Mechanism of NOH2 reaction over Rh foil and the role of chemisorbed nitrogen atoms

The behaviour of adsorbed nitrogen and the overall catalytic reaction between NO and H₂ on Rh foil were investigated in a pressure region around 10^?5–10^?4 Pa and a temperature range between 400 and 1200 K, using the flash desorption technique and ultraviolet photoelectron spectroscopy. In a reducing condition, the NOH₂ reaction proceeded rapidly in the temperature range between 500 and 1000 K, and the reaction probability of NO was almost unity in the temperature region studied. The major product was N₂, but NH₃ was also formed around 500 K. Chemisorbed nitrogen was accumulated during the NO-H₂ reaction and also during the NH₃ decomposition reaction. In both cases, the dependence of the rate of N₂ formation upon the amount of N(ad) estimated during the reaction was similar to that in the case of N(ad) flash desorption, which indicates that N₂ is formed by recombination of N(ad) in both the NO-H₂ reaction and the NH₃ decomposition reaction. The rate constant for the second order desorption of N(ad) was estimated to be $\text{10}{}^{\mathrm{?6.8\; \pm \; 0.3}}\text{exp(?97 ± 5(}\text{kJ}\text{mol}\text{) RT) (}\text{cm}{}^2\text{atom·s)}$. The overall reaction of NO-H₂ on Rh proceeds in a similar manner to Pd previously reported, but the dissociation of NO takes place more easily over Rh and O(ad) is more stable, being liable to cause an inhibition of the NO-H₂ reaction, especially at lower temperature.     

Study of Probe-Surface Interaction in Shear-Force Microscopy: Effects of Humidity and Lateral Spring Constant

The shear force between a glass probe and a mica surface has been investigated as a function of the relative humidity, H, and the lateral spring constant of the probe, K. It was found that the interaction length D_o decreases with increasing H and exhibits a sharp drop around H=40%. With increase in K from 5 to 40 N/m, D_o gradually increases, although this feature was absent when a probe with a softer tip-end was used. The latter result indicates that the shear force in an atmospheric condition is not a remote force but results from some contact between the tip and the surface. Our results that D_o is independent of the oscillating amplitude and that the resonance curve of the probe is almost symmetric except in close vicinity to the surface are not in accord with the force model proposed recently, i.e., the knocking mechanism. It is proposed that the probe can vibrate even if the probe touches the surface, and that the resonance frequency increases steeply as the contact tightens. Theoretical estimation of the contribution of noncontact forces is also described.This paper was originally presented at the seventh Meeting on Near Field Optics, which was held on July 1, 1998 at Nagoya University, Nagoya, organized by Research Group on Near Field Optics, the Optical Society of Japan, an affiliate of the Japan Society of Applied Physics.     

Adsorption behavior of methylene blue and its congeners on a stainless steel surface

Methylene blue and its congeners as model dyes were adsorbed onto stainless steel particles at different ionic strengths, pH values, and ethanol contents, and the adsorption mechanism was investigated. A Fourier transform infrared spectroscopy (FTIR) analysis of the dyes adsorbed on the stainless steel plate was carried out to determine the orientations of the adsorbed dyes on stainless steel surface. The adsorption isotherms for all the dyes tested were approximated by a Langmuir equation (Q=Kq(m)C/(1+KC)) in most cases except under strongly basic conditions. From the ionic strength and ethanol content dependencies of the K value in the Langmuir equations, both the electrostatic and hydrophobic interactions were indicated to contribute to the adsorption of the dyes at neutral pH. By comparing the K and q(m) values for the methylene blue congeners and with the aid of the FTIR analyses, it was found that the kind of substituent groups at most positions of the polyheterocycles of methylene blue strongly affects the adsorption behavior, particularly the area occupied by an adsorbed dye molecule, the affinity for the stainless steel surface, and the orientation of the adsorbed dye molecule on the stainless steel surface.     

