Propylamine Groups Research Articles

Exploring surface silanols in mesoporous Na-LTA zeolite to enhance its catalytic activity in knoevenagel condensation by grafting amino groups

Mesoporous Na-LTA zeolite was synthesized using the surfactant templating method with the organosilane surfactant [3-(trimethoxysilyl)propyl] octadecyldimethylammonium chloride (TPOAC). The formation of mesopores not only improved the accessibility of the basic catalytic sites but also led to the formation of isolated external silanols. These silanols were used to anchor propylamine groups by reacting with 3-aminopropyltrimethoxysilane (APTMS). The incorporation of propylamine groups in the mesoporous Na-LTA improved its catalytic activity in the Knoevenagel condensation reaction by 40 % due to the presence of extra basic catalytic sites from amino groups. The combination of mesopore generation and functionalization is an efficient strategy for enhancing the performance of Na-LTA zeolite in this reaction.

Amine-grafted H-MFI zeolite precursors as acidic-basic catalysts for deacetalization-Knoevenagel condensation

Amorphous and semi-crystalline precursors of zeolites have a large number of silanols that can be used to anchor organic functionalities, like silane-based amines, resulting in formation of basic sites. This work describes the use of amorphous and semi-crystalline precursors of H-MFI zeolite reacting with aminopropyltrimethoxysilane (APTMS) to produce bifunctional acidic-basic catalysts for the deacetalization-Knoevenagel condensation. The effect of precursors crystallinity on the catalytic performance is explained by the formation of Brønsted acidic sites, which catalyze the deacetalization step, and on the propylamine anchoring capacity, controlled by the amount of external silanols present in the aluminosilicate. It is shown that the aluminosilicates with lower crystallinity provide a higher yield of the end product ethyl trans-α-cyanocinnamate due to the greater number of grafted propylamine groups. These results provide new insights into the preparation of acidic-basic catalysts for converting bulky molecules.

Design and Synthesis of Novel Phenylahistin Derivatives Based on Co-Crystal Structures as Potent Microtubule Inhibitors for Anti-Cancer Therapy.

Phenylahistin is a naturally occurring marine product with a diketopiperazine structure that can bind to the colchicine site of microtubulin as a possible anticancer agent. To develop more potent microtubule inhibitors, novel phenylahistin derivatives were designed and synthesized based on the co-crystal complexes of phenylahistin derivatives and microtubulin. We established a focused library of imidazole-type molecules for the introduction of different groups to the C-ring and A-ring of phenylahistin. Structure-activity relationship studies indicated that appropriate hydrocarbon substituents and unsaturated alkenyl substituents at the 1-position of the imidazole group are important for improving the activity of such compounds. In addition, this study found that propylamine groups could maintain the activity of these compounds, as exemplified by compound 16d (IC50 = 5.38 nM, NCI-H460). Compound 15p (IC50 = 1.03 nM, NCI-H460) with an allyl group exhibited potent cytotoxic activity at the nanomolar level against human lung cancer cell lines. Immunofluorescence assay indicated that compound 15p could efficiently inhibited microtubule polymerization and induced a high expression of caspase-3. 15p also displayed good pharmacokinetic characteristics in vitro. Additionally, the growth of H22 transplanted tumors was significantly inhibited in BALB/c mice when 15p alone was administered at 4 mg/kg, and the tumor inhibition rate was as much as 65%. Importantly, the continuous administration of 15p resulted in a lower toxicity than that of docetaxel (10 mg/kg) and cyclophosphamide (20 mg/kg). Overall, the novel allyl-imidazole-diketopiperazine-type derivatives could be considered safe and effective potential agents for cancer treatment.

