Search

Nitroxide spin probes and spin labels are broadly utilized in EPR oximetry studies ranging from in vivo investigation to profiling heterogeneous environment of lipid bilayer membranes and proteins by site-specific oxygen-accessibility experiments. In such experiments, effective collision distances of the spin exchange interaction between the nitroxide and molecular oxygen are typically assumed to be the same even though localization of spin density over the nitroxide moiety is known to be affected by local polarity. Furthermore, some biophysical studies, such as those involving lipid bilayers, are often carried out with structurally different nitroxides but the results are analyzed under an assumption that proportionality between changes in the nitroxide electronic relaxation times and the product of the local oxygen concentration and translational diffusion coefficients remain the same. Here, we present an experimental verification of such a prevailing but not yet verified assumption by measuring effects of molecular oxygen in air and pure oxygen at atmospheric pressure on continuous wave EPR spectra of six structurally different nitroxides including those capable of reversible protonation. The data were analyzed using a convolution fitting model, which, by comparing EPR spectra measured at two different oxygen concentrations, allows one to extract the peak-to-peak width $${\Delta }B_{{{\text{p}} - {\text{p}}}}$$ of a Lorentzian function that characterizes the effect of oxygen broadening. While the data on oxygen broadening measured by comparing EPR spectra of nitroxide solutions equilibrated with nitrogen and pure oxygen show clear trends that are rationalized by differences in the nitroxide structure, the overall variations in $${\Delta }B_{{{\text{p}} - {\text{p}}}}$$ for various nitroxides fall within ca. ± 5%. Such variations are comparable to the effect of “salting-out” of molecular oxygen in aqueous solutions when electrolytes are present in physiological concentrations. Overall, the data further establish nitroxides as robust EPR molecular probes to measure the product of local oxygen concentration and its translational diffusion coefficient under a wide range of conditions such as pH and electrolyte concentrations.

We record stimulated Raman scattering spectra in chemically-pure glycerol with the formation of two Stokes satellites with equidistant Raman frequencies ν = 2889 cm−1. To excite the scattered radiation, we employ short pulses of the second optical harmonic of a YAG:Nd3+ laser with a wavelength of 532 nm. Using the fundamental harmonic of the YAG:Nd3+ laser λ = 1064 nm, we convert the infrared Stokes component of stimulated Raman scattering into the visible range of the spectrum with the help of a nonlinear crystal of barium titanate. The large Raman shift of the Stokes components of stimulated Raman scattering makes it possible to use glycerol to convert laser radiation into different spectral ranges.

The problem of microgeometry profiling of the lubricating layer of an irreversible plain bearing is considered with the assumption of the maximum lift force on the basis of a Rayleigh pocket in order to construct profiles easy to manufacture. To this end the lift force dependence on several selected parameters, which most accurately approximate the considered profile to the profile of the global extremum, is investigated. The formulated problem of parametric optimization is solved using the software packages IOSO and modeFrontier, whereas the pressure field in the bearing is determined by the Navier–Stokes equations using the ANSYS/CFX. The results may be used to construct optimal processable profiles of plain bearings applied in various power engineering and other machines and devices.

Interfacial electrostatic properties of monodisperse silica nanoparticles (SiNPs) in aqueous suspensions as a function of bulk pH were characterized by spin labeling EPR of two ionizable nitroxides...

A novel Dynamic Nuclear Polarization (DNP) NMR polarizing agent ToSMTSL-PTE representing a phospholipid with a biradical TOTAPOL tethered to the polar head group has been synthesized, characterized, and employed to enhance solid-state Nuclear Magnetic Resonance (SSNMR) signal of a lipid-reconstituted integral membrane protein proteorhodopsin (PR). A matrix-free PR formulation for DNP improved the absolute sensitivity of NMR signal by a factor of ca. 4 compared to a conventional preparation with TOTAPOL dispersed in a glassy glycerol/water matrix. DNP enhancements measured at 400 MHz/263 GHz and 600 MHz/395 GHz showed a strong field dependence but remained moderate at both fields, and comparable to those obtained for PR covalently modified with ToSMTSL. Additional continuous wave (CW) X-band electron paramagnetic resonance (EPR) experiments with ToSMTSL-PTE in solutions and in lipid bilayers revealed that an unfavorable conformational change of the linker connecting mononitroxides could be one of the reasons for moderate DNP enhancements. Further, differential scanning calorimetry (DSC) and CW EPR experiments indicated an inhomogeneous distribution and/or a possibility of a partial aggregation of ToSMTSL-PTE in DMPC:DMPA bilayers when the concentration of the polarizing agent was increased to 20 mol% to maximize the DNP enhancement. Thus, conformational changes and an inhomogeneous distribution of the lipid-based biradicals in lipid bilayers emerged as important factors to consider for further development of this matrix-free approach for DNP of membrane proteins.

The Raman spectra of different specimens of protium and deuterium water have been compared. The spectra have been recorded using a fiber-optic technique and a compact BWS465-785H spectrometer. The spectra of spontaneous Raman scattering have been excited using a cw laser with a wavelength of 785 nm. Significant differences in the low-frequency Raman spectra from different specimens of water have been observed, which were explained by the presence of structural changes and impurities in analyzed specimens. Stimulated Raman spectra in protium and deuterium water have been measured upon excitation by picosecond laser pulses at a wavelength of 532 nm. The presence of low-frequency satellites in the spectrum of stimulated Raman scattering, indicating the structuring of water due to the formation of clusters consisting of a few molecules, has been revealed.

