The fundamental roles
that peptides and proteins play in today’s
biology makes it almost indisputable that peptides were key players
in the origin of life. Insofar as it is appropriate to extrapolate
back from extant biology to the prebiotic world, one must acknowledge
the critical importance that interconnected molecular networks, likely
with peptides as key components, would have played in life’s
origin. In this review, we summarize chemical processes involving
peptides that could have contributed to early chemical evolution,
with an emphasis on molecular interactions between peptides and other
classes of organic molecules. We first summarize mechanisms by which
amino acids and similar building blocks could have been produced and
elaborated into proto-peptides. Next, non-covalent interactions of
peptides with other peptides as well as with nucleic acids, lipids,
carbohydrates, metal ions, and aromatic molecules are discussed in
relation to the possible roles of such interactions in chemical evolution
of structure and function. Finally, we describe research involving
structural alternatives to peptides and covalent adducts between amino
acids/peptides and other classes of molecules. We propose that ample
future breakthroughs in origin-of-life chemistry will stem from investigations
of interconnected chemical systems in which synergistic interactions
between different classes of molecules emerge.
Azobenzene-3,3'-dicarboxylic acid exists in photoisomerizable (E) and (Z)-forms. Deprotonation of the carboxylic acid groups from the (E)-form occurs simultaneously, whereas in the (Z)-form it occurs in a stepwise fashion. The mono anionic form of the (Z)-isomer acts as a glycosidase mimic that proceeds through a general acid-general base catalytic mechanism. This is the first example of a photoresponsive glycosidase mimic.
The discovery of photoswitchable azobenzene-systems that undergo trans-to-cis photoisomerisation was a milestone in supramolecular chemistry. Such photoswitches have possible applications in data storage, stimuli responsive delivery systems, and molecular machines due to fast and selective switching. However, the light induced cis isomer of azobenzene is rather unstable and reverts thermally and photochemically to the thermodynamically stable trans configuration. We report, for the first time, controlled photoswitching of an azo-naphthalenediimide (azo-NDI) which can be achieved upon binding of fluoride ions through anion-π interaction. This NDI-F–NDI “sandwich” stabilises the cis configuration through the generation of an NDI•− radical anion, and a dianionic, NDI2− species that becomes unusually stable in the cis form. The sandwiched cis form reverts to the trans form only upon decomplexation of F−. A model pollutant was successfully degraded using the photogenerated NDI-F–NDI sandwich. This opens a wide range of applications in molecular and supramolecular nanotechnology.
A new naphthalene diimide-dithiocarbamate based fluorescence probe was synthesized and its fluorogenic behavior towards various metal ions was studied. Upon addition of various metal ions, the probe afforded an irreversible change only with Hg(2+) ions in aqueous-ethanol media (4 : 1 v/v) with a fourfold enhancement of the fluorescence (Φ = 0.03 → 0.11) along with a distinct 43 nm blue shift of the emission maxima. The mechanism of the chemodosimetric behavior of the probe has been attributed to a Hg(2+) induced transformation of a weakly fluorescent dithiocarbamate to a highly fluorescent isothiocyanate which has been characterized by a number of spectroscopic techniques and a crystal structure. Intracellular detection of Hg(2+) ions was achieved using the probe.
Stimuli responsive hosts for C
60
can control its binding and release on demand. A photoswitchable TPE based supramolecular host can encapsulate C
60
in the
Z
-form with a markedly different visual change in the colour. In addition, the
Z
-1 bound C
60
has been characterized by various spectroscopic methods and mass spectrometry. Upon exposure to visible light (>490 nm), the host switches to the
E
-form where the structural complementarity with the guest is destroyed as a result of which the C
60
is disassembled from the host. The results described herein reveals an actionable roadmap to pursue further advances in component self-assembly particularly light-induced association and dissociation of a guest molecule.
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