Laser Raman and IR spectra and force fields for 2,4-dichlorobenzonitrile

Raman spectrum of 2,4-dichlorobenzonitrile (2,4-DCBN) in powder form has been recorded in the region 50-4000 cm(-1) on a Jasco K-500 Raman spectrophotometer using the 488.0 nm radiation from an argon laser. FTIR spectra in the region 200-4000 cm(-1) have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer. Using the observed Raman and IR frequencies, normal co-ordinate analysis has been carried out to support the vibrational analysis and to determine the planar and non-planar force fields.     

Spectroscopic studies of some antidiabetic drugs

The infrared absorption spectrum of antidiabetic drugs Pioglitazone and Pioglitazone.HCl has been recorded at high resolution in the spectral region 200-4000 cm(-1). Most of the frequencies in the latter compound are slightly lower in magnitude than corresponding value in the former. The absorption intensities are however slightly larger. In order to confirm the vibrational assignment of the bands obtained from experimental observation, a normal co-ordinate analysis has been carried out using semi empirical AM1 method through MOPAC 5.1 computer program. In addition to these compounds, the vibrational frequencies for some of the intermediate metabolite of Pioglitazone have also been calculated.     

Laser produced spectrum of Si(2) molecule in the region of 540-1010 nm

The laser produced spectrum of Si(2) molecule is recorded for the first time using laser ablation technique in the region of 540-1010 nm. About 110 bands are observed in the entire spectral region and all these bands are classified into three band systems, viz. E-X, F-X and G-X of Si(2) molecule lying in the region of 814-1010 nm, 630-900 nm and 546-710 nm, respectively. All these electronic transitions take place from ground state X(3)Sigma(g)(-) state. The molecular constants of all these states have been determined.     

Intensity analysis of overlapped discrete and continuous absorption by spectral simulation: the electronic transition moment for the B-X system in I2

The spectrum of I(2) is examined anew in the wavelength region 520-640 nm, where discrete absorption in the B-X transition is prominent. The spectrum is recorded with high quantitative precision at moderate resolution (0.1 nm) and is analyzed by least-squares spectral simulation, yielding the B-X electronic transition strength ∣μ(e)∣(2) with unprecedented precision (<2% relative standard error) over most of the studied region. The analysis also yields directly new estimates of the continuous absorption in this region, which support previous assessments of the A ← X transition but lower the C((1)Π(u)) ← X transition strength by 25%. The new analysis method is applicable to any situation where the discrete spectrum can be simulated reliably.     

FT-IR, UV-vis, 1H and 13C NMR spectra and the equilibrium structure of organic dye molecule disperse red 1 acrylate: a combined experimental and theoretical analysis

This study reports the characterization of disperse red 1 acrylate compound by spectral techniques and quantum chemical calculations. The spectroscopic properties were analyzed by FT-IR, UV-vis, (1)H NMR and (13)C NMR techniques. FT-IR spectrum in solid state was recorded in the region 4000-400 cm(-1). The UV-vis absorption spectrum of the compound that dissolved in methanol was recorded in the range of 200-800 nm. The (1)H and (13)C NMR spectra were recorded in CDCl(3) solution. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR spectrum. A satisfactory consistency between the experimental and theoretical spectra was obtained and it shows that the hybrid DFT method is very useful in predicting accurate vibrational structure, especially for high-frequency region. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties were performed by timedependent DFT (TD-DFT) and CIS(D) approach. To investigate non linear optical properties, the electric dipole moment μ, polarizability α, anisotropy of polarizability Δα and molecular first hyperpolarizability β were computed. The linear polarizabilities and first hyperpolarizabilities of the studied molecule indicate that the compound can be a good candidate of nonlinear optical materials.     

