Band Deconvolution Research Articles

Structural-functional organization of the main light harvesting complex and photosystem 2 of higher plants.

The interrelation between spectral and structural-functional properties of LhcIIb was studied. The dipole strength of the main Q(y )bands of chlorophylls (Chl a 30.8 D(2); Chl b 18.5 D(2)) and chlorophyll a/b ratio (Chl a/Chl b = 7 : 6) were determined for LhcIIb. The Chl a/Chl b value shows that the subunit of this complex contains seven Chl a and six Chl b molecules. Individual bands of chlorophylls (bands in stokes and anti-Stokes parts at 77 K were Lorentzian and Gaussian, respectively) were resolved using synchronized deconvolution of absorption, CD, and LD bands of chlorophylls. Seven of these bands belonged to Chl a. Parameters of absorption bands of Chl a indicate that seven molecules represent a united cluster (heptamer) with exciton interactions, determining the spectrum of LhcIIb in the Chl a absorption region. Parameters of absorption bands of Chl b show the existence of three clusters: monomer (639.6 nm), dimer (645.2 and 647.4 nm), and trimer (649.8 and 654.1 nm). These clusters and their properties agree with the well-known structure of porphyrin groups of the LhcIIb subunit (Kuhlbrandt, 1994). A distorted ring of seven porphyrins in the stromal range of the subunit corresponds to Chl a heptamer; a separately located molecule near the N-terminal domain on the stromal side of the subunit corresponds to Chl b monomer; a dimer and a trimer of porphyrins in the lumenal range of the subunit correspond to the dimer and trimer of Chl b, respectively. The calculated lifetimes of the excitation energy (exciton) transfer in subunit and trimer of LhcIIb confirm this location of pigments. The geometry of the Chl a heptamer (mutual orientation of transition dipole moments) was determined by the steady-state Kasha-Tinoco approximation using parameters of individual bands of exciton splitting. The calculated parameters of mutual orientation of Chl a dipoles agree with the topography of the stromal porphyrins found by electron crystallography (Kuhlbrandt, 1994). A structural model of the granal multicentral macrocomplex of PSII (MPSII) is suggested. The lifetimes of the exciton migration between the main pigment-protein compartments of MPSII were calculated. The results of calculation are consistent with the structural model of the photosystem. The location of pigments provides for fast exciton hopping between Chl a clusters of neighboring proteins in the MPSII along the stromal surface within the membrane (5-25 psec) and between stacked membranes (approximately 40 psec) of chloroplast grana.

Free Energy Relationships for the Outer-Sphere Anion–Anion and Anion–Cation Optical Electron Transitions Involving Common Cyanometalate (II) and (IV) Donors: Evidence for the Frequency-Distorted Reorganization Dynamics

This work is an extension of the research project on the outer-sphere optical charge transfer (CT) initiated by Prof. R.R. Dogonadze at the Laboratory founded by him in Tbilisi, Georgia. We report the band deconvolution procedures and accomplished free energy relationships for recently observed novel outer-sphere anion–anion and anion–cation optical electron transitions involving common cyanometalate II and IV ions, viz. [M(CN)x]4–, M = Fe, Ru, Os (x = 6) and M = Mo, W (n = 8) as electron donors, and [FeIII(CN)6]3– and [RuIII(NH3)6]3+ as electron acceptors, respectively. The CT band maximum vs. the redox asymmetry free energy relationships, constructed through the consideration of spin-orbit splitting effects, exhibit linear character with slopes close to unity as predicted theoretically, and fully confirm the assignment of these transitions to outer-sphere optical electron transitions as outlined in the preceding works. The preliminary comparative analysis of presented relationships based on the contemporary charge transfer theory and recent differential DO-D stretching overtone data strongly suggests the essential redox asymmetry for the reorganization free energy increments attributed to first solvating shells of cyanometalate ions involved.

