Palladium-catalyzed intramolecular asymmetric hydroamination, hydroalkoxylation, and hydrocarbonation of alkynes

A conceptually novel approach for asymmetric intramolecular hydroamination, hydroalkoxylation and hydrocarbonation of alkynes using chiral palladium catalysts are described. The reactions of the aminoalkynes 5, alkynols 7, and alkynylmethines 9 in the presence of Pd2(dba)3 x CHCl3/PhCOOH/renorphos 4 in benzene (or benzene-hexane) at 100 degrees C gave the corresponding cyclization products (nitrogen heterocycles 6, oxygen heterocycles 8, and carbocycles 10) in good yields with good enantioselectivities. The origins of enantioselectivities in the hydroamination reaction are discussed based on DFT computations.     

High-resolution separation of peptides by sodium dodecyl sulfate-polyacrylamide gel "focusing"

As a follow-up of our previous report (Anal. Chem. 2007, 79, 821-827) on analytical SDS-PAGE focusing, a refinement of the method for separation of peptides in the small to medium M(r) range (0.5-10 kDa) is here reported, based on a shallow gradient of immobilized positive charges (0-10 mM) onto a minimally sieving polyacrylamide gel matrix (4%T, 2.5%C). Unlike conventional SDS-PAGE, which rarely can achieve the separations of polypeptide chains below a critical value of 10 kDa, the present method can be fine-tuned to perform such separations even down to a size of only 500 Da. In the case of larger fragments, the major peptide zones are shown, under microscope observation, to be composed by envelopes of bands as narrow as 20-100 microm, spaced at regular intervals of 100-150 microm. It is hypothesized that such larger peptides could form complexes with rather small SDS micelles and that such peptide-SDS complexes could differ in charge by just a single negative charge.     

Development of a proficiency testing scheme for a limited number of participants in the field of natural water analysis

A proficiency testing (PT) scheme was developed for a limited number of analytical laboratories participating in the analysis of natural water in Israel. Three fit-for-intended-use reference materials (RMs) were prepared for a pilot PT from natural water: RM-blank and two in-house reference materials (IHRMs) with seven analytes fortified to achieve different levels of analyte concentrations. The measurands for the PT participants were the traceable spike values certified in the IHRMs, i.e., added mass concentrations of the analytes. The RM-blank and IHRMs were found to be homogeneous and stable over 11 days, the time necessary for the experimental part of the PT. The RMs were distributed to the PT participants as unknown test items similar to routine samples. The test results were evaluated using their deviations from the IHRM-certified values. Eight Israeli laboratories took part in the interlaboratory comparison. Individual laboratory performance and metrological compatibility of the PT results of the participants, as a local group of laboratories, were evaluated for every analyte.     

Assessment of Gaussian-4 theory for the computation of enthalpies of formation of large organic molecules

Gas-phase enthalpies of formation of 122 relatively large organic molecules with up to 15 non-hydrogen atoms have been calculated at the Gaussian-4 (G4) level of theory using the atomization reaction procedure. The calculated values were compared with experimental data published mainly last years. Particular attention has been given to nitro compounds and nitrogen, oxygen, and sulfur containing heterocyclic compounds. The expected accumulation of systematic errors as the molecular size increases was not observed with increasing the number of non-hydrogen atoms from 6 to 15. The largest mean absolute deviation between experimental and G4 enthalpies of formation, 10.7 kJ/mol, was revealed for nitro compounds. All theoretical values for nitro compounds were underestimated by 5–15 kJ/mol. The best agreement with experiment with mean absolute deviation of 4.5 kJ/mol was observed for compounds which types were widely presented in the original test set of G4 method. The mean absolute deviations for nitrogen heterocycles (6.8 kJ/mol) and oxygen and sulfur heterocycles (9.1 kJ/mol) are noticeably larger. Experimental enthalpies of formation of four compounds (N,N-dinitromethanamine, 2,3,5,6-tetrachloronitrobenzene, 2-methyl-2H-tetrazole, and proline) were suggested to be unreliable from comparison with the G4 values calculated from atomization energies and isodesmic reactions.     

