α-Cleavage of 2,2-Diazido-2,3-dihydroinden-1-one in Solution and Cryogenic Matrices.

The Norrish type I (α-cleavage) reaction is an excellent photochemical method for radical-pair formation in solution. However, in cryogenic matrices, the starting material typically re-forms before the radical pair diffuses apart. This study focused on N2 extrusion from an azido alkyl radical to prevent radical-pair recombination. Irradiation of 2,2-diazido-2,3-dihydroinden-1-one (1) in methanol mainly yielded methyl 2-cyanomethylbenzoate (2) and 2-cyanomethylbenzoic acid (3) via α-cleavage. Laser flash photolysis of 1 in argon-saturated acetonitrile resulted in α-cleavage to form triplet biradical 31Br1 (λmax ∼ 410 nm, τ ∼ 400 ns). In contrast, upon irradiation in glassy 2-methyltetrahydrofuran matrices, triplet alkylnitrene 31N was directly detected using electron spin resonance (D/hc = 1.5646 cm-1, E/hc = 0.00161 cm-1) and absorption spectroscopy (λmax = 276 and 341 nm). Irradiation of 1 in argon matrices generated 31N, benzoyl azide 4, singlet benzoylnitrene 14N, and isocyanide 5, as revealed by IR spectroscopy. The experimental results supported by density functional theory calculations [B3PW91/6-311++G(d,p)] suggest that irradiation of 1 in matrices results in α-cleavage to form biradical 31Br1, which extrudes N2 to yield 31Br2. Rearrangement of 31Br2 into 31N competes with cleavage of a N3 radical to form radical 1Ra3. The N3/1Ra3 radical pair combines to form 4, which upon irradiation yields 14N and 5.

Treating very preterm European infants with inhaled nitric oxide increased in-hospital mortality but did not affect neurodevelopment at 5 years of age.

AIM: We examined the outcomes of using inhaled nitric oxide (iNO) to treat very preterm born (VPT) infants across Europe. METHODS: This was a sub-study of the Screening to Improve Health in Very Preterm Infants in Europe research. It focused on all infants born between 22 + 0 and 31 + 6 weeks/days of gestation from 2011 to 2012, in 19 regions in 11 European countries. We studied 7268 infants admitted to neonatal care and 5 years later, we followed up the outcomes of 103 who had received iNO treatment. They were compared with 3502 propensity score-matched controls of the same age who did not receive treatment. RESULTS: All countries used iNO and 292/7268 (4.0%) infants received this treatment, ranging from 1.2% in the UK to 10.5% in France. There were also large regional variations within some countries. Infants treated with iNO faced higher in-hospital mortality than matched controls (odds ratio 2.03, 95% confidence interval 1.33-3.09). The 5-year follow-up analysis of 103 survivors showed no increased risk of neurodevelopmental impairment after iNO treatment. CONCLUSION: iNO was used for VPT patients in all 11 countries. In-hospital mortality was increased in infants treated with iNO, but long-term neurodevelopmental outcomes were not affected in 103 5-year-old survivors.

Unraveling the Solid-State Photoreactivity of Carbonylbis(4,1-Phenylene)dicarbonazidate with Laser Flash Photolysis.

Solid-state photoreactions are generally controlled by the rigid and ordered nature of crystals. Herein, the solution and solid-state photoreactivities of carbonylbis(4,1-phenylene)dicarbonazidate (1) were investigated to elucidate the solid-state reaction mechanism. Irradiation of 1 in methanol yielded primarily the corresponding amine, whereas irradiation in the solid state gave a mixture of photoproducts. Laser flash photolysis in methanol showed the formation of the triplet ketone (TK) of 1 (τ ∼ 99 ns), which decayed to triplet nitrene 31N (τ ∼ 464 ns), as assigned by comparison to its calculated spectrum. Laser flash photolysis of a nanocrystalline suspension and diffuse reflectance laser flash photolysis also revealed the formation of TK of 1 (τ ∼ 106 ns) and 31N (τ ∼ 806 ns). Electron spin resonance spectroscopy and phosphorescence measurements further verified the formation of 31N and the TK of 1, respectively. In methanol, 31N decays by H atom abstraction. However, in the solid state, 31N is sufficiently long lived to thermally populate its singlet configuration (11N). Insertion of 11N into the phenyl ring to produce oxazolone competes with 31N cleavage to form a radical pair. Notably, 1 did not exhibit photodynamic behavior, likely because the photoreaction occurs only on the crystal surfaces.

