Power law behavior of the isotope yield distributions in the multifragmentation regime of heavy ion reactions

Isotope yield distributions in the multifragmentation regime were studied with high-quality isotope identification, focusing on the intermediate mass fragments (IMFs) produced in semiviolent collisions. The yields were analyzed within the framework of a modified Fisher model. Using the ratio of the mass-dependent symmetry energy coefficient relative to the temperature, a(sym)/T, extracted in previous work and that of the pairing term, a(p)/T, extracted from this work, and assuming that both reflect secondary decay processes, the experimentally observed isotope yields were corrected for these effects. For a given I = N - Z value, the corrected yields of isotopes relative to the yield of C-12 show a power law distribution Y (N, Z)/Y(C-12) similar to A(-tau) in the mass range 1 <= A <= 30, and the distributions are almost identical for the different reactions studied. The observed power law distributions change systematically when I of the isotopes changes and the extracted tau value decreases from 3.9 to 1.0 as I increases from -1 to 3. These observations are well reproduced by a simple deexcitation model, with which the power law distribution of the primary isotopes is determined to be tau(prim) = 2.4 +/- 0.2, suggesting that the disassembling system at the time of the fragment formation is indeed at, or very near, the critical point.

Carbon monoxide adsorption on molybdenum phosphides: Fourier transform infrared spectroscopic and density functional theory studies

Molybdenum phosphide (MoP) and supported molybdenum phosphide (MoP/gamma-Al2O3) have been prepared by the temperature-programmed reduction method. The surface sites of the MoP/gamma-Al2O3 catalyst were characterized by carbon monoxide (CO) adsorption with in situ Fourier transform infrared (FT-IR) spectroscopy. A characteristic IR band at 2037 cm(-1) was observed on the MoP/gamma-Al2O3 that was reduced at 973 K. This band is attributed to linearly adsorbed CO on Mo atoms of the MoP surface and is similar to IR bands at 2040-2060 cm(-1), which correspond to CO that has been adsorbed on some noble metals, such as platinum, palladium, and rhodium. Density functional calculations of the structure of molybdenum phosphides, as well as CO chemisorption on the MoP(001) surface, have also been studied on periodic surface models, using the generalized gradient approximation (GGA) for the exchange-correlation functional. The results show that the chemisorption of CO on MoP occurred mainly on top of molybdenum, because the bonding of CO requires a localized mininum potential energy. The adsorption energy obtained is DeltaH(ads) approximate to -2.18 eV, and the vibrational frequency of CO is 2047 cm-1, which is in good agreement with the IR result of CO chernisorption on MoP/gamma-Al2O3.

Exploring the Origin of Power Law Distribution in Single-Molecule Conformation Dynamics: Energy Landscape Perspectives

We explored the origin of power law distribution observed in single-molecule conformational dynamics experiments. By establishing a kinetic master equation approach to study statistically the microscopic state dynamics, we show that the underlying landscape with exponentially distributed density of states leads to power law distribution of kinetics. The exponential density of states emerges when the system becomes glassy and landscape becomes rough with significant trapping.

Structural characterization and identification of dibenzocyclooctadiene lignans in Fructus Schisandrae using electrospray ionization ion trap multiple-stage tandem mass spectrometry and electrospray ionization Fourier transform ion cyclotron resonance multiple-stage tandem mass spectrometry

The electrospray ionization ion trap multiple-stage tandem mass spectrometry (ESI-MSn) and electrospray ionization Fourier transform ion cyclotron resonance multiple-stage tandem mass spectrometry (ESI-FT-ICR-MSn) have been applied successfully to the direct investigation of a number of dibenzocyclooctadiene lignan constituents from the methanol extracts of the Fructus Schisandrae in the positive ion mode. The detailed structural characterization of the same skeleton and different peripheral substituents had been studied and the precise elemental compositions of ions at high mass resolution had been obtained. So the fragmentation mechanisms could be clarified.

Studies of the intermolecular DNA triplexes of C+center dot GC and T center dot AT triplets by electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry

Formation and stabilities of four 14-mer intermolecular DNA triplexes, consisting of third strands with repeating sequence CTCT, CCTT, CTT, or TTT, were studied by electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) in the gas phase. The gas-phase stabilities of the triplexes were compared with their CD spectra and melting behaviors in solution, and parallel correlation between two phases were obtained. In the presence of 20 mm NH4+ (pH 5.5), the formation of the TTT triplex was not detected in both solution and the gas phase.

Structural analysis of monoterpene glycosides extracted from Paeonia lactiflora Pall. using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

Paeoniflorin standard was first investigated by electrospray ionization Fourier transform ion cyclotron resonance tandem mass spectrometry (ESI-FTICR-MS/MS) using a sustained off-resonance irradiation (SORI) collision-induced dissociation (CID) method at high mass resolution. The experimental results demonstrated that the unambiguous elemental composition of product ions can be obtained at high mass resolution. Comparing MS/MS spectra and the experimental methods of hydrogen and deuterium exchange, the logical fragmentation pathways of paeoniflorin have been proposed. Then, the extracts of the traditional Chinese medicine Paeonia lactiflora Pall. were analyzed by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS). By comparison with the ESI-FTICR-MS/MS data of paeoniflorin, the isomers paeoniflorin and albiflorin in Paeonia lactiflora Pall. have been identified using HPLC/MS with CID in an ion trap and in-source CID. Furthermore, using the characteristic fragmentation pathways, the retention times (t(R)) in HPLC and MS/MS spectra, the structures of three other kinds of monoterpene glycoside compounds have been identified on-line without time-consuming isolation.

