Vibrational Spectroscopy and Phonon-Related Properties of the L-Aspartic Acid Anhydrous Monoclinic Crystal

A highlightedly improved method for isolating and characterizing calcium oxalate crystals from tubercles of Mammillaria schumannii

BACKGROUND

Calcium oxalate (CaOx) is the most prevalent and widespread biomineral in plants and is involved in protective and/or defensive functions against abiotic stress factors. It is, however, expected that this function has an extremely significant contribution to growth processes in plants bearing large amounts of CaOx, such as cacti growing in desert environment.

RESULTS

In our research, small-sized CaOx crystals (≤ 20 µm) with tetrahedral or spherical shapes were observed to dominate in each epidermal and cortical cell from the tubercles of Mammillaria schumannii, a species from the Cereoideae subfamily, having tubercles (main photosynthetic organs) united with adjacent ones almost into ridges on its stem. Because they have potential significant functions, differential centrifugations after mechanical blending were used to obtain these small-sized CaOx crystals, which extremely tend to adhere to tissue or suspend in solution. And then the combined Scanning Electron Microscope Energy Dispersive System (SEM-EDS) and Raman spectroscopy were further performed to demonstrate that the extracted crystals were mainly CaC2O4·2H2O. Interestingly, spherical druses had 2 obvious abnormal Raman spectroscopy peaks of -CH and -OH at 2947 and 3290 cm-1, respectively, which may be attributed to the occluded organic matrix. The organic matrix was further extracted from spherical crystals, which could be polysaccharide, flavone, or lipid compounds on the basis of Raman spectroscopy bands at 2650, 2720, 2770, and 2958 cm-1.

CONCLUSIONS

Here we used a highlightedly improved method to effectively isolate small-sized CaOx crystals dominating in the epidermal and cortical cells from tubercles of Mammillaria schumannii, which extremely tended to adhere plant tissues or suspend in isolation solution. And then we further clarified the organic matrix getting involved in the formation of CaOx crystals. This improved method for isolating and characterizing biomineral crystals can be helpful to understand how CaOx crystals in cacti function against harsh environments such as strong light, high and cold temperature, and aridity.

Periodic DFT Calculations-Review of Applications in the Pharmaceutical Sciences

In the introduction to this review the complex chemistry of solid-state pharmaceutical compounds is summarized. It is also explained why the density functional theory (DFT) periodic calculations became recently so popular in studying the solid APIs (active pharmaceutical ingredients). Further, the most popular programs enabling DFT periodic calculations are presented and compared. Subsequently, on the large number of examples, the applications of such calculations in pharmaceutical sciences are discussed. The mentioned topics include, among others, validation of the experimentally obtained crystal structures and crystal structure prediction, insight into crystallization and solvation processes, development of new polymorph synthesis ways, and formulation techniques as well as application of the periodic DFT calculations in the drug analysis.

Vibrational Modes and Phonon and Thermodynamic Properties of the Metaboric Acid Polymorphs α-, β-, and γ-(BOH)3O3 within a Density Functional Theory Framework

A combined study of vibrational and thermodynamic properties of metaboric acid (BOH)₃O₃ crystal polymorphs α, β, and γ were obtained through density functional theory (DFT) calculations in an attempt to resolve the conflicting assignments that currently exist in the literature for them. A complete correlation between the normal-mode assignment and vibrational signatures to distinguish particular features of each metaboric acid polymorph, in particular, those related to motions of the planar layers in α-(BOH)₃O₃, with a level of detail surpassing essays based on previous published experimental works has been achieved. Besides, no DFT-based research work was published early on the (BOH)₃O₃ polymorph vibrational properties, and our DFT-simulated infrared and Raman spectra for all metaboric acid polymorphs agree very well with experiment. Comparison of the previously published experimental IR and Raman spectroscopic results with predictions from higher levels DFT calculations allows identification of the in-plane and out-of-plane B-O bending modes. For example, the strongest measured (DFT-calculated) Raman modes of α-(BOH)₃O₃ at 591 and 797 cm^-1 (599 and 810 cm^-1) are identified as vibrational signatures of breathing B₃O₃/A_g in-plane modes, while the shoulder in the lattice modes region at 135 (143) cm^-1 is the vibrational signature of the bending B₃O₃/B_1g out-of-plane mode. Phonon-dispersion bands and their respective phonon densities of states were also evaluated for each system, as well as temperature-dependent curves for entropy, enthalpy, free energy, heat capacity, and Debye temperature. Phonon dispersion curves are singular for each (BOH)₃O₃ species, and a consistent gap decrease between the lowest and highest frequency vibrational bands was observed. The DFT-based calculations also revealed that the noncovalent interactions prevalent in the α and β crystals lead to significant differences with respect to the thermodynamic properties in comparison with the γ phase.

The effect of the flexibility of hydrogen bonding network on low-frequency motions of amino acids. Evidence from Terahertz spectroscopy and DFT calculations

Low-frequency modes of L-Asp and L-Asn were studied in the range from 0.1 to 3.0THz using time-domain Terahertz spectroscopy and density functional theory calculation. The results show that PBE-D2 shows more success than BLYP-D2 in prediction of THz absorption spectra. To compare their low-frequency modes, we adopted "vibrational character ID strips" proposed by Schmuttenmaer and coworkers [Journal of Physical Chemistry B, 117, 10444(2013)]. We found that the most intense THz absorption peaks of two compounds both involve severe distortion of their hydrogen bonding networks. Due to less rigid hydrogen bonding network in L-Asp, the side chain (carboxyl group) of L-Asp exhibits larger motions than that (carboxamide group) of L-Asn in low-frequency modes.

The vibrational properties of the bee-killer imidacloprid insecticide: A molecular description

The chemical imidacloprid belongs to the neonicotinoids insecticide class, widely used for insect pest control mainly for crop protection. However, imidacloprid is a non-selective agrochemical to the insects and it is able to kill the most important pollinators, the bees. The high toxicity of imidacloprid requires controlled release and continuous monitoring. For this purpose, high performance liquid chromatography (HPLC) is usually employed; infrared and Raman spectroscopy, however, are simple and viable techniques that can be adapted to portable devices for field application. In this communication, state-of-the-art quantum level simulations were used to predict the infrared and Raman spectra of the most stable conformer of imidacloprid. Four molecular geometries were investigated in vacuum and solvated within the Density Functional Theory (DFT) approach employing the hybrid meta functional M06-2X and the hybrid functional B3LYP. The M062X/PCM model proved to be the best to predict structural features, while the values of harmonic vibrational frequencies were predicted more accurately using the B3LYP functional.

Changing the gap type of solid state boric acid by heating: a dispersion-corrected density functional study of α-, β-, and γ-metaboric acid polymorphs

The gap type of solid state metaboric acid can be changed by temperature changes near 100 °C according to DFT calculations.