In-Silico Investigation of Luminol, Its Analogues and Improved Mechanism of Chemiluminescence for Blood Identification Beyond Forensics

ABSTRACTThis study aimed to discover chemiluminescent analogues of luminol, understand their molecular binding to hemoglobin of bloodstains in the household crime, and the mechanism of chemiluminescence. Similarity and clustering analyses of luminol analogues were conducted, and molecular docking was carried out on hemoglobin from Homo sapiens and other four domestic organism namely Gallus gallus, Drosophila melanogaster, Rattus norvegicus, and Canis familiaris. The results show that the order of overall binding score is D. melanogaster > H. sapiens > C. familiaris > R. norvegicus > G. gallus. Seven compounds namely ZINC16958228, ZINC17023010, ZINC19915427, ZINC34928954, ZINC19915369, ZINC19915444, and ZINC82294978, were found to be consistently stable in binding to diverse hemoglobin and possibly have chemiluminescence than luminol. The amino acid residues involved in the interaction of human hemoglobin with the 30 test compounds, show that His45, Lys61, Asn68, Val73, Met76, Pro77, Ala79, Ala82, Leu83, Pro95, Phe98, Lys99, Ser102, Ser133, Ala134, and Thr134 are significant in the mechanism of action of presumptive test compounds. The improved mechanism of chemiluminescent identification of blood hypothesized that nitrite interact with the Fe(II) heme, with the cleavage of a hydroxide ion and the formation of the nitrosonium cation in peroxidase reaction. It was proposed that degradation of rhombic heme complex to fluorescent products is possibly inhibited by nitric oxide from the test compound luminol. This study provides novel insight on the luminol and its actual mechanism for broader possible applications of luminol with careful development of new methodologies.

Detailed mechanistic investigation into the S-nitrosation of cysteamine

The nitrosation of cysteamine (H2NCH2CH2SH) to produce cysteamine-S-nitrosothiol (CANO) was studied in slightly acidic medium by using nitrous acid prepared in situ. The stoichiometry of the reaction was H2NCH2CH2SH + HNO2 → H2NCH2CH2SNO + H2O. On prolonged standing, the nitrosothiol decomposed quantitatively to yield the disulfide, cystamine: 2H2NCH2CH2SNO → H2NCH2CH2S–SCH2CH2NH2 + 2NO. NO2 and N2O3 are not the primary nitrosating agents, since their precursor (NO) was not detected during the nitrosation process. The reaction is first order in nitrous acid, thus implicating it as the major nitrosating agent in mildly acidic pH conditions. Acid catalyzes nitrosation after nitrous acid has saturated, implicating the protonated nitrous acid species, the nitrosonium cation (NO+) as a contributing nitrosating species in highly acidic environments. The acid catalysis at constant nitrous acid concentrations suggests that the nitrosonium cation nitrosates at a much higher rate than nitrous acid. Bimolecular rate constants for the nitrosation of cysteamine by nitrous acid and by the nitrosonium cation were deduced to be 17.9 ± 1.5 (mol/L)–1 s–1 and 6.7 × 104 (mol/L)–1 s–1, respectively. Both Cu(I) and Cu(II) ions were effective catalysts for the formation and decomposition of the cysteamine nitrosothiol. Cu(II) ions could catalyze the nitrosation of cysteamine in neutral conditions, whereas Cu(I) could only catalyze in acidic conditions. Transnitrosation kinetics of CANO with glutathione showed the formation of cystamine and the mixed disulfide with no formation of oxidized glutathione (GSSG). The nitrosation reaction was satisfactorily simulated by a simple reaction scheme involving eight reactions.

Protein disulfide-isomerase mediates delivery of nitric oxide redox derivatives into platelets

S-nitrosothiol compounds are important mediators of NO signalling and can give rise to various redox derivatives of NO: nitrosonium cation (NO+), nitroxyl anion (NO−) and NO• radical. Several enzymes and transporters have been implicated in the intracellular delivery of NO from S-nitrosothiols. In the present study we have investigated the role of GPx (glutathione peroxidase), the L-AT (L-amino acid transporter) system and PDI (protein disulfide-isomerase) in the delivery of NO redox derivatives into human platelets. Washed human platelets were treated with inhibitors of GPx, L-AT and PDI prior to exposure to donors of NO redox derivatives (S-nitrosoglutathione, Angeli's salt and diethylamine NONOate). Rapid delivery of NO-related signalling into platelets was monitored by cGMP accumulation and DAF-FM (4-amino-5-methylamino-2′7′-difluorofluorescein) fluorescence. All NO redox donors produced both a cGMP response and DAF-FM fluorescence in target platelets. NO delivery was blocked by inhibition of PDI in a dose-dependent manner. In contrast, inhibition of GPx and L-AT had only a minimal effect on NO-related signalling. PDI activity is therefore required for the rapid delivery into platelets of NO-related signals from donors of all NO redox derivatives. GPx and the L-AT system appeared to be unimportant in rapid NO signalling by the compounds used in the present study. This does not, however, exclude a possible role during exposure of cells to other S-nitrosothiol compounds, such as S-nitrosocysteine. These results further highlight the importance of PDI in mediating the action of a wide range of NO-related signals.