Desorption Mass Spectrometry Research Articles

Characterization of Stable Fluorine-Doped Silicon Oxide Film Prepared by Biased Helicon Plasma Chemical Vapor Deposition

Fluorine-doped silicon oxide (SiOF) film prepared by biased helicon plasma chemical vapor deposition with SiF4 and O2 is characterized. In this characterization, the SiOF film is compared with that prepared using a nonbiased plasma. SiOF films prepared using a biased plasma are stable in air. Whereas films prepared using a nonbiased plasma are not stable in air and the relative dielectric constant and stress vary in the ranges 3.2 to 3.5 and from -35 MPa to 0 MPa, respectively. Analysis Fourier transform infrared (FT-IR) and thermal desorption mass spectroscopy (TDS) spectra, clarifies the following. (1) Si-F bonds are formed in SiOF films prepared using a biased plasma. (2) Not only Si-F bonds but also F-Si-F bonds are formed in SiOF films prepared using a nonbiased plasma. (3) The F-Si-F bond structure formed in SiOF films absorbs water easily.

Thermooxidation‐induced Surface Modifications of the Ethylene–Methyl Acrylate Copolymer as Investigated by Time‐of‐flight Particle‐induced Desorption Mass Spectrometry. Part II: The Copolymer

Thermooxidation‐induced Surface Modifications of the Ethylene–Methyl Acrylate Copolymer as Investigated by Time‐of‐flight Particle‐induced Desorption Mass Spectrometry. Part II: The Copolymer

Growth Rate Reduction of GaN Due to Ga Surface Accumulation

GaN(0001) has been grown on Al2O3 (0001) by molecular beam epitaxy where NH3 was used as the nitrogen precursor. Desorption mass spectroscopy and reflection high energy electron diffraction (RHEED) were used to monitor the relationship between growth rate and the incident fluxes during growth. Excess surface Ga decreases the GaN formation rate when the substrate temperature is too low or the Ga flux is too high. A simple rate equation is used to describe the observed behavior.

Effects of fires and biofractionation of carbon isotopes on results of radiocarbon dating of old textiles: the Shroud of Turin

A laboratory model especially created to “reproduce”, i.e. to simulate the physical/chemical conditions of the 1532 Chambéry fire was developed for the purpose of determining experimentally the probability that fire-induced chemical modifications of the Turin Shroud textile cellulose had occurred and evaluating its possible impact on the radiocarbon dating results. In these studies, both old Russian and old Middle Eastern (En Gedi, Israel, bc100– ad100) linen textile samples were tested by near-IR reflectance spectrophotometry, field ionization/field desorption mass spectrometry, and conventional AMS analysis. We found that the different fire-simulating model conditions were able to promote the carboxylation of unscreened OH-groups in textile cellulose molecules. This carboxylation process involves carbon-containing combustion gases, CO and CO 2, in the presence of silver cations, water and heat. As a result, a significant additional amount of 14C and 13C atoms incorporate into the textile cellulose structure as a portion of carboxy-groups. Radiocarbon ages of experimental textile samples incubated under fire-simulating conditions have been estimated by the common AMS technique with correction for C-isotopes fractionation. As seen from the resulting data, fire-induced carboxylation, i.e. “carbonization”, of the textile cellulose, leads to a significant error in the radiocarbon dating results. The extent and mechanism of this phenomenon as well as the problem of accuracy and the limitations of the radiocarbon method are discussed. All experimental data and theoretical statements presented in this work deal with the re-evaluation of the Shroud of Turin dating results obtained by Damon et al. using a conventional radiocarbon approach.

Synthesis of Symmetric Fluorescently Labeled Poly(ethylene glycols) Using Phosphoramidites of Pyrenebutanol and Their Characterization by MALDI Mass Spectrometry

We report the synthesis and characterization of a series of poly(ethylene oxide) [PEO] polymers in which two pyrene groups are separated by a common EO87 chain, and flanked by tails of varying EOx length. These polymers were prepared by reacting HO−EO87−OH (Mn = 3841, Mw/Mn = 1.01) with four different N,N-diisopropylphosphoramidites containing both pyrene (Py) and MeO−EOx− substituents. In this way, polymers of the form EOx−Py−EO87−Py−EOx (with MeO end groups) were obtained, with x = 2, 12, 17, and 47. These polymers are particularly useful for studying cyclization kinetics via pyrene excimer formation for two points labeled by pyrenes within the interior of a polymer chain. The polymers were characterized by NMR, size exclusion chromatography, and matrix-assisted laser desorption (MALDI) mass spectroscopy. The MALDI results were particularly informative since each of the oligomers of each of the components could be identified in each mass spectrum.

