IRRA Spectra Research Articles

Infrared Reflection-Absorption Spectroscopy of α-Keto Acids at the Air-Water Interface: Effects of Chain Length and Headgroup on Environmentally Relevant Surfactant Films.

A variety of organic surfactants are found at air-water interfaces in natural environments, including on the surfaces of aqueous aerosols. The structure and morphology of these organic films can have profound impacts on material transfer between the gas and condensed phases, the optical properties of atmospheric aerosol, and chemical processing at air-water interfaces. Combined, these effects can have significant impacts on climate via radiative forcing, but our understanding of organic films at air-water interfaces is incomplete. Here, we examine the impact of the polar headgroup and alkyl tail length on the structure and morphology of organic monolayers at the air-water interfaces. First, we focus on the substituted carboxylic acids, α-keto acids, using Langmuir isotherms and infrared reflection absorption spectroscopy (IR-RAS) to elucidate key structures and phase behaviors of α-keto acids with a range of surface activities. We show that the structure of α-keto acids, both soluble and insoluble, at water surfaces is a compromise between van der Waals interactions of the hydrocarbon tail and hydrogen bonding interactions involving the polar headgroup. Then, we use this new data set regarding α-keto acid films at water surfaces to examine the role of the polar headgroup on organic films using a similar substituted carboxylic acid (α-hydroxystearic acid), an unsubstituted carboxylic acid (stearic acid), and an alcohol (stearyl alcohol). We show that the polar headgroup and its hydrogen bonding interactions can significantly affect the orientation of amphiphiles at air-water interfaces. Here, we provide side-by-side comparisons of Langmuir isotherms and IR-RA spectra for a set of environmentally relevant organic amphiphiles with a range of alkyl tail lengths and polar headgroup structures.

Characterization of self-assembled Bis[2-(2-bromoisobutyryloxy) undecyl] disulphide (DTBU) on gold surfaces suitable for use in surface-initiated atom transfer radical polymerization (SI-ATRP)

• Initiator DTBU on gold electrode (SAM) enhances electrochemical mediation ATRP. • CV, EIS, CA, XPS and IRRAS methods are used for DTBU monolayer characterization. • Well organized DTBU SAM with polar head and non-polar inside. • EIS, CA and IRRAS prove preferential presence of 6MP in mixed SAM with DTBU. • Mixed monolayers with 6MP provide optimal conditions for adaptation and use in e-ATRP. Bis[2-(2-bromoisobutyryloxy) undecyl] disulphide (DTBU) is an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP) able to functionalize metal surfaces through formation of self-assembled monolayers (SAM). The goal of this work is the making monolayers with the DTBU initiator on gold polycrystalline electrodes and their study by electrochemical methods as cyclic voltammetry (CV), capacity-potential curves (C-E), electrochemical impedance spectroscopy (EIS), and angle contact measurements for their characterization. Information of the integrity and permeability of the monolayers has been obtained by capacitance-potential measurements and impedance spectra. Also, the blocking effect of the physical barrier that SAM can produce to different redox probes is explored by using voltammetry and impedance. DTBU forms a compact monolayer whose main features are related with heterogeneous chain structures, having a non-polar hydrocarbon internal part and a polar head group. This is confirmed by X-ray photoelectron spectroscopy (XPS) which shows the presence of the elements of the DTBU adsorbate of SAM. Moreover, mixed monolayers of DTBU and 6-mercaptopurine (6MP) have been prepared and characterized, to check if the thiol facilitates electron exchange through monolayers. On this approach, different DTBU:6MP ratios have been employed and characterized studying IRRAS spectra, electrochemical properties, and contact angle on the modified surface. These mixed monolayers provide optimal conditions for adaptation and use in e-ATRP.

Achieving High-Performance Molecular Rectification through Fast Screening Alkanethiol Carboxylate-Metal Complexes Electroactive Units

Achieving High-Performance Molecular Rectification through Fast Screening Alkanethiol Carboxylate-Metal Complexes Electroactive Units

What Does Ectoine Do to DNA? A Molecular-Scale Picture of Compatible Solute-Biopolymer Interactions.

