Search results for "bonds"
showing 10 items of 155 documents
Template-Free Supracolloidal Self-Assembly of Atomically Precise Gold Nanoclusters : From 2D Colloidal Crystals to Spherical Capsids
2016
We report supracolloidal self-assembly of atomically precise and strictly monodisperse gold nanoclusters involving p-mercaptobenzoic acid ligands (Au102-pMBA44) under aqueous conditions into hexagonally packed monolayer-thick two-dimensional facetted colloidal crystals (thickness 2.7 nm) and their bending to closed shells leading to spherical capsids (d ca. 200 nm), as controlled by solvent conditions. The 2D colloidal assembly is driven in template-free manner by the spontaneous patchiness of the pMBA ligands around the Au102-pMBA44 nanoclusters preferably towards equatorial plane, thus promoting inter-nanocluster hydrogen bonds and high packing to planar sheets. More generally, the findin…
Tertiary Chiral Nanostructures from C‐H∙∙∙F Directed Assembly of Chiroptical Superatoms
2021
Chiral hierarchical structures are universal in nature, whereas quite challenging to mimic in man-made synthesis. We report herein the synthesis and structure of tertiary chiral nanostructures with 100% optical purity. A novel synthetic strategy, using chiral reducing agent, R and S -BINAPCuBH 4 (BINAP is 2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl), is developed to access to atomically precise, intrinsically chiral [Au 7 Ag 6 Cu 2 ( R - or S -BINAP) 3 (SCH 2 Ph) 6 ]SbF 6 nanoclusters in one-pot synthesis. The clusters represent the first tri-metallic superatoms with inherent chirality and fair stability. Both metal distribution (primary) and ligand arrangement (secondary) of the enantiomer…
Designing portfolios of financial products via integrated simulation and optimization models
1999
We analyze the problem of debt issuance through the sale of innovative financial products. The problem is broken down to questions of designing the financial products, specifying the debt structure with the amount issued in each product, and determining an optimal level of financial leverage. We formulate a hierarchical optimization model to integrate these three issues and provide constructive answers. Input data for the models are obtained from Monte Carlo simulation procedures that generate scenarios of holding period returns of the designed products. The hierarchical optimization model is specialized for the problem of issuing a portfolio of callable bonds to fund mortgage assets. The …
The Molecular and Crystal Structure of tert-Butyl N.ALPHA.-tert-Butoxycarbonyl-L-(S-trityl)cysteinate and the Conformation-Stabilizing Function of We…
2001
The title compound, C31H37NO4S [systematic name: (R)-tert-butyl-2-[(tert-butoxycarbonyl)amino]-3-(tritylsulfanyl)propanoate] is an L-cysteine derivative with three functions: NH2, COOH and SH, blocked by protecting groups tert-butoxycarbonyl, tert-butyl and trityl, respectively. The main chain of the molecule adopts the extended, nearly all-trans C5 conformation with the intramolecular N-H...O=C hydrogen bond. The urethane group is not involved in any intermolecular hydrogen bonding. Only weak intermolecular hydrogen bonds and hydrophobic contacts are observed in the crystal structure. These are C-H...O hydrogen bonds and CH/pi interactions with donor...acceptor distances, C...O ca. 3.5 A a…
The Low Barrier Hydrogen Bond in the Photoactive Yellow Protein: A Vacuum Artifact Absent in the Crystal and Solution
2016
Journal of the American Chemical Society 138(51), 16620 - 16631 (2016). doi:10.1021/jacs.6b05609
Simple molecular model for the binding of antibiotic molecules to bacterial ion channels
2003
A molecular model aimed at explaining recent experimental data by Nestorovich et al. [Proc. Natl. Acad. Sci. USA 99, 9789 (2002)] on the interaction of ampicillin molecules with the constriction zone in a channel of the general bacterial porin, OmpF (outer membrane protein F), is presented. The model extends T. L. Hill’s theory for intermolecular interactions in a pair of binding sites [J. Am. Chem. Soc. 78, 3330 (1956)] by incorporating two binding ions and two pairs of interacting sites. The results provide new physical insights on the role of the complementary pattern of the charge distributions in the ampicillin molecule and the narrowest part of the channel pore. Charge matching of int…
Computational study of water adsorption on halloysite nanotube in different pH environments
2020
Abstract The comprehension of structural and energetic features of halloysite nanotube (HNT) in different chemical environments plays a crucial role in developing new HNT based materials. So far these aspects were investigated by means of laboratory techniques that hardly are able to provide hints at atomistic level of detail. Our investigation aims to obtain such accurate informations through density functional theory calculations on HNT models, in order to figure out the most stable forms of HNT under different pH conditions. It turns out that, at low pH, the preferred protonation sites are located in the inner aluminic surface while in alkaline medium the silicic layer can show delocaliz…
Magneto-structural and theoretical study of the weak interactions in a Mn(II) complex with a very unusual N,O-chelating coordination mode of 2-aminot…
2017
International audience; The Mn(II) complex {[Mn(atpa)(H2O)2]·H2O}n (1),with the dicarboxylate ligand 2-aminoterephthalic acid (H2atpa), has been synthesized and crystallographically, spectroscopically and magnetically characterized. Complex 1 shows a very unusual 1κ2N,O coordination mode of the aminoterephthalate dianion with the Mn(II) ion. One of the carboxylate groups shows a syn-anti-μ2-η1:η1 binding mode to form a 2D square grid. The magnetic properties of this compound can be very well reproduced with a regular S = 5/2 chain model with a very weak antiferromagnetic coupling constant of J = −0.2 cm−1 through the single syn-anti carboxylate bridges. EPR measurement also supports the exp…
Theoretical determination of the geometric and electronic structures of oligorylenes and poli(peri‐naphthalene)
1992
We present a theoretical investigation of the electronic structure of oligorylenes (from perylene to heptarylene, including also the naphthalene molecule) and their corresponding polymer poly(peri‐naphthalene) (PPN) using the nonempirical valence effective (VEH) method. The geometry of the unit cell used to generate the polymer is extrapolated from the PM3‐optimized molecular geometries of the longest oligorylenes. That geometry shows some bond alternation along the perimeter carbon chains and a bond length of ≊1.46 Å is calculated for the peri bonds connecting the naphthalene units. The VEH one‐electron energy level distributions calculated for oligorylenes are used to interpret the experi…
Experimental evidence for two different precursors of E’γ centers in silica
2004
Electron paramagnetic resonance measurements of concentration and line shape of centers induced by γ ray irradiation are presented for natural and synthetic commercial silica with different OH contents. Synthetic materials with OH content >200 ppm by weight show one line shape for all investigated doses. In contrast, the other materials show a different line shape at low irradiation doses. Differences are also observed in the concentration growth of the centers in synthetic wet materials and in the other materials. The results are interpreted as evidence of two centers distinguishable by their line shape and having different precursors.