Disorder-induced enhancement of local hexatic correlations in two-dimensional fluids.

Quenched disorder affects translational and orientational correlations in two-dimensional interacting particle systems. Such disorder always suppresses orientational order in crystalline states. Surprisingly, in fluid phases of particles interacting with a power-law repulsive interaction, increasing the strength of a quenched Gaussian random pinning potential appears to enhance hexatic order locally. We propose that nearby pairs of pinned particles lock in the relative orientation of neighbours around them, propagating hexatic orientational order across larger distances than in the unpinned fluid. We test this idea using Monte Carlo simulations of interacting particles in their fluid phase in two dimensions, where two of the particles are constrained to be permanently pinned at a fixed distance from each other. We use Voronoi tesselations of instantaneous particle configurations to demonstrate that these pinned particles create hexatic neighbourhoods that can extend well beyond the range of their separation. This structuring is enhanced when the particle density is increased and is most prominent in the vicinity of the liquid-solid transition. Testing these ideas experimentally using experiments on 2D colloidal systems should be feasible.

Orientational correlations in fluids with quenched disorder.

Snapshots of colloidal particles moving on disordered two-dimensional substrates can be used to extract equal-time many-body correlations in their positions. To understand the systematics of these correlations, we perform Monte Carlo simulations of a two-dimensional model fluid placed in a quenched disordered background. We use configurations generated from these simulations to compute translational and orientational two-point correlations at equal time, concentrating on correlations in local orientational order as a function of density and disorder strength. We calculate both the disorder averaged version of conventional two-point correlation functions for orientational order, as well as the disorder averaged version of a novel correlation function of time-averaged disorder-induced inhomogeneities in local orientation analogous to the Edwards-Anderson correlation function in spin systems. We demonstrate that these correlations can exhibit interesting nonmonotonic behavior in proximity to the underlying fluid-solid transition and suggest that this prediction should be experimentally accessible.

Golf-course and funnel energy landscapes: Protein folding concepts in martensites.

We use protein folding energy landscape concepts such as golf course and funnel to study re-equilibration in athermal martensites under systematic temperature quench Monte Carlo simulations. On quenching below a transition temperature, the seeded high-symmetry parent-phase austenite that converts to the low-symmetry product-phase martensite, through autocatalytic twinning or elastic photocopying, has both rapid conversions and incubation delays in the temperature-time-transformation phase diagram. We find the rapid (incubation delays) conversions at low (high) temperatures arises from the presence of large (small) size of golf-course edge that has the funnel inside for negative energy states. In the incubating state, the strain structure factor enters into the Brillouin-zone golf course through searches for finite transitional pathways which close off at the transition temperature with Vogel-Fulcher divergences that are insensitive to Hamiltonian energy scales and log-normal distributions, as signatures of dominant entropy barriers. The crossing of the entropy barrier is identified through energy occupancy distributions, Monte Carlo acceptance fractions, heat emission, and internal work.

Publisher's Note: Golf-course and funnel energy landscapes: Protein folding concepts in martensites [Phys. Rev. E 95, 063003 (2017)].

This corrects the article DOI: 10.1103/PhysRevE.95.063003.

Novel supramolecular palladium catalyst for the asymmetric reduction of imines in aqueous media.

A novel approach to the asymmetric reduction of dihydro-beta-carboline derivatives to the corresponding tetrahydro-beta-carbolines is described based on the supramolecular lyophilized complex formed from beta-cyclodextrin/imines as an enzyme mimetic and palladium hydride as the reducing agent. The methodology allowed us to develop a short and efficient preparation of (R)-harmicine and (R)-deplancheine alkaloids in high overall yields and ee of 89 and 90%, respectively.

Solid-phase synthesis of new pyrrolobenzodiazepine-chalcone conjugates: DNA-binding affinity and anticancer activity.

A new class of C8-linked pyrrolo[2,1-c][1,4]benzodiazepine-chalcone conjugates have been prepared by employing a solid-phase synthetic protocol. In this strategy an intramolecular aza-Wittig reductive cyclization approach has been utilized. Interestingly, some of these molecules have shown enhanced DNA-binding affinity and promising anticancer activity on a large number of human cancer cell lines.

Synthesis of 1,2,3-triazole-linked pyrrolobenzodiazepine conjugates employing 'click' chemistry: DNA-binding affinity and anticancer activity.

1,2,3-Triazole based molecules are useful pharmacophores for several DNA-alkylating and cross-linking agents. A series of A/C8, C/C2 and A/C8-C/C2-linked 1,2,3-triazole-PBD conjugates have been synthesized by employing 'click' chemistry. These molecules have exhibited promising DNA-binding affinity and anticancer activity in selected human cancer cell lines.

Efficient solid-phase synthesis of a library of imidazo[1,2-a]pyridine-8-carboxamides.

A versatile method for the solid-phase synthesis of imidazo[1,2-a]pyridine-based derivatives, imidazo[1,2-a]pyridine-8-carboxamides, has been developed. They were obtained by treatment of the amino group of the polymer-bound 2-aminonicotinate with different alpha-haloketones, followed by halogenation at the 3-position of the polymer-bound imidazo[1,2-a]pyridine. The derived polymer-bound imidazo[1,2-a]pyridines 5, 6, and 7 were finally cleaved from the solid-support with an excess of primary or secondary amines. The final crude products were purified from excess amines by solid-supported liquid-liquid extraction (SLE).

Solid-phase synthesis of a library of pyrrolo[2,1-c][1,4]benzodiazepine-5,11-diones with potential antitubercular activity.

A versatile combinatorial approach was developed and utilized for the rapid synthesis of pyrrolo[2,1-c]-[1,4]benzodiazepine-5,11-dione (PBD-5,11-dione) libraries 10, 15, and 19 containing 210 compounds with varied substitutions in A, B, and C rings. The key aspect of the synthetic strategy includes Staudinger, intermolecular aza-Wittig reaction followed by imine reduction and base-mediated cyclative cleavage results in the formation of final resin-free compounds. This strategy provides a highly efficient and practical protocol for the parallel synthesis of PBD-5,11-diones on solid support. The modifications in the C-ring of the PBD scaffold produced three types of sublibraries. Reactions were monitored by FT-IR spectroscopy on the resin beads. Further, from a generated library of 210 compounds, 142 compounds have been selected and evaluated for in vitro activity against Mycobacterium tuberculosis, and some of these compounds have exhibited promising activity.

Recent advances in the solid-phase combinatorial synthetic strategies for the benzodiazepine based privileged structures.

Benzodiazepine based heterocycles can be prepared efficiently on solid-support by employing different approaches. In this review, an effort has been made to highlight academic and industrial examples of combinatorial synthesis for this type of heterocycles published in the last decade. Therefore, it describes synthetic strategies for the generation of benzodiazepine privileged structures employing the corresponding resin-bound substrates. Further, the most relevant biological properties of these heterocycles have also been incorporated.

Recent advances in the solid-phase combinatorial synthetic strategies for the quinoxaline, quinazoline and benzimidazole based privileged structures.

Quinoxaline, quinazoline and benzimidazole based templates have been synthesized on solid-support employing different methodologies. This review enlightens academic and industrial examples of combinatorial synthesis for this type of heterocycles that appeared in the literature in the last decade. Hence, some of the important synthetic strategies for the generation of quinoxaline, quinazoline and benzimidazole based privileged structures, and the important biological activities for these heterocycles have been highlighted. Further, benzothiadiazinone, thioxoquinazolinone, cinnoline and indazole are also examined in this review.