Electronegative Properties Research Articles

Synthesis, spectroscopic properties, density functional theory calculations and nonlinear optical properties of novel complexes of 5‐hydroxy‐4,7‐dimethyl‐6‐(phenylazo)coumarin with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions

5‐Hydroxy‐4,7‐dimethyl‐6‐(phenylazo)coumarin (L) has been synthesized and its novel complexes with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions have also been prepared and identified using various analytical tools. The complexes are octahedral binding via one/two oxygen, nitrogen atoms for 1:1 and 1:2 complexes and two/three coordinated water molecules. All the prepared solid complexes behave as neutral in dimethylformamide. The optimized structures of the studied complexes were theoretically investigated at the B3LYP/6‐311G** level. Molecular stability and bond strengths were investigated by applying natural bond orbital analysis. The geometries of the studied complexes are non‐planar as indicated from the values of dihedral angles. The global properties of hardness, global softness and electronegativity were computed. The calculated small energy gap between highest occupied and lowest unoccupied molecular orbital energies shows that charge transfer occurs within the complexes. The obtained total static dipole moment, mean polarizability, anisotropy of polarizability and mean first‐order hyperpolarizability (<β>) were compared with those of urea as a reference material. The results for <β> showed that the complexes are excellent candidates as nonlinear optical materials. The three‐dimensional plots of the molecular electrostatic potential for some selected complexes were investigated.

Determination of pKa and the corresponding structures of quinclorac using combined experimental and theoretical approaches

As an emerging environmental contaminant, the herbicide quinclorac has attracted much attention in recent years. However, a very fundamental issue, the acid dissociation of quinclorac has not yet to be studied in detail. Herein, the pKa value and the corresponding structures of quinclorac were systematically investigated using combined experimental and theoretical approaches. The experimental pKa of quinclorac was determined by the spectrophotometric method to be 2.65 at 25 °C with ionic strength of 0.05 M, and was corrected to be 2.56 at ionic strength of zero. The molecular structures of quinclorac were then located by employing the DFT calculation. The anionic quinclorac was directly located with the carboxylic group perpendicular to the aromatic ring, while neutral quinclorac was found to be the equivalent twin structures. The result was further confirmed by analyzing the UV/Vis and MS-MS2 spectra from both experimental and theoretical viewpoints. By employing the QSPR approach, the theoretical pKa of QCR was determined to be 2.50, which is excellent agreement with the experimental result obtained herein. The protonation of QCR at the carboxylic group instead of the quinoline structure was attributed to the weak electronegative property of nitrogen atom induced by the electron-withdrawing groups. It is anticipated that this work could not only help in gaining a deep insight into the acid dissociation of quinclorac but also offering the key information on its reaction and interaction with others.

Structural Variability of R 2 C Adducts of 3a,6a-Diaza-1,4-diphosphapentalene: Tuning the N→P Bonding

3a,6a-Diaza-1,4-diphosphapentalene (DDP) reacts with hexachlorocyclopentadiene to form a stable adduct (ClC)4C=DDP (4). The phosphorus atom involved into coordination has a pyramidal arrangement but retains partial double bonding with carbon [1.752(3) Å]. At the same time, the P–N bond remains covalent [1.824(3) Å]. The adduct 4 is better described as a zwitterionic compound with strongly delocalized positive and negative charges. A similar zwitterionic adduct DDP=C(CN)2 was prepared by the reactions of dichloro-DDP (7) with malononitrile in the presence of Et3N. DFT calculations showed that related structures are formed in the case of the substituents (ClC)4C=, (HC)4C=, (NC)2C=, and (MeCO)2C=, possessing electron-delocalizing properties. Compounds with other R2C groups (R = Ph, Me, C6F5, Cl), possessing electronegative properties as well, but insufficient e-delocalization, demonstrate the noncovalent P–N bonding and a little shorter R2C–P bond lengths (ca. 1.70 Å).