Compatible solutes accumulate in the cytoplasm of halophilic microorganisms, enabling their survival in a high-salinity environment. Ectoine is such a compatible solute. It is a zwitterionic molecule that strongly interacts with surrounding water molecules and changes the dynamics of the local hydration shell. Ectoine interacts with biomolecules such as lipids, proteins, and DNA. The molecular interaction between ectoine and biomolecules, in particular the interaction between ectoine and DNA, is far from being understood. In this paper, we describe molecular aspects of the interaction between ectoine and double-stranded DNA (dsDNA). Two 20 base pairs-long dsDNA fragments were immobilized on a gold surface via a thiol-tether. The interaction between the dsDNA monolayers with diluted and concentrated ectoine solutions was examined by means of X-ray photoelectron and polarization modulation infrared reflection absorption spectroscopies (PM IRRAS). Experimental results indicate that the ability of ectoine to bind water reduces the strength of hydrogen bonds formed to the ribose-phosphate backbone in the dsDNA. In diluted (0.1 M) ectoine solution, DNA interacts predominantly with water molecules. The sugar-phosphate backbone is involved in the formation of strong hydrogen bonds to water, which, over time, leads to a reorientation of the planes of nucleic acid bases. This reorientation destabilizes the strength of hydrogen bonds between the bases and leads to a partial dehybridization of the dsDNA. In concentrated ectoine solution (2.5 M), almost all water molecules interact with ectoine. Under this condition, ectoine is able to interact directly with DNA. Density functional theory (DFT) calculations demonstrate that the direct interaction involves the nitrogen atoms in ectoine and phosphate groups in the DNA molecule. The results of the quantum-chemical calculations show that rearrangements in the ribose-phosphate backbone, caused by a direct interaction with ectoine, facilitates contacts between the O atom in the phosphate group and H atoms in a nucleic acid base. In the PM IRRA spectra, an increase in the number of IR absorption modes in the base pair frequency region proves that the hydrogen bonds between bases become weaker. Thus, a sequence of reorientations caused by interaction with ectoine leads to a breakdown of hydrogen bonds between bases in the double helix.

Monolayer behavior of pure F-DPPC and mixed films with DPPC studied by epifluorescence microscopy and infrared reflection absorption spectroscopy

The monolayer behavior of a l-DPPC derivative with a single fluorination in one of its terminal methyl groups (F-DPPC) at air-water interface was investigated by epifluorescence microscopy and infrared reflection absorption spectroscopy (IRRAS). Epifluorescence microscopy was utilized to study the shape and morphology of liquid-condensed (LC) domains observed upon compression of the film. IRRAS was employed for the determination of chain order and orientation. The shapes of LC-domains in a monolayer of F-DPPC are more dependent on the rate of compression than those of DPPC. The LC domains of F-DPPC display pronounced fractal growth patterns depending on the compression speed. The evolution of LC domain occurs under dominating electrostatic dipolar forces in F-DPPC. IRRAS measurements with the analysis of the frequency of the methylene stretching vibrations as a function of film compression show that the acyl chains in an F-DPPC monolayer in the LE-phase are more disordered than those in a DPPC film. The reason for the higher chain disorder in LE phase F-DPPC monolayers is a back folding of the fluorinated sn-2 chain terminus towards the air-water interface leading to larger molecular area requirement. Angular dependent IRRA spectra of monolayers at a surface pressure of 30 mN m−1 show that in the LC phase DPPC and F-DPPC exhibit a similar tilt of the acyl chains of ca. 28−30 ° relative to the surface normal. F-DPPC is ideally miscible with l-DPPC-d62 having the same chirality, as indicated by epifluorescence images and by IRRAS. However, the LC domains in an equimolar mixture of d-DPPC and F-DPPC having opposite chirality show multi-lobed complex domain patterns indicating chiral phase separation within LC domains.

