Bilayer Lipid Membrane-Semiconductor Junctions. Spectroscopic and Electrochemical Characterizations and Photoelectron Transfer

Three different systems of glyceryl monooleate (GMO) bilayer lipid membrane (BLM) supported semiconductor particles have been prepared and characterized. A single composition of particulate semiconductor deposited on only one side of the BLM constituted System A, two different compositions of particulate semiconductors sequentially deposited on the same side of the BLM represented System B, and two different compositions of particulate semiconductors deposited on the opposite sides of the BLM made up System C. Effective refractive indices and optical thicknesses of GMO-BLM-supported In₂S₃ and ZnS particles (System A), determined by Brewster-angle and reflection measurements, allowed the assessment of the maximum sizes and the volume fractions of semiconductor particles to be on the order of 1200 Å and 0.3, respectively. Since semiconductor particles are highly porous structures, only the first layer of particulates penetrated into the BLM and were considered in the proposed equivalent circuit and band models. The presence of semiconductors on the BLM surface has been established by voltage-dependent capacitance measurements, absorption spectroscopy, and optical microscopy. Subsequent to the injection of H₂S, the first observable change was the appearance of fairly uniform white dots on the black film. These dots rapidly moved around and grew in size, forming islands which then merged with themselves and with a second generation of dots, which ultimately led to a continuous film which continued to grow in thickness. Cyclic voltammetry established the current rectifying behavior for the semiconductor-particle-coated BLMs. CdS, ZnS, and In₂S₃ (System A) formed an n-type, while Cu_2-(x+y)S (System A) behaved like a p-type, electrolyte-semiconductor (ES) junction. Semiconductor-semiconductor heterojunction (SS') formation was established for System C. Transfer of conduction-band electrons to dissolved oxygen (for the n-type ES junction) and across the membrane was considered to be responsible for the observed dark currents. Steady-state illumination of a CdS-containing BLM resulted in the prompt development of -150 to -200 mV (cis side negative) potential difference in an open circuit across the GMO BLM. This initial photovoltage, V ₁, quickly decayed to a steady value, V _s (- 100 to -150 mV). When the illumination was turned off, the potential difference across the GMO BLM decreased to its dark value in 3-4 minutes.     

Automated SPE and nanoLC–MS analysis of somatostatin

Plasma peptides are widely used in clinical diagnosis and therapy monitoring. Our aim was an efficient system development for the enrichment of small, low abundant peptides from plasma by robotized sample preparation. The automation of SPE yields additional time saving and improves system robustness and repeatability. Automation is based on combining a Waters SPE kit with Oasis HLB sorbent and a multichannel liquid handling workstation with cheap commercially available electronic devices such as a programmable logic controller (PLC) and an AVR controller. Reversed phase nano liquid chromatography coupled with a sensitive quadrupole time of flight mass spectrometer (QTOF MS) was used for the quantitative determination of somatostatin (SST). We quantified SST from mouse plasma, where lower limit of detection (LLOD) and lower limit of quantification (LLOQ) were 2.5 and 8.3 fmol/ml, respectively. We investigated linearity of response, accuracy, precision, recovery, reproducibility and stability of SST during both short-term sample processing and long-term storage. This method allows reliable quantification of plasma peptides. The developed automated sample preparation solid phase extraction method can be easily and conveniently adopted for different volumes and amounts of sample in routine analysis using controlled vacuum. The highest advantage is enhanced reproducibility, which makes it suitable for the investigations of large sample cohorts in clinical studies.     

