Competition between photodetachment and autodetachment of the 2(1)pi pi* state of the green fluorescent protein chromophore anion

Using a combination of photoelectron spectroscopy measurements and quantum chemistry calculations, we have identified competing electron emission processes that contribute to the 350–315 nm photoelectron spectra of the deprotonated green fluorescent protein chromophore anion, p-hydroxybenzylidene-2,3-dimethylimidazolinone. As well as direct electron detachment from S0, we observe resonant excitation of the 21ππ* state of the anion followed by autodetachment. The experimental photoelectron spectra are found to be significantly broader than photoelectron spectrum calculated using the Franck-Condon method and we attribute this to rapid (∼10 fs) vibrational decoherence, or intramolecular vibrational energy redistribution, within the neutral radical

Three-dimensional lanthanide-organic frameworks based on di-, tetra-, and hexameric clusters

Three-dimensional lanthanide-organic frameworks formulated as (CH3)2NH2[Ln(pydc)2] · 1/2H2O [Ln3+ ) Eu3+ (1a) or Er3+ (1b); pydc2- corresponds to the diprotonated residue of 2,5-pyridinedicarboxylic acid (H2pydc)], [Er4(OH)4(pydc)4(H2O)3] ·H2O (2), and [PrIII 2PrIV 1.25O(OH)3(pydc)3] (3) have been isolated from typical solvothermal (1a and 1b in N,N-dimethylformamide - DMF) and hydrothermal (2 and 3) syntheses. Materials were characterized in the solid state using single-crystal X-ray diffraction, thermogravimetric analysis, vibrational spectroscopy (FT-IR and FT-Raman), electron microscopy, and CHN elemental analysis. While synthesis in DMF promotes the formation of centrosymmetric dimeric units, which act as building blocks in the construction of anionic ∞ 3{[Ln(pydc)2]-} frameworks having the channels filled by the charge-balancing (CH3)2NH2 + cations generated in situ by the solvolysis of DMF, the use of water as the solvent medium promotes clustering of the lanthanide centers: structures of 2 and 3 contain instead tetrameric [Er4(μ3-OH)4]8+ and hexameric |Pr6(μ3-O)2(μ3-OH)6| clusters which act as the building blocks of the networks, and are bridged by the H2-xpydcx- residues. It is demonstrated that this modular approach is reflected in the topological nature of the materials inducing 4-, 8-, and 14-connected uninodal networks (the nodes being the centers of gravity of the clusters) with topologies identical to those of diamond (family 1), and framework types bct (for 2) and bcu-x (for 3), respectively. The thermogravimetric studies of compound 3 further reveal a significant weight increase between ambient temperature and 450 °C with this being correlated with the uptake of oxygen from the surrounding environment by the praseodymium oxide inorganic core

Defining the molecular properties of N-nitrosodimethylamine (NDMA) precursors using computational chemistry

N-Nitrosodimethylamine (NDMA) is a potent carcinogen and can be produced during chloramination of drinking water and wastewater. Computational chemistry methods were used for the first time to calculate molecular descriptors for 64 NDMA precursors containing a dimethylamine (DMA) moiety. Descriptors were partial charge, bond length and pKa of the DMA nitrogen and planarity of the DMA group. Precursors classified on the basis of chemical functionality showed distinct relationships between partial charge and NDMA formation. Quaternary amines and tertiary amines with the DMA bonded to -COR and -CSR groups had a combination of low NDMA formation and high partial charge. The most potent NDMA precursors are tertiary amines with an acidic hydrogen and electron-donating group α and β to the DMA respectively. They also have comparable molecular descriptors: relatively negative partial charges, low planarity values, high bond lengths and pKa values from ∼8.3–10.1. A literature search identified 233 potential NDMA precursors that have never been tested experimentally. Of these chemicals 60% are therapeutics, 13% veterinary therapeutics and 10% natural products. Analysis combining qualitative assessment of chemical functionality and computational calculation of molecular descriptors successfully identified rivastigmine, a therapeutic, and conessine, a naturally occurring species, whose NDMA yields were determined experimentally to be 83.3 ± 0.5% and 42.3 ± 1.8% mol mol−1, respectively. This study defines the molecular properties associated with reactive NDMA precursors and the origin and identity of those amines which contribute to NDMA formation in drinking water

Defining the molecular properties of N-nitrosodimethylamine (NDMA) precursors using computational chemistry

N-nitrosodimethylamine (NDMA) is a potent carcinogen and can be produced during chlorarnination of drinking water and wastewater. Computational chemistry methods were used for the first time to calculate molecular descriptors for 64 NDMA precursors containing a dimethylamine (DMA) moiety. Descriptors were partial charge, bond length and pK. of the DMA nitrogen and planarity of the DMA group. Precursors classified on the basis of chemical functionality showed distinct relationships between partial charge and NDMA formation. Quaternary amines and tertiary amines with the DMA bonded to -COR and -CSR groups had a combination of low NDMA formation and high partial charge. The most potent NDMA precursors are tertiary amines with an acidic hydrogen and electron-donating group a and to the DMA respectively. They also have comparable molecular descriptors: relatively negative partial charges, low planarity values, high bond lengths and pK, values from -8.3- I0.1. A literature search identified 233 potential NDMA precursors that have never been tested experimentally. Of these chemicals 60% are therapeutics, 13% veterinary therapeutics and I 0% natural products. Analysis combining qualitative assessment of chemical functionality and computational calculation of molecular descriptors successfully identified rivastigmine, a therapeutic, and conessine, a naturally occurring species, whose NDMA yields were determined experimentally to be 83.3±0.5% and 42.3±1.8% mol/mol, respectively. This study defines the molecular properties associated with reactive NDMA precursors and the origin and identity of those amines which contribute to NDMA formation in drinking water

Field demonstration of mode-division multiplexing upgrade scenarios on commercial networks

We demonstrate three possible scenarios for upgrading current single-mode transmission networks with high capacity few-mode fiber technology using mode-division multiplexing (MDM). The results were obtained from measurements over a number of field-deployed single-mode fiber links with an additional experimental in-line amplified few-mode fiber link. The results confirm the viability of employing MDM using few-mode fiber technology to gradually replace legacy optical systems