Shift-Type Properties of Commuting,Completely Non Doubly Commuting Pairs of Isometries

Pairs (V, V′) of commuting, completely non doubly commuting isometries are studied. We show, that the space of the minimal unitary extension of V (denoted by U) is a closed linear span of subspaces reducing U to bilateral shifts. Moreover, the restriction of V′ to the maximal subspace reducing V to a unitary operator is a unilateral shift. We also get a new hyperreducing decomposition of a single isometry with respect to its wandering vectors which strongly corresponds with Lebesgue decomposition.     

Simultaneous projectional skeletons

We prove the existence of a simultaneous projectional skeleton for certain subspaces of C(K)$C(K)$ spaces. This generalizes a result on simultaneous projectional resolutions of identity proved by M. Valdivia. We collect some consequences of this result. In particular we give a new characterization of Asplund spaces using the notion of projectional skeleton.     

Experimental Study of Asphaltenes Flocculation Onset in Crude Oils Using the Densitometry Measurement Technique

The asphaltenes flocculation proceeds with changes of oil composition and causes significant losses in petroleum industry operations. The main objective of this work is to evaluate the reliability of the densitometry technique in studying experimentally the mechanism of aggregation and flocculation of asphaltenes occurring in crude oils. As asphaltene flocculation threshold in crude oils or mixture can be achieved by addition of n-heptane, various n-heptane concentrations were added to crude oil, and their effects have been investigated trough density measurements. Thereby, measurements were based on mixture of crude oil + toluene and cyclohexane + n-heptane, respectively. While asphaltene aggregates form clusters and flocculate, the mixture volumetric mass change and the reduced density of non-Newtonian fluids under investigation have been pointed out as one of appropriate measures of flocculation process. In particular, the curve representing the reduced density as function of the ratio between n-heptane concentration and concentration of crude oil under study featured a break point that well characterizes the flocculation threshold. Besides the quantity needed to initiate and to aggregate asphaltenes within crude oils, the amount required to completely achieve deposition of asphaltenes has also been identified. A quantity of 4 and 20 g of n-heptane per gram of crude oil was found necessary.     

Metallomesogens: enaminoketone derivatives of the 3-oxa, 3-thia- and 3-selena-butyric amides

Liquid crystalline Ni(II) and Cu(II) complexes of tetradentate ligands, enaminoketones and 3-oxa; 3-thia- and 3-selena-butyramides were synthesized and examined. The compounds show very low C ₁ symmetry resulting from the chiral donor atoms — oxygen, sulphur and selenium — incorporated in the butyric amide moiety. This chirality can be observed in NMR studies. The complexes exhibit enantiotropic as well as monotropic calamitic SmA and N phases.     

Influence of mesogenic core polarity and position of chains attachment on columnar phase stability

Series of new Ni(II) metalomesogens of triangular molecular shape and forming Col_h liquid crystalline (LC) phase were synthesised and described. Using in the molecular core the barbituric moieties that contain carbonyl or thiocarbonyl groups causes strong polarisation of the molecules and creates a permanent dipole moment μ, which was confirmed by quantum mechanical calculations. The relationship between molecular dipole moment and self-organisation of molecules into the columnar phase was considered. The position of alkyl and alkoxy chains substituted at phenyl ring that affects LC phase formation seems to be connected with planar conformation of the attached chains. These can broaden the mesogenic core and stabilise the Col_h mesophase.     

An Improved Synthesis and NMR Spectra of Benzylated Glycals

Abstract

Benzylated glycals, unlike their acylated congeners which easily undergo allylic rearrangement, are frequently employed as reactive enol ether type substrates in a variety of electrophilic addition reactions.^1–4 Although these compounds are considered to be readily available substrates, reported procedures for their syntheses involve some steps of limited efficiency, chromatographic separations or costly reagents,^5–7 and experimental requirements not amenable for large scale preparations. In view of the recent applications of benzylated glycals to syntheses of O-glycosides,^1,2 C-glycosyl compounds,³ and β-lactams,⁴ we have undertaken a study aimed at efficient one step benzylation procedures applicable to pyranoid 1-enitols as well as to their acylated derivatives. This goal was eventually achieved by employing a catalytic phase transfer alkylation system with     

