Synthesis and stereoselective DNA binding abilities of new optically active open-chain polyamines

The efficient synthesis of new open-chain enantiopure polyamines bearing (R,R)- and/or (S,S)-trans-cyclohexane-1,2-diamine moieties is described. The key step for the synthetic procedure is the selective monoalkylation of the cyclohexanebis(sulfonamide) core, which allows the subsequent functionalization of this moiety. Compounds bearing different combinations of absolute configurations, length of the aliphatic spacers and terminal groups have been prepared. As a demonstration of the potential utility of the obtained compounds, the preliminary DNA binding abilities of some of them have been studied by UV-measurements of melting temperatures (Tm). The effects of the absolute configuration of the corresponding chiral centers and the length of the spacer separating the cyclohexanediamine moieties on the strength of the interaction with DNA are also discussed.     

Polymerization of 1-vinylcyclohexene in the presence of group 4 metallocenes – MAO catalysts

1-Vinylcyclohexene was polymerized in the presence of several homogeneous catalytic systems consisting of methylaluminoxane and group 4 metallocenes such as CpTiCl₃, [isopropyl(cyclopentadienyl)(1-fluorenyl)]ZrCl₂,rac-[ethylenebis(1-indenyl)] ZrCl₂, (CH₃)₂Si(Cp)₂ZrCl₂, CpZrCl₃. The structure of the polymers depends on the catalyst. In fact, with CpTiCl₃, [isopropyl(cyclopentadienyl)(1-fluorenyl)]ZrCl₂ and rac-[ethylenebis-(1-indenyl)]ZrCl₂ the polymers are chemo-, regio- and stereoregular with 1,4 cis, 1,4 trans and 1,2 isotactic structure, respectively.     

General synthesis of 8-aryl-2-tetralones

Two alternative routes are described for the synthesis of 8-aryl-2-tetralones (1). Route A starts from alpha-tetralone 3 and involves 3 or 4 steps, with the selective Na-EtOH reduction of 1-aryl-7-methoxynaphthalenes 2 being the key step. The exclusive reduction of the A ring of naphthalenes 2 occurs when the aryl group at C-1 has no substituent at the ortho positions, affording tetrahydronaphthalenes 11. Reduction of the B ring of 2 becomes the major process when the aryl fragment has two substituents at the ortho positions, affording 8-aryl-2-tetralones 1 as the major component. Route B involves 5 steps starting from 2-tetralone 5, with the key step being the Suzuki coupling with triflate 4. This approach allows the synthesis of 8-aryl-2-tetralones 1 with no substituent at the ortho positions of the aryl fragment and with naphthalene and anthracene rings at C-8.     

Completeness of the Trajectories of Particles Coupled to a General Force Field

We analyze the extendability of the solutions to a certain second order differential equation on a Riemannian manifold (M, g), which is defined by a general class of forces (both prescribed on M or depending on the velocity). The results include the general time-dependent anholonomic case, and further refinements for autonomous systems or forces derived from a potential are obtained. These extend classical results for Lagrangian and Hamiltonian systems. Several examples show the optimality of the assumptions as well as the utility of the results, including an application to relativistic pp-waves.     

Topological phase diagram of a Kitaev ladder

We investigate the topological properties of a Kitaev ladder, i.e., a system made of two Kitaev chains coupled together by transversal hopping and pairing term, t₁ and Δ₁, respectively. Using the Chern number invariant, we present the topological phase diagram of the system. It is shown that beyond a non-topological phase, the system exhibits a topological phase either with four or two Majorana (zero energy) modes. In particular, we find that for some critical values of the transversal hopping t₁, and at a given transversal paring Δ₁, the topological phase survives also when the Kitaev criterion for the single chain (Δ > 0,   |μ| < 2t) is violated. Using a tight-binding analysis for a finite-size system we numerically check the bulk-edge correspondence.     

