Development of Antifouling Coatings Based on Quaternary Ammonium Compounds through a Multilayer Approach.

The development of polymeric materials as antifouling coatings for aquaculture nets is elaborated in the present work. In this context, cross-linked polymeric systems based on quaternary ammonium compounds (immobilized or releasable) prepared under mild aqueous conditions were introduced as a more environmentally friendly methodology for coating nets on a large scale. To optimize the duration of action of the coatings, a multilayer coating method was applied by combining the antimicrobial organo-soluble copolymer poly(cetyltrimethylammonium 4-styrenesulfonate-co-glycidyl methacrylate) [P(SSAmC16-co-GMA20)] as the first layer with either the water-soluble copolymer poly(vinylbenzyl trimethylammonium chloride-co-acrylic acid) [P(VBCTMAM-co-AA20)] or the water-soluble polymers poly(acrylic acid) (PAA) and poly(hexamethylene guanidine), PHMG, as the second layer. The above-mentioned approach, followed by thermal cross-linking of the polymeric coatings, resulted in stable materials with controlled release of the biocidal species. The coated nets were studied in terms of their antifouling efficiency under accelerated biofouling conditions as well as under real conditions in an aquaculture field. Resistance to biofouling after three water-nutrient replenishments was observed under laboratory accelerated biofouling conditions. In addition, at the end of the field test (day 23) the uncoated nets were completely covered by marine contaminants, while the coated nets remained intact over most of their extent.

pH-Sensitive Gold Nanorods for Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) Delivery and DNA-Binding Studies.

A facile experimental protocol for the synthesis of poly(ethylene glycol)-modified (PEGylated) gold nanorods (AuNRs@PEG) is presented as well as an effective drug loading procedure using the non-steroidal anti-inflammatory drug (NSAID) naproxen (NAP). The interaction of AuNRs@PEG and drug-loaded AuNRs (AuNRs@PEG@NAP) with calf-thymus DNA was studied at a diverse temperature revealing different interaction modes; AuNRs@PEG may interact via groove-binding and AuNRs@PEG@NAP may intercalate to DNA-bases. The cleavage activity of the gold nanoparticles for supercoiled circular pBR322 plasmid DNA was studied by gel electrophoresis while their affinity for human and bovine serum albumins was also evaluated. Drug-release studies revealed a pH-sensitive behavior with a release up to a maximum of 24% and 33% NAP within the first 180 min at pH = 4.2 and 6.8, respectively. The cytotoxicity of AuNRs@PEG and AuNRs@PEG@NAP was evaluated against MCF-7 and MDA-MB-231 breast cancer cell lines. The development of AuNRs as an efficient non-steroidal anti-inflammatory drugs (NSAIDs) delivery system for chemotherapy is still in its infancy. The present work can shed light and inspire other research groups to work in this direction.

Structural Identification of Metalloproteomes in Marine Diatoms, an Efficient Algae Model in Toxic Metals Bioremediation.

The biosorption of pollutants using microbial organisms has received growing interest in the last decades. Diatoms, the most dominant group of phytoplankton in oceans, are (i) pollution tolerant species, (ii) excellent biological indicators of water quality, and (iii) efficient models in assimilation and detoxification of toxic metal ions. Published research articles connecting proteomics with the capacity of diatoms for toxic metal removal are very limited. In this work, we employed a structural based systematic approach to predict and analyze the metalloproteome of six species of marine diatoms: Thalassiosira pseudonana, Phaeodactylum tricornutum, Fragilariopsis cylindrus, Thalassiosira oceanica, Fistulifera solaris, and Pseudo-nitzschia multistriata. The results indicate that the metalloproteome constitutes a significant proportion (~13%) of the total diatom proteome for all species investigated, and the proteins binding non-essential metals (Cd, Hg, Pb, Cr, As, and Ba) are significantly more than those identified for essential metals (Zn, Cu, Fe, Ca, Mg, Mn, Co, and Ni). These findings are most likely related to the well-known toxic metal tolerance of diatoms. In this study, metalloproteomes that may be involved in metabolic processes and in the mechanisms of bioaccumulation and detoxification of toxic metals of diatoms after exposure to toxic metals were identified and described.

