The greatest depth of Hb penetration into the lipid bilayer was observed in PC vesicles. In Chol-containing liposomes sterol condensing effect prevents deep protein penetration into the membrane. PG has an ability to stabilize lipid bilayers due to the ordered state of its lipid tails and H-bonding interactions between lipid molecules. This also can prevent Hb access to the inner membrane regions. KEY WORDS: hemoglobin, model membranes, protein-lipid complexes, pyrene, fluorescence spectroscopy. ДОСЛІДЖЕННЯ ЗВ'ЯЗУВАННЯ ГЕМОГЛОБІНУ З ФОСФОЛІПІДНИМИ МЕМБРАНАМИ ЗА ДОПОМОГОЮ ПІРЕНУ O.К. Куценко, Г.П. Горбенко, В.М. Трусова Харківський національний університет імені В.Н. Каразіна, пл. Свободи, 4, Харків, 61077 В даній роботі комплексоутворення гемоглобіну (Hb) з ліпідними бішарами різного складу досліджувалось за допомогою флуоресцентного зонду пірену. Зв'язування Hb з ліпідами характеризувалось гасінням флуоресценції зонда, що супроводжувалось зростанням відносної інтенсивності вібронних смуг. Можливо, Hb, проникаючи у бішар, розсуває сусідні молекули ліпідів, сприяючи проникненню води у мембрану. Гасіння випромінювання ексимерів інтерпретувалось у термінах резонансного переносу енергії. Найбільша глибина проникнення білка спостерігалась у РС везикулах. У ліпосомах, які містили Chol, конденсуючий ефект стерола перешкоджав проникненню білка у мембрану. Структурні властивості PG сприяють стабілізації ліпідного бішару, що також може перешкоджати проникненню Hb у внутрішні регіони мембрани. КЛЮЧОВІ СЛОВА: гемоглобін, модельні мембрани, білок-ліпідні комплекси, пірен, флуоресцентна спектроскопія. ИССЛЕДОВАНИЕ СВЯЗЫВАНИЯ ГЕМОГЛОБИНА С ФОСФОЛИПИДНЫМИ МЕМБРАНАМИ С ПОМОЩЬЮ ПИРЕНА O.К. Куценко, Г.П. Горбенко, В.М. Трусова Харьковский национальный университет имени В.Н. Каразина, пл. Свободы, 4, Харьков, 61077 В данной работе комплексообразование гемоглобина (Hb) с липидными бислоями различного состава исследовалось с помощью флуоресцентного зонда пирена. Связывание Hb с липидами характеризовалось тушением флуоресценции пирена, что сопровождалось увеличением относительной интенсивности вибронных полос пирена. Возможно, Hb, проникая в бислой, раздвигает соседние молекулы липидов, способствуя проникновению воды в мембрану. Тушение испускания эксимеров интерпретировалось в терминах резонансного переноса энергии. Наибольшая глубина проникновения белка наблюдалась в РС везикулах. В липосомах, содержащих Chol, конденсирующий эффект стерола препятствовал проникновению белка в мембрану. Структурные свойства PG способствуют стабилизации липидного бислоя, что также может препятствовать проникновению Hb во внутренние области мембраны. КЛЮЧЕВЫЕ СЛОВА: гемоглобин, модельные мембраны, белок-липидные комплексы, пирен, флуоресцентная спектроскопия

Phase diagram and isotope effect in (PrEu)_0.7Ca_0.3CoO_3 cobaltites exhibiting spin-state transitions

We present the study of magnetization, thermal expansion, specific heat, resistivity, and a.c. susceptibility of (Pr$_{1-y}$Eu$_y$)$_{0.7}$Ca$_{0.3}$CoO$_3$ cobaltites. The measurements were performed on ceramic samples with $y = 0.12 - 0.26$ and $y = 1$. Based on these results, we construct the phase diagram, including magnetic and spin-state transitions. The transition from the low- to intermediate-spin state is observed for the samples with $y > 0.18$, whereas for a lower Eu-doping level, there are no spin-state transitions, but a crossover between the ferromagnetic and paramagnetic states occurs. The effect of oxygen isotope substitution along with Eu doping on the magnetic/spin state is discussed. The oxygen-isotope substitution ($^{16}$O by $^{18}$O) is found to shift both the magnetic and spin-state phase boundaries to lower Eu concentrations. The isotope effect on the spin-state transition temperature ($y > 0.18$) is rather strong, but it is much weaker for the transition to a ferromagnetic state ($y < 0.18$). The ferromagnetic ordering in the low-Eu doped samples is shown to be promoted by the Co$^{4+}$ ions, which favor the formation of the intermediate-spin state of neighboring Co$^{3+}$ ions.Comment: 13 pages, including 11 figures, to be published in Phys. Rev.