Bifunctional hybrid organosiliceous catalysts for aldol condensation – hydrogenation tandem reactions of furfural in continuous-flow reactor

A series of organic-inorganic hybrid bifunctional organosiliceous catalysts with accessible pendant amine groups as single basic sites (such as propylamine, diethylamine, pyrrolidine) and Pd nanoparticles was prepared from suitable synthesis processes. Pd/MCM-41 silica decorated with propylamine groups was highly active and selective for the single-reactor tandem aldol condensation/crotonization reaction between furfural with methyl isobutyl ketone, followed by hydrogenation, to access renewable biosolvent and biofuel precursors in the branched alkane range at mild temperature (80–100 ºC). The catalyst was characterized in detail using XRD, C and N elemental analysis, ICP-OES, TGA/DTA, HR-TEM, N2 adsorption/desorption at 77 K, solid-state 13C and 29Si MAS NMR and FT-IR spectroscopy CO2 as acid probe. The catalyst was robust when operated in a dual fixed-bed reactor achieving steady 20 % furfural conversion for 12 h on stream with preferential formation of 1-(furan-2-yl)− 5-methylhexan-3-one.

Advantages of Covalent Immobilization of Metal‐Salophen on Amino‐Functionalized Mesoporous Silica in Terms of Recycling and Catalytic Activity for CO2 Cycloaddition onto Epoxides

AbstractNiII and MnIII Schiff base complexes (Salophen‐Ni and Salophen‐MnCl) bearing a pending carboxylic group were prepared and characterized. Both complexes were grafted onto a mesoporous amino‐functionalized SBA‐15 silica, by formation of an amide function between the propylamine groups of the support and the carboxylic acid functions of the salophen ligand (corresponding respective to 1.30 wt.% of Ni and 1.06 wt.% of Mn). The co‐catalytic behaviour of the free and grafted complexes was then evaluated in the CO2 cycloaddition reaction onto styrene oxide, using tetra‐butylammonium bromide (n−Bu4NBr) as the main catalyst. In homogeneous conditions, the MnIII Schiff base complex and the NiII one, to a lesser extent, behave as efficient co‐catalysts for this reaction (styrene conversion of 100 % and 65 % respectively after 3 h at 120 °C, under 15 bars of CO2). Upon immobilization at the surface of the amino‐functionalized SBA‐15, we showed that the co‐catalytic activity of the less efficient one, i. e. Ni2+ salophen complex, could be enhanced (reaching a full conversion after 7 h), hence highlighting a potential synergistic effect between the unused amine functions of the support and the Ni2+ salophen co‐catalyst. Both salophen complexes were successfully re‐used in homogeneous conditions or after their immobilization without any appreciable loss of activity. This work is only a first step towards a completely heterogeneous catalytic system, in which the tetraalkylammonium halide catalyst and the metal‐salophen co‐catalyst will both be covalently anchored on the same support.

Improving hydraulic permeability, mechanical properties, and chemical functionality of cellulose acetate-based membranes by co-polymerization with tetraethyl orthosilicate and 3-(aminopropyl)triethoxysilane

Composite cellulose acetate (CA) membranes are widely used but their multiphase nature results in additive losses, poor mechanical strength, low chemical resistance and thermal stability, limiting their separation/purification yields. To overcome this, we fabricated monophasic hybrid membranes using a modified phase inversion technique, where tetraethylorthosilicate and 3-(aminopropyl)triethoxysilane were added to the CA casting solution. The resulting co-polymerization between CA, silanols and amine-functionalized silica groups, through sol-gel chemistry, was proved by ATR-FTIR (1118 cm−1, ν(SiOC)). The presence of propyl-amine groups increases the hydraulic permeability (3×), the rupture elongation (×1.5), and decreases the Young modulus (×1/2), due to the disruption of the CA-silica 3D network. For high propyl-amine contents this behaviour is reversed due to intensive cross-linking between CA-silica chains (decrease in 903 cm−1, ν(CH3COOC-)). The addition of silica- and amine-based structures to the CA framework increases the system degrees of freedom, opening the door to the design of new CA membranes.