Probing the Coordination Environment of the Human Copper Chaperone HAH1: Characterization of HgII‐Bridged Homodimeric Species in Solution

Although metal ion homeostasis in cells is often mediated through metallochaperones, there are opportunities for toxic metals to be sequestered through the existing transport apparatus. Proper trafficking of Cu^I in human cells is partially achieved through complexation by HAH1, the human metallochaperone responsible for copper delivery to the Wilson and Menkes ATPase located in the trans‐Golgi apparatus. In addition to binding copper, HAH1 strongly complexes Hg^II, with the X‐ray structure of this complex previously described. It is important to clarify the solution behavior of these systems and, therefore, the binding of Hg^II to HAH1 was probed over the pH range 7.5 to 9.4 using ¹⁹⁹Hg NMR, ^199mHg PAC and UV–visible spectroscopies. The metal‐dependent protein association over this pH range was examined using analytical gel‐filtration. It can be concluded that at pH 7.5, Hg^II is bound to a monomeric HAH1 as a two coordinate, linear complex (HgS₂), like the Hg^II–Atx1 X‐ray structure (PDB ID: 1CC8). At pH 9.4, Hg^II promotes HAH1 association, leading to formation of HgS₃ and HgS₄ complexes, which are in exchange on the μs–ns time scale. Thus, structures that may represent central intermediates in the process of metal ion transfer, as well as their exchange kinetics have been characterized.     

Dehydrogenation Mechanism of Liquid Organic Hydrogen Carriers: Dodecahydro‐N‐ethylcarbazole on Pd(111)

Dodecahydro‐N‐ethylcarbazole (H₁₂‐NEC) has been proposed as a potential liquid organic hydrogen carrier (LOHC) for chemical energy storage, as it combines both favourable physicochemical and thermodynamic properties. The design of optimised dehydrogenation catalysts for LOHC technology requires a detailed understanding of the reaction pathways and the microkinetics. Here, we investigate the dehydrogenation mechanism of H₁₂‐NEC on Pd(111) by using a surface‐science approach under ultrahigh vacuum conditions. By combining infrared reflection–absorption spectroscopy, density functional theory calculations and X‐ray photoelectron spectroscopy, surface intermediates and their stability are identified. We show that H₁₂‐NEC adsorbs molecularly up to 173 K. Above this temperature (223 K), activation of C? H bonds is observed within the five‐membered ring. Rapid dehydrogenation occurs to octahydro‐N‐ethylcarbazole (H₈‐NEC), which is identified as a stable surface intermediate at 223 K. Above 273 K, further dehydrogenation of H₈‐NEC proceeds within the six‐membered rings. Starting from clean Pd(111), C? N bond scission, an undesired side reaction, is observed above 350 K. By complementing surface spectroscopy, we present a temperature‐programmed molecular beam experiment, which permits direct observation of dehydrogenation products in the gas phase during continuous dosing of the LOHC. We identify H₈‐NEC as the main product desorbing from Pd(111). The onset temperature for H₈‐NEC desorption is 330 K, the maximum reaction rate is reached around 550 K. The fact that preferential desorption of H₈‐NEC is observed even above the temperature threshold for H₈‐NEC dehydrogenation on the clean surface is attributed to the presence of surface dehydrogenation and decomposition products during continuous reactant exposure.     

The 2,2′-Coupled Pyrrolidine-Phospholane Ring System: A Highly Enantioselective Synthesis and Kinetic Resolution of the Phosphorus Centre

Abstract

Enantiopure five-membered ring nitrones derived from L-tartaric acid and from L-malic acid undergo highly regio- and stereoselective cycloaddition reactions with an excess of racemic 2,3-dihydro-1-phenyl-1H-phospholes producing two readily separable tricyclic cycloadducts and concomitantly effecting kinetic resolution of the dihydrophosphole derivative (diastereomeric ratio up to 10:l; stereoselectivity factor s = kS/kR = 14). The tricyclic cycloadducts feature 2,2′-connection of pyrrolidine and phospholane rings and five to seven contiguous stereogenic centers of which three are induced and one or two are kinetically resolved during the cycloaddition process.