Non-cyclic Analogues Research Articles

Thermodynamics of the formation of metal complexes of 1,4,10-trioxa-7,13-diazacyclopentadecane-N,N′-diacetic acid and of 1,4,10,13-tetraoxa-7,16-diazacyclo-octadecane-N,N′-diacetic acid

Thermodynamic functions for the formation of the alkaline-earth and some transition-metal complexes of the ligands L1(1,4,1O-trioxa-7,13-diazacyclopentadecane-N,N′-diacetic acid) and L2(1,4,10,13-tetraoxa-7,16-diazacyclo-octadecane-N,N′-diacetic acid) were determined by direct batch microcalorimetry. The ligand L1 gives more stable transition-metal complexes than L2 due to more favourable heats of reaction. The reverse situation is found for complexes of the alkaline-earth metals, although the differences in stability of the complexes of these metals with the two ligands are small due to less favourable entropy changes in the case of L2. The two macrocyclic ligands behave similarly to their non-cyclic analogues L3 and L4(3-oxapentane-1,5-diamine-and 3,6-dioxaoctane-1,8-diamine-N,N,N′,N′-tetra-acetic acid) but form less stable complexes due to less favourable heats of reaction. The transition-metal complexes of L1 do not follow the Irving-Williams order of stability, contrary to the situation with complexes of L2. The reason for the inversion of the stability order is discussed in terms of the changes in crystal field stabilization energies when the octahedrally co-ordinated aqueous ions form complexes of a different structure, either five-co-ordinated or tetrahedral.

The macrocyclic and cryptate effect. 2. Complexation of silver(I) by different ligands in methanol

The complex formation of Ag + with a variety of noncyclic ligands, crown ethers, aza crown ethers and cryptands has been studied in methanol by potentiometric and calorimetric titration. From the measured reaction enthalpies with different noncyclic ligands it is deduced that the bond strength between the silver ion and different donor atoms decrease in the order: N > S > O. A macrocyclic effects for ligands containing only oxygen as donor atoms was found, caused by a favourable entropic change. Complexes of aza crowns and their non-cyclic analogues have the same stabilities. The existence of different conformations of the cyclic ligands is mainly responsible for the absence of the macrocyclic effect. A cryptate effect for the complexation of Ag + was observed, due to an increase in Δ H.

HOST-GUEST-TYPE ACID CATALYSTS DERIVED FROM CALIX[6]ARENE

Abstract Water-soluble calix[6]arenes bearing both acidic protons and sulfonate groups were synthesized. They catalyzed a hydration reaction of 1-benzyl-1,4-dihydronicotinamide (BNAH) according to Michaelis-Menten kineticts and the rate constants were greater by 426–1220 fold than those for noncyclic analogues. Fluorescence data supported the complexation of BNAH with these water-soluble calixarenes. These findings indicate that calixarenes serve as a new starting material to design functionalized host molecules.

Nuclear magnetic resonance studies of the protonation sequence of cyclic tetra-azatetra-acetic acids

The protonation sequence of a cyclic tetra-azatetra-acetic acids(cDOTA, cTRITA, cTETA, and cPENTA) was studied by means of n.m.r. titration spectroscopy. The methods previously used for non-cyclic polyaminocarboxylates and for the most symmetrical members of the series, cDOTA and cTETA, did not prove adequate for the entire series. The shielding parameters CN and CN′ are different for each type of proton in the tetra-aza ring and acetate groups and vary with the pH of the medium. This behaviour can be attributed to changes in the conformation equilibria with the protonation of the various basic centres, in which electrostatic repulsions and hydrogen-bond formation play a role, and to the more restricted flexibility of these compounds compared to their non-cyclic analogues. CN and CN′, were estimated as functions of the probabilities of protonation of the carboxylate groups and used as such to derive protonation sequences of the cyclic polyaminocarboxylates by solving systems of linear equations relating chemical shifts to pH and to the number of equivalents of added acid. The results confirm that two nitrogens are protonated first in all four compounds and no protonation of the carboxylate groups occurs; further acidification results in preferential protonation of these groups from cDOTA to cTETA but not for cPENTA, which preferentially accepts a third proton in one nitrogen. cDOTA and cTRlTA do not protonate further in their nitrogens but such a tendency can be observed in cTETA and clearly in cPENTA which can be fully protonated in their nitrogens and carboxylates. The sequence of protonation in this case lends support to the formation of hydrogen bonds between protonated nitrogens and non-protonated carboxylates.

Binding specificity of serum amyloid P component for the pyruvate acetal of galactose.

