Langmuir-Blodgett films of phycobiliproteins (I)——Monomolecular film and conformational studies of R-phycoerythrin

The surface pressure-area (π-A) isotherm of R-phycoerythrin (R-PE) at the air-water interface has been measured. The results indicate that R-PE can form the monomolecular film. Moreover, the molecule-occupied area extrapolating the linear part of the n-A isotherm is identical with that when an R-PE molecule is located at the interface with its disk plane parallel to the air-water interface. The transmission electron micrograph (TEM) and the measurement of the thickness of the protein monolayer by ellipsometry show that the orientation of R-PE disk plane on the substrate is parallel to the plane of substrate. Absorption and fluorescence spectra of R-PE LB multilayers were obtained through transferring R-PE monolayer at the air-water interface to the substrates at the proper surface pressure by Langmuir-Blodgett (LB) technique. These spectra of R-PE LB films do not show distinct differences from those in aqueous solution. Comparative studies of circular dichroism (CD) spectra of the protein between in aq     

Infrared and Raman studies of hydrogen bonded complexes involving acetone,acetophenone and benzophenone—II. Raman intensity of the vCO band

The effect of hydrogen bond formation on the Raman intensity of the v_CO band of acetone, acetophenone and benzophenone complexed with phenol derivatives (pK_a = 10.30-7.75) is investigated. The Raman intensity enhancement brought about by complex formation lies between 1.1 and 2.5 and is inversely related to the Raman intensity in the free base. Linear correlations are found between the square root of the intensity enhancement and the enthalpy of complex formation, the intercepts and the slopes depending on the nature of the proton acceptor. The depolarization ratio of the carbonyl band remains practically unchanged. The results are discussed in terms of σ and π electronic densities on the carbon and oxygen atoms of the carbonyl function.     

Ag clusters electrochemically reduced in stearic acid Langmuir-Blodgett films and their structural characterizations

Silver ions confined in the silver stearate Langmuir-Blodgett (L-B) films of 8-14 layers were elec-trochernically reduced into Ag clusters,which made the observation of well-ordered scanning tunneling microscope (STM) images of the films with molecular resolution.A hexagonal packing of the hydrophobic chains was obtained,which was superimposed on the two-dimensional Ag clusters of 2-3 nm m diameter.Furthermore,a (2×1) struc-time of the hexagonal packing was observed.It was attributed to a self-assembled structure of the hydrophilic surface of the L-B films through hydrogen bonding.The strong surface enhanced Raman scattering (SERS) effect of Ag clusters made it possible to record Raman spectra of two-layer steanc acid L-B films in the region of C-C stretching vibration frequencies The appearance of the bands at 1 128 0 and 1 100.7 cm-1,which correspond to the antisymmetric C-C stretching model of the acyl chains m the all-trans conformation and the C-C stretching model of the acyl chains in the gauche     

Synthesis of α, ω-dihydroxymethylphenylsiloxanes and their reactions with silicon tetrachloride and tetrabutoxytitanium

Russian Chemical Bulletin -     

Infrared spectra of triacetylene in the 4000-220 cm−1 region: Absolute band intensity and implications for the atmosphere of Titan

The gas phase infrared spectra of triacetylene were studied at room temperature in the 4000-220 cm⁻¹ wavenumber region. The absolute intensity of all the bands of noticeable strength were experimentally determined and the associated uncertainties were systematically estimated. The data obtained were then used for studying the detectability of C₆H₂ in Titan's atmosphere by means of infrared spectroscopy. The upper limit of mean stratospheric abundance derived from the already available Titan IR spectra (a fraction of ppb) is in agreement with the photochemical model estimates.     

