Rate constants for the gas-phase reactions of O3 with a series of Terpenes and OH radical formation from the O3 reactions with Sesquiterpenes at 296 ± 2 K

Rate constants for the gas-phase reactions of O₃ with the sesquiterpenes α-cedrene, α-copaene, β-caryophyllene, α-humulene, and longifolene, and with the monoterpenes limonene, terpinolene, α-phellandrene, and α-terpinene, have been measured using a relative rate technique at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in units of 10^?17 cm³ molecule^?1 s^?1) are: limonene, 20.1 ± 5.1; terpinolene, 188 ± 67; α-phellandrene, 298 ± 105; α-terpinene, 2110 ± 770; α-cedrene, 2.78 ± 0.71; α-copaene, 15.8 ± 5.6; β-caryophyllene, 1160 ± 430; α-humulene, 1170 ± 450; and longifolene, <0.07, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference organics. Hydroxyl radical formation yields were also determined for the O₃ reactions with the sesquiterpenes, of 0.67 for α-cedrene, 0.35 for α-copaene, 0.06 for β-caryophyllene, and 0.22 for α-humulene, all with estimated overall uncertainties of a factor of ca. 1.5. The tropospheric lifetimes of the sesquiterpenes due to reaction with O₃ are calculated. © 1994 John Wiley & Sons, Inc.     

A New Desulfurization Method: Application to the Synthesis of 11-Deoxyprostaglandin E2

Alkylation at carbon attached to sulfur of α-phenylthio or α-alkylthioketones, or reductive-alkylation of α-phenylthioketones provided a new regiospecific alkylation method of ketones.^1,2 In these procedures, desulfurization was effected either by reduction with lithium in liquid ammonia^1,2 or by use of Raney Ni-W-2.² Recently, buffered sodium amalgam method has been reported to be effective for desulfurization of β-ketosulfides as well as for desulfonylation of aryl alkyl sulfones.³ We wish to report here that desulfurization of α-phenylthioketones was achieved by treatment of the ketones with zinc and chlorotrimethylsilane. This observation would lead to a facile synthesis of α-substituted ketones.     

Preparation of a Trans α,β-Epoxysilane by Selective Pyrolysis

α,β-Epoxysilanes have been shown to be useful synthetic intermediates² for the preparation of carbonyl compounds³ and stereoisomerically-pure olefins⁴ and heteroatom-substituted olefins⁵ (vinyl bromides,⁵ enol acetates,⁵ enol ethers,⁵ enamides,⁵ and vinyl mesylates⁶). In many of their reactions, α,β-epoxysilanes serve as stereospecific vinyl cation equivalents;⁴–6 therefore methods to prepare stereoisomerically-pure α,β-epoxysilanes are of considerable importance. Although other methods for preparing α,β-epoxysilanes have recently been developed,⁷ the only general method for preparing stereoisomerically-pure α,β-epoxysilanes is epoxidation of the corresponding vinylsilanes.     

CIDNP assisted assignment of carbon-13 NMR lines in α-tetralone and α-indanone

The reversible abstraction of hydrogen from benzene-1,3,5-triol by photoexcited α-tetralone or α-indanone in solutions of methanol leads to CIDNP in the ¹³C NMR spectra of these compounds. The information gained from the phase of the polarization in the CIDNP spectra is used to resolve the ambiguities in the assignment of the ¹³C NMR lines for α-indanone and α-tetralone, arising from conflicting literature data. Chemical shifts for both compounds in methanol are reported. 2′-Methylacetophenone does not exhibit CIDNP in the ¹³C spectrum under similar conditions.     

