Enhanced Antioxidant Activity of Fresh Fruits through Salicylic Acid/β-CD Hydroalcoholic Gels

Oxidation is an important cause of fruit spoilage, and therefore improving the antioxidant capacity of fresh fruits is beneficial to their preservation. Herein, fresh-cut bananas were used as a type of fresh fruit and soaked in 75% hydroalcoholic gels containing salicylic acid (SA) or SA/β-CD inclusion complex (SA/β-CD). After treatment, they were placed in an atmosphere at 85% relative humidity at 20 °C for 12 days. A significant reduction in spoilage in bananas treated with the hydroalcoholic gels in the presence of SA/β-CD was observed, compared with those treated with gels in the presence or absence of SA. The free-radical-scavenging performances of SA and its complex were investigated using the DPPH (1,1-diphenyl-2-picryl-hydrazil) method. Based on the results, the significant increase in antioxidant activity was attributed to the fact that the inclusion complex could break the intramolecular hydrogen bonding of SA, thus efficiently eliminating ROS in the fruits. The formation of the inclusion complex was confirmed by experiments and theoretical calculations. Our findings indicate that treatment with SA/β-CD can provide an efficient method of maintaining postharvest quality and extending the shelf life of bananas.

A new amino acid for improving permeability and solubility in macrocyclic peptides through side chain-to-backbone hydrogen bonding.

Despite the notoriously poor membrane permeability of peptides in general, many cyclic peptide natural products show high passive membrane permeability and potently inhibit a variety of “undruggable” intracellular targets. A major impediment to designing cyclic peptides with good permeability is the high desolvation energy associated with the peptide backbone amide NH groups. Strategies for mitigating the deleterious effect of the backbone NH group on permeability include N-methylation, steric occlusion, and the formation of intramolecular hydrogen bonds with backbone carbonyl oxygens, while there have been relatively few studies on the use of polar side chains to sequester backbone NH groups. We investigated the ability of N,N-pyrrolidinyl glutamine (Pye), whose side chain contains a powerful hydrogen bond accepting C=O amide group but no hydrogen bond donors, to sequester exposed backbone NH groups in a series of cyclic hexapeptide diastereomers. Analyses of partition coefficients, lipophilic permeability efficiencies (LPE), artificial and cell-based permeability assays revealed that specific Leu-to-Pye substitutions conferred dramatic improvements in aqueous solubility and permeability in a scaffold- and position-dependent manner. Introduction of the Pye residue thus offers a complementary tool, alongside traditional approaches, for improving membrane permeability and solubility in cyclic peptides.

Relationship between the Crystal Structure and Tuberculostatic Activity of Some 2-Amidinothiosemicarbazone Derivatives of Pyridine

Tuberculosis remains one of the most common diseases affecting developing countries due to difficult living conditions, the rapidly increasing resistance of M. tuberculosis strains and the small number of effective anti-tuberculosis drugs. This study concerns the relationship between molecular structure observed in a solid-state by X-ray diffraction and the 15N NMR of a group of pyridine derivatives, from which promising activity against M. tuberculosis was reported earlier. It was found that the compounds exist in two tautomeric forms: neutral and zwitterionic. The latter form forced the molecules to adopt a stable, unique, flat frame due to conjugation and the intramolecular hydrogen bond system. As the compounds exist in a zwitterionic form in the crystal state generally showing higher activity against tuberculosis, it may indicate that this geometry of molecules is the “active” form.

Halogen Bonding Organocatalysis Enhanced through Intramolecular Hydrogen Bonds

Recent results indicate a halogen bond donor is strengthened through direct interaction with a hydrogen bond to the electron-rich belt of the halogen. Here, this Hydrogen Bond enhanced Halogen Bond...

Theoretical Investigations of State Specific Hydrogen Atom Transfer in 8-Formyl-7-hydroxy-4-methylcoumarin

Excited state intramolecular hydrogen transfer (ESIHT) reaction of 8-formyl-7-hydroxy-4-methyl coumarin (FC) in its pure and hydrated state FC-(H2O)4 (FCH) has been studied by implementing state specific time dependent density functional theory (SS-TDDFT) along with the effective fragment potential (EFP1) method for solvation with discrete water molecules. The intramolecular hydrogen bond formed between hydroxyl hydrogen (H18) and formyl oxygen (O15) and intermolecular hydrogen bonds formed due to microsolvation were explored. The studies of electrostatic potential, natural charge analysis, difference electron density map and UV-Vis spectra of both FC and FCH molecules establish the intramolecular charge transfer (ICT) states of the molecules. The vertical excitation from S0 to S1 state causes the transfer of hydroxyl hydrogen to formyl oxygen and from S1 to S3 causes the transfer of the hydrogen atom back to hydroxyl oxygen. Potential energy surface scans along intramolecular hydrogen bonding at the ground and excited states confirm the state specific ESIHT reaction in both FC and FCH molecules.