Design (Docking and QSAR Studies) and synthesis of histone deacetylase 2 (HDAC2) inhibitors series

In recent years, it has been shown that histone deacetylase 2 (HDAC2) inhibitors increase histone acetylation and enhance memory processes, probably due to an increase in the gene transcription rate that emerges during memory formation. Histone acetylation generally favors long-term memory, whereas histone deacetylation impinges on it. However, until today there is no specific drug that can target the HDAC2 active site. In this work we applied the method of rational drug design, through enzyme-structural-chemical properties to generate new molecules as HDAC inhibitors. By the application of Quantitative Structure-Activity Relationship (QSAR) and molecular modeling methodologies our aim is to predict more potent HDAC inhibitors. 76 small molecules with potential activity were analyzed using QSAR methodology. The best model was constructed by merging the properties of electronegativity, atomic mass, polarizability, van der Waals forces and some conformational aspects, with the following statistical parameters: r 2 = 0.8935, q 2 LOO-CV = 0.8498, and q 2 LGO-CV = 0.7598. The molecular docking of the ligands on the template was performed by blind docking. The results showed intermolecular interactions between small molecules and some amino acids, such as His145, His146, Asp179, Asp186, and internal-H2O and Zn2+ of which IN01, IN04, and IN14 showed theoretically better biological activity compared with that of TSA and SAHA. Mainly, the IN14 synthesized molecule is a theoretical inhibitor of HDAC class I.

Ni/M-Al2O3 (M=Sm, Ce or Mg) for combined steam and CO2 reforming of CH4 from coke oven gas

Effects of structural promoters such as Sm, Ce, Mg metal oxides on the Ni/M-Al2O3 catalysts (where M=Sm, Ce, or Mg) were verified to elucidate different catalytic activity for a combined steam and CO2 reforming reaction with CH4 (CSCR) using H2-rich coke oven gases generated from steel industry. The enhanced catalytic performance and stability were explained in terms of the variations of surface basic sites with different aggregation phenomena of active nickel crystallites and resistances for a coke formation. The most efficient Sm promoter having a high electronegativity and basic property on the Ni/M-Al2O3 was found to largely suppress a coke deposition and less aggregation of active nickel crystallites by forming the strongly interacted nickel nanoparticles with an enhanced basic sites on the Sm-modified Al2O3. In addition, a larger amount of basic sites on the Ni/Sm-Al2O3 were responsible for a less coke deposition and best catalytic performances in terms of the conversions of CH4 and CO2. These positive effects of Sm promoter were also attributed to a relatively easy activation of CO2 and the formation of the strongly interacted smaller nickel crystallites on the newly formed basic perovskite-like SmAlO3 structures or segregated Sm2O3 species.

The novel properties of SF6 for directional dark matter experiments

SF6 is an inert and electronegative gas that has a long history of use in high voltage insulation and numerous other industrial applications. Although SF6 is used as a trace component to introduce stability in tracking chambers, its highly electronegative properties have limited its use in tracking detectors. In this work we present a series of measurements with SF6 as the primary gas in a low pressure Time Projection Chamber (TPC), with a thick GEM used as the avalanche and readout device. The first results of an 55Fe energy spectrum in SF6 are presented. Measurements of the mobility and longitudinal diffusion confirm the negative ion drift of SF6. However, the observed waveforms have a peculiar but interesting structure that indicates multiple drift species and a dependence on the reduced field (E/p), as well as on the level of water vapor contamination. The discovery of a distinct secondary peak in the waveform, together with its identification and use for fiducializing events in the TPC, are also presented. Our measurements demonstrate that SF6 is an ideal gas for directional dark matter detection. In particular, the high fluorine content is desirable for spin-dependent sensitivity, negative ion drift ensures low diffusion over large drift distances, and the multiple species of charge carriers allow for full detector fiducialization.

