Terminal Phenyl Group Research Articles

Ultrafast Excited-State Dynamics of ortho-Terphenyl and 1,2-Diphenylcyclohexene: The Role of "Ethylenic Twisting" in the Nonadiabatic Photocyclization of Stilbene Analogs.

Nonadiabatic photocyclization is the fundamental step underlying photoswitching and light-assisted bond formation within diarylethylenes, yet the details of the nuclear dynamics leading to cyclization remain unclear. We have examined the ultrafast excited-state dynamics of o-terphenyl (OTP) and 1,2-diphenylcyclohexene (DPCH) in solution to determine how variation in structural constraints impacts the course of nonadiabatic photocyclization specifically in stilbenoids. Measured spectral dynamics reflect cyclization through a S1-to-S0 transition for both systems on picosecond time scales, with excited-state decay appreciably faster for DPCH versus OTP. Supportive ab initio calculations reveal a higher energetic penalty in OTP versus DPCH for reaching the lowest-energy conical intersection from the S1 minimum; this penalty is associated primarily with twisting about the carbon-carbon bond that bridges terminal phenyl groups, a structural change that has a critical role in nonadiabatic cis-trans isomerization of diarylethylenes. Findings provide a new experimental perspective on the elusive nuclear dynamics underlying cis-stilbene photocyclization.

Electronic structure of octavinyl- and octaphenylsilsesquioxane from XPS and DFT data

X-ray photoelectron spectroscopy (XPS) and density functional theory are employed to study the electronic structure of octasilsesquioxanes (RSiO1.5)8 with vinyl and phenyl terminal groups. Quantitative compositions determined from the XPS data are close to those estimated by empirical formulas. Narrow spectral lines corresponding to ionization from C1s core levels indicate similar chemical states of carbon atoms for both compounds. Experimental data are confirmed by close calculated values of effective charges on carbon atoms when polarization functions are included in the basis set and also by small energy ranges of core level electrons. The valence spectral region is interpreted based on the calculated energy values of electronic levels with regard to the density of states and ionization cross-sections.

Biphenyl- and phenylnaphthalenyl-substituted 1H-imidazole-4,5-dicarbonitrile catalysts for the coupling reaction of nucleoside methyl phosphonamidites

Crystal structures are reported for three substituted 1H-imidazole-4,5-dicarbonitrile compounds used as catalysts for the coupling reaction of nucleoside methyl phosphonamidites, namely 2-(3',5'-dimethylbiphenyl-2-yl)-1H-imidazole-4,5-dicarbonitrile, C19H14N4, (I), 2-(2',4',6'-trimethylbiphenyl-2-yl)-1H-imidazole-4,5-dicarbonitrile, C20H16N4, (II), and 2-[8-(3,5-dimethylphenyl)naphthalen-1-yl]-1H-imidazole-4,5-dicarbonitrile, C23H16N4, (III). The asymmetric unit of (I) contains two independent molecules with similar conformations. There is steric repulsion between the imidazole group and the terminal phenyl group in all three compounds, resulting in the nonplanarity of the molecules. The naphthalene group of (III) shows significant deviation from planarity. The C-N bond lengths in the imidazole rings range from 1.325 (2) to 1.377 (2) Å. The molecules are connected into zigzag chains by intermolecular N-H···N(imidazole) [for (I)] or N-H····N(cyano) [for (II) and (III)] hydrogen bonds.

Nature of Chemical Bonding and Metalloaromaticity of Na2[(MArx′)3] (M = B, Al, Ga; Arx′ = C6H3-2,6-(C6H5)2)

The nature of chemical bonding and metalloaromaticity of Na(2)[(MArx')(3)] (M = B, Al, Ga) have been studied within the framework of the atoms in molecules (AIM) theory and using electron localization function (ELF) analysis. The π electrons of the studied systems were separated from the total electron density and analyzed. The calculated results indicate that there are closed-shell weak interactions between the sodium atom and the M(3) (M = B, Al, Ga) ring, between the sodium atom and the terminal phenyl group on each Arx', and between the terminal phenyl groups on Arx' in Na(2)[(MArx')(3)]. The Na(2)[(MArx')(3)] has metalloaromatic nature, and the sodium atoms have an active role in determining the computed aromatic properties of the three-numbered cycle.

