A zwitterion of 1,5‐bis­(2‐hydroxy­benzamido)‐3‐aza­pentane: a two‐dimensional hydrogen‐bonding network involving dimers

The title compound, 2‐{N‐[2‐(2‐hydroxy­benzamido)ethyl­ammonio­ethyl]amino­carbon­yl}phenolate, C₁₈H₂₁N₃O₄, crystallizes in a zwitterionic form as a result of inter­molecular proton transfer and possesses a negatively charged phenolate group and a protonated amino group. The 2‐hydroxy­benzamide and 2‐(amino­carbonyl)­phenolate moieties attached to the two ends of the C—C—N—C—C backbone adopt a cis conformation in relation to this backbone. All N‐ and O‐bound H atoms are involved in hydrogen‐bond formation; the zwitterions are first linked into head‐to‐tail dimers, which are further organized into a two‐dimensional network parallel to the crystallographic bc plane.     

Thermodynamics of solids: Corrections from electron-phonon interactions

Anomalous room-temperature specific heats have been seen experimentally by Knapp and coworkers in highT _c superconductors. The measurements depart from 3N k _B + ₀ T by an amount of order ₀ T. We present a theory for this, based on the fact that electronphonon interactions cause both electron band energies _{k n} and phonon frequencies _{Q µ} to be weakly temperature-dependent. First an observation is made which we call Brook's Theorem: the shiftE _{k n} (Q µ) of the electron energy _{k n} due to adding one phonon in modeQ µ, is identical to the shift _{Q µ} (k n) of the phonon energy _Qµ due to adding one electron in the statek n. Second, we assert that to sufficient accuracy whenT> _D , entropy of the system of interacting electrons and phonons equals the entropy which would be calculated for non-interacting particles, except that theT-dependent energiesE _kn (T) and _{Q µ} (T) should be used. A proof to orderu ² (whereu is phonon displacement amplitude) was given in the thesis of one of us. Third, we use Brook's Theorem to show that the corrections C _el and C _ph to the specific heat due toT-dependence of electron and phonon energies respectively, are identically equal and have order of magnitude ₀ T. All these results are valid in adiabatic approximation to orderu ², and fail at low temperatures where non-adiabatic corrections are large.     

Studies of the electrochemical behavior of epinephrine at a homocysteine self-assembled electrode

The self-assembled electrode with the homocysteine monolayer (Hcy/Au) has been characterized by infrared spectroscopy and ac impedance spectroscopy in electrolyte. The Hcy/Au electrode is demonstrated to promote the electrochemical response of epinephrine (E) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (k_s) is 2.1×10⁻² cm s⁻¹ at the self-assembled electrode. The reduction peak of E can be used to determine the concentration of E in presence of ascorbic acid (AA) owing to the Hcy/Au also promoting the electrochemical oxidation of AA.     

A new route for synthesizing cholesterol analogs with fluorocarbon side chains and their liquid-crystalline aliphatic esters

A new and efficient route has been developed to synthesize 17β-(1-methyl-3-perfluoroalkyl)propyl-3β-androsterol (1) in nine steps from hyodeoxycholic acid via selective addition of 1-perfluoroalkyl iodide to 24-norchola-5,22-dien-3β-ol. From (1), the first series of steroidal liquid crystalline aliphatic esters (smectic A) with fluorocarbon side chains has been prepared.     

On-line Separation and Detection of Peptides by Capillary Electrophoresis / Electrospray FT-ICR-MS

Recently, capillary electrophoresis/electrospray ionization mass spectrometry (CE/ESI- MS) has been rapidly developed as a powerful analytical tool for charged species ranged from small molecules such as carboxylic acids1, phenolic compounds2, metal species3, tetramines4, herbicides5, drugs and drug metabolites6 to peptides and proteins7, 8. The ESI mode has proven to be sensitive, versatile and relatively easy to use in combination with CE. CE confers rapid analysis and efficient separ…     

Palladium(II) complexes of bowls, pinwheels, cages, and N,C,N-pincers of starburst ligands 1,3,5-Tris(di-2-pyridylamino)benzene and 2,4,6-Tris(di-2-pyridylamino)-1,3,5-triazene

The reactions of Pd(II) ions with starburst ligands 1,3,5-tris(di-2-pyridylamino)benzene (tdab) and 2,4,6-tris(di-2-pyridylamino)-1,3,5-triazene (tdat) have been investigated. Complexes with the Pd:tdab (or tdat) ratio being 1:1 and 3:1 have been isolated and characterized. The structures of five new Pd(II) complexes containing the starburst ligands have been determined by X-ray diffraction analyses, which include chelate compounds [PdCl(2)(tdab)], 1, [(PdCl(2))(3)(tdab)], 2, [(Pd(OAc)(2))(3)(tdab)], 4, and [(Pd(OAc)(2))(3)(tdat)], 5, and a cyclometalated compound [Pd(OAc)(NCN-tdab)], 3. The Pd(II) ion in the 1:1 compound 1 is chelated by two pyridyl groups. Similarly, each Pd(II) center in the 3:1 compounds 2, 4, and 5 is chelated by two pyridyl groups. However, these three compounds display distinct structural features: 2 adopts a "bowl-shaped" structure, 4 has a "pinwheel"-like structure, and 5 has a "up-and-down" structure. Compounds 4 and 5 were examined in solution by variable-temperature (1)H NMR, which revealed that both compounds retain the "pinwheel" and the "up-and-down" structure, respectively. The observed structural preference by 4 and 5 is attributed to both electronic and steric factors.     

Co-C bond dissociation energy and reaction volume change of 2',5'-dideoxyadenosylcobalamin studied by laser-induced time-resolved photoacoustic calorimetry

Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B(12) analog 2',5'-dideoxyadenosylcobalamin, which lacks an -OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Phi(d) (0.25+/-0.02), Co-C bond dissociation energy (BDE; 31.8+/-2.5 kcal mol(-1)) and reaction volume change deltaV(R) (6.5+/-0.5 ml mol(-1)) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co-C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed.     

Magnetic beads as interfacial nanoprobes

We use paramagnetic beads to probe strongly localized magnetic fields from one-dimensional nanomagnets. Using a polarization microscope in reflection mode, we find that light reflected from beads exhibits intensity fluctuations which may help us understand Brownian motion near interfaces. We estimate the height fluctuations and femtonewton forces acting on the beads.     

Synthesis of new 1,3-bis（phenylethynyl）disilazanes

Three new 1,3-bis(phenylethynyl)disilazanes were synthesized from the reaction of 1,3-dichlorodisilazanes with (phenylethy- nyl)lithium,and characterized by infrared (IR) spectra,nuclear magnetic resonance (NMR) and mass spectrometry (MS).