Stacking-Conformations in Functionally Substituted Phosphines

The methods of synthesis and space structure of phosphorus-containing compounds, in which stacking conformation is realized, are considered. It is shown that intramolecular stacking can be observed in monoheterocyclic compounds, bi-and polycyclic compounds, complexes of metals and acyclic compounds.     

Mapping of Neuropeptides in the Crustacean Stomatogastric Nervous System by Imaging Mass Spectrometry

Considerable effort has been devoted to characterizing the crustacean stomatogastric nervous system (STNS) with great emphasis on comprehensive analysis and mapping distribution of its diverse neuropeptide complement. Previously, immunohistochemistry (IHC) has been applied to this endeavor, yet with identification accuracy and throughput compromised. Therefore, molecular imaging methods are pursued to unequivocally determine the identity and location of the neuropeptides at a high spatial resolution. In this work, we developed a novel, multi-faceted mass spectrometric strategy combining profiling and imaging techniques to characterize and map neuropeptides from the blue crab Callinectes sapidus STNS at the network level. In total, 55 neuropeptides from 10 families were identified from the major ganglia in the C. sapidus STNS for the first time, including the stomatogastric ganglion (STG), the paired commissural ganglia (CoG), the esophageal ganglion (OG), and the connecting nerve stomatogastric nerve (stn) using matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) and the MS/MS capability of this technique. In addition, the locations of multiple neuropeptides were documented at a spatial resolution of 25 μm in the STG and upstream nerve using MALDI-TOF/TOF and high-mass-resolution and high-mass-accuracy MALDI-Fourier transform ion cyclotron resonance (FT-ICR) instrument. Furthermore, distributions of neuropeptides in the whole C. sapidus STNS were examined by imaging mass spectrometry (IMS). Different isoforms from the same family were simultaneously and unambiguously mapped, facilitating the functional exploration of neuropeptides present in the crustacean STNS and exemplifying the revolutionary role of this novel platform in neuronal network studies.

Novel Copolymers of 4-Fluorostyrene. 9. Some Ring-Disubstituted 2-Phenyl-1,1-dicyanoethylenes

Novel copolymers of trisubstituted ethylene monomers, ring-disubstituted 2-phenyl-1,1-dicyanoethylenes, RC₆H₃CH=C(CN)₂ (where R = 3-Br-4-CH₃O, 5-Br-2-CH₃O, 2-F-5-CH₃, 2-F-6-CH₃, 3-F-2-CH₃, 3-F-4-CH₃, 4-F-2-CH₃, 4-F-3-CH₃) and 4-fluorostyrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r ₁) for the monomers is 3-F-4-CH₃(1.64) > 5-Br-2-CH₃O (1.62) > 3-Br-4-CH₃O (1.36) > 4-F-2-CH₃(1.3) > 4-F-3-CH₃(1.26) > 3-F-2-CH₃(1.11) > 2-F-5-CH₃ (0.98) > 2-F-6-CH₃ (0.97). High T_g of the copolymers, in comparison with that of poly(4-fluorostyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 290–400°C range with residue, which then decomposed in 400–800°C range.     

Novel Copolymers of 4-Fluorostyrene. 1. Alkyl Ring-Substituted 2-Phenyl-1,1-dicyanoethylenes

Novel copolymers of trisubstituted ethylene monomers, alkyl ring-substituted 2-phenyl-1,1-dicyanoethylenes, RC₆H₄CH = C(CN)₂ (where R is 2-methyl, 3-methyl, 4-methyl, 4-ethyl, 4-i-propyl, 4-butyl, 4-i-butyl, and 4-t-butyl) and 4-fluorostyrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r ₁) for the monomers is 4-ethyl (42.6) > 4-butyl (29.4) > 4-t-butyl (26.7) > 4-i-butyl (1.6) > 4-i-propyl (1.29) > 3-methyl (1.26) > 2-methyl (0.8) > 4-methyl (0.4). High T _g of the copolymers, in comparison with that of poly(4-fluorostyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in 183–500°C range with residue (5–30% wt.), which then decomposed in the 500–800°C range.     

