Pyrolysis of amines: Infrared spectrum of allylimine

Infrared absorption spectrum of allylimine in the gas phase was measured for the first time. The spectrum consisted of two rotational isomers, cis and trans, around the CC bond. The relative population of the trans form was 70–80%, and the rest was for the cis form at room temperature. This intermediate molecule was produced by the thermal decomposition of diallylamine and by the isomerization of propargylamine. The vibrational assignments were made with the help of an ab initio MO calculation. The half-life in the absorption cell was about 20 min.     

All-optical image processing with a supranonlinear dye-doped liquid-crystal film

We demonstrate a dynamic all-optical image-intensity-inversion technique that uses self- and mutual-phase-modulation effects with a highly nonlinear nematic liquid-crystal film placed in an intermediate focal plane. This process requires submilliwatt optical power, responds in a few milliseconds, and can be realized over a very broad spectral range.     

Bootstrap re-sampling technique to evaluate the optimal formulation of theophylline tablets predicted by non-linear response surface method incorporating multivariate spline interpolation

Optimal solutions of theophylline tablet formulations were derived from three types of experimental datasets, composed of different numbers of data-points using the response surface method incorporating multivariate spline interpolation (RSM(S)). The reliability of these optimal solutions was evaluated by a bootstrap re-sampling technique. Different levels of three causal factors were used as factors of response surface analysis: the lactose/cornstarch ratio (X(1)), the amount of carmellose calcium (X(2)), and the amount of hydroxypropylcellulose (X(3)). The target responses were the dissolution ratio of theophylline for the first 15 min (Y(1)) and the hardness (Y(2)) of each of the prepared tablets. Similar optimal solutions were estimated in three different sizes of datasets. A bootstrap re-sampling with replacements from the original dataset was applied, and optimal solutions for each bootstrap dataset were estimated. The frequency of the distribution of the optimal solution generated by the bootstrap re-sampling technique demonstrated almost normal distribution. The average and standard deviation of the optimal solution distribution were calculated as evaluation indices reflecting the accuracy and reproducibility of the optimal solution. It was confirmed that the accuracy was sufficiently high, irrespective of the dataset size; however, the reproducibility worsened with a decrease in the number of the experimental datasets. Consequently, it was considered that the novel evaluation method based on the bootstrap re-sampling technique was suitable for evaluating the reliability of the optimal solution.     

Transient diffusion and cluster formation of water molecules on Rh(111) at 20 K

The authors investigated the initial stage of water adsorption on Rh(111) at 20 K, using infrared reflection absorption spectroscopy. In this low coverage region, isolated water molecules and small water clusters are observed. Since thermal diffusion is suppressed at 20 K, the formation of water clusters at low coverage is controlled by both coverage and transient diffusion on the surface. Within a simple random walk model of the transient diffusion and clustering process, the authors estimate the mean lateral displacement from the first impact point to the final adsorption site to be 7.6 A; an incoming water molecule on Rh(111) is trapped with eight postcollision hops on the average.     

Diastereoselective construction of 7-methylenebicyclo[3.2.1]oct-3-en-2-one derivatives by palladium-catalyzed cyclization of propargylic acetates with 2-oxocyclohex-3-enecarboxylates

The reaction of propargylic acetates with 2-oxocyclohex-3-enecarboxylates in the presence of a palladium catalyst is described. Substituted 7-methylenebicyclo[3.2.1]oct-3-en-2-ones were synthesized in a highly diastereoselective manner.     

Two-dimensional superstructures and softened C-H stretching vibrations of cyclohexane on Rh(111): effects of preadsorbed hydrogen

Adsorption structures and interaction of cyclohexane molecules on the clean and hydrogen-preadsorbed Rh(111) surfaces were investigated using scanning tunneling microscopy, spot-profile-analysis low-energy electron diffraction, temperature-programmed desorption, and infrared reflection absorption spectroscopy (IRAS). Various ordered structures of adsorbed cyclohexane were observed as a function of hydrogen and cyclohexane coverages. When the fractional coverage (θ(H)) of preadsorbed hydrogen was below 0.8, four different commensurate or higher-order commensurate superstructures were found as a function of θ(H); whereas more densely packed incommensurate overlayers became dominant at higher θ(H). IRAS measurements showed sharp softened C-H vibrational peaks at 20 K, which originate from the electronic interaction between adsorbed cyclohexane and the Rh surface. The multiple softened C-H stretching peaks in each phase are due to the variation in the adsorption distance from the substrate. At high hydrogen coverages they became attenuated in intensity and eventually diminished at θ(H) = 1. The gradual disappearance of the soft mode correlates well with the structural phase transition from commensurate structures to incommensurate structures with increasing hydrogen coverage. The superstructure of adsorbed cyclohexane is controlled by the delicate balance between adsorbate-adsorbate and adsorbate-substrate interactions which are affected by preadsorbed hydrogen.     

