Ferrocene-containing polyesters and polyamides

A series of ferrocene-containing polyesters and polyamides were prepared by refluxing 1,1′-dichlorocarbonylferrocene with various diols and primary diamines in xylene–pyridine solvent. The polyamides were all solids, but some of the polyesters were liquids. Reported are the infrared spectra and solubility characteristics of all the polymers and, where possible, the molecular weight and molecular weight distributions. In general, these polyamides and polyesters were of relatively low molecular weight (below 4000), but the polyesters were readily chain extended and crosslinked by di- and triisocyanates. Elemental analyses are reported for all the polymers prepared.     

Ferrocene-containing polymers. I. Radiation-induced polymerization of ferrocenylmethyl methacrylate

γ-Ray-induced polymerizations of ferrocenylmethyl methacrylate (FMMA) in crystalline and amorphous states were investigated with kinetical and ESR methods. In the crystalline state the polymerization of FMMA proceeded slowly and gave low-molecular-weight polymers, whereas in the amorphous state it proceeded rapidly and gave polymers of much higher molecular weight. Molecular weight distributions of these polymers were binodal. The temperature dependence and the dose-rate dependence of the polymerization rates were different between the two states. Wide-line nuclear magnetic resonance (NMR) spectra of the amorphous monomer suggested that the polymerization proceeded in a supercooled state. Electron spin resonance (ESR) spectra of γ-irradiated FMMA and 1,1′-ferrocenyl-di(methyl methacrylate) showed that ferrocene radicals and methacrylic radicals were formed simultaneously at low temperature; with increasing temperature the former radicals disappeared, whereas the latter changed into growing chain radicals. The yields of radicals were relatively low; this means that ferrocene groups in the monomers behave as a radiation energy absorber.     

Effect of ion-molecule collisions in the vacuum chamber of an electrospray time-of-flight mass spectrometer on mass spectra of proteins

Electrospray ionization spectra of positive multiply charged ions of several proteins with molecular weight from 8565 to 339,100 u were recorded at different pressures of residual gas in the vacuum chamber of an electrospray time-of-flight mass spectrometer. The pressure was varied in the range (0.2 to 5) × 10^?6 torr. The effect of pressure was found to be significant even for the lightest protein investigated (ubiquitin), which resulted in a decrease of both sensitivity and resolution. Investigations of the arrival-time distributions and the energy distributions of ions showed that collision-induced dissociation (CID) of the protein ions in the drift region is the main process responsible for the effect. Several CID cross sections of proteins were estimated from a series of mass spectra recorded at different pressures in the reflecting mode: 1150 Ų for cytochrome c (averaged over charge states z = 14–18), 800 Ų for lysozyme (z = 8–10), 1840 Ų for apomyoglobin (z = 12–25), 800 Ų for holomyoglobin (z = 8), and 2500 Ų for carbonic anhydrase II (z = 22–35). Several experiments with large proteins in their native conformations and low charge states (m/z 0,000) demonstrate that these ions are less sensitive to high residual gas pressure.     

Molecular structure, vibrational spectroscopic, first hyperpolarizability, NBO and HOMO, LUMO studies of P-Iodobenzene sulfonyl chloride

In this work, the experimental and theoretical vibrational spectra of P-Iodobenzene sulfonyl chloride (P-IBSC) were studied. P-IBSC and its derivatives present in many biologically active compounds. Because of their spectroscopic properties and chemical significance in particular, sulfonyl chloride and its derivatives have been studied extensively by spectroscopic (FTIR and FT-Raman spectra) and theoretical methods. The infrared spectra of these compounds were recorded in condensed states, while the Raman spectra were measured without polarization using both parallel and perpendicular polarizations of scattered light. The molecular geometry, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), first order hyperpolarizability and thermodynamic properties of P-IBSC have been computed with the help of density functional theory (B3LYP) and ab initio (HF) methods with the LanL2DZ basis set. The HOMO and LUMO energy gap explains the charge transfer interactions taking place within the molecule. NBO study explains charge delocalization of the molecule. The contributions of the different modes to each wave number were determined using potential energy distributions (PEDs). The experimental and calculated results were consistent with each other.     

