Current Physical Chemistry - Volume 1, Issue 2, 2011

In order to examine new spectroscopic properties about intermolecular interactions, we prepared four Pd(II) complexes, trans-[Pd(phent)2(R-phenea)2] (1), trans-[Pd(phent)2(R-phenea)(S-phenea)] (2), trans-[Pd(succim)2 (12diphenea)2] (3), and trans-[Pd(succim)2(CH3NH2)2] (4), and we detected intensity and shift of absorption and fluorescence spectra with some photochromic dyes, azobenzene (AZ), stilbene (ST), 4-[ethyl(2-hydroxyethyl)amino]-4'- nitroazobenzene (DR1), 1,3,3-trimethylindolino-6'- nitrobenzopyrylospiran (SP1), and 1,3,3-trimethylindolino-8'- methoxybenzopyrilospiran (SP2), dissolved in several organic solvents before and after UV and visible light irradiation. Among them, a hybrid system of 4 and AZ in CHCl3 solution exhibited characteristic spectral enhancement by mixing at 320 nm of absorption spectra with a new peak emerging at 520 nm of fluorescence spectra accompanying by cis-trans photoisomerization of AZ.

A series of organic/inorganic hybrid materials containing two kinds of chiral Schiff base Mn(II) complexes, 1 and 2, with the photochromic compounds stilbene (ST) or 1,3,3-trimethylindolino-6'-nitrobenzopyrylospiran (SP) cast into polymethyl methacrylate (PMMA) films were prepared. To understand the efficiency of increasing optical anisotropy of ST or SP resulting from polarized UV light irradiation, we investigated the molecular alignment based on Weigert effect (only polarized UV light irradiation) and photoisomerization (alternate irradiations with polarized UV and visible light) for 1-ST-PMMA, 2-ST-PMMA, 1-SP-PMMA, and 2-SP-PMMA. Polarized electronic spectra and polarized IR spectra of the hybrid materials demonstrated gradually increasing anisotropy of both photochromic compounds and Mn(II) complexes and only Mn(II) complexes, respectively. These features suggest that interactions of ST are valid for both Weigert effects and photoisomerization, while those of SP are valid for photoisomerization mainly, and intermolecular interaction of 2 between photochromic compounds and Mn(II) complexes in PMMA cast films is weaker than that of 1.

The importance of nonfouling (bioadhesion-resistant) coatings of solid surfaces has been emerging in various fields ranging from biomedicine to shipbuilding. Although a large number of approaches to endow the solid surfaces with bioinertness have been reported, a thorough understanding of the mechanism underlying the bioinertness of surfaces at a molecular level has not been achieved. Self-assembled monolayers (SAMs) provide powerful platforms on which to systematically investigate the processes of adsorption and adhesion of biomolecules, because of the tunability of their surface chemical properties depending on terminal groups and well-defined structures. In this review, we introduce types of bioinert SAMs and focus especially on the SAMs of oligo(ethylene glycol)-terminated alkanethiols on gold surfaces (OEG-SAM), which have been the most investigated nonfouling monolayers. We survey works that elucidate the mechanism underlying the bioinertness of the nonfouling SAMs using experimental and theoretical techniques and summarize the present situation of this field. We also mention nonfouling polymer surfaces and discuss perspectives to bridge the findings of monolayers and polymers.

The role of lateral terminal (X2 and X3) and terminal (X1) positions of aryl ring on the second-order nonlinear optical (NLO) properties of arylimido derivatives of hexamolybdates have been examined by using time-dependent density functional response theory (TD-DFT). This group of organic-inorganic hybrid compounds holds considerable large molecular second-order NLO response, especially [Mo6O18 (NC6H2 (NH2)3)]2- (system 4) with the static secondorder polarizability (βvec) computed to be 4406.60 au. Hence, [Mo6O18 (NC6H4NH2)]2- (system 2) and [Mo6O18 (NC6H2 (CH3)2 NH2)]2- (system 3) have also possibility to be good second-order nonlinear optical materials as compared to [Mo6O18 (NC6H5)]2- (system 1). The study of the major contribution to the βvec value suggests that the charge transfer from arylimido to molybdate (D-A) along the z-axis plays an important part in the NLO response, arylimido acts as a donor (D) whereas molybdate (POM-cluster) acts as an acceptor (A) in all the studied systems. The computed βvec values increase by incorporation of an electron donor (-NH2) at the terminus of phenyl ring. Moreover, substitution of amino (-NH2) at the lateral terminal positions and the terminus of aryl ring is simultaneously dominant to increase the optical nonlinearity. The present exploration offers significant physical insight into the considerable large NLO properties of arylimido substituted hexamolybdates.