Alterations in the surface properties of sea spray aerosols introduced by the presence of sterols

The mixed stearic acid (SA)/sterol systems were used as sea spray aerosol mimics to get more insights into the alterations in surface properties of aerosols induced by sterols. By means of surface pressure (π)–area (A) isotherms and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS), the effect of cholesterol (chol), stigmasterol (stig) and ergosterol (erg) on the lateral packing and chain conformation of SA monolayer was explored. The fact that the excess areas of mixing of the mixed monolayers exhibit significant deviations from ideally mixed film proves that, the sterols are miscible with SA throughout all the monolayer compositions and surface pressures examined. The lift-off areas in π–A isotherms were found to increase with increasing mole fraction of sterols, indicating that expulsive interactions exist between SA and sterols, which are more pronounced when the mole fraction of sterols is 0.7. In addition, the peak intensities of νa(CH2) and νs(CH2) in IRRAS spectra decrease with increasing sterols levels, which is consistent with our findings in the π–A isotherms, that the addition of sterols leads to a looser chain packing in SA monolayer. The proportion of gauche defects in SA monolayer induced by the sterols follows the order cholesterol < stigmasterol < ergosterol at a certain sterol level, as reflected by the decreasing peak intensities of νa(CH2) and νs(CH2). Consequently, the sterols generally give rise to considerable expanding effects on SA monolayer, which are particularly pronounced for stigmasterol and ergosterol, suggesting that the additional alkyl side chains and double bonds of the sterols play a role on disordering SA monolayer. The present study is likely to shed light on many boundary processes take place at the interface of SSAs, in particular, transport processes of water and trace gases across the interface.

The film tells the story: Physical-chemical characteristics of IgG at the liquid-air interface.

The presence of liquid-air interfaces in protein pharmaceuticals is known to negatively impact product stability. Nevertheless, the mechanisms behind interface-related protein aggregation are not yet fully understood. Little is known about the physical-chemical behavior of proteins adsorbed to the interface. Therefore, the combinatorial use of appropriate surface-sensitive analytical methods such as Langmuir trough experiments, Infrared Reflection-Absorption Spectroscopy (IRRAS), Brewster Angle Microscopy (BAM), and Atomic Force Microscopy (AFM) is highly expedient to uncover structures and events at the liquid-air interface directly. Concentration-dependent adsorption of a human immunoglobulin G (IgG) and characteristic surface-pressure/area isotherms substantiated the amphiphilic nature of the protein molecules as well as the formation of a compressible protein film at the liquid-air interface. Upon compression, the IgG molecules do not readily desorb but form a highly compressible interfacial film. IRRA spectra proved not only the presence of the protein at the interface, but also showed that the secondary structure does not change considerably during adsorption or compression. IRRAS experiments at different angles of incidence indicated that the film thickness and/or packing density increases upon compression. Furthermore, BAM images exposed the presence of a coherent but heterogeneous distribution of the protein at the interface. Topographical differences within the protein film after adsorption, compression and decompression were revealed using underwater AFM. The combinatorial use of physical-chemical, spectroscopic and microscopic methods provided useful insights into the liquid-air interfacial protein behavior and revealed the formation of a continuous but inhomogeneous film of native-like protein molecules whose topographical appearance is affected by compressive forces.

Repercussion of the carbon matrix for the activity and stability of Fe/N/C electrocatalysts for the oxygen reduction reaction

Graphene-like (G), multiwalled carbon nanotubes (CNTs) and active carbon (AC) have been used as carbon matrix for the synthesis of Fe/N/C catalysts for the oxygen reduction reaction. A thorough physicochemical characterization of the electrocatalysts, including X-ray photoelectronic and X-ray absorption spectroscopies, reveal that the formation of Fe/Nx ensembles is favored when the graphene-like or the CNTs are used as the carbon matrix. As a result, the catalyst prepared with the graphene matrix (Fe/N/G) records the highest activity for the ORR in the series of 3.1Ag−1 at 0.9V. This very high ORR activity positions these catalysts as a realistic alternative to replace Pt/C cathodes in alkaline fuel cells. Moreover, using graphene as the carbon matrix endows the catalyst with very high stability during the ORR showing stable catalytic performance for the ORR even after being subjected to severe treatments of 3000 cycles up to 1.4V. In situ IRRA spectra demonstrate that such a high stability for the ORR relates to the excellent resistance against corrosion of the graphene-based catalyst.

