Density functional theory investigation of hydrogen bonding effects on the oxygen, nitrogen and hydrogen electric field gradient and chemical shielding tensors of anhydrous chitosan crystalline structure

Efficient delivery of anticancer 5-fluorouracil drug by alkaline earth metal functionalized porphyrin-like porous fullerenes: A DFT study

Finding and developing effective targeted drug delivery systems has emerged as an attractive approach for treating a wide range of diseases. In the present study, the potential of alkaline earth metal functionalized porphyrin-like porous C₂₄N₂₄ fullerenes for delivering 5-fluorouracil (5FU) anticancer drug is assessed using density functional theory calculations. The goal is to evaluate how the addition of alkaline earth metals to C₂₄N₂₄ enhances the adsorption capabilities of this system towards 5FU drug. The adsorption energies and charge transfers are determined in order to evaluate the strength of the interaction between the 5FU and fullerene surfaces. According to the results, adding alkaline earth metals increases the drug's adsorption energy on the C₂₄N₂₄ fullerene. In all cases, the drug molecule interacts with the metal atom through its CO group. Furthermore, the adsorption strength of the 5FU increases with metal atom size (Ca > Mg > Be), which is connected to the polarizability of these atoms. The adsorption energies of 5FU are shown to be highly sensitive on solvent effects and the acidity of the environment. The adsorption strength of 5FU decreases within the solvent (water), allowing it to be released more easily. The moderate adsorption energies and short desorption times of 5FU imply that it is reversibly adsorbed on the functionalized fullerenes.

Computational NMR of Carbohydrates: Theoretical Background, Applications, and Perspectives

This review is written amid a marked progress in the calculation of NMR parameters of carbohydrates substantiated by a vast amount of experimental data coming from several laboratories worldwide. By no means are we trying to cover in the present compilation a huge amount of all available data. The main idea of the present review was only to outline general trends and perspectives in this dynamically developing area on the background of a marked progress in theoretical and computational NMR. Presented material is arranged in three basic sections: (1)-a brief theoretical introduction; (2)-applications and perspectives in computational NMR of monosaccharides; and (3)-calculation of NMR chemical shifts and spin-spin coupling constants of di- and polysaccharides.

CHAL336 Benchmark Set: How Well Do Quantum-Chemical Methods Describe Chalcogen-Bonding Interactions?

We present the CHAL336 benchmark set-the most comprehensive database for the assessment of chalcogen-bonding (CB) interactions. After careful selection of suitable systems and identification of three high-level reference methods, the set comprises 336 dimers each consisting of up to 49 atoms and covers both σ- and π-hole interactions across four categories: chalcogen-chalcogen, chalcogen-π, chalcogen-halogen, and chalcogen-nitrogen interactions. In a subsequent study of DFT methods, we re-emphasize the need for using proper London dispersion corrections when treating noncovalent interactions. We also point out that the deterioration of results and systematic overestimation of interaction energies for some dispersion-corrected DFT methods does not hint at problems with the chosen dispersion correction but is a consequence of large density-driven errors. We conclude this work by performing the most detailed DFT benchmark study for CB interactions to date. We assess 109 variations of dispersion-corrected and dispersion-uncorrected DFT methods and carry out a detailed analysis of 80 of them. Double-hybrid functionals are the most reliable approaches for CB interactions, and they should be used whenever computationally feasible. The best three double hybrids are SOS0-PBE0-2-D3(BJ), revDSD-PBEP86-D3(BJ), and B2NCPLYP-D3(BJ). The best hybrids in this study are ωB97M-V, PW6B95-D3(0), and PW6B95-D3(BJ). We do not recommend using the popular B3LYP functional nor the MP2 approach, which have both been frequently used to describe CB interactions in the past. We hope to inspire a change in computational protocols surrounding CB interactions that leads away from the commonly used, popular methods to the more robust and accurate ones recommended herein. We would also like to encourage method developers to use our set for the investigation and reduction of density-driven errors in new density functional approximations.

