Isabel del Hierro

Adsorption of cadmium(II) from aqueous media onto a mesoporous silica chemically modified with 2-mercaptopyrimidine

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−1, whereas the adsorption capacity of the unmodified mesoporous silica was only 0.04 ± 0.02 mmol Cd(II) g−1. 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.

A New Generation of Anticancer Drugs: Mesoporous Materials Modified with Titanocene Complexes

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.

Preconcentration of Zn(II) in water samples using a new hybrid SBA-15-based material

A SBA-15 mesoporous silica has been chemically modified with 5-mercapto-1-methyltetrazole. The newly synthesized material (MTTZ-SBA-15) has been characterized, by powder X-ray diffraction, N(2) adsorption, FT-IR, (13)C NMR spectroscopy and elemental analysis, and used to preconcentrate Zn(II) in water samples. The effect of some variables on the adsorption capacity has been studied using the column techniques. The adsorption capacity of the prepared material followed the order: Zn>>Cu>Cd>>Mn, and under optimized conditions the maximum adsorption value for Zn(II) was 0.96+/-0.01 mmol/g with the adsorption efficiency of 0.76. In column experiments, adsorption was quantitative for 1000 mL of 7.65 x 10(-4)mM of Zn(II) solution and adsorbed ions were eluted out by 5 mL of 1M HCl (preconcentration factor of 200). Spiked tap water and mineral water were used for the preconcentration and determination of Zn(II) by flame atomic absorption spectrometry (FAAS), and a 102+/-2 and 98+/-3% recoveries were obtained. The LOD and LOQ values of the proposed method were found to be 8.0 x 10(-6) and 1.23 x 10(-5)mM, respectively. The relative standard deviation for four preconcentration experiments was found to be <or=4% in all cases.

Study of the influence of the metal complex on the cytotoxic activity of titanocene-functionalized mesoporous materials

Four different titanocene complexes, [Ti(η5-C5H5)2Cl2] (1), [Ti(η5-C5H5)(η5-C5H4Pri)Cl2] (2), [Ti(η5-C5H5)(η5-C5H4But)Cl2] (3) and [Ti(η5-C5H5){η5-C5H3(SiMe3)2}Cl2] (4), have been grafted onto dehydroxylated MCM-41 to give the novel materials MCM-41/[Ti(η5-C5H5)2Cl2] (S1), MCM-41/[Ti(η5-C5H5)(η5-C5H4Pri)Cl2] (S2), MCM-41/[Ti(η5-C5H5)(η5-C5H4But)Cl2] (S3) and MCM-41/[Ti(η5-C5H5){η5-C5H3(SiMe3)2}Cl2] (S4), which have been characterized by powder X-ray diffraction, X-ray fluorescence, nitrogen gas sorption, multinuclear MAS NMR spectroscopy, thermogravimetry, UV spectroscopy, SEM and TEM. The cytotoxicity of the non-functionalized MCM-41 and S1–S4 toward human cancer cell lines, such as adenocarcinoma HeLa, human myelogenous leukemia K562 and human malignant melanoma Fem-x, has been studied. Additional studies of the toxicity of these materials on stimulated and non-stimulated peripheral blood mononuclear cells (PBMC + PHA and PBMC − PHA; i.e. normal immunocompetent cells) have been also carried out. M50 values (quantity of material needed to inhibit normal cell growth by 50%) of the studied surfaces are reported observing that non-functionalized MCM-41 did not show notable antiproliferative activity, while the functionalized surfaces S1–S4 were active against all of the studied human cancer cells. The cytotoxic activities of surfaces S1–S3 were very similar on all the studied cancer cells, however, S4 showed M50 values that indicate the highest activity of all the analyzed materials on all the studied cells, being two to three times more cytotoxic than S1–S3. The same tendency in the cytotoxic activity of the metal complexes 1–3 compared with 4 was observed. Taking into account that all the studied surfaces had a very similar titanium content, the activity of these surfaces strongly depends on the grafted titanocene complex (1–4). This phenomenon indicates that, in contrast with that observed by other authors, the cytotoxicity of the studied materials may be due to action of the released metal complex and is probably not due to the particle action.

