Reduction of Methylene Green by EDTA:Kinetic and Thermodynamic Aspects

The reduction of methylene green (MG) into protonated leuco dye with ethylenediamine tetraacetic acid (EDTA) in aqueous alkaline medium was studied spectrophotometrically at λ_max 660 nm. EDTA behaved as an effective electron donor during the reduction of MG in an aerobic condition. Consumption of EDTA in the reduction of MG means that it is oxidized. This is an unexpected result since EDTA does not normally function as a reducing agent. The nitrogen-containing chelating agents with secondary or tertiary nitrogen behaved as an electron donor in photochemical reaction of dye. The rate of reduction depends upon pH in the same way as the base titration of EDTA. Effects of salt and temperature have been investigated for the reduction process. The salting agent KNO₃ has been found to uniquely enhance the rate of reduction of MG by EDTA in the aerobic condition. Detailed kinetic and thermodynamic aspects have been discussed to realize the interaction between MG and EDTA. Kinetic studies revealed that reaction was sensitive and regeneration of oxidized form of the dye was observed. Reversible first order reaction kinetics with respect to EDTA, MG and NaOH was found.     

Sulfate anion templation of a neutral pseudorotaxane assembly using an indolocarbazole threading component

The first example of anion templated pseudorotaxane formation between two neutral components in solution and in surface assembled monolayers is described.     

Bulky aryl functionalized carbazolyl ligands: amido alternatives to the 2,6-diarylphenyl ligand class?

Sterically encumbered amido ligands based on a 1,8-diarylcarbazol-9-yl backbone have been investigated as electronically distinct alternatives to the widely-used terphenyl ligand class in the stabilization of low-coordinate metal complexes, and structurally characterized for the first time. While 1,8-diphenylcarbazol-9-yl derivatives are readily available, facile rotation about the Cipso-Cipso bonds leads to structurally characterized main group derivatives {e.g., [(1,8-Ph,-3,6-Me2C12H4N)K]2} in which the coordination geometry at the metal centre is augmented by secondary metal arene interactions. By contrast, the extra bulk inherent in the corresponding 1,8-dimesityl ligand results in essentially perpendicular alignments of the arene and carbazole planes, and a substituent-enforced sterically protected pocket. Comparative structural studies of complexes containing the GaCl2 fragment imply that the 1,8-dimesitylcarbazol-9-yl framework offers greater steric protection at the metal centre than does the corresponding 2,6-dimesitylphenyl ligand.     

Microbial metabolism part 9. Structure and antioxidant significance of the metabolites of 5,7-dihydroxyflavone (chrysin), and 5- and 6-hydroxyflavones

5,7-Dihydroxyflavone (chrysin) (1) when fermented with fungal cultures, Aspergillus alliaceous (ATCC 10060), Beauveria bassiana (ATCC 13144) and Absidia glauco (ATCC 22752) gave mainly 4'-hydroxychrysin (4), chrysin 7-O-beta-D-4-O-methylglucopyranoside (5) and chrysin 7-sulfate (6), respectively. Mucore ramannianus (ATCC 9628), however, transformed chrysin into six metabolites: 4'-hydroxy-3'-methoxychrysin (chrysoeriol) (7), 4'-hydroxychrysin (apigenin) (4) 3',4'-dihydroxychrysin (luteolin) (8), 3'-methoxychrysin 4'-O-alpha-D-6-deoxyallopyranoside (9), chrysin 4'-O-alpha-D-6-deoxyallopyranoside (10), and luteolin 3'-sulfate (11). Cultures of A. alliaceous (ATCC 10060) and B. bassiana (ATCC 13144) metabolized 5-hydroxyflavone (2) into 5,4'-dihydroxyflavone (12) and 4'-hydroxyflavone 5-O-beta-D-4-O-methylglucopyranoside (13), respectively. 6-Hydroxyflavone (3) was transformed into 6-hydroxyflavanone (14), flavone 3-O-beta-D-4-O-methylglucopyranoside (15) and (+/-)-flavanone 6-O-beta-D-4-O-methylglucopyranoside (16) by cultures of Beauveria bassiana (ATCC 13144). The structures of the metabolic products were elucidated by means of spectroscopic data. The significance of the metabolites as antioxidants in relation to their structure is briefly discussed.     

Separation of substituted fullerenes using non-aqueous reversed-phase liquid chromatography-mass spectrometry

A simple non-aqueous reversed-phase separation HPLC-MS method has been developed to allow for the rapid screening and separation of fullerenes and substituted fullerenes. This procedure provides confirmation that the proposed substitution methodology for the fullerene is not only successful but that multiple substitution products are obtained. The methodology is being expanded to analyze other substituted fullerene product mixtures.     

