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An operationally simple and highly selective method for the decarboxylation of fatty acids under remarkably mild conditions is described herein. The activation of the aliphatic carboxylic acids by esterification with

The development of molecular and supramolecular optical devices for sensing ionic analytes in solution has emerged as a promissory field in the last decades. In this context, qualitative and quantitative analysis of metal cations based on chromogenic and fluorogenic chemosensors are particularly attractive, especially due to their successfully employment for biological and environmental purposes. In this work, the literature data associated to quinoxaline-based derivatives as chemosensors for metal cations in solution are comprehensively reviewed. Sensing mechanisms, detection limits, solvent effect, work concentration ranges, as well as examples of practical implementation are presented. We believe that the data compilation and pertinent discussion present in this survey should be of interest for researchers of heterocyclic-based chemosensors’ field.

Nucleophilic aromatic substitution (SNAr) is a class of reaction that has become very important over time. This type of transformation usually proceeds without the use of metal catalysts, making it very important for pharmaceutical and industrial purposes. Nevertheless, in order to obtain the desired substituted product, activated substrates are required to allow SNAr reactions under mild conditions. In this context, quinoxaline derivatives are one class of N-heteroarenes that has attracted great attention from the scientific community because of the large variety of applications for their derivatives in many fields, such as biological and technological areas. There are several reported methods for the synthesis of quinoxaline derivatives. Nonetheless, reactions of 2,3-dichloroquinoxaline (DCQX) with nucleophilic species has become a viable alternative because of the possibility to form new carbon-heteroatom bonds (e.g. CO, CN, and CS) directly at C2 and/or C3 positions of the quinoxaline moiety. This current review brings an overview of the last decade on the remarkable versatility of DCQX as a substrate for SNAr reactions. Herein, we show several examples in which DCQX reacts with N-, O-, S-, P- and C-nucleophiles, including controlled processes for the selective formation of mono- and disubstituted substrates. Almost all polyfunctionalized quinoxalines synthesized using this approach have shown applications in different areas such as in biological and technological fields. Keywords: 2,3-Dichloroquinoxaline, Building block, Heteroaromatic nucelophilic substitution, Organic synthesis

The one-pot synthesis of nine novel polyfunctionalized quinoxaline derivatives starting from l -ascorbic acid is described. Reaction products were obtained in moderate to good yields (65–84%) for an interesting scope of aldehydes after four synthetic transformations. Structural characterization of the molecules was performed by combined NMR (1H, 13C, DEPT-135 COSY and HSQC) techniques, infrared spectroscopy and theoretical calculations. Two selected target-compounds were evaluated as chromogenic chemosensors for ionic species in solution. One of the compounds was effective in the selective detection of Cu2+ in methanol-water 4:1 v/v solution. The other compound was applied as a chemosensor for F− in DMSO and aqueous DMSO solution. Binding mechanisms were proposed based on spectroscopic and theoretical data.

Self-assembly-based molecular structures have proven to be highly relevant to the development of soft materials. This work reports the synthesis, thermal behavior and computational analysis of two novel heterocyclic compounds with a non-symmetrical shape bearing a single long alkyl (C12) chain. The compounds 2-(4-dodecyloxy-phenyl)-1H-benzoimidazole, 1, with three-ring core mesogen with a more linear shape, and 1-dodecyl-1,4-dihydro-quinoxaline-2,3-dione, 2, with a condensed two-ring core with a more compact discotic shape, were obtained in good yields and investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) analysis. Benzimidazole derivative 1 was found to present liquid crystalline property, with a mesophase range from 85 to 177 °C, as verified by POM and DSC, with a smectogenic polymorphism assigned as a SmB and a more organized unidentified SmX phase. On the other hand, although quinoxaline 2 did not show liquid crystal behavior, POM analysis indicated an interesting spherulitic packing pattern, typical of a columnar arrangement of the molecules by possible H-bond interactions. Computational results indicated that combining intermolecular hydrogen bonds and hydrophobic interactions lead to a non-planar lamellar model for benzimidazole 1, consistent with the smectic packing found in the liquid crystalline phase and a twist-type packing for compound 2, which is consistent with a spherulitic model.

