Immobilization of Methyl Orange and Methylene Blue within the Matrix of Charge-Imbalanced Amphoteric Nanogels and Study of Dye Release Kinetics as a Function of Temperature and Ionic Strength

Cross-linked polyampholyte nanogels consisting of neutral N-isopropylacrylamide (NIPAM), negatively charged sodium salt of 2-acrylamido-2-methylpropanesulfonate (AMPS), and positively charged (3-acrylamidopropyltrimethylammonium chloride (APTAC) monomers were synthesized via conventional redox initiated free radical copolymerization using N,N-methylenebis(acrylamide) (MBAA) as a crosslinking agent. The resulting nanogels were characterized by means of FTIR and 1H NMR spectroscopy, dynamic light scattering (DLS) and zeta-potential measurements. Surface morphology was analyzed using scanning electron microscopy. Due to the presence of thermally responsive NIPAM units and varying molar ratios of anionic (AMPS) and cationic (APTAC) units, the resulting nanogels were responsive to multiple stimuli in aqueous media and can be used for controlled delivery of dyes. Thus, the NIPAM90-APTAC7.5-AMPS2.5 nanogel with an excess of the cationic units was chosen for immobilization of the anionic dye, methyl orange (MO), whereas the NIPAM90-APTAC2.5-AMPS7.5 nanogel with an excess of the anionic units was chosen for immobilization of the cationic dye, methylene blue (MB). The release kinetics of the dyes from the nanogel was studied depending on the phase transition temperature and the salt content. Mechanism of the dye release from the nanogel matrix was determined using the Ritger-Peppas equation. Disappearance of the ionic contacts between the charged groups of the nanogels and the ionic dyes was suggested to be the main reason for the diffusion of the dyes through the dialysis membrane into external solution.Peer reviewe

Synthesis and Characterization of Carboxymethylated Cornstarch

The aim of this study is preparation and characterization of carboxymethylated cornstarch (CMCS) for potential application as water based drilling fluids. The cornstarch was modified by sodium monochloroacetate. The structure of cornstarch and CMCS was established by H-1 NMR and FTIR spectroscopy. The degree of carboxymethylation of cornstarch determined by H-1 NMR spectroscopy was equal to 80%. The viscosity-average molecular weights (M-eta) of pristine cornstarch and CMCS calculated from Mark-Kuhn-Houwink equation [eta]=K-eta.M-a are equal to 2.15.10 (3) g.mol(-1) and 2.75.10(5 )g.mol(-1) respectively. The temperature dependent viscosity of CMCS was measured in water by Ubbelohde viscometer, while the rheological properties of CMCS in dependence of polymer concentration and ionic strength of the solution were evaluated by rheoviscometer. The thermal characteristics of samples were determined by differential scanning calorimeter (DSC) and thermogravimetric (TGA) and differential thermal analyzer (DTA). The morphological properties of cornstarch and CMCS were studied by scanning electron microscopy (SEM). The structural-mechanical, filtration and filter cake forming properties of drilling fluids and fluid loss indicators of CMCS were found.Peer reviewe

СВЕРХБЫСТРАЯ ПРОСВЕЧИВАЮЩАЯ ЭЛЕКТРОННАЯ МИКРОСКОПИЯ

Ultrafast laser spectral and electron diffraction methods complement each other and open up new possibilities in chemistry and physics to light up atomic and molecular motions involved in the primary processes governing structural transitions. Since the 1980s, scientific laboratories in the world have begun to develop a new field of research aimed at this goal. “Atomic-molecular movies” will allow visualizing coherent dynamics of nuclei in molecules and fast processes in chemical reactions in real time. Modern femtosecond and picosecond laser sources have made it possible to significantly change the traditional approaches using continuous electron beams, to create ultrabright pulsed photoelectron sources, to catch ultrafast processes in the matter initiated by ultrashort laser pulses and to achieve high spatio-temporal resolution in research. There are several research laboratories all over the world experimenting or planning to experiment with ultrafast electron diffraction and possessing electron microscopes adapted to operate with ultrashort electron beams. It should be emphasized that creating a new-generation electron microscope is of crucial importance, because successful realization of this project demonstrates the potential of leading national research centers and their ability to work at the forefront of modern science.Методы сверхбыстрой электронной дифракции, лазерной спектроскопии и квантовой химии, дополняя друг друга, открывают новые возможности изучения внутримолекулярной динамики веществ, участвующих в процессах химических реакций. Переходное состояние химических реакций определяет направление этих процессов. Начиная от первых работ 1980-х годов, выполненных в России и показавших принципиальную возможность исследования когерентной динамики ядер молекулярных систем, многие научные лаборатории в мире начали интенсивную разработку новой области исследований, направленную на экспериментальное исследование переходного состояния методом сверхбыстрой дифракции электронов. Последовательное развитие этого направления привело к созданию так называемого “атомно-молекулярного кино”, позволяющего визуализировать когерентную динамику ядер в молекулах и сверхбыстрые процессы в химических реакциях в режиме реального времени. В настоящее время ряд научно-исследовательских лабораторий в мире разрабатывают методы сверхбыстрой дифракции электронов и рентгеновского излучения, которые открыли возможность исследования переходного состояния химических реакций. Создание электронных микроскопов с высоким пространственно-временным разрешением является новым направлением в электронной микроскопии, близко примыкающим к этому новому направлению науки. Успешная реализация этого направления исследований демонстрирует потенциал ведущих национальных научно-исследовательских центров и их способность работать на переднем крае современной науки