Excited-State Intramolecular Proton Transfer in Salicylidene-α-Hydroxy Carboxylate Derivatives: Direct Detection of the Triplet Excited State of the cis-Keto Tautomer.

Excited-state intramolecular hydrogen transfer on the triplet surface of salicylideneaniline derivatives has received much less attention than the corresponding ultrafast process on the singlet surface. To enhance the understanding of this triplet reactivity, the photochemical properties of a series of salicylidene-α-hydroxy acid salts with different substituents on the phenol moiety (1-3) were characterized. UV/vis absorption and phosphorescence measurements in ethanol revealed that 1-3 exist as both enol and keto tautomers, with the enol form being predominant. Irradiation of 1 at 310 nm in ethanol glass (77 K) yielded an absorption band with a λmax at ∼405 nm, which was assigned to the trans-keto tautomer (trans-1K). In contrast, laser flash photolysis of 1-3 in methanol or acetonitrile resulted in a transient absorption with λmax at 440-460 nm. This transient, which decayed on the microsecond timescale and was significantly shorter lived in methanol than in acetonitrile, was assigned to the triplet excited state (T1) of the cis-keto tautomer (cis-1K-3K) and residual absorption of trans-1K-3K by comparison with TD-DFT calculations. The assignment of the T1 of cis-1K was further supported by quenching studies with anthracene and 2,5-dimethyl-2,4-hexadiene. Laser flash photolysis of 1 in the temperature range of 173-293 K gave an activation barrier of 6.7 kcal/mol for the decay of the T1 of cis-1K. In contrast, the calculated activation barrier for cis-1K to undergo a 1,5-H atom shift to reform 1 was smaller, indicating that intersystem crossing of the T1 of cis-1K is the rate-determining step in the regeneration of 1.

[Migraine prevalence, migraine incidence and migraine drug prescriptions in primary care in the capital region of Iceland].

INTRODUCTION: The study aim was to describe migraine incidence over the ten-year periods, 2000-2009 and 2010-2019, in individuals aged 10-79 years in primary healthcare centre (PHCC) Sólvangur and Fjörður, Hafnarfirði. Another aim was to estimate migraine prevalence in primary care clinics in the capital area of Iceland over the period 2010-2019 and describe prescriptions for migraine specific drugs and other drugs used for migraine. MATERIAL AND METHODS: This is a retrospective study based on data from medical records from the primary care clinics of the capital region of Iceland. The cohort consisted of individuals aged 10-79 years who were diagnosed with migraine, G43 according to the ICD-10 classification system. RESULTS: Migraine incidence at age 10-79 years over the ten-year period 2000-2009 at the primary care clinic Sólvangur was estimated 3.4 cases per 1000 person-years, during the period 2010-2019 in both Sólvangur and Fjörður clinics migraine incidence was estimated 2.9 cases per 1000 person-years. Increase was shown between the two periods in prescriptions of triptan drugs, opioids, and beta-blockers, where two-thirds of the migraineurs got prescription over the two periods. Women were three times more likely to be diagnosed with migraine than men, but men were diagnosed at younger age than women. Migraine prevalence at age 10-79 years in PHCCs in the capital area of Iceland was 4.4% over the period 2010-2019. CONCLUSION: Migraine prevalence in the PHCCs of the capital area of Iceland was only one third of migraine prevalence in the population-based cohort pilot study Heilsusaga Íslendinga. Increase in opioid drug prescriptions for individuals diagnosed with migraine is of concern and needs further study.