Scope for Spherical Bi2WO6 Quazi-Perovskites in the Artificial Photosynthesis Reaction—The Effects of Surface Modification with Amine Groups

The synthesis, characterisation, modification (with n-propyl amine groups) of Bi2WO6 particles and the scope for their application in artificial photosynthesis reactions is described. The synthesis involves microwave activation of spherical Bi2O3 precursors followed by a hydrothermal treatment in the presence of Na2WO4. These are characterised using electron microscopy (TEM and SEM), BET, XRD, FTIR, FT-Raman and UV–Visible spectroscopies and CO2 TPD. Subsequently this material is modified through the condensation of propyl amine groups to surface hydroxyl groups, and the composites prepared are characterised using FTIR and D-FTIR following exposure to CO2. Both the spherical particles and the amine-modified analogues are applied in the artificial photosynthesis reaction under batch conditions. O2, CO and CH4 are the observed gaseous products during the reaction and there is FTIR evidence for the formation of adsorbed alcohols and carbonylated products. Although the modification with amine groups decreased the overall photocatalytic reactivity, it also altered the product selectivity with respect to the CH4/CO ratio. The catalyst tends to improve the oxygen production ability after about 20 h of operation, with a decline in CH4 and CO production, indicating that other condensates are probably generated. This opens up new possibilities and scope for this catalyst and further research is required to understand the observations.

ACTOPROTECTOR ACTIVITY OF 4-R-(IDENEAMINO)- 5-R-4Н-1,2,4-TRIAZOLE-3-THIOLS

In this study, actoprotector activity of 1,2,4-triazole derivatives is described. The biological activity of synthetic 4-R-(ideneamino)-5-R-4Н-1,2,4-triazole-3- thiols was analyzed. The forced swim test with a weight load of 10% of the test animal’s body weight was applied. According to the obtained results, compounds that contained NH4+ and CuSO4 substituents were among the most active, potency of which was close to that of the reference drug Riboxin. Introduction of propylamine, isopropylamine and piperazine groups into the molecule decreases the actoprotector activity. Compounds containing monoethanolamine, diethylamine, ethylamine, and magnesium sulfate moieties almost did not exhibit actoprotector activity.

In Situ Growth of Chiral Gold Nanoparticles in Confined Silica Nanotube.

We reported here that chiral gold nanoparticles can be In Situ created inside a confined chiral silica nanotube. A bolaamphiphilic L-glutamic acid was found to self-assemble into nanotube and transcribed its chirality into the silica through co-assembly with ATPS and TEOS. After removing the bolaamphiphile, "chiral" alignment of propylamine groups or "chiral imprint" remained inside the silica nanotube. NaAuCl₄ was absorbed into silica nanotube via electrostatic and coordination interaction with propylamine groups. After In Situ reducing with ascorbic acid, the gold nanoparticles were formed inside the nanotube, which exhibited chiral optical activity. Interestingly, the chirality of gold nanoparticles still remained even after removing the silica nanotube template with HF, proved that the "chiral imprint" is strongly "memorized" by the gold nanoparticles.

Synthesis of a highly hydrophobic silica mesostructure by a modified co-condensation procedure and evaluation of its drug release capability

A highly hydrophobic silica mesostructure was synthesized by a modification on the conventional co-condensation procedure that involved the partial substitution of hexadecytltrimethylammonium, used as mesostructure directing agent, by hexadecyltrimethoxysilane. That modification allowed the production of a highly ordered hexagonal silica mesostructure with the mesopores partially filled with high amounts of hexadecyl chains, covalently bonded to inorganic framework. After extracting the reminiscent template molecules, ibuprofen was loaded into the mesostructure in order to evaluate its drug release properties. The drug loading amount (21 wt%) was comparable to the one reported for MCM-41 with grafted propylamine groups (25 wt%), indicating that C16-chains were not fully compacted occluding the pores. A slow ibuprofen release was observed in simulated body fluid (pH 7.2) by a process controlled by an anomalous transport with contribution of diffusional and relaxational components, according to the Korsmeyer-Peppas kinetics model. That hydrophobic mesostructure produced has the potential of being use as a carrier for low water soluble drugs with an extended delivery effect, but without the disadvantages of co-releasing toxic surfactant molecules or the need of non-toxic specific templates to be prepared.