Protein resistance of titanium oxide surfaces modified by biologically inspired mPEG-DOPA

In the present study, we have utilized X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (ELM), and optical waveguide lightmode spectroscopy (OWLS) to examine the surface adsorption and protein resistance behavior of bio-inspired polymers consisting of poly(ethylene glycol) (PEG) conjugated to peptide mimics of mussel adhesive proteins. Peptides containing up to three residues of 3,4-dihydroxyphenylalanine (DOPA), a key component of mussel adhesive proteins, were conjugated to monomethoxy-terminated PEG polymers. These mPEG-DOPA polymers were found to be highly adhesive to TiO2 surfaces, with quantitative XPS analysis providing useful insight into the binding mechanism. Additionally, the antifouling properties of immobilized PEG were reflected in the excellent resistance of mPEG-DOPA-modified TiO2 surfaces to protein adsorption. Measurements of mPEG-DOPA and human serum adsorption were related in terms of ethylene glycol (EG) surface density and serum mass adsorbed and demonstrated a threshold of approximately 15-20 EG/nm2, above which substantially little protein adsorbs. With respect to surface density of adsorbed PEG and the associated nonfouling behavior of the adlayers, strong parallels exist between the nonfouling properties of the surface-bound mPEG-DOPA polymers and PEG polymers immobilized to surfaces using other approaches. Peptide anchors containing three DOPA residues resulted in PEG surface densities higher than those achieved using several existing PEG immobilization strategies, suggesting that peptide mimics of mussel adhesive proteins may be useful for achieving high densities of protein-resistant polymers on surfaces.     

Coexistence of Three Ferroic Orders in the Multiferroic Compound [(CH3)4N][Mn(N3)3] with Perovskite‐Like Structure

The perovskite azido compound [(CH₃)₄N][Mn(N₃)₃], which undergoes a first‐order phase change at T_t=310 K with an associated magnetic bistability, was revisited in the search for additional ferroic orders. The driving force for such structural transition is multifold and involves a peculiar cooperative rotation of the [MnN₆] octahedral as well as order/disorder and off‐center shifts of the [(CH₃)₄N]⁺ cations and bridging azide ligands, which also bend and change their coordination mode. According to DFT calculations the latter two give rise to the appearance of electric dipoles in the low‐temperature (LT) polymorph, the polarization of which nevertheless cancels out due to their antiparallel alignment in the crystal. The conversion of this antiferroelectric phase to the paraelectric phase could be responsible for the experimental dielectric anomaly detected at 310 K. Additionally, the structural change involves a ferroelastic phase transition, whereby the LT polymorph exhibits an unusual and anisotropic thermal behavior. Hence, [(CH₃)₄N][Mn(N₃)₃] is a singular material in which three ferroic orders coexist even above room temperature.     

Single-particle inclusive spectra of charged particles in ¯pp interactions at 22·4 GeV/c

The inclusive spectra for ¯pp collisions at 22·4 GeV/c are investigated. The transversal momentum distribution resembles the corresponding one in high energy pp interactions. The cross section in the central region is 28±mb. They ^*-distribution of secondary particles in the central region indicates a charge asymmetry with the asymmetry parameter having the value 0.15±0·01. The upper limit of the diffraction dissociation of the beam particle is estimated to be mb.The authors want to express their gratitude to the staff responsible for the operation of the Serpukhov accelerator and of the beam channel no. 9 and to the technical staff of the LUDMI-LA HBC. We also thank the technicians and assistants at all laboratories for their excellent work. The authors from the Moscow State University want to express their gratitude to Prof. V. G.Shevchenko for his continuous support of this work.     

Adenosine Cyclic 3′, 5′-Phosphoramidate and N,N-Dimethylphosphoramidate: Synthesis Via Symmetrical and Mixed Anhydrides and Hydrolysis

Abstract

The title compounds were synthesized by converting cyclic AMP with a sulfonyl chloride to the symmetrical anhydride or with diphenyl phosphorochloridate to the mixed anhydride, then aminolyzing the anhydrides without isolation. The synthesis preferentially gave Sp-amides. Characteristic differences were observed in the behavior of the unsubstituted amide and the dimethylamide under hydrolysis conditions.     

适用于放大自发辐射平滑光束的脉宽压缩方法

为了增加靶上的功率密度和耦合效率,基于饱和增益开关原理,发展了一种适用于放大自发辐射平滑光束的脉宽压缩方法。利用该方法,在赛格德大学的一台放电泵浦KrF准分子激光器上进行了实验,将该激光器输出的脉宽为14.5 ns的放大自发辐射光束压缩到了7.5 ns,并且保持了光束原有的均匀性。