From Incident Light to Persistent and Regenerable Radicals of Urea-Assembled Benzophenone Frameworks: A Structural Investigation.

Herein we probe the effects of crystalline structure and geometry on benzophenone photophysics, self-quenching, and the regenerable formation of persistent triplet radical pairs at room temperature. Radical pairs are not observed in solution but appear via an emergent pathway within the solid-state assembly. Single crystal X-ray diffraction (SC-XRD) of two sets of constitutional isomers, benzophenone bis-urea macrocycles, and methylene urea-tethered dibenzophenones are compared. Upon irradiation with 365 nm light-emitting diodes (LEDs), each forms photogenerated radicals as monitored by electron paramagnetic resonance (EPR). Once generated, the radicals exhibit half-lives from 2 to 60 days before returning to starting material without degradation. Re-exposure to light regenerates the radicals with similar efficiency. Subtle differences in the structure of the crystalline frameworks modulates the maximum concentration of photogenerated radicals, phosphorescence quantum efficiency (φ), and n-type self-quenching as observed using laser flash photolysis (LFP). These studies along with the electronic structure analysis based on the time-dependent density functional theory (TD-DFT) suggest the microenvironment surrounding benzophenone largely dictates the favorability of self-quenching or radical formation and affords insights into structure/function correlations. Advances in understanding how structure determines the excited state pathway solid-state materials undertake will aid in the design of new radical initiators, components of OLEDs, and NMR polarizing agents.

The type and timing of patent ductus arteriosus treatment was associated with neurodevelopment when extremely preterm infants reached 6.5 years.

AIM: This study investigated patent ductus arteriosus (PDA) treatment and neurodevelopmental outcomes when extremely preterm born children reached 6.5 years. METHOD: Our cohort was 435 children with neonatal PDA treatment data and neurodevelopmental follow-up data, born in 2004-2007, who participated in the Extremely Preterm Infants in Sweden Study. Pharmacological or surgical PDA treatment and the age at PDA treatment, were investigated in relation to the risks of moderate to severe neurodevelopmental impairment (NDI) and full-scale intelligence quotient (FSIQ) at 6.5 years. RESULTS: The children who received PDA drug treatment, including those who also had surgery, had the same risk of moderate to severe NDI or lower FSIQ as untreated children. However, children who had primary PDA surgery faced increased risks of NDI, with an adjusted incidence rate ratio of 1.62 (95% confidence interval [CI] 1.28-2.06) and a lower adjusted mean difference FSIQ of -7.1 (95% CI -11 to -3.2). Surgery at less than 10 days of life was associated with a significantly increased risk of moderate to severe NDI and lower FSIQ than surgery after 20 days. CONCLUSION: Drug treatment followed by deferred surgery appeared to be a safer option for extremely preterm infants severely affected by PDA.

Cracking under Internal Pressure: Photodynamic Behavior of Vinyl Azide Crystals through N2 Release.

When exposed to UV light, single crystals of the vinyl azides 3-azido-1-phenylpropenone (1a), 3-azido-1-(4-methoxyphenyl)propenone (1b), and 3-azido-1-(4-chlorophenyl)propenone (1c) exhibit dramatic mechanical effects by cracking or bending with the release of N2. Mechanistic studies using laser flash photolysis, supported by quantum mechanical calculations, show that each of the vinyl azides degrades through a vinylnitrene intermediate. However, despite having very similar crystal packing motifs, the three compounds exhibit distinct photomechanical responses in bulk crystals. While the crystals of 1a delaminate and release gaseous N2 indiscriminately under paraffin oil, the crystals of 1b and 1c visibly expand, bend, and fracture, mainly along specific crystallographic faces, before releasing N2. The photochemical analysis suggests that the observed expansion is due to internal pressure exerted by the gaseous product in the crystal lattices of these materials. Lattice energy calculations, supported by nanoindentation experiments, show significant differences in the respective lattice energies. The calculations identify critical features in the crystal structures of 1b and 1c where elastic energy accumulates during gas release, which correspond to the direction of the observed cracks. This study highlights the hitherto untapped potential of photochemical gas release to elicit a photomechanical response and motility of photoreactive molecular crystals.

