Metal scrambling in the trinuclear (Pt(2)Se(2)M)(M = Pt, Pd, Au) system using an electrospray mass spectrometry (ESMS) directed synthetic methodology; isolation and crystallographic characterization of (Pt(2)(mu(3)-Se)(2)(PPh(3))(4)[Pt(cod)])(PF(6))(2) and (Pt(mu(3)-Se)(2)(PPh(3))(2)[Pt(cod)](2))(PF(6))(2) (cod = cyclo-octa-1,5-diene)

Pt(2)(mu-Se)(2)(PPh(3))(4) reacts with PtCl(2)(cod) to give (Pt(2)(mu(3)-Se)(2)(PPh(3))(4)[Pt(cod)])(2+) and an unexpected cod-rich product that arises from metal scrambling, viz. (Pt(mu(3)-Se)(2)(PPh(3))(2)[Pt(cod)](2))(2+). The formation of these species was detected and followed by electrospray mass spectrometry (ESMS) and subsequently verified by batch synthesis and crystallographic characterization. Other metal-scrambled aggregate products were successfully detected.     

Peptide Brush Polymers for Efficient Delivery of a Gene Editing Protein to Stem Cells

The scarcity of effective means to deliver functional proteins to living cells is a central problem in biotechnology and medicine. Herein, we report the efficient delivery of an active DNA‐modifying enzyme to human stem cells through high‐density cell penetrating peptide brush polymers. Cre recombinase is mixed with a fluorophore‐tagged polymer carrier and then applied directly to induced pluripotent stem cells or HEK293T cells. This results in efficient delivery of Cre protein as measured by activation of a genomically integrated Cre‐mediated recombination reporter. We observed that brush polymer formulations utilizing cell penetrating peptides promoted Cre delivery but oligopeptides alone or oligopeptides displayed on nanoparticles did not. Overall, we report the efficient delivery of a genome‐modifying enzyme to stem cells that may be generalizable to other, difficult‐to‐transduce cell types.     

A rotating elliptic airfoil in fluid at rest and in a parallel freestream

This paper reports results of DPIV measurements on a two-dimensional elliptic airfoil rotating about its own axis of symmetry in a fluid at rest and in a parallel freestream. In the former case, we examined three rotating speeds (Re _c,Ω = 400, 1,000 and 2,000), and in the later case, four rotating speeds (Ro _c,Ω = 2.4, 1.2, 0.6 and 0.4), together with two freestream velocities (Re _c,u  = 200 and 1,000) and two starting configurations of the airfoil (i.e., chord parallel to (α ₀ = 0°) or normal (α ₀ = 90°) to the freestream). Results show that a rotating airfoil in a stationary fluid produces two distinct types of vortex structures depending on the Reynolds number. The first type occurs at the lowest Reynolds number (Re _c,Ω = 400), where vortices shed from the two edges or tips of the airfoil dissipated quickly, resulting in the airfoil rotating in a layer of diffused vorticity. The second type occurs at higher Reynolds numbers (i.e., Re _c,Ω = 1,000 and 2,000), where the corresponding vortices rotated together with the airfoil. Due to the vortex suction effect, the torque characteristics are likely to be heavily damped for the first type because of the rapidly subsiding vortex shedding, and more oscillatory for the second type due to persistent presence of tip vortices. In a parallel freestream, increasing the tip-speed ratio (V/U) of the airfoil (i.e., decreasing the Rossby number, Ro _c,Ω) transformed the flow topology from periodic vortex shedding at Ro _c,Ω = 2.4 to the generation of a “hovering vortex” at Ro _c,Ω = 0.6 and 0.4. The presence of the hovering vortex, which has not been reported in literature before, is likely to enhance the lift characteristics of the airfoil. Freestream Reynolds number is found to have minimal effect on the vortex formation and shedding process, although it enhances shear layer instability and produces more small-scale flow structures that affect the dynamics of the hovering vortex. Likewise, initial starting configuration of the airfoil, while affecting the flow transient during the initial phase of rotation, has insignificant effect on the overall flow topology. Unfortunately, technical constraint of our apparatus prevented us from carrying out complimentary force measurements; nevertheless, the results presented herein, which are more extensive than those computed by Lugt and Ohring (1977), will provide useful benchmark data, from which more advanced numerical calculations can be carried out to ascertain the corresponding force characteristics, particularly for those conditions with the presence of hovering vortex.     

