Shock-Induced Degradation of Guanosine and Uridine Promoted by Nickel and Carbonate: Potential Applications

Experimental studies of the degradation of two ribonucleosides (guanosine and uridine) were carried out by making use of mechanochemistry. Mechanochemical experiments reveal the decomposition of guanosine and uridine, promoted by nickel(II) and carbonate ions, into guanine and uracil, respectively. These nucleobases were identified by HPLC and 1H NMR spectroscopy (this applied only to uracil). Additionally, density-functional theory (DFT) methodologies were used to probe the energetic viability of several degradation pathways, including in the presence of the abovementioned ions. Three mechanisms were analysed via ribose ring-opening: dry, single-molecule water-assisted, and metal-assisted, wherein the last two mechanisms confirmed the mechanochemical degradation of both ribonucleosides into respective nucleobase moieties. These results can contribute to an astrobiological interpretation of the extraterrestrial sample's contents.

Metal Coordination and Biological Screening of a Schiff Base Derived from 8-Hydroxyquinoline and Benzothiazole

Designing new metallodrugs for anticancer therapy is a driving force in the scientific community. Aiming to contribute to this field, we hereby report the development of a Schiff base (H2L) derived from the condensation of 2-carbaldehyde-8-hydroxyquinoline with 2-hydrazinobenzothiazole and its complexation with transition metal ions. All compounds were characterised by analytical and spectroscopic techniques, which disclosed their structure: [Cu(HL)Cl], [Cu(HL)2], [Ni(HL)(acetate)], [Ni(HL)2], [Ru(HL)Cl(DMSO)], [VO(HL)2] and [Fe(HL)2Cl(H2O)]. Different binding modes were proposed, showing the ligand’s coordination versatility. The ligand proton dissociation constants were determined, and the tested compounds showed high lipophilicity and light sensitivity. The stability of all complexes in aqueous media and their ability to bind to albumin were screened. Based on an antiproliferative in vitro screening, [Ni(HL)(acetate)] and [Ru(HL)Cl(DMSO)] were selected for further studies aiming to investigate their mechanisms of action and therapeutic potential towards colon cancer. The complexes displayed IC50 < 21 μM towards murine (CT-26) and human (HCT-116) colon cancer cell lines. Importantly, both complexes exhibited superior antiproliferative properties compared to the clinically approved 5-fluorouracil. [Ni(HL)(acetate)] induced cell cycle arrest in S phase in CT-26 cells. For [Ru(HL)Cl(DMSO)] this effect was observed in both colon cancer cell lines. Additionally, both compounds significantly inhibited cell migration particularly in the human colon cancer cell line, HCT-116. Overall, the therapeutic potential of both metal complexes was demonstrated.

Red-Purple Photochromic Indigos from Green Chemistry: Mono-tBOC or Di-tBOC N-Substituted Indigos Displaying Excited State Proton Transfer or Photoisomerization

In indigo, excited state proton transfer (ESPT) is known to be associated with the molecular mechanism responsible for highly efficient radiationless deactivation. When this route is blocked (partially or totally), new deactivation routes become available. Using new green chemistry procedures, with favorable green chemistry metrics, monosubstitution and disubstitution of N group(s) in indigo, by tert-butoxy carbonyl groups, N-(tert-butoxycarbonyl)indigo (NtBOCInd) and N,N'-(tert-butoxycarbonyl)indigo (N,N'tBOCInd), respectively, were synthetically accomplished. The compounds display red to purple colors depending on the solvent and substitution. Different excited-state deactivation pathways were observed and found to be structure- and solvent-dependent. Trans-cis photoisomerization was found to be absent with NtBOCInd and present with N,N'tBOCInd in nonpolar solvents. Time-resolved fluorescence experiments revealed single-exponential decays for the two compounds which, linked to time-dependent density functional theory (TDDFT) studies, show that with NtBOCInd ESPT is extremely fast and barrierless-predicted to be 1 kJ mol^-1 in methylcyclohexane and 5 kJ mol^-1 in dimethylsulfoxide-, which contrasts with ∼11 kJ mol^-1 experimentally obtained for indigo. An alternative ESPT, competitive with the N-H···O═C intramolecular pathway, involving dimer units is also probed by TDDFT and found to be consistent with the experimentally observed time-resolved data. N,N'tBOCInd, where ESPT is precluded, shows solvent-dependent trans-cis/cis-trans photoisomerization and is surprisingly found to be more stable in the nonemissive cis conformation, whose deactivation to S₀ is found to be solvent-dependent.

