Simple and regioselective oxyiodination of aromatic compounds with ammonium iodide and Oxone

A simple method for the iodination of aromatic compounds using NH₄I as the iodine source and Oxone^® as the oxidant is described.     

N7-guanine as a C+ mimic in hairpin aeg/aepPNA-DNA triplex: probing binding selectivity by UV-Tm and kinetics by fluorescence-based strand-invasion assay

N7-substituted guanine (N7G) has been introduced into aminoethylglycyl bisPNA (7) as a C(+) mimic to achieve pH-independent triplex formation with complementary DNA sequences. The introduction of chiral, cationic aminoethylprolyl units with C(+) and C(+) mimic N7G in the backbone of bisPNAs (8, 9) influenced the recognition of complementary DNA in an orientation-selective manner. A simple fluorescence assay is developed to examine the process of strand invasion of target DNA duplex by these modified bisPNAs and comparative results of the study employing triplex forming polypyrimidine (C/T) (6, 8) and purine-pyrimidine (N7G/T) mixmer-bisPNAs (7, 9) are presented.     

Identification of Inhibitors for Mycobacterial Protein Tyrosine Phosphatase B (MptpB) by Biology‐Oriented Synthesis (BIOS)

Protein phosphatases have recently emerged as important targets for research in chemical biology and medicinal chemistry, and new classes of phosphatase inhibitors are in high demand. BIOS (biology‐oriented synthesis) employs the criteria of relevance to nature and biological prevalidation for the design and synthesis of compound collections. In an application of the BIOS principle, an efficient solid‐phase synthesis of highly substituted indolo[2,3‐a]quinolizidines by using a vinylogous Mannich–Michael reaction in combination with phosgene‐ or acid‐mediated ring closure was developed. Screening of this library for phosphatase inhibitors yielded a new inhibitor class for the Mycobacterium tuberculosis phosphatase MptpB.     

Determination of nitrate in environmental water samples by conversion into nitrophenols and solid phase extraction−spectrophotometry, liquid chromatography or gas chromatography-mass spectrometry

Conversion of nitrate into a nitro-phenol derivative by reaction with 2-methylphenol or 2,6-dimethylphenol allowed at least 100-fold enrichment of the derivative on Lichrolut EN polymeric cartridge, and it is stable for up to 1 month on the cartridge. The derivative could be eluted with ammonia-methanol mixture. This reaction for nitrate determination has permitted a choice of final measurement by UV-Vis spectrophotometry, liquid chromatography or gas chromatography-mass spectrometry when the limits of detection were 10, 6 and 3 μg l⁻¹, respectively, and the calibration range 20 μg to 10 mg l⁻¹ nitrate. The method has been validated by spiking natural water samples, when the recovery of nitrate was 98.5-108.4% (relative standard deviation 2.5-6.1%).     

Diastereoselective Baylis-Hillman reaction: first use of chiral 2,3-epoxy aldehydes as novel electrophiles

Chiral 2,3-epoxy aldehydes have been effectively utilized for the first time as novel electrophiles in Baylis-Hillman reactions with activated alkenes to result in densely functionalized adducts in good yields (61-80%) and in moderate to good diastereoselectivities (40-72% de).     

A computational study of CO2, N2, and CH4 adsorption in zeolites

The adsorption properties of CO₂, N₂ and CH₄ in all-silica zeolites were studied using molecular simulations. Adsorption isotherms for single components in MFI were both measured and computed showing good agreement. In addition simulations in other all silica structures were performed for a wide range of pressures and temperatures and for single components as well as binary and ternary mixtures with varying bulk compositions. The adsorption selectivity was analyzed for mixtures with bulk composition of 50:50 CO₂/CH₄, 50:50 CO₂/N₂, 10:90 CO₂/N₂ and 5:90:5 CO₂/N₂/CH₄ in MFI, MOR, ISV, ITE, CHA and DDR showing high selectivity of adsorption of CO₂ over N₂ and CH₄ that varies with the type of crystal and with the mixture bulk composition.     