Synthesis of aromatic trifluoromethyl compounds by ring expansion of cyclodienes

Chlorotrifluoromethyl-1-diazirine was used for a source of chlorotrifluoromethyl carbene. The carbene added to cyclic dienes to give trifluoromethylated six-membered aromatic compounds. Thus, pyrrole gave 3-(trifluoromethyl)pyridine and cyclopentadiene gave benzotrifluoride.In the course of out research to develop a new synthetic method for aromatic trifluoromethyl compounds [1], we planned to use the reaction of chlorotrifluoromethyl carbene (1) with a five-membered cyclic diene. The reaction of pyrrole with dichlorocarbene was reported to give 3-chloropyridine [2]. Therefore, we expected that the similar type of reaction of 1 with a five-membered cyclic diene would provide a new method for the syntheses of aromatic trifluoromethyl compounds. We chose chlorotrifluoromethyl-1-diazirine (2) [3] as the precursor of 1.First, we examined the reaction of 2 with cyclohexene to learn the reactivity of 1. Heating the solution of 2 in cyclohexene at 120° for 3 h gave two adducts (3 and 4). Both products were separated by the preparative g.l.c. using a DEGS column of 7 m at 60°C. 3: 36%; m/e 198 (M⁺); ¹H-NMR δ(CDCl₃) 0.88?2.60 (m); ¹⁹F-NMR δ [4] 10.2. 4: 10% m/e 198; ¹H-NMR δ(CDCl₃) 0.80?2.60; ¹⁹F-NMR δ ?1.2. Compound 3 reacted with silver trifluoroacetate to give 2-(trifluoromethyl)cyclohepten-3-yl trifluoroacetate, while 4 did not. This result established the Stereochemistry of both products as shown in Chart 1. This reaction showed that 2 was a good precursor of 1 and that 1 had a high reactivity to a double bond.To utilized this reaction for the synthesis of an aromatic trifluoromethyl compound, thermolysis of 2 with five-membered cyclic dienes was investigated. A solution of 2 (230 mg) in pyrrole (500 mg) was sealed in a Pyrex tube under vacuum and heated at 120°C for 2 h. The reaction mixture was purified by a trap-to-trap distillation. Analysis of the distillate by g.l.c. showed that 3-(trifluoromethyl)pyridine (5) was obtained in 35% yield based on 2. The g.l.c-mass spectrum and ¹⁹F-NMR of 5 were identical with those of the authentic sample [5]. Similar thermolysis and work-up of a solution of 2 (160 mg) in cyclopentadiene (550 mg) at 140°C for 3 h gave benzotrifluoride in 23% yield. All the results are summarized in Chart 1.The characteristic point of this procedure is that a trifluoromethyl group was introduced to a five membered ring with one carbon atom under ring expansion. Yields shown above were not optimized and this method can be used for synthesis of some aromatic trifluoromethyl compounds, which are difficult to synthesize by the usual methods.     

Contribution of acidic amino residues to the adsorption of peptides onto a stainless steel surface

The role of the acidic amino acid residues in the adsorption of peptides/proteins onto stainless steel particles was investigated using a peptide fragment from bovine beta-lactoglobulin, Thr-Pro-Glu-Val-Asp-Asp-Glu-Ala-Leu-Glu-Lys (T5 peptide), which has a high affinity to a stainless steel surface at acidic pHs, and its mutant peptides substituted with different numbers of acidic amino acid residues. The adsorption behavior of the mutant peptides as well as the T5 peptide were studied at pH 3 with respect to concentration and ionic strength dependencies and the reversibility of the adsorption process. The behavior of the peptides was generally characterized as two distinct irreversible adsorption modes, Mode I and Mode II. In Mode I, the amounts adsorbed lay on the ordinate at zero equilibrium concentration in the solution, while in Mode II, the amount adsorbed increased with increased equilibrium concentration. The area occupied by the peptides was predicted by molecular mechanics and molecular dynamics. The state of the peptides, when adsorbed, was investigated using FT-IR analysis. The FT-IR analyses revealed that the side carboxylic groups of the peptides adsorbed on the stainless steel surface were ionized, while they were unionized in the solution at pH 3. Thus, the interactions between the carboxylic groups of the peptide and the stainless steel surface can be considered to be largely electrostatic. The peptide having four acidic amino acid residues took a maximum adsorbed amount, the reason for which is discussed.     

Identification of ammonia in gas emanated from human skin and its correlation with that in blood.

Identifying and measuring the ammonia gas that emanates from human skin, which we called skin gas, has been achieved using a modified gas chromatographic system with a nitrogen-selective detector (flame-thermoionic detector: FTD). The skin gas is collected with a home-made sampling probe or bag, which is used to cover the skin surface of a subject's wrist, or a finger, for 5 min. It was proved that ammonia was present in skin gas for healthy persons and patients with hepatic disease. The average amounts of ammonia were 1.7 +/- 0.4 and 2.7 +/- 0.8 ng/cm2; furthermore, there was a significant difference between them (p < 0.05). In addition, the ammonia levels present in skin gas were correlated with that in blood (r = 0.64, p < 0.05).     

Determination of some inorganic cations adsorbed on porous silica glass in a distilled water medium

Porous glass (1 g, 97 m²) composed of 96% silica adsorbed 3.2–3.7 μmol of cations, such as Na, K, Sr, Ca and Mg ions, in a distilled water medium. Cations adsorbed were exchanged with other ions by equilibrium reaction and adsorption of bivalent cations on the glass was stronger than those of monovalent cations. The minimum detection limit to be able to estimate the value of cations is nM when usual glassware is used for determination of cations.     

How have they started? – A brief guide for pedestrians

I shall present a very brief summary of subjects selected from what Prof. Akito Arima has done in the past years. I will focus on the initial works on the configuration mixing and on the Interacting Boson Model. Since there are many literatures on these subjects, I shall concentrate what have been done at the initial or at the pre-history stages. By doing this, we shall see how Prof. Akito Arima started from the scratch.