Gas-phase structure of a pi-allyl-palladium complex: efficient infrared spectroscopy in a 7 T Fourier transform mass spectrometer

The performance of infrared (IR) spectroscopy of gas-phase ions in a commercially available 7 T Fourier transform ion cyclotron resonance mass spectrometer has been characterized. A pi-allyl-palladium reactive intermediate, [(pi-allyl)Pd(P(C6H5)3)2]+, involved in the catalytic allylation of amine is studied. A solution of this transition metal complex is electrosprayed, and the IR multiple photon dissociation (IRMPD) spectrum of the mass-selected ions is recorded in two spectral ranges. The fingerprint spectrum (650-1550 cm(-1)) is recorded using the Orsay free-electron laser, and the dependence of the IRMPD efficiency on laser power and irradiation time is characterized. The DFT-calculated IR absorption spectrum of the [(pi-allyl)Pd(P(C6H5)3)2]+ complex shows good agreement with the experimental spectrum. The pi-interaction between the palladium and the allyl moiety is reflected by the assignment of the IRMPD bands, and the observed allylic CH2 wagging modes appear to form a sensitive probe for the pi-interaction strength in metal-pi-allyl complexes. This spectral assignment is further supported by the analysis of the different IRMPD photofragmentation patterns observed at different photon energies, which are found to result from wavelength-specific photofragmentations. Nine peaks are well-resolved in the experimental spectrum, for which the bandwidth (fwhm) is on the order of 15 cm(-1). Resonances with a calculated IR intensity of 5 km/mol or larger are shown to be amenable for IRMPD, indicating an excellent sensitivity of our new experimental setup. Finally, the IR spectrum has also been recorded in the CH stretching region (2950-3150 cm(-1)) using a tabletop IR optical parametric oscillator/amplifier (OPO/OPA) laser source.     

RELAXATION OF SUPERCOILED DNA BY AMINOMETHYL TRIMETHYLPSORALEN AND UV PHOTONS: ACTION SPECTRUM

Abstract— An action spectrum of the relaxation of supercoied plasmid DNA(induction fo the firt single-strand break) by photoactivated 4'-aminomethyl-4, 5',8-trimethylpsoralen(AMT) has been determined using monochormatic UV photons from 254 to 405 nm. The spectrum of AMT-induced plasmid DNA relaxation fits closely with the absorbance spectrum of AMT in the spectral region between 313 nm and 405nm but deviates at wavelengths shorter than 313nm. This asay also reveals that the psoralen photosensitization reaction with DNA also produces piperidinelabile sites. Addition of mannitol and azide partially quenches the supercoil realaxation reaction, evidence for a role of Type II photosensitization pathway.     

Laser Raman and IR spectra and force fields for 2,6-difluorobenzonitrile

Raman spectrum of 2,6-difluorobenzonitrile in the powder form has been recorded in the region 50–4000 cm⁻¹ on a Jasco K-500 spectrophotometer using the 488.0 nm radiation from an argon laser. IR spectra in the region 200–4000 cm⁻¹ have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer and in liquid and vapour phases on a Jasco FTIR/7000 spectrometer. Using these observed frequencies force field calculations for the planar and non-planar modes have been carried out assuming a general valence force field.     

ANALYSIS OF THE COMPLEX BAND SPECTRUM OF P700 BASED ON PHOTOSELECTION STUDIES WITH PHOTOSYSTEM I PARTICLES

Abstract— The linear dichroism of the flash induced absorption changes of immobilized photosystem I reaction center particles from spinach chloroplasts has been investigated by means of the photoselection technique. Under flash excitation of predominantly β-carotenes at 500 nm, the photoinduced linear dichroism of the absorption changes has been measured in the spectral region from 620–720 nm. The most prominent feature in the spectrum of the dichroic ratio is the symmetrical pole at 687 nm. In parallel to all photoselection experiments, we recorded the light induced absorption changes of P700 under saturating flash excitation. A Gaussian deconvolution of this well-known difference spectrum of P700 has been attempted taking the additional features of the linear dichroism spectrum into account. From 670-720 nm, the best fit for both spectra was obtained by the following components:

• (1) 

  a disappearing wide band at 695.5 nm (σ= 200.0 cm⁻¹) attributed to the reduced special pair of chlorophyll a (Ch1- a );
• (2) 

  an appearing narrower band at 690 nm (σ= 120.0 cm⁻¹) with half the oscillatory strength of the former tentatively attributed to the non-oxidized moiety in the special pair; and
• (3) 

  a bathochromic bandshift centered at 688.4 nm attributed to the local electrochromic response of certain antennae Ch1- a molecules close to the primary electron donor.

