Changes In Hydrogen-bonding Interactions Research Articles

Aromatic Zipper Topology Dictates Water-Responsive Actuation in Phenylalanine-Based Crystals.

Water-responsive (WR) materials that reversibly deform in response to relative humidity (RH) changes are gaining increasing interest for their potential in energy harvesting and soft robotics applications. Despite progress, there are significant gaps in the understanding of how supramolecular structure underpins the reconfiguration and performance of WR materials. Here, three crystals are compared based on the amino acid phenylalanine (F) that contain water channels and F packing domains that are either layered (F), continuously connected (phenylalanyl-phenylalanine, FF), or isolated (histidyl-tyrosyl-phenylalanine, HYF). Hydration-induced reconfiguration is analyzed through changes in hydrogen-bond interactions and aromatic zipper topology. F crystals show the greatest WR deformation (WR energy density of 19.8MJm-3 ) followed by HYF (6.5MJm-3 ), while FF exhibits no observable response. The difference in water-responsiveness strongly correlates to the deformability of aromatic regions, with FF crystals being too stiff to deform, whereas HYF is too soft to efficiently transfer water tension to external loads. Thesefindings reveal aromatic topology design rules for WR crystals and provide insight into general mechanisms of high-performance WR actuation. Moreover, the best-performing crystal, F emerges as an efficient WR material for applications at scale and low cost.

PH-shifting alters textural, thermal, and microstructural properties of mung bean starch-flaxseed protein composite gels.

The objective of this study was to investigate the effect of pH-shifting on the textural and microstructural properties of mung bean starch (MBS)-flaxseed protein (FP) composite gels. Results showed that different pH-shifting treatments caused changes in hydrogen bond interactions and secondary structures in composite gels, leading to the formation of loose or compact gel networks. The pH2-shifting modified protein and starch molecules with shorter chains tended to form smaller intermolecular aggregates, resulting in the formation of a looser gel network. For pH 12-shifting treatment, conformational change of FP caused the unfolding of protein and the exposure of more hydrophobic groups, which enhanced the hydrogen bond and hydrophobic interactions between polymers, contributing to the formation of a compact gel network. Furthermore, pH 12-shifting improved the water-holding capacity (WHC), storage modulus, and strength of gels, while pH2-treated gels exhibited lower WHC, hardness, and gumminess due to the degradation of MBS and denaturation of FP caused by extreme acid condition. These findings suggest that pH-shifting can alter the gel properties of bi-polymeric starch-protein composite systems by affecting the secondary structures of proteins and the hydrogen bonding between the polymers, and provide a promising way for a wide application of FP in soft gel-type food production.

Electrochemical Aziridination of Tetrasubstituted Alkenes with Ammonia

Ammonia (NH3) is an ideal nitrogen source in terms of availability, reactivity, safety, atom economy, environmental compatibility, and ease of isolation. However, its utility for amine synthesis is...

Multiresponsive Spin Crossover Driven by Rotation of Tetraphenylborate Anion in an Iron(III) Complex

Dynamic molecular materials, which involve mechanical motions in crystals, usually exhibit tunable properties related to conformational polymorphs. Herein, we describe a solvent-free molecular crys...

Pressure-dependent Fourier transform infrared spectroscopy of a poly (ester urethane)

The effects of hydrostatic pressure upon (1) a segmented poly (ester urethane), (2) a hydrolytically degraded sample of the same polymer, and (3) models for the polyurethane and polyester segments in this polymer have been studied by Fourier transform infrared spectroscopy using high-pressure diamond anvil cells (DACs). The pressure responses of the vibrational frequencies of specific functional groups of the poly (ester urethane) in the 0–100-kbar range are compared with data for individual segment models and the partially degraded sample. The results indicated that the polymer is highly stable in this pressure regime, with no measurable degradation or phase changes. Differences in the pressure dependency of specific infrared bands between the poly (ester urethane) sample and the partially degraded sample are slight and consistent with changes in hydrogen-bonding interactions and shorter chain lengths in the degraded sample.

Correlation between Multiple Hydrogen Bonding and Alteration of the Oxidation Potential of the Bacteriochlorophyll Dimer of Reaction Centers from Rhodobacter sphaeroides

The electronic absorption and vibrational Raman spectra of mutant reaction centers from Rhodobacter sphaeroides bearing multiple site-specific mutations near the primary electron donor (P), a bacteriochlorophyll dimer, are reported. These mutations bear double and triple combinations of single-point mutations that alter the H-bonding interactions between histidine residues and the C2- and C9-conjugated carbonyl groups of the primary donor [Mattioli, T.A., Williams, J.C., Allen, J.P., & Robert, B. (1994) Biochemistry 33, 1636-1643] and change the donor redox midpoint potential from 410 to 765 mV compared to 505 mV for wild type [Lin, X., Murchison, H.A., Nagarajan, V., Parson, W.W., Williams, J.C., & Allen, J.P. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. Near-infrared Fourier transform Raman spectroscopy was used to determine the changes in H-bonding interactions of the primary donor in these multiple mutants. The Fourier transform Raman spectra of the mutants exhibit the predicted changes in hydrogen bond interactions of the P carbonyl groups with the protein, and they are consistent with the designed mutations. Moreover, the Raman data verify that the H-bonds formed or broken in the multiple mutants are similar in strength to those observed in the corresponding single mutants. A correlation was observed between the change in P/P.+ redox midpoint potential and the total change in H-bonding interaction energy (from -207 to 364 meV relative to wild type) as gauged by the estimated enthalpy of each H-bond formed or broken on the four conjugated carbonyls of the primary donor. Only minor changes were observed in the optical spectra of the mutant reaction centers, indicating that the addition of H-bonds from histidines has little effect in destabilizing the first electronic excited state of the dimer relative to the ground state. However a blue shift in the dimer absorption band at ca. 890 nm at 20 K was associated with the removal of the H-bond to the C2 acetyl carbonyl group via His L168. A red shift of the oxidized dimer band at ca. 1250 nm was associated with the formation of each H-bond to the C9 keto carbonyl groups.