State-of-the-art computations of dipole moments using analytic gradients of high-level density-fitted coupled-cluster methods with focal-point approximations

Using the analytic derivatives approach, dipole moments of high-level density-fitted coupled-cluster (CC) methods, such as coupled-cluster singles and doubles (CCSD), and coupled-cluster singles and doubles with perturbative triples [CCSD(T)], are presented. To obtain the high accuracy results, the computed dipole moments are extrapolated to the complete basis set (CBS) limits applying focal-point approximations. Dipole moments of the CC methods considered are compared with the experimental gas-phase values, as well as with the common DFT functionals, such as B3LYP, BP86, M06-2X, and BLYP. For all test sets considered, the CCSD(T) method provides substantial improvements over Hartree–Fock (HF), by 0.076–0.213 D, and its mean absolute errors are lower than 0.06 D. Furthermore, our results indicate that even though the performances of the common DFT functionals considered are significantly better than that of HF, their results are not comparable with the CC methods. Our results demonstrate that the CCSD(T)/CBS level of theory provides highly-accurate dipole moments, and its quality approaching the experimental results. © 2019 Wiley Periodicals, Inc.     

Plantazolicin A and B: structure elucidation of ribosomally synthesized thiazole/oxazole peptides from Bacillus amyloliquefaciens FZB42

The structures of the ribosomally synthesized peptide antibiotics from Bacillus amyloliquefaciens FZB42, plantazolicin A and B, have been elucidated by high resolving ESI-MSMS, 2D (1)H-(13)C-correlated NMR spectroscopy as well as (1)H-(15)N-HMQC/(1)H-(15)N-HMBC NMR experiments. (15)N-labeling prior to the experiments facilitated the structure determination, unveiling a hitherto unusual number of thiazoles and oxazoles formed from a linear 14mer precursor peptide. This finding further extends the number of known secondary metabolites from B. amyloliquefaciens and represents a new type of secondary metabolites from the genus Bacillus.     

Grating coupler integrated photodiodes for plasmon resonance based sensing

In this work, we demonstrate an integrated sensor combining a grating-coupled plasmon resonance surface with a planar photodiode. Plasmon enhanced transmission is employed as a sensitive refractive index (RI) sensing mechanism. Enhanced transmission of light is monitored via the integrated photodiode by tuning the angle of incidence of a collimated beam near the sharp plasmon resonance condition. Slight changes of the effective refractive index (RI) shift the resonance angle, resulting in a change in the photocurrent. Owing to the planar sensing mechanism, the design permits a high areal density of sensing spots. In the design, absence of holes that facilitate resonant transmission of light, allows an easy-to-implement fabrication procedure and relative insensitivity to fabrication errors. Theoretical and experimental results agree well. An equivalent long-term RI noise of 6.3 × 10(-6) RIU/√Hz is obtained by using an 8 mW He-Ne laser, compared to a shot-noise limited theoretical sensitivity of 5.61 × 10(-9) RIU/√Hz. The device features full benefits of grating-coupled plasmon resonance, such as enhancement of sensitivity for non-zero azimuthal angle of incidence. Further sensitivity enhancement using balanced detection and optimal plasmon coupling conditions are discussed.     

Microscopic characterization of peptide nanostructures

Peptide-based nanomaterials have been utilized for various applications from regenerative medicine to electronics since they provide several advantages including easy synthesis methods, numerous routes for functionalization and biomimicry of secondary structures of proteins which leads to design of self-assembling peptide molecules to form nanostructures. Microscopic characterization at nanoscale is critical to understand processes directing peptide molecules to self-assemble and identify structure-function relationship of the nanostructures. Here, fundamental studies in microscopic characterization of peptide nanostructures are discussed to provide insights in widely used microscopy tools. In this review, we will encompass characterization studies of peptide nanostructures with modern microscopes, such as TEM, SEM, AFM, and advanced optical microscopy techniques. We will also mention specimen preparation methods and describe interpretation of the images.     

Solutions of the Duffin-Kemmer-Petiau equation in the presence of Hulthn potential in(1+2) dimensions for unity spin particles using the asymptotic iteration method

The relativistic Duffin-Kemmer-Petiau equation in the presence of Hulthn potential in(1+2) dimensions for spin-one particles is studied.Hence,the asymptotic iteration method is used for obtaining energy eigenvalues and eigenfunctions.     

