Structures and conformations of heteroatom-bridged calixarenes

Unraveling the role of superalkalis in modulating the static and dynamic hyperpolarizabilities of emerging calix[4]arenes

Calixarenes, as novel organic materials, can play a pivotal role in the development of high-performance nonlinear optical materials due to the ease of design and fabrication. In this study, DFT simulations were employed to investigate the geometric, electronic, and NLO responses of calix[4]arene doped with Li3O, Na3O, and K3O superalkalis. The computed values of the vertical ionization energies and interaction energies indicate the chemical and thermodynamic stabilities of the targeted M3O@calix[4]arene complexes. The corresponding energy gaps (2.01 to 3.49 eV) are notably reduced, indicating the semiconductor nature of the materials. Surprisingly, the M3O@calix[4]arene complexes exhibit transparency in the UV/visible range as the absorption peaks are shifted in the near infrared (NIR) region. The highest values of 5.9 × 105 a.u. and 2.3 × 108 a.u. for the respective first and second hyperpolarizabilities are observed for Na3O@calix[4]arene. Furthermore, the Na3O@calix[4]arene complex exhibits maximum values of 2.3 × 105 a.u. for second harmonic generation (SHG) and (K3O@calix[4]arene) 2.3 × 106 a.u. for the electro-optical Pockels effect (EOPE) at 1064 nm. Similarly, approximations are made for the dynamic second hyperpolarizability coefficients (EOKE and EFISHG) at different wavelengths. Notably, the Na3O@calix[4]arene complex demonstrates the highest quadratic nonlinear refractive index (n2) of 9.5 × 10-15 cm2 W-1 at 1064 nm. This research paves the way for the development of stable calix[4]arenes doped with superalkalis, leading to an improved nonlinear optical (NLO) response.

Redox-Induced Molecular Actuators: The Case of Oxy-Alternate Bridged Cyclotetraveratrylene

We report a practical two-step approach for the synthesis of hybrid-bridge macrocyclic molecules that has been used to synthesize two novel oxy-alternate-bridged macrocyclic molecules, oxy-alternate cyclotetraveratrylene (^O-altCTTV) and oxy-alternate cyclohexaveratrylene (^O-altCHV). Electrochemistry, absorption spectroscopy, X-ray crystallography, and DFT calculations demonstrate that ^O-altCTTV acts as a redox-induced molecular actuator, as its switches from the open conformation in the neutral state to the closed conformation in the cation-radical state.

Formation of the inclusion complex of water soluble fluorescent calix[4]arene and naringenin: solubility, cytotoxic effect and molecular modeling studies

Naringenin is considered as an important flavonoid in phytochemistry because of its important effect on cancer chemoprevention. Unfortunately its poor solubility has restricted its therapeutic applications. In this study, an efficient water-soluble fluorescent calix[4]arene (compound 5) was synthesized as host macromolecule to increase solubility and cytotoxicity in cancer cells of water-insoluble naringenin as well as to clarify localization of naringenin into the cells. Complex formed by host-guest interaction between compound 5 and naringenin was analyzed with UV-visible, fluorescence, FTIR spectroscopic techniques and molecular modeling studies. Stern-Volmer analysis showed binding constant value of K_sv 3.5 × 10⁷ M^-1 suggesting strong interaction between host and guest. Binding capacity shows 77% of naringenin was loaded on compound 5. Anticarcinogenic effects of naringenin complex were evaluated on human colorectal carcinoma cells (DLD-1) and it was found that 5-naringenin complex inhibits proliferation of DLD-1 cells 3.4-fold more compared to free naringenin. Fluorescence imaging studies show 5-naringenin complex was accumulated into the cytoplasm instead of the nucleus. Increased solubility and cytotoxicity of naringenin with fluorescent calix[4]arene makes it one of the potential candidates as a therapeutic enhancer. For deep understanding of host-guest interaction mechanisms, complementary multiscale molecular modeling studies were also carried out.Communicated by Ramaswamy H. Sarma.

Synthesis, structure, and anion binding of functional oxacalix[4]arenes

Oxacalix[4]arenes obtained from the highly efficient, one-pot S_NAr reaction were post-macrocyclization functionalized through the reduction of nitro groups and hydrolysis of the ester groups to obtain several derivatives of desired solubility. The difficulties in basic hydrolysis of ester groups were overcome via developing an acid hydrolysis method for tert-butyl ester derivatives of this class. The synthesis of symmetrical oxacalix[4]arenes from an unsymmetrically substituted precursor was also explored via a multiple step fragment coupling approach. Compounds 17 & 18 adopted 1,3-alternate conformations in the solid state as most oxacalix[4]arenes did, and a chair (zigzag) conformation was revealed for tetraamido oxacalix[4]arene (6a) by X-ray single crystal analysis. The tetraureido oxacalixarene (7) showed strong association towards various anions such as F^-, Cl^-, Br^-, I^-, Ac^-, and HSO₄^- with a 1 : 1 stoichiometry as revealed by ¹H NMR analysis and UV-vis measurements.

Synthesis of hydroxylated azacalix[1]arene[3]pyridines from hydrolysis of high valent arylcopper complexes and conversion to a double azacalix[1]arene[3]pyridine host molecule

Arylcopper(ii) compounds reacted efficiently with KOH at ambient temperature to produce exclusively lower-rim-hydroxylated azacalix[1]arene[3]pyridines which underwent further CuCl₂/TMEDA-catalyzed oxidative homocoupling to afford an unprecedented bisazacalix[1]phenol[3]pyridine host molecule.

Synthesis of trifluoromethylthiolated azacalix[1]arene[3]pyridines from the Cu(ii)-mediated direct trifluoromethylthiolation reaction of arenes via reactive arylcopper(iii) intermediates

Cu(ii)-mediated arene C–H bond trifluoromethylthiolation with Me₄NSCF₃proceedsviaarylcopper(iii) intermediates to produce functionalized azacalix[1]arene[3]pyridine macrocycles.