Rubber elasticity in the range of small uniaxial tensions and compressions. Results for poly(dimethylsiloxane)

Results of uniaxial tension and compression experiments are reported on crosslinked polydimethylsiloxane (PDMS) networks in the unswollen state over the range 0.5 < α^?1 < 1.2 where α is the extension ratio. Curves representing the reduced force [f] = f(V⁰/V)^1/3(α – α^?2)^?1 plotted against α^?1 can be approximated by straight lines for 0.5 < α^?1 < 0.9, in agreement with the phenomenological Mooney equation. As α^?1 approaches 1, however, they tend to level off and continue into the α^?1 > 1 region with decreasing slope. These results are in agreement with the predictions of recent elasticity theories that incorporate the effect of junction-chain entanglements in the elastic free energy.     

Acrolein and Copper as Competitive Effectors of α-Synuclein

Mounting evidence supports the role of amyloidogenesis, oxidative stress, and metal dyshomeostasis in the development of neurodegenerative disorders. Parkinson's Disease is characterized by α-synuclein (αSyn) accumulation and aggregation in brain regions, also promoted by Cu²⁺. αSyn is modified by reactive carbonyl species, including acrolein (ACR). Notwithstanding these findings, the interplay between ACR, copper, and αSyn has never been investigated. Therefore, we explored more thoroughly the effects of ACR on αSyn using an approach based on LC-MS/MS analysis. We also evaluated the influence of Cu²⁺ on the protein carbonylation and how the ACR modification impacts the Cu²⁺ binding and the production of Reactive Oxygen Species (ROS). Finally, we investigated the effects of ACR and Cu²⁺ ions on the αSyn aggregation by dynamic light scattering and fluorescence assays. Cu²⁺ regioselectively inhibits the modification of His50 by ACR, the carbonylation lowers the affinity of His50 for Cu²⁺ and ACR inhibits αSyn aggregation both in the presence and in the absence of Cu²⁺.     

Calorimetric measurement of the heat of desorption of water vapor from amorphous and crystalline lactose

The heat required to release and vaporize bound H₂O from crystalline α-lactose monohydrate and from lactose glass, as determined by differential scanning calorimetry is 12.3±0.7 and 10.8±0.5 kcal·mole⁻¹ of H₂O, respectively. Water vapor sorption by anhydrous α-lactose leads to the formation of the α-monohydrate. The isotherm, obtained gravimetrically for this process is Langmuir type. β-Lactose is completely non-hygroscopic below 97% relative humidity. Thereafter, it sorbs H₂O rapidly to form a concentrated solution wherein the lactose is capable of mutarotation. Densites of lactose forms determined pycnometrically by helium displacement are: 1.535 g/cm³ for α-lactose·H₂O; 1.547 g/cm³ for anhydrous α-lactose; and 1.576 g/cm³ for β-lactose.     

Sodium Hypochlorite Reactions. III. The Catalytic Nakagawa and Related Systems

Mainly through the extensive investigations of Nakagawa and coworkers, nickel peroxide has emerged as a powerful oxidant for organic compounds. For example, it has been used for the oxidation of alcohols to aldehydes or carboxylic acids,^2,3 allylic hydroxyl (selectively) to the carbonyl group,⁴ α-ketols to α-diketones,⁵ α-glycols, α-ketols, α-hydroxyl and α-keto acids to cleavage products,⁶ aldehydes to amides or nitriles in the presence of ammonia,⁷ phenols to quinones,^8,9 certain Schiff bases to benzoxazoles,¹⁰ amines to azo compounds or nitriles,^11,12 diarylamines to hydrazines,¹³ carbazoles to dimers and trimers,¹⁴ hydrazones to diazo compounds,^15,16 1-aminobenzotriazole to benzyne,¹⁷ N-substituted hydroxylamines to azoxy compounds,¹⁸ phenylacetonitrile to dimeric products,¹⁹ a thiouracil to a uracil derivative,²⁰ thiols to disulfides and sulfides to sulfones,²¹ N-substituted phenothiazines to sulfoxides and sulfones,²¹ haloforms to hexahaloethanes.²³     

On some relations of a one-electron reaction with two partial charge transfer steps

The experimentally established relations for the transfer coefficients, α_T<α_e, α_T^k+α_T^a<1, α_e^a+α_e^k=1, were explained on the basis of a reaction with partial charge transfer steps. (α_T is determined from the Tafel slope, α_e is determined from the concentration dependence of the polarization resistance.) For a one-electron reaction with two charge transfer steps these relations were theoretically obtained. The quantitative comparison between experimentally established α_e and the α_e calculated on the basis of the theoretically derived relations shows a good agreement.     

