Proton Domino Reactions at an Imidazole Relay Control the Oxidation of a TyrZ-His190 Artificial Mimic of Photosystem II.

A close mimic of P680 and the TyrosineZ-Histidine190 pair in photosystem II (PS II) has been synthesized using a ruthenium chromophore and imidazole-phenol ligands. The intramolecular oxidation of the ligands by the photoproduced Ru(III) species is characterized by a small driving force, very similar to PS II where the complexity of kinetics was attributed to the reversibility of electron transfer steps. Laser flash photolysis revealed biphasic kinetics for ligand oxidation. The fast phase (τ<50 ns) corresponds to partial oxidation of the imidazole-phenol ligand, proton transfer within the hydrogen bond, and formation of a neutral phenoxyl radical. The slow phase (5-9 µs) corresponds to full oxidation of the ligand which is kinetically controlled by deprotonation of the distant 1-nitrogen of the imidazolium. These results show that imidazole with its two protonatable sites plays a special role as a proton relay in a 'proton domino' reaction.

In Addition to Damaging the Plasma Membrane, Phenolic Monoterpenoid Carvacrol Can Bind to the Minor Groove of DNA of Phytopathogenic Fungi to Potentially Control Tea Leaf Spot Caused by Lasiodiplodia theobromae.

Carvacrol expresses a wide range of biological activities, but the studies of its mechanisms focused on bacteria, mainly involving the destruction of the plasma membrane. In this study, carvacrol exhibited strong activities against several phytopathogenic fungi and demonstrated a novel antifungal mechanism against Lasiodiplodia theobromae. RNA sequencing indicated that many genes of L. theobromae hyphae were predominately induced by carvacrol, particularly those involved in replication and transcription. Hyperchromic, hypsochromic, and bathochromic effects in the UV-visible absorption spectrum were observed following titration of calf thymus DNA (ctDNA) and carvacrol, which indicated the formation of a DNA-carvacrol complex. Circular dichroism (CD) spectroscopy indicated that the response of DNA to carvacrol was similar to that of 4',6-diamidino-2-phenylindole (DAPI) but different from that of ethidium bromide (EB), implying the ionic bonds between carvacrol and ctDNA. Fluorescence spectrum (FS) analysis indicated that carvacrol quenched the fluorescence of double-stranded DNA (dsDNA) more than single-stranded DNA, indicating that carvacrol mainly bound to dsDNA. A displacement assay showed that carvacrol reduced the fluorescence intensity of the DNA-DAPI complex through competition with DAPI, but this did not occur for DNA-EB. The FS assay revealed that carvacrol bound to the AAA sequence on the minor groove of ds-oligonucleotides. The hydroxyl of carvacrol was verified to bind to ctDNA through a comparative test in which structural analogs of carvacrol, including thymol and 4-ethyl-1,2-dimethyl, were analyzed. The current study indicated carvacrol can destruct plasma membranes and bind to the minor groove of DNA, inhibiting fungal proliferation by disturbing the stability of dsDNA.

Proton-controlled Action of an Imidazole as Electron Relay in a Photoredox Triad.

Electron relays play a crucial role for efficient light-induced activation by a photo-redox moiety of catalysts for multi-electronic transformations. Their insertion between the two units reduces detrimental energy transfer quenching while establishing at the same time unidirectional electron flow. This rectifying function allows charge accumulation necessary for catalysis. Mapping these events in photophysical studies is an important step towards the development of efficient molecular photocatalysts. Three modular complexes comprised of a Ru-chromophore, an imidazole electron relay function, and a terpyridine unit as coordination site for a metal ion were synthesized and the light-induced electron transfer events studied by laser flash photolysis. In all cases, formation of an imidazole radical by internal electron transfer to the oxidized chromophore was observed. The effect of added base evidenced that the reaction sequence depends strongly on the possibility for deprotonation of the imidazole function in a proton-coupled electron transfer process. In the complex with MnII present as a proxy for a catalytic site, a strongly accelerated decay of the imidazole radical together with a decreased rate of back electron transfer from the external electron acceptor to the oxidized complex was observed. This transient formation of an imidazolyl radical is clear evidence for the function of the imidazole group as an electron relay. The implication of the imidazole proton and the external base for the kinetics and energetics of the electron trafficking is discussed.

