Dihydroxy Derivatives Research Articles

Studies on Nitrogen Rich Benzoxazines Containing Schiff Base for Optical, Aggregation Induced Emission and Anti-Microbial Applications

ABSTRACT Dihydroxy derivative of vanillin-based diaminotriazole core monomer (DTV) has been synthesized using sustainable vanillin (V) and 3,5-diamino-1,2,4-triazole (DT) under appropriate experimental conditions and characterized with a view to develop Schiff base core nitrogen-rich benzoxazines capable of exhibiting excellent optical and anti-microbial properties. The monomer DTV has been subsequently converted into benzoxazines separately using six structurally varied amino compounds, viz. aniline (a), 1-(−2-aminoethyl)piperazine (aep), furfurylamine (ffa), 4-H-1,2,4-triazoal-4-amine (ta), 3-aminopyrazol (apy) and 1-(3-aminopropyl)imidazole (api) with paraformaldehyde through Mannich condensation. The corresponding Schiff base based benzoxazines, viz. DTV-a, DTV-aep, DTV-ffa, DTV-ta, DTV-apy and DTV-api were synthesized and characterized for their molecular structure, thermal stability, optical, hydrophobic and anti-microbial properties using different analytical techniques and methods. Data obtained from different analyses for DTV based benzoxazines can be used for wide range of industrial and engineering applications.

Pseudomonas aeruginosa quorum sensing and biofilm attenuation by a di-hydroxy derivative of piperlongumine (PL-18)

Bacterial communication, Quorum Sensing (QS), is a target against virulence and prevention of antibiotic-resistant infections. 16 derivatives of Piperlongumine (PL), an amide alkaloid from Piper longum L., were screened for QS inhibition. PL-18 had the best QSI activity. PL-18 inhibited the lasR-lasI, rhlR-rhlI, and pqs QS systems of Pseudomonas aeruginosa. PL-18 inhibited pyocyanin and rhamnolipids that are QS-controlled virulence elements. Iron is an essential element for pathogenicity, biofilm formation and resilience in harsh environments, its uptake was inhibited by PL-18. Pl-18 significantly reduced the biofilm biovolume including in established biofilms. PL-18-coated silicon tubes significantly inhibited biofilm formation. The transcriptome study of treated P. aeruginosa showed that PL-18 indeed reduced the expression of QS and iron homeostasis related genes, and up regulated sulfur metabolism related genes. Altogether, PL-18 inhibits QS, virulence, iron uptake, and biofilm formation. Thus, PL-18 should be further developed against bacterial infection, antibiotic resistance, and biofilm formation.

Anticancer Effect of PtIIPHENSS, PtII5MESS, PtII56MESS and Their Platinum(IV)-Dihydroxy Derivatives against Triple-Negative Breast Cancer and Cisplatin-Resistant Colorectal Cancer.

Development of resistance to cisplatin, oxaliplatin and carboplatin remains a challenge for their use as chemotherapies, particularly in breast and colorectal cancer. Here, we compare the anticancer effect of novel complexes [Pt(1,10-phenanthroline)(1S,2S-diaminocyclohexane)](NO3)2 (PtIIPHENSS), [Pt(5-methyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)](NO3)2 (PtII5MESS) and [Pt(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)](NO3)2 (PtII56MESS) and their platinum(IV)-dihydroxy derivatives with cisplatin. Complexes are greater than 11-fold more potent than cisplatin in both 2D and 3D cell line cultures with increased selectivity for cancer cells over genetically stable cells. ICP-MS studies showed cellular uptake occurred through an active transport mechanism with considerably altered platinum concentrations found in the cytoskeleton across all complexes after 24 h. Significant reactive oxygen species generation was observed, with reduced mitochondrial membrane potential at 72 h of treatment. Late apoptosis/necrosis was shown by Annexin V-FITC/PI flow cytometry assay, accompanied by increased sub-G0/G1 cells compared with untreated cells. An increase in S and G2+M cells was seen with all complexes. Treatment resulted in significant changes in actin and tubulin staining. Intrinsic and extrinsic apoptosis markers, MAPK/ERK and PI3K/AKT activation markers, together with autophagy markers showed significant activation of these pathways by Western blot. The proteomic profile investigated post-72 h of treatment identified 1597 MDA-MB-231 and 1859 HT29 proteins quantified by mass spectroscopy, with several differentially expressed proteins relative to no treatment. GO enrichment analysis revealed a statistically significant enrichment of RNA/DNA-associated proteins in both the cell lines and specific additional processes for individual drugs. This study shows that these novel agents function as multi-mechanistic chemotherapeutics, offering promising anticancer potential, and thereby supporting further research into their application as cancer therapeutics.

