Diffuse reflectance spectroscopy of powders

Diffuse reflectance (DRIFT) spectra in the mid-IR region, especially of inorganic powders, often reveal inverted or derivative-like structures (“reststrahlen” bands) which make their straightforward interpretation in terms of the Kubelka-Munk theory difficult. A simulation technique based on a combination of single scattering (Mie theory) and radiative transfer (with Kubelka-Munk as a special case) is reported that allows measured DRIFT spectra to be described without use of any free “fit” parameters. The results for silica glass microspheres and silicon carbide powder show that not specular reflectance but prominent structures in the single particle scattering cross-section are responsible for the reststrahlen features which cannot be suppressed even by diluting the powder in an excess of KBr. The efficiency of a “blocker” device in DRIFTS is also discussed.     

An infrared spectroscopic study of hydrogen bonding in ethyl phenol: A model system for polymer phenolics

A detailed analysis of the bands appearing in the OH stretching region of the infrared spectrum of ethyl phenol solutions is presented. In cyclohexane solutions, the band due to “free” (non-hydrogen-bonded groups) contains overlapping contributions from both monomeric and end-group species. Other assignments are made on the basis of whether the proton and oxygen in a particular OH group are both involved in hydrogen bonds (as “donors” and “acceptors”, respectively), or if only the proton is acting as a donor. The strongest band in the spectra obtained at the highest concentration of ethyl phenol is due to OH groups present in linear chains of hydrogen-bonded OH groups (as recognized in numerous other studies), but a band due to cyclic trimers has also been identified. The assignment of other modes is more uncertain and various possibilities are discussed. In toluene solutions, assignments are more complicated, because bands due to OH–π hydrogen bonds are observed instead of free groups. Finally, the data from cyclohexane solutions was used to calculate equilibrium constants capable of describing the distribution of species present. A new methodology for determining the equilibrium constant describing association in the form of dimers is described.     

Preparation of alpha-elastin nanoparticles by gamma irradiation

Nanoparticles were prepared by utilizing the thermosensitive aggregation of alpha-elastin and gamma ray crosslinking. Three different heating process, “Slow heating”, “Fast heating”, and “Heat shock”, were applied for the aggregation of the alpha-elastin and examined to yield nanoparticles by gamma rays crosslinking. As a result, only “Slow heating” process yielded nanoparticles with diameters of about ca. 300 nm above cloud point (CP) and about ca. 100 nm below CP, and a narrow size distribution above 1.0 mg/ml concentration (exclude 1.0 mg/ml).     

Investigation of the interactions between ginsenosides and amino acids by mass spectrometry and theoretical chemistry

In order to evaluate the essence of the interactions of ginsenosides and proteins which are composed by α-amino acids, electrospray ionization mass spectrometry was employed to study the noncovalent interactions between ginsenosides (Rb₂, Rb₃, Re, Rg₁ and Rh₁) and 18 kinds of α-amino acids (Asp, Glu, Asn, Phe, Gln, Thr, Ser, Met, Trp, Val, Gly, Ile, Ala, Leu, Pro, His, Lys and Arg). The 1:1 and 2:1 noncovalent complexes of ginsenosides and amino acids were observed in the mass spectra. The dissociation constants for the noncovalent complexes were directly calculated based on peak intensities of ginsenosides and the noncovalent complexes in the mass spectra. Based on the dissociation constants, it can be concluded that the acidic and the basic amino acids, Asp, Glu, Lys and Arg, bound to ginsenosides more strongly than other amino acids. The experimental results were verified by theoretical calculations of parameters of noncovalent interaction between ginsenoside Re and Arg which served as a representative example. Two kinds of binding forms, “head–tail” (“H–T”) and “head–head” (“H–H”), were proposed to explain the interaction between ginsenosides and amino acids. And the interaction in “H–T” form was stronger than that in “H–H” form.     

Amine groups functionalized gel-type resin supported Pd catalysts: Physicochemical and catalytic properties in hydrogenation of alkynes

Palladium catalysts (0.125–0.5 wt.% Pd) supported by amine groups—functionalized gel-type resin (FCN) were studied in the hydrogenation of alkynes reagents, 2-butyne-1,4-diol and phenylacetylene. The catalysts were prepared by two routes. The first, “OAc” is based on the immobilization of Pd-precursor in the pre-swollen resin from THF solution of Pd(OAc)₂, followed by chemical reduction of the Pd-centers. This method produces Pd particles of size in nano-scale. The second procedure, “aq” implies the deposition of Pd-species on dry resin beads using aqueous solution of PdCl₂. Reduction of these Pd-species gives relatively large Pd particles, dominating are 30–50 nm in size. The SEM studies performed over the cross-section of catalysts grains showed location of Pd in outer shell of polymer beads in both “OAc” and “aq” catalysts; however, thinner layer of Pd appears in “aq” series catalysts. In the presence of all catalysts, prepared by “OAc” and “aq” methods the selectivity towards alkenes is high, above 90%. The catalysts of “aq’ series are much more active and more selective than “OAc” analogues giving selectivity to alkene ca. 94% at almost complete conversion of alkynes. Moreover, catalytic performance of “aq’ series catalyst is unchanged under recycling use. The catalyst was recovered and reused 4 times, maintaining its catalytic efficiency.     

