Influence of Metal, Ligand and Solvent on Supramolecular Polymerizations with Transition-Metal Compounds: A Theoretical Study

The nature of intermolecular interactions governing supramolecular polymerizations is very important to control their cooperativity. In order to address this problem, supramolecular columns made of Pt(II) and Pd(II) complexes of oligo(phenyleneethynylene)-based pyridine (OPE) and tetrazolyl-pyridine ligands (TEP) were investigated through the dispersion-corrected PM6 method. Aromatic, CH-π, M-Cl and metallophilic interactions helped stabilize the supramolecules studied, and their geometries and associated cooperativities were in excellent agreement with experimental data. The OPE ligand and/or the presence of Pt(II) have led to stronger metallophilic interactions and also to cooperative supramolecular polymerizations, which clearly suggests that metallophilic interactions are a key factor to control cooperativity. The results indicate that sequential monomer addition is in general less spontaneous than the combination of two larger pre-formed stacks. The present theoretical investigations contribute to the further understanding of the relation between the thermodynamics of supramolecular polymerizations and the nature of different synthons

Secure Sharing of PHR Data Using Re-Encryption: SESPHR

We propose a technique called SeSPHR for secure sharing of the PHRs in the cloud. The SeSPHR plan guarantees tolerant driven control on the PHRs and jelly the classification of the PHRs. The patients store the scrambled PHRs on the un-confided in cloud servers and specifically award access to various kinds of clients on various segments of the PHRs. A semi-believed intermediary called Setup and Re-encryption Server (SRS) is acquainted with set up people in general/private key sets and to create the re-encryption keys. In addition, the strategy is secure against insider dangers and furthermore implements a forward and in reverse access control. Moreover, we officially examine and confirm the working of SeSPHR strategy through the High Level Petri Nets (HLPN)

Supramolecular Polymerization: A Coarse Grained Molecular Dynamics Study

A coarse-grained (CG) force field to model the self-assembly of benzene-1,3,5-tricarboxamide (BTA) class of compounds in nonpolar solvents has been developed. The model includes an intrinsic point dipole embedded on one of the CG beads so as to impart a macrodipole moment to the oligomer, one of its characteristic feature. Chemical specificity has been preserved by benchmarking against results, including dimerization and solvation free energies, obtained from an all-atom representation. Starting from a well-dispersed configuration in <i>n</i>-nonane, BTA molecules self-assemble to form one-dimensional stacks. Free energy (FE) changes for the various manner in which short oligomers can exchange between the assembled and the dispersed states have been calculated. These calculations show BTA to self-assemble via a downhill cooperative mechanism with a nucleus size of three

Adducts of N-Heterocyclic Drugs, Niacin, Allopurinol, and Amiloride, with 2,4-Pyridinedicarboxylic Acid Coformer

A co-crystallization of three drug molecules, niacin (3-pyridine-carboxylic acid = NIA), allopurinol (pyrazolo(3,4-d)pyrimidin-4-one = ALP), and amiloride (3,5-diamino-6-chloro-pyrazine-2-carbonyl)-guanidine = AMI), with the same coformer, 2,4-pyridinedicarboxylic acid (PDA), resulted in three new crystalline products, (NIA)(PDA) (1), (ALP)2(PDA)·1.5H2O (2), and (AMI)2(PDA)2(H2O)2 (3). The formation of new phases was confirmed by IR spectra and X-ray single-crystal and powder diffraction analysis. The proton transfer resulted in the zwitterionic co-crystal 1. In co-crystal 2, neutral ALP molecules existed in the oxo-tautomeric form. Compound 3 crystallizes as the salt with the guanidinium cationic part as in the started amiloride hydrochloride hydrate, and the PDA coformer as the zwitterionic pyridinium dicarboxylate anion. Thus, the diversity of the PDA coformer ionization states included the neutral, zwitterion, and zwitterion anionic forms. All compounds were layered structures where the heterocyclic molecules were linked in the H-bonded corrugated layers stabilized by the diverse conventional and charge-assisted hydrogen bonds with π-π stacking interactions between the layers supported by the mediated water molecules in 2 and 3. © 2017 American Chemical Society

Solvent clathrate driven dynamic stereomutation of a supramolecular polymer with molecular pockets