Investigation of optimum condition in oxygen gas-assisted laser cutting

Laser cutting characteristics including power level and cutting gas pressure are investigated in order to obtain an optimum kerf width. The kerf width is investigated for a laser power range of 50–170 W and a gas pressure of 1–6 bar for steel and mild steel materials. Variation of sample thickness, material type, gas pressure and laser power on the average cut width and slot quality are investigated. Optimum conditions for the steel and mild steel materials with a thickness range of 1–2 mm are obtained. The optimum condition for the steel cutting results in a minimum average kerf width of 0.2 mm at a laser power of 67 W, cutting rate of 7.1 mm/s and an oxygen pressure of 4 bar. A similar investigation for the mild steel cutting results in a minimum average kerf width of 0.3 mm at the same laser power of 67 W, cutting rate of 9.5 mm/s, and an oxygen pressure of 1 bar. The experimental average kerf is about 0.3 mm, which is approximately equal to the estimated focused beam diameter of 0.27 mm for our focusing lens (f=4 cm and 100 W power). This beam size leads to a laser intensity of about 1.74×10⁹ W/m² at the workpiece surface. The estimated cutting rate from theoretical calculation is about 8.07 mm/s (1.0 mm thickness and 100 W power), which agrees with the experimental results that is 7.1 mm/s for 1.0 mm thickness of mild steel at the laser power of 88 W.     

An improved synthesis of Biginelli-type compounds via phase-transfer catalysis

3,4-Dihydropyrimidin-2(1H)-one, 3,4-dihydropyrimidin-2(1H)-thione, and 3,4-dihydropyrimidin-2(1H)-imine derivatives were synthesized by modified Biginelli cyclocondensation reaction in a time-efficient manner with near quantitative yields starting from appropriately substituted aromatic aldehyde, β-ketoester and either urea, thiourea or guanidine as constituent synthons using tetra-butyl ammonium bromide (TBAB) as catalyst for the first time.     

Electrochemical preparation of graphite intercalation compounds containing a cyclic amide, [CF2(CF2SO2)2N]

Graphite intercalation compounds (GICs) containing the cyclo-hexafluoropropane-1,3-bis(sulfonyl)amide anion, [CF₂(CF₂SO₂)₂N]⁻, are prepared for the first time. Stages 2 and 3 GICs are obtained by electrochemical oxidation of graphite in a nitromethane electrolyte. Gallery heights of 0.85-0.86 nm are determined by powder X-ray diffraction, and the intercalate anion orientation within the intercalate galleries is modeled using an energy minimized anion structure. GIC compositions are determined by thermogravimetric, fluorine and nitrogen analyses. The chemical preparation and bifluoride displacement reactions are compared with a GIC containing the linear bis(trifluoromethanesulfonyl)amide anion, [(CF₃SO₂)₂N]⁻.     

Dentin Phosphoprotein Mimetic Peptide Nanofibers Promote Biomineralization

Dentin phosphoprotein (DPP) is a major component of the dentin matrix playing crucial role in hydroxyapatite deposition during bone mineralization, making it a prime candidate for the design of novel materials for bone and tooth regeneration. The bioactivity of DPP‐derived proteins is controlled by the phosphorylation and dephosphorylation of the serine residues. Here an enzyme‐responsive peptide nanofiber system inducing biomineralization is demonstrated. It closely emulates the structural and functional properties of DPP and facilitates apatite‐like mineral deposition. The DPP‐mimetic peptide molecules self‐assemble through dephosphorylation by alkaline phosphatase (ALP), an enzyme participating in tooth and bone matrix mineralization. Nanofiber network formation is also induced through addition of calcium ions. The gelation process following nanofiber formation produces a mineralized extracellular matrix like material, where scaffold properties and phosphate groups promote mineralization. It is demonstrated that the DPP‐mimetic peptide nanofiber networks can be used for apatite‐like mineral deposition for bone regeneration.     

Treatment in Swelling Solutions Modifying Cellulose Fiber Reactivity – Part 1: Accessibility and Sorption

Of prime importance in reactions involving insoluble cellulosic fibers is the sorption of reagents, which is governed by their degrees of accessibility in substrates. Swelling treatments of cellulosics in alkali solutions alter substrate accessibility leading to changes in their reactivity. In this paper, the first of a two-part series, we collate and examine the results from various studies involving different techniques to characterize modifications in cellulosic fibers after swelling treatments in alkali solutions. Results from measurements of structure and accessibility in fibers with techniques such as water retention, inverse size exclusion chromatography (ISEC), iodine sorption, fiber diameters, and fiber-splitting propensities indicate that the influence of swelling treatments on fiber structure/accessibility is differs with alkali type. The results show that a non-uniform rather than uniform distribution of reagents within structures is a more accurate representation of reactions involving swollen cellulosic fibers. Hence, the observed changes in cellulose-fiber reactivity are governed by the degrees of fiber swelling, and reagent sorption and accessibility during swelling treatments.