Viwat Vchirawongkwin

Symmetry Breaking and Hydration Structure of Carbonate and Nitrate in Aqueous Solutions: A Study by Ab Initio Quantum Mechanical Charge Field Molecular Dynamics

The ab initio quantum mechanical charge field molecular dynamics (QMCF MD) formalism was applied to simulate carbonate and nitrate anions in aqueous solution. The out-of-plane (ν(2)) spectra obtained from the velocity autocorrelation functions (VACFs) and the torsion angle-time functions indicate that the symmetry of carbonate is reduced from D(3h) to a lower degree by breaking up the molecular plane, whereas the planarity of nitrate anion is retained. The calculated frequencies are in good agreement with the Raman and IR data. Carbonate shows a stronger molecular hydration shell than the nitrate anion with the average molecular coordination numbers of 8.9 and 7.9, respectively. A comparison with the average number of ion-solvent hydrogen bonds (H-bonds) indicates the extra water molecules within the hydration shell of carbonate (∼2) and nitrate (∼3), readily migrating from one coordinating site to another. The mean residence times for water ligands in general classify carbonate and nitrate as moderate and weak structure-making anions, while the specific values for individual sites of nitrate reveal local weak structure-breaking properties.

Structural and Dynamical Properties and Vibrational Spectra of Bisulfate Ion in Water: A Study by Ab Initio Quantum Mechanical Charge Field Molecular Dynamics

The ab initio quantum mechanical charge field molecular dynamics (QMCF MD) formalism was applied to simulate the bisulfate ion, HSO4-, in aqueous solution. The averaged geometry of bisulfate ion supports the separation of six normal modes of the O*-SO3 unit with C3v symmetry from three modes of the OH group in the evaluation of vibrational spectra obtained from the velocity autocorrelation functions (VACFs) with subsequent normal coordinate analyses. The calculated frequencies are in good agreement with the observations in Raman and IR experiments. The difference of the averaged coordination number obtained for the whole molecule (8.0) and the summation over coordinating sites (10.9) indicates some water molecules to be located in the overlapping volumes of individual hydration spheres. The averaged number of hydrogen bonds (H-bonds) during the simulation period (5.8) indicates that some water molecules are situated in the molecular hydration shell with an unsuitable orientation to form a hydrogen bond with the ion. The mean residence time in the surroundings of the bisulfate ion classify it generally as a weak structure-making ion, but the analysis of the individual sites reveals a more complex behavior of them, in particular a strong interaction with a water molecule at the hydrogen site.

New turn-on fluorescent and colorimetric probe for cyanide detection based on BODIPY-salicylaldehyde and its application in cell imaging.

Development of cyanide sensor is important as the anion is harmful to human health and the environment. Herein, a new colorimetric and fluorescent probe GSB based on boron dipyrrole-methene (BODIPY) containing salicylaldehyde group for cyanide detection has been reported. GSB undergoes exclusive colorimetric change from orange to colorless and exhibits selective fluorescence turn-on at 504nm upon the addition of cyanide. Other 13 anions give almost no interference under physiological condition. Detection limit of the new cyanide-sensing GSB is 0.88μM, which is below World Health Organization (WHO) recommended level in drinking water. A calculation by density functional theory (DFT) shows suppression of photoinduced electron transfer (PET) mechanism along with the interruption of π-conjugation between salicylaldehyde and BODIPY core by cyanide anion. Cell imaging studies demonstrated that GSB is compatible and capable of sensing cyanide anion in living cells.

Ab Initio quantum mechanical charge field study of hydrated bicarbonate ion: Structural and dynamical properties

The ab initio quantum mechanical charge field molecular dynamics (QMCF MD) formalism was applied to simulate the bicarbonate ion, HCO3−, in aqueous solution. The difference in coordination numbers obtained by summation over atoms (6.6) and for the solvent‐accessible surface (5.4) indicates the sharing of some water molecules between the individual atomic hydration shells. It also proved the importance to consider the hydration of the chemically different atoms individually for the evaluation of structural and dynamical properties of the ion. The orientation of water molecules in the hydration shell was visualized by the θ–tilt surface plot. The mean residence time in the surroundings of the HCO3− ion classify it generally as a structure‐breaking ion, but the analysis of the individual ion‐water hydrogen bonds revealed a more complex behavior of the different coordination sites.