Compact Titanium Oxycarbide: A New Substrate for Quantitative Analysis of Molecular Films by Means of Infrared Reflection Absorption Spectroscopy

Titanium oxide–titanium carbide (TiOxCy) hybrid materials have tunable electronic properties ranging from semiconductive to semimetallic. They can therefore be employed in solar energy conversion applications and as potential substitute for carbon based electrocatalyst supports for use in fuel cells. Understanding of the optical properties of semimetallic TiOxCy is of great importance. In this paper we report on the optical properties of compact TiOxCy in the mid-IR spectral region. TiOxCy reflects the IR light similarly to metals and is therefore suitable as a new substrate for molecular adsorption studies with infrared reflection absorption spectroscopy. For the first time polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) is applied to study quantitatively at the submolecular level the structure and orientation of fatty acid molecules in monolayers adsorbed on the TiOxCy surface. The analysis of the IR band intensities provides information on the structure, packing, and orientation of the fatty acid molecules in the monolayer. The PM IRRA spectra provide evidence of an interaction between surface atoms and the carboxylic group leading to dissociation of the polar headgroup and bidentate canted coordination of the carboxylate at the TiOxCy surface.

Spectroscopy of Metal/Electrolyte Interfaces

It is still a long way to reach the same holistic understanding of properties and processes at metal/ electrolyte interfaces as has been reached for surfaces in ultrahigh vacuum (UHV). In order to over-come this backlog i) more surface physisists should venture to "interfacial electrochemistry", because ii) new analytical techniques need to developed which replace all particle beam based methods which work successfully only in vacuum.In this lecture I will present and discuss investigations of several electrochemical interface pheno-mena as they occur in electro-catalysis, anion-adsorption, metal-deposition, molecular self-assembly, structural phase transitions, etc., using a number of in-situ methods like various modes of optical spectroscopy (IRRAS, RAS, etc.), X-ray diffraction (XRD) and scanning tunneling microscopy/ spectros-copy (STM/STS) as well as (still unavoidably) ex-situ methods like electron spectroscopies (XPS; AES), low energy electron diffraction (LEED) and ion scattering spectroscopy (ISS). As an example Fig.1 shows EC-STM images and IRRAS spectra of a) the "stripe-structure" and b) the "cavitand-structure" of dibenzyl-viologen molecules adsorbed on Cu(100) in HCl-solution. XPS proves the monocationic [dicationic] state of the molecular building blocks in a) [b)], while IRRAS enables a structural refine-ment of the orientation of the individual molecular cations in the respective structure (see models).

Adsorption of hydrogen on the surface and sub-surface of Cu(111)

The interaction of atomic hydrogen with the Cu(111) surface was studied by a combined experimental-theoretical approach, using infrared reflection absorption spectroscopy, temperature programmed desorption, and density functional theory (DFT). Adsorption of atomic hydrogen at 160 K is characterized by an anti-absorption mode at 754 cm(-1) and a broadband absorption in the IRRA spectra, related to adsorption of hydrogen on three-fold hollow surface sites and sub-surface sites, and the appearance of a sharp vibrational band at 1151 cm(-1) at high coverage, which is also associated with hydrogen adsorption on the surface. Annealing the hydrogen covered surface up to 200 K results in the disappearance of this vibrational band. Thermal desorption is characterized by a single feature at ∼295 K, with the leading edge at ∼250 K. The disappearance of the sharp Cu-H vibrational band suggests that with increasing temperature the surface hydrogen migrates to sub-surface sites prior to desorption from the surface. The presence of sub-surface hydrogen after annealing to 200 K is further demonstrated by using CO as a surface probe. Changes in the Cu-H vibration intensity are observed when cooling the adsorbed hydrogen at 180 K to 110 K, implying the migration of hydrogen. DFT calculations show that the most stable position for hydrogen adsorption on Cu(111) is on hollow surface sites, but that hydrogen can be trapped in the second sub-surface layer.