Homo- and hetero-nuclear chromium(III) complexes with natural ligands. Part 3. Chromium(III)/vanadium(IV) species isolated from the redox systems

Four new heteronuclear CrIII/VIV complexes have been isolated from the redox [CrIII–Vv–L1–L2] systems (L1 = glycine, glutaminic and nicotinic acids, L2 = cysteine and glutathione). The complexes have been analysed by spectroscopic methods (diffuse reflectance u.v./vis., i.r.) and by FAB mass spectra. A significant bathochromic shift of the d–d CrIII and VIV transitions in heteronuclear complexes (d1–d3) in comparison to the CrIII homonuclear species (d3/d3) has been related to the interaction of two metal centres. Spectral analyses by the digital filter and band deconvolution methods are presented.

One‐step functionalization of an ethylene/propylene random copolymer with two different reactive groups

AbstractThe efficiency of a macromolecular compatibilizer for reactive blending is strongly dependent on its potentiality of producing a grafted or block copolymer during processing. For the preparation of such a compatibilizer, the grafting of two different reactive groups onto the backbones of ethylene/propylene copolymer macromolecules was performed. The ethylene/propylene (70/30) copolymer was then processed in a Brabender mixer at 190°C in the presence of a mixture of maleic anhydride and diethylmaleate with either dicumyl peroxide or di‐tert‐butyl peroxide as an initiator. The experiments clearly showed that the two functionalities, 2‐diethyl succinate and 2‐succinic anhydride, could be grafted in one step. The effect of the feed composition demonstrated that the two monomers influenced the reciprocal reactivity and the resulting product. A detailed Fourier transform infrared analysis of the grafted macromolecules was performed, and the respective amounts of ester and anhydride derived groups were detected by deconvolution of the vibrational bands in the carbonyl spectral region. The validity of the process on an industrial scale was tested by the successful performance of the reaction in a twin‐screw extruder. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 14–23, 2003

Electronic structure of reduced symmetry peripheral fused-ring-substituted phthalocyanines.

Reduced symmetry phthalocyanines are finding use in an increasing number of industrial applications. A detailed understanding of the electronic structure of the pi-system will greatly facilitate the design of new complexes, which fit the specifications required in many of these emerging high technology fields. NMR, electronic absorption, magnetic circular dichroism (MCD), and fluorescence emission and excitation spectra have been recorded for five generic metal phthalocyanine (MPc) derivatives in which additional benzene rings are fused either radially or obliquely onto at least one of the four peripheral benzo groups. The spectroscopy of four radially substituted compounds, zinc mononaphthotribenzotetraazaporphyrine (Zn3B1N), zinc monobenzotrinaphthotetraazaporphyrine (Zn1B3N), and two cis and trans zinc dibenzodinaphthotetraazaporphyrine (Zn2B2N) isomers, is compared to that of the obliquely fused structural isomer of Zn3B1N (Zn3BoN) and the D(4)(h)() symmetry parent compounds, ZnPc and zinc naphthalocyanine (ZnNc). The selection of Zn(II) as the central metal eliminates the possibility of charge transfer between the metal and ring. None of the complexes studied contain any sigma-bonded peripheral substituents. (1)H NMR signals of the seven compounds are assigned on the basis of the coupling patterns, integrated proton numbers, and decoupling experiments. The SIMPFIT program was used to perform spectral band deconvolution analyses of absorption and MCD spectra. ZINDO molecular orbital calculations are described, and the optical spectra are assigned on the basis of the MO models that have been developed previously to account for the spectral properties of metal porphyrin (MP(-2)) and metal phthalocyanine (MPc(-2)) complexes.

Mono-aromatic ring-fused versus adjacently di-aromatic ring-fused tetraazaporphyrins: regioselective synthesis and their spectroscopic and electrochemical properties.

