Tigerinins: novel antimicrobial peptides from the Indian frog Rana tigerina

Four broad-spectrum, 11 and 12 residue, novel antimicrobial peptides have been isolated from the adrenaline-stimulated skin secretions of the Indian frog Rana tigerina. Sequences of these peptides have been determined by automated Edman degradation, by mass spectral analysis and confirmed by chemical synthesis. These peptides, which we have named as tigerinins, are characterized by an intramolecular disulfide bridge between two cysteine residues forming a nonapeptide ring. This feature is not found in other amphibian peptides. Conformational analysis indicate that the peptides tend to form β-turn structures. The peptides are cationic and exert their activity by permeabilizing bacterial membranes. Tigerinins represent the smallest, nonhelical, cationic antimicrobial peptides from amphibians

Chiral discrimination of α-amino acids by the DNA triplet GCA

The DNA triplet GCA is successfully used for the first time as a chiral selector for the chiral discrimination and optical purity measurement of some α-amino acids by investigating the collision-induced dissociation spectra of the sodiated ternary complex ion formed by electrospray ionization

Photophysics of ruthenium(II) complexes carrying amino acids in the ligand 2,2'-bipyridine and intramolecular electron transfer from methionine to photogenerated Ru(III)

New ruthenium(II) complexes carrying methionine and phenylalanine in the bipyridine ligand, [Ru(bpy)2(4-Me-4'-(CONH-l-methionine methyl ester)-2,2'-bipyridine)](PF6)2 (IV) and [Ru(bpy)2(4-Me-4'-(CONH-l-phenylalanine ethyl ester)-2,2'-bpy)](PF6)2 (V) have been synthesized and characterized and their photophysical properties studied. Flash photolysis measurements of complex IV, in the presence of an electron acceptor, methyl viologen (MV2+) show that an intermolecular electron transfer from the excited state of Ru(II) in complex IV, to MV2+ takes place, forming Ru(III) and the methyl viologen cation radical, MV+. The formation of MV+ in this system is confirmed using time-resolved transient absorption spectroscopy. This intermolecular electron transfer is followed by intramolecular electron transfer from the thioether moiety (methionine) to the photogenerated Ru(III), regenerating Ru(II). Graphical abstract New ruthenium(II) complexes carrying methionine and phenylalanine in the bipyridine ligand, [Ru(bpy)2(4-Me-4'-(CONH-l-methionine methyl ester)-2,2'-bipyridine)](PF6)2 (IV) and [Ru(bpy)2(4-Me-4'-(CONH-l-phenylalanine ethyl ester)-2,2'-bpy)](PF6)2 (V) have been synthesized and characterized and their photophysical properties studied. Flash photolysis measurements of complex IV, in the presence of an electron acceptor, methylviologen (MV2+) show that an intermolecular electron transfer from the excited state of Ru(II) in complex IV, to MV2+ takes place, forming Ru(III) and the methylviologen cation radical, MV+. The formation of MV+ in this system is confirmed using time-resolved transient absorption spectroscopy. This intermolecular electron transfer is followed by intramolecular electron transfer from the thioether moiety (methionine) to the photogenerated Ru(III), regenerating Ru(II)

Differential interactions of isomeric amino sugars with insulin studied under electrospray ionisation mass spectrometry

Protein-ligand interactions were studied for bovine insulin-amino sugar systems under electrospray ionisation mass spectrometry conditions. The isomeric amino sugars showed differences in the relative abundance of 1:1 protein-ligand complex formation. The electrospray ionisation and tandem mass spectrometry results of the complex clearly demonstrated that the differences in the interaction of isomeric sugars with insulin are mainly due to the differences in their gas-phase basicity. The same phenomenon is replicated in the formation of complexes between insulin and other ligands, such as amino acids, as well as in the binding of the amino sugars with amyloid β 1-40 peptide

Generation and Characterization of Distonic Dehydrophenoxide Radical Anions under Electrospray and Atmospheric Pressure Chemical Ionizations

We have explored the possibilities of generating radical anions under electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions. By using different sets of ortho-, meta-, and para-isomers of nitrobenzoic acids, methylphenols, and nitrophenols, and m-, and p-isomers of hydroxybenzaldehydes and hydroxyacetophenones as the precursor molecules, we have successfully generated the isomeric distonic dehydrophenoxide radical anions (m/z 92) using the ESI process by applying relatively high capillary voltages, the in-source dissociation (ISD) condition. Under the same conditions, the o-hydroxybenzaldehyde and the o-hydroxyacetophenone yielded the even-electron dehydrophenoxide anion (m/z 93) due to the well-known ortho-effect. The distonic phenoxide radical anions at m/z 92 were also generated under APCI-ISD conditions by using m- and p-isomers of nitrobenzaldehydes and nitroacetophenones. While the o-nitrobenzaldehyde and the o-nitroacetophenone mainly yielded the phenoxide anion at m/z 93, due to the ortho-effect. The collision-induced dissociation (CID) experiments of all the anionic precursor molecules formed from either ESI or APCI produced comparable mass spectra as those observed in the ESI-ISD or the APCI-ISD experiments. The radical anions at m/z 92 reacted with CO2 and O2 to form the CO2 adduct and the oxygen atom abstraction product, respectively, revealing the dual-character of the distonic radical anions, the phenide ion and the phenyl radical. Computational studies support the results of the ion-molecule reactions

