Structure and formation of gaseous [C4H6O]+˙ ions: 1—The enolic ions [CH2C(OH)?CHCH2]+˙ and [CH2CH?CHCH(OH)]+˙ and their relationship with their keto counterparts

The [C₄H₆O]^+˙ ion of structure [CH₂?CHCH?CHOH]^+˙ (a) is generated by loss of C₄H₈ from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔH_f of [CH₂?CHCH?CHOH]^+˙ was estimated to be 736 kJ mol^?1. The isomeric ion [CH₂?C(OH)CH?CH₂]^+˙ (b) was shown to have ΔH_f, ? 761 kJ mol^?1, 54 kJ mol^?1 less than that of its keto analogue [CH₃COCH?CH₂]^+˙. Ion [CH₂?C(OH)CH?CH₂]^+˙ may be generated by loss of C₂H₄ from ionized hex-1-en-3-one or by loss of C₄H₈ from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C₄H₆O]^+˙ ion generated by loss of C₂H₄ from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH₂?CHCH?CHOH]^+˙ and [CH₂?C(OH)CH?CH₂]^+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH₃˙ and CO, [CH₂?CHCH?CHOH]⁺˙ and [CH₂?C(OH)CH?CH₂]^+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C₄H₆O]^+˙ ion [CH₂?C?CHCH₂OH]^+˙ are also reported.     

5,6-位烷氧基保护和3-/3,8-位三苯胺拓展1,10-菲咯啉衍生物与银离子识别

在1,10-菲咯啉的5,6-位引入烷氧基后,分子的反应活性明显提升,同时获得的三苯胺基（TPA）衍生物的溶解性也明显提高。晶体结构分析表明：烷氧基团是以六元环形式的乙撑二氧结构接入1,10-菲咯啉环的5,6-位。化合物TPA1和TPA2均对Ag+表现出选择性识别作用。其中,TPA1与Ag⁺作用后虽然荧光减弱不明显,但其发射波长明显红移（47 nm）。而TPA2和Ag⁺作用后,415和542 nm处荧光发射峰同时淬灭。化合物TPA3虽然也能与Ag⁺发生相互作用使荧光减弱,但是其荧光减弱幅度不大,很容易受到其它杂离子干扰影响,不适用于离子识别研究。     

Photoexcitation of CH3NCO,CH3NCS and CH3SCN in the vacuum ultraviolet: Rydberg states and photofragment emission

Photoabsorption cross sections and fluorescence excitation spectra of CH₃NCO, CH₃NCS and CH₃SCN vapor were measured in the vacuum ultraviolet using synchrotron radiation. Many sharp structures observed from CH₃NCO and CH₃SCN in the 120–180 nm region are classified into three Rydberg series and their vibrational progressions, whereas for CH₃NCS six broad bands exhibit no fine structure. The emission which starts to appear at 172.8 ± 1.0 nm excitation of CH₃NCO is attributed to the NCO(A²Σ⁺-X²Π) band. The emissions from CH₃NCS and CH₃SCN are assigned to the A²Π-X²Π and B²Σ⁺-X²Π bands of NCS; the CN(B²Σ⁺-X²Σ⁺) band is also observed at 125 nm excitation of CH₃SCN. The photodissociation processes are discussed in accord with the emission observed.     

Absolute and relative emission cross sections for electron impact on CH3F,CH2F2 and CHF3

Emission spectra following electron impact on CH₃F, CH₂F₂ and CHF₃ at various energies have been investigated in the spectral region from 200 nm to 700 nm. Emission thresholds and excitation functions for atomic and molecular fragments have been determined. Absolute emission cross sections were obtained for two band systems, ^{A 2} Δ → X ² Π, C ² Σ⁺ → X ² Π, observed in the emission spectrum of CH₃F and for the H-Balmer radiation, H _α ? H _γ, in the spectra of all compounds. The continuous emission between 200 nm and 400 nm in the spectra of CH₂F₂ and CHF₃ has been examined systematically. It was found that CF₂(Ã) is the main precursor in both spectra.     

