Structural features and bioactivities of the chitosan

Fourier transform infrared (FT-IR) spectroscopic studies (3500-600 cm⁻¹) showed some different bands of chitosan. The absorption at 3439 cm⁻¹ is stretching vibration of -OH and -NH₂ bonds, indicating the association of the hydrogen-bond between them. The bands at 1659, 1599 and 1321 cm⁻¹ are attributable to the peaks of stretching vibrations of amide I (ν_(CO)), II (δ_(N-H)), and the peak of stretching and bending vibrations of III (ν_(C-N)) (δ_(N-H)). The chitosan showed strong free radical scavenging activities. Pretreatment with chitosan significantly prevented the decrease of antioxidant enzymes activities and the increase of p-JNK at 3 h after renal ischemia and reduced renal tubular epithelial cell apoptosis.     

Conformational Flexibility of Choline Derivatives

CHOLINERGIC substrates have been found in a gauche conformation (G), skewed about the C_α–C_β bond of the (CH₃)₃N⁺–CH₂–CH₂–O cholinic fragment in a number of crystal structures^1–11. Sulphur and selenium isologues, on the other hand, with the (CH₃)₃N–CH₂–CH₂–(S,Se) group, are normally in the extended trans conformations (T)^10,12,13. In agreement with the assumption that the reduced spectrum of biological activity of many rigid analogues and C_α or C_β substituted derivatives of acetylcholine can be partially ascribed to the reduction in conformational flexibility^14–17, a theoretical investigation¹⁸ predicted the existence of four almost isoenergetic conformations TTTT, TGTT, TTGT and TGGT about the ψ₀, ψ₁, ψ₂ and ψ₃ internal rotation angles schematically represented in Fig. 1.     

Chiroptical properties of diastereomeric five-coordinate Pt(II)–olefin complexes. Molecular structure of [PtCl2{(S,S)-(E)-CNCHCHCN}(R,R)-{C6H5CH(CH3)N(CH3)CH2}2]·C6H6

The chiroptical properties of five-coordinate diastereomeric complexes of general formula [PtCl₂(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂{olefin}], with olefin ligands having electron-withdrawing substituents, have been investigated. The sign of CD bands in the 28 000–30 000 cm⁻¹ region appears to be correlated to the absolute configuration of the prochiral coordinated alkene. Single-crystal X-ray diffraction structure determination has been performed on the single diastereomer [PtCl₂(E-but-2-enedinitrile)(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂]· C₆H₆. The compound crystallizes in the monoclinic space group C2 with a = 17.842(2), b = 8.466(1), c = 10.464(1) Å, β = 109.34(1)°, Z = 2. The number of observed reflections was 1943 and the final R and R_w values were 0.020 and 0.028 respectively. Trigonal-bipyramidal geometry is observed around the Pt atom, with the two Cl atoms in axial positions. The unsaturated ligand lies in the equatorial plane disclosing S,S absolute configuration.     

Optically active iridium complexes with cyclopentadienyl-phosphine ligands: synthesis and oxidative addition of methyl iodide

The dimer [Ir(μ-Cl)(C₈H₁₄)₂]₂ reacts with the ligands (S)-(C₅H₄CH₂CH(Ph)PPh₂)Li and (R)-(C₅H₄CH(Cy)CH₂PPh₂)Li to give (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(C₈H₁₄)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(C₈H₁₄)], which upon treatment with CH₃I at room temperature afford the cationic iridium(III) compounds (S,S_Ir)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(C₈H₁₄)][I] as a single diastereomer, and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(C₈H₁₄)][I] as a 9:1 mixture of two diastereomers. If the oxidative addition reaction is performed at reflux in methylene chloride, the starting complexes convert to the neutral compounds (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(I)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(I)] as 1.6:1 and 3.3:1 mixtures of diastereoisomers, respectively. Carbonyl iridium complexes are synthesized by reacting [IrCl(CO)(PPh₃)₂] with the ligands to afford (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CO)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CO)]. They give upon treatment with CH₃I the cationic species (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(CO)][I] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(CO)][I] as 1.6:1 and 3:1 mixture of diastereomers, respectively. No migratory-insertion of the methyl group into the carbonyl-metal bond has been observed even after prolonged heating.     