Use of Auxiliary Functions for Construction of Series Expansion Relations of Noninteger Slater Functions in Standard Convention

Using complete orthonormal sets of ψ ^(α*) ‐self‐frictional exponential type orbitals (ψ ^(α*) ‐SFETOs) and Q^q‐noninteger auxiliary functions (Q^q‐NIAFs) introduced by the author, the combined formulas for the one‐ and two‐center one‐range addition theorems of χ‐noninteger Slater type orbitals (χ‐NISTOs) with arbitrary values of distances between centers R_ab (for R_ab = 0 and R_ab ≠ 0), and of integer (for α* = α, –∞ < α ≤ 2) and noninteger (for α* ≠ α, –∞ < α* < 3) self‐frictional (SF) quantum numbers are suggested. The presented relations for the one‐range addition theorems can be useful tools especially in the electronic structure studies of atoms, molecules and solids when χ‐NISTOs are employed as basis functions.     

Spectrometric study of a-methylene aromatic araminenone and aminoketone

Thirteen α-methylene aromatic araminenone and four α-methylene aromatic aminoketones were prepared by modified Mannich reaction. On the basis of isotopic labeling, a plausible way of cleavage was proposed for the formation of the M^＋- 17 fragment peak in the MS of the α-methylene aromatic araminenone and aminoketones. The characteristic chemical shift of the olefinic protons in ^1H NMR is also discussed.     

Production of vibrationally excited OH in chemiluminescent reactions of ozone with monoterpenes

Emission from vibrationally excited OH molecules (Meinel bands) has been observed in chemiluminescent gas-phase reactions of ozone with myrcene, α-phellandrene, α-pinene, limonene and linallol. In addition emission from HCHO(¹A₂) and methylglyoxal(³A_u) has also been identified in reactions with myrcene, α-pinene and α-phellandrene.     

Asymmetric transfer hydrogenation of α,β-unsaturated, α-tosyloxy and α-substituted ketones

Asymmetric transfer hydrogenation of cyclic and acyclic α,β-unsaturated ketones catalysed by η⁶-p-cymene/ruthenium(II) and η⁵-pentamethylcyclopentadienyl/rhodium(III) complexes have been investigated. Cyclic α,β-unsaturated ketones appeared to be more suitable substrates for the synthesis of enantiomerically pure allylic alcohols than do acyclic α,β-unsaturated ketones. A proposed mechanism for the formation of 4-phenyl-[1,3]-dioxolan-2-one from α-tosyloxy- and halo-substituted acetophenones is discussed. The results of further investigations into the reduction of a range of α-tosyloxyacetophenones and the dynamic kinetic resolution of α-substituted ketones is presented.     

Light weight,mechanically strong and biocompatible α-chitin aerogels from different aqueous alkali hydroxide/urea solutions

Light weight and mechanically strong α-chitin aerogels were fabricated using the sol-gel/self-assembly method from α-chitin in different aqueous alkali hydroxide(KOH, Na OH and Li OH)/urea solutions. All of the α-chitin solutions exhibited temperature-induced rapid gelation behavior. 13 C nuclear magnetic resonance(NMR) spectra revealed that the aqueous alkali hydroxide/urea solutions are non-derivatizing solvents for α-chitin. Fourier transform infrared(FT-IR), X-ray diffraction(XRD) and cross-polarization magic angle spinning(CP/MAS) 13 C NMR confirmed that α-chitin has a stable aggregate structure after undergoing dissolution and regeneration. Subsequently, nanostructured α-chitin aerogels were fabricated by regeneration from the chitin solutions in ethanol and then freeze-drying from t-Bu OH. These α-chitin aerogels exhibited high porosity(87% to 94%), low density(0.09 to 0.19 g/cm~3), high specific surface area(419 to 535 m~2/g) and large pore volume(2.7 to 3.8 cm~3/g). Moreover, the α-chitin aerogels exhibited good mechanical properties under compression and tension models. In vitro studies showed that m BMSCs cultured on chitin hydrogels have good biocompatibility. These nanostructured α-chitin aerogels may be useful for various applications, such as catalyst supports, carbon aerogel precursors and biomedical materials.     