Investigation of structural changes of β-casein and lysozyme at the gas–liquid interface during foam fractionation

Purification and separation of proteins play a major role in biotechnology. Nowadays, alternatives to multistep operations suffering from low product yields and high costs are investigated closely amidst which one of the promising options is foam fractionation. The molecular behavior at the gas-liquid interface plays an important role in the formation and stabilization of enriched foam. This study for the first time correlates the physico-chemical parameters to the molecular structure in view of protein enrichment during foam fractionation of the two relatively different proteins lysozyme and β-casein employing biophysical techniques such as circular dichroism (CD) spectroscopy and infrared reflection absorption spectroscopy (IRRAS). In case of lysozyme, high enrichment was achieved at pH<pI in contrast to current opinion. This is due to partial unfolding and aggregation of the lysozyme molecules under favorable foaming conditions that resulted with high enrichment of foamed protein. Under these favorable conditions, CD spectra and IRRA spectra show that the unfolding of lysozyme is partially irreversible. However, the unfavorable foaming conditions, giving low enrichment, promote only minor structural changes and these changes are fully reversible. In case of β-casein, no pronounced unfolding can be observed using CD spectroscopy and IRRAS. The β-casein molecules adsorb and purely reorient at the gas-liquid interface, depending on favorable or unfavorable conditions.

PM-IRRAS Investigation of Self-Assembled Monolayers Grafted onto SiO2/Au Substrates

Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was used to characterize self-assembled monolayers (SAMs). Novel ester-terminated organosilicon coupling agents possessing a trialkoxysilyl headgroup and a urea group in the linear alkyl chains (4) were synthesized and grafted onto SiO(2)/Au substrates (SiO(2) film of 200 Å thickness deposited on gold mirror). This composite substrate allowed the anchoring of SAMs and preserved the high reflectivity for infrared radiation. PM-IRRAS spectra with very high signal-to-noise ratios have been obtained in the mid-infrared spectral range allowing monitoring of the grafted SAMs. Quantitative analysis of the measured signal is described to compare PM-IRRAS and conventional IRRAS spectra. This quantitative analysis has been validated since the band intensities in the corrected PM-IRRAS and conventional IRRAS spectra are identical. Orientation information on the different functional groups has been obtained comparing the corrected PM-IRRAS spectrum with the one calculated using isotropic optical constants of ester-terminated organosilicon coupling agents 4. The carbonyls of the urea groups are preferentially parallel to the substrate surface favoring intermolecular hydrogen bonding and consequently a close packing of the molecules attached to the surface. By contrast, the alkyl chains present gauche defects and are poorly oriented.

A structural and corrosion study of triethoxysilyl and perfluorooctyl functionalized polyhedral silsesquioxane nanocomposite films on AA 2024 alloy

A tri-functional polyhedral oligomeric silsesquioxane (POSS) based silane precursor R x R y R z (SiO 3/2) n ( x + y + z = n = 6, 8, 10, ….) bearing 3-(N-(3-triethoxysilylpropyl)ureido)propyl, isooctyl and perfluoropropyl groups was synthesized and investigated as corrosion protective coating for AA 2024 alloy. Infrared reflection-absorption (IR RA) combined with X-ray photoelectron spectroscopy and atomic force microscopy provided information about partial self-assembling of coatings having a fluorine enriched upper layer with a low surface energy ( γ tot = 12.37 mN/m). The structural changes that accompanied corrosion produced under chronocoulometrical conditions were assessed from ex-situ IR RA spectra. A new band at 1690–1700 cm − 1 appeared above the corrosion potential, and was assigned to the formation of amidonium ions and consequent relaxation of urea–urea associations.

