Molecular Fluorescence Imaging Spectroscopy for Mapping Low Concentrations of Red Lake Pigments: Van Gogh's Painting The Olive Orchard

Vincent van Gogh used fugitive red lake pigments that have faded in some paintings. Mapping their distribution is key to understanding how his paintings have changed with time. While red lake pigments can be identified from microsamples, in situ identification and mapping remain challenging. This paper explores the ability of molecular fluorescence imaging spectroscopy to identify and, more importantly, map residual non-degraded red lakes. The high sensitivity of this method enabled identification of the emission spectra of eosin (tetrabromine fluorescein) lake mixed with lead or zinc white at lower concentrations than elemental X-ray fluorescence (XRF) spectroscopy used on account of bromine. The molecular fluorescence mapping of residual eosin and two carmine red lakes in van Gogh's The Olive Orchard is demonstrated and compared with XRF imaging spectroscopy. The red lakes are consistent with the composition of paint tubes known to have been used by van Gogh.     

Rapid radical formation by DNA charge transport through sequences lacking intervening guanines

Using the flash-quench technique to probe DNA charge transport in assemblies containing a tethered ruthenium intercalator, the kinetics and yield of methylindole radical formation as a function of DNA sequence were studied by laser spectroscopy and biochemical methods. In these assemblies, the methylindole moiety serves as an artificial base of low oxidation potential. Hole injection and subsequent formation of the methylindole radical cation were observed at a distance of over 30 A at rates >/=107 s-1 in assemblies containing no guanine bases intervening the ruthenium intercalator and GMG oxidation site. Radical yield was, however, strikingly sensitive to an intervening base mismatch; no significant methylindole radical formation was evident with an intervening AA mismatch. Also critical is the sequence at the injection site; this sequence determines initial hole localization and hence the probability of hole propagation. With guanine rather than inosine near the site of hole injection, decreased yields of radicals and long-range oxidative damage are observed. The presence of the low-energy guanine site in this case serves to localize the hole and therefore diminish charge transport through the base pair stack.     

Rapid formation of diphenylmethyl ethers and thioethers using microwave irradiation and protic ionic liquids

Using microwave irradiation and protic ionic liquids (pIL) as co-solvent and catalyst for the synthesis of several diphenylmethyl ethers was achieved. The desired ethers were isolated simply by filtration through a silica plug to remove the pIL and proceeded in high yields (60–98%). These reactions were extremely rapid (10–30 min) and occurred under mild conditions (80 °C). This protocol was also successfully applied to the synthesis of thioethers.     

Fddd network phase in ABA triblock copolymer melts

Using self‐consistent field theory, we investigate the stability of the orthorhombic Fddd network phase (O⁷⁰) in ABA triblock copolymer melt systems. Consistent with previous findings, we observe that the gross topology of phase behavior is unchanged with varying chain asymmetry. However, the mean field critical point is displaced from the diblock copolymer value of f_A = 0.5 (f_A is the A segment volume fraction) to larger values as the triblock copolymer symmetry is broken with unequal A block lengths. This deviation significantly shifts the order‐order phase boundaries, resulting in an appreciable region of O⁷⁰ stability in the phase diagram of asymmetric ABA triblock copolymers. More importantly, the stability of the O⁷⁰ phase extends to the intermediate segregation regime for select chain asymmetries. Both features are desirable for achieving a synthetic realization of the phase in binary AB block copolymer systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1112–1117     

Context-dependent mutagenesis by DNA lesions.

BACKGROUND: Detailed analyses of mutational hotspots following DNA damage provide an understanding of oncogene activation and tumor suppressor gene inactivation, and hence provide an insight into the earliest steps in the induction of cancer. A mutational hotspot might be created by preferential lesion formation, decreased lesion repair, or increased misinsertion past the lesion during DNA replication. The respective contribution of these factors might be influenced by the DNA sequence context of the hotspot. RESULTS: As a prelude to addressing the contribution of all possible nearest-neighbor contexts on the replication past O6-methylguanine (m6G) and repair of m6G in vivo, we have devised a mutation frequency (MF) detection strategy on the basis of the properties of type IIs restriction enzymes. We also report a method for constructing site-specific single-stranded viral DNA genomes that should yield identical ligation efficiencies regardless of the lesion or its surrounding sequence context. Using repair-deficient Escherichia coli, we discovered that m6G in three sequence contexts was nearly 100% mutagenic in vivo, showing that the DNA polymerase holoenzyme almost always placed a thymine base opposite m6G during replication. In partially repair-proficient cells, the Ada O6-methylguanine-DNA methyltransferase repair protein was twice as efficient on m6G when a guanine base rather than an adenine base was 5' to the lesion. CONCLUSIONS: The system allows the mutagenic potential of, theoretically, any DNA lesion that exhibits point mutations, in any varied local sequence context, to be rapidly determined. The assay demonstrates low background, high throughput, and does not require phenotypic selection, making it possible to discern the effects of sequence context on the processing of m6G.     

