Cryogenic ion trap vibrational spectroscopy of the microhydrated sulfate dianions SO42-(H2O)3-8

Infrared photodissociation spectra of the D2-tagged microhydrated sulfate dianions with three to eight water molecules are presented over a broad spectral range that covers the OH stretching and H2O bending modes of the solvent molecules at higher energies, the sulfate stretching modes of the solute at intermediate energies and the intermolecular solute librational modes at the lowest energies. A low ion temperature combined with messenger-tagging ensures well-resolved vibrational spectra that allow for structure assignments based on a comparison to harmonic and anharmonic IR spectra from density functional theory (DFT) calculations. DFT ab initio molecular dynamics simulations are required to disentangle the broad and complex spectral signatures of microhydrated sulfate dianions in the OH stretching region and to identify systematic trends in the correlation of the strength and evolution of the solute-solvent and solvent-solvent interactions with cluster size. The onset for the formation of the second solvation shell is observed for n = 8.

Measuring Electronic Structure of Multiply Charged Anions to Understand Their Chemistry: A Case Study on Gaseous Polyhedral closo-Borate Dianions

Research on multiply charged anions (MCAs) in the gas phase has been intensively performed during the past decades, mainly to understand fundamental molecular physics phenomena, for example, intramolecular Coulomb repulsion and existence of the repulsive Coulomb barrier. However, the relevance of these investigations with respect to understanding MCAs' chemistry appears often vague. Here, we discuss how insights into the electronic structure obtained from negative ion photoelectron spectroscopy (NIPES) combined with theoretical calculations and collision-induced dissociation can provide a fundamental understanding of the intrinsic chemical reactivity of MCAs and their fragments. This is exemplified in our studies on polyhedral closo-borate dianions [B_nX_n]^2- (n = 6, 10, 11, 12; X = H, F-I, CN) and their fragment ions. For example, the rational design of closo-borate dianions with specific electronic properties is described, which leads to generating highly reactive fragments. Depending on the dianionic precursor, these fragments are tuned to either bind noble gases effectively or activate small molecules like CO and N₂. The intrinsic electronic properties of closo-borate dianions are further compared to their electrochemistry in solutions, revealing solvent effects on the redox potentials. Neutral host molecules such as cyclodextrins are found to bind strongly to [B_nX_n]^2-, and gas phase NIPES provides insights into the intrinsic host-guest interactions. Finally, outlooks including the direct NIPES of molecular fragment ions that cannot be generated in the condensed phase and their utilization in preparative mass spectrometry are discussed.

Gaseous cyclodextrin-closo-dodecaborate complexes χCD·B12X122- (χ = α, β, and γ; X = F, Cl, Br, and I): electronic structures and intramolecular interactions

A fundamental understanding of cyclodextrin-closo-dodecaborate inclusion complexes is of great interest in supramolecular chemistry. Herein, we report a systematic investigation on the electronic structures and intramolecular interactions of perhalogenated closo-dodecaborate dianions B12X122- (X = F, Cl, Br and I) binding to α-, β-, and γ-cyclodextrins (CDs) in the gas phase using combined negative ion photoelectron spectroscopy (NIPES) and density functional theory (DFT) calculations. The vertical detachment energy (VDE) of each complex and electronic stabilization of each dianion due to the CD binding (ΔVDE, relative to the corresponding isolated B12X122-) are determined from the experiments along α-, β- and γ-CD in the form of VDE (ΔVDE): 4.00 (2.10), 4.33 (2.43), and 4.30 (2.40) eV in X = F; 4.09 (1.14), 4.64 (1.69), and 4.69 (1.74) eV in X = Cl; 4.11 (0.91), 4.58 (1.38), and 4.70 (1.50) eV in X = Br; and 3.54 (0.74), 3.88 (1.08), and 4.05 (1.25) eV in X = I, respectively. All complexes have significantly higher VDEs than the corresponding isolated dodecaborate dianions with ΔVDE spanning from 0.74 eV at (α, I) to 2.43 eV at (β, F), sensitive to both host CD size and guest substituent X. DFT-optimized complex structures indicate that all B12X122- prefer binding to the wide openings of CDs with the insertion depth and binding motif strongly dependent on the CD size and halogen X. Dodecaborate anions with heavy halogens, i.e., X = Cl, Br, and I, are found outside of α-CD, while B12F122- is completely wrapped by γ-CD. Partial embedment of B12X122- into CDs is observed for the other complexes via multipronged B-XH-O/C interlocking patterns. The simulated spectra based on the density of states agree well with those of the experiments and the calculated VDEs well reproduce the experimental trends. Molecular orbital analyses suggest that the spectral features at low binding energies originated from electrons detached from the dodecaborate dianion, while those at higher binding energies are derived from electron detachment from CDs. Energy decomposition analyses reveal that the electrostatic interaction plays a dominating role in contributing to the host-guest interactions for the X = F series partially due to the formation of a O/C-HX-B hydrogen bonding network, and the dispersion forces gradually become important with the increase of halogen size.