Isotope shift in the electron affinity of chlorine

The specific mass shift in the electron affinity between ^{35}Cl and ^{37}Cl has been determined by tunable laser photodetachment spectroscopy to be -0.51(14) GHz. The isotope shift was observed as a difference in the onset of the photodetachment process for the two isotopes. In addition, the electron affinity of Cl was found to be 29138.59(22) cm^{-1}, giving a factor of 2 improvement in the accuracy over earlier measurements. Many-body calculations including lowest-order correlation effects demonstrates the sensitivity of the specific mass shift and show that the inclusion of higher-order correlation effects would be necessary for a quantitative description.Comment: 16 pages, 6 figures, LaTeX2e, amsmat

Conformational Parameters and Hydrodynamic Behavior of Poly(2-Methyl-2-Oxazoline) in a Broad Molar Mass Range

In this work, we report our results on the hydrodynamic behavior of poly(2-methyl-2-oxazoline) (PMeOx). PMeOx is gaining significant attention for use as hydrophilic polymer in pharmaceutical carriers as an alternative for the commonly used poly(ethylene glycol) (PEG), for which antibodies are found in a significant fraction of the human population. The main focus of the current study is to determine the hydrodynamic characteristics of PMeOx under physiological conditions, which serves as basis for better understanding of the use of PMeOx in pharmaceutical applications. This goal was achieved by studying PMeOx solutions in phosphate-buffered saline (PBS) as a solvent at 37 °C. This study was performed based on two series of PMeOx samples; one series is synthesized by conventional living cationic ring-opening polymerization, which is limited by the maximum chain length that can be achieved, and a second series is obtained by an alternative synthesis strategy based on acetylation of well-defined linear poly(ethylene imine) (PEI) prepared by controlled side-chain hydrolysis of a defined high molar mass of poly(2-ethyl-2-oxazoline). The combination of these two series of PMeOx allowed the determination of the Kuhn–Mark–Houwink–Sakurada equations in a broad molar mass range. For intrinsic viscosity, sedimentation and diffusion coefficients, the following expressions were obtained: η=0.015M0.77, s0=0.019M0.42 and D0=2600M−0.58, respectively. As a result, it can be concluded that the phosphate-buffered saline buffer at 37 °C represents a thermodynamically good solvent for PMeOx, based on the scaling indices of the equations. The conformational parameters for PMeOx chains were also determined, revealing an equilibrium rigidity or Kuhn segment length, (A) of 1.7 nm and a polymer chain diameter (d) of 0.4 nm. The obtained value for the equilibrium rigidity is very similar to the reported values for other hydrophilic polymers, such as PEG, poly(vinylpyrrolidone) and poly(2-ethyl-2-oxazoline), making PMeOx a relevant alternative to PEG

Few cycle dynamics of multiphoton double ionization

In intense field ionization, an electron removed from the atomic core oscillates in the combined fields of the laser and the parent ion. This oscillation forces repeated revivals of its spatial correlation with the bound electrons. The total probability of double ionization depends on the number of returns and therefore on the number of optical periods in the laser pulse. We observed the yield of Ne\ub2\u207a relative to Ne\u207a with 12 fs pulses to be clearly less compared to 50 fs pulses in qualitative agreement with our theoretical model.Peer reviewed: YesNRC publication: Ye

Functional Changes in the Snail Statocyst System Elicited by Microgravity

BACKGROUND: The mollusk statocyst is a mechanosensing organ detecting the animal's orientation with respect to gravity. This system has clear similarities to its vertebrate counterparts: a weight-lending mass, an epithelial layer containing small supporting cells and the large sensory hair cells, and an output eliciting compensatory body reflexes to perturbations. METHODOLOGY/PRINCIPAL FINDINGS: In terrestrial gastropod snail we studied the impact of 16- (Foton M-2) and 12-day (Foton M-3) exposure to microgravity in unmanned orbital missions on: (i) the whole animal behavior (Helix lucorum L.), (ii) the statoreceptor responses to tilt in an isolated neural preparation (Helix lucorum L.), and (iii) the differential expression of the Helix pedal peptide (HPep) and the tetrapeptide FMRFamide genes in neural structures (Helix aspersa L.). Experiments were performed 13-42 hours after return to Earth. Latency of body re-orientation to sudden 90° head-down pitch was significantly reduced in postflight snails indicating an enhanced negative gravitaxis response. Statoreceptor responses to tilt in postflight snails were independent of motion direction, in contrast to a directional preference observed in control animals. Positive relation between tilt velocity and firing rate was observed in both control and postflight snails, but the response magnitude was significantly larger in postflight snails indicating an enhanced sensitivity to acceleration. A significant increase in mRNA expression of the gene encoding HPep, a peptide linked to ciliary beating, in statoreceptors was observed in postflight snails; no differential expression of the gene encoding FMRFamide, a possible neurotransmission modulator, was observed. CONCLUSIONS/SIGNIFICANCE: Upregulation of statocyst function in snails following microgravity exposure parallels that observed in vertebrates suggesting fundamental principles underlie gravi-sensing and the organism's ability to adapt to gravity changes. This simple animal model offers the possibility to describe general subcellular mechanisms of nervous system's response to conditions on Earth and in space