Møllerov polarimetar za elektrone u dvorani A u JLabu

As part of the spin-physics program at Jefferson Laboratory (JLab), a Moller polarimeter was developed to measure the polarization of electron beam of energies 0.8 to 5.0 GeV. A unique signature for Moller scattering is obtained using a series of three quadrupole magnets which provide an angular selection, and a dipole magnet for energy analysis. The design, commissioning and the first results of the polarization measurements of this polarimeter will be presented as well as future plans to use its small scattering angle capabilities to investigate physics in very low Q2 regime.Kao dio programa istraživanja spinske fizike, u Jeffersonovom se laboratoriju sagradio Møllerov polarimetar radi mjerenja polarizacije elektrona energije 0,8 do 5,0 GeV. Jedinstven signal za Møllerovo raspršenje se postiže nizom od tri kvadrupolna magneta koji određuju kut, te dipolnim magnetom za analizu impulsa elektrona. Opis, preuzimanje i prva mjerenja s tim polarimetrom se izlažu, kao i planovi za buduću upotrebu mogućnosti sustava za mjerenja na malim kutovima raspršenja radi istraživanja fizike za vrlo male Q2

Møllerov polarimetar za elektrone u dvorani A u JLabu

As part of the spin-physics program at Jefferson Laboratory (JLab), a Moller polarimeter was developed to measure the polarization of electron beam of energies 0.8 to 5.0 GeV. A unique signature for Moller scattering is obtained using a series of three quadrupole magnets which provide an angular selection, and a dipole magnet for energy analysis. The design, commissioning and the first results of the polarization measurements of this polarimeter will be presented as well as future plans to use its small scattering angle capabilities to investigate physics in very low Q2 regime.Kao dio programa istraživanja spinske fizike, u Jeffersonovom se laboratoriju sagradio Møllerov polarimetar radi mjerenja polarizacije elektrona energije 0,8 do 5,0 GeV. Jedinstven signal za Møllerovo raspršenje se postiže nizom od tri kvadrupolna magneta koji određuju kut, te dipolnim magnetom za analizu impulsa elektrona. Opis, preuzimanje i prva mjerenja s tim polarimetrom se izlažu, kao i planovi za buduću upotrebu mogućnosti sustava za mjerenja na malim kutovima raspršenja radi istraživanja fizike za vrlo male Q2

Interplaying Cassandra NoSQL Consistency and Performance: A Benchmarking Approach

This experience report analyses performance of the Cassandra NoSQL database and studies the fundamental trade-off between data consistency and delays in distributed data storages. The primary focus is on investigating the interplay between the Cassandra performance (response time) and its consistency settings. The paper reports the results of the read and write performance benchmarking for a replicated Cassandra cluster, deployed in the Amazon EC2 Cloud. We present quantitative results showing how different consistency settings affect the Cassandra performance under different workloads. One of our main findings is that it is possible to minimize Cassandra delays and still guarantee the strong data consistency by optimal coordination of consistency settings for both read and write requests. Our experiments show that (i) strong consistency costs up to 25% of performance and (ii) the best setting for strong consistency depends on the ratio of read and write operations. Finally, we generalize our experience by proposing a benchmarking-based methodology for run-time optimization of consistency settings to achieve the maximum Cassandra performance and still guarantee the strong data consistency under mixed workloads

Carbon nanotubes for polarization sensitive terahertz plasmonic interferometry

We report on helicity sensitive photovoltaic terahertz radiation response of a carbon nanotube made in a configuration of a field-effect transistor. We find that the magnitude of the rectified voltage is different for clockwise and anticlockwise circularly polarized radiation. We demonstrate that this effect is a fingerprint of the plasma waves interference in the transistor channel. We also find that the presence of the helicity- and phase-sensitive interference part of the photovoltaic response is a universal phenomenon which is obtained in the systems of different dimensionality with different single-particle spectrum. Its magnitude is a characteristic of the plasma wave decay length. This opens up a wide avenue for applications in the area of plasmonic interferometry

Polarization degrees of freedom in photoinduced two-nucleon knockout from finite nuclei

The polarization degrees of freedom in photoinduced two-nucleon knockout from finite nuclei are studied. It is pointed out that they open good perspectives to study the dynamics of dinucleons in the medium in detail. The ($\gamma,pp$) and ($\gamma,pn$) angular cross sections, photon asymmetries and outgoing nucleon polarizations are calculated for the target nuclei $^{16}$O and $^{12}$C and photonenergies ranging from 100 up to 500 MeV. It is investigated to which degree the two-nucleon emission reaction is dominated by photoabsorption on $^3S_1(T=0)$ proton-neutron and $^1S_0(T=1)$ proton-proton pairs in the nuclear medium. The calculations demonstrate that dominance of $S$ wave photoabsorption in the ($\gamma,pn$) channel does not necessarily imply that the reaction mechanism is similar to what is observed in deuteron photodisintegration.Comment: 27 pages, REVTeX 3.0 with epsf.sty, 11 figures in EPS forma