A method which preferentially produces adjacently di-aromatic ring-substituted tetraazaporphyrins (TAPs) has been developed, and their electrochemical and spectroscopic properties have been studied and compared with those of the corresponding series of mono-aromatic ring-fused TAPs. Mono-aromatic ring-fused TAPs show a split Q-band, and the splitting energy increases with increasing size of the aromatic ring. In addition, for the split Q-bands, the relative intensity of the band at longer wavelength decreases with increasing molecular size of the fused aromatics, compared with the shorter wavelength band. In the di-aromatic ring-fused TAPs, this kind of splitting is not seen, and only a shift of the band is observed. The intensity and band position of the split or unsplit Q-bands are quantitatively evaluated by simultaneous band deconvolution analysis, using both electronic absorption and magnetic circular dichroism spectra. The preparation of these TAP compounds has made it possible to adjust the Q-band position in a stepwise manner between ca. 600 and 750 nm. The first reduction and oxidation potentials of the TAP ring shift negatively with increasing number and size of the fused aromatics. The extent of the shift is found to be very small for the LUMOs but significant for the HOMOs. These spectroscopic and electrochemical properties are almost perfectly reproduced by molecular orbital calculations within the framework of the Pariser-Parr-Pople approximation. In particular, a small variation of the LUMO level and large destabilization of the HOMO level on ring expansion are rationalized from the extent of stretch of molecular orbitals: i.e., since the LUMOs are localized in the central TAP moiety irrespective of the molecular size, while the HOMOs have appreciable coefficients even over the fused aromatics, the HOMO level destabilizes while the LUMO level remains constant with increasing molecular size. In one CoTAP derivative, Co(III/II) and the first ligand oxidation couples occur experimentally at the same potential.

Identification of Surface−TiClx Groups on Silica by Raman Spectroscopy

The reaction of TiCl4 with the surface of silica gel was studied by Raman spectroscopy. New bands were observed which were attributed to low-frequency vibration modes of attached Ti-species. On the basis of band deconvolution and band integration, a model is proposed to determine the relative contribution of the occurring surface reactions. This new method yields results, which are in good agreement with the previously used techniques based on elemental analysis. However, this method provides both qualitative and quantitative information in a single nondestructive experiment.

Homo- and hetero-nuclear chromium(III) complexes with natural ligands. Part 1. Spectroscopic and mass spectra studies on ternary [M–L1–L2] systems

Seven new ternary mono- and poly-nuclear CrIII complexes with natural ligands: glycine, glutaminic, nicotinic and asparginic acids, cysteine and glutathione, have been isolated and physicochemically characterized. Four of them have been tested and appear to be non-toxic. The complexes have been analysed using spectroscopic (diffuse reflectance U.v–vis., i.r., f.i.r.), magnetic methods, and (some) by FAB mass spectra. Spectral analyses with the digital filter and band deconvolution methods have been also presented.

Homo- and hetero-nuclear chromium(III) complexes with natural ligands. Part 2. Oxo- and hydroxo-bridged chromium(III)/vanadium(V) species

Six new heteropolynuclear chromium(III)/vanadium(V) complexes with natural ligands: glycine, glutaminic, nicotinic and asparginic acids, have been isolated and physicochemically characterised. The complexes have been analysed using spectroscopic (diffuse reflectance u.v.–vis., i.r.), magnetic methods and by FAB mass spectra. Spectral analyses with the digital filter and band deconvolution methods are presented. Additionally, preliminary toxicity studies have been performed.

FT-IR spectroscopy study on cutaneous neoplasie

In this work we report a preliminary study of Fourier transform infrared spectroscopy on normal and neoplastic human skin samples suffering from two kinds of cancer, namely epithelioma and basalioma. The analyzed skin samples have been drawn from different parts of the human body, after biopsies. By performing a complex band deconvolution due to the complexity of the tissue composition, the analysis within the considered frequency region (900–4000 cm −1) of the collected IR spectra, allowed us, first of all, to characterize the presence of the pathologies and to show clear different spectral features passing from the normal tissue to the malignant one in particular within the region (1500–2000 cm −1) typical of the lipid bands.

Studies on Composite Electrolytes Composed of Thermoplastic Polyurethane and Polyacrylonitrile

Composite electrolytes comprised of thermoplastic polyurethane (TPU) with polyacrylonitrile (PAN) were investigated. Differential scanning calorimetry (DSC) and impedance spectroscopy were used to monitor the changes in the thermal characteristics and bulk conductivity of the composites due to the amounts of PAN in the composite. Fourier transform infrared spectroscopy (FTIR) was employed to identify the modifications in molecular interactions associated with TPU. The deconvolution of spectral bands associated with CO and the NH group of TPU and the C⋮N group of PAN was utilized to obtain such information. The bulk conductivity of the composites with different PAN content was determined, and the influence of PAN on that was brought out. The effects of temperature and lithium salt concentration on conductivity of the composites were analyzed with respect to TPU. The conductivity changes were correlated through DSC and FTIR results.

