Structure and Photochemical Behavior of the Cyclodextrin Inclusion Complexes of the Benzoylthiophene‐Derived Drugs Tiaprofenic Acid (=5‐Benzoyl‐α‐methylthiophene‐2‐acetic Acid) and Suprofen (=α‐Methyl‐4‐(2‐thienylcarbonyl)benzeneacetic Acid)

The effect of β‐cyclodextrin (β‐CD) on the excited‐state reactivity of the two benzoylthiophene derivatives, tiaprofenic acid (TPA; 2 ) and suprofen (SPF; 3 ) in their carboxylate forms is studied. The presence of β‐cyclodextrin does not affect the nature of the photoproduced transients and the photoproducts, but increases the photodegradation quantum yields of both drugs. The efficiency of the photodecarboxylation process is enhanced. This effect is rationalized in the light of the inclusion of 2 and 3 in the β‐CD cavity, affecting the energy of the lowest excited states of the drugs. The structure of the complexes is determined by induced circular dichroism, and molecular‐mechanics and dynamic Monte Carlo calculations. The photoreactivity of the decarboxylated photoproduct 7 of tiaprofenic acid ( 2 ) in presence of β‐CD is also examined.     

Novel Chitosan-Based Schiff Base Compounds: Chemical Characterization and Antimicrobial Activity

Chitosan (CS) and its derivatives are receiving considerable attention for their great biocompatibility and broad-spectrum activities in many fields. In this work, we aimed to characterize the antimicrobial activity of novel chitosan Schiff bases (CSSB). CS was synthesized by double deacetylation of chitin (Cn) after its extraction from the armors of crustaceans Astacus leptodactylus, and CSSB-1 and CSSB-2 were synthesized by interaction of CS with 4-(2-chloroethyl) benzaldehyde (aldehyde-1) and 4-(bromoethyl) benzaldehyde (aldehyde-2), respectively, at room temperature. The synthesized compounds were characterized by elemental analysis, gel permeation chromatography (GPC), infrared spectroscopy (FTIR), thermogravimetry (TG), and differential scanning calorimetry (DSC). The antimicrobial activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria and against yeasts (Candida albicans) was significantly increased due to their higher solubility as compared to unmodified CS opening perspectives for the use of these compounds for antimicrobial prevention in different fields as, for example, food industry, cosmetics, or restoration.     

Model with uniquely deducible parameters for the combined analysis of two resonating vibrational states. Anharmonic resonances in molecules of asymmetric-gyroscope type

A model of an effective Hamiltonian with parameters that are uniquely deducible from the spectrum for the combined analysis of the rotational structure of two resonating vibrational states is proposed and validated. Anharmonic resonances in molecules of asymmetric-gyroscope type are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 108–112, February, 1982.     

Redox-induced coordination isomerization of a phosphoniobenzophospholide

1-Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)(5)Br] (M = Mn, Re) and [Mn(CO)(3)(naphthalene)][BF(4)] to give complexes cis-[M(CO)(4)(1)Br] (5 a,b) and [Mn(CO)(3)(1)][BF(4)] (6 a[BF(4)]), respectively, featuring eta(1)(P)- and eta(5)(pi)-coordination of the phosphole ring. The corresponding reactions with [M(2)(CO)(10)] proceed with conservation of the metal-metal bond and yield, depending on the reaction temperature, dinuclear complexes [M(2)(CO)(8)(1)] (M=Mn, 7 a) or [M(2)(CO)(6)(1)(2)] (M=Mn, Re, 8 a,b) with mu(2)-bridging eta(1)(P):eta(2)(Pdbond;C) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF(4)], and 8 a,b were characterized by X-ray diffraction studies as well. The structural and (31)P NMR data of the dinuclear manganese complex 8 a suggest that the interaction between the metal atoms and the eta(2)-bound Pdbond;C double bond moieties is dominated by the L-->M charge-transfer contribution; this hints at a very low back-donation ability of the central M(2)(CO)(6) fragment. Investigation of the reactions of the Mn complexes 6 a and 8 a with Mg or ferrocenium hexafluorophosphate ([Fc][PF(6)]), respectively, revealed that the chemically reversible mutual interconversion between both species was feasible. Likewise, oxidation of the rhenium complex 8 b with [Fc][PF(6)] gave spectroscopic evidence for the formation of a Re analogue of 6 a. Electrochemical studies suggested that the oxidation 8 a-->2 6 a involves two consecutive single-electron-transfer steps, the first of which is electrochemically reversible and produces a metastable radical cation that is detectable by ESR spectroscopy. The mutual interconversion between 6 a and 8 a represents the first case of a reversible coordination isomerization of a phosphaarene that is triggered by a redox process and might stimulate further studies directed at the use of dinuclear phosphaarene complexes in redox-catalysis.     

