Photochemical Strain-Release-Driven Cyclobutylation of C(sp3)-Centered Radicals

A new photoredox-catalyzed decarboxylative radical addition approach to functionalized cyclobutanes is described. The reaction involves an unprecedented formal Giese-type addition of C(sp³)-centered radicals to highly strained bicyclo[1.1.0]butanes. The mild photoredox conditions, which make use of a readily available and bench stable phenyl sulfonyl bicyclo[1.1.0]butane, proved to be amenable to a diverse range of α-amino and α-oxy carboxylic acids, providing a concise route to 1,3-disubstituted cyclobutanes. Furthermore, kinetic studies and DFT calculations unveiled mechanistic details on bicyclo[1.1.0]butane reactivity relative to the corresponding olefin system.     

Structure, electronic properties and catalytic behaviour of an activity-enhancing CYP102A1 (P450(BM3)) variant

The substrate-free crystal structure of a five-mutation directed evolution variant of CYP102A1 (P450(BM3)) with generic activity-enhancing properties ("KT2") has been determined to 1.9-? resolution. There is a close resemblance to substrate-bound structures of the wild-type enzyme (WT). The disruption of two salt bridges that link the G- and I-helices in WT causes conformational changes that break several hydrogen bonds and reduce the angle of the kink in the I-helix where dioxygen activation is thought to take place. The side-chain of a key active site residue, Phe87, is rotated in one molecule of the asymmetric unit, and the side-chains of Phe158 and Phe261 cascade into the orientations found in fatty-acid-bound forms of the enzyme. The iron is out of the porphyrin plane, towards the proximal cysteine. Unusually, the axial water ligand to the haem iron is not hydrogen-bonded to Ala264. The first electron transfer from the reductase domain to the haem domain of substrate-free KT2 is almost as fast as in palmitate-bound WT even though the reduction potential of the haem domain is only slightly more oxidising than that of substrate-free WT. However, NADPH is turned over slowly in the absence of substrate, so the catalytic cycle is gated by a step subsequent to the first electron transfer-a contrast to WT. Propylbenzene binding slightly raises the first electron transfer rate in WT but not in KT2. It is proposed that the generic rate accelerating properties of KT2 arise from the substrate-free form being in a catalytically ready conformation, such that substrate-induced changes to the structure play a less significant role in promoting the first electron transfer than in WT.     

Crystal growth, structural, optical, dielectric and thermal studies of an amino acid based organic NLO material: L-phenylalanine L-phenylalaninium malonate

The mineral crandallite CaAl₃(PO₄)₂(OH)₅·(H₂O) has been identified in deposits found in the Jenolan Caves, New South Wales, Australia by using a combination of X-ray diffraction and Raman spectroscopic techniques. A comparison is made between the vibrational spectra of crandallite found in the Jenolan Caves and a standard crandallite. Raman and infrared bands are assigned to PO₄³⁻ and HPO₄²⁻ stretching and bending modes. The predominant features are the internal vibrations of the PO₄³⁻ and HPO₄²⁻ groups. A mechanism for the formation of crandallite is presented and the conditions for the formation are elucidated.     

Crystal growth, structural, optical, spectral and thermal studies of tris(L-phenylalanine)L-phenylalaninium nitrate: a new organic nonlinear optical material

Tris(L-phenylalanine)L-phenylalaninium nitrate, C(9)H(12)NO(2)(+)·NO(3)(-)·3C(9)H(11)NO(2) (TPLPN), a new organic nonlinear optical material was grown from aqueous solution by slow evaporation solution growth at room temperature. The grown crystals were subjected to powder X-ray diffraction and single crystal X-ray diffraction studies to confirm the crystalline nature and crystal structure. The modes of vibration of different molecular groups present in TPLPN have been identified by FTIR spectral analysis. The presence of hydrogen and carbon in the grown crystal were confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. The optical transmission spectral study establishes good transmitting ability of the crystal in the entire visible region. The thermogravimetric (TG) and differential thermal analyses (DTA) were carried out to understand the thermal stability of the sample. The nonlinear optical property of the compound observed using Kurtz powder second harmonic generation test assets the suitability of the grown material for the frequency conversion of laser radiation of Nd:YAG.     