New Perspectives in the Noble Gas Chemistry Opened by Electrophilic Anions

Binding of noble gases (NGs) is commonly considered to be the realm of highly reactive electophiles with cationic or at least non-charged character. Herein, we summarize our latest results evidencing that the incorporation of a strongly electrophilic site within a rigid cage-like anionic structure offers several advantages that facilitate the binding of noble gases and stabilize the formed NG adducts. The anionic superelectrophiles investigated by us are based on the closo-dodecaborate dianion scaffold. The record holder [B₁₂(CN)₁₁]⁻ binds spontaneously almost all members of the NG family, including the very inert argon at room temperature and neon at 50 K in the gas phase of mass spectrometers. In this perspective, we summarize the argumentation for the advantages of anionic electrophiles in binding of noble gases and explain them in detail using several examples. Then we discuss the next steps necessary to obtain a comprehensive understanding of the binding properties of electrophilic anions with NGs. Finally, we discuss the perspective to prepare bulk ionic materials containing NG derivatives of the anionic superelectophiles. In particular, we explore the role of counterions using computational methods and discuss the methodology, which may be used for the actual preparation of such salts.

Binding Properties of Small Electrophilic Anions [B6 X5 ]- and [B10 X9 ]- (X=Cl, Br, I): Activation of Small Molecules Based on π-Backbonding

Superelectrophilic anions constitute a special class of molecular anions that show strong binding of weak nucleophiles despite their negative charge. In this study, the binding characteristics of smaller gaseous electrophilic anions of the types [B6 X5 ]- and [B10 X9 ]- (with X=Cl, Br, I) were computationally and experimentally investigated and compared to those of the larger analogues [B12 X11 ]- . The positive charge of vacant boron increases from [B6 X5 ]- via [B10 X9 ]- to [B12 X11 ]- , as evidenced by increasing attachment enthalpies towards typical σ-donor molecules (noble gases, H2 O). However, this behavior is reversed for σ-donor-π-acceptor molecules. [B6 Cl5 ]- binds most strongly to N2 and CO, even more strongly than to H2 O. Energy decomposition analysis confirms that the orbital interaction is responsible for this opposite trend. The extended transition state natural orbitals for chemical valence method shows that the π-backdonation order is [B6 X5 ]- >[B10 X9 ]- >[B12 X11 ]- . This predicted order explains the experimentally observed red shifts of the CO and N2 stretching fundamentals compared to those of the unbound molecules, as measured by infrared photodissociation spectroscopy. The strongest red shift is observed for [B6 Cl5 N2 ]- : 222 cm-1 . Therefore, strong activation of unreactive σ-donor-π-acceptor molecules (commonly observed for cationic transition metal complexes) is achieved with metal-free molecular anions.

Isolated [B2(CN)6]2-: Small Yet Exceptionally Stable Nonmetal Dianion

We report the observation of a small, yet remarkably stable, metal-free hexacyanodiborate dianion [B₂(CN)₆]^2- in the gas phase. Negative ion photoelectron spectroscopy (NIPES) was employed to measure its spectra at multiple laser wavelengths, yielding a 1.9 eV electron binding energy (EBE) ─a remarkably high value of electronic stability and a ∼2.60 eV repulsive Coulomb barrier (RCB) for electron detachment. This rationalizes the observation of this dianion, although homolytic charge-separation dissociation into two [B(CN)₃]^•- is energetically favorable. Quantum chemical calculations demonstrate a D_3d staggered conformation for both the dianion and radical monoanion, and the calculated EBE and RCB match the experimental values well. The simulated density of states spectrum reproduces all measured electronic transitions, while the simulated vibrational progressions for the ground state transition cover a much narrower EBE range compared to the experimental band, indicating appreciable auto-photodetachment via electronically excited dianion resonances.