Indium(III) in the "Periodic Table" of Di(2-pyridyl) Ketone: An Unprecedented Transformation of the Ligand and Solid-State 115In NMR Spectroscopy as a Valuable Structural Tool.

Reactions of di(2-pyridyl) ketone, (py)2CO, with indium(III) halides in CH3NO2 have been studied, and a new transformation of the ligand has been revealed. In the presence of InIII, the C═O bond of (py)2CO is subjected to nucleophilic attack by the carbanion -:CH2NO2, yielding the dinuclear complexes [In2X4{(py)2C(CH2NO2)(O)}2] (X = Cl, 1; X = Br, 2; X = I, 3) in moderate to good yields. The alkoxo oxygens of the two η1:η2:η1-(py)2C(CH2NO2)(O)- ligands doubly bridge the InIII centers and create a {In2(µ2-OR)2}4+ core. Two pyridyl nitrogens of different organic ligands and two terminal halogeno ions complete a distorted-octahedral stereochemistry around each In(III) ion. After maximum excitation at 360 or 380 nm, the solid chloro complex 1 emits blue light at 420 and 440 nm at room temperature, the emission being attributed to charge transfer within the coordinated organic ligand. Solid-state 115In NMR spectra, in combination with DFT calculations, of 1-3 have been studied in detail at both 9.4 and 14.1 T magnetic fields. The nuclear quadrupolar and chemical shift parameters provide valuable findings concerning the electric field gradients and magnetic shielding at the nuclei of indium, respectively. The experimentally derived CQ values are 40 ± 3 MHz for 1, 46 ± 5 MHz for 2, and 50 ± 10 and 64 ± 7 MHz for the two crystallographically independent InIII sites for 3, while the δiso values fall in the range 130 ± 30 to -290 ± 60 ppm. The calculated CQ and asymmetry parameter (ηQ) values are fully consistent with the experimental values for 1 and 2 and are in fairly good agreement for 3. The results have been analyzed and discussed in terms of the known (1, 3) and proposed (2) structural features of the complexes, demonstrating that 115In NMR is an effective solid-state technique for the study of indium(III) complexes.

Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic, Structural, and Physical Studies.

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO3)3·nH2O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln2(O2CMe)4(NO3)2(mepaoH)2] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the LnIII-mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O2CMe)3·4H2O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy2(O2CMe)6(mepaoH)2] (6). Treatment of 6 with one equivalent of HNO3 gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2-4 display similar structural characteristics with 1 and 5. The structures of 1-5 consist of dinuclear molecules in which the two LnIII centers are bridged by two bidentate bridging (η1:η1:µ2) and two chelating-bridging (η1:η2:µ2) acetate groups. The LnIII atoms are each chelated by a N,N'-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate LnIII centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the TbIII atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0-300 K range reveal weak antiferromagnetic intramolecular GdIII…GdIII exchange interactions in 3; the J value is -0.09(1) cm-1 based on the spin Hamiltonian H = -J(SGd1·SGd2).

Polymeric Coatings Based on Water-Soluble Trimethylammonium Copolymers for Antifouling Applications.

Crosslinked polymeric materials based on a quaternary trimethylammonium compound were developed and evaluated as potential antifouling coatings. For this purpose, two water-soluble random copolymers, poly(4-vinylbenzyltrimethylammonium chloride-co-acrylic acid) P(VBCTMAM-co-AAx) and poly(N,N-dimethylacrylamide-co-glycidylmethacrylate) P(DMAm-co-GMAx), were synthesized via free radical polymerization. A water based approach for the synthesis of P(VBCTMAM-co-AAx) copolymer was used. Coatings of the complementary reactive copolymers in different compositions were obtained by curing at 120 °C for one day and were used to coat aquaculture nets. These nets were evaluated in respect to their release rate using Total Organic Carbon (TOC) and Total Nitrogen (TN) measurements. Finally, the antifouling efficacy of these newly-composed durable coatings was investigated for 14 days in accelerated conditions. The results showed that this novel polymeric material provides contact-killing antifouling activity for a short time period, whereas it functions efficiently in biofouling removal after high-pressure cleaning.

Multifunctionality in Two Families of Dinuclear Lanthanide(III) Complexes with a Tridentate Schiff-Base Ligand.

