Towards an understanding of the heat capacity of liquids. A simple two-state model for molecular association

A model for the temperature dependence of the isobaric heat capacity of associated pure liquids C(p,m)(o)(T) is proposed. Taking the ideal gas as a reference state, the residual heat capacity is divided into nonspecific C(p) (res,ns) and associational C(p) (res,ass) contributions. Statistical mechanics is used to obtain C(p)(res,ass) by means of a two-state model. All the experimentally observed C(p,m)(o)(T) types of curves in the literature are qualitatively described from the combination of the ideal gas heat capacity C(p)(id)(T) and C(p)(res,ass)(T). The existence of C(p,m)(o)(T) curves with a maximum is predicted and experimentally observed, for the first time, through the measurement of C(p,m)(o)(T) for highly sterically hindered alcohols. A detailed quantitative analysis of C(p,m)(o)(T) for several series of substances (n-alkanes, linear and branched alcohols, and thiols) is made. All the basic features of C(p,m)(o)(T) at atmospheric and high pressures are successfully described, the model parameters being physically meaningful. In particular, the molecular association energies and the C(p)(res,ns) values from the proposed model are found to be in agreement with those obtained through quantum mechanical ab initio calculations and the Flory model, respectively. It is concluded that C(p,m)(o)(T) is governed by the association energy between molecules, their self-association capability and molecular size.     

Photocontrolled mechanical phenomena in photochromic doped polymeric systems

This work examines volume changes at the sub-micron scale, induced photochemically in polymeric matrices doped with photochromic molecules. To achieve this, spiropyran is employed as a photochromic molecule embedded in polyethylmethacrylate-co-methylacrylate (PEMMA) matrices. Spiropyran can be reversibly interconverted to merocyanine, its coloured isomer, by irradiation at 248 nm and 532 nm, correspondingly. It is demonstrated that the interconversion between the two forms activates volume changes in the polymer matrix. To this end, off-axis reflection holographic interferometry is employed as a sensitive probe of the induced volume changes. This scheme provides a novel method for controlling sub-micron volume changes reversibly, as required in several microactuator designs. Received: 17 April 2002 / Accepted: 18 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +30-810/391-318, E-mail: nassia@iesl.forth.gr     

Custom‐Fit Ruthenium(II) Metallopeptides: A New Twist to DNA Binding With Coordination Compounds

A new bipyridine building block has been used for the solid‐phase synthesis of dinuclear DNA‐binding ruthenium(II) metallopeptides. Detailed spectroscopic studies suggest that these compounds bind to the DNA by insertion into the DNA minor groove. Moreover, the potential of the solid‐phase peptide synthesis approach is demonstrated by the straightforward synthesis of an octaarginine derivative that shows effective cellular internalization and cytotoxicity linked with strong DNA interaction, as evidenced by steady‐state fluorescence spectroscopy and AFM studies.     

DPPC/poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline) chimeric nanostructures as potential drug nanocarriers

In this study, we report on the self assembly behavior and on stability studies of mixed (chimeric) nanosystems consisting of dipalmitoylphosphatidylcholine (DPPC) and poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline) (MPOx) gradient copolymer in aqueous media and in fetal bovine serum (FBS). A gamut of light scattering techniques and fluorescence spectroscopy were used in order to extract information on the size and morphological characteristics of the nanoassemblies formed, as a function of gradient block copolymer content, as well as temperature. The hydrodynamic radii (R _h) of nanoassemblies decreased in the process of heating up to 50 °C, while the fractal dimension (d _f) values, also increased. Indomethacin was successfully incorporated into these chimeric nanocarriers. Drug release was depended on the components ratio. The present studies show that there are a number of parameters that can be used in order to alter the properties of chimeric nanosystems, and this is advantageous to the development of “smart” nanocarriers for drug delivery.     