Preparation and catalytic activity of titanium silicalite-1 zeolite membrane with TPABr as template

The preparation of the supported titanium silicalite-1 (TS-1) zeolite membrane with inexpensive tetrapropylammonium bromide (TPABr)/weak base synthesis system was studied by three methods, and the catalytic activity of the obtained TS-1 zeolite membrane was evaluated with the oxidation of 2-propanol (IPA) under pervaporation condition. It was found that TS-1 zeolite membrane could be successfully prepared with “seeding” or “seeding in situ” method, but could not be achieved with “in situ” method. Adding a little amount of promoter ions of PO₄³⁻ into the synthesis gel was of benefit to the catalytic activity of the prepared TS-1 zeolite membrane, but had no obvious effect on the membrane layer formation on the mullite porous support. For “seeding” method, the membrane prepared with the synthesis gel having molar composition of SiO₂:0.1TPABr:0.9Et₂NH:0.03TiO₂:80H₂O:0.06H₃PO₄ at 150 °C for 48 h showed the highest oxidation conversion of IPA of 72% accompanied by a flux of 0.35 kg/m² h. Further more, much higher IPA oxidation conversion of 76% accompanied by a flux of 0.65 kg/m² h was obtained for the TS-1 zeolite membrane prepared with the same synthesis gel by “seeding in situ” method at 150 °C for 72 h.     

Superconductivity—a source of surprises

Superconductivity is ascribed to a tendency of pairwise localization of conduction electrons. As a necessary condition in k space bands with very small as well as large dispersion need to be present at the Fermi level (“flat band/steep band”). The sufficient condition is a strong enough coupling of the flat band states to specific phonons in case of phonon-mediated superconductivity. The electron–phonon coupling parameter λ reveals a peak structure in the phonon q-space. These aspects are discussed for actual examples, e.g., rare earth carbides and carbide halides as well as MgB₂.     

Mutational pressure is a cause of inter- and intragenomic differences in GC-content of simplex and varicello viruses

Total GC-content (G + C), GC-content in codon positions and 0-fold, 2-fold and 4-fold degenerated sites in all coding districts from 10 completely sequenced genomes of simplex and varicello viruses have been calculated by the original “Coding Genome Scanner” algorithm. The low coefficient of correlation (R < 0.5) between 3GC and G + C in all coding districts from unique regions (UL and US) of alphaherpesvirus genome is a new criterion of the strong mutational pressure that is the process of increasing the rates of nonsynonymous mutations because of the extreme saturation (GC-pressure) or desaturation (AT-pressure) of third (liberal) codon positions with G and C. Unique regions of HSV1, HSV2, CeHV1, CeHV2, CeHV16 and BoHV5 are under the influence of strong GC-pressure caused mostly by AT to GC transversions. Unique regions of EqHV1 are under the influence of weak GC-pressure. In unique regions of CeHV9 AT-pressure is strong; in EqHV4 and VZV unique regions AT-pressure is weak. Mutational AT-pressure in CeHV9 and VZV is caused mostly by transitions, while in EqHV4 it is caused mostly by transversions. The level of 3GC in coding districts situated in long terminal inverted repeats (LTR) of all these viruses is much higher than in coding districts from UL and US. Higher GC-content does not seem to depend on the gene itself, but it does depend on its location. V67 gene of EqHV1 is situated in LTR (3GC = 0.853), while V67 gene of EqHV4 is situated in US (3GC = 0.397). Higher rates of AT to GC transversions in coding districts situated in LTR should be due to the “anatomy” of long terminal inverted repeats. The process of AT to GC transversions is thought to take place only in doublestranded DNA. Indeed, in the potential secondary structure formed by singlestranded genomic DNA of alphaherpesviruses only joined inverted repeats should be doublestranded.     

“Hole-burning spectra”. A new method for obtaining fine structure in absorption spectra of organic molecules

A new method is proposed for obtaining fine structure in broad-band absorption spectra of organic molecules in solid solutions at low temperature. This method is based on the laser burning of a series of narrow gaps in inhomogeneously broadened absorption spectra. A special spectral set-up has been developed for the measurement of the differential spectrum (a “hole-burning spectrum”) of “burnt” and “unburnt” samples. As an example the hole-burning spectrum of Zn-tetraphenylporphine in ethanol has been considered.     

