Patent Application
20090203930
The present invention relates to the field of tunable spatial dispersion of functionality onto inorganic surface with a one-pot procedure.
The attachment of molecular organic structures to inorganic surface provides a unique opportunity to engineer the surface properties. Several approaches have been used to incorporate organic groups and molecules onto the surface of inorganic materials. Hybrid organic-inorganic materials were prepared by direct grafting or deposition onto inorganic surface (metal oxides such as silica, titania, alumina, zirconia, etc. or metals such as silicon, gold, platinum . . . ) with organic moieties containing coupling functionalities such as alkoxy or halogeno-silane, phosphonate, phosphinate, sulfonate, carboxylate, olefin, thiol, or disulfide as disposed for example in W. A. Aue and C. R. Hastings, J. Chromatog., 42 (1969) 319, in K. G. Allum, R. D. Hancok, I. V. Howell, S. McKenzie, R. C. Pitkethly and P. J. Robinson, J. Organometal. Chem., 87 (1975) 203, in O. Leal, D. L. Anderson, R. G. Bowman, F. Basolo and R. L. Burwell, Jr, J. Am. Chem. Soc., 97 (1975) 5125, in J. F. Fritz and J. N. King, Anal. Chem., 48 (1976) 570, in P. Tundo and P. Venturello, J. Am. Chem. Soc., 101 (1979) 6606, in H. Engelhardt and P. Orth, J. Liq. Chromatog., 10 (1987) 1999, in A. Cauvel, G. Renard, and D. Brunei, J. Org. Chem., 1997. 62: p. 749, in H. D. Abruna, T. L. Meyer and R. W. Murray, Inorg. Chem., 18 (1979) 3233, in H. D. Abruna, T. L. Meyer and R. W. Murray, Inorg. Chem., 20 (1981) 1481, in P. Supra, F. Fajula, D. Brunei, P. Lentz, G. Daelen and J. B. Nagy, Colloid and Surfaces, 158 (1999) 21, in D. Brunei, A. Cauvel, F. Di Renzo, F. Fajula, B. Fubini, B. Onida and E. Garrone, New J. Chem., 24 (2000) 807-813, in M. Etienne, J. Bessière and A. Walcarius, Sens. Actuators B, 76 (2001) 531.
A more recent procedure for the preparation of hybrid functionalised silica consists in the one-pot sol-gel synthesis using organic trialkoxysilanes which co-condensate with the tetraalkoxysilane or silicates as silica source as disclosed for example in K. J. Shea, D. A. Loy and D. W. Webster, Chem. Mater., 1 (1989) 574, in D. J. Macquarrie, Chem. Commun., (1996) 1775, in S. L. Burkitt, S. D. Sims and S. Mann, Chem. Commun. (1996) 1367, in R. J. P. Corriu, J. J. E. Moreau, P. Thépot, M. Wong Chi Man, Chem. Mater., 4 (1992), in M. H. Lim, C. F. Blanford and A. Stein, Chem. Mater., 10 (1998) 467.
Assembled monolayer structures possessing functional groups on inorganic surface have wide scientific and practical implications in several fields such as for example adsorption, ion exchange, catalysis, sensing, non-linear optics and biomolecular recognition.
The control of the distribution, mainly the dispersion of the functionalities is crucial to improve the performance of these materials in most of their applications. There are however only few examples in literature dealing with site isolation and controlled distance between the grafted functions. In a first aspect, two amine groups were grafted at a fixed distance from one another by linking them with spacer bearing carbonyl function able to form imine junctions, which had to be removed by a specific reaction after grafting. This method is described for example by Wulff et al. in G. Wulff, B. Heide, G. Helmeier, in J. Amer. Chem. Soc., 1986, 108, 1089; or in G. Wulff, B. Heide, G. Helmeier, in React. Polym., 1987, 6, 299. This strategy was adapted from previous works on molecular imprinting into cross-linked porous polymeric matrix mainly initiated by Shea et al (K. J. Shea and E. A. Thompson, J. Org. Chem 1978, 43, 4253; K. J. Shea, E. A. Thompson, S. D. Pandey and P. S. Beauchamp, J. Am. Chem; Soc., 1980, 102, 3149; K. J. Shea and T. K. Dougherty, J. Am. Chem. Soc., 1986, 108, 1091) and has spurred others for creating more tailorable active sites inside imprinted polymeric chiral cavity as disclosed by J. J. Becker and M. R Gagné, in Acc. Chem. Res., 2004, 37, 798-804.
