Chemistry

Solutions of cyclamate in water were characterized by HATR and Raman spectroscopies. The vibrational spectra were assigned taking into account the factor group analysis. The solvent effects for the four species were simulated using the IEFPCM model. The principal donor and acceptor sites in solution were predicted by calculations. The SQM force fields were obtained and the force constants were reported.

In the present study, a complete assignment of the vibrational spectra of sucrose in aqueous medium was performed combining Pulay's Scaled Quantum Mechanics Force Field (SQMFF) methodology with selfconsistent reaction field (SCRF) calculations. Aqueous saturated solutions of sucrose and solutions at different molar concentrations of sucrose in water were completely characterized by infrared, HATR, and Raman spectroscopies. In accordance with reported data of the literature for sucrose, the theoretical structures of sucrose penta and sucrose dihydrate were also optimized in gas and aqueous solution phases by using the density functional theory (DFT) calculations. The solvent effects for the three studied species were analyzed using the solvation PCM/SMD model and, then, their corresponding solvation energies were predicted. The presence of pure water, sucrose penta-hydrate, and sucrose dihydrate was confirmed by using theoretical calculations based on the hybrid B3LYP/6-31G ⁄ method and the experimental vibrational spectra. The existence of both sucrose hydrate complexes in aqueous solution is evidenced in the IR and HATR spectra by means of the characteristic bands at 3388, and 668 cm À1 while in the Raman spectrum, the groups of bands in the regions 3159-3053 cm À1 , 2980, 2954, and 1749-1496 cm À1 characterize the vibration modes of those complexes. The inter and intra-molecular H bond formations in aqueous solution were studied by Natural Bond Orbital (NBO) and Atoms in Molecules theory (AIM) investigation.

Due to environmental concerns, it is highly desirable to replace liquid HF or H 2 SO 4 by more benign solid acid such as sulfated zirconia (SZ). Sulfated zirconia materials have been demonstrated to be a good catalyst for the isomerization of lineal alkanes at relatively low temperatures. Our objective was: (1st) prepare nanostructured materials either by controlled hydrolysis of zirconium alkoxide or by impregnation of tetragonal zirconia with H 2 SO 4 1 M or ammonium sulfate, (2nd) carry out the characterization by conventional techniques (X ray diffraction, electron microscopy, N 2 adsorption, FT-IR/Raman spectroscopy, UV diffuse reflectance) and (3 rd ) evaluate the acidity through the transesterification reaction of vinyl acetate with i-amyl alcohol to give i-amyl acetate and acetaldehyde and using toluene as solvent.

Zirconia samples prepared from Zr(n-OC 3 H 7) 4 and ZrOCl 2 were characterized by XRD, BET surface area, TG-DTA, TEM/SEM, FTIR, and D 2 O exchange. Oxides obtained from the alkoxide contain two types of hydroxyl groups at 3704 and 3597 cm-1 , which do not exchange with D 2 O. Those obtained from ZrOCl 2 produced three types of hydroxyl groups at 3774, 3733 and 3671 cm-1 , which do exchange with D 2 O. Surface acidity was determined by FTIR of adsorbed lutidine. Only Lewis acid sites were found on samples from ZrOCl 2 hydrolysis. FTIR spectra of calcined samples exhibited strong absorption bands in the 1800 to 1000 cm-1 region, which are ascribed to various types of carbonate and bicarbonate species. These ones are strongly adsorbed on the surface oxide and they are removed only after 3 hours at 600 ºC in stream of H 2. Samples derive from the alkoxide precursor restore the original carbonate species after exposure to O 2 at 600ºC. Catalytic activity for i-propanol dehydration/dehydrogenation showed the absence of basic centers and an intermediate dehydration activity between that of silica and alumina.

The structural and vibrational properties of the α-adrenergic agonist clonidine hydrochloride agent and their anionic and dimeric species were studied combining the experimental FT-IR and Raman spectra in solid phase with ab-initio calculations based on the density functional theory (DFT). All the calculations were performed by using the hybrid B3LYP with the 6-31G* and 6-311++G** basis sets. The structural properties for those species were studied employing the Natural Bond Orbital (NBO), Atoms in Molecules theory (AIM) and frontier orbitals calculations. The complete assignments of the FTIR and Raman spectra were performed combining the DFT calculations with the Pulay´s Scaled Quantum Mechanics Force Field (SQMFF) methodology. Very good concordances between the theoretical and experimental spectra were found. In addition, the force constants for those three species were computed and compared with the values reported for similar antihypertensive agents. The ionic nature of the H→Cl bond and the high value of the LP(1)N4 → LP*(1)H18 charge transfer could explain the high reactivity of clonidine hydrochloride in relation to other antihypertensive agent and the strong shifthing of the band assigned to the N-H stretching mode linked to the H-Cl bond toward lower wavenumbers.

