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A mesoporous silica (SBA-15) has been chemically modified with 2-mercaptopyrimidine using the homogeneous route. This synthetic route involved the reaction of 2-mercaptopyrimidine with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry and elemental analysis. The solid was employed as a Cd(II) adsorbent from aqueous solutions at room temperature. The effects of several variables (stirring time, pH, metal concentration and presence of other ions in the medium) have been studied using the batch technique. Flame atomic absorption spectrometry was used to determine the Cd(II) concentration in the filtrate after the adsorption process. The results indicate that under the optimum conditions, the maximum adsorption value for Cd(II) was 0.99 ¡ 0.03 mmol Cd(II) g 21 , whereas the adsorption capacity of the unmodified mesoporous silica was only 0.04 ¡ 0.02 mmol Cd(II) g 21 . On the basis of these results, it can be concluded that it is possible to modify chemically SBA-15 with 2-mercaptopyrimidine and to use the resulting modified mesoporous silica as an effective adsorbent for Cd(II) in aqueous media.

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Recent advances in the development of new materials are having a major impact on Analytical Chemistry. For example, the unique properties of ordered mesoporous silicas have been shown to enhance the analytical performance of many existing techniques or allow new, exciting ones to be developed. Likewise, the introduction of organo-functional groups makes mesoporous silicas highly versatile and enables them to perform specialized tasks, such as the adsorption of toxic heavy metals from aqueous solutions. In this tutorial review, we present readers with a brief introduction to the most relevant achievements in the preparation of hybrid mesoporous silicas functionalized with chelating ligands for the complexation of heavy metals. We also provide some recent examples from the last ten years regarding the analytical applications of such hybrid silicas. Two topics of great current interest in environmental water analysis for heavy metal detection, namely the use of hybrid mesoporous silicas as sorbents for solid-phase extraction and the use of these materials to develop new strategies for electrochemical detection of heavy metals by stripping voltammetry, are addressed.

The strong therapeutic potential of an organotin(IV) compound loaded in nanostructured silica (SBA-15pSn) is demonstrated: B16 melanoma tumor growth in syngeneic C57BL/6 mice is almost completely abolished. In contrast to apoptosis as the basic mechanism of the anticancer action of numerous chemotherapeutics, the important advantage of this SBA-15pSn mesoporous material is the induction of cell differentiation, an effect unknown for metal-based drugs and nanomaterials alone. This non-aggressive mode of drug action is highly efficient against cancer cells but is in the concentration range used nontoxic for normal tissue. JNK (Jun-amino-terminal kinase)-independent apoptosis accompanied by the development of the melanocyte-like nonproliferative phenotype of survived cells indicates the extraordinary potential of SBA-15pSn to suppress tumor growth without undesirable compensatory proliferation of malignant cells in response to neighboring cell death.

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Dehydroxylated MCM-41 and SBA-15 surfaces were modified by the grafting of two different titanocene complexes ([Ti(eta(5)-C(5)H(4)Me)(2)Cl(2)] and [Ti{Me(2)Si(eta(5)-C(5)Me(4))(eta(5)-C(5)H(4))}Cl(2)]) to give new materials, which have been characterized by powder X-ray diffraction, X-ray fluorescence, nitrogen gas sorption, MAS-NMR spectroscopy, thermogravimetry, SEM, and TEM. The toxicity of the resulting materials toward human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x, and normal immunocompetent cells, such as peripheral blood mononuclear cells PBMC has been studied. Estimation of the number of particles per gram of material led to the calculation of Q(50) values for these samples, which is the number of particles required to inhibit normal cell growth by 50%. In addition, M(50) values (quantity of material needed to inhibit normal cell growth by 50%) of the studied surfaces is also reported. Nonfunctionalized MCM-41 and SBA-15 did not show notable antiproliferative activity, whereas functionalization of these materials with different titanocene based anticancer drugs led to very promising antitumoral activity. The best Q(50) values correspond to titanocene functionalized MCM-41 surfaces (MCM-41/[Ti(eta(5)-C(5)H(4)Me)(2)Cl(2)] (1) and MCM-41/[Ti{Me(2)Si(eta(5)-C(5)Me(4))(eta(5)-C(5)H(4))}Cl(2)] (2)) with Q(50) values between 3.8+/-0.6x10(8) and 24.5+/-3.0x10(8) particles. Titanocene functionalized SBA-15 surfaces (SBA-15/[Ti(eta(5)-C(5)H(4)Me)(2)Cl(2)] (3) and SBA-15/[Ti{Me(2)Si(eta(5)-C(5)Me(4))(eta(5)-C(5)H(4))}Cl(2)] (4)) gave higher Q(50) values, showing lower activity from 73.2+/-9.9x10(8) to 362+/-7x10(8) particles. The best response of the studied materials in terms of M(50) values was observed against Fem-x (309+/-42 microg for 4) and K562 (338+/-18 microg for 2), whereas moderate activities were observed in HeLa cells (from 508+/-63 microg of 2 to 912+/-10 microg of 1). In addition, the analyzed surfaces presented only marginal activity against unstimulated and stimulated PBMC, showing a slight selectivity on human cancer cells. Comparison of the in vitro cytotoxicity in solution of the titanocene complexes [Ti(eta(5)-C(5)H(4)Me)(2)Cl(2)] and [Ti{Me(2)Si(eta(5)-C(5)Me(4))(eta(5)-C(5)H(4))}Cl(2)] and the corresponding titanocene functionalized materials is also described.

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