Conspectus
Hydrogen bonds (H-bonds) play important roles
in imparting functionality
to the basic molecules of life by stabilizing their structures and
directing their interactions. Numerous studies have been devoted to
understanding H-bonds involving highly electronegative atoms like
nitrogen, oxygen, and halogens and consequences of those H-bonds in
chemical reactions, catalysis, and structure and function of biomolecules;
but the involvement of less electronegative atoms like sulfur and
selenium in H-bond formation establishes the concept of noncanonical
H-bonds. Initially belittled for the “weak” nature of
their interactions, these perceptions have gradually evolved over
time through dedicated efforts by several research groups. This has
been facilitated by advancements in experimental methods for their
detection through gas-phase laser spectroscopy and solution NMR spectroscopy,
as well as through theoretical predictions from high level quantum
chemical calculations.
In this Account, we present insights
into the versatility of the
sulfur and selenium centered H-bonds (S/SeCHBs) by highlighting their
multifarious applications in various fields from chemical reactions
to optoelectronic properties to structural biology. Our group has
highlighted the significance and strength of such H-bonds in natural
and modified biomolecules. Here, we have reviewed several molecular
assemblies, biomolecules, and functional materials, where the role
of these H-bonds is pivotal in influencing biological functions. It
is worth mentioning here that the precise experimental data obtained
from gas-phase laser spectroscopy have contributed considerably to
changing the existing perceptions toward S/SeCHBs. Thus, molecular
beam experiments, though difficult to perform on smaller model thio-
or seleno-substituted Molecules, etc. (amides, nucleobases, drug molecules),
are inevitable to gather elementary knowledge and convincing concepts
on S/SeCHBs that can be extended from a small four-atom sulfanyl dimer
to a large 14 kDa iron–sulfur protein, ferredoxin. These H-bonds
can also tailor a fascinating array of molecular frameworks and design
supramolecular assemblies by inter- and intralinking of individual
“molecular Lego-like” units.
The discussion is
indeed intriguing when it turns to the usage
of S/SeCHBs in facile synthetic strategies like tuning regioselectivity
in reactions, as well as invoking phenomena like dual phosphorescence
and chemiluminescence. This is in addition to our investigations of
the dispersive nature of the hydrogen bond between metal hydrides
and sulfur or selenium as acceptor, which we anticipate would lead
to progress in the areas of proton and hydride transfer, as well as
force-field design. This Account demonstrates how ease of fabrication,
enhanced efficiency, and alteration of physicochemical properties
of several functional materials is facilitated owing to the presence
of S/SeCHBs. Our efforts have been instrumental in the evaluation
of various S/SeCHBs in flue gas capture, as well as design of organic
ene...
Effects of dimethyl-sulfoxide (DMSO) on the hydrogen bonding structure and dynamics in aqueous N-methylacetamide (NMA) solution are investigated by classical molecular dynamics simulations. The modifications of structure and interaction between water and NMA in presence of DMSO molecules are calculated by various site-site radial distribution functions and average interaction energies between these species in the solution. It is observed that the aqueous peptide hydrogen bond interaction is relatively stronger with increasing concentration of DMSO, whereas methyl-methyl interaction between NMA and DMSO decreases significantly. The DMSO molecule prefers to interact with amide-hydrogen of NMA even at lower DMSO concentration. The lifetimes and structural-relaxation times of NMA-water, water-water and DMSO-water hydrogen bonds are found to increase with increasing DMSO concentration in the solution. The slower translational and rotational dynamics of NMA is observed in concentrated DMSO solution due to formation of stronger inter-species hydrogen bonds in the solution.
Extensions of the ideal
associated solution theory which take into account intermolecular interaction
and/or size factors are derived and applied to triethylamine+ CHCl3
and diethyl ether+CHCl3. Evidence is presented for
non-hydrogen-bonding specific interactions between the unlike molecules in
these systems. Theories that do not take this into consideration are likely to
be unsatisfactory for the determination of hydrogen-bond properties. With
respect to the evaluation of ?net complex formation? properties, the extensions
considered do not represent significant improvements of the simple theory. The
molar enthalpies of mixing of triethylamine+CH3CCl, and diethyl
ether+ CH3CCl3 have been measured at 288.15 and 298.15 K.
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