Novel Copolymers of 4-Fluorostyrene. 3. Some Ring-Substituted 2-Phenyl-1,1-dicyanoethylenes

Novel copolymers of trisubstituted ethylene monomers, ring-substituted 2-phenyl-1,1-dicyanoethylenes, RC₆H₄CH=C(CN)₂ (where R is 4-dimethylamino, 4-diethylamino, 3-phenoxy, 3-benzyloxy, 4-benzyloxy, 4-acetoxy, 2-cyano, 3-cyano, and 4-cyano) and 4-fluorostyrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r ₁) for the monomers is 3-benzyloxy (2.9) > 4-cyano (2.7) > 3-phenoxy (1.9) > 4-acetoxy (1.8) > 3-cyano (1.7) > 2-cyano (1.6) > 4-benzyloxy (0.6) > 4-dimethylamino (0.4) = 4-diethylamino (0.4). High T _g of the copolymers, in comparison with that of poly (4-fluorostyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 290–400°C range with residue, which then decomposition in 400–800°C range.     

New Tools for Investigating Electromagnetic Hot Spots in Single‐Molecule Surface‐Enhanced Raman Scattering

Surface‐enhanced Raman scattering (SERS) is quickly growing as an analytical technique, because it offers both molecular specificity and excellent sensitivity. For select substrates, SERS can even be observed from single molecules, which is the ultimate limit of detection. This review describes recent developments in the field of single‐molecule SERS (SM‐SERS) with a focus on new tools for characterizing SM‐SERS‐active substrates and how they interact with single molecules on their surface. In particular, techniques that combine optical spectroscopy and microscopy with electron microscopy are described, including correlated optical and transmission electron microscopy, correlated super‐resolution imaging and scanning electron microscopy, and correlated optical microscopy and electron energy loss spectroscopy.     

Characterization of NIST food-matrix standard reference materials for their vitamin C content

The vitamin C concentrations in three food-matrix Standard Reference Materials (SRMs) from the National Institute of Standards and Technology (NIST) have been determined by liquid chromatography (LC) with absorbance detection. These materials (SRM 1549a Whole Milk Powder, SRM 1849a Infant/Adult Nutritional Formula, and SRM 3233 Fortified Breakfast Cereal) have been characterized to support analytical measurements made by food processors that are required to provide information about their products’ vitamin C content on the labels of products distributed in the United States. The SRMs are primarily intended for use in validating analytical methods for the determination of selected vitamins, elements, fatty acids, and other nutrients in these materials and in similar matrixes. They can also be used for quality assurance in the characterization of test samples or in-house control materials, and for establishing measurement traceability. Within-day precision of the LC method used to measure vitamin C in the food-matrix SRMs characterized in this study ranged from 2.7 % to 6.5 %.     

Deoxygenation of Aromatic Ketones Using Transfer Hydrogenolysis with Raney Nickel in 2-Propanol

Aryl ketones are readily deoxygenated to their corresponding aryl alkanes upon treatment with Raney nickel catalyst in boiling 2-propanol.

Disassembly Kinetics of Quinone‐Methide‐Based Self‐Immolative Spacers that Contain Aromatic Nitrogen Heterocycles

We prepared several pyridine‐ and pyrimidine‐based self‐immolative spacer groups to evaluate the significance of the resonance energy of the spacer aromatic ring on the kinetics of 1,4‐ and 1,6‐elimination reactions, which govern spacer disassembly. Subsequently, we relied on a photoactivation procedure to accurately analyze the disassembly kinetics. Beyond providing new results that are relevant for deriving quantitative structure–property relationships, herein, we demonstrate that pH value can be used as an efficient parameter to finely control the disassembly time of a self‐immolative spacer after an initial activation.