Does Hydrogen Bonding Matter in Crystal Engineering? Crystal Structures of Salts of Isomeric Ions

The preparation and structure determinations of the crystalline salts [3,3'-H(2)bipy][PtCl(4)] (2), [2,2'-H(2)bipy][PtCl(4)] (3) and [1,4'-Hbipy][PtCl(4)] (4) and [3,3'-H(2)bipy][SbCl(5)] (6) and [1,4'-Hbipy][SbCl(5)] (8) are reported. In addition a redetermination of the structure of the metastable salt [4,4'-H(2)bipy][SbCl(5)] (5 b) in the corrected space group Pbcm is described. These structures are compared to those of the known salt [4,4'-H(2)bipy][PtCl(4)] (1), the stable triclinic form of [4,4'-H(2)bipy][SbCl(5)] (5 a) and [2,2'-H(2)bipy][SbCl(5)] (7). In the case of the salts of the rigid [PtCl(4)](2-) ion, structures 2, 3 and 4 are essentially isostructural despite the differing hydrogen-bonding capability of the cations. Similarly, among the salts of [SbCl(5)](2-) ions, structures 7 and 8 are essentially isostructural. Structure 6 differs from these in having a differing pattern of aggregation of the [SbCl(5)](2-) ions to form polymeric rather than tetrameric units. It is evident that local hydrogen-bonding interactions, although significant, are not the only or even the decisive influence on the crystal structures formed by these salts. These observations are not in good accord with the heuristic "sticky tecton" or supramolecular synthon models for synthetic crystallography or crystal engineering.     

Using molecular similarity to construct accurate semiempirical electronic structure theories

Ab initio electronic structure methods give accurate results for small systems, but do not scale well to large systems. Chemical insight tells us that molecular functional groups will behave approximately the same way in all molecules, large or small. This molecular similarity is exploited in semiempirical methods, which couple simple electronic structure theories with parameters for the transferable characteristics of functional groups. We propose that high-level calculations on small molecules provide a rich source of parametrization data. In principle, we can select a functional group, generate a large amount of ab initio data on the group in various small-molecule environments, and "mine" this data to build a sophisticated model for the group's behavior in large environments. This work details such a model for electron correlation: a semiempirical, subsystem-based correlation functional that predicts a subsystem's two-electron density matrix as a functional of its one-electron density matrix. This model is demonstrated on two small systems: chains of linear, minimal-basis (H-H)(5), treated as a sum of four overlapping (H-H)(2) subsystems; and the aldehyde group of a set of HOC-R molecules. The results provide an initial demonstration of the feasibility of the approach.     

Immobilized pH gradients as a first dimension in shotgun proteomics and analysis of the accuracy of pI predictability of peptides

In this work, we demonstrate the potential use of immobilized pH gradient isoelectric focusing as a first dimension in shotgun proteomics. The high resolving power and resulting reduction in matrix ionization effects due to analyzing peptides with almost the exact same physiochemical properties, represents a significant improvement in performance over traditional strong cation-exchange first-dimensional analysis associated with the shotgun proteomics approach. For example, using this technology, we were able to identify more than 6000 peptides and > 1200 proteins from the cytosolic fraction of Escherichia coli from approximately 10 microg of material analyzed in the second-dimensional liquid chromatography-tandem mass spectrometry experiment. Sample loads on the order of 1 mg can be resolved to 0.25 isoelectric point (pI) units, which make it possible to analyze organisms with significantly larger genomes/proteomes. Accurate pI prediction can then be employed using currently available algorithms to very effectively filter data for peptide/protein identification, and thus lowering the false-positive rate for cross-correlation-based peptide identification algorithms. By simplifying the protein mixture problem to tryptic peptides, the effect of specific amino acids on pI prediction can be evaluated as a function of their position in the peptide chain.     