Vibrational, electronic and quantum chemical studies of 1,2,4-benzenetricarboxylic-1,2-anhydride

The FTIR and FT-Raman spectra of 1,2,4-benzenetricarboxylic-1,2-anhydride (BTCA) have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. The complete vibrational assignments and analysis of BTCA have been performed. More support on the experimental findings was added from the quantum chemical studies performed with DFT (B3LYP, MP2, B3PW91) method using 6-311++G(**), 6-31G(**) and cc-pVTZ basis sets. The structural parameters, energies, thermodynamic parameters, vibrational frequencies and the NBO charges of BTCA were determined by the DFT method. The (1)H and (13)C isotropic chemical shifts (δ ppm) of BTCA with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. The delocalization energies of different types of interactions were determined.

Structural, vibrational and nuclear magnetic resonance investigations of 4-bromoisoquinoline by experimental and theoretical DFT methods

Quantum chemical calculations of energy, structural parameters and vibrational wavenumbers of 4-bromoisoquinoline (4BIQ) were carried out by using B3LYP method using 6-311++G(**), cc-pVTZ and LANL2DZ basis sets. The optimised geometrical parameters obtained by DFT calculations are in good agreement with electron diffraction data. Interpretations of the experimental FTIR and FT-Raman spectra have been reported with the aid of the theoretical wavenumbers. The differences between the observed and scaled wavenumber values of most of the fundamentals are very small. The thermodynamic parameters have also been computed. Electronic properties of the molecule were discussed through the molecular electrostatic potential surface, HOMO-LUMO energy gap and NBO analysis. To provide precise assignments of (1)H and (13)CNMR spectra, isotropic shielding and chemical shifts were calculated with the Gauge-Invariant Atomic Orbital (GIAO) method.

15N CHEMICAL SHIFT CALCULATIONS AND NATURAL BONDING ORBITAL ANALYSES OF (BENZAMIDE)n = 1 - 6 CLUSTERS

A DFT/B3LYP study was performed to calculate 15 N chemical shielding tensors in ( benzamide )n = 1-6 clusters. We found that N–H⋯O hydrogen bonds around the benzamide molecule in crystalline lattice have significant influences on the 15 N chemical shielding tensors. For ( benzamide )n clusters, the n-dependent trend in 15 N chemical shielding appears to be correlated with cooperative effects in R [N–H⋯O ] bond distance. Natural bonding orbital (NBO) analysis was used to rationalize the chemical shielding results in terms of [Formula: see text] charge delocalization effects in the benzamide clusters. This suggests that 15 N chemical shielding measurements can provide a useful probe of electron delocalization phenomena in both gaseous and condensed media.

Intra- and inter-molecular interactions in salicylic acid — Theoretical calculations of 17O and 1H chemical shielding tensors and QTAIM analysis

A density functional theory (DFT) study was performed to examine intra- and inter-molecular hydrogen bond (HB) properties in crystalline salicylic acid (SA). BLYP, B3LYP, and M06 functionals with 6–311++G** basis set were employed to calculate NMR chemical shielding isotropy (σiso) and anisotropy (Δσ) at the sites of the 17O and 1H nuclei of SA. From this study, it appears that the intra- and inter-molecular O–H···O as well as C–H···O HBs around the SA molecule in the crystal lattice have a major influence on the chemical shielding tensors and more specifically on the carbonyl 17O isotropy value. The quantum theory of atoms in molecules (QTAIM) analysis was also employed to elucidate the interaction characteristics in SA H-bonded network. Based on QTAIM results, a partial covalent character is attributed to the intra- and inter-molecular O–H···O HBs in SA.

