Zipper assembly of photoactive rigid-rod naphthalenediimide pi-stack architectures on gold nanoparticles and gold electrodes

We introduce zipper assembly as a simple and general concept to create complex functional architectures on conducting surfaces. Rigid-rod pi-stack architecture composed of p-oligophenyl rods and blue naphthalenediimide (NDI) stacks is selected as an example. First, short p-quaterphenyl initiators with four anionic NDIs are deposited on gold. Then, long p-octiphenyl propagators with eight cationic NDIs are added. The lower half of the propagator pi-stacks with the initiator, whereas the upper half of the molecule remains free. These cationic sticky-ends zip up with anionic propagators to produce anionic sticky-ends, and so on. Zipper assembly on gold nanoparticles is demonstrated by the appearance of the absorption of face-to-face NDI pi-stacks and the shift of the surface plasmon resonance band with increasing layer thickness. Complete inhibition by zipper capping demonstrates that zipper assembly affords complex architectures that are more ordered than those obtained by conventional layer-by-layer (LBL) approaches. Zipper assembly on gold electrodes produces increasing photocurrents with increasing number of zipped layers. The photocurrents obtained by this method are much higher than those obtained by conventional LBL controls; zipper termination by capping cleanly stops any increase in photocurrent.     

Nuclear magnetic resonance of mass-limited samples using small RF coils

Figure Schematic diagram of a typical arrangement used for hyphenating chemical microseparations (e.g. capillary HPLC, CE, or CEC) with microcoil NMR detection     

Hsp90 inhibitors disrupt mitochondrial homeostasis in cancer cells

Hsp90 is a cytosolic molecular chaperone whose paralog in mitochondria, TRAP1, protects cells from oxidative stress. The recent study in Cell by Kang et al. now identifies the molecular components of the proapoptotic network regulated by TRAP1, that includes Hsp90. Targeting Hsp90/TRAP1 inhibitors to mitochondria induces rapid tumor cell-specific apoptosis.     

Luminescent chemical waves in the Cu(II)-catalyzed oscillatory oxidation of SCN- ions with hydrogen peroxide

The oscillatory oxidation of thiocyanate ions with hydrogen peroxide, catalyzed by Cu2+ ions in alkaline media, was so far observed as occurring simultaneously in the entire space of the batch or flow reactor. We performed this reaction for the first time in the thin-layer reactor and observed the spatiotemporal course of the above process, in the presence of luminol as the chemiluminescent indicator. A series of luminescent patterns periodically starting from the random reaction center and spreading throughout the entire solution layer was reported. For a batch-stirred system, the bursts of luminescence were found to correlate with the steep decreases of the oscillating Pt electrode potential. These novel results open possibilities for further experimental and theoretical investigations of those spatiotemporal patterns, including studies of the mechanism of this chemically complex process.     

Contrasting singlet-triplet dynamical behavior of two vibrational levels of the acetylene S1 2(1)3(1)B2 polyad

Surface electron ejection by laser-excited metastables (SEELEM) and LIF spectra of acetylene were simultaneously recorded in the regions of the A1Au-X1Sigmag+ nominal 2(1)3(1)4(2) Ka=1<--00 and 2(1)3(1)6(2) Ka=1<--00 bands near 46,140 cm(-1). The upper states of these two bands are separated by only approximately 100 cm(-1), and the two S1 vibrational levels are known to be strongly mixed by anharmonic and Coriolis interactions. Strikingly different patterns were observed in the SEELEM spectra in the regions of the 2(1)3(1)4(2) and 2(1)3(1)6(2) vibrational levels. Because the equilibrium structure of the T3 electronic state is known to be nonplanar, excitation of nu4 (torsion) and nu6 (antisymmetric in-plane bend) are expected respectively to promote and suppress vibrational overlap between low-lying S1 and T3 vibrational levels. The nearly 50:50 mixed 2(1)3(1)4(2)-2(1)3(1)6(2) character of the S1 vibrational levels rules out this simple Franck-Condon explanation for the different appearance of the SEELEM spectra. A simple model is applied to the SEELEM/LIF spectra to explain the differences between spectral patterns in terms of a T3 doorway-mediated singlet-triplet coupling model.     

Controlled diastereoselectivity at the alkene-geometry through selective encapsulation: E-Z photoisomerization of oxazolidinone-functionalized enecarbamates within hydrophobic nano-cavities

Photoisomerization of encapsulated Z-enecarbamates within the hydrophobic chiral cavities of gamma-CD showed higher diastereoselectivities in the photoproducts than those obtained in solution. The selective encapsulation of the enecarbamates and the following isomerization process are both diastereoselectively controlled by gamma-CD.     