Serum amyloid P component (SAP) is a normal plasma protein that is of interest because of its presence in amyloid deposits, its presence in normal human glomerular basement membrane, and its stable evolutionary conservation. It has calcium-dependent ligand-binding specificity for amyloid fibrils, fibronectin (Fn), C4-binding protein (C4bp), and agarose. Although the binding to agarose, a linear galactan hydrocolloid derived from some marine algae, is unlikely per se to be related to the physiological function of SAP, it does provide a model system in which to explore the precise ligand requirements of SAP. We report here that the amount of SAP from human, mouse, and plaice (Pleuronectes platessa L.) serum able to bind to agarose from different sources reflect precisely their pyruvate content. Methylation with diazomethane of the carboxyl groups in the pyruvate moiety of agarose completely abolishes SAP binding to agarose. The pyruvate in agarose exists as the 4,6-pyruvate acetal of beta-D-galactopyranose. We have therefore synthesized this galactoside, using a novel procedure, established its structure by analysis of its nuclear magnetic resonance spectra, and shown that it completely inhibits all known calcium-dependent binding reactions of SAP. The R isomer of the cyclic acetal, methyl 4,6-O-(1-carboxyethylidene)-beta-D-galactopyranoside (MO beta DG) was effective at millimolar concentration and was more potent than its noncyclic analogue, while pyruvate, D-galactose, and methyl beta-D-galactopyranoside were without effect. The autologous protein ligands of SAP presumably, therefore express a structural determinant(s) that stereochemically resembles MO beta DG. Availability of this specific, well-characterized, low molecular weight ligand for SAP should facilitate further investigation of the function of SAP and its role in physiological and pathophysiological processes.

Conformational effects upon the stability and reactivity of the [1.1]ferrocenophan-1-yl and diferrocenylmethyl cations

Rate and equilibrium constants have been measured for the interconversion of the [1.1]ferrocenophan-1-yl cation and [1.1]ferrocenophan-1-ol in H2O–MeCN (1 : 1 w/w) and compared with the corresponding values for interconversion of the diferrocenylmethyl cation and diferrocenylmethanol. The former cation is ca. 30 times more reactive towards addition of H2O than is the non-cyclic analogue and is formed ca. 325 times faster by heterolysis of the alcohol at a given acid concentration.

Enamines. 8. Polarographic study of the reactions of a number of enamino ketones with nucleophilic reagents

The hydrolysis and hydrazinolysis of cyclic enamino ketones of the pyrrolidine, piperidine, and hexahydroazepine series, as well as their noncyclic analogs, were investigated. It is shown that these processes have several principles in common. A bell-shaped dependence of kobs on the pH of the medium is characteristic for hydrolysis; the reaction of the enamino ketones with hydrazine hydrate in absolute ethanol is accelerated in the presence of p-toluenesulfonic acid. It is shown that the rates of hydrolysis and hydrazinolysis depend on the size of the saturated azaheteroring and change in the order 6 > 5 > 7. A possible mechanism for the processes in which the slow step is C-protonation and(or) attack by the nucleophilic reagent in the “enamine” α position is discussed.

Lactam acetals and acid amides. 31. Synthesis, protonation, and basicities of some heterocyclic enamino ketones

The protonation of cyclic enamino ketones of the pyrrolidine, piperidine, and hexahydroazepine series, as well as their noncyclic analogs, was studied by PMR spectroscopy. It is shown that the presence of a CH2 or CH3 group in the “enamine” position leads to C protonation (in CF3COOH). In the case of enamino ketones that do not contain substituents in the “enamine” α position N-and O-protonated forms are observed in CF3COOH. The measured pKa values (in 10% alcohol) and the ΔpKa values (in nitromethane) of the enamino ketones show that the compounds for which C protonation is characteristic are two to three orders of magnitude more basic than in the case of compounds that do not contain substituents in the “enamine” α position; this is explained by the different character of protonation.

Durable‐press cotton with improved retentions of strength and abrasion resistance via N‐methylolpolyethyleneurea D.P. 2

AbstractDiethylenetriamine was reacted with urea to form a noncyclic analog of ethyleneurea (one of the lowest members of a series of linear polyethyleneureas) which was characterized spectroscopically. Its reaction with formaldehyde to yield the N‐methylol derivative (N‐methylolpolyethyleneurea, degree of polymerization 2; NMP‐2) was investigated. The polymerization characteristics of the NMP‐2 were studied and compared with those of N‐methylol derivatives of cyclic ethyleneurea (related structurally) and melamine (related polyfunctionally). The NMP‐2 was applied to cotton fabrics by a pad–dry–cure process with Al2(OH)5Cl·2H2O as the polymerization crosslinking catalyst. Fabrics treated with the experimental reagent developed high levels of resilience (durable press appearance) and were characterized by significantly higher than conventional levels of retained strength and abrasion resistance. Analyses by electron microscopy of fibers treated with NMP‐2 and with the predominant conventional reagent, dimethyloldihydroxyethyleneurea, are reported. Attractive performance properties are discussed and attributed, at least in part, to rapid polymerization accompanying, or in advance of, etherification of cellulosic hydroxyl groups.