Electronegativity of capacitively coupled Ar+O2 plasma excited at very high frequency

By using pulsed laser induced detachment technique assisted with a Langmuir probe, the electronegative characteristics of the capacitively coupled Ar plasma doped with 5% O2 are studied in this paper. We first focus on the electrical signal of the probe after laser pulse has induced negative ion detachment, and then analyze characteristics of the probe signal with the probe bias below or above the plasma space potential. When the bias is set to be lower than the plasma potential, the probe signal usually shows a downward surge signal. As the bias is higher than the plasma potential, the main characteristics of the signal takes on an upward wide wave packet. The evolution behavior of the probe signal with bias from the downward surge valley to the upward wide wave packet might be due to the potential difference between the plasma space potential and the probe bias voltage. Furthermore, it shows that the position of the upward peak appears later than that of the downward surge valley, which may be related to the changing of the rate of the electron diffusion flux and the electric field drift flux. According to the dependence of probe collection signal on bias, the electronegativity describing the Ar+O2 plasma electronegative property is defined as saturation ratio of electron current after pulsed laser radiation to that of collection probe at a potential above plasma spatial potential. Plasma electronegativity is diagnosed with discharge pressure, radio-frequency (RF) input power and axial position. The experimental results show that the electronegativity of plasma decreases with input RF power increasing. As the gas pressure is kept at 12.0 Pa, the plasma electronegativity decreases from 5.05 to 0.98 with RF input power increasing from 50 to 300 W. It also shows an increasing trend of electronegativity with plasma discharge pressure increasing. Due to asymmetrical distribution of electrodes, the plasma electronegativity also takes on asymmetric one with respect to the axial position. In our experiments, the electronegativity near the power electrode shows about 1-4 times higher than that near the ground electrode, the lowest point of the plasma electronegativity seems to be located in the center of the plasma discharge. This may be related to the dynamics of the secondary electrons emitted from electrode and the competition processes between negative ion production in collisional dissociation of oxygen molecules and the losses of high energy electron and negative ion in collisional detachment of negative ion with oxygen molecule.

Triboelectric Nanogenerators Based on Melamine and Self‐Powered High‐Sensitive Sensors for Melamine Detection

Melamine (Mel) is added illegally to foods and feeds due to its high nitrogen content and high intake, and it causes serious health problems, so it is urgent to build a simple and quick method for detecting Mel in our daily life. In this work, a self‐powered Mel detection method is developed that is based on the newly invented triboelectric nanogenerator (TENG) by using the strong electronegativity property of Mel. In addition, Mel can enhance the electrical output signals of the TENGs by pairing with other triboelectric materials. Thus a high‐sensitive Mel sensor is designed based on polytetrafluoethylene (PTFE) TENG; the output current of TENG increases with the addition of Mel, resulting in largely improved detection limit of Mel with 0.5 ppb and a linear increase range from 1 to 500 ppb. This study not only develops a new type of material for TENG, but also demonstrates an innovative and convenient method for the detection of Mel and other biomaterials.

An assessment of triboelectrification effects on co-ground solid dispersions of carbamazepine

One of strategies adopted to improve the dissolution rates of poorly soluble drugs is by co-grinding the drug with a hydrophilic carrier. However, the introduction of mechanical forces during the grinding process can lead to changes in the physicochemical characteristics as well as an increase in the surface free energy of the ground particles, which causes an alteration in the electrostatic properties of these particles. The solid state characteristics of glucosamine hydrochloride (GLU) and carbamazepine (CBZ) and their co-ground mixtures were studied using DSC, XRPD and SEM. These revealed that polymorphic transformations occurred due to the grinding process. The influence of grinding time on the triboelectrification properties of the formulations was also studied. Both pure CBZ and GLU powders were predominantly electro-positively charged and their charging properties increased with increasing grinding time. CBZ:GLU physical mixtures exhibited complicated bipolar charging behaviour, however, when subjected to grinding, these mixtures demonstrated mainly electronegative charge properties. The influence of both grinding time and CBZ content within CBZ:GLU mixtures was examined. The value of net-electronegative-charge density of CBZ:GLU mixtures was shown to increase with grinding time and/or when increasing the percentage proportion of CBZ up to 30% w:w. This study helps to provide information about the handling of these formulations and gives a formulator tools to ascertain appropriate ratios for handling and possible simultaneous dissolution improvements.

