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This article presents the design of cyclometalated platinum(ii) complexes incorporating pyridyl-appended acetylide ligands of the form Pt–CC–py, acting either as sites for protonation or methylation reactions or as a host receptor for binding metal cations. The complexes studied are Pt(t-Bu2phbpy)(–CC–py), 2, which can undergo protonation at the pyridyl N; its cationic N-methylated derivative [Pt(t-Bu2phbpy)(–CC–pyMe)]+, 4, which serves as a model of the N-protonated species; and a derivative in which the pyridyl ring is incorporated into a macrocyclic diamide-crown ether ligand (3). The co-ligand t-Bu2phbpy is a cyclometalated, NNC-coordinated phenylbipyridine ligand carrying tert-butyl groups at the 4-positions of the pyridyl rings. The photophysical properties of the neutral compounds 2and 3have been compared to those of the pyridinium, methyl-pyridinium or metal-complexed species (namely 2-H+, 4and 3-Pb2+). Detailed TD-DFT calculations provide a theoretical basis to account for the experimentally-observed changes upon protonation/methylation/complexation. The joint TD-DFT and experimental studies provide evidence for an unprecedented molecular switch in the nature of the excited state (from mixed L′LCT/MLCT to ML′CT) in which the acceptor ligand in the CT process switches from being the NNC ligand to the pyridyl acetylide. [ABSTRACT FROM AUTHOR]

The detection of methylation in DNA and RNA is essential for the diagnosis and treatment of a wide range of diseases. A one-step fabricated laser-induced graphene (LIG) electrode has received increasing attention due to its good electrical conductivity, large specific surface area, ease of miniaturization, low cost and flexibility. Herein, a potential biosensor for N6-methyladenosine (m6A-RNA) and 5-methylcystosine-single strand DNA (5mC-ssDNA) detection was designed. The aim of this paper is to address the problem of detecting the m6A-RNA and 5mC-ssDNA content in cells. By stepwise modification of gold nanoparticles (AuNPs), sulfhydryl-modified nucleic acid chains, biotin-modified antibodies, and streptavidin-modified horseradish peroxidase (SA-HRP) at the LIG electrode, the peak current responses exhibited an increase proportional to the concentration of m6A-RNA and 5mC-ssDNA in the hydrogen peroxide–hydroquinone (H2O2–HQ) system. This method demonstrated a low detection limit of 2.81 pM for m6A-RNA and 9.53 pM for 5mC-ssDNA, with a linear detection range of 0.01 nM to 10 nM for both targets. The regression equation was determined as ΔI = 4.83 log c + 12.32 (R2 = 0.9980) for m6A-RNA and ΔI = 9.82 log c + 22.09 (R2 = 0.9903) for 5mC-ssDNA. Our method has good selectivity toward different detection targets of nucleic acid chains, stability for long-term storage and consecutive scanning (RSD of 9.42% and 2.08%, respectively) and reproducibility of 5 electrodes (RSD of 6.85%). This method utilizes gold–sulfur bonding to immobilize the detection target, which improves the conductivity of the LIG electrode and introduces an amplified portion of the signal by taking advantage of antigen–antibody specific binding. Thus, dual detection of m6A-RNA and 5mC-ssDNA was realized. Importantly, this approach is successfully applied for the detection of targets in spiked samples extracted from HeLa cells, suggesting its potential for clinical applications and providing a new perspective for the development of point-of care testing (POCT) techniques. [ABSTRACT FROM AUTHOR]

A variety of sulfonic acids have been trifluoromethylated using 1-trifluoromethyl-1,2-benziodoxol-3(1H)-one under mild conditions in good to excellent yields. Initial mechanistic investigations of this reaction show a clean second-order kinetics and only very weak substrate electronic effects. [ABSTRACT FROM AUTHOR]

A homodinuclear Ni2-Schiff base 1complex (0.1–1 mol%) promoted the direct catalytic asymmetric aldol reaction of β-keto esters with formaldehyde, giving hydroxymethylated adducts in 94–66% ee. [ABSTRACT FROM AUTHOR]