Hemiphasmidic Side-Chain Liquid Crystalline Polymer: From Smectic C Phase to Columnar Phase with a Bundle of Chains as Its Building Block.

We synthesized a new hemiphasmidic side-chain liquid crystalline polymer (P-n, n is the number of carbons in alky tail of the side chain, n = 4-12) using free radical polymerization. The side chain of P-n has a biphenyl in the middle, linked to the polystyrene backbone and to the terminal phenyl group with three alkyl tails via only methyleneoxy units. Upon increasing n, the mesophase of P-n changes from bilayer smectic C to hexagonal columnar (Φh) phase with the a-dimension of ∼6 nm. Both of the mesophases are long-range ordered, which can be well aligned by simple shearing. The oriented Φh shows a quite low rotational disorder around the shear direction. Most likely, the Φh phase takes a bundle of chains (e.g., ∼five chains) rather than a single chain as its building block. This "multi-chain model" of the Φh phase may represent a new type of self-assembly in side-chain polymers.

Solitonic waves in polyene dications and principles of charge carrier localization in π-conjugated organic materials

The quantum-chemical investigations by ab initio method (restricted Hartree–Fock/6-31G**) have been performed for a series of unsubstituted, monosubstituted, and disubstituted neutral polyenes and their double charged cations. The waves of charge alternation (characterized by the difference in the electron densities at the nearest carbon atoms or Δq function) and bond length alternation (characterized by the lengths difference of the nearest carbon–carbon bonds or Δl function) are reported. Comparisons are made with the corresponding monocationic polymethine molecules. We found that ionization by two electrons results in formation of two solitonic waves of charge alternation, rather than superposition of two overlapping solitonic waves into one. These waves behave similar to two independent elastic particles, which do not penetrate into each other despite the special confinement by the length of chromophore π-system. In monosubstituted polyene dication, Δq and Δl functions contain two waves each; however, only one wave is mobile and sensitive to a change of the chemical nature of the terminal group, whereas the second wave remains practically unchanged. The introduction of one oxymethyl or phenyl terminal groups leads to a relatively small shift of the mobile wave from the center to a direction of the terminal group. The effect of the amino or tropilium terminal groups is much more pronounced and leads to a shift of the mobile wave to the end of the molecule. In disubstituted polyene dication, both solitonic waves become mobile and shift symmetrically to both ends. The general principles of the charge localization described in this study may be used in molecular design and fine-tuning of the charge transport properties in plastic photovoltaics and other organic semiconducting materials. © 2012 Wiley Periodicals, Inc.

Biophysical Studies on the Effect of the 13 Position Substitution of the Anticancer Alkaloid Berberine on Its DNA Binding

The structural effects and thermodynamics of the DNA binding of six berberine analogues with alkyl chains of varying length and a terminal phenyl group at the C-13 position were investigated. All the analogues bound DNA noncooperatively in contrast to the cooperative binding of berberine. The binding affinity was higher and the effect of the chain length was only up to (CH(2))(3), after which the binding affinity decreased slightly. Intercalative binding with strong stabilization of the DNA helix was revealed. Binding resulted in the weakening of the base stacking with moderate conformational changes within the B-form. The binding was entropy driven in each case, the entropy contribution to the free energy increasing with the chain length up to the threshold (CH(2))(3). The complexation was dominated by nonpolyelectrolytic forces in each case; polyelectrolytic forces contributed only a quarter to the total free energy at 50 mM [Na(+)]. Overall, the phenylalkyl substitution at the C-13 position considerably enhanced the DNA binding and was highest for the analogue with (CH(2))(3). Structural and thermodynamic data on the DNA binding aspects of the substituted berberines are presented in comparison with berberine.

