Dendritic molecular capsules for hydrophobic compounds

Reichardt's dye, a highly solvatochromic dye, was encapsulated within poly (glycerol succinic acid) ([Gn]-PGLSA-OH) dendrimers to investigate the interior environment of these dendritic macromolecules. The absorption maximum for the encapsulated Reichardt's dye in water was indicative of a relatively high dielectric constant present within the dye/dendrimer complex. (1)H NMR of the encapsulated complex showed the presence of aromatic protons from Reichardt's dye along with the aliphatic protons of the dendrimer. Additionally, there were substantial changes in T(1) and T(2) times of the encapsulated dye when compared with the free dye, and (1)H NOESY spectra for the complex showed a significant number of intermolecular NOE cross-peaks. These data reveal the close through-space proximity of the dye to the dendrimer and the restricted motion of the encapsulated dye. To demonstrate the potential use of these macromolecules as drug delivery vehicles, the poorly water-soluble anticancer drug 10-hydroxycamptothecin (10HCPT) was encapsulated within a carboxylated PGLSA dendrimer ([G4]-PGLSA-COONa). Cytotoxicity assays with human breast cancer cells showed a significant reduction of cell viability, demonstrating that 10HCPT retains activity upon encapsulation.     

A first-principles density-functional calculation of the electronic and vibrational structure of the key melanin monomers

We report first-principles density-functional calculations for hydroquinone (HQ), indolequinone (IQ), and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of biomacromolecules with important biological functions (including photoprotection) and with the potential for certain bioengineering applications. We have used the difference of self-consistent fields method to study the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, Delta(HL). We show that Delta(HL) is similar in IQ and SQ, but approximately twice as large in HQ. This may have important implications for our understanding of the observed broadband optical absorption of the eumelanins. The possibility of using this difference in Delta(HL) to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules have significantly different infrared and Raman signatures, and so these spectra could be used in situ to nondestructively identify the monomeric content of macromolecules. It is hoped that this may be a helpful analytical tool in determining the structure of eumelanin macromolecules and hence in helping to determine the structure-property-function relationships that control the behavior of the eumelanins.     

OXIDATIVE DEGRADATION OF LIGNIN BY PHOTOCHEMICAL AND CHEMICAL RADICAL GENERATING SYSTEMS

Oxidation of specifically radiolabeled ¹⁴C-lignins by UV/H₂0₂. Fenton's reagent, photosesitizing riboflavin. UV- and γ-irradiation was examined. In the presence of UV/H₂O₂, a hydroxyl radical (·OH) generating system. ¹⁴C-methoxy. 2-[¹⁴C-sidechain] and ¹⁴C-ring labeled lignin were rapidly and extensively degraded as measured by gel filtration of the reaction products on Sephadex LH-20. This suggested that exposure to OH leads to rapid, nonspecific lignin degradation. Rapid degradation of 14C-methoxy, 2-[¹⁴C-sidechain] and ¹⁴C-ring labeled lignin also occurred in the presence of the ·OH generating system, Fenton's reagent, confirming the primary role of ·OH in these reactions. Photosensitizing riboflavin, also capable of effecting transformation of organic compounds via Type I hydrogen radical abstractions, caused extensive oxidative degradation of ¹⁴C-methoxy labeled lignin and significant degradation of 2-(¹⁴C-sidechain] and ¹⁴C-ring labeled lignin. In addition, UV- and γ-irradiation caused slower but extensive degradation of the polymers, probably via radical type mechanisms. All of these results indicate that ·OH as well as organic radical generating systems are effective agents for the purpose of degrading this heterogeneous, optically inactive and random biopolymer.     

Absorption and fluorescence spectroscopy of rhodamine 6G in titanium dioxide nanocomposites

A comparison has been made between the spectroscopic properties of the laser dye rhodamine 6G (R6G) in mesostructured titanium dioxide (TiO(2)) and in ethanol. Steady-state excitation and emission techniques have been used to probe the dye-matrix interactions. We show that the TiO(2)-nanocomposite studied is a good host for R6G, as it allows high dye concentrations, while keeping dye molecules isolated, and preventing aggregation. Our findings have important implications in the context of solid state dye-lasers and microphotonic device applications.     