Self-assembled monolayers prepared from ω-thiophene-functionalized n-alkyltrichlorosilane on silicon substrates

Self-assembled monolayers (SAMs) of thienyl-functionalized n-alkyltrichlorosilane (11-(3-thienyl)undecyltrichlorosilane [TUTS]) have been prepared by adsorption from solution and characterized by using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle measurements, ellipsometry, and scanning electron microscopy (SEM). Using contact angle and SEM measurements, the film preparation protocol was optimized, resulting in reproducible SAM formation with no adverse deposition of polysiloxane particles. XPS and ellipsometry studies confirmed the existence of SAM formation. AFM results show a smooth and homogeneous SAM, with surface roughness of Ra≤0.2 nm, which is slightly higher than the corresponding values for octadecyltrichlorosilane (OTS) SAMs. Such thiophene-based SAM surfaces can be used for surface-initiated polymerization of thiophene. The resulting formed polythiophene layers at non-compatible surfaces offer some practical applications in manufacturing [W. Plieth, A. Fikus, D. Appelhans, H.-J. Adler, German Patent Application No. 2661977 (1998); D. Appelhans, D. Ferse, H.-J. Adler, A. Fikus, W. Plieth, B. Aldolphi et al., J. Electrochem. Soc. (accepted)].     

Deracemization of unnatural amino acid: homoalanine using D-amino acid oxidase and ω-transaminase

A deracemization method was developed to generate optically pure L-homoalanine from racemic homoalanine using D-amino acid oxidase and ω-transaminase. A whole cell reaction using a biphasic system converted 500 mM racemic homoalanine to 485 mM L-homoalanine (>99% ee).     

Langmuir-Blodgett films of phycobiliproteins (II) --Photoelectrochemical property of R-phycoerythrin

Through an electrochemical cell deposited with R-phycoerythrin (R-PE) monolayer on SnO2 optically transparent electrode (SnO2 OTE), charge transport phenomenon and the photoelectrochemical behavior of R-PE have been investigated. The experimental results indicate that the cell is able to generate photocurrent; moreover, the signal increases apparently in the presence of electron donor or acceptor in the electrolyte solution, showing that the photocurrent of R-PE would originate from its charge transfer. Further comparative test showed that the photocurrent came from the photo-induced charge separation property of the chromorphores attached covalently to the apoprotein of R-PE. The photocurrent spectrum of R-PE LB films verified the above viewpoint, from which the mechanism of photo-induced charge transfer of R-PE is suggested. The quantum yield for photoelectric conversion of R-PE LB films was measured to be φ520nm=3.4% and the photovoltage approached 400 mV. Moreover, the protein is stable for a long     

Theoretical studies on the inactivation mechanism of γ-aminobutyric acid aminotransferase

The inactivation mechanism of γ-aminobutyric acid aminotransferase (GABA-AT) in the presence of γ-vinyl-aminobutyric acid, an anti-epilepsy drug, has been studied by means of theoretical calculations. Density functional theory methods have been applied to compare the three experimentally proposed inactivation mechanisms (Silverman et al., J. Biol. Chem., 2004, 279, 363). All the calculations were performed at the B3LYP/6-31+G(d,p) level of theory. Single point solvent calculations were carried out in water, by means of an integral equation formalism-polarizable continuum model (IEFPCM) at the B3LYP/6-31+G(d,p) level of theory. The present calculations provide an insight into the mechanistic preferences of the inactivation reaction of GABA-AT. The results also allow us to elucidate the key factors behind the mechanistic preferences. The computations also confirm the importance of explicit water molecules around the reacting center in the proton transfer steps.     

Biophysical and electrochemical studies of protein–nucleic acid interactions

Monatshefte für Chemie - Chemical Monthly - This review is devoted to biophysical and electrochemical methods used for studying protein–nucleic acid (NA) interactions. The importance of...     

Admittance studies of hydrogen-induced states at the silicon—silicon dioxide interface

The admittance of Pd-thin SiO₂Si MOSCAP devices was studied as a function of the following variables: temperature, measurement frequency, oxide preparation conditions, applied gate voltage and ambient atmospheres of 100 ppm hydrogen in nitrogen and pure oxygen. Transient current, capacitance and annealing studies were also conducted for many of these variables. It is shown that hydrogen atoms produced by the catalytic action of the Pd on hydrogen molecules can be injected into the oxide—semiconductor interface where, depending on the choice of oxidation conditions for growing the oxide, they modify the density and capture cross-sections of the hydrogen-induced interfacial states. It is also demonstrated that below 125 °C, the injected hydrogen can be reversibly removed by changing the ambient gas from the H₂/N₂ mixture to pure oxygen.     