Gas Phase Reactivity of [Mo6X14]2- Dianions (X = Cl - I)

We investigate collision-induced dissociation (CID) of [Mo₆X₁₄]^2- (X = Cl, Br, I) and the reactivity of fragment ions of these precursors with background gases. Ion mobility measurements and theoretical calculations provide structural information for some of the observed ions. Sequential losses of MoX₂ units dominate the dissociation pathways of [Mo₆Cl₁₄]^2-. Meanwhile, loss of X radicals is the main channel for X = Br and I. Ion mobility measurements and computational investigations indicate minor structural changes in the octahedral Mo₆ unit for [Mo₆I_m]^- (m = 6-13) fragments. We observe that mass spectra obtained using CID substantially vary among mass spectrometers: Specifically, ions with molecular formula [Mo₆X_m(O₂)_n]^- (X = Br and I) are observed as dominant species produced through reactions with O₂ in several mass spectrometers, but also adduct free fragment ions were observed in other instruments, depending on the background conditions. Ion-trap fragmentation combined with theoretical investigations indicates that spontaneous losses of X radicals occur upon binding of O₂ to [Mo₆I_m]^- fragments (m ≤ 12). Theoretical investigations indicate that both oxygen atoms are bound to the vacant sites of the Mo₆ units. This study opens up a new vista to generate and study a large variety of hexanuclear Mo₆X_m(O₂)_n anions.

B12X11(H2)−: exploring the limits of isotopologue selectivity of hydrogen adsorption

We study the isotopologue-selective binding of dihydrogen at the undercoordinated boron site of B₁₂X₁₁⁻ (X = H, F, Cl, Br, I, CN) using ab initio quantum chemistry. With a Gibbs free energy of H₂ attachment reaching up to 80 kJ mol⁻¹ (ΔG at 300 K for X = CN), these sites are even more attractive than most undercoordinated metal centers studied so far. We thus believe that they can serve as an edge case close to the upper limit of isotopologue-selective H₂ adsorption sites. Differences of the zero-point energy of attachment average 5.0 kJ mol⁻¹ between D₂ and H₂ and 2.7 kJ mol⁻¹ between HD and H₂, resulting in hypothetical isotopologue selectivities as high as 2.0 and 1.5, respectively, even at 300 K. Interestingly, even though attachment energies vary substantially according to the chemical nature of X, isotopologue selectivities remain very similar. We find that the H–H activation is so strong that it likely results in the instantaneous heterolytic dissociation of H₂ in all cases (except, possibly, for X = H), highlighting the extremely electrophilic nature of B₁₂X₁₁⁻ despite its negative charge. Unfortunately, this high reactivity also makes B₁₂X₁₁⁻ unsuitable for practical application in the field of dihydrogen isotopologue separation. Thus, this example stresses the two-edged nature of strong H₂ affinity, yielding a higher isotopologue selectivity on the one hand but risking dissociation on the other, and helps define a window of adsorption energies into which a material for selective adsorption near room temperature should ideally fall.

The extreme H₂ affinity of B₁₂X₁₁⁻ gives a glimpse of how higher selectivities in adsorptive isotopologue separation may be achieved.

Binding of Saturated and Unsaturated C6-Hydrocarbons to the Electrophilic Anion [B12Br11]−: A Systematic Mechanistic Study

The highly reactive gaseous ion [B12Br11]– is a metal-free closed-shell anion which spontaneously forms covalent bonds with hydrocarbon molecules, including alkanes. Herein, we systematically investigate the reaction mechanism for binding...

Synthesis, Structure, and Surface Adsorption Characteristics of a Polynuclear MnII,IV-YbIII Complex

The controlled adsorption of polynuclear coordination compounds with specific structural and electronic characteristics on surfaces is crucial for the prospective implementation of molecule-surface interfaces into practical electronic devices. From this perspective, a neutral 3d,4f-coordination cluster [Mn^II₃Mn^IVYb₃O₃(OH)(L·SMe)₃(OOCMe)₉]·2MeCN·3EtOH (1·2MeCN·3EtOH), where L·SMe^- is a Schiff base, has been synthesized and fully characterized and its adsorption on two different solid substrates, gold and graphite, has been studied. The mixed-valence compound with a bilayered metal core structure and the structurally exposed thioether groups exhibits a substantially different surface bonding to metallic gold and semimetallic graphite substrates. While on graphite the adsorption takes place only on distinguished attraction points with a locally increased number of potential bonding sites such as terrace edges and other surface defects, on gold the molecules were found to adsorb rather weakly on randomly distributed adsorption sites of the surface terraces. This entirely different behavior provides important information for the development of advanced surface materials that may enable well-distributed ordered molecular assemblies.