The nitrogen-vacancy colour centre in diamond

The nitrogen-vacancy (NV) colour centre in diamond is an important physical system for emergent quantum technologies, including quantum metrology, information processing and communications, as well as for various nanotechnologies, such as biological and sub-diffraction limit imaging, and for tests of entanglement in quantum mechanics. Given this array of existing and potential applications and the almost 50 years of NV research, one would expect that the physics of the centre is well understood, however, the study of the NV centre has proved challenging, with many early assertions now believed false and many remaining issues yet to be resolved. This review represents the first time that the key empirical and ab initio results have been extracted from the extensive NV literature and assembled into one consistent picture of the current understanding of the centre. As a result, the key unresolved issues concerning the NV centre are identified and the possible avenues for their resolution are examined.     

In Vitro and In Vivo Sequestration of Methamphetamine by a Sulfated Acyclic CB[n]-Type Receptor

We report the synthesis of two new acyclic sulfated acyclic CB[n]-type receptors ( TriM0 and Me₄TetM0 ) and investigations of their binding properties toward a panel of drugs of abuse ( 1 – 13 ) by a combination of ¹H NMR spectroscopy and isothermal titration calorimetry. TetM0 is the most potent receptor with K_a≥10⁶ M⁻¹ toward methamphetamine, fentanyl, MDMA and mephedrone. TetM0 is not cytotoxic toward HepG2 and HEK 293 cells below 100 μM according to MTS metabolic and adenylate kinase release assays and is well tolerated in vivo when dosed at 46 mg kg⁻¹. TetM0 does not inhibit the hERG ion channel and is not mutagenic based on the Ames fluctuation test. Finally, in vivo efficacy studies show that the hyperlocomotion of mice treated with methamphetamine can be greatly reduced by treatment with TetM0 up to 5 minutes later. TetM0 has potential as a broad spectrum in vivo sequestrant for drugs of abuse.     

Heteroleptic copper dipyrromethene complexes: synthesis, structure, and coordination polymers

The synthesis of neutral [Cu(dpm)2] and [Cu(dpm)(acac)] (dpm = dipyrromethene, acac = acetylacetonato) complexes is presented. The formation of the asymmetric metal complexes was monitored by electronic absorption and infrared spectroscopy. Two of the complexes investigated, containing pyrdpm ligands (pyrdpm = pyridyldipyrromethene), form 1-dimensional coordination polymers. The coordination polymers formed by these complexes have been characterized by single-crystal X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. The complexes possess square pyramidal coordination geometries with the apical position occupied by the meso-pyridyl donor of a neighboring complex in the crystal lattice. The features of these coordination complexes that facilitate formation of extended solids have been probed. Symmetric [Cu(pyrdpm)2] complexes are unable to form coordination solids due to steric hindrance at the metal center. Use of cyano donors in complexes such as [Cu(cydpm)(acac)] (cydpm = cyanodipyrromethene) in lieu of pyridyl donors also fail to form network solids. Through these systematic studies, both the basic coordination chemistry of these complexes and the fundamental design requirements for synthesizing this novel class of coordination polymers have been defined.     

Complementary Standoff Chemical Imaging to Map and Identify Artist Materials in an Early Italian Renaissance Panel Painting

Two imaging modalities based on molecular and elemental spectroscopy were used to characterize a painting by Cosimo Tura. Visible‐to‐near‐infrared (400–1680 nm) reflectance imaging spectroscopy (RIS) and X‐ray fluorescence (XRF) imaging spectroscopy were employed to identify pigments and determine their spatial distribution with higher confidence than from either technique alone. For example, Mary’s red robe was modeled through the distribution of an insect‐derived red lake (RIS map) and lead white (XRF lead map), rather than a layer of red lake on vermilion. The RIS image cube was also used to isolate the preparatory design by mapping the reflectance spectra associated with it. In conjunction with results from an earlier RIS study (1650–2500 nm) to map and identify the binding media, a more thorough understanding was gained of the materials and techniques used in the painting.