Protonated Research Articles

Impact of the Solar Flares on the SER Dynamics on Micro and Nanometric Technologies

The objective of this paper is to study the impact of the solar flares on the single event rate (SER) dynamics investigating the influence of shielding, the technological integration level and the contribution of the direct ionization of protons for a 65 nm technology. This paper proposes a comparison of MUSCA SEP3 calculations and SAC-C satellite in-flight data in terms of SEU “instantaneous” rate and total count.

Infrared Spectra and Hydrogen‐Bonded Network Structures of Large Protonated Water Clusters H+(H2O)n (n=20–200)

Infrared Spectra and Hydrogen‐Bonded Network Structures of Large Protonated Water Clusters H⁺(H₂O)_<i>n</i> (<i>n</i>=20<b>–</b>200)

On the molecular mechanisms of the acid-induced dissociation of hydroxy-apatite in water

The enamel/saliva interface is mimicked by the comparably much simpler model of (001) surfaces of hydroxy-apatite ( Ca(10)(PO(4))(6)(OH)(2) ) in contact with aqueous solution. At neutral pH, the dissociation of ions is penalized by more than 150 kJ mol(-1) giving rise to very stable apatite-water interfaces. This picture changes drastically with decreasing pH, as the protonation of phosphate and hydroxide ions lowers the free energy of calcium ions dissociation. Our simulations suggest the mechanism of acid-induced apatite decomposition to i) require a considerable degree of protonation of the apatite surface. The first ion dissociation step ii) involves calcium ions which electrostatic binding has been locally destabilized through phosphate and hydroxide protonation. The depletion of calcium ions embedding the anions then allows iii) the dissociation of the anionic species. Along this line, the protective role of fluoride in caries prevention is related to the stabilization of the calcium triangles embedding the OH(-)/F(-) ions.

Ionization signals from electrons and alpha-particles in mixtures of liquid Argon and Nitrogen – perspectiveson protons for Gamma Resonant Nuclear Absorption applications

In this paper we report on a detailed study of ionization signals produced by Compton electrons and alpha-particles in a Time Projection Chamber (TPC) filled with different mixtures of liquid Argon and Nitrogen. The measurements were carried out with Nitrogen concentrations up to 15% and a drift electric field in the range 0-50 kV/cm. A prediction for proton ionization signals is made by means of interpolation. This study has been conducted in view of the possible use of liquid Ar−N2 TPCs for the detection of gamma-rays in the resonant band of the Nitrogen absorption spectrum, a promising technology for security and medical applications.

Structure–activity studies of GmSubPep, a soybean peptide defense signal derived from an extracellular protease

GmSubPep, a 12-amino acid peptide isolated from soybean leaves, induces the expression of genes in soybean suspension-cultured cells that encode proteins involved in defense against pathogens. The peptide is derived from an extracellular subtilisin-like protease (subtilase) and binds a putative cell-surface receptor that initiates a defense signaling cascade. Interaction of the peptide with its receptor results in alkalinization of soybean suspension cell media which can be utilized to analyze the kinetics of receptor binding. Substitutions of alanine at each of the 12 amino acid positions revealed that the amino acids at positions 10 (arginine) and 12 (histidine) were essential for activity. Both analogs were able to reduce the physiological effects of GmSubPep associated with receptor binding. Deletion of the C-terminal histidine [GmSubPep(1-11)] abolished the alkalinizing activity and this peptide was also a strong competitor for receptor binding. Deletion of N-terminal amino acids from GmSubPep caused a sequential loss of activity with no alkalinizing activity for GmSubPep(4-12). However, the N-terminal deleted peptides did not compete with GmSubPep for receptor binding. Further modifications at the arginine-10 position indicated that an ionizable proton was not essential for activity as an attenuated response was found for a citrulline substitution. Substitution of the histidine-12 with methylated histidine at position N-1 of the imidazole group abolished activity, whereas substitution at N-3 was completely active, indicating that the N-3 analog retains important receptor binding properties. This study indicates that the extreme C-terminal of GmSubPep has important signal transduction properties while the C-terminal is essential for receptor interaction.

Directional fast neutron detection using a time projection chamber

Measurement of the three dimensional trajectory and specific ionization of recoil protons using a hydrogen gas time projection chamber provides directional information about incident fast neutrons. Here we demonstrate directional fast neutron detection using such a device. The wide field of view and excellent gamma rejection that are obtained suggest that this device is well suited to searches for special nuclear materials, among other applications.