A Structural and Corrosion Study of Triethoxysilyl Functionalized POSS Coatings on AA 2024 Alloy

A novel bifunctional polyhedral oligomeric silsesquioxane (POSS) based silane precursor R(x)R'(y)(SiO(3/2))(8), (x + y = 8), bearing 3-(N-(3-triethoxysilylpropyl)ureido)propyl (ureasil - U) and isooctyl (IO) groups (i.e., U(2)IO(6) POSS) was synthesized, and the corresponding coatings, prepared under the acid hydrolysis conditions, were studied in order to assess their corrosion inhibition of the AA 2024-T3 alloy. The U(2)IO(6) POSS precursor was made in two steps: in the first, an appropriate stoichiometric (2:6) mixture of 3-aminopropyltriethoxysilane (AP(2)) and isooctyltrimethoxysilane (IO(6)) was autoclaved under basic hydrolysis conditions giving AP(2)IO(6)(SiO(3/2))(8) cubes, which were reacted in the second step with 3-isocyanatopropyltriethoxysilane (ICPTES), leading to the bis end-capped sol-gel precursor U(2)IO(6) POSS having a cube-like structure. Coatings were made from sols catalyzed with acidified water. IR and (29)Si NMR spectroscopic studies combined with mass spectrometric measurements were employed to confirm the cube-like structure of AP(2)IO(6) and U(2)IO(6) POSS. The structure and morphology of the U(2)IO(6) POSS coatings were studied with the help of infrared reflection-absorption (IR RA) spectroscopic measurements combined with XPS and AFM measurements, providing information about the formation of partially self-assembled coatings. The degree of corrosion inhibition was assessed from the potentiodynamic measurements showing around 10 times smaller current densities for the coatings only 30-40 nm thick. Ex situ IR RA spectroelectrochemical measurements were performed by consecutive measurements of the IR RA spectra of U(2)IO(6) POSS coatings which were chronocoulometrically charged at different potentials. At potentials more positive than the corrosion potential (E(corr) approximately -0.5 V), the amide I bands shifted, indicating the formation of new urea-urea aggregations and associations, with the newly formed strong band at 1680-1690 cm(-1) suggesting the formation of amidonium ions. These results showed that the urea groups represented the weakest part of the coatings due to their tendency to protonation.

Interfacial properties and structural analysis of the antimicrobial peptide NK‐2

The structure of the antimicrobial peptide NK-2 has been studied at the air-water interface and in different solutions using spectroscopic methods such as circular dichroism (CD) and infrared reflection absorption spectroscopy (IRRAS) as well as specular X-ray reflectivity (XR). NK-2 adopts an unordered structure in water, buffer, and in the presence of monomeric cationic and noncharged amphiphiles. However, it forms a stable alpha-helix in 2,2,2-trifluoroethanol (TFE) and in micellar solutions of anionic, cationic as well as nonionic amphiphiles, whereas only in sodium dodecyl sulfonate solutions the alpha-helical structure can also be found below the critical micellar concentration (cmc). The amphiphilic molecule NK-2 is surface active and forms a Gibbs monolayer at the air-buffer interface. In contrast, no adsorption was observed if NK-2 is dissolved in water. During the adsorption process in buffer solutions, NK-2 undergoes a conformational transition from random coil in bulk to alpha-helix at the interface. This change of the peptide's secondary structure is known to be associated with its antimicrobial activity. A comparison of the experimental IRRA spectra with the simulated spectra indicates that the adsorbed NK-2 alpha-helix lies flat at the interface. This is confirmed by XR measurements which show that the thickness of the NK-2 layer is approximately 17 A, which is the average diameter of a alpha-helix, indicating that only a monomolecular adsorption layer is formed.