Key Parameters on the Antibacterial Activity of Silver Camphor Complexes

Nine new complexes with camphor imine or camphor sulfonimine ligands were synthesized and analytically and spectroscopically characterized, aiming to identify the key parameters that drive the antibacterial activity of the complexes with metal cores and imine substituents with distinct electronic and steric characteristics. The antimicrobial activity of all complexes was evaluated by determining their minimum inhibitory concentrations (MIC) against the Gram-negative Escherichia coli ATCC25922, Pseudomonas aeruginosa 477, and Burkholderia contaminans IST408, and the Gram-positive Staphylococcus aureus Newman. Camphor imine complexes based on the hydroxyl silver center ({Ag(OH)}) typically perform better than those based on the nitrate silver center ({Ag(NO₃)}), while ligands prone to establish hydrogen bonding facilitate interactions with the bacterial cell surface structures. A different trend is observed for the silver camphor sulfonimine complexes that are almost non-sensitive to the nature of the metal cores {Ag(OH)} or {Ag(NO₃)} and display low sensitivity to the Y substituent. The antibacterial activities of the Ag(I) camphor sulfonimine complexes are higher than those of the camphor imine analogues. All the complexes display higher activity towards Gram-negative strains than towards the Gram-positive strain.

Deep in blue with green chemistry: influence of solvent and chain length on the behaviour of N- and N,N′- alkyl indigo derivatives

Using green chemistry procedures the synthesis of N-alkyl (NC_nInd) and N,N′-dialkyl (N,N′C_nInd) indigo derivatives, with n = 1–3, 6, 8, 12 and 18, was undertaken, leading to compounds with blueish to greenish colors in solution. The effect of the alkyl chain length on the spectral (including color) and photophysical properties of the compounds was explored. This was done with solvents of different viscosities and polarities (dielectric constants). From time-resolved fluorescence and femtosecond-transient absorption (fs-TA) for the NC_nInd derivatives with n = 1 and 2, the decays are, in methylcyclohexane (MCH) and n-dodecane, single-exponential, while in 2-methyltetrahydrofuran (2MeTHF) they are bi-exponential. The excited state proton transfer (ESPT) is ultrafast (<1 ps) for NC_1,2Ind in MCH and n-dodecane, supported by time-dependent density functional theory (TDDFT) calculations, thus showing that both the chain length and solvent influence the ESPT process. For N,N′C_nInd, from time-resolved experiments, and with the exception of the shortest member of the series, N,N′C₁Ind, two conformers are found to be present in the excited state.

Using green chemistry procedures the synthesis of N- and N,N′-alkyl indigo derivatives was undertaken and the effect of the alkyl chain length on the spectral (including color) and photophysical properties of the compounds explored.

Correction: Deep in blue with green chemistry: influence of solvent and chain length on the behaviour of N- and N,N′-alkyl indigo derivatives

Correction for ‘Deep in blue with green chemistry: influence of solvent and chain length on the behaviour of N- and N,N′-alkyl indigo derivatives’ by Daniela Pinheiro et al., Chem. Sci., 2020, DOI: 10.1039/d0sc04958a.