This work investigates the quality of the ENDF 56Fe cross-section libraries for describing the transport of fast neutrons in iron. We have used the D(d,n)3He reaction with a pulsed 7-MeV deuteron beam energy as a neutron source and analyzed the neutrons transmitted through two natural iron spheres of thicknesses 3 and 8 cm. The experimental neutron time-of-flight transmitted spectra for various angles are compared with MCNP simulations. Our result indicates the possibility of an underestimation of the nonelastic cross section and an overestimation of the elastic cross section for 56Fe in the ENDF/B-VII.1 library for the neutron energy range of 7.2 to 10.2 MeV. Our result agrees qualitatively with the Ramsauer model and optical model calculations. This discrepancy in the library cross section might lead to an underestimation/overestimation of material damage in nuclear reactor calculations. A newer evaluation, ENDF/B-VIII.0, was released subsequent to the completion of the majority of this project....

The spectra of multifrequency parametric stimulated Raman scattering in a barium nitrate single crystal is investigated. When this single crystal is excited by ultrashort (80 ps) YAG : Nd3+ laser pulses with a wavelength of 1064 nm, a frequency comb of eight anti-Stokes components is observed in the visible spectral range. The Raman satellites are due to the totally symmetric vibrational modes of barium nitrate single crystal. The frequencies of the corresponding Raman Stokes components in the IR range (from 1193 to 9662 nm) are calculated. The results of the study open the way to form an array of laser frequencies from the IR to green spectral range with a period of 1047 cm–1.

In this paper we present the first systematic analysis of the impact of the populated vs. intrinsic spin distribution on the nuclear level density and γ-ray strength function retrieved through the Oslo Method. We illustrate the effect of the spin distribution on the recently performed 239Pu(d,pγ)240Pu experiment using a 12 MeV deuteron beam performed at the Oslo Cyclotron Lab. In the analysis we couple state-of-the-art calculations for the populated spin-distributions with the Monte-Carlo nuclear decay code RAINIER to compare Oslo Method results to the known input. We find that good knowledge of the populated spin distribution is crucial and show that the populated distribution has a significant impact on the extracted nuclear level density and γ-ray strength function for the 239Pu(d,pγ)240Pu case.

At the present time, the Dubna gas-filled separator is the world’s leading physical facility in the field of synthesis of superheavy elements. This is the device where new elements with Z = 114–118 (Fl, Mc, Lv, Ts, Og) were synthesized. The original tools and methods considered in this paper are applied in reactions of complete fusion of actinide target + 48Ca → SHN + xn type. Modification of the active correlation method is planned after the launch of new DC-280 cyclotron developed at the Flerov Laboratory of Nuclear Reactions in 2019.

Compared to traditional collision induced dissociation methods, electron capture dissociation (ECD) provides more comprehensive characterization of large peptides and proteins as well as preserves labile post-translational modifications. However, ECD experiments are generally restricted to the high magnetic fields of FTICR-MS that enable the reaction of large polycations and electrons. Here, we demonstrate the use of an electromagnetostatic ECD cell to perform ECD and hybrid ECD methods utilizing 193 nm photons (ECuvPD) or collisional activation (EChcD) in a benchtop quadrupole–Orbitrap mass spectrometer. The electromagnetostatic ECD cell was designed to replace the transfer octapole between the quadrupole and C-trap. This implementation enabled facile installation of the ECD cell, and ions could be independently subjected to ECD, UVPD, HCD, or any combination. Initial benchmarking and characterization of fragmentation propensities for ECD, ECuvPD, and EChcD were performed using ubiquitin (8.6 kDa). ECD yielded extensive sequence coverage for low charge states of ubiquitin as well as for the larger protein carbonic anhydrase II (29 kDa), indicating pseudo-activated ion conditions. Additionally, relatively high numbers of d- and w-ions enable differentiation of isobaric isoleucine and leucine residues and suggest a distribution of electron energies yield hot-ECD type fragmentation. We report the most comprehensive characterization to date for model proteins up to 29 kDa and a monoclonal antibody at the subunit level. ECD, ECuvPD, and EChcD yielded 93, 95, and 91% sequence coverage, respectively, for carbonic anhydrase II (29 kDa), and targeted online analyses of monoclonal antibody subunits yielded 86% overall antibody sequence coverage.

The results of studying the process of distillation in a column with 21 vortex contact stages have been reported. The partial condensation of an ascending ethanol–water mixture vapor at the contact stages has been shown to intensify the mixture distillation process by threefold compared to adiabatic distillation. The process parameters that intensify heat and mass transfer in thermal distillation have been established. Some relationships for estimating the efficiency of a vortex contact stage have been derived.

The problem solution for the thrust sector bearing of a hydrogenerator with oil lubrication is considered. The value of the most important hydrodynamic characteristic of the thrust bearing, which is the lifting force, is defined. The pressure field is determined by the direct numerical integration of the Navier-Stokes equations for a lubricating oil layer. The case of the absence of heat exchange between the lubrication layer and solid-state components of the thrust bearing and the case when the heat exchange is taken into account are considered. The calculation results, which are compared with an experiment, are presented. The research results can serve as the basis to develop automation systems for designing hydrogenerator thrust bearings.