ChemInform Abstract: Synthesis of the First Heterobimetallic Rhenium-Ruthenium η2- Dihydrogen Complexes.

The complex [(PPh3)2HRe(µ-H)3(µ-CO)RuH(PPh3)2]1, resulting from the reaction of [ReH6(PPh3)2]– with [RuHCl(CO)(PPh3)3], reacts with chloroform to give [(PPh3)2HRe(µ-Cl)2(µ-H)(µ-CO)RuH(PPh3)2]2; protonation of 1 and 2 with HBF4·Et2O leads to the formation of the fluxional [(PPh3)2HRe(µ-H)3(µ-CO)Ru(η2-H2)(PPh3)2][BF4]3, and the rigid [(PPh3)2HRe(µ-H)(µ-Cl)2(µ-CO)Ru(η2-H2)(PPh3)2][BF4]4 complexes.

Absolute total and partial cross sections for ionization of nucleobases by proton impact in the Bragg peak velocity range

We present experimental results for proton ionization of nucleobases (adenine, cytosine, thymine, and uracil) based on an event-by-event analysis of the different ions produced combined with an absolute target density determination. We are able to disentangle in detail the various proton ionization channels from mass-analyzed product ion signals in coincidence with the charge-analyzed projectile. In addition we are able to determine a complete set of cross sections for the ionization of these molecular targets by 20--150 keV protons including the total and partial cross sections and the direct-ionization and electron-capture cross sections.

Selective Isolation of Component Myristicine from Ligustium sinense oliv by Second-Sphere Coordination Inclusion Crystallization

The first ligand of [CoCl4 ]2 - and the second ligand of protonated N,N,N',N'-tetra-p-methyl- benzyl-ethylenediamine were used to construct a second-sphere coordination complex as the host framework. Myristicine was selectively isolated from the volatile oil of Ligustium sinense oliv by the inclusion crystalline method as the guest molecules. IR,NMR,X-ray diffraction were used to determine the structure of the inclusion complex,and the host-guest molar ratio in the complex was found to be 2∶ 1. The myristicine was isolated from the inclusion complex via Kugelrohr vacuum distillation technique and was characterized by IR, NMR and GC. According to the result of GC,the content of myristicine in the volatile oil of Ligustium sinense oliv is 60. 4% ,and the purity of isolated myristicine reaches 100% .

Dissolution kinetics and mechanism of Mg–Al layered double hydroxides: A simple approach to describe drug release in acid media

Layered double hydroxides (LDHs) weathering in acidic media is one of the main features that affects their applications in drug delivery systems. In this work, the dissolution kinetics of biocompatible Mg-Al LDHs was studied at different initial pH values and solid concentrations using a simple and fast experimental method that coupled flow injection analysis and amperometric detection. A carbonate intercalated sample was used to determine the controlling step of the process and the dissolution mechanism. Finally, the study was extended to an ibuprofen intercalated LDH. The obtained results showed that the weathering process was mainly controlled by the exposed area and surface reactivity of LDHs particles. The dissolution mechanism at the particle surface was described in two steps: fast formation of surface reactive sites by hydroxyl group protonation and slow detachment of metal ions from surface. At strongly acidic conditions, the reaction rate was pH dependent due to the equilibrium between protonated (active) and deprotonated (inactive) hydroxyl groups. On the other hand, at mildly acidic conditions, the dissolution behavior was also ruled by the equilibrium attained between the particle surface reactive sites and the dissolved species. LDHs solubility and dissolution rate presented strong dependence with the interlayer anion. The ibuprofen intercalated sample was more soluble and more rapidly dissolved than the carbonate intercalated one in acetic/acetate buffer. On the other hand, the dissolution mechanism was invariant with the interlayer anion.

Degradation of a COTS linear CCD induced by proton irradiation

A Commercial Off-The-Shelf (COTS) linear CCD irradiated by protons is examined experimentally in this study. A dummy output voltage, the charge transfer efficiency (CTE) and a dark signal were degraded by 2-, 5-, and 10-MeV proton irradiation for comparison. The CCDs irradiated by 2-MeV protons were damaged most seriously, and the CCDs irradiated by 5-MeV protons were damaged more than those irradiated by 10-MeV protons. Biased CCDs were damaged more seriously than unbiased CCDs with the same proton irradiation conditions. The vacancy density and distribution induced by proton displacement damage and the ionizing energy loss induced by proton ionization damage were calculated using TRIM software. The correlation between CTE degradation and nonionizing energy loss is analyzed.

