Microwave Heating of Liquid Crystals and Ethanol-Hexane Mixed Solution and Its Features (Review)

Microwave heating is widely used to accelerate organic reactions in the chemistry field. However, the effect of microwaves on chemical reaction has not yet been well characterized at the molecular level. In this review chapter, microwave heating processes of liquid crystals and an ethanol-hexane mixed solution under microwave irradiation were experimentally and theoretically investigated using in situ microwave irradiation nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulation, respectively. The temperature of the solution under microwave irradiation was estimated from a chemical shift calibrated temperature (CSC-temperature) which was determined from the temperature dependence of the 1H chemical shift. The CSC-temperatures of CH2 and CH3 non-polar protons of ethanol reflect the bulk temperature of a solution by the thermal microwave effect. The lower CSC-temperature of the OH polar protons in ethanol and much higher CSC-temperature of H-C=N (7′) and CH3-O (α’) protons of N-(4-methoxybenzyliden)-4-butylaniline with respect to the bulk temperature are attributed to the non-thermal microwave effects. According to the MD simulation under microwave irradiation, the number of hydrogen bonds increased in the ethanol-hexane mixed solution as a result of a non-thermal microwave effect. It is concluded that a coherently ordered low entropy state of polar molecules is induced by a non-thermal microwave effect. The ordered state induces molecular interaction, which may accelerate the chemical reaction rate between molecules with polar groups

Retinal Configuration of ppR Intermediates Revealed by Photoirradiation Solid-State NMR and DFT

Pharanois phoborhodopsin (ppR) from Natronomonas pharaonis is a transmembrane photoreceptor protein involved in negative phototaxis. Structural changes in ppR triggered by photoisomerization of the retinal chromophore are transmitted to its cognate transducer protein (pHtrII) through a cyclic photoreaction pathway involving several photointermediates. This pathway is called the photocycle. It is important to understand the detailed configurational changes of retinal during the photocycle. We previously observed one of the photointermediates (M-intermediates) by in situ photoirradiation solid-state NMR experiments. In this study, we further observed the 13C cross-polarization magic-angle-spinning NMR signals of late photointermediates such as O- and N'-intermediates by illumination with green light (520 nm). Under blue-light (365 nm) irradiation of the M-intermediates, 13C cross-polarization magic-angle-spinning NMR signals of 14- and 20-13C-labeled retinal in the O-intermediate appeared at 115.4 and 16.4 ppm and were assigned to the 13-trans, 15-syn configuration. The signals caused by the N'-intermediate appeared at 115.4 and 23.9 ppm and were assigned to the 13-cis configuration, and they were in an equilibrium state with the O-intermediate during thermal decay of the M-intermediates at -60°C. Thus, photoirradiation NMR studies revealed the photoreaction pathways from the M- to O-intermediates and the equilibrium state between the N'- and O-intermediate. Further, we evaluated the detailed retinal configurations in the O- and N'-intermediates by performing a density functional theory chemical shift calculation. The results showed that the N'-intermediate has a 63° twisted retinal state due to the 13-cis configuration. The retinal configurations of the O- and N'-intermediates were determined to be 13-trans, 15-syn, and 13-cis, respectively, based on the chemical shift values of [20-13C] and [14-13C] retinal obtained by photoirradiation solid-state NMR and density functional theory calculation

Soft chromophore featured liquid porphyrins and their utilization toward liquid electret applications

Optoelectronically active viscous liquids are ideal for fabricating foldable/stretchable electronics owing to their excellent deformability and predictable π-unit-based optoelectronic functions, which are independent of the device shape and geometry. Here we show, unprecedented 'liquid electret' devices that exhibit mechanoelectrical and electroacoustic functions, as well as stretchability, have been prepared using solvent-free liquid porphyrins. The fluidic nature of the free-base alkylated-tetraphenylporphyrins was controlled by attaching flexible and bulky branched alkyl chains at different positions. Furthermore, a subtle porphyrin ring distortion that originated from the bulkiness of alkyl chains was observed. Its consequences on the electronic perturbation of the porphyrin-unit were precisely elucidated by spectroscopic techniques and theoretical modelling. This molecular design allows shielding of the porphyrin unit by insulating alkyl chains, which facilitates its corona-charged state for a long period under ambient conditions

