Masahiro Kotaka

Bio: Masahiro Kotaka is an academic researcher from Tokyo Institute of Technology. The author has contributed to research in topics: Ion chromatography & Hydrogen atom. The author has an hindex of 9, co-authored 20 publications receiving 652 citations.

Fundamental studies on the ion-exchange separation of boron isotopes

Abstract: The single-stage separation factors for boron isotopes between an ion-exchange resin and an external solution were determined, using an ion-exchange breakthrough operation. The lighter isotope boron-10 was considerably enriched in the anion-exchange resin phase. The separation factor was very much influenced by the boric acid concentration in the external solution, but not as much influenced by the kind of the anion exchange resin used and operation temperature. The separation factor increased with a decrease in the boric acid concentration of external solution from 1.008 (0.501 mol/l) to 1.016 (0.010 mol/l). The value of the separation factors obtained experimentally were compared with those estimated on the basis of the theory of the two-phase distribution of isotopes.

11B-NMR Study of the Complex Formation of Borate with Catechol and L-Dopa

Abstract: In the solution of catechol and borax at pH 11, the equilibria between catechol and the monomeric borate anion to form the 1 : 1 and 2 : 1 (catechol: boron) anionic complexes have been demonstrated by the existence of 11B-NMR signals for the two complexes and the monomeric borate anion. In the solution of L-dopa and borax at pH 11, however, the signal for the 2 : 1 anionic complex was not observed, though it was observed below pH 7. By the 11B-NMR spectra at pH 6.5, the complex formation constants, logK1 and logK2, have been estimated as 3.9 and 4.4 for catechol, and as 4.3 and 5.0 for L-dopa, respectively.

Vibrational analysis of pyruvate ion molecules and estimation of equilibrium constants for their hydrogen isotopic exchange reactions

Abstract: The infrared spectra (4000-300 cm/sup -1/) of CH/sub 3/COONa and its five isotopic substitutions including D- and /sup 13/C-labeled modifications suspended in KBr disks were measured at 80 and 290 K. Excellent resolutions were obtained by recording the spectra at low temperature. Complete vibrational assignments were established on the basis of correlations of group modes and the /sup 13/C shifts of the fundamentals. From a normal coordinate analysis a general valence force field involving 26 force constants has been determined, which reproduces 82 experimental frequencies with a root-mean-squares deviation of 3.3 cm/sup -1/. The composition of the normal vibrations from the symmetry coordinates has been given in terms of the potential energy distribution which makes it possible to inspect the relation between the normal modes and the group vibrations. The valence force field was used to predict fundamental frequencies which were not available from experiments, and the reduced partition function ratios of acetate ion molecules were calculated by using the spectroscopic data including the predicted values of the fundamentals. Calculated equilibrium constants of some hydrogen isotopic exchange reactios between the acetate ion molecules are reported.

Atmospheric carbon dioxide concentrations over the past 60 million years

Abstract: Knowledge of the evolution of atmospheric carbon dioxide concentrations throughout the Earth's history is important for a reconstruction of the links between climate and radiative forcing of the Earth's surface temperatures. Although atmospheric carbon dioxide concentrations in the early Cenozoic era (about 60Myr ago) are widely believed to have been higher than at present, there is disagreement regarding the exact carbon dioxide levels, the timing of the decline and the mechanisms that are most important for the control of CO2 concentrations over geological timescales. Here we use the boron-isotope ratios of ancient planktonic foraminifer shells to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used to reconstruct atmospheric CO2 concentrations. We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene and earliest Eocene periods (from about 60 to 52 Myr ago), and ®nd an erratic decline between 55 and 40 Myr ago that may have been caused by reduced CO2 outgassing from ocean ridges, volcanoes and metamorphic belts and increased carbon burial. Since the early Miocene (about 24Myr ago), atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more stable than before, although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately 15 and 3 Myr ago.

Applying Stable Isotope Fractionation Theory to New Systems

Abstract: A basic theoretical understanding of stable isotope fractionations can help researczzzhers plan and interpret both laboratory experiments and measurements on natural samples. The goal of this chapter is to provide an introduction to stable isotope fractionation theory, particularly as it applies to mass-dependent fractionations of non-traditional elements and materials. Concepts are illustrated using a number of worked examples. For most elements, and typical terrestrial temperature and pressure conditions, equilibrium isotopic fractionations are caused by the sensitivities of molecular and condensed-phase vibrational frequencies to isotopic substitution. This is explained using the concepts of vibrational zero-point energy and the partition function, leading to Urey’s (1947) simplified equation for calculating isotopic partition function ratios for molecules, and Kieffer’s (1982) extension to condensed phases. Discussion will focus on methods of obtaining the necessary input data (vibrational frequencies) for partition function calculations. Vibrational spectra have not been measured or are incomplete for most of the substances that Earth scientists are interested in studying, making it necessary to estimate unknown frequencies, or to measure them directly. Techniques for estimating unknown frequencies range from simple analogies to well-studied materials to more complex empirical force-field calculations and ab initio quantum chemistry. Mossbauer spectroscopy has also been used to obtain the vibrational properties of some elements, particularly iron, in a variety of compounds. Some kinetic isotopic fractionations are controlled by molecular or atomic translational velocities; this class includes many diffusive and evaporative fractionations. These fractionations can be modeled using classical statistical mechanics. Other kinetic fractionations may result from the isotopic sensitivity of the activation energy required to achieve a transition state, a process that (in its simplest form) can be modeled using a modification of Urey’s equation (Bigeleisen 1949). Theoretical estimates of isotopic fractionations are particularly powerful in systems that are difficult to characterize experimentally, or when empirical …