Primary Alkylammonium Cations Research Articles

Structural characterization of organo-montmorillonites prepared from a series of primary alkylamines salts: Mid-IR and near-IR study

Primary alkylammonium cations with progressively increasing chain length from methylammonium (CH3-NH3+) to nonadecylammonium (CH3-(CH2)18-NH3+) were used to prepare unique series of organo-montmorillonites (O-Mts). Infrared spectroscopy in the mid-IR and near-IR regions and XRD were used to characterize samples and to investigate the effect of the chain length on the arrangement of cations confined in montmorillonite (Mt) interlayers. For the first time detailed assignment of the vibration bands in the near-IR region (8000–4000 cm−1) was provided not only for O-Mts but also for selected primary alkylamines and alkylammonium salts, used for their preparation. The IR spectra showed that both, type of head-group, i.e. NH2 vs NH3+, and nature of the anionic counterpart, i.e. chloride vs Mt layer, significantly affected the positions the NH vibration modes as a result of different H-bonds in O-Mts. The alkyl chain length had significant effect on the arrangement of the intercalated cations. With increasing chain length the stretching (νCH2) and first overtone (2νCH2) bands were shifted to lower wavenumbers indicating decreasing amount of disordered gauche in favor of ordered all-trans conformers. Significantly higher shift of the 2νasCH2 band than νasCH2 benefits the NIR region for conformational studies more than MIR.

Influence of Different Organoclays on the Curing, Morphology, and Dynamic Mechanical Properties of an Epoxy Adhesive

The thermal, mechanical, and adhesive properties of nanoclay-modified adhesives were investigated. Two organically modified montmorillonites: Cloisite 93A (C93A) and Nanomer I.30E (I.30E) were used as reinforcement of an epoxy adhesive. C93A and I.30E are modified with tertiary and primary alkyl ammonium cations, respectively. The aim was to study the influence of the organoclays on the curing, and on the mechanical and adhesive properties of the nanocomposites. A specific goal was to compare their behavior with that of Cloisite30B/epoxy and Cloisite15A/epoxy nanocomposites that we have previously studied. Both C30B and C15A are modified with quaternary alkyl ammonium cations. Differential scanning calorimetry results showed that the clays accelerate the curing reaction, an effect that is related to the chemical structure of the ammonium cations. The three Cloisite/nanocomposites showed intercalated clay structures, the interlayer distance was independent of the clay content. The I.30E/epoxy nanocomposites presented exfoliated structure due to the catalytic effect of the organic modifier. Clay-epoxy nanocomposites showed lower glass transition temperature (T g ) and higher values of storage modulus than neat epoxy thermoset, with no significant differences between exfoliated or intercalated nanocomposites. The shear strength of aluminum joints using clay/epoxy adhesives was lower than with the neat epoxy adhesive. The water aging was less damaging for joints with I.30E/epoxy adhesive.

Rescue of K12G Triosephosphate Isomerase by Ammonium Cations: The Reaction of an Enzyme in Pieces

The K12G mutation at yeast triosephosphate isomerase (TIM) results in a 5.5 × 10(5)-fold decrease in k(cat)/K(m) for isomerization of glyceraldehyde 3-phosphate, and the activity of this mutant can be successfully "rescued" by NH(4)(+) and primary alkylammonium cations. The transition state for the K12G mutant TIM-catalyzed reaction is stabilized by 1.5 kcal/mol by interaction with NH(4)(+). The larger 3.9 kcal/mol stabilization by CH(3)CH(2)CH(2)CH(2)NH(3)(+) is due to hydrophobic interactions between the mutant enzyme and the butyl side chain of the cation activator. There is no significant transfer of a proton from alkylammonium cations to GAP at the transition state for the K12G mutant TIM-catalyzed reaction, because activation by a series of RNH(3)(+) shows little or no dependence on the pK(a) of RNH(3)(+). A comparison of k(cat)/K(m) = 6.6 × 10(6) M(-1) s(-1) for the wildtype TIM-catalyzed isomerization of GAP and the third-order rate constant of 150 M(-2) s(-1) for activation by NH(4)(+) of the K12G mutant TIM-catalyzed isomerization shows that stabilization of the bound transition state by the effectively intramolecular interaction of the cationic side chain of Lys-12 at wildtype TIM is 6.3 kcal/mol greater than that for the corresponding intermolecular interaction of NH(4)(+) at K12G mutant TIM.

