The first quantitative model for the partially reversible thermochromism in Langmuir-Blodgett films of the polymerized Cd2+ salts of 10,12-tricosadiynoic acid (TCDA) and 10,12-pentacosadiynoic acid (PCD A) is presented. The visible spectrum as a function of temperature provides evidence for two parallel processes, one of which is reversible. The following kinetic model is proposed which qualitatively and quantitatively accounts for the observed reversible thermochromism: B R (kf, fer); P -* R (fe2). B and P stand for two distinct forms of the blue polymer, and R stands for the red form of the polymer. Activation barriers of E{ = 22.5 kcal/mol, Et = 21.4 kcal/mol, and E2 -23.0 kcal/mol are obtained from the TCDA spectra as a function of temperature using a "normal" preexponential factor of 1012 s-1 and Et and Et as adjustable parameters. The same model can be fit to films of PCDA and gives activation barriers of Et = 21.5 kcal/mol, Et = 21.0 kcal/mol, and E2 = 22.5 kcal/mol.

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We have evaluated in a microchip format the photochemical solid-phase phosphoramidite DNA synthesis method we previously developed. A set of nucleoside building blocks with “easy-off” base protecting groups was prepared bearing photolabile 5‘-O-dimethoxybenzoincarbonate (DMBOC) groups. Photolysis rates and cycle yields for these DMBOC-protected nucleotides covalently attached to planar, derivatized glass surfaces were determined by fluorescence imaging-based methods earlier developed by McGall et al. and described in detail elsewhere. Data were obtained for both 280/310 and 365/400 nm irradiation in a range of solvents. Deprotection of the DMBOC occurs fastest in a nonpolar medium or without solvent. The coupling efficiency of these amidites in the synthesis of homopolymers was determined to be in the range 80−97%, with purines generally showing lower efficiency than pyrimidines. These DMBOC-protected monomers were used to prepare a 4 × 4 array of 16 decanucleotides of the sequence 5‘-AAXTAXCTAC−chip, where X = A, C, G, or T. The array was hybridized with a target deoxyeicosanucleotide of the sequence fluorescein-5‘-CTGAACGGTAGCATCTTGAC. Surface fluorescence imaging demonstrated sequence-specific hybridization to this probe.

A method has been developed to prepare short DNA sequences using light to deprotect a nucleoside 3‘-phosphotriester, generating a phosphodiester useful for coupling with a free 5‘-OH-nucleotide. The dimethoxybenzoin group is used as the photochemically-removable protecting group for the 3‘-phosphate. Cyanoethyl is most effective as the second protecting group on the phosphodiester. Because the method is directed at the preparation and use of the DNA sequences while still bound to the support, allyl and allyloxycarbonyl protecting groups are used for the nitrogenous bases since, based on the work of Hayakawa and Noyori, they can be removed without cleaving the DNA from the support. Two simple trinucleotides have been prepared in solution using this method. It has been demonstrated that the photochemical deprotection conditions do not lead to the formation of cyclobutane dimers from adjacent T residues.