Vibrational-torsional excitation and direct overtone photodissociation of ethyl hydroperoxide at 5nuOH

We have observed OH radical products from the unimolecular dissociation of ethyl hydroperoxide (CH3-CH2OOH) excited to 5nuOH and have collected an action spectrum from 15,600 to 16,800 cm(-1) and an OH product state distribution at the maximum (16,119 cm(-1)). We use a vibrational-torsional model to simulate spectra in the 5nuOH region for the trans and gauche conformers. A combination of the two simulated spectra resembles the experimental action spectrum, provided that the trans conformer is assumed to dominate at room temperature. Energy disposal in the OH fragment yields an upper limit for the O-O bond dissociation energy at D0 < 44 kcal mol(-1).     

Ground and low-lying excited states of propadienylidene (H2C=C=C:) obtained by negative ion photoelectron spectroscopy

A joint experimental-theoretical study has been carried out on electronic states of propadienylidene (H(2)CCC), using results from negative-ion photoelectron spectroscopy. In addition to the previously characterized X(1)A(1) electronic state, spectroscopic features are observed that belong to five additional states: the low-lying ?(3)B(1) and b(3)A(2) states, as well as two excited singlets, ?(1)A(2) and B(1)B(1), and a higher-lying triplet, c(3)A(1). Term energies (T(0), in cm(-1)) for the excited states obtained from the data are: 10,354±11 (?(3)B(1)); 11,950±30 (b(3)A(2)); 20,943±11 (c(3)A(1)); and 13,677±11 (?(1)A(2)). Strong vibronic coupling affects the ?(1)A(2) and B(1)B(1) states as well as ?(3)B(1) and b(3)A(2) and has profound effects on the spectrum. As a result, only a weak, broadened band is observed in the energy region where the origin of the B(1)B(1) state is expected. The assignments here are supported by high-level coupled-cluster calculations and spectral simulations based on a vibronic coupling Hamiltonian. A result of astrophysical interest is that the present study supports the idea that a broad absorption band found at 5450 ? by cavity ringdown spectroscopy (and coincident with a diffuse interstellar band) is carried by the B(1)B(1) state of H(2)CCC.     

Molecular thin films on solid surfaces: mechanisms of melting

We use molecular dynamics simulations to study the melting of pentane and hexane monolayers adsorbed on the basal plane of graphite. For both of these systems, the temperature-dependent structures and the melting temperatures agree well with experiment. A detailed analysis reveals that a mechanism involving the promotion of molecules to the second layer underlies melting in these systems. In the second-layer promotion mechanism, a small fraction of molecules transition into the second layer around the melting temperature, leaving vacant space in the first layer to facilitate disordering. The second-layer promotion mechanism arises because of the weaker molecule-surface interaction in our study than that in previous studies. The weaker molecule-surface interaction is consistent with experimental temperature-programmed desorption studies.     

Enhanced Biomimetic Performance of Ionic Polymer–Metal Composite Actuators Prepared with Nanostructured Block Ionomers

Ionic polymer–metal composites (IPMCs) represent an important class of stimuli‐responsive polymers that are capable of bending upon application of an electric potential. Conventional IPMCs, prepared with Nafion and related polyelectrolytes, often suffer from processing challenges, relatively low actuation levels and back relaxation during actuation. In this study, we examine and compare the effects of fabrication and solvent on the actuation behavior of a block ionomer with a sulfonated midblock and glassy endblocks that are capable of self‐organizing and thus stabilizing a molecular network in the presence of a polar solvent. Unlike Nafion, this material can be readily dissolved and cast from solution to yield films that vary in thickness and exhibit enormous solvent uptake. Cycling the initial chemical deposition of Pt on the surfaces of swollen films (the compositing process) increases the extent to which the electrodes penetrate the films, thereby improving contact along the polymer/electrode interface. The maximum bending actuation measured from IPMCs prepared with different solvents is at least comparable, but is often superior, to that reported for conventional IPMCs, without evidence of back relaxation. An unexpected characteristic observed here is that the actuation direction can be solvent regulated. Our results confirm that this block ionomer constitutes an attractive alternative for use in IPMCs and their associated applications.     