The development of nanoprobes for selective detection of metal ions in solution has attracted great attention due to their impact on living organisms. As a contribution to this field, this paper reports the synthesis of silver nanoparticles modified with rutin in the presence of ascorbic acid and their successful use as a chromogenic probe for the selective detection of Fe3+ in aqueous solution. Limits of detection and quantification were found to be 17 nmol L−1 and 56 nmol L−1, respectively. The sensing ability is proposed to proceed via an iron-induced nanoparticle growth/aggregation mechanism. A practical approach using image analysis for quantification of Fe3+ is also described.

Biothiols such as l-cysteine, l-homocysteine, and glutathione play essential roles in many biological processes, and are directly associated with several health conditions. Therefore, the development of fast, selective, sensitive, and inexpensive methods for quantitatively analyzing biothiols in aqueous solution, but especially in biological samples, is a very attractive research field. In this feature review, we have approached the relevance of biothiols' nucleophilicity to develop selective fluorogenic probes. Since biothiols have considerable structural similarity, relevant strategies are in full development, including several fluorescent molecular platforms, specific receptor sites, reaction conditions, and optical responses. All of these features are properly presented and discussed. Biothiol sensing protocols are based on traditional organic chemistry reactions such as (hetero)aromatic nucleophilic substitution, addition, and substitution at carbonyl carbon, conjugate addition, and nucleophilic substitution at saturated carbon, amongst others including combined processes; furthermore, mechanistic aspects are detailed herein, including some interesting historical contexts. The feasibility of related fluorogenic probes is illustrated by analysis in complex matrices such as serum, cells, tissues, and animal models. Applications of these reactions in more complex systems such as sulfhydryl-based peptides and proteins are also presented, aiming at functionalizing and detecting these nucleophiles. Most literature cited in this review is recent; however, some other prominent works are also detailed. It is believed that this review may be accessible for many academic levels and may efficiently contribute not only to popularizing science but also to the rational development of fluorogenic probes for biothiol sensing.

A multicomponent synthesis of substituted 3-styryl-1H-quinoxalin-2-ones is described. Sequential reactions of o-phenylenediamine with sodium pyruvate and aldehydes in 20% aqueous acetic acid containing sodium acetate provided the target products in good to high yields. The reaction is proposed to proceed via initial condensation of the diamine and pyruvate partners followed by an aldol condensation-type mechanism.

Herein we report the successful synthesis of stable silver nanoparticles (AgNPs) using 1,1′-(quinoxaline-2,3-diylbis(azanediyl))diethanol (QX) as the only stabilizer. The QX-AgNPs system was then employed as chromogenic probe for the selective detection of L -cysteine (Cys), Mg2+, and Sn2+ in the presence of interfering species. We discuss the role of pH for differentiation between Mg2+ and Sn2+ in terms of analyte-induced aggregation mechanisms. Limits of detection reached 2.7 nmol L−1, 15 nmol L−1 and 18 nmol L−1 for Cys, and Mg2+ and Sn2+, respectively, which are levels comparable to other reported probes. Concerning Mg2+, the LOD found in this study was the lowest ever reported. The QX-AgNPs were also successfully employed in the quantification of Cys in urine and Mg2+ in tap water.

