Living photolytic ring-opening polymerization of amino-functionalized [1]ferrocenophanes: synthesis and layer-by-layer self-assembly of well-defined water-soluble polyferrocenylsilane polyelectrolytes

Facile synthetic routes have been developed that provide access to cationic and anionic water-soluble polyferrocenylsilane (PFS) polyelectrolytes with controlled molecular weight and narrow polydispersity. Living photolytic ring-opening polymerization of amino-functionalized [1]ferrocenophane (fc) monomers [fcSiMe{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}] (3), [fcSi{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}(2)] (10), [fcSiMe(C[triple chemical bond]CCH(2)NMe(2))] (14), and [fcSiMe(p-C(6)H(4)CH(2)NMe(2))] (20) yielded the corresponding polyferrocenylsilanes [(fcSiMe{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)})(n)](5), [(fcSi{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}(2))(n)] (11), [{fcSiMe(C[triple chemical bond]CCH(2)NMe(2))}(n)] (15), and [{fcSiMe(p-C(6)H(4)CH(2)NMe(2))}(n)] (21) with controlled architectures. Further derivatization of 5, 15, and 21 generated water-soluble polyelectrolytes [(fcSiMe{C[triple chemical bond]CCH(2)N(CH(2)CH(2)CH(2)SO(3)Na)(2)})(n)] (6), [{fcSiMe(C[triple chemical bond]CCH(2)NMe(3)OSO(3)Me)}(n)] (7), and [{fcSiMe(p-C(6)H(4)CH(2)NMe(3)OSO(3)Me)}(n)] (22), respectively. The polyelectrolytes were readily soluble in water and NaCl aqueous solutions, with 6 and 22 exhibiting long-term stability in aqueous media. The PFS materials 6 and 22, have been utilized in the layer-by-layer (LbL) self-assembly of electrostatic superlattices. Our preliminary studies have indicated that films made from controlled low molecular-weight PFSs possess a considerably thinner bilayer thickness and higher refractive index than those made from PFSs that have an uncontrolled high molecular-weight. These results suggest that the structure and optical properties of LbL ultra-thin films can be tuned by varying polyelectrolyte chain length. The water-soluble low molecular weight PFSs are also useful materials for a range of applications including LbL self-assembly in highly confined spaces.     

Boron-pnictogen multiple bonds: donor-stabilized P=B and As=B bonds and a hindered iminoborane with a B-N triple bond

Reaction of the hindered phosphino- and arsinoboranes, Ar*Pn(H)-B(Br)Tmp (Ar* = -C6H3-2,6-(C6H2-2,4,6-iPr3)2; Tmp = 2,2,6,6-tetramethylpiperidino; Pn = P and As, 1 and 3, respectively) with 4-dimethylaminopyridine, DMAP, afforded the boranylidenephosphane and arsane, Ar*Pn=B(DMAP)Tmp (Pn = P and As, 2 and 4) as deep red-purple solids. The analogous aminoboranes Ar'N(H)-B(X)Tmp (Ar' = -C6H3-2,6-(C6H2-2,4,6-Me3)2; X = Cl and Br; 5 and 6) did not display any reactivity with DMAP, but in the presence of the amide base, Na[N(SiMe3)2], the clean formation of the uncomplexed iminoborane Ar'NBTmp (7) was observed. Attempts to generate an Sb=B bond were unsuccessful, as the required stibinoborane precursor, Ar*Sb(H)-B(Br)Tmp, could not be prepared; in place of clean Sb-B bond formation, the reduced product Ar*Sb=SbAr* was obtained. All compounds were characterized spectroscopically, and the X-ray crystal structures of 1, 2, 4, 6, and 7 were determined.     

Facile synthesis of BiCuOS by hydrothermal methods

BiCuOS, which is isostructural to the layered rare-earth oxysulfides LnCuOS (Ln = La-Eu), was synthesized by a single-step hydrothermal reaction at low temperature (250 degrees C) and pressure (<20 atm). Particular emphasis is placed on how the selection of the proper reaction conditions, such as temperature and pH, achieves a mutual high solubility of the metal-oxide reactants, Bi2O3 and Cu2O, and thus generates BiCuOS in a good yield. The optical and electrical properties of BiCuOS were measured to determine the influence of replacing a rare-earth cation with bismuth. The electrical conductivity of BiCuOS is increased over that of certain layered rare-earth oxysulfides, LnCuOS (Ln = La, Pr, and Nd), and is similar to that of the cerium members, CeCuOS and CeAgOS. Band structure calculations reveal that, similar to other potential transparent conductors containing sixth-row elements, relativistic effects significantly lower the energy of the conduction band, and thus narrow the optical band gap. These low-energy conduction bands are responsible for the electrical and optical properties of BiCuOS.     