Photoinduced whispering gallery mode microcavity resonator in a chalcogenide microfiber

We demonstrate an approach to creating localized whispering gallery mode (WGM) microcavities by exploiting the photosensitivity of a chalcogenide (As2S3) microfiber. A highly prolate WGM microcavity with cavity quality factors (Q) exceeding 2×10(5) is fabricated and characterized. Without the need for geometrical shaping, our approach enables the cavity properties to be monitored during fabrication for the first time.     

Solvent Effects on Acrylate kp in Organic Media?—A Systematic PLP–SEC Study

The Arrhenius parameters of the propagation rate coefficient, k_p, are determined employing high‐frequency pulsed laser polymerization–size exclusion chromatography (PLP–SEC) for the homologous series of five linear alkyl acrylates (i.e., methyl acrylate (MA), butyl acrylate (BA), dodecyl acrylate (DA), stearyl acrylate (SA), and behenyl acrylate (BeA)) in 1 m solution in butyl acetate (BuAc) as well as in toluene. The comparison of the obtained k_p values with the literature known values for bulk demonstrates that no significant solvent influence neither in BuAc nor in toluene on the propagation reaction compared to bulk is detectable. Concomitantly, the k_p values in toluene and in BuAc solution display a similar increase with increasing number of C‐atoms in the ester side chain as was previously reported for the bulk systems. These findings are in clear contrast to earlier studies, which report a decrease of k_p with increasing ester side chain length in toluene. The additional investigation of the longest and shortest ester side chain acrylate (i.e., BeA and MA) over the entire experimentally available concentration range at one temperature (i.e., 50 °C) does not reveal any general concentration dependence and all observed differences in the k_p are within the experimental error.

     

Rational forms for twistings of enveloping algebras of simple Lie algebras

We give rational forms for twistings of classical enveloping algebras. We also remark a link with the generalized formalism of Gurevich, Manin, and Cartier.     

Quantum information processing with delocalized qubits under global control

Conventional quantum computing schemes are incompatible with nanometer-scale "hardware," where the closely packed spins cannot be individually controlled. We report the first experimental demonstration of a global control paradigm: logical qubits delocalize along a spin chain and are addressed via the two terminal spins. Using NMR studies on a three-spin molecule, we implement a globally clocked quantum mirror that outperforms the equivalent swap network. We then extend the protocol to support dense qubit storage and demonstrate this experimentally via Deutsch and Deutsch-Jozsa algorithms.     

Design and fabrication of optical filters with very large stopband (≈500 nm) and small passband (1 nm) in silicon-on-insulator

In this paper, we report on the design, fabrication and characterization of a broadband photonic crystal filter. Modeling with a genetic algorithm (GA) was used to investigate the effect of changing the number of periods and thickness ratios of a photonic crystal filter structure with two alternating materials. Theoretical optimized parameters were obtained as a function of wavelength for a photonic crystal filter with a very broad filter bandwidth as well as a very narrow transmission window. We used the determined optimum parameters at a wavelength of 1550 nm to fabricate the structure using e-beam lithography and inductively coupled plasma (ICP) etching. Experimental results show that the structure indeed has a very narrow transmission window and a low loss of just 4 dB. Hence, this structure can be regarded as a high precision filter for optical communication and photonic integrated chip technologies.     

DNA separation at a liquid-solid interface

We demonstrate that it is possible to separate a broad band of DNA on a solid substrate without topological obstacles. The mobility was found to scale with molecular size (N) as N(-0.25), while the resolution scaled as N(0.75) indicating that diffusivity on this substrate was minimal. By varying the buffer concentration we were able to show that the mobility for a given chain length scaled with the persistent length (p) as p(1/2). This could be shown to be related to the Gaussian conformation of the chains adsorbed on the surface. A two-dimensional corrugated surface of nonporous silica beads was produced using a self-assembling process at the air/water interface. Even though the surface corrugations were comparable to persistence length we show that they do not affect the mobility, indicating that surface friction rather than topological constraints are the predominant mechanism of separation on a surface.