Almost Minimum Diameter Orientations of Semicomplete Multipartite and Extended Digraphs

 An orientation of a digraph D is a spanning subdigraph of D obtained from D by deleting exactly one arc between x and y for every pair x≠y of vertices such that both x y and y x are in D. Almost minimum diameter orientations of certain semicomplete multipartite and extended digraphs are considered, several generalizations of results on orientations of undirected graphs are obtained, some conjectures are posed. Received: August 31, 2000 Final version received: October 30, 2001 Acknowledgments. Part of this work was done when the first author was visiting the Department of Mathematics, National University of Singapore. The departmental hospitality and financial support are very much appreciated.     

The vibrational spectra of the boron halides and their molecular complexes, part 5 An ab initio study of the infrared spectrum of the boron trifluoride-carbon dioxide complex

The optimized structures, interaction energies, Mulliken charges and vibrational spectra of three conformers of a 1:1 complex between boron trifluoride and carbon dioxide have been determined by means of ab initio calculations at the second-order level of M?ller-Plesset perturbation theory, using the 6-31G* basis set. All three structures feature a B⋯O electron donor-acceptor interaction. One of the structures, in which the carbon dioxide axis eclipses one of the BF bonds, was found to be a genuine minimum, one (the corresponding staggered form) a first-order saddle point and the third (a linearly bonded B⋯OCO species) a second-order transition state. The computed infrared spectrum of the preferred conformer has been used to predict the appearance of the spectrum of boron trifluoride and carbon dioxide co-deposited in cryogenic matrices, which will be reported in a forthcoming publication. Received: 18 November 1996 / Accepted: 11 March 1997     

Surface vibration induced spatial ordering of periodic polymer patterns on a substrate

We demonstrate the possibility of producing regular, long-range, spatially ordered polymer patterns without requiring the use of physical or chemical templating through the interfacial destabilization of a thin polymer film driven by surface acoustic waves (SAWs). The periodicity and spot size of the pattern are observed to be dependent on a single parameter, that is, the SAW frequency (or wavelength), therefore offering a rapid, simple, yet novel method for self-organized regular spatial polymer pattern formation that is far more tunable than conventional polymer patterning procedures.     

Exploring the subtleties of drug-receptor interactions: the case of matrix metalloproteinases

By solving high-resolution crystal structures of a large number (14 in this case) of adducts of matrix metalloproteinase 12 (MMP12) with strong, nanomolar, inhibitors all derived from a single ligand scaffold, it is shown that the energetics of the ligand-protein interactions can be accounted for directly from the structures to a level of detail that allows us to rationalize for the differential binding affinity between pairs of closely related ligands. In each case, variations in binding affinities can be traced back to slight improvements or worsening of specific interactions with the protein of one or more ligand atoms. Isothermal calorimetry measurements show that the binding of this class of MMP inhibitors is largely enthalpy driven, but a favorable entropic contribution is always present. The binding enthalpy of acetohydroxamic acid (AHA), the prototype zinc-binding group in MMP drug discovery, has been also accurately measured. In principle, this research permits the planning of either improved inhibitors, or inhibitors with improved selectivity for one or another MMP. The present analysis is applicable to any drug target for which structural information on adducts with a series of homologous ligands can be obtained, while structural information obtained from in silico docking is probably not accurate enough for this type of study.     

Microparticle collection and concentration via a miniature surface acoustic wave device

The ability to detect microbes, pollens and other microparticles is a critically important ability given the increasing risk of bioterrorism and emergence of antibiotic-resistant bacteria. The efficient collection of microparticles via a liquid water droplet moved by a surface acoustic wave (SAW) device is demonstrated in this study. A fluidic track patterned on the SAW device directs the water droplet's motion, and fluid streaming induced inside the droplet as it moves along is a key advantage over other particle collection approaches, because it enhances microparticle collection and concentration. Test particles consisted of 2, 10, 12 and 45 microm diameter monodisperse polystyrene and melamine microparticles; pollen from the Populus deltoides, Kochia scoparia, Secale cerale, and Broussonetia papyrifera (Paper Mulberry) species; and Escherichia coli bacteria. The collection efficiency for the synthetic particles ranged from 16 to 55%, depending on the particle size and surface tension of the collection fluid. The method was more effective in collecting pollen and the bacteria with an efficiency of 45-68% and 61.0-69.8%, respectively. Pollen collection was strongly influenced by its diameter, size, and surface geometry in a manner contrary to initial expectations. Reasons for the consistent yet unexpected collection results include leaky SAW pressure boundary segregation and shear-induced concentration of larger particles, and the subtle effects of wetting interactions. These results demonstrate a new method for collecting microparticles requiring only about one second per run, and illustrate the inadequacy of using synthetic microparticles as a substitute for their biological counterparts in experiments studying particle collection and behavior.