The genus Callyspongia (Callyspongiidae) encompasses a group of demosponges including 261 described species, of which approximately 180 have been accepted after taxonomic reviews. The marine organisms of Callyspongia are distributed in tropical ecosystems, especially in the central and western Pacific, but also in the regions of the Indian, the West Atlantic, and the East Pacific Oceans. The reason for the interest in the genus Callyspongia is related to its potential production of bioactive compounds. In this review, we group the chemical information about the metabolites isolated from the genus Callyspongia, as well as studies of the biological activity of these compounds. Through NMR data, 212 metabolites were identified from genus Callyspongia (15 species and Callyspongia sp.), belonging to classes such as polyacetylenes, terpenoids, steroids, alkaloids, polyketides, simple phenols, phenylpropanoids, nucleosides, cyclic peptides, and cyclic depsipeptides. A total of 109 molecules have been reported with bioactive activity, mainly cytotoxic and antimicrobial (antibacterial and antifungal) action. Thus, we conclude that polyacetylenes, terpenoids and steroids correspond to the largest classes of compounds of the genus, and that future research involving the anticancer action of the species’ bioactive metabolites may become relevant.

The acidity of organic compounds is highly relevant to understanding several biological processes. Although the relevance and challenges in estimating pKa values of organic acids is recognized by several reported works in the literature, there is a lack in determining the acidity of amides. This paper presents an experimental/theoretical combined investigation on the acid dissociation of the compound 6,7-dinitro-1,4-dihydroquinoxaline-2,3-dione (DNQX), a well-established antagonist of ionotropic glutamate receptor GluA2. DNQX was synthesized, and its two acidic constants were determined by UV–vis spectroscopy. The experimental pKa of 6.99 ± 0.02 and 10.57 ± 0.01 indicate that DNQX mainly exists as an anionic form (DNQXA1) in physiological media, which was also confirmed by 1H NMR analysis. Five computational methods were applied for estimating the theoretical pKa values of DNQX, including B3LYP, M06-2X, ωB97XD, and CBS-QB3, which were able to provide reasonable estimates for pKa associated with DNQX. Mole...

The development of nanoprobes for selective detection of metal ions in solution has attracted great attention due to their impact on living organisms. As a contribution to this field, this paper reports the synthesis of silver nanoparticles modified with rutin in the presence of ascorbic acid and their successful use as a chromogenic probe for the selective detection of Fe

Quinoxaline derivatives have attracted considerable attention due to their vast range of applications that includes electroluminescence and biomedicine. Concerning the latter, the literature has shown that compounds with a quinoxaline motif bind quite efficiently to phosphatidylinositol-4,5-bisphosphate 3-kinases (PI3Ks), which are enzymes found to be overexpressed in some types of neoplasms. In the present study, gold nanoparticles (AuNPs) were easily functionalized with 2,3-diethanolminoquinoxaline (DEQX) and 2-(2,3-dihydro-[1,4]oxazino[2,3-b]quinoxalin-4-yl)ethanol (OAQX). We made use of glycerol in alkaline media as reducing agent and the quinoxalines served as capping ligands to stabilize the AuNPs. This is the first report on the modification of a nanostructure with quinoxalines. Functionalization confers nanoparticles the required specificity to target only cancer cells, which opens possibilities for phototherapy since the modified AuNPs would concentrate in the tumor tissue as a consequence of PI3Kα overexpression. Molecular dynamics simulations have shown that DEQX and OAQX are potential inhibitors of PI3Kα since they bind to the active site of the enzyme in a way similar to other known inhibitors.

Despite the fact that silver nanoparticles (AgNPs) have been widely studied in medical and correlated fields, details on their mechanisms are yet to be fully understood. Herein we present the first study on the combination of infrared spectroscopy and chemometrics as an analytical tool to investigate the mechanism of action of AgNPs against Escherichia coli by comparison with popular and commercially available antibiotics. The rationale behind this study is that the selected antibiotics act on bacteria in specific and distinct manners (DNA, cell membrane, mitochondria, etc.). Hence, via multivariate analysis we were able to compare the spectra of bacteria treated with the antibiotics and AgNPs to determine the main target of the latter. Spectral comparison, exploratory analysis, clustering and classification based on infrared spectra were carried out for E. coli samples in the absence and presence (treated) of four widely known antibiotics (ampicillin, ciprofloxacin, gentamicin and sulfadiazine) as well as RA-AgNPs and ERA-AgNPs. Chemometrics models indicated an interesting similarity between infrared spectra from E. coli treated with sulfadiazine and AgNPs, in which vibrational modes associated to phosphate groups were found to be the most representative. This result suggests that both AgNPs and sulfadiazine affects DNA structural features and availability, but not necessarily through the same mechanism. This biospectroscopy-based approach opens an interesting possibility for the understanding over the mechanism of antibacterial activity of AgNPs.

