Photochemical reactions in organized assemblies. 40. Amylose and carboxymethylamylose inclusion complexes with photoreactive molecules

Suddaby, Brian R.; Dominey, Raymond N.; Yang, Hui; Whitten, David G.

doi:10.1139/v85-223

Cited by 13 publications

(4 citation statements)

References 21 publications

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“…The inner diameter of these helical structures is 4.5−7.0 Å and, thus, in the same range as that of the urea channels. Indeed, amylose has previously been used as a ‘reaction vessel' for photochemical reactions. 29b, This hunch proved to be correct in that amylose served as a host for the MTO-catalyzed silane oxidation; unfortunately, the silane conversions were lower than those with urea (Table , entries 11−13). Presumably, this is due to the more polar environment and the conformationally fixed structure of the amylose compared to the urea channels.…”

Section: Discussionmentioning

confidence: 99%

Host−Guest Chemistry in a Urea Matrix: Catalytic and Selective Oxidation of Triorganosilanes to the Corresponding Silanols by Methyltrioxorhenium and the Urea/Hydrogen Peroxide Adduct

et al. 1999

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The oxidation of silanes to silanols, catalyzed by methyltrioxorhenium (MTO), proceeds in high conversions and excellent selectivities in favor of the silanol (no disiloxane product) when the urea/hydrogen peroxide adduct (UHP) is used as oxygen source instead of 85% aqueous H 2 O 2 . It is proposed that this novel Si-H oxidation takes place in the helical urea channels, in which the urea matrix serves as host for the silane substrate, the H 2 O 2 oxygen source, and the MTO metal catalyst as guests. In this confined environment, the metal catalyst is stabilized against decomposition, and this enhances higher conversions while condensation of the silanol to its disiloxane is avoided for steric reasons. The oxidation of the optically active silane (S)-(R-Np)PhMeSiH proceeds with retention of configuration in excellent yield. To date, no catalytic Si-H oxygen insertion has been reported for the preparation of optically active silanols. In analogy with the stereoselectivity in the dioxirane oxidation of (+)-(R-Np)PhMeSiH to (+)-(R-Np)PhMeSiOH, a concerted spiro-type transitionstate structure is proposed for this novel Si-H oxidation. Herewith, a valuable synthetic method for the preparation of silanols has been made available through catalytic and selective oxidation of silanes to silanols by the MTO/UHP system.

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Section: Discussionmentioning

confidence: 99%

Host−Guest Chemistry in a Urea Matrix: Catalytic and Selective Oxidation of Triorganosilanes to the Corresponding Silanols by Methyltrioxorhenium and the Urea/Hydrogen Peroxide Adduct

et al. 1999

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“…Carboxymethylamylose was synthesized in this laboratory by Ray Dominey as previously described (Suddaby et al, 1985); (M) = 4.7X104 (average molecular weight), (DP) = 230 (degree of polymerization), DS = 0.52 (degree of substitution).…”

Section: Synthesismentioning

confidence: 99%

“…During the past several years there has been an increasing interest in the photochemistry of a "guest" molecule incorporated into "hosts" such as zeolites, cyclodextrins, cryptates and amylose. In these complexes the host may either provide a rather fixed rigid environment as is the case for cyclodextrins (Turro et al, 1982;Raniamurthy and Eaton, 1988), a variety of sites having specific compartment size (zeolites) (Turro et al, 1988), or an adjustable cavity as is the case for amylose (Suddaby et al, 1985). Depending upon both the specific host and guest, the guest in these complexes may be anticipated to be held in a somewhat restricted environment with some limitation as to the possible conformation it can assume.…”

Section: Introductionmentioning

confidence: 99%

MONOALKYL α‐OXOAMIDES: PHOTOCHEMISTRY IN HOMOGENEOUS and IN MICROHETEROGENEOUS MEDIA*

Richard

Chesta

Whitten

1991

Photochem & Photobiology

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An investigation of the photoreactivity of the amphiphilic α‐oxoamide, N‐(12‐dodecanoic acid)benzoylformamide, (1), in aqueous (pH 10) solution and its inclusion complexes with β‐cyclodextrin (β‐CD) and carboxymethylamylose (CMA). In all three media photolysis of 1 yields predominantly the fragmentation products from hydrolysis, mandelamide and the corresponding aldehyde. The most reasonable mechanism for the reaction is an intramolecular quenching of a ketone‐localized excited state by electron transfer from the amide nitrogen followed by proton transfer and a second electron transfer (zwitterion‐1 → diradical ⇄ zwitterion‐2) to yield ultimately the mandelamide‐imine precursor which hydrolyzes to the observed products. The quantum yields for 1 decomposition and mandelamide appearance in aqueous solution (pH 10) are 0.21 and 0.16, respectively. Compound 1 forms a 1:1 and 1:2 complex with β‐CD and shows enhanced quantum efficiencies for reaction, especially the 1:2 complex. 1 also forms a complex with CMA which shows a similar binding constant to other similar chain length amphiphiles in other studies. Here again reactivity is enhanced for the photoreaction of 1 upon complexation, indicating that neither the electron transfer quenching of the excited states nor reaction of subsequent intermediates is prohibited in the complexes. Mechanistic implications of these results are discussed.