4-((E)-{2-[N-(1,5-Dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)carboximidoyl]benzylidene}amino)-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-one

The title compound, C30H28N6O2, is a symmetric diimine derived from ortho-dibenzaldehyde. Both C=N bonds are (E)-configured. The terminal N-bonded phenyl groups adopt staggered conformations relative to their respective parent heterocycles, the relevant least-squares planes inter­sect at angles of 32.35 (11) and 38.59 (10)°. In the crystal, C—H⋯O contacts connect the mol­ecules into chains along the b axis and give rise to a C 1 1(14)C 1 1(14) and a R 2 2(12) pattern on different levels of graph-set analysis. The shortest inter­centroid distance between two centroids was found at 4.2074 (11) Å between the two five-membered heterocycles.

Polymers with Carbazole-Oxadiazole Side Chains as Ambipolar Hosts for Phosphorescent Light-Emitting Diodes

Polymethacrylates, polystyrenes, and polynorbornenes bearing 2-(3-(carbazol-9-yl)phenyl)-5-phenyl-1,3,4-oxadiazole, 2-(4-(carbazol-9-yl)phenyl)-5-phenyl-1,3,4-oxadiazole, 2-(3,5-di(carbazol-9-yl)phenyl)-5-phenyl-1,3,4-oxadiazole) groups linked to the polymer backbone through the 3-position of their terminal phenyl groups have been synthesized for use as solution-processable ambipolar hosts for phosphorescent light-emitting diodes. The polymers exhibit good thermal stabilities, with no weight loss below 350 °C, and have glass-transition temperatures in the range 118–209 °C. Spectroscopic, electrochemical, and quantum-chemical data for small-molecule model compounds suggest that the side chain groups are suitable hosts for a range of phosphors, including the green-emitter fac-tris(2-phenylpyridinato-N,C2′)iridium (Ir(ppy)3). Light-emitting diodes were fabricated, each with a solution-processed photo-cross-linked hole-transport layer, a solution-processed emissive layer composed of a carbazole-oxadiazole-fun...

Electrochemical synthesis of dendritic diarylcarbenium ion pools

Dendritic diarylcarbenium ion pools were synthesized by the low temperature electrochemical oxidation of the corresponding dendritic (diarylmethyl)trimethylsilanes, which were prepared by use of the iterative method consisting of electrochemical activation and Friedel–Crafts type coupling. Time-course NMR studies revealed that thermal stability of dendritic diarylcarbenium ions depends both on the generation of the dendritic structure and on the para-substituents of the terminal phenyl groups. Dendritic diarylcarbenium ions up to the third generation exhibited high reactivity as a carbon electrophile.

Fluoride-mediated capture of a noncovalent bound state of a reversible covalent enzyme inhibitor: X-ray crystallographic analysis of an exceptionally potent α-ketoheterocycle inhibitor of fatty acid amide hydrolase.

Two cocrystal X-ray structures of the exceptionally potent α-ketoheterocycle inhibitor 1 (K(i) = 290 pM) bound to a humanized variant of rat fatty acid amide hydrolase (FAAH) are disclosed, representing noncovalently and covalently bound states of the same inhibitor with the enzyme. Key to securing the structure of the noncovalently bound state of the inhibitor was the inclusion of fluoride ion in the crystallization conditions that is proposed to bind the oxyanion hole precluding inhibitor covalent adduct formation with stabilization of the tetrahedral hemiketal. This permitted the opportunity to detect important noncovalent interactions stabilizing the binding of the inhibitor within the FAAH active site independent of the covalent reaction. Remarkably, noncovalently bound 1 in the presence of fluoride appears to capture the active site in the same "in action" state with the three catalytic residues Ser241-Ser217-Lys142 occupying essentially identical positions observed in the covalently bound structure of 1, suggesting that this technique of introducing fluoride may have important applications in structural studies beyond inhibiting substrate or inhibitor oxyanion hole binding. Key insights to emerge from the studies include the observations that noncovalently bound 1 binds in its ketone (not gem diol) form, that the terminal phenyl group in the acyl side chain of the inhibitor serves as the key anchoring interaction overriding the intricate polar interactions in the cytosolic port, and that the role of the central activating heterocycle is dominated by its intrinsic electron-withdrawing properties. These two structures are also briefly compared with five X-ray structures of α-ketoheterocycle-based inhibitors bound to FAAH recently disclosed.

