Synthesis, structures and ε-caprolactone polymerization activity of aluminum N,N′-dimethyloxalamidates

Alkyl aluminum N,N′-dimethyloxalamidates R₄Al₂(dmoa) (1, R = Me; 2, R = Et; 3, R = ⁱBu; 4, R = ^tBu) (dmoa-H₂ = N,N′-dimethyloxalamide) have been prepared and characterized. Molecular structures of the compounds 1 and 4 have been determined by X-ray crystallography. The centrosymmetric molecules of the compounds consist of one N,N′-dimethyloxalamidate unit bonded to two four-coordinated aluminum atoms. Each of the aluminum atoms is bonded to two alkyl groups, and oxygen and nitrogen atoms originating from two different amidate groups. A skeleton framework of the molecules of 1 and 4 consists of two fused AlNOC₂ heterocyclic rings, which are flat and positioned in one plane. It was shown that compounds 1-3 were initiators in a process of ring opening polymerization (ROP) of ε-caprolactone. The compound 4 exhibited low activity in ROP.     

Electrical energy required to form large conducting pores

This study computes the contribution of the externally induced transmembrane potential to the energy of large, highly conductive pores. This work was undertaken because the pore energy formulas existing in the literature predict qualitatively different behavior of large pores: the original formula proposed by Abidor et al. in 1979 implies that the electrical force expanding the pore increases linearly with pore radius, while later extensions of this formula imply that this force decreases to zero for large pores. Starting from the Maxwell stress tensors, our study derives the formula for the mechanical work required to deform a dielectric body in an ionic solution with steady-state electric current. This formula is related to a boundary value problem (BVP) governing electric potentials and fields in a proximity of a pore. Computer simulations yield estimates of the electrical energy for pores of two different shapes: cylindrical and toroidal. In both cases, the energy increases linearly for pore radii above approximately 20 nm, implying that the electrical force expanding the pore asymptotes to a constant value for large pores. This result is different from either of the two energy formulas mentioned above. Our study traces the source of this disagreement to approximations made by previous studies, which are suitable only for small pores. Therefore, this study provides a better understanding of the energy of large pores, which is needed for designing pulsing protocols for DNA delivery.     

How natural materials remove heavy metals from water: mechanistic insights from molecular dynamics simulations

Water pollution by heavy metals is of increasing concern due to its devastating effects on the environment and on human health. For the removal of heavy metals from water sources, natural materials, such as spent-coffee-grains or orange/banana/chestnut peels, appear to offer a potential cheap alternative to more sophisticated and costly technologies currently in use. However, in order to employ them effectively, it is necessary to gain a deeper understanding – at the molecular level – of the heavy metals-bioorganic-water system and exploit the power of computer simulations. As a step in this direction, we investigate via atomistic simulations the capture of lead ions from water by hemicellulose – the latter being representative of the polysaccharides that are common components of vegetables and fruit peels − as well as the reverse process. A series of independent molecular dynamics simulations, both classical and ab initio, reveals a coherent scenario which is consistent with what one would expect of an efficient capture, i.e. that it be fast and irreversible: (i) binding of the metal ions via adsorption is found to happen spontaneously on both carboxylate and hydroxide functional groups; (ii) in contrast, metal ion desorption, leading to solvation in water, involves sizable free-energy barriers.

We investigate via atomistic simulations the capture of lead ions from water by hemicellulose – as representative of the polysaccharides that are common components of vegetables and fruit peels – and the reverse process.     

Electron impact-induced decomposition of some substituted 7-ethoxycarbonylpyridopyrrolidenequinolines

The electron impact ionization mass spectrometric behaviour of three cycloadducts of 4,6-benzo[h]naphthyridinum ethoxycarbonylmethylide with acrylonitrile, ethyl acrylate and diethyl maleate was studied with the aid of exact mass measurements and metastable transitions. The study showed that the electron impact-induced decomposition of substituted pyridopyrrolidenequinolines occurs exclusively on the aliphatic five-membered ring.     