Calixarenes as Hosts for Ammonium Cations: A Quantum Chemical Study and Mass‐Spectrometric Investigations

Host-guest complexes of tetramethylcavitand with different ammonium cations were investigated by using a quantum chemical method at the density functional level (BP86, B3 LYP). The NH4+ cation is strongly bound to the host. Increasing methyl substitution at the cation decreases its inclination towards the complex formation. The calculated data are in line with results from electrospray ionization mass spectrometry (ESI-MS) experiments. They reveal stable aggregates only for the NH4+ cation and for the primary alkylammonium cations.

Extraction of cesium and barium by dicarbollide and polyethylene glycol in the presence of alkylammonium cations

The extraction of cesium and barium cations into nitrobenzene and 60% (vol.%) nitrobenzene +40% CCl4 mixture in the presence of dicarbollide (+Slovafol 909), and primary alkylammonium cations has been studied. Extraction constants determined for three methylammonium cations correlate well with their hydration enthalpies. Reverse order of the hydrophobicity of methylammonium cations (competition with bare Cs+ ion) and of their tendency to enter the polyethylene glycol complex (competition with polyethylene glycol complexed Cs+ and Ba2+ ions) is recorded. The possibility of the regeneration of the organic phase after stripping of Cs+ and Ba2+ ions with methylammonium cations has been investigated.

Macrocyclic and macropolycyclic compounds based upon 1,3-disubstituted propane units

Synthetic routes to the macrocyclic polyamine derivatives (1) and (3) are described, together with an investigation of the complexing properties of the triamines (1d) and (3d) with primary alkylammonium cations. Macrotricyclic and macrotetracyclic compounds may be obtained from the macrocycle (1) by a stepwise procedure whereas macrocycle (3b) can be converted into a macrotricyclic derivative in a one step alkylation procedure. The alkylation of the tetrahydropyrimidone (18) with αα′-dibromo-m-xylene gives the calix[4] arene analogue (19) which adopts the ‘cone’(21a) and ‘1,3-alternate’(21b) conformations. The macrocyclic hexa-amine (23) may be synthesized by a simple alkylation procedure whereas the octa-amine (27) required a systematic stepwise synthesis. The hexa-amine salt (23)·6 HBr shows selectivity in forming inclusion complexes with the dicarboxylate anions –O2C(CH2)nCO2–.

Cation exchange in synthetic manganates: II. The structure of an alkylammonium-saturated phyllomanganate

AbstractA synthetic phyllomanganate saturated with a series of primary alkylammonium cations has been examined using XRD, chemical analysis and X-ray photoelectron spectroscopy. A linear relationship exists between the basal spacing of the saturated alkylammonium-manganate and the hydrocarbon chain length in the interlayer, and from the gradient it is concluded that the alkyl chains are perpendicular to the manganate sheet. This orientation is a function of both the charge density and the presence of a layer of water molecules immediately adjacent to the manganate basal surfaces. Evacuation results in the loss of this interlayer water and the structure of the organo-manganate is considerably disrupted. The extent to which the interlayer arrangement can be reinstated by rehydration is dependent on the chain length of the saturating organo-cation. For cations of chain length > C6 the C contents suggest that cation in excess of the exchange capacity is present in the interlayer, but the absence of any compensating anion and the release of amine on evacuation suggests that the excess C arises from the presence of free amine.

