Ultraviolet Absorption Wavelength Research Articles

Synthesis of near infrared absorbing cationic zinc aminophthalocyanine and its application as an efficient photo-sensitizing nanoparticle in anti-drug-resistant bacteria

The emergence of drug-resistant bacteria threatens human health, and photodynamic therapy and photothermal therapy are promising methods to eliminate drug-resistant bacteria. However, the key to photodynamic and photothermal therapy is efficient photosensitizers, which are not fully developed. Herein, a novel cationic zinc aminophthalocyanine, zinc tetrakis(dimethyloctylammonium bromide) phthalocyanine (DMAZnPc-C8), is synthesized and investigated. The structures of the cationic zinc aminophthalocyanines are characterized by Fourier transform infrared spectrometer (FTIR), nuclear magnetic resonance hydrogen spectrum (1H NMR)，Mass spectrometry and X-ray spectroscopy. The singlet oxygen generation ability, photo-thermal properties and antibacterial properties against methicillin-resistant Staphylococcus aureus (MRSA) of cationic zinc aminophthalocyanine nanoparticles (DMAZnPc-C8 NP) in aqueous dispersion are investigated. The results show that the maximum ultraviolet absorption wavelength of DMAZnPc-C8 in DMSO is at 764 nm, and DMAZnPc-C8 shows good response to near-infrared light. DMAZnPc-C8 NP has good photo-thermal performance. After irradiation with an 808 nm laser (0.5 W/cm2) for 10 min, the temperature of DMAZnPc-C8 NP dispersion (0.05 mg/mL) is increased by 7.4 °C. And DMAZnPc-C8 NP has good singlet oxygen production capacity. DMAZnPc-C8 NP has excellent antibacterial effect against MRSA-resistant bacteria. When the concentration of DMAZnPc-C8 NP is 0.03 mg/mL, the growth of MRSA is almost completely inhibited after 10 min of laser irradiation at 808 nm (0.5 W/cm2), the antibacterial rate reach over 99 %. This study shows that cationic zinc aminophthalocyanine has promising application prospects in the field of anti-drug-resistant bacteria.

Preparing bright Monascus yellow pigments by loading quercetin-Sn(II)- albumin –chitosan: Enhanced stability and bioactivity

Natural Monascus yellow pigments (MYPs) have received considerable attention due to their great safety and biological activities, but their unsatisfactory color tonality and stability limit their applications. A novel encapsulate system for hydrophilic yellow pigments (HYPs) were investigated through stable ternary nanocomplexes using quercetin-Sn (II), bovine serum albumin (BSA), and chitosan (CS) in this work. Layer-by-layer assembly preparation of HYPs-loaded quercetin-Sn (II)-BSA-CS nanocomplexes were verified by fluorescence spectroscopy, fourier transform infrared spectroscopy, X-ray photoelectron spectra, and 1H nuclear magnetic resonance. A hyperchromic effect on HYPs was obtained since their maximum ultraviolet absorption wavelength redshifted from 352 nm to 364 nm first due to the interaction with quercetin-Sn (II) and further redshifted to 408 nm due to ternary conjugation, greatly improved the color tonality and dye-uptake. The HYPs-loaded nanocomplexes showed irregular glomerate nanosphere with 252–382 nm of particle size. Their conjugation remitted HYPs degradation under various environmental stresses (thermal, light, and ascorbic acid treatment), and had a great color stability response to pH change. Higher lipid-lowering and antioxidant activities were detected in the nanocomplexes than free HYPs. This study provides a new way for fabricating novel MYPs with great physicochemical stability, bright color and hypolipidemic activities.