Challenges in semiconductor single-entity photoelectrochemistry

It is challenging to study the single semiconductor nanocrystal electrochemistry and photoelectrochemistry. The photocatalytic processes, such as the oxidation of methanol and iodide, that result from the electron–hole pair formed within a nanoparticle (NP) allow the detection of discrete current transient events assigned to single entities. Photocatalytic current amplification allows detection of collisions between the semiconductor NPs and the ultramicroelectrode that produce current transient. Staircase responses and blips in the i vs. t response indicate that irreversible and reversible NP/electrode interactions result depending on the experimental conditions. Dye sensitization increases the photocurrent magnitude of ZnO and TiO₂ with respect to bare TiO₂ NPs. The microelectrodes used are Pt, TiO₂/Pt, TiO₂/Au, and F-doped SnO₂.     

Application of voltammetric methods for the analysis of gold and other transition metals in quartzite rock

Simple, rapid and accurate voltammetric methods viz. DCP, DPP and DPASV have been presented for the trace determination of gold and other transition metals in quartzite rock sample. The analysis has been performed using 0.1 M(NH4)2 tartrate, 0.1 M NaClO4 and 1 M NaOH as supporting electrolyte with 0.001% gelatin as maximum suppressor. The results show the presence of CuII(10.70), CoII(4.72), FeIII(66.96), AuIII(0.066), ZnII(1.68) and CdII(0.62) mg x g(-1) metal ions from the sample. Gold produced a well defined wave/peak with E1,2/Ep = -0.61 V/-0.64 V vs SCE, in 1 M NaOH supporting electrolyte. The quantitative analysis of metal inos was carried out by the method of standard addition. Statistical treatment of the observed voltammetric data reveals high accuracy and good precision of determination. The observed voltammetric results are comparable with those obtained using AAS method.     

Determination of the conformation of trimethoprim in the binding pocket of bovine dihydrofolate reductase from a STD-NMR intensity-restrained CORCEMA-ST optimization

Dihydrofolate reductase (DHFR) is a pharmacologically important intracellular target enzyme for folate antagonists, including the antibacterial agent trimethoprim (TMP). The structures of DHFR from various sources with and without the bound ligands have been determined by X-ray crystallography and solution NMR spectroscopy. However, there is no crystal or solution NMR structure for the bovine DHFR/TMP complex. Here we report the solution structure of TMP within the binding pocket of bovine DHFR using a novel method developed in our laboratory, viz., STD-NMR intensity-restrained CORCEMA-ST optimization (SICO) utilizing experimental STD data on this complex, and demonstrate that its solution structure is essentially identical to the one in the crystal structure of the homologous chicken liver DHFR/TMP complex. The excellent agreement we obtain between the experimental and predicted STDs also serves as a validation of the CORCEMA-ST methodology.     

Cross-Polarisation Applied to the Study of Liquid Crsytalline Ordering

 Cross polarisation is extensively used in solid state NMR for enhancing signals of nuclei with low gyromagnetic ratio. However, the use of the method for providing quantitative structural and dynamics information is limited. This arises due to the fact that the mechanism which is responsible for cross polarisation namely, the dipolar interaction, has a long range and is also anisotropic. In nematic liquid crystals these limitations are easily overcome since molecules orient in a magnetic field. The uniaxial ordering of the molecules essentially removes problems associated with the angular dependence of the interactions encountered in powdered solids. The molecular motion averages out intermolecular dipolar interaction, while retaining partially averaged intramolecular interaction. In this article the use of cross polarisation for obtaining heteronuclear dipolar couplings and hence the order parameters of liquid crystals is presented. Several modifications to the basic experiment were considered and their utility illustrated. A method for obtaining proton–proton dipolar couplings, by utilizing cross polarisation from the dipolar reservoir, is also presented.