Effect of cholesterol on diffusion in surfactant bilayers

Biological membranes consist of lipid bilayers with liquid-ordered and liquid-disordered phases. It is believed that cholesterol controls the size of the microdomains in the liquid-ordered phase and thereby affects the mobility as well as the permeability of the membrane. We study this process in a model system consisting of the nonionic surfactant C(12)E(5) and water in the lamellar phase. We measure the diffusion of fluorescent probe molecules (rhodamine B) by fluorescence correlation spectroscopy. For different surfactant to water ratios, we measure how the molecular mobility varies with the amount of cholesterol added. We find that a reduction of the diffusion coefficient is already detectable at a molar ratio of 8 mol % cholesterol.     

Synthesis of thieno[2,3-d]pyrimidin-2-ylmethanamine combinatorial library with four diversity points

The parallel solution-phase synthesis of more than 230 substituted thieno[2,3-d]pyrimidin-2-ylmethanamines has been accomplished. This strategy is based on the cyclization of 2-aminothiophen-3-carboxylates with chloroacetonitrile to construct the thieno[2,3-d]pyrimidine core with two diversity points. Derivatization of the active chlorine and functionalization of C-4 position of the pyrimidine ring allow the introduction of other diversity points. The products containing ester groups at the 6-position of the thieno[2,3-d]pyrimidine were used in amide synthesis. Simple manual techniques for parallel reactions, coupled with simple purification procedures, gave highly pure final products. The scope and limitations of the approach are discussed.     

Separation and evaluation of free radical-scavenging activity of phenol components of green, brown, and black leaves of Bergenia crassifolia by using HPTLC-DPPH* method

A new procedure has been developed to separate and quantify the free radical-scavenging activity of individual compounds from green, brown, and black leaves of Bergenia crassifolia based on the combination of high performance TLC (HPTLC) with a diode array detector (DAD) and postchromatographic 1,1-diphenyl-2-picrylhydrazyl radical (DPPH(*)) derivatization. Free gallic and ellagic acids, arbutin, hydroquinone, and bergenin in the B. crassifolia leaves' extracts were separated by HPTLC and identified. All compounds of the extract excluding bergenin were capable of scavenging DPPH * radicals. From the estimated ID(50) values, it can be seen that the increasing order of activity was gallic acid > arbutin > ellagic acid > hydroquinone > ascorbic acid. The antiradical activity of leaves of B. crassifolia is probably associated to the presence of phenol.     

Heterocyclic analogues of cyclohexene: theoretical studies of the molecular structures and ring-inversion processes

The equilibrium geometry, ring-inversion barrier, and pathway for heterocyclic analogues of cyclohexene have been studied using the MP2/6-311G(d,p) level of theory. It is concluded that the replacement of one methylene group in cyclohexene by heteroatom results in significant changes in the character of the potential-energy surface in comparison with cyclohexene. The equilibrium conformation of ring strongly depends on the position of the heteroatom due to the existence of the n-pi conjugation. However, the character of the ring-inversion process is determined by the nature of the heteroatom. In the case of sulfur- and selenium-containing rings, the boat or twist-boat conformation corresponds to an additional minimum on the potential-energy surface. Moreover, the barriers of the conformational transition from this conformer to two different half-chair forms are significantly different. Nitrogen-containing heterocycles possess two pairs of minima corresponding to the different configurations of the nitrogen atom. However, the transition between the two minima with the same configuration of the heteroatom proceeds only in two steps that include ring inversion and nitrogen inversion.     

Rapid ligand substitution reactions in ionic liquids studied by stopped-flow technique

Detailed kinetic studies on ligand substitution reactions of [M(II)(terpy)Cl](+) complexes (M = Pt, Pd; terpy = 2,2':6',2'-terpyridine) with thiourea as entering nucleophile were for the first time performed in the imidazolium based ionic liquid [emim][NTf(2)] using stopped-flow techniques, opening the route to study fast reactions of transition metal complexes in ionic liquids.     

Three-component coordination networks based on [Ru(phen)(CN)4(2-) anions, near-infrared luminescent lanthanide(III) cations, and ancillary oligopyridine ligands: structures and photophysical properties

A series of cyanide-bridged coordination networks has been prepared which contain [Ru(phen)(CN)4](2-) anions, Ln(III) cations, and additional oligopyridine ligands (1,10-phenanthroline, 2,2':6',2'-terpyridine or 2,2'-bipyrimidine) which coordinate to the Ln(III) centres. Five structural types have been identified and examples of each type of structure are described: these are hexanuclear Ru4Ln2 clusters; two-dimensional Ru-Ln sheets with a honeycomb pattern of edge-linked Ru6Ln6 hexagons; one-dimensional chains consisting of two parallel cross-linked strands in a ladder-like arrangement; simple single-stranded chains of alternating Ru/Ln components; and a one-dimensional 'chain of squares' in which Ru2Ln2 squares are linked by bipyrimidine bridging ligands which connect to the Ln(III) corners of adjacent squares in the sequence. The 3MLCT luminescence characteristic of the [Ru(phen)(CN)4](2-) units is quenched in those networks containing Ln(III) which have low-lying near-infrared luminescent f-f states [Pr(III), Nd(III), Er(III), Yb(III)], with sensitised Ln(III)-based near-IR luminescence generated by d --> f energy-transfer. The rate of d --> f energy-transfer, and hence the degree of quenching of the 3MLCT luminescence from the [Ru(phen)(CN)4](2-) units, depends on the availability of f-f levels of an appropriate energy on the Ln(III) centre, with Nd(III) (with a high density of low-lying f-f states) being the most effective energy-acceptor and Yb(III) (with a single low-lying f-f state) being the least effective. Rates of d --> f energy-transfer to different Ln(III) centres could be determined from both the residual (partially quenched) lifetimes of the 3MLCT luminescence, and--in the case of the Yb(III) networks--by a rise-time for the sensitised near-IR luminescence. The presence of the 'blocking' polypyridyl ligands, which reduced the number of cyanide and water ligands that would otherwise coordinate to the Ln(III) centres, resulted in increases in the Ln(III)-based emission lifetimes compared to networks where these blocking ligands were not used.     

