Reactivity of β-aluminas with water

The reactivity with air moisture of finely divided crystals of Na β and Li⁺-containing β-aluminas is analyzed with thermogravimetric and X-ray techniques. For Na β-alumina two distinct water intake processes are evident: 1) a fast one, controlled by the elastic interactions among water molecules near the crystal boundaries; 2) a slow one, driven by water diffusion away from the boundaries. For finely divided crystals of Li β-alumina the two processes cannot be distinguished but the slow one is observable in crystals of macroscopic dimensions. The water intake is generally accompanied by an expansion of the c-axis. However, the relationship between water content and c-parameter is highly non-linear and the c-axis length at room temperature depends upon the thermal history of the sample. Our results confirm previous reports suggesting that β-aluminas absorb about one water molecule per cation of the conducting plane.     

Smooth and discontinuous junctions in the p-system

Consider the p-system describing the subsonic flow of a fluid in a pipe with section a=a(x). We prove that the resulting Cauchy problem generates a Lipschitz semigroup, provided the total variation of the initial datum and the oscillation of a are small. An explicit estimate on the bound of the total variation of a is provided, showing that at lower fluid speeds, higher total variations of a are acceptable. An example shows that the bound on TV(a) is mandatory, for otherwise the total variation of the solution may grow arbitrarily.     

Arithmetical Rank of Squarefree Monomial Ideals Generated by Five Elements or with Arithmetic Degree Four

Let I be a squarefree monomial ideal of a polynomial ring S. In this article, we prove that the arithmetical rank of I is equal to the projective dimension of S/I when one of the following conditions is satisfied: (1) μ(I) ≤5; (2) arithdeg I ≤ 4.     

Oxygen‐Triggered Switchable Polymerization for the One‐Pot Synthesis of CO2‐Based Block Copolymers from Monomer Mixtures

Switchable polymerization provides the opportunity to regulate polymer sequence and structure in a one‐pot process from mixtures of monomers. Herein we report the use of O₂ as an external stimulus to switch the polymerization mechanism from the radical polymerization of vinyl monomers mediated by (Salen)Co^III?R [Salen=N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine; R=alkyl] to the ring‐opening copolymerization (ROCOP) of CO₂/epoxides. Critical to this process is unprecedented monooxygen insertion into the Co?C bond, as rationalized by DFT calculations, leading to the formation of (Salen)Co^III?O?R as an active species to initiate ROCOP. Diblock poly(vinyl acetate)‐b‐polycarbonate could be obtained by ROCOP of CO₂/epoxides with preactivation of (Salen)Co end‐capped poly(vinyl acetate). Furthermore, a poly(vinyl acetate)‐b‐poly(methyl acrylate)‐b‐polycarbonate triblock copolymer was successfully synthesized by a (Salen)cobalt‐mediated sequential polymerization with an O₂‐triggered switch in a one‐pot process.     

Optical saturation driven by exciton confinement in molecular chains: a time-dependent density-functional theory approach

We identify excitonic confinement in one-dimensional molecular chains (i.e., polyacetylene and H2) as the main driving force for the saturation of the chain polarizability as a function of the number of molecular units. This conclusion is based on first principles time-dependent density-functional theory calculations using a recently developed exchange-correlation kernel that accounts for excitonic effects. The failure of simple local and semilocal functionals is shown to be linked to the lack of memory effects, spatial ultranonlocality, and self-interaction corrections. These effects get smaller as the gap reduces, in which case such simple approximations do perform better.     

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.     

A domino approach to pyrazino- indoles and pyrroles using vinyl selenones

Herein we disclose an efficient and flexible approach to biologically relevant 3,4-dihydropyrazino[1,2-a]indol-1(2H)ones and 3,4-dihydropyrrolo[1,2-a]pyrazin-1(2H)ones through a domino Michael/intramolecular nucleophilic substitution pathway using potassium hydroxide in dichloromethane. Variously substituted vinyl selenones and 1H-indole-2-carboxamides or 1H-pyrrole-2-carboxamides have been employed with success in chemo and regio-selective processes. The introduction of an amino acid portion on the amidic function is well tolerated without racemization.     

Some properties of third order differential operators

Consider the third order differential operator L given by and the related linear differential equation L(x)(t) + x(t) = 0. We study the relations between L, its adjoint operator, the canonical representation of L, the operator obtained by a cyclic permutation of coefficients a _i , i = 1,2,3, in L and the relations between the corresponding equations.We give the commutative diagrams for such equations and show some applications (oscillation, property A).     

Effect of the nature of the metal atom on hydrogen bonding and proton transfer to [Cp*MH3(dppe)]: tungsten versus molybdenum

The hydrogen-bonding and proton-transfer pathway to complex [Cp*W(dppe)H(3)] (Cp*=eta(5)-C(5)Me(5); dppe=Ph(2)PCH(2)CH(2)PPh(2)) was investigated experimentally by IR, NMR, UV/Vis spectroscopy in the presence of fluorinated alcohols, p-nitrophenol, and HBF(4), and by using DFT calculations for the [CpW(dhpe)H(3)] model (Cp=eta(5)-C(5)H(5); dhpe=H(2)PCH(2)CH(2)PH(2)) and for the real system. A study of the interaction with weak acids (CH(2)FCH(2)OH, CF(3)CH(2)OH, (CF(3))(2)CHOH) allowed the determination of the basicity factor, E(j)=1.73+/-0.01, making this compound the most basic hydride complex reported to date. A computational investigation revealed several minima for the [CpW(dhpe)H(3)] adducts with CF(3)CH(2)OH, (CF(3))(2)CHOH, and 2(CF(3))(2)CHOH and confirms that these interactions are stronger than those established by the Mo analogue. Their geometries and relative energies are closely related to those of the homologous Mo systems, with the most stable adducts corresponding to H bonding with M-H sites, however, the geometric and electronic parameters reveal that the metal center plays a greater role in the tungsten systems. Proton-transfer equilibria are observed with the weaker proton donors, the proton-transfer step for the system [Cp*W(dppe)H(3)]/HOCH(CF(3))(2) in toluene having DeltaH=(-3.9+/-0.3) kcal mol(-1) and DeltaS=(-17+/-2) cal mol(-1) K(-1). The thermodynamic stability of the proton-transfer product is greater for W than for Mo. Contrary to the Mo system, the protonation of the [Cp*W(dppe)H(3)] appears to involve a direct proton transfer to the metal center without a nonclassical intermediate, although assistance is provided by a hydride ligand in the transition state.