The linear dichroism gives no evidence for any substructure within the absorption band of the reduced special pair.     

Fluorescence spectral imaging of dihydroxyacetone on skin in vivo

Dihydroxyacetone (DHA) has been proposed as a potential alternative to dansyl chloride for use as a fluorescence marker on skin to assess stratum corneum turnover time in vivo. However, the fluorescence from DHA on skin has not been adequately studied. To address this void, a noninvasive, noncontact spectral imaging system is used to characterize the fluorescence spectrum of DHA on skin in vivo and to determine the optimal wavelengths over which to collect the DHA signal that minimizes the contributions from skin autofluorescence. The DHA-skin fluorescence signal dominates the 580-680 nm region of the visible spectrum when excited with ultraviolet radiation in the 320-400 nm wavelength region (UVA). An explanation of the time-dependent spectral features is proposed in terms of DHA polymerization and binding to skin.     

Limonene: electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, electron scattering, He(I) photoelectron spectroscopy and ab initio calculations

Electronic state spectroscopy of limonene has been investigated using vacuum ultraviolet photoabsorption spectroscopy in the energy range 5.0-10.8 eV. The availability of a high resolution photon beam (~0.075 nm) enabled detailed analysis of the vibrational progressions and allowed us to propose, for the first time, new assignments for several Rydberg series. Excited states located in the 7.5-8.4 eV region have been studied for the first time. A He(I) photoelectron spectrum has also been recorded from 8.2 to 9.5 eV and compared to previous low resolution works. A new value of 8.521 ± 0.002 eV for the ground ionic state adiabatic ionisation energy is proposed. Absolute photoabsorption cross sections were derived in the 10-26 eV range from electron scattering data. All spectra presented in this paper represent the highest resolution data yet reported for limonene. These experiments are complemented by new ab initio calculations performed for the three most abundant conformational isomers of limonene, which we then used in the assignment of the spectral bands.     

FT-IR, FT-Raman, NMR and UV-vis spectra, vibrational assignments and DFT calculations of 4-butyl benzoic acid

The solid phase FTIR and FT-Raman spectra of 4-butyl benzoic acid (4-BBA) have been recorded in the regions 400-4000 and 50-4000cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-311++G(d,p) as basis set. The vibrational frequencies were calculated for monomer and dimer by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. (13)C and (1)H NMR spectra were recorded and (13)C and (1)H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-visible spectrum of the compound was recorded in the region 200-400nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman intensities, chemical shifts and absorption wavelengths were compared with the available experimental data of the molecule.     

THE ''Q-BAND'' ABSORPTION spECTRA OF HEMATOPORPHYRIN MONOMER AND AGGREGATE IN AQUEOUS SOLUTION

Abstract The resolution of the absorption spectra in the Q band (480 nm-620 nm) spectral region of monomeric and dimeric hematoporphyrin species present in aqueous solutions has been achieved using absorption, fluorescence and computer analysis methods. The absorption maxima of the dimer in this spectral region are red shifted about 12 nm with respect to those of the monomer. The significance of this finding in relationship to the well documented blue shift of hematoporphyrin aggregate observed in the Soret band region (λ_malx∼400 nm) of the absorption spectrum is discussed.     

An investigation of the hydrogen-bonding structure in bilirubin by 1H double-quantum magic-angle spinning solid-state NMR spectroscopy.

The complex hydrogen-bonding arrangement in the biologically important molecule bilirubin IXalpha is probed by using 1H double-quantum (DQ) magic-angle spinning (MAS) NMR spectroscopy. Employing fast MAS (30 kHz) and a high magnetic field (16.4 T), three low-field resonances corresponding to the different hydrogen-bonding protons are resolved in a 1H MAS NMR spectrum of bilirubin. These resonances are assigned on the basis of the proton-proton proximities identified from a two-dimensional rotor-synchronized 1H DQ MAS NMR spectrum. An analysis of 1H DQ MAS spinning-sideband patterns for the NH protons in bilirubin allows the quantitative determination of proton-proton distances and the geometry. The validity of this procedure is proven by simulated spectra for a model three-spin system, which show that the shortest distance can be determined to a very high degree of accuracy. The distance between the lactam and pyrrole NH protons in bilirubin is determined to be 0.186 +/- 0.002 nm (corresponding to a dominant dipolar coupling constant of 18.5 +/- 0.5 kHz). The analysis also yields a distance between the lactam NH and carboxylic acid OH protons of 0.230 +/- 0.008 nm (corresponding to a perturbing dipolar coupling constant of 9.9 +/- 1.0 kHz) and an H-H-H angle of 122 +/- 4 degrees. Finally, a comparison of 1H DQ MAS spinning-sideband patterns for bilirubin and its dimethyl ester reveals a significantly longer distance between the two NH protons in the latter case.     