Detection of cationic species represents an important field due to its importance in biological and environmental processes. This communication shows the synthesis and application of an ascorbic acid-based quinoxaline derivative (1) in the colorimetric detection of Cu2 + against several other cationic species, including Sr2 +, Fe2 +, Pb2 +, Mn2 +, Mg2 +, Ni2 +, Zn2 +, Sn2 +, Hg2 +, Ca2 +, Ba2 +, Co2 +, Cr3 +, Al3 +, and Fe3 +. Based on experimental and theoretical results, a 1:2 binding model involving 1 and Cu2 + is proposed.

This paper presents a simple, fast and inexpensive way to measure serum protein content (albumin and total proteins) by integration of color images acquired with a cell phone camera and multiple linear regression (MLR). MLR models were built using the RGB-HSV image systems from the color changes induced by bromocresol green and Biuret methods on solutions containing albumin (0.24 to 5.03 g dL−1) and total proteins (0.25 to 8.20 g dL−1), respectively, acquired from a cell phone camera. These methods were adapted to a microscale analysis by using an ELISA 96-microwell plate of 250 μL as a reaction container, and subsequently were statistically validated. The RMSEP values obtained for albumin and total protein models were respectively equal to 0.28 and 0.12 g dL−1, and their precision was respectively equal to 6.16 and 4.85%. No statistical difference was observed at a confidence level of 95% between the protein concentration calculated by the proposed method and those found by the reference method, proving the reliability of the imaging method as an alternative approach for these assays.

Natural products-mediated synthesis has become quite an interesting route for the ecofriendly production of nanomaterials . However, products employed in natura may require long reaction times and high temperatures that lead to non-ideal particle-size distribution. In this work, we developed an optimized one-pot synthesis of silver nanoparticles using isolated ricinoleic acid (extracted from castor bean plant) and its epoxidized form as both reducer and stabilizer agents to convert silver ions into silver nanoparticles at room temperature. Through a design of experiments, we discovered that the epoxidized form of the ricinoleic acid is far more effective than its unmodified counterpart in terms of reaction time and homogeneity of nanoparticles. The silver nanoaparticles were then evaluated as functional chromogenic probes for cysteine sensing, allowing for direct naked-eye detection and a limit of detection of 25.37 μmol L −1. Cysteine sensing mechanisms are also discussed in this work. This approach reinforces the advantages in using purified natural products over their direct natural sources.

This paper presents a low-cost reflectometer for selective detection of Cu2+. The reflectometer is based on an emission light source using five light-emitting diodes at different wavelengths and a detector using a webcam. The samples were prepared using a filter paper-based colorimetric sensor with ascorbic acid-based quinoxaline derivative. Video analysis using gray color intensity was used to perform both copper ion screening (Cu2+, Pb2+, Cr+3, Ni2+, Fe2+, Sn2+, Mg2+, Cd2+, Ag+ and Co2+) and quantification of Cu2+ in spiked samples. In addition, a multivariate validation was performed. The system proved to be selective to Cu2+ among the screened ions, and its quantification was performed using partial least square regressions. Good linearity (R2 = 0.979, coefficient of determination), low root-mean-square error of prediction (RMSEP = 5.20 × 10-3 mol L-1) and high recovery (93.39-128.64%) were achieved. This method has potential to be employed for rapid and selective determination of Cu2+ in water using low-cost instrumentation.

