Microwave promoted improved regioselective synthesis of 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones by radical cyclisation

In this work, two new effective methodologies have been adopted for the preparation of 5-(2′-bromobenzyloxy)pyrimidine-2,4-diones 6(a–k). In the first methodology, 5-hydroxy uracils 4(a–f) were alkylated with 2-bromobenzyl bromide 5a or 2-bromo-5-methoxy benzyl bromide 5b under phase transfer catalysis condition using lithium hydroxide/tetrabutyl ammonium bromide in N,N-dimethylformamide at 45 °C, and in the second method, the microwave irradiation (MWI) protocol has been exploited by mixing 5-hydroxy uracils 4(a–f) with 30 % excess of 2-bromobenzyl bromide 5a or 2-bromo-5-methoxy benzyl bromide 5b. A catalytic amount of TBAB and potassium carbonate was added and irradiated in an open Erlenmeyer flask in a microwave oven for 3–12 min. The tributyltin hydride-mediated radical cyclisation of 6(a–k) was carried out under MWI to generate 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones 7(a–k) in 80–89 % yield, and the reaction time was shortened compared to the previously reported conventional radical cyclisation method.     

Exploring the Effect of Bioisosteric Replacement of Carboxamide by a Sulfonamide Moiety on N‐Glycosidic Torsions and Molecular Assembly: Synthesis and X‐ray Crystallographic Investigation of N‐(β‐D‐Glycosyl)sulfonamides as N‐Glycoprotein Linkage Region Analogues

N‐Glycoprotein linkage region constituents, 2‐acetamido‐2‐deoxy‐β‐D ‐glucopyranose (GlcNAc) and asparagine (Asn) are conserved among all the eukaryotes. To gain a better understanding for nature’s choice of GlcNAcβAsn as linkage region constituents and inter‐ and intramolecular carbohydrate–protein interactions, a detailed systemic structural study of the linkage region conformation is essential. Earlier crystallographic studies of several N‐(β‐glycopyranosyl)alkanamides showed that N‐glycosidic torsion, ?_N, is influenced to a larger extent by structural variation in the sugar part than that of the aglycon moiety. To explore the effect of the bioisosteric replacement of a carboxamide group by a sulfonamide moiety on the N‐glycosidic torsions as well as on molecular assembly, several glycosyl methanesulfonamides and glycosyl chloromethanesulfonamides were synthesized as analogues of the N‐glycoprotein linkage region, and crystal structures of seven of these compounds have been solved. A comparative analysis of this series of crystal structures as well as with those of the corresponding alkanamido derivatives revealed that N‐glycosidic torsion, ?_N, does not alter significantly. Methanesulfonamido and chloromethanesulfonamido derivatives of GlcNAc display a different aglycon conformation compared to other sulfonamido analogues. This may be due to the cumulative effect of the direct hydrogen bonding between N1 and O1′ and C? H???O interactions of the aglycon chain, revealing the uniqueness of the GlcNAc as the linkage sugar.     

Multi-way modeling of hydro-chemical data of an alluvial river system--a case study

A large data set pertaining to water quality of an alluvial river was analyzed using multi-way data analysis methods with a view to extract the hidden information, spatial and temporal variation trends in the river water quality. Four-way data (8 monitoring sites × 22 water quality variables × 10 monitoring years × 12 sampling months) analysis was performed using PARAFAC and Tucker3 models. A two component PARAFAC model, although explained 35.1% of the data variance, could not fit to the data set. Tucker3 model of optimum complexity (2,3,1,3) explaining 39.7% of the data variance, allowed interpretation of the data information in four modes. The model explained spatial and temporal variation trends in terms of water quality variables during the study period and revealed that sampling sites in mid-stretch of the river were dominated mainly by the variables of anthropogenic origin. The results delineated the mid stretch of the river as critical from pollution point of view and also identified summer months as having high influence on river water quality in this stretch. The information regarding spatial and temporal variations in water quality generated by the four-way modeling of data would be useful in developing long-term water resources management strategies in the river basin.     

Competing magnetic interactions in a dinuclear Ni(II) complex: antiferromagnetic O-H...O moiety and ferromagnetic N3- ligand

Synthesis, structural characteristics, magnetic studies and DFT calculations in Ni(II) dinuclear complexes containing two bridging N3- and an O-H...O linkage reveal the existence of ferromagnetic interactions between Ni(II) centers via N3- ligands and antiferromagnetic interactions through the H-bonded moiety. The overall magnetic behavior of the system depends on the delicate balance between these two competing interactions.     

Insights into the role of Val45 and Gln182 of Escherichia coli MutY in DNA substrate binding and specificity

Background  

Escherichia coli MutY (EcMutY) reduces mutagenesis by removing adenines paired with guanines or 7,8-dihydro-8-oxo-guanines (8-oxoG). V45 and Q182 of EcMutY are considered to be the key determinants of adenine specificity. Both residues are spatially close to each other in the active site and are conserved in MutY family proteins but not in Methanobacterium thermoautotrophicum Mig.MthI T/G mismatch DNA glycosylase (A50 and L187 at the corresponding respective positions).     

