Doxorubicin Encapsulation in Carbon Nanotubes Having Haeckelite or Stone–Wales Defects as Drug Carriers: A Molecular Dynamics Approach

Doxorubicin (DOX), a recognized anticancer drug, forms stable associations with carbon nanotubes (CNTs). CNTs when properly functionalized have the ability to anchor directly in cancerous tumors where the release of the drug occurs thanks to the tumor slightly acidic pH. Herein, we study the armchair and zigzag CNTs with Stone–Wales (SW) defects to rank their ability to encapsulate DOX by determining the DOX-CNT binding free energies using the MM/PBSA and MM/GBSA methods implemented in AMBER16. We investigate also the chiral CNTs with haeckelite defects. Each haeckelite defect consists of a pair of square and octagonal rings. The armchair and zigzag CNT with SW defects and chiral nanotubes with haeckelite defects predict DOX-CNT interactions that depend on the length of the nanotube, the number of present defects and nitrogen doping. Chiral nanotubes having two haeckelite defects reveal a clear dependence on the nitrogen content with DOX-CNT interaction forces decreasing in the order 0N > 4N > 8N. These results contribute to a further understanding of drug-nanotube interactions and to the design of new drug delivery systems based on CNTs.     

An NMR study of merocyanine-type dyes derived from barbituric acid

The 13C NMR of two solvatochromic dyes derived from a barbituric acid acceptor and dimethylaminophenyl donor fragments, compound 1 and the related merocyanine 2, were recorded in various solvents. The observed chemical-shift variations were used to interpret their structural differences and solvatochromic behavior in solution.     

On the Kadomtsev-Petviashvili Equation and Associated Constraints

The initial-boundary-value problem for the Kadomtsev-Petviashvili equation in infinite space is considered. When formulated as an evolution equation, found that a symmetric integral is the appropriate choice in the nonlocal term; namely, . If one simply chooses , then an infinite number of constraints on the initial data in physical space are required, the first being . The conserved quantities are calculated, and it is shown that they must be suitably regularized from those that have been used when the constraints are imposed.     

Dynamics of Lump Solutions in a 2 + 1 NLS Equation

We derive a class of localized solutions of a 2+1 nonlinear Schrödinger (NLS) equation and study their dynamical properties. The ensuing dynamics of these configurations is a superposition of a uniform, "center of mass" motion and a slower, individual motion; as a result, nontrivial scattering between humps may occur. Spectrally, these solutions correspond to the discrete spectrum of a certain associated operator, comprised of higher-order meromorphic eigenfunctions.     

Electromagnetic properties of a chiral-plasma medium

The theoretical properties of a composite chiral-plasma medium are developed. By using the reaction theorem for a magnetized chiroplasma, we obtain the proof of nonreciprocity based upon the constitutive relationships between electromagnetic vectorsE, B, H, D. Using the Maxwell’s equations and the proposed constitutive relations for a chiral-plasma medium, we derive the vectorsE andH and from these equations, dispersion relations andE-field polarizations are based. The obtained results for waves propagating parallel to the external magnetic field in a cold magnetized chiro-plasma are compared with typical results obtained for a cold plasma. For circulary polarized waves, a new mode conversion is founded with the chiral effect. The chiral rotation is obtained and compared with the Faraday rotation. For waves propagating across the magnetic field, we found a shift of the cut-offs of ordinary and extraordinary waves. On the lower branch of the extraordinary wave mode there is no bands of forbidden frequencies and the reflection point vanishes when the chiral parameter increases.     

Stochastic model for market stocks with floors

We present a model to describe the stochastic evolution of stocks that show a strong resistance at some level and generalize to this situation the evolution based upon geometric Brownian motion. If volatility and drift are related in a certain way we show that our model can be integrated in an exact way. The related problem of how to prize general securities that pay dividends at a continuous rate and earn a terminal payoff at maturity T is solved via the martingale probability approach.     

Solvability of the Direct and Inverse Problems for the Nonlinear Schrödinger Equation

In this paper we study rigorous spectral theory and solvability for both the direct and inverse problems of the Dirac operator associated with the nonlinear Schrödinger equation. We review known results and techniques, as well as incorporating new ones, in a comprehensive, unified framework. We identify functional spaces in which both direct and inverse problems are well posed, have a unique solution and the corresponding direct and inverse maps are one to one.Mathematics Subject Classifications (2000) 34A55, 35Q55.     

Bioactive eremophilanolides from Senecio poepigii

A new bioactive eremophilanolide, 1alpha-tigloyloxy-8betaH,10betaH-eremophil-7(11)-en-8alpha,12-olide, was isolated from Senecio poepigii and its structure was elucidated by spectral analysis. 1alpha-Angeloyloxy-8beta-methoxy-10betaH-eremophil-7(11)-en-8alpha,12-olide was also isolated. Antifungal and insect antifeedant properties were evaluated.     

Molecular dynamics assessment of doxorubicin–carbon nanotubes molecular interactions for the design of drug delivery systems

Carbon nanotubes (CNTs) constitute an interesting material for nanomedicine applications because of their unique properties, especially their ability to penetrate membranes, to transport drugs specifically and to be easily functionalized. In this work, the energies of the intermolecular interactions of single-walled CNTs and the anticancer drug doxorubicin (DOX) were determined using the AMBER 12 molecular dynamics MM/PBSA and MM/GBSA methods with the aim of better understanding how the structural parameters of the nanotube can improve the interactions with the drug and to determine which structural parameters are more important for increasing the stability of the complexes formed between the CNTs and DOX. The armchair, zigzag, and chiral nanotubes were finite hydrogen-terminated open tubes, and the DOX was encapsulated inside the tube or adsorbed on the nanotube surface. Pentagon/heptagon bumpy defects and polyethylene glycol (PEG) nanotube functionalization were also studied. The best interaction occurred when the drug was located inside the cavity of the nanotube. Armchair and zigzag nanotubes doped with nitrogen, favored interaction with the drug, whereas chiral nanotubes exhibited better drug interactions when having bumpy defects. The π-π stacking and N-H…π electrostatic interactions were important components of the attractive drug-nanotube forces, enabling significant flattening of the nanotube to favor a dual strong interaction with the encapsulated drug, with DOX–CNT equilibrium distances of 3.1–3.9 Å. These results can contribute to the modeling of new drug-nanotube delivery systems.