Please login first

List of accepted submissions

Show results per page
Find papers
  • Open access
  • 319 Reads
A novel and efficient magnetic nanocatalyst functionalized with 1,3,5-tris(2-hydroxyethyl)isocyanurate and boric acid for the synthesis of symmetric and asymmetric Hantzsch esters

A new magnetic core/shell nanocatalyst functionalized with 1,3,5-tris(2-hydroxyethyl)isocyanurate and boric acid (Fe3O4/SiO2/CPTS/THEIC/(CH2)3B(OH)2) was designed and properly characterized by the Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption–desorption technique (BET), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) spectroscopy. The catalytic activity of Fe3O4/SiO2/CPTS/THEIC/(CH2)3B(OH)2, as an efficient magnetically recoverable catalyst, was investigated for the synthesis of polyhydroquinolines (PHQs) as well as polyhydroacridines (PHAs) via one-pot multicomponent reactions of ethyl acetoacetate and / or dimedone, different aldehydes and ammonium acetate in EtOH under reflux conditions. High to quantitative yields of the desired PHQs or PHAs products, wide scope of the substrates, eliminating of any toxic heavy metals or corrosive reagents for modification of the catalyst, simple work-up procedure, short reaction times and low loading of the catalyst are remarkable advantages of this green protocol. An additional advantage of this magnetic nanoparticles catalyst is its ability to be separated and recycled easily from the reaction mixture with minimal efforts in six subsequent runs without significant loss of its catalytic activity.

  • Open access
  • 66 Reads
Synthesis of 3-tetrazolylmethyl-4H-chromen-4-ones via Ugi-azide reaction catalyzed by ZnO nanoparticles

A serie of novel 3-tetrazolylmethyl-4H-chromen-4-ones were synthesized via Ugi-azide reaction under mild ultrasound-assisted conditions (room temperature, EtOH, 10% mol ZnO nanoparticles). The products containing two privileged heterocyclic frameworks: 1,5- disubstituted-1H-tetrazole and 3-substituted-4H-chromen chromen-4-ones, which are present in a variety of bioactive compounds and commercial drugs.

  • Open access
  • 66 Reads

Cholinesterase inhibitors (ChEI) play a significant role in enhancing synaptic cholinergic activity avoiding cholinergic poisoning, and consequently have therapeutic relevance related to Alzheimer's disease (AD), myasthenia gravis, and glaucoma. In this sense, photochromic ChEI have become interesting due to the expansion of photopharmacological approach towards the remote control of acetylcholinesterase (AChE). Inspired in the concept of “azologization” as the rational introduction of the azobenzene group into the structure of a designed active compound, and based on our previous results, indicating aza-stilbene activity as dual ChEI, we synthesized several azoderivatives with potential application as reversible photochromic AChE inhibitors. In this work we present 1,2-bis(4-(4-(pyrrolidin-1-yl)butoxy)phenyl)diazene (di-PRLC4OAzo), obtained by microwave assisted synthesis, which showed in vitro enzymatic response for its (E) isomer (IC50: 1,08 µM) beside a stable photostationary state, indicating it might be an efficient photo-responsible probe to remote control the activity of the enzyme. Ellman´s assay was performed for measuring AChE activity in the presence of the reversible photoswitchable blocker, whose in vitro photoisomerization efficiency was evaluated by UV/Vis absorption spectroscopy.

  • Open access
  • 55 Reads
Effects of ethylimidazolium nitrate and the aluminium nitrate salt mixtures on germination of three forest species

Ionic liquids are synthetic compounds with melting temperatures lower than 100 ºC and with high ability of modification of their physical and chemical properties from changes on their chemical structure. Although the number of applications in the last years has been continuously increasing, their effects on the different terrestrial ecosystems have been scarcely studied.

In this work, the effects of the ionic liquid ethylammonium nitrate (EAN), the aluminium nitrate salt (Al(NO3)3) and the saturated mixture of both components on germination of three forest species have been studied. Different doses from control to 10% weight of the three treatments were applied at seeds of three different forest species (Eucalyptus globulus Labill, Pinus radiata D. Don and Pinus Sylvestris L.) and the germination of these seeds were continuously monitored during 35 days.

The results showed that the addition of ionic liquid, salt and mixture provoke the reduction of germination for all the species. Concentrations of 5% and higher incite the total inhibition of the germination of all species for all the treatments, being EAN treatment the most harmful.

  • Open access
  • 71 Reads
Comparison of thermophysical properties of pure imidazolium nitrate and doped with a lithium nitrate salt in liquid and gel forms as potential electrolytes.