Visible Light Absorption and Long-Lived Excited States in Dinuclear Silver(I) Complexes with Redox-Active Ligands.

Well-defined dinuclear silver(I) complexes have been targeted for applications in catalysis and materials chemistry, and the effect of close silver-silver interactions on electronic structure remains an area of active inquiry. In this study, we describe the synthesis, structure, and photophysical properties of dimeric silver complexes featuring a redox-active naphthyridine diimine ligand. Unusually for silver(I), these complexes display absorption features in the visible region due to metal-metal to ligand charge transfer (MMLCT) transitions, which arise from the combination of close silver-silver interactions and low-lying ligand π* orbitals. The complexes' photophysical properties are explored via a combination of spectroscopic and computational studies, revealing MMLCT excited state lifetimes that exceed 1 µs. These results portend previously unforeseen applications of silver(I) dimers in visible light absorption and excited state reactivity.

Comparison of the Photochemistry of Acyclic and Cyclic 4-(4-Methoxy-phenyl)-4-oxo-but-2-enoate Ester Derivatives.

To clarify the cis-trans isomerization mechanism of simple alkenes on the triplet excited state surface, the photochemistry of acyclic and cyclic vinyl ketones with a p-methoxyacetophenone moiety as a built-in triplet sensitizer (1 and 2, respectively) was compared. When irradiated, ketone 1 produces its cis-isomer, whereas ketone 2 does not yield any photoproducts. Laser flash photolysis of ketone 1 yields a transient spectrum with λmax ∼ 400 nm (τ ∼ 125 ns). This transient is assigned to the first triplet excited state (T1) of 1, which presumably decays to form a triplet biradical (1BR) that is shorter lived than the triplet ketone. In comparison, laser flash photolysis of 2 reveals two transients (τ ∼ 20 and 440 ns), which are assigned to T1 of 2 and triplet biradical 2BR, respectively. Density functional theory calculations support the characterization of the triplet excited states and the biradical intermediates formed upon irradiation of ketones 1 and 2 and allow a comparison of the physical properties of the biradical intermediates. As the biradical centers in 2BR are stabilized by conjugation, 2BR is more rigid than 1BR. Therefore, the longer lifetime of 2BR can be attributed to less-efficient intersystem crossing to the ground state.

Photolysis of 5-Azido-3-Phenylisoxazole at Cryogenic Temperature: Formation and Direct Detection of a Nitrosoalkene.

To enhance the versatility of organic azides in organic synthesis, a better understanding of their photochemistry is required. Herein, the photoreactivity of azidoisoxazole 1 was characterized in cryogenic matrices with IR and UV-Vis absorption spectroscopy. The irradiation (λ = 254 nm) of azidoisoxazole 1 in an argon matrix at 13 K and in glassy 2-methyltetrahydrofuran (mTHF) at 77 K yielded nitrosoalkene 3. Density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations were used to aid the characterization of nitrosoalkene 3 and to support the proposed mechanism for its formation. It is likely that nitrosoalkene 3 is formed from the singlet excited state of azidoisoxazole 1 via a concerted mechanism or from cleavage of an intermediate singlet nitrene that does not undergo efficient intersystem crossing to its triplet configuration.

Formation and Reactivity of Triplet Vinylnitrenes as a Function of Ring Size.