Assignment of the optical spectrum of metal porphyrin and phthalocyanine radical anions

The approach developed previously to assign the major π → π* and π* → π* bands in the optical spectra of metallophthalocyanine radical species [ MPc (−n)](n−2)−(n = 1–6), which was based on spectral band deconvolution analyses of the UV-vis absorption and magnetic circular dichroism (MCD) spectra and ZINDO calculations, is reviewed in this paper and extended to the major bands observed in the spectrum of the zinc tetraphenylporphyrin radical anion [ ZnTPP (−3)]−. The magnetic circular dichroism spectrum is dominated by an intense pseudo A term associated with the B (or Soret) transition with bands at 445 and 465 nm. Weaker bands associated with the π* → π* transition out of the partially filled LUMO give rise to two widely separated, oppositely signed, coupled B terms in the MCD spectrum at 538 and 910 nm. The Q transition is assigned to a weak absorption band at 750 nm and a shoulder slightly to the blue at 728 nm.

A Holistic Approach for Protein Secondary Structure Estimation from Infrared Spectra in H2O Solutions

We present an improved technique for estimating protein secondary structure content from amide I and amide III band infrared spectra. This technique combines the superposition of reference spectra of pure secondary structure elements with simultaneous aromatic side chain, water vapor, and solvent background subtraction. Previous attempts to generate structural reference spectra from a basis set of reference protein spectra have had limited success because of inaccuracies arising from sequential background subtractions and spectral normalization, arbitrary spectral band truncation, and attempted resolution of spectroscopically degenerate structure classes. We eliminated these inaccuracies by defining a single mathematical function for protein spectra, permitting all subtractions, normalizations, and amide band deconvolution steps to be performed simultaneously using a single optimization algorithm. This approach circumvents many of the problems associated with the sequential nature of previous methods, especially with regard to removing the subjectivity involved in each processing step. A key element of this technique was the calculation of reference spectra for ordered helix, unordered helix, sheet, turns, and unordered structures from a basis set of spectra of well-characterized proteins. Structural reference spectra were generated in the amide I and amide III bands, both of which have been shown to be sensitive to protein secondary structure content. We accurately account for overlaps between amide and nonamide regions and allow different structure types to have different extinction coefficients. The agreement between our structure estimates, for proteins both inside and outside the basis set, and the corresponding determinations from X-ray crystallography is good.

Band deconvolution analysis of the absorption and magnetic circular dichroism spectral data of a planar phthalocyanine dimer.

The electronic absorption and magnetic circular dichroism spectral data of a phthalocyanine dicopper complex that is deduced to be very planar and to share a common benzene ring have been studied by band deconvolution analysis. The results were compared with those of the molecular orbital (MO) calculations within the framework of the Pariser-Parr-Pople (PPP) approximation. The results of the band deconvolution analysis are in good agreement with those of the PPP calculations, allowing many bands to be reasonably assigned on the basis of the MO calculations. The validity of the PPP method for the MO calculation of large molecules is also emphasized.

Comparative spectroscopic and electrochemical properties of bis(octakis(dodecylthio)naphthalocyaninato)europium(III) and bis(tetra-tert-butylnaphthalocyaninato)europium(III) complexes.