Effects of Protonation State on a Tyrosine−Histidine Bioinspired Redox Mediator

The conversion of tyrosine to the corresponding tyrosyl radical in photosystem II (PSII) is an example of proton-coupled electron transfer. Although the tyrosine moiety (Tyr(Z)) is known to function as a redox mediator between the photo-oxidized primary donor (P680(•+)) and the Mn-containing oxygen-evolving complex, the protonation states involved in the course of the reaction remain an active area of investigation. Herein, we report on the optical, structural, and electrochemical properties of tyrosine-histidine constructs, which model the function of their naturally occurring counterparts in PSII. Electrochemical studies show that the phenoxyl/phenol couple of the model is chemically reversible and thermodynamically capable of water oxidation. Studies under acidic and basic conditions provide clear evidence that an ionizable proton controls the electrochemical potential of the tyrosine-histidine mimic and that an exogenous base or acid can be used to generate a low-potential or high-potential mediator, respectively. The phenoxyl/phenoxide couple associated with the low-potential mediator is thermodynamically incapable of water oxidation, whereas the relay associated with the high-potential mediator is thermodynamically incapable of reducing an attached photoexcited porphyrin. These studies provide insight regarding the mechanistic role of the tyrosine-histidine complex in water oxidation and strategies for making use of hydrogen bonds to affect the coupling between proton and electron transfer in artificial photosynthetic systems.

The Conversion of l-Phenylalanine to (S)-2-Hydroxy-3-phenylpropanoic Acid: A Simple, Visual Example of a Stereospecific SN2 Reaction

We report a simple, inexpensive, visual, and environmentally friendly SN2 reaction appropriate for the second-year organic chemistry laboratory that illustrates stereospecificity, dependence of water solubility on the state of ionization, optical activity, and effect of diastereotopic protons in 1H NMR spectroscopy. The reaction converts readily available l-phenylalanine in a double SN2 reaction to enantiomerically pure (S)-2-hydroxy-3-phenylpropanoic acid. The optical purity and absolute stereochemistry are determined by the specific rotation of the product.

Ion Chemistry of VX Surrogates and Ion Energetics Properties of VX: New Suggestions for VX Chemical Ionization Mass Spectrometry Detection

Room temperature rate constants and product ion branching ratios have been measured for the reactions of numerous positive and negative ions with VX chemical warfare agent surrogates representing the amine (triethylamine) and organophosphonate (diethyl methythiomethylphosphonate (DEMTMP)) portions of VX. The measurements have been supplemented by theoretical calculations of the proton affinity, fluoride affinity, and ionization potential of VX and the simulants. The results show that many proton transfer reactions are rapid and that the proton affinity of VX is near the top of the scale. Many proton transfer agents should detect VX selectively and sensitively in chemical ionization mass spectrometers. Charge transfer with NO(+) should also be sensitive and selective since the ionization potential of VX is small. The surrogate studies confirm these trends. Limits of detection for commercial and research grade CIMS instruments are estimated at 80 pptv and 5 ppqv, respectively.

The structures of free-base carbahemiporphyrazines

In this report we present an X-ray crystallographic study of two N -deficient hemiporphyrazines: dicarbahemiporphyrazine (1) and benziphthalocyanine (2). Both compounds can be isolated in multiple crystal forms, and five different solvated forms of macrocycle 1 are presented. Four of the five are non-planar, showing the high degree of flexibility and capacity for hydrogen bonding from solvent to N-H groups in the macrocycle. The remaining structure of 1 is a planar dicationic species that represents a tautomeric form of the macrocycle often seen in metal binding. Four structures of macrocycle 2 are also presented in this report. The structure of 2 is also planar due to the tautomerism of the internal protons, and structural elucidation of this macrocycle reveals the presence of three ionizable protons rather than the expected single proton postulated by Elvidge and Golden.