Effect of maltodextrin combination with gum arabic and whey protein isolate on the microencapsulation of gurum seed oil using a spray-drying method.

This study aimed to evaluate the potential of maltodextrin (MD) combination with gum arabic (GA), and whey protein isolate (WPI) on the microencapsulation of gurum seeds oil by a spray-drying method. Three formulations of protein-based (PB) (WPI: MD, 2:1), carbohydrate-based (CHOB) (GA: MD, 2:1), and mixed (MIX) (WPI: GA: MD, 1:1:1) wall materials were designed. The moisture content and water activity were in the range of 1.65-3.67% and 0.17-0.31, respectively, which is suitable for long-term storage. The best results were achieved when gurum seed oil was microencapsulated with carbohydrate-based, where it had the highest microencapsulation yield (92.80%) and microencapsulation efficiency (97.38%). Carbohydrate-based showed the highest relative crystallinity (32.25%) and the temperature of the glass transition (58.20 °C). FT-IR revealed that the oil was well encapsulated in the microcapsules. SEM of microcapsules showed spherical shapes without any apparent cracking on the surfaces. During the oxidative stability study, carbohydrate-based microencapsulation was the wall material that best protected the active materials against lipid oxidation.

Luminescent Chemosensor Based on Ru(II) Bipyridine Complex for Detection of Sudan I through Inner Filter Effect.

Presence of Sudan I in food stuff can be problematic and need to be checked in order to protect our health from possible carcinogen. Therefore, it is essential to detect Sudan I by efficient, rapid and reliable method. In this work, we have designed a Ru(II) polypyridyl complex, [Ru(bpy)2(CIP)]2+ probe for the selective and sensitive detection of Sudan I. Upon addition of Sudan I to the solution of [Ru(bpy)2(CIP)]2+ in ethanol, the luminescence quenched rapidly, and linear concentration range with analyte has been obtained from 0.8 to 100 µM with the limit of detection as low as 0.26 µM (S/N = 3). The effective luminescence quenching was resulted due to the inner filter effect (IFE) between luminophore, [Ru(bpy)2(CIP)]2+ and quencher, Sudan I. Our spectroscopic study was essentially provided sufficient analytical evidences in order to prove occurrence of IFE mechanism. As there were no interferences observed in luminescence measurement from the other substances the present probe has been successfully applied for the detection of Sudan I in commercial chili powder sample, making the probe suitable for practical usage.

Highly selective detection of l-Phenylalanine by molecularly imprinted polymers coated Au nanoparticles via surface-enhanced Raman scattering.

Molecularly imprinted film coated gold nanoprticles (MIP-AuNPs) were employed as surface-enhanced Raman scattering (SERS) substrate for sensitive and selective recognition and quantification of l-Phenylalanine (L-Phe). The MIP was in-situ formed on the AuNPs by sol-gel technique using L-Phe as the template molecule, tetraethyl orthosilicate as the crosslinker and phenyltrimethoxysilane as the functional monomer. The efficient removal of template was achieved by ultrasonic treatment. The as-prepared MIP-AuNPs sensor showed a good linear relationship with the concentration of L-Phe in the range of 1.0 × 10-8-1.0 × 10-4 mol L-1 with a limit of detection as low as 1.0 nmol L-1. The sensor also showed an excellent selectivity as L-Phe can be determined in the presence of other amino acid analogues, D-Phe and bovine serum. The stability of the MIP-AuNPs was manifested by the low deviation (RSD = 3.7%) for 40 days subsequent measurements.

Direct Electrochemical Sensing of Phosphate in Aqueous Solutions Based on Phase Transition of Calcium Phosphate.