Infrared laser spectroscopy of the fundamental band of a 3π CO

Many rotational components of the fundamental band of metastable a ³Π CO have been measured in absorption using diode laser spectroscopy with concentration modulation detection. Line positions are in good agreement with predictions from optically derived parameters. Resolved or partially resolved splittings arising from lambda-doubling appear for the three Ω components. Splittings in the Ω = 1 and 2 spectra agree satisfactorily with molecular beam (rf) and microwave results while those in the Ω = 0 fundamental deviate by several linewidths (up to 0.015 cm-⁻¹) from calculated values.     

Physicochemical studies of metal haloacetates—VI Infrared spectra of alkaline-earth metals and lead trifluoroacetates

The i.r. spectra of crystalline Mg, Ca and Pb trifluoroacetates have been investigated between 400—300 cm⁻. The trihaloacetate group vibrations are found to be more influenced by the mass and steric hindrance of the CX₃ group as compared to the electron withdrawing ability of the halogens.     

Pulse radiolysis studies on reactions of α-hydroxyalkyl radicals with nicotinamide and 6-methyl nicotinic acid

Reactions of α-hydroxyalkyl radicals derived from 2-propanol, ethanol and methanol with nicotinamide (NICAM) and 6-methyl nicotinic acid (6-MNA) were studied at various pHs using pulse radiolysis technique. It is found that α-hydroxyalkyl radicals react with NICAM and 6-MNA at pHs when nitrogen is in the protonated state. In these reactions, radical adducts of NICAM/6-MNA with α-hydroxyalkyl radicals are formed which have absorption maxima at about 340–350 nm which subsequently decay to give pyridinyl type of radicals of NICAM and 6-MNA having λ_max at 410 nm. Rate constants for the reactions of (CH₃)₂COH, CH₃CHOH and CH₂OH radicals with NICAM and 6-MNA were found to have linear dependence on reduction potentials of corresponding α-hydroxyalkyl radicals. Adducts formed in the reactions of CH₃CHOH and CH₂OH radicals with both NICAM and 6-MNA decayed slowly compared to the decay of adduct formed in reactions with (CH₃)₂COH radicals.     

Synthesis, characterization, and antifungal studies of transition metal complexes of ω-bromoacetoacetanilide isonicotinylhydrazone

Isonicotinic acid hydrazide or isonicotinylhydrazide, commonly known as isoniazid, is an antibacterial agent that has been used to treat tuberculosis. It interacts with microbial cell walls. Schiff’s bases or anils are the compounds having >C=N−N< linkages, which have immense applications as catalysts, stabilizers, pigments, dyes, and drugs. They have good ability to form chelates with many metal ions. Isoniazid can form Schiff’s bases with diketones such as acetoacetanilide. Acetoacetanilide isonicotinylhydrazone and its metal chelates exhibit anticancer activity. Our studies on N-methyl-acetoacetanilide isonicotinylhydrazone and its metal chelates revealed that they are active against pathogenic fungal strains. Hence, it is worthwhile to synthesize new complexes of ligands having different substituents on the acetoacetanilide moiety. We synthesized five new metal chelates of ω-bromoacetoacetanilide isonicotinylhydrazone. The ligand behaved as a tridentate monoanion or as a tridentate dianion in the complexes. These compounds were characterized mainly by elemental analysis; conductivity measurements; and electronic, infrared, and nuclear magnetic resonance spectral studies. We also carried out antifungal studies of these compounds against four selected pathogenic fungal strains using a cup-plate technique. Both the ligand and its metal chelates were active against all fungal strains investigated. However, the chelates were found to be more active than the ligand.     