Decorating the lanthanide terminus of self-assembled heterodinuclear lanthanum(iii)/gallium(iii) helicates

Arylacylhydrazones of 2,3-dihydroxybenzaldehyde are appropriate ligands for the preparation of heterodinuclear triple-stranded helicates involving high coordinated lanthanide(III) ions. In the present study, three different kinds of substituents are introduced at the ligands in order to modify the organic periphery of the coordination compounds: (1) alkoxy groups are attached to the terminal phenyl groups, (2) NH protons of the hydrazones are substituted by phenyl moieties and (3) amino acid bearing units are attached to the terminus of the ligand. The new ligands nicely form the desired triple-stranded gallium(III)-lanthanum(III) complexes [(5a-c,7,12,15)(3)GaLa] of which the highly phenylated derivative was crystallized and studied by X-ray diffraction.

Modulating the Light Switch by 3MLCT-3ππ* State Interconversion

The spectroscopic, electronic, and DNA-binding characteristics of two novel ruthenium complexes based on the dialkynyl ligands 2,3-bis(phenylethynyl)-1,4,8,9-tetraaza-triphenylene (bptt, 1) and 2,3-bis(4-tert-butyl-phenylethynyl)-1,4,8,9-tetraaza-triphenylene (tbptt, 2) have been investigated. Electronic structure calculations of bptt reveal that the frontier molecular orbitals are localized on the pyrazine-dialkynyl portion of the free ligand, a property that is reflected in a red shift of the lowest energy electronic transition (1: λmax = 393 nm) upon substitution at the terminal phenyl groups (2: λmax = 398 nm). Upon coordination to ruthenium, the low-energy ligand-centered transitions of 1 and 2 are retained, and metal-to-ligand charge transfer transitions (MLCT) centered at λmax = 450 nm are observed for [Ru(phen)2bptt]2+(3) and [Ru(phen)2tbptt]2+(4). The photophysical characteristics of 3 and 4 in ethanol closely parallel those observed for [Ru(bpy)3]2+ and [Ru(phen)3]2+, indicating that the MLCT excited state is primarily localized within the [Ru(phen)3]2+ manifold of 3 and 4, and is only sparingly affected by the extended conjugation of the bptt framework. In an aqueous environment, 3 and 4 possess notably small luminescence quantum yields (3: ϕH2O = 0.005, 4: ϕH2O = 0.011) and biexponential decay kinetics (3: τ1 = 40 ns, τ2 = 230 ns; 4: τ1 ∼ 26 ns, τ2 = 150 ns). Addition of CT-DNA to an aqueous solution of 3 causes a significant increase in the luminescence quantum yield (ϕDNA = 0.045), while the quantum yield of 4 is relatively unaffected (ϕDNA = 0.013). The differential behavior demonstrates that tert-butyl substitution on the terminal phenyl groups inhibits the ability of 4 to intercalate with DNA. Such changes in intrinsic luminescence demonstrate that 3 binds to DNA via intercalation (Kb = 3.3 × 104 M−1). The origin of this light switch behavior involves two competing 3MLCT states similar to that of the extensively studied light switch molecule [Ru(phen)2dppz]2+. The solvent- and temperature-dependence of the luminescence of 3 reveal that the extended ligand aromaticity lowers the energy of the 3ππ* excited state into competition with the emitting 3MLCT state. Interconversion between these two states plays a significant role in the observed photophysics and is responsible for the dual emission in aqueous environments.

