Controlling the DNA binding specificity of bHLH proteins through intramolecular interactions

Reversible control of the conformation of proteins was employed to probe the relationship between flexibility and specificity of the basic helix-loop-helix protein MyoD. A fusion protein (apaMyoD) was designed where the basic DNA binding helix of MyoD was stablized by an amino-terminal extension with a sequence derived from the bee venom peptide apamin. The disulfide-stabilized helix from apamin served as a nucleus for a helix that extended for a further ten residues, thereby holding apaMyoD's DNA recognition helix in a predominantly alpha-helical conformation. The thermal stability of the DNA complexes of apaMyoD was increased by 13 degrees C relative to MyoD-bHLH. Measurements of the fluorescence anisotropy change on DNA binding indicated that apaMyoD bound to E-box-containing DNA sequences with enhanced affinity relative to MyoD-bHLH. Consequently, the DNA binding specificity of apaMyoD was increased 10-fold.     

Oxidation of isobutane catalyzed by vanadyl, copper and cesium substituted H3PMo12O40

Effects of Cs⁺, H⁺ and Cu²⁺ counterions in the vanadium containing heteropoly compounds Cs_xH_1-xVO[PMo₁₂O₄₀] and Cs_yH_0.5-yCu_0.25VO[PMo₁₂O₄₀] on the catalytic oxidation of isobutane and characterization by TGA, IR and ESR spectroscopies are reported. A high selectivity of 76% for methacrylic acid and methacrolein together has been obtained with Cs_0.75H_0.25VO[PMo₁₂O₄₀] catalysts at a reactivity of 5.3x10^-1 mmol/h cm³.     

Pinkment: a synthetic platform for the development of fluorescent probes for diagnostic and theranostic applications

Reaction-based fluorescent-probes have proven successful for the visualisation of biological species in various cellular processes. Unfortunately, in order to tailor the design of a fluorescent probe to a specific application (i.e. organelle targeting, material and theranostic applications) often requires extensive synthetic efforts and the synthetic screening of a range of fluorophores to match the required synthetic needs. In this work, we have identified Pinkment-OH as a unique “plug-and-play” synthetic platform that can be used to develop a range of ONOO⁻ responsive fluorescent probes for a variety of applications. These include theranostic-based applications and potential material-based/bioconjugation applications. The as prepared probes displayed an excellent sensitivity and selectivity for ONOO⁻ over other ROS. In vitro studies using HeLa cells and RAW 264.7 macrophages demonstrated their ability to detect exogenously and endogenously produced ONOO⁻. Evaluation in an LPS-induced inflammation mouse model illustrated the ability to monitor ONOO⁻ production in acute inflammation. Lastly, theranostic-based probes enabled the simultaneous evaluation of indomethacin-based therapeutic effects combined with the visualisation of an inflammation biomarker in RAW 264.7 cells.

Pinkment, a resorufin based ONOO⁻ selective and sensitive ‘plug and play’ fluorescence-based platform for in vitro and in vivo use, enables facile functionalisation for various imaging and theranostic applications.     

Syntheses and Structures of Two New Cu/Nb/pyrazine Complexes: Three dimensional CuNb(pyz)2OF5 · (pyz)(H2O) and two dimensional [Cu(pyz)2.5]+ [NbF6]− · (pyz)

Crystals of CuNb(pyz)₂OF₅ · (pyz)(H₂O) ( 1 ) and [Cu(pyz)_2.5]⁺ [NbF₆]^? · (pyz) ( 2 ) were grown (150°C and autogeneous pressures) from CuO, 1/2(Nb₂O₅), (HF)_x · pyridine, and H₂O in excess pyrazine. Light blue single crystals of ( 1 ) are orthorhombic, crystallizing in space group Cccm (No. 66), with a = 14.547(1) Å, b = 16.135(2) Å, c = 13.803(2) Å, and Z = 8. The structure of ( 1 ) contains corner shared [Cu(pyz)_4/2F_2/2]⁺, [Cu(pyz)_4/2O_2/2], and [NbF₄O_1/2F_1/2]^?0.5 octahedra. Orange crystals of ( 2 ) are monoclinic, crystallizing in space group C2/c (No. 15), with a = 11.792(8) Å, b = 17.123(3) Å, c = 17.051(5) Å, β = 90.04(4)°, and Z = 8. The structure of ( 2 ) contains puckered rings of corner shared [Cu(pyz)(pyz)_3/2]⁺ tetrahedra and isolated [NbF₆]^? anions within the rings.     

Determination of dissolved organic nitrogen in natural waters using high-temperature catalytic oxidation

Studies on nitrogen in natural waters have generally focussed on dissolved inorganic nitrogen (DIN), primarily because of relative ease of analysis and the important influence of DIN on water quality. Advances in analytical techniques now permit the systematic study of dissolved organic nitrogen (DON), and this work has shown that DON is quantitatively significant in many waters. This article describes the sampling and analytical protocols required for rapid, precise and reliable determinations of DON, involving high-temperature catalytic oxidation (HTCO), coupled to chemiluminescence detection. This approach simultaneously determines dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), and DON is derived by subtraction of DIN measured by colorimetry. The DON determination is simple to perform, exhibits excellent precision (<1% for C and 1.5% for N) and is applicable to a wide range of natural waters.     