Ag(I) camphor complexes: antimicrobial activity by design

Eleven new complexes of general formula [Ag(NO₃)(L-Y)₂] corresponding to Ag(I) camphorimine complexes [Ag(NO₃)(OC₁₀H₁₄NY)₂] (Y=NMe₂ (1); OH (2); C₆H₅ (3); 4-MeC₆H₄, (4); 3,5-(CH₃)₂C₆H₃ (5); 3-OHC₆H₄, (6); 3-ClC₆H₄ (7); 4-ClC₆H₄ (8); 4-FC₆H₄ (9); 4-CF₃C₆H₄ (10)) and the camphor sulfonylimine complex [Ag(NO₃)(O₂SNC₁₀H₁₄NY)₂] (Y=NH₂) were synthesized/characterized and their structural properties and antibacterial activity studied to gain insights into the structure-antimicrobial activity relationships. Five of the complexes were selected as representative examples and structures were optimized by Density Functional Theory calculations. The results show that the imine substituents (Y) at the camphor ligands drive the structure of the complexes from distorted octahedral to trigonal prismatic or linear ionic while the effect of the sulfonylimine ring does not appreciably affects the geometry of the complex. The lipophilicity and polarity which are important parameters concerning the biological activity of the complexes are also high dependent of the characteristics of the camphor ligands. The redox properties of the complexes studied by cyclic voltammetry showed that their reduction potentials are essentially independent of their electronic and steric properties. The antibacterial activity of all the complexes, against Gram-positive (S. aureus Newman) and Gram-negative (Escherichia coli ATCC25922, Pseudomonas aeruginosa 477, Burkholderia contaminans IST408) strains was evaluated through calculation of MIC values. Results show that complexes with camphor imine ligands (1-10) that combine high lipophilicity with low dipolar moment (3-5) exhibit enhanced antibacterial activity. The ability to establish hydrogen bonding emerged as an important contribution to the antibacterial activity of the camphor sulphonylimine complex 11 (Y=NH₂).

Structural dependence of the optical properties of narrow band gap thiophene–thiadiazoloquinoxaline derivatives and their application in organic photovoltaic cells

The structural causes for NIR absorption bands on new [1,2,5]thiadiazolo[3,4-g]quinoxaline derivatives were determined on the basis of DFT calculations and organic photovoltaic cells incorporating the new compounds were fabricated.

Band-gap tunable thiadiazolo[3,4-g]quinoxaline derivatives as non-fullerene acceptors in organic photovoltaic cells processed from low toxic ethanol/anisole mixtures

New non-fullerene acceptors were combined with a new polythiophene donor and processed from solvent mixtures of low toxicity in organic photovoltaic cells.

Naphthoylhydrazones: coordination to metal ions and biological screening

V^IVO, Cu^II and Zn^II complexes from three new naphthoylhydrazones were screened towards their ability to bind albumin and their cytotoxicity.

Photophysical properties and biological evaluation of a Zinc(II)-5-methyl-1H-pyrazole Schiff base complex

A new ZnL₂ complex containing two molecules of a tridentate Schiff base derived from 5-methyl-1H-pyrazole (HL) is synthesized and characterized. The photophysical properties of HL and ZnL₂ are disclosed and supported by CAMB3LYP DFT/TDDFT calculations. It is shown that there is keto-tautomer stabilization upon excitation with an energetically accessible triplet state in HL, not present in ZnL₂, this explaining the differences found in the emissions of the compounds. The intrinsic fluorescence of ZnL₂ is used as probe for a detailed study of its binding to human serum albumin. The protein-complex association is thermodynamically favourable and it is shown by fluorescence quenching and time-resolved analysis that the fluorescence quenching involves a mixed mechanism with prevalence of static quenching, which corroborates adduct formation at site I, close to the Trp214 residue. The ability of ZnL₂ to bind DNA was also evaluated, as well as its cytotoxic activity against MCF7 (breast), PC3 (prostate) cancer cells and hamster V79 fibroblasts. ZnL₂ is a moderate DNA intercalator (K_app = 3.9 × 10⁴ M^-1) and depicts a quite low IC₅₀ value at 48 h against MCF7 cells (IC₅₀ = 530 nM), but much higher for PC3 and V79 cells. The relevance of a more careful speciation evaluation of ZnL₂ and other potential metal-based drugs in incubation media used in in vitro tests is highlighted.

Synthesis of Ag(I) camphor sulphonylimine complexes and assessment of their cytotoxic properties against cisplatin-resistant A2780cisR and A2780 cell lines