Similar methodologies were adopted by Tahmassebi and Sasaki (D. C. Tahmassebi, T. Sasaki, J. Org. Chem., 1994, 59, 679) and by Hwang et al. (K.-O. Hwang, Y. Yakura, F. S. Ohuchi, T. Sasaki, Mater. Sci. Eng., C 1995, 3, 137) or by Liu et al. (J. Liu, Y. Shin, L.-Q. Wang, Z. Nie, J W. D. Samuels, H. Chang, G. Fryxell, and G. J. Exarhos, in J. Phys. Chem. A 2000, 104, 8328) or by Shin et al. (Y. Shin, J. Liu, L.-Q. Wang, Z. Nie, G. Fryxell, W. D. Samuels and G. J. Exarhos, Ang. Chem. Int. Ed. 2000, 39, 2702). They anchored two or three aminopropylsilanes using different types of dipod or tripod templates bound by imine bonds for protecting part of the surface during the monolayer coverage with long chain organic silanes. These template molecules were subsequently removed by acid hydrolysis, to leave imprinted rectangular or triangular microcavities in the monolayer coating. It should be noted that this procedure did not give liberated single-surface point but surface portion. Moreover, the distribution of templates on the surface was hardly homogeneous due to possible aggregation of these molecules, resulting in negative effects on the size and shape of the cavities.
Katz and Davis used a similar approach to graft isolated amine groups by direct synthesis of imprinted silica using an in-situ sol-gel methodology (A. Katz and M. E. Davis, Nature, 2000, 403, 286). In this work, the amine functions were protected by a carbamate linkage bearing the imprint that, in addition to providing site isolation, also generates a spatially organised void space when removed. It should be noted that the formation of the final gel with tethered and dispersed amine sites requires also subsequent removal of the imprint molecule and that the control of the site dispersion is provided by two-point bound or one-point bound probe molecule.
Recently, Jones et al have investigated the grafted amine function isolation through a molecular patterning technique using a large tritylimine individually anchored on the silica surface (M. W. McKittrick and C. W. Jones, Chem. Mater. 2003, 15, 1132-1139; M. W. McKittrick and C. W. Jones, J. Am. Chem. Soc., 2004, 126, 3052-3053.) The amine site isolation after silanol capping and hydrolysis of imine bonding function, was controlled by contacting the amine functionalised materials with terephthaloyl chloride, leading to mono or di-amide bonded linkage and probing the unreacted monoacid chloride functionality as previously mentioned.
Another strategy was adopted by Bonneviot et al. to create hydrophilic sites in partially silylated micelle-templated silicas (L. Bonneviot, A. Badiei, N. Crowther, US-A-2004/0035791. As the MCM-41-type silica are usually prepared by cooperative assembly of silicates with a long chain alkyltrimethyl ammonium cation as templating agent, the authors took advantage of the presence of the positively charged surfactant as counter-ion of silicates in the as-made mesoporous silica, to graft the accessible surrounding silanols with a base-generating trimethylsilating agent. After removal of the surfactant, the partially trimethylated material surface contained silanol groups arising from the silicates after displacement of the surfactant, that were uniformly distributed along the mineral surface. These materials with silanol groups surrounded by a hydrophobic environment were available for further surface modification such as for example, further functionalisation by catalytic site grafting. This strategy involved a multi-step procedure and was applicable only with micelle-templated silicas.
These methods are complex and require a long and tedious treatment.
The present invention discloses an alternative strategy to design hybrid materials based on tethered organic chains onto mineral framework and possessing single-site functional chains -LX dispersed between non-functional chains -L. It is based on the dilution of the functional tethering precursor agent with non-functional ones with a ratio larger than 1:4, anticipating a random distribution of functional groups. Preferably, the separating agent has the same organo-chain L as the functional ones.
