An iron catalyzed regioselective oxidation of terminal alkenes to aldehydes

Fe(BF(4))(2)·6H(2)O with pyridine-2,6-dicarboxylic acid and PhIO can efficiently catalyze the regioselective oxidation of terminal alkene derivatives to aldehydes under mild and benign reaction conditions.     

Combined experimental-theoretical characterization of the hydrido-cobaloxime [HCo(dmgH)2(PnBu3)

A combined theoretical and experimental approach has been employed to characterize the hydrido-cobaloxime [HCo(dmgH)(2)(PnBu(3))] compound. This complex was originally investigated by Schrauzer et al. [Schrauzer et al., J. Am. Chem. Soc. 1971, 93,1505] and has since been referred to as a key, stable analogue of the hydride intermediate involved in hydrogen evolution catalyzed by cobaloxime compounds [Artero, V. et al. Angew. Chem., Int. Ed. 2011, 50, 7238-7266]. We employed quantum chemical calculations, using density functional theory and correlated RI-SCS-MP2 methods, to characterize the structural and electronic properties of the compound and observed important differences between the calculated (1)H NMR spectrum and that reported in the original study by Schrauzer and Holland. To calibrate the theoretical model, the stable hydrido tetraamine cobalt(III) complex [HCo(tmen)(2)(OH(2))](2+) (tmen = 2,3-dimethyl-butane-2,3-diamine) [Rahman, A. F. M. M. et al. Chem. Commun. 2003, 2748-2749] was subjected to a similar analysis, and, in this case, the calculated results agreed well with those obtained experimentally. As a follow-up to the computational work, the title hydrido-cobaloxime compound was synthesized and recharacterized experimentally, together with the Co(I) derivative, giving results that were in agreement with the theoretical predictions.     

A Self-Healing Metal–Organic Hydrogel for an All-Solid Flexible Supercapacitor

A zinc containing metal–organic gel (Zn-MOG) with embedded free ions, which exhibits self-healing properties, has been synthesized for application in supercapacitors. The activated carbon-based flexible supercapacitor device with the MOG electrolyte has a broad potential window of 2.1 V, with high retention of specific capacitance compared to the traditional polyvinyl alcohol (PVA)-based gel. The Zn-MOG does not require an additional electrolyte. The sodium and sulphate ions embedded in the MOG are sufficient enough for the charge storage.     

Hierarchical Order Parameters for Macromolecular Assembly Simulations I: Construction and Dynamical Properties of Order Parameters

Macromolecular assemblies often display a hierarchical organization of macromolecules or their sub-assemblies. To model this, we have formulated a space warping method that enables capturing overall macromolecular structure and dynamics via a set of coarse-grained order parameters (OPs). This article is the first of two describing the construction and computational implementation of an additional class of OPs that has built into them the hierarchical architecture of macromolecular assemblies. To accomplish this, first, the system is divided into subsystems, each of which is described via a representative set of OPs. Then, a global set of variables is constructed from these subsystem-centered OPs to capture overall system organization. Dynamical properties of the resulting OPs are compared to those of our previous nonhierarchical ones, and implied conceptual and computational advantages are discussed for a 100ns, 2 million atom solvated Human Papillomavirus-like particle simulation. In the second article, the hierarchical OPs are shown to enable a multiscale analysis that starts with the N-atom Liouville equation and yields rigorous Langevin equations of stochastic OP dynamics. The latter is demonstrated via a force-field based simulation algorithm that probes key structural transition pathways, simultaneously accounting for all-atom details and overall structure.     

A review on thiocyanate methods for the estimation of molybdenum by molecular absorption spectroscopy

A review is presented on thiocyanate methods for the estimation of molybdenum in a wide variety of samples. They include conventional thiocyanate methods in which molybdenum forms an orange red complex with the thiocyanate ions and improved thiocyanate methods where the sensitivity is increased through the formation of ternary ion association complex.     

