Theoretical Study of the Stability of the DNA Duplexes Modified by a Series of Hydrophobic Base Analogues

The geometries of a 13 mer of a DNA double helix (5′‐GCGTAC A CATGCG‐3′) were determined by molecular dynamics simulations using a Cornell et al. empirical force field. The bases in the central base pair (shown in bold) were replaced (one or both) by a series of hydrophobic base analogues (phenyl, biphenyl, phenylnaphathalene, phenylanthracene and phenylphenanthrene). Due to the large fluctuations of the systems, an average geometry could not be determined. The interaction energies of the Model A, which consisted of three central steps of a duplex without a sugar phosphate backbone, taken from molecular dynamics simulations (geometry sampled every 1 ps), were calculated by the self‐consistent charge density functional based tight‐binding (SCC‐DFTB‐D) method and were subsequently averaged. The higher the stability of the systems the higher the aromaticity of the base analogues. To estimate the desolvation energy of the duplex, the COSMO continuum solvent model was used and the calculations were provided on a larger model, Model B (the three central steps of the duplex with a sugar phosphate backbone neutralised by H atoms), taken from molecular dynamics simulations (geometry sampled every 200 ps) and subsequently averaged. The selectivity of the base analogue pairs was ascertained (Model B) by including the desolvation energy and the interaction energy of both strands, as determined by the SCC‐DFTB‐D method. The highest selectivity was found for a phenylphenanthrene. Replacing the nucleic acid bases with a base analogue leads to structural changes of the central pair. Only with the smallest base analogues (phenyl) does the central base pair stay planar. When passing to larger base analogues the central base pair is usually stacked.     

Impact of position of electron withdrawing cyano groups on nonlinear optical properties of centrosymmetric donor‐π‐acceptor system

Two symmetrically substituted phenylenevinylene D‐A‐D′‐A‐D type siblings, (2Z,2′Z)‐2,2′‐(2,5‐dimethoxy‐1,4‐phenylene)bis(3‐(4‐(dimethylamino)phenyl)acrylonitrile) (↑‐dscn) and (2Z,2′Z)‐3,3′‐(2,5‐dimethoxy‐1,4‐phenylene)bis(2‐(4‐(dimethylamino)phenyl)acrylonitrile) (↓‐dscn), are prepared. We investigate the effect of different but symmetrical location of these cyano groups in vinylene bridges on the 1‐photon and 2‐photon absorption behaviors. We report that the closeness of CN group on the vinyl group to the central phenyl ring in ↑‐dscn induces an intramolecular geometric distortion between the central phenyl ring and vinylene group, preventing the effective π‐conjugation length in ground and excited states. Thus, the transition energy that is observed in 1‐photon absorption and fluorescence is larger in ↑‐dscn than in ↓‐dscn. This leads to a different intramolecular charge distribution, as a result of which the linear and nonlinear optical properties strongly depend on the position of acceptors. These results are theoretically unraveled in terms of charge transfer pathways, charge distribution, and charge distribution differences on transition.     

Theoretical Investigation on the Electron and Energy Transfer between Peripheral Carrier Transport Groups and Central Chromophores in Electroluminescent Materials

The molecular materials with structures of luminescent core and peripheral carrier groups (e.g. carbazoles), have exhibited high‐performance in organic light‐emitting diodes (OLEDs). Present work is to understand the basic process of electronic and energy exchange between the peripheral functional groups and the central core through quantum chemical analysis. As an example, 4,7‐bis(9,9‐bis(6‐(9H‐carbazol‐9‐yl)hexyl)‐9H‐fluoren‐2‐yl)benzo[c]‐[1,2,5]thiadiazole (TCBzC) is investigated in regards to optoelectronic properties using density functional theory (DFT). The results suggest that the forbidden transition from peripheral carbazole to the central chromophore core makes for separated electrical and optical properties, and high performance electroluminescence (EL) is mainly attributed to the energy‐transfer from carbazoles to the fluorene derivative core     

Rational Design of a Lanthanide‐Based Complex Featuring Different Single‐Molecule Magnets