Current electrolytes for electrochemical energy storage devices are made of solvent which often present problems of flammability, corrosion and high toxicity. Ionic liquids and mixtures with metal salts are proposed as a good selection for more safety electrolytes due to their properties as, among others, non-flammability, negligible vapour pressure, high ionic conductivity and wide electrochemical window.

In this work, electrical conductivity of solutions of the ionic liquid 1-Ethyl-3-methylimidazolium nitrate ([EIm][NO3]) with lithium nitrate salt in four different concentrations has been analysed, for liquid and gel states.

Temperature and salt concentration dependences of electrical conductivity have been studied for liquid and gel states. As expected, an increase of conductivity with temperature and a decrease whit salt concentration were observed, except for the case of gel [EIm][NO3] with salt concentration of 0.5 m which shows a little increase of conductivity compared to the pure gel.

Comparison of conductivity of the liquid and gel states shows a significant increase for gel state at low concentrations of the added salt.

  • Open access
  • 89 Reads
Synthesis of new bis 1-substituted 5H-tetrazoles via efficient heterocyclizations from symmetric dianilines, methyl orthoester and sodium azide

Then, we herein describe the synthesis and characterization of three new bis 1-substituted-5H-tetrazoles. Two were synthesized in a single step via a heterocyclization involving primary amines, an orthoester and sodium azide in 30 to 91% yield. Besides, one was prepared via a three-step-based synthetic methodology: SNAr (32%), nitro group reduction (66%) and primary amine heterocyclization (83%) for an overall yield of 18%. It is noteworthy that those ligands neither have been synthesized nor isolated before. The aim of these syntheses is the use of new tetrazole-based ligands for the construction of novel MOF structures to evaluate their gas capture properties, such as CO2 under relative humidity conditions.

  • Open access
  • 64 Reads
Diplodomica I. Chemical composition of repugnatorial secretions of Cuban endemic millipede gen. Rhinocricus sp. A case of Applied Chemical Ecolgy

Analysis of the chemical composition of the ejaculated repugnatorial secretion of some populations of the Cuban endemic millipede Rhinocricus inhabiting in the western eco-geographical region of the Cuban archipelago has been developed. During research has been identified several quinonoids metabolites (quinones and phenols natural products) as an active components.

Many species of millipedes (Diplopoda) respond to disturbance by coiling up into a tight spiral keeping the head in the centre and ejecting, if further disturbed as defensive strategy, a noxious, topically irritant, with variable composition, fluid, being highly toxic an even cytotoxic.

In the defensive secretions of millipedes have been identified hydrocyanic acid, esters, acids, aldehydes, terpenoids, cyanogenic compounds, phenols, 1,4-benzoquinones, quinazolines, alkaloids, aromatic nitriles, and amino-nitro compounds. The most frequently detected are substituted quinonoids (phenols and 1,4-benzoquinones).

Some individuals (males) gathered from raked forest soil at the edge of the tropical forest, in some cases in typical carst region, were collected and studied. 850 μg of a deep brown-red secretion obtained by means of glass capillary from the individual studied, and directly introduced into analytical instrumental (GC-MS and FTIR)

The analysis of FTIR spectrum and mass spectrum show that the main components of secretions are substituted hydroquinones, substituted 1,4-benzoquinones and aldehydes.

The biological effects of these defensive secretions were evaluated experimentally, on ants (Atta spp.) and on pathogenic microorganisms. The results of the experiments showed a quick repellent effect and very interesting antimicrobial action. The ecological and evolutionary significance of chemical differentiation in millipedes populations are under study.

  • Open access
  • 61 Reads
Multicomponet Synthesis of Pyrrolo[3,4-a]carbazole-1,3-diones

Pyrrolocarbazoles are important structural motives present in many natural products and pharmaceuticals. Particularly, pyrrolo[3,4-a]carbazole-1,3-diones have attracted much attention as analogues of bioactive compounds, such as anticancer agent granulatimide. Surprisingly, only a few methods for the synthesis of these compounds have been reported in the literature, and they are almost limited to the Diel-Alder cycloaddition of 3-vinylindoles.

We have recently developed a multicomponent synthesis of polysubstituted anilines starting from a,b-unsaturated carbonyls, isocyanides and dienophiles. Here we report the application of this tandem [4+1]-[4+2] cycloaddition procedure for the synthesis of 4-amino-5-arylisoindoline-1,3-diones, which are then cyclized by means of a metal catalyzed intramolecular C-N coupling, affording structurally diverse, natural product-like pyrrolo[3,4-a]carbazole-1,3-diones with high yields and selectivities.