Chiral discrimination of drugs by DNA tetranucleotides under electrospray ionisation conditions

The DNA tetranucleotides, extended versions of GCA at the 3'-end or 5'-end, were used as chiral selectors for the chiral discrimination of atenolol, DOPA, tamsulosin, valacyclovir and zolmitriptan. Chiral discrimination was achieved by investigating the collision-induced dissociation spectra of the [X+Y-2H]2- ion generated by electrospraying a solution mixture of tetranucleotide (X) and R- or S-analyte drug (Y). The relative abundances of the precursor ion and the product ion, resulting from the loss of drug, were considered for measuring the degree of chiral discrimination. Among all the tetranucleotides studied, AGCA showed the highest chiral discrimination. The present study emphasised the position of an adenine base in the tetranucleotide in chiral discrimination. The suitability of the method for the measurement of optical purity was also demonstrated in the case of zolmitriptan

Chiral discrimination of α-amino acids by the DNA triplet GCA using amino acids as a co-selector

The DNA triplet GCA is successfully used as a chiral selector for the chiral discrimination of amino acids using amino acids themselves as a co-selector. Chiral discrimination was achieved by investigating the collision-induced dissociation spectra of the [XA + XR + 2Y - 2H]2- ion generated by electrospraying a mixture of analyte amino acid (XA), reference amino acid (XR) and GCA (Y). The relative abundances of fragment ions resulting from the competitive loss of reference and XA's are considered for measuring the degree of chiral discrimination. GCA successfully shows D-selectivity for all the amino acids, except Tyr and Lys. The success of the method lies in the selection of a suitable 10R that has closer GCA binding affinity to that of analyte. The degree of discrimination by GCA is improved in the presence of the reference, and the chirality of the reference does not change the selectivity of GCA. The suitability of the method for the measurement of optical purity is also demonstrated

Separation and determination of process-related impurities of industrial chlorpyriphos by reversed- phase high performance liquid chromatography

Samples were dissolved in the mobile phase and applied to a reversed-phase C18 column with acetonitrile/aqueous acetic acid as mobile phase and diode array detection. Typical content of chlorpyriphos was 978.8-990.6 g/kg with a RSD of 1.45%. Impurities were 0.1-2.5 g/kg with RSD of 1.63-2.56

Carbohydrate-based switch-On molecular sensor for Cu(II) in buffer: absorption and fluorescence study of the selective recognition of Cu(II) ions by galactosyl derivatives in HEPES buffer

1-(β-D-Galactopyranosyl-1'-deoxy-1'-iminomethyl)-2-hydroxynaphthalene (L1), possessing an ONO binding core, was found to be selective for Cu2+ ions in N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] buffer, at concentrations ≤ 580 ppb, at physiological pH by eliciting switch-on behavior, whereas the other ions, viz., Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+, and Cd2+, caused no significant change in the fluorescence. Whereas the binding characteristics were ascertained by absorption spectroscopy, the species formed were shown by Q-TOF ES MS

Estimation of Gas-Phase Acidities of Deoxyribonucleosides: An Experimental and Theoretical Study

We determined the gas-phase acidities (ΔHacid) of four deoxyribonucleosides, i.e., 2′-deoxyadenosine (dA), 2′-deoxyguanosine (dG), 2′-deoxycytidine (dC), and 2′-deoxythymidine (dT) by applying the extended kinetic method. The negatively charged proton-bound hetero-dimeric anions, [A − H − B]− of the deoxyribonucleosides (A) and reference compounds (B) were generated under electrospray ionization conditions. Collision-induced dissociation spectra of [A − H − B]− were recorded at four different collision energies using a triple quadrupole mass spectrometer. The abundance ratios of the individual monomeric product ions were used to determine the ΔHacid of the deoxyribonucleosides. The obtained ΔHacid value follows the order dA > dC > dT > dG. The ΔGacid (298 K) values were determined by using ΔGacid = ΔHacid -TΔSacid where the ΔHacid and ΔSacid values were determined directly from the kinetic method plots. The ΔHacid values were also predicted for the deoxyribonucleosides at the B3LYP/6-311+G**//B3LYP/6-311G** level of theory. The acidity trend obtained from the computational investigation shows good agreement with that obtained experimentally by the extended kinetic method. Theoretical calculations provided the most preferred deprotonation site as C5′-OH from sugar moiety in case of dA, and as −NH2 (dC and dG) or −NH- (dT) from nitrogenous base moiety in the case of other deoxyribonucleosides