Gheorghe Surpateanu

Analytical Improvement in Measuring Formation Constants of Inclusion Complexes between β-Cyclodextrin and Phenolic Compounds

Inclusion complex formation betweensixteen para-substituted phenols andβ-cyclodextrin have been investigated in orderto establish Quantitative Structure AffinityRelationships. An analytical methodology is proposed,in order to obtain reliable evaluation of bindingaffinities. Potentiometry and circular dichroism havebeen applied to define experimental conditions and toconfirm postulated equilibriums. In addition, the useof algorithmic treatments and concentrationoptimisation to determine formation constants leads tocoherent values between 1H NMR, direct UVSpectroscopy and the spectral displacement method. Theresults emphasise the contribution of van der Waalsinteractions, provided that no significant differencein the dipole of the molecule arises from thepara-substituent.

Fenton degradation assisted by cyclodextrins of a high molecular weight polycyclic aromatic hydrocarbon benzo[a]pyrene.

This paper investigates the effect of native beta-cyclodextrin (beta-CD) and its CD derivatives, such as hydroxypropyl-beta-cyclodextrin (HPBCD) and randomly methylated-beta-cyclodextrin (RAMEB), on the solubilization of a high molecular weight polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) and on its degradation by Fentons reaction. The results show that BaP apparent solubility was significantly increased in the presence of cyclodextrin (CD) in the following order: beta-CD<RAMEB<HPCD. BaP Fenton degradation was strongly dependent on the capacity of cyclodextrin to solubilize BaP. In the presence of a radical scavenger (mannitol), BaP Fenton degradation was inhibited with RAMEB but not in the presence of HPCD. Molecular modelisation was used to visualize the steric complementarity of these host-guest systems. No significant difference of encapsulation between the two modified CDs was observed. Nevertheless, the results suggest a probable existence of a ternary complex HPCD-BaP-iron permitting the generation of hydroxyl radicals in close proximity to BaP. On the basis of these results, it appears that HPCD may be useful for developing targeted BaP degradation system.

Benzo[a]pyrene degradation using simultaneously combined chemical oxidation, biotreatment with Fusarium solani and cyclodextrins.

The interest of simultaneously combining chemical (Fentons reaction) and biological treatments for the degradation of a high molecular weight polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) has been studied in laboratory tests. An optimal concentration of 1.5x10(-3) M H(2)O(2) as Fentons reagent was firstly determined as being compatible with the growth of Fusarium solani, the Deuteromycete fungus used in the biodegradation process. For the enhancement of BaP solubilisation, cyclodextrins were also used in the performed tests. The best degradation performance was achieved through the use of 5x10(-3) M hydroxypropyl-beta-cyclodextrin (HPBCD) in comparison with randomly methylated-beta-cyclodextrin (RAMEB). When Fentons treatment was combined with biodegradation, a beneficial effect on BaP degradation (25%) was obtained in comparison with biodegradation alone (8%) or with chemical oxidation alone (16%) in the presence of HPBCD for 12 days of incubation.

Experimental and Theoretical Study on the Inclusion Compounds of Aroma Components with β-Cyclodextrins

Inclusion equilibria between four aroma components suspected to be allergen and various β-cyclodextrins were investigated. The association constants of inclusion complexes were measured in aqueous solution by UV/VIS spectroscopy by competition method with methyl orange and direct titration. The data indicated the formation of 1:1 inclusion compounds. In addition, a theoretical study using MM3 force field was conducted and the computed formation energy, e.g. the stability of the complexes, were in good agreement with the calculated formation constants.

Microwave effects in the synthesis of polyethers by phase transfer catalysis

Phase transfer catalysis processes with or without microwave fields are studied. A polycondensation reaction was used as a model, starting from 3,3-bis(chloromethyl)oxetane and various bisphenols. The results obtained show the advantages of microwave fields, concerning the molecular weights for crystalline polymers and the reaction time for all types of structures.

