Human Enamel and Dentin: Effect of Gender,Geographic Location and Smoking Upon Metal Concentrations

Abstract

The goal of this study was to determine the content of 12 metals in 23 samples of teeth from two cities in Bosnia and Herzegovina (B&H): Sarajevo, a capital city with heavy traffic, industrial facilities, and long periods of smog during winter and Bihac, a picturesque small city, with no industrialization, settled among vivid national park and rivers. The teeth were separated into enamel and dentin. Dissolution of samples was performed in concentrated HNO₃ with the addition of H₂O₂ followed by flame atomic absorption spectroscopy (FAAS) analysis. The results showed expected high contents of Ca, Na, Mg, and K, while elevated contents of Cu, Fe, and Zn were present in some samples. K and Na showed uniform distributions throughout enamel and dentin. Alkaline and earth-alkaline metals showed significant positive correlations. Zinc and manganese exhibited differences in the dentin content based on the place of residence. Zinc also displayed statistically significant differences between smokers’ and nonsmokers’ dentin samples. The differences were more pronounced between intra groups (within one sample) than for inter groups (within different groups, such as location, gender, and smoking).     

DFT study on [4+2] and [2+2] cycloadditions to [60] fullerene

The functionalisation of C₆₀ fullerene with 2,3-dimethylene-1,4-dioxane (I) and 2,5-dioxabicyclo [4.2.0]octa-1(8),6-diene (II) was investigated by the use of density functional theory calculations in terms of its energetic, structural, field emission, and electronic properties. The functionalisation of C₆₀ with I was previously reported experimentally. The I and II molecules are preferentially attached to a C—C bond shared and located between two hexagons of C₆₀ via [4+2] and [2+2] cycloadditions bearing reaction energies of ?15.9 kcal mol^?1 and ?72.4 kcal mol^?1, respectively. The HOMO-LUMO energy gap and work function of C₆₀ are significantly reduced following completion of the reactions. The field electron emission current of the C₆₀ surface will increase after functionalisation of either the I or II molecule.     

Über quantitative Beziehungen zwischen Fragmenten und ihren relativen Intensitäten im Massenspektrometer. V—Untersuchungen an N-t-Alkylaminen und -acetamiden

The ion intensity ratios from α-fissions of N-t-alkylethylamines are independent of electron energy above 18 eV and they directly follow the ‘ion mass effect’ in this region. The course of the intensity ratios over the whole energy range can be explained by combination of appearance energy differences and the ion mass effect. In the upper energy region the increase of the ion intensity ratios I(M? R_large): I(M? R_small) normally found with increasing electron energy is mainly caused by successive decomposition of the ions. This is shown from investigations of N-t-alkylacetamides. A correlation is found between the masses of the primary ions and the tendency towards secondary ion formation, and the internal energy of the primary ions is found to have an influence too. The ‘ion mass effect’ is not a direct effect of the ion masses.     

Cleaning time and fate of phosphoric acid as conditioning agent on human dental enamel and dentin. An in vitro radiotracer study

In this study the cleaning time and fate of phosphoric acid on human dental enamel and dentin has been investigated, using the radioactive tracer technique with³²P as an indicator of phosphorus. Twenty seconds were found to be sufficient for cleaning the enamel from phosphoric acid, which is used for conditioning, and from formulations produced from its interaction with enamel. It was also found that dentin protection is necessary before conditioning with phosphoric acid due to the retention penetration of the latter through subsurface dentinal tubules. In addition, there seems to be an interaction between phosphoric acid and Ca(OH)₂ leading to the formation of a sparingly soluble compound.     

Silver-palladium alloyed clusters synthesized by radiolysis

Bimetallic Ag—Pd clusters have been synthesized by radiation-induced reduction of aqueous solutions of metal sulfate salts with different Ag^I/Pd^II ratios in the presence of polyacrylic acid. The mixed clusters have been characterized by TEM and UV-visible spectra. The evolution of the optical absorption spectrum with the dose absorbed and the electron diffractograms support the conclusion of the formation of an intimately alloyed cluster of Ag_xPd_1-x. The maximum wavelengths of the experimental absorption spectra at variable x coincide with those calculated from the electron density in an alloyed cluster.     