Photoelectron spectroscopy of anilinide and acidity of aniline

The photoelectron spectrum of the anilinide ion has been measured. The spectrum exhibits a vibrational progression of the CCC in-plane bending mode of the anilino radical in its electronic ground state. The observed fundamental frequency is 524 ± 10 cm(-1). The electron affinity (EA) of the radical is determined to be 1.607 ± 0.004 eV. The EA value is combined with the N-H bond dissociation energy of aniline in a negative ion thermochemical cycle to derive the deprotonation enthalpy of aniline at 0 K; Δ(acid)H(0)(PhHN-H) = 1535.4 ± 0.7 kJ mol(-1). Temperature corrections are made to obtain the corresponding value at 298 K and the gas-phase acidity; Δ(acid)H(298)(PhHN-H) = 1540.8 ± 1.0 kJ mol(-1) and Δ(acid)G(298)(PhHN-H) = 1509.2 ± 1.5 kJ mol(-1), respectively. The compatibility of this value in the acidity scale that is currently available is examined by utilizing the acidity of acetaldehyde as a reference.     

Gel-induced selective crystallization of polymorphs

Although nanoporous materials have been explored for controlling crystallization of polymorphs in recent years, polymorphism in confined environments is still poorly understood, particularly from a kinetic perspective, and the role of the local structure of the substrate has largely been neglected. Herein, we report the use of a novel material, polymer microgels with tunable microstructure, for controlling polymorph crystallization from solution and for investigating systematically the effects of nanoconfinement and interfacial interactions on polymorphic outcomes. We show that the polymer microgels can improve polymorph selectivity significantly. The polymorphic outcomes correlate strongly with the gel-induced nucleation kinetics and are very sensitive to both the polymer microstructure and the chemical composition. Further mechanistic investigations suggest that the nucleation-templating effect and the spatial confinement imposed by the polymer network may be central to achieving polymorph selectivity. We demonstrate polymer microgels as promising materials for controlling crystal polymorphism. Moreover, our results help advance the fundamental understanding of polymorph crystallization at complex interfaces, particularly in confined environments.     

Preparation of azulene-derived fulvenedialdehydes and their application to the synthesis of stable adj-dicarbaporphyrinoids

A "2 + 2" strategy for synthesizing adj-dicarbaporphyrinoid systems has been developed. In a model study, an azulenylmethylpyrrole dialdehyde was condensed with a dipyrrylmethane in the presence of HCl, followed by oxidation with ferric chloride, to give a modest yield of an azuliporphyrin. Fulvene aldehydes were prepared by reacting an indene-derived enamine with azulene aldehydes in the presence of Bu(2)BOTf, and azulene dialdehydes similarly reacted to give fulvene dialdehydes. The dialdehydes were condensed with dipyrrylmethanes in TFA/dichloromethane to afford good to excellent yields of dicarbaporphyrinoids with adjacent indene and azulene subunits. These 22-carbaazuliporphyrins exhibited significant diatropic character, and this property was magnified upon protonation. These characteristics are attributed to tropylium-containing resonance contributors that possess 18π electron delocalization pathways. Protonation studies demonstrated that C-protonation readily occurred at the interior indene carbon, but deuterium exchange also occurred at the internal azulene CH as well as at the meso-positions with TFA-d. Reaction of a carbaazuliporphyrin with silver(I) acetate in methanol or ethanol solutions also gave unusual nonaromatic dialkoxy derivatives.     

Characterization of the 1st and 2nd EF-hands of NADPH oxidase 5 by fluorescence, isothermal titration calorimetry, and circular dichroism

Background

Superoxide generated by non-phagocytic NADPH oxidases (NOXs) is of growing importance for physiology and pathobiology. The calcium binding domain (CaBD) of NOX5 contains four EF-hands, each binding one calcium ion. To better understand the metal binding properties of the 1^st and 2^nd EF-hands, we characterized the N-terminal half of CaBD (NCaBD) and its calcium-binding knockout mutants.