Metabolic Engineering of Yarrowia lipolytica for Zeaxanthin Production.

Zeaxanthin is a carotenoid, a dihydroxy derivative of β-carotene. Zeaxanthin has antioxidant, anti-inflammatory, anticancer, and neuroprotective properties. In this study, Yarrowia lipolytica was used as a host for the efficient production of zeaxanthin. The strain Y. lipolytica PO1h was used to construct the following engineered strains for carotenoid production since it produced the highest β-carotene among the Y. lipolytica PO1h- and Y. lipolytica PEX17-HA-derived strains. By regulating the key nodes on the carotenoid pathway through wild and mutant enzyme comparison and successive modular assembly, the β-carotene concentration was improved from 19.9 to 422.0 mg/L. To provide more precursor mevalonate, heterologous genes mvaE and mvaSMT were introduced to increase the production of β-carotene by 27.2% to the yield of 536.8 mg/L. The β-carotene hydroxylase gene crtZ was then transferred, resulting in a yield of zeaxanthin of 326.5 mg/L. The oxidoreductase RFNR1 and CrtZ were then used to further enhance zeaxanthin production, and the yield of zeaxanthin was up to 775.3 mg/L in YPD shake flask.

Information potential of an ubiquitous phytochemical cue.

This article is a Commentary on Li et al. (2023), 238: 2099–2112.

Carbonylation of Polyfluorinated 1-Arylalkan-1-ols and Diols in Superacids.

We describe the carbonylation of a series of mono and dihydroxy derivatives of polyfluorinated alkylbenzenes and benzocycloalkenes with OH groups at benzylic positions using carbon monoxide in the presence of a superacid (TfOH, a TfOH-SbF5 mixture, or a FSO3H-SbF5 mixture). It was shown that the superacid-catalyzed addition of CO to various primary and secondary polyfluorinated alcohols and diols gives the corresponding mono- and dicarboxylic acids or lactones. The efficiency of various superacids depending on alcohol structure was evaluated, and FSO3H-SbF5 yielded the best results in most transformations. The addition of CO to secondary 1-arylalkan-1-ols containing vicinal fluorine atoms was found to be accompanied by elimination of HF with the formation of α,β-unsaturated aryl-carboxylic acids. In contrast to primary and secondary alcohols, conversion of tertiary perfluoro-1,1-diarylalkan-1-ols into carbonylation products is not complete, and the resulting carboxylic acids are easily decarboxylated after water treatment of the reaction mixture.

Isolation and characterization of carpaine and dihydroxy derivative of carpaine from leaves of Carica papaya: Development of fast HPLC method and standardization of formulations

Carpaine, a major alkaloid of Carica papaya leaves, is widely studied for its anti-thrombocytopenic activity. The objective of present work was to isolate carpaine from dried leaves of Carica papaya. Isolation of carpaine was carried out by solvent extraction techniques followed by column chromatography by gradient elution using dichloromethane: methanol (80:20, v/v) as eluent. Dihydroxy derivative of carpaine was also identified for the first time from leaves of Carica papaya. Structures of carpaine and dihydroxy derivative of carpaine were confirmed by LC-MS/MS followed by IR studies. Fast HPLC method was developed using Sunniest C18 column (150 mm × 4.6 mm) as stationary phase and water (pH 8.5): acetonitrile (60: 40, v/v) as mobile phase at flow rate of 1.0 mL/min. Carpaine was eluted with mean retention time of 6.017 min. The developed HPLC method was used to estimate carpaine in extract and marketed formulations containing Carica papaya leaves.

Search for new antimicrobials: spectroscopic, spectrometric, and in vitro antimicrobial activity investigation of Ga(III) and Fe(III) complexes with aroylhydrazones.

