Dipole-bound anions of highly polar molecules: ethylene carbonate and vinylene carbonate

Results of experimental and theoretical studies of dipole-bound negative ions of the highly polar molecules ethylene carbonate (EC, C3H4O3, mu=5.35 D) and vinylene carbonate (VC, C3H2O3, mu=4.55 D) are presented. These negative ions are prepared in Rydberg electron transfer (RET) reactions in which rubidium (Rb) atoms, excited to ns or nd Rydberg states, collide with EC or VC molecules to produce EC- or VC- ions. In both cases ions are produced only when the Rb atoms are excited to states described by a relatively narrow range of effective principal quantum numbers, n*; the greatest yields of EC- and VC- are obtained for n*(max)=9.0+/-0.5 and 11.6+/-0.5, respectively. Charge transfer from low-lying Rydberg states of Rb is characteristic of a large excess electron binding energy (Eb) of the neutral parent; employing the previously derived empirical relationship Eb=23/n*(max)(2.8) eV, the electron binding energies are estimated to be 49+/-8 meV for EC and 24+/-3 meV for VC. Electron photodetachment studies of EC- show that the excess electron is bound by 49+/-5 meV, in excellent agreement with the RET results, lending credibility to the empirical relationship between Eb and n*(max). Vertical electron affinities for EC and VC are computed employing aug-cc-pVDZ atom-centered basis sets supplemented with a (5s5p) set of diffuse Gaussian primitives to support the dipole-bound electron; at the CCSD(T) level of theory the computed electron affinities are 40.9 and 20.1 meV for EC and VC, respectively.     

Rapid deposition of triangular silver nanoplates on planar surfaces: application to metal-enhanced fluorescence

A simple and rapid wet-chemical technique for the deposition of silver triangles on conventional glass substrates, which alleviates the need for lithography, has been developed. The technique is based on the seed-mediated cetyltrimethylammonium-bromide-directed growth of silver triangles on glass surfaces, where smaller spherical silver seeds that were attached to the surface were subsequently converted and grown into silver triangles in the presence of a cationic surfactant and silver ions. The size of the silver triangles was controlled by sequential immersion of silver seed-coated glass substrates into a growth solution and by the duration time of immersion. Atomic force microscopy studies revealed that the size of the silver triangles ranged between 100 and 500 nm. Interestingly, these new surfaces are a significant improvement over traditional silver island films for applications in metal-enhanced fluorescence. A routine 16-fold enhancement in emission intensity was typically observed, for protein-immobilized indocyanine green, with a relatively very low loading density of silver triangles on the glass surface.     

On the contribution of vibrational anharmonicity to the binding energies of water clusters

The second-order vibrational perturbation theory method has been used together with the B3LYP and MP2 electronic structure methods to investigate the effects of anharmonicity on the vibrational zero-point energy (ZPE) contributions to the binding energies of (H2O)n, n = 2-6, clusters. For the low-lying isomers of (H2O)6, the anharmonicity correction to the binding energy is calculated to range from -248 to -355 cm(-1). It is also demonstrated that although high-order electron correlation effects are important for the individual vibrational frequencies, they are relatively unimportant for the net ZPE contributions to the binding energies of water clusters.     

A Grafting Study on Partially Dehydrochlorinated Poly(vinyl chloride) by Atom Transfer Radical Polymerization

HCl elimination in low ratio was first carried out from poly(vinyl chloride) to increase allylic chlorines. Partially dehydrochlorinated poly(vinyl chloride), having a macroinitiator effect, was grafted with tert‐butyl methacrylate via atom transfer radical polymerization in the presence of CuBr/2,2′‐bipyridine at 64°C in tetrahydrofuran. Original poly(vinyl chloride) was also grafted with tert‐butyl methacrylate under the same conditions to compare with that of partially dehydrochlorinated poly(vinyl chloride). The graft copolymers were characterized by elemental analysis, FTIR, ¹H and ¹³C‐NMR, differential scanning calorimetry, and gel permeation chromatography (GPC). Thermal stabilities of the graft copolymers were investigated by thermogravimetric analysis as compared with those of the macroinitiators.     

