Growth,structural, optical and thermal properties of potential THz material: N,N-dimethylamino-N′-methylstilbazolium 4-styrenesulphonate

N,N-dimethylamino-N′-methylstilbazolium 4-styrenesulphonate (DSSS), was synthesized by metathesization of the N,N-dimethylamino-N′-methylstilbazolium iodide (DASI) salt with sodium 4-styrenesulfonate. The growth of DSSS single crystal was carried out by adopting the slope nucleation coupled slow evaporation method. DSSS crystals with size 4×2×1 mm³ were grown within a period of 15 days. The structure and composition of the crystal were studied by single crystal X-ray diffraction, CHN and nuclear magnetic resonance (NMR) analyses. The FTIR results reveal the existence of the vinyl groups and their corresponding vibrational modes. The melting point and thermal behavior of DSSS were investigated using differential scanning calorimetric (DSC) and thermogravimetric analyses (TGA).     

Nanotube-grafted polyacrylamide hydrogels for electrophoretic protein separation

Multiwalled carbon nanotube-modified polyacrylamide gels have been employed for the electrophoretic separation of proteins. Two approaches are compared in this investigation, one using nanotubes only as fillers inside the gel matrix and the other using nanotubes as catalyst for polymerization of acrylamide. In both the cases, polymerization of acryl-amide/bisacrylamide has been carried out in situ in the presence of nanotubes dispersed in the gel buffer containing monomer and cross-linker. In the former case, initiator and catalyst have been added after ultrasonication of nanotubes in the gel buffer mixture where the nanotubes play the role of filler. On the other hand, the second approach precludes use of catalyst and involves addition of initiator alone during ultrasonication of nanotubes in the gel buffer containing monomer and cross-linker, which leads to the formation of nanotube-grafted gel after 25 min. When nanotubes are used as a catalyst instead of N,N,N',N'-tetramethylethylenediamine, pore size distribution of the gel matrix and linearity of molecular weight calibration plots are found to be improved. In addition, other issues associated with the use of an external catalyst like handling the moisture-sensitive and corrosive reagent and associated irreproducibility are addressed in this approach.     

UV irradiation affects melanocyte stimulatory activity and protein binding of piperine

Piperine, the major alkaloid of black pepper (Piper nigrum L.; Piperaceae), stimulates melanocyte proliferation and dendrite formation in vitro. This property renders it a potential treatment for the skin depigmentation disorder vitiligo. However, piperine does not stimulate melanin synthesis in vitro, and treatments based on this compound may therefore be more effective with concomitant exposure of the skin to ultraviolet (UV) radiation or sunlight. The present study investigated the effect of UVA and simulated solar radiation (SSR) on the chemical stability of piperine, its melanocyte stimulatory effects and its ability to bind protein and DNA. Chromatographic and spectroscopic analysis confirmed the anticipated photoisomerization of irradiated piperine and showed the absence of any hydrolysis to piperinic acid. Isomerization resulted in the loss of ability to stimulate proliferation of a mouse melanocyte cell line, and to bind to human serum albumin. There was no evidence of DNA binding by piperine either before or after irradiation, showing the absence of photoadduct formation by either piperine or its geometric isomers. This is unlike the situation with psoralens, which form DNA adducts when administered with UVA in treating skin diseases. The present study suggests that exposure to bright sunlight should be avoided both during active application of piperine to the skin and in the storage of piperine products. If UVA radiation is used with piperine in the treatment of vitiligo, application of the compound and irradiation should be staggered to minimize photoisomerization. This approach is shown to effectively induce pigmentation in a sparsely pigmented mouse strain.     

Are deterministic expert systems for computer-assisted structure elucidation obsolete?

Expert systems for spectroscopic molecular structure elucidation have been developed since the mid-1960s. Algorithms associated with the structure generation process within these systems are deterministic; that is, they are based on graph theory and combinatorial analysis. A series of expert systems utilizing 2D NMR spectra have been described in the literature and are capable of determining the molecular structures of large organic molecules including complex natural products. Recently, an opinion was expressed in the literature that these systems would fail when elucidating structures containing more than 30 heavy atoms. A suggestion was put forward that stochastic algorithms for structure generation would be necessary to overcome this shortcoming. In this article, we describe a comprehensive investigation of the capabilities of the deterministic expert system Structure Elucidator. The results of performing the structure elucidation of 250 complex natural products with this program were studied and generalized. The conclusion is that 2D NMR deterministic expert systems are certainly capable of elucidating large structures (up to about 100 heavy atoms) and can deal with the complexities associated with both poor and contradictory spectral data.     