Mutable Lewis and Brønsted acidity of aluminated SBA-15 as revealed by NMR of adsorbed pyridine-15N

(1)H and variable-temperature (15)N NMR techniques have been used to study the effect of the gradual alumination of SBA-15 on the structure and adsorption properties of this mesoporous material. The interpretation of experimental spectra suggests that aluminum chlorhydrol most effectively reacts with silica surfaces in the confinement of the cavities of rough mesopore walls, instead of forming a homogeneous aluminum film. This first leads to a gradual filling of the cavities and finally results in aluminum islands on the inner surfaces of mesopores. In the sample with a Si/Al atomic ratio of 4.1, up to half of the inner surface area of the mesopores is covered with aluminum. The alumination produces Br?nsted acid sites attributed to silanol groups interacting with aluminum but does not affect the proton-donating ability of isolated silanol groups. At high Si/Al ratios, the surface contains only one type of Lewis site attributed to tetracoordinated aluminum. At lower Si/Al ratios, Lewis acid sites with a lower electron-accepting ability appear, as attributed to pentacoordinated aluminum. The numerical values of the surface densities of all chemically active sites have been estimated after annealing at 420 and 700 K. We were surprised to observe that gaseous nitrogen can occupy Lewis acid sites and hinder the interaction of the aluminum with any other electron donor. As a result, aluminated surfaces saturated with nitrogen do not exhibit any Br?nsted or Lewis acidity. At room temperature, it takes days before pyridine replaces nitrogen at the Lewis acid sites.     

Convenient synthesis of non-conjugated alkynyl ketones from keto aldehydes by a chemoselective one-pot nonaflation—base catalyzed elimination sequence

Keto aldehydes were selectively converted to non-conjugated alkynyl ketones possessing an unsubstituted alkyne terminus using one-pot nonaflation—base catalyzed elimination reaction sequences. Consecutive one-pot nonaflation of keto aldehydes with perfluorobutane-1-sulfonyl fluoride and elimination of the nonaflyl group using the P₁ phosphazene base resulted in the formation of a terminal CC triple bond with the keto group remaining intact. Careful optimization of the reaction conditions enabled a highly chemoselective conversion of the aldehyde function in the presence of unprotected keto groups exploiting a minor difference in acidity of their α-hydrogen atoms. Scope and limitations of the protocol as well as possible implementation of these substrates in Sonogashira coupling were explored.     

C76 fullerene chlorides and cage transformations. Structural and theoretical study

Chlorination of the D(2)-C(76) fullerene under various conditions is studied in detail. It is found that, in addition to the previously known C(76)Cl(18) and C(76)Cl(34), a number of intermediate chlorides are formed, with all molecules falling into two structural types. The first type is observed in the C(76)Cl(18)-C(76)Cl(28) range, whereas further chlorination provides the C(76)Cl(30)-C(76)Cl(34) compounds of the second type exhibiting a major change in the addition motif. We also present a detailed theoretical rationalization of the previously observed skeletal rearrangement in the D(2)-C(76) that affords the non-IPR (18917)C(76)Cl(24) compound.     

Size-selective molecular transport through silica colloidal nanopores

Diffusion rate of dye-labelled PAMAM dendrimers through free-standing silica colloidal crystals was studied as a function of the dendrimer generation and nanopore size to determine the transport selectivity.     

Copper-catalyzed arylation of 1H-perfluoroalkanes

A general method has been developed for arylation of readily available 1H-perfluoroalkanes. The method employs aryl iodide and 1H-perfluoroalkane reagents, DMPU solvent, TMP(2)Zn base, and a copper chloride/phenanthroline catalyst. Preliminary mechanistic studies are reported.     

Microgels for the encapsulation and stimulus-responsive release of molecules with distinct polarities

A microfluidic strategy for the encapsulation and stimulus-responsive release of molecules with distinct polarities from the interior of microgels is reported. The approach relies on (i) the generation of a primary O/W emulsion by the ultrasonication method, (ii) MF emulsification of the primary emulsion, and (iii) photopolymerization of the monomer present in the aqueous phase of the droplets, thereby transforming them into microgels. Non-polar molecules are dissolved in oil droplets embedded in the microgels. Polar molecules are physically associated with the hydrogel network. Upon heating, the microgels contract and release polar and non-polar cargo molecules. The approach paves the way for stimuli-responsive vehicles for multiple drug delivery.