An investigation into the role of macromolecules of different polarity as passivating agent on the physical,chemical and structural properties of fluorescent carbon nanodots

In this study, comparative evaluation of fluorescent carbon nanodots (C-Dots) prepared using carob molasses was reported by screening various biocompatible macromolecules as passivating agent (PA). Incorporation of PAs with different molecular weight, polarity, and chemical structure was examined, and compared with the polyethylene glycol (PEG, Mn = 10 kN) passivated and pristine C-Dots. Not only the fluorescence properties but also many other features including size, crystal structure, colloidal conductivity, resistance to photobleaching, quantum yield, and UV-modulated surface interaction of them with the reactive oxygen species (ROS) as well as ROS production were investigated. Photoluminescence (PL) capacity of C-Dots was found to be associated with the number of surface alkyl groups and polymeric hydrogen bounding present on the C-Dot surface (increased number is associated with decreased PL) while surface conductivity of C-Dots in water was proportional to the PL intensity. More importantly, C-Dots with relatively poorer fluorescent were investigated in various organic solvents (hexane, methanol, acetone, ethanol, dimethylformamide (DMF), and DMSO). As happens with the fluorescent dyes, their PL intensities were significantly enhanced (even for pristine C-Dots) depending on the solvent characteristics. All of the C-Dots synthesized were further evaluated by means of UV-induced generation of ROS and inhibition of ROS by using H₂O₂ as model. In contrary to other carbonaceous nanomaterials, they did not show any ROS generation, on the contrary, they showed ROS scavenging activity that can be modulated by UV-irradiation (λ _exc = 365 nm). PEG and alginate passivated C-Dots inhibited H₂O₂ activity at LC₅₀ values below 10 mg/mL.

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Anion reaction of 1,3-benzoxathiole-3-oxide with several electrophilic compounds

The reaction of benzoxathiole-3-oxide with LDA in THF or THF/hexane or THF/HMPA gave a carbanion which was reacted with methyl iodide, aromatic aldehydes or carbon dioxide. The conformational stability (-diastereoselectivity) of the carbanion and the asymmetric induction due to the prochiral electrophiles (β-diastereoselectivity) was studied. The temperature and the solvent effects on the - and β-diastereoselectivity are discussed.     

Polybutylene terephthalate reactive blending with polymethylhydrosiloxane by ruthenium‐catalyzed carbonyl hydrosilylation reaction

Carbonyl hydrosilylation reaction was developed to prepare reactive blending between PBT and polymethylhydrosiloxane (PMHS). It focused on the addition reaction of Si–H groups from PMHS onto carbonyl groups from PBT catalyzed by triruthenium dodecacarbonyl (Ru₃(CO)₁₂). An approach on PBT model compounds was carried out and investigated by NMR spectroscopy to evidence the potentiality and efficiency of carbonyl hydrosilylation reaction. At temperatures up to 100 °C, the hydrosilylation reaction can reach 33 mol% conversion in a few hours. Side reactions were also highlighted. Such side reactions can reach more than 23 mol% of the final products when temperature increases to 180 °C. Then hydrosilylation reaction was extended to PBT modification with a molar ratio of ester group/SiH = 3.5 and viscosity ratio polysiloxane/PBT = 4.0 × 10^?5. The reaction was carried out in an internal mixer at 220 °C and followed through the evolution of the torque of the reactional medium. Samples for different processing times were investigated by SEM and rheology. From these analyses, the dispersion of PMHS was promoted with diameters of few micrometers. The elastic behavior of final material was characteristic of solid or gel‐like structures, suggesting a network structure formation consistent with the gel fraction increase from 0 to 0.55. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1855–1868     

An unusual behaviour of N-(tert-butoxycarbonyl)- and N-pivaloyl-(methylthio)anilines in metallation reactions

The metallation reaction of N-Boc-and N-Piv-(methylthio)anilines are here described. The results show that N-Boc derivatives are metallated only by superbases to give products substituted at the thiomethylic group. N-Piv derivatives show a different behaviour: ortho-derivative is metallated by both butyllithium and superbase at the thiomethylic carbon atom, while para-derivative is metallated in ortho to the N-Piv group by butyllithium and at the thiomethylic carbon atom by superbase. The meta-derivative is metallated only by superbase at the thiomethylic carbon atom.     

