The 1:1 adduct of 4‐aminobenzoic acid with 4‐aminobenzonitrile

The 1:1 adduct of 4‐amino­benzoic acid (PABA) with 4‐am‐inobenzonitrile (PABN), C₇H₇NO₂·C₇H₆N₂, consists of a primary centrosymmetric cyclic hydrogen‐bonded PABA dimer interaction [O?O 2.640 (3) Å] peripherally linked into chains by weaker hydrogen bonds via a head‐to‐tail PABN interaction [N?N 3.179 (4) and N?O 3.062 (4) Å], and is linked between the chains by amine‐N (PABN) to amine‐N (PABA) interactions [N?N 3.233 (5) Å]. No proton transfer occurs.     

NMR method for the determination of solute hydrogen bond acidity

It is shown that the difference in the 1H NMR chemical shift of a protic hydrogen in DMSO and CDCl3 solvents is directly related to the overall, or summation, hydrogen bond acidity for a wide range of solutes. This provides a new and direct method of measuring the hydrogen bond acidity. For 54 compounds, the observed shifts for 72 protic hydrogens could be correlated to the Abraham solute hydrogen bond acidity parameter, A, with a correlation coefficient squared, R2, of 0.938 and a standard deviation, SD, of 0.054 units in A. A training equation that used half the data could predict A values for the remaining data with an average error of 0.001 and a standard deviation, SD, of 0.053 units, thus demonstrating the predictive power of the method. Unlike any previous method for the determination of solute hydrogen bond acidities, the NMR method allows the determination of A values for individual protic hydrogens in multifunctional solutes.     

Excited-state absorption properties of platinum(II) terpyridyl acetylides

A comprehensive photophysical study is presented which compares the ground- and excited-state properties of four platinum(II) terpyridyl acetylide compounds of the general formula [Pt(tBu3tpy)(CCR)]+, where tBu3tpy is 4,4',4' '-tri-tert-butyl-2,2':6',2' '-terpyridine and R is an alkyl or aryl group. [Ru(tBu3tpy)3]2+ and the pivotal synthetic precursor [Pt(tBu3tpy)Cl]+ were also investigated in the current work. The latter two complexes possess short excited-state lifetimes and were investigated using ultrafast spectrometry while the other four compounds were evaluated using conventional nanosecond transient-absorption spectroscopy. The original intention of this study was to comprehend the nature of the impressive excited-state absorptions that emanate from this class of transition-metal chromophores. Transient-absorbance-difference spectra across the series contain the same salient features, which are modulated only slightly in wavelength and markedly in intensity as a function of the appended acetylide ligand. More intense absorption transients are observed in the arylacetylide structures relative to those bearing an alkylacetylide, consistent with transitions coupled to the pi system of the ancillary ligand. Reductive spectroelectrochemical measurements successfully generated the electronic spectrum of the tBu3tpy radical anion in all six complexes at room temperature. These measurements confirm that electronic absorptions associated with the tBu3tpy radical anion simply do not account for the intense optical transitions observed in the excited state of the Pt(II) chromophores. Transient-trapping experiments using the spectroscopically silent reductive quencher DABCO clearly demonstrate the loss of most transient-absorption features in the acetylide complexes throughout the UV, visible, and near-IR regions following bimolecular excited-state electron transfer, suggesting that these features are strongly tied to the photogenerated hole which is delocalized across the Pt center and the ancillary acetylide ligand.     

A silicone-based stretchable micropost array membrane for monitoring live-cell subcellular cytoskeletal response

External forces are increasingly recognized as major regulators of cellular structure and function, yet the underlying mechanism by which cells sense forces and transduce them into intracellular biochemical signals and behavioral responses ('mechanotransduction') is largely undetermined. To aid in the mechanistic study of mechanotransduction, herein we devised a cell stretching device that allowed for quantitative control and real-time measurement of mechanical stimuli and cellular biomechanical responses. Our strategy involved a microfabricated array of silicone elastomeric microposts integrated onto a stretchable elastomeric membrane. Using a computer-controlled vacuum, this micropost array membrane (mPAM) was activated to apply equibiaxial cell stretching forces to adherent cells attached to the microposts. Using the mPAM, we studied the live-cell subcellular dynamic responses of contractile forces in vascular smooth muscle cells (VSMCs) to a sustained static equibiaxial cell stretch. Our data showed that in response to a sustained cell stretch, VSMCs regulated their cytoskeletal (CSK) contractility in a biphasic manner: they first acutely enhanced their contraction to resist rapid cell deformation ('stiffening') before they allowed slow adaptive inelastic CSK reorganization to release their contractility ('softening'). The contractile response across entire single VSMCs was spatially inhomogeneous and force-dependent. Our mPAM device and live-cell subcellular contractile measurements will help elucidate the mechanotransductive system in VSMCs and thus contribute to our understanding of pressure-induced vascular disease processes.     

Phenyliodine(III) bis(trifluoroacetate) (PIFA)-promoted synthesis of Bodipy dimers displaying unusual redox properties

Phenyliodine(III) bis(trifluoroacetate) (PIFA) in conjunction with a Lewis acid promotes C-C coupling of Bodipy monomers leading to mixtures of various oligomers. When a single position is blocked with an iodo or phenyl group, formation of the dimer is favored. These dimers display two successive oxidation and two reduction waves separated on average by 260 and 130 mV, respectively, corresponding to each Bodipy subunit.     

Chiral separation using cyclodextrins as mobile phase additives in open-tubular liquid chromatography with a pseudophase coating

The chiral separation of various analytes (dichlorprop, mecoprop, ibuprofen, and ketoprofen) was demonstrated with different cyclodextrins as mobile phase additives in open-tubular liquid chromatography using a stationary pseudophase semipermanent coating. The stable coating was prepared by a successive multiple ionic layer approach using poly(diallyldimethylammonium chloride), polystyrene sulfonate, and didodecyldimethyl ammonium bromide. Increasing concentrations (0–0.2 mM) of various native and derivatized cyclodextrins in 25 mM sodium tetraborate (pH 9.2) were investigated. Chiral separation was achieved for the four test analytes using 0.05–0.1 mM β-cyclodextrin (resolution between 1.11 and 1.34), γ-cyclodextrin (resolution between 0.78 and 1.27), carboxymethyl-β-cyclodextrin (resolution between 1.64 and 2.59), and 2-hydroxypropyl-β-cyclodextrin (resolution between 0.71 and 1.76) with the highest resolutions obtained with 0.1 mM carboxymethyl-β-cyclodextrin. %RSD values were <10%. This is the first demonstration of chiral open-tubular liquid chromatography using achiral chromatographic coatings and cyclodextrins as mobile phase additives.