Control over the helical organization of synthetic supramolecular systems is intensively pursued to manifest chirality in a wide range of applications ranging from electron spin filters to artificial enzymes. Typically, switching the helicity of supramolecular assemblies involves external stimuli or kinetic traps. However, efforts to achieve helix reversal under thermodynamic control and to understand the phenomena at a molecular level are scarce. Here we present a unique example of helix reversal (stereomutation) under thermodynamic control in the self-assembly of a coronene bisimide that has a 3, 5- dialkoxy substitution on the imide phenyl groups (CBI-35CH), leading to "molecular pockets" in the assembly. The stereomutation was observed only if the CBI monomer possesses molecular pockets. Detailed chiroptical studies performed in alkane solvents with different molecular structures reveal that solvent molecules intercalate or form clathrates within the molecular pockets of CBI-35CH at low temperature (263 K), thereby triggering the stereomutation. The interplay among the helical assembly, molecular pockets, and solvent molecules is further unraveled by explicit solvent molecular dynamics simulations. Our results demonstrate how the molecular design of selfassembling building blocks can orchestrate the organization of surrounding solvent molecules, which in turn dictates the helical organization of the resulting supramolecular assembly

Sulfuric acid and Amberlyst-H\u3csup\u3e+\u3c/sup\u3e catalyzed condensation reactions of renewable keto acids with paraformaldehyde: Synthesis of a new dispiro bis-lactone ring system 2,9,13-trioxadispiro[4.1.4.3]tetradecane-3,6,10-trione

The sulfuric acid and Amberlyst-H+ catalyzed condensation reactions of renewable feedstock levulinic acid with paraformaldehyde under neat conditions at 80 °C gives 2,9,11,14-tetraoxadispiro[4.1.5.3]pentadecane-3,6-dione in 91-93% yield, in which the structure was confirmed by single crystal X-ray crystallography. A similar condensation reaction between 4-ketopimelic acid and paraformaldehyde at 80 °C gives 2,9,13-trioxadispiro[4.1.4.3]tetradecane-3,6,10-trione. This new dispiro bis-lactone was found to composed of a 1.6 : 1 mixture of isomers with planes of symmetry bisecting the tetrahydro-2H-pyran-4-one rings through the carbonyl groups

Development of New Transferable Coarse-Grained Models of Hydrocarbons

We have utilized an approach that integrates molecular dynamics (MD) simulations with particle swarm optimization (PSO) to accelerate the development of coarse-grained (CG) models of hydrocarbons. Specifically, we have developed new transferable CG beads, which can be used to model the hydrocarbons (C5 to C17) and reproduce their experimental properties with good accuracy. First, the PSO method was used to develop the CG beads of the decane model represented with a 2:1 (2-2-2-2-2) mapping scheme. This was followed by the development of the nonane model described with hybrid 2-2-3-2 and 3:1 (3-3-3) mapping schemes. The force-field parameters for these three CG models were optimized to reproduce four experimentally observed properties including density, enthalpy of vaporization, surface tension, and self-diffusion coefficient at 300 K. The CG MD simulations conducted with these new CG models of decane and nonane, at different timesteps, for various system sizes, and at a range of different temperatures, were able to predict their density, enthalpy of vaporization, surface tension, self-diffusion coefficient, expansibility, and isothermal compressibility with good accuracy. Moreover, a comparison of structural features obtained from the CG MD simulations and the CG beads of mapped all-atom trajectories of decane and nonane showed very good agreement. To test the chemical transferability of these models, we have constructed the models for hydrocarbons ranging from pentane to heptadecane, by using different combinations of the CG beads of decane and nonane. The properties of pentane to heptadecane predicted by these new CG models showed excellent agreement with the experimental data

Supramolecular Polymerization of <i>N</i>,<i>N</i>′,<i>N</i>″,<i>N</i>‴-<i>tetra</i>-(Tetradecyl)-1,3,6,8-pyrenetetracarboxamide: A Computational Study

The role of molecular dipole orientations and intermolecular interactions in a derivative of pyrene on its supramolecular self-assembly in solution has been investigated using quantum chemical and force field based computational approaches. Five possible dipole configurations of the molecule have been examined, among which the one in which adjacent dipole vectors are antiparallel to each other is determined to be the ground state, on electrostatic grounds. Self-assembly of this molecule under realistic conditions has been studied using MD simulations. Dipolar relaxation in its liquid crystalline (LC) phase has been investigated and contrasted against that in the well-established benzene-1,3,5-tricarboxamide (BTA) family. The dihedral barrier related to the amide dipole flip is larger in the pyrene system than in BTA which explains the differences in their dipolar relaxation behaviors. The mechanism underlying polarization switching upon the application of an external electric field in the LC phase is investigated. Unlike in BTA, this switching is not associated with a reversal of the helical sense of the hydrogen bonded chains, due to differences in molecular symmetry. The observations enable general conclusions on the relationship between electric field induced chiral enhancement and symmetry to be drawn