The photoreactivity of cyclic vinyl azides 1 (3-azido-2-methyl-cyclopenten-1-one) and 2 (3-azido-2-methyl-2-cyclohexen-1-one), which have five- and six-membered rings, respectively, was characterized at cryogenic temperature with electron paramagnetic resonance (EPR), IR, and UV spectroscopy. EPR spectroscopy revealed that irradiating (λ > 250 nm) vinyl azides 1 and 2 in 2-methyltetrahydrofuran at 10 K resulted in the corresponding triplet vinylnitrenes 31N (D/hc = 0.611 cm-1 and E/hc = 0.011 cm-1) and 32N (D/hc = 0.607 cm-1 and E/hc = 0.006 cm-1), which are thermally stable at cryogenic temperature. Irradiation of vinyl azides 1 (310 nm light-emitting diode at 12 K) and 2 (xenon arc lamp through a 310-350 nm filter at 8 K) in argon matrices showed that in competition with intersystem crossing to form vinylnitrenes 31N and 32N, vinyl azide 1 formed a small amount of ketenimine 3, whereas vinyl azide 2 formed significant amounts of azirine 7 and ketenimine 6. Thus, vinyl azide 1 undergoes intersystem crossing more efficiently than vinyl azide 2. Similarly, vinylnitrene 31N is much more photoreactive than vinylnitrene 32N. Quantum chemical calculations were used to support the mechanisms for forming vinylnitrenes 31N and 32N and their reactivity.

Laser flash photolysis of nanocrystalline α-azido-p-methoxy-acetophenone.

Irradiation of nanocrystals of azide 1 results in a solid-to-solid reaction that forms imine 2 in high chemical yield. In contrast, solution photolysis of azide 1 yields a mixture of products, with 7 as the major one. Laser flash photolysis (LFP) of a nanocrystalline suspension of azide 1 in water shows selective formation of benzoyl radical 4 (λmax ∼ 400 nm), which is short-lived (τ = 833 ns) as it intersystem crosses to form imine 2. In comparison, LFP of azide 1 in methanol reveals the formation of triplet alkylnitrene 10 (λmax ∼ 340 nm). The selectivity observed in the solid-state is related to stabilization of the triplet ketone with (n,π*) configuration by the crystal lattice, which results in α-cleavage being favored over triplet energy transfer to the azido chromophore. Both the solid-state and solution reaction mechanisms are further supported by density functional theory calculations. Thus, laser flash photolysis has been used to effectively elucidate the medium dependent reaction mechanisms of azide 1.

Using Molecular Architecture to Control the Reactivity of a Triplet Vinylnitrene.

Photolysis of 3-azido-1-indenone (1) with a light-emitting diode (LED, λ = 405 nm) or mercury arc lamp (Pyrex) resulted in the formation of heterodimer 3 in excellent yield, through dimerization of triplet vinylnitrene 32. At ambient temperature, vinylnitrene 32 (λmax at 340 and 480 nm) was detected directly with laser flash photolysis of vinyl azide 1. The vinylnitrene intermediate was also characterized directly with IR and ESR spectroscopy in cryogenic matrices. The ESR spectrum of vinylnitrene 32 yielded a zero-field splitting parameter |D/hc| of 0.460 cm-1 and |E/hc| of 0.015 cm-1, which reveals that vinylnitrene 32 has significant 1,3-biradical character. The proposed mechanism for the formation and reactivity of triplet vinylnitrene 32 was supported with density functional theory (DFT) calculations, which highlight that the steric demand of the five-membered ring in vinylnitrene 32 prevents intersystem crossing to the corresponding azirine (10). CASSCF and CASPT2 calculations showed that the energy gap between the singlet and triplet configurations of vinylnitrene 2 is only 10 kcal/mol. In spite of this small energy gap, vinylnitrene 32 does not decay by intersystem crossing, but rather by dimerization. Thus, triplet vinylnitrenes can be selectively formed with visible light and used to form new C-N bonds in synthetic applications.

Respiratory symptoms, sleep-disordered breathing and biomarkers in nocturnal gastroesophageal reflux.