One and Two-dimensional NMR Investigations of the Inclusion of the Monosulfonated Triphenylphosphine in the β-cyclodextrin

The interaction between the sodium salt of the monosulfonated triphenylphosphine and the g -cyclodextrin has been investigated in aqueous solution by high field nuclear magnetic resonance and UV-Vis spectroscopies. Continuous variation and titration plots obtained from NMR and UV-Vis data indicate formation of a 1:1 inclusion complex and allow to calculate an association constant of 12,000 M m 1 at 25C. The T-ROESY NMR experiments complemented by molecular modelling suggest that one of non-sulfonated aromatic rings is included into the hydrophobic cavity of the g -cyclodextrin from the side of secondary hydroxyl groups. Formation of inclusion complex with the f - and n -cyclodextrin is also briefly discussed.

A comparative study by AM1, PM3 and ab initio HF/3-21G methods on the structure and reactivity of monosubstituted carbanion 1,2,4-triazolium ylides

Abstract A full conformational analysis of six 1,2,4-monosubstituted carbanion 1,2,4-triazolium ylides 4 a – f was performed using AM1, PM3 and HF/3-21G methods. The C -type conformers were found as the most stable structures by these different methods. This study also includes a qualitative estimation of the chemical behavior of triazolium ylides 4 a – f as nucleophilic agents on the level of ylide carbon atoms. The ab initio 3-21G method seems to be the most suitable in the characterization of these molecular systems.

Structure and reactivity of cycloimmonium ylides. Theoretical study in triazolium ylides by AM1, PM3 and DFT procedure methods

Abstract This paper reports some general remarks on structure and reactivity of monosubstituted and disubstituted cycloimmonium ylides. The results have been achieved by calculations on ylide bond lengths, bond orders, dipolar moments and rotational barriers. Some aspects have been followed on charges and high-occupied molecular orbital coefficients of ylide carbon atoms during rotation around ylide bond. The AM1, PM3 and DFT procedure methods have been used in this study. Three ylidic systems have been selected as models of cycloimmonium ylides: (a) 1-ethoxycarbonylmethyl 1,2,4-triazol-1-ium 4′-nitrobenzoyl 2″,4″,6″-trinitrophenyl methylides, (b) 4-phenylbenzoyl 1,2,4-triazol-1-ium methylide and (c) 4-phenyl dibenzoyl 1,2,4-triazol-1-ium methylide. DFT and AM1 procedure methods are appropriate for the description of monosubstituted cycloimmonium ylides. Only DFT procedure method is recommended for the description of the non-planar disubstituted cycloimmonium ylides. The resonance interaction in planar monosubstituted and planar disubstituted cycloimmonium ylide systems permits to carry out 3+2 cycloadditions preferably in non or less polar solvents.

Study of the Inclusion Complexes of β-Cyclodextrin with the Sodium Salt of Trisulfonated Triphenylphosphine

The formation of inclusion complexesbetween the sodium salt of trisulfonatedtriphenylphosphine and β-cyclodextrin has beeninvestigated at two temperatures by high field nuclearmagnetic resonance, electrospray mass and UV-visspectroscopies. At 268 K, titration experiments andJobs method suggest that the major species insolution is a 1 : 1 inclusion complex. The moleculargeometry of this inclusion complex was studied usingthe ROESY NMR technique complemented by molecularmodelling. All these methods converged towards thestructure attained by inserting one aromatic ring intothe hydrophobic cavity of the host from the side ofthe secondary hydroxyls. At 298 K, a higher proportionof 2 : 1 and 3 : 1 complexes induces strong alterations ofthe NMR signals, preventing an easy and reliabledetermination of association constants. Nevertheless,an apparent association constant can be determinedfrom UV-vis data by assuming a 1 : 1 equilibrium. Thegeometry of the 2 : 1 and 3 : 1 complexes is also brieflydiscussed from ROESY NMR experiments.

A comparative study by AM1 and PM3 methods on the structure and reactivity of disubstituted carbanion 1,2,4-triazolium ylides

Abstract A full conformational analysis of six 1,2,4-disubstituted carbanion 1,2,4-triazolium ylides 1a – f was performed using AM1 and PM3 methods. The D type conformers were found to be the most stable structures by these different methods. This study also includes a qualitative estimation of the chemical behavior of these disubstituted ylides in electrocyclization reactions, in order to form 1H-1,2,4-triazolo[5,1a] isoindoles 3 .