Spectroscopic studies of the Ã-X̃ electronic spectrum of the β-hydroxyethylperoxy radical: structure and dynamics

The jet-cooled A?-X? near IR origin band spectra of the G(1)G(2)G(3) conformer of four β-hydroxyethylperoxy isotopologues, β-HEP (HOCH(2)CH(2)OO), β-DHEP (DOCH(2)CH(2)OO), β-HEP-d(4) (HOCD(2)CD(2)OO), and β-DHEP-d(4) (DOCD(2)CD(2)OO), have been recorded by a cavity ringdown spectrometer with a laser source linewidth of ~70 MHz. The spectra of all four isotopologues have been analyzed and successfully simulated with an evolutionary algorithm, confirming the cyclic structure of the molecule responsible for the observed origin band. The analysis also provides experimental A? and X? state rotational constants and the orientation of the transition dipole moment in the inertial axis system; these quantities are compared to results from electronic structure calculations. The observed, broad linewidth (Δν > 2 GHz) is attributed to a shortened lifetime of the A? state associated with dynamics along the reaction path for hydrogen transfer from the OH to OO group.     

Global ab initio potential energy surfaces for both the ground (X̃1A') and excited (Ã1A') electronic states of HNO and vibrational states of the Renner-Teller Ã1A'-X̃1A' system

The global potential energy surfaces for both the ground (X?(1)A(')) and excited (A?(1)A(')) electronic states of the HNO molecule have been constructed by three-dimensional cubic spline interpolation of more than 17,000 ab initio points, which have been calculated at the internal contracted multi-reference configuration interaction level with the Davidson correction using an augmented correlation-consistent polarized valence quadruple zeta basis set. The low-lying vibrational energy levels for the two electronic states of HNO have also been calculated on our potential energy surfaces including the diagonal Renner-Teller terms. The calculated results have shown a good agreement with the experimental vibrational frequencies of HNO and its isotopomers.     

The Ã-state dissociation continuum of NO-Ar and its near infrared spectrum

After preparing NO-Ar in a vibrational state correlating with the first overtone vibration in NO, we recorded its hot band UV spectrum by monitoring simultaneously the intensity in the NO(+) and the NO(+)-Ar ion channels. In this way, the bound as well as the continuous part of the electronic A?←X? spectrum are observed directly. Below the dissociation threshold, the intensity is found exclusively in the NO(+)-Ar ion channel while above it is found in the NO fragment ion channel. We observe simultaneously intensity in both ion channels only for a very narrow frequency range near the dissociation threshold. Structures in the dissociation spectrum correlate well with the thresholds for production of NO(A) in different rotational states. At frequencies well above the dissociation threshold, NO-Ar is detected efficiently as a NO fragment. This fact has been exploited to record the near IR spectrum of NO-Ar with significantly increased sensitivity. The dissociation detected spectra are essentially identical to our previous constant photon energy sum (CONPHOENERS) scans [B. Wen, Y. Kim, H. Meyer, J. K?os, and M. H. Alexander, J. Phys. Chem. A 112, 9483 (2008)]. Several hot band spectra have been remeasured with improved sensitivity enabling a comprehensive analysis yielding for the first time spectroscopic constants for levels associated with the potential surfaces of NO-Ar correlating with NO(v(NO) = 0 and 2). Since many NO-X complexes do not have a strong bound A?-state spectrum, although they do have a A?-state dissociation continuum, there is the possibility to record their near IR spectra by employing dissociation detection.     

Optical Stark spectroscopy of the 2(0)(6) Ã1A'-X̃1A' band of chloro-methylene, HCCl

The laser induced fluorescence spectra of the 2(0)(6)A?(1)A(')-X?(1)A(') band of a rotationally cold (<20 K) molecular beam sample of chloro-methylene, HCCl, has been recorded, field-free and in the presence of a static electric field. The field-free spectrum has been analyzed to produce an improved set of spectroscopic parameters for the A?(1)A(') (060) vibronic state. The magnitude of the a-component of the permanent electric dipole moment, μ(a), for the X?(1)A(') (000) vibronic state has been determined to be 0.501(1) D from the analysis of the observed electric field induced shifts. Comparisons with theoretical predictions and flouro-methylene, HCF, are presented.     