Bis(substituted-2,3-naphthalocyaninato)europium(III) complexes: bis(octakis(dodecylthio)-2,3-naphthalocyaninato)europium(III) (Eu[2,3-Nc(SC12H25)8]2, 1) and bis(tetra-tert-butyl-2,3- naphthalocyaninato)europium(III) (Eu[2,3-Nc(t-Bu)4]2, 2) have been synthesized by cyclic tetramerization of naphthalonitriles with Eu(acac)3.H2O in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in refluxing n-octanol. These compounds were characterized by UV-visible, magnetic circular dichroism (MCD), near-IR, IR, EPR, and mass spectroscopies. The absorption and MCD spectra of 1 showed splitting of the Q band, with peaks at 700 and 784 nm, red shifted from the Q band of 2 at 763 nm. The absorption and MCD spectral band deconvolution calculations of complex 1 gave two A terms in the Q-band region. The A terms are assigned to 2A2-->2E1 transitions. Cyclic voltammograms of 1 and 2 showed reversible oxidation couples at E1/2 = -0.28 V (for 2) and -0.25 V (for 1) vs ferrocenium/ferrocene (Fc+/Fc). The second oxidation exhibited a complicated behavior for both complexes. The reduction couples for 2 were observed at E1/2 = -0.61, -1.64, -1.97, and -2.42 V, and for 1 they were observed at E1/2 = -0.62, -1.60, -1.86, and -2.27 V vs Fc+/Fc. Spectral changes observed on chemical oxidation and reduction of the complexes are presented, and the behaviors of 1 and 2 are compared.

Interactions between Betacarboline and Benzenoid π Bases: FTIR Evidence for the Formation of NH−π Hydrogen Bonds

In the presence of benzene, naphthalene, or phenanthrene, the NH stretching band of betacarboline in tetrachloroethane diminishes in intensity while a new red-shifted band grows. These changes are attributed to the formation of molecular association complexes between betacarboline and the benzenoid compounds. Deconvolution of these IR bands allowed us to calculate their association constants, which increase linearly with the number of π electrons of the benzenoid substrates. The shifts of the associated bands were, however, independent of the bases. These results suggest that the complexes are stabilized by the hydrogen-bonding interaction between the pyrrolic NH group of betacarboline and the π-delocalized electrons of the benzenoid substrates. Low-level semiempirical calculations (AM1/MOPAC) also predict T-shaped structures as the most stable. On the other hand, experiments using harmane, the 1-methylated betacarboline, proved steric hindrance for naphthalene and phenanthrene, which should be a conseque...

Synthesis, Spectroscopy, and Molecular Orbital Calculations of Subazaporphyrins, Subphthalocyanines, Subnaphthalocyanines, and Compounds Derived Therefrom by Ring Expansion1

A subazaporphyrin (SubAP), tert-butylated and crowned subphthalocyanines (tBSubPc and SubCRPc), a μ-oxo dimer of tert-butylated SubPc {(tBSubPc)2O}, a subnaphthalocyanine (SubNc), and monosubstituted type unsymmetrical phthalocyanine (Pc) and naphthalocyanine (Nc) analogues have been synthesized. In particular, unsymmetrical Pc's and Nc's have been prepared in moderate yields by the ring expansion reaction of structurally distorted SubPc's and SubNc's with isoindolediimine derivatives in dimethyl sulfoxide−chloronaphthalene (or chlorobenzenes or aromatic hydrocarbons such as toluene and xylene) mixtures. The compounds have been characterized by electronic absorption, magnetic circular dichroism (MCD), fluorescence emission, and nuclear magnetic resonance spectroscopy. Both the Soret bands and Q-bands shift to longer wavelength and gain intensity in the order SubAP, SubPc, and SubNc. Fluorescence quantum yields and lifetimes generally decrease with decreasing molecular symmetry. Circular dichroism and NMR spectroscopy have revealed that a SubPc with three 15-crown-5 ether voids having a phenyl group as an axial ligand (SubCRPc) forms inclusion complexes with 2,6-dimethyl-β-cyclodextrin in acetonitrile or water−acetonitrile mixtures, while the electronic absorption spectroscopy suggests that it is not dimerized by the addition of cations such as K+, Rb+, Ce+, i.e., cations which are effective in dimerizing Pc's with 15-crown-5 ether voids. Molecular orbital (MO) calculations within the framework of the Pariser−Parr−Pople approximation have succeeded in reproducing the optical absorption experimental data of not only the parent subazamacrocycles but also Pc derivatives with lower symmetry obtained by the ring expansion reaction. The correspondence between MO calculations and experiments suggests strongly that, in the metal-free unsymmetrical Pc's, two pyrrole hydrogen atoms are bound to the nitrogens along the short axis. Comparison of formation, bonding, and donation energies between SubPc and typical Pc, i.e., MgPc by natural bond orbital analysis, suggests that the distortion energy is not the major reason for the ring expansion reactivity of SubPc, and that the lack of donor−acceptor stabilization in B−N(pyrrole) bonds destabilizes SubPc. Band deconvolution of the electronic absorption and MCD spectra of SubPc with the same set of bands (with the same centers and width) experimentally identified that the excited state of the Q-band of SubPc is orbitally degenerate, with three degenerate transitions located in the 250−450-nm region. In particular, the transition at 359 nm corresponds to a shoulder seen on the red side of the Soret band tail. Time-resolved EPR analysis has shown that the size of the π-system of SubPc is, indeed, smaller than that of Pc's.