Benzyl coupling on bismuth-modified Pt(111)

It has been found that adsorbed benzyl (O-CH2(a)), produced from methylcyclohexane, can undergo dimerisation to adsorbed bibenzyl (O-CH2-CH2-O) on a bismuth-modified Pt(111) surface. In this case, the bismuth was postdosed to the benzyl adlayer, as in bismuth postdosing thermal desorption mass spectroscopy (BPTDS). The bibenzyl product desorbs to give bibenzyl gas in good yield with respect to the starting benzyl or the reacted methylcyclohexane. This reaction competes poorly with simple hydrogenation of the benzyl species to toluene when adsorbed hydrogen is also present on the bismuth-dosed surface. In the absence of hydrogen, dimerization dominates the chemistry of this intermediate, although some direct desorption of benzyl radical also occurs. The dependence of the activation energy for benzyl coupling on the thickness of the bismuth film suggests that the bismuth resides between the Pt surface and the benzyl adlayer. Benzyl coupling and desorption occurs on Bi/Pt, whereas only its decomposition occurs on clean Pt. This is attributed to two effects: the weakness of C-Bi bond leads to a low barrier for benzyl coupling or desorption; and, (2) bismuth blocks Pt sites needed to stabilize the fragments of decomposition. Both D2-BPTDS and this bismuth-induced coupling reaction in simple BPTDS were used to monitor the coverage of benzyl during its thermal decomposition on bismuth-free Pt(111), and the temperature dependence of the rate of its decomposition. Estimates of the bismuth-carbon bond strengths are also presented.

Chemical Properties of Zn/S/Mo(110) and Co/S/Mo(110) Surfaces: Reaction with Hydrogen and Formation of Hydrogen Sulfide

The chemical and electronic properties of a series of Zn/S/Mo(110) and Co/S/Mo(110) systems have been investigated using photoemission, thermal desorption mass spectroscopy, and hydrogen (H2, D2, or D) chemisorption. Sulfur multilayers supported on Mo(110) are very reactive toward admetals like Zn and Co. The behavior of the Zn/S/Mo(110) and Co/S/Mo(110) systems indicates that Zn and Co promote Mo ↔ S interactions, inducing the formation of molybdenum sulfide films. The ZnMoS and CoMoS films were unreactive toward H2 or D2 under ultrahigh vacuum conditions. As gas-phase hydrogen atoms (D) impinged on the surfaces, gaseous hydrogen sulfide was formed. Thus, the slow step in the D2,gas + Ssolid → D2Sgas reaction is the dissociation of molecular hydrogen. A good correlation exists between trends seen in the hydrodesulfurization (HDS) activity of ZnMoS and CoMoS catalysts and trends found for the sulfidation of Mo and hydrogenation of S in ZnMoS and CoMoS films. The systems that contain Co show the larger HDS activity, the stronger metal ↔ metal interactions with a subsequent increase in the reactivity of Mo toward S-containing molecules, and the bigger tendency to create unsaturated Mo sites through the hydrogenation of Mo-bonded S atoms.

Interaction of Zinc with Transition-Metal Surfaces: Electronic and Chemical Perturbations Induced by Bimetallic Bonding

The addition of zinc can induce significant changes in the chemical and catalytic properties of a transition-metal surface. The properties of a series of bimetallic surfaces that combine Zn with Rh or group 10 elements (TM = Ni, Pd, or Pt) have been examined using thermal desorption mass spectroscopy, core- and valence-level photoemission, CO chemisorption, and ab initio self-consistent-field calculations. The deposition of Zn on Rh(111) or polycrystalline surfaces of group 10 metals leads to the formation of alloys. These surface alloys decompose at high temperatures: 600−800 K, ZnNi; 650−850 K, ZnRh; 750−950 K, ZnPt; 850−1000 K, ZnPd. In the alloys, the core levels and valence d band of the transition metals exhibit positive binding energy shifts, while negative shifts are observed for the Zn 2p levels and 3d band. For CO/ZnRh and CO/ZnTM surfaces, the CO adsorption bond is weaker than for CO/Rh and CO/TM surfaces: 1−2 kcal/mol on ZnNi; 4−5 kcal/mol on ZnRh; 4−8 kcal/mol on ZnPt; and 12−16 kcal/mol on...

