Designed Synthesis of a 1D Polymer in Twist-Stacked Topology via Single-Crystal-to-Single-Crystal Polymerization

To synthesize a fully organic 1D polymer in a novel twist-stacked topology, we designed a peptide monomer HC≡CCH₂-NH-Ile-Leu-N₃, which crystallizes with its molecules H-bonded along a six-fold screw axis. These H-bonded columns pack parallelly such that molecules arrange head-to-tail, forming linear non-covalent chains in planes perpendicular to the screw axis. The chains arrange parallelly to form molecular layers which twist-stack along the screw axis. Crystals of this monomer, on heating, undergo single-crystal-to-single-crystal (SCSC) topochemical azide–alkyne cycloaddition (TAAC) polymerization to yield an exclusively 1,4-triazole-linked polymer in a twist-stacked layered topology. This topologically defined polymer shows better mechanical strength and thermal stability than its unordered form, as evidenced by nanoindentation studies and thermogravimetric analysis, respectively. This work illustrates the scope of topochemical polymerizations for synthesizing polymers in pre-decided topologies.     

Cytotoxicity assessment based on the AUC50 using multi-concentration time-dependent cellular response curves

Although many indices have been developed to quantify chemical toxicity, substantial shortcoming is inherent in most of them, such as observation time dependence, insufficient robustness, and no comparison with the negative control. To assess the extent of exposure of the tested substance, a cytotoxicity assay named AUC₅₀ was developed to describe the time and concentration-dependent cellular responses. By monitoring the dynamic cytotoxicity response profile of living cells via the xCELLigence real-time cell analysis high-throughput (RTCA HT) system, changes in cell number (named cell index, CI) were recorded and analyzed subsequently. A normalized cell index (NCI) is introduced to reduce the influence of inter-experimental variations. The log-phase of cellular growth is considered, which alleviates the cell's spontaneous effect. The area between the control line and the assessed time-dependent cellular response curve (TCRC) of the tested substance was calculated, and the corresponding exponential kill model (concentration–response curve) was developed along with exploiting the concept of AUC₅₀. The validation of the proposed method is demonstrated by exposing HepG2 cell line to seven chemical compounds. Our findings suggested that the proposed AUC-based toxicity assay could be an alternative to the traditional single time-point assay, and it has potential to become routine settings for evaluating the cell-based in vitro assay. Furthermore, the AUC₅₀ combined with RTCA HT assay can be used to achieve a high-throughput screening that conventional cellular assay cannot achieve.     

Joule heating and viscous dissipation effects on MHD flow past a semi-infinite inclined plate with variable surface temperature

A numerical investigation is performed to study the MHD free convection flow past a semi-infinite inclined plate subjected to a variable surface temperature. The Joule heating and viscous dissipation effects are taken into account in the energy equation. The governing equations of the flow are transformed into a nondimensional form using suitable dimensionless quantities. A fully developed implicit finite-difference scheme of Crank-Nicolson type is engaged to solve the dimensionless governing equations, which is more accurate, fast convergent, and unconditionally stable. The effects of the MHD, inclination angle, power law, Grashof number, Prandtl number, Joule heating, and viscous dissipation effects are studied on the velocity, temperature, shear stress, and heat transfer coefficients during transient periods. It is observed that the MHD has retarding effects on velocity.     

Picking Out Logic Operations in a Naphthalene β-Diketone Derivative by Using Molecular Encapsulation,Controlled Protonation,and DNA Binding

On–off switching and molecular logic in fluorescent molecules are associated with what chemical inputs can do to the structure and dynamics of these molecules. Herein, we report the structure of a naphthalene derivative, the fashion of its binding to β-cyclodextrin and DNA, and the operation of logic possible using protons, cyclodextrin, and DNA as chemical inputs. The compound crystallizes out in a keto-amine form, with intramolecular N−H⋅⋅⋅O bonding. It shows stepwise formation of 1:1 and 1:2 inclusion complexes with β-cyclodextrin. The aminopentenone substituents are encapsulated by β-cyclodextrin, leaving out the naphthalene rings free. The binding constant of the β-cyclodextrin complex is 512 m⁻¹. The pK_a value of the guest molecule is not greatly affected by the complexation. Dual input logic operations, based on various chemical inputs, lead to the possibility of several molecular logic gates, namely NOR, XOR, NAND, and Buffer. Such chemical inputs on the naphthalene derivative are examples of how variable signal outputs based on binding can be derived, which, in turn, are dependent on the size and shape of the molecule.     

Combined effects of viscous dissipation and MHD on free convection flow past a semi-infinite vertical plate with variable surface temperature in the presence of heat source

An unsteady MHD laminar viscous dissipative fluid flow past a semi-infinite vertical plate with variable surface temperature in the presence of heat source is considered in the present analysis. The present approach transforms the governing boundary layer equations into nondimensional form using the appropriate nondimensional quantities, which is valid in the free convection region. The resulting governing equations are solved numerically using the Crank–Nicolson method, an efficient implicit finite-difference scheme. Numerical results are obtained and presented in the form of local as well as average shearing stress, local and average heat transfer rate, velocity and temperature during the transient period. The present results are compared with the available results in the literature and are found to be in an excellent agreement.     

What Controls the Magnetic Exchange Interaction in Mixed‐ and Homo‐Valent Mn7 Disc‐Like Clusters? A Theoretical Perspective

Density functional theory (DFT) studies have been undertaken to compute the magnetic exchange and to probe the origin of the magnetic interactions in two hetero‐ and two homo‐valent heptanuclear manganese disc‐like clusters, of formula [Mn^II₄Mn^IV₃(tea)(teaH₂)₃(peolH)₄] ( 1 ), [Mn^II₄Mn^III₃F₃(tea)(teaH)(teaH₂)₂(piv)₄(Hpiv)(chp)₃] ( 2 ), [Mn^II₇(pppd)₆(tea)(OH)₃] ( 3 ) and [Mn^II₇ (paa)₆(OMe)₆] ( 4 ) (teaH₃=triethanolamine, peolH₄=pentaerythritol, Hpiv=pivalic acid, Hchp=6‐chloro‐2‐hydroxypyridine, pppd=1‐phenyl‐3‐(2‐pyridyl) propane‐1,3‐dione; paaH=N‐(2‐pyridinyl)acetoacetamide). DFT calculations yield J values, which reproduce the magnetic susceptibility data very well for all four complexes; these studies are also highlighting the likely ageing/stability problems in two of the complexes. It is found that the spin ground states, S, for complexes 1 – 4 are drastically different, varying from S=29/2 to S=1/2. These values are found to be controlled by the nature of the oxidation state of the metal ions and minor differences present in the structures. Extensive magneto–structural correlations are developed for the seven building unit dimers present in the complexes, with the correlations unlocking the reasons behind the differences in the magnetic properties observed. Independent of the oxidation state of the metal ions, the Mn‐O‐Mn/Mn‐F‐Mn angles are found to be the key parameters, which significantly influence the sign as well as the magnitude of the J values. The magneto–structural correlations developed here, have broad applicability and can be utilised to understand the magnetic properties of other Mn clusters.