h i g h l i g h t s " Vibrational spectra of zinc difluoromethanesulfinate salt were recorded. " The theoretical structures of Zn(SO 2 CF 2 H) 2 and a monohydrated complex were determined. " A complete assignment of the observed spectral features is proposed. " The theoretical calculations allowed obtaining a set of scaled force constants. " The nature of the compound was studied by NBO and AIM analyses.

Dieldrin was characterized by using Fourier Transform infrared (FT-IR) and Raman (FT-Raman), Ultraviolet-Visible (UV-Visible) spectroscopies. The structural and vibrational properties for dieldrin in gas phase and in aqueous solution were computed combining those experimental spectra with hybrids B3LYP and WB97XD calculations by using the 6-31G* and 6-311++G** basis sets. Here, the experimental available Hydrogen and Carbon Nuclear Magnetic Resonance (1 Hand 13 C-NMR) for dieldrin were also used and compared with those predicted by calculations.The B3LYP/6-311++G** method generates the most stable structures while the results have demonstrated certain dependence of the volume and dipole moment values with the method, size of the basis set and, with the studied media. The lower solvation energy for dieldrin (-32.94 kJ/mol) is observed for the higher contraction volume (-2.4 Å 3) by using the B3LYP/6-31G* method. The NBO studies suggest a high stability of dieldrin in gas phase by using the WB97XD/6-31G* method due to the n→π* and n*→π* interactions while the AIM analyses support this high stability by the C18-H26 and C14-O7 contacts. The different topological properties observed in the R5 ring suggest that probably this ring plays a very important role in the toxics properties of dieldrin. The frontier orbitals show that when dieldrin is compared with other toxics substances the reactivity increases in the following order: CO < STX < dieldrin < C 6 Cl 6 <TCAB < TCAOB < CNwhere evidently, the presence of five rings and six Cl atoms decrease the reactivity of dieldrin, as compared with hexachlorobencene. The WB97XD method and the two basis sets predicted for dieldrin in both media low reactivities, higher nucleophilicity and, low electrophilicity. All the bands observed in the IR and Raman spectra were completely assigned to the 75 vibration normal modes and their harmonic force fields and force constants for first time are reported for dieldrin. The predicted FTIR, FT-Raman, UV-Visible and 1 H and 13 C-NMR spectra for dieldrin show a reasonable concordance with the experimental ones.

In this work, the a and b isomers, the a-lactose monohydrate and dihydrate and the dimeric species of lactose were studied from the spectroscopic point of view in gas and aqueous solution phases combining the infrared, Horizontal Attenuated Total Reflectance (HATR) and Raman spectra with the density functional theory (DFT) calculations. Aqueous saturated solutions of a-lactose monohydrate and solutions at different molar concentrations of a-lactose monohydrate in water were completely characterized by infrared, HATR and Raman spectroscopies. For all the species in solution, the solvent effects were studied using the solvation polarizable continuum (PCM) and solvation (SM) models and, then, their corresponding solvation energies were predicted. The vibrational spectra of those species in aqueous solution were completely assigned by employing the Scaled Quantum Mechanics Force Field (SQMFF) methodology and the self-consistent reaction field (SCRF) calculations. The stabilities of all those species were studied by using the natural bond orbital (NBO), and atoms in molecules (AIM) calculations.