The in vitro antimicrobial activity of Fe(III) and Ga(III) complexes with N'-(2,3-dihydroxy-phenylmethylidene)-3-pyridinecarbohydrazide (H2L1), N'-(2,4-dihydroxy-phenyl-methylidene)-3-pyridinecarbohydrazide (H2L2), N'-(2,5-dihydroxy-phenylmethylidene)-3-pyridinecarbohydrazide (H2L3), N'-(2-hydroxy-3-methoxyphenyl-methylidene)-3-pyridine-carbohydrazide (H2L4), N'-(2-hydroxy-4-methoxyphenylmethyl-idene)-3-pyridine-carbohydrazide (H2L5), and N'-(2-hydroxy-5-methoxyphenylmethylidene)-3-pyridinecarbo-hydrazide (H2L6) toward several Gram-positive strains of Staphylococcus aureus, a Gram-negative strain of Escherichia coli, and a yeast Candida albicans were investigated. Fe(III)-complexes do not possess antimicrobial activity against all tested strains at concentrations up to 10mgmL-1. Ga(III) complexes with dihydroxy derivatives showed selective activity, while the broadest range of antibacterial and antifungal activities was observed for complex with 2-hydroxy-3-methoxy-derivative, ligand H2L5. In addition, the coordination properties of ligands H2L1-H2L3 in solution were investigated by UV-Vis spectroscopy. The stability constants (logK) for Ga(III)-H2L 1:1 complexes in MeOH/H2O 1/1 at pH 2.52 were determined, and amounted to 5.8, 5.68, and 4.7, respectively. Detailed characterization of complexes was performed by high-resolution mass spectrometry. The fragmentation pathways for dimer [Fe2(L1)2]2+, [Fe(HL)2]+, [Ga(HL2)2]+ and adduct ions are given. The comparison with analogue Ga(III) and Fe(III) complexes with compounds H2L4-H2L6 was made as well.

Hydroxylation of Progesterone and Its Derivatives by the Entomopathogenic Strain Isaria farinosa KCh KW1.1.

Progesterone biotransformation is worth studying because of the high industrial value of its derivatives. This study investigated the catalytic ability of the entomopathogenic filamentous fungus strain Isaria farinosa KCh KW1.1 to transform progesterone derivatives: 11α-hydroxyprogesterone, 17α-hydroxyprogesterone, 16α,17α-epoxyprogesterone and pregnenolone. In the culture of Isaria farinosa KCh KW1.1, 11α-hydroxyprogesterone was effectively transformed into only one product: 6β,11α-dihydroxyprogesterone. Transformation of 17α-hydroxyprogesterone gave three hydroxy derivatives: 6β,17α-dihydroxyprogesterone, 12β,17α-dihydroxyprogesterone and 6β,12β,17α-trihydroxyprogesterone. Two products: 6β-hydroxy-16α,17α-epoxyprogesterone and 6β,11α-dihydroxy-16α,17α-epoxyprogesterone, were obtained from the 16α,17α-epoxyprogesterone transformation. We isolated two compounds from the biotransformation medium with pregnenolone: 11α-hydroxy-7-oxopregnenolone and 5α,6α-epoxy-3β,11α-dihydroxypregnan-7,20-dione. In this study, we observed only mono- and dihydroxy derivatives of the tested substrates, and the number of obtained products for each biotransformation did not exceed three.

Hexokinase 2 Inhibition and Biological Effects of BNBZ and Its Derivatives: The Influence of the Number and Arrangement of Hydroxyl Groups.

Hexokinase 2 (HK2), an enzyme of the sugar kinase family, plays a dual role in glucose metabolism and mediating cancer cell apoptosis, making it an attractive target for cancer therapy. While positive HK2 expression usually promotes cancer cells survival, silencing or inhibiting this enzyme has been found to improve the effectiveness of anti-cancer drugs and even result in cancer cell death. Previously, benitrobenrazide (BNBZ) was characterized as a potent HK2 inhibitor with good anti-cancer activity in mice, but the effect of its trihydroxy moiety (pyrogallol-like) on inhibitory activity and some cellular functions has not been fully understood. Therefore, the main goal of this study was to obtain the parent BNBZ (2a) and its three dihydroxy derivatives 2b–2d and to conduct additional physicochemical and biological investigations. The research hypothesis assumed that the HK2 inhibitory activity of the tested compounds depends on the number and location of hydroxyl groups in their chemical structure. Among many studies, the binding affinity to HK2 was determined and two human liver cancer cell lines, HepG2 and HUH7, were used and exposed to chemicals at various times: 24 h, 48 h and 72 h. The study showed that the modifications to the structures of the new BNBZ derivatives led to significant changes in their activities. It was also found that these compounds tend to aggregate and exhibit toxic effects. They were found to contribute to: (a) DNA damage, (b) increased ROS production, and (c) disruption of cell cycle progression. It was observed that, HepG2, occurred much more sensitive to the tested chemicals than the HUH7 cells; However, regardless of the used cell line it seems that the increase in the expression of HK2 in cancer cells compared to normal cells which have HK2 at a very low level, is a serious obstacle in anti-cancer therapy and efforts to find the effective inhibitors of this enzyme should be intensified.