Nucleation and growtn of polythiophene films on gold electrodes

The nucleation and growth of polythiophene films on gold electrodes has been studied using potentiostatic steps. The mechanism has been deduced and estimates made of the kinetic parameters. Dissolution of the gold substrate at potentials where thiophene polymerisation occurs is suppressed by the initial rapid formation of a monolayer of polymer. The data indicate that formation of bulk film occurs by the instantaneous nucleation and three-dimensional growth of polymer on top of this monolayer. Rate constants for growth parallel to the surface on the bare gold substrate and the covering polymer layer are surprisingly very similar. Growth perpendicular to the surface is slightly more rapid, typically by a factor of 1.5–3, although it is less dependent on potential. The high density of nuclei results in their overlap at an early stage, after which growth is only possible perpendicular to the surface. Within a narrow potential range, the observation of maxima and minima in current-time transients is interpreted in terms of the “death” and “rebirth” of growing centres.     

Reminiscences and lessons on the occasion of a silver jubilee

This paper, written to commemorate the publication of Walsh's classical paper on the potentialities of atomic absorption spectroscopy (AAS) 25 years ago, contains nothing new. It is a personal recollection of the work done independently at our laboratory prior to 1955 which resulted in the construction of a “negative filter” (for use in atomic emission spectroscopy) and an “absorption flame photometer.” Some lessons are drawn from the historical development of AAS about the inventing of new analytical methods in general.     

Measurement of surface orientation in uniaxial poly(ethylene terephthalate) films using polarised specular reflectance Fourier transform infrared microscopy

Polarised Fourier transform infrared (FT-IR) external-reflection spectroscopy has been used to measure molecular orientation at the surface of uniaxially drawn poly(ethylene terephthalate) (PET) films as a function of draw ratio. The spectra, which were obtained using an FT-IR microscope operating in the reflectance mode, were of high signal-to-noise (S/N) ratio, and contained only the specular component of the reflected radiation. The dichroic ratio of the 1019 cm⁻¹ ring stretching band was used to measure the PET orientation function, P₂₀₀. Prior to quantifying band intensities, the reflectance spectra were either transformed using the Kramers-Kronig algorithm, or simply differentiated; it was found that the dichroic ratios obtained using either pretreatment were similar. It was shown that the P₂₀₀ values obtained using the FT-IR method compared well with those obtained using surface refractive index measurements, provided that the intensity of the 1019 cm⁻¹ band was normalised relative to a non-dichroic band in the spectrum prior to computing dichroic ratios. The use of a reflecting microscope to perform the analysis of surface orientation not only simplifies sample alignment compared with “macro” reflectance accessories, but also allows awkward-shaped or small samples to be examined with relative ease. Unfortunately, a significant current limitation is that samples must be sufficiently “optically thick” to prevent double-pass (“transflectance”) radiation reaching the detector and yielding non-specular features in the reflectance spectrum. For polyaromatics, this probably means thicknesses in excess of 50 μm to obtain good spectra in the fingerprint region. Polarised attenuated total reflectance microscopy may present an alternate approach for examining thinner films.     

On the ionic conductivity and phase transitions in the Li2SO4---Li2WO4 system and their relation to ion transport mechanism

Secco et al. have performed several measurements of ionic conductivity, which they have considered as “convincing evidence” that the “paddle-wheel” mechanism does not contribute significantly to ion conductivity in Li₂SO₄-based compositions. However, a comparison of their results in the high-conductivity range with those of other investigators suggests that their data are artifacts. The cause of this is that the resistance of their sulfate-rich samples is about 0.1 ohm at high temperatures. Thus, their results are reliable only for “normal,” i.e., low, conductivities. It is briefly summarized why the “paddle-wheel” mechanism for ion transport is superior to a percolation-type mechanism for a few high-conducting phases.     

Ir spectra of the simplest stable proton solvates in methanol and ethanol

The spectra of (MeOH)₂H⁺ and (EtOH)₂H⁺ proton disolvates formed by strong symmetrical hydrogen bonding were separated from the multiple frustrated total internal reflection (MFTIR) IR spectra of solutions of HCl in methanol and ethanol. These spectra show a large number of rather narrow bands, exceeding the number of bands in the spectra of the pure alcohols and are in accord with a model, in which the generation of continuous absorption in solutions of strong acids is a consequence of the interaction of vibrations for protons in a strong, symmetrical hydrogen bond with the vibrations of other groups of proton disolvates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 217–220, January, 1991.     

