Charting a course for chemistry

To mark the occasion of Nature Chemistry turning 10 years old, we asked scientists working in different areas of chemistry to tell us what they thought the most exciting, interesting or challenging aspects related to the development of their main field of research will be — here is what they said

Small-Molecule-Induced Folding of a Synthetic Polymer

Small-Molecule-Induced Folding of a Synthetic Polymer

Core-Substituted Naphthalene-Diimides (cNDI) and Related Derivatives: Versatile Scaffold for Supramolecular Assembly and Functional Materials

Abstract Naphthalene-diimide (NDI)-derived building blocks have been explored extensively for supramolecular assembly as they exhibit attractive photophysical properties, suitable for applications in organic optoelectronics. Core-substituted derivatives of the NDI chromophore (cNDI) differ significantly from the parent NDI dye in terms of optical and redox properties. Adequate molecular engineering opportunities and substitution-dependent tunable optoelectronic properties make cNDI derivatives highly promising candidates for supramolecular assembly and functional materials. This short review discusses recent development in the area of functional supramolecular assemblies based on cNDIs and related molecules. Table of contents 1. Introduction 2. General Supramolecular Assemblies of cNDI Derivatives 3. cNDI-Based Chiral Supramolecular Assemblies and Functional Materials 4. Controlled Supramolecular Polymerization with cNDI Derivatives 5. Dimeric Naphthalimide-Based Building Blocks 6. Conclusions and Outloo

Small-molecule-induced folding of a synthetic polymer

Small-Molecule-Induced Folding of a Synthetic Polymer

Aromatic Donor-Acceptor Charge-Transfer and Metal-Ion-Complexation-Assisted Folding of a Synthetic Polymer

Aromatic Donor-Acceptor Charge-Transfer and Metal-Ion-Complexation-Assisted Folding of a Synthetic Polyme

Structural Fine-Tuning of (-Donor-spacer-acceptor-spacer-)n_n Type Foldamers. Effect of Spacer Segment Length, Temperature, and Metal-Ion Complexation on the Folding Process

The synthesis of a series of polymers (PDA-nOE) containing an alternating arrangement of electron rich (donor) and electron deficient (acceptor) aromatic units, which are linked by flexible oligo(oxyethylene) (nOE) spacers, is reported. The length of the oligo(oxyethylene) spacer was varied from tetra(oxyethylene) (n = 4) to hexa(oxyethylene) (n = 6), to examine the relative propensities of these polymers to form folded structures by virtue of intrachain charge-transfer interactions between the adjacent donor and acceptor units. Comparison of the proton NMR and UV-visible spectra of the three different polymers clearly reveals that PDA-4OE, which has the shortest tetra(oxyethylene) spacer, exhibits the greatest propensity to fold in the nascent form. A significant upfield shift of the aromatic protons upon lowering of temperature confirmed this greater tendency of the PDA-4OE to fold; the spectra of polymers with longer spacers, on the other hand, exhibited a very weak temperature dependence indicating their sluggishness to fold in nascent form. However, in the presence of suitable alkali-metal ions (or a polar solvent), the spectra of the polymers with longer oligo(oxyethylene) spacers also exhibit a much stronger temperature dependence (similar to the PDA-4OE case), implying the occurrence of a metal-ion (and solvophobic effect) assisted formation of folded structures. These NMR studies corroborate well with similar variable temperature UV-visible spectral studies, wherein the intensities of the D-A charge-transfer band is monitored as a signature of the folded structure; there were, however, some distinct differences in the nature of the variation in the case of nascent polymer samples that appear to reflect the differences in sensitivities of the two spectral techniques to the folding process. In an effort to better understand the folding process, model compounds of the type donor-spacer-acceptor and analogous DAD and ADA were synthesized. Comparison of the spectral changes seen in model compounds, both as a function of temperature and during alkali-metal ion titrations, with those seen in the analogous polymers helped confirm that the folded structures in the polymer clearly must involve intrachain charge-transfer interactions that exceeds simple pairing of adjacent donor and acceptor units; i.e., the acceptors in the folded polymer are sandwiched between donors and vice versa, thereby forming extended stacks

Fracture toughness characteristics of ultrafine grained Nb–Ti stabilized microalloyed and interstitial free steels processed by advanced multiphase control rolling