Fluorescence of sanguinarine: fundamental characteristics and analysis of interconversion between various forms

The quaternary isoquinoline alkaloid, sanguinarine (SG) plays an important role in both traditional and modern medicine, exhibiting a wide range of biological activities. Under physiological conditions, there is an equilibrium between the quaternary cation (SG⁺) and a pseudobase (SGOH) forms of SG. In the gastrointestinal tract, SG is converted to dihydrosanguinarine (DHSG). All forms exhibit bright fluorescence. However, their spectra overlap, which limited the use of powerful techniques based on fluorescence spectroscopy/microscopy. Our experiments using a combination of steady-state and time-resolved techniques enabled the separation of individual components. The results revealed that (a) the equilibrium constant between SG⁺ and SGOH is pK _a = 8.06, while fluorescence of DHSG exhibited no changes in the pH range 5–12, (b) the SGOH has excitation/emission spectra with maxima at 327/418 nm and excited-state lifetime 3.2 ns, the spectra of the SG⁺ have maxima at 475/590 nm and excited-state lifetime 2.4 ns. The DHSG spectra have maxima at 327/446 nm and 2-exponential decay with components 4.2 and 2.0 ns, (c) NADH is able to convert SG to DHSG, while there is no apparent interaction between NADH and DHSG. These techniques are applicable for monitoring the SG to DHSG conversion in hepatocytes.     

Photochemistry of trimethylene oxide and trimethylene sulfide radical cations in freonic matrices at 77 K

It was shown that trimethylene oxide (oxetane) radical cations were converted at 77 K into either distonic radical cations ·CH₂CH₂CH=OH⁺ or 2-oxetanyl radicals, depending on the freonic matrix used, by the action of light at λ = 546 nm and trimethylene sulfide radical cations transformed into distonic radical cations CH₂CHSH⁺CH ₂ ^· under 436-nm irradiation. The quantum yields of the photochemical reactions were determined. Quantum-chemical calculations on the structure and HFC constants of the radical cations and possible paramagnetic products of their transformation were performed. The reasons behind the observed difference in reactivity between the radical cations under the action of light are discussed.     

Synthesis,spectroscopic and spectrophotometric study of BODIPY appended crown ether sensor for ion detection

A novel fluoroionophore compound was synthesized from a boron dipyrromethene (BODIPY) fluorophore and 4′-formylbenzo-15-crown-5 ionophore groups. Photophysical properties of the BODIPY-crown compound were studied with UV–Vis and fluorescence spectroscopy. The effect of metalic cations (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Al³⁺, Fe³⁺, Cu²⁺, Co²⁺, Zn²⁺, Ag⁺, Hg²⁺, Pb²⁺) on the absorption and fluorescence spectra of compound 2 was investigated. Blue shifts were detected in UV–Vis spectra upon addition of some metal ions (Al³⁺ > Fe³⁺ > Na⁺). At the same time, the emission intensity of this complex increased due to binding of Na⁺ ion to the benzo crown cavity. Additionally, a decrease in the intensity of the 630 nm emission peak and an increase in the intensity of the 570 nm emission peak was observed in the fluorescence emission spectra following addition of Al³⁺ and Fe³⁺ ions.     