Insertion of Lipidated Ras Proteins into Lipid Monolayers Studied by Infrared Reflection Absorption Spectroscopy (IRRAS)

Ras proteins have to be associated with the inner leaflet of the plasma membrane to perform their signaling functions. This membrane targeting and binding is controlled by post-translational covalent attachment of farnesyl and palmitoyl chains to cysteines in the membrane anchor region of the N- and H-Ras isoforms. Two N-Ras lipoproteins were investigated, namely a farnesylated and hexadecylated protein, presenting the natural hydrophobic modifications and a doubly hexadecylated construct, respectively. The proteins are surface active and form a Gibbs monolayer at the air-D 2O interface. The contours of the amide-I bands were analyzed using infrared reflection absorption spectroscopy (IRRAS). Langmuir monolayers of a mixture of POPC, brain sphingomyelin, and cholesterol were used as half of a model biomembrane to study the insertion of these N-Ras proteins. They insert with their hydrophobic anchors into lipid monolayers but at higher surface pressures (30 mN/m); the farnesylated and hexadecylated protein desorbs completely from the monolayer, whereas the doubly hexadecylated protein remains incorporated. During the insertion process, changes in the orientation of the protein secondary structure were detected by comparison with simulated IRRA spectra, based on the information on the relative orientation of the secondary structure elements from the protein crystal structure data.

Quantitative determination of corrosion products and adsorbed water on copper in humid air containing SO 2 by IR-RAS measurements

The time dependency of the amounts of corrosion products and co-existing adsorbed water on copper in humid air containing SO 2 was estimated from a series of in situ time-resolved IR-RAS spectra on the basis of the relations between the band intensities and the mass changes of the corrosion products, which were determined by simultaneous measurement of IR-RAS and QCM. The amounts of both corrosion products increased slowly at the initial stage and later increased rapidly. Although the relative humidity was kept constant, the amount of adsorbed water increased nearly the same behavior as that of corrosion products in the stage of relatively small amounts of corrosion products and later increased rapidly when the amounts of corrosion products increased. In humid air without SO 2, sulfite gradually decomposed and some of it changed into sulfate.

Vanadyl naphthalocyanine and vanadyl porphine phenyl substituted macrocycles: SERS and thin film organisation studies

Infrared (middle and far) and Raman spectroscopy were used to study the adsorption of vanadylnaphthalocyanine and vanadylporphine tetraphenyl substituted macrocycles adsorbed onto metallic surfaces. The IR spectra of the compounds deposited onto a KBr monocrystal and onto a smooth copper surface suggest a weak adsorbate–substrate interaction and no significant structural modifications imposed by surface effect. The reflection–absorption IR (IRRAS) spectra allowed to propose a preferential molecular orientation of the molecules deposited onto the copper surface. Surface-enhanced Raman spectral data obtained on colloidal Ag as well as Ag island films suggest a weak macrocycle interaction and small structural modifications of the naphthalocyanine complex on the surface. The whole spectral data indicate that the naphthalocyanine complex is orientated with the naphthalocyanine plane face-on to the surface. In both complexes the vanadyl group is perpendicular to the coordination site and opposed to the surface. In both molecular systems the phenyl substituents, oriented perpendicular to the macrocycle plane, are responsible of the weak adsorbate–substrate interaction. Porphine complex has no interaction with the surface. This different behaviour of the above complexes is related to the different extent of the π-electronic size.

Effect of magnetic field on growth of bianthrone thin films

The authors investigated the influence on the properties of vacuum-deposited thin films of organic dyes prepared during application of magnetic fields. In spite of weak magnetic field intensity (0.1–0.3 T), the effect of the magnetic field could be observed in the PL spectra and IR-RAS spectra for 10,10′-bianthrone (BA) thin films. BA molecules in a vacuum-deposited thin film are oriented comparatively randomly; they are found to be oriented as perpendicular and parallel molecular planes to the substrate in the presence of the perpendicular and parallel magnetic fields, respectively. The magnetic orientation is effective for facilitating the orientation of organic low-molecular-weight molecules with high coplanarity.