Polyynes Formation from Electric Arc in Liquid Argon in Presence of Methane

The carbon arc in liquid argon in presence of methane produces the complete series of polyynes from C₄H₂ to C₁₂H₂ which have been collected in a cold trap and analyzed by electronic absorption spectroscopy and by liquid chromatography (HPLC-diode array). The relative abundance of the polyynes series has been determined. In addition to polyynes the decomposition of methane in the argon arc produces also vinylacetylene and naphthalene. Thermodynamic calculations explain why the polyynes are formed so easily in the carbon arc.     

Polyynes Production in a Solvent-Submerged Electric Arc Between Graphite Electrodes. III. Chemical Reactivity and Stability Toward Air, Ozone, and Light

Since polyynes are easily accessible with the submerged electric arc synthesis between graphite electrodes, the chemical behavior of polyynes solutions in different solvents has been explored. It has been found that surprisingly the polyynes solutions, with polyynes having up to 16 carbon atoms arranged in a chain, are stable in air over 1 week time in the dark. These solutions react relatively slowly with ozone while add rapidly and completely bromine. The polyynes solutions are instead quite easily photolyzed under the action of UV radiation both in air and under N₂. Two different light sources were used in the study: a low pressure mercury lamp emitting almost a monochromatic radiation at 254 nm and an high pressure mercury lamp emitting in a broad wavelength range in the ultraviolet. With the former monochromatic light source, it has been demonstrated the possibility to perform a selective photolysis of selected polyynes in a mixture of homologous series.     

γ-Radiolysis of Polyynes in Heptane

The polyynes in heptane solution were γ-radiolyzed at a total dose of 150, 300 and 600 kGy. After radiolysis the products were analyzed by electronic absorption spectroscopy, by HPLC (liquid chromatography) and by FT-IR spectroscopy. Even at 150 kGy the polyynes disappear completely from the solution and the chromatographic analysis shows that the acetylenic chains undergo fragmentation, addition and crosslinking reactions with other chains and with solvent. The oxidative interference from air has been detected by FT-IR.     

Soot and other Products Formation from the Submerged Carbon Arc in Halogenated Solvents

A series of selected halomethanes were treated with the submerged carbon arc using graphite electrodes at 10A. CCl₄ and CHCl₃ produce abundant soot which is double in comparison to the soot produced by arcing CH₂Cl₂ and is one order of magnitude higher than the amount of soot produced by arcing hydrocarbons such as n-hexane or decalin and two orders of magnitudes higher in comparison to the amounts of soot produced by arcing alcohols. It was found a anticorrelation between the amount of polyynes present in the solution of the arced solvent and the amount of soot produced by arcing. In the case of CCl₄ and CHCl₃ no polyynes were detected by liquid chromatographic analysis (HPLC-DAD), while polyynes were detected in CH₂Cl₂ and are present in higher concentration in arced hydrocarbon solutions. The soot produced from halomethanes was analyzed by FT-IR spectroscopy in comparison to the soot produced by arcing hydrocarbons and alcohols. Furthermore, the soot from halomethanes was analyzed by HPLC-DAD after extraction with acetonitrile and found to contain a mixture of halogenated polycyclic aromatic hydrocarbons (PAHs). Also CHClBr and CH₂I₂ were arced between graphite electrodes. The former compound produces free bromine and soot; bromine causes halogenation of the polyynes. In the case of the latter compound, free iodine is released from the arc and the amount of soot produced is comparable to that obtained by arcing CH₂Cl₂.     

