Evolution of the Pt layer deposited on MgO(001) by pulsed laser deposition as a function of the deposition parameters: a scanning tunneling microscopy and energy dispersive X-ray diffractometry/reflectometry study

A combined ultrahigh vacuum scanning tunneling microscopy (STM-UHV) and energy dispersive X-ray diffractometry/reflectometry (EDXD/EDXR) study of the evolution of face-centered cubic (fcc) Pt layer growth on MgO(100) by pulsed laser deposition as a function of the process parameters such as deposition temperature and deposition duration has been carried out. The aim of this study is to define the best experimental conditions to obtain a controlled film deposition selective on the Pt growth direction (either [111] or [002]). The evolution of the Pt surface morphology as a function of the deposition temperature (T(dep)) from 300 to 700 degrees C has been studied with STM and ED techniques. Results show that the Pt surface, characterized at T(dep) = 300 degrees C by a 3D island morphology, evolves at higher temperatures to a morphology in which the original islands coexist with a distribution of orthogonal 2D stripes. The two features can be associated with the [111] and [002] Pt growth directions of the fcc phase, respectively. For T(dep) = 700 degrees C, the island morphology of the (111) face completely disappears, while the merging process of the (002) stripes reaches completion. The evolution of the morphology at T(dep) = 600 degrees C as a function of the deposition time and thickness has then been studied with STM-UHV, revealing an initial growth of mosaic-like 3D islands. These independent islands, already interconnected, expand along two orthogonal directions and, for longer deposition times, lead to the texture of orthogonal stripes. The EDXR characterization providing the morphological parameters of the films, i.e., thickness and roughness, confirms the above observation and quantifies the effect of such morphological changes on the surface roughness of the Pt film, an important parameter for applications of Pt films as underlayer in magnetic recording media.     

Cyclic Hilbert Spaces and Connes’ Embedding Problem

Let M be a II ₁-factor with trace τ, the finite dimensional subspaces of L ²(M, τ) are not just common Hilbert spaces, but they have an additional structure. We introduce the notion of a cyclic linear space by taking these additional properties as axioms. In Sect. 3 we formulate the following problem: “does every cyclic Hilbert space embed into L ²(M, τ), for some M?”. An affirmative answer would imply the existence of an algorithm to check Connes’ embedding Conjecture. In Sect. 4 we make a first step towards the answer of the previous question.     

Morse–Smale Regression

This article introduces a novel partition-based regression approach that incorporates topological information. Partition-based regression typically introduces a quality-of-fit-driven decomposition of the domain. The emphasis in this work is on a topologically meaningful segmentation. Thus, the proposed regression approach is based on a segmentation induced by a discrete approximation of the Morse–Smale complex. This yields a segmentation with partitions corresponding to regions of the function with a single minimum and maximum that are often well approximated by a linear model. This approach yields regression models that are amenable to interpretation and have good predictive capacity. Typically, regression estimates are quantified by their geometrical accuracy. For the proposed regression, an important aspect is the quality of the segmentation itself. Thus, this article introduces a new criterion that measures the topological accuracy of the estimate. The topological accuracy provides a complementary measure to the classical geometrical error measures and is very sensitive to overfitting. The Morse–Smale regression is compared to state-of-the-art approaches in terms of geometry and topology and yields comparable or improved fits in many cases. Finally, a detailed study on climate-simulation data demonstrates the application of the Morse–Smale regression. Supplementary Materials are available online and contain an implementation of the proposed approach in the R package msr, an analysis and simulations on the stability of the Morse–Smale complex approximation, and additional tables for the climate-simulation study.     

Multi-level Dynamical Systems: Connecting the Ruelle Response Theory and the Mori-Zwanzig Approach

We consider the problem of deriving approximate autonomous dynamics for a number of variables of a dynamical system, which are weakly coupled to the remaining variables. In a previous paper we have used the Ruelle response theory on such a weakly coupled system to construct a surrogate dynamics, such that the expectation value of any observable agrees, up to second order in the coupling strength, to its expectation evaluated on the full dynamics. We show here that such surrogate dynamics agree up to second order to an expansion of the Mori-Zwanzig projected dynamics. This implies that the parametrizations of unresolved processes suited for prediction and for the representation of long term statistical properties are closely related, if one takes into account, in addition to the widely adopted stochastic forcing, the often neglected memory effects.     

Synthesis of potential HIV integrase inhibitors inspired by natural polyphenol structures

Drawing inspiration from the structural features of some natural polyphenols, the synthesis of two different model compounds as potential inhibitors of HIV integrase (IN) has been described. The former was characterised by a diketo acid (DKA) bioisostere, such as a β-hydroxycarbonyl moiety, between two fragments containing aromatic groups, while in the latter an epoxide linked two polyoxygenated aromatic residues. The moieties present in the structures are thought to function by chelating divalent metal ions on the enzyme catalytic site. Overall, 10 compounds were prepared and some of that submitted to molecular modelling studies (to investigate their interactions with the active site of IN), to metal titration studies (to detect their chelating capability) and to biological assays.     

