Dendrimers as scaffolds for multifunctional reversible addition–fragmentation chain transfer agents: Syntheses and polymerization

The synthesis and characterization of novel first‐ and second‐generation true dendritic reversible addition–fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3‐benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z‐group architecture based on 1,1,1‐hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1.3 for PS) via bulk free‐radical polymerization at 60 °C. The novel dendrimer‐based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number‐average molecular weight (M_n) with the monomer–polymer conversion, yielding star polymers with molecular weights of up to M_n = 160,000 g mol^?1 for PBA (based on a linear PBA calibration) and up to M_n = 70,000 g mol^?1 for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1‐hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star‐shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star‐shaped polymeric materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5877–5890, 2004     

The preparation theorem on banach spaces

We give a generalization, for smooth Fredholm maps between Banach spaces, of the Preparation Theorem known in finite dimension. As an application we obtain the Prepared Form Theorem which is a basic tool in singularity theory.     

The membrane free sonoelectroanalytical determination of trace levels of lead and cadmium in human saliva

In this paper, square wave anodic stripping voltammetry (SWASV), synergistically coupled with an ultrasonically enhanced preconcentration step has been shown to yield a quantitative determination of lead and cadmium in human saliva at a membrane free in situ plated mercury thin film glassy carbon electrode. The sensitivity was facilitated by acoustic streaming which promoted efficient mass transport to the electrode thus reducing sampling times. Cavitation was responsible for cleaning and activating the electrode surface, this was essential in order to obtain a reproducible and representative signal. In silent conditions electrode fouling leading to fluctuations in the baseline current and signal depression, precluded accurate quantitative analyses. The results presented herein provide an extension to the proof of concept given in the authors' earlier work, with the analysis of lead in human saliva as opposed to artificial saliva reported. We also address the hitherto unreported detection and determination of cadmium in this medium. Results for both were independently verified by inductively coupled plasma-mass spectroscopy (ICP-MS). Close agreement between lead concentration determined by sono-SWASV and independent and blind ICP-MS is reported for human saliva samples having a total lead content of 0.92 microg L(-1) and 5 microg L(-1) with a detection limit of 0.5 microg L(-1). Microaddition calibration data for cadmium additions of 0.0125 microg L(-1) to samples spiked with 2.5 microg L(-1) and 5.0 microg L(-1) (reflecting levels in workers occupationally exposed) exhibited close agreement with the known total cadmium in the samples. A detection limit of 1 microg L(-1) cadmium in saliva has been established.     

Regiochemical Control and Suppression of Double Bond Isomerization in the Heck Arylation of 1-(Methoxycarbonyl)-2,5-dihydropyrrole

Arylation of 1-(methoxycarbonyl)-2,5-dihydropyrrole under standard Heck reaction conditions produces a mixture of compounds. The olefin undergoes two types of palladium-catalyzed reactions: (a) arylation to provide C-3 arylated derivatives and (b) competing double bond isomerization. Addition of silver carbonate and thallium acetate fully suppressed the isomerization, and good yields of C-3 substituted compounds were achieved after arylation with aryl halides. With regard to aryl triflates as arylating agents, addition of lithium chloride was necessary to promote the Heck reaction. This additive excluded the use of silver and thallium salts, but high regioselectivity and good yields could be obtained by employing tri-2-furylphosphine as ligand. Arylation was rendered both regioselective and enantioselective (58% ee) with 1-naphthyl triflate as substrate utilizing a (R)-BINAP/thallium acetate combination. The C-3 arylated enamides were converted further into the corresponding 3-arylpyrrolidines.     

The Small Molecule PPARγ Agonist GL516 Induces Feeding-Stimulatory Effects in Hypothalamus Cells Hypo-E22 and Isolated Hypothalami

PPARγ agonists are implicated in the regulation of diabetes and metabolic syndrome and have therapeutic potential in brain disorders. PPARγ modulates appetite through its central effects, especially on the hypothalamic arcuate nucleus (ARC). Previous studies demonstrated that the small molecule GL516 is a PPARγ agonist able to reduce oxidative stress and apoptosis with a potential neuroprotective role. Herein, we investigated the effects of GL516, in vitro and ex vivo, on the levels of hypothalamic dopamine (DA) and serotonin (5-HT). The gene expressions of neuropeptide Y, CART, AgRP, and POMC, which play master roles in the neuroendocrine regulation of feeding behavior and energy balance, were also evaluated. HypoE22 cells were treated with H₂O₂ (300 μM) for 2 h e 30’ and with different concentrations of GL516 (1 nM-100 µM). The cell viability was evaluated after 24 and 48 h of culturing using the MTT test. DA and 5-HT levels in the HypoE22 cell supernatants were analyzed through HPLC; an ex vivo study on isolated hypothalamic specimens challenged with scalar concentrations of GL516 (1–100 µM) and with pioglitazone (10 µM) was carried out. The gene expressions of CART, NPY, AgRP, and POMC were also determined by a quantitative real-time PCR. The results obtained showed that GL516 was able to reduce DA and 5-HT turnover; moreover, it was effective in stimulating NPY and AgRP gene expressions with a concomitant reduction in CART and POMC gene expressions. These results highlight the capability of GL516 to modulate neuropeptide pathways deeply involved in appetite control suggesting an orexigenic effect. These findings emphasize the potential use of GL516 as a promising candidate for therapeutical applications in neurodegenerative diseases associated with the reduction in food intake and stimulation of catabolic pathways.     