Camphorsulphonylimine complexes [Ag(NO₃)(^IL)₂] (^IL=C₁₂H₁₉N₃SO₂, 1) and [(AgNO₃)₂(^IIL)] (^IIL=C₂₂H₂₃N₃SO₂, 2) were synthesized and characterized by elemental analysis, spectroscopy (IR, NMR) and cyclic voltammetry. [Ag(NO₃)(^IL)₂] crystalizes in the monoclinic C2 space group with a triangular geometry assuming a chalice-type shape. The anti-proliferative properties of the new complexes 1 and 2 and those of the previously reported [Ag(NO₃)(^IIIL)] (^IIIL=C₁₆H₁₈N₃SO₂, 3) were assessed against the human ovarian cancer cells (cisplatin-sensitive A2780, cisplatin-resistant A2780cisR) and the non-tumoral human HEK 293 cell line, using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. The NR (3-amino-7-dimethylamino-2-methylphenazine hydrochloride) assay was alternatively used to assess the cytotoxicity on the A2780 cells. Results from the MTT assay (48h exposure) show that the complexes display IC₅₀ values lower (by at least one order of magnitude) than cisplatin, while the cytotoxicity of AgNO₃ is of the same order of cisplatin. The camphorsulphonylimine ligands display irrelevant (^IL, ^IIIL) or no cytotoxicity (^IIL). The highest cytotoxicity (lower IC₅₀) was found for [(AgNO₃)₂(^IIL)]. The binding ability of the complexes to calf thymus-deoxyribonucleic acid (CT-DNA) was studied by fluorescence. Constants (K_sv, K_a) and the number (n) of binding centres to DNA were calculated showing that DNA intercalation possibly occurs in the cases of complexes 2 and 3, while a more complicated process operates for 1. As expected from the cytotoxicity, [(AgNO₃)₂(^IIL)] displays the highest binding affinity (K_a=1.61×105 M^-1). No binding to DNA was detected for AgNO₃ or ^IIL under the experimental conditions used. The binding trend to CT-DNA found by fluorescence was corroborated by cyclic voltammetry.

Antibacterial activity of silver camphorimine coordination polymers

[Ag(NO₃)(OC₁₀H₁₄NC₆H₄NC₁₀H₁₄O)] is the first bi-camphor silver coordination polymer structurally characterized. It displays bactericidal activity against Gram-negative and Gram-positive strains comparable to drugs in use.

Oxygen activation by copper camphor complexes

In situreduction of CuCl₂enables formation of Cu(i) complexes prone to activate molecular oxygen from air towards catalytic oxidation of 1,3-dicarbonyls.

Reactivity Trends in the Reaction of Alkynes with 3-Oxo-camphorsulfonylimine

The regioselective addition of deprotonated alkynes (phenyl-1-propyne, propargyl ether or tetrahydropyran-protected 3-butyn-1-ol) to the imine group was identified as a competitive process to the nucleophilic addition to the keto group of (1S)-3-oxo-camphorsulfonylimine. The selectivity of the process depends on the characteristics of the nucleophile and the reaction conditions. In the case of propargyl ether it was possible to render the imine addition the main process.

The structural characterization of compounds 1, 2, 6 by X-ray diffraction analysis show that the C2 - C3 bond becomes longer upon nucleophilic addition to the imine group of (1S)-3-oxo-camphorsulfonylimine. This trend is believed to favour the ring opening process that undergoes the formation of the spiro type compound 7.

Role of tumor necrosis factor-α, interferon-γ and Fas-ligand on in vitro nitric oxide activity in the corpus luteum

Normal reproductive function involves the expression of inflammatory mediators. Regarding the corpus luteum (CL), cytokines promote the cross-talk between immune, vascular and steroidogenic cells, among others. Moreover, TNF, IFNG and FASL were shown to regulate equine CL establishment and regression. We hypothesized that cytokines action on equine CL may be mediated by nitric oxide (NO), through the regulation of endothelial NO synthase (eNOS) expression. TNF increased eNOS mRNA level and NO metabolite (nitrite) production during CL growth. Cytokines combined action (TNF+IFNG+FASL) promoted eNOS protein upregulation in mid-CL and nitrite production in mid and late-CL. However, in late-CL, TNF alone decreased nitrite secretion. These results indicate that in equine CL, cytokines TNF, IFNG and FASL regulate NO activity, via eNOS expression modulation.