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“…As a result, the rotational freedom around the chromophore (in the inclusion) is substantially restricted even at an elevated temperature in solution, compared to the case of the noninclusion free dye. This results in an enhanced fluorescence emission of the chromophore. , Our earlier fluorescence study 3 suggests that the binding of DASPC 22 to the host amylose (at room temperature) is reduced with increasing water content in DMSO−H 2 O mixtures, anticipating that, in 100% water, conformation of the included dye becomes less restrictive and that, at a critical temperature, some of the bound dye may be freed from the inclusion and moves into bulk water.…”

mentioning

confidence: 95%

Unusual Thermochromic Behavior of Photoreactive Dyes Confined in Helical Amylose as Inclusion Complex

Choi

Kim

1998

Macromolecules

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Molecular environment has a significant impact on the dynamics and reactivity of molecules, particularly when the molecules are confined in a rigidly tied space. 1,2 In such a surrounding, guest molecules may experience a different reaction pathway due to chemical as well as steric interactions with the host environment. Unlike the case where reactive species are embedded in vesicle membranes and Langmuir-Blodgett films, in inclusion complexation, guest molecules are supramolecularly encapsulated by host molecules through binding interactions such that the confined guest becomes rigidified and loses conformational freedom. These are part of the consequence, and further, a number of uncommon chemical/physical properties are anticipated to result, depending on the inclusion structure and external conditions.Taking advantage of part of the above notion, we have developed a new strategy for nonlinear optical (NLO) materials whose chromophores are supramolecularly included in the helical cavity of amylose. 3 It was found that solution-cast thin films of the supramolecular complex displayed a self-assembly/self-poling, which induced a significantly large second harmonic generation 4,5 and an excellent long-term polar stability. 4 Further advantages for the material properties are enhanced thermal and photochemical stabilities and mechanical integrity of chromophores. 4,6,7 A recent observation 8 revealed that the hyperpolarizability of the chromophores is doubled by the inclusion complexation with a helical amylose 9 relative to the noninclusion free state in solution.Few studies have been made with respect to thermal stability 6 of the bound guest in amylose inclusion. In this communication, we report thermally induced conformational transitions of a hemicyanine dye, 4-[4-(dimethylamino)styryl]-1-docosylpyridinium bromide (DASPC 22 ), confined in a helical amylose (forming a 1:1 complex) 12 in the solid state, making a comparison with that in solution. This is the first report of an unusual thermochromism of the dye that is associated with restricted chromophore conformations in the confinement of the rigid helical host in the solid state.It is known that conjugated dyes in amphiphilic multilayers 16 as well as in solution 17 and conjugated polymers 18,19 in solid films and in solution as well undergo a marked conformational transition with increasing temperature, exhibiting a reversible thermochromism that is commonly represented by a linearly increasing blue shift of the absorption maximum, λ max , with temperature. This is largely due to the loss of coplanarity in the conjugated chromophore.Since amylose is a polymeric host with multiple binding sites, once incorporated, the guest molecules are rigidly bound (K a ) 2 × 10 5 M -1 ) with increasing carbon chain length or hydrophobicity. As a result, the rotational freedom around the chromophore (in the inclusion) is substantially restricted even at an elevated temperature in solution, compared to the case of the noninclusion free dye. This results in an enhanced flu...

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Photochemical reactions in organized assemblies. 40. Amylose and carboxymethylamylose inclusion complexes with photoreactive molecules

Cited by 13 publications

References 21 publications

Host−Guest Chemistry in a Urea Matrix: Catalytic and Selective Oxidation of Triorganosilanes to the Corresponding Silanols by Methyltrioxorhenium and the Urea/Hydrogen Peroxide Adduct

Host−Guest Chemistry in a Urea Matrix: Catalytic and Selective Oxidation of Triorganosilanes to the Corresponding Silanols by Methyltrioxorhenium and the Urea/Hydrogen Peroxide Adduct

MONOALKYL α‐OXOAMIDES: PHOTOCHEMISTRY IN HOMOGENEOUS and IN MICROHETEROGENEOUS MEDIA*

Unusual Thermochromic Behavior of Photoreactive Dyes Confined in Helical Amylose as Inclusion Complex

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