Size-dependent photocurrent switching in chemical bath deposited CdSe quantum dot films

Journal of Solid State Electrochemistry - Size-dependent photocurrent switching has been investigated in chemical bath deposited CdSe quantum dot (QD) films with band gaps 2.26, 2.09, and...     

Nucleotides. Part XLV. Synthesis of new (2′–5′)adenylate trimers,containing 5′-amino-5′-deoxyadenosine residues at the 5′-end of the oligoadenylate chain,and of its analogues,carrying a 9-[(2-hydroxyethoxy)methyl]adenine residue at the 2′-terminus

The 5′-amino-5′-deoxy-2′,3′-O-isopropylideneadenosine ( 4 ) was obtained in pure form from 2′,3′-O-isopropylideneadenosine ( 1 ), without isolation of intermediates 2 and 3 . The 2-(4-nitrophenyl)ethoxycarbonyl group was used for protection of the NH₂ functions of 4 (→7) . The selective introduction of the palmitoyl (= hexadecanoyl) group into the 5′-N-position of 4 was achieved by its treatment with palmitoyl chloride in MeCN in the presence of Et₃N (→ 5 ). The 3′-O-silyl derivatives 11 and 14 were isolated by column chromatography after treatment of the 2′,3′-O-deprotected compounds 8 and 9 , respectively, with (tert-butyl)dimethylsilyl chloride and 1H-imidazole in pyridine. The corresponding phosphoramidites 16 and 17 were synthesized from nucleosides 11 and 14 , respectively, and (cyanoethoxy)bis(diisopropylamino)phosphane in CH₂Cl₂. The trimeric (2′–5′)-linked adenylates 25 and 26 having the 5′-amino-5′-deoxyadenosine and 5′-deoxy-5′-(palmitoylamino)adenosine residue, respectively, at the 5′-end were prepared by the phosphoramidite method. Similarly, the corresponding 5′-amino derivatives 27 and 28 carrying the 9-[(2-hydroxyethoxy)methyl]adenine residue at the 2′-terminus, were obtained. The newly synthesized compounds were characterized by physical means. The synthesized trimers 25–28 were 3-, 15-, 25-, and 34-fold, respectively, more stable towards phosphodiesterase from Crotalus durissus than the trimer (2′–5′)ApApA.     

Bragg diffraction of light by a hypersound in gyrotropic cubic crystals

Noncollinear acousto-optical interaction of light beams in acoustically gyrotropic cubic crystals is considered. The dependences of the diffraction efficiency of the parameters of the optical and acoustical gyrotropy have been established. The attainability of the optimal efficiency of diffraction by shear ultrasonic waves due to the anisotropy electrically induced by the external field under conditions of longitudinal electro-optical effect is shown.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 80–84, January–February, 2005.     

Amino Acid Assisted Incorporation of Dye Molecules within Calcite Crystals

Biomineralisation processes invariably occur in the presence of multiple organic additives, which act in combination to give exceptional control over structures and properties. However, few synthetic studies have investigated the cooperative effects of soluble additives. This work addresses this challenge and focuses on the combined effects of amino acids and coloured dye molecules. The experiments demonstrate that strongly coloured calcite crystals only form in the presence of Brilliant Blue R (BBR) and four of the seventeen soluble amino acids, as compared with almost colourless crystals using the dye alone. The active amino acids are identified as those which themselves effectively occlude in calcite, suggesting a mechanism where they can act as chaperones for individual molecules or even aggregates of dyes molecules. These results provide new insight into crystal–additive interactions and suggest a novel strategy for generating materials with target properties.     

Physicochemical Properties of Nanoparticles: Interaction of Supported Platinum Nanoparticles with Gaseous Reactants

The shapes, sizes, and electronic structures of platinum nanoparticles supported onto highly oriented pyrolytic graphite and oxidized silicon by different methods and their adsorptive properties with respect to hydrogen, oxygen, water, and ammonia were established. The apparent activation energy of the reduction of single oxidized platinum nanoparticles with molecular hydrogen was determined. The possibility of controlling the rate of ammonia decomposition by a nanostructured platinum coating by the application of electric potentials of different values and polarities to it was demonstrated.     

Forty Years after the Discovery of Its Nucleolytic Activity: [Cu(phen)2]2+ Shows Unattended DNA Cleavage Activity upon Fluorination

[Cu( phen )₂]²⁺ ( phen =1,10-phenanthroline) is the first and still one of the most efficient artificial nucleases. In general, when the phen ligand is modified, the nucleolytic activity of its Cu^II complex is significantly reduced. This is most likely due to higher steric bulk of such ligands and thus lower affinity to DNA. Cu^II complexes with phen ligands having fluorinated substituents (F, CF₃, SF₅, SCF₃) surprisingly showed excellent DNA cleavage activity—in contrast to the unsubstituted [Cu( phen )₂]²⁺—in the absence of the otherwise required classical, bioabundant external reducing agents like thiols or ascorbate. This nucleolytic activity correlates well with the half-wave potentials E_1/2 of the complexes. Cancer cell studies show cytotoxic effects of all complexes with fluorinated ligands in the low μm range, whereas they were less toxic towards healthy cells (fibroblasts).