Effect of π–π stacking on the atom transfer radical polymerization of styrene

The atom transfer radical polymerization (ATRP) of styrene (St) was carried out in the presence of varying equivalents (eq) of hexafluorobenzene (HFB) to probe the effect of pi–pi stacking on the rate of the polymerization and the resulting tacticity of polystyrene (PSt) formed. The extent of interaction between the electron deficient face of the HFB and the electron rich face of the styrenic or polystyrenic phenyl ring was also examined as a function of reaction solvent, incorporating both non-aromatics (hexanes and THF) and aromatics (benzene and toluene). It was found that in all cases the rate of the ATRP of St was slowed by the addition of HFB to the reaction mixture, with increasing amounts of HFB (1 full eq. compared to St) retarding the rate to a relatively greater extent compared to smaller amounts (0.5 eq). Additionally, when aromatic solvents were used instead of hydrocarbons the effect of HFB on the rate of the ATRP was minimized, consistent with the solvent itself competing with the styrenic phenyl groups for pi–pi stacking interactions with HFB. The decreased rate in the presence of HFB is consistent with a reduced ability of the terminal phenyl group on the PSt chain to stabilize the active polymer radical, pushing the equilibrium further to the dormant alkyl halide. This interaction between the dormant alkyl bromide and HFB was verified by 1H NMR, with 1-bromoethylbenzene used as the alkyl bromide. When the ATRP of non-aromatic vinyl monomers was studied (butyl acrylate and methyl methacrylate), the effect of HFB on the system was almost unnoticeable as expected due to their inability to participate in pi–pi stacking interactions. The tacticity of the PSt formed in the presence of HFB was compared to PSt formed in its absence by observing the C1 resonance on 13C NMR, but no change in the shape or chemical shift of the signal was observed.

(3R,4R,5R)-5-(Acetamidomethyl)-N-benzyl-3,4-dihydroxytetrahydrofuran-3-carboxamide

X-ray crystallographic analysis with Cu Kα radiation established the relative configurations of the stereogenic centers in the title compound, C15H20N2O5, and clarified mechanistic ambiguities in the synthesis. The conformation of the five-membered ring approximates twisted, about a C—O bond. The absolute configuration of this carbon-branched dipeptide isostere was known based on the use of d-ribose as the starting material. Refinement of the Flack parameter gave an ambiguous result but the refined Hooft parameter is in agreement with the assumed (d-ribose) absolute structure. The crystal structure consists of N—H⋯O and O—H⋯O hydrogen-bonded bi-layers, with the terminal methyl and phenyl groups forming a hydro­phobic inter-layer inter­face. Some weak C—H⋯O inter­actions are also present.

A Novel Competitive Class of α‐Glucosidase Inhibitors: (E)‐1‐Phenyl‐3‐(4‐Styrylphenyl)Urea Derivatives

Competitive glycosidase inhibitors are generally sugar mimics that are costly and tedious to obtain because they require challenging and elongated chemical synthesis, which must be stereo- and regiocontrolled. Here, we show that readily accessible achiral (E)-1-phenyl-3-(4-strylphenyl)ureas are potent competitive α-glucosidase inhibitors. A systematic synthesis study shows that the 1-phenyl moiety on the urea is critical for ensuring competitive inhibition, and substituents on both terminal phenyl groups contribute to inhibition potency. The most potent inhibitor, compound 12 (IC(50)=8.4 μM, K(i)=3.2 μM), manifested a simple slow-binding inhibition profile for α-glucosidase with the kinetic parameters k(3)=0.005256 μM(-1) min(-1), k(4)=0.003024 min(-1), and K(i)(app) =0.5753 μM.