Electrodeposition of hyaluronic acid and hyaluronic acid–bovine serum albumin films from aqueous solutions

Hyaluronic acid (HYH) films were prepared from aqueous sodium hyaluronate (HYNa) solutions by anodic electrodeposition. The film thickness was varied in the range of 0–20 μm by the variation of the deposition time and HYNa concentration. The deposition rate was low at HYNa concentration below 1 g L⁻¹ and increased significantly in the range of 3–5 g L⁻¹. The addition of bovine serum albumin (BSA) to the HYNa solutions resulted in increased deposition yield, which was attributed to the formation of composite HYH–BSA films. The thickness of the HYH–BSA films deposited by anodic electrodeposition was varied in the range of 0–80 μm. The HYH and composite HYH–BSA films were studied by scanning electron microscopy, thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and circular dichroism spectroscopy. The deposition mechanism and kinetics of deposition are discussed.     

Spectroscopic studies on the inclusion behavior between caffenic acid and ��-cyclodextrin

To investigate the inclusion ability of ??-cyclodextrin (??-CD) for caffenic acid (CA). The conditions for the formation of inclusion complex and the binding constant between ??-CD and CA were determined by fluorescent and ultraviolet spectroscopic methods. The behavior of CA as a free radical scavenger before and after its inclusion was investigated. In addition, solid samples of the inclusion complex, prepared through the co-precipitation and grinding methods, were characterized via IR spectroscopy and differential scanning calorimetry. The inclusion complex was further characterized with ¹H NMR spectroscopy. By using fluorescent and ultraviolet spectroscopy, the conditions for the formation of inclusion complex between ??-CD and CA were optimized and the binding constant determined. It was observed that the guest molecule behaves as a better anti-oxidant after its inclusion into ??-CD.     

Infrared spectral studies on the stability of some binuclear transition metal—Schiff base complexes

Some di-Schiff bases like N,N′-o-phenylene-bis-salicylaldimine (DSB₁), N,N′-m-phenylene-bis-salicylaldimine (DSB₂) and N,N′-p-phenylene-bis-salicylaldimine (DSB₃) have been synthesized by the condensation of salicylaldehyde with o-, m- and p-phenylenediamines, respectively. The synthesized complexes of Cu(II), Ni(II) and Co(II) with these ligands have been assigned their molecular structure on the basis of their elemental analyses, molecular weight determination, magnetic measurements, electronic spectra, molar volume and infrared spectral studies. The nature of bonding between metal ion and Schiff bases is studied by i.r. spectrophotometry. The shift in the band position of the groups involved in coordination has been utilized to estimate the coordination bond lengths. The value of the coordination bond length of Cu(II) complexes is shorter than the corresponding values for Ni(II) and Co(II) complexes.     

Synthesis of arsonium salts and betaines based on triphenylarsine and ω-bromoalkanoic acids

The reactions between Ph₃As and ω-bromoalkanoic acids with the length of polymethylene fragment n = 5, 7, 9 afford quaternary arsonium salts. Their treatment with alkali gives biologically active arsenobetaines. Solvent-free reactions of Ph₃P or Ph₃As with 2,3-dibromopropionic acid lead to the corresponding arsonium and phosphonium salts bearing (CH₂)₂COOH substituent.     

ClH(ClD) stretching band shape analysis in isolated 1−1 complexes of hydrochloric acid with ethers

A new theoretical approach is proposed for a quantitative representation of the v_ClH(ClD) band profiles in 1−1 complexes of ethers with hydrochloric acid in the gas phase and isolated in matrices at very low temperature. Several band shaping mechanisms are proposed. In solid matrices of gas at very low temperature, beside secondary environmental effects, the band profile is dominated by the vibrational interaction of the two stretching modees of the hydrogen bond (v_ClH(ClD) and v_Cl…O, respectively) which induces a homogeneous broadening for the v_ClH(ClD) band. In the gas phase, the same mechanism, including hot transitions, determines the shape of each subband. The band manifold is ascribed to an additional coupling wiht a low-frequency bending mode of the hydrogen bond. The rovibrational structure turns out to be only a minor band shaping factor. Born-Oppenheimer potential functions for the v_Cl…O mode are determined and a simple model is proposed to account for their particular shapes which are extremely sensitive to the isotopic substitution.