The rational synthesis of the 2‐{1‐methylpyridine‐N‐oxide‐4,5‐[4,5‐bis(propylthio)tetrathiafulvalenyl]‐1H‐benzimidazol‐2‐yl}pyridine ligand ( L ) is described. It led to the tetranuclear complex [Dy₄(tta)₁₂( L )₂] ( Dy‐Dy₂‐Dy ) after coordination reaction with the precursor Dy(tta)₃?2 H₂O (tta^?=2‐thenoyltrifluoroacetonate). The X‐ray structure of Dy‐Dy₂‐Dy can be described as two terminal mononuclear units bridged by a central antiferromagnetically coupled dinuclear complex. The terminal N₂O₆ and central O₈ environments are described as distorted square antiprisms. The ac magnetism measurements revealed a strong out‐of‐phase signal of the magnetic susceptibility with two distinct sets of data. The high‐ and low‐frequency components were attributed to the two terminal mononuclear single‐molecule magnets (SMMs) and the central dinuclear SMM, respectively. A magnetic hysteresis loop was detected at very low temperature. From both structural and magnetic points of view, the tetranuclear SMM Dy‐Dy₂‐Dy is a self‐assembly of two known mononuclear SMMs bridged by a known dinuclear SMM.     

A Theoretical Study on Hydrogen‐Bonded Complex of Proflavine Cation and Water: The Site‐dependent Feature of Hydrogen Bond Strengthening and Weakening

The intermolecular hydrogen‐bonds between proflavine cation (PC) and water molecules are investigated by density functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods. The ground‐state geometry optimizations, electronic excitation energies and corresponding oscillation strengths of the low‐lying electronically excited states for the isolated proflavine cation, the hydrogen‐bonded PC–H2O dimer and PC–(H2O)2 trimer are calculated. Intermolecular hydrogen bonds at the central site of proflavine molecule are found to be stronger than the peripheral site. The hydrogen bond N–H???O for the hydrogen‐bonded dimer are indicated to be weakened in the excited states, since the excitation energy is increased slightly comparing to the monomer. Hydrogen bonds of PC–(H2O)2 trimer with the same type as the dimer are strengthened in the excited state, which is demonstrated by the decrease of the excited energies. Thus, hydrogen bond strengthening and weakening are observed to reveal site dependent feature in proflavine molecule. Furthermore, the hydrogen bond at central site induces the blue‐shift of the absorption spectrum, while the ones at peripheral site induce red‐shift. Hydrogen bonds with the same type at peripheral and central sites of proflavine molecule provide different effects on the photochemical and photophysical properties of proflavine.     

Solid‐State 1H NMR Studies of Degradable Poly(ethylene oxide) Based Hydrogels

Summary: Hydrogels, the elastic chains of which are constituted of a short central poly(1,3‐dioxolane) (PDXL) block surrounded by two hydrophilic poly(ethylene oxide) (PEO) blocks, were obtained by free radical homopolymerization of α,ω–methacryloyloxy PEO‐block‐1,3‐PDXL‐block‐PEO macromonomers. The central PDXL block is known to be sensitive to acidic degradation due to the presence of acetal groups. Once swollen to equilibrium, these hydrogels were characterized for their equilibrium swelling degree and their mechanical properties and network degradation studies were carried out.

Representation proposed for the breaking of a PEO‐block‐PDXL‐block‐PEO block copolymer.     

Construction of an Internally B3N3‐Doped Nanographene Molecule

The synthesis of a hexa‐peri‐hexabenzocoronene (HBC) with a central borazine core is described. The solid‐state structure of this BN‐doped HBC (BN‐HBC) is isotypic with that of the parent HBC. Scanning tunneling microscopy shows that BN‐HBC lies flat on Au(111) in a two‐dimensional pattern.     

Low‐cost bifunctional initiators for bidirectional living cationic polymerization of olefins. III. centrally functionalized polyisobutylenes

Allyl‐telechelic polyisobutylene (A‐PIB‐A) produced by the bis‐benzocyclobutane dichloride (bBCB‐diCl) initiator contains the bis‐benzocyclobutane (bBCB) fragment at the center of the macromolecule (A‐PIB‐bBCB‐PIB‐A). Thermolysis of A‐PIB‐bBCB‐PIB‐A quantitatively converts the central bBCB fragment to a substituted conjugated tetraene (A‐PIB‐tetraene‐PIB‐A). The structure of A‐PIB‐tetraene‐PIB‐A was anticipated from small molecule models and identified/quantitated by ¹H NMR spectroscopy. This is the first time a reactive functional group was introduced at the statistical center of a (telechelic) PIB. Subsequently, the A‐PIB‐tetraene‐PIB‐A was peroxidized to an epoxy derivative. Reaction of the A‐PIB‐tetraene‐PIB‐A with HSCH₂CH₂OH produced HOCH₂‐telechelic PIB containing a central  CH₂OH function, and hydrosilation with HSi(Me₂)‐O‐Si(Me₂)H produced SiH‐telechelic PIB with a central  SiH function. Reactions with maleic anhydride, tetracyanoethylene, butyl lithium, and potassium permanganate have also been examined. In sum, A‐PIB‐bBCB‐PIB‐A and A‐PIB‐tetraene‐PIB‐A are useful intermediates for the synthesis of novel PIB‐based materials for various end uses under investigation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1140–1145     