Structure and spectroscopic properties of cyclodextrin inclusion complexes

We compare spectroscopic properties of higher order complexes of organic guests (e.g. naphthalene, phenols, indole, C₆₀ fullerene) with cyclodextrins (CDx) to results of molecular modeling investigations. Naphthalene 1:2 complexes with -CDx show high spectral resolution and peculiar triplet properties. Molecular simulations and calculation of the experimentally measured induced circular dichroism (ICD) provide detailed structural information.     

Photodecarboxylation of ketoprofen in aqueous solution. A time-resolved laser-induced optoacoustic study

The photodecarboxylation reaction of 2-(3-benzoylphenyl)propionate (ketoprofen anion, KP-) was studied in water and in 0.1 M phosphate buffer solutions in the pH range 5.7-11.0 by laser-induced optoacoustic spectroscopy (LIOAS, T range 9.5-31.6 degrees C). Upon exciting KP- with 355 nm laser pulses under anaerobic conditions, two components in the LIOAS signals with well-separated lifetimes were found (tau 1 < 20 ns; 250 < tau 2 < 500 ns) in the whole pH range, whereas a long-lived third component (4 < tau 3 < 10 microseconds) was only detected at pH < or = 6.1. The heat and structural volume changes accompanying the first step did not depend on pH or on the presence of buffer. The carbanion resulting from prompt decarboxylation within the nanosecond pulse (< 10 ns) drastically reduces its molar volume ([-18.9 +/- 2.0] cm3/mol) with respect to KP- and its enthalpy content is (256 +/- 10) kJ/mol. At acid pH (ca 6), a species is formed with a lifetime in the hundreds of ns. The enthalpy and structural volume change for this species with respect to KP- are (181 +/- 15) kJ/mol and (+0.6 +/- 2.0) cm3/mol, respectively. This species is most likely a neutral biradical formed by protonation of the decarboxylated carbanion, and decays to the final product 3-ethylbenzophenone in several microsecond. At basic pH (ca 11), direct formation of 3-ethylbenzophenone occurs in hundreds of ns involving a reaction with the solvent. The global decarboxylation reaction is endothermic ([45 +/- 15] kJ/mol) and shows an expansion of (+14.5 +/- 0.5) cm3/mol with respect to KP-. At low pH, the presence of buffer strongly affects the magnitude of the structural volume changes associated with intermolecular proton-transfer processes of the long-lived species due to reactions of the buffer anion with the decarboxylated ketoprofen anion.     

Co-conformational variability of cyclodextrin complexes studied by induced circular dichroism of azoalkanes.

