Theory of the two step enantiomeric purification of 1,3 dimethylallene

An application of a recently proposed [P. Kral et al., Phys. Rev. Lett. 90, 033001 (2003)] two step optical control scenario to the purification of a racemic mixture of 1,3 dimethylallene is presented. Both steps combine adiabatic and diabatic passage phenomena. In the first step, three laser pulses of mutually perpendicular linear polarizations, applied in a "cyclic adiabatic passage" scheme, are shown to be able to distinguish between the L and D enantiomers due to their difference in matter-radiation phase. In the second step, which immediately follows the first, a sequence of pulses is used to convert one enantiomer to its mirror-imaged form. This scenario, which only negligibly populates the first excited electronic state, proves extremely useful for systems such as dimethylallene, which can suffer losses from dissociation and internal conversion upon electronic excitation. We computationally observe conversion of a racemic mixture of dimethylallene to a sample containing approximately 95% of the enantiomer of choice.     

Comparison of uranyl extraction mechanisms in an ionic liquid by use of malonamide or malonamide-functionalized ionic liquid

The extraction of uranyl from acidic (HNO(3)) aqueous solutions toward an ionic liquid phase, C(1)-C(4)-imTf(2)N (1-methyl,3-butylimidazolium Tf(2)N), has been investigated as a function of initial acid concentration and ligand concentration for two different extracting moieties: a classical malonamide, N,N'-dimethyl-N,N'-dibutylmalonamide (DMDBMA) and a functionalized IL composed of the Tf(2)N(-) anion and an imidazolium cation on which a malonamide pattern has been grafted (FIL-MA). The extraction mechanism, as demonstrated through the influence of added C(1)-C(4)-imCl or added LiTf(2)N in the aqueous phase, is slightly different between the DMDBMA and FIL-MA extracting agents. Modeling of the extraction data evidences a double extraction mechanism, with cation exchange of UO(2)(2+)versus 2 H(+) for DMDBMA or versus C(1)-C(4) -im(+) and H(+) for FIL-MA at low acidic values, and through anion exchange of [UO(2)(NO(3))(3)](-)versus Tf(2)N(-) for both ligands at high HNO(3) concentrations. The FIL-MA molecule is more efficient than its classical DMDBMA parent.     

Band gaps and structural properties of graphene halides and their derivates: a hybrid functional study with localized orbital basis sets

Density functional theory calculations of the electronic structure of graphane and stoichiometrically halogenated graphene derivatives (fluorographene and other analogous graphene halides) show: (i) localized orbital basis sets can be successfully and effectively used for such two-dimensional materials; (ii) several functionals predict that the band gap of graphane is greater than that of fluorographene, whereas HSE06 gives the opposite trend; (iii) HSE06 functional predicts quite good values of band gaps with respect to benchmark theoretical and experimental data; (iv) the zero band gap of graphene is opened by hydrogenation and halogenation and strongly depends on the chemical composition of mixed graphene halides; (v) the stability of graphene halides decreases sharply with increasing size of the halogen atom--fluorographene is stable, whereas graphene iodide spontaneously decomposes. In terms of band gap and stability, the C(2)FBr and C(2)HBr derivatives seem to be promising materials, e.g., for (opto)electronics applications, because their band gaps are similar to those of conventional semiconductors, and they are expected to be stable under ambient conditions. The results indicate that other fluorinated compounds (C(a)H(b)F(c) and C(a)F(b)Y(c), Y = Cl, Br, I) are stable insulators.     

Iterative operations on microdroplets and continuous monitoring of processes within them; determination of solubility diagrams of proteins

We demonstrate a technique for controlling the content of multiple microdroplets in time. We use this system to rapidly and quantiatively determine the solubility diagrams of two model proteins (lysozyme and ribonuclease A).     

Time-dependent partitioning theory of the control of radiationless transitions in 24-mode pyrazine

We consider the control of internal conversion between the S(2)((1)B(2u)) excited electronic state of pyrazine and the S(1)((1)B(3u)) state. The study is performed both during and after the femtosecond excitation of the ground electronic state S(0)((1)A(g)) to form the S(2) state. The dynamics is examined using the newly developed "effective modes" technique which enables the full computation of quantum dynamics in multi-dimensional spaces. Using this technique, we also investigate the coherent control of population transfer from S(0) to the S(2) and S(1) electronic states. We find that the use of shaped laser pulses enables a significant delay of the internal conversion. For example, after 60 fs, the S(2) population amounts to ～60% of the initial S(0) population, and remains at ～20% after 100 fs, in contrast to the S(0) electronic state which is completely depopulated within 75 fs.     