Synthesis of central functionalized asymmetric triblock copolymers for surface modification and switchable surface properties

Well‐defined central functionalized asymmetric triblock copolymers (CFABC) were designed as a new type of polymer‐brush surface modifier with a short central functionalized block that could form chemical bonds with a suitable substrate surface. A combination of sequential living anionic polymerization and polymer modification reactions was used for the synthesis of two CFABCs: polystyrene‐b‐poly(4‐hydroxystyrene)‐b‐poly(methyl methacrylate) (3) and polystyrene‐b‐poly(4‐urethanopropyl triethoxysilylstyrene)‐b‐poly(methyl methacrylate) (4). The central block of 3, poly(4‐hydroxystyrene), was synthesized with a protected monomer, p‐[(tert‐butyldimethylsilyl)oxy]styrene, for the polymerization step, and this synthesis was followed by the hydrolysis of the silyl protecting group. To obtain polymer 4, the phenol functionality in 3 was converted to triethoxysilyl groups by a quantitative reaction with isocyanato propyl triethoxysilane. Gel permeation chromatography and NMR characterization indicated that the block copolymers possessed controlled molecular weights and narrow molecular weight distributions. Preliminary atomic force microscopy and X‐ray photoelectron spectroscopy analysis of the polymer brushes were reported. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3742–3750, 2000     

Crystallographic report: Crystal structure of tetra(4‐methyl‐5‐imidazole‐carboxyaldehyde)zinc(II) diperchlorate

The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd.     

Bimodal Functionality in a Porous Covalent Triazine Framework by Rational Integration of an Electron‐Rich and ‐Deficient Pore Surface

A porous covalent triazine framework (CTF) consisting of both an electron‐deficient central triazine core and electron‐rich aromatic building blocks is reported. Taking advantage of the dual nature of the pore surface, bimodal functionality has been achieved. The electron deficiency in the central core has been utilized to address one of the pertinent problems in chemical industries, namely separation of benzene from its cyclic saturated congener, that is, cyclohexane. Also, by virtue of the electron‐rich aromatic rings with Lewis basic sites, aqueous‐phase chemical sensing of a nitroaromatic compound of highly explosive nature (2,4,6‐trinitrophenol; TNP) has been achieved. The present compound supersedes the performance of previously reported COFs in both the aspects. Notably, this reports the first example of pore‐surface engineering leading to bimodal functionality in CTFs.     

Mixed‐Valent Molecular Triple Deckers

Two phenothiazine (PTZ) moieties were connected via naphthalene spacers to a central arene to result in stacked PTZ‐arene‐PTZ structure elements. Benzene and tetramethoxybenzene units served as central arenes mediating electronic communication between the two PTZ units. Based on cyclic voltammetry, UV/Vis‐NIR absorption, EPR spectroscopy, and computational studies, the one‐electron oxidized forms of the resulting compounds behave as class II organic mixed‐valence species in which the unpaired electron is partially delocalized over both PTZ units. The barrier for intramolecular electron transfer depends on the nature of the central arene sandwiched between the two PTZ moieties. These are the first examples of rigid organic mixed‐valent triple‐decker compounds with possible electron‐transfer pathways directly across a stacked structure, and they illustrate the potential of oligo‐naphthalene building blocks for long‐range electron transfer and a future molecular electronics technology.     