Matrix-assisted and polymer-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of low molecular weight polystyrenes and polyethylene glycols

Recently, matrices based on oligomers of dioxin and thiophene (polymer-assisted laser desorption/ionization (PALDI)) have been described for mass spectrometric (MS) analysis of low molecular weight compounds (Woldegiorgis A, von Kieseritzky F, Dahlstedt E, Hellberg J, Brinck T, Roeraade J. Rapid Commun. Mass Spectrom. 2004; 18: 841-852). In this paper, we report the use of PALDI matrices for low molecular weight polymers. An evaluation with polystyrene and polyethylene glycol showed that no charge transfer ionization occurs. Ionization is mediated through metal ion adduction. Comparison of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) data for two very low molecular weight polymers with data obtained from size-exclusion chromatography (SEC) revealed a systematic difference regarding mean molecular weight and dispersity. Further, the mass spectra obtained with PALDI matrices had a higher signal-to-noise ratio than the spectra obtained with conventional matrices. For polymers with higher molecular weights (>1500 Da), the conventional matrices gave better performance. For evaluation of the MALDI spectra, three non-linear mathematical models were evaluated to model the cumulative distributions of the different oligomers and their maximal values of Mw, Mn and PDI. Models based on sigmoidal or Boltzmann equations proved to be most suitable. Objective modeling tools are necessary to compare different sample and instrumental conditions during method optimization of MALDI analysis of polymers, since the bias between MALDI and SEC data can be misleading.     

The conformation and vibrational spectra of 1,5-hexadiene-3-yne (divinylacetylene) and perchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene)

Infrared spectra of 1,5-hexadiene-S-yne (divinylacetylene) have been recorded in the vapour phase, in solution and in the amorphous and crystalline solid states at 90 K in the region 4000–4020 cm^?1. Correspondingly, IR spectra ofperchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene) as a melt, as a solute in various solvents and as a solid at 90 K have been obtained. Raman spectra of the two compounds were recorded in the liquid (molten) state including polarization measurements, and as crystalline solids at 90 K.The spectral data indicate that each compound exists as one conformer only in the various states of aggregation. In divinylacetylene the molecular symmetry appears to be anti (C_2h) while for perchlorodivinylacetylene the symmetry is either C_2v (syn) or C₂ (gauche). Vibrational assignments for the spectra of both molecules are presented and the values are compared with the results of normal coordinate analyses.     

Infrared, surface-assisted laser desorption ionization mass spectrometry on frozen aqueous solutions of proteins and peptides using suspensions of organic solids

Surface-assisted, laser desorption ionization (SALDI) time-of-flight mass spectra of proteins and peptides have been obtained from bulk frozen aqueous solutions by adding solid organic powders to the solutions before freezing. Abundant analyte ions were obtained with a 3.28 µm Nd:YAG/OPO laser. 20 compounds were evaluated as solid additives, and 16 yielded protein mass spectra. Successful solids included compounds like pyrene, aspartic acid, and polystyrene. The best results were obtained with nicotinic acid and indole-2-carboxylic acid, which yielded protein mass spectra anywhere on the sample and with every laser shot. Compared with ultraviolet-matrix-assisted laser desorption ionization on the same instrument, cryo-IR-SALDI had a comparable detection limit (≈1 µM), a lower mass resolution for peptides, and a higher mass resolution for large proteins. Approximately 2500 cryo-IR-SALDI mass spectra were obtained from a single spot on a 0.3-mm-thick frozen sample before the metal surface was reached. About 0.1 nL of frozen solution was desorbed per laser shot. The extent of protein charging varied between the SALDI solids used. With thymine, myoglobin charge states up to MH ₁₂ ⁺¹² were observed. It is tentatively concluded that observed ions are preformed in the frozen sample.     