Characterization of five [C4H7O]+ Ion structures. Fragmentation of the 2-pentanone molecular ion

The [C₄H₇0]⁺ ions [CH₂?CH? C(?OH)CH₃]⁺ (1), [CH₃CH?CH? C(?OH)H]⁺ (2), [CH₂?C(CH₃)C(?OH)H]⁺ (3), [Ch₃CH₂CH₂C?O]⁺ (4) and [(CH₃)₂CHC?O]⁺ (5) have been characterized by their collision-induced dissociation (CID) mass spectra and charge stripping mass spectra. The ions 1–3 were prepared by gas phase protonation of the relevant carbonyl compounds while 4 and 5 were prepared by dissociative electron impact ionization of the appropriate carbonyl compounds. Only 2 and 3 give similar spectra and are difficult to distinguish from each other; the remaining ions can be readily characterized by either their CID mass spectra or their charge stripping mass spectra. The 2-pentanone molecular ion fragments by loss of the C(1) methyl and the C(5) methyl in the ratio 60:40 for metastable ions; at higher internal energies loss of the C(1) methyl becomes more favoured. Metastable ion characteristics, CID mass spectra and charge stripping mass spectra all show that loss of the C(1) methyl leads to formation of the acyl ion 4, while loss of the C(5) methyl leads to formation of protonated vinyl methyl ketone (1). These results are in agreement with the previously proposed potential energy diagram for the [C₅H₁₀O]⁺˙ system.     

QUENCHING OF METHYLCYCLOHEXANE FLUORESCENCE BY METHANOL*

We measured the fluorescence emission spectrum and intensity decays of methylcyclohexane (MCH) when excited by simultaneous absorption of two photons at 298 nm. The steady-state intensities and lifetimes were both decreased by methanol, which was found to be an efficient quencher of MCH fluorescence. Methanol quenching of MCH is clearly dynamic, but the exact mechanism of quenching is unclear. Dynamic quenching of MCH was also observed by water and n-propanol. These results suggest that alkane fluorescence from biopolymers, if observable, will only occur from regions of the macromolecules that are not exposed to water.     

The ions [CH3S]+, [C2H5S]+ and [CH3O]+ formed by electron-impact

The mass spectra of deuterated species shows that both the isomeric ions [CH₂?SH]⁺ and [CH₃? S]⁺ are formed in the ratio 2:1 from CH₃SH; the ions [CH₃CH?SH]⁺ and [CH₃CH₂S]⁺ in the ratio 0·8:1 from CH₃CH₂SH; and [CH₂?OH]⁺ and [CH₃? O]⁺ in the ratio 6·7:1 from methanol. The heats of formation of [CH₃S]⁺ and [C₂H₅S]⁺ are of the order of 222 and 203 Kcal.mole^?1 respectively. The isomeric ions cannot be distinguished on thermodynamic grounds.     

Study of the temperature effect on IR spectra of crystalline amino acids,dipeptides, and polyamino acids. IV. L-cysteine and DL-cysteine

A study of the IR spectra of L- and DL-cysteine is carried out in a range of frequencies from 4000 cm^?1 to 600 cm^?1 and temperatures from 333 K to 83 K. Changes in the spectra of L- and DL-cysteine (NH ₃ ⁺ CH(CH₂SH)-COO^?) on cooling are analyzed in comparison with the spectra of L- and DL-serine (NH ₃ ⁺ CH(CH₂OH)-COO^?) and three polymorphs of glycine (NH ₃ ⁺ CH₂-COO^?) previously studied under temperature variation. Changes in the IR spectra at variable temperatures are correlated with previously obtained diffraction data on anisotropic compression of the structure and changes in the geometric parameters of hydrogen bonds. Special attention is paid to temperature regions in which anomalies were detected by vibrational spectroscopy, X-ray diffraction, and calorimetry.     

Comparison of the bis(ferrocenylethynyl)phenylmethylium cation with bis(ferrocenylethenyl)methylium analogues

Several new ferrocenylethynyl derivatives, (FcCC)₂CHOH, (FcCC)₂CH₂, (FcCC)₂CPhOH have been synthesised from ethynylferrocene. Attempts to synthesise the corresponding bis(ferrocenylethynyl)-stabilised carbocations by hydroxyl or hydride abstraction from the bridging group was unsuccessful for (FcCC)₂CHOH and (FcCC)₂CH₂, respectively. In the case of (FcCC)₂CPhOH, the [(FcCC)₂CPh]⁺ cation could be observed by ¹H and ¹³C NMR, and by UV-Vis-NIR spectroscopy, but was too unstable for isolation or prolonged study in solution. The UV-Vis-NIR spectrum of [(FcCC)₂CPh]⁺ is compared to that of the considerably more stable cations, [Fc(CHCH)₂CH]⁺ and [(FcCHCH)₂CPh]⁺.     