Accretion disks around the Gibbons–Maeda–Garfinkle–Horowitz–Strominger charged black holes

It seems surprising that the emissivity properties of the accretion disk (à la Page and Thorne) surrounding the Gibbons–Maeda–Garfinkle–Horowitz–Strominger (GMGHS) black holes of heterotic string theory have not yet been studied. To fill this gap in the literature, we study the emissivity properties of the thin accretion disks around these black holes both in the Einstein and in the string frame using the Page–Thorne model. For illustration, we choose as a toy model a stellar-sized spherically symmetric black hole and find that, while the emissivity properties do not significantly differ from those of Reissner–Nordström and Schwarzschild black holes, they remarkably differ at GMGHS extreme limits corresponding to naked singularity and wormhole at higher frequencies. These differences provide a novel way to speculatively conclude about different types of objects from the observational point of view.     

Family of mixed-valence oxovanadium(IV/V) dinuclear entities incorporating N4O3-coordinating heptadentate ligands: synthesis, structure, and EPR spectra

Dinuclear (V(IV)V(V)) oxophenoxovanadates of general formula [V2O3L] have been synthesized in excellent yields by reacting bis(acetylacetonato)oxovanadium(IV) with H3L in a 2:1 ratio in acetone under an N2 atmosphere. Here L3- is the deprotonated form of 2,6-bis[{{(2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L1), 2,6-bis[{{(5-methyl-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L2), 2,6-bis[{{(5-tert-butyl-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L3), 2,6-bis[{{(5-chloro-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol(H3L4), 2,6-bis[{{(5-bromo-2-hydroxybenzyl)(N'N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L5), or 2,6-bis[{{(5-methoxy-2-hydroxybenzyl)(N'N'-(dimethylamino)ethyl)}methyl]-4-methylphenol (H3L6). In [V2O3L1], both the metal atoms have distorted octahedral geometry. The relative disposition of two terminal V=O groups in the complex is essentially cis. The O=V...V=O torsion angle is 24.6(2) degrees . The V-O(oxo)-V and V-O(phenoxo)-V angles are 117.5(4) and 93.4(3) degrees , respectively. The V...V bond distance is 3.173(5) A. X-ray crystallography, IR, UV-vis, and 1H and 51V NMR measurements show that the mixed-valence complexes contain two indistinguishable vanadium atoms (type III). The thermal ellipsoids of O2, O4, C10, C14, and C15 also suggests a type III complex in the solid state. EPR spectra of solid complexes at 77 K display a single line indicating the localization of the odd electron (3d(xy)1). Valence localization at 77 K is also consistent with the 51V hyperfine structure of the axial EPR spectra (3d(xy)1 ground state) of the complexes in frozen (77 K) dichloromethane solution: S = 1/2, g(parallel) approximately 1.94, g(perpendicular) approximately 1.98, A(parallel) approximately 166 x 10(-4) cm(-1), and A(perpendicular) approximately 68 x 10(-4) cm(-1). In contrast isotropic room-temperature solution spectra of the family have 15 hyperfine lines (g(iso) approximately 1.974 and A(iso) approximately 50 x 10(-4) cm(-1)) revealing that the unpaired electron is delocalized between the metal centers. Crystal data for the [V2O3L1].CH2Cl2 complex are as follows: chemical formula, C32H43O6N4Cl2V2; crystal system, monoclinic; space group, C2/c; a = 18.461(4), b = 17.230(3), c = 13.700(3) A; beta = 117.88(3) degrees ; Z = 8.     

Rh(i)- and Rh(ii)-catalyzed C–H alkylation of benzylamines with alkenes and its application in flow chemistry

The Rh-catalyzed C–H alkylation of benzylamines with alkenes using a picolinamide derivative as a directing group is reported. Both Rh(i) and Rh(ii) complexes can be used as active catalysts for this transformation. In addition, a flow set up was designed to successfully mimic this process under flow conditions. Several examples are presented under flow conditions and it was confirmed that a flow process is advantageous over a batch process. Deuterium labelling experiments were performed to elucidate the mechanism of the reaction, and the results indicated a possible carbene mechanism for this C–H alkylation process.

Rh(i)- and Rh(ii)-catalyzed C–H alkylation of benzylamines with alkenes using a picolinamide derivative as a directing group is reported under both batch and flow.     

Selective Colorimetric Sensing of Geometrical Isomers of Dicarboxylates in Water by Using Functionalized Gold Nanoparticles

A colorimetric sensing system based on gold nanoparticles functionalized with a water‐soluble anion‐recognition motif, an o‐(carboxamido)trifluoroacetophenone analogue, has been developed. The nanoparticle system selectively senses specific isomers of dicarboxylates that are geometrically favorable for the binding‐induced aggregation process; thus, it discriminates a trans‐dicarboxylate fumarate from its cis‐isomer maleate, and benzene‐1,4‐dicarboxylate from its isomeric benzene‐1,2‐and benzene‐1,3‐dicarboxylates in water, exhibiting a color change from red to blue.     

Recovery and Reuse of Composite Cathode Binder in Lithium Ion Batteries

Here, we investigate the recovery and reuse of polyvinylidene fluoride (PVDF) binders from both homemade and commercial cathode films in Li ion batteries. We find that PVDF solubility depends on whether the polymer is an isolated powder or cast into a composite film. A mixture of tetrahydrofuran:N-methyl-2-pyrrolidone (THF : NMP, 50 : 50 v/v) at 90 °C delaminates composite cathodes from Al current collectors and yields pure PVDF as characterized by ¹H nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), wide-angle X-ray scattering (WAXS), and scanning electron microscopy (SEM). PVDF recovered from Li ion cells post-cycling exhibits similar performance to pristine PVDF. These data suggest that PVDF can be extracted and reused during Li ion battery recycling while simultaneously eliminating the formation of HF etchants, providing an incentive for use in direct cathode recycling.