X-Ray crystal structure determination of a series of 1-aryl- 2-[3-(3-[2-aryl-1-diazenyl]-1,3-diazepan-1-ylmethyl)-1, 3-diazepan-1-yl]-1-diazenes obtained from the reaction of diazonium salts with mixtures of formaldehyde and 1,4-diaminobutane

A new series of bis-triazenes, the 1-aryl-2-[3-(3-[2-aryl-1-diazenyl]-1,3-diazepan-1-ylmethyl)-1,3-diazepan-1-yl]-1-diazenes has been synthesized from the reaction of diazonium salts with a mixture of 1,4-diaminobutane and formaldehyde. The structures of 1-(p-bromophenyl)-2-[3-{3-[2-(p-bromophenyl)-1-diazenyl]-1,3-diazepan-1-ylmethyl}-1,3-diazepan-1-yl]-1-diazene(1), 1-(p-cyanophenyl)-2-[3-{3-[2-(p-cyanophenyl)-1-diazenyl]-1,3-di azepan-1-ylmethyl}-1,3-diazepan-1-yl]-1-diazene(2), and 1-(p-methoxyphenyl)-2-[3-{3-[2-(p-methoxy-phenyl)-1-diazenyl]-1,3-diazepan-1-ylmethyl}-1,3-diazepan-1-yl]-1 diazene(3) have been unequivocally determined by X-ray crystallography. The new bis-triazenes are important since the structure contains the novel saturated heterocycle, 1,3-diazepane. The general conclusion of this study is that alkanediamines with 3 or 4 carbon atoms in the spacer link between the nitrogen atoms give rise to the linear bicyclic molecules of type 5, in contrast to the case of ethylenediamine (spacer link 2 carbon atoms), which affords molecules of type 6, which exemplify the general cage structure of type 4. The crystal structures of 1, 2 and 3 are compared with the previously reported structure of the hexahydropyrimidine analogue 8a(X=CN); compounds 2 and 8a(X=CN) are homologous with respect to the alkane spacer moiety. The structures of 2 and 8a(X=CN) are very different in one respect; in 2 the aryldiazenyl-1,3-diazepanyl groups are in the s-trans orientation around the central methylene group whereas in 8a(X=CN) the arrangement of the aryldiazenyl-hexahydropyrimidinyl groups is the s-cis orientation.Crystal data: 1 C₂₃H₃₀N₈Br₂, triclinic, space group P-1, a=8.3979(2), b=10.7828(3), c=14.4692(5) ?, α=83.670(1), β=78.662(1), γ=78.758(1)°, V=1256.48(6) ?³, for Z=2. 2 C₂₅H₃₀N₁₀, monoclinic, space group P2 ₁ /n, a=13.4046(6), b=9.4482(4), c=10.6913(4)?, β=103.239(2)°, V=2490.5(2) ?³, for Z=4. 3 C₂₅H₃₆N₈O₂, triclinic, space group P-1, a=8.5223(3), b=10.6913(4), c=14.4034(7)?, α=85.657(2), β=78.731(2), γ=80.153(1)°, V=1266.88(9) ?³, for Z=2.     

Methyl 4-((E)-2-{3-[(3-{ (E)-2-[4-(methoxycarbonyl)phenyl]- 1-diazenyl}-5,5-dimethylhexahydro-1-pyrimidinyl)methyl]-5,5-dimethylhexahydro-1-pyrimidinyl-1-diazenyl) benzoate. X-ray crystal structure

Methyl 4-((E)-2-{3-[(3-{(E)-2-[4-(methoxycarbonyl)phenyl]-1-diazenyl}-5, 5-dimethyl hexahydro-1-pyrimidinyl)methyl]-5, 5- dimethylhexahydro-1- pyrimidinyl}-1- diazenyl) benzoate (1) has been synthesized by reaction of a mixture of formaldehyde and 2,2-dimethyl-1,3-propanediamine with p-methoxycarbonylbenzenediazonium chloride. The crystal structure of 1 has been determined by single crystal X-ray diffraction analysis. The crystals of 1 displayed problems of disorder; the asymmetric unit is built up by two independent molecules, which display disorder within a methoxycarbonyl group. The two independent molecules in the asymmetric unit are very similar, differing only slightly about the mutual orientation of the aryltriazenyl groups. With respect to the N–C–N bridge between the hexahydropyrimidinyl rings, the two equivalent fragments containing the triazene moieties are in a cis orientation. The N–N single bonds, in the range 1.319(4)–1.348(4) Å, and the N=N double bonds, in the range 1.255(5)–1.275(4) Å, indicate significant conjugations within the triazene moieties. All the hexahydropyrimidine six-membered rings adopt a chair conformation as shown by their puckering parameters. The crystal packing is determined only by simple van der Waals interactions. The crystal structure of 1 is compared with the previously reported structure of the unbranched hexahydropyrimidine analogue 2. Crystal data: 1 C29H40N8O4, triclinic, space group P-1, a = 13.9652(2), b = 14.2908(3), c = 16.6129(4) Å, = 97.279(1), = 90.872(1), = 107.385(1), V = 3133.6(1) ų, for Z = 4.     

A novel [Cu II 4] cluster from the assembly of two [Cu II 2L]+ units by a central mu4-1,1,2,2 perchlorate ligand

A perchlorate ligand in the rare mu4-1,1,2,2 binding mode is seen for the first time as the sole support for the assembly of two cationic [Cu II 2L]+ fragments (H3L = a dinucleating ligand) in the formation of a magnetically-exchanged tetranuclear cluster.     

Sequential one-pot glycosidations catalytically promoted: unprecedented strategy in oligosaccharide synthesis for the straightforward assemblage of the antitumor PI-88 pentasaccharide

The pentasaccharide sequence of the most active components of the antitumor drug PI-88, currently in phase II clinical trial, has been rapidly assembled in high overall yield and in only three steps starting from three monosaccharide building blocks. The procedure takes advantage of the first reported strategy of sequential one-pot glycosidations conducted exclusively under catalytic activation. In addition, the procedure relies only on shelf-stable and mild promoters such as Yb(OTf)(3) and Bi(OTf)(3).