Protonation, deprotonation, and protonation: conjugated photochemical reactions of ferrocenylazophenol

4-Ferrocenylazophenol (FAP) and 8-(4-ferrocenylazophenoxy)octanyl-1-bromide (FAOB) have been synthesized and their protonation and photochemical behavior have been investigated. FAP showed reversible protonation and deprotonation behavior in the presence of trifluoroacetic acid and potassium tert-butylate, respectively. FAP and FAOB exhibit high photoreactivity, which was induced through excitation of not only the pi-pi* band by UV light but also the d-pi* band by green light. The photoreaction of FAP and FAOB in ethanol or acetonitrile with a trace amount of water afforded phenylhydrazonocyclopentadiene (PHP) derivatives, indicating that hydrolysis of the photoexcited species occurs.     

Enthalpy of vaporization measurements by calorimetric techniques

Journal of Thermal Analysis and Calorimetry - Enthalpies of vaporization, $$ \Delta _{\text{vap}} H^{\circ }_{298} $$ , were determined for perfluorooctyl-1-bromide (PFOB) at the temperature...     

Die Schwingungsspektren von Mesitylverbindungen—I. Mesitylhalogenide

The infrared and Raman vibrational frequencies of mesitylfluoride, -chloride, -bromide and -iodide are reported and completely assigned to the normal vibrations. The results of a partially successfull normal coordinate analysis are also presented.     

Electrophile-driven copper-catalyzed one-pot synthesis of 3-halogen quinoline derivatives

A convenient and regioselective one-pot synthesis of 3-chloride or 3-bromide quinoline derivatives was achieved through a Grignard addition reaction by alkynyl Grignard regent to o-trifluoroacetyl aniline and a Cu(II)-catalyzed cyclization–halogenation tandem reaction with aqueous HCl or HBr as electrophilic reagent.     

Rapid enrichment of phosphopeptides by BaTiO3 nanoparticles after microwave-assisted tryptic digest of phosphoproteins, and their identification by MALDI-MS

We show that BaTiO₃ nanoparticles (NPs) can be used as a novel substrate for the rapid enrichment of phosphopeptides from microwave tryptic digests of α-casein and non-fat milk prior to their identification by MALDI-MS. Protein digestion is achieved by microwave tryptic digest for 50?s, and the resulting phosphopeptides can be effectively adsorbed on the surfaces of the NPs. The phosphopeptides were selectively detected via MALDI-MS. Digestion, enrichment and detection are accomplished within ～60?min. The method was applied to the indentification of 24 phosphopeptides from α-casein and of 21 phosphopeptides (of the α-casein type) from nonfat milk.

The nature of pb(II)-bromide complexes in propylene carbonate

The greatly increased solubility of PbBr₂ in propylene carbonate (PC) caused by addition of LiBr indicates that PB(II) interacts strongly with bromide ion in propylene carbonate to form stable Pb(II)-bromide complexes. Solubility and spectrophotometric data for LiBr solutions saturated with PbBr₂ indicate the presence of two Pb(II)-bromide complexes whose bromide:lead ratios are respectively 3.00 and 2.75. The former, which predominates in dilute (<0.03 m) solutions of LiBr saturated with PbBr₂, was shown by potentiometry and solubility data to be PbBr₃^?, a species also formed when PbBr₂ dissolves in PC in the absence of LiBr. The latter, which is predominant in more concentrated LiBr solutions saturated wih PbBr₂, was shown by spectrophotometry and solubility data to be the polynuclear complex Pb₄Br₁₁^?3. Both complexes are sufficiently stable that the free bromide ion concentration in these solutions corresponds to only a small fraction of the total bromide concentration. In LiBr solutions unsaturated with respect to PbBr₂, the major Pb(II) species are PbBr₃^? and PbBr₄^?2.     

3,5-二(4-甲基苯基)吡啶的Suzuki偶联合成及其光学性能

以3,5-二溴吡啶和对甲基苯硼酸为原料,醋酸钯为催化剂,经Suzuki偶联反应合成了3,5-二(4-甲基苯基)吡啶(1),收率73%,其结构和性能经¹H NMR, ¹³C NMR, IR, 元素分析, UV-Vis, FL和X-射线单晶衍射表征。结果表明：1（CCDC: 1509844）属正交晶系,空间群P2₁2₁2₁,晶胞参数a=6.447 8(12) , b=7.240 2(14) , c=29.890 0(6) ,β=90°。1为非平面刚性共轭分子,荧光量子产率13.9%。     

Syntheses of (−)-gabosine A, (+)-4-epi-gabosine A, (−)-gabosine E, and (+)-4-epi-gabosine E

(+)-4-epi-Gabosine A 1 and (−)-gabosine A 2 have been synthesized starting from methyl α,d-glucopyranoside and methyl α,d-mannopyranoside, respectively, by utilizing Pd(0) catalyzed Stille coupling as the key step. On the other hand, syntheses of (+)-4-epi-gabosine E 3 and (−)-gabosine E 4 have been accomplished from methyl α,d-glucopyranoside and from methyl α,d-mannopyranoside, respectively, by utilizing DMAP catalyzed Morita-Baylis-Hillman reaction as the key step. Presence of acetyl group at C-6 position of sugar derived cyclic enone prevented the aromatization of MBH adduct. A plausible mechanism is also described.     