Estimation of rutin‐loaded chitosan sodium alginate nanoparticles in rat plasma using a chemometrics‐assisted bioanalytical high‐performance liquid chromatography method

AbstractRutin, a flavonoid glycoside is mostly made up of phenolic compounds and is involved in a variety of biological processes. Rutin‐loaded chitosan‐alginate nanoparticles were prepared for enhancing the site specificity and bioavailability. The main focus of the current research work was to develop and validate a simple, accurate, and robust bioanalytical reverse‐phase high‐performance liquid chromatography method using the Design of Experiments principles for the estimation of rutin‐loaded chitosan‐alginate nanoparticles in plasma. A mixture of methanol and phosphate buffer in the ratio of 45:55 v/v was used as the mobile phase. The pH of the mobile phase is adjusted to 3.2 with 80% orthophosphoric acid; the flow rate was optimized to 1.0 ml/min and the ultraviolet absorption wavelength at 254 nm. Critical analytical attributes were screened with Taguchi orthogonal array model design. To develop and analyze a “Design Space,” Box‐Behnken three‐level, three‐factorial design in the design of experiment was employed. Analysis of variance, contour plots, and three‐dimensional surface response plots were used to statistically assess this design, and the model was shown to be statistically significant. The devised approach was validated according to the recommendations of the International Council for Harmonization (Q2 R1). The linearity of the developed method showed excellent in the range of 100 to 900 ng/ml with good regression (R2 > 0.998), the limit of quantitation (30 ng/ml), and the limit of detection (10 ng/ml). The validation findings of the parameters were examined and found to be within acceptable limits. The study findings stated that the Quality by Design‐driven bioanalytical approach is applicable for the in vivo and in vitro quantification of rutin derived from bulk and rutin‐loaded chitosan‐alginate nanoparticles formation.

Original boron cluster covalent with poly-zwitterionic BODIPYs for boron neutron capture therapy agent

Currently, boron neutron capture therapy（BNCT） is the most innovative and promising highly selective targeted radiotherapy for cancer. Therefore, this paper designed and synthesized two kinds of boron-polymers, wrapped in the same fluorophore -BODIPYs, as fluorescent targeting markers for rapid, accurate, real-time, and inexpensive detection of boron-containing drugs. The spherical polymer o-carborane (PBC) in different polar solvents, the ultraviolet maximum absorption wavelength is in the range of 530–545 nm. The maximum ultraviolet absorption wavelength of PBD is in the range of 440–520 nm. The fluorescence spectra of the two boron-polymer are very similar, and the maximum emission wavelength is concentrated in the range of 550–560 nm. In terms of cytotoxicity and in vitro cell imaging, the in vitro biological toxicity evaluation of the two boron-polymer reached the expected high level, especially the cytotoxic concentration of PBD reached 1.347 ± 0.033 μM, which was higher than the 2.829 ± 0.351 μM of PBC. By transmission electron microscopy, it was found that the two terminal zwitterions of BODIPY polymer tightly wrapped boron clusters to form small particle nanoclusters. The imaging of the two boron-polymers was tested in the Hera cell lines of low, medium, and high densities. The in vitro study results revealed high levels of accumulation in HeLa cells with higher cytotoxicity and boron uptake compared to L-boron-phenylalanine (BPA). In vivo imaging, large number of borane polymers were observed to accumulate in the subcutaneous tumor sites of mice over time, indicating that it has high selectivity and high aggregation.

A strong acid-resistant flavanthrone with excellent photophysical properties

Based on a vat dye of anthraquinone type, simple modification of the structure of flavanthrone (Benzo[h]Benz[5,6]Acridino[2,1,9,8-Klmna]Acridine-8,16-Dione). By introducing the electrochemically inert group 1-bromo-3,5-di-tert-butylbenzene after the reduction of the carbonyl group, increasing the probability of fluorescence transition. And discussed the new simple compound that under different strongly acidic conditions, the optical properties are obviously distinction. Sulfuric acid, methanesulfonic acid and hydrochloric acid were added, the maximum ultraviolet absorption wavelength of the original product is redshifted from 510 nm to about 590 nm, and the fluorescence emission wavelength is around 523 nm to 526 nm and the fluorescence intensity decreased significantly. Especially, the addition of trifluoromethanesulfonic acid, the maximum ultraviolet absorption wavelength is redshifted to 602 nm, and the fluorescence quenching. Nevertheless, the addition of nitric acid, hydrofluoric acid and phosphoric acid had no obvious effect on the optical properties of the flavanthrone compound. Also, even in different strong acid conditions the flavanthrone compound has excellent fluorescence stability and high fluorescence quantum yield of about 50%. To better comprehend the electronic properties, the values of the energy levels of the highest occupied molecular orbitals (HOMOs, EHOMO = -5.2937 eV) and the lowest unoccupied molecular orbitals (LUMOs, ELUMO = −2.7021 eV) of the flavanthrone as well as energy band gaps determined electrochemically (△E = 2.5916 eV) were carried out at the B3LYP/6-311G** level of the density functional theory (DFT) calculations.

