Chemical absorption of CO2 employing alkanolamines is currently considered to be the most promising approach for CO2 emission reduction from power plants. Extensive efforts have been devoted by experimental and theoretical researchers in the development of amine solutions, with the main purpose of reducing the energy cost of solvent regeneration. In the present Commentary, we show how theoretical calculations have been utilized in the analysis of the amine-CO2 reaction mechanism. Theoretical studies with quantum chemistry calculations and ab initio molecular dynamics are mainly focused on.
Illustration of the chemical absorption process using amines as CO2 absorber.Fullsize Image
In the 20th century, transistor, computer, and LASER were invented. New spectroscopic methods have been developed along with electronics and opt-electronics. The development of the LASER and computer technology strongly stimulated the unique LASER Raman spectroscopy, which is still opening the door of biomolecluar science.
The solutions (χnlm) of the Schrödinger equation for the hydrogen atom contain the term exp(imφ). When m = 0, functions χnlm are real, however, in the cases of m ≠ 0, functions χnlm are complex. Probability density distribution of χn,n−1,m ( n = 1, 2, 3,…, 6 ) was sculptured in a glass block (Figures 1, 2). Each picture is symmetrical about the z axis. It was compared with a 3-D isosurface model such as Figure 4. Isosurface models can hardly show the entire region where an electron can be found. On the other hand, in the diagram of probability density distribution models, an electron is found everywhere around the nucleus. The number and shape of the planar and conical nodes symmetrical about the z axis are summarized in Figure 3.
Schematic representation of the planar (orange) and conical (blue) nodes symmetrical about the z axis.Fullsize Image
Membrane bioreactors (MBRs) are a system integrating biological degradation of waste products and solid-liquid separation by membrane filtration. One of the obstacles to wide application of MBRs is membrane fouling, which is a phenomenon whereby particles deposit on the membrane surface or in the pores. Fouling decreases membrane permeability and increases operating costs. In order to reduce fouling, chemical cleaning must be performed at an appropriate time. However, chemicals used in cleaning are costly and preparation time is needed to do chemical cleaning. Hence, a fouling prediction model is required. Although statistical models have been proposed in previous studies, it is difficult to predict fouling in newly constructed MBRs or when operating conditions are changed. We focused on the fact that the fouling mechanism is common in various MBRs and to predict fouling in a certain newly established MBR, we developed a statistical model trained by data measured in other MBRs. Through case studies using data sets measured in real MBRs, it was confirmed that a constructed model using the proposed method could predict fouling more accurately than a model which was trained by data measured in the newly constructed MBR (Figures 4, 5, Table 2).
Urethane resins show peculiar coatings, adhesives and cushions. The urethane formations from isocyanates with alcohols etc. are accompanied by carbamic acids, the esters, and their decomposed compounds for material performances. The steric and energy changes in the basic reaction processes of isocyanates、and the catalytic reaction by triethylamine were speculated by MOPAC-PM6 simulation, and the simulations compared with them by other methods. Thus, K. C. Frischs' analysis that the reactivities between substituted phenylisocyanates and an alcohol are related to Hammett substituent constants,σ (R = 0.97), was correlated with Mulliken's electronegativity, (IP + EA)/2 by PM6 method (R = 0.97). The reactions were speculated to proceed via hydrogen-bondings and six-membered ring 1:2 complexes of isocyanate with alcohol (water or amine) and by the activation energy of Ea = 4∼13 kcal mol−1. The higher reactivity is pointed out by the calculated smaller Ea value. The calculations including PM6-D3H4 were also effective for the reactivity of X-NCO. The 4 molecules' catalytic reaction of PhNCO with 2MeOH by Et3N was speculated to be accelerated from Ea = 7.23 kcal mol−1 to Ea = 3.92 kcal mol−1. The transition state structure showed the easy proton transfer by Et3N. Hydrolyses of carbamic acid and the methyl carbamate ester were compared for urethane properties, and the decomposition of the acid to diphenylurea via aniline etc. and the stability of the ester were speculated by the calculated Ea and transition state structures.
The catalytic reaction with 2MeOH for the urethane. IRC data of catalytic urethane formation via the complex (Bcom) from PhNCO and 2MeOH by Et3N.Fullsize Image
ABSTRACT: Dynorphin-A (1–17) and its variant, R6W-DNYA, are known to penetrate into the plasma membrane and to cause lysis and fusion. Peptide-membrane interactions promote α -helix formations of these peptides. To investigate the membrane-promoting α -helix formation, we systematically compute low-energy α -helical conformations using the Wang- Landau method, and evaluate their solvation free-energies in cyclohexane solvent corresponding to the hydrophobic environment of a membrane. The result suggests that Dynorphin-A (1–17) and R6W-DNYA existing in a membrane may form α -helices in two regions of Gly3-Ile8 and Leu12-Gln17.