A technique of probe photoluminescence and Raman spectroscopy has been developed. This technique makes it possible to detect small (10−6 to 10−8 g) amounts of uranyl compounds at short exposure times (1−10 s). The photoluminescence spectra of Na[UO2CH3(COO)3] polycrystals recorded upon excitation by short-wavelength radiation of LEDs and lasers are found to contain equidistant bands with a shift of 854 cm−1, which corresponds to the frequency of totally symmetric uranyl vibration also manifesting itself in Raman spectra.

The synthesis and characterization of a lipidlike electrostatic spin probe, (S)-2,3-bis(palmitoyloxy)propyl 2-((4-(4-(dimethylamino)-2-ethyl-1-oxyl-5,5-dimethyl-2,5-dihydro-1H-imidazol-2-yl)benzyl)disulfanyl)ethyl phosphate (IKMTSL-PTE), are being reported. The intrinsic pKa0 of IKMTSL-PTE was determined by X-band (9.5 GHz) electron paramagnetic resonance (EPR) titration of a water-soluble model compound, 4-(dimethylamino)-2-ethyl-2-(4-(((2-hydroxyethyl)disulfanyl)methyl)phenyl)-5,5-dimethyl-2,5-dihydro-1H-imidazol-1-oxyl (IKMTSL-ME), an adduct of methanethiosulfonate spin label IKMTSL and 2-mercaptoethanol. The pKa0 of IKMTSL-ME in bulk aqueous solutions was found to be significantly higher than that of 4-(((2-hydroxyethyl)disulfanyl)methyl)-2,2,3,5,5-pentamethylimidazolidin-1-oxyl (IMTSL-ME), an adduct of the corresponding methanethiosulfonate spin label IMTSL and 2-mercaptoethanol (17 °C, pKa0 = 6.16 ± 0.03 vs 20 °C, pKa0 = 3.33 ± 0.03, respectively). A series of EPR titration experiments with IKMTSL-ME in aqueous solutions containing 0-60% v/v isopropanol have been carried out at 17 and 48 °C to determine the effects of temperature and bulk dielectric permittivity constant, e, on the probe pKa. A linear relationship between the probe pKa and e has been established and found to be essentially the same at 17 and 48 °C. The polarity term contributing to the pKa of IKMTSL-PTE at an uncharged lipidlike interface was determined by incorporating the probe into electrically neutral micelles formed from nonionic detergent Triton X-100, and it was found, similar to IMTSL-PTE, to be negative. In negatively charged DMPG lipid bilayers, IKMTSL-PTE exhibits ionization transitions with significantly higher pKa values than those previously reported for IMTSL-PTE (e.g., at 17 °C, pKai = 7.80 ± 0.03 vs pKa0 = 5.70 ± 0.05). The surface electrostatic potentials of DMPG lipid bilayers calculated using IKMTSL-PTE titration data were found to be somewhat lower than those calculated using IMTSL-PTE. The lower values measured by IKMTSL-PTE are the likely consequences of the structure of the linker that positions the reporter nitroxide further away from the bilayer plane into aqueous phase. Overall, the ionization transitions of IKMTSL-PTE with pKa values close to the neutral pH range make this lipidlike molecule a valuable spectroscopic EPR probe for studying the electrostatic phenomena at biological interfaces, including lipid bilayer/membrane protein systems, that could be unstable in the acidic pH range accessible by the previously available probes.

Spin probe and spin labeling Electron Paramagnetic Resonance methods are indispensable research tools for solving a wide range of bioanalytical problems—from measuring microviscosity and polarity of phase-separated liquids to oxygen concentrations in tissues. One of the emerging uses of spin probes are the studies of proton transfer-related and surface electrostatic phenomena. The latter Electron Paramagnetic Resonance methods rely on molecular probes containing an additional functionality capable of reversible ionization (protonation, in particular) in the immediate proximity to an Electron Paramagnetic Resonance-active reporter group, such as (N–O•) for nitroxides. The consequent formation of protonated and nonprotonated nitroxide species with different magnetic parameters (A iso, g iso) could be readily distinguished by Electron Paramagnetic Resonance. Bioanalytical Electron Paramagnetic Resonance studies employing pH-sensitive paramagnetic probes typically involve determination of the equilibrium constant (pK a) between the protonated and nonprotonated forms of the nitroxide. However, any chemical equilibrium involving charged species, such as ionization of acids and bases, and so the reversible protonation of the nitroxide, is known to be affected by an ionic strength of the solution. Currently, only scarce data for the effect of the solution ionic strength on the experimental pK a’s of the ionizable nitroxides can be found in the literature. Here we have carried out a series of Electron Paramagnetic Resonance titration experiments for aqueous solutions of 2,2,3,4,5,5-hexamethylimidazolidin-1-oxyl (HMI) nitroxide known for one of the largest differences in the isotropic nitrogen hyperfine coupling constant A iso between the protonated and nonprotonated forms. Electrolyte concentration was varied over an exceptionally large range (i.e., from 0.05 to 5.0 M) to elucidate the effect of ionic strength on the ionization constant of this pH-sensitive Electron Paramagnetic Resonance probe and the data were compared to the Debye–Huckel limiting law. Effects of the ionic strength on the magnetic parameters of the ionizable nitroxides are also discussed.