A near-infrared azadipyrromethene dye: Photophysical properties under different acidity conditions

We designed and synthesized the new structure azadipyrromethene from 4-bromo-2-hydroxyacetophenone through five steps, and tested the compound via five different acid conditions. The results indicated that the maximum ultraviolet absorption wavelength of azadipyrromethene is 763 nm, and the addition of methanesulfonic acid and hydrochloric acid solution significantly increased the ultraviolet absorbance of the compound within 10 h, but the fluorescence quantum yield decreased from 0.71 to around 0.05. However, under the condition of phosphoric acid, the photophysical properties of azadipyrromethene did not change significantly.

Spectral Calculation of Cucurbituril[n] Molecule Based on Density Functional Theory

The cucurbituril[n] (CB[n]) is a class of chemical supramolecular substances. In order to calculate the spectrum ofthe cucurbituril[n] molecules, the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT) are used to optimize the geometrical structure of CB[n](n=5-10) at the level of 6-311g(d) in the gas phase environment. Then, the infrared (IR) spectrum and ultraviolet (UV) spectrum of CB[n] (n=5-10) are calculated respectively. The results show that: (1) The absorption peaks of two vibration modes of ν(β-H) and ν(γ-H) of CB[n](n = 7,8) are degenerated. (2) The absorption frequency of the stretching vibration ν(α=O) is red shifted. (3) The increase of the absorption peak intensity in the vibration mode near the 1200 cm-1 wavenumber is especially noticeable. (4) The ring tension of CB[n](n=5∼10) gradually decreases with n increasing. (5) The UV absorption wavelength of the maximum absorption peak of CB[n](n=5-10) increases from 198.8317nm to 202.2633nm with n from 5 to 10. The methylene CH2 has isolating action in the formation process of the UV spectrum of CB[n] (n=5-10). The distribution of electron and hole is symmetric and locally excitated (LE) for CB[n] (n=5-10).

Investigation on the UV spectra of the supermolecular system involving silver nanoparticles–substituted N‐(phenyl‐ethylene)‐anilines

AbstractThe ultraviolet (UV) absorption spectra of the supermolecular system involving silver nanoparticles–substituted N‐(phenyl‐ethylene)‐anilines were investigated. Silver nanoparticles (AgNPs) and 77 kinds of substituted N‐(phenyl‐ethylene)‐anilines ZArC (Me)═NArY (ZPEAY, including 40 compounds 2‐H‐XPEAY without ortho‐hydroxyl and 37 compounds 2‐OH‐XPEAY with ortho‐hydroxyl) were prepared. The size of AgNPs was measured with transmission electron microscopy. To study the effect of substituents X and Y on the UV spectra of the supermolecular system of AgNPs‐ZPEAY, the authors measured the UV absorption spectra of AgNPs, ZPEAY, and AgNPs‐ZPEAY solutions. The experimental results show that (a) the size of AgNPs increases in AgNPs‐ZPEAY solution compared with that in AgNPs solution, due to the absorption of ZPEAY molecules on the surface of AgNPs; (b) the UV absorption wavelength of ZPEAY changes in AgNPs‐ZPEAY solution and there is a limitation for the wavelength shift (λWSL) between ZPEAY and AgNPs‐ZPEAY system; (c) there is a quantitative correlation between the wavenumber ΔνWSL of λWSL and the substituent constants (Hammett constant σ and excited‐state substituent constant ) of substituents X and Y; (d) the intramolecular hydrogen bonding in 2‐OH‐XPEAY makes the ΔνWSL a red shift in AgNPs‐ZPEAY system.