Controlling the reversible wetting capability of smart photochromic-polymer surfaces by micro patterning

We demonstrate the wetting behavior control of polymer surfaces doped with photochromic molecules by modifying the surface patterning features introduced by soft molding lithography. Such surfaces enhance their hydrophilicity upon UV irradiation due to conversion of the non-polar spiropyran dopant molecules to their polar merocyanine isomers. The process is reversed upon visible light irradiation. By changing the topological parameters of the introduced pattern, one achieves surface tuning from hydrophobic to hydrophilic situations. The difference for the contact angles between UV- and green-irradiated surfaces may become significantly higher than for the flat surfaces, for the specific patterning parameters analyzed. PACS 42.62.-b; 68.08.Bc; 83.50.Uv; 42.70.Jk; 42.70.Gi     

Simultaneous ultrasound-assisted emulsification-derivatization as a simple and miniaturized sample preparation method for determination of nitrite in cosmetic samples by microvolume UV-vis spectrophotomety

A simple and miniaturized approach based on ultrasound-assisted emulsification-derivatization is proposed for the determination of nitrite in cosmetic samples by UV-vis micro-spectrophotometry. Oil/water emulsions were formed using 15 mg of cosmetic sample and 1 mL of an aqueous medium containing 0.5% w/v SDS and 1% v/v acetic acid. When powerful sonication systems were used to make emulsions, i.e. probe or cup-horn sonoreactor, stable and transparent emulsions were obtained in one or half minute per sample, respectively. The Griess reaction in these special conditions (i.e. sonication and the presence of an organized medium) was investigated. The absence of matrix effects allows external calibration with aqueous standards for nitrite quantification. Analytical features were compared to those of the European official method 82/434/EEC. Detection limit, sample throughput and reagent consumption were significantly improved.     

Molecular mechanism of acid-triggered aryl-halide reductive elimination in well-defined aryl-Cu(III)-halide species

Well-defined aryl-Cu(III)-halide species undergo reductive elimination upon acid addition resulting in the formation of strong aryl-halide bonds. The computationally studied mechanism points towards ligand protonation as the rate-determining step, in agreement with previous experimental data.     

Optically implemented broadband blueshift switch in the terahertz regime

We experimentally demonstrate, for the first time, an optically implemented blueshift tunable metamaterial in the terahertz (THz) regime. The design implies two potential resonance states, and the photoconductive semiconductor (silicon) settled in the critical region plays the role of intermediary for switching the resonator from mode 1 to mode 2. The observed tuning range of the fabricated device is as high as 26% (from 0.76 THz to 0.96 THz) through optical control to silicon. The realization of broadband blueshift tunable metamaterial offers opportunities for achieving switchable metamaterials with simultaneous redshift and blueshift tunability and cascade tunable devices. Our experimental approach is compatible with semiconductor technologies and can be used for other applications in the THz regime.     

Classification of heterotic Pati–Salam models

We extend the classification of free fermionic heterotic-string models to vacua in which the SO(10)$\mathit{SO}(10)$ GUT symmetry is broken at the string level to the Pati–Salam subgroup. Using our classification method we recently presented the first example of a quasi-realistic heterotic-string vacuum that is free of massless exotic states. Within this method we are able to derive algebraic expressions for the Generalised GSO (GGSO) projections for all sectors that appear in the models. This facilitates the programming of the entire spectrum analysis in a computer code. The total number of vacua in the class of models that we classify is ²⁵¹∼¹⁰¹⁵$2^{51}\sim {10}^{15}$. We perform a statistical sampling in this space of models and extract 10¹¹ GGSO configurations with Pati–Salam gauge group. Our results demonstrate that one in every 10⁶ vacua correspond to a three generation exophobic model with the required Higgs states, needed to induce spontaneous breaking to the Standard Model.     

Combined land-use and water allocation planning

A general framework for a combined land use and water management is described. An optimization problem is formulated that combines combinatorial and spatial characteristics. The aim of the planning is to maximize economic benefit, while minimizing water extraction and transportation cost under ecological constraints. A genetic algorithm is employed endowed with a new neighborhood operator. This operator acts on a local level, but it produces global results. Although the computational scheme does not include compactness as a separate objective, compact patterns are produced as emergent results. The algorithm is tested on a fictive area represented as a grid with 15×15 land blocks and, also, on a real-world case study.