Communication: Stereoselective Addition of Phenylsulfonylmethides and Methylmagnesium Halides to Pentodialdo-1,4-Furanoses

Additions of organometallics to chiral α-alkoxy and α,β-dialkoxy carbonyl compounds have recently attracted a great deal of attention since this methodology has a great potential for the synthesis of a variety of polyoxy natural products such as macrolide antibiotics and polyether ionophores. Interpretation of the stereochemical outcome of the addition of organometallics to α,β-dialkoxy carbonyls, however, is rather complex and inconclusive¹ compared to that of α-alkoxy carbonyls.².     

Regioselective α(2→3)-Sialylation of LeX and Lea by Sialidase-Catalyzed Transglycosylation

Considerable effort has been devoted to the development of new methods for α-selective sialylation due to the growing importance of the synthetic sialoglycoconjugates in glycobiology³. The synthesis of α-sialoside has been establised by chemical routes,⁴ which often involve many steps and are complicated. The promising chemoenzymatic procedure through the use of sialyltransferases has already become a preparative technique.⁵ However, laborious isolation and the pronounced acceptor specificity of the transferases limit their synthetic potential. Recently, a novel procedure for α-sialylation has been reported, which uses sialosides of synthetic substrate as donors and is catalyzed by sialidase in place of sialyltransferase. Thiem et a1.⁶ have reported the enzymatic synthesis of α(2→6)-linked sialyl galactose, glucose, lactose and lactosamine in preference to the corresponding α(2→3)-linked derivatives employing sialidase from vibrio cholerae, while Ajisaka et al.⁷ have synthesized α(2→3)-linked sialyl lactose and lactosamine with sialidase from new castle disease virus.

     

Sulfurisation of Amino Tetraphosphorus Trichalcogenide Compounds

Amino tetraphosphorus trisulfides α-P₄S₃(NR¹R²)₂ reacted with S₈ under photolysis using visible light, in moderate or low conversion, to give α-P₄S₃(S)(NR¹R²)₂, in which the added sulfur atom was exocyclic. For NR¹R² = NPr₂ⁱ, three isomers were found: a pair of diastereomers corresponding to attachment of the sulfur atom to a nitrogen-carrying phosphorus atom either with retention or with inversion of its configuration, and an isomer containing a sulfurised bridgehead phosphorus atom. For NR¹R² = NMePh, only the two diastereomers were seen. Photolysis of a mixture of α-P₄Se₃(NMePh)₂ and α-P₄Se₃(NMePh)I with S₈ gave as major products α-P₄SSe₂(NMePh)₂ and α-P₄SSe₂(NMePh)I, in which sulfur had replaced the bridging selenium atom in the starting compounds. This provides a synthesis of compounds α-P₄SSe₂XY in which sulfur occupies a specific skeletal position, rather than being randomly distributed. All products were characterised by ³¹P NMR in unseparated solutions. Ab initio MO calculations of geometry and of GIAO NMR chemical shifts at the 3-21G* level for three isomers of the unknown model compound α-P₄S₃(S)(NH₂)₂, and two isomers of α-P₄S₃(NH₂)₂, allowed identification of the observed isomer of α-P₄S₃(S)(NPr₂ⁱ)₂ with a sulfurised bridgehead, but relative assignment of the two diastereomers to their NMR parameters remains a hypothesis.     

