Octaoctyl-substituted lutetium bisphthalocyanine for NADH biosensing

Cyclic voltammetric and Raman and UV-vis spectroscopic measurements were performed on thin films of nonperipherally substituted bis[1,4,8,11,15,18,22,25-octakis(octyl)phthalocyaninato] lutetium(III) (R16LuPc2). Voltammograms exhibit one-electron quasi-reversible redox processes in 1.5 M LiClO4 aqueous solutions. The red-shift of the Q-band of R16LuPc2 in the UV-visible absorption spectra upon oxidation is attributed to the shortening of the inter-ring distance between the two phthalocyanine moieties. This observation is also consistent with the shift in the redox-sensitive vibrational modes in the Raman spectra due to the localization of the positive charge on phthalocyanine moieties. Neutralization of the oxidized R16LuPc2(+) film by dihydronicotinamide adenine dinucleotide (NADH) using different concentrations varying from 0.05 to 1 mM has been studied by UV-vis absorption and Raman spectroscopies. The reduction processes for a three month old film were found to be slower than those for freshly prepared films and showed a dependence upon NADH concentration. The data provide a basis for application of R16LuPc2 as a sensor for NADH.

Routes to some 3,6-disubstituted phthalonitriles and examples of phthalocyanines derived therefrom: An overview

The paper reviews a selection of synthetic pathways that provide access to 3,6-disubstituted phthalonitriles, precursors for the synthesis of 1,4,8,11,15,18,22,25-octasubstituted phthalocyanine derivatives. Early routes using Diels–Alder reactions for the synthesis of 3,6-dialkyl, 3,6-dialkoxymethyl, 3,6-dialkenyl and 3,6-diphenylphthalonitriles are appraised. However, the emphasis of the review focuses on the scope and applications of 2,3-dicyanohydroquinone as a starting material for obtaining 3,6-disubstituted phthalonitriles. The earliest example of the use of 2,3-dicyanohydroquinone concerned its O -alkylation to afford 3,6-dialkoxyphthalonitriles. These are immediate precursors to near-infrared absorbing phthalocyanine derivatives. Triflation of 2,3-dicyanohydroquinone extends the scope of the compound for phthalocyanine synthesis; the bis-triflate derivative is susceptible to S N Ar reactions and readily reacts with thiols to provide 3,6-bis(alkylsulfanyl) and 3,6-bis(arylsulfanyl)phthalonitriles. 3,6-Bis(phenylselenyl)phthalonitrile has also been obtained recently from the same precursor. Phthalocyanine derivatives obtained from them typically show a strongly bathochromically shifted Q-band absorption that is particularly sensitive to the central metal ion. The bis-triflate of 2,3-dicyanohydroquinone is also an ideal precursor for participation in cross-coupling reactions. Examples from the University of East Anglia group and elsewhere are presented which show the application of the nickel-catalyzed Negishi coupling reaction using alkylzinc halide derivatives. Yields of 3,6-dialkylphthalonitriles and 3,6-bis(substituted alkyl)phthalonitriles range from ca. 40 to 70%. Direct comparison for one example shows that the yield from the Negishi coupling method is higher than that using the Suzuki coupling protocol. Examples of the preparation of 3,6-diarylphthalonitriles from 2,3-dicyanohydroquinone bis-triflate using the Suzuki coupling reaction are reported with yields of the order of 65–70%. The review also includes a further application of 2,3-dicyanohydroquinone as a precursor to both monobromo and dibromo derivatives of 3,6-dibutoxyphthalonitrile. These compounds provide opportunities for cross-coupling at the brominated sites to provide more complex derivatives with the potential to serve as precursors of highly substituted phthalocyanine derivatives.

