Homochiral or Heterochiral: A Systematic Study of Threonine Clusters Using a FT ICR Mass Spectrometer

The strong chiral preferences of some magic clusters of amino acids have attracted continually increasing interests due to their unique structures, properties and possible roles in homochirogenesis. However, how chirality can influence the generation and stability of cluster ions in a wild range of cluster sizes is still unknown for most amino acids. In this study, the preference for threonine clusters to form homochiral and heterochiral complex ions has been investigated by electrospray ionization (ESI) mass spectrometry. Abundant cluster [Thrn+mH]m+ ions (7 ≤ n ≤ 78, 1 ≤ m ≤ 5) have been observed for both samples of enantiopure (100% L) and racemic (50:50 L:D) threonine solutions. Further analyses of the spectra show that the [Thr14+2H]2+ ion is characterized by its most outstanding homochiral preference, and [Thr7+H]+ and [Thr8+H]+ ions also clearly exhibit their homochiral preferences. Although most of the triply charged clusters (20 ≤ n ≤ 36) are characterized by heterochiral preferences, the quadruply charged [Thrn+4H]4+ ions (40 ≤ n ≤ 59) have no obvious chiral preference in general. On the other hand, a weak homochiral preference exists for most of the quintuply charged ions observed in the experiment.

Study on Metakaolin Impact on Concrete Performance of Resisting Complex Ions Corrosion

The main purpose of this study is to determine the metakaolin (MK) impacts on the concrete durability when the concrete is subjected to joint corrosion of SO42−,Mg2+ and, Cl−. Four groups of concrete test samples, which contained different MK contents, were designed and tested in order to see their physical property changes and macro-morphology differences during the cyclic corrosion process. And a series of approaches, including XRD, FTIR, SEM, and EDS, were applied to study the concrete phase composition changes and the micro-morphology features of all groups. According to the test results, when reaching 20 cycles, the concrete sample with 10% MK showed the best concrete physical properties; when reaching 120 cycles, the concrete with 5% MK content showed the best durability, produced similar amount of corrosion products to ordinary concrete, and presented relatively compacted micro-structure and small internal porosity. Mg2+ actually has a great impact on metakaolin. The corrosion product quantity increased significantly when MK admixture reached 15%. Due to the great number of produced M-S-H, the corrosive ions damaged the concrete for a second time, leading to serious aggregate peeling-off, powder surface of test samples, and porous micro-structure.

TD-DFT: An Exploration of the Energies and Structures of Crystal Violet and a Variety of Cr(III) Complex Ions

<p>Spectroscopy is the science of utilising light in order to divine information about a molecule or system of molecules. Specifically, the absorption, emission, and scattering of different wavelengths of light can provide data about bond strength, bond order, vibrational frequency, and excitation energy [1, 2]. As the wavelength and therefore energy of the incident photons can be set by the instrument, the exact energies of absorbance or emission of the molecule can be measured. This data can be gathered experimentally using specialised equipment however some molecules resist synthesis, and so a wealth of data about many theoretically possible species eludes us. We may also want to isolate the molecule in “empty space” whereas “gas phase” measurements are not always possible. This is one place where computational chemistry comes to the fore. Using an appropriate computational method such as density functional theory (DFT), data can be theoretically derived and calculated for many interesting areas of chemistry. DFT is a computational method based on the findings of Hohenberg and Kohn in 1964 that the ground state electronic energy of a system can be determined completely by the electron density [3-6]. This means that it has a considerably higher efficiency as a computational method compared to the wave function approach, where the number of variables increases exponentially as your system increases in size, as the electron density has the same number of variables regardless of the size of the system [7]. The use of an appropriate functional to map the electron density and the energy is one of the vital choices in utilising this method, but if chosen well can provide good results with a much lower computational cost than other methods, while still accounting for electron correlation effects [8]. It has become a very popular method due to its versatility and generally good accuracy with relatively low computational expense when compared to ab initio methods [9].</p>

TD-DFT: An Exploration of the Energies and Structures of Crystal Violet and a Variety of Cr(III) Complex Ions

<p>Spectroscopy is the science of utilising light in order to divine information about a molecule or system of molecules. Specifically, the absorption, emission, and scattering of different wavelengths of light can provide data about bond strength, bond order, vibrational frequency, and excitation energy [1, 2]. As the wavelength and therefore energy of the incident photons can be set by the instrument, the exact energies of absorbance or emission of the molecule can be measured. This data can be gathered experimentally using specialised equipment however some molecules resist synthesis, and so a wealth of data about many theoretically possible species eludes us. We may also want to isolate the molecule in “empty space” whereas “gas phase” measurements are not always possible. This is one place where computational chemistry comes to the fore. Using an appropriate computational method such as density functional theory (DFT), data can be theoretically derived and calculated for many interesting areas of chemistry. DFT is a computational method based on the findings of Hohenberg and Kohn in 1964 that the ground state electronic energy of a system can be determined completely by the electron density [3-6]. This means that it has a considerably higher efficiency as a computational method compared to the wave function approach, where the number of variables increases exponentially as your system increases in size, as the electron density has the same number of variables regardless of the size of the system [7]. The use of an appropriate functional to map the electron density and the energy is one of the vital choices in utilising this method, but if chosen well can provide good results with a much lower computational cost than other methods, while still accounting for electron correlation effects [8]. It has become a very popular method due to its versatility and generally good accuracy with relatively low computational expense when compared to ab initio methods [9].</p>

The Thermodynamics of Copper (II) and Nickel (II)- Diamine Complex Formation in Aqueous Solution

<p>This work describes the accurate measurement of the thermodynamic functions Delta G degree and Delta H degree for the step-wise coordination equilibria between each of the ions H+, Ni2+, Cu2+, and, a series of C1-substituted 1,2-diaminoethanes in aqueous solution. The study Involved. (a) The construction of a sensitive constant temperature environment calorimeter for measuring the enthalpy changes in the complex-formation reactions, (b) The rigorous calibration of an electrode system, incorporating a glass electrode, for the direct potentiometric measurement of equilibrium hydrogen ion concentrations in the solutions containing complex ions. The thermodynamic functions Delta G degree and Delta H degree led to accurate Delta S degree values for the step-wise complex-formation reactions. The thesis considers the contribution of the entropy of ligation to the stability of complex ions. The molar entropies of the complex ions have been calculated and their values considered with respect to the coordination number and the possible structure, degree of hydration and steric properties of the ions.</p>

The Thermodynamics of Copper (II) and Nickel (II)- Diamine Complex Formation in Aqueous Solution

<p>This work describes the accurate measurement of the thermodynamic functions Delta G degree and Delta H degree for the step-wise coordination equilibria between each of the ions H+, Ni2+, Cu2+, and, a series of C1-substituted 1,2-diaminoethanes in aqueous solution. The study Involved. (a) The construction of a sensitive constant temperature environment calorimeter for measuring the enthalpy changes in the complex-formation reactions, (b) The rigorous calibration of an electrode system, incorporating a glass electrode, for the direct potentiometric measurement of equilibrium hydrogen ion concentrations in the solutions containing complex ions. The thermodynamic functions Delta G degree and Delta H degree led to accurate Delta S degree values for the step-wise complex-formation reactions. The thesis considers the contribution of the entropy of ligation to the stability of complex ions. The molar entropies of the complex ions have been calculated and their values considered with respect to the coordination number and the possible structure, degree of hydration and steric properties of the ions.</p>