Direct synthesis of aryl substituted pyrroles from calcium carbide: an underestimated chemical feedstock

In this work, a novel synthetic methodology for the preparation of aryl pyrroles directly from the reaction of calcium carbide with oxime is reported. Various pyrrole derivatives are generated from the corresponding oximes in satisfactory yields (49–88%) under the optimized conditions. The one-pot synthesis of aryl pyrrole from widely available ketone is also successfully developed. A new near-infrared fluorescent BODIPY dye containing a phenyl substitution at the C-3 position is expediently prepared from the aryl pyrrole derived from this methodology. The key benefit of this methodology is the use of an inexpensive and less hazardous primary chemical feedstock, calcium carbide, in a wet solvent without any metal catalysts. This process offers a novel cost-efficient route for the synthesis of functionalized pyrrole.

Tl(I)‐the strongest structure‐breaking metal ion in water? A quantum mechanical/molecular mechanical simulation study

Structural and dynamical properties of the Tl(I) ion in dilute aqueous solution have been investigated by ab initio quantum mechanics in combination with molecular mechanics. The first shell plus a part of the second shell were treated by quantum mechanics at Hartree‐Fock level, the rest of the system was described by an ab initio constructed potential. The radial distribution functions indicate two different bond lengths (2.79 and 3.16 Å) in the first hydration shell, in good agreement with large‐angle X‐ray scattering and extended X‐ray absorption fine structure spectroscopy results. The average first shell coordination number was found as 5.9, and several other structural parameters such as coordination number distributions, angular distribution functions, and tilt‐ and θ‐angle distributions were evaluated. The ion–ligand vibration spectrum and reorientational times were obtained via velocity auto correlation functions. The TlO stretching force constant is very weak with 5.0 N m−1. During the simulation, numerous water exchange processes took place between first and second hydration shell and between second shell and bulk. The mean ligand residence times for the first and second shell were determined as 1.3 and 1.5 ps, respectively, indicating Tl(I) to be a typical “structure‐breaker”. The calculated hydration energy of −84 ± 16 kcal mol−1 agrees well with the experimental value of −81 kcal mol−1. All data obtained for structure and dynamics of hydrated Tl(I) characterize this ion as a very special case among all monovalent metal ions, being the most potent “structure‐breaker”, but at the same time forming a distinct second hydration shell and thus having a far‐reaching influence on the solvent structure.

Dynamics and mechanism of structural diffusion in linear hydrogen bond

Dynamics and mechanism of proton transfer in a protonated hydrogen bond (H‐bond) chain were studied, using the CH3OH2+(CH3OH)n complexes, n = 1–4, as model systems. The present investigations used B3LYP/TZVP calculations and Born‐Oppenheimer MD (BOMD) simulations at 350 K to obtain characteristic H‐bond structures, energetic and IR spectra of the transferring protons in the gas phase and continuum liquid. The static and dynamic results were compared with the H3O+(H2O)n and CH3OH2+(H2O)n complexes, n = 1–4. It was found that the H‐bond chains with n = 1 and 3 represent the most active intermediate states and the CH3OH2+(CH3OH)n complexes possess the lowest threshold frequency of proton transfer. The IR spectra obtained from BOMD simulations revealed that the thermal energy fluctuation and dynamics help promote proton transfer in the shared‐proton structure with n = 3 by lowering the vibrational energy for the interconversion between the oscillatory shuttling and structural diffusion motions, leading to a higher population of the structural diffusion motion than in the shared‐proton structure with n = 1. Additional explanation on the previously proposed mechanisms was introduced, with the emphases on the energetic of the transferring proton, the fluctuation of the number of the CH3OH molecules in the H‐bond chain, and the quasi‐dynamic equilibriums between the shared‐proton structure (n = 3) and the close‐contact structures (n ≥ 4). The latter prohibits proton transfer reaction in the H‐bond chain from being concerted, since the rate of the structural diffusion depends upon the lifetime of the shared‐proton intermediate state.