Moderately concentrated solutions of polystyrene. I. Viscosity as a function of concentration,temperature, and molecular weight

Data on the viscosity η of moderately concentrated solutions of polystyrene are reported. Several solvents were investigated, including cyclopentane solutions over a temperature span between θ_U = 19.5°C and θ_L = 154.5°C. The data were analyzed in terms of a relation giving η as a function of αφM, where α_φ is the expansion factor for the chain dimensions in a solution with volume fraction φ of polymer with molecular weight M. It is shown that values of α_φ so determined decrease as ? lnα_φ/? lnφ = (1 ? 2μ)/6μ for φ greater than φ^* = 0.2M/s³ for moderately concentrated solutions, where s is the root-mean-square radius of gyration and μ = ? ln[η]/? lnM with [η] the intrinsic viscosity.     

Synthesis and biological evaluation of quinocarcin derivatives

Cyanation of quinocarcin readily opened the oxazolidine ring to provide DX-52-1 (2), which was a key compound in the synthesis of quinocarcin derivatives. Various electrophilic reactions toward aromatic ring of DX-52-1 were examined, and 10-substituted (e.g., halogen, nitro, formyl, cyano, hydroxy, etc.) analogs were prepared. Dehydrocyanation of the derivatives could be achieved to reproduce the oxazolidine ring upon treatment with HCl or AgNO3. 10-Chloride 10 and 10-bromide 11 were the most promising among the derivatives prepared. Antitumor activity of 10 was extended to B-16 melanoma.     

Generation and Reactions of ε-Carbonyl Cations via Group 13 Catalysis

The generation of ε-carbonyl cations and their reactions with nucleophiles is accomplished readily without transition metal cation stabilization, using the ε-bromide dienoate or dienone starting materials and GaCl₃ or InCl₃ catalysis. Arene nucleophiles are somewhat more straightforward than allyltrimethylsilane, but allyltrimethylsilane and propiophenone trimethysilyl enol ether each react successfully with InCl₃ catalysis. The viability of these cations is supported by DFT calculations.     

Internal field of polymer crystals: Polarizability tensor of the methylene group from the birefringence of paraffin crystal

Using the concept of a point dipole lattice, it is shown that the internal field of induced dipoles can be calculated for crystals comprised of simple chain molecules. The only structure which must be taken into account accurately is that of the chain molecule itself. From the calculations, reliable values of the polarizability tensor of the CH₂ unit are deduced from the birefringence of the paraffin crystal. In addition, it is shown that birefringence measurements provide a method for demonstrating the consistency of polarizability data so that no detailed structural information is needed. For the CH₂ unit, it is found by both methods that α^∥ ? α^? = ? 0.63 with respect to the chain direction [the units of polarizability α are 10^?24 cm³ (cgs)]. The most probable anisotropies for the bond polarizabilities are α ? α = 0.30, α ? α = ? 0.62.     

Binding of Dopamine to Alpha-Synuclein is Mediated by Specific Conformational States

Parkinson’s disease is the second most common neurodegenerative disorder, in which both alpha-synuclein (α-syn) and dopamine (DA) have a critical role. α-Syn is known to be natively unstructured in equilibrium with subpopulations of more compact structures. It is these compact structures that are thought to be linked to amyloid formation. In the presence of DA, α-syn yields a diverse range of SDS-resistant, non-amyloid oligomers, however the precursor state conformation has not been established. Here, three DA molecules have been observed to bind per α-syn monomer by electrospray-ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS). Each of these DA molecules binds exclusively to the extended conformation of α-syn, and binding is not observed in the compact state of the protein. Measurements of collisional cross sectional areas show that the incremental uptake of DA pushes the protein towards a highly extended population, becoming fully populated upon the binding of three DA ligands. Tyrosine (Tyr) as a closely related structural analog, exhibited limited binding to the protein as compared with DA, with a maximum of two ligands being observed. Those Tyr ligands that do bind were observed as adducts to the extended conformation akin to DA. These findings suggest DA is able to modulate α-syn self-assembly by inducing the population of a highly extended state.

Reaction of Aziridinones with 2-Lithio-1, 3-Dithiane: Selective Cleavage of the Aziridinone Ring

The reaction of aziridinones (1a-1d) with tert-butyllithium at room temperature affords α-hydroxy imines (5ax-5dx).¹ One possible pathway leading to these products involves the formation of 2 as an intermediate, followed by rearrangement to 3. In fact, under carefully controlled conditions that prevent the rearrange-of 2 to 3, α-amino ketones (4ax-4dx), which arise from the protonation of 2, can be isolated. Other α-amino ketones were synthesized in a like manner from aziridinones by treatment with a variety of alkyllithium reagents.² Baumgarten and co-workers³ subsequently reported similar products from the reaction of phenyllithium and methyllithium with an aziridinone. In an attempt to extend this study to other organolithium reagents, especially those bearing functional groups, we have investigated the reaction of     

Chemical and structural characterization of α-N-acetylgalactosaminidase I and II from starfish, <Emphasis Type="Italic">asterina amurensis</Emphasis>

Background

The marine invertebrate starfish was found to contain a novel α-N-acetylgalactosaminidase, α-GalNAcase II, which catalyzes removal of terminal α-N-acetylgalactosamine (α-GalNAc), in addition to a typical α-N-acetylgalactosaminidase, α-GalNAcase I, which catalyzes removal of terminal α-N-acetylgalactosamine (α-GalNAc) and, to a lesser extent, galactose. The interrelationship between α-GalNAcase I and α-GalNAcase II and the molecular basis of their differences in substrate specificity remain unknown.

