Supramolecular helical fluid columns from self-assembly of homomeric dipeptides

Herein, we demonstrate that with the widespread theme of residue patterning and stereochemical restraints of self-complimenting proteinogenic amino acids, a new and rich class of homomeric dipeptides exhibiting two-dimensional fluid aggregates with hierarchical ordering can be obtained. In particular, a simple way of achieving a class of functional dipeptides, wherein the first and the second residues chosen are L-/D-alanines and L-/D-leucines, has been accomplished. The supramolecules synthesized can be regarded as intermediates between polycatenars and taper-shaped amphiphiles because they possess two lipophilic segments interlinked by a peptide unit (spacer). Two pairs of enantiomers and their respective diastereomers derived from these amino acids are evidenced to self-organize into a helical columnar phase through hydrogen bonding by means of FTIR, UV/Vis, and chiroptical circular dichroism (CD) spectral analyses as well as by optical, calorimetric, electrical switching, and X-ray studies. The CD and X-ray studies have revealed that the form chirality (handedness) and the magnitude of out-of-plane fluctuations of the lattice planes of the fluid supramolecular columnar structures are solely directed by the stereochemistry encoded in the spacer. Of special significance, the less frequently found oblique helical columnar phase formed by a pair of enantiomers derived from L-/D-alanines, unlike those derived from other amino acids, exhibit ferroelectric behavior; the measured spontaneous polarization is as high as 440 nC cm(-2). Besides, all these supramolecules form stable organogels in ethanol and the CD and SEM studies on a representative gel suggest the presence of helical structures.     

Synthesis of functionalized pyrroles and fused pyrroles through intermolecular [3 + 2] cycloaddition reaction

A facile and efficient synthesis of pyrrole and pyrrole-fused heterocyclic compounds has been demonstrated. The current protocol involves the in situ generation of azomethine ylides which undergoes intermolecular cycloaddition reaction and subsequent treatment with DDQ provides the pyrrole and fused heterocyclic compounds in good yields.     

Towards green synthesis of nanoparticles: From bio-assisted sources to benign solvents. A review

Current advancements in green synthesis of materials especially nanoparticles have led to conservation of natural and non-renewable resources along with reduction in environmental pollution. Development of cost-effective, simple and eco-friendly routes for the synthesis of nanoparticles is very important. All over the world, a wide variety of biogenic sources have been put to trial as a source of green agents to facilitate synthesis process. In addition to this, environmentally benign solvents are also being used these days in order to promote green synthesis. In this review, an attempt has been made to familiarise the readers with the different green routes for the synthesis of nanoparticles.     

Challenge in understanding size and shape dependent toxicity of gold nanomaterials in human skin keratinocytes

As the nanotechnology field continues to develop, assessing nanoparticle toxicity is very important for advancing nanoparticles for biomedical application. Here we report cytotoxicity of gold nanomaterial of different size and shape using MTT test, absorption spectroscopy and TEM. Spherical gold nanoparticles of different sizes are not inherently toxic to human skin cells, but gold nanorods are highly toxic due to the presence of CTAB as coating material. Due to toxicity of CTAB, and aggregation of gold nanomaterials in the presence of cell media, we have demonstrated that it is difficult to understand the cytotoxicity of gold nanomaterials individually.     

Separation and quantification of lignans in Phyllanthus species by a simple chiral densitometric method

A sensitive, selective, and robust high-performance TLC (HPTLC) method using chiral TLC plates for qualitative and quantitative analysis of phyllanthin (A), hypophyllanthin (B), niranthin (C), and nirtetralin (D), the active lignans of Phyllanthus species, was developed and validated. The effectiveness and role of various stationary phases viz TLC silica gel 60F(254), HPTLC silica gel 60F(254), and chiral TLC plates in the quantitation were evaluated. A precoated chiral TLC plate was found suitable for the simultaneous analysis of four pharmacologically active lignans. For achieving good separation, the optimized mobile phase of n-hexane/acetone/1,4-dioxane (9:1:0.5 by volume) was used (R(f) = 0.30, 0.36, 0.41, and 0.48 for compounds A, B, C, and D, respectively). A densitometric determination of the above compounds was carried out in reflection/absorption mode at 620 nm. Optimized chromatographic conditions provide well-separated compact bands for the tested lignans. The calibration curves were found linear in the concentration range of 100-500 ng/band. Recoveries of A-D were 99.98, 100.51, 99.22, and 98.74%, respectively. The method was validated according to ICH guidelines. The method reported here is reproducible and applied for the quantitative analysis of the above lignans in the leaves of four Phyllanthus species, i. e., P. amarus, P. maderaspatensis, P. urinaria, and P. virgatus.     

