Parametrically shaped femtosecond pulses in the nonlinear regime obtained by reverse propagation in an optical fiber

We present the experimental realization of a method to generate predetermined, arbitrary pulse shapes after transmission through an optical fiber in the nonlinear regime. The method is based on simulating the reverse propagation of the desired pulse shape in the fiber. First, linear and nonlinear parameters of a single-mode step-index fiber required for the simulation are determined. The calculated pulse shapes are then generated in a pulse shaper.     

Tale of the Breslow intermediate,a central player in N-heterocyclic carbene organocatalysis: then and now

N-Heterocyclic carbenes (NHCs) belong to the popular family of organocatalysts used in a wide range of reactions, including that for the synthesis of complex natural products and biologically active compounds. In their organocatalytic manifestation, NHCs are known to impart umpolung reactivity to aldehydes and ketones, which are then exploited in the generation of homoenolate, acyl anion, and enolate equivalents suitable for a plethora of reactions such as annulation, benzoin, Stetter, Claisen rearrangement, cycloaddition, and C–C and C–H bond functionalization reactions and so on. A common thread that runs through these NHC catalyzed reactions is the proposed involvement of an enaminol, also known as the Breslow intermediate, formed by the nucleophilic addition of an NHC to a carbonyl group of a suitable electrophile. In the emerging years of NHC catalysis, enaminol remained elusive and was largely considered a putative intermediate owing to the difficulties encountered in its isolation and characterization. However, in the last decade, synergistic efforts utilizing an array of computational and experimental techniques have helped in gaining important insights into the formation and characterization of Breslow intermediates. Computational studies have suggested that a direct 1,2-proton transfer within the initial zwitterionic intermediate, generated by the action of an NHC on the carbonyl carbon, is energetically prohibitive and hence the participation of other species capable of promoting an assisted proton transfer is more likely. The proton transfer assisted by additives (such as acids, bases, other species, or even a solvent) was found to ease the kinetics of formation of Breslow intermediates. These important details on the formation, in situ detection, isolation, and characterization of the Breslow intermediate are scattered over a series of reports spanning well over a decade, and we intend to consolidate them in this review and provide a critical assessment of these developments. Given the central role of the Breslow intermediate in organocatalytic reactions, this treatise is expected to serve as a valuable source of knowledge on the same.

Molecular insights on the formation, detection, and even isolation of the Breslow intermediate, which is the most important species in N-heterocyclic carbene (NHC) catalysis, as obtained from experimental and computational studies, are presented.     

α‐Amino Acid‐Isosteric α‐Amino Tetrazoles

The synthesis of all 20 common natural proteinogenic and 4 otherα‐amino acid‐isosteric α‐amino tetrazoles has been accomplished, whereby the carboxyl group is replaced by the isosteric 5‐tetrazolyl group. The short process involves the use of the key Ugi tetrazole reaction followed by deprotection chemistries. The tetrazole group is bioisosteric to the carboxylic acid and is widely used in medicinal chemistry and drug design. Surprisingly, several of the common α‐amino acid‐isosteric α‐amino tetrazoles are unknown up to now. Therefore a rapid synthetic access to this compound class and non‐natural derivatives is of high interest to advance the field.     

Cis-coordination of the chromate anions in helical Co/Ni block-type polymeric systems. Structural and spectroscopic characteristics of catena(μ-CrO4-O,O′)[Co(HIm)3H2O] and catena(μ-CrO4-O,O′)[Co0.43Ni0.57(HIm)3H2O]

Two polymeric complexes: catena(μ-CrO₄-O,O′)[Co(HIm)₃H₂O] (1) and catena(μ-CrO₄-O,O′)[Co_0.43Ni_0.57(HIm)₃H₂O] (2) (where HIm=imidazole) with a cis-bridging coordination mode of the CrO₄ ²⁻ anion have been synthesized and characterized by X-ray and spectroscopic methods. These crystals were isolated from nine systems of varying reagent molar ratios and three excluding anions: Cl⁻, NO₃ ⁻ and SO₄ ²⁻ exclusively as mer [M(HIm)₃O₃]-type isomers. The unit cell of these isostructural complexes (monoclinic crystal system P2₁ /n) contains two independent helixes, left- and right handed, stabilized by intrahelical and interhelical hydrogen bonding and π–π interaction between pairs of the imidazole rings from neighbouring helixes. The Raman spectra at 77 K of 1 and 2 deconvoluted into lorentzian components revealed the block-type polymeric structure of the complexes. Moreover, the solution studies at millimolar concentrations of 1 and 2 indicated their complete decomposition in water. Four K electronic spectral analysis of the crystals (band deconvolution into gaussian components) enhanced with the data obtained in the polarized light allowed for assignment of the bands to the respective d–d transition (D_4h symmetry). It was found that the metallic centres are independently absorbing species, which supports the suggestion of a block-type structure of the polymers. The respective crystal field parameters for Co and Ni were calculated.     