Factors affecting outcome in locally advanced breast cancer

Patients presenting with locally advanced breast cancer (LABC) constitute a diverse group for which a variety of treatment modalities have been instituted. To assess which factors have a direct impact on outcome, we reviewed the medical records of 104 patients diagnosed with stage IIIA, stage IIIB and T3N0M0 breast carcinoma. When considered individually (univariate analysis), clinical stage, pathological stage, oestrogen receptor status and type of therapy were significant predictors for disease-free survival (DFS) and overall survival (OS). However, in a multivariate analysis, only clinical stage was a significant predictor for both DFS and OS, while ER status was a significant predictor for OS. There was a high degree of correlation between clinical and pathological staging. Nearly two-thirds of the patients developed a recurrence by 5 years. Loco-regional recurrence was the site of first recurrence in one-third of the patients by 5 years. The prognosis for patients presenting with LABC is poor, and they should be treated aggressively with loco-regional and systemic multimodality therapy. Although groups of patients with improved outcome could be identified by clinical or pathological staging, no group demonstrated an outcome good enough to be spared from multimodality therapy.

Influence of local treatment on the recurrence rate of ductal carcinoma in situ

BACKGROUND

Screening mammography has resulted in a significant increase in the diagnosis of ductal carcinoma in situ (DCIS). The role of breast conservation therapy and the long-term recurrence rate are still controversial. This article compares mastectomy, wide excision alone, and wide excision with radiation as treatments for DCIS.

STUDY DESIGN

One hundred twenty-four cases of DCIS were retrospectively reviewed and were found to be pure DCIS by a senior pathologist. The mean age at diagnosis was 60 years (range, 33 to 81). Originally, 101 patients (81 percent) presented with calcification on mammogram, and 23 (19 percent) presented with a palpable mass. Histologic data showed that 54 (44 percent) had noncomedo type lesions, 46 (37 percent) had comedo type, and 24 (19 percent) had unknown type DCIS.

RESULTS

Four of the 124 patients had a recurrence during a mean follow-up period of 43 months. Recurrence is defined as any development of DCIS or invasive carcinoma in the ipsilateral breast. There was one (1.3 percent) recurrence in the 75 patients treated with mastectomy (an adenocarcinoma of the chest wall), which occurred at 59 months. Treatment was 5,750 cGy to the chest wall and the patient is free of disease 37 months postradiation. There were three (11 percent) recurrences at 14, 21, and 29 months, respectively, in the 28 patients treated with wide excision alone. All three recurrences were found by calcifications on mammogram and all patients had comedo type original lesions. Two recurrences were pure DCIS of the breast. Both patients were treated with mastectomy and are free of disease at 33 and five months, respectively. The third recurrence was an invasive colloid carcinoma of the breast. Treatment was a modified radical mastectomy; the patient is free of disease after 62 months. There were no recurrences in the 21 patients who were treated with wide excision and radiation. Average total dose of radiation was 5,835 cGy (range, 4,500 to 6,480).

CONCLUSIONS

The results of this study indicate that both mastectomy and wide excision with radiation are associated with very low recurrence rates. Wide excision alone is associated with a higher recurrence rate. However, all recurrences were detected mammographically and all lesions were salvaged by mastectomy. Therefore, the ultimate local control and survival rates were similar for all three modalities.

