We have synthesized and characterized TCAB by infrared, Raman, multidimensional nuclear magnetic resonance (NMR) and ultraviolet–visible spectroscopies. The assignments of the 66 normal modes of vibration corresponding to both cis and trans isomers of the UNC669 are reported. The theoretical structures of two cis and trans forms of TCAB were determined by using the 6-31G* and 6-311++G** basis sets. The molecular electrostatic potentials, atomic charges and bond orders support the high stability of the trans forms together with the NBO studies, which suggest that the electronic transitions of the two cis forms are n → π* transitions while for the trans forms are n → π* and π* → π* transitions. Thus, the topological parameters and the main delocalization energies favor to the trans forms. The calculated highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gaps for the four conformations of TCAB follow the trend: cis I > trans II > trans I > cis II. The SQM/B3LYP/6-31G* force field for the two pairs of conformers of TCAB were obtained together with the more important force constants. This study shows that the cis and trans isomers exhibit different structural and vibrational properties and absorption bands. Additionally, the size of the basis set reveals the importance of it in all the studied properties.
This analysis was performed taking into account the energetical stabilities of the two pairs of conformers of TACB and the small difference energies among them. This way, the vibration normal modes corresponding to the two pairs of conformers were considered in the study. The comparison of the calculated infrared and Raman spectra for TCAB by using B3LYP/6-31G* VX-745 level with the corresponding experimental ones demonstrate a good correlation, as observed respectively in Fig. 2 and Fig. 3. Note that the strong bands between 1500 and 1000 cm−1 in the experimental IR spectrum are justified by the presence of both trans forms while probably in this region these bands overlap those bands attributed to the cis forms. On the other hand, the bands observed in the higher and lower wavenumbers regions in the Raman spectrum are probably attributed to the two cis forms and, this way, those bands justify the existence of both forms in the solid phase. The two pairs of conformations of TCAB have C1 symmetries and 66 normal vibration modes where all the vibrations are IR and Raman active. The assignment of the experimental bands to the expected normal vibration modes were made on the PED ?10% contributions, by using of symmetry coordinates and taking into account the assignments for similar compounds , , , , ,  and . Table 3, Tables S9 and S10 show the experimental and calculated frequencies, potential energy distribution based on the 6-31G* basis set, and assignment for the two pairs of conformers of TCAB. We considered the B3LYP/6-31G* calculations because the used scale factors are defined for this basis set. The SQM force fields for this compound can be obtained upon request.
3.4. Cellular uptake in Sulfo-NHS-LC-Biotin Caco-2 cell model
The addition of RRH to a solution of FITC-dextran did not improve cellular uptake of FITC-dextran (Fig. 4). Encapsulation FITC-dextran in PECA nanoparticles increased the cellular uptake to approximately 16%, significantly higher than FITC-dextran in solution (P < 0.001). Associating the nanoparticles with RRH, either by a physical mix or RRH-tagging did not further improve the cellular uptake ( Fig. 4). However, increasing the amount of RRH used for tagging by 10-fold (to 100 μmol) significantly increased the cellular uptake of the FITC-dextran to 45% (P < 0.001) compared to unmodified nanoparticles ( Fig. 4).
Fig. 4. Cellular uptake of different nanoparticle formulations in Caco-2 cells at 37 °C over 2 h. Data are means ± SD (n ? 6).Figure optionsDownload full-size imageDownload high-quality image (168 K)Download as PowerPoint slide
3.5. Release profile of FITC-dextran in HBSS