Lysine pyrrolation is a naturally-occurring covalent modification involved in the production of DNA mimic proteins.

Covalent modification of proteins exerts significant effects on their chemical properties and has important functional and regulatory consequences. We now report the identification and verification of an electrically-active form of modified proteins recognized by a group of small molecules commonly used to interact with DNA. This previously unreported property of proteins was initially discovered when the γ-ketoaldehydes were identified as a source of the proteins stained by the DNA intercalators. Using 1,4-butanedial, the simplest γ-ketoaldehyde, we characterized the structural and chemical criteria governing the recognition of the modified proteins by the DNA intercalators and identified Nε-pyrrolelysine as a key adduct. Unexpectedly, the pyrrolation conferred an electronegativity and electronic properties on the proteins that potentially constitute an electrical mimic to the DNA. In addition, we found that the pyrrolated proteins indeed triggered an autoimmune response and that the production of specific antibodies against the pyrrolated proteins was accelerated in human systemic lupus erythematosus. These findings and the apparent high abundance of Nε-pyrrolelysine in vivo suggest that protein pyrrolation could be an endogenous source of DNA mimic proteins, providing a possible link connecting protein turnover and immune disorders.

Optical emission spectroscopic diagnostics of a non-thermal atmospheric pressure helium-oxygen plasma jet for biomedical applications

In this work, we have applied optical emission spectroscopy diagnostics to investigate the characteristics of a non-thermal atmospheric pressure helium plasma jet. The discharge characteristics in the active and afterglow region of the plasma jet, that are critical for biomedical applications, have been investigated. The voltage-current characteristics of the plasma discharge were analyzed and the average plasma power was measured to be around 18 W. The effect of addition of small fractions of oxygen at 0.1%–0.5% on the plasma jet characteristics was studied. The addition of oxygen resulted in a decrease in plasma plume length due to the electronegativity property of oxygen. Atomic and molecular lines of selected reactive plasma species that are considered to be useful to induce biochemical reactions such as OH transitions A2Σ+(ν=0,1)→X2Π(Δν=0) at 308 nm and A2Σ+(ν=0,1)→X2Π(Δν=1) at 287 nm, O I transitions 3p5P→3s5S0 at 777.41 nm, and 3p3P→3s3S0 at 844.6 nm, N2(C-B) second positive system with electronic transition C3Πu →B3Πg in the range of 300–450 nm and N2+(B-X) first negative system with electronic transition B2Σu+→X2Σg+(Δν=0) at 391.4 nm have been studied. The atomic emission lines of helium were identified, including the He I transitions 3p3P0→2s3S at 388.8 nm, 3p1P0→ 2s1S at 501.6 nm, 3d3D→2p3P0 at 587.6 nm, 3d1D→2p1P0 at 667.8 nm, 3s3S1→2p3P0 at 706.5 nm, 3s1S0→2p1P0 at 728.1 nm, and Hα transition 2p-3d at 656.3 nm. Using a spectral fitting method, the OH radicals at 306–312 nm, the rotational and vibrational temperatures equivalent to gas temperatures of the discharge was measured and the effective non-equilibrium nature of the plasma jet was demonstrated. Our results show that, in the entire active plasma region, the gas temperature remains at 310 ± 25 K and 340 ± 25 K and it increases to 320 ± 25 K and 360 ± 25 K in the afterglow region of the plasma jet for pure helium and helium/oxygen (0.1%) mixture, respectively. Additionally, the vibrational temperatures range from 2200 ± 100 K and 2500 ± 100 K for pure helium and helium/oxygen (0.1%) mixture, respectively. The plasma jet was tested on heat sensitive polymer films used in biomedical applications such as polyethylene terephthalate and poly-L-lactide samples continuously for several minutes without causing any physical or thermal damage to the films. The plasma jet produces significant reactive species of interest while the gas temperatures remain very low demonstrating its potential for a range of biomedical applications.