Frustrated beta-chloride elimination. Selective arene alkylation by alpha-chloronorbornene catalyzed by electrophilic metallocenium ion pairs

Single-site polymerization catalysts generated in situ via activation of Cp*MMe(3) (Cp* = C(5)Me(5); M = Ti, Zr), (CGC)MMe(2) (CGC = C(5)Me(4)SiMe(2)NBu(t)(); M = Ti, Zr), and Cp(2)ZrMe(2) with Ph(3)C(+)B(C(6)F(5))(4)(-) catalyze alkylation of aromatic molecules (benzene, toluene) with alpha-chloronorbornene at room temperature, to regioselectively afford the 1:1 addition products exo-1-chloro-2-arylnorbornane (aryl = C(6)H(5) (1a), C(6)H(4)CH(3) (1b)) in good yields. Analogous deuterium-labeled products exo-1-chloro-2-aryl-d(n)-norbornane-7-d(1) (aryl-d(n) = C(6)D(5) (1a-d(6)), C(6)D(4)CD(3) (1b-d(8))) are obtained via catalytic arylation of alpha-chloronorbornene in either benzene-d(6) or toluene-d(8). Isolated ion-pair complexes such as (CGC)ZrMe(toluene)(+)B(C(6)F(5))(4)(-) and Cp(2)ThMe(+)B(C(6)F(5))(4)(-) also catalyze the reaction of alpha-chloronorbornene in toluene-d(8) to give 1b-d(8) in good yields, respectively. Small quantities of the corresponding bis(1-chloronorbornyl)aromatics 2 are also obtained from preparative-scale reactions. These reactions exhibit turnover frequencies exceeding 120 h(-1) (for the Cp*TiMe(3)/Ph(3)C(+)B(C(6)F(5))(4)(-)-catalyzed system), and chlorine-free products are not observed. Compounds 1 and 2 were characterized by (1)H, (2)H, (13)C, and 2D NMR, GC-MS, and elemental analysis. The aryl group exo-stereochemistry in 1a and 1b is established using (1)H-(1)H COSY, (1)H-(13)C HMBC, and (1)H-(1)H NOESY NMR, and is further corroborated by X-ray analysis of the product 1,4-bis(exo-1-chloro-2-norbornyl)benzene (2a). Control experiments and reactivity studies on each component step suggest a mechanism involving participitation of the metal electrophiles in the catalytic cycle.     

Is bismuth subsalicylate an effective nontoxic catalyst for plga synthesis?

Poly(d,l ‐lactide‐co‐glycolide) (PLGA) copolyesters are commonly used in biomedical applications. Researches were carried out on nontoxic or low‐toxic catalysts that are enough efficient to provide short polymerization times, adequate microstructure chains and similar properties than the commercial PLGA materials. In this study, PLGA were synthesized by ring‐opening copolymerization (ROP) using three different catalysts. Stannous octoate is the first catalyst we used, as it is very efficient, even its toxicity is still on debate. Two others low‐toxic catalysts [zinc lactate and bismuth subsalicylate (BiSS)] were also evaluated. The comparison of these ROP was realized in terms of kinetics and control of the polymerization. Then, the influence of the catalyst on the PLGA microstructure chains is reported. Finally, abiotic hydrolytic degradation rate is studied. Results described in this article show that BiSS is one very attractive catalyst to produce low toxic PLGA for biomedical applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1130–1138     

Dual Electroactivity in a Covalent Organic Network with Mechanically Interlocked Pillar[5]arenes

The synthesis and characterization of a polyrotaxanated covalent organic network (CON) based on the association between the viologen and pillar[5]arene (P[5]OH) units are reported. The mechanical bond allows for the irreversible insertion of n-type redox centers (P[5]OH macrocycles) within a pristine structure based on p-type viologen redox centers. Both redox units are active on a narrow potential range and, in water, the presence of P[5]OH greatly increases the electroactivity of the material.     

Influence of Equilibration Time in Solution on the Inclusion/Exclusion Topology Ratio of Host–Guest Complexes Probed by Ion Mobility and Collision‐Induced Dissociation

Host–guest complexes are formed by the creation of multiple noncovalent bonds between a large molecule (the host) and smaller molecule(s) or ion(s) (the guest(s)). Ion‐mobility separation coupled with mass spectrometry nowadays represents an ideal tool to assess whether the host–guest complexes, when transferred to the gas phase upon electrospray ionization, possess an exclusion or inclusion nature. Nevertheless, the influence of the solution conditions on the nature of the observed gas‐phase ions is often not considered. In the specific case of inclusion complexes, kinetic considerations must be taken into account beside thermodynamics; the guest ingression within the host cavity can be characterized by slow kinetics, which makes the complexation reaction kinetically driven on the timescale of the experiment. This is particularly the case for the cucurbituril family of macrocyclic host molecules. Herein, we selected para‐phenylenediamine and cucurbit[6]uril as a model system to demonstrate, by means of ion mobility and collision‐induced dissociation measurements, that the inclusion/exclusion topology ratio varies as a function of the equilibration time in solution prior to the electrospray process.