3,4'-Linked bis(piperidines) related to the haliclonacyclamine class of marine alkaloids: synthesis using crossed-aldol chemistry and preliminary biological evaluations

Compounds 2-5, incorporating various elements of the 3,4'-bis(piperidine) core associated with the sponge-derived alkaloid haliclonacyclamine A (HA, 1), have been prepared through, inter alia, aldol-type reactions of N-substituted piperidin-4-ones and certain derivatives. Screening of these compounds in various assays, including an ecological one, reveals that compound 5 exhibits allelochemical properties similar to those associated with HA itself.     

Conversion of a ribozyme to a deoxyribozyme through in vitro evolution

An RNA ligase ribozyme was converted to a corresponding deoxyribozyme through in vitro evolution. The ribozyme was prepared as a DNA molecule of the same sequence, and had no detectable activity. A population of randomized variants of this DNA was constructed and evolved to perform RNA ligation at a rate similar to that of the starting ribozyme. When the deoxyribozyme was prepared as an RNA molecule of the same sequence, it had no detectable activity. Thus, the evolutionary transition from an RNA to a DNA enzyme represents a switch, rather than a broadening, of the chemical basis for catalytic function. This transfer of both information and function is relevant to the transition between two different genetic systems based on nucleic acid-like molecules, as postulated to have occurred during the early history of life on Earth.     

Local Fredholm Spectra and Fredholm Properties of Singular Integral Operators on Carleson Curves Acting on Weighted Hölder Spaces

We study the local Fredholm spectra and global Fredholm properties for singular integral operators on composed Carleson curves with discontinuous coefficients acting on weighted H?lder spaces. We consider the curves, coefficients, and weights which are slowly oscillating at the nodes of the curve. Application of pseudodifferential operators technique allows us to explain the influence of oscillation of curves, coefficients, and weights on the appearance of massive local Fredholm spectra. We obtain a criterion of Fredholmness and index formula for operators under consideration.     

Cross-coupling reactions of gold(I) alkynyl and polyyndiyl complexes

Gold(I) alkynyl complexes are shown to efficiently couple with aryl iodides under mild conditions in the presence of both Pd(II) and Cu(I) co-catalysts. The reaction is not gold catalysed, but rather the Au(I) centre serves to transfer the alkynyl moiety to Cu(I), which then enters the conventional Sonogashira cycles. Using this method, a small range of 1,4-disubstituted diynes, including examples of differentially substituted compounds ArCCCCAr′, have been prepared directly from [(Ph₃P)AuCCCCAu(PPh₃)] and aryl iodides ArI.     

Aurones: Small Molecule Visible Range Fluorescent Probes Suitable for Biomacromolecules

Aurones, derivatives of 2-benylidenebenzofuran-3(2H)-one, are natural products that serve as plant pigments. There have been reports that some of these substances fluoresce, but little information about their optical properties is in the literature. In this report, series of aurone derivatives were synthesized as possible fluorescent probes that can be excited by visible light. We found that an amine substituent shifted the lowest energy absorption band from the near-UV to the visible region of the electromagnetic spectrum. Four amine-substituted aurone derivatives were synthesized to explore the effect of this substituent on the absorption and emission properties of the aurone chromophore. The emission maxima and intensities of the molecules are strongly dependent on the nature of the substituent and the solvent polarity. Overall, the emission intensity increases and the maximum wavelength decreases in less polar solvents; thus, the aurones may be useful probes for hydrophobic sites on biological molecules. A limited investigation with model protein, nucleic acid and fixed cells supports this idea. It is known that the sulfur analog of aurone can undergo photo-induced E/Z isomerization. This possibility was investigated for one of the aminoaurones, which was observed to reversible photoisomerize. The two isomers have similar absorption spectra, but the emission properties are distinct. We conclude that appropriately substituted aurones are potentially useful as biological probes and photoswitches.     

Phonetic variability of stops and flaps in spontaneous and careful speech

Variability is perhaps the most notable characteristic of speech, and it is particularly noticeable in spontaneous conversational speech. The current research examines how speakers realize the American English stops /p, k, b, g/ and flaps (? from /t, d/), in casual conversation and in careful speech. Target consonants appear after stressed syllables (e.g., "lobby") or between unstressed syllables (e.g., "humanity"), in one of six segmental/word-boundary environments. This work documents the degree and types of variability listeners encounter and must parse. Findings show greater reduction in connected and spontaneous speech, greater reduction in high frequency phrases (but not within high frequency words), and greater reduction between unstressed syllables than after a stress. Although highly reduced productions of stops and flaps occur often, with approximant-like tokens even in careful speech, reduction does not lead to a large amount of overlap between phonological categories. Approximant-like realizations of expected stops and flaps in some conditions constitute the majority of tokens. This shows that reduced speech is something that listeners encounter, and must perceive, in a large proportion of the speech they hear.     

The hydrogenation of α-methylstyrene by tricarbonyl(cyclopentadienyl)hydride compounds of tungsten and molybdenum; support for a radical mechanism

Rates of reaction of the hydrides of tungsten and molybdenum of the form HM(η5-C₅H₅(CO)₃, with β-methylstyrene have been determined. The rate law is first order in olefin and in hydride. A mechanism involving a rate limiting step of hydrogen atom transfer to the olefin is consistent with the rate law, isotope effect and the absence of CO inhibition. The activation enthalpy for the reactions of HW(η5-C₅H₅)(CO)₃ and HMo(η5-C₅H₅)(CO)₃ are 97.5 ± 4.2 and 89.1 ± 3.3 kJ/mol, respectively. The rate constant for the reaction of styrene and HW(β5-C₅H₅)(CO)₃ is approximately that of β-methylstyrene, while β-methylstyrene was not observed to react under the conditions of the previous determinations. This suggests that attack by the hydride occurs at the β-carbon and this process is inhibited by substituents at that location.