The employment of N-(2-carboxyphenyl)salicylideneimine in 4f metal chemistry has led to two families of dinuclear complexes depending on the lanthanide(III) used. Representative members exhibit interesting magnetic, optical, and catalytic properties.

Tetranuclear lanthanide(III) complexes with a zigzag topology from the use of pyridine-2,6-dimethanol: synthetic, structural, spectroscopic, magnetic and photoluminescence studies.

Reaction between Ln(NO3)3·xH2O (x = 5 or 6) and the potentially tridentate (N,O,O) chelating/bridging ligand pyridine-2,6-dimethanol (pdmH2), in the presence of base NEt3, affords a family of isostructural tetranuclear [Ln(III)4(NO3)2(pdmH)6(pdmH2)2](NO3)4 (Ln(III) = Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Yb(III)) complexes with a rare zigzag topology. All complexes contain a [Ln4(µ-OR)6](6+) core with bridging ligation provided by the alkoxido arms of six η(1):η(1):η(2):µ pdmH(-) groups. The Ln(III) ions are eight coordinate with distorted geometries. Direct current magnetic susceptibility studies revealed predominant weak antiferromagnetic exchange interactions between the metal centers, which were quantified in the case of isotropic Gd(III)4 to give J = -0.09(1) cm(-1) and g = 2.00(1). The observation of out-of-phase (χ″M) ac susceptibility signals suggested that the Dy(III)4 analogue might be a molecular nanomagnet. Solid-state photoluminescence studies showed that the Eu(III)4 and Tb(III)4 compounds exhibit intense, sharp, and narrow emission bands in the red and green visible regions, respectively, which arise from the characteristic (5)D0 → (7)FJ and (5)D4 → (7)FJ transitions. The combined results demonstrate the ability of pdmH2 ligand to yield homometallic 4f clusters with interesting magnetic and optical properties.

Fluorescent naphthalene diols as bridging ligands in Ln(III) cluster chemistry: synthetic, structural, magnetic, and photophysical characterization of Ln(III)8 "Christmas stars".

The initial employment of the fluorescent bridging ligand naphthalene-2,3-diol in 4f-metal coordination chemistry has provided access to a new family of Ln(III)8 clusters with a "Christmas-star" topology, single-molecule magnetism behavior, and ligand-centered emissions.

Dinuclear lanthanide(III) complexes by metal-ion-assisted hydration of di-2-pyridyl ketone azine.

The initial employment of di-2-pyridyl ketone azine in 4f metal chemistry has led to a unique ligand transformation; the resulting anionic ligand is able to bridge two Ln(III) ions, affording neutral and cationic dinuclear complexes with interesting properties.

Interesting chemical and physical features of the products of the reactions between trivalent lanthanoids and a tetradentate Schiff base derived from cyclohexane-1,2-diamine.

The initial use of a tetradentate Schiff base (LH2) derived from the 2 : 1 condensation between 2-hydroxyacetophenone and cyclohexane-1,2-diamine in 4f-metal chemistry is described. The 1 : 2 reaction of Ln(NO3)3·xH2O (Ln = lanthanoid or yttrium) and LH2 in MeOH/CH2Cl2 has provided access to isostructural complexes [Ln(NO3)3(L'H2)(MeOH)] in moderate to good yields. Surprisingly, the products contain the corresponding Schiff base ligand L'H2 possessing six aliphatic -CH2- groups instead of the -CH-(CH2)4-CH- unit of the cyclohexane ring, i.e. an unusual ring-opening of the latter has occurred. A mechanism for this LnIII-assisted/promoted LH2 → L'H2 transformation has been proposed assuming transient LnII species and a second LH2 molecule as the H2 source for the reduction of the cyclohexane moiety. DFT calculations provide strong evidence for the great thermodynamic stability of the products in comparison with analogous complexes containing the original intact ligand. The structures of the PrIII, SmIII, GdIII, TbIII, and HoIII complexes have been determined by single-crystal X-ray crystallography. The 9-coordinate LnIII centre in the molecules is bound to six oxygen atoms from the three bidentate chelating nitrato groups, two oxygen atoms that belong to the bidentate chelating organic ligand, and one oxygen atom from the coordinated MeOH group. In the overall neutral bis(zwitterionic) L'H2 ligand, the acidic H atoms are clearly located on the imino nitrogen atoms and this results in the formation of an unusual 16-membered chelating ring. The coordination polyhedra defined by the nine donor atoms around the 4f-metal-ion centres can be best described as distorted, spherical capped square antiprisms. The EuIII, TbIII, and DyIII complexes exhibit LnIII-based luminescence in the visible region, with the coordinated L'H2 molecule acting as the antenna. Ac magnetometry experiments show that the DyIII member of the family behaves as an SIM at zero field and under external dc fields of 0.1 and 0.2 T without the enhancement of the peaks' maxima, suggesting that QTM is not the relaxation path. The GdIII complex behaves, rather unexpectedly, as a SIM with two different magnetic relaxation paths occurring at very close temperatures; this behaviour is tentatively attributed to a very small axial zero-field splitting (D ∼ 0.1 cm-1), which cannot be detected by magnetization or susceptibility experiments. The prospects of the present, first results in the lanthanoid(III)-LH2 chemistry are discussed.