Coupling of whispering-gallery modes in size-mismatched microdisk photonic molecules

Mechanisms of whispering-gallery (WG)-mode coupling in microdisk photonic molecules (PMs) with slight and significant size mismatches are numerically investigated. The results reveal two different scenarios of modes interaction depending on the degree of this mismatch and offer new insight into how PM parameters can be tuned to control and modify WG-mode wavelengths and Q factors. From a practical point of view, these findings offer a way to fabricate PM microlaser structures that exhibit low thresholds and directional emission and at the same time are more tolerant to fabrication errors than previously explored coupled-cavity structures composed of identical microresonators.     

High-efficiency 1.5 microm thick optical axis grating and its use for laser beam combining

We demonstrate an optical axis grating (OAG) recorded in a nematic liquid crystal that yields a higher than 80% diffraction efficiency and over 800:1 switching contrast between diffraction orders for a laser beam of a red wavelength in a material layer only 1.5 microm thick. The grating was used for combining two laser beams with high efficiency. These observations prove the feasibility of new generation high-efficiency diffractive optical components, which are most promising for infrared and high-power applications owing to their enhanced transparency and reduced thermal effects in thin material layers.     

One-dimensional manganese coordination polymers composed of polynuclear cluster blocks and polypyridyl linkers: structures and properties

The synthesis, crystal structures and magnetic properties of five new manganese compounds are reported. These include a linear trinuclear cluster [Mn(II)(3)(O(2)CCHMe(2))(6)(dpa)(2)].2MeCN (1) (dpa = 2,2'-dipyridylamine), a tetranuclear cluster [Mn(II)(2)Mn(III)(2)O(2)(O(2)CCMe(3))(6)(bpy)(2)] (3) (bpy = 2,2'-bipyridine), and chain coordination polymers composed of cluster blocks such as Mn(3), Mn(3)O, and Mn(4)O(2) bridged by 2,2'-bipyrimidine (bpm) or hexamethylentetramine (hmta) ligands to give ([Mn(II)(3)(O(2)CCHMe(2))(6)(bpm)].2EtOH)(n) (2), [Mn(II)(2)Mn(III)(2)O(2)(O(2)CCHMe(2))(6)(bpm)(EtOH)(4)](n) (4), and (([Mn(II)Mn(III)(2)O(O(2)CCHMe(2))(6)(hmta)(2)].EtOH)(n) (5). The magnetic analysis of the compounds was achieved using a combination of vector coupling and full-matrix diagonalization methods. Susceptibility data for compound 1 was fitted using a vector coupling model to give g = 2.02(1) and 2J/k(B) = -5.38(2) K. To model the trimer chain, we used vector coupling for initial values of J(1) and then diagonalization techniques to estimate J(2) to give g = 1.98(1), 2J(1)/k(B) = -3.3(1) K and 2J(2)/k(B) = -1.0(1) K by approximating the system to a dimer of trimers. The analysis of 3 was made difficult by the mixture of polymorphs and the difficulties of a three-J model, while for 4 an analysis was not possible because of the size of the computation and the relative magnitudes of the three couplings. Compound 5 was modeled using the same techniques as 2 to give g = 1.99(1), 2J(1)/k(B) = +32.5(2) K, 2J(2)/k(B) = -16.8(1) K, and 2J(3)/k(B) = +0.4(1) K. The combination of techniques has worked well for compounds 2 and 5 and thus opens up a method of modeling complex chains.     

Vapour pressure and enthalpy of vaporization of aliphatic dialkyl carbonates

Molar enthalpies of vaporization of aliphatic alkyl carbonates: dimethyl carbonate [616-38-6], diethyl carbonate [105-58-8], di-n-propyl carbonate [623-96-1], di-n-butyl carbonate [542-52-9], and dibenzyl carbonate [3459-92-5] were obtained from the temperature dependence of the vapour pressure measured by the transpiration method. A large number of the primary experimental results on temperature dependences of vapour pressures have been collected from the literature and have been treated uniformly in order to derive vaporization enthalpies of dialkyl carbonates at the reference temperature 298.15 K. An internal consistency check was performed on enthalpy of vaporization values for dialkyl carbonates studied in this work.