Experimental and DFT studies on the antioxidant activity of a C-glycoside from Rhynchosia capitata

Rhynchosia capitata (=Glycine capitata) Heyne ex roth, was found to possess polyphenolics including flavonoids, which acts as potential antioxidant. The study of ethanolic extract of roots and leaves reveals that the leaves possess high polyphenolics including flavonoids than roots. This was also confirmed by DPPH radical scavenging activity. Leaf powder of the plant was extracted with different solvents by soxhlet apparatus in the order of increasing polarity. The DPPH scavenging activity of methanol fraction was found to be high compared to the crude extract and other fractions. Nitric oxide scavenging activity was dominant in chloroform fraction compared to methanol fraction. Presence of flavonoids especially vitexin, a C-glycoside in methanol and chloroform fractions were confirmed by high pressure thin layer chromatography (HPTLC) analysis. The structural and molecular characteristics of naturally occurring flavonoid, vitexin was investigated in gas phase using density functional theory (DFT) approach with B3LYP/6-311G(d,p) level of theory. Analysis of bond dissociation enthalpy (BDE) reveals that the OH site that requires minimum energy for dissociation is 4′-OH from B-ring. To explore the radical scavenging activity of vitexin, the adiabatic ionization potential, electron affinity, hardness, softness, electronegativity and electrophilic index properties were computed and interpreted. The nonvalidity of Koopman’s theorem has been verified by the computation of Eo and Ev energy magnitudes. Interestingly, from BDE calculations it was observed that BDE for 4′-OH, 5-OH and 7-OH are comparatively low for vitexin than its aglycone apigenin and this may be due to the presence of C-8 glucoside in vitexin. To substantiate this, plot of frontier molecular orbital and spin density distribution analysis for neutral and the corresponding radical species for the compound vitexin have been presented.

Enhanced heavy metals removal and recovery by mesoporous adsorbent prepared from waste rubber tire

A novel carbon (RTAC) developed by physical activation from waste tire rubber, was used as adsorbent for assessing its removal capacity of lead and nickel ions from aqueous solutions. A well developed mesoporous structure in RTAC was conducive for its enhanced batch adsorption capacity of the studied metal ions removal in comparison to a microporous commercial carbon (CAC). Uptake trend of RTAC for Pb2+>Ni2+ revealed the adsorbate properties of electronegativity and ionic radii to play a contributory role. Effect of various operating parameters along with equilibrium, kinetic and thermodynamic studies reveal the efficacy of the RTAC for lead and nickel removal. The adsorption equilibrium data obeyed the Langmuir model and the kinetic data were well described by the pseudo-second-order model. A physical electrostatic adsorbate–adsorbent interaction is revealed from pHPZC studies and from D–R model constants. The adsorption process is believed to proceed by an initial surface adsorption followed by intraparticle diffusion. Thermodynamic studies revealed the feasibility and endothermic nature of the system. Such promising results were confirmed by column experiments. Adequate desorption as well as reusability without significant loss of efficiency established the practicality of the developed system and demonstrated an important criterion of advanced adsorbent in RTAC for waste water treatment. Approximately 96% and 87% lead and nickel removal was achieved by RTAC from a simulated electroplating industry wastewater. The experimental results reveal the technical feasibility of RTAC, its easy synthesis, economic, eco-friendly and a promising advanced adsorbent in environmental pollution cleanup.

Interaction of Au16 Nanocluster with Defects in Supporting Graphite: A Density-Functional Study

Soft-landed adsorption of Au16 on bilayered graphene is investigated using density functional theory. The orientation of the Au16 cluster and number of neighboring surface vacancies affect the overall structural and electronic properties of the cluster. The results of the PBE, vdW-DF, and vdW-DF2 exchange-correlation functionals are compared for the cluster-substrate interaction for systems with and without defects. In the presence of defects size two and greater, an Au atom adsorbs into the topmost graphene layer; this strongly influences the binding energy (>3 eV), while inducing substantial bending in the carbon plane and altering electronic properties of the system. Though the Td-symmetry and electronegative properties of the Au16 structure change in the presence of greater neighboring defects, elements of the cagelike starting structure remain throughout. The electron localization function shows that the in-plane Au–C bonds are of delocalized (metallic) nature and there is a local charge transfer to ...