Synthesis, spectral characterization, electron microscopic study and thermogravimetric analysis of a phosphorus containing dendrimer with diphenylsilanediol as core unit

A phosphorus containing dendrimer with a diphenylsilanediol core was synthesized using a divergent method. Several types of reactions were performed on dendrons of several sizes, either at the level of the core or the surface. The giant Schiff’s base macro molecule possesses 12 imine bonds and 8 hydroxy groups on the terminal phenyl groups. The structures of the intermediate compounds were confirmed by IR, GCMS and 31P NMR. The final compound was characterized by 1H, 13C, 31P NMR, MALDI-TOF MS and CHN analysis. Scanning electron microscopic and thermogravimetric analysis/differential scanning calorimetric studies were also performed on the final dendritic molecule.

Identification of Novel Synthetic Toll-like Receptor 2 Agonists by High Throughput Screening

Toll-like receptors (TLRs) play a central role in host defense by inducing inflammatory and adaptive immune responses following infection. Drugs that target TLRs are of considerable interest as potential inflammatory regulators, vaccine adjuvants, and novel immunotherapeutics. TLR2, in cooperation with either TLR1 or TLR6, mediates responses to a wide variety of microbial products as well as products of host tissue damage. In an effort to understand the structural basis of TLR2 recognition and uncover novel TLR2 agonists, a synthetic chemical library of 24,000 compounds was screened using an IL-8-driven luciferase reporter in cells expressing these human receptors. The screening yielded several novel TLR2-dependent activators that utilize TLR1, TLR6, or both as co-receptors. These novel small molecule compounds are aromatic in nature and structurally unrelated to any known TLR2 agonists. The three most potent compounds do not exhibit synergistic activity, nor do they act as pseudoantagonists toward natural TLR2 activators. Interestingly, two of the compounds exhibit species specificity and are inactive toward murine peritoneal macrophages. Mutational analysis reveals that although the central extracellular region of TLR1 is required for stimulation, there are subtle differences in the mechanism of stimulation mediated by the synthetic compounds in comparison with natural lipoprotein agonists. The three most potent compounds activate cells in the nanomolar range and stimulate cytokine production from human peripheral blood monocytes. Our results confirm the utility of high throughput screens to uncover novel synthetic TLR2 agonists that may be of therapeutic benefit.

Leukotriene B4 inhibitors: US2009054466; US2009227603 and US2009253684

Three US applications describing a narrow, closely related series of antagonists of the action of leukotriene B4 on the BLT1 and BLT2 receptors are described. The generic structure claimed is a lipophilic linked diphenyl core containing two acid groups appended to the central phenyl ring. The terminal phenyl moiety contains disubstitution at the 3′- and 5′-positions. These three applications differ in the nature of the substituent on the terminal phenyl group as well as the linking moiety between the two phenyl rings. These compounds are claimed to have utility in inflammatory diseases such as severe asthma and chronic obstructive pulmonary disease.

Odd–Even Effects in the Friction of Self-Assembled Monolayers of Phenyl-Terminated Alkanethiols in Contacts of Different Adhesion Strengths

We have studied the frictional properties of self-assembled monolayers (SAMs) of phenyl-terminated alkanethiols, C6H5(CH2) n SH (n = 13–16) on template-stripped gold. The friction force was measured with atomic force microscopy (AFM), and the magnitude of the adhesion was controlled by immersing the sliding contact in ethanol (giving low adhesion) or dry N2 gas (giving enhanced adhesion relative to ethanol). We observed a linear friction force as a function of load (F = μL) in the systems with low adhesion and a non-linear friction force when the adhesion was higher. The non-linear behavior in the adhesive systems appeared to be area-dependent (F = S c A) and was compared to contact areas calculated using the extended Thin-Coating Contact Mechanics (TCCM) model. In ethanol, the coefficient of friction μ was found to be systematically higher for odd values of n (i.e., for the monolayers in which the terminal phenyl group was oriented closer to the surface normal).