Structure-Antioxidant Capacity Relationships of the Dihydroxy Derivatives of Benzaldehyde and Benzoic Acid

In this paper, the antioxidant capacities (AOC) of the dihydroxybenzaldehyes (DHB) and dihydroxybenzoic acids (DHBA) are determined by two single electron transfer (SET) assays, namely CUPRAC and e-CUPRAC (CUPric Reducing Antioxidant Capacity), and a SET + hydrogen atom transfer (HAT) assay: 2,2-diphenyl-1-picrylhydrazyl (DPPH). It is found that the oxidation potential (EOX) determined by voltammetry can be used as a structural parameter in the same way as the HOMO energy. From the dependencies of the AOC with EOX, it follows that only the electrondonor derivatives of DHB and DHBA exhibit antioxidant activity, which means that the number of hydroxyl groups, two for all molecules, is not the only factor related to the AOC. A relationship between the position of the hydroxyl groups and the AOC is shown. Moreover, the value of the AOC also has a contribution of dissociation of the hydroxyl groups.

New macrocycles incorporating glycolipids via copper-catalyzed triazole coupling

A series of new macrocycles based on alkyl glycosides derived from D-glucose and D-galactose was synthesized. The macrocycles were easily obtained by the reaction of dialkynyl derivatives with diazides via copper-catlyzed 1,3-cycloaddition reaction. Simple protecting group strategies were applied to obtain the vicinal dihydroxy derivatives, followed by Williamson etherification with propargyl bromides to get the dialkynyl derivatives. These derivatives were subjected to 1,3-Hüisgen triazole coupling with diazides furnishing the macrocycles in good yields. The 1,3-Hüisgen reaction used to build these macrocycles was investigated thoroughly with respect to reaction time, catalysts, solvents, and temperature for optimum macrocyclisation.

Characterization of Non-volatile Oxidation Products Formed from Triolein in a Model Study at Frying Temperature.

Frying allows cooking food while promoting their organoleptic properties, imparting crunchiness and flavor. The drawback is the oxidation of triacylglycerides (TAGs), leading to the formation of primary oxidized TAGs. Although they have been associated with chronic and degenerative diseases, they are precursors of pleasant flavors in fried foods. Nevertheless, there is a lack of knowledge about the oxidation species present in foods and their involvement in positive/negative health effects. In this work, high-resolution (HR) C30 reversed-phase (RP)-liquid chromatography (LC)-tandem HR mass spectrometry (MS/MS) was used to identify primary oxidation TAGs resulting from heating triolein (160 °C, 5 min). This allows simulating the initial heating process of frying oils usually used to prepare fried foods, such as chips, crisps, and snacks. Beyond hydroxy, dihydroxy, hydroperoxy, and hydroxy-hydroperoxy derivatives, already reported in phospholipids oxidized by Fenton reaction, new compounds were identified, such as dihydroxy-hydroperoxy-triolein derivatives and positional isomers (9/10- and 9/12-dihydroxy-triolein derivatives). These compounds should be considered when proposing flavor formation pathways and/or mitigating lipid-derived reactive oxygen species occurring during food frying.

Eicosanoids

This article describes the pathways of eicosanoid synthesis, eicosanoid receptors, the action of eicosanoids in different physiological systems, the roles of eicosanoids in selected diseases, and the major inhibitors of eicosanoid synthesis and action. Eicosanoids are oxidised derivatives of 20-carbon polyunsaturated fatty acids (PUFAs) formed by the cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (cytP450) pathways. Arachidonic acid (ARA) is the usual substrate for eicosanoid synthesis. The COX pathways form prostaglandins (PGs) and thromboxanes (TXs), the LOX pathways form leukotrienes (LTs) and lipoxins (LXs), and the cytP450 pathways form various epoxy, hydroxy and dihydroxy derivatives. Eicosanoids are highly bioactive acting on many cell types through cell membrane G-protein coupled receptors, although some eicosanoids are also ligands for nuclear receptors. Because they are rapidly catabolised, eicosanoids mainly act locally to the site of their production. Many eicosanoids have multiple, sometimes pleiotropic, effects on inflammation and immunity. The most widely studied is PGE2. Many eicosanoids have roles in the regulation of the vascular, renal, gastrointestinal and female reproductive systems. Despite their vital role in physiology, eicosanoids are often associated with disease, including inflammatory disease and cancer. Inhibitors have been developed that interfere with the synthesis or action of various eicosanoids and some of these are used in disease treatment, especially for inflammation.

