Re-examination of the anion derivatives of isoflavones by radical fragmentation in negative electrospray ionization tandem mass spectrometry: experimental and computational studies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Metabolic fingerprinting using direct flow injection electrospray ionization tandem mass spectrometry for the characterization of proanthocyanidins from the barks of Hancornia speciosa

Direct flow injection electrospray ionization ion trap tandem mass spectrometry (ESI-IT-MS/MS) was used to investigate the polyphenolic compounds present in an infusion from the barks of Hancornia speciosa Gom. (Apocynaceae), a native Brazilian plant popularly known as 'mangabeira', used as a source of nutrition and against gastric disorders. After a simple sample filtration pretreatment the characteristic fingerprint of the infusion was performed in negative ion ESI mode in a few minutes. At low capillary-voltage activation, the deprotonated molecules ([M-H](-)) were observed and using collision-induced dissociation the product ion spectra showed the presence of a homologous series of B-type proanthocyanidins, as well as another series containing their respective C-glycosylated derivatives, with a degree of polymerization from 1 up to 6 units of interlinked catechins. Therefore, direct flow injection allowed us to identify the key compounds without preparative isolation of the components. Copyright (C) 2007 John Wiley & Sons, Ltd.

Integrated analysis of halogenated organic pollutants in sub-millilitre volumes of venous and umbilical cord blood sera

A rapid, robust and economical method for the analysis of persistent halogenated organic compounds in small volumes of human serum and umbilical cord blood is described. The pollutants studied cover a broad range of molecules of contemporary epidemiological and legislative concern, including polychlorobiphenyls (PCBs), polychlorobenzenes (CBs), hexachlorocyclohexanes (HCHs), DDTs, polychlorostyrenes (PCSs) and polybromodiphenyl ethers (PBDEs). Extraction and clean-up with n-hexane and concentrated sulphuric acid was followed with analysis by gas chromatography coupled to electron capture (GC-ECD) and GC coupled to negative ion chemical ionisation mass spectrometry (GC-NICI-MS). The advantages of this method rest in the broad range of analytes and its simplicity and robustness, while the use of concentrated sulphuric acid extraction/clean-up destroys viruses that may be present in the samples. Small volumes of reference serum between 50 and 1000 μL were extracted and the limits of detection/quantification and repeatability were determined. Recoveries of spiked compounds for the extraction of small volumes (≥300 μL) of the spiked reference serum were between 90% and 120%. The coefficients of variation of repeatability ranged from 0.1-14%, depending on the compound. Samples of 4-year-old serum and umbilical cord blood (n = 73 and 40, respectively) from a population inhabiting a village near a chloro-alkali plant were screened for the above-mentioned halogenated pollutants using this method and the results are briefly described. © 2010 Springer-Verlag.

Optimal single-embryo mass spectrometry fingerprinting

In pre-implantation embryos, lipids play key roles in determining viability, cryopreservation and implantation properties, but often their analysis is analytically challenging because of the few picograms of analytes present in each of them. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) allows obtaining individual phospholipid profiles of these microscopic organisms. This technique is sensitive enough to enable analysis of individual intact embryos and monitoring the changes in membrane lipid composition in the early stages of development serving as screening method for studies of biology and biotechnologies of reproduction. This article introduces an improved, more comprehensive MALDI-MS lipid fingerprinting approach that considerably increases the lipid information obtained from a single embryo. Using bovine embryos as a biological model, we have also tested optimal sample storage and handling conditions before the MALDI-MS analysis. Improved information at the molecular level is provided by the use of a binary matrix that enables phosphatidylcholines, sphingomyelins, phosphatidylserines, phosphatidylinositols and phosphoethanolamines to be detected via MALDI(±)-MS in both the positive and negative ion modes. An optimal MALDI-MS protocol for lipidomic monitoring of a single intact embryo is therefore reported with potential applications in human and animal reproduction, cell development and stem cell research. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of target bias on magnetic field enhanced plasma immersion ion implantation

Recent studies have demonstrated that sheath dynamics in plasma immersion ion implantation (PIII) is significantly affected by an external magnetic field, especially in the case when the magnetic field is parallel to the workpiece surface or intersects it at small angles. In this work we report the results from two-dimensional, particle-in-cell (PIC) computer simulations of magnetic field enhanced plasma immersion implantation system at different bias voltages. The simulations begin with initial low-density nitrogen plasma, which extends with uniform density through a grounded cylindrical chamber. Negative bias voltage is applied to a cylindrical target located on the axis of the vacuum chamber. An axial magnetic field is created by a solenoid installed inside the target holder. A set of simulations at a fixed magnetic field of 0.0025 T at the target surface is performed. Secondary electron emission from the target subjected to ion bombardment is also included. It is found that the plasma density around the cylindrical target increases because of intense background gas ionization by the electrons drifting in the crossed E x B fields. Suppression of the sheath expansion and increase of the implantation current density in front of the high-density plasma region are observed. The effect of target bias on the sheath dynamics and implantation current of the magnetic field enhanced PIII is discussed. (C) 2007 Elsevier B.V. All rights reserved.