1H-nmr study on the preferred conformations of chiral pyridine-dinucleotide models

The synthesis of four chiral NAD⁺ models 1 and their 1,4-dihydro analogs 2 is described. From the temperature dependence of the ¹H-nmr spectra it is concluded that for these compounds two preferred conformations I and II, differing slightly in energy, exist. Both conformations are “folded” with the more or less parallel p-anisyl and pyridine groups mutually gauche, but in I the pyridine group is rotated by about 180° as compared with II, thus leading to a conspicuous difference in orientation of the substituent Z (NH₂CO, C₆H₅NHSO₂, (CH₂)₄NSO₂, or (C₄H₈ON)SO₂) in the pyridine ring toward the anisyl group. The most stable conformation (I) has Z closest to the center of the p-anisyl group. In 360-MHz spectra of the dihydropyridines at low temperature (?10°C), slow interconversion of I and II leads to the observation of an XY pattern for the C-4 methylene protons of the 1,4-dihydropyridine system. The anisochronity in this methylene group is caused mainly by the anisotropy of the neighboring p-anisyl group.     

Selective distortion of the planar group CαC'(O)O to a chiral flat tetrahedron in the amino acid alanine

Based on a Cambridge Structural Database (CSD) search, a meta‐analysis of 116 structures of alanine H₃NC_αH(CH₃)C′(O)O and its derivatives H₃NC_αH(CH₃)C′(O)O(H/R/M), protonated, esterified, or coordinated at the carboxylic group, shows that in the first step of a chirality chain, the L configuration at C_α induces (M) and (P) conformations with respect to rotation around the central C′─C_α bond. In the second step, the (M) and (P) conformations selectively distort the planar carboxylic group C_αC'(O_cis)O_trans to asymmetric flat (R) and (S) tetrahedra. High diastereoselectivities are caused by the two players attraction N…O_cis and repulsion O_trans…C_Me, which work together in (L,M,R) configurations but against each other in (L,P,S) configurations.     

Crystallographic characterization of the α,γ C12 helix in hybrid peptide sequences

The solid‐state conformations of two αγ hybrid peptides Boc‐[Aib‐γ⁴(R)Ile]₄‐OMe 1 and Boc‐[Aib‐γ⁴(R)Ile]₅‐OMe 2 are described. Peptides 1 and 2 adopt C₁₂‐helical conformations in crystals. The structure of octapeptide 1 is stabilized by six intramolecular 4 → 1 hydrogen bonds, forming 12 atom C₁₂ motifs. The structure of peptide 2 reveals the formation of eight successive C₁₂ hydrogen‐bonded turns. Average backbone dihedral angles for αγ C₁₂ helices are peptide 1 , Aib; φ (°) = ?57.2 ± 0.8, ψ (°) = ?44.5 ± 4.7; γ⁴(R)Ile; φ (°) = ?127.3 ± 7.3, θ₁ (°) = 58.5 ± 12.1, θ₂ (°) = 67.6 ± 10.1, ψ (°) = ?126.2 ± 16.1; peptide 2 , Aib; φ (°) = ?58.8 ± 5.1, ψ (°) = ?40.3 ± 5.5; ψ⁴(R)Ile; φ (°) = ?123.9 ± 2.7, θ₁ (°) = 53.3 θ 4.9, θ ₂ (°) = 61.2 ± 1.6, ψ (°) = ?121.8 ± 5.1. The tendency of γ⁴‐substituted residues to adopt gauche–gauche conformations about the C^α–C^β and C^β–C^γ bonds facilitates helical folding. The αγ C₁₂ helix is a backbone expanded analog of α peptide 3₁₀ helix. The hydrogen bond parameters for α peptide 3₁₀ and α‐helices are compared with those for αγ hybrid C₁₂ helix. Copyright © 2016 European Peptide Society and John Wiley & Sons.     