Glycosynthase-mediated synthesis of glycosphingolipids

Glycosphingolipids play crucial roles in virtually every stage of the cell cycle, and their clinical administration has been proposed as a treatment for Alzheimer's, Parkinson's, stroke, and a range of other conditions. However, lack of supply has severely hindered testing of this potential. A novel glycosynthase-based synthetic strategy is demonstrated, involving a mutant of an endoglycoceramidase in which the catalytic nucleophile has been ablated. This mutant efficiently couples a range of glycosyl fluoride donors with a range of sphingosine-based acceptors in yields around 95%. This technology opens the door to large-scale production of glycosphingolipids and, thus, to clinical testing.     

Spectral characteristics of 2-amino-3-benzyloxy pyridine: Effects of solvents,pH, and β-cyclodextrin

Spectral characteristics of 2-amino-3-benzyloxypyridine (2ABP) has been studied in solvents of different polarity, pH, and β-cyclodextrin (β-CD) and compared with 2-amino pyridine (2AP). The inclusion complex of both amino pyridine (AP) molecules with β-CD are analysed by UV-visible, fluorimetry, FTIR, ¹H NMR, SEM and AM1 methods. The solvent studies shows no significant shift observed in absorption maxima between both AP molecules, but in the excited state a slight red shift is noticed in 2ABP than in 2AP which indicates that the addition of benzyloxy group in 2AP does not effectively increase the resonance interaction in 2ABP. The regular red shift observed in acidic pH solutions suggests intramolecular proton transfer (IPT) interaction in both molecules. β-CD studies shows that in pH ∼7, 2ABP forms 1: 2 inclusion complex from 1: 1 inclusion complex and 1: 1 inclusion complex is formed in pH ∼ 1. In pH ∼ 7, a red shift observed in 2ABP with lower β-CD concentration suggests aromatic ring encapsulated in the β-CD cavity and blue shift noticed at higher β-CD concentrations indicates pyridine ring encapsulated in the β-CD cavity.     

Unusual spectral shifts on fast violet-B and benzanilide: Effect of solvents, pH and β-cyclodextin

The absorption and fluorescence spectra of fast violet-B (FVB) and benzanilide (BA) have been analysed in different solvents, pH and β-cyclodextrin. The inclusion complex of FVB with β-CD is investigated by UV–visible, fluorimetry, AM 1, FTIR and SEM. The absorption maximum of FVB (anilino substitution) is red shifted than that of BA, but the benzoyl substitution hardly changed the ground state structure of BA. Compared to BA, the emission maxima of FVB largely blue shifted in cyclohexane and aprotic solvents, but red shifted in protic solvents and the longer wavelength maxima in FVB is due to the intramolecular charge transfer (TICT). In BA, the normal emission originates from a locally excited state and the longer wavelength band due to intramolecular proton transfer in non-polar/aprotic solvents and in protic solvents it is due to TICT state. β-CD studies reveal that, FVB forms 1:2 complex from 1:1 complex and BA forms 1:2 complex with β-CD.     

Steady state dynamics of a moving model cell

Crawling cell motility results due to treadmilling of a polymerized actin network at the leading edge. Steady state dynamics of a moving cell are governed by actin concentration profiles across the cell. Branching of new filaments implicating Arp2/3 and capping of existing filaments with capZ or Gelsolin are central to the robust functioning of the actin network. Using computer simulations, steady state concentration profiles of globular actin (G actin) and filamentous actin (F actin) are computed. The profiles are in agreement with experimentally observed ones. Simulations unveil that there is an optimal capping and branching rate for which the velocity of the model cell is maximum. Our simulations also indicate that the capping of actin filaments results in an increase in nucleation of new filaments by Arp2/3-induced branching and is in agreement with a recently observed monomer gating model. We observe that Arp2/3 and capping protein exhibit a functional antagonism with respect to the actin network treadmilling.     

CuAAC Click Reactions in the Gas Phase: Unveiling the Reactivity of Bis‐Copper Intermediates

Copper‐catalysed azide alkyne cycloaddition (CuAAC) has been considered a breakthrough transformation over the last 15 years. Its debated mechanism arouses continuously growing interest. By means of a mass spectrometer modified ad hoc, the entire catalytic cycle of CuAAC reaction has been investigated in the gas phase. Ion‐molecule reactions were performed inside the mass spectrometer to reproduce step‐by‐step, at a molecular level, the complete catalytic cycle of the click reaction. We successfully challenged the reactivity of elusive mono‐ and bis‐copper intermediates by ion‐molecule reactions leading to the production of mass‐characterized triazole products, paving the way for detailed energetic studies to be performed in the gas phase. The structures of the relevant species, calculated at a DFT level, helped rationalise our experimental results.