Electrochemical determination of phosphate in aqueous solutions attracts considerable interests in both biological and environmental fields. Because of the electrochemically inactive nature of phosphate, direct electrochemical detection of phosphate is still a highly challenging task. Herein, we reported a direct electrochemical approach for the determination of phosphate based on the oxidation of coordinated OH during the phase transition of calcium phosphates (CaPs). The mixture of amorphous CaPs and octacalcium phosphate (Ca8(HPO4)2(PO4)4·5H2O), which acts as the starting material for hydroxyapatite (Ca10(PO4)6(OH)2), was self-assembled on a Nafion-modified glassy carbon electrode. The as-prepared electrode (CaPs/Nafion) showed a distinct oxidation peak at 1.0 V versus Ag/AgCl in phosphate solution. The peak heights were directly proportional to the concentration of phosphate from 0.1 to 10 µM in the presence of 1 mM Ca2+. After comprehensive characterization of the CaPs/Nafion electrode, it was understood that phosphate ions as a proton acceptor could stimulate the generation of coordinated OH from coordinated water (H2O) in CaP. The addition of Ca2+ could magnify the coordinated H2O source because of its hydration to H2O. The CaPs/Nafion electrode also displayed good selectivity as the electrochemical oxidization response was not affected by up to 10 µM of potentially competitive species like CO32-, NO3-, CH3COO-, SO42-, and Cl-. The results obtained in this work not only provided a new method for direct detection of phosphate in aqueous solution but also suggested that Ca2+ could be a promoter for electrochemical oxygen generation.

A potential new source: Nutritional and antioxidant properties of edible oils from cucurbit seeds and their impact on human health.

Seeds from the cucurbitaceae plant family are discarded as the byproducts which generally obtained after extraction of oil during food processing. Recently, found a great deal of interest as cucurbit seeds are found to be rich source of nutrients such as monounsaturated fatty acids, polyunsaturated fatty acids, tocopherols (α-Tocopherol, ß-Tocopherol, δ-Tocopherol, γ-Tocopherol), carotenoids, ß-carotene, phytosterol, proteins, minerals, vitamins, phenolic compounds, and antioxidants. Despite the potential nutritional benefits, the commercial product of cucurbit plants are lacking in the market. Therefore, there is an urgent need to increase production and utilization of cucurbit seed oil for human nutrition. The main purpose of the present review is to sum up the published information on the nutritional potential of cucurbit seed oils to promote industrial production and stimulates further research on commercial use of cucurbit seeds. PRACTICAL APPLICATIONS: The aims of this review are to highlight the nutritional values and antioxidant properties of cucurbit seed and their impact on the overall human health. These cucurbit seeds are rich source of vitamins and minerals which are necessary for healthy human diet. In addition to other commercial oils, cucurbits oils are equally important and rich in essential active ingredients. Quite abundance of cucurbit seeds in African continents can pave way to enhance production on the industrial scale which can create employability ranging from farmers to skilled workers. In all, the oil produced from the cucurbit seeds can be applied practically to implement large-scale production as a part of food industry and dietary supplement industry in paramedical sector.

Rapid and selective luminescent sensing of allergenic gluten by highly phosphorescent switch-on probe.

First time the luminescent switch-on probe using novel water-soluble cyclometallated iridium complex (Ir-dc) has been developed for sensitive and selective detection of gluten in the presence of several interfering elements. Linear concentration range of gluten is obtained from 5 to 200 µg/mL with a limit of detection 2.6 µg/mL. The Ir-dc complex responded to the broad pH range which is advantageous for the detection of gluten in various food samples. Additionally, It has been successfully employed for the detection of gluten in commercial food samples of wheat flour and oats with highest recovery values, indicating applicability of Ir-dc for practical usage.

Light-induced tryptophan radical generation in a click modular assembly of a sensitiser-tryptophan residue.

Click chemistry was used as an efficient method to covalently attach a chromophore to an amino acid. Such easily prepared model systems allow for time-resolved studies of one-electron oxidation reactions by the excitation of the chromophore by a laser flash. The model complex ruthenium-tryptophan (Ru-Trp) has been synthesised and studied for its photophysical and electrochemical properties. Despite a small driving force of less than 100 meV, excitation with a laser flash results in fast internal electron transfer leading to the formation of the protonated radical (Trp˙H(+)). At neutral pH electron transfer is followed by deprotonation to form the neutral Trp˙ radical with the rate depending on the concentration of water acting as the proton acceptor. The formation of the tryptophan radical was confirmed by EPR.