In this paper, a dual-signal ratiometric electrochemiluminescence (ECL) assay was developed to detect human DNA (cytosine-5)-methyltransferase1 (DNMT1) activity. Mercaptopropionic acid (MPA)-modified Eu3+-doped CdS nanocrystals (MPA-CdS:Eu NCs) and luminol were used as two different ECL emitters, which showed ECL signals at different electrochemical potentials. The resultant ECL peaks exhibited opposite trends in the DNMT1 system. According to the ratio of the ECL responses of CdS to luminol, the DNMT1 activity was detected in the range of 1.0–30.0 U mL−1 in buffer solution. The limit of detection (LOD) was estimated to be 0.07 U mL−1 at a signal-to-noise ratio of 3. The assay was extended to detect the DNMT1 activity from crude lysates of cancer cells, along with the effect of DNMT1 inhibitors such as 5-aza and 5-aza-2′-dC. [ABSTRACT FROM AUTHOR]

The reactivity and functionality of technical lignin requires reliable modulation in order to be used as a precursor for a variety of applications. A green alternative for lignin methylation using dimethyl carbonate (DMC) is reported and this paper discusses our efforts toward optimization and structural elucidation for such reactions. It is demonstrated that softwood kraft lignin can be progressively and reproducibly methylated to different extents using DMC in the presence of sodium hydroxide or cesium carbonate as bases with the latter requiring milder reaction conditions. 13C NMR, FT-IR, and quantitative 31P NMR spectroscopic analyses were used to document and understand the structural changes occurring within the methylated lignin derivatives. While the phenolic hydroxyl groups of lignin are methylated, the reduction in aliphatic –OHs is also observed in control and methylation reactions, most likely via a solvent mediated intramolecular rearrangement reaction. As anticipated, the methylation induced thermal stability, elimination of thermally induced crosslinking and lowering of the glass transition temperature. Overall, the developed chemistry offers a green alternative to a much sought derivatization reaction that adds value to an otherwise intractable and underutilized biopolymer. [ABSTRACT FROM AUTHOR]

This contribution reports about an in situFT-IR investigation and the catalytic reactivity of Mg/Me3+mixed oxides (Me = Cr, Fe, or Al; Mg/Me = 2, atomic ratio) in the gas-phase methylation of phenol with methanol. It is the second of two papers concerning the mentioned systems, and its purpose is twofold: to confute the classic and not accurate theory concerning the reaction mechanism, and to propose a novel interpretation based on the combined use of catalytic tests and in situmolecular spectroscopy. Results here reported highlight that: (i) the reaction mechanism in phenol methylation, when catalysed by basic systems, is not a classical electrophylic substitution, as generally reported in the literature, but proceeds through the formation of formaldehyde as an intermediate, and (ii) the catalytic behaviour in respect to both methanol and phenol reactants is strictly dependent on catalyst features. Although all investigated systems exhibit a basic-type behaviour with regard to phenol, which dissociates to yield an adsorbed phenolate species, the distribution of phenolic compounds obtained with the Mg/Al/O catalyst was that typically observed with acid catalysts, with prevailing formation of anisole when the reaction was carried out below 350 °C and of mono and poly-C-alkylated compounds when the reaction temperature was above 350 °C. On the contrary, the reactivity shown by both Mg/Fe/O and Mg/Cr/O systems was that reported in the literature as typical of mixed oxides possessing basic features. The extent of methanol decomposition into light compounds was maximum in the case of Mg/Fe/O catalysts, because of the pronounced redox behaviour typical of Fe3+species, whereas neither methanol dehydrogenation nor decomposition were ever observed with Mg/Al/O up to 400 °C. Reactivity tests and spectroscopic experiments hinted for methanol dehydrogenation to formaldehyde as the first step in the ring-methylation of phenol with Mg/Cr/O and Mg/Fe/O: in that case, o-cresol and 2,6-xylenol were the only reaction products. But, with Mg/Al/O systems, for which no methanol dehydrogenation occurred, the formation of anisole was due to the synergistic effect of stronger basic features and the presence of Lewis acidic sites, that facilitate the reaction between phenol and methanol after activation over the two different types of catalytic sites. [ABSTRACT FROM AUTHOR]