The Oslo method has been applied to particle-$\ensuremath{\gamma}$ coincidences following the $^{239}\mathrm{Pu}(d,p)$ reaction to obtain the nuclear level density (NLD) and $\ensuremath{\gamma}$-ray strength function ($\ensuremath{\gamma}\mathrm{SF}$) of $^{240}\mathrm{Pu}$. The experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron Laboratory. The low spin transfer of this reaction leads to a spin-parity mismatch between populated and intrinsic levels. This is a challenge for the Oslo method as it can have a significant impact on the extracted NLD and $\ensuremath{\gamma}\mathrm{SF}$. We have developed an iterative approach to ensure consistent results even for cases with a large spin-parity mismatch, in which we couple Green's function transfer calculations of the spin-parity dependent population cross-section to the nuclear decay code rainier. The resulting $\ensuremath{\gamma}\mathrm{SF}$ shows a pronounced enhancement between 2--4 MeV that is consistent with the location of the low-energy orbital $M1$ scissors mode.

The photoluminescence spectra of sodium uranyl acetate polycrystals are recorded under excitation by different sources (semiconductor light-emitting diodes, cw lasers, and repetitively pulsed lasers). The excitation wavelengths fall into the absorption band of this solid, which makes it possible to record photoluminescence beginning from an extremely small volume of the material (10–10 cm3) at exposures of ~10–3 s.

Secondary emission spectra of globular silica photonic crystals when their surfaces were exposed to laser pulses 250 fs long at a power density to 1 TW/cm2 have been studied. Optical harmonics and plasma emission were detected in this case. For the opal matrix containing pores filled with air, in the reflection mode, the third optical harmonic with a conversion efficiency of ∼10% arises. The highest conversion efficiency for exciting radiation with wavelengths of 1026 or 513 nm is implemented when the frequencies of the exciting radiation or the second harmonic are near the stop band edge. In globular photonic crystals filled with sodium nitrite or barium titanate ferroelectrics, the second optical harmonic is observed. The exciting radiation conversion efficiency to the second optical harmonic was a few percent and depended on the frequency of exciting radiation and photonic crystal globule diameters. It is found that the plasma emission intensity increases with the exciting radiation power density. The dependences of the intensity of the second and third optical harmonics on the pump intensity are constructed for various photonic crystal globule diameters.

The technique for recording Raman spectra in uranium compounds using a probe minispectrometer with a multielement radiation detector has been developed. A selective filter, which reflects exciting laser radiation and transmits Raman signals, has been used to suppress the exciting radiation. It is shown that the technique developed makes it possible to record Raman spectra from a small amount (~10–5 g) of sodium uranyl-acetate polycrystals in a wide spectral range for several seconds.

EPR pulsed dipolar spectroscopy (PDS) is indispensable for measurements of nm-scale distances between electronic spins in biological and other systems. While several useful modifications and pulse sequences for PDS have been developed in recent years, DEER experiments utilizing pump and observer pulses at two different frequencies remain the most popular for practical applications. One of the major drawbacks of all the available DEER approaches is the presence of a significant unmodulated fraction in the detected signal that arises from an incomplete inversion of the coupled spins by the pump pulse. The latter fraction is perceived as one of the major sources of error for the reconstructed distance distributions. We describe an alternative detection scheme – a R efocused O ut- O f- Ph ase DEER (ROOPh-DEER) – to acquire only the modulated fraction of the dipolar DEER signal. When Zeeman splitting is small compared to the temperature, the out-of-phase magnetization components cancel each other and are not observed in 4-pulse DEER experiment. In ROOPh-DEER these components are refocused by an additional pump pulse while the in-phase component containing an unmodulated background is filtered out by a pulse at the observed frequency applied right at the position of the refocused echo. Experimental implementation of the ROOPh-DEER detection scheme requires at least three additional pulses as was demonstrated on an example of a 7-pulse sequence. The application of 7-pulse ROOPh-DEER sequence to a model biradical yielded the interspin distance of 1.94 ± 0.07 nm identical to the one obtained with the conventional 4-pulse DEER, however, without the unmodulated background present as a dominant fraction in the latter signal.

As the application of mass spectrometry intensifies in scope and diversity, the need for advanced instrumentation addressing a wide variety of analytical needs also increases. To this end, many modern, top-end mass spectrometers are designed or modified to include a wider range of fragmentation technologies, for example, ECD, ETD, EThcD, and UVPD. Still, the majority of instrument platforms are limited to more conventional methods, such as CID and HCD. While these latter methods have performed well, the less conventional fragmentation methods have been shown to lead to increased information in many applications including middle-down proteomics, top-down proteomics, glycoproteomics, and disulfide bond mapping. We describe the modification of the popular Q Exactive Orbitrap mass spectrometer to extend its fragmentation capabilities to include ECD. We show that this modification allows ≥85% matched ion intensity to originate from ECD fragment ion types as well as provides high sequence coverage (≥60%) of intact proteins and high fragment identification rates with ∼70% of ion signals matched. Finally, the ECD implementation promotes selective disulfide bond dissociation, facilitating the identification of disulfide-linked peptide conjugates. Collectively, this modification extends the capabilities of the Q Exactive Orbitrap mass spectrometer to a range of new applications.

