Excited state dynamics of the11BO2 free radical

The excitation spectrum of the double-headed 00°0-00°0 band of BO₂ (A²Π_u-X²Π_g) was recorded by LIF. Special attention was paid to determine the dependence of the radiative lifetime of (00°0) A²Π state with J and the quenching by bath gases N₂, Ar, O₂. The determinations of fluorescence decay were made in real time. The mean radiative lifetime τ_r of the A²Π_3/2(00°0) state of ¹¹ BO₂ was determined to be 91 ± 4 ns (1σ).     

S(N)2 Mechanism for Alcoholysis, Aminolysis, and Hydrolysis of Acetyl Chloride

First-order solvolysis rate constants are reported for solvolyses of acetyl chloride in methanol and MeOD, and in binary aqueous mixtures with acetone, acetonitrile, ethanol, methanol, and trifluoroethanol at 0 degrees C. Product selectivities (S = [MeCOOR]/[MeCOOH] x [water]/[alcohol]) are reported for solvolyses in ethanol/ and methanol/water at 0 degrees C. Solvolyses of acetyl chloride show a high sensitivity to changes in solvent ionizing power, consistent with C-Cl bond cleavage. As the solvent is varied from pure ethanol (or methanol) to water, S values and rate-rate profiles show no evidence for the change in reaction channel observed for solvolyses of benzoyl and trimethylacetyl chlorides. However, using rate ratios in 40% ethanol/water and 97% trifluoroethanol/water (solvents of similar ionizing power but different nucleophilicities) to compare sensitivities to nucleophilic attack, solvolyses of acetyl chloride are over 20-fold more sensitive to nucleophilic attack than benzoyl chloride. The solvent isotope effect of 1.29 (MeOH/MeOD) for acetyl chloride is similar to that for p-methoxybenzoyl chloride (1.22) and is lower than for benzoyl chloride (1.55). Second-order rate constants for aminolyses of acetyl chloride with m-nitroaniline in methanol at 0 degrees C show that acetyl chloride behaves similarly to p-methoxybenzoyl chloride, whereas benzoyl chloride is 40-fold more sensitive to the added amine. The results indicate mechanistic differences between solvolyses of acetyl and benzoyl chlorides, and an S(N)2 mechanism is proposed for solvolyses and aminolyses by m-nitroaniline of acetyl chloride (i.e. these reactions are probably not carbonyl additions, but a strong sensitivity to nucleophilic attack accounts for their high rates).     

PRODUCTS OF CHLOROPHYLL PHOTODEGRADATION–1. DETECTION and SEPARATION

Abstract— The photodegradative fate of ¹⁴C-radiolabelled phaeophytin a adsorbed on hydrophobic particles in an aqueous suspension is followed. An approximate mass balance is made for the hydrophilic, hydrophobic and CO, fractions. In addition, components of the colourless hydrophilic fraction produced from photodegrading chlorophyll a, phaeophytin a, phaeophorbide a and chlorophyll b are detected and separated using reverse-phase ion-pair and ion-exclusion HPLC with UV detection. The increase in the hydrophilic molecules and the decrease in chlorophyll a are measured as the photodegradation proceeds.     

The Direct Heat Measurement of Mechanical Energy Storage Metal–Organic Frameworks

In any process, the heat exchanged is an essential property required in its development. Whilst the work related to structural transitions of some flexible metal–organic frameworks (MOFs) has been quantified and linked with potential applications such as molecular springs or shock absorbers, the heat related to such transitions has never been directly measured. This has now been carried out with MIL‐53(Al) using specifically devised calorimetry experiments. We project the importance of these heats in devices such as molecular springs or dampers.     

Tuning the Properties of MOF-808 via Defect Engineering and Metal Nanoparticle Encapsulation

Defect engineering and metal encapsulation are considered as valuable approaches to fine-tune the reactivity of metal–organic frameworks. In this work, various MOF-808 (Zr) samples are synthesized and characterized with the final aim to understand how defects and/or platinum nanoparticle encapsulation act on the intrinsic and reactive properties of these MOFs. The reactivity of the pristine, defective and Pt encapsulated MOF-808 is quantified with water adsorption and CO₂ adsorption calorimetry. The results reveal strong competitive effects between crystal morphology and missing linker defects which in turn affect the crystal morphology, porosity, stability, and reactivity. In spite of leading to a loss in porosity, the introduction of defects (missing linkers or Pt nanoparticles) is beneficial to the stability of the MOF-808 towards water and could also be advantageously used to tune adsorption properties of this MOF family.     

A Robust Infinite Zirconium Phenolate Building Unit to Enhance the Chemical Stability of Zr MOFs

A novel Zr‐chain based MOF, namely MIL‐163, was designed and successfully synthesized using a bis‐1,2,3‐trioxobenzene ligand. Endowed with large square‐shaped channels of 12 Å width, it shows remarkable water uptake (ca. 0.6 cm³ g^?1 at saturating vapor pressure) and a remarkable stability in simulated physiological media, where archetypical Zr carboxylate MOFs readily degrade.     

High uptakes of CO2 and CH4 in mesoporous metal-organic frameworks MIL-100 and MIL-101

Mesoporous MOFs MIL-100 and MIL-101 adsorb huge amounts of CO2 and CH4. Characterization was performed using both manometry and gravimetry in different laboratories for isotherms coupled with microcalorimetry and FTIR to specify the gas-solid interactions. In particular, the uptake of carbon dioxide in MIL-101 has been shown to occur with a record capacity of 40 mmol g(-1) or 390 cm3STP cm(-3) at 5 MPa and 303 K.     

Comparison of the biological properties of several marine sponge-derived sesquiterpenoid quinones

Eight naturally occurring marine-sponge derived sesquiterpenoid quinones were evaluated as potential inhibitors of pyruvate phosphate dikinase (PPDK), a C4 plant regulatory enzyme. Of these, the hydroxyquinones ilimaquinone, ethylsmenoquinone and smenoquinone inhibited PPDK activity with IC50's (reported with 95% confidence intervals) of 285.4 (256.4-317.7), 316.2 (279.2-358.1) and 556.0 (505.9-611.0) microM, respectively, as well as being phytotoxic to the C4 plant Digitaria ciliaris. The potential anti-inflammatory activity of these compounds, using bee venom phospholipase A2 (PLA2), was also evaluated. Ethylsmenoquinone, smenospongiarine, smenospongidine and ilimaquinone inhibited PLA2 activity (% inhibition of 73.2 +/- 4.8 at 269 microM, 61.5 +/- 6.1 at 242 microM, 41.0 +/- 0.6 at 224 microM and 36.4 +/- 8.2 at 279 microM, respectively). SAR analyses indicate that a hydroxyquinone functionality and a short, hydroxide/alkoxide side-chain atC-20 is preferred for inhibition of PPDK activity, and that a larger amine side-chain at C-20 is tolerated for PLA2 inhibitory activity.