Synthesis and characterization of some octaalkyl substituted lead phthalocyanines and unexpected variations in lead lability arising from the position of substituents and their chain length

The preparation of some peripherally substituted (2,3,9,10,16,17,23,24) and non-peripherally substituted (1,4,8,11,15,18,22,25) octaalkyl lead(II) phthalocyanines with different alkyl chain lengths (6, 7, 8 or 9 carbons) is described and a comparison of some of their properties reported. X-ray structure analyses of the isomeric peripheral and non-peripheral octakis(octyl)phthalocyaninato lead(II) compounds reveal a greater degree of distortion of the ligand ring system from planarity in the former derivative. The series of peripherally substituted octaalkyl lead(II) phthalocyanines exhibit columnar liquid crystal behavior whereas the non-peripherally substituted isomers do not. The lability of the lead ion was investigated using 1 H NMR spectrometry under a specific set of conditions (8.8 × 10-4 M solutions of the phthalocyanine in d8-toluene containing d4-acetic acid 2.06 × 10-5 M). All the compounds underwent acid catalyzed demetalation at rates dependent upon the location of the substituents and, more surprisingly, the chain length of the alkyl groups. Under these conditions the lead ion within each of the peripherally substituted octaalkyl lead phthalocyanines was more labile than that in the non-peripherally substituted isomer.

Evanescent wave excitation of palladium metalated porphyrins as self-assembled monolayers and phosphorescence quenching by oxygen

The novel palladium metalated derivatives of 5,5′-[8,8′-di(thiooctyloxy)-4,4′-phenyl)]-10,10′,15,15′,20,20′-hexakis(4,4′-t-butylphenyl)diporphyrin and 5,5′-[8,8′-di(thiooctyloxy)-4,4′-phenyl)]- 10,10′,15,15′,20,20′-hexakis(3,3′,4,4′,5,5′-hexakisdecyloxyphenyl)diporphyrin, 1 and 2 respectively, have been synthesized and deposited to form self-assembled monolayer (SAM) films on gold-coated glass slides that served as substrates. The SAM films have been characterised by RAIR spectroscopy. Excitation of the molecules within the films has been achieved using the evanescent field arising when the glass substrate was used as a waveguide. Luminescence spectroscopy detected both fluorescence and phosphorescence emission from the SAM films under an argon atmosphere. Quenching of the phosphorescence emission by dioxygen was investigated for both films. Greater reproducibility of data was achieved from the SAM films of compound 2. The phosphorescence quenching from these films followed the Stern–Volmer relationship.

Epilepsy: Ever-changing states of cortical excitability

It has been proposed that the underlying epileptic process is mediated by changes in both excitatory and inhibitory circuits leading to the formation of hyper-excitable seizure networks. In this review we aim to shed light on the many physiological factors that modulate excitability within these networks. These factors have been discussed extensively in many reviews each as a separate entity and cannot be extensively covered in a single manuscript. Thus for the purpose of this work in which we aim to bring those factors together to explain how they interact with epilepsy, we only provide brief descriptions. We present reported evidence supporting the existence of the epileptic brain in several states; interictal, peri-ictal and ictal, each with distinct excitability features. We then provide an overview of how many physiological factors influence the excitatory/inhibitory balance within the interictal state, where the networks are presumed to be functioning normally. We conclude that these changes result in constantly changing states of cortical excitability in patients with epilepsy.

Characterization, liquid crystallinity and spin-coated films of some metalated 1,4,8,11,15,18,22,25-octaalkyl tetrabenzo [b,g,l,q][5,10,15]triazaporphyrin derivatives

The preparation and characterization of a number of metalated derivatives of 1,4,8,11,15,18,22,25-octahexyl and 1,4,8,11,15,18,22,25-octadecyl tetrabenzotriazaporphyrins (TBTAPs) are reported. The mesophase behavior of the compounds has been characterized by differential scanning calorimetry (DSC) and by polarized light optical microscopy. Mesophase behavior is compared with data for the corresponding phthalocyanine derivatives reported earlier. The temperature range of the mesophase(s) exhibited by the title compounds is generally broader than those of their phthalocyanine analogs. UV-vis data for examples of the TBTAP compounds as spin-coated films reveal differences in the type of molecular packing in the as-deposited films that is largely dependent upon the length of the alkyl chain substituents. On heating, the films undergo molecular reorganizations at temperatures corresponding to the mesophase transitions of bulk material observed by DSC.

The prevalence and demographic distribution of treated epilepsy: a community-based study in Tasmania, Australia

OBJECTIVES

To estimate the prevalence and demographic distribution of treated epilepsy in a community-based population.

MATERIALS & METHODS

We surveyed all residents in Tasmania, Australia, who were supplied at least one antiepileptic drug prescription between July 1, 2001 and June 30, 2002, recorded on the national prescription database. We adjusted for the effect of disease-related non-response bias by imputation methods.

