Determination of <Emphasis Type="Italic">N</Emphasis>-nitrosodiethanolamine in cosmetic products by LC–MS–MS

We have developed and validated in-house a liquid chromatography and mass spectrometry (LC-MS-MS) method for determination of N-nitrosodiethanolamine (NDELA) in cosmetics. The sample is diluted with water and then a C18 clean-up is performed. The average recovery of NDELA is 88.3%, range 48.3-112.7%, and the limit of detection is 22.8 microg kg-1. The repeatability is 7.6%, and the intermediate precision is 8.7%. Surveys were carried out in the Netherlands in September and October 2002 to determine the quantities of NDELA in cosmetics marketed in the Netherlands. The LC-MS-MS method was used to determine the NDELA content of 140 cosmetic products including shower gels, hair oils, shampoos and conditioners, cream and foam baths, mud baths, scrubs, creme and other soaps, and body washes. NDELA at levels ranging from 23 to 992 microg kg-1 was found in 35 cosmetic products.     

The max-flow problem with parametric capacities

In this paper we present a comprehensive analysis of the max-flow problem with n parametric capacities, and give the basis for an algorithm to solve it. In particular we give a method for finding the max-flow value as a function of the parameters, and max-flows for all parameter points, in terms of max-flow values to problems at certain key parameter points. In the problem with nonzero lower bounds on the arc flows, we derive a set of linear constraints whose solution set is identical to the set of all feasible parameter points.The intrinsic difficulty of the problem is compared with that of the general multiparametric linear programming problem, and thus light is shed on the difficulty of the latter problem, whose complexity is currently unknown.     

Structure-based design of estrogen receptor-beta selective ligands

We present the structure-based optimization of a series of estrogen receptor-beta (ERbeta) selective ligands. X-ray cocrystal structures of these ligands complexed to both ERalpha and ERbeta are described. We also discuss how molecular modeling was used to take advantage of subtle differences between the two binding cavities in order to optimize selectivity for ERbeta over ERalpha. Quantum chemical calculations are utilized to gain insight into the mechanism of selectivity enhancement. Despite only two relatively conservative residue substitutions in the ligand binding pocket, the most selective compounds have greater than 100-fold selectivity for ERbeta relative to ERalpha when measured using a competitive radioligand binding assay.     

Stereoelectronic Control of Additions of Vinylmagnesium Bromide to 1-Methyland 3-Methylpentacyclo[5.4.0.02,6.03,10.05.9]undecane-8,11-diones and to 1-Methylhexacyclo[10.2.1.0.02,11.04,9.04,14.09,13]pentadeca-5,7-diene-3,10-dione

Grignard addition of excess vinylmagnesium bromide to 1-methyland 3-methylpentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane-8,11-diones (1a and 1b, respectively) and to 1-methylhexacyclo[10.2.1.0^2,11.0^4,9.0^4,14.0^9,13]pentadeca-5,7-diene-3,10-dione (4) each proceed regiospecifically to afford a single hemiketal adduct (i.e., 2a, 3a, and 5a, respectively). The structure of each of the three reaction products was established unequivocally via application of X-ray crystallographic methods. Relative energies for the model transition states obtained from geometry optimizations at the Hartree–Fock level of theory in basis set 3-21G(d) indicate that these reactions are kinetically controlled.     

Tailored thioxanthone‐based photoinitiators for two‐photon‐controllable polymerization and nanolithographic printing

Printing of high‐resolution three‐dimensional nanostructures utilizing two‐photon polymerization has gained significant attention recently. In particular, isopropyl thioxanthone (ITX) has been implemented as a photoinitiator due to its capability of initiating and depleting polymerization on demand, but new photoinitiating materials are still needed in order to reduce the power requirements for the high‐throughput creation of 3D structures. To address this point, a suite of new thioxanthone‐based photoinitiators were synthesized and characterized. Then two‐photon polymerization was performed using the most promising photoinitiating molecule. Importantly, one of the initiators, 2,7‐bis[(4‐(dimethylamino)phenyl ethynyl)‐9H‐thioxanthen‐9‐one] (BDAPT), showed a fivefold improvement in the writing threshold over the commonly used ITX molecule. To elucidate the fundamental mechanism, the excitation and inhibition behavior of the BDAPT molecule were evaluated using density functional theory (DFT) calculations, low‐temperature phosphorescence spectroscopy, ultra‐fast transient absorption spectroscopy, and the two‐photon Z‐scan spectroscopic technique. The improved polymerization threshold of this new photoinitiator presents a clear pathway for the modification of photoinitiators in 3D nanoprinting. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1462–1475     

Evaporative micro-particle self assembly influenced by capillary evacuation

As evaporation does not incur energy introduction, the droplet coffee-stain patterning approach is attractive for biochemical tests conducted in the field or in third world environments. A practical strategy uses chemically functionalized microbeads for the coffee stain deposition process. From an application perspective, it will be necessary to minimize the coffee stain deposition time, as evaporation, depending on the volume of the droplet, can be a slow process. The introduction of a porous media will generate a capillary flow (or wicking) that removes any remnant liquid in the droplet, thus permitting it to be done inexpensively and in the field. Using optical profilometry, we were able to establish that polystyrene microspheres developed more copious and defined single ring coffee depositions than silica of the same size and concentration in a suspension. In analyzing the droplet capillary evacuation process with a porous media, we found the liquid bridge formed during the later stages to rupture and leave behind some liquid material for a second stage evaporation process. This was responsible for a two ring structure that was more visible with silica microspheres. A high degree of hysteresis of the contact angle was found to develop at the contact line in which values below 5° could be achieved. Dynamic observations showed the copious and dense packing of polystyrene particles to be more resistant to ring break up from the evacuation flow. Nevertheless, erosion of the back array portions of the ring was evident notwithstanding either type of microsphere used.     

Experimental and theoretical study of rotationally inelastic diffraction of D2 from NiAl(110)

We present a detailed experimental and theoretical study of elastic and rotationally inelastic diffraction of D(2) from NiAl(110) in the energy range 85-150 meV. The experiments were performed using a high-resolution, fixed angle geometry apparatus. Quantum and classical dynamical calculations were performed by using a six-dimensional potential energy surface constructed upon interpolation of a set of DFT (density functional theory) data. We show that, although elastic diffraction peak intensities are accurately described by theory in the whole range of incidence energies and angles explored, significant discrepancies are obtained for RID peaks, especially for those involving rotational initial states with j(i) > 0. Possible reasons for this discrepancy are discussed.     

A ratiometric CdSe/ZnS nanocrystal pH sensor

The development of a reversible chemical sensor based on a CdSe/ZnS nanocrystal (NC) is described. Signal transduction is accomplished by fluorescence resonance energy transfer (FRET) between the NC and a fluorescent pH-sensitive squaraine dye attached to the surface of the NC. The efficiency of FRET, and consequently the relative intensity of NC and dye emissions, is modulated with the pH-dependent absorption cross section of the squaraine dye. The design of a NC sensor based on FRET results in a ratiometric sensor since the emission intensities of dye and NC may be referenced to the isosbestic point between NC and dye emissions. The ratiometric approach allows sensing to be performed, regardless of issues surrounding collection efficiency (scattering environment, light fluctuations, etc.) and dye:NC loadings.