Identification of oxidative post-translational modification of serum albumin in patients with idiopathic pulmonary arterial hypertension and pulmonary hypertension of sickle cell anemia

Pulmonary hypertension (PH) in sickle cell anemia (SCA) is characterized by decreased nitric oxide bioavailability that might, in part, be related to oxidative stress. Oxidative post-translational modifications of plasma proteins may serve as hallmarks of disease severity and could result in altered protein function and structure. We hypothesized that serum albumin in patients with PH of SCA undergoes oxidative post-translational modification and that this modification may reflect important mediators of disease pathogenesis that are common to both idiopathic pulmonary arterial hypertension (IPAH) and PH of SCA. To explore this hypothesis, we studied albumin purified from the plasma of patients in four subject groups: SCA and PH, SCA steady-state without PH, IPAH, and normal volunteers. Purified albumin was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). Using MALDI-TOFMS, we identified that an ion corresponding to a malondialdehyde (MDA)-modified albumin peptide was differentially present in patients with IPAH and PH of SCA. These results were confirmed by dot-blotting and Western analysis. We localized the site of MDA modification to albumin residue K159 using LC/MS/MS. Thus, we have identified an MDA modification of serum albumin that appears to be a common link between PH of SCA and IPAH. This finding supports the notion that oxidative stress modulates the pathogenesis of PH of SCA and suggests that this and other post-translational modifications may be important biomarkers of disease.     

Synthesis and characterization of ruthenium bis(beta-diketonato) pyridine-imidazole complexes for hydrogen atom transfer

Ruthenium bis(beta-diketonato) complexes have been prepared at both the RuII and RuIII oxidation levels and with protonated and deprotonated pyridine-imidazole ligands. RuII(acac)2(py-imH) (1), [RuIII(acac)2(py-imH)]OTf (2), RuIII(acac)2(py-im) (3), RuII(hfac)2(py-imH) (4), and [DBU-H][RuII(hfac)2(py-im)] (5) have been fully characterized, including X-ray crystal structures (acac = 2,4-pentanedionato, hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato, py-imH = 2-(2'-pyridyl)imidazole, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene). For the acac-imidazole complexes 1 and 2, cyclic voltammetry in MeCN shows the RuIII/II reduction potential (E1/2) to be -0.64 V versus Cp2Fe+/0. E1/2 for the deprotonated imidazolate complex 3 (-1.00 V) is 0.36 V more negative. The RuII bis-hfac analogues 4 and 5 show the same DeltaE1/2 = 0.36 V but are 0.93 V harder to oxidize than the acac derivatives (0.29 and -0.07 V). The difference in acidity between the acac and hfac derivatives is much smaller, with pKa values of 22.1 and 19.3 in MeCN for 1 and 4, respectively. From the E1/2 and pKa values, the bond dissociation free energies (BDFEs) of the N-H bonds in 1 and 4 are calculated to be 62.0 and 79.6 kcal mol(-1) in MeCN - a remarkable difference of 17.6 kcal mol(-1) for such structurally similar compounds. Consistent with these values, there is a facile net hydrogen atom transfer from 1 to TEMPO* (2,2,6,6-tetramethylpiperidine-1-oxyl radical) to give 3 and TEMPO-H. The DeltaG degrees for this reaction is -4.5 kcal mol(-1). 4 is not oxidized by TEMPO* (DeltaG degrees = +13.1 kcal mol(-1)), but in the reverse direction TEMPO-H readily reduces in situ generated RuIII(hfac)2(py-im) (6). A RuII-imidazoline analogue of 1, RuII(acac)2(py-imnH) (7), reacts with 3 equiv of TEMPO* to give the imidazolate 3 and TEMPO-H, with dehydrogenation of the imidazoline ring.     

Autocorrelation infrared analysis of mineralogical samples: the influence of user controllable experimental parameters

Autocorrelation infrared (ACIR) analysis is based upon the application of the autocorrelation function corr(alpha,omega') = integral(-infinity)(infinity) alpha(omega + omega') alpha(omega) d omega to standard Fourier transform infrared (FTIR) transmission spectra. We present a rigorous examination of the effect of experimental parameters such as dilution ratio, spectral resolution, grinding time and pressing conditions upon the ACIR analysis of haematite. Results were found to vary by less than 4.5% irrespective of sample preparation, instrumental and data collection parameters. For a series of perovskite samples, the relationship between the measured effective linewidth and material composition appears to be reproducible, even though the absolute magnitudes of delta corr values do not. Our results further indicate that the ACIR technique is indeed valid for comparative analysis of synthetic sample sequences that vary slightly in composition or structural state, provided that primary spectra are all recorded by the same instrument.     

Observation of the A1A" state of isocyanogen

The A1A" state of isocyanogen, CNCN, is observed using photofragment fluorescence excitation spectroscopy in a room temperature cell and in a molecular beam. The spectra are highly congested, but progressions that correspond to the Franck-Condon active C-N-C bending vibration in the excited state are evident. Linewidth measurements indicate that the excited state lifetime is <10 ps. These measurements are consistent with previous ab initio calculations, which predicted a bent excited state with a short lifetime due to predissociation. Although we do not believe that we have observed the origin band of the electronic transition, we place an upper limit of 42,523 cm(-1) on the energy of the excited state zero point level.