The effect of composite resonances on Higgs decay into two photons

In scenarios of strongly coupled electroweak symmetry breaking, heavy composite particles of different spin and parity may arise and cause observable effects on signals that appear at loop levels. The recently observed process of Higgs to $\gamma \gamma $ at the LHC is one of such signals. We study the new constraints that are imposed on composite models from $H\rightarrow \gamma \gamma $ , together with the existing constraints from the high precision electroweak tests. We use an effective chiral Lagrangian to describe the effective theory that contains the Standard Model spectrum and the extra composites below the electroweak scale. Considering the effective theory cutoff at $\Lambda = 4\pi v \sim 3\text { TeV}$ , consistency with the $T$ and $S$ parameters and the newly observed $H\rightarrow \gamma \gamma $ can be found for a rather restricted range of masses of vector and axial-vector composites from 1.5 to 1.7 and 1.8 to 1.9 TeV, respectively, and only provided a non-standard kinetic mixing between the $W^{3}$ and $B^{0}$ fields is included.     

A Strategy to Locate Fixed Points and Global Perturbations of ODE’s: Mixing Topology with Metric Conditions

In this paper we discuss a topological treatment for the planar system 0.1 $$\begin{aligned} z'=f(t,z)+g(t,z) \end{aligned}$$ where $f:\mathbb {R}\times \mathbb {R}^{2}\longrightarrow \mathbb {R}^{2}$ and $g:\mathbb {R}\times \mathbb {R}^{2}\longrightarrow \mathbb {R}^{2}$ are $T$ -periodic in time and $g(t,z)$ is bounded. Namely, we study the effect of $g(t,z)$ in two different frameworks: isochronous centers and time periodic systems having subharmonics. The main tool employed in the proofs consists of a topological strategy to locate fixed points in the class of orientation preserving embedding under the condition of some recurrence properties. Generally speaking, our topological result can be considered as an extension of the main result in Brown (Pac J Math 143:37–41, 1990) (concerning two cycles) to any recurrent point.     

β-Fe2O3 nanomaterials from an iron(II) diketonate-diamine complex: a study from molecular precursor to growth process

Iron oxide is a key multi-functional material in many different fields of modern technology. The β-Fe(2)O(3) cubic phase, one of the least studied Fe-O systems, was obtained by Chemical Vapor Deposition (CVD) using for the first time a Fe(II) β-diketonate diamine complex, Fe(hfa)(2)·TMEDA, as the molecular source (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N',N'-tetramethylethylenediamine). The strong visible light absorption of β-Fe(2)O(3) deposits highlights their possible functional application in photocatalytic hydrogen production under solar light. A comprehensive investigation on the Fe(ii) complex, performed by a joint experimental-theoretical approach, explains the molecular origin of its excellent thermal behaviour and reveals why this species is a successful precursor for the CVD of iron oxide nanostructures.     

Experimental and computational investigation of Au25 clusters and CO2: a unique interaction and enhanced electrocatalytic activity

Atomically precise, inherently charged Au(25) clusters are an exciting prospect for promoting catalytically challenging reactions, and we have studied the interaction between CO(2) and Au(25). Experimental results indicate a reversible Au(25)-CO(2) interaction that produced spectroscopic and electrochemical changes similar to those seen with cluster oxidation. Density functional theory (DFT) modeling indicates these changes stem from a CO(2)-induced redistribution of charge within the cluster. Identification of this spontaneous coupling led to the application of Au(25) as a catalyst for the electrochemical reduction of CO(2) in aqueous media. Au(25) promoted the CO(2) → CO reaction within 90 mV of the formal potential (thermodynamic limit), representing an approximate 200-300 mV improvement over larger Au nanoparticles and bulk Au. Peak CO(2) conversion occurred at -1 V (vs RHE) with approximately 100% efficiency and a rate 7-700 times higher than that for larger Au catalysts and 10-100 times higher than those for current state-of-the-art processes.