Rational design of single-composition ABC collagen heterotrimers

Design of heterotrimeric ABC collagen triple helices is challenging due to the large number of competing species that may be formed. Given the required one amino acid stagger between adjacent peptide strands in this fold, a ternary mixture of peptides can form as many as 27 triple helices with unique composition or register. Previously we have demonstrated that electrostatic interactions can be used to bias the helix population toward a desired target. However, homotrimeric assemblies have always remained the most thermally stable species in solution and therefore comprised a significant component of the peptide mixture. In this work we incorporate complementary modifications to this triple-helical design strategy to destabilize an undesirable competing state while compensating for this destabilization in the desired ABC composition. The result of these modifications is a new ABC triple-helical system with high thermal stability and control over composition, as observed by NMR. An additional set of modifications, which exchanges aspartate for glutamate, results in an overall lowering of stability of the ABC triple helix yet shows further improvement in the system's specificity. This rationally designed system helps to elucidate the rules governing the self-assembly of synthetic collagen triple helices and sheds light on the biological mechanisms of collagen assembly.     

Selective recognition of fluoride and acetate by a newly designed ruthenium framework: experimental and theoretical investigations

An effective anion sensor, [Ru(II)(bpy)(2)(H(2)L(-))](+) (1(+)), based on a redox and photoactive {Ru(II)(bpy)(2)} moiety and a new ligand (H(3)L = 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid), has been developed for selective recognition of fluoride (F(-)) and acetate (OAc(-)) ions. Crystal structures of the free ligand, H(3)L and [1](ClO(4)) reveal the existence of strong intramolecular and intermolecular hydrogen bonding interactions. The structure of [1](ClO(4)) shows that the benzimidazole N-H of H(2)L(-) is hydrogen bonded with the pendant carboxylate oxygen while the imidazole N-H remains free for possible hydrogen bonding interaction with the anions. The potential anion sensing features of 1(+) have been studied by different experimental and theoretical (DFT) investigations using a wide variety of anions, such as F(-), Cl(-), Br(-), I(-), HSO(4)(-), H(2)PO(4)(-), OAc(-) and SCN(-). Cyclic voltammetry and differential pulse voltammetry established that 1(+) is an excellent electrochemical sensor for the selective recognition of F(-) and OAc(-) anions. 1(+) is also found to be a selective colorimetric sensor for F(-) or OAc(-) anions where the MLCT band of the receptor at 498 nm is red shifted to 538 nm in the presence of one equivalent of F(-) or OAc(-) with a distinct change in colour from reddish-orange to pink. The binding constant between 1(+) and F(-) or OAc(-) has been determined to be logK = 7.61 or 7.88, respectively, based on spectrophotometric titration in CH(3)CN. The quenching of the emission band of 1(+) at 716 nm (λ(ex) = 440 nm, Φ = 0.01 at 298 K in CH(3)CN) in the presence of one equivalent of F(-) or OAc(-), as well as two distinct lifetimes of the quenched and unquenched forms of the receptor 1(+), makes it also a suitable fluorescence-based sensor. All the above experiments, in combination with (1)H NMR, suggest the formation of a 1:1 adduct between the receptor (1(+)) and the anion (F(-) or OAc(-)). The formation of 1:1 adduct {[1(+)·F(-)] or [1(+)·OAc(-)]} has been further evidenced by in situ ESI-MS(+) in CH(3)CN. Though the receptor, 1(+), is comprised of two N-H protons associated with the coordinated H(2)L(-) ligand, only the free imidazole N-H proton participates in the hydrogen bonding interactions with the incoming anions, while the intramolecularly hydrogen bonded benzimidazole N-H proton remains intact as evidenced by the crystal structure of the final product (1). The hydrogen bond mediated anion sensing mechanism, over the direct deprotonation pathway, in 1(+) has been further justified by a DFT study and subsequent NBO analysis.     

Direct heteroarylation of tautomerizable heterocycles into unsymmetrical and symmetrical biheterocycles via Pd/Cu-catalyzed phosphonium coupling

The direct cross-coupling of tautomerizable heterocycles with various unfunctionalized heteroarenes has been achieved through PyBroP-mediated and Pd/Cu-catalyzed sequential C-OH/C-H activation. The methodology allows a facile entry into novel diazine-azole biheterocyclic frameworks. Moreover, an unprecedented Pd-catalyzed phosphonium homocoupling of tautomerizable heterocycles was also developed to afford a direct synthetic route to symmetrical 1,2-, 1,3-, and 1,4-bidiazine units.