Energy‐induced polymorphic changes in poly(vinylidene fluoride): How ultrasonication results in polymer with predominantly γ phase

Self‐polarized poly(vinylidene fluoride) (PVDF) films were prepared via solution crystallization technique wherein the polymorphism of the films was controlled from α phase (>85%) to γ phase (>90%) by varying the time of ultrasonication. On increasing ultrasonication time up to 60 min, γ phase crystallites were found to be self‐aligned in the matrix while an equal proportion of α and γ phases coexist in the PVDF films ultrasonicated for 120 min. The phase conversion as well as inversion was evident from Fourier transform infrared, X‐ray diffraction, and differential scanning calorimetry analyses. Microscopic images of films ultrasonicated for 60 min showed a scrolled lamellar morphology while those sonicated for 120 min showed mixture of scrolled lamellar and spherulitic morphology. With the help of computational studies, it is explained that a large amount of energy is required for transforming trans‐gauche‐trans‐gauche into trans‐trans‐trans‐gauche conformation which is provided by ultrasonication. The mechanism of γ phase formation is proposed based on the experimental and theoretical approaches. Our studies show that just by tuning the time of ultrasonication, PVDF films with various morphologies can be processed; either one with predominantly electroactive γ phase with superior electrical properties or one with equal proportion of α and γ phases with superior mechanical properties. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 40–50     

Vibronic spectra of jet-cooled 2-aminopurine·H2O clusters studied by UV resonant two-photon ionization spectroscopy and quantum chemical calculations

For understanding the major- and minor-groove hydration patterns of DNAs and RNAs, it is important to understand the local solvation of individual nucleobases at the molecular level. We have investigated the 2-aminopurine·H(2)O monohydrate by two-color resonant two-photon ionization and UV/UV hole-burning spectroscopies, which reveal two isomers, denoted A and B. The electronic spectral shift δν of the S(1) ← S(0) transition relative to bare 9H-2-aminopurine (9H-2AP) is small for isomer A (-70 cm(-1)), while that of isomer B is much larger (δν = -889 cm(-1)). B3LYP geometry optimizations with the TZVP basis set predict four cluster isomers, of which three are doubly H-bonded, with H(2)O acting as an acceptor to a N-H or -NH2 group and as a donor to either of the pyrimidine N sites. The "sugar-edge" isomer A is calculated to be the most stable form with binding energy D(e) = 56.4 kJ/mol. Isomers B and C are H-bonded between the -NH2 group and pyrimidine moieties and are 2.5 and 6.9 kJ/mol less stable, respectively. Time-dependent (TD) B3LYP/TZVP calculations predict the adiabatic energies of the lowest (1)ππ* states of A and B in excellent agreement with the observed 0(0)(0) bands; also, the relative intensities of the A and B origin bands agree well with the calculated S(0) state relative energies. This allows unequivocal identification of the isomers. The R2PI spectra of 9H-2AP and of isomer A exhibit intense low-frequency out-of-plane overtone and combination bands, which is interpreted as a coupling of the optically excited (1)ππ* state to the lower-lying (1)nπ* dark state. In contrast, these overtone and combination bands are much weaker for isomer B, implying that the (1)ππ* state of B is planar and decoupled from the (1)nπ* state. These observations agree with the calculations, which predict the (1)nπ* above the (1)ππ* state for isomer B but below the (1)ππ* for both 9H-2AP and isomer A.     

Formic Acid as a Potential Pretreatment Agent for the Conversion of Sugarcane Bagasse to Bioethanol

In recent years, growing attention has been focused on the use of lignocellulosic biomass as a feedstock for the production of ethanol, a possible renewable alternative to fossil fuels. Several pretreatment processes have been developed for decreasing the biomass recalcitrance, but only a few of them seem to be promising. In this study, effect of various organic solvents and organic acids on the pretreatment of sugarcane bagasse was studied. Among the different organic acids and organic solvents tested, formic acid was found to be effective. Optimization of process parameters for formic acid pretreatment was carried out. The structural changes before and after pretreatment was investigated by scanning electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared (FTIR) analysis. The X-ray diffraction profile showed that the degree of crystallinity was more for pretreated biomass than that of untreated. The FTIR spectra shown at the stretching of hydrogen bonds of pretreated sugarcane bagasse arose at higher number. It also revealed that the cellulose content in the solid residue increased because the hemicelluloses fraction in raw materials was released by acid hydrolytic reaction.     

Chemical cationization of cotton fabric for improved dye uptake

Cotton fabric is usually dyed with reactive dyes. During the dyeing process, a large amount of salt is required to achieve higher exhaustion of the dye from the dyebath onto the fiber. Dyeing of cotton with reactive dyes has a substantial environmental impact due to the discharge of a large volume of highly colored and saline effluents. Chemical cationization allows cotton fibers to be dyed without salt by chemically modifying cellulosic macromolecules to introduce positively charged sites. In this study, cotton fabric was cationized using (3-chloro-2-hydroxylpropyl) trimethyl-ammonium chloride (CHPTAC). Dye uptake was assessed using two reactive dyes, CI Reactive Blue 235 and CI Reactive Blue 19. Dye exhaustion kinetics were determined using a Datacolor-HueMetrix Monitor system. Analysis of variance demonstrated significant effects of CHPTAC concentration and exhaustion time on the percent exhaustion. Color strength at the end of the dyeing cycle was significantly higher for cationized fabrics compared to the control fabric. This work shows that treatment of cotton with CHPTAC enhanced dye uptake properties due to the introduction of cationic sites and resulted in superior dyeing without the addition of salt.     