Semiorganic nonlinear optical material for frequency doubling: preparation and properties of sodium p-nitrophenolate dihydrate (SPNP)

Sodium p-nitrophenolate (SPNP), a semiorganic nonlinear optical (NLO) material useful for frequency doubling in the IR region, has been synthesized. The solubility studies have been carried out in the temperature range 30-50 degrees C. Single crystals (size 12 mmx7 mmx4 mm) have been grown by slow evaporation of the saturated aqueous solution (methanol as solvent) at 30 degrees C. The lattice parameters of the grown crystals have been determined by single crystal X-ray diffraction technique. The UV-vis-NIR transmittance spectrum has been recorded in the range 200-1500 nm. The molecular structure was confirmed by FT-IR and FT-NMR. SPNP was thermally stable up to 103 degrees C as determined by TG/DTA curves. By a modified Kurtz and Perry method, the powder SHG efficiency was found to be five times that of KDP and its phase matching property was established. Laser damage threshold of SPNP was determined using a Nd:YAG laser.     

Fluorescence Excitation Spectrum of Bilirubin in Blood: A Model for the Action Spectrum for Phototherapy of Neonatal Jaundice

A recent report (Lamola et al. 2013 Pediatric Research, 74, 54–60) presents a semiempirical model for facile calculation of an action spectrum for bilirubin photochemistry in vivo using the most current knowledge of the optics of neonatal skin. The calculations indicate that competition for phototherapy light by hemoglobin in the skin is the predominant factor that defines the spectrum of light absorbed by bilirubin. If the latter is correct, a valid physical analog of the calculated spectrum is the excitation spectrum of bilirubin in blood. The fluorescence excitation spectrum was recorded and, indeed, found to be very similar to the calculated spectrum. Both spectra exhibit maxima near 476 nm and widths at half height of about 50 nm. This result supports the conclusion that light between 460 and 490 nm is most effective for phototherapy of neonatal jaundice.     

DECONVOLUTION OF THE RED P700 DIFFERENCE SPECTRUM BASED ON A SET OF THREE GAUSSIAN COMPONENTS: FURTHER EVIDENCE FROM LITERATURE SPECTRA

Abstract Literature data on the light induced difference spectrum of the photosynthetic reaction centre complex P700 were analysed in the spectral region from 670-700 nm. In accordance to our previous Gaussian deconvolution of the flash induced difference spectrum and the linear dichroism spectrum of photosystem I particles from green plants, we present here fits of three representative difference spectra that were recorded at room temperature and at low temperature conditions, respectively. These fits are generated by using the same set of only three Gaussian components that we specified previously: (1) a disappearing wide band around 695 nm representing the absorption of the reduced special-pair of chlorophyll- a ; (2) an appearing narrower band at slightly shorter wavelength (In agreement with our previous results, this band shows half the oscillatory strength of the former band. It is therefore attributed to the non-oxidized chlorophyll- a in the special pair); and (3) a bathochromic bandshift centered around 688 nm, which indicates the local electrochromic response of chlorophyll-a antennae molecule(s) close to the site of the primary donor. Among the reports by several authors we attribute the variation of the difference spectra of P700 in the region from 670-720 nm mainly to a variation in the magnitude of the third component, the local electrochromic one. We can also account for the peculiar shape of the low temperature spectra, mainly by alteration of the extent of the electrochromic component. It seems reasonable that the electrochromic component reacts most sensitively against structural changes of the reaction centre protein complex (brought forth by different degrees of depletion from antennae or by variation of the temperature).     