The solution structures of the beta-cyclodextrin complexes between 2,3-diazabicyclo[2.2.2]oct-2-ene (1) and its 1-isopropyl-4-methyl derivative 2 have been investigated by means of induced circular dichroism (ICD) and MM3-92 force-field calculations, which considered the effect of solvation within a continuum approximation. Of primary interest was the so-called co-conformation of the host-guest complex, i.e., the relative orientation of the guest within the host. A pool of low-energy complex structures, which were located by means of a Monte Carlo simulated annealing routine, was generated to evaluate the dynamic co-conformational variability of the complexes. The ICD effects were calculated for the computed low-energy structures by applying a semiempirical method. The experimental and theoretical ICD as well as the calculated low-energy complex geometries suggest solution co-conformations in which the parent compound 1 adapts a lateral arrangement with the ethano bridge of the guest penetrating deepest into the cavity and the azo group aligning parallel to the plane of the upper rim. In contrast, the alkyl derivative 2 prefers a frontal co-conformation with the isopropyl group penetrating deepest into the cavity and the azo group aligning perpendicular to the plane of the upper rim. The validity of the predictions of the Harata rule regarding the sign and the intensity of the ICD signals for the n(-)pi, n(+)pi, and pipi transition of the azo chromophore in dependence on the complex co-conformation are discussed. With respect to the co-conformational variability of the complexes of the two azoalkanes, it was observed that the nearly spherical guest 1 forms a geometrically better defined complex than the sterically biased, alkyl-substituted derivative 2. This dichotomy is attributed to the largely different modes of binding for azoalkanes 1 and 2. It is concluded that the goodness-of-fit in a host-guest complex cannot be directly related to the "tightness-of-fit".     

Charge-transfer complexes betweenp-toluidine and iodine in solution: A kinetic study

The kinetics of charge-transfer interaction betweenp-toluidine and iodine in methylene chloride was investigated in depth. Thethermal process of formation of theinner complex was found to proceed to an equilibrium. Thephotochemical process follows a different reaction coordinate, going through the formation of an exciplex between the excitedouter complex and the amine ground state. In both cases the same ionic complex (Am ₂I⁺I ₃ ^– , whereAm stands forp-toluidine) was detected as the final product.

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Kinetische Untersuchung der Charge-Transfer-Komplexe zwischenp-Toluidin und Jod

Zusammenfassung Die Kinetik der Charge-Transfer-Wechselwirkung zwischenp-Toluidin und Jod in Methylenchlorid wurde ausführlich untersucht. Derthermische Prozeß, der zur Bildung desinner-Komplexes führt, geht bis zu einem Gleichgewicht. Derphotochemische Prozeß folgt einer unterschiedlichen Reaktionskoordinate und verläuft über die Bildung eines Exziplexes zwischen dem angeregtenouter-Komplex und dem Amin im Grundzustand. In beiden Fällen wurde derselbe ionische Komplex (Am ₂I⁺I ₃ ^– , wobeiAm fürp-Toluidin steht) als Endprodukt festgestellt.

     

High-order anharmonicity parameters in various representations of the diatomic potential function and exact relations between spectroscopic constants. application to the co molecule

Closed formulae for Born—Oppenheimer anharmonicity parameters a_n in terms of isotopically invariant constants U_mj are derived for Dunham, Simons—Parr—Finlan, Ogilvie—Tipping and Thakkar representations and are applied to the CO molecule. Models for a fit of vibration—rotation and pure rotational transitions based on the exact relations U_mj = f(U_k,o, U_k-1.1) and U_mj = α(U_k,1, U_k,2) are discussed.     

Effective potential method for active particles

ABSTRACT

We investigate the steady-state properties of an active fluid modelled as an assembly of soft repulsive spheres subjected to Gaussian coloured noise. Such a noise captures one of the salient aspects of active particles, namely the persistence of their motion and determines a variety of novel features with respect to familiar passive fluids. We show that within the so-called multidimensional unified coloured noise approximation, recently introduced in the field of active matter, the model can be treated by methods similar to those employed in the study of standard molecular fluids. The system shows a tendency of the particles to aggregate even in the presence of purely repulsive forces because the combined action of coloured noise and interactions enhances the effective friction between nearby particles. We also discuss whether an effective two-body potential approach, which would allow to employ methods similar to those of density functional theory, is appropriate. The limits of such an approximation are discussed.