Repulsive Interactions between Au and S on Mo(110) and Rh(111): An Experimental and Theoretical Study

The coadsorption of Au and S on Mo(110) and Rh(111) has been examined using thermal desorption mass spectroscopy, photoemission, and ab initio self-consistent-field calculations. On both surfaces, the interactions between Au and S are repulsive. S reduces the adsorption energy of Au. In some cases, the weakening of the Mo−Au and Rh−Au bonds is so large (5−7 kcal/mol) that the Au adatoms “ball up” on the surface instead of “wetting” the Mo(110) and Rh(111) substrates. The ab initio SCF calculations show that a S adatom modifies the chemical behavior of adjacent Mo and Rh sites by reducing their contribution to the density of states around the Fermi level of the system, weakening in this way their ability to form strong bonds with Au. In the Au/S/Mo(110) and Au/S/Rh(111) surfaces, Au and S compete for the electrons of the transition-metal substrate. Gold produces dramatic changes in the reaction pathways for the removal of sulfur from the Mo and Rh surfaces. In the Au/S/Rh(111) system, S2 desorbs at much lo...

Peptide mass fingerprinting of chaperonin-containing TCP-1 (CCT) and copurifying proteins.

The chaperonin-containing TCP-1 (CCT), found in the eukaryotic cytosol, is currently the focus of extensive research, CCT isolated from mouse testis lysate sediments at 20S in a sucrose gradient and accounts for about 70% of the total protein in this fraction. We intend to identify all the other proteins that copurify with CCT and to compile a reference profile for future studies. Their identification can be accelerated by a combination of protease digestion, matrix-assisted laser desorption-mass spectrometry, and database matching known as peptide mass fingerprinting. We applied this strategy to 32 polypeptides resolved by 2-dimensional gel electrophoresis, and 23 known proteins and 6 novel proteins were identified. We analyzed isoelectric variants of the CCT subunits and differences in the peptide mass spectra of two CCT theta isoforms indicated a novel posttranslational modification of this subunit.

Coadsorption of Chlorine and Carbon Monoxide on a Pt(100) Face

Coadsorption of chlorine and carbon monoxide on a Pt(100) face is studied in an ultrahigh vacuum system using line-of-sight desorption mass spectrometry and LEED. Adsorption of the single components as well as coadsorption of both species removes the reconstruction of the clean Pt(100) hex surface. On a partially chlorine-precovered Pt(100) (1x1) surface, adsorption of CO occurs with high efficiency via a precursor state up to the completion of a mixed CO/Cl c(2x2) adlayer. The rate of the slow CO uptake that occurs further is determined by the transformation of the adlayer into a densely packed arrangement with a total adsorbate-to-surface Pt atom ratio of about 0.6. Depending on the dosing conditions, the mixed high-coverage adlayer exhibits the LEED patterns of a c(2x2) or of a ( 5 1 0 1 ) structure. Temperature-programmed desorption produces separate carbon monoxide and Cl atom peaks. The desorption kinetics indicate that both electronegative adsorbates, CO and Cl, destabilize CO in the c(2 x 2) adlayer to a comparable extent.

DIBs in captivity (?)