Interactions of functions between themselves and interactions between function and support as for instance, hydrogen bond for amine, can create some functional chain packing during grafting. The closeness of functions can lead to patches of anchored functional chains despite dilution. This is detrimental to a true molecular dispersion of the functions as represented in
Moreau et al. (J. J. E. Moreau, Luc Vellutini, Michel Wong Chi Man, and Catherine Bied, Chem. Eur. J. 2003, 9, 1594-1599) have developed the synthesis of organised tri-dimensional hybrid structures via a homogeneous hydrolysis-condensation reaction of appropriate silylated organic molecules. The method takes into account the possible, self-association of classes of compounds by supra-molecular assembly, which is able to direct the spatial organisation of functional organic entities into elongated nanofibre-like structure by making use of multiple hydrogen bondings. This is described for example in J. van Esch, S. de Feyter, R. M. Kellogg, F. de Schryver and B. L. Feringa, Chem. Eur. J. 1997, 3, 1238-1243; in J. van Esch, F. Schoonbeek, M. de Loos, H. Kooijman, A. L. Spek, R. M. Kellogg and B. L. Feringa, Chem. Eur. J. 1999, 5, 937-950; in M. Suzuki, Y. Nakajima, M. Yumoto, M. Kimura, H. Shirai and K. Hanabusa, Org. Biomol. Chem., 2004, 2, 1155-1159; in J. M. Lehn, Angew. Chem. Inter. Ed., 1990, 29, 1304-1319. Thanks to bis-urea groups borne by such precursors, molecules assemble by supra-molecular association caused by multiple hydrogen bondings as described in J. J. E. Moreau, B. P. Pichon, M. Wong Chi Man, C. Bied, H. Pritzkow, J.-L. Bantignies, P. Dieudonne and Jean-Louis Sauvajol, Angew. Chem. Int. Ed. 2004, 43, 203-206. Interestingly, a chiral silylated diureidocyclohexyl derivative led to hybrid materials with helical morphology and with handedness reflecting the configuration of the organic sub-structure. This is described in J. J. E. Moreau, L. Velluti, M. Wong Chi Man and C. Bied, J. Am. Chem. Soc, 2001, 123, 1509-1510.
It is an aim of the present invention to use an associative process to allow building patterning during the dual functionalisation of inorganic structures.
It is also an aim of the present invention to develop a one-pot method to disperse functionality on the surface of the support.
It is another aim of the present invention to improve the dispersion of functionality on the surface of the support.
It is a further aim of the present invention to control the dispersion of functionality on the surface of the support.
Accordingly, the present invention provides a method for spatially separating tethered functional organo-chains, through their dilution with tethered non-functional oragno-chains, in the presence of soluble molecular derivatives that are able to self-assemble and to interact with the functional organo-silane.
The separation is effected by spatial occupation provided by the solvating agent that acts as a space-filling agent. It is a non-functional group that preferably has the same nature as the functional groups in order to efficiently avoid aggregation and occupy the space between the active groups.
In a preferred embodiment, the present invention provides a method for functionalising an inorganic support that comprises the steps of:
The auxiliary agent is typically selected from urea derivatives, bis-urea derivatives, thiourea derivatives, triethanolamine, 2,6-aminopyridine, amides, aminoalcohols, aminoacids, cyanuric acid, barbituric acid derivatives, mono-, bi- or tri-glycerides or combinations thereof.
Preferably, it is selected as a function of the functional group as described in Table I.
Preferably, the functional group X is halogen and the auxiliary agent is diol or aminoacid or X is amine and the auxiliary agent is urea derivative, amide or carbamate. The most preferred combination is an amine functional group X with a urea derivative auxiliary agent.
The auxiliary agent, acting as separating agent is preferably compatible with the silane in morphology, and/or in size, and/or in nature, and/or in anchoring capability onto the support, but it has no functional groups X. The amount of separating agent useful in the present invention is at least equal to the amount of grafts. The upper limit is function of its level of solubility. The ratio of silane to separating agent is preferably of from 1:20 to 1:1, more preferably of from 1:10 to 1:8.