5,6-位烷氧基保护和3-/3,8-位三苯胺拓展1,10-菲咯啉衍生物与银离子识别

在1,10-菲咯啉的5,6-位引入烷氧基后,分子的反应活性明显提升,同时获得的三苯胺基(TPA)衍生物的溶解性也明显提高。晶体结构分析表明:烷氧基团是以六元环形式的乙撑二氧结构接入1,10-菲咯啉环的5,6-位。化合物TPA1和TPA2均对Ag+表现出选择性识别作用。其中,TPA1与Ag+作用后虽然荧光减弱不明显,但其发射波长明显红移(47 nm)。而TPA2和Ag+作用后,415和542 nm处荧光发射峰同时淬灭。化合物TPA3虽然也能与Ag+发生相互作用使荧光减弱,但是其荧光减弱幅度不大,很容易受到其它杂离子干扰影响,不适用于离子识别研究。     

Photoexcitation processes of CH3OH: Rydberg states and photofragment fluorescence

Photoabsorption and fluorescence cross sections of methanol vapor were mearured using synchrotron radiation. Weak structures observed in the 110–140 nm region are classified into three Rydberg series. Quasidiatomic repulsive potential curves for the states dissociating into CH₃ + OH(A²Σ⁺) are obtained from the measured fluorescence cross section. The photodissociation processes are discussed in accord with the fluorescence observed. The fluorescence quantum yield (< 0.8%) for photodissociation of CH₃OH is one order of magnitude smaller than that of H₂O, indicating a correlation that the fluorescence quantum yield decreases with increasing number of molecular orbitals.     

Structures and stabilities of [C3H3O]+ ions in the gas phase: A molecular orbital study

The relative energies of 11 [C₃H₃O]⁺ ions are calculated by different molecular orbital methods (MINDO/3, MNDO, ab initio with 3-21G and 4-31G* basis set and configuration interaction). The four most stable structures are: a ([CH₂?CH? CO]⁺), b c ([CH?C? CHOH]⁺) and d ([CH₂?C?COH]⁺); their relative energies at the CI/4-31G*//3-21G level are 0, 117, 171 and 218 kJ mol^?1, respectively. The isomerizations c→[CH?CH? CHO]⁺→[CH₂?C? CHO]⁺→ a and dissociations into [C₂H₃]⁺+CO and [HCO]⁺+C₂H₂ are explored. The calculated potential energy profile reveals that the energy-determining step is the 1,3-H migration c→[CH?CH? CHO]⁺. This explains the value of unity of the branching ratio and the spread of kinetic energy released for the two dissociation channels.     

Polar and Hydrogen-Bonding Effects of Alcohols on the Emission Spectrum of Styrene–Triethylamine System

The emission spectra of styrene (ST)–triethylamine (TEA) systems were measured under steady-state illumination conditions in some tetrahydrofuran (THF)–protic solvent mixtures. The fluorescence spectrum of the ST–TEA system in THF consists of two bands (band A at 304 nm (fluorescence of ST) and band B at 460 nm (emission from an exciplex)). The intensity of band A increased and that of band B decreased with increasing amounts of protic solvents in THF–protic solvent mixtures. The increase in the intensity of band A was explained by the decrease in the concentration of free amine owing to the hydrogen-bonding interaction (or protonation) between TEA and protic solvents. The decrease in the intensity of band B was considered to be caused by the decrease in the concentration of free amine upon the addition of protic solvents and the enhanced conversion of the exciplex to an ion pair with increasing solvent polarity. The polar effect was expressed as a function of the relative permittivity of the solution.     