Conformations of model compounds of proteins. II. Infrared spectra of N-acetyl-amino acid methylamides

N-Acetyl-amino acid methylamides CH₃CONHCHRCONHCH₃ were prepared from L - and DL -alanine, L and DL -α-amino-n-butyric acid, L - and DL -norvaline, DL -norleucine, L - and DL -methionine, L - and DL -leucine, L -aspartic acid and DL -phenylalanine. The deuterium homologs of the type CH₃CONDCHRCONDCH₃, CD₃CONHCHRCONHCH₃, and CH₃CONHCHRCONHCD₃ were also prepared. The infrared spectra of these compounds were measured down to 300 cm^?1 in the crystalline state. The infrared spectra of N-isopropylacetamide CH₃CONHCH(CH₃)₂, N-methylisobutyramide (CH₃)₂CHCONHCH₃ and their deuterium homologs were also measured. The C?O in-plane and out-of-plane bending vibration bands of the CH₃CONHC^α group (amide IVa and VIa) and those of the –C^αCONHCH₃ group (amide IVb and VIb) were assigned from these data. Two crystalline modifications, form I and form II, were found for the compounds prepared from L -alanine, DL -leucine, L -aspartic acid and DL -phenylalanine. The two forms show quite different skeletal vibrations, which suggest, rotational isomerism. Two distinct patterns were found as to the positions of the amide IVa and VIa bands for the above compounds. The two amide bands were found near 630 and 600 cm^?1 in form I, whereas they were found near 600 cm^?1 in form II. The crystals of the remaining compounds were also classified into form I or form II on the basis of the arrangement of the amide bands. The X-ray structure analyses suggest that these two forms have different hydrogen-bond structures.     

Organic derivatives of aluminium. Part I. Reactions of alkanolamines with aluminium isopropoxide

Reactions of alkanolamines [R₁R₂NXOH; R₁ = H, CH₃, C₂H₅; R₂ = H, CH₃, C₂H₅ and X = -CH₂CH₂-, -CH₂CH₂CH₂-, -CH₂CHCH₃, -C₆H₄CH₂CH₂-] with aluminium isopropoxide in different molar ratios (1 to 3) yield compounds of the type Al(OPrⁱ)_3?n(OXNR₁R₂)_n, where ‘n’ can be 1, 2 and 3. Most of the derivatives are distillable liquids, soluble in common organic solvents and susceptible to hydrolysis even by atmospheric moisture. The new derivatives are characterized by elemental analysis, IR and ¹H NMR spectra. Molecular weight measurements of Al(OPrⁱ)_3?n(OXNR₁R₂)_n reveal them to be tetrameric in nature.     

H-nmr study on the preferred conformations of chiral pyridine-dinucleotide models

The synthesis of four chiral NAD⁺ models 1 and their 1,4-dihydro analogs 2 is described. From the temperature dependence of the ¹H-nmr spectra it is concluded that for these compounds two preferred conformations I and II, differing slightly in energy, exist. Both conformations are “folded” with the more or less parallel p-anisyl and pyridine groups mutually gauche, but in I the pyridine group is rotated by about 180° as compared with II, thus leading to a conspicuous difference in orientation of the substituent Z (NH₂CO, C₆H₅NHSO₂, (CH₂)₄NSO₂, or (C₄H₈ON)SO₂) in the pyridine ring toward the anisyl group. The most stable conformation (I) has Z closest to the center of the p-anisyl group. In 360-MHz spectra of the dihydropyridines at low temperature (−10°C), slow interconversion of I and II leads to the observation of an XY pattern for the C-4 methylene protons of the 1,4-dihydropyridine system. The anisochronity in this methylene group is caused mainly by the anisotropy of the neighboring p-anisyl group.     