Synthesis of Dopamine,Rotigotin, Ladostigil,Rasagiline Analogues 2-Amino-4,5,6-trimethoxyindane, 1-Amino-5,6,7-trimethoxyindane,and Their Sulfamide Derivatives

Dopamine, rotigotin, ladostigil, and rasagiline analogues 2-amino-4,5,6-trimethoxyindane and 1-amino-5,6,7-trimethoxyindane were synthesized starting from 5,6,7-trimethoxyindan-1-one for the first time with 34% and 45% total yields. α-Carboxylation of indanone, reduction of ketone group with Et₃SiH, basic hydrolysis of ester, Curtius reaction of the acid, and addition of BnOH afforded the corresponding carbamate. Pd-C-catalyzed hydrogenolysis of carbamate and deprotonation of amine hydrochloride with NaOH gave the dopamine and rotigotin analogue 2-aminoindane. Reduction of 5,6,7-trimethoxyindan-1-one with NaBH₄ afforded the alcohol, which was then converted to the azide derivative via Mitsunobu reaction with diphenylphosphoryl azide; Pd-C catalyzed hydrogenation of the azide to the amine hydrochloride and then deprotonation of the amine hydrochloride with NaOH furnished the ladostigil and rasagiline analogue 1-aminoindane. These amines and BnOH were reacted with CSI to produce sulfamoyl carbamates, which were converted to sulfamides via Pd-C-catalyzed hydrogenolysis reaction with 20% and 25% total yields.     

Determination of europium(III) in environmental samples using a flow injection analysis system with on-line preconcentration and spectrophotometric detection

A simple and accurate flow injection analysis system coupled with spectrophotometric detector was developed for preconcentration and determination of europium(III) in aqueous samples. The developed flow system includes a europium preconcentration step in a column packed with Amberlite XAD-4 resin impregnated with nalidixic acid at pH 7.0. The europium complex was desorbed from the resin by 0.1 mol L^?1 HCl and mixed with arsenazo-III solution (0.05 % solution in 0.1 mol L^?1 HCl) and taken to the flow through cell of spectrophotometer where its absorbance was measured at 661 nm. The optimum preconcentration system, chemical and FIA variables were investigated. The preconcentration factors obtained were 115 and 500, detection limits of 0.43 and 0.1 μg L^?1, sample throughputs of 40 and 10 were obtained for preconcentration time of 60 and 300 s respectively. The proposed system showed good precision and accuracy with relative standard deviation of 1.5 %. The method has been applied to the determination of europium(III) in real water samples and certified reference material IAEA-SL-1 (Lake sediment).     

Synthesis and inverse virtual screening of new bi-cyclic structures towards cancer-relevant cellular targets

Structural Chemistry - We report here synthetic approaches to access new classes of small molecules based on three heterocyclic scaffolds, i.e. 3,7-dihydropyrimido[4,5-d]pyridazine-4,8-dione,...     

Low Temperature Metal-Enhanced Fluorescence

In this short letter, we describe the effects of low temperature on the Metal-Enhanced Fluorescence (MEF) phenomenon. Fluorophores close to Silver Island Films (SiFs) show on average two- to ten-fold enhancements in their fluorescence signatures at room temperature. However, at 77 K, we have observed that MEF is even more pronounced as compared to an identical glass control sample. We also demonstrate that the further enhancements in MEF occur at low temperature over a range of visible wavelengths for different fluorophores, for both SiFs and 20 nm surface deposited gold colloids.     

Automated,Accelerated Nanoscale Synthesis of Iminopyrrolidines

Miniaturization and acceleration of synthetic chemistry is an emerging area in pharmaceutical, agrochemical, and materials research and development. Herein, we describe the synthesis of iminopyrrolidine-2-carboxylic acid derivatives using chiral glutamine, oxo components, and isocyanide building blocks in an unprecedented Ugi-3-component reaction. We used I-DOT, a positive-pressure-based low-volume and non-contact dispensing technology to prepare more than 1000 different derivatives in a fully automated fashion. In general, the reaction is stereoselective, proceeds in good yields, and tolerates a wide variety of functional groups. We exemplify a pipeline of fast and efficient nanomole-scale scouting to millimole-scale synthesis for the discovery of a useful novel reaction with great scope.     

TEAD–YAP Interaction Inhibitors and MDM2 Binders from DNA-Encoded Indole-Focused Ugi Peptidomimetics

DNA-encoded combinatorial synthesis provides efficient and dense coverage of chemical space around privileged molecular structures. The indole side chain of tryptophan plays a prominent role in key, or “hot spot”, regions of protein–protein interactions. A DNA-encoded combinatorial peptoid library was designed based on the Ugi four-component reaction by employing tryptophan-mimetic indole side chains to probe the surface of target proteins. Several peptoids were synthesized on a chemically stable hexathymidine adapter oligonucleotide “hexT”, encoded by DNA sequences, and substituted by azide-alkyne cycloaddition to yield a library of 8112 molecules. Selection experiments for the tumor-relevant proteins MDM2 and TEAD4 yielded MDM2 binders and a novel class of TEAD-YAP interaction inhibitors that perturbed the expression of a gene under the control of these Hippo pathway effectors.