Diego Sampedro

Reversible Photocontrol of Peptide Conformation with a Rhodopsin-like Photoswitch

Reversible photocontrol of biomolecules requires chromophores that can efficiently undergo large conformational changes upon exposure to wavelengths of light that are compatible with living systems. We designed a benzylidene-pyrroline chromophore that mimics the Schiff base of rhodopsin and can be used to introduce light-switchable intramolecular cross-links in peptides and proteins. This new class of photoswitch undergoes an ~10 Å change in end-to-end distance upon isomerization and can be used to control the conformation of a target peptide efficiently and reversibly using, alternately, violet (400 nm) and blue (446 nm) light.

E/Z Photochemical switches: syntheses, properties and applications

Molecular switches based on E/Z photoisomerization have been used in different contexts in order to control a variety of processes in different systems, from peptide conformation control to molecular data storage devices, from catalysis to smart materials. The syntheses, properties and applications of several types of E/Z photochemical switches are presented with special attention paid to azobenzenes, overcrowded alkenes and switches based on the protonated Schiff base chromophore of rhodopsins.

Benzylidene-oxazolones as molecular photoswitches.

The synthesis and photochemical study of a family of molecular switches inspired by the green fluorescent protein (GFP) chromophore is presented. These compounds can be easily synthesized, and their photophysical properties may be tuned. Due to their efficient photoisomerization and high stability, these compounds can be switched on/off by using light and heat or light with different wavelengths.

Chiral Hydrogen Bond Environment Providing Unidirectional Rotation in Photoactive Molecular Motors

Generation of a chiral hydrogen bond environment in efficient molecular photoswitches is proposed as a novel strategy for the design of photoactive molecular motors. Here, the following strategy is used to design a retinal-based motor presenting singular properties: (i) a single excitation wavelength is needed to complete the unidirectional rotation process (360°); (ii) the absence of any thermal step permits the process to take place at low temperatures; and (iii) the ultrafast process permits high rotational frequencies.

Photocyclization of Iminyl Radicals: Theoretical Study and Photochemical Aspects

The irradiation of acyloximes was studied by theoretical methods. CASPT2/6-31G*//CASSCF/6-31G* calculations, using an active space of 14 electrons in 11 orbitals, indicate that S2 should be the spectroscopic state, and its relaxation leads directly to N-O bond breakage due to coupling between the imine pi* and the sigma* N-O orbitals. Subsequent calculations at the B3PW91/6-31+G* level suggest that the resulting iminyl radicals are able to cyclize to the five- or six-membered ring, depending on the presence of a phenyl group as a spacer, a process that has been verified experimentally. The photochemical aspects of the more common five-membered ring formation, such as excited-state quenching, quantum yield, excited-state sensitizers, laser flash photolysis experiments, Stern-Volmer plot, and luminescence measurements, were investigated. These studies indicate that singlet and triplet excited states undergo the same reaction. Emission lifetimes of ca. tau = 10.6 micros for compound 11 are suggestive of triplet parentage, while no fluorescence was detected, in agreement with the computed MEP energy profile.

Fluorenylidene-pyrroline biomimetic light-driven molecular switches.

A new family of biomimetic photoactivated molecular switches based in the retinal chromophore is described. Expedient synthesis allows a library of compounds with a different substitution pattern, including chiral substituents, to be obtained. The effect of substitution, solvent, and light source on the photoisomerization step has been assessed. The absorption maximum has been red-shifted ca. 50 nm with respect to related systems and rotation is now easily achieved by using visible light.

PREPARATION AND APPLICATION OF CYCLOPROPYLIMINES IN ORGANIC SYNTHESIS. A REVIEW

INTRODUCTION ...................................................................................................................... 563 I . SYNTHESIS ............................................................................................................................. 564 1 . C-Cyclopropylimines ........................................................................................................ 564 a) From Cyclopropylcarbonyl Compounds ........................................................................ 5~ b) Cyclopropanations to C-Cyclopropylimines .................................................................. 567 2 . N-Cyclopropylimiies ......................................................................................................... 568 a) From Cyclopropylamines ............................................................................................... 569 b) Cyclopropanations to N-Cyclopropylimines .................................................................. 571 I1 . REACTIVITY ........................................................................................................................ 576 1 . Rearrangements of C-Cyclopropylimines ....................................................................... 576 a) Rearrangement of C-Cyclopropylimines to 2-Pyrrolines .............................................. 576 i . Cloke-Stevens-Boeckman Rearrangements ............................................................... 576 ii . Thermal Rearrangements without AcidlNucleophilic Catalyst ................................ 578 iii . Carbene-carbene Rearrangements ............................................................................ 579 iv . Metal-catalyzed Rearrangements ............................................................................. 580 v . Photochemistry of C-Cyclopropylimines .................................................................. 580 b) Rearrangements to Larger Heterocycles ....................................................................... 5g1 c) Cycloaddition Reactions ................................................................................................. 582 2 . Rearrangements of N-Cyclopropylimin es ....................................................................... 582 a) Rearrangements of N-Cyclopropylimines to I -Pyrrolines ............................................ 583 i . Thermal Rearrangements ............................................................................................ 583 ii . Photochemical Rearrangements ................................................................................ 583

Hydantoin-Based Molecular Photoswitches

A new family of molecular photoswitches based on arylidenehydantoins is described together with their synthesis and photochemical and photophysical studies. A series of hydantoin derivatives have been prepared as single isomers using simple and versatile chemistry in good yields. Our studies show that the photostationary states of these compounds can be easily controlled by means of external factors, such as the light source or filters. Moreover, the detailed investigations proved that these switches are efficient (i.e., they make efficient use of the light energy, are high fatigue resistant, and are very photostable). In some cases, the switches can be completely turned on/off, a desirable feature for specific applications. A series of theoretical calculations have also been carried out to understand the photoisomerization mechanism at the molecular level.

Simple and versatile synthesis of 1-pyrroline derivatives through thermal rearrangement of N-cyclopropylimines

N-Cyclopropylimines rearrange under thermal conditions to give 1-pyrrolines. The effect of imine and cyclopropane substitution is explored. This methodology allows the presence of different substituents (alkyl, alkenyl, aryl) and the reaction proceeds regiospecifically.

DFT Rationalization of the Diverse Outcomes of the Iodine(III)‐Mediated Oxidative Amination of Alkenes

A computational study of the mechanism for the iodine(III)-mediated oxidative amination of alkenes explains the experimentally observed substrate dependence on product distribution. Calculations with the M06 functional have been carried out on the reaction between PhI(N(SO2 Me)2 )2 and three different representative substrates: styrene, α-methylstyrene, and (E)-methylstilbene. All reactions start with electrophilic attack by a cationic PhI(N(SO2 Me)2 )(+) unit on the double bond, and formation of an intermediate with a single C-I bond and a planar sp(2) carbocationic center. The major path, leading to 1,2-diamination, proceeds through a mechanism in which the bissulfonimide initially adds to the alkene through an oxygen atom of one sulfonyl group. This behavior is now corroborated by experimental evidence. An alternative path, leading to an allylic amination product, takes place through deprotonation at an allylic C-H position in the common intermediate. The regioselectivity of this amination depends on the availability of the resonant structures of an alternate carbocationic intermediate. Only in cases where a high electronic delocalization is possible, as in (E)-methylstilbene, does the allylic amination occur without migration of the double bond.