Active site of the solvated thiosulfate ion characterized by hydration structures and dynamics

The reactivity of the terminated sulfur atom within the thiosulfate ion (S2O3(2-)) when it is involved in chemical reactions was investigated through the properties of the molecular hydration shell, obtained from the ab initio quantum mechanical change field molecular dynamics (QMCF MD) simulation. The average geometry indicated the significant effect of explicit water on the reduction of the S-S length, which was reflected in the splitting peaks of the spectrum for the stretching mode of this bond (ν(SS)). A further investigation on a simple model with various theoretical levels exhibited the hydrophobicity of the S-S bond. The evaluation of the molecular coordination number was sensitive to the radii of the atomic hydration spheres, which were obtained from the vague boundaries of the first peak in the atomic radial distribution functions. The number of actual contacts specified 6.8 water molecules interacting with the thiosulfate ion, and 2.4 extra waters located in the molecular hydration shell, forming a H-bonding network with the bulk water. The mean residence times for the water ligands distinguished the asymmetric strength of the hydration shell into a weaker sulfur and three stronger oxygen sites, instigating the terminated sulfur atom as the active site that is involved in chemical reactions.

Paclitaxel Delivery Using Carrier made from Curcumin Derivative: Synergism Between Carrier and the Loaded Drug for Effective Cancer Treatment

To fully make use of the synergism between paclitaxel and curcumin (CUR) in cancer treatment, carrier made from CUR derivative was synthesized and used to deliver paclitaxel into cancer cells. The methoxylpolyethylene oxide-linked palmitate-modified curcumin (mPEO-CUR-PA) was synthesized and the obtained amphiphilic mPEO-CUR-PA molecules were allowed to self-assemble into microspheres. In vitro release of free CUR from mPEO-CUR-PA in the presence of lipase was proofed and the ability of cells to endocytose mPEO-CUR-PA microspheres was verified. Cytotoxic activity of the mPEO-CUR-PA microspheres toward cancer cell lines (S102 and A549) was evaluated and compared with that of the unmodified CUR. Paclitaxel was then loaded into the microspheres and the paclitaxel-loaded mPEO-CUR-PA microspheres showed up to fivefold to 44-fold increased in vitro cytotoxicity (in terms of % cell mortality) in susceptible (HCC-S102 and A549) and paclitaxel-resistant (A549RT-eto) cancer cells, respectively, compared with that of free paclitaxel.

Determination of structure and dynamics of the solvated bisulfide (HS-) ion by ab initio QMCF molecular dynamics.

The hydration structure of the bisulfide (HS(-)) ion in dilute aqueous solution was characterized by means of an ab initio quantum mechanical charge field (QMCF) molecular dynamics simulation at the Hartree-Fock level employing Dunning double-ζ plus polarization function (DZP) basis sets. An average H-S bond distance of 1.35 Å resulted from the simulation and a hydration shell located at 2.42 Å S(HS(-))···H(w) and 3.97 Å HS(-) distances, respectively. At the sulfur site, the average coordination number is 5.9 ± 1.1, while the value for the hydrogen site is 9.2 ± 1.6. The calculated H(HS(-))-S(HS(-)) stretching frequency of 2752 cm(-1) obtained from the QMCF MD simulation is in good agreement with that reported from the Raman spectrum (2570 cm(-1)) only if a scaling factor of 0.89 is applied. The stability of the nondissociated HS(-) structure is reflected by the force constants of 436.1 and 4.5 N/m determined for the H(HS(-))-S(HS(-)) and H(HS(-))···O(w) bonds, respectively. A weak structure-making effect of the hydrated HS(-) ion results from the mean residence times of 1.5 and 2.1 ps of coordinated water molecules at the sulfur and hydrogen sites of the HS(-) ion, respectively.