Biological Effects of Human Exposure to Environmental Cadmium.

Cadmium (Cd) is a toxic metal for the human organism and for all ecosystems. Cd is naturally found at low levels; however, higher amounts of Cd in the environment result from human activities as it spreads into the air and water in the form of micropollutants as a consequence of industrial processes, pollution, waste incineration, and electronic waste recycling. The human body has a limited ability to respond to Cd exposure since the metal does not undergo metabolic degradation into less toxic species and is only poorly excreted. The extremely long biological half-life of Cd essentially makes it a cumulative toxin; chronic exposure causes harmful effects from the metal stored in the organs. The present paper considers exposure and potential health concerns due to environmental cadmium. Exposure to Cd compounds is primarily associated with an elevated risk of lung, kidney, prostate, and pancreatic cancer. Cd has also been linked to cancers of the breast, urinary system, and bladder. The multiple mechanisms of Cd-induced carcinogenesis include oxidative stress with the inhibition of antioxidant enzymes, the promotion of lipid peroxidation, and interference with DNA repair systems. Cd2+ can also replace essential metal ions, including redox-active ones. A total of 12 cancer types associated with specific genes coding for the Cd-metalloproteome were identified in this work. In addition, we summarize the proper treatments of Cd poisoning, based on the use of selected Cd detoxifying agents and chelators, and the potential for preventive approaches to counteract its chronic exposure.

Stimuli-responsive spin crossover nanoparticles for drug delivery and DNA-binding studies.

Aminated silica hybrid, spin-crossover (SCO) nanoparticles (AmNPs) coupled with (S)-naproxen (NAP) were proposed for potential drug nanocarriers through drug release experiments at various pH values. DNA- and albumin-binding studies were also carried out using diverse techniques in order to investigate the interaction of the nanoparticles with calf-thymus DNA and serum albumins and to determine the corresponding binding constants.

Two different coordination modes of the Schiff base derived from ortho-vanillin and 2-(2-aminomethyl)pyridine in a mononuclear uranyl complex.

This work describes the reaction of the potentially tetradentate Schiff-base ligand N-(2-pyridylmethy)-3-methoxysalicylaldimine (HL) with UO2(O2CMe)2·2H2O and UO2(NO3)2· 6H2O in MeOH in the absence or presence of an external base, respectively. The product from these reactions is the mononuclear complex [UO2(L)2] (1). Its structure has been determined by single-crystal, X-ray crystallography. The anionic ligand adopts two different coordination modes (1.1011, 1.1010; Harris notation) in the complex. The new compound was fully characterized by solid-state (IR, Raman and Photoluminescence spectroscopies) and solution (UV-Vis and 1H NMR spectra, conductivity measurements) techniques.

A new family of nonanuclear lanthanide clusters displaying magnetic and optical properties.

The initial employment of 2-(hydroxymethyl)pyridine in 4f metal chemistry has afforded a new family of Ln(III)(9) clusters with a sandglass-like topology and dual physical properties; the Dy(III) member shows single-molecule magnetism behavior, while the Eu(III) analogue exhibits intense red photoluminescence.