BACKGROUND: Nocturnal gastroesophageal reflux (nGER) is associated with respiratory symptoms and sleep-disordered breathing (SDB), but the pathogenesis is unclear. We aimed to investigate the association between nGER and respiratory symptoms, exacerbations of respiratory symptoms, SDB and airway inflammation. METHODS: Participants in the European Community Respiratory Health Survey III in Iceland with nGER symptoms (n = 48) and age and gender matched controls (n = 42) were studied by questionnaires, exhaled breath condensate (EBC), particles in exhaled air (PEx) measurements, and a home polygraphic study. An exacerbation of respiratory symptoms was defined as an episode of markedly worse respiratory symptoms in the previous 12 months. RESULTS: Asthma and bronchitis symptoms were more common among nGER subjects than controls (54 % vs 29 %, p = 0.01; and 60 % vs 26 %, p < 0.01, respectively), as were exacerbations of respiratory symptoms (19 % vs 5 %, p = 0.04). Objectively measured snoring was more common among subjects with nGER than controls (snores per hour of sleep, median (IQR): 177 (79-281) vs 67 (32-182), p = 0.004). Pepsin (2.5 ng/ml (0.8-5.8) vs 0.8 ng/ml (0.8-3.6), p = 0.03), substance P (741 pg/ml (626-821) vs 623 pg/ml (562-676), p < 0.001) and 8-isoprostane (3.0 pg/ml (2.7-3.9) vs 2.6 pg/ml (2.2-2.9), p = 0.002) in EBC were higher among nGER subjects than controls. Albumin and surfactant protein A in PEx were lower among nGER subjects. These findings were independent of BMI. CONCLUSION: In a general population sample, nGER is associated with symptoms of asthma and bronchitis, as well as exacerbations of respiratory symptoms. Also, nGER is associated with increased respiratory effort during sleep. Biomarker measurements in EBC, PEx and serum indicate that micro-aspiration and neurogenic inflammation are plausible mechanisms.

Definition of nocturnal gastroesophageal reflux for studies on respiratory diseases.

OBJECTIVE: Nocturnal gastroesophageal reflux (nGER) has been associated with respiratory diseases. Our aim was to study a questionnaire method to identify nGER subjects with respiratory involvement in a general population. MATERIAL AND METHODS: A subgroup of Icelandic participants in the European Community Respiratory Health Survey III (ECRHS III) reporting symptoms of nGER (n = 48) as well as age and gender paired controls (n = 42) were studied further by a structured interview, questionnaires, laryngeal fibrescopy, and exhaled breath condensate. A subgroup underwent 24-h oesophageal pH impedance (24-h MII-pH) measurements. Symptoms of nGER were assessed with a modified version of the reflux disease questionnaire (RDQ), where symptoms were divided into daytime and nocturnal. A report of nGER both at baseline and at follow-up was defined as persistent nGER. RESULTS: Participants reporting persistent nGER had significantly more signs of laryngopharyngeal reflux according to the reflux finding score than those without nGER (Mean ± SD: 5.1 ± 2.3 vs. 3.9 ± 2.2, p = 0.02). Of the 16 persistent nGER subjects that underwent 24-h MII-pH, 11 had abnormal gastroesophageal reflux, but none of three control subjects (69% vs. 0%). Pepsin was more commonly found in exhaled breath condensate in the nGER group (67% vs. 45%, p = 0.04). CONCLUSIONS: Participants with nGER symptoms at least once a month, reported on two occasions, had a high level of positive 24-h MII-pH measurements, laryngeal inflammation and pepsin in exhaled breath condensate. This nGER definition identified a representable group for studies on nGER and respiratory diseases in a general population.

Direct detection of a triplet vinylnitrene, 1,4-naphthoquinone-2-ylnitrene, in solution and cryogenic matrices.

The photolysis of 2-azido-1,4-naphthoquinone (1) in argon matrices at 8 K results in the corresponding triplet vinylnitrene (3)2, which was detected directly by IR spectroscopy. Vinylnitrene (3)2 is stable in argon matrices but forms 2-cyanoindane-1,3-dione (3) upon further irradiation. Similarly, the irradiation of azide 1 in 2-methyltetrahydrofuran (MTHF) matrices at 5 K resulted in the ESR spectrum of vinylnitrene (3)2, which is stable up to at least 100 K. The zero-field splitting parameters for nitrene (3)2, D/hc = 0.7292 cm(-1) and E/hc = 0.0048 cm(-1), verify that it has significant 1,3-biradical character. Vinylnitrene (3)2 (λmax ∼ 460 nm, τ = 22 µs) is also observed directly in solution at ambient temperature with laser flash photolysis of 1. Density functional theory (DFT) calculations support the characterization of vinylnitrene (3)2 and the proposed mechanism for its formation. Because vinylnitrene (3)2 is relatively stable, it has potential use as a building-block for high-spin assemblies.

