Yields of Br* (4P1/2) as a function of wavelength in the photodissociation of Br2 and IBr

A flashlamp-pumped tunable dye laser has been used to study the photochemical production of Br* (4²P_1/2) atoms from Br₂ and IBr exc     

β-lithiations of carboxamides. Synthesis of β-substituted-α,β-unsaturated amides

N-Methyl-2-methyl-3-(benzotriazol-l-yl)propanamide, on treatment with butyllithium forms a dianion which on treatment with alkyl and benzyl halides, aldehydes and ketones affords monosubstituted products; with ethyl p-toluate, a lactam is formed. The alkylated derivatives eliminate benzotriazole in the presence of base to afford trisubstituted α,β-unsaturated amides.     

Homopolar- and Heteropolar Bond Dissociation Energies and Heats of Formation of Radicals and Ions in the Gas Phase. I. Data on organic molecules

The literature data on heteropolar and homopolar 2-center bond dissociation energies in organic molecules in the gas phase and the corresponding heats of formation of radicals and ions have been critically evaluated. Data for more than 500 bonds are represented in tabular form together with the pertinent literature references. Selected electron affinities and π-bond dissociation energies have also been incorporated. The follow-up paper will discuss some empirical general aspects of these data particularly regarding the effect of structure on the bond dissociation energies.     

Construction of functional porphyrin polystyrene nano-architectures by ATRP

A series of mono-functionalized metallo-porphyrin polystyrenes have been synthesized using atom transfer radical polymerization and their self-assembling behavior was studied by electron microscopy showing that the polystyrene tail-length influences the aggregate architecture.     

Site-specific detection of S-nitrosylated PKB alpha/Akt1 from rat soleus muscle using CapLC-Q-TOF(micro) mass spectrometry

Protein Kinase Balpha(PKBalpha, or Akt1) is believed to play a crucial role in programmed cell death, cancer progression and the insulin-signaling cascade. The protein is activated by phosphorylation at multiple sites and subsequently phosphorylates and activates eNOS. Free cysteine residues of the protein may capture reactive, endogenously produced nitric oxide (NO) as S-nitrosothiols. Site-specific detection of S-nitrosylated cysteine residues, usually at low stoichiometry, has been a major challenge in proteomic research largely due to the lack of mass marker for S-nitrosothiols that are very labile under physiologic conditions. In this report we describe a sensitive and specific MS method for detection of S-nitrosothiols in PKB alpha/Akt1 in rat soleus muscle. PKB alpha/Akt1 was isolated by immunoprecipitation and 2D-gel electrophoresis, subjected to in-gel tryptic digestion, and cysteinyl nitrosothiols were reacted with iodoacetic acids [2-C(12)/C(13) = 50/50] under ascorbate reduction conditions. This resulted in the production of relatively stable carboxymethylcysteine (CMC) immonium ions (m/z 134.019 and m/z 135.019) within a narrow argon collision energy (CE = 30 +/- 5 V) in the high MS noise region. In addition, free and disulfide-linked cysteine residues were converted to carboxyamidomethylcysteines (CAM). Tryptic S-nitrosylated parent ion was detected with a mass accuracy of 50 mDa for the two CMC immonium ions at the triggered elution time during capillary liquid chromatography (LC) separation. A peptide containing Cys(296) was discriminated from four co-eluting tryptic peptides under lock mass conditions (m/z 785.8426). S-nitrosothiol in the tryptic peptide, ITDFGLBKEGIK (B: CAM, [M + 2H](2+) = 690.86, Found: 690.83), is believed to be present at a very low level, since the threshold for the CMC immonium trigger ions was set at 3 counts/s in the MS survey. The high levels of NO that are produced under stress conditions may result in increased S-nitrosylation of Cys(296) which blocks disulfide bond formation between Cys(296) and Cys(310) and suppresses the biological effects of PKB alpha/Akt1. With the procedures developed here, this process can be studied under physiological and pathological conditions.     

Radical mediated synthesis of 6-arylphenanthridines via benzotriazole ring-opening

Lithiation of diarylbenzotriazol-1-ylmethanes followed by addition of copper( I ) iodide gave 6-arylphenanthridine derivatives in moderate yields. When the two aryl groups were the same or contained very different electron densities, only one product was obtained. However, when the two aryl groups exhibited electron densities of similar magnitude, two isomers were afforded. According to the substituent effect, we believe that the reactions proceed via radical intermediates formed by copper( I ) iodide.     

