A turn on ESIPT probe for rapid and ratiometric fluorogenic detection of homocysteine and cysteine in water with live cell-imaging

5(Benzothiazol-2-yl)-4-hydroxyisophthalaldehyde (BHI), an intense ESIPT containing molecule in mixed media loses its properties due to resonance-assisted H-bond (RAHB) in absolute water. Due to resonance-assisted H-bond the o-aldehyde is more reactive than the other one. With addition of cysteine/homocysteine into this solution the o-aldehyde group gets transformed into thiazolidine/thiazine ring, respectively, and the phenolic proton becomes free enough for transfer to nitrogen of the benzothiazole ring in excited state, that is, the ESIPT of BHI is turned on. Thus we can detect cysteine/homocysteine in water as well as in live cells.     

Crack tortuousity in the nacreous layer – Topological dependence and biomimetic design guideline

The nacreous layer in seashells is known for two phenomenal aspects: light-weightiness and superior fracture toughness. Of a multitude of toughening mechanisms, the highly meandering nature of the crack path through its staggered architecture has been reported to contribute approximately a third of its overall toughness. In the current article, we are trying to establish the scientific rationale associated with the influence of overlap length on the crack-tip driving force from a local perspective via development of a simplified analytical model. Characteristic overlap lengths computed showed reasonable agreement with the values reported in the nacreous layer and previously published experimental data. Biomimetic design guideline obtained from the current investigation would thereby lead to development of synthetic staggered architecture materials with improved stiffness, load-transfer and toughness.     

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.     

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.     

The antimony(III)-bridged heteropolyanion sandwich dimers [Sb(II3(A-α-XW9O34)2]11- (X = SiIV, GeIV and C-shaped double-sandwich [SbIII6O2(PW6O26)(A-α-PW9O34)2]15-

Interaction of potassium antimony(iii) tartrate hydrate K(2)(SbC(4)H(2)O(6))(2)·3H(2)O with the trilacunary Keggin derivatives [A-α-XW(9)O(34)](10-) (X = Si(IV), Ge(IV)) and [A-α-PW(9)O(34)](9-) in aqueous acidic medium (pH 4.8) resulted in three novel polyanions, [Sb(3)(A-α-XW(9)O(34))(2)](11-) (X = Si(IV) (1), Ge(IV) (2)) and [Sb(6)O(2)(A-PW(6)O(26))(A-α-PW(9)O(34))(2)](15-) (3), which were isolated as the hydrated potassium salts K(11)[Sb(3)(A-α-XW(9)O(34))(2)]·31H(2)O (X = Si(IV) (K-1), Ge(IV) (K-2)) and the mixed potassium-sodium salt K(14)Na[Sb(6)O(2)(A-PW(6)O(26))(A-α-PW(9)O(34))(2)]·61H(2)O (KNa-3) salts, respectively, and characterized by single-crystal X-ray diffraction, IR spectroscopy, as well as elemental and thermogravimetric analyses. The Sb(III)-containing polyanions 1-3 possess unique structural features, as they represent the first examples of sandwich-type POMs with trigonal-pyramidal Sb(III)O(3) linkers. The stability of 1-3 in aqueous media was investigated by multinuclear ((183)W, (31)P) NMR and UV-Vis spectroscopy.     

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.     

Ba(1-x)K(x)Mn2As2: an antiferromagnetic local-moment metal

The compound BaMn2As2 with the tetragonal ThCr2Si2 structure is a local-moment antiferromagnetic insulator with a Néel temperature T(N)=625 K and a large ordered moment μ=3.9μ(B)/Mn. We demonstrate that this compound can be driven metallic by partial substitution of Ba by K while retaining the same crystal and antiferromagnetic structures together with nearly the same high T(N) and large μ. Ba(1-x)K(x)Mn2As2 is thus the first metallic ThCr2Si2-type MAs-based system containing local 3d transition metal M magnetic moments, with consequences for the ongoing debate about the local-moment versus itinerant pictures of the FeAs-based superconductors and parent compounds. The Ba(1-x)K(x)Mn2As2 class of compounds also forms a bridge between the layered iron pnictides and cuprates and may be useful to test theories of high T(c) superconductivity.