Dielectric properties of thin-film ZrO<Subscript>2</Subscript> up to 50 GHz for RF MEMS switches

The dielectric properties of zirconium dioxide (ZrO₂) ceramic thin films were characterized up to 50 GHz using coplanar waveguides (CPWs) and metal–insulator–metal (MIM) capacitors with top circular electrodes. The ZrO₂ films were deposited using a chemical solution onto high-resistivity Si wafers and metal layers. The real part of the dielectric constant of approximately 22 and 26 was extracted at 50 GHz for CPW and MIM structures, respectively, and the loss tangent was approximately 0.09 at 50 GHz. C–V and I–V measurements were carried out to determine low-frequency and DC dielectric properties. The measurement results indicate that ZrO₂ is a promising material to be used as a dielectric layer for radio-frequency (RF) microelectromechanical systems (MEMS) capacitive switches.     

Strong-field multiphoton ionization of hydrogen. TheS-matrix treatment of the elementary process

Summary A theoretical model is presented to treat the elementary act of strong-field multiphoton ionization of atoms when the electron continuum final-state distribution is important. It is based on theS-matrix formalism and treats the final-state electron-radiation interaction in an essentially nonperturbative way. Selected numerical calculations concern the ionization of hydrogen atoms and include differential and total cross-sections of several multiphoton channels as a function of the laser intensity. Good, qualitative agreement with the experimental observations is found for values of the field intensity which are not critical with respect to the simplifications adopted in constructing the theoretical model. It applies particularly to the use of an ideal model for the laser field. Significant departure from observations is instead found when the implications of the ideal laser model play a critical role, as occurs at channel inversion and suppression. It is concluded that the theoretical treatment to be completely satisfactory needs essentially to incorporate a more realistic laser model such as a multimode one.

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Riassunto Si presenta un modello teorico per il processo elementare della ionizzazione multifotonica di atomi da parte di un forte campo laser quando diventa importante la distribuzione degli stati finali del continuo dell'elettrone. Il modello si fonda sul formalismo della matriceS e tratta l'interazione elettrone-radiazione nello stato finale in modo non perturbativo. I calcoli numerici qui riportati si riferiscono alla ionizzazione di atomi d'idrogeno e includono sezioni d'urto totali e differenziali per diversi canali multifotonici in funzione dell'intensità del laser. Si trova un accordo qualitativo con i dati sperimentali per valori dell'intensità del campo che non sono critici rispetto alle semplificazioni adottate nella costruzione del modello teorico. Un significativo distacco dai dati sperimentali si ha quando le implicazioni del modello di laser ideale giocano un ruolo critico, come si ha per l'inversione e la scomparsa dei canali. Si conclude che il trattamento teorico per essere completamente soddisfacente necessita dell'introduzione di un modello di laser piú realistico, quale, ad esempio, quello a molti modi.

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Резюме Предлагается теоретическая модель для рассмотрения элементарного акта многофотонной ионизации атомов в сильном поле, когда распределение электронных непрерывных конечных состояний является существенным. Подход базируется на формализмеS-матрицы и взаимодействие электронов в конечном состоянии с полем излучения рассматривается непертурбационным образом. Численные вычисления касаются ионизации атомов водорода и включают дифференциальные и полные поперечные сечения для некоторых многофотонных каналов, как функции интенсивности лазерного излучения. Получено хорошее качественное согласие с экспериментальными результатами для значений интенсивности поля, которые не являются критическими по отношению к упрощениям, используемым при конструировании теоретической модели. Используется идеальная модель для лазерного поля. Обнаружено существенное отклонение от экспериментальных результатов в тех случаях, когда имеет место инверсия и подавление каналов. Делается вывод, что теоретический подход становится удовлетворительным, если используется более реалистическая модель лазера, как например, многомодовая модель.

     

The hydrogen molecule in an arbitrarily oriented magnetic field

Summary The modifications induced by a magnetic field of arbitrary direction and intermediate strength (i.e not larger than 2.35·10⁵ tesla, the ?atomic tesla?) on the lowest singlet and triplet energy states of the hydrogen molecule are studied. Using a linear combination of products of field-modified atomic orbitals, it is found that increasing the field strength the depth of the singlet energy well increases and the equilibrium internuclear distance decreases, yielding more rigid and localized nuclear vibrations. For sufficiently strong fields perpendicular to the internuclear axis, the triplet state exhibits a bonding behaviour. An explanation of the above results is given in terms of the field-modified electronic-charge distributions in the internuclear region. Based on the thesis submitted by S. Basile to the University of Palermo for graduation in Physics.     

Multiphoton free-free transitions in a spatially inhomogeneous laser field

Summary The results of an investigation are presented in which it is shown how the spatial inhomogeneity of a laser field modifies the multiphoton free-free transition cross-sections compared to the case of a homogeneous field. This kind of investigation is required to make more close contact with experiments in intense fields, as in these cases the inhomogeneity is produced by the focusing of the laser beam. Furthermore, taking into account the intensity spatial distribution allows us to achieve in an effective way the asymptotic decoupling of the scattered particles from the field, which is very important for theoretical models using asymptotic initial and final states embedded in the field. Differential and total cross-sections are calculated over a wide range of parameters as functions of the scattering angle, of the incoming-particle energy and of the laser intensity and frequency. The laser spatial inhomogeneity is found to wash out most of the oscillating behaviour of multiphoton differential cross-sections, derived within the model of a homogeneous laser. Little modifications are, instead, found in the total cross-sections which are simply scaled to slightly lower values. Crosssections with zero photon exchange are increased, while those with photon exchanges are lowered. This yields the result that the sum of all the ≪inhomogeneous≫ cross-sections is equal to the sum of all the ≪homogeneous≫ ones (sum rule). The multiphoton free-free transition differential cross-sections are found to be very sensitive quantities which may be used to get information on the laser properties and on their nonlinear behaviour, when these are not precisely known. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.