Characterization of cooperative effects in linear alpha-glycylglycine clusters

The aspects of N-H...O=CNH, N-H...O=CO and C-H...O=CNH interactions are analyzed by applying ab initio and DFT methods as well as Bader theory. We investigated geometry, binding energies, (17)O, (15)N chemical shift tensors, and Atoms in Molecules (AIM) properties of alpha-glycylglycine (alpha-glygly) clusters, via MP2, B3LYP and PW91(XC) methods. Dimer stabilization energies and equilibrium geometries are studied in various levels of theory. MP2 and DFT calculations reveal that for alpha-glygly clusters, stability of N-H...O and C-H...O hydrogen bonds are enhanced significantly as a result of cooperativity effects. Furthermore, a covalent nature is also detected for some hydrogen bondings. The n-dependent trend of (17)O and (15)N chemical shift tensors was reasonably correlated with cooperative effects in hydrogen-bond interactions. Regarding the various N-H...O=CNH, N-H...O=CO and C-H...O=CNH hydrogen bondings, capability of the alpha-glygly clusters for electron localization at the N-H...O and C-H...O bond critical points, depends on the cluster size. This leads to cooperative changes in the hydrogen-bond length and strength as well as (17)O and (15)N chemical shift tensors.

Theoretical investigation of hydrogen bonding effects on oxygen, nitrogen, and hydrogen chemical shielding and electric field gradient tensors of chitosan/HI salt

A density functional theory study has been carried out to calculate the (17)O, (15)N, (13)C, and (1)H chemical shielding as well as (17)O, (14)N, and (2)H electric field gradient tensors of chitosan/HI type I salt. These calculations were performed using the B3LYP functional and 6-311++G (d,p) and 6-31++G (d,p) basis sets. Calculated EFG and chemical shielding tensors were used to evaluate the (17)O, (14)N, and (2)H nuclear quadruple resonance, NQR, and (17)O, (15)N, (13)C, and (1)H nuclear magnetic resonance, NMR, parameters in the cluster model, which are in good agreement with the available experimental data. The difference in the isotropic shielding (sigma(iso)) and quadrupole coupling constant (C(Q)) between monomer and target molecule in the cluster was analyzed in detail. It was shown that both EFG and CS tensors are sensitive to hydrogen-bonding interactions, and calculating both tensors is an advantage. A different influence of various hydrogen bond types, N-Hcdots, three dots, centeredI, O-Hcdots, three dots, centeredI, and N-Hcdots, three dots, centeredO was observed on the calculated CS and EFG tensors. On the basis of this study, nitrogen and O-6 are the most important nuclei to confirm crystalline structure of chitosan/HI. These nuclei have large change in their CS and EFG tensors because of forming intermolecular hydrogen bonds. Moreover, the quantum chemical calculations indicated that the intermolecular hydrogen-bonding interactions play an essential role in determining the relative orientation of CS and EFG tensors of O-6 and nitrogen atoms in the molecular frame axes.

Influence of N–H…O and O–H…O hydrogen bonds on the 17O, 15N and 13C chemical shielding tensors in crystalline acetaminophen: A density functional theory study

A computational investigation was carried out to characterize the (17)O, (15)N and (13)C chemical shielding tensors in crystalline acetaminophen. We found that N-H...O and O-H...O hydrogen bonds around the acetaminophen molecule in the crystal lattice have different influences on the calculated (17)O, (15)N and (13)C chemical shielding eigenvalues and their orientations in the molecular frame of axes. The calculations were performed with the B3LYP method and 6-311++G(d, p) and 6-311+G(d) standard basis sets using the Gaussian 98 suite of programs. Calculated chemical shielding tensors were used to evaluate the (17)O, (15)N, and (13)C NMR chemical shift tensors in crystalline acetaminophen, which are in reasonable agreement with available experimental data. The difference between the calculated NMR parameters of the monomer and molecular clusters shows how much hydrogen-bonding interactions affect the chemical shielding tensors of each nucleus. The computed (17)O chemical shielding tensor on O(1), which is involved in two intermolecular hydrogen bonds, shows remarkable sensitivity toward the choice of the cluster model, whereas the (17)O chemical shielding tensor on O(2) involved in one N-H...O hydrogen bond, shows smaller improvement toward the hydrogen-bonding interactions. Also, a reasonably good agreement between the experimentally obtained solid-state (15)N and (13)C NMR chemical shifts and B3LYP/6-311++G(d, p) calculations is achievable only in molecular cluster model where a complete hydrogen-bonding network is considered. Moreover, at the B3LYP/6-311++G(d, p) level of theory, the calculated (17)O, (15)N and (13)C chemical shielding tensor orientations are able to reproduce the experimental values to a reasonably good degree of accuracy.