Metallocyclodextrin catalysts for hydrolysis of phosphate triesters

Cyclodextrines as Functional Agents for Decontamination of the Skin Contaminated by Nerve Agents

Three decontamination solutions of β-cyclodextrines were prepared. Their abilities to decontamine rat skin contamined with nerve agent soman were tested. Decontamination efficacy of the tested cyclodextrine solutions was compared with the same decontamination means but without the cyclodextrines. The efficacy of tested decontaminants was evaluated by the assessment of the ID50 values. Two decontamination prescriptions with cyclodextrines (tetraborate buffer and tetraborate buffer with acetone) do not show significantly better decontamination efficacies in comparison with prescriptions without cyclodextrines. Only in case of aqueous solution of 2–aminoethanol the addition of β-cyclodextrine resulted in significant increase (32%) in decontamination efficacy.

A Cyclodextrin-Based Photoresponsive Molecular Gate that Functions Independently of Either Solvent or Potentially Competitive Guests

The photoinduced interconversion between cinnamido-substituted cyclodextrins constitutes a gating switch through which the substituent moves to open or block access to the cyclodextrin cavity. Most unusually for a cyclodextrin-based device, the operation of this gate is solvent-independent and unaffected by potentially competitive guests. It occurs in MeOH and DMSO, as well as in water. This contrasts with other cyclodextrin inclusion phenomena that are usually driven by hydrophobic effects and limited to aqueous media.

Molecular Commonality Detection Using an Artificial Enzyme Membrane for in Situ One-Stop Biosurveillance

Biodetection and biosensing have been developed based on the concept of sensitivity toward specific molecules. However, current demand may require more levelheaded or far-sighted methods, especially in the field of biological safety and security. In the fields of hygiene, public safety, and security including fighting bioterrorism, the detection of biological contaminants, e.g., microorganisms, spores, and viruses, is a constant challenge. However, there is as yet no sophisticated method of detecting such contaminants in situ without oversight. The authors focused their attention on diphosphoric acid anhydride, which is a structure common to all biological phosphoric substances. Interestingly, biological phosphoric substances are peculiar substances present in all living things and include many different substances, e.g., ATP, ADP, dNTP, pyrophosphate, and so forth, all of which have a diphosphoric acid anhydride structure. The authors took this common structure as the basis of their development of an artificial enzyme membrane with selectivity for the structure common to all biological phosphoric substances and studied the possibility of its application to in situ biosurveillance sensors. The artificial enzyme membrane-based amperometric biosensor developed by the authors can detect various biological phosphoric substances, because it has a comprehensive molecular selectivity for the structure of these biological phosphoric substances. This in situ detection method of the common diphosphoric acid anhydride structure brings a unique advantage to the fabrication of in situ biosurveillance sensors for monitoring biological contaminants, e.g., microorganism, spores, and viruses, without an oversight, even if they were transformed.

Reversal of Regioselectivity and Enhancement of Rates of Nitrile Oxide Cycloadditions through Transient Attachment of Dipolarophiles to Cyclodextrins

The reactions of nitrile oxides with monosubstituted dipolarophiles, such as propiolamide, typically afford proportionally 80 % or more of the 3,5-disubstituted cycloadducts. By contrast, the reactions of 6(A)-deoxy-6(A)-propynamido-beta-cyclodextrin with 4-tert-butylbenzonitrile oxide and 4-phenylbenzonitrile oxide afford >90 % and approximately 85 % of the corresponding 3,4-disubstituted isoxazoles, respectively. As well as reversing the regioselectivity, the cyclodextrin increases the rates of these cycloadditions. The extent of the acceleration is up to more than three orders of magnitude for the production of the cycloadduct preferred by the cyclodextrin, but even the rate of reaction to give the less favored regioisomer is increased. With 6(A)-deoxy-6(A)-propynamido-beta-cyclodextrin, the cycloadducts are not easily separated from the cyclodextrin, as the amide bond is not readily cleaved. In comparison, the regioselectivity of the cycloadditions of 4-tert-butylbenzonitrile oxide with acrylic acid, methacrylic acid, and crotonic acid is also altered by formation of the corresponding cyclodextrin esters, by factors of 500, >10, and >100, respectively. The rates of cycloaddition are also increased by up to 475 times, and in these cases the products of cycloaddition are readily released from the cyclodextrin through ester hydrolysis. Incorporating these processes into a reaction cycle, acylation of beta-cyclodextrin with p-nitrophenyl acrylate and subsequent treatment first with 4-tert-butylbenzonitrile oxide and then with base, the latter to catalyze ester hydrolysis and regenerate the beta-cyclodextrin, affords proportionally fivefold more of the 3,4-disubstituted isoxazoline than is produced directly from acrylic acid.

Rapid phosphorus triester hydrolysis catalyzed by bimetallic tetrabenzimidazole complexes

Bimetallic complexes based on the binucleating ligand N,N,N',N'-tetrakis[(2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane (1L) and its new toluoyl ester derivative (2L) catalyze the hydrolysis of phosphorus triesters at ambient temperature with activities rivalling the fastest known systems.

