Spin-coupled theory for 'N electrons in M orbitals' active spaces

Spin-coupled (SC) theory, an ab initio valence bond (VB) approach which uses a compact and an easy-to-interpret single-orbital product wave function comparable in quality to a ‘N in N’ complete-active-space self-consistent field [CASSCF(N,N)] construction, is extended to ‘N in M’ (N ≠ M) active spaces. The SC(N,M) wave function retains the essential features of the original SC model: It involves just the products of nonorthogonal orbitals covering all distributions of N electrons between M orbitals in which as few orbitals as possible, |N – M|, are doubly occupied (for N > M) or missing (for N < M) and all other orbitals are singly occupied; each of these products is combined with a flexible spin function which allows any mode of coupling of the spins of the orbitals within the product. The SC(N,M) wave function remains much more compact than a CASSCF(N,M) construction; for example, the SC(6,7) wave function includes 35 configuration state functions (CSFs) as opposed to the 490 CSFs in the CASSCF case. The essential features of the SC(N,M) method are illustrated through a SC(6,5) calculation on the cyclopentadienyl anion, C5H5(–), and a SC(6,7) calculation on the tropylium cation, C7H7(+). The SC(6,5) and SC(6,7) wave functions for C5H5(–) and C7H7(+) are shown to provide remarkably clear modern VB models for the electronic structures of these aromatic cyclic ions which closely resemble the well-known SC model of benzene and yet recover almost all of the correlation energy included in the corresponding CASSCF(6,5) and CASSCF(6,7) wave functions: over 97% in the case of C5H5(–) and over 95% in the case of C7H7(+).     

Layer-by-layer quantum dot constructs using self-assembly methods

We describe the creation of CdSe/ZnS quantum dot assemblies using layer-by-layer construction strategies, using self-assembly. In the first approach, a dithiol linker was used to make multilayers of CdSe/ZnS quantum dots, while in the second biotin- and streptavidin-conjugated CdSe/ZnS quantum dots were used to make multilayer constructs. Both the chemical bonding nature and fluorescence spectroscopic properties of quantum dot films were characterized using X-ray photoelectron spectroscopy (XPS) and fluorescence spectroscopy.     

Stabilization of All-trans-retinol by Cyclodextrins: A Comparative Study Using HPLC and Fluorescence Spectroscopy

Purpose: To formulate preparations incorporating cyclodextrins (CDs) which could be used for direct delivery to the retina of vitamin A (all-trans-retinol), while also protecting it from degradation in the aqueous environment. Vitamin A supplementation is being considered for treatment of several ophthalmic diseases characterised by progressive photoreceptor degeneration. Methods: The complexation between vitamin A and ten cyclodextrins, Captisol^®(sulfobutyl ether-7--cyclodextrin), hydroxypropyl--CD, 2-hydroxypropyl--CD, -CD, hydroxypropyl--CD, hydroxypropyl--CD, -CD, methyl--CD,Heptakis-(2,6-di-O-methyl)--CD andHeptakis-(2,3,6-tri-O-methyl)--CD,was investigated using bothhigh sensitivity fluorescence spectrometry and HPLC (high pressure liquid chromatography). Samples of retinol-CD complexes in phosphate buffer, pH 7.4 were analysed for up to 72 hours. Optimum conditions for formation of the Captisol-retinol complexes were investigated. Results: Using spectroscopic measurements and HPLC, the complexes formed between ten cyclodextrins and all-trans-retinol were evaluated. The results indicate that all cyclodextrins tested were able to form inclusion complexes as shown by the fluorescence signals which are considerably larger than those obtained in the absence of cyclodextrin. Only minimal degradation of retinol over 48 hours was observed with three of these cyclodextrins. Captisol was able to stabilise all-trans-retinol for up to 72 hours, as shown by HPLC, and the optimum ratio of Captisol to retinol was determined to be 50 to 1. Addition of glutathione and decrease in pH did not improve stability of the complex. Conclusions: This survey suggests that Captisol and other cyclodextrins could be used to stabilise and solubilise vitamin A in aqueous media and this establishes the basis for an ocular Captisol-retinol drug delivery system now under development in our laboratory.     

Theoretical electronic transition moments for the Ballik-Ramsay,Fox-Herzberg,and Swan systems OF C2

Potential energy curves and spectroscopic constants T_e, r_e, ω_e, and ω_eχ_e have been calculated for the a³Π_u, b³Σ^-_g, d³Π_g and e³Π_g electronic states of C₂ using self-consistent-field plus configuration-interaction techniques. These results are in excellent agreement with those obtained from experiments. The variation of the electronic transition moment with internuclear separation has been calculated for the Ballik-Ramsay system (b³Σ^-_g-a³Π_u), Fox-Herzberg (e³Π_g-a³Π_u), and Swan (d³Π_g-a³Π_u) band systems. These results are in good agreement with existing experimental and theoretical data.     

Digital biomagnetism: Electrodeposited multilayer magnetic barcodes

A novel magnetic encoding technique for performing high-throughput biological assays is presented. Electrodeposited Ni/Cu and Co/Cu multilayer pillar structures with a diameter of 15 μm and a thickness up to 10 μm are presented as “magnetic barcodes”, where the number of unique codes possible increases exponentially with a linear increase in length. A gold cap facilitates the growth of self-assembled monolayers (SAMs), while microdrop printing allows efficient generation of large libraries of tagged probes. Coercivity-tuning techniques are used to exploit a non-proximity encoding methodology compatible with microfluidic flow.     

Plasmonic enhancement of the two photon absorption cross section of an organic chromophore using polyelectrolyte-coated gold nanorods

The effect of plasmonic enhancement on the two-photon absorption cross section of organic chromophores attached to polyelectrolyte-coated gold nanorods was investigated. The magnitudes of such enhancements were confirmed using single and two photon excitations of the chromophore molecules bound to polyelectrolyte-coated gold nanorods. By synthesizing two-, four-, six-, and eight-polyelectrolyte layer coated nanorods of a particular aspect ratio, the distance dependence of the evanescent electromagnetic field on molecular two-photon absorption was observed. Enhancements of 40-fold were observed for the chromophores nearest to the surface.     

The influence of linguistic and musical experience on Cantonese word learning

Adult non-native speech perception is subject to influence from multiple factors, including linguistic and extralinguistic experience such as musical training. The present research examines how linguistic and musical factors influence non-native word identification and lexical tone perception. Groups of native tone language (Thai) and non-tone language listeners (English), each subdivided into musician and non-musician groups, engaged in Cantonese tone word training. Participants learned to identify words minimally distinguished by five Cantonese tones during training, also completing musical aptitude and phonemic tone identification tasks. First, the findings suggest that either musical experience or a tone language background leads to significantly better non-native word learning proficiency, as compared to those with neither musical training nor tone language experience. Moreover, the combination of tone language and musical experience did not provide an additional advantage for Thai musicians above and beyond either experience alone. Musicianship was found to be more advantageous than a tone language background for tone identification. Finally, tone identification and musical aptitude scores were significantly correlated with word learning success for English but not Thai listeners. These findings point to a dynamic influence of musical and linguistic experience, both at the tone dentification level and at the word learning stage.