Measurement Bias on Nanoparticle Size Characterization by Asymmetric Flow Field-Flow Fractionation Using Dynamic Light-Scattering Detection

In this work, we highlight the influence of the particle–particle interaction on the retention behavior in asymmetric flow field-flow fractionation (A4F) and the misunderstanding considering the size determination by a light-scattering detector (static and dynamic light scattering) by comparing fullerene nanoparticles to similar sized polystyrene nanoparticle standards. The phenomena described here suggest that there are biases in the hydrodynamic size and diffusion determination induced by particle–particle interactions, as characterized by their virial coefficient. The dual objectives of this paper are to (1) demonstrate the uncertainties resulting from the current practice of size determination by detectors coupled to an A4F system and (2) initiate a discussion of the effects of particle–particle interactions using fullerene nanoparticles on their characterization as well as their origins. The results presented here clearly illustrate that the simple diffusion coefficient equation that is generally used to calculate the hydrodynamic size of nanoparticles (NPs) cannot be considered for whole fractograms according to their size distribution. We tried to identify particle interactions that appear during fractionation and demonstrated using the fully developed diffusion coefficient equation. We postulate that the observed interaction-dependent retention behavior may be attributed to differences in the virial coefficient between NPs and between NPs and the accumulation wall (membrane surface) without quantifying it. We hope that our results will stimulate discussion and a reassessment of the size determination procedure by A4F-LS to more fully account for all the influential material parameters that are relevant to the fractionation of nanoscale particles by A4F.     

Isomeric effects on the self‐assembly of a plausible prebiotic nucleoside analogue: A theoretical study

The self‐assembly properties of N(9)‐(2,3‐dihydroxypropyl adenine) (DHPA), a plausible prebiotic nucleoside analogue of adenosine, were investigated using density functional theory. Two different isomers were considered, and it is found that while both isomers can form a variety of structures, including chains, one of them is also able to form cages and helixes. When these results were put in the context of substrate supported molecular self‐assembly, it is concluded that gas‐phase self‐assembly studies that consider isomer identity and composition not only can aid interpreting the experimental results, but also reveal structures that might be overlooked otherwise. In particular, this study suggest that a double‐helical structure made of DHPA molecules which could have implications in prebiotic chemistry and nanotechnology, is stable even at room temperature. For example electrical properties (energy gap of 4.52eV) and a giant permanent electrical dipole moment (49.22 Debye) were found in our larger double‐helical structure (3.7 nm) formed by 14 DHPA molecules. The former properties could be convenient for construction of organic dielectric‐based devices.     

Absolute Configuration of Two New 6‐Alkylated α‐Pyrones (=2H‐Pyran‐2‐ones) from Ravensara crassifolia

The stem bark CH₂Cl₂ extract of Ravensara crassifolia showed antifungal activity against the phytopathogenic fungus Cladosporium cucumerinum in a bioautographic TLC assay. Activity‐guided fractionation afforded two new α‐pyrones : (6S)‐5,6‐dihydro‐6‐[(2R)‐2‐hydroxy‐6‐phenylhexyl]‐2H‐pyran‐2‐one ( 1 ) and (6R)‐6‐[(4R,6R)‐4,6‐dihydroxy‐10‐phenyldec‐1‐enyl]‐5,6‐dihydro‐2H‐pyran‐2‐one ( 2 ). Their structures and absolute configurations were established by NMR spectroscopy, chemical methods, and CD spectroscopy. The antifungal activity against C. cucumerinum was determined for both compounds.     

HTMoL: full-stack solution for remote access,visualization, and analysis of molecular dynamics trajectory data

Research on biology has seen significant advances with the use of molecular dynamics (MD) simulations. The MD methodology enables explanation and discovery of molecular mechanisms in a wide range of natural processes and biological systems. The need to readily share the ever-increasing amount of MD data has been hindered by the lack of specialized bioinformatic tools. The difficulty lies in the efficient management of the data, i.e., in sending and processing 3D information for its visualization. In this work, we present HTMoL, a plug-in-free, secure GPU-accelerated web application specifically designed to stream and visualize MD trajectory data on a web browser. Now, individual research labs can publish MD data on the Internet, or use HTMoL to profoundly improve scientific reports by including supplemental MD data in a journal publication. HTMoL can also be used as a visualization interface to access MD trajectories generated on a high-performance computer center directly. Furthermore, the HTMoL architecture can be leveraged with educational efforts to improve learning in the fields of biology, chemistry, and physics.     