Storage Stability of Polyynes and Cyanopolyynes in Solution and the Effect of Ammonia or Hydrochloric Acid

The storage stability of an acetonitrile solution of polyynes and monocyanopolyynes was studied by liquid chromatographic analysis for about 50 days at room temperature in a closed Pyrex flask. Monocyanopolyynes decomposition starts immediately after their synthesis; the decomposition can be approximated by a pseudo-first-order kinetic law and the rate constant is dependent from the length of the monocyanopolyyne chains, being faster for longer chains. For instance, for HC₇N the decomposition rate is k=-3.4×10^-7 s^-1 but becomes -7.0×10^-5 s^-1 for HC₁₃N decay, 204 times faster than the decay of the former compound. Polyynes mixed with monocyanopolyynes in the same CH₃CN show an induction time before starting to decompose. The induction time appears linked to the decomposition of monocyanopolyynes, which seems to protect the polyynes from the decomposition. Once the monocyanopolyynes are vanished also the decomposition of polyynes starts with a slower kinetics than monocyanopolyynes and following the rule that longer chains disappear at higher speed than shorter chains. For example, the pseudo-first-order rate constant for C₈H₂ is k=-1.31×10^-8 s^-1. Ammonia exerts a deleterious effect on monocyanopolyynes. In fact, ammonia addition to an acetonitrile solution of monocyanopolyynes causes their immediate decomposition due to a nucleophilic addition of ammonia to the polyyne chains. Instead, hydrogen-teminated polyynes are much more resistant toward the nucleophilic addition of ammonia. Hydrochloric acid does not influence the stability of polyynes and monocyanopolyynes.     

On the Action of Ozone on Polyynes and Monocyanopolyynes: Selective Ozonolysis of Polyynes

Ozone reacts selectively with hydrogen-terminated polyynes when they are present in a mixture with monocyanopolyynes. The latter class of molecules reacts more slowly with ozone. Since the ozone attack to double or triple bonds is essentially electrophilic in its nature, the lower reactivity with ozone of monocyanopolyynes has been interpreted in terms of lower π-electron charge concentration at the conjugated triple bonds because of the electron-withdrawing effect exerted by the nitrile group at one end of the monocyanopolyynes molecules. This experimental result demonstrates the presence of conjugation among adjacent triple bonds in the polyynes molecules: the electron-withdrawing effect of the -CN group propagates along the entire polyyne chains.     

Synthesis of Polyynes with Electric Arc Part 5: Detection of PAHs as Minor Products

The main products of the submerged electric arc between graphite electrodes in n-hexane and in methanol are the polyynes series. The liquid chromatographic analysis (HPLC) of the arcing products in n-hexane reveals also the presence of a mixture of polycyclic aromatic hydrocarbons (PAHs) as minor products. Naphthalene, acenaphthylene, phenanthrene, perylene, fluoranthene, benzo[b]fluoranthene, pyrene, and the related compound cyclopenta[c,d]pyrene have been identified. Even crysene and acenaphthene were reasonably identified from the PAHs mixture. The PAHs mixture appears to derive essentially from the plasmalysis of the solvent where the electric arc is conducted, while the polyynes are formed from the elemental carbon supplied from the graphite electrodes. Another minor product is represented in all cases by the formation of carbon black or carbon coke, which appears more abundant in n-hexane rather than in methanol. The different results are explained thermodynamically in terms of different carbonization tendency of the solvents used.     

Toluene pyrolysis in an electric ARC: Products analysis

Toluene pyrolysis in a submerged carbon arc produced at least 72 different molecular species as detected by gas-chromatography coupled with mass spectrometry (GC-MS). The most abundant products found were bibenzyl (1,2-diphenylethane), naphthalene and biphenylene. Furthermore, also diethynylbenzene isomers, fluorene, diphenymethane, indene and biphenyl were produced in appreciable amounts. The formation mechanisms of these and other minor products are discussed mainly in the light of the benzyl radical and its decay into other products. Among polyynes, only 1,3,5,7-octatetrayne was produced above 1% relative yield. The results are discussed in comparison to the products detected in toluene pyrolysis under other experimental conditions, such as shock tube pyrolysis and toluene flames. Furthermore, a comparison with the products obtained from the benzene pyrolysis is reported.     