Critical behavior of megabase-size DNA toward the transition into a compact state

We studied the changes in the higher-order structure of a megabase-size DNA (S120-1 DNA) under different spermidine (SPD) concentrations through single-molecule observations using fluorescence microscopy (FM) and atomic force microscopy (AFM). We examined the difference between the folding transitions in S120-1 DNA and sub-megabase-size DNA, T4 DNA (166 kbp). From FM observations, it is found that S120-1 DNA exhibits intra-chain segregation as the intermediate state of transition, in contrast to the all-or-none nature of the transition on T4 DNA. Large S120-1 DNA exhibits a folding transition at lower concentrations of SPD than T4 DNA. AFM observations showed that DNA segments become aligned in parallel on a two-dimensional surface as the SPD concentration increases and that highly intense parallel alignment is achieved just before the compaction. S120-1 DNA requires one-tenth the SPD concentration as that required by T4 DNA to achieve the same degree of parallel ordering. We theoretically discuss the cause of the parallel ordering near the transition into a fully compact state on a two-dimensional surface, and argue that such parallel ordering disappears in bulk solution.     

On-line mass spectrometric analysis of hydrothermal reactions for biomass model sample containing sulfur compounds

Biomass gasification using supercritical water is a promising way to produce hydrogen gas. However, this method might release toxic heteroatomic compounds. It is therefore important to clarify reaction pathways for efficiently obtaining hydrogen gas and suppressing environmental burden. L-cysteine was adopted for a test reagent containing sulfur and determination of the sulfur compound reaction pathways was studied by Li⁺-ion attachment mass spectrometry. It was found that H₂S, CO, CO₂, SO, SO₂ and SO₃ gasses were released at high concentrations in the gas phase during the hydrothermal reaction. By adding Ca(OH)₂ as alkali, the pathway of these gasses were, however, suppressed into the liquid phase so that the toxic emissions to the gas phase could be avoided.     

Control of Exchange Interactions in π Dimers of 6‐Oxophenalenoxyl Neutral π Radicals: Spin‐Density Distributions and Multicentered–Two‐Electron Bonding Governed by Topological Symmetry and Substitution at the 8‐Position

The tri‐tert‐butylphenalenyl (TBPLY) radical exists as a π dimer in the crystal form with perfect overlapping of the singly occupied molecular orbitals (SOMOs) causing strong antiferromagnetic exchange interactions. 2,5‐Di‐tert‐butyl‐6‐oxophenalenoxyl (6OPO) is a phenalenyl‐based air‐stable neutral π radical with extensive spin delocalization and is a counter analogue of phenalenyl in terms of the topological symmetry of the spin density distribution. X‐ray crystal structure analyses showed that 8‐tert‐butyl‐ and 8‐(p‐XC₆H₄)‐6OPOs (X=I, Br) also form π dimers in the crystalline state. The π‐dimeric structure of 8‐tert‐butyl‐6OPO is seemingly similar to that of TBPLY even though its SOMO–SOMO overlap is small compared with that of TBPLY. The 8‐(p‐XC₆H₄) derivatives form slipped stacking π dimers in which the SOMO–SOMO overlaps are greater than in 8‐tert‐butyl‐6OPO, but still smaller than in TBPLY. The solid‐state electronic spectra of the 6OPO derivatives show much weaker intradimer charge‐transfer bands, and SQUID measurements for 8‐(p‐BrC₆H₄)‐6OPO show a weak antiferromagnetic exchange interaction in the π dimer. These results demonstrate that the control of the spin distribution patterns of the phenalenyl skeleton switches the mode of exchange interaction within the phenalenyl‐based π dimer. The formation of the relevant multicenter–two‐electron bonds is discussed.