Mechanistic studies of La3+ and Zn2+-catalyzed methanolysis of O-ethyl O-aryl methylphosphonate esters. An effective solvolytic method for the catalytic destruction of phosphonate CW simulants

The kinetics of methanolysis of six O-ethyl O-aryl methylphosphonates (6a-f) promoted by methoxide, La3+ and 1,5,9-triazacyclododecane complex of Zn2+(-OCH3) (5:Zn2+(-OCH3)) were studied as simulants for chemical warfare (CW) agents, and analyzed through the use of Brønsted plots. The beta(lg) values are, respectively, -0.76, -1.26 and -1.06, pointing to significant weakening of the P-OAr bond in the transition state. For the metal-catalyzed reactions the data are consistent with a concerted process where the P-OAr bond rupture has progressed to the extent of 84% in the La3+ reaction and ca. 70% in the Zn2+ catalyzed reaction. The catalysis afforded by the metal ions is remarkable, being about 10(6)-fold and 10(8)-fold for poor and good leaving groups, respectively, relative to the background reactions at pH 9.1. Solvent deuterium kinetic isotope studies for two of the substrates promoted by 5:Zn2+(-OCH3) give kH/kD = 1.0 +/- 0.1, consistent with a nucleophilic mechanism. A unified mechanism for the metal-catalyzed reactions is presented which involves pre-equilibrium coordination of the substrate to the metal ion followed by intramolecular delivery of a coordinated methoxide.

Aminocyclodextrins to facilitate the deprotonation of 4-tert-butyl-α-nitrotoluene

6A-Amino-6A-deoxy-beta-cyclodextrin enhances the rate of the deprotonation of 4-tert-butyl-alpha-nitrotoluene. The rate constants for reaction of the cyclodextrin-bound species, kinc = 4 x 10(-3), 9 x 10(-3) and 19 x 10(-3) s(-1), at pH 6.0, 6.5 and 7.0, respectively, in 0.1 mol dm(-3) aqueous phosphate buffer containing 1% methanol at 298 K. These rate constants correspond to a rate acceleration (kinc/kun) of ca. 10 times at each pH. Under the same conditions, 6A-dimethylamino-6A-deoxy-beta-cyclodextrin and 6A-(2-aminoethylamino)-6A-deoxy-beta-cyclodextrin are more effective; at pH 6.0, 6.5 and 7.0, for the former, kinc = 3 x 10(-2), 7 x 10(-2) and 12 x 10(-2) s(-1), whilst for the latter, kinc = 4 x 10(-2), 5 x 10(-2) and 9 x 10(-2) s(-1), respectively. Each cyclodextrin also decreases the pKa of the nitrotoluene, from 6.8 in free solution, to 6.2 when bound. The accelerated deprotonation by 6A-amino-6A-deoxy-beta-cyclodextrin is reflected in the enhanced rates of hydrogen-deuterium exchange of the nitrotoluene in deuterium oxide, and in the conjugate addition of the nitrotoluene to methyl vinyl ketone in aqueous solution.

Solvent deuterium kinetic isotope effects for the methanolyses of neutral CO, PO and PS esters catalyzed by a triazacyclododecane : Zn2+-methoxide complex

The methanolyses of several organophosphate/phosphonate/phosphorothioate esters (O,O-diethyl O-(4-nitrophenyl) phosphate, paraoxon, ; O,O-diethyl S-(3,5-dichlorophenyl) phosphorothioate, ; O-ethyl O-(2-nitro-4-chlorophenyl) methylphosphonate, ; O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate, fenitrothion, ; O-ethyl S-(3,5-dichlorophenyl) methylphosphonothioate ) and a carboxylate ester (p-nitrophenyl acetate, ) catalyzed by methoxide and the Zn(2+)((-)OCH(3)) complex of 1,5,9-triazacyclododecane ( : Zn(2+)((-)OCH(3))) were studied in methanol and d(1)-methanol at 25 degrees C. In the case of the methoxide reactions inverse skie's were observed for the series with values ranging from 2 to 1.1, except for where the k(D)/k(H) = 0.90 +/- 0.02. The inverse k(D)/k(H) values are consistent with a direct nucleophilic methoxide attack involving desolvation of the nucleophile with varying extents of resolvation of the TS. With the : Zn(2+)((-)OCH(3)) complex all the skie values are k(D)/k(H) = 1.0 +/- 0.1 except for where the value is 0.79 +/- 0.06. Arguments are presented that the fractionation factors associated with complex : Zn(2+)((-)OCH(3)) are indistinguishable from unity. The skie's for all the complex-catalyzed methanolyses are interpreted as being consistent with an intramolecular nucleophilic attack of the Zn(2+)-coordinated methoxide within a pre-equilibrium metal : substrate complex.