Optionally, the functionalised material is subsequently cured and passivated.
The procedure of the present invention is based on the formation of supra-molecular assemblies by association of functional organic-bearing moieties and self-assembled auxiliary molecules. This prevents aggregation of the functional organic precursor during the organic-inorganic interface formation.
The auxiliary molecules are capable to self-assemble and to specifically interact with functional groups X as depicted in
The method can be used for dual functionalisation, either via one-pot sol-gel assembly or via one-pot mineral surface grafting.
In a more preferred embodiment according to the present invention, a silica surface is functionalised with a mixture comprising aminoalkyl or aminoaryl silane and alkylsilane or phenylsilane, according to a sol-gel surface polymerisation described for example in T. Martin, A. Galarneau, D. Brunei, V. Izard, V. Hulea, A. C. Blanc, S. Abramson, F. Di Renzo and F. Fajula, in Stud. Surf Sci. Catal., 135 (2001) 29-O-02or in S. Abramson, M. Laspéras, A. Galarneau, D. Desplantier-Giscard and D. Brunel in Chem. Comm., (2000), 1773-1774. This functionalisation is carried out in the presence of urea derivative as auxilliary molecules. The dual function patterning onto inorganic surface toward single-site functional materials is performed in a single step. The auxiliary urea molecules are subsequently removed during a washing step with polar solvents usually performed after the grafting step.
Preferably, the inorganic support is made from porous mineral oxide particles that have at least one of the following characteristics:
The support may be of various kinds. Depending on its nature, its state of hydration or hydroxylation and its ability to retain water, it may be necessary to submit it to a dehydration treatment of greater or lesser intensity depending upon the desired surface content of —OH radicals.
Those skilled in the art may determine, by routine tests, the dehydration and possibly also of dehydroxylation treatments that should be applied to the support, depending on the desired surface content of —OH radicals.
More preferably, the starting support is made of silica. Typically, the silica may be heated between 100 and 1000° C. and preferably between 140 and 800° C., under an inert gas atmosphere, such as for example under nitrogen or argon, at atmospheric pressure or under a vacuum of about 10−5 bars, for at least 60 minutes. For such heat treatment, the silica may be mixed, for example, with NH4Cl so as to accelerate the dehydration.
In the silane of step b (i), if the “linker” L is a flexible arm, it can be selected from an alkyl having from 1 to 12 carbon atoms, an ether or a thioether. If the “linker” is a rigid arm, it can be selected from an aryl, a mono- or bi-phenyl, a naphtalene, a polyarylether or an ether di-phenol. Preferably the “linker” is a rigid arm and more preferably it is a phenyl. The effect of the rigid linker is to keep away the active sites from the support surface in order to limit undesirable interactions.
The functional group X enables covalent bonding by addition or substitution reaction. It can be selected from halogen, hydroxyl, carboxyl, amino, isocyanate, thiol, or glycidyl. Preferably, it is halogen or amino.
Preferably, the separating agent has the same reacting group as the silane with respect to Si in the support.
The separating agent keeps the functional groups X away from one another thereby creating mono-sites as depicted in
The dispersion of the amino groups tethered on the silica surface can be probed by fluorescence studies of pyrene molecules anchored on the amine functions by covalent linkage.
Detection of excimers can be used to determine the efficiency of dispersion as the emission spectra of the monomer or the excimer allow to determine whether molecular entities are close to one another or not, said molecular entities being either free or linked to large molecules or to solids.
Excimer designate a pair of molecules, preferably identical molecules, formed by diffusion in a medium and wherein one of the molecules M* is in an excited state and the other molecule M is in the fundamental state. The interaction occurring between M and M* consumes a portion of M*'s excitation energy, the remaining energy being shared between the pair MM*. The pair MM* exists for a period of time of a few nanoseconds and then emits photons when returning towards a repulsive ground state as can be seen in
The grafted functional groups are reacted with molecules such as pyrene, that may form excimers if sufficiently close, in order to test their dispersion.