Polarised raman and infrared spectra and vibrational analysis forα-naphthylamine

The Raman spectrum of polycrystalline α-naphthylamine was recorded in the region 100–4000 cm⁻¹. Polarisation measurements were made in CS₂ and CHCl₃ solutions. The infrared spectrum was recorded in nujol mull in the region 200–4000 cm⁻¹. The resolution was better than 2 cm⁻¹ and the accuracy of the measurements was within ± 2 cm⁻¹ for all the spectra. Vibrational assignments have been proposed for the observed frequencies. Out of the 54 normal modes of vibrations, 51 modes could be observed experimentally.     

A comparative study of Keane''s and Stacey''s equations of state

Chitosan acetate-ammonium nitrate (NH₄NO₃) films have been prepared by the solution-cast technique. Fourier transform infrared spectroscopy (FTIR) showed that complexation has occurred. FTIR exhibited shifts in amine and carbonyl bands from 1553 to 1520 cm⁻¹ and 1636 to 1617 cm⁻¹. A new peak was also observed at 1746 cm⁻¹. XRD shows that all complexes are amorphous. The highest conductivity at room temperature is 2.53×10⁻⁵ S cm⁻¹ for the film containing 45 wt% NH₄NO₃. The conductivity of the samples is dependent on the number of mobile ions and mobility.     

Energy and angular distributions of electrons ejected from CH<Subscript>4</Subscript> and C<Subscript>3</Subscript>H<Subscript>8</Subscript> under 16.0 keV electron impact

Relative cross sections, differential in energy and angle, for electrons ejected from CH₄ and C₃H₈ molecules under 16.0 keV electron impact have been measured. Electrons were analyzed by a 45° parallel plate electrostatic analyzer at emission angles varying from 60° to 135° with energies from 50 eV to 1000 eV. The angular distributions of electrons exhibit structures which are found to arise from Coulomb and non-Coulomb interactions. Furthermore, the double differential cross sections of electrons ejected from C₃H₈ molecule are found to be higher in magnitude than those from CH₄. This result supports the fact that the number of ejected electrons participating in collisions with C₃H₈ molecules is more than that in CH₄. Also, the angular distributions of C-K-shell Auger electrons emitted from the target molecules have been studied and shown to be isotropic within the experimental uncertainty     

Adaptable Optical Microwaveguides From Mechanically Flexible Crystalline Materials

Flexible organic crystals (elastic and plastic) are important materials for optical waveguides, tunable optoelectronic devices, and photonic integrated circuits. Here, we present highly elastic organic crystals of a Schiff base, 1-((E)-(2,5-dichlorophenylimino)methyl)naphthalen-2-ol ( 1 ), and an azine molecule, 2,4-dibromo-6-((E)-((E)-(2,6-dichlorobenzylidene)hydrazono)methyl)phenol ( 2 ). These microcrystals are highly flexible under external mechanical force, both in the macroscopic and the microscopic regimes. The mechanical flexibility of these crystals arises as a result of weak and dispersive C−H⋅⋅⋅Cl, Cl⋅⋅⋅Cl, Br⋅⋅⋅Br, and π⋅⋅⋅π stacking interactions. Singly and doubly-bent geometries were achieved from their straight shape by a micromechanical approach using the AFM cantilever tip. Crystals of molecules 1 and 2 display a bright-green and red fluorescence (FL), respectively, and selective reabsorption of a part of their FL band. Crystals 1 and 2 exhibit optical-path-dependent low loss emissions at the termini of crystal in their straight and even in extremely bent geometries. Interestingly, the excitation position-dependent optical modes appear in both linear and bent waveguides of crystals 1 and 2 , confirming their light-trapping ability.     

Morphogenetic and chemical stability of long-term maintained Agrobacterium-mediated transgenic Catharanthus roseus plants

Transgenic Catharanthus roseus plants (transgenic Dhawal [DT] and transgenic Nirmal [NT]) obtained from the Agrobacterium tumefaciens and Agrobacteriumrhizognenes-mediated transformations, respectively, have been maintained in vitro for 5 years. Plants were studied at regular intervals for various parameters such as plant height, leaf size, multiplication rate, alkaloid profile and presence of marker genes. DT plant gradually lost the GUS gene expression and it was not detected in the fifth year while NT plant demonstrated the presence of genes rolA, rolB and rolC even in the fifth year, indicating the more stable nature of Ri transgene. Vindoline content in the DT was two times more than in non-transformed control plants. Alkaloid and tryptophan profiles were almost constant during the 5 years. The cluster analysis revealed that the DT plant is more close to the control Nirmal plant followed by NT plant.