Synthesis of glycolurils and hydantoins by reaction of urea and 1, 2-dicarbonyl compounds using etidronic acid as a “green catalyst”

Most of the known methods for the synthesis of heterocyclic compounds have disadvantages, such as a long reaction time and aggressive conditions. We have developed a new, rather simple and efficient method for the synthesis of a number of glycoluryls and hydantoins in water using a etidronic acid (HEDP) as “Green catalyst.” So, for the first time, the condensation reaction of ureas with 1, 2-dicarbonyl compounds was carried out in the presence of HEDP. Also based on NMR studies, a chemism of these reactions, which is stepwise, is proposed. It has been established that the optimal conditions for the synthesis of glycoluryls and hydantoins using HEDP are: temperature 80°C-90°C, 40-20 minutes, and the ratio of urea and HEDP is 1:1. In all cases, the remaining aqueous filtrate containing HEDP after the reaction can be reused for other cycles synthesis of glycoluril and other compounds, because HEDP is not converted during the reaction.     

The effective local potential method: implementation for molecules and relation to approximate optimized effective potential techniques

We have recently formulated a new approach, named the effective local potential (ELP) method, for calculating local exchange-correlation potentials for orbital-dependent functionals based on minimizing the variance of the difference between a given nonlocal potential and its desired local counterpart [V. N. Staroverov et al., J. Chem. Phys. 125, 081104 (2006)]. Here we show that under a mildly simplifying assumption of frozen molecular orbitals, the equation defining the ELP has a unique analytic solution which is identical with the expression arising in the localized Hartree-Fock (LHF) and common energy denominator approximations (CEDA) to the optimized effective potential. The ELP procedure differs from the CEDA and LHF in that it yields the target potential as an expansion in auxiliary basis functions. We report extensive calculations of atomic and molecular properties using the frozen-orbital ELP method and its iterative generalization to prove that ELP results agree with the corresponding LHF and CEDA values, as they should. Finally, we make the case for extending the iterative frozen-orbital ELP method to full orbital relaxation.     

Self-consistent effective local potentials

An effective local potential (ELP) is a multiplicative operator whose deviation from a given nonlocal potential has the smallest variance evaluated with a prescribed single-determinant wave function. ELPs are useful in density functional theory as alternatives to optimized effective potentials (OEPs) because they do not require special treatment in finite basis set calculations as OEPs do. We generalize the idea of variance-minimizing potentials by introducing the concept of a self-consistent ELP (SCELP), a local potential whose deviation from its nonlocal counterpart has the smallest variance in terms of its own Kohn-Sham orbitals. A semi-analytical method for computing SCELPs is presented. The OEP, ELP, and SCELP techniques are applied to the exact-exchange-only Kohn-Sham problem and are found to produce similar results for many-electron atoms.     

Exact algorithms for the traveling salesman problem with draft limits

This paper deals with the Traveling Salesman Problem (TSP) with Draft Limits (TSPDL), which is a variant of the well-known TSP in the context of maritime transportation. In this recently proposed problem, draft limits are imposed due to restrictions on the port infrastructures. Exact algorithms based on three mathematical formulations are proposed and their performance compared through extensive computational experiments. Optimal solutions are reported for open instances of benchmark problems available in the literature.     

Redox‐Switchable Supramolecular Graft Polymer Formation via Ferrocene–Cyclodextrin Assembly