CH2 b̃1B1-ã1A1 band origin at 1.20 μm

The origin band in the b?(1)B(1)-a?(1)A(1) transition of CH(2) near 1.2 μm has been recorded at Doppler-limited resolution using diode laser transient absorption spectroscopy. The assignments of rotational transitions terminating in upper state levels with K(a) = 0 and 1, were confirmed by ground state combination differences and extensive optical-optical double resonance experiments. The assigned lines are embedded in a surprisingly dense spectral region, which includes a strong hot band, b?(0,1,0) K(a) = 0 - a?(0,1,0) K(a) = 1 sub-band lines, with combination or overtone transitions in the a?(1)A(1) state likely responsible for the majority of unassigned transitions in this region. From measured line intensities and an estimate of the concentration of CH(2) in the sample, we find the transition moment square for the 0(00) ← 1(10) transition in the b?(1)B(1)(0,0,0)(0)-a?(1)A(1)(0,0,0)(1) sub-band is 0.005(1) D(2). Prominent b?(1)B(1)(0,1,0)(0)-a?(1)A(1)(0,1,0)(1) hot band lines were observed in the same spectral region. Comparison of the intensities of corresponding rotational transitions in the two bands suggests the hot band has an intrinsic strength approximately 28 times larger than the origin band. Perturbations of the excited state K(a) = 0 and 1 levels are observed and discussed. The new measurements will lead to improved future theoretical modeling and calculations of the Renner-Teller effect between the a? and b? states in CH(2).     

Thermodynamic and spectroscopic properties of 2-pyrrolidinones. 7. ΔE T N for binary solvent mixtures of 2-pyrrolidinone andN-methylbenzenesulfonamide at 30 and 50°C

ΔE _T ^N values for 2-pyrrolidinone and N-methylbenzenesulfonamide solvent systems, in which the solvents were benzyl alcohol, 1,4-dioxane and hexamethylphosphoric triamide, were determined over the whole mole fraction range. The study was carried out at 30 and 50°C. The ΔE _T ^N values were positive for all of these systems, with the exception of the 2-pyrrolidinone-hexamethylphosphoric triamide system, which was slightly negative. The results are discussed in terms of intermolecular interactions and preferential solvation.     

Detection of vibrational bending mode ν8 and overtone bands of the propargyl radical, HCCCH2 X̃ 2B1

Infrared (IR) absorption spectra of matrix-isolated HCCCH(2) have been measured. Propargyl radicals were generated in a supersonic pyrolysis nozzle, using a method similar to that described in a previous study (Jochnowitz, E. B.; Zhang, X.; Nimlos, M. R.; Varner, M. E.; Stanton, J. F.; Ellison, G. B. J. Phys. Chem. A 2005, 109, 3812-3821). Besides the nine vibrational modes observed in the previous study, this investigation detected the HCCCH(2) X? (2)B(1) out-of-plane bending mode (ν(8)) at 378.0 (±1.9) cm(-1) in a cryogenic argon matrix. This is the first experimental observation of ν(8) for the propargyl radical. In addition, seven overtone and combination bands have also been detected and assigned. Ab initio coupled-cluster anharmonic force field calculations were used to guide the analysis. Furthermore, ν(12), the HCCCH(2) in-plane bending mode, has been assigned to 333 (±10) cm(-1) based on the detection of its overtone (2ν(12), 667.7 ± 1.0 cm(-1)) and a possible combination band (ν(10) + ν(12), 1339.0 ± 0.8 cm(-1)). This is the first experimental estimation of ν(12) for the propargyl radical.     

The ν2 bending vibrational structure of the X̃2Σ+ state of MgNC

We have generated MgNC in supersonic free jet expansions and observed the laser induced fluorescence (LIF) of the A?(2)Π-X?(2)Σ(+) transition. We measured the LIF dispersed spectra from the single vibronic levels of the A?(2)Π electronic state of MgNC, following excitation of each ν(2) bending vibronic band observed, i.e., the κ series of the (0,v(2)('),0)-(0,0,0), v(2)(') = 0, 1, 2, 4, and 6 vibronic bands. In the vibrational structure in the dispersed fluorescence spectra measured, the long progression of the ν(2) bending mode in the X?(2)Σ(+) state is identified, e.g., up to v(2)(')=14 in the (0,6,0)-(0,v(2)('),0) spectrum. This enables us to derive the potential curve of the ν(2) bending mode in the X?(2)Σ(+) state. We used two kinds of models to obtain the potential curve; (I) the customary formula expressed in the polynomial series of the (v(2)(')+(d(2)/2)) term and (II) the internal rotation model. The potential curve derived from model (I) indicates the convergence of the bending vibrational levels at about 800 cm(-1) from the vibrationless level of MgNC, which may correspond to the barrier height of the isomerization reaction, MgNC ? MgCN, in the X?(2)Σ(+) state. Model (II) gives a simple picture for the isomerization reaction pathway with a barrier height of about 630 cm(-1) from the vibrationless level of the more stable species, MgNC. This shows that the v(2)(')=8 bending vibrational level of MgNC is already contaminated by the v(2)(')=2 bending vibrational level of the isomer, MgCN, and implies that the isomerization reaction begins at the v(2) (')=8 level. The bending potential surface and the isomerization reaction pathway, MgNC ? MgCN, in the X?(2)Σ(+) state are discussed by comparing the potential derived in this study with the surface obtained by quantum chemical calculation.     