Experiments involving the electrical discharge of trace amounts (0.5%) of methane in argon gas followed by freezing out of products of the discharge in an argon matrix at 10 K have produced absorption bands of known interstellar molecular species, including CH, C 2 (anion form), C 3 and HCO (“a frozen interstellar cloud”). These experiments also repeatedly produce absorption bands that correlate in approximate wavelength with those of some of the stronger diffuse interstellar bands (DIBs). Among the interesting absorption bands produced in our experiments is a strong, broad band at 4500 Å. It is well known that because there is a difference between interaction of lower and higher energy states of a molecule or ion with the matrix, the absorption for a matrix-isolated species occurs at a different wavelength(s) than for the gas phase. Progressing from polar matrices to argon. and on to neon, the absorption wavelength converges toward what occurs in or is expected for the gas phase. Neon matrices affect an isolated species the least, with the result that wavelengths of absorptions are very close (∼ 0.1%) to that of the gas phase. The two 9700 Å region bands of the matrix-isolated C 60 cation shift blueward when isolated in neon, by 94 and 86 Å from what they are in argon (Gasyna. Z. et al., J. phys. Chem., 96, 1525–1527. 1992; Joblin. C. M., Ph.D. thesis, University of Paris. 1992). Isolated in neon, the pyrene cation exhibits an absorption at 4395 Å. which is blueward by 40 Å from the wavelength measured in argon (Salami, F. and Allamandola, L. J., Astrophys. J., 395, 301–306, 1992; Nature, 358, 42–43, 1992). These results strongly suggested that the 4500 Å band due to a reactive and as yet unidentified species isolated in argon in our experiments could shift blueward in the gas phase to coincide with the strong DIB at 4428 Å (Wdowiak. T. J. et al., The Diffuse Interstellar Bands, 1994; Molecules and Grains in Space, 1994). Recently, it has been demonstrated that the absorption seen in an argon matrix at 4500 Å for the photolysis product of methylpyrene shifts 60 Å to 4440 Å (Leger, A. and d'Hendecourt, L., The Diffuse Interstellar Bands, 1995) or 4442 Å (Salarna, F. and Allamandola, L. J., The Diffuse Interstellar Bands, 1995). All of this strongly argues for intensive investigation of the band found in our experiments at 4500 Å as a significant laboratory analog for the 4428 Å DIB. Efforts are in progress to better characterize the nature of the absorption, optimize its production in a more controlled manner and identify the ‘culprit’. This report discusses the relative strength of the 4500 Å band as compared with that of those bands due to identified species such as C 2 (anion) and C 3, and the results of laser-induced fluorescence experiments. Future experiments will include the more difficult neon matrix isolation technique and laser desorption mass spectroscopy.

Nonselective and Efficient Fluorescent Labeling of Glycans Using 2-Amino Benzamide and Anthranilic Acid

Reaction conditions for conjugation of two fluorescent ortho-substituted aniline derivatives, 2-amino benzamide (2-AB) and 2-anthranilic acid (2-AA), to N- and O-glycans have been investigated. Conjugation conditions for attaching 2-AB and 2-AA to core-fucosylated and nonfucosylated glycans were developed using complex N-glycans radiolabeled at the nonreducing terminus with [ 3H]C6-galactose. Optimal conditions for each of the following reaction parameters were experimentally defined: [glycans], [2-AB] or [2-AA], solvent and acid composition, temperature and time of Schiff′s base formation, nature of reductant, and temperature and time of reduction. Using the optimized reaction conditions it has been shown with several standard glycans and glycoprotein-derived glycan libraries that (i) molar labeling efficiencies are high and essentially independent of the amount of glycans; (ii) negligible (< 2 mol %) desialylation occurs during conjugation; (iii) glycan labeling is nonselective, i.e., independent of glycan structure; and (iv) insignificant fluorescent or chemical "blank" is recovered during the glycan-labeling and purification protocol. Labeling glycan pools with 2-AB or 2-AA therefore allows representative glycan profiles to be obtained and also allows relative molar quantitation of individual glycans in a pool. The 2-AB label is compatible with several chromatographic means for separation of carbohydrates including Bio Gel P4 gel permeation, high-performance anion-exchange chromatography with fluorescence detection, and a variety of HPLC procedures, as well as with mass spectrometric methods including matrix-assisted laser desorption-mass spectrometry and electrospray-mass spectrometry. The 2-AA label is particularly well-suited for electrophoretic separations by polyacrylamide gel electrophoresis. These fluorophores show high intrinsic sensitivity and thus facilitate very sensitive analysis of protein glycosylation.

Particle‐induced desorption in mass spectrometry. Part II. Effects and applications

AbstractIn the second part of this review (see preceding article for Part I), desorption‐induced processes by polyatomic projectiles over a broad energy range is described. The nonlinear increase in secondary ion yields as a function of the number of constituent atoms, which is evidence for “collective” effects, is discussed. Effects accompanying ion ejection upon monotornic or polyatomic particle impact, namely secondary electron emission, impact‐induced luminescence (photon emission), and sputtering of clusters (fullerenes in particular) by energetic ions, are intimately related to the mechanisms of desorption, and for that reason are also reviewed. Some of these phenomena, linked to, e.g., methods of ion detection, have (or may have in the future) practical applications in analytical mass spectrometry. In conclusion, selected examples for useful analytical applications of desorption methods like PDMS and FAB mainly in the biochemical field, which may illustrate current and emerging trends and perspectives, are discussed. © 1996 John Wiley &amp; Sons, Inc.

