Evaluation of the binding of oxovanadium(IV) to human serum albumin

The understanding of the biotransformations of insulin mimetic vanadium complexes in human blood and its transport to target cells is an essential issue in the development of more effective drugs. We present the study of the interaction of oxovanadium(iv) with human serum albumin (HSA) by electron paramagnetic resonance (EPR), circular dichroism (CD) and visible absorption spectroscopy. Metal competition studies were done using Cu(II) and Zn(II) as metal probes. The results show that V(IV)O occupies two types of binding sites in albumin, which compete not only with each other, but also with hydrolysis of the metal ion. In one of the sites the resulting V(IV)O-HSA complex has a weak visible CD signal and its X-band EPR spectrum may be easily measured. This was assigned to amino acid side chains of the ATCUN site. The other binding site shows stronger signals in the CD in the visible range, but has a hardly measurable EPR signal; it is assigned to the multi metal binding site (MBS) of HSA. Studies with fatted and defatted albumin show the complexity of the system since conformational changes, induced by the binding of fatty acids, decrease the ability of V(IV)O to bind albumin. The possibility and importance of ternary complex formation between V(IV)O, HSA and several drug candidates - maltol (mal), picolinic acid (pic), 2-hydroxypyridine-N-oxide (hpno) and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone (dhp) was also evaluated. In the presence of maltol the CD and EPR spectra significantly change, indicating the formation of ternary VO-HSA-maltol complexes. Modeling studies with amino acids and peptides were used to propose binding modes. Based on quantitative RT EPR measurements and CD data, it was concluded that in the systems with mal, pic, hpno, and dhp (V(IV)OL(2))(n)(HSA) species form, where the maximum value for n is at least 6 (mal, pic). The degree of formation of the ternary species, corresponding to the reaction V(IV)OL(2) + HSA -->/<-- V(IV)OL(2)(HSA) is hpno > pic ≥ mal > dhp. (V(IV)OL)(n)(HSA) type complexes are detected exclusively with pic. Based on the spectroscopic studies we propose that in the (V(IV)OL(2))(n)(HSA) species the protein bounds to vanadium through the histidine side chains.     

Determination of Cd levels in smoke condensate of Brazilian and Paraguayan cigarettes by Thermospray Flame Furnace Atomic Absorption Spectrometry (TS-FF-AAS)

In this study, the concentrations of Cd in smoke condensate of Paraguayan and Brazilian full flavor normal size cigarettes were determined. A “fishtail” chimney was used to confine and direct cigarette smoke to an impaction trap followed by 3 MCE (mixed cellulose ester) filters for smoke collection. The smoke condensate collected at the first two collection stages (chimney and impactor) was prepared as Triton X-100 slurry samples and the 3 MCE filters (third collection stage) used to collect smoke were microwave digested. Samples were analyzed by Thermospray Flame Furnace Atomic Absorption Spectrometry (TS-FF-AAS) for Cd and the results obtained were compared with Graphite Furnace Atomic Absorption Spectrometry (GFAAS). No significant differences were found between the values obtained with TS-FF-AAS and GFAAS at a 95% confidence level. The total concentration of Cd in the smoke of Brazilian and Paraguayan cigarettes tested ranged from 187 to 281 ng/cigarette and from 176 to 271 ng/cigarette, respectively. The LODs for Cd using TS-FF-AAS and GFAAS, were 5.8 and 1.5 ng/cigarette, respectively, for the analysis of smoke condensate from 1 cigarette. The main advantages of using the simple TS-FF-AAS system are its low running costs and the analysis time when compared to GFAAS.     

1H and 13C NMR spectral assignments of four dammarane triterpenoids from carnauba wax

The phytochemical investigation of carnauba wax led to the isolation of three new dammarane triterpenoids 1, 2 and 4, together with the known triterpene 3. The structures of the new compounds were determined by 1D and 2D NMR spectroscopy and by comparison with published data for closely related compounds.     