Growth, structural, vibrational, optical, laser and dielectric aspects of L-alanine alaninium nitrate single crystal

Bulk single crystals of l-alanine alaninium nitrate [abbreviated as LAAN], an intriguing material for frequency conversion has been grown from its aqueous solution by both slow solvent evaporation and by slow cooling techniques. The optimized pH value to grow good quality LAAN single crystal was found to be 2.5. The grown crystals were subjected to single crystal X-ray diffraction studies to determine the unit cell dimensions and morphology. Vibrational frequencies of the grown crystals by Fourier transform infrared spectroscopic technique were investigated. Also, the presence of hydrogen and carbon atoms in the grown sample was confirmed using proton and carbon NMR analyses. The dielectric constant and dielectric loss measurements of the as grown crystal at different temperatures and frequencies of the applied field are measured and reported. LAAN has good optical transmission in the entire visible region with cutoff wavelength within the UV region confirms its suitability for device fabrications. The existence of second harmonic generation signals was observed using Nd:YAG laser with fundamental wavelength of 1064 nm. Its Laser Damage Threshold (LDT) was measured and also tested by using a Q-switched Nd:YAG laser and the value of LDT of LAAN is 17.76GW/cm2 respectively, is found to be better than certain organic and semiorganic materials.     

Phthalocyanine analogues: unexpectedly facile access to non-peripherally substituted octaalkyl tetrabenzotriazaporphyrins, tetrabenzodiazaporphyrins, tetrabenzomonoazaporphyrins and tetrabenzoporphyrins

Controlled syntheses of phthalocyanine/benzoporphyrin hybrid structures have been achieved. We report a simple means for obtaining non-peripherally octaalkyl-substituted derivatives of tetrabenzotriazaporphyrin (TBTAP), tetrabenzodiazaporphyrin (TBDAP), tetrabenzomonoazaporphyrin (TBMAP) and tetrabenzoporphyrin (TBP) macrocycles by treating 3,6-dialkyl phthalonitriles with differing amounts of the Grignard reagent MeMgBr. This range of macrocyclic products is not obtained from corresponding reactions of a Grignard reagent with 4-substituted phthalonitriles, reported previously, or reaction of MeMgBr with a 4,5-dialkyl phthalonitrile. Attempts to form a meso-substituted TBTAP from 3,6-dialkyl phthalonitriles by reaction with benzyl and long-chain alkyl Grignard reagents unexpectedly gave only the parent macrocycle unsubstituted at the meso position. The synthetic protocols are by far the most straightforward and convenient means to access these interesting, but scarcely studied, classes of material. The new series of substituted macrocyclic compounds, obtained as the metal-free and magnesium- and copper(II)-metallated derivatives, show trends in the UV/Vis spectra consistent with those predicted elsewhere by Kobayashi. Characterisation of the new families allows further trends to be identified as meso-nitrogen atoms are sequentially replaced by methine bridges, for example, the compounds provide novel examples of macrocyclic structures that show columnar mesophase behaviour. Single-crystal X-ray structure determinations have been obtained for three magnesium-metallated derivatives bearing eight hexyl substituents and constitute the first set of structural data obtained for such a series.     