Results

The isothermal titration calorimetry measurement for NCaBD reveals that the calcium binding of two EF-hands are loosely associated with each other and can be treated as independent binding events. However, the Ca²⁺ binding studies on NCaBD(E31Q) and NCaBD(E63Q) showed their binding constants to be 6.5 × 10⁵ and 5.0 × 10² M^-1 with ??Hs of -14 and -4 kJ/mol, respectively, suggesting that intrinsic calcium binding for the 1^st non-canonical EF-hand is largely enhanced by the binding of Ca²⁺ to the 2^nd canonical EF-hand. The fluorescence quenching and CD spectra support a conformational change upon Ca²⁺ binding, which changes Trp residues toward a more non-polar and exposed environment and also increases its ??-helix secondary structure content. All measurements exclude Mg²⁺-binding in NCaBD.

Conclusions

We demonstrated that the 1^st non-canonical EF-hand of NOX5 has very weak Ca²⁺ binding affinity compared with the 2^nd canonical EF-hand. Both EF-hands interact with each other in a cooperative manner to enhance their Ca²⁺ binding affinity. Our characterization reveals that the two EF-hands in the N-terminal NOX5 are Ca²⁺ specific.

Graphical abstract

     

Exponential distance dependence of photoinitiated stepwise electron transfer in donor-bridge-acceptor molecules: implications for wirelike behavior

Donor-bridge-acceptor (D-B-A) systems in which a 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ-An) chromophore and a naphthalene-1,8:4,5-bis(dicarboximide) (NI) acceptor are linked by oligomeric 2,7-fluorenone (FN(n)) bridges (n = 1-3) have been synthesized. Selective photoexcitation of DMJ-An quantitatively produces DMJ(+?)-An(-?), and An(-?) acts as a high-potential electron donor. Femtosecond transient absorption spectroscopy in the visible and mid-IR regions showed that electron transfer occurs quantitatively in the sequence: DMJ(+?)-An(-?)-FN(n)-NI → DMJ(+?)-An-FN(n)(-?)-NI → DMJ(+?)-An-FN(n)-NI(-?). The charge-shift reaction from An(-?) to NI(-?) exhibits an exponential distance dependence in the nonpolar solvent toluene with an attenuation factor (β) of 0.34 ?(-1), which would normally be attributed to electron tunneling by the superexchange mechanism. However, the FN(n)(-?) radical anion was directly observed spectroscopically as an intermediate in the charge-separation mechanism, thereby demonstrating conclusively that the overall charge separation involves the incoherent hopping (stepwise) mechanism. Kinetic modeling of the data showed that the observed exponential distance dependence is largely due to electron injection onto the first FN unit followed by charge hopping between the FN units of the bridge biased by the distance-dependent electrostatic attraction of the two charges in D(+?)-B(-?)-A. This work shows that wirelike behavior does not necessarily result from building a stepwise, energetically downhill redox gradient into a D-B-A molecule.     

A robust small-molecule microarray platform for screening cell lysates

Herein we report the expanded functional group compatibility of small-molecule microarrays to include immobilization of primary alcohols, secondary alcohols, phenols, carboxylic acids, hydroxamic acids, thiols, and amines on a single slide surface. Small-molecule "diversity microarrays" containing nearly 10,000 known bioactive small molecules, natural products, and small molecules originating from several diversity-oriented syntheses were produced by using an isocyanate-mediated covalent capture strategy. Selected printed bioactive compounds were detected with antibodies against compounds of interest. The new surface of the diversity microarrays is highly compatible with approaches involving cellular lysates. This feature has enabled a robust, optimized screening methodology using cellular lysates, allowing the detection of specific interactions with a broad range of binding affinity by using epitope-tagged or chimeric fluorescent proteins without prior purification. We believe that this expanded research capability has considerable promise in biology and medicine.