Tautomeric and conformational properties of β-diketones

Available literature data about keto–enol equilibrium in β-diketones with different substituents in β-positions (R1C(O)–CH 2–C(O)R2) has been analyzed. It was concluded that substituents from group I (R = H, CH 3, CF 3, C(CH3) 3) strongly favour the enol tautomer, whereas substituents from group II (R = F, Cl, OCH 3, NH 2) favour the keto form. To understand the influence of the nature of the substituents on the keto–enol tautomerism, quantum chemical calculations (B3LYP/aug-cc-pVTZ) were performed for the series of β-diketones with substituents from both groups, with R1 = R2 or R1 ≠ R2. Equilibrium structures of enol and keto forms and vibrational spectra were analyzed for all investigated molecules. The electron density distribution was studied by NBO-analysis. Experiments and quantum chemical calculations demonstrate, that the keto form is preferred only in β-diketones with R1 and R2 from group II. This result can be explained by hyperconjugation between lone pairs of these substituents and the C O double bond in both R–C O fragments. Thus, lone pairs at the atom, connected with the C(O)–C–C(O) skeleton, which are present in the substituents from group II, are the reason for favouring to the keto form rather than electronegativity or other properties. In β-diketones with at least one substituent from group I the enol tautomer is preferred. Obviously, the strong hydrogen bond and π-conjugation in the ring are the reasons for stabilizing the enol form. Optimized geometrical parameters of the molecules are in a good agreement with the experimental gas-phase structures. The calculations predict reasonably well the energetically most preferred tautomer. However, exact prediction of the keto/enol equilibrium composition apparently requires methods, more sophisticated than B3LYP or MP2.

Structural stability, electronegativity and electronic property of endohedral TM@C 24 and exohedral TM [sbnd]C 24 (TM = Sc, Y and La) metallofullerene complexes: Density-functional theory investigations

The structural stability, electronegativity and electronic property of endohedral TM@C 24 and exohedral TM C 24 (TM = Sc, Y and La) complexes have been systematically investigated using the hybrid DFT-(U)B3PW91 functional. The calculated results show that the endohedral complexes do not undergo any major deformation in the structures, and the Sc atom is energetically favorable to be encapsulated into the centre of the cage. But in the Y and La cases the exohedral structure is more stable than the endohedral structure. The frontier orbital analyses indicate that the exohedral TM C 24 complexes have the high kinetic stabilities, which are consistent with their thermodynamic stabilities. Additionally, natural population analyses also tell us that the natural charges on TM atoms are obviously increased with the increasing atomic radii except for the endohedral La@C 24. In the La@C 24, the La atom acts as an electron acceptor with the negative charges. And its 4f orbitals are significantly involved in the formation of the chemical bonding.

Charge transfer and trapping properties in polymer gate dielectrics for non-volatile organic field-effect transistor memory applications

We investigate here charge transfer and trapping characteristics of various chargeable polymer dielectric layers, polystyrene (PS), poly(4-vinyl naphthalene) (PVN), and amorphous fluoropolymer (Teflon ® AF) in non-volatile pentacene field-effect transistor (FET) memory devices. Non-volatile memory properties, i.e., the degree of threshold voltage ( V Th) shifts (memory window), the programming and erasing bias, and the retention time, strongly depended on the selection of a charge storage layer, due to its electronic and dielectric properties. The pentacene FETs with PVN or PS showed reversible positive and negative V Th shifts by an application of external gate bias. In Teflon ® AF device, most significant positive V Th shift was obtained indicating a efficient electron injection whereas showed inefficient erasing characteristics via hole injection and storing due to a high electronegative properties of fluorine units in the dielectric. This result indicates importance of a selection of the chargeable polymer dielectric to obtain efficient organic non-volatile memory with a long retention time.