Impact of replacement of the central benzene ring in anthracene by a heterocyclic ring on electronic excitations and reorganization energies in anthratetrathiophene molecules

The impact of changing the central benzene ring on the electronic excitations and reorganization energies (λ) of the anthratetrathiophene (ATT) molecules is studied by density functional theory (DFT) and time‐dependent DFT (TD‐DFT) quantum chemical calculations. The effect of changing the position of the sulfur atom at the periphery of anthracene on the optical and charge transfer properties is also studied. The calculated results suggest that the HOMO, LUMO, HOMO–LUMO energy gap, ionization potential (IP), electron affinity (EA), hole extraction potential (HEP), electron extraction potential (EEP), and reorganization energies (λ) are affected by replacing the central ring with different heterocyclic rings and the position of the sulfur atom. In addition, all molecules show good hole‐ and electron‐transport properties. This work may be helpful for future design and preparation of high‐performance charge‐transport materials.     

Enantiomeric differentiation of β‐amino alcohols under electrospray ionization mass spectrometric conditions

The enantiomeric differentiation of a series of chiral β‐amino alcohols (A) is attempted, for the first time, by applying the kinetic method using L‐proline, L‐tryptophan, 4‐iodo‐L‐phenylalanine or 3, 5‐diiodo‐L‐tyrosine as the chiral references (Ref) and Cu²⁺ or Ni²⁺ ion (M) as the central metal ion. The trimeric diastereomeric adduct ions, [M+(Ref)₂+A‐H]⁺, formed under electrospray ionization conditions, are subjected for collision‐induced dissociation (CID) experiments. The products ions, formed by the loss of either a reference or an analyte, detected in the CID spectra are evaluated for the enantiomeric differentiation. All the references showed enantiomeric differentiation and the R_chiral values are better for the aromatic alcohols than for aliphatic alcohols. Notably, the R_chiral values of the aliphatic amino alcohols enhanced when Ni²⁺ is used as the central metal ion. The experimental results are well supported by computational studies carried out on the diastereomeric dimeric complexes. The computational data of amino alcohols is correlated with that of amino acids to understand the structural interaction of amino alcohols with reference molecule and central metal ion and their role on the stabilization of the dimeric complexes. Application of flow injection MS/MS method is also demonstrated for the enantiomeric differentiation of the amino alcohols. Copyright © 2014 John Wiley & Sons, Ltd.     

Combining Organocatalysis with Central‐to‐Axial Chirality Conversion: Atroposelective Hantzsch‐Type Synthesis of 4‐Arylpyridines

Suitably substituted enantioenriched 4‐aryl‐1,4‐dihydro‐pyridines prepared by an organocatalytic enantioselective Michael addition were oxidized with MnO₂ into axially chiral 4‐arylpyridines with central‐to‐axial chirality conversion. Moderate to complete percentages (cp) were observed, and a model for the conversion of chirality is discussed.     

Synthesis of Hexahydro‐2‐pyrindine (=Hexahydrocyclopenta[c]pyridine) Derivatives as Conformationally Restricted Analogs of the Nicotinic Ligands Arecolone and Isoarecolone

Two hexahydropyrindine derivatives, 1,2,3,4,6,7‐hexahydro‐2‐methyl‐5H‐cyclopenta[c]pyridin‐5‐one ( 1 ) and 1,2,3,4,5,6‐hexahydro‐2‐methyl‐7H‐cyclopenta[c]pyridin‐7‐one ( 2 ), and their methiodides 14 and 26 , respectively, were synthesized. They can be considered rigid analogues of the known nicotinic agonists arecolone (=1‐(1,2,5,6‐tetrahydro‐1‐methylpyridin‐3‐yl)ethanone) and isoarecolone (=1‐(1,2,3,6‐tetrahydro‐1‐methylpyridin‐4‐yl)ethanone). The affinity for the central nicotinic receptor were measured on rat cerebral cortex. Although only the methiodide 14 , among the four conformationally restricted compounds, shows an appreciable affinity, the results obtained provide useful information on the molecular requirements at the interaction site of the central nicotinic receptors.     