Particle‐induced desorption in mass spectrometry. Part I. Mechanisms and processes

AbstractDesorption of (predominantly) organic molecules, induced by particles with keV to MeV energy incident on a condensed phase target, is the topic of this review. The focus is on MeV atomic ion‐induced desorption–plasma desorption (PD). Parallels with keV particle desorption–secondary ion mass spectrometry (SIMS) and fast atom bombardment (FAB)–will be presented more schematically and chiefly for comparison purposes. Current understanding of desorption mechanisms by referring to insights from theory of the processes is surveyed, and the underlying similarities as well as differences between keV and MeV particle desorption are addressed. Several connections between particle‐induced desorption and photon‐induced desorption (e.g., matrix‐assisted laser desorption/ionization‐MALDI) are briefly outlined. Results from computer simulations are used to visualize the dynamics of the desorption process. A brief description of experimental characteristics of desorbed species, aimed at elucidating the mechanisms of desorption, is given, partly to illustrate the use of mass spectrometry in fundamental studies of ion–solid interactions. Ionization pathways in PD and molecular SIMS are briejy summarized. No special emphasis is placed in describing the “generic” instrumental setup f o r particle desorption and only specific technical aspects, not treated elsewhere, eg., time and spatial correlation of the ejected species, are discussed here.In the second part of this review (subsequent article) desorption induced by polyatomic projectiles, and effects, accompanying ion ejection, namely secondary electron emission, impact‐induced photon emission, and sputtering of clusters (fullerenes in particular), are also reviewed. In conclusion, selected examples for analytical applications of desorption methods that may illustrate current and emerging trends and perspectives are discussed. © 1996 John Wiley &amp; Sons, Inc.

The Interaction of Sulfur with Ag/Pt(111) Surfaces: Silver-Promoted Sulfidation of Platinum

The coadsorption of sulfur and silver on Pt(111) has been examined using thermal desorption mass spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), and X-ray excited Auger electron spectroscopy (XAES). The results of XPS and XAES indicate that at temperatures between 300 and 700 K, S2 gas reacts with Pt(111) producing a chemisorbed layer of sulfur without forming bulk-like platinum sulfides. The sulfidation of platinum occurs after vapor depositing Ag on S/Pt(111) surfaces, or after exposing Ag/Pt(111) surfaces to S2 gas. At temperatures from 400 to 700 K, the reaction of S2 gas with Ag/Pt(111) surfaces produces silver sulfides that catalyze the sulfidation of platinum by providing surface sites for the dissociation of S2, and by favoring the diffusion of S into the bulk of the Pt substrate. The silver and platinum sulfides in the S/Ag/Pt(111) systems decompose at temperatures between 750 and 850 K, with S2 and S evolving into gas phase and metallic Ag remaining on top of a Pt(111) substrate partially covered by chemisorbed S. At submonolayer coverages of Ag and S on Pt(111), θAg + θs < 1 ML, the presence of sulfur significantly weakens the strength of the Pt ↔ Ag interactions, and the desorption temperature of Ag is ∼90 K smaller than on clean Pt(111). The TDS results indicate that a S adatom reduces the ability for bimetallic bonding of several (3-4) platinum surface atoms.

Isolation, Characterization, and Primary Structure of Rubredoxin from the Photosynthetic Bacterium, Heliobacillus mobilis

Rubredoxin is a small nonheme iron protein that serves as an electron carrier in bacterial systems. Rubredoxin has now been isolated and characterized from the strictly anaerobic phototroph, Heliobacillus mobilis. The molecular mass (5671.3 Da from the amino acid sequence) was confirmed and partial formylation of the N-terminal methionyl residue was established by matrix-assisted laser desorption mass spectroscopy. The complete 52-amino-acid sequence was determined by a combination of N-terminal sequencing by Edman degradation and C-terminal sequencing by a novel method using carboxypeptidase treatment in conjunction with amino acid analysis and laser desorption time of flight mass spectrometry. The molar absorption coefficient of Hc. mobilis rubredoxin at 490 nm is 6.9 mM−1 cm−1 and the midpoint redox potential at pH 8.0 is −46 mV. The EPR spectrum of the oxidized form shows resonances at g = 9.66 and 4.30 due to a high-spin ferric iron. The amino acid sequence is homologous to those of rubredoxins from other species, in particular, the gram-positive bacteria, and the phototrophic green sulfur bacteria, and the evolutionary implications of this are discussed.