Determination of Na, K, Ca and Mg in biodiesel samples by flame atomic absorption spectrometry (F AAS) using microemulsion as sample preparation

This study proposes a procedure for determining sodium, potassium, calcium and magnesium in biodiesel samples by flame atomic absorption spectrometry (F AAS). The sample was prepared as a microemulsion without surfactant. The optimized composition of the microemulsion was 10% (w/v) biodiesel, 75% (v/v) n-propanol, 1% (v/v) concentrated nitric acid and 14% (v/v) of aqueous solution formed by 0.2% (v/v) of nitric acid and 0.5% (v/v) of ionization suppressor. Analyte signals in the samples as microemulsion were found to be stable for a period of 15 days. Analytical curves were obtained using organometallic standard solutions. The limits of detection (LOD) found for the proposed procedure were 0.1 µg g^− 1, 0.01 µg g^− 1, 0.04 µg g^− 1, and 0.004 µg g^− 1 for Na, K, Ca and Mg, respectively. The reference method established by ABNT (Brazilian Association of Technical Norms) NBR 15556:2008 was used to verify the accuracy of the proposed procedure. No significant statistical difference was found between the results obtained with the proposed and the chosen reference procedure. The proposed procedure showed no matrix influence when recovery tests were performed (89%-103%). The results found in this study show that the proposed procedure is a good alternative for determining Na, K, Ca, and Mg by F AAS in biodiesel samples.     

Phase portraits for quadratic homogeneous polynomial vector fields on $$ \mathbb{S}^2 $$

Let X be a homogeneous polynomial vector field of degree 2 on $ \mathbb{S}^2 $ \mathbb{S}^2 . We show that if X has at least a non-hyperbolic singularity, then it has no limit cycles. We give necessary and sufficient conditions for determining if a singularity of X on $ \mathbb{S}^2 $ \mathbb{S}^2 is a center and we characterize the global phase portrait of X modulo limit cycles. We also study the Hopf bifurcation of X and we reduce the 16 ^th Hilbert’s problem restricted to this class of polynomial vector fields to the study of two particular families. Moreover, we present two criteria for studying the nonexistence of periodic orbits for homogeneous polynomial vector fields on $ \mathbb{S}^2 $ \mathbb{S}^2 of degree n.     

Green Synthesis of Spiro Compounds with Potential Anticancer Activity through Knoevenagel/Michael/Cyclization Multicomponent Domino Reactions Organocatalyzed by Ionic Liquid and Microwave-Assisted

In this work a microwave-assisted Knoevenagel/Michael/cyclization multicomponent domino methodology, using ethanol as solvent and the ionic liquid 1-methylimidazolium chloride as catalyst was developed for the synthesis of spiro compounds. The reaction conditions considered ideal were determined from a methodological study varying solvent, catalyst, amount of catalyst, temperature, and heating mode. Finally, the generality of the methodology was evaluated by exploring the scope of the reaction, varying the starting materials (isatin, malononitrile, and barbituric acid). Overall, the twelve spiro compounds were synthesized in good yields (43–98%) and the X-ray structure of compound 1b was obtained. In addition, the in vitro antiproliferative activities of the spirocycles against four types of human cancer cell lines including HCT116 (human colon carcinoma), PC3 (prostate carcinoma), HL60 (promyelocytic leukemia), and SNB19 (astrocytoma) were screened by MTT-based assay. It is noteworthy that spiro compound 1c inhibited the four cell lines tested with the lowest IC₅₀ values: 52.81 µM for HCT116, 74.40 µM for PC3, 101 µM for SNB19, and 49.72 µM for HL60.     

Electrochemical Sulphenylation/Cyclization of Quinones: A Rapid,Green, and Efficient Access to Cytotoxic Compounds

Undivided electrochemical cells enable economical preparation of sulphur-containing naphthoquinones through electrochemical sulphenylation of quinoidal compounds. The environmentally friendly and efficient protocol eliminates the use of chemical oxidants and facilitates the synthesis of the desired molecules. This approach offers an efficient and versatile method to synthesize quinones that exhibit cytotoxicity against cancer cell lines.