Photophysical and self‐assembly behavior of poly(amidoamine) dendrons with chromophore as scaffold: The effect of dendritic architecture

Two series of amphiphiles composed of hydrophilic poly(amidoamine) dendrons (from the first to the third generation) as the shell and hydrophobic aromatic chromophores (3,6‐di(maleimidyl)‐9‐phenyl carbazole and 9‐(4′‐maleimidyl phenyl)‐3‐maleimidyl carbazole) as the central scaffold were synthesized. The effect of dendritic architecture on the photophysical properties and the self‐assembly behavior of these amphiphiles were studied by UV–vis absorption spectroscopy, fluorescence spectroscopy, and transmission electron microscopy (TEM) measurements. Both the generation of dendritic shell and the location of dendrons at the chromophoric scaffold had great effect on the photophysical properties of these amphiphiles. In addition, different spherical aggregates were formed from these amphiphiles in the aqueous solution at different concentrations. Because of the combined effects of steric hindrance and architecture of dendritic shells, the amphiphiles from G2 dendron with central chromophore self‐organized into ordered aggregates more readily than that from G1 and G3. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4584–4593, 2008     

Synthesis and Supramolecular Self‐Assembly of Coil‐Rod‐Coil Molecules: The Relationship between Self‐Assembled Nanostructures and Molecular Structures

Herein, the relationship between the supramolecularly self‐assembled nanostructures and the chemical structures of coil‐rod‐coil molecules is discussed. A series of nonamphiphilic coil‐rod‐coil molecules with different alkyl chains, central mesogenic groups, and chemical linkers were designed and synthesized. The solvent‐mediated supramolecular self‐assembling of these coil‐rod‐coil molecules resulted in rolled‐up nanotubes, nanofibers, submicron sized belts, needle‐like microcrystals, and amorphous structures. The self‐assembling behaviors of these coil‐rod‐coil molecules have been systematically investigated to reveal the relationship between the supramolecularly self‐assembled nanostructures and their chemical structures. With respect to the formation of rolled‐up nanotubes by self‐assembly of coil‐rod‐coil molecules, we have systematically investigated the following three influencing structural factors: 1) the alkyl chain length; 2) the central mesogenic group; (3) the linker type. These studies disclosed the key structural features of coil‐rod‐coil molecules for the formation of rolled‐up nanotubes.     

10‐(4‐Fluorophenyl)‐3,3,6,6,9‐pentamethyl‐3,4,6,7,9,10‐hexahydroacridine‐1,8(2H,5H)‐dione and 10‐(4‐fluorophenyl)‐3,3,6,6‐tetramethyl‐9‐­propyl‐3,4,6,7,9,10‐hexahydroacridine‐1,8(2H,5H)‐dione

10‐(4‐Fluoro­phenyl)‐3,3,6,6,9‐penta­methyl‐3,4,6,7,9,10‐hexa­hydro­acridine‐1,8(2H,5H)‐dione, C₂₄H₂₈FNO₂, (I), crystallizes with two crystallographically independent mol­ecules (which differ slightly in conformation), while 10‐(4‐fluoro­phenyl)‐9‐propyl‐3,3,6,6‐tetra­methyl‐3,4,6,7,9,10‐hexa­hydro­acridine‐1,8(2H,5H)‐dione, C₂₆H₃₂FNO₂, (II), crystallizes with one mol­ecule per asymmetric unit. In both structures, the central ring in the acridine moiety is in a sofa conformation, while the outer rings adopt intermediate half‐chair/sofa conformations. The central pyridine ring is orthogonal to the substituted phenyl ring. In both structures, the packing of the crystal is stabilized by C—H?O intermolecular hydrogen bonds.     

Steric‐Structure‐Dependent Gel Formation,Hierarchical Structures,Rheological Behavior,and Surface Wettability

A series of bicholesteryl‐based gelators with different central linker atoms C, N, and O (abbreviated to GC , GN , and GO , respectively) have been designed and synthesized. The self‐assembly processes of these gelators were investigated by using gelation tests, field‐emission scanning electron microscopy, field‐emission transmission electron microscopy, UV/Vis absorption, IR spectroscopy, X‐ray diffraction, rheology, and contact‐angle experiments. The gelation ability, self‐assembly morphology, rheological, and surface‐wettability properties of these gelators strongly depend on the central linker atom of the gelator molecule. Specifically, GC and GN can form gels in three different solvents, whereas GO can only form a gel in N,N‐dimethylformamide (DMF). Morphologies from nanofibers and nanosheets to nanospheres and nanotubes can be obtained with different central atoms. Gels of GC , GN , and GO formed in the same solvent (DMF) have different tolerances to external forces. All xerogels gave a hydrophobic surface with contact angles that ranged from 121 to 152°. Quantum‐chemical calculations indicate that the GC , GN , and GO molecules have very different steric structures. The results demonstrate that the central linker atom can efficiently modulate the molecular steric structure and thus regulate the supramolecular self‐assembly process and properties of gelators.