Establishing a method of HPLC involving precolumn derivatization by 2,2'-dithiobis (5-nitropyridine) to determine the sulfites in shrimps in comparison with ion chromatography.

Although sulfites are widely used in shrimp processing, the contents of residual sulfite need to be strictly controlled due to their potential toxicity. In this paper, a novel method was developed for determination of the free and total sulfites in shrimps. Major procedures of the method includes separation of free and total sulfites with ultrasound‐assisted extraction and pH adjustment for 20 min, then a precolumn derivatization was conducted by 2,2′‐Dithiobis (5‐nitropyridine) and verified by LC‐MS, and finally HPLC coupled with an ultraviolet (UV) detector was carried out. Results indicated that the UV absorption wavelength shifted from 213 (sulfites) to 320 nm (new disulfide compounds), significantly reducing the interference of natural occurring compounds and solvents in the matrix. The standard curves exhibited a good linear range of 3.2–51.2 mg/L (R 2 = 0.9996). The limit of detection (LOD) and limit of quantification (LOQ) were 0.3 and 1.0 mg/L, respectively. The contents of free and total sulfite in frozen shrimps were 26.58 ± 0.48 and 31.44 ± 0.83 mg/kg calculated by SO2, respectively. These were similar (p > 0.05) to the data obtained by the method of ion chromatography. In conclusion, the new developed method has been proved to be a reliable and economic method for effective determination of free and total sulfites in the shrimps, and the method could be expanded in determination of the sulfites in other food products.

Direct determination of ultra-trace polycyclic aromatic hydrocarbons in water by liquid chromatography coupled with online solid phase extraction

A method was developed for the direct determination of 16 ultra-trace polycyclic aromatic hydrocarbons (PAHs) in water by liquid chromatography (LC) coupled with online solid phase extraction (online SPE). The water sample was centrifuged at a high speed to remove the particulate matter and prepared into an aqueous solution containing 40% (v/v) methanol. A 2 mL-sample was directly injected into the online SPE flow path. Online purification and enrichment of the samples were carried out on the SPE column (Acclaim PA Ⅱ, 50 mm×4.6 mm, 3 μm). The PAHs eluted from the SPE column were transferred to the analytical flow path by valve switching, and were separated on a Hypersil Green PAHs column (150 mm×3 mm, 3 μm). Water and acetonitrile were used as the mobile phases. The flow rates of 1.0 mL/min and 0.4 mL/min were used in the extraction and balance processes, respectively. The flow rate of 0.6 mL/min was used to separate the PAHs in the analytical flow path. Acenaphthylene without a fluorescent signal was detected at the ultraviolet absorption wavelength of 220 nm, while other PAHs were measured by the fluorescence signal via the special excitation/emission wavelength program. The entire analysis could be completed within 37 min. The linear correlation coefficients of the 16 PAHs were greater than 0.996. The limits of detection of the PAHs were 0.14-12.50 ng/L (S/N=3) with only 0.38 ng/L for benzo(a)pyrene (B(a)P). The recoveries of PAHs at spiked levels of 10, 40 and 200 ng/L in the water samples were 76.1%-134.9%. The RSDs (n=3) were 0.3%-16.6%. Furthermore, the recoveries and RSDs (n=3) of B(a)P were 71.8%-92.7% and 3.9%, respectively. The proposed method is simple, rapid, solvent-saving, stable and sensitive, and can meet the ultra-trace analysis requirements of the PAHs (especially B(a)P) in various water samples.