Study of the cytotoxicity and particle action in human cancer cells of titanocene-functionalized materials with potential application against tumors

Titanocene dichloride [Ti(η(5)-C(5)H(5))(2)Cl(2)] (1), has been grafted onto dehydrated hydroxyapatite (HAP), Al(2)O(3) and two mesoporous silicas MSU-2 (Michigan State University Silica type 2) and HMS (Hexagonal Mesoporous Silica), to give the novel materials HAP/[Ti(η(5)-C(5)H(5))(2)Cl(2)] (S1) (1.01 wt.% Ti), Al(2)O(3)/[Ti(η(5)-C(5)H(5))(2)Cl(2)] (S2) (2.36 wt.% Ti), HMS/[Ti(η(5)-C(5)H(5))(2)Cl(2)] (S3) (0.75 wt.% Ti) and MSU-2/[Ti(η(5)-C(5)H(5))(2)Cl(2)] (S4) (0.74 wt.% Ti), which have been characterized by powder X-ray diffraction, X-ray fluorescence, nitrogen gas sorption, multinuclear magic angle spinning NMR spectroscopy, IR spectroscopy, thermogravimetry analysis, UV spectroscopy, scanning electronic microscopy and transmission electronic microscopy. The cytotoxicity of the titanocene-functionalized materials toward human cancer cell lines from five different histogenic origins: 8505C (anaplastic thyroid cancer), A253 (head and neck cancer), A549 (lung carcinoma), A2780 (ovarian cancer) and DLD-1 (colon cancer) has been determined. M(50) values (quantity of material needed to inhibit normal cell growth by 50%) and Ti-M(50) values (quantity of anchored titanium needed to inhibit normal cell growth by 50%) indicate that the activity of S1-S4 against studied human cancer cells depended on the surface type as well as on the cell line. In addition, studies on the titanocene release and the interaction of the materials S1-S4 with DNA show that the cytotoxic activity may be due to particle action, because no release of titanium complexes has been observed in physiological conditions, while electrostatic interactions of titanocene-functionalized particles with DNA have been observed.

Synthesis and structure of titanium alkoxide complexes with bulky ligands derived from natural products: Asymmetric epoxidation of cinnamyl alcohol

Abstract A family of titanium(IV) alkoxide compounds [{Ti(OPr i ) 3 (OR)} 2 ], [{Ti(OPr i ) 2 (OR) 2 } 2 ], and Ti(OR) 4 ( 1 – 12 ) have been prepared using two different routes: by metathesis reaction of TiCl(OPr i ) 3 and TiCl 2 (OPr i ) 2 with ROH in the presence of Et 3 N and alternatively by alcohol exchange of Ti(OPr i ) 4 and the corresponding higher boiling alcohol (ROH=adamantanol, 1,2:3,4-di- O -isopropylidene-α- d -galactopyranose, 1,2:5,6-di- O -isopropylidene-α- d -glucofuranose, 1 R ,2 S ,5 R -(−)-menthol). These tetra alkoxide titanium(IV) compounds have been characterized by spectroscopic techniques. In addition, some of these chiral Lewis acid titanium compounds, derived from diacetone galactose and diacetone glucose, have been studied in the asymmetric epoxidation of cinnamyl alcohol in order to evaluate their catalytic activity and stereoselectivity.

Synthesis and Reactivity of Novel Niobocene Complexes Containing Allyl or 1-Azaallyl Ligands. X-ray Crystal Structure of [Li{η3-N(SiMe3)C(tBu)CH2}]3

The lithium 1-azaallyl complex [Li{η3-N(SiMe3)C(tBu)CH2}]3 (1), has been prepared, and its X-ray crystal structure was determined. The niobocene(III) allyl and 1-azaallyl complexes Cp‘2Nb[η3-CH2C(R)CH2] (Cp‘ = η5-C5H4SiMe3; R = H (2), Me (3)) and Cp‘2Nb[N(SiMe3)C(tBu)CH2] (4) have been synthesized. Oxidation of 2 and 3 by O2 yields Cp‘2Nb[η1-CH2C(R)CH2](O) (R = H (5), Me (6)). The complexes CpNb(NtBu)[η1-CH2C(R)CH2]Cl (Cp = η5-C5H5; R = H (7), Me (8)) have also been prepared. Oxidation of 2−4 by PbCl2 gave Cp‘2Nb[η1-CH2C(R)CH2]Cl (R = H (9), Me (10)) and Cp‘2Nb[N(SiMe3)C(tBu)CH2]Cl (11). Cp‘2Nb[η1-CH2C(R)CH2](L) (L = CO (12), CN(2,6-Me2−C6H3) (13)) were prepared by the reaction of Cp‘2NbCl(L) with ClMg(CH2CHCH2).