Mechanistic studies of La3+- and Zn2+-catalyzed methanolysis of aryl phosphate and phosphorothioate triesters. Development of artificial phosphotriesterase systems

The methanolyses of a series of O,O-diethyl O-aryl phosphates (2,5) and O,O-diethyl S-aryl phosphorothioates (6) promoted by methoxide and two metal ion systems, (La3+)2(-OCH3)2 and 4:Zn2+:-OCH3 (4 = 1,5,9-triazacyclododecane) has been studied in methanol at 25 degrees C. Brønsted plots of the logk2 values vs. pKa for the phenol leaving groups give beta(lg) values of -0.70, -1.43 and -1.12 for the methanolysis of the phosphates and -0.63, -0.87 and -0.74 for the methanolysis of the phosphorothioates promoted by the methoxide, La3+ and Zn2+ systems respectively. The kinetic data for the metal-catalyzed reactions are analyzed in terms of a common mechanism where there is extensive cleavage of the P-XAr bond in the rate-limiting transition state. The relevance of these findings to the mechanism of action of the phosphotriesterase enzyme is discussed.

Zn2+-Catalyzed Methanolysis of Phosphate Triesters: A Process for Catalytic Degradation of the Organophosphorus Pesticides Paraoxon and Fenitrothion

The methanolyses of two neutral phosphorus triesters, paraoxon (1) and fenitrothion (3), were investigated as a function of added Zn(OTf)(2) or Zn(ClO(4))(2) in methanol at 25 degrees C either alone or in the presence of equimolar concentrations of the ligands phenanthroline (4), 2,9-dimethylphenanthroline (5), and 1,5,9-triazacyclododecane (6). The catalysis requires the presence of methoxide, and when studied as a function of added NaOCH(3), the rate constants (k(obs)) for methanolysis of Zn(2+) alone or in the presence of equimolar 4 or 5 maximize at different [(-)OCH(3)]/[Zn(2+)](total) ratios of 0.3, 0.5, and 1.0, respectively. Plots of k(obs) vs [Zn(2+)](total) either alone or in the presence of equimolar ligands 4 and 5 at the [(-)OCH(3)]/[Zn(2+)](total) ratios corresponding to the rate maxima are curved and show a nonlinear dependence on [Zn(2+)](total). In the cases of 4 and 5, this is explained as resulting from formation of a nonactive dimer, formulated as a bis-mu-methoxide-bridged form (L:Zn(2+)((-)OCH(3))(2)Zn(2+):L) in equilibrium with an active monomeric form (L:Zn(2+)((-)OCH(3))). In the case of the Zn(2+):6 system, no dimeric forms are present as can be judged by the strict linearity of the plots of k(obs) vs [Zn(2+)](total) in the presence of equimolar 6 and (-)OCH(3). Analysis of the potentiometric titration curves for Zn(2+) alone and in the presence of the ligands allows calculation of the speciation of the various Zn(2+) forms and shows that the binding to ligands 4 and 6 is very strong, while the binding to ligand 5 is weaker. Overall the best catalytic system is provided by equimolar Zn(2+), 5, and (-)OCH(3), which exhibits excellent turnover of the methanolysis of paraoxon when the substrate is in excess. At a concentration of 2 mM in each of these components, which sets the pH of the solution at 9.5, the acceleration of the methanolysis of paraoxon and fenitrothion relative to the methoxide reaction is 1.8 x 10(6)-fold and 13 x 10(6)-fold, respectively. A mechanism for the catalyzed reactions is proposed which involves a dual role for the metal ion as a Lewis acid and source of nucleophilic Zn(2+)-bound (-)OCH(3).

Cu(ii)-Mediated decomposition of phosphorothionate PS pesticides. Billion-fold acceleration of the methanolysis of fenitrothion promoted by a simple Cu(ii)–ligand system

The kinetics of methanolysis of the title compound (3) were studied in the presence of Cu(2+), introduced as Cu(OTf), in the presence of 0.5-1.0 eq. of methoxide and in the presence of 1.0 eq. of a ligand such as bipyridyl (5), phenanthroline (6) or 1,5,9-triazacyclododecane (4). In all cases the active species involve Cu(2+)((-)OCH(3)). In the case of added strong-binding ligands 5 or 6, a plot of the observed rate constant for methanolysis of 3 vs. [Cu(2+)](total) gives a curved line modelled by a process having a [Cu(2+)](1/2) dependence consistent with an active monomeric species in equilibrium with an inactive dimer i.e.[LCu(2+)((-)OCH(3))](2) <==> 2LCu(2+)((-)OCH(3)). In the case of the added strong binding ligand 4, the plot of the observed rate constant for methanolysis of 3 vs.[Cu(2+)](total) gives a straight line consistent with the catalytically active species being Cu(2+)(OCH(3)) which shows no propensity to form inactive dimers. Turnover experiments where the [3] > [Cu(2+)](total) indicate that the systems are truly catalytic. In the optimum case a catalytic system comprising 1 mM of the complex 4Cu(2+)((-)OCH(3)) catalyzes the methanolysis of 3 with a t(1/2) of approximately 58 s accounting for a 1.7 x 10(9)-fold acceleration relative to the background reaction at near neutral (s)(s)pH (8.75).