Amorphous carbon nitrogenated films prepared by plasma immersion ion implantation and deposition

In this work, an investigation was conducted on amorphous hydrogenated-nitrogenated carbon films prepared by plasma immersion ion implantation and deposition. Glow discharge was excited by radiofrequency power (13.56 MHz, 40 W) whereas the substrate-holder was biased with 25 kV negative pulses. The films were deposited from benzene, nitrogen and argon mixtures. The proportion of nitrogen in the chamber feed (R-N) was varied against that of argon, while keeping the total pressure constant (1.3 Pa). From infrared reflectance-absorbance spectroscopy it was observed that the molecular structure of the benzene is not preserved in the film. Nitrogen was incorporated from the plasma while oxygen arose as a contaminant. X-ray photoelectron spectroscopy revealed that N/C and O/C atomic ratios change slightly with R-N. Water wettability decreased as the proportion of N in the gas phase increased while surface toughness underwent just small changes. Nanoindentation measurements showed that film deposition by means of ion bombardment was beneficial to the mechanical properties of the film-substrate interface. The intensity of the modifications correlates well with the degree of ion bombardment. (c) 2006 Elsevier B.V. All rights reserved.

Thin polymer films prepared by plasma immersion ion implantation and deposition

This work describes an investigation of the properties of polymer films prepared by plasma immersion ion implantation and deposition. Films were synthesized from low pressure benzene glow discharges, biasing the samples with 25 W negative pulses. The total energy deposited in the growing layer was varied tailoring simultaneously pulse frequency and duty cycle. The effect of the pulse characteristics on the chemical composition and mechanical properties of the films was studied by X-ray photoelectron spectroscopy (XPS) and nanoindentation, respectively. Analysis of the deconvoluted C 1s XPS peaks demonstrated that oxygen was incorporated in all the samples. The chemical modifications induced structural reorganization, characterized by chain cross-linking and unsaturation, affecting material properties. Hardness and plastic resistance parameter increased under certain bombardment conditions. An interpretation is proposed in terms of the total energy delivered to the growing layer. (C) 2004 Elsevier B.V. All rights reserved.

Numerical simulation of magnetic field enhanced plasma immersion ion implantation

The behavior of plasma and sheath characteristics under the action of an applied magnetic field is important in many applications including plasma probes and material processing. Plasma immersion ion implantation (PIII) has been developed as a fast and efficient surface modification technique of complex shaped three-dimensional objects. The PIII process relies on the acceleration of ions across a high-voltage plasma sheath that develops around the target. Recent studies have shown that the sheath dynamics is significantly affected by an external magnetic field. In this work we describe a two-dimensional computer simulation of magnetic field enhanced plasma immersion implantation system. Negative bias voltage is applied to a cylindrical target located on the axis of a grounded cylindrical vacuum chamber filled with uniform nitrogen plasma. An axial magnetic field is created by a solenoid installed inside the cylindrical target. The computer code employs the Monte Carlo method for collision of electrons and neutrals in the plasma and a particle-in-cell (PIC) algorithm for simulating the movement of charged particles in the electromagnetic field. Secondary electron emission from the target subjected to ion bombardment is also included. It is found that a high-density plasma region is formed around the cylindrical target due to the intense background gas ionization by the magnetized electrons drifting in the crossed ExB fields. An increase of implantation current density in front of high density plasma region is observed. (C) 2007 Elsevier B.V. All rights reserved.

Argon ion implantation inducing modifications in the properties of benzene plasma polymers

Benzene plasma polymer films were bombarded with Ar ions by plasma immersion ion implantation. The treatments were performed using argon pressure of 3 Pa and 70 W of applied power. The substrate holder was polarized with high voltage negative pulses (25 kV, 3 Hz). Exposure time to the immersion plasma, t, was varied from 0 to 9000 s. Optical gap and chemical composition of the samples were determined by ultraviolet-visible and Rutherford backscattering spectroscopies, respectively. Film wettability was investigated by the contact angle between a water drop and the film surface. Nanoindentation technique was employed in the hardness measurements. It was observed growth in carbon and oxygen concentrations while there was decrease in the concentration of H atoms with increasing t. Furthermore, film hardness and wettability increased and the optical gap decreased with t. Interpretation of these results is proposed in terms of the chain crosslinking and unsaturation. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Thin films generated by plasma immersion ion implantation and deposition of hexamethyldisilazane mixed with nitrogen in different proportions

In this work, it was used a plasma system composed of a cylindrical stainless steel reactor, a radio-frequency (13.56MHz) power source fixed at either 25 W or 70 W, a power source with a negative bias of 10kV and a 100Hz pulse. The system worked at an operational pressure of 80mTorr which consisted of varying concentrations of the monomer HMDSN and gaseous nitrogen in ratios: HMDSN (mTorr)/nitrogen (mTorr) from 70/10 to 20/60 in terms of operational pressure. The structural characterization of the films was done by FTIR spectroscopy. Absorptions were observed between 3500 cm(-1) to 3200 cm(-1), 3000 cm(-1) to 2900 cm(-1), 2500 cm(-1) to 2000 cm(-1), 1500 cm(-1) to 700 cm(-1), corresponding, respectively, to OH radicals, C-H stretching bonds in CH2 and CH3 molecules, C-N bonds, and finally, strain C-H bonds, Si-CH3 and Si-N groups, for both the 70 W and the 25 W. The contact angle for water was approximately 100 degrees and the surface energy is near 25mJ/m(2) which represents a hydrophobic surface, measured by goniometric method. The aging of the film was also analyzed by measuring the contact angle over a period of time. The stabilization was observed after 4 weeks. The refractive index of these materials presents values from 1.73 to 1.65 measured by ultraviolet-visible technique.