Synthesis, electrochemistry and reactivity of formato– and acetato–niobocene complexes

The complex [Nb(η5-C5H4SiMe3)2H3]1 reacted with CO2 to give the formato complex [Nb(η5-C5H4SiMe3)2{OC(O)H-O,O′}]2, which can alternatively be prepared from a two-electron reduction of [Nb(η5-C5H4SiMe3)2Cl2]3 in the presence of formic acid. The reaction of 2 with different π-acids or heterocumulene molecules resulted in opening of the bidentate formate ligand giving rise to the monodentate formato-containing complexes [Nb(η5-C5H4SiMe3)2{OC(O)H-O}L], L = CS24, CO 5 or 2,6-Me2C6H3NC 6. On the other hand, [Nb(η5-C5H4SiMe3)2{OC(O)Me-O,O′}]8 was prepared from either the reaction of [Nb(η5-C5H4SiMe3)2Cl]7 with 1 equivalent of Tl(O2CMe) or from a two-electron reduction of 3 in the presence of acetic acid. The complex [Nb(η5-C5H4SiMe3)2(MeCOCHCOMe-O,O′)]9 can also be isolated from the reaction of 7 with 1 equivalent of Tl(acac)(acac = acetylacetonate). Complex 8 reacted with oxygen to give [Nb(η5-C5H4SiMe3)2O{OC(O)Me-O}]10, and with π-acids or heterocumulenes to give products with a monodentate OC(O)Me ligand, namely [Nb(η5-C5H4SiMe3)2{OC(O)Me-O}L], L = CS211, SCNPh 12, PhNCCPhEt 13, MeO2CCCCO2Me 14, ButNC 15 or CO 16. The structures of all complexes have been established by spectroscopic methods.

Solid-State 49/47Ti NMR of Titanium-Based MCM-41 Hybrid Materials

Titanium solid-state NMR spectroscopy data for a series of organic-inorganic titanium MCM-41 based materials have been collected. These materials have been synthesized by first modifying the mesoporous silica MCM-41 in one step with a mixture of silanes: a triazine propyl triethoxysilane acting as functional linker and methyltrimethoxysilane or hexamethyldisilizane as capped agents to mask the remaining silanol groups. Second, the appropiate titanium precursor Ti(OPr(i))(4), [{Ti(OPr(i))(3)(OMent)}(2)] (OMent = 1R,2S,5R-(-)-menthoxo), Ti(OPr(i))(4), or [Ti(eta(5)-C(5)HMe(4))Cl(3)], has been immobilized by reaction with the modified MCM-41. Finally, after Ti(OPr(i))(4) immobilization onto the organomodified support the reaction with the chiral (+)-diethyl-l-tartrate was accomplished. The materials without functional linker have been also prepared by reaction in one step of the capped agent and the titanium precursor with the mesoporous silica. Relevant correlations of titanium NMR resonance chemical shifts and line widths can be inferred depending on different factors. The immobilization procedure used to prepare titanium-based MCM-41 hybrid materials and the choice of the silylating reagents employed to mask the silanol groups present on the silica surfaces produce significant differences in the Ti NMR spectra. Furthermore, depending on the electronic and sterical influence of the substituents directly attached to the titanium center, chemical shifts and line widths are modified providing novel information about titanium structure.

Synthesis and electrochemistry of niobium complexes incorporating asymmetrically substituted ansa-ligands

Abstract The following asymmetric ansa -niobocene(IV) dichloride complexes have been prepared: [Nb{Me 2 Si(η 5 -C 5 Me 4 )(η 5 -C 5 H 3 R)}Cl 2 ] (R=H ( 1a ), Me ( 2a ), SiMe 3 ( 3a ), Pr i ( 4a ), PPh 2 ( 5a )). The ESR spectra of 1a – 5a have been recorded. Oxidation and reduction potentials have also been measured and compared with non ansa -niobocene complexes. The new niobocene complexes [Nb(η 5 -C 5 H 4 R) 2 }Cl 2 ] (R=Pr i ( 6a ), PPh 2 ( 7a )) have been also synthesized. In addition, reduction of 1a in the presence of ligand (RCCR) (R=Me, Ph) to give [Nb{Me 2 Si(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl(RCCR)] (R=Me ( 8a ), Ph ( 9a )) is described.