The Conductance- and Capacitance-Frequency Characteristics of the Rectifying Junctions Formed by Sublimation of Organic Pyronine-B on p-Type Silicon

The rectifying junction characteristics of the organic compound pyronine-B film on a p-type Si substrate has been studied. The pyronine-B has been sublimed on the top of p-Si surface. The barrier height and ideality factor values of 0.79±0.04 and 1.13±0.06 eV for this structure have been obtained from the forward bias current-voltage (I-V) characteristics. From the low capacitance-frequency (C-f) characteristics as well as conductance-frequency (G-f) characteristics, the energy distribution of the interface states and their relaxation time have been determined in the energy range of (0.53−E_v)-(0.79−E_v) eV taking into account the forward bias I-V data. The interface state density N_ss ranges from 4.93×10¹⁰ cm⁻² eV⁻¹ in (0.79−E_v) eV to 3.67×10¹³ cm⁻² eV⁻¹ in (0.53−E_v) eV. Furthermore, the relaxation ranges from 3.80×10⁻³ s in (0.53−E_v) eV to 4.21×10⁻⁴ s in (0.79−E_v) eV. It has been seen that the interface state density has an exponential rise with bias from the midgap towards the top of the valence band. The relaxation time shows a slow exponential rise with bias from the top of the valence band towards the midgap.     

Backbonding contributions to small molecule chemisorption in a metal–organic framework with open copper(i) centers

Metal–organic frameworks are promising materials for applications such as gas capture, separation, and storage, due to their ability to selectively adsorb small molecules. The metal–organic framework Cu^I-MFU-4l, which contains coordinatively unsaturated copper(i) centers, can engage in backbonding interactions with various small molecule guests, motivating the design of frameworks that engage in backbonding and other electronic interactions for highly efficient and selective adsorption. Here, we examine several gases expected to bind to the open copper(i) sites in Cu^I-MFU-4l via different electronic interactions, including σ-donation, π-backbonding, and formal electron transfer. We show that in situ Cu L-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy can elucidate π-backbonding by directly probing excitations to unoccupied backbonding orbitals with Cu d-character, even for gases that participate in other dominant interactions, such as ligand-to-metal σ-donation. First-principles calculations based on density functional theory and time-dependent density functional theory additionally reveal the backbonding molecular orbitals associated with these spectroscopic transitions. The energies of the transitions correlate with the energy levels of the isolated small molecule adsorbates, and the transition intensities are proportional to the binding energies of the guest molecules within Cu^I-MFU-4l. By elucidating the molecular and electronic structure origins of backbonding interactions between electron rich metal centers in metal–organic frameworks and small molecule guests, it is possible to develop guidelines for further molecular-level design of solid-state adsorbents for energy-efficient separations of relevance to industry.

In situ near edge X-ray absorption fine structure spectroscopy directly probes unoccupied states associated with backbonding interactions between the open metal site in a metal–organic framework and various small molecule guests.     

A study of the electronic structure of phenylsilanes by X-ray emission spectroscopy and quantum chemical calculation methods

The electronic structure of a series of phenylsilanes Ph_4?n SiH _n (n = 0?C3) is studied by X-ray emission spectroscopy and quantum chemical calculations by the density functional theory method. Based on the calculations theoretical X-ray emission SiK??₁ spectra of phenylsilanes Ph_4?n SiH _n (n = 0?C4) are constructed and their energy structure and shape turn out to be well consistent with experiment. The distribution of the electron density of states with different symmetry of Si, C, H atoms are also constructed. An analysis of the obtained X-ray fluorescent SiK??₁ spectra and the distribution of the electron density of states in Ph₄Si and Ph₃SiH compounds shows that their energy structure is mainly determined by a system of the energy levels of phenyl ligands weakly perturbed by interactions with valence AOs of silicon. In the energy structure of MOs of the PhSiH₃ compound, energy orbitals related to t ₂ and a ₁ levels of tetrahedral SiH₄ are mainly presented.     