Solid-state NMR characterization of triacylglycerol and polysaccharides in coffee beans

<p>It is important to understand the structural characteristics of triacylglycerol (TAG), polysaccharides and trace elements in coffee beans, so that residues can be reutilized in applications including biodiesel oils. Here, we performed ¹H and ¹³C solid-state NMR measurements on Indonesian green beans, roasted beans, and spent coffee grounds (SCGs). In the NMR spectra, there were liquid-like TAG containing linoleic acids based on observed signals of -CH=CH-CH₂-CH=CH- group in an acyl chain, which play a role in decreasing TAG’s melting point. We found TAG was still abundant in the SCGs from NMR spectra. After lipids were removed from SCGs, the intensity of the TAG signal decreased considerably, with approximately 64% of the TAG was successfully extracted. We described the chemical structure of TAG in coffee beans and demonstrated that it is possible quantify the amount of extracted TAG using solid-state NMR.</p> <p>Triacylglycerol as a source of biodiesel fuel in spent coffee grounds, green and roasted coffee beans was thoroughly characterized by ¹H and ¹³C solid-state NMR spectroscopy.</p

Solid-State NMR Characterization of the Structure of Self-Assembled Ile–Phe–OH

Solid-state nuclear magnetic resonance (NMR) spectroscopy provides significant structural information regarding the conformation and dynamics of a variety of solid samples. In this study, we recorded the 13C and 15N solid-state NMR spectra of a self-assembled isoleucine-phenylalanine (Ile&ndash;Phe&ndash;OH) dipeptide. Immediately after the addition of hexane to a solution of concentrated peptide in ethyl acetate, the peptide visually aggregated into a nanofiber. Then, we obtained well-resolved 13C and 15N NMR signals of the natural, isotopic-abundant Ile&ndash;Phe&ndash;OH peptide in the nanofiber. Furthermore, we calculated the chemical shift values of the reported crystal structure of the Ile&ndash;Phe dipeptide via the density functional theory (DFT) calculation and compared these results with the experimental values. Notably, the two sets of values were in good agreement with each other, which indicated that the self-assembled structure closely reflected the crystal structure. Therefore, herein, we demonstrated that solid-state NMR characterization combined with DFT calculations is a powerful method for the investigation of molecular structures in self-assembled short peptides

A Comparative Study on Interactions of Antimicrobial Peptides L- and D-phenylseptin with 1,2-dimyristoyl-sn-glycero-3-phosphocholine

L-phenylseptin (L-Phes) and D-phenylseptin (D-Phes) are amphibian antimicrobial peptides isolated from the skin secretion of Hypsiboas punctatus. In the N-termini, L-Phes and D-Phes contain three consecutive phenylalanine residues, l-Phe-l-Phe-l-Phe and l-Phe-d-Phe-l-Phe, respectively. They are known to exhibit antimicrobial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Xanthomonas axonopodis pv. Glycines. However, their mechanism of action and the role of the D-amino acid residue have not been elucidated yet. In this study, the interactions of both peptides with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were investigated by means of quartz crystal microbalance, circular dichroism, vibrational circular dichroism, 31P solid-state NMR, and molecular dynamics simulation. Both peptides have similar binding constants to the DMPC lipid bilayers, in the order of 106 M&minus;1, and form an &alpha;-helix structure in the DMPC lipid bilayers. Both the peptides induce similar changes in the dynamics of DMPC lipids. Thus, in spite of the difference in the conformations caused by the chirality at the N-terminus, the peptides showed similar behavior in the membrane-bound state, experimentally and computationally