The characteristics of stimulated Raman scattering in benzene and carbon disulfide introduced in pores of globular photonic crystals—opal matrices formed from close-packed balls (globules) of amorphous quartz (silica)—have been experimentally studied. Stimulated Raman scattering spectra have been excited by giant pulses of the second optical harmonic (532 nm) of a YAG laser. The spectra have been recorded in the direction of mirror reflection from the (111) growth surface of a globular photonic crystal at various angles of incidence (10°–70°) of laser radiation. It has been shown that the threshold of stimulated Raman scattering decreases sharply (by more than an order of magnitude) at a certain angle of mirror reflection and additional Stokes and anti-Stokes Raman satellites appear in the spectrum. The observed sharp decrease in the threshold of stimulated Raman scattering has been explained by an increase in the spectral density of the electromagnetic field in the surface region of the photonic crystal because of the approach of the spectral position of the stopband of the photonic crystal to the exciting line (532 nm) under variation of the angle of incidence of pump radiation on the (111) surface.

This paper reports on the results of experimental investigations of the generation of the second optical harmonic localized in a thin subsurface layer of ferroelectric photonic crystals and photon traps. To excite the second optical harmonic, a KGW: Yb solid-state pulsed-periodic laser generating the radiation with a wavelength of 1026 nm in a form of pulses ∼10−13 s long with a repetition frequency of 200 kHz at the average power of 0.1–3.5 W and power density of ∼109−1012 W/cm2 in a spot less than 100 μm in diameter focused near the surface was used. Ferroelectrics, notably, barium titanate or sodium nitrite, were introduced into the pores between SiO2 nanoglobules. It is established that the maximal conversion efficiency of the exciting radiation into the second optical harmonic was several percents. The generation characteristics of the second optical harmonic near the surface of photonic crystals filled with ferroelectrics are compared with the generation of the second optical harmonic in ferroelectric photon traps of barium titanate ceramics and sodium nitrite microcrystals.

We present the results of an experimental study of the spontaneous and stimulated Raman scattering (SRS) spectra and luminescence spectra of light and heavy waters. Also we investigate various samples of light water. We show the possibility of using spectral methods to detect impurities in water and determine the degree of its structuredness, which can serve as an additional criterion of the water quality. We find a fine structure in the SRS spectrum of heavy water in the low-frequency region.

Known since the ancient times, cotton continues to be one of the essential materials for the human civilization. Cotton fibers are almost pure cellulose and contain both crystalline and amorphous nanodomains with different physicochemical properties. While understanding of interactions between the individual cellulose chains within the crystalline phase is important from a perspective of mechanical properties, studies of the amorphous phase lead to characterization of the essential transport parameters, such as solvent diffusion, dyeing, drug release, and toxin absorption, as well as more complex processes of enzymatic degradation. Here, we describe the use of spin probe electron paramagnetic resonance methods to study local polarity and heterogeneous viscosity of two types of unprocessed cotton fibers, G. hirsutum and G. barbadense, harvested in the State of North Carolina, USA. These fibers were loaded with two small molecule nitroxide probes that differ in polarity—Tempo and its more hydrophilic derivative Tempol—using a series of polar and non-polar solvents. The electron paramagnetic resonance spectra of the nitroxide-loaded cotton fibers were analyzed both semi-empirically and by least-squares simulations using a rigorous stochastic theory of electron paramagnetic resonance spectra developed by Freed and coworkers. A software package and least-squares fitting protocols were developed to carry out automatic simulations of multi-component electron paramagnetic resonance spectra in both first-derivative and the absorption forms at multiple resonance frequencies such as X-band (9.5 GHz) and W-band (94.3 GHz). The results are compared with the preceding electron paramagnetic resonance spin probe studies of a commercial bleached cotton sheeting carried out by Batchelor and coworkers. One of the results of this study is a demonstration of a co-existence of cellulose nanodomains with different physicochemical properties such as polarity and microviscosity that are affected by solvents and temperature. Spin labeling studies also revealed a macroscopic heterogeneity in the domain distribution along the cotton fibers and a critical role the cuticular layer is playing as a barrier for spin probe penetration. Finally but not lastly, the simultaneous multi-component least-squares simulation method of electron paramagnetic resonance spectra acquired at different resonant frequencies and the display forms (e.g., absorption and first-derivative displays) and the strategy of spectral parameter sharing could be potentially applicable to other heterogeneous biological systems in addition to the cotton fibers studies here.

Many biophysical processes such as insertion of proteins into membranes and membrane fusion are governed by bilayer electrostatic potential. At the time of this writing, the arsenal of biophysical methods for such measurements is limited to a few techniques. Here we describe a, to our knowledge, new spin-probe electron paramagnetic resonance (EPR) approach for assessing the electrostatic surface potential of lipid bilayers that is based on a recently synthesized EPR probe (IMTSL-PTE) containing a reversibly ionizable nitroxide tag attached to the lipids' polar headgroup. EPR spectra of the probe directly report on its ionization state and, therefore, on electrostatic potential through changes in nitroxide magnetic parameters and the degree of rotational averaging. Further, the lipid nature of the probe provides its full integration into lipid bilayers. Tethering the nitroxide moiety directly to the lipid polar headgroup defines the location of the measured potential with respect to the lipid bilayer interface. Electrostatic surface potentials measured by EPR of IMTSL-PTE show a remarkable (within ±2%) agreement with the Gouy-Chapman theory for anionic DMPG bilayers in fluid (48°C) phase at low electrolyte concentration (50 mM) and in gel (17°C) phase at 150-mM electrolyte concentration. This agreement begins to diminish for DMPG vesicles in gel phase (17°C) upon varying electrolyte concentration and fluid phase bilayers formed from DMPG/DMPC and POPG/POPC mixtures. Possible reasons for such deviations, as well as the proper choice of an electrostatically neutral reference interface, have been discussed. Described EPR method is expected to be fully applicable to more-complex models of cellular membranes.