Sterically crowded diolates of group 13 metals

The dependence of the structure of complexes of sterically crowded 2,4-dimethylpentane-2,4-diol with group 13 metals trialkyls on the kind of metal, as well as steric bulk of the substituents on the metal atoms is reported. The reaction of ^tBu₃Ga with 2,4-dimethylpentane-2,4-diol leads to the formation of an unstable dimeric product {^tBu₂Ga[(OC(CH₃)₂CH₂C(CH₃)₂OH]}₂ (1) possessing a four-membered Ga₂O₂ core and two unreacted hydroxyl groups. Compound 1 undergoes further intramolecular reaction to yield the unusual (monoalkyl)gallane O,O^′-chelate complex {^tBuGa[OC(CH₃)₂CH₂C(CH₃)₂O]}₂ (2). In contrast to ^tBu₃Ga, ^tBu₃In reacts with 2,4-dimethylpentane-2,4-diol to give the stable dimeric complex ^tBu₄In₂[OC(CH₃)₂CH₂C(CH₃)₂OH]₂ (4) stabilised by two intramolecular O-H?O bonds. At higher temperature compound 4 reacts with an excess of ^tBu₃In to form the trinuclear complex ^tBu₅In₃[OC(CH₃)₂CH₂C(CH₃)₂O]₂ (5). The reactions of 2,4-dimethylpentane-2,4-diol with trialkylmetallane with small alkyl groups, i.e. Me₃Ga and Me₃In allow for the isolation of the trinuclear diolates {Me₅M₃[OC(CH₃)₂CH₂C(CH₃)₂O]₂} [M=Ga (3), M=In (6)]. The crystal structures of 2, 3 and 4 have been determined by single crystal X-ray diffraction. The reactions of tert-butylmetallane diolates with trimethyl metallanes have been studied. The interaction of the allane complex {^tBuAl[OC(CH₃)₂CH₂C(CH₃)₂O]}₂ with Me₃Al results in the formation of the trialuminium mixed-ligand product {Me₃(^tBu)₂Al₃[OC(CH₃)₂CH₂C(CH₃)₂O]₂} (7). Compounds 2 and 4 undergo a total transmetallation reaction in the presence of Me₃M to yield [Me₅M₃(diol-(2H))₂] [M=Al, Ga] products.     

Relativistic corrections in the multiple-scattering method

We show how to introduce the Foldy-Wouthuysen relativistic corrections in the multiple-scattering method, for the determination of the electronic energy levels of molecules. The present derivation begins from a variational expression where the Foldy-Wouthuysen hamiltonian is inserted, instead of the Schrödinger hamiltonian. The resulting secular equation becomes identical with the standard multiple-scattering secular equation, if one neglects the relativistic correction terms.     

(+)-(S)-α-diethoxyphosphorylvinyl p-tolyl sulfoxide: A new chiral Michael acceptor and dienophile

The tittle reagent, (+)-(S)-1, was prepared from (+)-(S)_s-α-diethoxy-phosphorylethyl p-tolyl sulfoxide 2 by phenylselenylation-deselenylation procedure. Its reactivity was demonstrated by diastereoselective Michael addition of ethanethiol giving rise to 3, tandem Michael addition/intramolecular Horner--Wittig reaction with 2-formyl pyrrole leading to the corresponding pyrrolizine sulfoxide 5 and cycloaddition with cyclopentadiene affording the diastereomeric adducts 6. The steric course of the Diels-Alder reaction is briefly discussed.     

Spectral and thermal studies of Y(III) and heavy lanthanide 4-chlorophthalates

Summary Complexes of heavy lanthanide(III) (Gd-Lu) and Y(III) with 4-chlorophthalic acid were prepared and their IR spectra, solubility in water at 295 K and thermal decomposition were investigated. When heated the complexes with general formula Ln₂[ClC₆H₃(CO₂)₂]₃·nH₂O where n=6 for Tb, Dy(III), n=4 for Gd, Ho and Er(III), n=2 for Tm-Lu(III) and n=3 for Y(III) decompose to the oxides Ln₂O₃, Tb₄O₇ with intermediate formation of oxochlorides LnOCl.