Computational prediction and experimental selectivity coefficients for hydroxyzine and cetirizine molecularly imprinted polymer based potentiometric sensors

In spite of the increasing usages number of molecularly imprinted polymers (MIPs) in many scientific applications, the theoretical aspects of participating intra molecular forces are not fully understood. This work investigates effects of the electrostatic force, the Mulliken charge and the role of cavity's backbone atoms on the selectivity of MIPs. Moreover, charge distribution, which is a computational parameter, was proposed for the prediction of the selectivity coefficients of MIP-based sensors. In the computational approaches and experimental study, methacrylic acid (MAA) was chosen as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the cross linker for hydroxyzine and cetirizine imprinted polymers. Ab initio, DFT B3LYP method was carried out on molecular optimization. With regard to results obtained from molecules optimization and hydrogen bonding properties, possible configurations of 1:n (n ≤ 5) template/monomer complexes were designed and optimized. The binding energy for each complex in gas phase was calculated. Depending on the most stable configuration, hydroxyzine and cetirizine imprinted polymer models were designed. The calculations including the porogen were also investigated. The theoretical charge distributions for the template and some potential interfering molecules were calculated. The results showed a correlation between the selectivity coefficients and the theoretical charge distributions. The results surprisingly show that charge distribution based model was able to predict the selectivity coefficients of MIP based potentiometric sensors.     

Conformer selection of protein ions by ion mobility in a triple quadrupole mass spectrometer

Electrospray mass spectra of multiply charged protein molecules show two distinct charge state distributions proposed to correspond to a more highly charged, open conformational form and a lower charged, folded form. Elastic collisions carried out in the radiofrequency-only collision cell of a triple quadrupole mass spectrometer have dramatic effects on the appearance of the mass spectra. The different cross sectional areas of the conformers allow preferential selection of one charge state distribution over the other on the basis of ion mobility. Preferential selection is dependent on the nature and pressure of the target gas as well as the nature of the protein. In the case of positively charged horse heart apomyoglobin (MW 16,951 da), a high charge state distribution centered around (M + 20H)²⁰⁺ predominates at low target gas pressures and a second distribution centered around (M + 10H)¹⁰⁺ predominates at high target gas pressures. Bimodal distributions are observed at intermediate pressures and, remarkably, charge states between the two distributions are not effectively populated under most of the conditions examined. Hard sphere collision calculations show large differences in collision frequencies and in the corresponding kinetic energy losses for the two conformational states and they demonstrate that the observed charge state selectivity can be explained through elastic collisions.     

Local many-electron states in transition metal oxides and their surface complexes with atomic and molecular oxygen

The local many-electron states in transition metal oxides (TMOs) are considered in the framework of the effective Hamiltonian of the crystal field (EHCF) method. The calculations are performed with use of the 5×5×5 clusters modeling TMOs with the rock salt crystal structure. The d-d excitation spectra are calculated and discussed with the aim of interpreting the experimental data on optical adsorption and electron energy loss spectra. The EHCF method is extended to account for the electron correlation in the d-shell and some electronic variables of ligands simultaneously. This approach is used to calculate the states of atomic and molecular oxygen on the surfaces of the TMOs. The possible role of geometric parameters of the adsorption complex is evaluated. The metal-oxygen distance and the exit of the metal ion from the surface plane are varied in a wide range. In the case of molecular oxygen different coordination forms are considered and for all adsorption systems the weights of different oxygen states (triplet, singlet, and charge transfer) are estimated.     

The conformation and vibrational spectra of trans-1,4-dihalocyclohexanes: Part II. trans-1,4-Chlorobromocyclohexane and trans-1,4-chloroiodocyclohexane