The structures of α-and β-maltose anhydrous and their corresponding monohydrated species were studied combining the FT-IR, FT-Raman and HATR spectra with DFT calculations. The four structures were optimized in gas and aqueous solution by using the hybrid B3LYP/6-31G* method. The self-consistent force field (SCRF) calculations together with the polarized continuum (PCM) model were used to study the systems in solution while the solvation energies were computed using the solvation model (SM). The calculated structural and vibrational properties could explain the anomerization of maltose in solution, as was reported in the literature while the natural bond orbital (NBO) analyses for those species support clearly the mutarotation equilibria between both forms in solution, evidencing the anhydrous forms the equilibrium: α (45%) ⇔ β (55%), similar to that experimentally reported at 20°C. Bands of all the species observed in the vibrational spectra support the presence of the anomeric species of maltose in solution while the presence of dimeric species justify the intense IR bands observed in the higher wavenumbers region. The similar gap values for maltose and lactose probably justify that these sugars are reducing sugars while the high values in sucrose could explain that it is a non-reducing sugar. On the other hand, the sweeteners cyclamate and saccharine are most reactive in solution than the sugars maltose, lactose and sucrose, as expected due to their ionic characteristics. The predicted vibrational spectra for the four species of maltose show reasonable concordances with the corresponding experimental ones. The f(δC-O-C) force constants of the glycosidic bonds follow the tendency: maltose > lactose > sucrose.

Due to environmental concerns, it is highly desirable to replace liquid HF or H 2 SO 4 by more benign solid acid such as sulfated zirconia (SZ). Sulfated zirconia materials have been demonstrated to be a good catalyst for the isomerization of lineal alkanes at relatively low temperatures. Our objective was: (1st) prepare nanostructured materials either by controlled hydrolysis of zirconium alkoxide or by impregnation of tetragonal zirconia with H 2 SO 4 1 M or ammonium sulfate, (2nd) carry out the characterization by conventional techniques (X ray diffraction, electron microscopy, N 2 adsorption, FT-IR/Raman spectroscopy, UV diffuse reflectance) and (3 rd) evaluate the acidity through the transesterification reaction of vinyl acetate with i-amyl alcohol to give i-amyl acetate and acetaldehyde and using toluene as solvent.

The potassium 3-furoyltrifluoroborate salt has been experimentally characterized by means of FT-IR, FT-Raman and UVeVisible spectroscopies. Here, the predicted FT-IR, FT-Raman and UVevisible spectra by using theoretical B3LYP/6-31G* and 6-311þþG** calculations show very good correlations with the corresponding experimental ones. The solvation energies were predicted by using both levels of calculations. The NBO analyses reveal the high stability of the salt by using the B3LYP/6-31G* level of theory while the AIM studies evidence the ionic characteristics of the salt in both media. The strong blue colour observed on the K atom by using the molecular electrostatic potential mapped suggests that this region act as typical electrophilic site. The gap values have revealed that the salt in gas phase is more reactive than in solution, as was reported in the literature while, the F13/H6 interaction together with the KeO bond observed by the studies of their charges could probably modulate the reactivities of this salt in aqueous solution. The force fields were computed with the SQMFF methodology and the Molvib program to perform the complete vibrational analysis. Then, the 39 vibration normal modes classified as 26 A'þ 13 A 00 were completely assigned and their force constants are also reported.

FT-IR, FT-Raman and ultravioletevisible spectroscopies were used to characterize the potassium 5hydroxypentanoyltrifluoroborate salt (HTFB) while the theoretical structures of this salt in gas and aqueous solution phases were studied by using hybrid B3LYP/6-311þþG** calculations and the self consistent reaction field (SCRF) and solvation (SM) models because these models consider the solvent effects. Good concordance were obtained among the predicted 1 H-, 13 C and 19 F-NMR chemical shifts for HTFB in aqueous solution with the corresponding experimental available data for this salt in CDCl 3. The corrected solvation energy by using ZPVE and non electrostatic terms is higher for this salt (À103.73 kJ/ mol) than those reported for furoyl (À84.72 kJ/mol) and isonicotinoyl (À95.05 kJ/mol). Evidently, the side chain in HTFB increase the solubility of this salt in water, as compared with furoyl and isonicotinoyl. The NBO analyses show that the potassium 2-isonicotinoyltrifluorborate salt in both media is most stable than hydroxypentanoyl and furoyl salts and, in particular, the side chain in HTFB generates a diminishing of its stability in aqueous solution. Probably, this low stability of HTFB in solution is due to the higher solvation energy and to the n/s * transitions no observed in the other salts. The AIM studies support the high stability of isonicotinoyl than the other two salts and, also, reveal the ionic characteristics of the Ke-O and Ke-F interactions observed in those three salts. The comparisons of the gap values for the three species suggest that the most reactive salt is isonicotinoyl while furoyl salt is the less reactive. The descriptors show the importance of study these salts in different media because the values in solution are slightly different in the three salts from those computed in gas phase. In addition, the harmonic force fields and the scaled internal force constants for the salt in both media are reported together to their complete vibrational assignments.