Analysis of the diffuse bands near 6100 Å in the fluorescence spectrum of Cs2

The diffuse bands near 6100 Å in the laser-induced fluorescence spectrum of Cs₂ are analyzed through quantum-mechanical spectral simulations. These bands are interpreted as bound-free emission to the vibrational continuum of the ground state from an excited state of ion-pair character. The lower region of this state, which we have labeled E′, is described approximately by the spectroscopic constants, T_e = 19400 cm⁻¹, R_e = 9 Å, and ω_e = 13 cm⁻¹. Experiments with a single-mode Ar⁺ laser as excitation source clearly reveal fine structure in the E′ → X spectrum, which was not evident for multimode laser excitation. This fine structure confirms our analysis and supports our suggestion that extensive averaging over initial (υ′, J′) levels is responsible for the absence of fine structure in the spectra excited by a multimode laser. Various averaging mechanisms are investigated in the spectral calculations. The paper includes a brief review of other work on “structured continua” in diatomic spectra, and a semiclassical treatment of such structure, with emphasis on the distinction between “reflection” structure and “interference” structure.     

A thermodynamic interpretation of the behavior of higher fatty alcohols and acids upon the chromatographic paper

An idea was presented of treating the chromatographed substance as a “solute,” and the chromatographic system, composed of the stationary and the mobile phase as a “solvent.” Moreover the concept of “local equilibrium” was introduced, allowing to regard a given chromatographic spot as a “binary solution.” Thus a possibility arose to apply the classical thermodynamic approach, normally used for binary solutions, and namely: μ_i = μ_i + RT ln x_iƒ_i, where μ_i—chemical potential of the “i”-th compound in the solution, μ_i—chemical potential of the pure “i”-th compound, x_i-molar fraction of the “i”-th compound, ƒ_i—its activity coefficient, in a modified form, suitable for the chromatographic purpose.     

The question of timescale associated with the determination of molecular structures

A critical view of the “timescale” problem arising in spectroscopic and diffraction experiments is presented and a comparison made between the different types of information on dynamic processes obtainable from these methods. X-ray structural data on solids are intrinsically time-averaged over the period of data collection, and therefore contain information on dynamic processes which must be considered when interpreting solid-state NMR spectra. Intramolecular rearrangements in solid Fe₃(CO)₁₂ (tri-iron dodecacarbonyl) and C₁₀H₁₀ (bullvalene) are discussed as examples.     

Epithermal neutron flux characterization of the IEA-R1 research reactor,Sao Paulo,Brazil

Summary The nonideality of the epithermal neutron flux distribution at a reactor site parameter (α) and the thermal-to-epithermal neutron ratio (ƒ) were determined in three typical irradiation positions of the IEA-R1 reactor of IPEN-CNEN/SP, Sao Paulo, Brazil, using the “Cd-ratio for multimonitor” and “bare bi-isotopic monitor” methods, respectively. This characterization is to be used in the k₀-method of NAA, recently introduced at the IPEN.     

Effects of strong inter-hydrogen bond dynamical couplings in the polarized IR spectra of adipic acid crystals

This paper presents the results of the re-investigation of polarized IR spectra of adipic acid and of its d₂, d₈ and d₁₀ deuterium derivative crystals. The spectra were measured at 77 K by a transmission method using polarized light for two different crystalline faces. Theoretical analysis concerned linear dichroic effects and H/D isotopic effects observed in the spectra of the hydrogen and deuterium bonds in adipic acid crystals at the frequency ranges of the ν_O–H and the ν_O–D bands. The two-branch fine structure pattern of the ν_O–H and ν_O–D bands and the basic linear dichroic effects characterizing them were ascribed to the vibronic mechanism of vibrational dipole selection rule breaking for IR transitions in centrosymmetric hydrogen bond dimers. It was proved that for isotopically diluted crystalline samples of adipic acid, a non-random distribution of protons and deuterons occurs in the dimers (H/D isotopic “self-organization” effect). This effect results from the dynamical co-operative interactions involving the dimeric hydrogen bonds.     

Comparison of chemometric methods for brand classification of cigarettes by near-infrared spectroscopy

The combinations of NIR spectroscopy and three classification algorithms, i.e., multi-class support vector machine (BSVM), k-nearest neighbor (KNN) and soft independent modeling of class analogies (SIMCA), for discriminating different brands of cigarettes, were explored. The influence of the training set size on the relative performance of each algorithm was also investigated. A NIR spectral dataset involving the classification of cigarettes of three brands was used for illustration. Three performance criteria based on “correctly classified rate (CCR)”, i.e., “Average CCR”, “95 percentile of CCR” and “S.D. of CCR”, were defined to compare different algorithms. It was revealed that BSVM is significantly better than KNN or SIMCA in the statistical sense, especially in cases where the training set is relatively small. The results suggest that NIR spectroscopy together with BSVM could be an alternative to traditional methods for discriminating different brands of cigarettes.