Abstract Aim of the current study is to analyze the fracture toughness values along with other mechanical properties and correlating the microstructures of ultrafine grained (UFG) microalloyed and interstitial free (IF) steels produced through advanced 3-steps control multiphase rolling. The analysis of fracture toughness was carried out through computing KQ (conditional fracture toughness), J-integral (crack initiation energy) and Kee (equivalent energy fracture toughness) values from 3-point bend test data of rolled specimens. Microstructural analysis was performed through transmission electron microscopy (TEM) along with selected area electron diffraction (SAED) and Electron backscatter diffraction (EBSD). The quantitative measurement of low and high angle grain boundaries and their distribution in the deformed state were determined through EBSD analysis. The good combinations of fracture toughness, yield strength (YS) and percent elongation (%El.) (i.e. ductility) were achieved through innovative 3-phase control rolling (microalloyed steel: Kee = 68.9MPa√m, J = 81.4 kJ/m2, YS = 923MPa, %El. = 13.6; IF steel: Kee = 72MPa√m, J = 87.7 kJ/m2, YS = 623Mpa and %El. = 19). This is ascribed to the development of homogeneously distributed submicron size (0.69μm) ferritic + martensitic structure in the microalloyed steel and submicron size (0.83μm) ferritic grains along with high density dislocation substructure in the IF steel. These dislocation cells and substructures could effectively block the crack initiation and propagation. The development of UFG microstructure has been analyzed in the light of deformation induced ferrite transformation (DIFT) and dynamic recrystallization (DRX) mechanisms. Superior fracture toughness of the UFG steels along with better combination of mechanical properties is very demanding for high strength structural applications

Improvement of fracture toughness of Ti+Nb stabilized microalloyed and interstitial free steels processed through single phase regime control multiaxial forging

Abstract Objective of the current study is to enhance the mechanical properties, with a special emphasis on fracture toughness, of Ti + Nb stabilized interstitial free and microalloyed steels through microstructural modification by single-phase controlled multiaxial forging at large cumulative strains. Analysis of fracture toughness was executed through calculating KQ (conditional fracture toughness), Kee (equivalent energy fracture toughness) and J-integral (crack initiation energy) values from single-edge bend test data of the forged specimens. The effect of strain hardening rate and strain hardening exponent on deformation behavior were examined to correlate the yield strength (YS) and uniform elongation. Also, theoretically calculated YS (obtained from analysis of strengthening mechanisms) was correlated well with the experimentally obtained results. The quantitative measurement of grain size, low- and high-angle grain boundaries and their distribution in the deformed state were investigated through EBSD/TEM analysis. Superior combinations of the YS, ductility (%El.) and fracture toughness were obtained through intercritical (α+γ) phase regime (~Ar1) control 15 cycles multiaxially forged (MAFed) microalloyed steel (YS = 1027 MPa, %El. = 8.3% and Kee = 90 MPa√m) and pure α-ferritic region (<Ar1) control 18 cycles MAFed IF steel (YS = 881 MPa, %El. = 11.2% and Kee = 97 MPa√m) specimens. Enhancement of the fracture toughness is ascertained to the formation of uniformly distributed nanosize fragmented cementite (Fe₃C) particles (~35 nm size) within the submicron size (~280 nm size) ferritic microstructure in the microalloyed steel; whereas in case of the IF steel, this is attributed to the formation of ultrafine ferrite grain (~320 nm) along with dense dislocation substructures. These dislocation cells and fine substructures as well as nanosize Fe₃C could effectively block the crack initiation and propagation and thereby enhance the fracture toughness

Binding of 9-N-Butyladenine by Carboxylic Acids: Evidence that Hoogsteen Binding Can Dominate in Solution

H-1 NMR titration of 9-N-butyladenine (1) with a series of 1 1 rt presentative carboxylic acids has been carried out in CDCl3 by following the chemical shifts of delta(H-2) and delta(H-8) of 1 to determine the association constants for the Watson-Crick and the Hoogsteen modes of binding. Compound 1 has been found to bind carboxylic acids through the Watson-Crick (WC) site or the Hoogsteen (I-IG) site. The binding of carboxylic acids from the WC site shifts the delta(H-2) signal upfield, whereas the binding from the HG site shifts the delta(H-8) Signal downfield. Analyses of binding-induced shifts of delta(H-2) and delta(H-8) of 1 in the presence of the carboxylic acids have indicated a distinct preference Sor the HG site by aromatic carboxylic acids, such as benzoic acid and monobenzyl isophthalate. On the other hand, aliphatic acids such as 4-nitrophenylacetic acid and propanoic acid are found to prefer the WC site for complexing 1. Binding affinities of a few alkenoic and alkynoic acids were also determined. In addition to the complexes (1/acid) of I:I stoichiometry, the possibility of a 1:2 complexation between 1 and the carboxylic acids is addressed. A possible rationale for the upfield shift of H-2 (of 1) upon binding by a carboxylic acid is discussed. The K-a's were found to increase in general with enhanced acidity of the carboxylic acids. However, the pK(a) values of the acids do not appear to determine the site-specificity of the binding of 1