In many cases model integration treats models as software components only, ignoring the fluid relationship between models and reality, the evolving nature of models and their constant modification and recalibration. As a result, with integrated models we find increased complexity, where changes that used to impact only relatively contained models of subsystems, now propagate throughout the whole integrated system. This makes it harder to keep the overall complexity under control and, in a way, defeats the purpose of modularity, when efficiency is supposed to be gained from independent development of modules. Treating models only as software in solving the integration challenge may give birth to 'integronsters' - constructs that are perfectly valid as software products but ugly or even useless as models. We argue that one possible remedy is to learn to use data sets as modules and integrate them into the models. Then the data that are available for module calibration can serve as an intermediate linkage tool, sitting between modules and providing a module-independent baseline dynamics, which is then incremented when scenarios are to be run. In this case it is not the model output that is directed into the next model input, but model output is presented as a variation around the baseline trajectory, and it is this variation that is then fed into the next module down the chain. However still with growing overall complexity, calibration can become an important limiting factor, giving more promise to the integral approach, when the system is modeled and simplified as a whole.

Recently, in the DGFRS related experiments the discoveries of new superheavy elements Z=114-118 were successfully performed. As concerns to a background radical suppression in those experiments it was namely “active correlations” method which was applied to this goal. Note, that application of DSSSD detector allows one to apply this method more effectively, although with some difficulties due to neighbor strips edge effects. Present version of the DGFRS spectrometer is presented. First results of its application in the 240Pu+48Ca→Fl∗ complete fusion nuclear reaction are presented too.

We have measured visible to near-UV reflection spectra of opal photonic crystals infiltrated with ferroelectrics: barium titanate, sodium nitrite, potassium iodate, and triglycine sulfate. An experimental procedure has been developed for the infiltration of various ferroelectrics into opal pores through laser ablation and laser implantation. Using a fiber-optic probe, we were able to analyze surface reflection spectra of photonic crystals with a 0.2-mm resolution. A deuterium lamp was used as a broadband UV source, which allowed us to observe both the first and second [111] photonic band gaps in the reflection spectrum of opal crystals.

A method for diagnosing the molecular structure and composition of aromatic bioactive preparations is developed by the example of pharmaceutical objects: analgin, citramon, aspirin, and paracetamol. The method is based on fiber-optic measurements of fluorescence spectra upon laser ultraviolet (266 nm) excitation with high (0.1 mm) spatial resolution. It is shown that the inhomogeneity of a pharmaceutical preparation containing several components is observed at a distance of a few millimeters. Difference fluorescence spectra are constructed, which allow detection of differences in preparation compositions and structures even in the case of closeness of their fluorescence spectra. The developedmethod can be used to control quality of a large class of bioactive structures luminescing under ultraviolet light.

The possibilities of the extraction and collimation of a circulating beam by a new method due to the reflection of particles in crystals with axial orientation were experimentally investigated in the Fall-2010 run at the U_70 synchrotron. Such crystals have positive features, because the axial potential is five times larger than the planar potential. It has been shown that the collimation efficiency can reach 90% due to axial effects in the crystal. Losses of the circulating beam on a collimator have been reduced by several times; this makes it possible to suppress the muon jet near the steel collimator of the circulating beam.

We present experimental results on the introduction (laser implantation) of ferroelectric NaNO2 into artificial opal pores upon exposure of a thin powder layer of sodium nitrite applied on the artificial opal surface to radiation of the ultraviolet excimer laser. Reflection spectra of broadband radiation from the laser-implanted sample surface are compared with the reflection spectra of pure initial opals, artificial opals impregnated with a saturated aqueous solution of sodium nitrite and evaporated from solvent, and samples in which NaNO2 was directly introduced in the form of a melt.

We present the experimental results on implantation of NaNO2 ferroelectric into pores of synthetic opal by illuminating with focused ultraviolet excimer-laser radiation of a sodium nitrite film located on the synthetic-opal surface. The reflection spectra of broadband radiation from the surface of implanted specimens are compared with the reflection spectra of initial (without any treatment) opals, synthetic opals filled with a saturated aqueous solution of sodium nitrite with subsequently evaporated solvent, and specimens with NaNO2 embedded as a melt. The possible mechanisms of shifts of reflected- and transmitted-radiation peaks are analyzed. Methods of implanting materials with high melting points into pores of 3D photonic crystals are proposed.

We have studied the optical properties of gold- and silver-infiltrated opal photonic crystals composed of close-packed SiO2 spheres ∼200 nm in diameter. The reflectivity spectra obtained are used to assess the photonic band gap of the crystals in the visible range. We present the characteristics of the emission induced in the opal photonic crystals by monochromatic and broadband light sources and calculated reflectances of the synthetic opal samples.