Nuclear magnetic resonance study of ring conformations of cyclic tetradepsipeptide AM-toxins and related peptides

Cyclic tetradepsipeptides, AM-toxin I and II, are the host-specific phytotoxins of Alternaria mali. In order to elucidate conformation-toxicity relationships, we analyzed the 270-MHz proton nmr spectra of AM-toxins and hydrogenated analogs, (D -Ala²)AM-toxin I (toxic) and (L -Ala²)AM-toxin I (not toxic), in (C²H₃)₂SO. These cyclic tetradepsipeptides do not contain N-substituted amino acid residues, and all the peptide and ester groups have been found to be transoid. Two conformers with very unequal populations have been found for AM-toxin I and II; the C^β?C^α? C?O conformations of the Dha² residues are nonplanar S-trans in the major conformer and nonplanar S-cis in the minor conformer. Only one ring conformation has been found for each of (L -Ala²) and (D -Ala²)AM-toxin I. (L -Ala²)AM-toxin I takes a C₄-type ring conformation; all the C?O groups and C^α-H bonds are oriented to the same side of the ring. (D -Ala²)AM-toxin I takes a new ring conformation; the side chain and C?O group of the L -Amp¹ residue are oriented to the same side of the ring. This new conformation is also found for the major conformers of AM-toxin I and II and thus appears to be required for the toxicity. The ring conformations of Tyr(OCH₃)¹-bearing analog tetradepsipeptides have been found to be much the same as those of Amp¹-bearing depsipeptides. Furthermore, on the basis of the two distinct conformations of (D -Ala²) and (L -Ala²)AM-toxin I, an empirical rule is proposed for the stable ring conformations of cyclic tetra-D ,L -peptides, not containing N-substituted amino acid residues.     

Synthesis and characterization of silver(I) derivatives containing acylpyrazolonate and phosphino ligands: X-ray crystal structures of monomeric [Ag(Q)(PPh3)2] and of dimeric [{Ag(Q)(PiBu3)}2] (Q = 1-phenyl-3-methyl-4-tert-butylacetylpyrazolon-5-ato)

New silver(I) acylpyrazolonate derivatives [Ag(Q)], [Ag(Q)(PR₃)]₂ and [Ag(Q)(PR₃)₂] (HQ = 1-R¹-3-methyl-4-R²(CO)pyrazol-5-one, HQ^Bn = R¹ = C₆H₅, R² = CH₂C₆H₅; HQ^CHPh2 = R¹ = C₆H₅, R² = CH(C₆H₅)₂; HQ^nPe = R¹ = C₆H₅, R² = CH₂C(CH₃)₃; HQ^tBu = R¹ = C₆H₅, R² = C(CH₃)₃; HQ^fMe = R¹ = C₆H₄-p-CF₃, R² = CF₃; HQ^fEt = R¹ = C₆H₅, R² = CF₂CF₃; R = Ph or iBu) have been synthesized and characterized in the solid state and solution. The crystal structure of 1-(4-trifluoromethylphenyl)-3-methyl-5-pyrazolone, the precursor of proligand HQ^fMe and of derivatives [Ag(Q^nPe)(PPh₃)₂] and [Ag(Q^nPe)(PiBu₃)]₂ have been investigated. [Ag(Q^nPe)(PPh₃)₂] is a mononuclear compound with a silver atom in a tetrahedrally distorted AgO₂P₂ environment, whereas [Ag(Q^nPe)(PiBu₃)]₂ is a dinuclear compound with two O₂N-exotridentate bridging acylpyrazolonate ligands connecting both silver atoms, their coordination environment being completed by a phosphine ligand.     