RESULTS

After three mail contacts, 54.0% (4072/7541) responded, with 1774 (43.6%) indicating treatment for epilepsy, representing 86.0% of the estimated total possible cases in Tasmania. The adjusted treated epilepsy prevalence was 4.36 per 1000 (95% CI 4.34, 4.39); lower in women (prevalence ratio 0.92 (95% CI 0.84, 1.00)); greater with increasing age (P < 0.001); similar in the three main geographic regions; and similar with socioeconomic status of postcode of residence.

CONCLUSIONS

Although our estimates are likely to be affected by access to health services, overall treated epilepsy prevalence of 4.4 per 1000 is similar to previous studies. Our finding of high elderly prevalence has been reported in a few recent studies in developed countries and has important clinical and public health implications in populations with similar aging demographics.

Synthesis of tetra(trimethylammonio)phthalocyanato zinc tetraiodide, [ZnPc(NMe3)4]I4, and a spectrometric investigation of its interaction with calf thymus DNA

The phthalocyanine salt [ ZnPc(NMe3)4]I4was synthesized from 4-nitrophthalonitrile using a three-step procedure. The interaction of [ ZnPc(NMe3)4]4+with calf thymus DNA (CT DNA) has been investigated by UV-vis and fluorescence spectrometric methods. [ ZnPc(NMe3)4]4+exists in a non-monomeric form, proposed to be a dimer, in phosphate buffer solution (pH 6.82). Spectral changes show that in the presence of high concentrations of CT DNA added to the solution, [ ZnPc(NMe3)4]4+is bound in a monomeric state with evidence suggesting it is located in a DNA groove. At lower concentrations of DNA there is evidence of stacking of non-monomeric [ ZnPc(NMe3)4]4+onto the DNA. Two intrinsic binding constants for the interaction of [ ZnPc(NMe3)4]4+with CT DNA, 1.33 × 105and 2.56 × 104M-1have been obtained. Electrostatic binding is shown to play an important role in the interaction of [ ZnPc(NMe3)4]4+with nucleic acids.

Unmasking the chemistry and properties of non-peripherally octasubstituted phthalocyanines

The paper reviews the development of the chemistry, properties and applications of 1,4,8,11,15,18,22,25- (or non-peripheral) octasubstituted phthalocyanines that has been undertaken at the University of East Anglia over the last quarter of a century. The research has proved valuable for initiating and developing a number of areas of phthalocyanine science, not least because the compounds exhibit a number of properties seldom shared by Pc derivatives with other substitution patterns. In particular the compounds are obtained isomerically pure and the substituents' location at the non-peripheral sites as opposed to the peripheral positions ensures superior solubility and lower aggregation in most hydrophobic solvents. A further significant difference between isomeric non-peripheral (np)- and peripheral (p)-octasubstituted compounds is the effect of substituents on the energy of the Q-band, those at the former positions leading to more significant bathochromic shifts of this absorption band into the near infra-red. Examples of np-octasubstituted derivatives exhibit columnar mesophase behavior, a property shared by their p-octasubstituted counterparts. The favorable solubility of the np-octasubstituted compounds, including examples in which one of the four benzenoid rings bears different substituents from those on the other three (so called AAAB structures), in organic solvents facilitates their deposition as thin film formulations. A high degree of molecular organisation within Langmuir-Blodgett (LB) films of amphiphilic AAAB compounds has been investigated using various methods. Spin-coated films of certain AAAA and AAAB series of compounds have been shown to contain layer structuring and purpose designed AAAB compounds have been used in formation of self-assembled monolayers (SAMs). The use of LB and spin-coated films within electrical devices is described. Various applications of SAMs deposited on gold surfaces have been explored including gas sensing. Recent attention has focused on their use, when deposited onto gold nanoparticles, for applications in PDT, an approach complementing more conventional PDT studies. The principal challenge for obtaining the np-octasubstituted compounds is in preparing the precursor phthalonitriles. Though 3,6-dialkoxyphthalonitriles are readily prepared, early access to the 3,6-dialkylphthalonitriles was somewhat laborious. However, more convenient syntheses of the latter are now available through metal catalyzed cross-coupling reactions. Interesting contrasts in the reactivity of 3,6-dialkylphthalonitriles and 4,5-dialkylphthalonitriles have been uncovered. Thus reactions of the former with excess lithium in alcoholic solvents or with excess MeMgBr provide particularly ready access to examples of macrocycles that are hybrids of the Pc and tetrabenzoporphyrin structures. This level of reactivity is very different among the 4,5-dialkylphthalonitriles. Unexpectedly limited reactivity of np-octahexylsubstituted Si(OH)2Pc in condensation reactions has been exploited to provide a basis for the stepwise construction of m-oxo linked hetero-chromophore arrays. Finally, the unexpected construction of the novel EPR active Cd2Pc3 complexes from both np- and p-octaalkyl substituted CdPcs provided examples where both series behaved similarly – in contrast to behavior exhibited by alternatively substituted CdPcs investigated to date.