We study 3D globular photonic crystals based on synthetic opals filled with semiconductor core/shell quantum dots CdSe/CdS by measuring the photoluminescence spectra. The spectra were obtained using 369, 384, and 408 nm LED light excitation and involving a pulse YAG laser operating at 365 and 266 nm. The study shows that the photoluminescence spectra of opal filled with CdSe/CdS changes sufficiently in comparison with spectra taken for pure opal and a reference colloidal solution of CdSe/Cds quantum dots in toluene. Such opals may be used to fabricate a narrow-band light sources.

Generation of droplets on a surface of the water thin film at upflow and down flow is considered. Expressions for computation of splash type mass transfer were developed.

A first thiol-specific pH-sensitive nitroxide spin-label of the imidazolidine series, methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester (IMTSL), has been synthesized and characterized. X-Band (9 GHz) and W-band (94 GHz) EPR spectral parameters of the new spin-label in its free form and covalently attached to an amino acid cysteine and a tripeptide glutathione were studied as a function of pH and solvent polarity. The pKa value of the protonatable tertiary amino group of the spin-label was found to be unaffected by other ionizable groups present in side chains of unstructured small peptides. The W-band EPR spectra were shown to allow for pKa determination from precise g-factor measurements. Is has been demonstrated that the high accuracy of pKa determination for pH-sensitive nitroxides could be achieved regardless of the frequency of measurements or the regime of spin exchange: fast at X-band and slow at W-band. IMTSL was found to react specifically with a model protein, iso-1-cytochrome c from the yeast Saccharomyces cerevisiae, giving EPR spectra very similar to those of the most commonly employed cysteine-specific label MTSL. CD data indicated no perturbations to the overall protein structure upon IMTSL labeling. It was found that for IMTSL, g iso correlates linearly with A iso, but the slopes are different for the neutral and charged forms of the nitroxide. This finding was attributed to the solvent effects on the spin density at the oxygen atom of the NO group and on the excitation energy of the oxygen lone-pair orbital.

Nuclear level densities and radiative strength functions (RSFs) in 56Fe and 57Fe were measured using the 57Fe(3He, αγ) and 57Fe(3He, 3He′γ) reactions, respectively, at the Oslo Cyclotron Laboratory. A low-energy enhancement in the RSF below 4-MeV energy was observed. This finding cannot be explained by common theoretical models. In a second experiment, two-step cascade intensities with soft primary transitions from the 56Fe(n, 2γ) reaction were measured. The agreement between the two experiments confirms the low-energy enhancement in the RSFs. In a third experiment, the neutron evaporation spectrum from the 55Mn(d, n)56Fe reaction was measured at 7-MeV deuteron energy at the John Edwards Accelerator Laboratory at Ohio University. Comparison of the level density of 56Fe obtained from the first and third experiments gives an overall good agreement. Furthermore, observed enhancement for soft γ rays is strengthened by the last experiment.

Dynamic nuclear polarization (DNP) enhances the signal in solid-state NMR of proteins by transferring polarization from electronic spins to the nuclear spins of interest. Typically, both the protein and an exogenous source of electronic spins, such as a biradical, are either codissolved or suspended and then frozen in a glycerol/water glassy matrix to achieve a homogeneous distribution. While the use of such a matrix protects the protein upon freezing, it also reduces the available sample volume (by ca. a factor of 4 in our experiments) and causes proportional NMR signal loss. Here we demonstrate an alternative approach that does not rely on dispersing the DNP agent in a glassy matrix. We synthesize a new biradical, ToSMTSL, which is based on the known DNP agent TOTAPOL, but also contains a thiol-specific methanethiosulfonate group to allow for incorporating this biradical into a protein in a site-directed manner. ToSMTSL was characterized by EPR and tested for DNP of a heptahelical transmembrane protein, Anabaena sensory rhodopsin (ASR), by covalent modification of solvent-exposed cysteine residues in two (15)N-labeled ASR mutants. DNP enhancements were measured at 400 MHz/263 GHz NMR/EPR frequencies for a series of samples prepared in deuterated and protonated buffers and with varied biradical/protein ratios. While the maximum DNP enhancement of 15 obtained in these samples is comparable to that observed for an ASR sample cosuspended with ~17 mM TOTAPOL in a glycerol-d8/D2O/H2O matrix, the achievable sensitivity would be 4-fold greater due to the gain in the filling factor. We anticipate that the DNP enhancements could be further improved by optimizing the biradical structure. The use of covalently attached biradicals would broaden the applicability of DNP NMR to structural studies of proteins.