Oriented confined water induced by cationic lipids

We report on attenuated total reflection Fourier-transform infrared (ATR FTIR) spectroscopic measurements on oriented lipid multilayers of N,N-dimethyl-N,N-dioctadecyl-ammonium halides (DODAX, X = F, Cl, Br, I). The main goal of this study is the investigation of the structure and spectroscopic properties of water absorbed to these model membranes. Intensities of the water stretch absorptions were used to determine the amount of bound water. At high water activity, DODAF membranes bind ~11 water molecules/lipid while DODAC and DODAB adsorb 1-2 water/lipid and DODAI was hydrophobic. By adjustment of DODAF hydration to ~2 water molecules, stretching absorptions from water of the first hydration shell were accessible for the fluoride, chloride, and bromide analogs. The polarized measurements demonstrate highly confined and oriented water with infrared (IR) order parameters ranging from 0.2 to -0.4. Resolved IR water band components are attributed to different hydrogen-bonded populations. Complementary molecular dynamics simulations of DODAB strongly support the existence of differently hydrogen-bonded and oriented water within DODAB multilayers. A combination of both techniques was used for an assignment of water stretch band components to structures. The described cationic lipid systems are a prototype for a bottom-up approach to understand the IR spectroscopy of structured water at biological interfaces since they permit a defined increase of hydrophilic water-anionic interactions leading to extended water networks at membranes.     

A study of the atmospherically important reactions of dimethylsulfide (DMS) with I2 and ICl using infrared matrix isolation spectroscopy and electronic structure calculations

The reactions of dimethylsulfide (DMS) with molecular iodine (I(2)) and iodine monochloride (ICl) have been studied by infrared matrix isolation spectroscopy by co-condensation of the reagents in an inert gas matrix. Molecular adducts of DMS + I(2) and DMS + ICl have also been prepared using standard synthetic methods. The vapour above each of these adducts trapped in an inert gas matrix gave the same infrared spectrum as that recorded for the corresponding co-condensation reaction. In each case, the infrared spectrum has been interpreted in terms of a van der Waals adduct, DMS?:?I(2) and DMS?:?ICl, with the aid of infrared spectra computed for their minimum energy structures at the MP2 level. Computed relative energies of minima and transition states on the potential energy surfaces of these reactions were used to understand why they do not proceed further than the reactant complexes DMS?:?I(2) and DMS?:?ICl. The main findings of this research are compared with results obtained earlier for the DMS + Cl(2) and DMS + Br(2) reactions, and the atmospheric implications of the conclusions are also considered.     

Enhancing the photocatalytic efficiency of TiO(2) nanopowders for H(2) production by using non-noble transition metal co-catalysts

Co and Ni-nanoclusters are attractive alternatives to Pt catalysts for hydrogen generation. These earth abundant elements when loaded onto the TiO(2) nanopowders surface act as efficient co-catalysts. Co, Ni-decorated TiO(2) photocatalysts display only three (3) times lower catalytic activities for H(2) evolution under UV illumination compared with Pt-decorated TiO(2) photocatalysts.     

Proposed mechanisms for the fragmentation of doubly allylic alkenamides (tingle compounds) by low energy collisional activation in a triple quadrupole mass spectrometer

Tingle compounds are a class of alkenamides with organoleptic properties that include a numbing or a pins and needles effect that is generally perceived on the lips and in the mouth when consumed. They occur in nature in a number of botanical species. Spilanthol and Pellitorine are important examples of tingle compounds. A number of homologs and analogs were synthesized to study the effect of chain length, double bond location, and amide moiety on the tingle effect. This also provided the opportunity to study the behavior of these compounds in the collision cell of a triple quadrupole mass spectrometer. The doubly allylic 2E,6Z-alkenamides, which made up the largest class studied, fragmented in a characteristic way to produce a distonic radical cation and a cyclopropene cation. Mechanisms for the formation of these ions are proposed. The mechanisms are supported by energy-resolved mass spectrometric data, the analysis of deuterated analogs and homologs that are not doubly allylic, and exact mass measurements. Exceptions to the proposed mechanisms are also presented. These data represent the first attempt to apply mechanistic principles to the product ions observed in the MS/MS spectra of these compounds. The authors believe the results of this study will facilitate the identification of these and similar compounds and contribute to the fundamental understanding of the behavior of alkenamides in the collision cell of a triple quadrupole mass spectrometer.