Structural Investigation of Hybrid Peptide Foldamers Composed of α-Dipeptide Equivalent β-Oxy-δ5-amino Acids

Due to their equivalent lengths, δ-amino acids can serve as surrogates of α-dipeptides. However, δ-amino acids with proteinogenic side chains have not been well studied because of synthetic difficulties and because of their insolubility in organic solvents. Recently we reported the spontaneous supramolecular gelation of δ-peptides composed of β(O)-δ⁵-amino acids. Here, we report the incorporation of β(O)-δ⁵-amino acids as guests into the host α-helix, α,γ-hybrid peptide 12-helix and their single-crystal conformations. In addition, we studied the solution conformations of hybrid peptides composed of 1:1 alternating α and β(O)-δ⁵-amino acids. In contrast to the control α-helix structures, the crystal structure of peptides with β(O)-δ⁵-amino acids exhibit α-helical conformations consisting of both 13- and 10-membered H-bonds. The α,δ-hybrid peptide adopted mixed 13/11-helix conformation in solution with alternating H-bond directionality. Crystal-structure analysis revealed that the α,γ⁴-hybrid peptide accommodated the guest β(O)-δ⁵-amino acid without significant deviation to the overall helix folding. The results reported here emphasize that β(O)-δ⁵-amino acids with proteinogenic side chains can be accommodated into regular α-helix or 12-helix as guests without much deviation of the overall helix folding of the peptides.     

Microwave measurement of the α3 vibrationrotation constant of ClCN and BrCN vibrational energy transfer from active nitrogen

Vibrational energy transfer between active nitrogen N*₂, and the (0,0⁰, 1) state of ClCN and BrCN has allowed the determination of the α₃ vibrationrotation constant by microwave spectroscopy, with the values: α₃(³⁵ClCN) = 32.25 MHz, α₃(³⁷ClCN) = 31.68 MHz, α₃(⁷⁹BrCN) = 20.37 MHz and α₃(⁸¹BrCN) = 20.24 MHz. For ³⁵ClCN the α₁ vibrationrotation constant has also been determined with a standard technique, giving α₁ = 24.65 MHz. A new evaluation has been made of the equilibrium structure of ClCN as follows: r_e(CN) = 1.1606 A, r_e(CCL) = 1.6290 A.     

Capillary electrophoretic study of thiolated α-cyclodextrin-capped gold nanoparticles with tetraalkylammonium ions

Capillary zone electrophoresis (CZE) has been employed to characterize nanometer-sized thiolated α-cyclodextrin-capped gold nanoparticles (α-CD-S-AuNPs). The addition of tetrabutylammonium (Bu₄N⁺) ions to the run buffer greatly narrows the migration peak of α-CD-S-AuNP. The optimal run buffer was determined to be 10 mM Bu₄N⁺ in 30 mM phosphate buffer at pH 12 and an applied voltage of 15 kV. The effect of various tetraalkylammonium ions on the peak width and electrophoretic mobility (μ_e) of α-CD-S-AuNP was studied in detail. Bu₄N⁺ ions assist in inter-linking the α-CD-S-AuNPs and narrowing the migration peak in CZE. This observation can be explained by the fact that each Bu₄N⁺ ion can simultaneously interact with several hydrophobic cavities of the surface-attached α-CDs on AuNPs. The TEM images show that α-CD-S-AuNPs with Bu₄N⁺ are linked together but in the absence of Bu₄N⁺, they are more dispersed. The migration mechanism in CZE is based on the formation of inclusion complexes between Bu₄N⁺ and α-CD-S-AuNPs which induces changes in the charge-to-size ratio of α-CD-S-AuNPs and μ_e. An inverse linear relationship (r² > 0.998) exists between the μ_e and size of α-CD-S-AuNPs in the core range 1.4–4.1 nm. The CZE analyses are rapid with migration time less than 4 min. A few nanoliters of each of the α-CD-S-AuNP samples were injected hydrodynamically at 0.5 psi for 5 s. Our work confirms that CZE is an efficient tool for characterizing the sizes of α-CD-S-AuNPs using Bu₄N⁺ ions.