Proteomic analysis of transducin beta-subunit structural heterogeneity

Partially purified transducin was resolved using two-dimensional gel electrophoresis (2-DE). Peptide mass fingerprinting of several different spots believed to correspond to the 37 kDa beta-subunit of transducin (T(beta)) was performed. Spots were excised and proteolyzed using modified trypsin. Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) was performed on the peptide mixture resulting from each spot. As many as six spots with different pI, ranging from 5.2 to 6.1, were observed when separated using 2-DE. MALDI peptide mass fingerprinting determined with high probability that all of the spots were the same gene product, guanine nucleotide-binding protein G(I)/G(S)/G(T) beta-subunit 1 (GNB1; T(beta1)). This suggested that post-translational modification was responsible for the differences in pI. Phosphorylation experiments showed that at least one T(beta1) spot was phosphorylated in vitro with [gamma-(32)P]ATP by an endogenous kinase. Treatment of T(beta) with alkaline phosphatase caused a large change in the spot pattern of T(beta), suggesting that phosphorylated T(beta) is a substrate for alkaline phosphatase. We conclude that T(beta1) constitutes over 99% of the T(beta) expressed in bovine rod outer segments and displays structural heterogeneity that is due to post-translational modification. We also conclude that some, but not all, of the heterogeneity observed is due to phosphorylation of Tb1.     

Hydrogenation of

The course of the hydrogenation of [5]- and [6]metacyclophane (1b and 1c) and their thermochemistry is described. Both compounds are hydrogenated rapidly (within 10 s) to furnish the bridgehead olefins 13b and 12c. The accompanying hydrogenation enthalpies are -220 and -141 kJmol(-1), respectively. Strain energies (SE) and olefinic strains (OS) of a number of bridgehead olefins have been evaluated by DFT calculations; it was concluded that 13b belongs to the class of hyperstable olefins which correlates nicely with its reluctance to undergo hydrogenation. By combining experimental hydrogenation enthalpies and DFT calculations, SE of 187 and 121 kJmol(-1) were derived for 1b and 1c.     

Vibrational relaxation in liquid diethylamine

Two types of time resolved experiments have been performed on the intermediate sized polyatomic molecule diethylamine, in the liquid phase, in order to elucidate the pathway for vibrational relaxation of the ν = 3 level of the NH stretching mode, which has 9420 cm^?1 of energy. Both techniques had calibrated absolute sensitivities and were specific for vibrational modes of ca. 3000 cm^?1, yet with neither were transient populations in such modes observable. It is inferred that population relaxation in this highly excited room temperature system proceeds on the subpicosecond time scale to lower lying levels. The importance of intramolecular channels for this decay is suggested.     

Spirans XX. Synthesis of 8,8-dialkylazaspiro[4.5] decanes and 9,9-dialkylazaspiro[5.5]undecanes

N-(2-Dimethylaminopropyl)-8,8-dimethyl-2-azaspiro[4.5]decane ( 1 ), N-(2-dimethylaminopropyl)-8,8-diethyl-2-azaspiro[4.5]decane ( 2 ), N-(3-dimethylaminopropyl)-9,9-dimethyl-3-azaspiro[5.5]undecane ( 3 ), and N-(3-dimethylaminopropyl)-9,9-diethyl-3-azaspiro[5.5]undecane ( 4 ) have been synthesized from 4,4-dimethylcyclohexanone ( 5 ) and 4,4-diethylcyclohexanone ( 6 ). Biological evaluation of these amines showed significant inhibition of cancer cell growth in human cancer cells grown in tissue culture.     

Probing solution behaviour of metallosupramolecular complexes using pyrene fluorescence

A new method for assessing the topology of metallosupramolecular assemblies using pyrene-appended ligands is reported. Two potentially tetradentate ligands containing one (L(1)) and two (L(2)) terminal pyrene moieties were synthesised and their complexes with Cu(+) and Cd(2+) were characterised. Photophysical measurements demonstrate that in [Cu(2)(L(1))(2)](2+), [CdL(1)](2+) and [Cu(2)(L(2))(2)](2+) the emission spectra are dominated by monomeric emission but in the cadmium complex of L(2) (where the pyrene units are in close proximity) a quenching of the luminescence coupled with weak emission at 540 nm is indicative of excimer formation.     

Unexpected efficiency of cyclic amidine catalysts in depolymerizing poly(ethylene terephthalate)

This article describes studies on the catalytic activity of several nitrogen‐based organic catalysts for the depolymerization of poly(ethylene terephthalate) (PET), in which a few cyclic amidines work more effectively than a potent, bifunctional guanidine‐based catalyst 1,5,7‐triazabicyclo‐[4,4,0]‐dec‐5‐ene (TBD) in the presence of short chain diols that play a role in activation of carbonyl groups through hydrogen bonding. Further studies prove that the catalytic efficiency at the above specific conditions depends only on the extent of activation of a hydroxyl group rather than simply the pK_a of the bases. For glycolysis with excess short‐chain alkanediols, 1,8‐diazabicyclo[5.4.0]undec‐7‐ene is the best catalyst. In contrast, TBD shows outstanding catalytic activity in depolymerizations of PET with mono‐alcohols and longer‐chain diols. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

The Effect of Carbon Dioxide on the Alkali-Metal Initiation of Polyisoprene

The structures of polymers formed when alkali metals are placed in the vapor phase above isoprene monomer, both in the presence and absence of carbon dioxide, were investigated. In the absence of carbon dioxide, the polymers were all gel-like and soluble. In the presence of carbon dioxide, however, insoluble popcorn polymers were formed. The structures of the soluble polymers varied from primarily cis in the case of lithium to trans for sodium and potassium initiation. In the presence of carbon dioxide the three alkali metals produced polymers having similar structures, predominantly trans. In the absence of carbon dioxide most of the polymerization proceeds anionically with the majority of the free radical sites of the initially formed radical anion being removed by a transfer reaction or by dianion formation. The presence of carbon dioxide, however, leads to the formation of car boxy late ions that prevent anionic polymerization. Then, due to the structural orientation of the radical anion on the surface, free-radical polymerization occurs, leading to microgelation and popcorn polymerization. This results from cross-linking caused by mechanical rupture of the growing chains.