Morphology of self assembled monolayers using liquid phase reaction on silica and their effect on the morphology of adsorbed insulin

The effect of roughness of two different categories of self-assembled monolayers (SAMs) with propyl amine and propyl groups respectively on the morphology of adsorbed insulin is observed. SAMs are obtained by liquid phase reaction of silica with organo silane coupling agents (SCA). The influence of the morphology and physical characteristics of the SAMs on the reaction time and concentration of the modifiers are explored.We have tested three SCA containing propyl amine with varying groups linked to Si present on it. In addition, we have used a silane coupling agent to prepare SAM of methyl head group. The approach of these molecules towards the surface depends on the head group and the groups linked to Si of the SCA. The morphology of the surfaces is analysed using power spectral density distribution (PSD), skewness, ellipsometry thickness and surface energy.Both chemical nature and physical morphology of the adsorbent influence the morphology of the adsorbed insulin. In general, a low number of aggregates of big size are formed on the surfaces obtained from low concentration of SAMs, while a higher number but of smaller size of aggregates are formed over surfaces obtained from 1% concentration of SAMs modifiers. The peak to valley ratio of the aggregates of insulin is strongly influenced by the size of grains of SCA over the adsorbent.

Multinuclear nuclear magnetic resonance spectroscopic and high-performance liquid chromatographic characterization of silica, grafted with specifically deuterated 4-((propylamino)methyl)benzoic acid

Specifically deuterated 4-((propylamino)methyl)benzoic acid-grafted silica (PAMBA-silica) was prepared by benzylation of propylamino-grafted silica (PA-silica) by either in situ reduction by sodium cyanoborodeuteride (NaCNBD3) of the Schiff base, formed by the reaction between PA-silica and 4-formylbenzoic acid, or by NaCNBD3 reduction of the isolated Schiff base. The PAMBA-silicas, which contain amine and carboxylic acid functionalities, were characterized by elemental analysis, 13C, 29Si, and 2H solid state NMR, and HPLC. Solid state 13C NMR revealed that PAMBA-silica prepared by the in situ method consists of di-benzylated, mono-benzylated, and unreacted amino-groups while PAMBA-silica prepared by the two-step synthesis consists of only mono-benzylated and unreacted amino-groups. 29Si solid-state NMR spectra indicated that no significant loss of propylamine groups had occurred during benzylation. Nearly ideal uniaxial rigid-limit 2H NMR spectra of grafted 4-PAMBA ligands indicates that they form a rigid structure, which provides effective electrostatic screening of inner positive charges when the ligands are in zwitterionic form. HPLC columns packed with PAMBA-silica and PA-silica were evaluated for ionic solutes at different pH of the mobile phase. Retention times increased for cations and decreased for anions at increasing pH. These trends show that PAMBA-silicas act as cation and anion exchangers at high and low pH, respectively. The pKa values of grafted carboxylic acid, determined from HPLC of weakly retaining solutes, are close to pKa of the solution PAMBA.

Dealing with Confounding pH-Dependent Surface Charges in Immobilized Artificial Membrane HPLC Columns.