Adsorption of sulfur on bimetallic surfaces: Formation of copper sulfides on Pt(111) and Ru(001)

The interaction of sulfur and copper on Pt(111) and Ru(001) has been examined using x-ray photoelectron spectroscopy and thermal desorption mass spectroscopy. Cu/Pt(111) and Cu/Ru(001) surfaces were exposed to S2 gas at 300 K. It was found that for both substrates stable copper–sulfide films were formed, of which the Cu–S/Ru(001) system was the more stable. The decomposition of the Cu2S films on Pt(111) occurred at 600–850 K and on Ru(001) at 900–1000 K. Breakdown of the films led to evolution into the gas phase of sulfur (mainly as S2) without desorption of copper or the sulfur chemisorbed on the substrate. This chemisorbed sulfur desorbed in a broad feature from 1000 to 1500 K. For the Ru(001) substrate the Cu atoms remained on the surface until they desorbed at 1080 K, while on Pt(111) the Cu atoms migrated into the Pt(111) surface to form a subsurface Cu–Pt alloy; no Cu desorption features were seen at temperatures as high as 1300 K. On Pt(111), copper sulfide promoted the formation of a bulklike platinum sulfide. No sulfidation of ruthenium was detected in the presence of copper–sulfide films. For both substrates the sulfur atoms were found to highly perturb the copper sites, decreasing the ability of the noble-metal adatoms to adsorb CO.

Photochemical transformation of C 60 and C 70 films

Thin solid films of C 60 and C 70 have been found to be sensitive to UV-visible light. In the absence of oxygen, which acts as a triplet state quencher, C 60 and C 70 have been observed to phototransform from a toluene-soluble to a toluene-insoluble state. This phototransformation has been studied via Raman and FTIR spectroscopies, UV-visible transmission spectroscopy and laser desorption mass spectroscopy. The results of these experiments have been interpreted as evidence for a phototransformation from a van der Waals solid to one in which the fullerenes are linked by covalent bonds. For C 60, it is proposed that a transformation to a polymeric solid has occurred, whereas a similar flux of UV-visible light applied to C 70 is proposed to lead to a random dimerization of the lattice and a much smaller population of higher oligomers. For both phototransformed C 60 and C 70, the covalent bonds between fullerenes can be broken thermally and the phototransformed material returns to the pristine, toluene-soluble state. UV-visible light can also be used to photochemically assist the diffusion of dioxygen into the interstitial voids in the solid C 60 and C 70 lattices. For C 60, a photochemical enhancement of the O 2 diffusion rate by a factor of ~ 10 is observed by alpha particle backscattering, leading to a stoichiometry of ~ C 60O 2. Similar to C 60-polyfullerene, C 60(O 2) x is also toluene insoluble. As a result, these C 60-based films might find photolithographic applications.

Purification and amino acid sequence of the insecticidal neurotoxin T×4(6-1) from the venom of the ‘armed’ spider Phoneutria nigriventer (keys)

An insecticidal peptide referred to as Tx4(6-1) was purified from the venom of the spider Phoneutria nigriventer by a combination of gel filtration, reverse-phase fast liquid chromatography on Pep-RPC, reverse-phase high performance liquid chromatography (HPLC) on Vydac C 18 and ion-exchange HPLC on cationic columns. Tx4(6-1) is highly toxic to house flies. At levels of 0.5 ng/house fly it caused excitatory symptoms immediately after intrathoracical injection. However, in mice injections of 0.03 mg of the toxin intracerebroventricularly resulted in no apparent symptoms of intoxication. These results demonstrate that Tx4(6-1) of P. nigriventer has no toxicity for mice, and suggest that it is a specific anti-insect toxin. The mol. wt (5244.6) and purity of the toxin were determined by desorption mass spectroscopy. The complete amino acid sequence of this toxin was established by direct automated Edman degradation and manual 4- N, N′-dimethylaminoazobenzene-4′isothiocyanate/phenyl-isothiocyanate microsequence analyses of peptides obtained from digests with various proteases. The protein contains 48 amino acids including 10 Cys and 6 Lys. The N-terminal and C-terminal residues were Cys. The Tx4(6-1) sequence differs from that of previously characterized neurotoxins found in the same and other venom spiders, but exhibited sequence similarities in the location of the Cys residues.