Amino Acid-Based Molecular and Membranous Chiral Tools for Enantiomeric Recognition.

Given the need, both academic and industrial, for new approaches and technologies for chiral discrimination of enantiomers, the present work demonstrates the development through rational design and integration of two new chiral platforms (molecular and membranous) for enantioselective recognition through visual as well as microscopic observation. The molecular platform (TPT) is based on the tryptophan derivative developed through the condensation of two tryptophan units with terepthaloyl chloride. While TPT based on l-tryptophan recognizes R-mandelic acid over the S-isomer, the host with reverse chirality (TPDT) recognizes S-mandelic acid over R-isomer. The role of chemical functionality in this sensitive recognition process was established experimentally by developing an analogue of TPT and by judiciously using different chiral analytes. Importantly, a detailed theoretical study at the molecular level revealed the U-shaped conformation of TPT, creating a cavity for accommodating a chiral guest with selective functional interaction resulting in the discrimination of enantiomers. Finally, a chiral polymeric mat of poly(methyl methacrylate) (PMMA)/polyacrylonitrile (PAN) (2:3) impregnated with TPT was developed via electrospinning. The resulting fibrous mat was successfully utilized for chiral recognition through microscopic and architectural observation. Hence, the present work reports simple chiral tools for enantiomeric recognition.

Enamine/Iminium-based Dual Organocatalytic Systems for Asymmetric Catalysis and Synthesis.

The rational combination of two catalysts to expedite the construction of chiral complex biologically and pharmacologically relevant chiral compounds has widely gained momentum over the past decade. In particular, enamine or iminium catalysis ensuing from the activation of aldehyde or ketone by chiral amine catalysts in conjugation with other organocatalytic cycles has facilitated several asymmetric transformations to yield the enantioenriched products. Regardless of the considerable discussion on the various dual catalytic approaches, literature lacks a comprehensive review focusing on the enamine and iminium-based dual organocatalytic systems. Thus, this review article has discussed the noteworthy achievements in the field of asymmetric catalysis and synthesis catalyzed by the enamine and iminium-based dual organocatalytic systems.

Evolution of a ZW sex chromosome system in willows.

Transitions in the heterogamety of sex chromosomes (e.g., XY to ZW or vice versa) fundamentally alter the genetic basis of sex determination, however the details of these changes have been studied in only a few cases. In an XY to ZW transition, the X is likely to give rise to the W because they both carry feminizing genes and the X is expected to harbour less genetic load than the Y. Here, using a new reference genome for Salix exigua, we trace the X, Y, Z, and W sex determination regions during the homologous transition from an XY system to a ZW system in willow (Salix). We show that both the W and the Z arose from the Y chromosome. We find that the new Z chromosome shares multiple homologous putative masculinizing factors with the ancestral Y, whereas the new W lost these masculinizing factors and gained feminizing factors. The origination of both the W and Z from the Y was permitted by an unexpectedly low genetic load on the Y and this indicates that the origins of sex chromosomes during homologous transitions may be more flexible than previously considered.

Phylogenomics reveals patterns of ancient hybridization and differential diversification that contribute to phylogenetic conflict in willows, poplars, and close relatives.

Despite the economic, ecological, and scientific importance of the genera Salix L. (willows) and Populus L. (poplars, cottonwoods, and aspens) Salicaceae, we know little about the sources of differences in species diversity between the genera and of the phylogenetic conflict that often confounds estimating phylogenetic trees. Salix subgenera and sections, in particular, have been difficult to classify, with one recent attempt termed a "spectacular failure" due to a speculated radiation of the subgenera Vetrix and Chamaetia. Here, we use targeted sequence capture to understand the evolutionary history of this portion of the Salicaceae plant family. Our phylogenetic hypothesis was based on 787 gene regions and identified extensive phylogenetic conflict among genes. Our analysis supported some previously described subgeneric relationships and confirmed the polyphyly of others. Using an fbranch analysis, we identified several cases of hybridization in deep branches of the phylogeny, which likely contributed to discordance among gene trees. In addition, we identified a rapid increase in diversification rate near the origination of the Vetrix-Chamaetia clade in Salix. This region of the tree coincided with several nodes that lacked strong statistical support, indicating a possible increase in incomplete lineage sorting due to rapid diversification. The extraordinary level of both recent and ancient hybridization in both Salix and Populus have played important roles in the diversification and diversity in these two genera.