Infrared matrix isolation study of the thermal and photochemical reactions of ozone with trimethylgallium.

The thermal and photochemical reactions of (CH3)3Ga and O3 have been explored using a combination of matrix isolation, infrared spectroscopy, and theoretical calculations. Experimental data using twin jet deposition and theoretical calculations demonstrate the formation of multiple product species after deposition, annealing to 35 K, and UV irradiation of the matrices. The products were identified as (CH3)2GaOCH3, (CH3)2GaCH2OH, (CH3)(CH3O)Ga(OCH3), (CH3)2GaCHO, and (CH3)Ga(OCH3)(CH2OH). Product identifications were confirmed by annealing and irradiation behavior, (18)O substitution experiments, and high level theoretical calculations. Merged jet deposition led to a number of stable late reaction products, including C2H6, CH3OH, and H2CO. A white solid film was also noted on the walls of the merged (flow reactor) region of the deposition system, likely due to the formation of Ga2O3.

Synthesis of enantiopure reversed structured ether lipids of the 1-O-alkyl-sn-2,3-diacylglycerol type.

This report describes the synthesis of reversed structured 1-O-alkyl-2,3-diacyl-sn-glycerols (DAGEs) possessing a pure saturated even number fatty acid (C6:0-C16:0) at the sn-2 position along with a pure EPA or DHA located at the terminal sn-3 position of the glycerol backbone of chimyl, batyl and selachyl alcohols. These adducts were synthesized by a highly efficient two-step chemoenzymatic process involving an immobilized Candida antarctica lipase to introduce pure EPA and DHA activated as oxime esters exclusively to the sn-3 terminal position of enantiopure chimyl, batyl and selachyl alcohols in excellent yields. The saturated fatty acids were subsequently incorporated to the remaining sn-2 position of the resulting 3-monoacylglyceryl ethers (3-MAGEs) using EDAC coupling agent in the presence of DMAP in very high to excellent yields (85%-98%). No losses of enantiomeric composition were observed during these processes. The multiple utilities of the resulting focused library of reversed structured DAGEs are discussed including how such compounds may possibly be utilized within the pharmaceutical area.

Comparison of the photochemistry of 3-methyl-2-phenyl-2H-azirine and 2-methyl-3-phenyl-2H-azirine.

Photolysis of 3-methyl-2-phenyl-2H-azirine (1a) in argon-saturated acetonitrile does not yield any new products, whereas photolysis in oxygen-saturated acetonitrile yields benzaldehyde (2) by interception of vinylnitrene 5 with oxygen. Similarly, photolysis of 1a in the presence of bromoform allows the trapping of vinylnitrene 5, leading to the formation of 1-bromo-1-phenylpropan-2-one (4). Laser flash photolysis of 1a in argon-saturated acetonitrile (λ = 308 nm) results in a transient absorption with λ(max) at ~440 nm due to the formation of triplet vinylnitrene 5. Likewise, irradiation of 1a in cryogenic argon matrixes through a Pyrex filter results in the formation of ketene imine 11, presumably through vinylnitrene 5. In contrast, photolysis of 2-methyl-3-phenyl-2H-azirine (1b) in acetonitrile yields heterocycles 6 and 7. Laser flash photolysis of 1b in acetonitrile shows a transient absorption with a maximum at 320 nm due to the formation of ylide 8, which has a lifetime on the order of several milliseconds. Similarly, photolysis of 1b in cryogenic argon matrixes results in ylide 8. Density functional theory calculations were performed to support the proposed mechanism for the photoreactivity of 1a and 1b and to aid in the characterization of the intermediates formed upon irradiation.