Synthesis and Expression of a Gene From Kringle-2 Domain of Tissue Plasminogen Activator in E. coli

The DNA fragment corresponding to the tissue plasminogen activator (tPA) sequence 174-262 (Kringle-2 domain) has been synthesized by using the solid phase phosphotriester method. The Kringle-2 domain of human tPA was expressed in Escherichia colt by secretion into the periplasmic space using the Lpp-Lac promoter and PIN-Ⅲ OmpA2 signal sequence. About two thirds of the expression product was secreted into the periplasmic space , and purified with ammonium sulfate fractionation, affinity chro-matography on Lysine-Sepharose, and FPLC-Mono Q exchange chromatography. The amino acid composition observed from the Kringle-2 purified from E. coli is identical with that expected for the 174-262 fragment of human tPA. Radio binding assay shows that the recombinant Kringle-2 domain possesses the activity of fibrin binding.     

Total synthesis of violaceimides A–E and consideration of the reported stereochemistry

Here we report the first total synthesis of violaceimides A–E, a family of sulfur-containing metabolites from Aspergillus violaceus, a sponge-associated fungus. A concise, convergent and enantioselective synthesis was developed for all five family members, from a common advanced intermediate. However, while the NMR spectral data matched that of the reported natural products, the optical rotations were of opposite sign. This result prompted the enantioselective synthesis of all four diastereomeric pairs of violaceimide E, and suggests that the stereochemistry might have been misassigned.     

The C3-bending vibrational levels of the C3-Kr and C3-Xe van der Waals complexes studied by their Ã-X̃ electronic transitions and by ab initio calculations

Fluorescence excitation spectra and wavelength-resolved emission spectra of the C(3)-Kr and C(3)-Xe van der Waals (vdW) complexes have been recorded near the 2(2-)(0), 2(2+)(0), 2(4-)(0), and 1(1)(0) bands of the A?(1)Π(u)-X?(1)Σ(g)(+) system of the C(3) molecule. In the excitation spectra, the spectral features of the two complexes are red-shifted relative to those of free C(3) by 21.9-38.2 and 34.3-36.1 cm(-1), respectively. The emission spectra from the A? state of the Kr complex consist of progressions in the two C(3)-bending vibrations (ν(2), ν(4)), the vdW stretching (ν(3)), and bending vibrations (ν(6)), suggesting that the equilibrium geometry in the X? state is nonlinear. As in the Ar complex [Zhang et al., J. Chem. Phys. 120, 3189 (2004)], the C(3)-bending vibrational levels of the Kr complex shift progressively to lower energy with respect to those of free C(3) as the bending quantum number increases. Their vibrational structures could be modeled as perturbed harmonic oscillators, with the dipole-induced dipole terms of the Ar and Kr complexes scaled roughly by the polarizabilities of the Ar and Kr atoms. Emission spectra of the Xe complex, excited near the A?, 2(2-) level of free C(3), consist only of progressions in even quanta of the C(3)-bending and vdW modes, implying that the geometry in the higher vibrational levels (υ(bend) ≥ 4, E(vib) ≥ 328 cm(-1)) of the X? state is (vibrationally averaged) linear. In this structure the Xe atom bonds to one of the terminal carbons nearly along the inertial a-axis of bent C(3). Our ab initio calculations of the Xe complex at the level of CCSD(T)∕aug-cc-pVTZ (C) and aug-cc-pVTZ-PP (Xe) predict that its equilibrium geometry is T-shaped (as in the Ar and Kr complexes), and also support the assignment of a stable linear isomer when the amplitude of the C(3) bending vibration is large (υ(4) ≥ 4).     