Application of a catalytic oxidation method for the simultaneous determination of total organic carbon and total nitrogen in marine sediments and soils.

This study presents the application of a simultaneous method for the determination of total organic carbon (TOC) and total nitrogen (TN) in marine sediments and soils, using a data set of 206 samples collected from coastal lagoonal/marine sedimentary environments and certified reference materials (CRMs). TOC and TN were determined using the high temperature (720°C) catalytic (Pt/Al2O3) oxidation method and the detection of TOC and TN was performed using an infrared or a chemiluminescence detector, respectively. Results from the abovementioned TOC method were compared with the results from the widely used Wakley-Black titration method, while TN results with these from elemental analysis. Analytical quality control experiments were performed using CRM samples. Method characteristics such as range of measurement, calibration, method detection limit (MDL), limit of quantification (LOQ), repeatability and reproducibility, were calculated. The precision and the accuracy of the methods are also discussed. Comparison of the two TOC methods of 206 data set yields a regression line of correlation coefficient with R2 = 0.985. Additional different levels of TOC concentrations of low <1%, moderate 1-5% and high 5-40% level were examined indicating very good correlations. The lowest correlation coefficient was observed in low concentrations TOC<1% (R2 0.825), mainly as a result of the limitation of titration method. The evaluation of TN results indicated that the catalytic oxidation method and the elemental analysishave a significant good correlation with R2 = 0.977. The results of precision and accuracy, as well as the calculated MDL and LOQ show that this is a reliable method. Moreover, it requires a small amount of the analyzed sample and the total analysis time is 10 min. Therefore, it can be easily applied for the fast and precise simultaneous determination of TOC and TN in sediment and soil samples.

Tetranuclear oxido-bridged thorium(iv) clusters obtained using tridentate Schiff bases.

Thorium(iv) complexes are currently attracting intense attention from inorganic chemists due to the development of liquid-fluoride thorium reactors and the fact that thorium(iv) is often used as a model system for the study of the more radioactive Np(iv) and Pu(iv). Schiff-base complexes of tetravalent actinides are useful for the development of new separation strategies in nuclear fuel processing and nuclear waste management. Thorium(iv)-Schiff base complexes find applications in the colorimetric detection of this toxic metal ion and the construction of fluorescent on/off sensors for Th(iv) exploiting the ligand-based light emission of its complexes. Clusters of Th(iv) with hydroxide, oxide or peroxide bridges are also relevant to the environmental and geological chemistry of this metal ion. The reactions between Th(NO3)4·5H2O and N-salicylidene-o-aminophenol (LH2) and N-salicylidene-o-amino-4-methylphenol (L'H2) in MeCN have provided access to complexes [Th4O(NO3)2(LH)2(L)5] (1) and [Th4O(NO3)2(L'H)2(L')5] (2) in moderate yields. The structures of 1·4MeCN and 2·2.4 MeCN have been determined by single-crystal X-ray crystallography. The complexes have similar molecular structures possessing the {Th4(µ4-O)(µ-OR')8} core that contains the extremely rare {Th4(µ4-O)} unit. The four ThIV atoms are arranged at the vertexes of a distorted tetrahedron with a central µ4-O2- ion bonded to each metal ion. The H atom of one of the acidic -OH groups of each 3.21 LH- or L'H- ligand is located on the imine nitrogen atom, thus blocking its coordination. The ThIV centres are also held together by one 3.221 L2- or (L')2- group and four 2.211 L2- or (L')2- ligands. The metal ions adopt three different coordination numbers (8, 9, and 10) with a total of four coordination geometries (triangular dodecahedral, muffin, biaugmented trigonal prismatic, and sphenocorona). A variety of H-bonding interactions create 1D chains and 2D layers in the crystal structures of 1·4 MeCN and 2·2.4 MeCN, respectively. The structures of the complexes are compared with those of the uranyl complexes with the same or similar ligands. Solid-state and IR data are discussed in terms of the coordination mode of the organic ligands and the nitrato groups. 1H NMR data suggest that solid-state structures are not retained in DMSO. The solid complexes emit green light at room temperature upon excitation at 400 nm, the emission being ligand-centered.

Slow magnetic relaxation and luminescence properties in lanthanide(iii)/anil complexes.

