Isotopes as Tracers of the Hawaiian Coffee-Producing Regions

Green coffee bean isotopes have been used to trace the effects of different climatic and geological characteristics associated with the Hawaii islands. Isotope ratio mass spectrometry (IRMS) and inductively coupled plasma mass spectrometry ((MC)-ICP-SFMS and ICP-QMS) were applied to determine the isotopic composition of carbon (δ¹³C), nitrogen (δ¹⁵N), sulfur (δ³⁴S), and oxygen (δ¹⁸O), the isotope abundance of strontium (⁸⁷Sr/⁸⁶Sr), and the concentrations of 30 different elements in 47 green coffees. The coffees were produced in five Hawaii regions: Hawaii, Kauai, Maui, Molokai, and Oahu. Results indicate that coffee plant seed isotopes reflect interactions between the coffee plant and the local environment. Accordingly, the obtained analytical fingerprinting could be used to discriminate between the different Hawaii regions studied

Conjugation Length Distribution in Poly(<i>p</i>‑phenylenevinylene) (PPV) Films

We studied the absorption line-shape of poly­(<i>p</i>-phenylenevinylene) (PPV) films deposited via spin coating and Langmuir–Blodgett techniques with the intent of identifying the conjugation length distribution in these two types of films, a key morphological aspect of conjugated polymer films. We treated the excitons in the polymer as independent oligomer excitons and modeled the absorption spectra of the individual oligomers using simple expressions for the oligomer size dependence of the gap energy, the line-broadening factor, the transition dipole moment and the Huang–Rhys parameter. We validated these expressions by independent measurements on phenyl-based oligomers and Density Functional Theory calculations. Our results show clear evidence that, for both types of PPV films, the conjugation length distribution depends exponentially on the segment size. Our results also set a lower limit, of about ten repeat units, for the maximum exciton length of three different phenyl-based oligomers

An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

A silsesquioxane cage polymer functionalized with eight chloropropyl arms (<b>1</b>, T₈-PrCl) reacted with 2,2′-dipyridiylamine (DPA) to afford a new derivative with eight pendant linear chains (<b>2</b>, T₈-Pr-DPA). Further reaction with [Mo­(η³-C₃H₅)­Br­(CO)₂(NCMe)₂] afforded another derivative containing three molybdenum units (<b>3</b>, T₈-Pr-DPA-Mo), after substitution of the two nitrile ligands in each complex. These are the first silsesquioxane species containing DPA and the Mo­(η³-C₃H₅)­Br­(CO)₂ fragment. The three materials were characterized by ¹H, ¹³C, ²⁹Si, and ⁹⁵Mo NMR, FTIR, XRD, and elemental analysis, and T₈-PrCl (<b>1</b>) was also structurally characterized by single-crystal X-ray diffraction. It was identified as a low-temperature polymorph of this material. Elemental analysis indicated that all Cl atoms in the parent material T₈-PrCl (<b>1</b>) were substituted by the deprotonated DPA group in T₈-Pr-DPA (<b>2</b>). However, only three [Mo­(η³-C₃H₅)­Br­(CO)₂(DPA)] units were detected in T₈-Pr-DPA-Mo (<b>3</b>). A comprehensive NMR study, complemented with DFT calculations, was carried out in order to detect the effect of Mo coordination on the cage silicon and on the protons and carbons of the propyl chain, but no significant effects were observed. Both ¹H and ²⁹Si chemical shifts vary upon introducing DPA but remain the same after reaction with the Mo­(II) precursor. The ⁹⁵Mo NMR data reveal that the metal is not sensitive to the cage. The catalytic activity of <b>3</b> was tested as a precursor in the epoxidation of cyclooctene and styrene in the presence of TBHP. Despite the high selectivity toward the epoxides, the conversion and turnover frequencies were low, reflecting the behavior of the [Mo­(η³-C₃H₅)­Br­(CO)₂(DPA)] complex

An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

A silsesquioxane cage polymer functionalized with eight chloropropyl arms (<b>1</b>, T₈-PrCl) reacted with 2,2′-dipyridiylamine (DPA) to afford a new derivative with eight pendant linear chains (<b>2</b>, T₈-Pr-DPA). Further reaction with [Mo­(η³-C₃H₅)­Br­(CO)₂(NCMe)₂] afforded another derivative containing three molybdenum units (<b>3</b>, T₈-Pr-DPA-Mo), after substitution of the two nitrile ligands in each complex. These are the first silsesquioxane species containing DPA and the Mo­(η³-C₃H₅)­Br­(CO)₂ fragment. The three materials were characterized by ¹H, ¹³C, ²⁹Si, and ⁹⁵Mo NMR, FTIR, XRD, and elemental analysis, and T₈-PrCl (<b>1</b>) was also structurally characterized by single-crystal X-ray diffraction. It was identified as a low-temperature polymorph of this material. Elemental analysis indicated that all Cl atoms in the parent material T₈-PrCl (<b>1</b>) were substituted by the deprotonated DPA group in T₈-Pr-DPA (<b>2</b>). However, only three [Mo­(η³-C₃H₅)­Br­(CO)₂(DPA)] units were detected in T₈-Pr-DPA-Mo (<b>3</b>). A comprehensive NMR study, complemented with DFT calculations, was carried out in order to detect the effect of Mo coordination on the cage silicon and on the protons and carbons of the propyl chain, but no significant effects were observed. Both ¹H and ²⁹Si chemical shifts vary upon introducing DPA but remain the same after reaction with the Mo­(II) precursor. The ⁹⁵Mo NMR data reveal that the metal is not sensitive to the cage. The catalytic activity of <b>3</b> was tested as a precursor in the epoxidation of cyclooctene and styrene in the presence of TBHP. Despite the high selectivity toward the epoxides, the conversion and turnover frequencies were low, reflecting the behavior of the [Mo­(η³-C₃H₅)­Br­(CO)₂(DPA)] complex