Non-trivial length dependence of the conductance and negative differential resistance in atomic molecular wires

We study the electronic and transport properties of two novel molecular wires made of atomic chains of carbon atoms (polyynes) capped with either benzene-thiols or pyridines. While both molecules are structurally similar, the electrical conductance of benzene-thiol-capped chains attached to gold electrodes is found to be much higher than that of pyridine-capped chains. We predict that the conductance is almost independent of molecular length, which suggests that these molecules could be ideal molecular wires for sub-10?nm circuitry. Both systems exhibit negative differential resistance (NDR) but its origin and characteristics depend on the type of molecule. We find a novel type of NDR mechanism produced by the movement of the lowest unoccupied molecular orbital (LUMO) resonance with bias. We also show that by gating the pyridine-capped molecules it is possible to make the NDR disappear and dramatically modify the I-V characteristics and the length dependence.     

Optical beating of polychromatic light and its impact on time-resolved spectroscopy. Part II: Strategies for spectroscopic sensing in the presence of optical beating

Time-resolved spectroscopy can be compromised by optical beating, which is inherent to polychromatic light sources and signals. For incoherent light sources, the random interference can partially or completely mask the spectroscopic signature of interest if the time dynamics of the interference are similar to or faster than that of the signature. Part I of this review focused on the theory of this process with an emphasis on thermal light sources, and in this part, four methods to mitigate or circumnavigate the detrimental impact of interference on time-resolved spectroscopy are reviewed: use of light with a controlled, non-stochastic phase, use of narrow-bandwidth light, averaging, and pulse referencing.     

R.f. plasma deposition from hexamethyldisiloxane-oxygen mixtures

Hexamethyldisiloxane (HMDSO) has been used as a precursor for the deposition of silicon dioxide films at low substrate temperature (25–400°C) by plasma enhanced chemical vapour deposition processing. Effects of the partial pressure of oxygen in the discharge on the deposition rate and the composition of the films are investigated. The deposition rate is found to decrease with increasing oxygen concentration in the HMDSO/O₂ mixture. The chemical composition of the formed films was characterized by X-ray photoelectron spectroscopy and infrared spectroscopy. Over 40% of the oxygen in the gas phase the carbon content of films deposited from HMDSO/O₂ mixtures is less than 5%.     

Near-infrared spectroscopy for cocrystal screening. A comparative study with Raman spectroscopy

Near-infrared (NIR) spectroscopy is a well-established technique for solid-state analysis, providing fast, noninvasive measurements. The use of NIR spectroscopy for polymorph screening and the associated advantages have recently been demonstrated. The objective of this work was to evaluate the analytical potential of NIR spectroscopy for cocrystal screening using Raman spectroscopy as a comparative method. Indomethacin was used as the parent molecule, while saccharin and l-aspartic acid were chosen as guest molecules. Molar ratios of 1:1 for each system were subjected to two types of preparative methods. In the case of saccharin, liquid-assisted cogrinding as well as cocrystallization from solution resulted in a stable 1:1 cocrystalline phase termed IND-SAC cocrystal. For l-aspartic acid, the solution-based method resulted in a polymorphic transition of indomethacin into the metastable alpha form retained in a physical mixture with the guest molecule, while liquid-assisted cogrinding did not induce any changes in the crystal lattice. The good chemical peak selectivity of Raman spectroscopy allowed a straightforward interpretation of sample data by analyzing peak positions and comparing to those of pure references. In addition, Raman spectroscopy provided additional information on the crystal structure of the IND-SAC cocrystal. The broad spectral line shapes of NIR spectra make visual interpretation of the spectra difficult, and consequently, multivariate modeling by principal component analysis (PCA) was applied. Successful use of NIR/PCA was possible only through the inclusion of a set of reference mixtures of parent and guest molecules representing possible solid-state outcomes from the cocrystal screening. The practical hurdle related to the need for reference mixtures seems to restrict the applicability of NIR spectroscopy in cocrystal screening.     