Model for conformational relaxation of flexible conjugated polymers: application to p-phenylenevinylene trimers in nonpolar solvents

Photoexcitation of flexible conjugated polymers is invariably followed by a fast conformational/torsional relaxation towards a configuration favouring coplanarity of the conjugated segments. In general, the experimental relaxation rate constant (k(CR)) depends on the solvent viscosity (η) and temperature (T), and is not proportional to T/η. A theory capable of explaining the observed dependence of k(CR) on T and η over a wide range of these variables is not available. This gap is filled here by presenting a stochastic model that includes the participation of the oligomer side chain in storing and dissipating the stresses induced by photoexcitation. The model is able to account for the softening of solute-solvent interactions and its predictions are found to be in excellent agreement with the observed relaxation rate constants of a series of substituted p-phenylenevinylene trimers [ChemPhysChem 2009, 10, 448-454] on T, η and the size of the side-chains.

mRNA transcription of prostaglandin synthases and their products in the equine endometrium in the course of fibrosis

Accurate regulation of the reproductive cycle and successful implantation depend on proper functioning of the endometrium. The aim of this study was to determine whether mRNA transcription of specific enzymes responsible for prostaglandin (PG) synthesis (prostaglandin-endoperoxide synthase, PTGS-2; prostaglandin F(2α) synthase, PGFS; and prostaglandin E(2) synthases, PGES) and PG concentrations in endometrial extracts would change in moderate (Kenney's Category II) and severe phases of fibrosis (Kenney's Category III; endometrosis), compared with healthy endometrium (Kenney's Category I), during the estrous cycle. Endometrial tissues samples were obtained from mares at the early (n = 12), mid (n = 12) and late (n = 12) luteal phases and the follicular phase (n = 12) of the estrous cycle. Additionally, all endometria were classified microscopically as belonging to Categories I and II or III according to the Kenney classification, resulting in allocation of 4 samples for each subcategory, e.g., mid luteal I, II and III. Relative mRNA transcription was quantified using Real-time PCR. Concentrations of PGE(2) and PGF(2α) in the endometrial extracts were determined using enzyme-linked immunosorbent assay (EIA). In Category I, PTGS-2 mRNA transcription was upregulated at the mid (P < 0.05) and late luteal phases (P < 0.001) and at the follicular phase (P < 0.05) compared to the early luteal phase. PGFS mRNA transcription as well as PGF(2α) concentrations increased at the mid (P < 0.01) and late (P < 0.05) luteal phases compared to the early luteal phase in Category I. PGES mRNA transcription was higher at the mid (P < 0.01) and late luteal phases (P < 0.05) compared to the early luteal and follicular phases in Category I. Prostaglandin E(2) concentration in Category I was higher at the mid luteal phase (P < 0.01) compared to all other phases of the estrous cycle. During incipient endometrosis (Category II) and under full endometrosis (Category III), PTGS-2, PGFS and PGES mRNA transcription and PG concentration were altered compared to the respective estrous phases in healthy endometria (P < 0.05). It may be concluded that serious changes in mRNA transcription of PG synthases and PG production that occur in the equine endometrium during the course of fibrosis in the estrous cycle could be responsible for disturbances leading to disorders of the estrous cycle and early embryo losses.

Eggplant (Solanum melongena) infusion has a modest and transitory effect on hypercholesterolemic subjects

Eggplant (Solanum melongena) is consumed extensively in Brazil. It has been believed that infusion of a powdered preparation of the fruit may reduce serum cholesterol. However, there are few documented reports on its effects on cholesterol metabolism and its possible hypocholesterolemic effect has not been proved by well-controlled studies. The aim of the present study was to observe the effects of S. melongena on the serum cholesterol and triglycerides of 38 hypercholesterolemic human volunteers ingesting S. melongena infusion for five weeks. Thirty-eight hypercholesterolemic subjects receiving either S. melongena infusion (N = 19) or placebo (N = 19) participated in two clinical experiments in which the effect of S. melongena infusion was studied with (N = 16) or without (N = 38) dietary orientation. Total cholesterol and its fractions, triglycerides, and apolipoproteins A and B were measured in blood at the beginning of the experiment and three and five weeks thereafter. No differences were observed compared to control. Intraindividual analysis showed that S. melongena infusion significantly reduced the blood levels of total and LDL cholesterol and of apolipoprotein B. After dietary orientation, no intra- or intergroup differences were seen for any of the parameters analyzed. The results suggest that S. melongena infusion had a modest and transitory effect, which was not different from that obtained with standard orientation for dyslipidemia patients (diet and physical activities).