The retention capacity factor (k(IAM)) on immobilized artificial membrane chromatography columns (IAM-HPLC) is widely used as experimental descriptor of lipophilicity. For predominantly ionized compounds, however, unexpected and significant effects of pH, buffers, and salinity on k(IAM) have been reported. Besides zwitterionic phospholipids, IAM particles contain acidic silanol moieties and positively charged propylamine groups. The electrostatic model and experimental k(IAM) values presented in this study for organic cations show that the net IAM surface charge is positive below pH 5 and negative above pH 5. The resulting confounding electrostatic repulsion/attraction is strongly influenced by eluent salinity: k(IAM) values for cations differ by more than 2 orders of magnitude over the tested range of aqueous eluents. In phosphate buffered saline medium the actual lipophilicity of cationic drugs (K(PLIPW,cation)) is overestimated by at least a factor of 2. The K(PLIPW,cation) can be readily determined by IAM-HPLC in any 10 mM buffered eluent at pH 5. Accounting for, or avoiding, confounding electrostatic effects in IAM-HPLC considerably advances assessments of (phospho)lipophilicity for drug discovery and for environmental risk assessment of organic cations.

The role of hydroxyl group acidity on the activity of silica-supported secondary amines for the self-condensation of n-butanal.

The catalytic activity of secondary amines supported on mesoporous silica for the self-condensation of n-butanal to 2-ethylhexenal can be altered significantly by controlling the Brønsted acidity of M--OH species present on the surface of the support. In this study, M--OH (M=Sn, Zr, Ti, and Al) groups were doped onto the surface of SBA-15, a mesoporous silica, prior to grafting secondary propyl amine groups on to the support surface. The catalytic activity was found to depend critically on the synthesis procedure, the nature and amount of metal species introduced and the spatial separation between the acidic sites and amine groups. DFT analysis of the reaction pathway indicates that, for weak Brønsted acid groups, such as Si--OH, the rate-limiting step is C--C bond formation, whereas for stronger Brønsted acid groups, such as Ti and Al, hydrolysis of iminium species produced upon C--C bond formation is the rate-limiting step. Theoretical analysis shows further that the apparent activation energy decreases with increasing Brønsted acidity of the M--OH groups, consistent with experimental observation.

ChemInform Abstract: In situ Preparation of a Multifunctional Chiral Hybrid Organic—Inorganic Catalyst for Asymmetric Multicomponent Reactions.

AbstractThe utilized catalyst is made of a chiral mesoporous organosilica material incorporating a urea‐based cinchona derivative and propylamine groups, generated by a co‐condensation method.

In situ preparation of a multifunctional chiral hybrid organic–inorganic catalyst for asymmetric multicomponent reactions

A chiral mesoporous organosilica material incorporating a urea based-cinchona derivative and propylamine groups was prepared by a co-condensation method. The multisite solid catalyst efficiently promoted the asymmetric multicomponent reaction of aldehydes, malonates and nitromethane.

Quantification of chemisorption and physisorption of carbon dioxide on porous silica modified by propylamines: Effect of amine density

Detailed molecular aspects of carbon dioxide sorption on porous silica with different amounts of tethered and cross-linked n-propylamine groups were investigated. Infrared spectroscopy was applied to directly quantify physisorbed and chemisorbed CO2 on the amine modified silicas. The fractions of physisorbed CO2 and various chemisorbed species were determined as functions of CO2 pressure and the amine density on the modified silica. Physisorbed CO2 was a minor portion of the total CO2 uptake at low pressures, but its contribution increased to ∼35% at 1bar of CO2 when the propylamine surface density was low or medium (0.87–1.67 NH2/nm2). Chemisorption of CO2 dominated when the propylamine content was high (2.74 NH2/nm2). The quantities of propylammonium propylcarbamate ion pairs increased with increasing propylamine content. At low or medium amine surface densities (0.87–1.67 NH2/nm2) this increase was approximately proportional to the amine density, but the quantity of ion pairs increased very significantly when the propylamine content was high (2.74 NH2/nm2). This dependency on amine density is consistent with the idea that a sufficiently close proximity of propylamine groups allows a formation of ion pairs. The relative fractions of carbamic acid and silylpropylcarbamate were significant for materials on which ion pairs could not form in significant amounts. Furthermore, the quantities of carbamic acid increased with increasing amine densities suggesting that the ion pairs have a role to stabilize the labile carbamic acid through hydrogen bonds.