Synthesis, Structural Analysis, and Functional Group Interconversion in the [closo‐B10H8‐1,10‐X2]2– (X = CN, [OCRNMe2]+, OCOR, and [OH2]+) Derivatives

Derivatives [closo‐B10H8‐1,10‐(CN)2]2– and [closo‐B10H8‐1,10‐(OCHNMe2)2], efficiently obtained from [closo‐B10H8‐1,10‐(IPh)2] by nucleophilic substitution with CN– and DMF, were envisioned as precursors to diacid [closo‐B10H8‐1,10‐(COOH)2]2– and to dihydroxy derivative [closo‐B10H8‐1,10‐(OH)2]2–, respectively. Attempts at hydrolysis or reduction of the dinitrile gave no reaction or complex mixtures of products. In contrast, the DMF adduct was cleanly hydrolyzed to diformate [closo‐B10H8‐1,10‐(OCHO)2]2– and subsequently to protonated dihydroxy [closo‐B10H8‐1,10‐(OH2)2]. The latter was O‐acylated with PhCOCl. Crystal and molecular structures of five derivatives were established by single crystal XRD methods and compared to those for other [closo‐B10H8‐1,10‐X2]2– derivatives. Trends in molecular geometry in the series and also reactivity of the dinitrile and intermediates were corroborated and correlated with DFT results (B3LYP/TZVP) by analysis of bonding, charge distribution and vibrational frequencies.

Pro-oxidative and antioxidant effects of salicylates

The antioxidant or pro-oxidant properties of dihydroxybenzoic acid (DHBA) derivatives, salicylates, as well as the standard antioxidant compound trolox, were evaluated for inhibition or promotion of the selected reactive oxygen and nitrogen species (O2·−, ·OH, NO, ONO2−) under physiological conditions (pH value 7.4) and at five concentrations (5 to 100 μg ml−1). Tests were also carried out on their ability to influence the antioxidant system on isolated liver mitochondria. According to the findings, selected salicylic acid dihydroxy derivatives do not exhibit significant scavenging activity towards O2·; nor do they differ greatly in activity against ·OH (~ − 6–34%). By comparing their scavenging capabilities with the activity of selected enzyme antioxidants and the concentration of reduced glutathione, 2,5- and 3,4-DHBA in particular are considered able to modulate H2O2 concentrations and thus mediate signalling pathways. The effects on NO were much more pronounced (~ 14–78%) with 2,6-DHBA and 3,5-DHBA causing a decrease in NO inhibitory activity together with ONO2− overproduction. This leads to the prediction that they may act as selective effectors of NO levels. In summary, we can say that selected salicylic acid dihydroxy derivatives predominantly interfere with redox homeostasis by reactions with ·OH and NO.

Methylene Oxidation of Alkyl Sulfates by Cytochrome P450BM-3 and a Role for Conformational Selection in Substrate Recognition.

Cytochrome P450BM-3 (P450BM-3) is a flavoprotein reductase-heme fusion protein from the bacterium Bacillus megaterium that has been well-characterized in many biophysical aspects. Although the enzyme is known to catalyze the hydroxylation of medium and long-chain fatty acids at high rates, no definitive physiological function has been associated with this process in the organism other than a possible protective role. We found that P450BM-3 rapidly hydroxylates alkyl sulfates, particularly those with 12-16 carbons (i.e., including dodecyl sulfate) in a similar manner to the fatty acids. The products were characterized as primarily ω-1 hydroxylated alkyl sulfates (plus some ω-2 and ω-3 hydroxylation products), and some further oxidation to dihydroxy and keto derivatives also occurred. Binding of the alkyl sulfates to P450BM-3 converted the iron from the low-spin to high-spin form in a saturable manner, consistent with the catalytic results. Rates of binding decreased as a function of increasing concentration of dodecyl sulfate or the fatty acid myristate. This pattern is consistent with a binding model involving multiple events and with conformational selection (equilibrium of the unbound enzyme prior to binding) instead of an induced fit mechanism. Neither C-H bond-breaking nor product release was found to be rate-limiting in the oxidation of lauric acid. The conformational selection results rationalize some known crystal structures of P450BM-3 and can help explain the flexibility of P450BM-3 and engineered forms in accepting a great variety of substrates.