A comparison of two-component and four-component approaches for calculations of spin-spin coupling constants and NMR shielding constants of transition metal cyanides

Relativistic density functional theory (DFT) calculations of nuclear spin-spin coupling constants and shielding constants have been performed for selected transition metal (11th and 12th group of periodic table) and thallium cyanides. The calculations have been carried out using zeroth-order regular approximation (ZORA) Hamiltonian and four-component Dirac-Kohn-Sham (DKS) theory with different nonrelativistic exchange-correlation functionals. Two recent approaches for representing the magnetic balance (MB) between the large and small components of four-component spinors, namely, mDKS-RMB and sMB, have been employed for shielding tensor calculations and their results have been compared. Relativistic effects have also been analysed in terms of scalar and spin-orbit contributions at the two-component level of theory, including discussion of heavy-atom-on-light-atom effects for (1)J(CN), σ(C), and σ(N). The results for molecules containing metals from 4th row of periodic table show that relativistic effects for them are small (especially for spin-spin coupling constants). The biggest effects are observed for the 6th row where nonrelativistic theory reproduces only about 50%-70% of the two-component ZORA results for (1)J(MeC) and about 75% for heavy metal shielding constants. It is important to employ a full Dirac picture for calculations of heavy metal shielding constants, since ZORA reproduces only 75%-90% of the DKS results. Smaller discrepancies between ZORA-DFT and DKS are observed for nuclear spin-spin coupling constants. No significant differences are observed between the results obtained using mDKS-RMB and sMB approaches for magnetic balance in four-component calculations of the shielding constants.     

The Simple Synthesis of Chiral Polyazaoxacoronands Derived from α-Amino Acids

Abstract

Bisamidation of oxaloyl chloride using L-amino acid methyl ester hydrochlorides afforded chiral diesters. The following reactions of diesters with 2,2-(ethylene-dioxy)diethylamine, afforded tetramides possessing C₂ symmetry. Coupling of N-hydroxysuccinimide ester of N-benzyloxycarbonyl-L-alanine with 1,5-diamino-3-oxapentane, followed by cleavage of protecting groups, afforded an optically active diamine, which was transformed consequently into tetramide via the reaction with diglycolic acid dimethyl ester under high pressure conditions.     

Interfacial reciprocal grafting by free radical reactions in polymer blends

Recent developments in the field of reactive compatibilization of polymer blends prepared by melt processing focus on the addition of low molecular weight compounds. This work deals with in situ compatibilization through the formation of graft or crosslinked copolymers at the interface. Mixtures of semicrystalline hydrocarbon polymers have been subjected to free radical reactivity, in a co-rotating twin screw extruder (ZSK 30) in a single step. The particular system, high density polyethylene and polyamide 6, was blended in the presence of a peroxide and a reactive bifunctional monomer, maleic anhydride. Because of a combined effect, the reaction appears to occur mainly at the interface, where the resulting grafted copolymer acts as an anchor for the final stabilization of the biphasic system. Different analytical techniques, such as differential scanning calorimetry, scanning electron microscopy and tensile testing, helped in characterizing the resulting blends and confirmed the high level of interfacial grafting and the expected improvement in mechanical properties.     

Formation of ti(28) ln cages, the highest nuclearity polyoxotitanates (ln=la, ce)

The solvothermal reactions of Ti(OEt)(4) with LnCl(3) (Ln=La, Ce) produced new Ti(28) Ln cages, in which the Ln(3+) ions are coordinated within a metallocrown arrangement, which represents the highest nuclearity cages of this type.     

Enantioselective Reformatsky reaction of ethyl iododifluoroacetate with ketones

Two approaches have been developed for the enantioselective Reformatsky reaction of ethyl iododifluoroacetate with ketones to form a quaternary carbon centre using (1R,2S)-1-phenyl-2-(1-pyrrolidinyl)-1-propanol as the chiral ligand. Good yields and high enantioselectivities (80-91% ee) were achieved with a range of alkyl aryl ketones in a convenient one-pot protocol using ethyl iododifluoroacetate and diethylzinc to form the difluorinated Reformatsky reagent homogeneously. In the traditional two-step Reformatsky reaction using the preformed Reformatsky reagent generated from ethyl iododifluoroacetate and zinc dust, good yields and good enantioselectivities (75-84% ee) were also obtained.