20–150-keV proton-impact-induced ionization of uracil: Fragmentation ratios and branching ratios for electron capture and direct ionization

Fragmentation ratios and branching ratios are measured for ionization and dissociative ionization for 20–150 keV (0.9–2.4v0) proton collisions with gas-phase uracil molecules. Through event-by-event determination of the postcollision projectile charge, it is possible for such a key biomolecule to distinguish between electron capture (EC) by the incident proton and direct ionization (DI) without projectile neutralization. While the same fragment ion groups are observed in the mass spectra for both processes, EC induces dissociation with greater efficiency than DI in the impact energy range of 35–150 keV (1.2–2.4v0). In this range EC is also less abundant than DI with a branching ratio for EC/total ionization of <50%. Moreover, whereas fragmentation ratios do not change with energy in the case of EC, DI mass spectra show a tendency for increased fragmentation at lower impact energies.

Thermodynamic Study on the Interaction between Phenylglycine and Some Transition Metal Ions

The proton ionization constants (pK011 and pK012) of phenylglycine were determined in aqueous solution using Bjerrum’s potentiometric technique. The measurements were carried out at three ionic str...

Survivin expression is an independent prognostic factor in rectal cancer patients with and without preoperative radiotherapy

A study of liquid chromatography-triple quadrupole mass spectrometry (LC-MS-MS) with positive electrospray ionisation (ESI) for the determination of selected drugs in human tissues and body fluids such as blood, urine and hair is described. The possibility to screen for and quantify the 19 most commonly prescribed neuroleptics on the Swedish market and determine the presence of their major metabolites within a single LC-MS-MS analysis was evaluated on a PE Sciex API2000 instrument. Chromatographic conditions were optimised and the best separation, with individual retention times for most of the analytes, was obtained on a Zorbax SB-CN column within a 9-min gradient run. The MS-MS fragmentation conditions were optimised for each compound in order to obtain both specific fragments and high signal intensity. Since neuroleptics are a heterogeneous group of compounds, a markedly difference in collision energy needed to achieve fragments of the selected parent ions was seen and the number of fragments achieved varied as well. For sensitive quantification the transition of the most intense fragment of the protonated molecular ion (M + 1)(+) was selected for multiple reaction monitoring analysis. More than 70 transitions were finally included in the assay. Detection levels down to the lower ng/ml level were achieved for all analytes, but between analytes more than a 10-fold difference in signal response was seen. By evaluation of extracted ion chromatograms from the analysis of authentic human blood, urine and hair sample the proposed concept for rational drug analysis was found to be both selective and sensitive for the neuroleptics included. A great number of metabolites could be determined in blood, urine and hair as well. A full method validation was not performed since the objective was to evaluate the method design rather than to validate a final method set-up.

Operational SER Calculations on the SAC-C Orbit Using the Multi-Scales Single Event Phenomena Predictive Platform (MUSCA ${\rm SEP}^{3}$)

In this paper, the Multi-Scales Single Event Phenomena Predictive Platform (MUSCA SEP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) is presented. This platform is dedicated to predicting SEE cross sections or rates and evaluated thanks to on-board operational results on memories from the ICARE experiment (SAC-C mission). It allows for investigating the single and multiple events thus, MUSCA SEP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> helps at estimating sensitivity trend for nano-metric technology and more particularly investigating the emerging effect related to the direct proton ionization. It is a critical problematic which concerns both the space and atmospheric environments.

Reactivity ofortho-Substituted Aryl–Palladium Complexes towards Carbodiimides, Isothiocyanates, Nitriles, and Cyanamides

Complexes [Pd(C(6)H(3)XH-2-R'-5)Y(N;N)] (X=O, NH; Y=Br, I; R'=H, NO(2); N;N=N,N,N',N'-tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), 4,4'-di-tert-butyl-2,2'-bipyridine (dtbbpy)) react with RN=C=E (E=NR, S) or RC identical withN (R=alkyl, aryl, NR''(2)) and TlOTf (OTf=CF(3)SO(3)) to give, respectively, 1) products of the insertion of the C=E group into the C--Pd bond, protonation of the N atom, and coordination of X to Pd, [Pd{kappa(2)-X,E-(XC(6)H(3){EC(NHR)}-2-R'-4)}(N;N)]OTf or [Pd(kappa(2)-X,N-{ZC(6)H(3)(NH=CR)-2-R'-4})(N;N)]OTf, or products of the coordination of carbodiimides and OH addition, [Pd{kappa(2)-C,N-(C(6)H(4){OC(NR)}NHR-2)}(bpy)]OTf; or 2) products of the insertion of the C identical withN group to Pd and N-protonation, [Pd(kappa(2)-X,N-{XC(6)H(3)(NH=CR)-2-R'-4})(N;N)]OTf.