Photonic band gaps analysis of Thue-Morse multilayers made of porous silicon

Dielectric aperiodic Thue-Morse structures up to 128 layers have been fabricated by using porous silicon technology. The photonic band gap properties of Thue-Morse multilayers have been theoretically investigated by means of the transfer matrix method and the integrated density of states. The theoretical approach has been compared and discussed with the reflectivity measurements at variable angles for both the transverse electric and transverse magnetic polarizations of light. The photonic band gap regions, wide 70 nm and 90 nm, included between 0 and 30°, have been observed for the sixth and seventh orders, respectively

Quantitative dominances of taxa structuring the macrozoobenthic communities living in different coastal habitats.

The aim of this study was to quantify the dominance of macrozoobenthic taxa structuring the benthic assemblages associated to 6 coastal habitats, which occur from the mesolittoral to the circalittoral zone of the Campania coast. Crustaceans, polychaetes and molluscs were the main taxonomic groups structuring all the benthic assemblages, representing an average of 89.20% of the total taxa. However, each habitat showed the dominance of only one peculiar taxon

Development of Lewis Acid Catalyzed Asymmetric Ring Expansion Reactions and Catalysis of Etherification Reactions with sp3 Electrophiles

Thesis advisor: Marc L. SnapperChapter 1: Over the past 100 years, ring expansion chemistry with non-stabilized diazoalkanes has grown slowly. While the intrinsic hazards and stigma associated with the use of diazoalkanes has been a serious impediment to more widespread development, a number of groups have made significant advances over the years. This chapter aims to provide a brief historical account of the most significant developments related to diazoalkane- based ring expansion methods. Chapter 2: The construction of stereogenic centers adjacent to ketones remains a challenging synthetic problem for chemists. Deficiencies with regard to reaction scope, efficiency, and generality remain. In contrast to the majority of other methods in the literature, stereoselective insertion of diazoalkanes provides a pathway to directly access enantiomerically enriched α-substituted cycloalkanones. In this chapter, an account of how we developed the first catalytic asymmetric diazoalkane-based ring expansion reactions is presented. Ring expansion of unfunctionalized cycloalkanones with diazoalkanes efficiently affords α-aryl substituted cycloalkanones with high enantiopurity. Additionally, this work led to the synthesis of new chiral bis(oxazoline) ligands and the discovery of a rapid method to assay the concentration of diazoalkane solutions. Chapter 3: Single-carbon ring expansion is a powerful synthetic disconnection, allowing chemists to construct or purchase the lower homologue of a ring system before expanding to the target ring size. Starting from a smaller ring size can often allow access to a broader array of transformations that proceed with greater stereoselection. In our approach to a class of natural products bearing a cis-decalin core, we successfully implemented a catalytic regioselective single-carbon ring expansion reaction in the context of an advanced synthetic intermediate. This chapter describes the experimental details behind the first catalytic single carbon cyclopentanone homologations and how we extended the method to more complex substrates. Chapter 4: Catalytic activation of sp2 hybridized electrophiles by nucleophilic catalysts has been studied extensively and proceeds through a well-defined mechanistic pathway. In constrast, activation of sp3 hybridized electrophiles in a similar fashion with small-molecule organocatalysts remains an elusive endeavor for chemists. This chapter describes prelimi- nary studies towards this lofty goal and how we discovered a new class of imidazole-based catalysts. Thorough mechanistic studies with the newly discovered catalysts ultimately proved that the reactions proceeded through a pathway that does not involve electrophile activation. However, inexpensive and commercially available imidazolium salts were found to catalyze Williamson etherification reactions under mild conditions through a mechanism that involves an unusual imidazolium alkoxide ion-pair.Thesis (PhD) — Boston College, 2013.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Chemistry

Red coral (Corallium rubrum) populations and coralligenous characterization within "Regno di Nettuno MPA" (Tyrrhenian Sea, Italy)

Red coral is one of the most important species belonging to the coralligenous habitats, being a structuring organism and highly sensitive to human pressure. The presence of red coral populations is historically well documented along the Campania coast (Tyrrhenian Sea), and, due to its high economic value, it has been commercially overharvested since ancient times. Red coral populations along several cliffs on the "Regno di Nettuno" MPA of the Gulf of Naples were investigated using ROV-imaging techniques. Coralligenous habitats were characterized in terms of percent cover and number of morphological groups. Pizzaco site showed the richest and most diverse community. Density of red coral colonies was calculated and compared with morphometric parameters. Results show an inversely correlated trend between colonies density and their size. Finally, fishing pressure was estimated through frequency of lost fishing gears, and S. Angelo site resulted the most stressed one. Anthropic stress plays a key role in the degradation of coralligenous habitats and the dramatic reduction of red coral populations recorded in recent years allows to suspect a more extensive degradation of the entire community. An assessment of the distribution and state of the populations can provide useful information to take measures for a better MPAs management

ESI-MS and thermal melting studies of nanoscale platinum(ii) metallomacrocycles with DNA