The complex spectrum of a "simple" free radical: the Ã-X̃ band system of the jet-cooled boron difluoride free radical

The near-ultraviolet band system of the jet-cooled boron difluoride free radical has been studied by a combination of laser-induced fluorescence and single vibronic level wavelength resolved emission spectroscopies. The radical was produced in a supersonic discharge jet using a precursor mixture of 1%-3% of BF(3) or (10)BF(3) in high pressure argon. A large number of bands were found in the 340-286 nm region and assigned as transitions from the X?(2)A(1) ground state to the lower Renner-Teller component of the A?(2)Π excited state, based on our previous ab initio potential energy surface predictions, matching the emission spectra Franck-Condon profiles of (11)BF(2) and (10)BF(2), and comparison of observed and calculated boron isotope effects. Several bands have been rotationally analyzed providing ground state structural parameters of r(0)(') (BF) = 1.3102(9) ? and θ(0)(') (FBF) = 119.7(6)°. The ground state totally symmetric vibrational energy levels of both boron isotopologues have also been measured and assigned up to energies of more than 8000 cm(-1). Although BF(2) might be considered to be a "simple" free radical, understanding the details of its electronic spectrum remains a major challenge for both theory and experiment.     

Partial Protection of Carbohydrate Derivatives. Part 13.1 Chemical Conversion of Kanamycin A Into 2′-Deoxykanamycin A, 2′-Epi-Kanamycin A,and 2′-Epi-Kanamycin B

Abstract

Hydrazinolyses of hexa-0-benzoyl-tetra-N-benzyloxycarbonyl-and N-ethoxycarbonylkanamycin A were performed and found to be sufficiently regioselective to give the corresponding 2′-hydroxyl derivatives in good yields under controlled conditions. The products were converted into the corresponding 2′-triflates, which were then subjected to nucleophilic substitution reactions with sodium benzenethioxide, sodium benzoate, and sodium azide to give the corresponding d-mannopyranosyl derivatives in good yields. Deprotection of the phenylthio (10) and azido (12) derivatives, and hydrogenolysis, gave 2′-deoxykankmycin A and 2′-epi-kanamycin B, respectively. Moreover, deprotection of the benzoyl compound 11 gave 2′-epi-kanamycin A.     

Two-fragment α-adrenolytics. 4. Synthesis of phosphorylated derivatives of 2-aryloxyethylamines and N-phenylpiperazine

The reactions of 3-chloropropylphosphonates, 3-chloropropylthiophosphonates, or 3-chloropropylphosphinates with 2-aryloxyethylamines or N-phenylpiperazine afford the corresponding 3-(2-aryloxyethylamino)propylphosphonates and -phosphinates or 3-(4-phenylpiperazin-1-yl)propylphosphonates and -phosphinates. The compounds obtained exhibit -adrenolytic and hypotensive activities, the latter being found to depend on the substituents at the P atom.     

The microwave and millimeter spectrum of ZnCCH (X̃2Σ+): a new zinc-containing free radical

The pure rotational spectrum of the ZnCCH (X?(2)Σ(+)) radical has been measured using Fourier transform microwave (FTMW) and millimeter direct-absorption methods in the frequency range of 7-260 GHz. This work is the first study of ZnCCH by any type of spectroscopic technique. In the FTMW system, the radical was synthesized in a mixture of zinc vapor and 0.05% acetylene in argon, using a discharge assisted laser ablation source. In the millimeter-wave spectrometer, the molecule was created from the reaction of zinc vapor, produced in a Broida-type oven, with pure acetylene in a dc discharge. Thirteen rotational transitions were recorded for the main species, (64)ZnCCH, and between 4 and 10 for the (66)ZnCCH, (68)ZnCCH, (64)ZnCCD, and (64)Zn(13)C(13)CH isotopologues. The fine structure doublets were observed in all the data, and in the FTMW spectra, hydrogen, deuterium, and carbon-13 hyperfine splittings were resolved. The data have been analyzed with a (2)Σ Hamiltonian, and rotational, spin-rotation, and H, D, and (13)C hyperfine parameters have been established for this radical. From the rotational constants, an r(m) ((1)) structure was determined with r(Zn-C) = 1.9083 A?, r(C-C) = 1.2313 A?, and r(C-H) = 1.0508 A?. The geometry suggests that ZnCCH is primarily a covalent species with the zinc atom singly bonded to the C≡C-H moiety. This result is consistent with the hyperfine parameters, which suggest that the unpaired electron is localized on the zinc nucleus. The spin-rotation constant indicates that an excited (2)Π state may exist ～19,000 cm(-1) in energy above the ground state.