N-Methylolpolyethyleneureas-Reagents Yielding Durable-Press Cotton Fabrics with Improved Retention of Strength-Abrasion Resistance

Polyethylenimines, degree of polymerization = 1-5, 7, and 14, were reacted with urea to form oligomeric noncyclic analogues of ethyleneurea that were subsequently treated with formaldehyde to yield the corresponding N-methylol polyethyleneureas. All seven of these oligomers were shown to undergo facile acid-catalyzed gelation at 50°C. They were applied to cotton twill with Al2(OH)2Cl.2NH2O as the crosslinking/polymerization catalyst. The textile properties of these fabrics were compared with those of fabrics treated with ten conventional crosslinking reagent/catalyst systems. The fabrics finished with the N methylolpolyethyleneureas had significantly higher than conventional levels of retained strength and abrasion resistance at comparable durable-press appearance ratings. The best balance of properties oc curred when the degree of polymerization of the N-methylolpolyethyleneurea was in the 2-4 range. Microscopical studies indicated a more open, less tightly cross-linked structure in the N-methylolpolyethyleneurea fabrics relative to fabrics treated with conventional reagents. The attractive performance properties conferred by the N-methylolpolyethyl eneureas are attributed to the ability of the reagent to penetrate the cotton fiber, undergo facile polymerization and moderate cellulosic crosslinking, deposit small amounts of resin on fiber surfaces, and yield modified fibers that are more open and less tightly crosslinked than are conventionally crosslinked fibers.

Improved Durable-Press Cotton via Polymeric N-Methylol Reagents

Polyethylenimines, degree of polymerization = 7 and 14, were reacted with urea to form polymeric noncyclic analogues of ethyleneurea that were subsequently treated with formaldehyde to yield N-methylol derivatives. These reagents were applied to cotton fabric both alone and in combination with dimethyloldihydroxyethyleneurea. Al2(OH)5Cl·2H2O was the preferred crosslinking catalyst. Fabrics finished with these crosslinking reagent systems had durable-press properties generally comparable to those of fabrics prepared by conventional techniques but were characterized by significantly higher levels of retained strength and abrasion resistance.

The stabilities of Meisenheimer complexes. Part VIII. Equilibrium and kinetic data for spiro-complex formation in water

Equilibrium and rate constants for the formation in water of spiro-complexes from four ring-activated aromatic glycol ethers are reported. Values of the rate constants K–1 for opening of the dioxolan ring of these complexes are much higher than those for the expulsion of base from non-cyclic analogues. This may indicate ring strain in the spiro-complexes.

The stabilities of Meisenheimer complexes. Part IX. The general acid catalysed ring opening of spiro-complexes

The ring opening of two spiro-Meisenheimer complexes to give respectively 1-(2-hydroxyethoxy)-2,4,6-trinitrobenzene and 1-(2-hydroxyethoxy)-2,4-dinitronaphthalene is found to be subject to general acid catalysis in water. The α value of the Bronsted equation is 0·5. The isotope effect of the hydronium ion catalysed reaction KD3O+/KH3O+= 1·5. A mechanism is proposed involving concerted oxygen protonation and C–O bond breaking. The uncatalysed reaction is shown to proceed by a unimolecular mechanism rather than a bimolecular reaction with water. The results are compared with those for non-cyclic analogues.

The molecular association of small organosilicon heterocycles and their analogs

The molecular association of derivatives of the 1-silacycloalkanes CH2(CH2)n−1SiXY and their saturated and unsaturated noncyclic analogs has been studied by cryoscopy in cyclohexane. It has been established that in this series of heterocycles the tendency to association falls with an increase in their size and is a maximum in the case of the silacyclobutanes (n=4). Derivatives of 1-silacyclobutane are associated considerably more strongly than their noncyclic analogs CH2=CH(CH3)XiXY and CH3CH2(CH3)SiXY. The relationship found between the degree of association and the structure is in harmony with the results of studies of molecular association by UV spectroscopy and also with data on reactivities.

The effect of spatial factors on the reaction of arylmercuric hydroxides with N-acids

1. The reaction of phenylmercuric hydroxide with a series of cyclic-N-acids and sulfamides was investigated. 2. The compounds mentioned above, in contrast to the noncyclic analogs studied earlier with a conformation stabilized by conjugation, form C6H5Hg derivatives. 3. Steric hindrances, created by groups whose conformation is not immobilized by resonance, do not hinder the formation of phenylmercuric derivatives of the N-acids.