The hydrophilic, long-chain diamine PEGda (O,O′-bis(2-aminoethyl)octadeca(ethylene glycol)), when complexed with cis-protected Pt(II) ions afforded water-soluble complexes of the type [Pt(N,N)(PEGda)](NO3)2 (N,N = N,N,N′,N′-tetramethyl-1,2-diaminoethane (tmeda), 1,2-diaminoethane (en), and 2,2′-bipyridine (2,2′-bipy)) featuring unusual 62-membered chelate rings. Equimolar mixtures containing either the 16-mer duplex DNA D2 or the single-stranded D2a and [Pt(N,N)(PEGda)]2+ were analyzed by negative-ion ESI-MS. Analysis of D2-Pt(II) mixtures showed the formation of 1:1 adducts of [Pt(en)(PEGda)]2+, [Pt(tmeda)(PEGda)]2+ and the previously-described metallomacrocycle [Pt2(2,2′-bipy)2{4,4′-bipy(CH2)44,4′-bipy}2]8+ with D2; the dinuclear species bound to D2 most strongly, consistent with its greater charge and aromatic surface area. D2 formed 1:2 complexes with the acyclic species [Pt(2,2′-bipy)(Mebipy)2]4+ and [Pt(2,2′-bipy)(NH3)2]2+. Analyses of D2a-Pt(II) mixtures gave results similar to those obtained with D2, although fragmentation was more pronounced, indicating that the nucleobases in D2a play more significant roles in mediating the decomposition of complexes than those in D2, in which they are paired in a complementary manner. Investigations were also conducted into the effects of selected platinum(II) complexes on the thermal denaturation of calf thymus DNA (CT-DNA) in buffered solution. Both [Pt2(2,2′-bipy)2{4,4′-bipy(CH2)64,4′-bipy}2]8+ and [Pt(2,2′-bipy)(Mebipy)2]4+ stabilized CT-DNA. In contrast, [Pt(tmeda)(PEGda)]2+ and [Pt(en)(PEGda)]2+ (as well as free PEGda) caused negligible changes in melting temperature (ΔTm), suggesting that these species interact weakly with CT-DNA

Playing with light in diatoms: microalgae with a natural photonic crystal structure

Complex micro- and nano-structured materials for photonic applications are designed and fabricated using top technologies. A completely different approach to engineering systems at the sub-micron-scale consists in recognizing the nanostructures and morphologies that nature has optimized during life’s history on earth. In fact, biological organisms could exhibit ordered geometries and complex photonic structures which often overcome the products of the best available fabrication technologies [1]. An example is given by diatoms, microalgae with a peculiar cell wall consisting of amorphous hydrated silica valves reciprocally interconnected in a structure called the frustule. Valve surfaces exhibit specie-specific patterns of regular arrays of chambers, called areolae, developed into the frustule depth. Areolae range in diameter from few hundreds of nanometers up to few microns, and can be circular, polygonal or elongate [2]. The formation of these patterns can be modeled by self-organised, genetically controlled processes. Despite of the high level of knowledge on the genesis and morphology of diatom frustules, their functions are not completely understood [2]. In this work, we show that the silica valves of marine diatoms, characterized by a photonic crystal-like structure, have surprising optical properties, being capable of filtering and focalizing light, as well as exhibiting optical sensing capabilities

The ligand-receptor interactions based on silicon technology

We explored the use of porous silicon (pSi) technology for the construction of a biotechnological device, in which the ligand-receptor interactions are revealed by means of laser optical measurements. Here we report the settling of chemical procedures for the functionalization of the silicon wafers and for the subsequent anchoring of biological molecules such as a purified murine monoclonal antibody (UN1 mAb), an antibody anti-P8 protein of M13 phage and an antibody anti-A20 murine lymphoma cell line. The optical analysis of the interaction on the biochips between the bound biomolecules and their corresponding ligands indicated that the pSi is suitable for thi

Muscle sympathetic nerve activity in patients with acromegaly

Muscle sympathetic nerve activity was measured in nine acromegalic patients (age, 35 +/- 4 yr; body mass index, 28 +/- 2 kg/m2) and eight healthy subjects (age, 32 +/- 3 yr; body mass index, 25 +/- 2 kg/m2) by combining the forearm arterial-venous difference technique with the tracer method [infusion of tritiated norepinephrine (NE)]. Muscle NE release was quantified both at rest and during physiological hyperinsulinemia while maintaining euglycemia (approximately 90 mg/dL) by means of the euglycemic clamp. Arterial plasma NE was similar in the two groups at rest (197 +/- 28 and 200 +/- 27 pg/mL (-1) and slightly increased during insulin infusion. Forearm NE release was 2.33 +/- 0.55 ng x liter(-1) x min(-1) in healthy subjects and 2.67 +/- 0.61 ng x liter(-1) x min(-1) in acromegalic subjects in the basal state and increased to a similar extent during insulin infusion in both groups (3.13 +/- 0.71 and 3.32 +/- 0.75 ng x L(-1) x min(-1), P < 0.05 vs. basal), indicating a normal stimulatory effect of insulin on muscle sympathetic activity. In contrast, insulin-stimulated forearm glucose uptake was markedly lower in acromegalic patients (2.3 +/- 0.4 mg x L(-1) x min(-1)) than in control subjects (7.9 +/- 1.3 mg x L(-1) x min(-1), P < 0.001), indicating the presence of severe insulin resistance involving glucose metabolism. Our data demonstrate that patients with long-term acromegaly have normal sympathetic activity in the skeletal muscle in the basal, postabsorptive state and normal increments in NE spillover in response to the sympatho-excitatory effect of insulin. Thus, the presence of severe insulin resistance in acromegaly is not accounted for by adrenergic mechanisms