Alkali-metal-intercalated transition metal disulfides: A thermodynamic model

In the lithium-intercalated disulfides, Li_xMS₂, where M = Ti, Ta, a nearly linear compositional variation of the lithium chemical potential is observed throughout the composition range 0 < x < 1.0. For most sodium-intercalated disulfides, chemical potential plateaus are observed between regions exhibiting linear variations of sodium chemical potential. Our thermodynamic model indicates that the two most important factors which determine the compositional variation of the alkali metal chemical potential are the interaction energy between intercalated alkali-metal atoms and the compositional variation of the electron chemical potential. Although these two factors determine the compositional variation of chemical potential in single-phase regions, the existence of two-phase regions in the concentration range x = 0?0.15 are influenced by the energy required to expand the interlayer gap and the configurational entropy.     

CdS and CdSe quantum dots subsectionally sensitized solar cells using a novel double-layer ZnO nanorod arrays

We report a novel approach for synthesizing CdS and CdSe quantum dots subsectionally sensitized double-layer ZnO nanorods for solar cells, which are comprised of CdS QDs-sensitized bottom-layer ZnO NRs and CdSe QDs-sensitized top-layer ZnO NRs. X-ray diffraction study and scanning electron microscopy analysis indicate that the solar cells of subsectionally sensitized double-layer ZnO NRs, which are the hexagonal wurtzite crystal structure, have been successfully achieved. The novel structure enlarged the range of absorbed light and enhanced the absorption intensity of light. The I-V characteristics show that the double-layer structure improved both the current density (J_sc) and fill factor (FF) by 50%, respectively, and power conversion efficiency (η) was increased to twice in comparison with the CdS QDs-sensitized structure.     

Energy dependence of the energy absorption buildup factor of HCO-materials

The energy absorption G-P fitting parameters and respective buildup factors for seven HCO-materials have been generated using the interpolation method in the energy range 0.015–15.0 MeV and up to a penetration depth of 40 mean free path. The generated buildup factor data has been studied as a function of incident photon energy and is presented in the form of graphs.     

Dispersion of carbon nanotubes by the branched block copolymer Tetronic 1107 in an alcohol–water solution

The dispersion of carbon nanotubes (CNTs) by the branched block copolymer Tetronic 1107 was investigated in mixed solvents consisting of water and one of the following alcohols: ethanol, n-propanol, ethylene glycol (EG), or glycerol (GLY). The maximum concentration of dispersed CNTs (C _limit) and the optimum T1107 concentration (C _opt) to disperse the maximum amount of CNTs in different solvents were obtained from UV–vis–NIR absorbance spectra. The addition of ethanol or n-propanol to water dramatically increases the C _limit. The value of C _opt follows the order: n-propanol–water?>?ethanol–water?>?EG–water?≈?GLY–water mixtures. I _D/I _G was used to characterize the defect density of CNTs dispersed in the mixed solvents, which was investigated by Raman spectroscopy. The I _D/I _G values in n-propanol–water and ethanol–water mixtures are higher than those in EG–water and GLY–water mixtures. High-resolution transmission electron microscopy is used to confirm a favorable dispersion in the presence of different alcohols.     

Physical aspects of charge transfer theory

The possible shapes of the ground (U_I) and first excited (U_II) adiabatic potentials are discussed in connection with the electron transfer problem. If U_I has two minima the electron transfer process is adiabatic, regardless of the value of the gap 2Γ between U_I and U_II; the transfer rate W has the form W = B exp(?E_A/T), the pre-exponential factor B can be influenced by the size of the gap, especially when Γ is small. For the fluctuation model of the medium in the case of purely adiabatic transfer (large Γ) the value of W corresponds to diffusional penetration through the potential barrier. A barrier of arbitrary shape is considered and an expression for W obtained, which matches with the corresponding expression for the “hindered adiabatic” case of small Γ.     