HETEROGENEITY OF THE PHOTOCHEMICAL CENTERS IN SYSTEM II OF CHLOROPLASTS*

Abstract— In 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) poisoned chloroplasts of algae and‘ higher plants the area over the fluorescence induction curve increases with biphasic first order kinetics (Melis and Homann, 1975). Two possibilities are considered to explain the biphasic nature of the area growth. The first is a sequential double reduction of the primary electron acceptor in system II while the second envisages a heterogeneity of its photochemical centers. The kinetic properties of the area growth after firing a single saturating flash proved to be incompatible with the predictions of the “sequential double reduction” model. This conclusion was corroborated by results obtained from a kinetic analysis of the area restoration process in the dark, and an analysis of the partially restored areas. Assuming an existence of a heterogeneous pool of photochemical centers, the growth of the area over the fluorescence curve could be further analyzed to yield two components, a fast a-component, and a relatively slow β-component. The kinetic characteristics of these components, and the effect of a short saturating flash on their respective size, led to the conclusion that one type of photochemical center had a faster recombination rate of the photochemically separated charges and was less efficient in trapping excitation energy.     

BIMANES—26. AN ELECTRON TRANSFER REACTION BETWEEN PHOTOSYSTEM I1 AND MONOBROMOBIMANE INDUCES STATIC CHLOROPHYLL a QUENCHING IN SPINACH CHLOROPLASTS

Abstract— Monobromobimane in chloroplasts lowers both the quantum yield of system II photochemistry and the yield of chlorophyll a fluorescence. Illumination of the chloroplasts in the presence of monohromobimane is an absolute prerequisite to the manifestation of this phenomenon, which proceeds via the Photosystem II intermediate, the semiquinone radical anion, Q_A-. The latter transfers an electron to monobromobimane to yield an anion radical (mBBr^·), which may either lose bromide ion to yield a reactive radical (mB^·), or acquire a proton and undergo further reduction, eventually forming syn-(methyl, methyl) bimane. In turn, mB reacts with the protein of the light-harvesting complex, to form a product which acts as static excitation energy quencher in the chlorophyll pigment bed of photosystem 11. Polarographic reduction of monobromobimane shows an adsorption wave at O V and two reduction waves. Prolonged reduction in water at -0.5 V yields syn-(methyl, methyl) bimane (which is further reduced at more negative potentials) and bromide ion. Thus, both electrochemical and chloroplast-induced reduction produce syn-(methyl, methyl) bimane. Monobromobimane may then serve as a Photosystem II activated probe in elucidating the conformation of intrinsic thylakoid membrane polypeptides.     

OH−-induced β-elimination reactions with 1-(2-Xethyl)-4-nitrobenzene substrates in solvent mixture H2O/CH3CN and H2O/DMSO: Reactivity and mechanism

The behaviour of 1-(2-bromoethyl) 4-nitrobenzene (1), N,N,N-triethyl-2-(4-nitrophenyl)ethanaminium bromide (2) and N,N-diethyl-N-[2-(4-nitrophenyl)ethyl]octan-1-aminium bromide (3) in the OH⁻-induced elimination reactions with formation of 1-nitro-4-vinylbenzene in mixtures of DMSO/H₂O or CH₃CN/H₂O has been investigated. With all three substrates an increase in dipolar aprotic solvent content implies a limited increase of the second-order rate constant k _OH up to ≅605, and then an exponential increase is observed. The variation of activation parameters ΔH ^# and dGS ^#, measured in DMSO/H₂O mixtures, is parallel for 1 and 2. This similar behaviour of 1 and 2 with respect to variation in solvent composition is evidence that it is not possible to use this technique of solvent effect for the mechanistic diagnosis of elimination reactions.     

Metallation reactions XXVII.: Metallation of (methylthio)anilines

The metallation reactions of (methylthio)anilines with organolithium reagents and with the butyllithium–potassium tert-butoxide superbasic mixture are here described. The results show that the para isomer when treated with butyllithium gave a mixture of products with no selectivity. Using tert-butyllithium or superbases we obtained the substitution of the thiomethyl hydrogen. Moreover, superbase allowed to prepare the disubstituted product with the new groups in the thiomethyl and in ortho to this group. On the other side, both ortho and meta isomers were lithiated at the thiomethyl carbon by butyllithium and the other reagents. Starting from the unalkylated amine we prepared through three successive one-pot monometallations N,N-disubstituted amines with equal or different groups and bearing an alkylthio chain as long as wanted.     

Monte Carlo simulations for 1- and 2D spin crossover compounds using the atom–phonon coupling model

In this contribution we have simulated, using the Monte Carlo–Metropolis technique, the thermal behavior of an one dimensional and of a square lattice spin crossover system.In the one dimensional case, a long-range interaction parameter must be included in order to obtain a thermal hysteresis. For the square lattice we have tacked into account the nearest as well the next-nearest neighbors. We show the role of the elastic constant ratio on the hysteresis width.     

Investigation of Vipera Anatolica Venom Disintegrin via Intracellular Uptake with Radiolabeling Study and Cell-Based Electrochemical Biosensing Assay

Applied Biochemistry and Biotechnology - Snake venoms are a natural biological source that has potential therapeutic value with various protein compounds. Disintegrins originally were discovered as...