Cooperative Gold Nanoparticle Stabilization by Acetylenic Phosphaalkenes

Acetylenic phosphaalkenes (APAs) are used as a novel type of ligands for the stabilization of gold nanoparticles (AuNP). As demonstrated by a variety of experimental and analytical methods, both structural features of the APA, that is, the P?C as well as the C?C units are essential for NP stabilization. The presence of intact APAs on the AuNP is demonstrated by surface‐enhanced Raman spectroscopy (SERS), and first principle calculations indicate that bonding occurs most likely at defect sites on the Au surface. AuNP‐bound APAs are in chemical equilibrium with free APAs in solution, leading to a dynamic behavior that can be explored for facile place‐exchange reactions with other types of anchor groups such as thiols or more weakly binding phosphine ligands.     

Sensing Characteristics of a Graphene‐like Boron Carbide Monolayer towards Selected Toxic Gases

By using first‐principles calculations based on density functional theory, we study the adsorption efficiency of a BC₃ sheet for various gases, such as CO, CO₂, NO, NO₂, and NH₃. The optimal adsorption position and orientation of these gas molecules on the BC₃ surface is determined and the adsorption energies are calculated. Among the gas molecules, CO₂ is predicted to be weakly adsorbed on the graphene‐like BC₃ sheet, whereas the NH₃ gas molecule shows a strong interaction with the BC₃ sheet. The charge transfer between the molecules and the sheet is discussed in terms of Bader charge analysis and density of states. The calculated work function of BC₃ in the presence of CO, CO₂, and NO is greater than that of a bare BC₃ sheet. The decrease in the work function of BC₃ sheets in the presence of NO₂ and NH₃ further explains the affinity of the sheet towards the gas molecules. The energy gap of the BC₃ sheets is sensitive to the adsorption of the gas molecules, which implies possible future applications in gas sensors.     

Microbial quality evaluation and effective decontamination of nutraceutically valued lotus seeds by electron beams and gamma irradiation

Lotus seeds are nutraceutically valued natural plant produce, which succumbs to microbial contamination, predominantly to toxigenic moulds. Results of the present study revealed seed coat portion to harbor higher proportion of microbial load, particularly fungi than cotyledon portion. Among the mycotoxins analyzed, aflatoxins (B₁, B₂, G₁ and G₂) were below detectable limits, while the seeds were devoid of Ochratoxin-A (OTA). Application of different doses of electron beam and gamma irradiation (0, 2.5, 5, 7.5, 10, 15 and 30 kGy) for decontamination purpose revealed significant dose-dependent decrease in the fungal contaminants (P<0.05). However, the contaminant yeasts could survive up to 10 kGy dose, which could be completely eliminated at 15 kGy. From the results obtained, a dose range between 10 and 15 kGy is recommended for complete decontamination, as these doses have also been shown earlier to have minimal effects on nutritional and functional properties of lotus seeds.     

Microwave‐Assisted Expedite Synthesis of 2‐Phenylimidazo[1,2‐a]pyridylquinoxalin‐2(1H)‐ones

An efficient methodology has been developed for the synthesis of quinoxalin‐2(1H)‐one derivatives of 2‐phenylimidazo[1,2‐a]pyridines by microwave‐irradiated Hinsberg heterocyclization between 2‐phenylimidazo[1,2‐a]pyridine‐3‐glyoxalates and o‐phenylenediamine using either montmorillonite K‐10 or Yb(OTf)₃ as catalysts. Montmorillonite K‐10 was proven to be an efficient catalyst for the heterocyclization reaction between sterically hindered glyoxalate and o‐phenylenediamine only under microwave conditions. The use of Yb(OTf)₃/tetrahydrofuran was also found to be an effective catalyst for the above chemical transformation among a series of Lewis acids screened under microwave conditions; however, comparatively lesser yields were obtained as compared with the use of montmorillonite K‐10.     

Insights into the mechanism of methionine oxidation catalyzed by metal (Cu2+, Zn2+, and Fe3+)—Amyloid beta (Aβ) peptide complexes: A computational study

In this DFT study, a mechanism of the oxidation of methionine (Met) amino acid residue catalyzed by the metal (Cu²⁺, Zn²⁺, and Fe³⁺) bound amyloid beta (Aβ) peptide has been proposed. Based on experimental information, two different mechanisms: (1) stepwise and (2) concerted mechanisms for this important process have been investigated. The B3LYP calculations suggest that in the stepwise mechanism, the two separate pathways leading to the same sulfoxide product [Met(O)] go through prohibitively high barriers of 27.3 and 35.1 kcal/mol, therefore it is ruled out. In the concerted mechanism, the Cu²⁺‐Aβ complex has been found to be the most efficient catalyst with the computed barrier of 14.3 kcal/mol. The substitutions of Cu²⁺ by Zn²⁺ and Fe³⁺ increase barriers to 19.6 and 16.9 kcal/mol, respectively and make the reaction thermodynamically less favorable. It was also found that, in comparison with the cysteine (Cys) residue, Met is more susceptible toward oxidation. Its substitution with Cys slightly increased the barrier to 15.8 kcal/mol for the Cu²⁺‐Aβ complex. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009