Ion implantation modified stainless steel as a substrate for hydroxyapatite deposition. Part I. Surface modification and characterization

Material surfaces play critical role in biology and medicine since most biological reactions occur on surfaces and interfaces. There are many examples showing that the surface properties of the materials control and are directly involved in biological reactions and processes in-vitro like blood compatibility, protein absorption, cell development, etc. The rules that govern the diversity of biological surface phenomenon are fundamental physical laws. Stainless steel doped with Cr, Ni and Mo is widely used material in medicine and dentistry due to its excellent corrosion resistance and mechanical properties. The interest in this material has stimulated extensive studies on improving its bone-bonding properties. This paper describes the surface modification of Cr-Ni stainless steel (AISI 316) by a whole surface sequential implantation of Ca and P ions (the basic ions of hydroxyapatite). Three groups of stainless steel samples are prepared: (i) ion-implanted, (ii) ion-implanted and thermally treated at 600^∘C in air for 1 h and (iii) initials. The surface chemistry and topography before and after the surface modification are characterized by X-ray photoelectron spectroscopy, Auger electron spectroscopy, magic mirror method, atomic force microscopy and contact angle measurements.     

Sub critical crack advance vs. impact fracture on high impact polystyrene with different second phase volume contents and structures

Also for polymers, many fractures in service occurs after a period in which an existing crack has propagated in a sub-critical manner, while the laboratory tests are mainly concentrated on impact fractures. Aim of this paper is then to investigate the sub critical fracture in some high impact polystyrene (HIPS) materials with different second phase volume fraction and particle size and to compare it with the outcomes of impact Fracture Mechanics experiments. Large differences in the results of the two mechanical test procedures are evidenced: the materials behaviour is then examined from the structural point of view and an interesting case of interfacial failure, which disappears at high strain rate, is attested on some HIPSs by means of different techniques, i.e. electron microscopy, nuclear magnetic resonance spectroscopy and dynamic mechanical spectroscopy, indicating that the slow crack fracture behaviour can be influenced by parameters that do not affect ordinary mechanical tests.     

A novel method for the preparation of biodegradable microspheres for protein drug delivery.

Microspheres are potential candidates for the protein drug delivery. In this work, we prepared polymer-coated starch/bovine serum albumin (BSA) microspheres using co-axial electrohydrodynamic atomization (CEHDA). First, starch solution in dimethyl sulphoxide (DMSO) was prepared and then an aqueous solution of BSA was added to it to make a starch-BSA solution. Subsequently, this solution was made to flow through the inner capillary, while the polymer, polydimethylsiloxane (PDMS), flowed through the outer capillary. On collection, filtration and subsequent drying, near-monodisperse microspheres of 5-6microm in size were obtained. The microspheres were characterized by Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscopy. Cumulative BSA release was investigated by UV spectroscopy. BSA structure and activity was preserved in the microspheres and its release in 0.01M phosphate buffered saline (PBS) was studied over a period of 8 days. There was an initial burst with 32wt% of total BSA released in 2h. Overall 75wt% of BSA was released over a 7 day period.     

Statistical two-dimensional correlation spectroscopy: its theory and applications to sets of vibrational spectra

The present study aims at developing a new form of two-dimensional (2D) correlation spectroscopy, statistical 2D correlation spectroscopy. Statistical 2D spectroscopy differs from the widely used generalized 2D correlation spectroscopy in that the former abstracts spectral features by pretreatment and by 2D maps that are limited by the correlation coefficients in the range from 1 to -1. In this paper, the theory of the new 2D method is briefly described, and then its applications are discussed to reveal spectral and concentration features of artificial model spectra, infrared spectra of polycondensation of bis(hydroxyethyl terephthalate) measured on-line, and short-wave near-infrared spectra of raw milk. The results are analyzed thoroughly and compared with those from generalized 2D correlation spectroscopy and partial least-squares loadings and scores. The most significant advantage of statistical 2D correlation spectroscopy is that the 2D correlation spectra are easy to calculate and are purely mathematical in nature, thereby eliminating any subjective involvement of an experimenter, while the inherent weakness of the method lies in its sensitivity to the noise.     