Stability in solution of indolium heptamethine cyanines and related pH‐sensitive systems

Relative stabilities of methanolic solutions of dyes that are potentially important for labeling of biological macromolecules with a visible‐red or near‐infrared fluorophore were evaluated in the presence of molecular oxygen under dark and light conditions.     

High-throughput direct-infusion ion trap mass spectrometry: a new method for metabolomics

A fast method was developed to directly infuse raw plant extracts into a linear ion trap mass spectrometer, using the ion trap to isolate and fragment as many ions as possible from the extract. The full mass spectra can be analysed by multivariate statistics to determine discriminating ions, and the fragmentation data allows rapid classification or identification of these ions. The methodology was used to screen a wide range of strains of endophytic fungi in perennial ryegrass seeds for differences in metabolic profiles. The results show that this newly developed methodology is able to determine discriminating ions that can be present in very low concentrations. It also yielded sufficient fragmentation data to classify or identify the discriminating ions.     

Numerical methods for the computation of the confluent and Gauss hypergeometric functions

The two most commonly used hypergeometric functions are the confluent hypergeometric function and the Gauss hypergeometric function. We review the available techniques for accurate, fast, and reliable computation of these two hypergeometric functions in different parameter and variable regimes. The methods that we investigate include Taylor and asymptotic series computations, Gauss–Jacobi quadrature, numerical solution of differential equations, recurrence relations, and others. We discuss the results of numerical experiments used to determine the best methods, in practice, for each parameter and variable regime considered. We provide “roadmaps” with our recommendation for which methods should be used in each situation.     

High-field (75)As NMR study of arsenic oxysalts

Arsenic is an important environmental hazard, but there have been few NMR investigations of its molecular scale structure and dynamics, due principally to the large quadrupole moment of (75)As and consequent large quadrupole couplings. We examine here the potential of existing, single-field solid-state NMR technology to investigate solids containing arsenate and arsenite oxyanions. The results show that current techniques have significant potential for arsenates that do not contain both protonated H(x)AsO4-(3-x) groups and structural water molecules, but that the quadrupole couplings for the arsenites examined here are large enough that interpretation of the spectra is difficult, even at 21.1T. Compounds that contain both structural H(2)O molecules and protonated arsenate groups do not yield resolvable signal, likely a result of T(2) effects related to a combination of strong quadrupolar interactions and proton exchange. Spin-echo experiments at 11.7 and 14.1T were effective for Li(3)AsO(4) and CsH(2)AsO(4), as were whole-pattern spikelet experiments for arsenate oxide (As(2)O(5)) at 17.6 and 21.1T. The central transition resonance of Ca(3)(AsO(4))(2).8H(2)O is approximately 6 MHz broad and required a non-conventional, histogram-style spikelet method at high field to improve acquisition efficiency. This approach reduces the acquisition time due to the sensitivity enhancement of the spikelet sequence and a reduction in the number of frequency increments required to map the resonance. Despite the large quadrupole couplings, we have identified a correlation between the (75)As isotropic chemical shift and the electronegativity of the next-nearest neighbor cation in arsenate compounds.     

"Tetrahedrality" and the relationship between collective structure and radial distribution functions in liquid water

Molecular dynamics simulations of pure liquid water under ambient conditions using four common empirical water models have been analyzed to determine how well the oxygen-oxygen radial distribution function, g(OO)(r), used as the sole criterion of congruence with experiment, captures variations in the actual anisotropic collective structuring for these models. The largest systematic deviations from tetrahedrality were found to be due to deformations of the angle between the two closet hydrogen bond donor neighbors, but for intrinsic geometric reasons, these were found to contribute less to g(OO)(r) than deformations of the angles between one hydrogen bond donor neighbor and one hydrogen bond acceptor neighbor. Relying exclusively on a qualitative characterization of the second peak in g(OO)(r) seems to overemphasize the differences between the structuring in some of these models.     

Carbonylation of epoxides to substituted 3-hydroxy-delta-lactones

Substituted 3-hydroxy-delta-lactones (3HLs) are valuable intermediates in the synthesis of pharmaceuticals and other biologically active natural products. Herein we report the first example of the catalytic carbonylation of substituted homoglycidols to 3HLs using HCo(CO)4. Upon optimization of the catalyst and reaction conditions, a functionally diverse set of 3HLs was prepared. Mechanistic insight was gained by observation of the carbonylation reaction using in situ IR spectroscopy, and we propose a mechanism that is consistent with previously studied epoxide carbonylation systems.