Effect of electron magnetic trapping in a plasma immersion ion implantation system

In this work we describe a two-dimensional computer simulation of magnetic field enhanced plasma immersion implantation system. Negative bias voltage of 10.0 kV is applied to a cylindrical target located on the axis of a grounded vacuum chamber filled with uniform nitrogen plasma. A pair of external coils creates a static magnetic field with main vector component along the axial direction. Thus, a system of crossed ExB field is generated inside the vessel forcing plasma electrons to rotate in azimuthal direction. In addition, the axial variation of the magnetic field intensity produces magnetic mirror effect that enables axial particle confinement. It is found that high-density plasma regions are formed around the target due to intense background gas ionization by the trapped electrons. Effect of the magnetic field on the sheath dynamics and the implantation current density of the PIII system is investigated. By changing the magnetic field axial profile (varying coils separation) an enhancement of about 30% of the retained dose can be achieved. The results of the simulation show that the magnetic mirror configuration brings additional benefits to the PIII process, permitting more precise control of the implanted dose.

Treatment of PVC using an alternative low energy ion bombardment procedure

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Study of the mechanism of action of anoplin, a helical antimicrobial decapeptide with ion channel-like activity, and the role of the amidated C-terminus

Anoplin, an antimicrobial, helical decapeptide from wasp venom, looses its biological activities by mere deamidation of its C-terminus. Secondary structure determination, by circular dichroism spectroscopy in amphipathic environments, and lytic activity in zwitterionic and anionic vesicles showed quite similar results for the amidated and the carboxylated forms of the peptide. The deamidation of the C-terminus introduced a negative charge at an all-positive charged peptide, causing a loss of amphipathicity, as indicated by molecular dynamics simulations in TFE/water mixtures and this subtle modification in a peptide's primary structure disturbed the interaction with bilayers and biological membranes. Although being poorly lytic, the amidated form, but not the carboxylated, presented ion channel-like activity on anionic bilayers with a well-defined conductance step; at approximately the same concentration it showed antimicrobial activity. The pores remain open at trans-negative potentials, preferentially conducting cations, and this situation is equivalent to the interaction of the peptide with bacterial membranes that also maintain a high negative potential inside. Copyright (C) 2007 European Peptide Society and John Wiley & Sons, Ltd.

Plasma immersion ion implantation of nitrogen into H13 steel under moderate temperatures

Ion implantation of nitrogen into samples of tempered and quenched H13 steel was carried out by plasma immersion technique. A glow discharge plasma of nitrogen species was the ion source and the negative high voltage pulser provided 10-12 kV, 60 mu s duration and 1.0-2.0 kHz frequency, flat voltage pulses. The temperatures of the samples remained between 300 and 450 degrees C, sustained solely by the ion bombardment. In some of the discharges, we used a N-2 + H-2 gas mixture with 1:1 ratio. PIII treatments as long as 3, 6, 9 and up to 12 h were carried out to achieve as thickest treated layer as possible, and we were able to reach over 20 mu m treated layers, as a result of ion implantation and thermal (and possibly radiation enhanced) diffusion. The nitrogen depth profiles were obtained by GDOS (Glow Discharge Optical Spectroscopy) and the exact composition profiles by AES (Auger Electron Spectroscopy). The hardness of the treated surface was increased by more than 250%, reaching 18.8 GPa. No white layer was seen in this case. A hardness profile was obtained which corroborated a deep hardened layer, confirming the high efficacy of the moderate temperature PIII treatment of steels. (c) 2005 Elsevier B.V. All rights reserved.

Numerical simulation of magnetic-field-enhanced plasma immersion ion implantation in cylindrical geometry

Recent studies have demonstrated that the sheath dynamics in plasma immersion ion implantation (PIII) is significantly affected by an external magnetic field. In this paper, a two-dimensional computer simulation of a magnetic-field-enhanced PHI system is described. Negative bias voltage is applied to a cylindrical target located on the axis of a grounded vacuum chamber filled with uniform molecular nitrogen plasma. A static magnetic field is created by a small coil installed inside the target holder. The vacuum chamber is filled with background nitrogen gas to form a plasma in which collisions of electrons and neutrals are simulated by the Monte Carlo algorithm. It is found that a high-density plasma is formed around the target due to the intense background gas ionization by the magnetized electrons drifting in the crossed E x B fields. The effect of the magnetic field intensity, the target bias, and the gas pressure on the sheath dynamics and implantation current of the PHI system is investigated.