The initial use of anils, i.e. bidentate Schiff bases derived from the condensation of anilines with salicylaldehyde or its derivatives, in 4f-metal chemistry is described. The 1 : 1 reactions between Ln(NO3)3·xH2O (Ln = lanthanide) or Y(NO3)3·6H2O and N-(5-bromosalicylidene)aniline (5BrsalanH) in MeCN has provided access to complexes [Ln(NO3)3(5BrsalanH)2(H2O)]·MeCN (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) and [Y(NO3)3(5BrsalanH)2(H2O)]·MeCN, respectively, in good yields. The structures of the isomorphous complexes with Ln = Pr(1·MeCN), Sm(3·MeCN), Gd(5·MeCN), Dy(7·MeCN) and Er(9·MeCN) have been determined by single-crystal X-ray crystallography. The other complexes were proven to be isostructural with the fully structurally characterized compounds based on elemental analyses, IR spectra, unit cell determinations and powder X-ray patterns. The 9-coordinate LnIII centre in the [Ln(NO3)3(5BrsalanH)2(H2O)] molecules is bound to six oxygen atoms from the three bidentate chelating nitrato groups, two oxygen atoms that belong to the organic ligands and one oxygen atom from the aquo ligand. The 5BrsalanH molecules behave as monodentate O-donors; the acidic H atom is clearly located on the imino N atom and thus the formally neutral ligands adopt an extremely rare coordination mode participating in the zwitterionic form. The coordination polyhedra defined by the nine donor atoms around the LnIII centres are best described as spherical capped square antiprisms. Various intermolecular interactions build the crystal structures and Hirshfeld surface analysis was applied to evaluate the magnitude of interactions between the molecules. Solid-state IR and UV/VIS data are discussed in terms of structural features. 1H NMR data prove that the diamagnetic [Y(NO3)3(5BrsalanH)2(H2O)] complex decomposes in DMSO. Combined dc and ac magnetic susceptibility, as well as magnetization data for 7 suggest that this complex shows field-induced slow magnetic relaxation. Two magnetization relaxation processes are evident. The fit to the Arrhenius law has been performed using the 6.5-8.5 K ac data, affording an effective barrier for the magnetization reversal of 27 cm-1. Cole-Cole plot analysis in the temperature range in which the Orbach relaxation process is assumed, reveals a narrow distribution of relaxation times. The solid Dy(iii) complex 7 emits green light at 338 nm, the emission being ligand-centered. The perspectives of the present, first results in the lanthanide(iii)-anil chemistry are critically discussed.

Use of Ureasil gels to extract ions from aqueous solutions.

Nanocomposite organic-inorganic gels synthesized through the sol-gel procedure by using Ureasil precursors can be employed as efficient sorbents for retaining metal cations and small anions from aqueous solutions. Sulfate or sulfonate as well as nitrate ions demonstrate a high affinity for Ureasils. High affinity was also demonstrated by trivalent metal cations. This affinity was explained by the presence of urea and of ether groups in Ureasils, which have the ability to complex many different types of ionic species.

Study of the conditions affecting dye adsorption on titania films and of their effect on dye photodegradation rates.

Nanocrystalline titania films have been deposited on glass slides by the sol-gel technique in the presence of surfactant, which plays the role of template of the nanostructure. Several different dyes, both anionic and cationic, have been adsorbed on these films from aqueous solutions. Some of these dyes were adsorbed at large quantities some at lower quantities. Some of them were adsorbed in monomeric form and others formed aggregates. Aggregates are easily distinguished by absorption spectrophotometry, since absorption of light is observed at a different wavelength than monomer absorption in a dilute solution. In all cases, aggregation demonstrated a hypsochromic shift, indicating repulsive interactions, which are justified in view of the fact that titania surface is charged and that adsorbed molecules are aligned in parallel. The above titania films are hydroxylated. Therefore, cationic dyes were readily adsorbed. Anionic dyes could be adsorbed only from aqueous solutions brought at low pH. Photodegradation rates of adsorbed dyes were generally fast since these films are efficient photocatalysts. Nevertheless, photodegradation of an adsorbed dye was faster when the quantity of the dye was smaller. When the adsorbed dyes formed aggregates, aggregation had adverse effect on photodegradation rates.