The adsorption of organic vapors on alkylammonium smectites. The influence of mineral charge density and monofunctional ammonium cation type

Exchanging smectites (from Otay, Moosburg, Wyoming, and Hector) with long-chain monofunctional ammonium cations of appropriate chain length produces monolayer, double-layer, and pseudothree-layer complexes or paraffin-type structures. These adsorbents have an interesting affinity for single vapors such as ethanol and benzene. At different threshold pressures there is an expansion of the complexes accompanied by a reorientation of the organic cations which occurs at a lower p p 0 the higher the charge density of the mineral. Double-layer complexes are not expanded by n-hexane vapor sorption. In monolayer complexes, expansion only occurs for the ethanol-primary alkylammonium system irrespective of the smectite used and an expansion on contact with the first traces of ethanol at 20°C could be predicted for a smectite with an octahedral charge distribution of ξ = 0.433 e (Si, Al) 4O 10 unit. In double-layer complexes the monotrimethylammonium alkane (MTM) systems expand in contact with benzene and a MTM bilayer complex with a mineral of ξ = 0.401 e (Si, Al) 4O 10 will expand with the first traces of C 6H 6. With double layers of primary alkylammonium cations and monotriethylammonium alkanes expansion with benzene only occurs when the number of functional groups per unit surface is high enough, i.e., when the Otay clay is utilized. Partial exchange of MTM double-layer complexes with Cu decreases the adsorption capacity of the adsorbent. The pseudo-three-layer complexes and paraffin-type structures readily expand in benzene vapor and sorb large amounts of adsorbate.

To enzyme analogues by lock and key chemistry with crown compounds. Part 1. Enantiomeric differentiation by configurationally chiral cryptands synthesised from L-tartaric acid and D-mannitol.

The requirements of an enzyme analogue are discussed in terms of (i) binding, (ii) chirality, and (iii) functionality. The ability of 18-crown-6 derivatives to complex with primary alkylammonium cations indicates the potential of the 18-crown-6 constitution to provide the binding requirement of an enzyme analogue. Attention is drawn to the fact that carbohydrates provide not only functionality but also a relatively inexpensive source of chiral bismethylenedioxy units for incorporation into the 18-crown-6 framework. The optically pure configurationally chiral cryptands L-(14), LL-(15), LL-(16), LL-(17), DD-(17), LL-(18), DD-(28), D-(29), DDD-(30), DD-(31), DD-(32), and DD-(33) have been synthesised from L-tartaric acid and D-mannitol. The 18-crown-6 locks excluding the tetraol LL-(16) and the octaol DD-(31), have been shown by 1H n.m.r. spectroscopy to form complexes in CD2Cl2 with primary alkylammonium salts. The stability constants for complexes formed in CDCl3 solution between (i) t-butylammonium thiocyanate and (ii) benzylammonium thiocyanate and some of these 18-crown-6 locks have been determined by an 1H n.m.r. spectroscopic method and compared with the complexing ability of 18-crown-6 (34). 1H and 13C N.m.r. spectroscopy has been used to demonstrate that the locks LL-(18) and DD-(28) exhibit enantiomeric differentiation in complexation equilibria towards (RS)-α-phenylethylammonium hexafluorophosphate [(RS)-(8),HPF6]. The tetraol LL-(16) and the octaol DD-(31) have been shown by 1H n.m.r. spectroscopy to form complexes in CD3OD and D2O with primary alkylammonium salts. The tetra-O-isopropylidene derivative DD-(28) forms strong complexes in methanolic solution with alkali metal cations.

Stereoselectivity in complexation of primary alkylammonium cations by the diastereotopic faces of chiral asymmetric crowns

The temperature-dependent 1H n.m.r. spectra of the 1:1 complexes formed between crowns D-(1), DD-(2), D-(3), and DD-(4) and primary alkylammonium cations in solution are interpreted in terms of equilibria involving diastereoisomeric complexes of (i) similar strengths in the case of the galacto-crowns D-(1) and DD-(2) and (ii) dissimilar strengths in the case of the gluco-crowns D-(3) and DD-(4) where a secondary interaction of a dipole-induced dipole type appears to be responsible for the stereoselectivity.

Synthesis of configurationally chiral cryptands and cryptates from carbohydrate precursors

Optically pure configurationally chiral 18-crown-6 and 9-crown-3 cryptands have been synthesised from L-tartaric acid and D-mannitol and some of the 18-crown-6 derivatives have been shown to form cryptates with metal and primary alkylammonium cations.