The redox switchable formation of very well‐defined supramolecular graft polymers in aqueous solution driven by host–guest interactions between ferrocene (Fc) and cyclodextrin (CD) is presented. The Fc‐containing acrylic backbone copolymer (PDMA‐stat‐Fc) is prepared via reversible addition–fragmentation chain transfer (RAFT) copolymerization of N,N‐dimethyl­acrylamide (DMA) and the novel monomer N‐(ferrocenoylmethyl)acrylamide (NFMA). Via the RAFT process, copolymers containing variable Fc ratios (5‐10 mol%) are prepared, affording polymers of molecular masses of close to 11 000 g mol⁻¹ and molar mass dispersities (Đ) of 1.2. The β‐cyclodextrin (β‐CD) containing building block is synthesized via RAFT‐polymerization, too, in order to afford a polymer with well‐defined molecular mass and low dispersity ( = 10 300 g mol⁻¹, Đ = 1.1), employing a propargyl‐functionalized chain transfer agent for the polymerization of N,N‐diethylacrylamide (DEA). The polymerization product is subsequently terminated with β‐CD via the regiospecific copper (I)‐catalyzed 1,3‐cycloaddition (PDEA‐βCD). Host–guest interactions between Fc and CD lead to the formation of supramolecular graft‐polymers, verified via nuclear Overhauser enhancement spectroscopy (NOESY). Importantly, their redox‐responsive character is clearly confirmed via cyclic voltammetry (CV). The self‐assembly of the statistical Fc‐containing lateral polymer chain in aqueous solution leads to mono‐ and multi‐core micelle‐aggregates evidenced via TEM. Only diffused cloud‐like, non‐spherical nanostructures are observed after addition of PDEA‐βCD (TEM).

     

Transport properties of aqueous solutions of calcium lactate in the absence and presence of β-cyclodextrin

Mutual diffusion coefficients and electrical conductivity of a well-known food additive and supplement, or excipient in pharmaceutical formulations, calcium lactate, have been measured in the absence and presence of β-cyclodextrin in aqueous solutions, at 298.15 K. The dependence of conductivity on concentration has been analysed using the Fuoss-Edelson method. The values of the Nernst diffusion coefficients, for binary solutions, derived from conductance and from diffusion experiments are in good agreement. The presence of β-cyclodextrin leads to a non-expected effect on the transport properties of the aqueous solutions of calcium lactate. These data have been justified with help of ¹H NMR spectroscopy. The effect on the water structure, reducing the hydration shell of lactate, is argued. This leads to an increase of the effective concentration of calcium lactate in solution contributing to an increase in the diffusion coefficients and a decrease in the dependence of the electrical conductance on the concentration.     

High spin metastable state relaxation of spin-crossover solids driven by white noise

The mean first passage time (MFPT) as dwell time in high spin metastable state of spin-crossover solids is investigated both analytically and numerically. Calculations showed that the MFPT decreases with the increases of a distance from metastable state. The probability density function has also been examined.     

Intense red upconversion fluorescence emission in NIR-excited erbium-ytterbium doped laponite-derived phosphor

In this report the optical properties and energy-transfer frequency upconversion luminescence of Er³⁺/Yb³⁺-codoped laponite-derived powders under 975 nm infrared excitation is investigated. The 75%(laponite):25%(PbF₂) samples doped with erbium and ytterbium ions, generated high intensity red emission around 660 nm and lower intensity green emission around 525, and 545 nm. The observed emission signals were examined as a function of the excitation power and annealing temperature. The results indicate that energy-transfer, and excited-state absorption are the major upconversion excitation mechanism for the erbium excited-state red emitting level. The precursor glass samples were also heat treated at annealing temperatures of 300 °C, 400 °C, 500 °C, and 600 °C, for a 2 h period. The dependence of the visible upconversion luminescence emission upon the annealing temperature indicated the existence of an optimum temperature which leads to the generation of the most intense and spectrally pure red emission signal.     

Pre-inflationary homogenization of scalar field cosmologies

We consider the evolution of covariant and gauge invariant linear density perturbations of scalar field cosmologies using a dynamical systems? approach. We find conditions for which the perturbations decay in time, so that the spacetime approaches a homogeneous solution which inflates, for quadratic and exponential potentials. This pre-inflationary homogenization is found to be stable in the potentials? parameter spaces. Furthermore, in each case, we determine the minimum size of the resultant homogeneous patch and show that, for quadratic potentials, the resulting inflationary solutions include those with the necessary number of e-folds.