Crystal Structures of the Potassium and Silver Salts of Nitroform

The solid state structures of three nitroformate (NF) salts were determined using single crystal X‐ray crystallography. The NF anion was found to be a non‐planar moiety which adopts either the commonly observed C_2v conformation or distorted propeller conformation (D₃) in the case of the silver salts, or, a C₂ conformation in the case of the potassium salt. This latter C₂ conformation has been uniquely observed for potassium nitroformate. All structures exhibit cation‐anion interactions that influence the structure of the anion. The ¹³C and ¹⁴N NMR spectra of the NF anion show broad singlets, which indicates the equivalence of the nitro groups in solution within the NMR time‐scale. In addition, the vibrational and mass spectra of potassium nitroformate and silver nitroformate monohydrate were recorded. Furthermore, the gaseous decomposition products of potassium nitroformate at 25 °C were detected using IR spectroscopy and mass spectrometry.     

Vibrational spectroscopy of 3,4-difluorocyclobutenes: cis-d0, trans-d0 and trans-d4 species

Infrared and Raman spectra were recorded for cis-3,4-difluorocyclobutene (cDFCB) and trans-3,4-difluorocyclobutene-d4. Unscaled density functional theory (DFT) calculations of frequencies and intensities at the B3LYP/6-311++G(d,p) level supported the complete assignment of the vibrational fundamentals. The previous assignment of fundamentals of trans-3,4-difluorocyclobutene was revised. An unusual blue shift occurs for the methylenic CH-stretching frequencies of cis-3,4-difluorocyclobutene in going from the gas phase to the liquid phase. This hydrogen bond effect is related to similar observations recently reported and interpreted. The blue shift does not occur for the vinylic CH bonds of the cis isomer and does not occur for either type of CH bond in the trans isomer.     

Capillary electrophoresis of single mammalian cells

Capillary electrophoresis (CE) has been established as powerful tool for single cell analysis. Newly developed sampling, separation and detection methods have allowed the investigation of single mammalian cells with CE despite their small size and complex composition. Advances in sample injection techniques include several novel methods for the injection of whole cells and sampling techniques for the study of cellular secretion. CE of single mammalian cells has been applied in a wide range of fields including protein analysis, neuroscience, and oncology. The development of new detection schemes in the analysis of single mammalian cells with CE has included studies of protein expression and the utilization of mass spectrometric and electrochemical detection. Subcellular mammalian cell analysis with CE also has been investigated.     

Enantioselective [4 + 2] cycloadditions of o-quinone methides: total synthesis of (+)-mimosifoliol and formal synthesis of (+)-tolterodine

The first example of an enantioselective cycloaddition of an o-quinone methide (o-QM) with a chiral enol ether is described along with the total synthesis of (+)-mimosifoliol and the formal synthesis of (+)-tolterodine. These syntheses exemplify a three-component, one-pot benzopyran approach for the construction of chiral benzylic junctions. Cycloadditions of various enol ethers and o-QMs are examined, and diastereoselectivities >95% are obtained with trans-2-phenyl-1-cyclohexanol and 2,2-diphenylcyclopentanol vinyl ethers.     

DNA interchain cross-links formed by acrolein and crotonaldehyde

Acrolein and higher alpha,beta-unsaturated aldehydes are bifunctional genotoxins. The deoxyguanosine adduct of acrolein, 3-(2-deoxy-beta-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a]purin-10(3H)-one (8-hydroxy-1,N(2)-propanodeoxyguanosine, 2a), is a major DNA adduct formed by acrolein. The potential for oligodeoxynucleotide duplexes containing 2a to form interchain cross-links was evaluated by HPLC, CZE, MALDI-TOF, and melting phenomena. Interchain cross-links represent one of the most serious types of damage in DNA since they are absolute blocks to replication. In oligodeoxynucleotides containing the sequence 5'-dC-2a, cross-linking occurred in a slow, reversible manner to the extent of approximately 50%. Enzymatic digestion to form 3-(2-deoxy-beta-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-(N(2)-2'-deoxyguanosinyl)pyrimido[1,2-a]purin-10(3H)one (5a) and reduction with NaCNBH(3) followed by enzymatic digestion to give 1,3-bis(2'-deoxyguanosin-N(2)-yl)propane (6a) established that cross-linking had occurred with the exocyclic amino group of deoxyguanosine. It is concluded that the cross-link is a mixture of imine and carbinolamine structures. With oligodeoxynucleotide duplexes containing the sequence 5'-2a-dC, cross-links were not detected by the techniques enumerated above. In addition, (15)N-(1)H HSQC and HSQC-filtered NOESY spectra carried out with a duplex having (15)N-labeling of the target amino group established unambiguously that a carbinolamine cross-link was not formed. The potential for interchain cross-link formation by the analogous crotonaldehyde adduct (2b) was evaluated in a 5'-dC-2b sequence. Cross-link formation was strongly dependent on the configuration of the methyl group at C6 of 2b. The 6R diastereomer of 2b formed a cross-link to the extent of 38%, whereas the 6S diastereomer cross-linked only 5%.     

Poly-N-hydroxyethylacrylamide as a novel, adsorbed coating for protein separation by capillary electrophoresis.