NADH Electrooxidation Using Bis(1,10-phenanthroline-5,6-dione) (2,2'-bipyridine)ruthenium(II)-Exchanged Zirconium Phosphate Modified Carbon Paste Electrodes

We present a carbon paste electrode (CPE) modified using the electron mediator bis(1,10‐phenanthroline‐5,6‐dione)(2,2′‐bipyridine)ruthenium(II) ([Ru(phend)₂bpy]²⁺) exchanged into the inorganic layered material zirconium phosphate (ZrP). X‐Ray powder diffraction showed that the interlayer distance of ZrP increases upon [Ru(phend)₂bpy]²⁺ intercalation from 10.3 Å to 14.2 Å. The UV‐vis and IR spectroscopies results showed the characteristic peaks expected for [Ru(phend)₂bpy]²⁺. The UV‐vis spectrophotometric results indicate that the [Ru(phend)₂bpy]²⁺ concentration inside the ZrP layers increased as a function of the loading level. The exchanged [Ru(phend)₂bpy]²⁺ exhibited luminescence even at low concentration. Modified CPEs were constructed and analyzed using cyclic voltammetry. The intercalated mediator remained electroactive within the layers (E°′=–38.5 mV vs. Ag/AgCl, 3.5 M NaCl) and electrocatalysis of NADH oxidation was observed. The kinetics of the modified CPE shows a Michaelis–Menten behavior. This CPE was used for the oxidation of NADH in the presence of Bakers' yeast alcohol dehydrogenase. A calibration plot for ethanol is presented.     

Periodic orbits of nonscaling Hamiltonian systems from quantum mechanics

Quantal (E,tau) plots are constructed from the eigenvalues of the quantum system. We demonstrate that these representations display the periodic orbits of the classical system, including bifurcations and the transition from stable to unstable. (c) 1995 American Institute of Physics.     

Two-photon spectra of gases by three-wave mixing

We show that the two-photon resonances in the third-order susceptibility can be exploited to yield two-photon spectra of molecular gases at moderately high spectral resolution. This form of spectroscopy does not depend on the occurrence of processes (such as fluorescence of photoionization) leading to indirect methods of two-photon absorption. The method is direct and leads in principle to values for a two-photon cross section. Comparisons of two-photon and coherent anti-Stokes Raman resonances leads to ratios of Raman and two-proton cross sections independent of the laser powers and spatial characteristics. The technique is documented with rotationally resolved spectra of SO₂ and NO. A value for |α_xxα_yy| of 1.5 × 10^?52 cm⁶ was measured for the O₁₂ (6$\text{built:1}\text{2}$) component of the (A)²Σ ← (X)² Π_{$\text{1}\text{2}$} transition of nitric oxide.     

Immobilisation of electroactive macrocyclic complexes within titania films

The 4-carboxyphenyl-appended macrocyclic ligand trans-6,13-dimethyl-6-((4-carboxybenzyl)amino)-1,4,8,11-tetraazacyclotetradecane-6-amine (HL10) has been synthesised and complexed with Co(III). The mononuclear complexes [Co(HL10)(CN)]2+ and [CoL10(OH)]+ have been prepared and the crystal structures of their perchlorate salts are presented, where the ligand is bound in a pentadentate mode in each case while the 4-carboxybenzyl-substituted pendent amine remains free from the metal. The cyano-bridged dinuclear complex [CoL10-mu-NC-Fe(CN)5]2- was also prepared and chemisorbed on titania-coated ITO conducting glass. The adsorbed complex is electrochemically active and cyclic voltammetry of the modified ITO working electrode in both water and MeCN solution was undertaken with simultaneous optical spectroscopy. This experiment demonstrates that reversible electrochemical oxidation of the Fe(II) centre is coupled with rapid changes in the optical absorbance of the film.