Interactions of NO2 with Amine-Functionalized SBA-15: Effects of Synthesis Route

SBA-15 mesoporous silica was modified using (3-aminopropyl)trimethoxysilane (APTMS) following co-condensation or grafting methods and then used as a NO(2) adsorbent at room temperature. The samples were characterized before and after exposure to NO(2) by SEM-EDX, N(2) adsorption at 77 K, potentiometric titration, thermal analysis, and FTIR spectroscopy. Even though, regardless of the synthesis route, the addition of propylamine groups leads to a significant enhancement in the amount of NO(2) adsorbed (from 21 to 124 mg(NO(2))/g), a higher retention of NO(2) and NO (released as a result of surface reactions) was measured on the grafted silica than on all of the co-condensed samples. In the case of the latter materials, improvements in both NO(2) adsorption capacity and NO retention were found for the samples treated with NaOH. This behavior is related to the higher reactivity of deprotonated propylamine groups (formed during NaOH treatment) with NO(2), the presence of silanol groups, and the residual amount of sodium present in the samples. The mechanism of NO(2) adsorption on propylamine groups involves the formation of nitramine and/or nitrosamine. Analysis of the spent materials indicates that the porosity of co-condensed materials is not affected to the same extent by adsorption of NO(2) as that of the grafted silica.

Normal Phase HPLC as a Model System of Specific Benzodiazepine-receptor Binding

The hypothesis that benzodiazepines interact with their receptors in the CNS via hydrogen bonding mediated by the carbonyl and imine groups has been studied by correlating a physicochemical parameter affected by hydrogen bonds potentially accepted or donated by benzodiazepines with their binding constants to synaptosomal rat brain membranes. The reference physicochemical system chosen was normal phase high-performance liquid chromatography on mu-Bondapack NH2 (propylamine groups chemically bonded to porous silica) eluted with mixtures of n-hexane and 2-propanol. A strong correlation has been found for binding of the implicated groups to the column and to the receptor.

Carbon Dioxide Sorbents with Propylamine Groups−Silica Functionalized with a Fractional Factorial Design Approach

Mesoporous silica particles (Davisil) were functionalized with aminopropyltriethoxysilane (APTES) in a fractional factorial design with 19 different synthesis and uptake experiments. The number of amino groups and the uptake of CO(2) were optimized in a 2(V)(5-1) design. Most important to functionalization was the amount of water present during synthesis, the reaction time, and pretreating the silica with a mineral acid; certain two-way interactions were shown to be statistically significant as well. Modifications performed at 110 or 80 °C showed no significant differences concerning amine content or uptake of CO(2). Properly choosing center points for the discrete variables is problematic and is somewhat related to the lack of fit with respect to CO(2) uptake; the regression was good. Solid-state (29)Si NMR showed that the APTES was mainly fully condensed. Specific surface areas did not correlate with the number of n-propylamine groups on the silica, which is indicative of differential levels of heterogeneity in the coverage of propylamines. The uptake of CO(2) and N(2) was measured from -20 to 70 °C and from 0 to 1 bar and parametrized by the Freundlich isotherm. Amine-modified silica adsorbed significant amounts of CO(2), especially at the low partial pressure, which is important for CO(2) capture from flue gas. At such pressures, samples with a high density of amine (4 amines/nm(2)) showed a much higher uptake of CO(2) than did those with densities of ∼2-3 amines/nm(2), reflecting differential tendencies to form propylammonium-propylcarbamate ion pairs; these require close proximity among amine groups to form. Water affected the uptake of carbon dioxide in different ways. Certain samples took up more moist CO(2) gas than dry CO(2), and others took up less moist CO(2) than dry CO(2), which is indicative of differential tendencies toward water adsorption. We conclude that experimental design is a time-efficient approach to the functionalization of silica with propylamine groups.