New fluorescent sensor for antimony and transition metal cations based on rhodamine amide-arm homotrioxacalix[3]arene

A new fluorescent sensor 1 based on the rhodamine amide-armed homotrioxacalix[3]arene was synthesized, and its sensing behavior toward metal ions was investigated by UV–vis and fluorescence spectroscopies. Upon the addition of metal cations (Sb³⁺, Fe³⁺, Ni²⁺), a significant fluorescent enhancement in the range of 500–600 nm and colorimetric change was observed.     

Effect of primary filter using theoretical intensity of fluorescent X‐rays and scattered X‐rays

A primary filter is often used for low‐concentration analysis by energy‐dispersive X‐ray fluorescence spectrometer. We determined the material and thickness of the primary filter and calculated the theoretical intensities of the fluorescent X‐rays and scattered X‐rays using lead in brass, for which the concentration is known. The filter materials were zirconium, nickel, titanium, aluminum, and molybdenum with a thickness between 20 and 125 µm. For verification, we calculated the lower limits of detection using theoretical intensities for several filters and compared them with values calculated using the measured intensities. For example, both values were similar for a 125 µm zirconium filter: 128.0 ppm using theoretical intensities and 147.7 ppm using measured intensities. The theoretical intensity values are obtained by measurements and calculations, but require no primary filters for the measurements. This method is extremely effective for selecting the optimal filter for multiple samples and elements. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterization of aluminum species with nitrate, perchlorate and sulfate ions in the positive and negative ion mode by electrospray ionization mass spectrometry

The application of electrospray ionization mass spectrometry (ESI-MS) for aluminum speciation in the positive and negative ion modes was discussed. Aluminum nitrate, perchlorate and sulfate solutions were measured by ESI-MS. In the positive ion mode, aluminum species containing anions (Al-L; L=NO3, ClO4 and SO4) were identified, while [Al(OH)2(H2O)n]+ (n=2-4) were the main species. The affinity of the anions with Al3+ estimated by ESI-MS was consistent with the hardness of the anions (hard and soft acids and bases principle) and the results from 27Al nuclear magnetic resonance studies. This indicates that the results observed from the positive ion mode preserved the chemical state of aluminum in the solution. In the negative ion mode, [Al(OH)4-nLn]- (n=0-2, L=NO3, ClO4) were the main species, which were considered to be converted from positive aluminum species, [Al(OH)(H2O)n]+ (n=2-4), by the successive addition of anions. Anions did not only attach to one aluminum ion but also bridged two aluminum ions. In Al2(SO4)3 solution, the behavior of SO4(2-) in the negative ion mode differed from that of NO3- and ClO4-. This may reflect the affinity of SO4(2-) with Al3+ in the solution or in the mass spectrometer or in both. Finally, detection mechanisms for the aluminum species in the solution are proposed for both the positive and negative ion modes. It is shown that ESI-MS can be used to observe the interaction between Al3+ and anions. We show the importance of the interpretation of the results by ESI-MS for obtaining new information of the metal species in the solution.     

Asymmetric synthesis of aerothionin, a marine dimeric spiroisoxazoline natural product, employing optically active spiroisoxazoline derivative

Successful first synthesis of optically pure (+)- and (−)-aerothionins (1) from the racemic spiroisoxazoline derivative 8 has been accomplished. The absolute configuration of natural (+)-1 was determined by comparison of (+)- and (−)-8 with related derivatives.     

Optical emission spectroscopy of benzyl radicals produced in a radio-frequency plasma

The benzyl radical was studied by optical emission spectroscopy in gas phase. This radical was produced in a radio-frequency (RF, 13.56 MHz) discharge, using benzyl alcohol (?CH(2)OH) as a precursor. The fluorescence from the first excited electronic state 1(2)A(2) to ground state 1(2)B(2) (450 nm) was studied as a function of several external parameters (pressure, RF power, electrodes and mixtures of the inert gases Ar, Ne, He, N(2), with the precursor). We also used a DC discharge to produce this radical but, in this case, the decomposition was fast. We observed changes in the electronic transitions of this radical, and found the best conditions to study it by optogalvanic spectroscopy.     

Free-energy calculation of structure-H hydrates

A molecular-dynamics (MD) simulation of structure-H hydrates was performed under constant pressure and temperature with 6120 TIP4P water molecules, 900 OPLS-UA methane molecules, and 180 large molecular guest substance (LMGS) molecules. The LMGS molecules were represented in the form of a one-site Lennard-Jones (LJ) model using the LJ parameters sigma and epsilon. In order to clarify the thermodynamic stability of structure-H hydrates, we calculated the free-energy difference, changing on the sigma and epsilon only of the LMGS molecules. In this simulation, stable crystals of structure-H hydrates and a minimum value of DeltaG were obtained at sigma approximately 6.2 A and large values of epsilon. All simulations were performed using the special-purpose computer hardware MDGRAPE-2.     

Interference, fluctuation, and alternation of electron tunneling in protein media. 1. Two tunneling routes in photosynthetic reaction center alternate due to thermal fluctuation of protein conformation

Electron tunneling routes for the electron transfer from the bacteriopheophytin anion to the primary quinone in the bacterial photosynthetic reaction center of Rhodobactor sphaeroides are investigated by a combined method of molecular dynamics simulations for the protein conformation fluctuation and quantum chemical calculations for the electronic states of the donor, acceptor, and protein medium. The analysis of the tunneling route is made by mapping interatomic electron tunneling currents for each protein conformation. We found that there are two dominant routes mainly passing through Trp(M252) (Trp route) or mainly passing through Met(M218) (Met route). Actual electron tunneling pathways alternate between the two routes, depending on the protein conformation which varies with time. When either the Trp route or the Met route dominates, the electron tunneling matrix element /T(DA)/ becomes large. When both the Trp route and the Met route dominate, /T(DA)/ becomes very small due to the destructive interference of the electron tunneling currents between the two routes. We found that a linear relationship exists between the value of /T(DA)/ and the inverse of the degree of destructive interference Q for a wide range of values (ca. 3-10(3) for Q). A similar relationship was also found previously for electron transfer in ruthenium-modified azurins, suggesting that this relationship holds true in general. From these results, we are led to the conclusion that /T(DA)/ cannot exceed a maximum value at Q = 1, even if much variation of /T(DA)/ happens due to the fluctuation of protein conformation. We also conclude that the property of the electron transfer alternates between constructive and destructive interference, due to the fluctuation of protein conformation. It is impossible to keep a system in either constructive or destructive interference because thermal fluctuation of protein conformation takes place.     

Ladderlike ferromagnetic spin coupling network on a pi-conjugated pendant polyradical

A poly(9,10-anthryleneethynylene)-based polyradical with two pendant stable phenoxyls in one anthracene skeleton was newly synthesized via polymerization of the corresponding bromoethynylanthracene monomer using a Pd(0) catalyst. The average molecular weight of the polymer reached M(n) = 5 x 10(3) and was soluble in common organic solvents. The polyradical was prepared from the corresponding hydroxyl precursor polymer and was appropriately stable at room temperature. The ESR spectrum of the corresponding monomeric radical suggested an effectively delocalized spin density distribution on the backbone anthracene. The magnetization and the static magnetic susceptibility of the polyradical were measured using a SQUID magnetometer. The large average spin quantum number (S = (5)/(2)) of the polyradical indicated that the ferromagnetic spin coupling network of the polyradical had spread throughout the pi-conjugated chain and that it was considerably insensitive to spin defects.