The IR spectra of trans-1,4-chlorobromo- and trans-1,4-chloroiodocyclohexane were recorded in the region 4000–30 cm^?1 as solutes in various solvents, as KI and polyethylene pellets and as solids under high pressure (1–50 kbar at ambient temperature). Additional spectra of the melts, amorphous and annealed crystalline solids at 90 K and dichroism of oriented polycrystalline films were obtained above 200 cm^?1. Raman spectra of the compounds were recorded in the amorphous and crystalline states at 90 K, and polarization measurements were made in CCl₄ CS₂ and C₆H₆ solution.The title compounds existed as an equilibrium mixture of ee and aa conformers in solution, in the melts and in the amorphous solids at 90 K. When heated to temperatures in the region 165–195 K the amorphous solids apparently crystallized into a metastable form containing the aa conformer, while above 200 K the solids were converted to a stable crystal containing the ee conformer. Under high pressure the concentration of the aa conformer increased and this form was almost exclusively present at ca. 50 kbar nominal pressure.The fundamental frequencies for both conformers were assigned in terms of C_smolecular symmetry. An extensive normal coordinate analysis on six trans-1,4-dihalocyclohexanes was carried out using the overlay technique.     

RG+ formation following photolysis of NO-RG via the Ã-X transition: a velocity map imaging study

Kr(+) and Xe(+) formation following photodissociation of NO-RG (RG = Kr or Xe) molecules via the ?-X electronic transition in the 44,150-44,350 cm(-1) region has been investigated using velocity map imaging. Nuclear kinetic energy release (nKER) spectra indicate that the NO cofragment is produced in multiple vibrational states of the electronic ground state, with a high degree of rotational excitation. Photofragment angular distributions and nKERs are consistent with photo-induced charge transfer at the two-photon level followed by dissociative ionization at the three-photon level. RG(+) angular distributions showing highly parallel character relative to the laser polarization axis are indicative of a high degree of molecular alignment in the dissociating species.     

Electronic structure of benzaldehyde: A comparative study of the lowest excited singlet π* ← π and π* ← n states

VE-PPP, CNDO/2, and CNDO/s-CI methods have been used to investigate the electronic spectrum and structure of benzaldehyde. Electronic charge distributions and bond orders in the ground and lowest excited singlet π* ← π and π* ← n states of the molecule have been studied. The molecule has been shown to be nonplanar in the lowest π* ← n excited singlet state, in agreement with the conclusions drawn from the study of vibrational spectra. Dipole moments in both excited states have been shown to be larger than the ground-state value. Thus, the ambiguity in the experimental result for the π* ← π n excited singlet state dipole moment has been resolved. It has been shown that the n orbital is mainly localized on the CHO group. Furthermore, charge distributions, dipole moments, and molecular geometries are shown to be very different in the excited singlet π* ← π and π* ← n states.     

Collisional activation and collision-activated dissociation of large multiply charged polypeptides and proteins produced by electrospray ionization

Collisional activation (CA) and collision-activated dissociation (CAD) of multiply protonated molecular ions produced by electrospray ionization using an atmospheric pressure source are described. A TAGA 6000E triple-quadrupole mass spectrometer, in both unmodified and differentially pumped inlet arrangements, was used to investigate CA and CAD during transfer through the atmosphere-vacuum interface and subsequent CAD in the tandem instrument. Melittin, which has a molecular weight (M _r ) of 2846, is efficiently dissociated in the interface at higher nozzle-skimmer voltages, yielding fragmentation that can be assigned to the various charge states. Selection of such product ions formed in the interface for subsequent tandem mass spectrometry allows confirmation of earlier sequence assignments and extends the utility of these methods. Various charge states of larger polypeptides, such as human parathyroid hormone (1–44) (M _r 5064), can be efficiently collisionally dissociated in the second (rf-only) quadrupole. However, for molecular ions of this size, the low-energy collisions used for CAD yield only partial sequence information. For large molecules such as horse heart myoglobin (M _r 16,951), the effects of nozzle-skimmer bias are explored, and it is shown that higher charge states (at ≤ m/z 1400) can be effectively dissociated in the interface. Initial results for both metastable (unimolecular) and CAD for myoglobin are reported. The potential and limitations of CAD for large biomolecular ions are discussed. The feasibility of fingerprinting for proteins is illustrated by the CAD spectra of cytochrome c from nine species.     