Gordy’s electrostatic scale of electronegativity revisited

Gordy identified electronegativity of an atom with the electrostatic potential felt by one of its valence electrons and suggested an ansatz, χ = Z eff/ r cov where χ is the electronegativity, Z eff is the effective nuclear charge and r cov is the radial distance equal to atom’s single bond covalent radius. In this report we have elucidated that the use of covalent radius in evaluating the electronegativity, ( χ), of atoms through Gordy’s formula, χ = Z eff/ r cov, is not justified. Armed with this knowledge and relying upon the electronegativity equalization principle, we have argued that the most probable radius (Slater radius), and not the covalent radius, is the fundamental size descriptor of atoms in mathematical formulation of electronegativity property of atoms. We have also suggested that the electronegativity, χ, is not equal to Z eff/ r according to Gordy’s original formula rather it is proportional to Z eff/ r and the new electronegativity ansatz is χ = [ a( Z eff/ r) + b], where a and b are constants and r is the Slater (most probable) radius of atoms. We have taken care so that the electronegativity is evaluated in proper unit i.e. energy unit. We have computed the electronegativity of 103 elements of the periodic table through the new suggested ansatz and using Slater radii and effective nuclear charge computed by us. The evaluated new electronegativities are found to satisfy the sine qua non of a reasonable scale of electronegativity by exhibiting periodicity of periods and groups, and observing silicon rule and correlating many physico-chemical properties of elements. The intrinsic inertness of Hg atom is revealed in the present scale.

Anomalies in oxygen-induced quenching of electronically excited states of 4,4′-bis[2-(1,3)-benzoxazol-2-yl)ethenyl]biphenyl in the vapor phase

From oxygen-induced quenching of polarized fluorescence of 4,4′-bis[2-(1,3-benzoxazol-2-yl)ethenyl]biphenyl, we have observed structural transformation in electronically excited molecules with retention of fluorescent capability, initiated by collisions with oxygen. Replacing two hydrogen atoms with fluorine in the ortho positions of the diphenyl moiety of the molecule leads to absence of quenching upon collisions with oxygen molecules, owing to the electronegative properties of fluorine atoms.

Surface chemistry and reactivity of well-defined multilayered supported M 1O x/M 2O x/SiO 2 catalysts

A series of group 5–7 transition metal oxides (TMOs) were supported on SiO 2 and surface-modified SiO 2 containing surface AlO x , ZrO x , and TiO x species. The surface reactivity of these silica supported oxides was chemically probed with CH 3OH-temperature-programmed surface reaction (TPSR) spectroscopy. The selectivity of the model supported MO x catalytic active sites on SiO 2 generally reflect the same product distribution as their corresponding bulk MO x counterparts toward dimethyl ether (DME), formaldehyde (HCHO) and CO 2 from surface acidic, redox, and basic sites, respectively. The reactivity of the surface MO x sites generally was suppressed by anchoring of the surface MO x species onto the SiO 2 support. The general surface chemistry trend followed the known inorganic chemistry of the corresponding bulk MO x TMOs. For the multilayered supported M 1O x /M 2O x /SiO 2, with M 1 representing the group 5–7 TMOs and M 2 representing Al, Zr or Ti, the selectivity of the catalytic active sites was generally comparable to that for the model-supported M 1O x /SiO 2 catalysts. The reactivity of the surface VO x , MoO x , and ReO x redox sites increased by one to four orders of magnitude with the introduction of the surface modifiers; however, the reactivity of the surface WO x acidic site was mildly suppressed by the presence of the surface modifiers. The reactivity of the basic CrO x site was only mildly perturbed by the surface modifiers. The reactivity trend of the catalytic TMOs sites was related to the electronegativity properties of the anchoring substrate cations (Si > Al > Zr ∼ Ti).