The IINS, IR and DFT studies of hydrogen bonds in 6-Furfuryl and 6-Benzylaminopurines

Modification of the Release of Poorly Soluble Sulindac with the APTES-Modified SBA-15 Mesoporous Silica

The effectiveness of oral drug administration is related to the solubility of a drug in the gastrointestinal tract and its ability to penetrate the biological membranes. As most new drugs are poorly soluble in water, there is a need to develop novel drug carriers that improve the dissolution rate and increase bioavailability. The aim of this study was to analyze the modification of sulindac release profiles in various pH levels with two APTES ((3-aminopropyl)triethoxysilane)-modified SBA-15 (Santa Barbara Amorphous-15) silicas differing in 3-aminopropyl group content. Furthermore, we investigated the cytotoxicity of the analyzed molecules. The materials were characterized by differential scanning calorimetry, powder X-ray diffraction, scanning and transmission electron microscopy, proton nuclear magnetic resonance and Fourier transformed infrared spectroscopy. Sulindac loaded on the SBA-15 was released in the hydrochloric acidic medium (pH 1.2) and phosphate buffers (pH 5.8, 6.8, and 7.4). The cytotoxicity studies were performed on Caco-2 cell line. The APTES-modified SBA-15 with a lower adsorption capacity towards sulindac released the drug in a less favorable manner. However, both analyzed materials improved the dissolution rate in acidic pH, as compared to crystalline sulindac. Moreover, the SBA-15, both before and after drug adsorption, exhibited insignificant cytotoxicity towards Caco-2 cells. The presented study evidenced that SBA-15 could serve as a non-toxic drug delivery system that enhances the dissolution rate of sulindac and improves its bioavailability.

Tautomeric purine forms of 2-amino-6-chloropurine (N9H10 and N7H10): structures, vibrational assignments, NBO analysis, hyperpolarizability, HOMO-LUMO study using B3 based density functional calculations

Two purine tautomers of 2-amino-6-chloropurine (ACP), in labeled as N(9)H(10) and N(7)H(10), were investigated by vibrational spectroscopy and quantum chemical method. The FT-IR and FT-Raman spectra of ACP have been recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The measured spectra were interpreted by aid of a normal coordinate analysis following DFT full geometry optimization and vibrational frequency calculations at B3LYP/6-311++G(d,p) level. First-order hyperpolarizability, HOMO and LUMO energies were calculated at same level of theory. The calculated molecular geometry has been compared with the X-ray data. The observed and calculated frequencies were found in good agreement. The obtained NBO data and second-order perturbation energy values to elucidate the Lewis and non-Lewis types of bonding structures in the purine tautomer N(9)H(10), have indicated the presence of an intramolecular hyperconjucative interaction between lone pair N and N-C bond orbital.

Inelastic Neutron Scattering (INS) Study of Low Frequency Vibrations and Hydrogen Bonding of (E)-2-Hydroxyimino-2-Cyanoacetic Acid Ethyl Ester

The title unsubstituted (normal) (E)-2-hydroxyimino-2-cyanoacetic acid ethyl ester (the abbreviated name: (E)-2-cyanoethyl ester-2-oxime or 2-oxime) and its 2-deuterated analogue have been prepared and characterized using infrared, Raman and inelastic, incoherent neutron scattering (IINS) spectroscopy. Molecular structures (molecular conformations) of the compounds are proposed for the vapour state. Four molecular conformers, namely two pairs of the s-cis, s-trans rotational isomers (rotamers) from six lower energetic conformations of E-2-hydroxyimino-2-cyanoacetic ethyl ester, are predominating for the single molecule of the compound. They amount together to almost 100% of the conformational populations of both rotational isomers as it was theoretically calculated using DFT (B3LYP) method with 6-311G++(d,p) basis set. Additionally dimers of 2-oxime were considered using B3LYP/6-31G* method in order to improve the results obtained for single molecule. In both parent (=N–OH) and deuterated (=N–O–D) molecules of the (E)-2-ethylcyano ester-2-oxime respectively, extra bands corresponding primarily to hydrogen (deuterium) bond vibrations (γ–bending out of plane of hydrogen bond, σ–stretching of hydrogen bond bridge, δ–bending in plane of hydrogen bond, λ–bending of hydrogen bond bridge have been identified, namely σ (N–O–H···O) at 132.8, 212.5, 279, 358.7, 424, 448, 523.6, 872, γ (N–O–H···O) at 334, 564, 592, 745, 820, δ (N–OH···O) at 1461, 1600, 1862cm−1 in the low temperature IINS spectrum, whereas the frequency at 365cm−1 has been assigned as the out of plane (o.o.p.) (γ O–D···O) vibrational mode. Formation of the O–H···O hydrogen bridge is reflected in shifting of the bands of the stretching and bending vibrations of OH group as well as arising of the bridge vibrations in the low frequency range. Moreover, equilibrium geometries and all harmonic vibrational frequencies of the (E)-2-cyano ethyl ester-2-oxime molecules with potential energy distribution (PED) were also calculated by means of the above mentioned theoretical programs.