Electrochemical and photophysical characterization of non-peripherally-octaalkyl substituted dichlorotin(IV) phthalocyanine and tetrabenzotriazaporphyrin compounds

Three non-peripherally substituted tin(IV) macrocylic compounds, octahexylphthalocyaninato dichlorotin(IV) (3a), octahexyltetrabenzo-5,10,15- triazaporphyrinato dichlorotin(IV) (3b) and octadecylphthalocyaninato dichlorotin(IV) (3c) were synthesized and their photophysical and electrochemical behavior studied. Complex 3b, containing a CH group in place of one of the aza nitrogen atoms of the phthalocyanine core, shows a split Q-band due to its lower symmetry. The triplet state quantum yields were found to be lower than would be expected on the basis of the heavy atom effect of tin as the central metal for phthalocyanine derivatives (3a and 3c). In contrast, 3b shows a triplet quantum yield Φ T = 0.78. The triplet state lifetimes were solvent dependent, and were higher in tetrahydrofuran than in toluene. Cyclic voltammetry and spectroelectrochemistry of the complexes revealed only ring-based redox processes.

NMR spectroscopic evidence for the self-association of some asymmetrically substituted phthalocyanines in solution

1 H NMR data obtained for two series of asymmetrically octasubstituted metal-free and zinc phthalocyanines, bearing one or two hydroxyalkyl groups, indicate a degree of solution phase aggregation particular to the systems. The metal-free derivatives appear to stack cofacially through the interaction of their π systems and give rise to unusually well resolved, solvent, temperature and concentration dependent 1 H NMR spectra. Structural features for the aggregates, in which the phthalocyanine rings are cofacial but offset in a particular way, are proposed based on the NMR data. The zinc derivatives appear to form dynamic aggregates in solution in which the oxygen borne by one of the substituents coordinates to the zinc at the centre of the core through an inter- and/or intramolecular interaction leading to the temperature dependent 1 H NMR spectra that are observed.

Stepwise syntheses of complex μ-oxo-linked heterochromophore arrays containing phthalocyanine, porphyrin and subphthalocyanine ligands

The article reviews the exploitation of the serendipitous discovery that dihydroxysilicon 1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyanine 1 reacts at one face only to form a μ-oxo linked bond to dichlorosilicon phthalocyanine. Reaction of 1 with dihydroxysilicon octaethylporphyrin led to an unstable μ-oxo linked Pc-O-Pn heteroligand dyad that could not be isolated. However, reaction with dihydroxygermanium octaethylporphyrin gave a stable dyad that showed substantial broad band absorption attributable to exciton effects. A small amount of the μ-oxo linked homo dyad formed by self-condensation of dihydroxygermanium octaethylporphyrin was detected by MALDI-TOF mass spectrometry but was not isolated. Reaction of 1 with chloroboron subphthalocyanine afforded the stable Pc-O-SubPc heterodyad as the main product and the SubPc-O-Pc-O-SubPc triad as a minor side product. Both gave absorption spectra that showed the main features of the ligands present, implying limited exciton coupling. A further reaction of 1 with axial-hydroxy, axial-methyl silicon phthalocyanine provided a key Pc-O-Pc′ dyad that proved to be an ideal intermediate for developing a synthetic strategy to access a series of hetero-metalloid/hetero-ligand Pc-O-Pc′-O-Pn triads. X-ray structural data for examples of these arrays are discussed. A feature of the triad compounds is their very broad band absorption spectra that extends from the UV through the visible region to near IR wavelengths.