Modified UBFF calculations of the alpha-L-fucopyranose molecule in the crystalline state

Normal co-ordinate analysis has been realised in the crystalline state using a modified Urey-Bradley-Shimanouchi force field combined with an intermolecular potential energy function that includes van der Waals interactions, some electrostatic terms and an explicit hydrogen bond function. The vibrational spectra of the alpha-L-fucose molecule have been recorded in the crystalline state, in the 4000-500 cm(-1) spectral region for the mid-IR spectra, in the 500-100 cm(-1) spectral region for the far-IR spectra, and in the 4000-20 cm(-1) spectral range for Raman spectra. These spectra constitute the experimental support for the establishment of a force field for the molecule in the crystalline state through a normal co-ordinate analysis.     

Heavy hydrides: H2Te ultraviolet photochemistry

The room-temperature ultraviolet absorption spectrum of H2Te has been recorded. Unlike other group-6 hydrides, it displays a long-wavelength tail that extends to 400 nm. Dissociation dynamics have been examined at photolysis wavelengths of 266 nm (which lies in the main absorption feature) and 355 nm (which lies in the long-wavelength tail) by using high-n Rydberg time-of-flight spectroscopy to obtain center-of-mass translational energy distributions for the channels that yield H atoms. Photodissociation at 355 nm yields TeH(2Pi1/2) selectively relative to the TeH(2Pi3/2) ground state. This is attributed to the role of the 3A' state, which has a shallow well at large R(H-TeH) and correlates to H+TeH(2Pi1/2). Note that the 2Pi1/2 state is analogous to the 2P1/2 spin-orbit excited state of atomic iodine, which is isoelectronic with TeH. The 3A' state is crossed at large R only by 2A", with which it does not interact. The character of 3A' at large R is influenced by a strong spin-orbit interaction in the TeH product. Namely, 2Pi1/2 has a higher degree of spherical symmetry than does 2Pi3/2 (recall that I(2P1/2) is spherically symmetric), and consequently 2Pi1/2 is not inclined to form either strongly bonding or antibonding orbitals with the H atom. The 3A'<--X transition dipole moment dominates in the long-wavelength region and increases with R. Structure observed in the absorption spectrum in the 380-400 nm region is attributed to vibrations on 3A'. The main absorption feature that is peaked at approximately 240 nm might arise from several excited surfaces. On the basis of the high degree of laboratory system spatial anisotropy of the fragments from 266 nm photolysis, as well as high-level theoretical studies, the main contribution is believed to be due to the 4A" surface. The 4A"<--X transition dipole moment dominates in the Franck-Condon region, and its polarization is in accord with the experimental observations. An extensive secondary photolysis (i.e., of nascent TeH) is observed at 266 and 355 nm, and the corresponding spectral features are assigned. Analyses of the c.m. translational energy distributions yield bond dissociation energies D0. For H2Te and TeH, these are 65.0+/-0.1 and 63.8+/-0.4 kcalmol, respectively, in good agreement with predictions that use high-level relativistic theory.     

BEHAVIOR OUTDOORS AND ITS EFFECTS ON PERSONAL ULTRAVIOLET EXPOSURE RATE MEASURED USING AN AMBULATORY DATALOGGING DOSIMETER

We describe the construction of a small device incorporating a UVB (290–320 nm) sensor that can be worn on the lapel site or waistband and which is electrically coupled to a portable data logger carried in a trouser pocket or worn on a belt. The detector has an approximate cosine-weighted angular response and is linear over a wide dynamic range. It has a spectral sensitivity that follows closely the erythema action spectrum in the UVB region, is less than one order of magnitude greater than this action spectrum in the UVAII region (320–340 nm) and between one to two orders of magnitude greater in the UVAI region (340–400 nm). The instrument has been used to monitor variations in erythemally effective exposure rate that occurred during three outdoor activities with differing weather conditions. Erythemal irradiance incident on the trunk was recorded every 2 s for periods ranging from 1 to 2.2 h. The results demonstrated that behavior outdoors can be a more dominant factor in determining personal exposure than ambient ultraviolet and highlighted the very important role that shade from trees plays in reducing exposure.