Effect of substituents on the UV spectra of supermolecular system: Silver nanoparticles with bi‐aryl Schiff bases containing hydroxyl

AbstractEffect of substituents on the ultraviolet (UV) spectra of supermolecular system involving silver nanoparticles (AgNPs) and Schiff bases was investigated. AgNPs and 49 samples of model compounds (MC), bi‐aryl Schiff bases containing hydroxyl (XBAY, involving 4‐OHArCHNArY, 2‐OHArCHNArY, XArCHNAr‐4′‐OH, and XArCHNAr‐2′‐OH), were synthesized. The size of AgNPs was characterized by transmission electron microscopy (TEM), and the UV absorption spectra of AgNPs, XBAYs, and MC‐AgNPs mixed solutions were measured, respectively. The results show that (1) the size of AgNPs is larger in MC‐AgNPs solutions than that in AgNPs solution due to the distribution of MC molecules on the surface of AgNPs; (2) the UV absorption wavelength of XBAYs changes in the action of AgNPs and their wavelength shift exists limitation between XBAY and MC‐AgNPs solutions; and (3) the wavelength shift limit of MC‐AgNPs (λWSL) is influenced by the substituents X and Y and the position of hydroxyl OH. The wavenumber ΔνWSL of λWSL can be quantified by employing the excited‐state substituent constant and Hammett constant σ of substituents X and Y. Comparing with the 4‐OH, the 4′‐OH makes the ΔνWSL a red shift, whereas the 2′‐OH, comparing with the 2‐OH, makes the ΔνWSL a blue shift.

Microbiological synthesis of zinc sulfide nanoparticles using Desulfovibrio desulfuricans

ABSTRACTZinc sulfide (ZnS) nanoparticles were synthesized in a single-step process using Desulfovibrio desulfuricans at room temperature and atmospheric pressure. The kinetics of ZnS biosynthesis and the cellular distribution of Zn were also studied by measuring the Zn2+ and ZnS concentrations. The microstructure of the ZnS nanoparticles was characterized by means of high-resolution transmission electron microscopy and X-ray diffraction. The particles were essentially granular, and the particle size ranged from approximately 5 to 8 nm. The total UV–Vis spectrum of the product migrated toward blue wavelengths compared with the ultraviolet absorption wavelength of the ZnS bulk material. The yield of ZnS nanoparticles was 97.8% after 96 h. A mechanistic experiment showed that ZnS nanoparticles were produced inside the cells and released into the solution. In the cells, Zn was the most highly concentrated in the membrane, followed by the cell wall and cytoplasm.

UV Detection on Artificial Uric Acid Using UV-Vis Spectrometer

The aim of this research work is to measure the concentration and absorption cross-section of artificial uric acid in the Ultraviolet (UV) region using UV-Vis spectrometer. The uric acid sample comes in powder form which has to be dissolved with distilled water to convert it into liquid form. Therefore, it can be placed in the cuvette for the analysis purposes. This research study was proposed to make a comparison with the previous research studies that uric acid was normally extracted from human serum as a real sample. This research study was carried out using an artificial sample of uric acid with the suspended or grits of uric acid which were not totally dissolved. These grits might be artificially assumed as crystallites which is common with Gout disease. Based on the medical perspective, crystallites normally inhibit the human joints which may cause intense pain to the human bones or tissues. In the experiment, the distilled water was used a background or reference spectrum which can be stored and automatically deducted using the Spectra suite software application. Thus, Spectra suite only measures the pure concentration and UV absorption wavelength of the uric acid through the use of the spectrometer. The absorbance data was extracted and substituted into Beer’s Lambert Law formula to calculate the value of absorption cross-section. The result shows that the value of UV absorption wavelength and absorption cross-section is really close as reported in the previous research studies. It proves that even the artificial sample of uric acid with the grits still can give a very close result. The UV absorption of uric acid was obtained at 293.99 nm by four different concentrations. The response time was successfully done in 3 seconds. The resulting curves have noise signals which can be analyzed and reduced using an averaging method to make the curve look sharper and lack of noise.