We present the polymer poly-N-hydroxyethylacrylamide (PHEA) (polyDuramide) as a novel, hydrophilic, adsorbed capillary coating for electrophoretic protein analysis. Preparation of the PHEA coating requires a simple and fast (30 min) protocol that can be easily automated in capillary electrophoresis instruments. Over the pH range of 3-8.4, the PHEA coating is shown to reduce electroosmotic flow (EOF) by about 2 orders of magnitude compared to the bare silica capillary. In a systematic comparative study, the adsorbed PHEA coating exhibited minimal interactions with both acidic and basic proteins, providing efficient protein separations with excellent reproducibility on par with a covalent polyacrylamide coating. Hydrophobic interactions between proteins and a relatively hydrophobic poly-N,N-dimethylacrylamide (PDMA) adsorbed coating, on the other hand, adversely affected separation reproducibility and efficiency. Under both acidic and basic buffer conditions, the adsorbed PHEA coating produced an EOF suppression performance comparable to that of covalent polyacrylamide coating and superior to that of adsorbed PDMA coating. The protein separation performance in PHEA-coated capillaries was retained for 275 consecutive protein separation runs at pH 8.4, and for more than 800 runs at pH 4.4. The unique and novel combination of hydrophilicity and adsorptive coating ability of PHEA makes it a suitable wall coating for automated microscale analysis of proteins by capillary array systems.     

Controlled structural variations in templated uranium sulfates

A series of experiments in the UO(2)(CH(3)CO(2))(2).2H(2)O/H(2)SO(4)/1-(2-aminoethyl)piperazine/H(2)O system were conducted to determine the effects of variation in initial reactant concentrations on the reaction products. Several reaction gels were produced, in which the composition varied from 16:80:4:500 UO(2)(CH(3)CO(2))(2).2H(2)O/H(2)SO(4)/1-(2-aminoethyl)piperazine/H(2)O to 4:92:4:500 UO(2)(CH(3)CO(2))(2).2H(2)O/H(2)SO(4)/1-(2-aminoethyl)piperazine/H(2)O. Single crystals of two new organically templated uranium sulfates, [N(3)C(6)H(18)](2)[(UO(2))(5)(H(2)O)(SO(4))(8)].5H(2)O and [N(3)C(6)H(18)][(UO(2))(2)(H(2)O)(SO(4))(3)(HSO(4))].4.5H(2)O, were isolated. Both compounds exhibit structures in which the inorganic frameworks are two-dimensional and the protonated amines reside between layers, participating in extensive hydrogen bonding. The composition and structure of each compound is dependent on the nature of the starting concentrations. Crystal data: for [N(3)C(6)H(18)](2)[(UO(2))(5)(H(2)O)(SO(4))(8)].5H(2)O, monoclinic, space group P2(1)/n (No. 14), a = 21.5597(3) A, b = 10.2901(2) A, c = 22.8403(3) A, beta = 96.7436(7) degrees, and Z = 4; for [N(3)C(6)H(18)][(UO(2))(2)(H(2)O)(SO(4))(3)(HSO(4))].4.5H(2)O, monoclinic, space group P2(1)/a (No. 14), a = 15.7673(4) A, b = 10.5813(3) A, c = 16.7710(5) A, beta = 99.9216(9) degrees, and Z = 4.     

A mixed‐valence chloride‐bridged (pincer)IrIII–(diene)IrI complex

The title compound, [2,6‐bis(di‐tert‐butylphosphino)phenyl‐1κ³P,C¹,P′]di‐μ‐chlorido‐1:2κ⁴Cl:Cl‐(2η⁴‐cycloocta‐2,5‐diene)hydrido‐1κH‐diiridium(I,III) hexane hemisolvate, [Ir₂(C₈H₁₂)(C₂₄H₄₃P₂)Cl₂H]·0.5C₆H₁₄ or [(^tBuPCP)IrH(μ₂‐Cl)₂Ir(COD)][^tBuPCP is κ³‐2,6‐(^tBu₂PCH₂)₂C₆H₃ and COD is η⁴‐2,5‐cyclooctadiene], is an Ir^III/Ir^I dimer bridged by two chloride ions. The Ir₂Cl₂ framework is nearly planar, with a dihedral angle of 13.04 (4)° between the two Ir centers. The compound was isolated as a hexane hemisolvate. A list of distances found in Ir(PCP) compounds is given.     

Application of ESCA to polymer chemistry. XVI. Electron mean free paths as a function of kinetic energy in polymeric films determined by means of ESCA

Electron mean free paths as a function of kinetic energy have been measured by the substrate overlayer technique for in situ-polymerized films of poly(p-xylylene) and the monochloro- and monobromo-substituted derivatives. The results are compared with previous estimates of mean free paths available in the literature for organic materials. Comparison is also drawn with corresponding experimental data for typical metals and semiconductors, and it is shown that organic polymers fit into a consistent picture which may be rationalized on the basis of existing theory. For electrons of kinetic energy ～969 eV, ～1170 eV, 1202 eV, and 1403 eV, mean free paths of ～14 Å, ～22 Å, ～23 Å, and ～29 Å, respectively, are obtained for the poly(p-xylylene) polymer films studied in this work.     

Optical rotatory dispersion and circular dichroism. LXXV. Circular dichroism of some aryl-amino acids

CD. curves have been recorded for α-aryl-α-amino acids, esters and amides related to α-phenylglycine, α-phenyl-alanine and their N-dimethyl derivatives, and for the corresponding α-cyclohexyl-α-amino acids and esters. Compounds with the (S)-configuration at the single asymmetric carbon atom give strong positive Cotton effects near 220 nm. The conformations of the acids are discussed and compared with those of other α-amino acids.