Halomethyl-metal compounds : LVII. The insertion of phenyl(bromodichloromethyl)mercury-derived dichlorocarbene into CH bonds. Further studies of the β-metal activated Cz.sbnd;H insertion reaction

Phenyl(bromodichloromethyl)mercury-derived dichlorocarbene inserts into the β CH bonds of Me₃MCH(CH₃)CH₂CH₃ and Me₃MCD(CH₃)CH₂CH₃ (M = Si and Sn) to give Me₃MCH(CH₃)CH(CH₃)CCl₂H and Me₃MCD(CH₃)CH(CH₃)CCl₂H, respectively. That no rearrangement of deuterium to the β position occured was suggested by the ¹³C and ¹H NMR spectra of the products. This result is taken to speak against the intervention of sila- and stannacyclopropenium ion intermediates in the insertion process and in favor of stabilization of the transition state of the insertion reaction by metalcarbon bond hyperconjugation (σ-π stabilization, a vertical stabilization process).     

Synthesis,fluorescence properties,and conformational analysis of ether-linked (1,8)pyrenophanes

Mono-, di- and oligo-ether linked (1,8)pyrenophanes 1–7 were synthesized, and their fluorescence and conformational properties in the absence and presence of metal ions were elucidated. Fluorescence spectra of 1.0 × 10⁻⁵ M solutions of the mono- and di-ether linked pyrenophanes 1–5 were comprised of only monomer emission bands, while those of the oligoethylene glycol linked analogs 6 and 7 contained both monomer and intramolecular excimer emission bands. Addition of perchlorate salts of Ba²⁺, Na⁺ and Li⁺ to 1:1 v/v CH₃CN:CH₂Cl₂ solutions of 6 and 7 caused decreases in the intensities of the corresponding intramolecular excimer emission bands and, in some cases, increases in the intensities of the monomer emission. Monomer and intramolecular excimer emission from the (1,8)pyrenophanes are suggested to arise from the respective anti and syn conformers, whose ratios are dependent on solvent polarity, temperature and kinds of added metal ions.     

Mass spectrometric investigation of stereosomeric 1,2-dimethyl-4-substituted decahydroquinol-4-ol N-oxides. Concerning the configuration of the asymmetric nitrogen atom

The main fragmentation pathways of the N-1, C-2 and C-4 stereoisomers of the 1,2-dimethyl-4-R-transdecahydroquinoline-4-ol N-oxides (R=C?CH, CH?CH₂ and C₂H₅) under electron impact are discussed. The correlation between the mass spectrometric chromatographic behaviour and the configuration of polar groups in the N-oxides examined is discussed. The mass spectra of the N-1 stereoisomers may be subdivided into two groups, depending only on the orientation of N→O group and not of the 4-OH group. The spectra of N-oxides with the axial N-oxide group reveal less intense ions and much more intense [M? CH₃]⁺, [M? O]⁺, [M? OH]⁺ and ions, whereas in the spectra of their equatorial epimers the abundance of the ions exceeds the intensities of the latter ions.     

Novel fluorescent 2‐(2‐aminofluorophenyl)benzoxazoles: Syntheses and photophysical properties

2‐(2‐Amino‐3,4,5,6‐tetrafluorophenyl)benzoxazole ( 2 ) absorbs in long wavelength band (λ_abs^max = 346 nm in methanol) and in the normal wavelength band (λ_abs^max = 285.5 nm), and emits blue fluorescence. The emission intensity is highly affected by the solvent polarity and is large in a polar solvent such as methanol. 2‐(2‐Pentafluorobenzamido‐3,4,5,6‐ tetrafluorophenyl)benzoxazole ( 5 ) emits green fluorescence along with the short wavelength emission around 380 nm and their relative intensity depends on the solvent polarity. Green fluorescence is enhanced in nonpolar solvents such as chloroform and toluene, resulting in the considerably large Stokes shift.