The radiative strength function (RSF) is key for understanding nuclear reaction rates in areas ranging from astrophysics to radiochemical diagnostics. The RSF also provides a tool for understanding the characteristics of gamma-ray cascades. Unresolved transitions in nuclear deexcitation processes are best described by statistical properties such as the radiative strength function. The sequential extraction method developed at the Oslo Cyclotron Laboratory provides data for radiative strength functions for gamma-ray energies from 1 MeV to the neutron binding energy. The data are averaged over about 100 keV energy bin and normalized to the average total radiative width of neutron resonances. The radiative strength functions in all nuclei studied show a characteristic increase with increasing gamma-ray energy. However, the detailed structures in the radiative strength function for various nuclei show different behavior in various mass regions. In rare-earth nuclei, a resonance structure near 3 MeV is observed. For several lighter nuclei (A

[reaction: see text] An approach to the synthesis of new imidazoline nitroxides bearing an N',N'-disubstituted amidine group is reported. The approach is based on the alkylation of diamagnetic 4-R-amino-1,2,2,5,5-pentamethyl-3-imidazolines with bromoacetic acid ethyl ester; the products of alkylation are further oxidized to the corresponding nitroxides. The approach allows a variety of functional groups to be introduced into the nitroxide molecule structure. Alkylation with bromoacetic acid ethyl ester was found to proceed with high regioselectivity and afford the products of exo-alkylation. The regiochemical assignment is made on the basis of 13C NMR spectra and confirmed by X-ray diffraction study. All of the nitroxides synthesized here were shown to have pH-dependent EPR spectra with pKa ranging from 3.5 to 6.2. For nitroxides 13 bearing the carboxylic group remote to the nitroxide moiety, the changes in isotropic magnetic parameters of EPR spectra due to reversible deprotonation of the carboxylic group were found to be small. For these nitroxides, we demonstrate an alternative approach for pKa determination that is based on measuring the peak-to-peak line width of the EPR spectrum in the presence of the paramagnetic broadening agent potassium ferricyanide. The partition coefficients of nitroxides in octanol/H2O and octanol/phosphate buffer solution mixtures were measured to reveal a range of their lipophilicities.

The approximate dependences of the contact angle on the dimensionless velocity α0 ~ Ca1/3 for the wetting of a surface, as well as on the dimensionless time for the spreading of a drop on a wall, are known [1–3], having been treated by De Gennes [4] as similarity laws in wetting dynamics. However, due to the effect of the scaling factor [1, 2], such a treatment is possible only in a narrow approximate sense.

The characteristics of the neutron fields (spectrum, fluence) at four points of the GIR-2 reactor are measured. It is shown experimentally that the energy spectrum of leakage neutrons from the reactor core through an opening in a spherical converter, which consists of light elements and inside which the core is placed, becomes harder. This effect is due to the shift of the region in the core where the number density of fissions is high toward the lateral surface of the core as a result of the presence the converter, consisting of light elements, outside the core. On the basis of the results of these investigations, GIR-2 neutron fields are certified as reference standards for measurements.

Electrostatic interactions are known to play one of the major roles in the myriad of biochemical and biophysical processes. In this Chapter we describe biophysical methods to probe local electrostatic potentials of proteins and lipid bilayer systems that is based on an observation of reversible protonation of nitroxides by EPR. Two types of the electrostatic probes are discussed. The first one includes methanethiosulfonate derivatives of protonatable nitroxides that could be used for highly specific covalent modification of the cysteine’s sulfhydryl groups. Such spin labels are very similar in magnetic parameters and chemical properties to conventional MTSL making them suitable for studying local electrostatic properties of protein-lipid interfaces. The second type of EPR probes is designed as spin-labeled phospholipids having a protonatable nitroxide tethered to the polar head group. The probes of both types report on their ionization state through changes in magnetic parameters and a degree of rotational averaging, thus, allowing one to determine the electrostatic contribution to the interfacial pKa of the nitroxide, and, therefore, determining the local electrostatic potential. Due to their small molecular volume these probes cause a minimal perturbation to the protein or lipid system while covalent attachment secure the position of the reporter nitroxides. Experimental procedures to characterize and calibrate these probes by EPR and also the methods to analyze the EPR spectra by least-squares simulations are also outlined. The ionizable nitroxide labels and the nitroxide-labeled phospholipids described so far cover an exceptionally wide pH range from ca. 2.5 to 7.0 pH units making them suitable to study a broad range of biophysical phenomena especially at the negatively charged lipid bilayer surfaces. The rationale for selecting proper electrostatically neutral interface for calibrating such probes and example of studying surface potential of lipid bilayer is also described.

The influence of dislocations on the parameters of diodes fabricated on p-type Cd 0.22 Hg 0.78 Te layers grown by molecular beam epitaxy (MBE) has been investigated. The n-region of diodes was formed by mercury thermodiffusion from anodic oxide, To introduce dislocations some diodes from the array were subjected to a pressure of (1-6) x 10 7 N/m 2 . It was found that after applying a pressure of more than 4 × 10 7 N/m 2 the diode parameters degraded due to an increasing trap concentration with energies E t1 E v + 0.035 eV and E t2 E v + 0.043 eV. It is suggested that these traps are connected with dislocations.

The reported neutron spectrometry method is based on primary γ-transition energy shifts. It has been demonstrated in measurements of the partial radiative capture cross-section of the 58 Ni(n,γ) 59 Ni reaction at the example of γ-transitions to the ground and second excited states of 59 Ni. The reaction 7 Li(p, n) is used to produce resonance neutrons by means of the proton beam of a Van de Graaff accelerator. A compact geometry allows one to improve the luminosity and to employ a rather wide neutron spectrum of up to ∼100 keV. Both partial radiative parameters of some neutron resonances and partial cross sections for population of the low-lying states of the daughter nucleus 59 Ni are obtained. The results are compared with the data obtained by the time-of-flight method.