“Light on” fluorescence carbon dots with intramolecular hydrogen bond-regulated co-planarization for cell imaging and temperature sensing

Turn-on thermosensitive carbon dots (CDs) with dual function of imaging and sensing are desirable for biological research and clinical diagnosis at cellular level. Herein, we synthesized eight types of novel...

Anti-Solvatochromic and Highly Emissive Twisted D-A structure with Intramolecular Hydrogen Bond

Electron donor-acceptor (D-A) structure are the most common strategy to develop fluorescent dyes with high quantum yield in solution and the solid state. However, most of the D-A type fluorescent...

Crystallographic structure, activity prediction, and hydrogen bonding analysis of some CSD-based 3,3'-bis-indole derivatives: A review

Herein we report crystallographic comparison of some geometrical and structural features for a series of biologically relevant bis-indole derivatives. Selected bond distances and bond angles of interest in a series of bis-indole derivatives have been discussed in detail. The biological activity of the substances has been correlated with based the structure-activity relationships (SAR) base which provides the different possibility of activity (Pa) and possibility of inactivity (Pi). For a better understanding of the packing interactions existing among these derivatives, an overview of crystal structure analysis with emphasis on the intramolecular hydrogen bonding in some bis-indole derivatives is presented. The role of hydrogen bonding in the crystal structure assembly of bis-indole derivatives has been found to be predominant and this observation reveals significant impact of hydrogen bonding in high value of drug-likeness of these bio-molecules.

Crystal structure, Hirshfeld surface analysis, and DFT studies of N-(2-chlorophenylcarbamothioyl)cyclohexanecarboxamide

N-(2-Chlorophenylcarbamothioyl)cyclohexanecarboxamide was characterized by a single crystal X-ray diffraction study. Crystal data for this compound, C14H17ClN2OS; Monoclinic, space group P21/n with Z = 4, a = 5.2385(10) Å, b = 17.902(4) Å, c = 15.021(3) Å, β = 90.86(3)°, V = 1408.5(5) Å3, T = 153(2) K, μ(MoKα) = 0.413 mm-1, Dcalc = 1.400 g/cm3, 9840 reflections measured (7.082° ≤ 2Θ ≤ 50.378°), 2519 unique (Rint = 0.0406, Rsigma = 0.0335) which were used in all calculations. The final R1 was 0.0397 (I > 2σ(I)) and wR2 was 0.0887 (all data). The puckering parameters (q2 = 0.019(3) Å, q3 = 0.578(3) Å, θ = 1.0(3)° and φ = 51(8)°) of the title compound show that the cyclohexane ring adopts a chair conformation. The molecular conformation of the title compound is stabilized by intramolecular hydrogen bonds (N2-H2⋅⋅⋅Cl1, N2-H2⋅⋅⋅O1, and C2-H2A⋅⋅⋅S1) and intermolecular hydrogen bonds (N1-H1⋅⋅⋅S1i and C9-HA⋅⋅⋅S1ii: 2-x, 2-y, 1-z). The intramolecular hydrogen bonds (N2-H2⋅⋅⋅O1 and C2-H2A⋅⋅⋅S1) are also form two pseudo-six-membered rings. Density functional theory optimized structure in the gaseous phase at B3LYP/6-311G(d,p) level of theory has been compared with the experimentally defined molecular structure. The molecular orbitals HOMO and LUMO with the energy gap for the title compound are calculated and the estimated energy gap (ΔE) between the HOMO and LUMO energies levels of the title compound is 3.5399 eV, which implies that the title molecule is very reactive. The Hirshfeld surface analysis reveals that the most important contributions to crystal packing are from H···H (49.0%), H···C/C···H (12.5%), H···Cl/Cl···H (10.9%), and H···S/S···H (10.0%) interactions. The energy-framework calculations are used to analyze and visualize the three-dimensional topology of the crystal packing. The intermolecular energy analysis confirmed a significant contribution of dispersion to the stabilization of molecular packings in the title compound.

Thermal Analysis of Plastics Used in the Food Industry

Fires in landfills, where used plastic packaging waste is discarded, have shown how great a fire hazard these types of materials pose. In this study, the course of thermo-oxidation of samples made of polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) based plastics was determined. Based on an analysis of the dissociation energy of bonds between atoms in a polymer molecule, the mechanisms responsible for the character and course of degradation were observed. It was found that the degradation rate of PP and PS could be a result of the stability of C-H bonds on the tertiary carbon atom. In the case of PS, due to facilitated intramolecular hydrogen transfer, stabilization of hydroperoxide, and formation of a stable tertiary alcohol molecule, the onset of degradation is shifted towards higher temperatures than in the case of PP. Notably, the PP fragmentation occurs to a greater extent due to the easier course of β-scission. In addition, it was found that during a fire, the least amount of heat would be generated by thermo-oxidation of PS-based plastics. This is a result of the formation of a styrene molecule during decomposition that, due to the high stability of bonds in the aromatic ring, escapes from the combustion zone without oxidation. It has been proven that the greatest thermal effect accompanies PET decomposition, during which a phenyl radical is produced, where the C-H bonds break more easily in comparison with the bonds of an intact ring.