Ab initio SCF MO study of the hydrogen-bonded dimers of cyanogen with HF and HCl

Large-scale gaussian orbital SCF MO calculations are presented for the hydrogen-bonded complexes NCCN…HF and NCCN…HCl. Calculated equilibrium geometries, hydrogen-bond dissociation energies and selected one-electron properties are given to supplement available experimental data. Changes of electron distribution on complex formation are discussed in terms of Mulliken population indices.     

Inelastic incoherent neutron scattering measurements of intact cells and tissues and detection of interfacial water

We have previously used inelastic incoherent neutron scattering spectroscopy to investigate the properties of aqueous suspensions of biomolecules as a function of hydration. These experiments led to the identification of signals corresponding to interfacial (hydration) water at low water content. A prediction from these studies was that in the crowded environment inside living cells, a significant proportion of the water would be interfacial, with profound implications for biological function. Here we describe the first inelastic incoherent neutron scattering spectroscopy studies of living cells and tissues. We find that the interfacial water signal is similar to that observed for water interacting with purified biomolecules and other solutes, i.e., it is strongly perturbed in the librational and translational intermolecular optical regions of the spectrum at 20-150 meV. The ratio of interfacial water compared to total water in cells (approximately 30%) is in line with previous experimental data for hydration water and calculations based on simple assumptions.     

Intermolecular packing and alignment in an ordered beta-hairpin antimicrobial peptide aggregate from 2D solid-state NMR

The aggregation and packing of a membrane-disruptive beta-hairpin antimicrobial peptide, protegrin-1 (PG-1), in the solid state are investigated to understand its oligomerization and hydrogen-bonding propensity. Incubation of PG-1 in phosphate buffer saline produced well-ordered nanometer-scale aggregates, as indicated by 13C and 15N NMR line widths, chemical shifts, and electron microscopy. Two-dimensional 13C and 1H spin diffusion experiments using C-terminus strand and N-terminus strand labeled peptides indicate that the beta-hairpin molecules in these ordered aggregates are oriented parallel to each other with like strands lining the intermolecular interface. In comparison, disordered and lyophilized peptide samples are randomly packed with both parallel and antiparallel alignments. The PG-1 aggregates show significant immobilization of the Phe ring near the beta-turn, further supporting the structural ordering. The intermolecular packing of PG-1 found in the solid state is consistent with its oligomerization in lipid bilayers. This solid-state aggregation approach may be useful for determining the quaternary structure of peptides in general and for gaining insights into the oligomerization of antimicrobial peptides in lipid bilayers in particular.     

Application of laser ablation–inductively coupled plasma-mass spectrometry (LA–ICP–MS) to investigate trace metal spatial distributions in human tooth enamel and dentine growth layers and pulp

Human tooth enamel provides a nearly permanent and chronological record of an individuals nutritional status and anthropogenic trace metal exposure during development; it might thus provide an excellent bio archive. We investigated the micro-spatial distribution of trace metals (Cu, Fe, Mg, Sr, Pb, and Zn) in 196×339 m² raster pattern areas (6.6×10⁴ m²) in a deciduous tooth using laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS). Ablated areas include prenatal and postnatal enamel, the neonatal line, the dentine–enamel junction (DEJ), dentine, and the dentine–pulp junction. Topographic variations in the surface elemental distribution of lead, zinc, strontium, and iron intensities in a deciduous tooth revealed heterogeneous distribution within and among regions. ⁴³Ca normalized elemental intensities showed the following order: Sr>Mg>>Zn>Pb>Fe>Cu. Elevated zinc and lead levels were present in the dental pulp region and at the neonatal line. This study demonstrates the ability of LA–ICP–MS to provide unique elemental distribution information in micro spatial areas of dental hard tissues. Elemental distribution plots could be useful in decoding nutrition and pollution information embedded in their bio apatite structure.Presented in part at the 2002 Winter Conference on Plasma Spectrochemistry, Scottsdale, AZ, January 6–12, 2002. The poster was selected as an outstanding poster presentation.