Photoionization of aqueous indole: Conduction band edge and energy gap in liquid water

Previous work on the determination of the photoionization threshold (I_sol) of tryptophan has now been extended to indole as a solute, both in tetramethylsilane (TMSi) and H₂O solvents. In TMSi, electron scavenging by N₂O or photoconductivity measurements lead to the same I_sol value: 4.95 ± 0.1 eV. In water, I_sol is found equal to 4.35 ± 0.1 eV. From these experiments, information on the ionization mechanism, on the oxidized solute and on the solvent can be gained: (i) the scavenger electron affinity does not intervene in the energy balance providing I_sol; (ii) an “effective” ionic radius of indole (1.40 Å) is estimated which suggests that the positive charge remains highly localized on the N-atom of the indole ring; (iii) a value of ?1.2 ± 0.1 eV can be deduced for V_o, the conduction band edge of water; (iiii) from the above findings, the energy gap E_G of pure water, considered as a semi-conductor, would be close to 7 eV. Such a result is discussed in terms of literature data pertaining to electron ejection in pure liquid water and X-ray photoelectron spectroscopy of amorphous ice.     

Lithium ion penetration depth profiles and reversibility of electrochromic reaction for TiO2 thin films

We investigated the penetration depth profiles of lithium ions in titanium oxide thin film during electrochromic reactions. The penetration depth profiles were obtained using time-of-flight secondary ion mass spectrometry (TOF-SIMS) for various states associated with coloring and bleaching reactions. It was found that the amount of penetrated lithium ions in the coloring process decreased sharply with increasing depth for samples in which lithium ions were inserted by applying a voltage, Vi, for 50 s in electrolyte. Over 70 % of the total lithium ions were detected within 10 nm from the surface of the film. The amount of ions in each depth was represented as a function of 1/d ² (d, depth), and the penetration depth of the lithium ions increased by increasing Vi. Furthermore, we found that the de-intercalation of the lithium ions by applying a reverse voltage arise preferentially near the surface of the film. The de-intercalated (released) lithium ion ratio seems to decrease with increasing the penetration depth. Hence, we expected that an electrochromic device using nanorod-structured titanium oxide film would improve reproducibility owing to a small number of unreleased ions. A film composed of nanorods was made by oblique evaporation. The electrochromic device using the nanorod-structured film showed excellent reproducibility for small value of driving voltage. The number of possible switching increased by a factor of 30 according to the driving voltage. In this paper, we discuss the details of the relationship between the lithium ion penetration depth profile and the electrochromic reactions.     

Nonequilibrium vibrational populations and dissociation rates of oxygen in electrical discharges

Nonequilibrium vibrational distributions and dissociation rates of molecular oxygen in both electrical and thermal conditions have been calculated by solving a system of master equations including V-V (vibration-vibration), V-T (vibration-translation) and e-V (electron-vibration) energy exchanges. The dissociation constant under thermal conditions (i.e. without electrons) follows an Arrhenius law with an activation energy of 120 kcal/mole, while the corresponding rates under electrical conditions (5000 ? T_e ? 15000 K, 300 ? T_g ? 1000 K, 10¹¹ ? n_e ? 10¹² cm^?3,5 ? p ? 20 torr) increase with decreasing gas (T_g) and electron (T_e) temperatures and pressure (p) and with increasing electron density (n_e). These results are explained on the basis of the different interplay of V-V and V-T energy exchanges and are rationalized by means of simplified models proposed in the literature. The accuracy of the present results is discussed paying particular attention to the dependence of V-V and V-T rate coefficients on the vibrational quantum number. A comparison of the calculated dissociation rates with the corresponding ones obtained by the direct electron impact mechanism shows that the present mechanism prevails at low electron and gas temperatures. Finally a comparison is shown between theoretical and experimental dissociation rates under electrical and thermal conditions.     