Formation of HETE-EAs and dihydroxy derivatives in mouse kidney tissue and analysis by high-performance liquid chromatography tandem mass spectrometry

The kidneys play an important role in the long-term regulation of blood pressure by control of salt and water balance in the body through various systems including the endocannabinoid system. The endocannabinoid system consists of the two major cannabinoid receptor agonists, anandamide (AEA) and 2-arachidonylglycerol (2-AG), their hydrolyzing enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), and the cannabinoid receptors, CB1 and CB2. AEA can be converted into 12- and 15(S)-hydroperoxyeicosatetraenoic acid ethanolamides by 12-LOX and 15-LOX, respectively and can form epoxyeicosatrienoic acid- (EET-EAs) (5,6-, 8,9-, 11,12-, 14,15-) and hydroxyeicosatetraenoic acid- (HETE) ethanolamides. Furthermore, the EET-EAs produce a secondary metabolism by microsomal epoxide hydrolase to form the corresponding dihydroxyeicosatetraenoic acid-EAs (DiHETE-EA). Reference material was not available for DiHETE-EA. These metabolites were synthesized by incubation of the corresponding EET-EAs with mouse liver cytosol containing epoxide hydrolases. Presented is a solid phase extraction and high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) for the extraction and quantitation of AEA, 2-AG, their metabolites, oleoylethanolamide (OEA), and palmitoylethanolamide (PEA), and the in vivo formation of the DiHETE-EAs in kidney after a single intravenous bolus administration of 20 mg/kg of anandamide in C57BL/6 J and FAAH KO mice.

Development of a liquid chromatography Q Exactive high resolution mass spectrometry method by the Box-Behnken design for the investigation of sibutramine urinary metabolites

Sibutramine is cited by the World Anti-Doping Agency as a stimulant. According to the literature, sibutramine is extensively metabolized into N-desmethyl-sibutramine (M1), N-bisdesmethyl-sibutramine (M2) and monohydroxy derivatives of M1 and M2. Therefore, it is important to verify new sibutramine metabolites through current analytical methodologies, such as liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS). Furthermore, the development of a comprehensive approach to investigate sibutramine metabolism can increase the detection window for stimulant misuse and enable advancements in pharmacological studies. This work aimed to develop and evaluate the performance of an LC-HRMS method applying Design of Experiments (DoE) for sibutramine metabolite analysis in human urine. After optimizing the method by DoE, the final chromatographic conditions were based on reversed-phase chromatography using a C18 column with a ramp time of 25 min, a flow rate of 0.17 mL min−1 and a temperature of 50 °C. Mobile phase A consisted of water with 0.1% formic acid and 5 mM ammonium formate, and mobile phase B consisted of methanol with 0.1% formic acid; the initial gradient percent was 15% B, and the injection volume was 5 μL. In addition to the hydroxylated metabolites previously described in human urine, dihydroxy derivatives of M1 and M2 were observed for the first time. These dihydroxy derivative metabolites can be applied as new targets for doping control.

Relationships between chemical properties of the dihydroxy derivatives of benzaldehyde and benzoic acid and HOMO energies using electrochemical measurements

The possible relationships between the HOMO energies and chemical properties (acid dissociation constants) is explored for the dihydroxybenzaldehydes (DHBs) and dihydroxy benzoic acids (DHBAs). The pK values are obtained by UV–visible spectroscopy, except for 2,6DHBA for which the pK was determined by electrochemical measurements. Cyclic voltammograms of the different compounds showed the occurrence of reversible or quasi-reversible processes, for half of the derivatives, and irreversible oxidations for the rest. From the pH dependence of the peak potentials of the oxidation peaks, the differences of the peak potentials of the dissociated and undissociated species were obtained in the same conditions of pH, buffer solution and ionic strength. These differences, showed good correlations with the values of pK, being the correlation for the aldehydes more reliable than that observed for the acids. It was concluded that the oxidation peak potentials in solution can be related to the HOMO energies. A relation between structure and chemical reactivity is proved for these derivatives.