The use of digital image analysis as an analytical tool is a reality nowadays, and the use of smartphones stands out due to its high accessibility and practicality. Ascorbic acid (AA) is a natural and essential vitamin available as a supplement as a result of its use in preventing and treating several pathologies. This paper reports a simple, fast and low cost method using smartphone image analysis for quantification of AA based on its interfering effect in the enzymatic colorimetric detection of glucose. Commercial vitamin C tablets were used as prediction set for AA quantification, showing very satisfactory results (relative errors < 4%), where no statistical difference at a 95% confidence level was observed between the AA content estimated by the imaging method and the labeled reference values. As advantages, this method does not use expensive reagents neither laborious procedures to carry out the analysis.

The inhibitory ability of an oxazinoquinoxaline derivative (OAQX) against the corrosion of AISI 1018 mild steel induced by aqueous 0.6 mol L-1 NaCl solution is herein evaluated. Linear polarization resistance studies showed the inhibitory efficiency of OAQX varying from 62.75% to 75.93% with OAQX concentration ranged from 0.259 x 10-4 mol L-1 to 3.243 x 10-4 mol L-1. Aiming at to investigate the Tafel curves on the OAQX electrochemical behavior at saline (0.6 mol L-1 NaCl) aqueous media the linear Tafel segments of anodic and cathodic curves were extrapolated to the intersection point which afforded corrosion potential (Ecorr) and corrosion current density (icorr) data. By applying Tafel approach the efficiency of OAQX ranges from 55.30% to 87.60%. In both analysis Langmuir isotherm lead to optimized adsorption parameter. The adsorption mechanism of OAQX is proposed from FTIR experiments and quantum calculations. The theoretical employed method is hybrid B3LYP combined with 6-311++G(d,p). Theoretical results showed OAQX as a promising inhibitor that form a stable protective metal-ligand film on metal surfaces, and differs from several heterocyclic compounds due to its solubility in small amount of DMSO (0.627 x 10-4 mol L-1) which is resistant to a saline aqueous media (0.6 mol L-1 NaCl).

Bioorganic and biological chemistry have been found to be highly motivating to undergraduate students and in this context, biochemical blood parameter analysis emerges as highly attractive content. In this proposal, several aspects related to analyses of glucose, cholesterol and triglycerides using the enzymatic colorimetric method were involved, and the findings have at least two relevant implications: i) introducing students to connections between organic chemistry and biology based on enzymatic processes, including reactivity and mechanistic aspects; ii) performing a micro scale bioassay analysis. The proposal requires two theoretical classes (2 h per class) and one practical class (4 h).

Polar microemulsion systems (SME) based on saponified coconut oil (OCS) as surfactant were prepared in order to increase the solubility of the heterocycle isatin (IST) aiming at its application as corrosion inhibitor against AISI 1020 mild steel, in saline medium. The adsorptions phenomena of the tested SME systems (SME-OCS1-IST and SME-OCS2-IST) in the liquid/gas interface were evaluated by surface tension measurements which do not show significant differences in the presence of ion Cl-. The free energy values of the micellization proved the occurrence of spontaneous process. The corrosion inhibition effectiveness of SME-OCS2, SME-OCS1-IST and SME-OCS2-IST samples was evaluated in 0.5% aqueous NaCl using voltammetry linear scan method (LPR). The maximum efficiency findings were 73.2% for SME-OCS2, 88.2% for SME-OCS2-IST and 97.6% for SME-OCS1-IST. The spontaneity of the adsorption phenomena was also observed in the liquid/metal interface by analyzes of the adsorption free energy. In addition, since computational calculations have been found as a very relevant tool in the corrosion field, a theoretical study was performed in attempt to give support to the observed experimental results, in which B3LYP and 6-311++G(d,p) were applied aiming at investigation of geometry, electronic density aspects, HOMO-LUMO energy gap, as well as the binding between isatin and metal surface.