Synthesis, lead lability and ring deformation of three 1,4,8,11,15,18,22,25-octasubstituted phthalocyaninato lead derivatives

The syntheses and attempted syntheses of some non-peripherally (1,4,8,11,15,18,22,25) octasubstituted lead phthalocyanines from their corresponding metal-free derivatives are described. Some compounds exhibited lability of the lead ion during work-up to regenerate the starting material. The results of single crystal X-ray diffraction analyses of 1,4,8,11,15,18,22,25-octahexyl-, 1,4,8,11,15,18,22,25-octa-iso-pentyl- and 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanines are reported and cast some light on the greater stability of 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine, in terms of ease of loss of the lead ion, over the other two substituted lead phthalocyanines studied. The phthalocyanine cores of all three derivatives adopt a saddle-shaped geometry rather than the saucer-shaped conformation exhibited by unsubstituted lead phthalocyanine. The saddle-shaped conformation would appear to offer a means of relieving steric interactions between the substituents on adjacent benzene rings. That steric interactions are a feature of these molecules is perhaps reflected in the different distortions of the saddle conformations. This is greatest for compound 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanine bearing the isopentyl groups, expected to introduce the most interactions, and least for compound 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine where S atoms rather than methylene groups are adjacent to the benzene ring. The molecules of 1,4,8,11,15,18,22,25-octahexyl- and 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine pack together in pairs with their nearest neighbouring molecule; their lead atoms, displaced from the core and directed towards each other. The presence of the S atoms in 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine leads to close Pb … S contacts between the molecules. Attractive Pb … S interactions in this compound may also account for the larger displacement of the Pb from the mean-plane of the four coordinated nitrogen atoms at the centre of the phthalocyanine core than is found for 1,4,8,11,15,18,22,25-octahexyl- and 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanines. The molecular packing of 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanine is more complex because of the presence of tetrahydrofuran molecules (the solvent of recrystallisation) within the crystal, offering additional interactions with the Pb atoms.

Triple-decker cadmium phthalocyanine sandwich complexes: self-assembled EPR active complexes

The discovery and characterization of the first example of a bis-cadmiumtris-phthalocyanine triple-decker sandwich complex is reviewed. The compound, with each Pc ring substituted at the eight non-peripheral positions with hexyl chains, was obtained unexpectedly during recrystallization of the corresponding monomeric 1,4,8,11,15,18,22,25-octa-hexyl cadmium phthalocyanine from CH 2 Cl 2 and methanol. The scope for obtaining further examples of this new class of complex bearing different ring substituents is also described. A feature of the compounds is that they give an EPR signal. An electrochemical study has shown that the rest state of the core of the sandwich structure is a dianion arising from the imbalance of the charges on the two cadmium atoms and the three Pc 2- ligands. This is a spin 0 species. It is proposed that the free radical character arises because the potential for the first one-electron oxidation is unusually low for a phthalocyanine, allowing for the partial presence of the spin ½ species for non-peripherally substituted complexes and a more extensive presence of the EPR active redox state for peripherally substituted analogs. Results of chemical oxidation using iodine are also discussed. A spectroscopic and electrochemical study on the monomeric precursors revealed the mode of formation of the triple-decker complexes. It has been established that octa-alkyl cadmium phthalocyanines unexpectedly exist very predominantly as dimeric structures in CH 2 Cl 2 and these are proposed to be intermediates in the formation of the triple-decker complexes. Results from a series of cross experiments using differently substituted Pcs indicate that cadmium can be scrambled between a CdPc and a metal-free Pc . Furthermore, when either species is added to a solution of a triple-decker complex, the ligand from the added species becomes incorporated into new "mixed" triple-decker complexes. From these results it is proposed that the triple-decker structures are formed by self-assembly processes and that they can disassemble and reassemble in the solution phase. Preliminary measurements have identified ring substitution patterns that lead to higher oligomers.