Results

Chemical and structural comparisons between α-GalNAcase I and II using immunostaining, N-terminal amino acid sequencing and peptide analysis showed high homology to each other and also to other glycoside hydrolase family (GHF) 27 members. The amino acid sequence of peptides showed conserved residues at the active site as seen in typical α-GalNAcase. Some substitutions of conserved amino acid residues were found in α-GalNAcase II that were located near catalytic site. Among them G171 and A173, in place of C171 and W173, respectively in α-GalNAcase were identified to be responsible for lacking intrinsic α-galactosidase activity of α-GalNAcase II. Chemical modifications supported the presence of serine, aspartate and tryptophan as active site residues. Two tryptophan residues (W16 and W173) were involved in α-galactosidase activity, and one (W16) of them was involved in α-GalNAcase activity.

Conclusions

The results suggested that α-GalNAcase I and II are closely related with respect to primary and higher order structure and that their structural differences are responsible for difference in substrate specificities.

     

Neues über den Mechanismus der retentiven Substitution am Dreiring von Propellanen. Vorläufige Mitteilung

New results concerning the mechanism of retentive substitution at the three membered ring of propellanes The reaction of the endo- and exo-bromide 1a and 1b with acetate ion in aprotic polar solvents carried out at high concentrations of 1 furnishes the dimeric dehydro-halogenation products 3a and 3b , the structures of which are determined by x-ray crystallography (Fig. 1). The formation of 3a and 3b as well as of the products 2 of a retentive substitution process can be explained by assuming that the strained benzo-tropones 4 are intermediates. Their high barrier to inversion is confirmed by π-SCF-molecular mechanics calculations.     

Selenylated dienes: synthesis, stereochemical studies by Se NMR, and transformation into functionalized allenes

2-Phenylselanyl-1,3-dienes 3-8 were prepared by a Wittig or Wittig-Horner-Emmons procedure starting from α-phenylselanyl α,β-unsaturated aldehydes. Ratio and configuration of each diene isomers were determined by ⁷⁷Se and ¹H NMR. These dienes were then oxidized into selenoxides, which could be isolated in some cases. In THF, [2,3]-sigmatropic rearrangement of allylic selenoxides, selenimides, and dihalo-selenuranes occurred, yielding allenyl alcohols 12-15, allenyl carbamates 16c-19c, and 1-haloalkyl allenes 20c-22c, respectively.     

Isomerization of unsaturated radicals. V. Unimolecular isomerization of hot α,α- and α,β-dimethallyl radicals

The 147 nm photolysis of 3,3 dimethylbut-1-ene leads mainly to the formation of very hot (?375 kJ/mol) α,α-dimethallyl radicals. On the other hand, that of 3-methyl-cis-and trans-pentene-2, as well as that of 2,3-dimethylbut-1-ene is a source of very hot α,β-dimethallyl radicals. These allylic radicals are coolled down using pressure and are allowed to combine with available methyl radicals. From the formation of various C₆H₁₂ products, it is concluded that the very hot α,α- radical isomerizes towards the α,β-structure at low pressures and vice versa. The equilibrium constant of the following process has been evaluated to be 1.72 ± 0.30.      

The facile conversion of T-2 toxin and neosolaniol into anguidine

T-2 Toxin (5) and neosolaniol (6) are readily converted into anguidine (1) by a procedure where deoxygenation at the C-8 position is achieved, after conversion of the 3-TBDMS ether 7 of neosolaniol (6) to the β-bromide 11 for reduction to the anguidine precursor 12.     

Experimental validation of the α-effect in the gas phase

The α-effect-enhanced nucleophilicity of an anion with a lone pair of electrons adjacent to the attacking atom-has been well documented in solution; however, there is continuing disagreement about whether this effect is a purely solvent-induced phenomenon or an intrinsic property of the α-nucleophiles. To resolve these discrepancies, we explore the α-effect in the bimolecular nucleophilic substitution reaction in the gas phase. Our results show enhanced nucleophilicity for HOO(-) relative to "normal" alkoxides in three separate reaction series (methyl fluoride, anisole, and 4-fluoroanisole), validating an intrinsic origin of the α-effect. Caution must be employed when making comparisons of the α-effect between the condensed and gas phases due to significant shifts in anion basicity between these media. Variations in electron affinities and homolytic bond strengths between the normal and α-anions indicate that HOO(-) has distinctive thermochemical properties.