Tamarindus indica mucilage and its acrylamide-grafted copolymer as flocculants for removal of dyes

The application of Tamarindus indica seed mucilage (Tam), a food grade polysaccharide, and its acrylamide grafted copolymer as flocculants was assessed for the first time for removal of various types of dyes from model textile wastewater containing azo, basic, and reactive dyes. Acrylamide grafted T. indica mucilage (Tam-g-PAM) was obtained by ceric ion initiated polymerization technique. A series of contact time experiments were conducted to assess the system variables such as concentrations of mucilage and dyes and pH. These flocculants reduce the dye concentration by flocculation and settling. The grafted copolymer, Tam-g-PAM showed better results for dye removal. The optimal flocculant concentration, which was required to effect flocculation, was independent of dye concentration within the range examined. Both the flocculants performed better for removal of azo dyes than for reactive and basic dyes.     

Photopolymers for Rapid Prototyping of Soluble Mold Materials and Molding of Cellular Biomaterials

To substitute cross-linked photopolymers in rapid prototyping of mold materials and therefore extend the range of materials which can be casted, organo-soluble photopolymers were developed. Branched bisalkylacrylamides were suitable as base component for such formulations, due to their high reactivity, good mechanical properties, and excellent solubility of the formed polymers. These molding materials were used to prepare cellular biocompatible materials which could be used as bone replacement materials. Biocompatible crosslinkers based on methacrylates from hydrolyzed gelatine or lactic acid ethyleneglycol blockcopolymers and commercially available reactive diluents are the base components of such a formulation. Biocompatibility was investigated by osteoblast-like cells. Cellular biocompatible parts were obtained by thermal polymerization in soluble mould materials prepared by 3D-photoshaping.     

Rime samples characterization and comparison using classical and fuzzy principal components analysis

The main objective of this paper is to introduce principal component analysis and two robust fuzzy principal component algorithms as useful tools in characterizing and comparing rime samples collected in different locations in Poland (2004–2007). The efficiency of the applied procedures was illustrated on a data set containing 108 rime samples and concentration of anions, cations, HCHO, as well as pH and conductivity. The fuzzy principal component algorithms achieved better results mainly because they are more compressible than classical PCA and very robust to outliers. For example, a three component model, fuzzy principal component analysis-first component (FPCA-1) accounts for 62.37% of the total variance and fuzzy principal component analysis-orthogonal (FPCA-o) 90.11%; PCA accounts only for 58.30%. The first two principal components explain 51.41% of the total variance in the case of FPCA-1 and 79.59% in the case of FPCA-o as compared to only 47.55% for PCA. As a direct consequence, PCA showed only a partial differentiation of rime samples onto the plane or in the space described by different combination of two or three principal components, whereas a much sharper differentiation of the samples, regarding their origin and location, is observed when FPCAs are applied.      

Scaling law of poly(ethylene oxide) chain permeation through a nanoporous wall

This paper presents a study of the permeation of poly(ethylene oxide) (PEO) chains through the nanoporous wall of hollow polymeric capsules prepared by self-assembly of polyelectrolytes. We employ the method of pulsed field gradient (PFG) NMR diffusion to distinguish chains in different sites, i.e., in the capsule interior and free chains in the dispersion, by their respective diffusion coefficient. From a variation of the observation time, the time scale of the molecular exchange between both sites and thus the permeation rate constant is extracted from a two-site exchange model. Permeation rate constants show two different regimes with a different dependence on chain length. This suggests a transition between two different mechanisms of permeation as the molecular weight is increased. In either regime, the permeation time can be described by a scaling law tau approximately N (b) , with b = (4)/ 3 for short chains and b = (1)/ 3 for long chains. We discuss these exponents, which clearly differ from the theoretical predictions for chain translocation.     

Molecular dynamics modeling in quantum chemical calculations. Optical absorption spectra of 1,3-Dimethyl-1H-Pyrazolo[3,4-b]quinoline derivatives

Paper presents the quantum chemical modeling of the optical absorption spectra of 6-fluoro, 6-bromo, 7-trifluoromethyl, 6-cyano and 6-carboethoxy derivatives of 1,3-Dimethyl-1H-Pyrazolo[3,4-b]quinoline. The calculations are performed by means of the semiempirical quantum chemical methods (AM1 or PM3) in combination with molecular dynamics (MD) simulations at T=300 K. It is shown that a particular rotational dynamics of the methyl, trifluoromethyl or ethyl groups practically does not influence the optical absorption in the spectral range 200-500 nm whereas broadening of absorption bands may be well reproduced within MD simulations including all types of nuclei vibrations. The results of calculations are compared with the measured spectra of optical absorption. The quantum chemical method AM1 in combination with MD simulations gives for all dyes the best agreement between the calculated and measured spectral positions of the first absorption band (absorption threshold).     

Study of the role of ceramic filler in composite gel electrolytes based on microporous polymer membranes

The presented contribution aims at reconsidering the role of filler in affecting the ionic transport in composite gel electrolytes for Li-ion cells based on microporous polymer membranes. The gels have been prepared by swelling thin PVdF/HFP membranes either with conventional liquid electrolyte or with pure propylene carbonate solvent. The membranes contained dispersed submicron-size modified silica filler added in a wide range of weight ratios. The effect of filler content on the kinetics of liquid phase absorption and evaporation from the composite membranes, as well as on the conductivity of the corresponding gel electrolytes, has been studied and discussed in terms of the “colloidal” and “soggy sand” electrolyte concepts. It has been found that conductivity increase of composite gels is not directly correlated with the liquid electrolyte uptake. On this basis it is concluded that important part of ionic transport in this type of composite gel polymer electrolytes is realized on the filler grain boundaries, through overlapping space charge layers of the silica grains.