Laser-flash photolysis of dialkylbenzodipyridoporphyrazines

In the course of a fundamental study of photosensitizers for photodynamic therapy of cancer, a non-peripheral substituted phthalocyanine analogue, zinc bis(1,4-didecylbenzo)bis(3,4-pyrido)porphyrazine and its position isomers were examined to measure their photoexcited triplet state lifetimes in poly(methyl methacrylate) film using laser-flash photolysis. The isomer mixture of zinc bis(1,4-didecylbenzo)bis(3,4-pyrido)porphyrazine showed the most intense absorption in the 660-710 nm region, and the longer triplet state lifetime. The lowest symmetry isomer of zinc bis(1,4-didecylbenzo)bis(3,4-pyrido)porphyrazine was found to have the longest triplet state lifetime when all isomers were separated. The compound is proposed to be suitable for use as a photosensitizer for photodynamic therapy of cancer.

Porphyrin self-assembled monolayers and photodynamic oxidation of tryptophan

The zinc and magnesium metalated derivatives of 5,5′-[12,12′-di(thiododecyloxy)-4,4′-phenyl)]-10,10′,15,15′,20,20′-hexakis(3,3′,4,4′,5,5′-hexakisdecyloxyphenyl)diporphyrin, 1b and 1c, have been synthesised and deposited to form self-assembled monolayer (SAM) films on the surface of gold-coated glass substrates. The SAM films have been characterized by RAIR spectroscopy and fluorescence spectroscopy. The potential for the porphyrin films to catalyze the oxidation of tryptophan within human serum albumin upon irradiation with white light has been demonstrated and attributed to the porphyrins acting as photosensitizers of oxygen to form oxidizing species.

In situ chemichromic studies of interactions between a lutetium bis-octaalkyl-substituted phthalocyanine and selected biological cofactors

Spin-coated films, approximately 100 nm thick, of a newly synthesized bis[octakis(octyl)phthalocyaninato] lutetium(III) complex on ultrasonically cleaned glass substrates exhibit pronounced chemichromic behaviour with potential application in healthcare. In situ kinetic optical absorption spectroscopic measurements show that the phthalocyanine Q-band is red shifted by 60 nm upon oxidation arising from exposure to bromine vapour. Recovery to the original state is achieved by the treatment of the oxidized films with nicotinamide adenine dinucleotide and l-ascorbic acid (vitamin C) in an aqueous solution containing 1.5 M lithium perchlorate. The neutralization process is found to be governed by first-order kinetics. The linear increase of the reduction rate with increasing concentration of cofactors provides a basis for calibration of analyte concentrations ranging from 3.5 mM down to 0.03 mM.

Targeted photodynamic therapy of breast cancer cells using antibody-phthalocyanine-gold nanoparticle conjugates

A 4-component antibody-phthalocyanine-polyethylene glycol-gold nanoparticle conjugate is described for use as a potential drug for targeted photodynamic cancer therapy. Gold nanoparticles (4 nm) were stabilised with a self-assembled layer of a zinc-phthalocyanine derivative (photosensitiser) and a heterobifunctional polyethylene glycol. Anti-HER2 monoclonal antibodies were covalently bound to the nanoparticles via a terminal carboxy moiety on the polyethylene glycol. The nanoparticle conjugates were stable towards aggregation, and under irradiation with visible red light efficiently produced cytotoxic singlet oxygen. Cellular experiments demonstrated that the nanoparticle conjugates selectively target breast cancer cells that overexpress the HER2 epidermal growth factor cell surface receptor, and that they are effective photodynamic therapy agents.

High-mobility solution-processed copper phthalocyanine-based organic field-effect transistors

Solution-processed films of 1,4,8,11,15,18,22,25-octakis(hexyl) copper phthalocyanine (CuPc₆) were utilized as an active semiconducting layer in the fabrication of organic field-effect transistors (OFETs) in the bottom-gate configurations using chemical vapour deposited silicon dioxide (SiO₂) as gate dielectrics. The surface treatment of the gate dielectric with a self-assembled monolayer of octadecyltrichlorosilane (OTS) resulted in values of 4×10^-2 cm² V^-1 s^-1 and 10⁶ for saturation mobility and on/off current ratio, respectively. This improvement was accompanied by a shift in the threshold voltage from 3 V for untreated devices to -2 V for OTS treated devices. The trap density at the interface between the gate dielectric and semiconductor decreased by about one order of magnitude after the surface treatment. The transistors with the OTS treated gate dielectrics were more stable over a 30-day period in air than untreated ones.