Vapor Treatment of Electrospray Droplets: Evidence for the Folding of Initially Denatured Proteins on the Sub-Millisecond Time-Scale

The exposure of electrospray droplets generated from either highly acidic or highly basic solutions to basic or acidic vapors, respectively, admitted into the counter-current drying gas, has been shown to lead to significant changes in the observed charge state distributions of proteins. In both cases, distributions of charge states changed from relatively high charge states, indicative of largely denatured proteins, to lower charge state distributions that are more consistent with native protein conformations. Ubiquitin, cytochrome c, myoglobin, and carbonic anhydrase were used as model systems. In some cases, bimodal distributions were observed that are not noted under any solution pH conditions. The extent to which changes in charge state distributions occur depends upon the initial solution pH and the pK_a or pK_b of the acidic or basic reagent, respectively. The evolution of charged droplets in the sampling region of the mass spectrometer inlet aperture, where the vapor exposure takes place, occurs within roughly 1 ms. The observed changes in the spectra, therefore, are a function of the magnitude of the pH change as well as the rates at which the proteins can respond to this change. The exposure of electrospray droplets in this fashion may provide means for accessing transient folding states for further characterization by mass spectrometry.     

Analysis of thermal reactions of photochromic species in glassy matrices based on the concept of dispersive processes

Thermal decoloration reactions of photochromic spiroindolinonaphthoxazine in glassy polymer matrices have been studied. The non-exponential kinetic behaviour in these systems was analyzed using the phenomenological equation with an exp(-t^α) dependency describing dispersive processes in glassy solids. The dispersive parameter α represents the molecular environmental characteristics of matrix polymers.     

Thiol-terminated hydroxy-functional polymer as a transtab toward polymer latex particles

Hydroxy-functional macrodisulfides have been synthesized by atom transfer radical polymerization of 2-hydroxyethyl methacrylate or 2-hydroxypropyl methacrylate in 2-propanol. Mean degrees of polymerization of the polymer chains beside the disulfide were fixed at 30, 60, and 90; since ATRP has reasonably good living character, the molecular weight distribution is relatively narrow. Furthermore, the macrodisulfides were reduced to synthesize corresponding thiol-terminated polymers with relatively narrow molecular weight distributions. ¹H nuclear magnetic resonance and gel permeation chromatography were used to characterize the macrodisulfides and thiol-terminated polymers in terms of their chemical structure, molecular weight, and polydispersity, respectively. Dispersion polymerizations of styrene using the thiol-terminated hydroxy-functional polymers as a transtab (chain transfer agent + colloidal stabilizer) in ethanol resulted in colloidally stable submicrometer-sized polystyrene latex particles. Scanning electron microscopy, Fourier transform infrared spectroscopy, and elemental microanalysis were used to characterize the particles in terms of their morphologies, particle sizes and their distributions, and chemical compositions.     

Unusual effect of carborane ligands on the electronic properties of <Emphasis Type="Italic">d</Emphasis><Superscript>0</Superscript>-metal complexes

Modern quantum-chemical and photophysical methods have been used to study the structure of the frontier molecular orbitals and the nature of ligand-to-metal charge transfer (LMCT) transitions of structurally complex d ⁰-metallocenes. It has been shown that such metal complexes with carboranyl ligands have emissive LMCT states with preferential charge transfer from aromatic π-ligands to the metal and a large electric dipole moment. The electronic excitation and absorption spectra were simulated for the first time, and dipole moments of metal complexes containing metal–carbon σ- and π-bonds were estimated, which is of fundamental importance for the development of molecular photonics.     

Synthesis, characterization and properties of naphthoxazine-functional poly(propyleneoxide)s

Thermally curable naphthoxazine-functionalized polymers were synthesized by the reaction of linear (diamines) and branched (triamines) poly(propyleneoxide)s (Jeffamine series) having various molecular weights, with p-formaldehyde, and 2-naphthol. The structures of the resulting polymers were characterized by using FT-IR and ¹H-NMR. In addition, curing behavior of these polymers was studied using differential scanning calorimeter (DSC). Hydrophilicity of these polymers, both in cured and non-cured states, was investigated by water contact angle measurements. The surface topographies of the polymers were also examined by atomic force microscope (AFM).