A study of isomeric diglycosyl flavonoids by SORI CID of Fourier transform ion cyclotron mass Spectrometry in negative ion mode

High-resolution Sustained off resonance irradiation (SORI) CID was employed to distinguish four pairs of isomeric diglycosyl flavonoids in the negative mode using the electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FTICR MS). All of these isomers can be distinguished via MS/MS data. For these diglycosyl flavones and flavanones, the deprotonated alpha 1-->6 linkage diglycosyl flavonoids produce fewer fragments than the alpha 1-->2 linkage type compounds and the Retro-Diels-Alder (RDA) reaction in MS/MS only takes place when the aglycone is a flavanone and glycosylated with an alpha 1-->2 intersaccharide linkage disaccharide. The deprotonation sites after collisional activation are discussed according to the high mass accuracy and high-resolution data of tandem spectrometry. Some of these high-resolution SORI CID product ions from alpha 1-->2 linkage diglycosyl flavonoids involve multibond cleavages; the possible mechanism is discussed based on the computer modeling using Gaussian 03 program package at the B3LYP/6-31G level of theory. Unambiguous elementary composition data provides fragmentation information that has not been reported previously.

Analysis of strychnos alkaloids using electrospray ionization Fourier transform ion cyclotron resonance multi-stage tandem mass spectrometry

The fragmentations of four strychnos alkaloids have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) in the positive ion mode. Experiments using multi-stage tandem mass spectrometry (ESI-FT-ICR-MSn) allowed us to obtain precise elemental compositions of product ions at high mass resolution. The experimental data demonstrated that the nitrogen bridge and the coordinated oxygen atom on the nitrogen bridge in the alkaloid compounds were the active sites in the MS2 fragmentations. The loss of CH3 or the OCH3 group in those alkaloids, which have an OCH3 substituent, was the dominant fragmentation mode in the MS3 fragmentations. Logical fragmentation schemes for strychnos alkaloids have been proposed and these should be useful for the identification of these compounds.

Self-assembled monolayer growth of octanol on mica: Atomic force microscopy and Fourier-transform infrared spectroscopy studies

The growth kinetics of self-assembled monolayers formed by exposing freshly cleaved mica to octanol solution has been studied by atomic force microscopy (AFM) and Fourier-transform infrared spectroscopy (FTIR). AFM images of samples immersed in octanol for varying exposure times showed that before forming a complete monolayer the octanol molecules aggregated in the form of small islands on the mica surface. With the proceeding of immersion, these islands gradually grew and merged into larger patches. Finally, a close-packed film with uniform appearance and few defects was formed. The thickness of the final film showed 0.8 nm in height, which corresponded to the 40degrees tilt molecular conformation of the octanol monolayer. The growth mechanisms consisted of nucleation, growth, and coalescence of the submonolayer films. The growth process was also confirmed by FTIR. And the surface coverage of the submonolayer islands estimated from AFM images and FTIR spectra as a function of immersion time was quite consistent.

Investigation of thermal unfolding process of cyanic adduct of horseradish peroxidase by Fourier transform infrared and circular dichroism spectrometry

Detailed circular dichroism(CD) and Fourier transform infrared (FTIR) studies have been carried out to monitor thermal unfolding of horseradish peroxidase isoenzyme C(HRP) inhibited by CN(HRP-CN). The results suggest that HRP-CN is quite different from native HRP with different spin states of Fe of heme and different coordinated states. Cyanide becomes the sixth ligand of Fe(I) of heme and the hydrogen-binding network is destroyed partly at the same time, which cause the drastic decrease of thermal stability of HRP. The FTIR and Soret-CD spectra analysis demonstrate that during the heating process there is an intermediate state(I') which has both partly destroyed secondary and tertiary structures of native HRP, then it is the appearance of protein aggregation state(A) after fully unfolding. The unfolding pathway thus can be shown as follows: I -->I'-->U -->A.

In-situ microscopic Fourier transform infrared spectroelectrochemistry of redox mechanism for electroactive species in polyelectrolyte

Studies for the development of the in-situ microscopic FTIR spectroelectrochemistry (MFTIRS) have been carried out in polyethylene glycol(PEG) polyelectrolyte, Redox reaction mechanisms of various electroactive substances involving inorganic salt, organic compound and inorganic polymeric particles have been studied.

In-situ Fourier transform infrared spectroelectrochemistry as a probe of the glassy carbon electrode chemically modified by nickel (II)-cyanometallates

A new nickel (II)-cyanometallates modified on glassy carbon electrode was prepared by a new method and studied by cyclic voltammetry and in situ Fourier transform infrared (FTIR) spectroelectrochemistry. It was found that the NiHCF film existed in two forms: Ni2Fe(II)-(CN)(6) and M2NiFe(II)(CN)(6), Fe(CN)(3)(6-) codeposited in the NiHCF film existing in free cation or bridged-bond state depended on the property of the cations in electrolyte: in NaCl and LiCl solution, it is in bridges-bonded, but in HCl and KCl, it is free.