The grafting reaction is carried out at a temperature in the range of 60 to 120° C. under inert atmosphere.
The washing step is carried out at room temperature with a polar solvent that removes the auxiliary separating agent. The polar solvent can be selected from alcohol or water or a mixture thereof.
The curing, if present, is carried out at a temperature that can be selected between 110 and 200° C. depending upon the functional groups. The passivation step, if present, eliminates residual silanol. It is carried out with a silylation agent such as chlorotrimethylsilane, hexamethyldisilazane, trimethylsilylimidazole, N,O-Bis(trimethylsilyl)trifluoroacetamide or another passivation agent that is inert with respect to the functional groups X of the grafted silane.
The present invention also discloses the grafted inorganic supports wherein the functional grafts are efficiently dispersed on the surface of the support.
The functionalised supports of the present invention can be used to prepare new single site catalyst components by metallation reaction.
These supported catalyst components, when activated with suitable activating agents can be used as oligomerisation or polymerisation catalyst systems.
The starting material for the support was silica purchased from Grace Davisson under the name G5H. It had a specific surface area of 515 m2/g, a pore volume of 1.85 cm3/g, a pore diameter of 14.3 nm and a CBET (Brunauer-Emmet-Teller) index of 103.
The general procedure for grafting by coating was adapted from previous work by Martin et al. (“Towards total hydrophobisation of MCM-41 silica surface,” by T. Martin, A. Galarneau, D. Brunei, V. Izard, V. Hulea, A. C. Blanc, S. Abramson, F. Di Renzo and F. Fajula. in Stud. Surf. Sci. Catal., 2001, 135, 29-O-02.
Several grafted silica were prepared.
In S1, the grafting agent is para-aminophenyltrimethoxysilane (n-NH2-Ph-Si) alone. 3 g of silica support (3 g) were pre-activated by heating at 180° C. under vacuum (1 Torr) for 18 h. It was then cooled to room temperature under argon, and 90 mL of dry toluene were added along with 2.66 g (12.48 mmol) of para-aminophenyltrimethoxysilane (n-NH2Ph-Si) as grafting agents (5 molecules per nm2). The suspension was stirred under argon at room temperature for 1 h. Then, 224 mL of water (1.5 equiv per added silane), 118 mg of para-toluene sulfonic acid (0.05 equiv per added silane), 23 mg of ammonium fluoride (0.05 equiv. per added silane) were added to the reaction mixture that was stirred for 1 h at room temperature, then heated at 60° C. for 6 h, then at 120° C. for 1 h. During this last step an azeotropic distillation was carried out using a Dean-Starck apparatus.
The functionalised silica was separated by filtration and successively washed twice with 200 mL of toluene, twice with 200 mL of methanol, twice with 200 mL of a mixture of methanol and water in a 1:1 volume ratio, once with 200 mL of methanol and twice with 200 mL of diethyl ether. Finally, the separated samples were subjected to Soxhlet extraction with a mixture of dichloromethane and diethyl ether in a 1:1 volume ratio.
After grafting by coating, the grafted support was cured by heating under wet nitrogen atmosphere at a temperature of 130° C. overnight. The porous texture was preserved.
Passivation was then carried out as follows. The materials containing tethered amino chains were evacuated at a temperature of 130° C. for 8 h, then after cooling to room temperature, they were suspended in dry toluene. 2.8 mL (14 mmol·g−1) of trimethylsilylimidazole were added and the reaction mixtures were stirred at a temperature of 60° C. overnight.
The solids were separated by filtration and successively washed twice with 200 mL of toluene, twice with 200 mL of methanol, twice with 200 mL of dichloromethane, and twice with 200 mL of diethyl ether. Finally, the solids were subjected to Soxhlet extraction with a mixture of dichloromethane and diethyl ether in a 1:1 volume ratio.
In S2, the same grafting agent n-NH2-Ph-Si was diluted with phenyltrimethoxysilane (n-Ph-Si) in a ratio n-Ph-Si/n-NH2Ph-Si of 2.