Determination of some trace elements in human tooth enamel

Determination of seven elements (Cu, Fe, Mg, Mn, Pb, Sr and Zn) in whole enamel and surface layers of extracted non-carious human teeth by FAAS, ETA AAS, ICP-AES and ICP-MS (Pb) is demonstrated. Techniques are described for obtaining whole enamel and its acid dissolution. Fifty microm width enamel layers from outer enamel surface to a 200 microm depth were successively etched in 1 mL of 3 M HClO4 for 3 min dissolution periods. Enamel samples were analyzed for populations under and over 20 years of age and enamel from Bronze Age teeth. Concentrations of microelements in the whole enamel and in the first surface layer (50 microm depth) were compared. With exception of Sr and Mg, all elements show significantly higher concentrations in the first layer than in whole enamel and higher concentration in teeth of individuals over 20 years, which demonstrate the cumulative effect of these elements. The Cu, Fe, Mn, Pb and Zn concentrations in four layers of erupted and non-erupted teeth decreased while Mg and Sr concentrations increased toward enamel-dentine junction. The concentrations of most elements were almost constant as they approached the 150 microm layer. This concentration gradient may result from interaction between saliva and teeth and supports the hypothesis that the surface de- and re-mineralization process is effective at most to 150 microm from the enamel surface.     

Density functional calculation on a high energy density compound having the formula C2OH4?n (NO2) n

A series of ethylene oxide derivations, C₂OH_4?Cn (NO2) _n (x?=?1?C4), has been designed computationally. We calculated the heats of formation (HOFs), bond dissociation energy (BDE), and explosive performances (detonation velocity and detonation pressure) of the title compounds by using density functional theory with 6-311G** basis set. The results show that most of ethylene oxide derivations have positive HOFs values except I. All the calculated BDE and the bond dissociation energies without zero-point energy corrections (BDE⁰) are larger than 200?kJ?mol^?1, which indicate that all the ethylene oxide derivations have good thermal stabilities. The explosive performances of most of ethylene oxide derivations would rank up with cyclotrimethylenetrinitramine (RDX). The results have not only shown that these compounds may be used as high energy density compounds, but also provide some useful information for further syntheses.     

Stark-broadening regularities of lithium-like and sodium-like isoelectronic sequences

The Stark width (w) of spectral lines of multiply ionized atoms as a function of the upper-level ionization potential (I), the net core charge (z) and the electron temperature (T), was found to be of the form: w=az ² T ^?1/2 I ^?b normalized to 1×10²³ m^?3 electron density for a given transition array. Coefficientsa andb are independent of the upper-level ionization potential, the net core charge, the electron temperature and density. This paper proves the validity of this equation for Stark widths in domains of electron densities of (0.5–1.5)×10²³ m^?3 and temperatures of 20 000–80 000 K. The reduced Stark width (wT ^1/2/z ²) dependence on the inverse value of upper-level ionization potential is represented by a linear trend (in log-log scale) of the experimental and relevant theoretical results within maximal scatter of less than ±30%. For a givenns-np transition array, this trend is equally applicable to spectral lines of (i) successive ionization stages of the same atom and (ii) ions of isoelectronic sequences of the second and third periods of the periodic system. It is also shown that coefficientsa andb depend on the energy state of the electron emitter core. Using the obtained trends, one can quite successfully predict the Stark width of spectral lines of corresponding transitions that have not yet been measured.     

Stark broadening and shift of multiply ionized carbon spectral lines

Stark widths and shifts of sixCII, threeCIII and twoCIV spectral lines have been measured in a linear pinch discharge plasma and compared with available experimental and theoretical data. Electron density, (0.86?1.64)×10²³ m^?3, was determined by single wavelength laser interferometry using the visible 632.8 nm transition of He-Ne laser. The electron temperature of 38000 K was derived from the Boltzmann slope of severalCII spectral lines, and ratios of severalCII toCIII spectral lines. The stark widths (w) dependence on:(i) the upper-level ionization potential (I) of corresponding lines;(ii) net charge (z) of the emitter core seen by the optical electron undergoing transition, and(iii) electron temperature (T) was found to be of the form:w=az ² T ^?1/2 I ^?b . However, it should be noticed that the essential role in the obtained trends belongs to the energy of the emitter core. The established overall trend is used to predict Stark widths of uninvestigated spectral lines originating from the given transition arrays.