Copper catalytic effect on the thermal deterioration and surface morphology performance of transformer oil–paper insulation

Transformer failure caused by copper corrosion in oil–paper insulation has been attracting much attention in recent years. It is necessary to get a better understanding the effect of copper on the degradation rate and the microcosmic performance of the oil–paper insulation. In this way, targeted measures could be taken to prevent harm to the transformer. The catalytic effect of copper on the thermal aging rate and the micro‐/nano‐level morphology of oil–paper insulation aged with and without copper are compared in this paper. The dynamic behavior of copper compounds dissolved in oil and deposited on the insulation paper surface is discussed. Results show that copper plays a catalytic role in the deterioration of oil–paper insulation, and this role becomes obvious in the later stages of aging. Compared to the oil–paper insulation sample aged without copper, in the oil–paper insulation sample aged with copper the oil has higher acidity and higher ultraviolet absorption wavelength. Besides, the degree of polymerization of the paper is lower. Scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) results show that copper is present on the innermost paper surface. SEM and atomic force microscopy clearly show the deposition of copper compounds. Higher deterioration of the paper results in more roughness of the paper surface. The content of copper compounds dissolved in oil was found to be increasing first and then decreasing in the later process of aging. The content of copper compounds deposited on the paper increases significantly when the oil is aged for a long time. The catalytic effect of copper on the thermal aging rate and the surface morphology of oil–paper insulation should be paid more attention even for a noncorrosive oil. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Uric acid detection using uv-vis spectrometer

The aim of this research is to detect uric acid (UA) concentration using Ultraviolet-Visible (UV-Vis) spectrometer in the Ultraviolet (UV) region. Absorption technique was proposed to detect different uric acid concentrations and its UV absorption wavelength. Current practices commonly take a lot of times or require complicated structures for the detection process. By this proposed spectroscopic technique, every concentration can be detected and interpreted into an absorbance value at a constant wavelength peak in the UV region. This is due to the chemical characteristics belong to the uric acid since it has a particular absorption cross-section, σ which can be calculated using Beer’s Lambert law formula. The detection performance was displayed using Spectrasuite sofware. It showed fast time response about 3 seconds. The experiment proved that the concentrations of uric acid were successfully detected using UV-Vis spectrometer at a constant absorption UV wavelength, 294.46 nm in a low time response. Even by an artificial sample of uric acid, it successfully displayed a close value as the ones reported with the use of the medical sample. It is applicable in the medical field and can be implemented in the future for earlier detection of abnormal concentration of uric acid.

Successive stepwise evolution of host layer-stacking framework upon the intercalation of mobile vapor guests within side-chain layers

For the ordered phases of hairy-rod semiconductive poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT) sandwiched in between crystalline platelets of hexamethylbenzene, the successive stepwise evolution of layer-stacking framework upon guest intercalation has been studied in this research. The direct consequence of the guest intercalation into side-chain layers is evaluated to cause the lateral shift of thiophene backbones along π–π stacking, resulting in stepwise shift of ultraviolet absorption wavelength. The thermal motions of vapor guests within disordering side-chain layers subsequently cause progressive expansion of host stacking framework. With the increase in side-chain length, thicker layers of disordering side chains in liquid crystals (LCs) accommodate additional vapor guests and larger amplitudes of thermal motions of guests, hence promoting the level of reversible d-spacing change. The mixing between mobile vapor guests and aliphatic side chains is clarified as the mechanism of guest intercalation, which rationalizes successive guest intercalation during heating and the contribution of disordering side-chain layers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

QSAR Model-assisted Prediction of Largest Ultraviolet Absorption Wavelength of PCBs Based on Solvent Effects

This paper calculated the structure parameters, energy parameters, thermodynamic parameters, and ultraviolet absorption spectrum of 2,2′,5,5′-tetrachlorobiphenyl (PCB-52) in 12 polar solvents and g...