The procedure was the same as that use to prepare grafted support S1 except that a mixture of 0.9 g (4.2 mmol) of n-NH2-Ph-Si and 1.68 mg (1.85 mL; 8.48 mmol) of n-Ph-Si were used.
In S3, the same grafting agent n-NH2-Ph-Si was diluted with phenyltrimethoxysilane (n-Ph-Si) in a ratio n-Ph-Si/n-NH2-Ph-Si of 4.
The procedure was the same as that use to prepare grafted support S1 except that a mixture of 0.53 g (2.5 mmol) of n-NH2-Ph-Si and 1.97 mg (1.86 mL; 9.96 mmol) of n-Ph-Si were used.
In S4, the same grafting agent n-NH2-Ph-Si was diluted with phenyltrimethoxysilane (n-Ph-Si) in a ratio n-Ph-Si/n-NH2-Ph-Si of 9.
The procedure was the same as that use to prepare grafted support S1 except that a mixture of 0.266 g (1.25 mmol) of n-NH2-Ph-Si and 2.23 mg (2.1 mL; 11.25 mmol) of n-Ph-Si were used.
In S5, the same grafting agent n-NH2-Ph-Si was diluted with n-Ph-Si in a ratio n-Ph-Si/n-NH2-Ph-Si of 19.
The procedure was the same as that use to prepare grafted support S1 except that a mixture of 0.13 g (0.6 mmol) of n-NH2-Ph-Si and 2.34 g (2.21 mL; 11.83 mmol) of n-Ph-Si were used.
The procedure used for the preparation of S6, S7 and S8 was the same as that used to prepare respectively S2, S3 and S4, except that 0.9 g of methylurea in solution in 6 mL of methanol was added to the reacting silane mixture in solution in 60 mL of dry toluene.
0.9 g (12.2 mmol) of methylurea (5 molecules per nm2) as auxillary agent were dissolved in 6 mL of dry methanol, then added to a solution, in 60 mL of dry toluene, of the mixture of appropriate amounts of para-aminophenyltrimethoxysilane and phenyl-trimethoxysilane corresponding respectively to those of S2, S3 and S4 for the preparation of S6, S7 and S8, respectively. After homogenisation, each of the three solutions was added to a separate sample of silica support (3 g) already pre-activated by heating at 180° C. under vacuum (1 Torr) for 18 h, and then cooled to room temperature under argon. After a contacting time of 1 h, 224 mL (1.5 equiv per added silane) of water, 118 mg (0.05 equiv. per added silane) of paratoluenesulfonic acid and 23 mg (0.05 equiv. per added silane) of ammonium fluoride were added to the reaction mixture that was stirred for 1 hour at room temperature, then for 6 hours at a temperature of 60° C. and for 1 hour at a temperature of 120° C. During this last step an azeotropic distillation was carried out using a Dean-Starck apparatus.
The functionalised silica was separated by filtration and successively washed twice with 200 mL of toluene, twice with 200 mL of methanol, twice with 200 mL of a mixture of methanol and water in a 1:1 volume ratio, once with 200 mL of methanol and twice with 200 mL of diethyl ether. Finally, the separated samples were subjected to Soxhlet extraction with a mixture of dichloromethane and diethyl ether in a 1:1 volume ratio.
After grafting by coating, the grafted support was cured by heating under wet nitrogen atmosphere at a temperature of 130° C. overnight. The porous texture was preserved.
The passivation step was identical to that used in the preparation of S1 to S5. The characteristics of the grafted supports are displayed in Table II.
The dispersion of the functional groups on the surface of the support was then determined by reacting these functional groups with pyrene.
Pyrenesulfonylchloride (PSC) was first synthesised. A solution of 0.41 g (1.45 mmol) of pyrenesulfonic acid in 16 mL of thionylchloride was heated at a temperature of 80° C. until the emanation of SO2 and HCl stopped. Then, the excess thionylchloride was distilled under reduced pressure and the residue was dissolved in 20 mL of dimethylformamide.
Pyrenesulfonylchloride was then anchored onto the aminohydrocarbylsilane-grafted silica as represented in
The characteristics of the samples after anchorage of pyrenesulfonylchloride are summarised in Table III.