Determination of nitrite in waters by microplate fluorescence spectroscopy and HPLC with fluorescence detection.

A selective and versatile fluorescence spectroscopic method for the determination of nitrite in waters has been developed. Nitrite reacts in the presence of mineral acids with the nonfluorescent N-methyl-4-hydrazino-7-nitrobenzofurazan forming N-methyl-4-amino-7-nitrobenzofurazan, which can be detected by fluorescence spectroscopy with an excitation maximum at lambda = 468 nm and an emission maximum at lambda = 537 nm in acetonitrile. Three new methods based on this reaction have been developed: Direct fluorescence spectroscopy, HPLC/fluorescence, or HPLC with UV/vis detector may be selected as detection techniques. On microplates, high-throughput fluorescence spectroscopy is achieved, while HPLC/fluorescence provides lower limits of detection, and HPLC with UV/vis detection enables evaluation of the reaction with standard instrumentation. Different water samples were investigated using all detection modes, and a photometric standard procedure was successfully employed to validate the new methods with an independent technique.     

Fluorinated polymer films from r.f. plasmas containing benzene and sulfur hexafluorine

Mixtures of C₆H₆ and SF₆ were polymerized in an r.f. discharge. Actinometry (quantitative optical emission spectroscopy) was used to determine trends in the plasma concentrations of the species F, H and CH as a function of the proportion of SF₆ in the feed. Infrared spectroscopy and electron spectroscopy for chemical analysis were employed to characterize the deposited material. Increasing proportions of SF₆ in the feed produced increased fragmentation of the benzene molecules and greater fluorination of the deposited material. The deposition rate, as determined by optical interferometry, was found to be enhanced about 4 times by the presence of 10–20% SF₆ in the feed. At 50% SF₆ in the feed, deposition rates were greater than in pure C₆H₆ plasmas despite the (probably large) etching effect of atomic fluorine from the discharge. Relationships between the plasma composition, electron density and temperature, film composition and growth rate are discussed.     

用交流阻抗法研究碳纤维混凝土导电性

随着水泥基材料的发展 ,人们对水泥基材料提出的更新的要求 ,其中水泥基导电复合材料的研究引起了广泛的兴趣。制备水泥基导电复合材料的方法是在水泥基材料中掺入各种导电组分 ,目前较常用的是掺入碳纤维 ,它不仅可以大幅度提高水泥基复合材料的电导率 ,还能够改善水泥基材料的力学性能、增加其韧性。本研究主要通过对碳纤维混凝土的交流阻抗谱进行分析 ,研究其导电性能与内部微结构的关系。     

Parallel high-resolution confocal Raman SEM analysis of inorganic and organic bone matrix constituents.

In many multi-disciplinary fields of science, such as tissue engineering, where material and biological sciences are combined, there is a need for a tool that combines ultrastructural and chemical data analysis in a non-destructive manner at high resolution. We show that a combination of confocal Raman spectroscopy (CRS) and scanning electron microscopy (SEM) can be used for such analysis. Studies of atomic composition can be done by X-ray microanalysis in SEM, but this is only possible for atomic numbers greater than five and does not reveal molecular identity. Raman spectroscopy, however, can provide information on molecular composition and identity by detection of wavelength shifts caused by molecular vibrations. In this study, CRS-SEM revealed that early in vitro-formed bone extracellular matrix (ECM) produced by rat osteoprogenitor cells resembles mature bone chemically. We gained insight into the structure and chemical composition of the ECM, which was composed of mainly mineralized collagen type I fibres and areas of dense carbonated calcium phosphate related to the collagen fibre density, as revealed by Raman imaging of SEM samples. We found that CRS-SEM allows the study of specimens in a non-destructive manner and provides high-resolution structural and chemical information about inorganic and organic constituents by parallel measurements on the same sample.