Spontaneous ligand loss by soft landed [Ni(bpy)3]2+ ions on perfluorinated self-assembled monolayer surfaces

Transition metal (TM) complexes are widely used in catalysis, photochemical energy conversion, and sensing. Understanding factors that affect ligand loss from TM complexes at interfaces is important both for generating catalytically-active undercoordinated TM complexes and for controlling the degradation pathways of photosensitizers and photoredox catalysts. Herein, we demonstrate that well-defined TM complexes prepared on surfaces using ion soft landing undergo substantial structural rearrangements resulting in ligand loss and formation of both stable and reactive undercoordinated species. We employ nickel bipyridine (Ni-bpy) cations as a model system and explore their structural reorganization on surfaces using a combination of experimental and computational approaches. The controlled preparation of surface layers by mass-selected deposition of [Ni(bpy)3]2+ cations provides insights into the chemical reactivity of these species on surfaces. Both surface characterization using mass spectrometry and electronic structure calculations using density functional theory (DFT) indicate that [Ni(bpy)3]2+ undergoes a substantial geometry distortion on surfaces in comparison with its gas-phase structure. This distortion reduces the ligand binding energy and facilitates the formation of the undercoordinated [Ni(bpy)2]2+. Additionally, charge reduction by the soft landed [Ni(bpy)3]2+ facilitates ligand loss. We observe that ligand loss is inhibited by co-depositing [Ni(bpy)3]2+ with a stable anion such as closo-dodecaborate dianion, [B12F12]2-. The strong electrostatic interaction between [Ni(bpy)3]2+ and [B12F12]2- diminishes the distortion of the cation due to interactions with the surface. This interaction stabilizes the soft landed cation by reducing the extent of charge reduction and its structural reorganization. Overall, this study shows the intricate interplay of charge state, ion surface interactions, and stabilization by counterions on the structure and reactivity of metal complexes on surfaces. The combined experimental and computational approach used in this study offers detailed insights into factors that affect the integrity and stability of active species relevant to energy production and catalysis.

Probing the Electronic Structure of [B10H10]2- Dianion Encapsulated by an Octamethylcalix[4]pyrrole Molecule

Despite being an important closo-borate in condensed phase boron chemistry, isolated [B10H10]2- is electronically unstable and has never been detected in the gas phase. Herein, we report a successful capture of this fleeting species through binding with an octamethylcalix[4]pyrrole (omC4P) molecule to form a stable gaseous omC4P·[B10H10]2- complex and its characterizations utilizing negative ion photoelectron spectroscopy (NIPES). The recorded NIPE spectrum, contributed by both omC4P and [B10H10]2-, is deconvoluted by subtracting the omC4P contribution to yield a [B10H10]2- spectrum. The obtained [B10H10]2- spectrum consists of four major bands spanning the electron binding energy (EBE) range from 1 to 5 eV, with the EBE gaps matching excellently with the energy intervals of computed high-lying occupied molecular orbitals of the [B10H10]2- dianion. This study showcases a generic method to utilize omC4P to capture unstable multiply charged anions in the gas phase for experimental determination of their electronic structures.

Generation and reactivity of the fragment ion [B12I8S(CN)]- in the gas phase and on surfaces

Gaseous fragment ions generated in mass spectrometers may be employed as "building blocks" for the synthesis of novel molecules on surfaces using ion soft-landing. A fundamental understanding of the reactivity of the fragment ions is required to control bond formation of deposited fragments in surface layers. The fragment ion [B12X11]- (X = halogen) is formed by collision-induced dissociation (CID) from the precursor [B12X12]2- dianion. [B12X11]- is highly reactive and ion soft-landing experiments have shown that this ion binds to the alkyl chains of organic molecules on surfaces. In this work we investigate whether specific modifications of the precursor ion affect the chemical properties of the fragment ions to such an extent that attachment to functional groups of organic molecules on surfaces occurs and binding of alkyl chains is prevented. Therefore, a halogen substituent was replaced by a thiocyanate substituent. CID of the precursor [B12I11(SCN)]2- ion preferentially yields the fragment ion [B12I8S(CN)]-, which shows significantly altered reactivity compared to the fragment ions of [B12I12]2-. [B12I8S(CN)]- has a previously unknown structural element, wherein a sulfur atom bridges three boron atoms. Gas-phase reactions with different neutral reactants (cyclohexane, dimethyl sulfide, and dimethyl amine) accompanied by theoretical studies indicate that [B12I8S(CN)]- binds with higher selectivity to functional groups of organic molecules than fragment ions of [B12I12]2- (e.g., [B12I11]- and [B12I9]-). These findings were further confirmed by ion soft-landing experiments, which showed that [B12I8S(CN)]- ions attacked ester groups of adipates and phthalates, whereas [B12I11]- ions only bound to alkyl chains of the same reagents.