Equilibrium and fractal-like kinetic studies of the sorption of acid and basic dyes onto watermelon shell (<Emphasis Type="Italic">Citrullus vulgaris</Emphasis>)

In the present study, batch experiments were used to determine adsorption characteristics of Watermelon Shell Biosorbent (WSB) for the uptake of anionic and cationic dyes from aqueous solution. Various factors such as initial dye concentration, adsorbent dosage, pH, contact time and temperature were systematically investigated and discussed. WSB was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and Fourier Transform Infrared Spectroscopy. The adsorption kinetics was best described by Elovich and Diffusion-Chemosorption models for Basic red 2 (BR2) (cationic dye) and Orange G (OG) (anionic dye) respectively. However, the fractional time index “α” and non-integer “n” order by Fractal-like pseudo-first order kinetic affirmed that the mechanism of interaction of both dyes with WSB was by chemical reaction. The applicability of four adsorption isotherm models for the present system was tested. The equilibrium data were found to be well represented by the Extended Langmuir isotherm equation. The monolayer adsorption capacity of WSB for BR2 and OG adsorption was found to be 125 and 27 mg/g, respectively. The effect of temperature on the adsorption process was also investigated and the values of thermodynamic parameters ΔG°, ΔH° and ΔS° revealed that the adsorption system was spontaneous.     

“α-Methylene-γ-phostones”1 (5,5-di- and 5-monoalkyl-2-methoxy-3-methylene-1,2-oxaphospholan-2-ones). A phosphorus analog of the one-step reformatsky synthesis of α-methylene-γ-butyrolactones from ketones and aldehydes

The first synthesis of “α-methylene-γ-phostones” (propylphostonates) using dimethyl bromo-3-propen-2 ylphosphonate and ketones and aldehydes, in the presence of zinc, is described.     

First measurements of the HCFC-142b trend from atmospheric chemistry experiment (ACE) solar occultation spectra

The first measurement of the HCFC-142b (CH₃CClF₂) trend near the tropopause has been derived from volume mixing ratio (VMR) measurements at northern and southern hemisphere mid-latitudes for the 2004–2008 time period from spaceborne solar occultation observations recorded at 0.02 cm⁻¹ resolution with the ACE (atmospheric chemistry experiment) Fourier transform spectrometer. The HCFC-142b molecule is currently the third most abundant HCFC (hydrochlorofluorocarbon) in the atmosphere and ACE measurements over this time span show a continuous rise in its volume mixing ratio. Monthly average measurements at northern and southern hemisphere mid-latitudes have similar increase rates that are consistent with surface trend measurements for a similar time span. A mean northern hemisphere profile for the time span shows a near constant VMR at 8–20 km altitude range, consistent on average for the same time span with in situ results. The nearly constant vertical VMR profile also agrees with model predictions of a long lifetime in the lower atmosphere.     

Modal decomposition method for modeling the interaction of Lamb waves with cracks

The interaction of the low-order antisymmetric (a0) and symmetric (s0) Lamb waves with vertical cracks in aluminum plates is studied. Two types of slots are considered: (a) internal crack symmetrical with respect to the middle plane of the plate and (b) opening crack. The modal decomposition method is used to predict the reflection and transmission coefficients and also the through-thickness displacement fields on both sides of slots of various heights. The model assumes strip plates and cracks, thus considering two-dimensional plane strain conditions. However, mode conversion (a0 into s0 and vice versa) that occurs for single opening cracks is considered. The energy balance is always calculated from the reflection and transmission coefficients, in order to check the validity of the results. These coefficients together with the through-thickness displacement fields are also compared to those predicted using a finite element code widely used in the past for modeling Lamb mode diffraction problems. Experiments are also made for measuring the reflection and transmission coefficients for incident a0 or s0 lamb modes on opening cracks, and compared to the numerical predictions.     

Theory of Extended Solutions¶for Fast-Diffusion Equations¶in Optimal Classes of Data.¶Radiation from Singularities

This paper is devoted to constructing a general theory of nonnegative solutions for the equation called “the fast-diffusion equation” in the literature. We consider the Cauchy problem taking initial data in the set ?⁺ of all nonnegative Borel measures, which forces us to work with singular solutions which are not locally bounded, not even locally integrable. A satisfactory theory can be formulated in this generality in the range 1 > m > m _c = max {(N? 2)/N,0}, in which the limits of classical solutions are also continuous in ? ^N as extended functions with values in ?₊∪{∞}. We introduce a precise class of extended continuous solutions ? _c and prove (i) that the initial-value problem is well posed in this class, (ii) that every solution u(x,t) in ? _c has an initial trace in ?⁺, and (iii) that the solutions in ? _c are limits of classical solutions. Our results settle the well-posedness of two other related problems. On the one hand, they solve the initial-and-boundary-value problem in ?× (0,∞) in the class of large solutions which take the value u=∞ on the lateral boundary x∈??, t>0. Well-posedness is established for this problem for m _c < m > 1 when ? is any open subset of ? ^N and the restriction of the initial data to ? is any locally finite nonnegative measure in ?. On the other hand, by using the special solutions which have the separate-variables form, our results apply to the elliptic problem Δf=f ^q posed in any open set ?. For 1 > q > N/(N? 2)₊ this problem is well posed in the class of large solutions which tend to infinity on the boundary in a strong sense. As is well known, initial data with such a generality are not allowed for m≧ 1. On the other hand, the present theory fails in several aspects in the subcritical range 0> m≦m _c , where the limits of smooth solutions need not be extended-continuously.