Synthesis of Al-doping ZnO nanoparticles via mechanochemical method and investigation of their structural and optical properties

In this study, pure and Al-doped ZnO nanoparticles were successfully synthesized by the mechanochemical method. The effect of doping on structural and optical properties was studied. The structural investigations of products confirmed the hexagonal wurtzite structure for all products and also it was observed that doping caused a little change in lattice parameters. The results obtained by SEM revealed that the average particle size of products increases by doping and nanoparticles have almost spherical morphology. UV–visible absorption and PL spectra showed that the maximum ultraviolet absorption wavelength of products increases and the optical band gap shifts from 3.15eV to 3.11eV, with increasing the Al concentration.

UV-spectroscopy, electronic structure and ozonolytic reactivity of sesquiterpenes: a theoretical study

Sesquiterpenes, one of the most important classes of biogenic volatile organic compounds, are potentially significant precursors to secondary organic aerosols (SOAs) in nature. The electronic structure of sesquiterpenes and their reactivity in the ozonolysis reaction were investigated by density functional theory. Results from the CIS calculations combined with an analysis of transition intensities show that the first peaks in the ultraviolet (UV) spectra for saturated and unsaturated isomers are σ-σ and π-π transitions, respectively. The UV absorption wavelength and absorbency are dictated by the electronic structures of these compounds. An increase in the number of double bonds and formation of a conjugated system expand the range of absorption in the UV region. An isomer with an endocyclic C = C bond presents weaker UV transition intensity than its corresponding exocyclic isomer. Results from conceptual DFT chemical reactivity indices of isomers suggest that no quantitative linear relationships between the structural changes and their reactivity, such as different degrees of unsaturated C = C double bonds, or the number of substituents attached to the C = C bond were discovered. In the ozonolysis reaction of sesquiterpenes, isomers with larger steric hindrance of substituents or endocyclic C = C bond possess higher chemical reactivity compared to isomers with smaller steric hindrandce or with an exocyclic C = C bond. These results are imperative to a better understanding of SOAs production mechanisms in the troposphere.

The ?-bromocyclohexanone ring: The relationship between its conformation and the ultraviolet and infrared absorption of the keto group

A series of diterpenoids whose C-ring was an α-bromocyclohexanone showed a discontinuity in the relationship between the BrCCO torsion angle and the Br…O contact distance at about 50°, below which the Br…O distance remained effectively constant at about 3.0 A. This effect is caused by the non-compressibility of the van der Waals radii of the Br and O atoms. Analysis of the parameters for all compounds in the Cambridge Data File containing an α-bromocyclohexanone ring confirmed this phenomenon. Once the Br…O distance approaches 3.0 A, the BrCC and CCO angles are forced open to accommodate the Br…O compression strain as the torsion angle is further reduced. An approximate value of the Br…O distance, d in A, can be estimated for any torsion angle, o, by the empirical equation d2 = R – S cos ϕ + T cos2 ϕ where R = 11.73, S = 3.62 and T = 0.75. There is a linear relationship between the Br…O separation and both the infrared vibration frequency v and the ultraviolet absorption wavelength δmax of the CO group: the greater the distance, the lower is the frequency v and longer the wavelength δmax. Thus measurement of the ultraviolet and infrared spectra of a compound containing an α-bromocyclohexanone system can yield information about the Br…O distance and hence the conformation of the six-membered ring. There are also systematic trends in the effect on the spectroscopic properties of the keto group that accompany changing the halogen from fluorine through to iodine. When the halogen is axial, its electronegativity has a maximum influence on the CO vibration frequency by a ‘through-bond’ inductive process. When the halogen is equatorial, it exerts a steric compression on the non-bonded electrons in the 2p orbital of the oxygen atom. This enhances hybridization to the sp2 state and this simultaneously strengthens the CO bond and enlarges the n π* energy gap. This ‘through-space’ influence is simply a process of steric compression, dependent on the size of the halogen atom. It accounts well for all of the systematic trends in both infrared and ultraviolet frequencies of the CO group when the halogen is equatorial and eclipses the CO bond.