Amino decorated adenine based metal-organic framework for multi-faceted applications.

Multifunctional metal-organic frameworks with luminescence properties are promising materials for the detection and treatment of toxic pollutants in aqueous media. Herein, an adenine-based multifunctional Zn-MOF {[Zn3.5(AIPA)2(Ade)3(H2O)2]n using linkers adenine (Ade) and 5-aminoisophthalic acid (AIPA)} was prepared that could selectively detect particular classes of explosives and antibiotics, namely, nitrophenols, tetracyclines and nitrofurans. Moreover, the as-synthesized Zn-MOF displayed a remarkable efficiency for the treatment of antibiotics in water through adsorption and photocatalytic degradation. A subtle balance between photoinduced electron transfer (PET), resonance energy transfer (RET) and competitive excitation energy absorption enabled detection selectivity towards the pollutants. On the other hand, intermolecular interactions of free functional groups assisted the treatment process and thereby highlighted the crucial role of the linkers in furnishing multifunctional behavior without the need for any postsynthetic modifications.

Cu(II)-Based Coordination Polymer as a Pristine Form Usable Electrocatalyst for Oxygen Reduction Reaction: Experimental Evaluation and Theoretical Insights into Biomimetic Mechanistic Aspects.

As the postsynthesis-processed metal-organic material-based catalysts for energy applications add additional cost to the whole process, the importance of developing synthesized usable pristine catalysts is quite evident. The present work reports a new Cu-based coordination polymer (Cu-CP) catalyst to be used in its pristine form for oxygen reduction reaction (ORR) application. The catalyst was characterized using single-crystal X-ray diffraction, field emission scanning electron microscopy, and X-ray photoemission spectroscopy. The Cu-CP exhibits admirable electrocatalytic ORR activity with an onset potential of 0.84 V versus RHE and a half wave potential of 0.69 V versus RHE. As revealed by the density functional theory-based computational mechanistic investigation of the electrocatalytic ORR process, the electrochemically reduced Cu(I) center binds to the molecular O2 through an exergonic process (ΔG = -6.8 kcal/mol) and generates the Cu(II)-O2•- superoxo intermediate. Such superoxo intermediates are frequently encountered in the catalytic cycle of the Cu-containing metalloenzymes in their O2 reduction reaction. This intermediate undergoes coupled proton and electron transfer processes to give OH- in an alkaline medium involving H2O2 as the intermediate. The electrocatalytic performance of Cu-CP remained stable even up to 3000 cycles. Overall, the newly developed Cu-CP-based electrocatalyst holds promising potential for efficient biomimetic ORR reactivity, which opens new possibilities toward the development of robust coordination polymer-based electrocatalysts.

Chiral gelators for visual enantiomeric recognition.

Introduction of chirality in supramolecular gels has allowed the effective translation and amplification of molecular chirality. Upon integrating the stimuli-responsive nature of these gels with supramolecular chirality, a new platform for the discrimination of the enantiomeric guests through naked eye can be developed. Over the past decade, several groups have reported the development of chiral supramolecular gels for enantioselective recognition through gel formation or collapse. However, to the best of our knowledge, we are yet to come across a review highlighting the utilization of chiral supramolecular gels for macroscopic discrimination of enantiomers. In this article, we have articulated the chiral gelators developed to date for the recognition of different enantiomeric analytes focusing on their mode of recognition with an in-depth analysis of the mechanism of interactions assisting the recognition process.