A micro static-bomb combustion calorimeter has been developed in our laboratory designing one small cell to obtain combustion heats, which requires only a smaller sample quantity. The energy equivalent of the combustion system has been provided with a new micro-bomb. In the best conditions of operation, the energy equivalent of this calorimetric arrangement is just ε(calor)= (1,1679 ± 0,0004) kJK-1, which means an uncertainty of 0,03% for the calibration with benzoic acid NIST 39 Joule. This combustion calorimeter has been used in the measurement of the enthalpy of combustion of m-methoxybenzoic acid and salicylic acid, giving (-24,21876 ± 0,00102) kJg-1 and (-21,0078 ± 0,0025) kJg-1, respectively, for these substances.

Five levels for emphasizing the electronegativity and chemical hardness quantum chemical differences were reviewed: the analysis of their quantum definitions in Fock space, their reliability in providing atomic patterns of periodicity within density functional softness as well as the semiclassical quantum propagator/Green function based theories as compared to the traditional finite difference methods based on ionization potential and electronic affinity, in providing viable relationships with other aromaticity energetic, magnetic, topologic and geometric criteria, and exposing their sensitivity to the media or solvent effects. The revealed differences reflect the special role electronegativity and chemical hardness play in modeling chemical reactivity and chemical bonding by associating fundamental principles along with the conceptual and computational quantum methods in approximating, implementing, and combining the energy and density quantities and related properties of a multi-electronic multi-nuclei system; still, based on revealed quantum differences, the associate hierarchy of principles in chemical bonding is established and the idea of chemical orthogonal space having electronegativity and chemical hardness as main vectors is advanced.

First derivative fluorescence spectroscopy was used to monitor the kinetics of SN38 hydrolysis in the presence and absence of serum albumins at physiological pH. In plain phosphate-buffered saline (PBS) pH 7.4, it was found that SN38-lactone hydrolysis exhibited a positive Enthalpy (12.08 ± 3.8 kJ · mol-1) and Entropy (54.40 ± 12.8 J · K-1 · mol-1) indicating that SN38-lactone hydrolysis is endothermic and entropically driven. Hydrolysis of SN38 observed at multiple temperatures in the presence of serum albumin revealed that despite the similar values of activation energy involved in all the reaction media, SN38-lactone hydrolysis was prevented to a greater extent by the presence of human serum albumin (HSA), compared to the absence or in presence of bovine serum albumin (BSA). Taken together with the association constants KA, as estimated from static fluorescence quenching experiments and steady-state emission anisotropy, it is suggested that the greater stabilization of SN38-lactone in the presence of HSA is due to the significantly higher binding affinity of the SN38-lactone species and the weaker binding of the SN38-carboxylate moiety as opposed to the binding of the respective species to BSA.

In 1998 the American Chemical Society and the Indian Association for the Cultivation of Science, Kolkata (India) designated the discovery of the Raman effect as an International Historic Chemical Landmark. Today it is well-known that Raman spectroscopy and Infrared spectroscopy are supplementary so far the chemical-structure analysis based on vibration of the atoms and molecules is concerned. In the present communication a short history of the discovery of the two techniques as well as their applications by the chemists until 1940 are given.

A transmission line model was employed to interpret the impedance response of pol(o-aminophenol) (POAP) film electrodes in contact with sulfate and benzenesulfonate (BS) solutions. These two different anions were chosen due to their different characteristics of size and electron distribution, which assures a different interaction with the redox centers of the polymer. Electron (De) and ion (Di) diffusion coefficient values were separately obtained. Both diffusion constants depend on the type of anion present in the electrolyte solution. The effect of sulfate and BS anions on the electron conduction of poly(o-aminophenol) was explained in terms of their abilities to reduce repulsive interactions between redox sites of the polymer. In this regard, sulfate anions seem to be more effective than BS ones to attenuate repulsive interactions between redox centers of POAP. Also, both parameters depend on the electrolyte concentration and film thickness. These effects were attributed to incorporation of electrolyte into the porous structure of POAP. The increase of the ion conduction of POAP with the incorporation of electrolyte was attributed to a contribution of the counterions, contained in the inner electrolyte, to the charge transport process.