High Overtones of C−H Stretching Vibrations in Isoxazole, Thiazole, and Related Methyl and Dimethyl Derivatives

The high overtone spectra of liquid isoxazole and thiazole, two five-membered heterocyclic molecules with different aromaticity characters, have been investigated in the C−H stretching region by visible absorption spectroscopy. The local-mode model describes satisfactorily the C−H stretching vibrations at the fifth and sixth quanta of excitation, where the localized character is increased. Each overtone band generally displays a number of peaks corresponding to the different types of C−H oscillators. Comparison between the overtone spectra of the parent molecules and those of the methyl derivatives provided sufficient information for a conclusive assignment of the progressions. Deconvolution of the fifth overtone bands gave further evidence regarding the shape and the width of the distinct peaks. Anharmonicity values of the overtone vibrations, C−H bond lengths, and force constants were obtained from the local-mode analysis and discussed in comparison with the results obtained from the normal-mode approximation. A correlation between overtone frequencies and chemical shifts in proton magnetic resonance, generally observed in aromatic compounds, has been found only for thiazole, whose aromaticity is responsible for a significant electron current in the ring.

Raman spectroscopic study of acetone–phenol mixtures

Acetone–phenol mixtures with phenol mole fractions in the range 0.079–0.6000 were studied by Raman spectroscopy. Spectra were obtained in the regions of acetone C=O stretching and C–C symmetric stretching bands. Principal factor analysis applied to the set of C=O stretching bands revealed two independent components belonging to free and hydrogen-bonded acetone. Interaction with phenol produces a new band at a lower wavenumber in the C=O vibration region and an additional band at a higher wavenumber in the C–C symmetric stretch region. These changes were explained by charge delocalization induced by the hydrogen bond. On applying band deconvolution and target factor analysis, it was deduced that the equilibrium constant K of 1:1 acetone–phenol complex formation is too high to be determined by Raman spectroscopy in the range 0.079–0.400 mole fraction of phenol. At equal mole fractions of acetone and phenol, values of K=2.61 and 3.22 dm3 mol-1 were obtained by deconvolution and target factor analysis, respectively. An investigation of ternary solutions with an inert solvent showed no significant differences in acetone–phenol interaction between this system and binary mixtures. © 1998 John Wiley & Sons, Ltd.

Raman spectroscopic study of acetone–phenol mixtures

Acetone–phenol mixtures with phenol mole fractions in the range 0.079–0.6000 were studied by Raman spectroscopy. Spectra were obtained in the regions of acetone C=O stretching and C–C symmetric stretching bands. Principal factor analysis applied to the set of C=O stretching bands revealed two independent components belonging to free and hydrogen-bonded acetone. Interaction with phenol produces a new band at a lower wavenumber in the C=O vibration region and an additional band at a higher wavenumber in the C–C symmetric stretch region. These changes were explained by charge delocalization induced by the hydrogen bond. On applying band deconvolution and target factor analysis, it was deduced that the equilibrium constant K of 1:1 acetone–phenol complex formation is too high to be determined by Raman spectroscopy in the range 0.079–0.400 mole fraction of phenol. At equal mole fractions of acetone and phenol, values of K=2.61 and 3.22 dm3 mol-1 were obtained by deconvolution and target factor analysis, respectively. An investigation of ternary solutions with an inert solvent showed no significant differences in acetone–phenol interaction between this system and binary mixtures. © 1998 John Wiley & Sons, Ltd.