Through structural isomerism: positional effect of alkyne functionality on molecular optical properties.

Literature studies on the effects of alkyne functionality in manipulating the optical properties of donor-π-acceptor-type molecular scaffolds have been scarce compared to those on the alkene functional group. Here, two structurally isomeric donor-acceptor (D-A) dyes were synthesized to study the positional effect of alkyne functionality (triple bond) on their optical, electrochemical and charge generation properties in order to design efficient dyes for possible application in dye sensitized solar cells (DSSCs). These dyes, named CAPC and PACC, contain carbazole and cyanoacrylic acid as the donor and acceptor units, respectively, and the π-conjugation length within the molecules was controlled by the introduction of an alkyne group. The D-π-A design was followed in designing CAPC with the alkyne serving as the π-spacer, while in PACC, alkyne was placed on the donor, which was directly in conjugation with the acceptor. This rendered equal conjugation lengths within the designed dyes. With the help of photophysical characterizations, it was concluded that CAPC featured better characteristics for a DSSC dye than PACC. Our conclusions were further supported by the results of transient absorption spectroscopy, electrochemical analysis, fluorescence lifetime studies and density functional theory.

Molecular-level insights into the self-assembly driven enantioselective recognition process.

The importance of the orientation of functional groups in a chiral environment on enantioselective recognition has been demonstrated. Orientation controlled interactions of functional groups in (R)/(S)-MA lead to a visually differentiable morphology with an arginine-based gelator. The crucial role of various molecular-level interactions discriminating the enantioselective self-assembly has been established using different analytical techniques, crystal structure analysis, and DFT calculations.

Preferential intermolecular interactions lead to chiral recognition: enantioselective gel formation and collapse.

Interesting self-assembly of an amino acid based molecular material into a hydrogel in the presence of selective enantiomeric chiral amines leading to chiral recognition has been demonstrated. Moreover, collapse of a metallogel formed from the same material in the presence of selective enantiomers validated its enantioselective affinity. Importantly, in addition to relevant experimental techniques, DFT studies have been successfully explored to establish chiral recognition through enantioselective gelation.

A long-range emissive mega-Stokes inorganic-organic hybrid material with peripheral carboxyl functionality for As(v) recognition and its application in bioimaging.

We demonstrate a strategy for the recognition of As5+ in aqueous solution using a red-emissive probe based on a perylene-Cu2+ ensemble decorated with peripheral free carboxyl functionality. Single crystal analysis helped us to understand the chemical structure of the probe. To the best of our knowledge, this is the first probe for arsenic detection which emits in the red region (λem = 600 nm). The perylene-Cu2+ ensemble exhibited a mega-Stokes shift (>100 nm) with a high degree of selectivity upon interaction with As5+, which indicated that the present probe has the potential to be used as a turn-on optical sensor for selective detection of As5+ with fewer experimental limitations. The detection limit was found to be 26 nM. Inspired by its good emissive properties, the ensemble was further explored for imaging As5+ in live cells. Because of its long-range emissive nature, no autofluorescence from the cellular species was observed during the imaging process. The probe was evaluated to be non-toxic and successfully permeated the cell membrane without the help of any permeabilizing agent to image As5+.

Plant leaves as natural green scaffolds for palladium catalyzed Suzuki-Miyaura coupling reactions.

This work presents a novel approach of using natural plant leaf surfaces having intricate hierarchical structures as scaffolds for Pd nanoparticles and demonstrated it as a Green dip catalyst for Suzuki-Miyaura coupling reactions in water. The influence of the topographical texture of the plant leaves on the deposition and catalytic properties of Pd nanoparticles are presented and discussed. The catalytic activity can be correlated to the surface texture of the leaves, wherein it has been found that the micro/nanostructures present on the surface strongly influence the assembly and entrapment of the nanoparticles, and thereby control aggregation and leaching of the catalysts. This approach can provide insights for the future design and fabrication of bioinspired supports for catalysis, based on replication of leaf surfaces.