Absorption spectra of hybrid material in the UV-visible portion were measured with an apparatus based on diffuse reflection, Perkin-Elmer Lambda 14, equipped with an integrating sphere Labsphere, North Sutton, USA. Silica was deposited in a well, having a depth of 0.05 mm, dug in a quartz slide which was then covered with a standard quartz slide (QS-100 cell, Hellma). The reference cell was filled with BaSO4. The spectra were obtained using the Kubelka-Munk (KM) transform.
KM=(1−reflectance)2/2·reflectance
After the anchoring of pyrene, a new absorption zone appearing beyond 320 nm, up to over 420 nm was linked to the presence of pyrene, as shown on
Absorption increased with increasing functional graft content thereby showing that the amount of pyrene anchored was proportional to the density of functional grafts. In addition, all infrared spectra after pyrene anchorage showed that bands v(N—H) at 3480-3390 cm-1 and o(N—H) at 1625 cm-1 were less intense than those of the parent material thereby showing that amine groups had reacted and thus that the anchoring reaction was successful. This is represented in
The adsorption and desorption isotherms of nitrogen at 77°K, before and after grafting, were similar, indicating that the material porous structure was preserved. Chemical reactions thus did not affect the material's structure.
Fluorescence spectra were also obtained. They were carried out on a spectrofluorimeter built around two Jobin Yvon M25 mono-chromators each carrying a 1200 lines/mm grid (Czerny-turner, ¼ m). Each mono-chromator carries continuously adjustable slits. Detection is carried out with a R928 photomultiplier (Hamatsu). For the recording of spectra, the pass-band was fixed at 8 nm. Measurements were carried out with a right angle or with a frontal geometry, with the cell at an angle of 60 degrees with respect to the incident beam. The samples were placed:
These spectra are represented in
In addition to the monomer fluorescence bands at 376 and 390 nm, a broad peak centered at about 460 nm was observed for samples S1 to S3 and S6 to S7, prepared with and without methylurea. This peak corresponds to the fluorescence emission of the excimer. This implies that mixing two organosilanes could globally dilute the para-aminophenylsilane while keeping the number of grafts constant, but it also implies that a fraction of the functional grafts were not dispersed as evidenced by the presence of excimers. This lack of dispersion could be attributed to interactions between the amine groups of several para-aminophenylsilane favouring their packing.
The ratios of monomer (M) versus excimer (E) as a function of dilution are reported in Table IV.
The spectral area deconvolution is approximative due to the fact that the results are not corrected for the detector response as a function of wavelength.
The addition of methylurea as auxiliary according to the present invention, led to an increase in monomer/excimer ratio as compared to the samples without such addition. It was observed on the fluorescence spectra of all samples.
On the contrary, sample S5 corresponding to a very high dilution did not show this excimer emission, as monomer emission is only present at 376 and at 390 nm. It should be noted that this very diluted and dispersed anchored pyrene exhibited the band at 376 nm with a much larger intensity than that at 390 nm. Indeed, the fluorescence of monomer possesses a fine structure as a series of fine bands associated to vibrational modes of the molecule. The vibrational band said III, situated in the range 390-400 nm is known to have a constant intensity, while band said I, appearing in the range 372-384 nm, varies a lot in intensity according to the polarity of the environment of the pyrene (example: 0.48 in acetonitrile, 0.88 in benzene and 1.65 in hexane—K. Kalyanasundaram and J. K Thomas, J. Am. Chem. Soc, 99 (1977) 2039-2044).
When dilution increases, with or without the addition of methylurea as dispersing agent, the fluorescence emission of the monomer at 372-384 nm increases with respect to that at 390-400 nm. So the spectral analysis shows that, the use of urea further places the graft in an environment that is slightly less polar, for rates of grafting lower than 33%.
Hence the fluorescence results are consistent with a better separation versus dilution in the presence of methylurea. The addition of methyl urea was thus efficient in separating the functional grafts on the surface of the support.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04292817.6 | Nov 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/56056 | 11/18/2005 | WO | 00 | 10/15/2008 |