Control of Intermediates and Products by Combining Droplet Reactions and Ion Soft-Landing

Despite being recognized primarily as an analytical technique, mass spectrometry also has a large potential as a synthetic tool, enabling access to advanced synthetic routes by reactions in charged microdroplets or ionic thin layers. Such reactions are special and proceed primarily at surfaces of droplets and thin layers. Partial solvation of the reactants is usually considered to play an important role for reducing the activation barrier, but many mechanistic details still need to be clarified. In our study, we showcase the synergy between two sequentially applied "preparative mass spectrometry" methods: initiating accelerated reactions within microdroplets during electrospray ionization to generate gaseous ionic intermediates in high abundance, which are subsequently mass-selected and soft-landed to react with a provided reagent on a substrate. This allows the generation of products at a nanomolar scale, amenable to further characterization. In this proof-of-concept study, the contrasting reaction pathways between intrinsically neutral and pre-charged reagents, respectively, both in microdroplets and in layers generated by ion soft-landing are investigated. This provides new insights into the role of partially solvated reagents at microdroplet surfaces for increased reaction rates. Additionally, further insights into reactions of ions of the same polarity under various conditions is obtained.

The failure of conventional methods to promote spontaneous transpyloric feeding tube passage and the safety of intragastric feeding in the critically ill ventilated patient

Nasoenteral tube feedings are often recommended in critically ill patients when gastrointestinal tract function is intact. Conventional methods of placement include turning the patient on the right side and the use of drugs that stimulate peristalsis to promote transpyloric passage. A prospective study was initially performed to assess the success of conventional methods used to promote transpyloric feeding tube placement in patients requiring assisted ventilation admitted to the Surgical Intensive Care Unit (SICU) (Part I of the study). In 68 critically ill ventilated patients, placement of nasoduodenal feeding tubes was attempted. Successful transpyloric placement was achieved in only ten patients. There was no correlation between age, gender, admitting diagnosis, time of tube placement and successful placement. The second part of the study was initiated to assess the safety of nasogastric feeding in critically ill ventilated patients. Forty-two patients admitted to the SICU were considered candidates for gastrointestinal tract feeding and were fed through the gastric route. Twenty-five patients reached enteral feeding goal rate within 72 hours, while 34 patients achieved goal rate by five days. Eight patients required total parenteral nutrition to meet nutritional needs because of an inability to achieve adequate nutritional support enterally. There were 11 complications noted in ten patients, including one episode of aspiration pneumonia. The presence of complications was not related to age, gender, admitting diagnosis, infusion method or type of formula used. Duodenal intubation using conventional methods in critically ill ventilated patients is unsuccessful in most patients. Nasogastric feeding in this group of patients can be safely administered in selected instances.

Thioredoxin and thioredoxin reductase gene expression in human tumors and cell lines, and the effects of serum stimulation and hypoxia

Thioredoxin and thioredoxin reductase are redox proteins that have been implicated in the control of cell proliferation and transformation. We report the levels and activity of these proteins and their mRNAs in human primary tumors and tumor cell lines. Half of human primary colorectal carcinomas (5/10) examined had increased thioredoxin mRNA, of 3- to over 100-fold, compared to adjacent normal colonic mucosa from the same subject. Thioredoxin reductase protein and activity were increased an average of 2-fold in human colorectal tumors compared to normal mucosa. A number of human hematologic and solid tumor cell lines were studied and showed a 10-fold range of thioredoxin mRNA and a 23-fold range of thioredoxin reductase mRNA. Increased proliferation and hypoxia are factors that might contribute to the increased expression in solid tumors. We found that serum stimulation of growth arrested MCF-7 breast cancer cells caused a 59% increase in thioredoxin mRNA and a 62% increase in thioredoxin reductase mRNA by 24 hours. Exposure of HT-20 colon cancer cells to hypoxia resulted in a 14-fold increase in thioredoxin mRNA by 16 hours, and a transient 4-fold increase in thioredoxin reductase mRNA at 1 hour that had returned to control levels by 8 hours. Cancer cells were found to release thioredoxin into the medium at rates between 1 to 2 pmole/10(6) cells/3 hours. The rate of secretion was not, however, related to cellular-levels of thioredoxin. The results of the study show that the expression of thioredoxin and thioredoxin reductase are increased several fold in some human solid tumors compared to normal tissue. Secretion of thioredoxin, which is known to have a direct growth stimulating activity, by human tumor cells might lead to the stimulation of cancer cell growth.