N-silyl protecting groups for labile aziridines: application toward the synthesis of N-H aziridinomitosenes

Hindered N-silylamines were examined for their utility to serve as protecting groups for the labile aziridine nitrogen found within the highly sensitive aziridinomitosene framework. tert-Butyldiphenylsilyl and modified tert-butyldiphenylsilyl groups were the most resistant to nitrogen-silicon bond cleavage under various reaction conditions and were thus employed in transformations relevant to aziridinomitosene synthesis. The N-silylaziridines 7a, 21a, and 21b underwent azomethine ylide cycloaddition and afforded, upon deprotection, the N-H aziridine 24 in 18-32% overall yield for the three steps.     

Electron capture atmospheric pressure photoionization mass spectrometry: analysis of fullerenes, perfluorinated compounds, and pentafluorobenzyl derivatives

An electron capture (EC) ionization mechanism has been found to be highly efficient in negative-ion atmospheric pressure photoionization (APPI) for the analysis of compounds with positive electron affinity (EA). Using negative-ion APPI, we first report the sensitive detection of natural electrophores with limited polarity, such as fullerenes and perfluorinated compounds, by mass spectrometry (MS). Using direct infusion on a quadrupole time-of-flight (QTOF) mass spectrometer, the limits of detection (LODs) for C(60) and perfluoromethylcyclohexane were determined to be 0.15 pg (0.2 fmol) and 1 femtoliter (fL) ( approximately 1.5 pg or 4.3 fmol), respectively. As the EA of the analyte increases, the detection sensitivity is enhanced. Making use of the accurate mass measurement capability of the QTOF mass spectrometer, we were able to investigate the elemental composition of the ions in each spectrum and attribute the observed high sensitivity to an EC-initiated ionization process. The proposed EC ionization mechanism is further supported by the observation of a dissociative EC reaction of pentafluorobenzyl (PFB)-derivatized phenols. The analysis of phenols by EC-APPI of their PFB derivatives resulted in very high sensitivity, with the lowest reported LOD of approximately 0.17 pg (0.5 fmol) being for 2,4-dinitrophenol. For future LC/EC-APPI-MS applications, the effect of additives and solvents on sensitivity was also tested and reported.     

Negative ion-atmospheric pressure photoionization: Electron capture,dissociative electron capture,proton transfer,and anion attachment

To better guide the development of liquid chromatography/electron capture-atmospheric pressure photoionization-mass spectrometry (LC/EC-APPI-MS) in analysis of low polarity compounds, the ionization mechanism of 19 compounds was studied using dopant assisted negative ion-APPI. Four ionization mechanisms, i.e., EC, dissociative EC, proton transfer, and anion attachment, were identified as being responsible for the ionization of the studied compounds. The mechanisms were found to sometimes compete with each other, resulting in multiple ionization products from the same molecule. However, dissociative EC and proton transfer could also combine to generate the same [M - H](-) ions. Experimental evidence suggests that O(2)(-*), which was directly observed in the APPI source, plays a key role in the formation of [M - H](-) ions by way of proton transfer. Introduction of anions more basic than O(2)(-*), i.e., C(6)H(5)CH(2)(-), into the APPI source, via addition of di-tert-butyl peroxide in the solvent and/or dopant, i.e., toluene, enhanced the deprotonation ability of negative ion-APPI. Although the use of halogenated solvents could hinder efficient EC, dissociative EC, and proton transfer of negative ion-APPI due to their EC ability, the subsequently generated halide anions promoted halide attachment to compounds that otherwise could not be efficiently ionized. With the four available ionization mechanisms, it becomes obvious that negative ion-APPI is capable of ionizing a wider range of compounds than negative ion chemical ionization (NICI), negative ion-atmospheric pressure chemical ionization (negative ion-APCI) or negative ion-electrospray ionization (negative ion-ESI).     

Experimental performance analysis of two different passive cooling techniques for solar photovoltaic installations

Journal of Thermal Analysis and Calorimetry - At higher ambient temperatures during summer months, the cell temperature of a photovoltaic (PV) module increases to 50–60 °C and sometimes...     

Some experimental aspects of absolute configuration determination using single crystal X-ray diffraction

Students of single crystal X-ray diffraction are often give advice as to how best to collect their data when attempting absolute configuration determination. These ‘rules’ often have more grounding in gut-feeling than evidence. Thus, in an effort to provide advice and evidence that today’s crystallographers can pass onto to tomorrow’s young scientists, we present a systematic study of 1-deoxy-l-arabinitol, a straight chain sugar which crystalises well in the space group $\text{I}{4}_1$.