Heteroleptic dipyrrinato complexes containing 5-ferrocenyldipyrromethene and dithiocarbamates as coligands: selective chromogenic and redox probes

Six heteroleptic dipyrrinato complexes [Ni(fcdpm)(dedtc)] (1), [Ni(fcdpm)(dipdtc)] (2), [Ni(fcdpm)(dbdtc)] (3), [Pd(fcdpm)(dedtc)] (4), [Pd(fcdpm)(dipdtc)] (5), and [Pd(fcdpm)(dbdtc)] (6) (fcdpm = 5-ferrocenyldipyrromethene; dedtc = diethyldithiocarbamate; dipdtc = diisopropyldithiocarbamate; dbdtc = dibutyldithiocarbamate) have been synthesized and characterized by elemental analyses and spectral (ESI-MS, IR, (1)H, (13)C NMR, UV-vis) and electrochemical studies. Crystal structures of 1, 2, 4, and 5 have been authenticated by X-ray single-crystal analyses. Nickel-based complexes 1-3 display selective chromogenic and redox sensing for Hg(2+) and Pb(2+) ions, while palladium complexes 4-6 display selective chromogenic and redox sensing only for Hg(2+). Electronic absorption, ESI-MS, and electrochemical studies indicated that sensing arises from interaction between 1-3 and Hg(2+)/Pb(2+) through sulfur of the coordinated dithiocarbamates, while it arises from the pyrrolic nitrogen of fcdpm and dithiocarbamate sulfur from 4-6 and Hg(2+). Different modes of binding between Ni and Pd complexes have further been supported by theoretical studies. The receptor-cation binding constants (K(a)) and stoichiometry between probes and Hg(2+)/Pb(2+) have been estimated by the Benesi-Hildebrand method and Job's plot analysis. Detection limits for 1-3 toward Hg(2+)/Pb(2+) and 4-6 for Hg(2+) have been found to be reasonably high.     

Cyanuric chloride catalyzed mild protocol for synthesis of biologically active dihydro/spiro quinazolinones and quinazolinone-glycoconjugates

We have developed an efficient cyanuric chloride (2,4,6-trichloro-1,3,5-triazine, TCT) catalyzed approach for the synthesis of 2,3-dihydroquinazolin-4(1H)-one (3a-3x), 2-spiroquinazolinone (5, 7), and glycoconjugates of 2,3-dihydroquinazolin-4(1H)-one (10a, 10b) derivatives. The reaction allows rapid cyclization (8-20 min) with 10 mol % cyanuric chloride to give skeletal complexity in good to excellent yield. We believe that this novel procedure may open the door for the easy generation of new and bioactive quinazolinones.     

O-Tolyl/benzyl dithiocarbonates of phosphorus(III) and (V): syntheses and characterization

Abstract  

O-Tolyl/benzyl dithiocarbonates, ROCS₂Na (R = o-, m-, or p-CH₃C₆H₄–, and –CH₂C₆H₅), were synthesized and characterized. These new ligands reacted with PCl₃/POCl₃ in refluxing toluene which resulted in the formation of phosphorus(III) and phosphorus(V) tolyl/benzyl dithiocarbonates corresponding to [(ROCS₂) _n PCl_3−n ] and [(ROCS₂) _n POCl_3−n ] (R = o-, m-, or p-CH₃C₆H₄–, and –CH₂C₆H₅; n = 1, 2, 3). These pale yellow liquid compounds were characterized by IR, mass, and NMR (¹H, ¹³C, and ³¹P) spectral studies, which suggest the dithiocarbonate ligands bind in a monodentate mode leading to P–S–C linkages in these derivatives.     

Size-dependence enhancement in electrocatalytic activity of NiHCF-gold nanocomposite: potential application in electrochemical sensing

A nanocomposite of nickel hexacyanoferrate (NiHCF) was made with gold nanoparticles (AuNPs) of two different sizes (20 and 80 nm as AuNP(red) and AuNP(blue) respectively), synthesized via 3-glycidoxypropyltrimethoxysilane mediated reduction of 3-aminopropyltrimethoxysilane treated gold chloride and characterized by scanning electron microscopy and UV-VIS spectroscopy. The size of AuNPs was found to influence the two pairs of reversible voltammetric peaks of cation rich and cation deficient NiHCF. Such influence was identified from cyclic voltammetry of nanocomposite modified electrodes and applications during electrochemical sensing of two different analytes hydrazine and glutathione (GSH). Electrochemical sensing of hydrazine was based on cyclic voltammetry and differential pulse voltammetry (DPV) found as a function of sodium deficient NiHCF and was greatly amplified with increasing AuNPs nanogeometry. NiHCF alone is not an efficient electrode material for GSH analysis at the level required, however, the presence of AuNPs introduces size dependent sensitive and selective detection of GSH. GSH sensing based on linear sweep voltammetry (LSV) was found to be mediated by the potassium rich form of NiHCF redox couple in the presence of AuNPs. The results justified electrochemical detection of these analytes based on a mediated mechanism and support the role of AuNPs for facilitated electrochemical activity of NiHCF based systems as a function of nanogeometry.     

Visible light photoredox catalysis: generation and addition of N-aryltetrahydroisoquinoline-derived α-amino radicals to Michael acceptors

The photoredox-catalyzed coupling of N-aryltetrahydroisoquinoline and Michael acceptors was achieved using Ru(bpy)(3)Cl(2) or [Ir(ppy)(2)(dtb-bpy)]PF(6) in combination with irradiation at 455 nm generated by a blue LED, demonstrating the trapping of visible light generated α-amino radicals. While intermolecular reactions lead to products formed by a conjugate addition, in intramolecular variants further dehydrogenation occurs, leading directly to 5,6-dihydroindolo[2,1-a]tetrahydroisoquinolines, which are relevant as potential immunosuppressive agents.     

Alkaloids and flavonoids of Argemone mexicana

A new protopine alkaloid, protomexicine and a new isoflavonoid, mexitin, together with 8-methoxydihydrosanguinarine, 13-oxoprotopine, rutin and quercetrin have been isolated from the aerial part of the methanolic extract of Argemone mexicana. The structures of these compounds have been established by various spectral data. The structure of protomexicine was further confirmed by heteronuclear multiple bond correlation experiment. Protomexicine and mexitin are new compounds, and other compounds are first reported from A. mexicana and genus Argemone.     

Evaluation of the solid-phase extraction (SPE) cartridge method in combination with thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) for the analysis of different VOCs in liquid matrices in varying pH conditions

In this study, the solid-phase extraction (SPE) method combined with thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method is evaluated for the analysis of liquid-phase volatile organic compounds (LVOCs). Calibration experiments were performed on a number of polar and nonpolar LVOCs (including aromatic compounds, ester, ketones, and alcohol) as a function of solution pH. If the relative sensitivity of the SPE-TD-GC-MS method is compared between different VOCs across a wide range of pH (1, 4, 7, 10, and 13), optimum sensitivities for most VOCs are derived at the neutral pH. However, there were some exceptions to the general trend with the maximum sensitivity occurring either at a moderately basic pH (methyl isobutyl ketone and butyl acetate) or extremely acidic conditions (isobutyl alcohol). It was also noticed that the relative ordering of sensitivity was changed, as the pH conditions of the solution vary. The use of internal standard (IS: chlorobenzene) resulted in a notable improvement in both relative sensitivity and reproducibility for most compounds.     

FTIR structural investigation of gamma irradiated BaO–Na2O–B2O3–SiO2 glasses

Fourier transform infrared (FT-IR) spectra of xBaO–15Na₂O–(70−x)B₂O₃–15SiO₂ glass system with x=0, 5, 10, 15 and 20 (mol%) has been measured in the spectral range 400–4000 cm⁻¹ at room temperature in order to understand the characteristic frequencies of the chemical bonds and bonding mechanisms, which are susceptible to the structural and spectral changes. The effect of gamma irradiation in the dose range 0.1 kGy–60 kGy on the infrared absorption spectra of these glasses is also reported. The change in the glass structure due to the effect of composition is also discussed. It has been observed that irradiation of the glasses with the gamma rays increases the BO₃ groups and the non bridging oxygens which make the network loose.     

Implication of local moment at Ti and Fe sites for the electrical and magneto-transport properties of degenerate semiconducting Ti?-xFexO?-d epitaxial films

We have investigated the effect of local magnetic moment on the electrical and magneto-transport properties of thin films of the degenerate semiconductor Ti(1-x)Fe(x)O(2-d) (x = 0,0.04). The electrical measurements of these films reveal high temperature metallic behavior and resistivity minima. The behavior below the resistivity minimum temperature is ascribed to Kondo like scattering. The coupling between the local moment and the charge carriers is reflected in the magnetoresistance measurements in these films. This work indicates competition between the magnetic ordering mechanism by J(RKKY) and the moment screening mechanism by J(Kondo). Accordingly the role of carrier density in achieving the magnetic ordering in such materials either by defect engineering or by transition metal doping is discussed.     

Multiple electron injection dynamics in linearly-linked two dye co-sensitized nanocrystalline metal oxide electrodes for dye-sensitized solar cells

Understanding the electron transfer dynamics at the interface between dye sensitizer and semiconductor nanoparticle is very important for both a fundamental study and development of dye-sensitized solar cells (DSCs), which are a potential candidate for next generation solar cells. In this study, we have characterized the ultrafast photoexcited electron dynamics in a newly produced linearly-linked two dye co-sensitized solar cell using both a transient absorption (TA) and an improved transient grating (TG) technique, in which tin(IV) 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (NcSn) and cis-diisothiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(II) bis(tetrabutylammonium) (N719) are molecularly and linearly linked and are bonded to the surface of a nanocrystalline tin dioxide (SnO(2)) electrode by a metal-O-metal linkage (i.e. SnO(2)-NcSn-N719). By comparing the TA and TG kinetics of NcSn, N719, and hybrid NcSn-N719 molecules adsorbed onto both of the SnO(2) and zirconium dioxide (ZrO(2)) nanocrystalline films, the forward and backward electron transfer dynamics in SnO(2)-NcSn-N719 were clarified. We found that there are two pathways for electron injection from the linearly-linked two dye molecules (NcSn-N719) to SnO(2). The first is a stepwise electron injection, in which photoexcited electrons first transfer from N719 to NcSn with a transfer time of 0.95 ps and then transfer from NcSn to the conduction band (CB) of SnO(2) with two timescales of 1.6 ps and 4.2 ps. The second is direct photoexcited electron transfer from N719 to the CB of SnO(2) with a timescale of 20-30 ps. On the other hand, back electron transfer from SnO(2) to NcSn is on a timescale of about 2 ns, which is about three orders of magnitude slower compared to the forward electron transfer from NcSn to SnO(2). The back electron transfer from NcSn to N719 is on a timescale of about 40 ps, which is about one order slower compared to the forward electron transfer from N719 to NcSn. These results demonstrate that photoexcited electrons can be effectively injected into SnO(2) from both of the N719 and NcSn dyes.