Synthesis and crystal and molecular structure of a methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate complex

Bis-Methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate, Dy[O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂]₂(NCS) was prepared from the combination of ethanolic solutions of Dy(NCS)₃·xH₂O and (CH₃O)₂P(O)CH₂C(O)N(C₂H₅)₂. The complex was characterized by infrared and NMR spectroscopy, and single crystal X-ray diffraction methods. The crystal structure was determined at 25 °C from 3727 independent reflections by using a standard automated diffractometer. The complex was found to crystallize in the monoclinic space group P2₁/c with a = 13.282(4) Å, b = 19.168(5) Å, c = 9.648(2) Å, β = 90.09(2)°, Z = 4, V = 2456.4 ų and ?_cald = 1.72 g cm^?3. The structure was solved by standard heavy atom techniques, and blocked least-squares refinement converged with R_f = 4.7% and R_wF = 4.9%. The Dy atom is seven coordinate and bonded in a bidentate fashion to two anionic phosphonate ligands [O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂^?] through the carbonyl oxygen atoms and one of two phosphonate oxygen atoms. In addition, each Dy atom is coordinated to two phosphonate oxygen atoms from two neighboring complexes and to the nitrogen atom of a thiocyanate ion. This coordination scheme gives rise to a two-dimensional polymeric structure. Some important bond distances include DyNCS 2.433(8) Å, DyO(carbonyl)_avg 2.39(2) Å, DyO(equat. phosphoryl)_avg 2.303(8) Å, DyO(axial phosphoryl)_avg 2.25(2), PO(phosphoryl)_avg 1.493(3) Å and CO(carbonyl)_avg 1.25(1) Å.     

Raman spectra and conformations of the cis-unsaturated fatty-acid chains

Raman spectra of low (13°C) and high (16°C) m.p. crystals of oleic acid were recorded and the spectral differences were ascribed to different conformations around a pair of sp², CC axes, i.e. (skew, skew′) and (skew, skew). Crystalline modifications (m.p. 29°C and 29.5°C) of petroselinic acid were found for the first time; after spectral comparison with oleic acid conformations in those crystals were predicted to be (skew, skew′) and (skew, skew). Raman spectra of dioleoyl- and dipetroselinoyl-l-α-phosphatidylcholines were measured for different crystalline phases and the conformation was examined.The skeletal vibration bands of the polymethylene chains of cis- and trans-unsaturated fatty-acids were analysed by using the frequency-phase difference relationships of saturated fatty-acids. The ν₄ (stretching) vibrations were localised within each polymethylene chain and the bands of an acid CH₃(CH₂)_m?2CHCH(CH₂)_n?2COOH were explained in terms of the set of phase differences δ = kπ/m and kπ/n (k = 1, 2,..). A unique ν₄ vibration with δ = π/2m was also found. The ν₅ (bending) vibrations sometimes couple strongly with each other to form overall vibrations characterised by δ = kπ/(m + n).Implications of the cis-olefin group for the physical properties of phospholipid bilayers and the applicability of Raman spectroscopy in probing chain conformations were discussed.     

On the identification of ionic species of neutral halogen dimers, monomers and pincer type palladacycles in solution by electrospray mass and tandem mass spectrometry

Electrospray (ESI) mass spectra analysis of acetonitrile solutions of a series of neutral chloro dimers, pincer type, and monomeric palladacycles has enabled the detection of several of their derived ionic species. The monometallic cationic complexes Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (1a) and [Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)]⁺ (1b) and the bimetallic cationic complex [κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]Pd-Cl-Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (1c) were detected from an acetonitrile solution of the pincer palladacycles Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Cl) 1. For the dimeric compounds {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](μ-Cl)}₂ (2, Y=H and 3, CF₃), highly electronically unsaturated palladacycles [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (2d, 3d) and their mono and di-acetonitrile adducts, namely, [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)]⁺ (2e, 3e) and [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)₂]⁺ (2f and 3f) were detected together with the bimetallic complex [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]-Cl-Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N](CH₃)₂]⁺ (2a, 3a) and its acetonitrile adducts [κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)Pd-Cl-Pd[ κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (2b, 3b) and [κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)Pd-Cl-Pd[κ¹-C, κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂(CH₃CN)]⁺ (2c, 3c). The dimeric palladacycle {Pd[κ¹-C,κ¹-N-C(CH₃O-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](μ-Cl)}₂ (4) is unique as it behaves as a pincer type compound with the OCH₃ substituent acting as an intramolecular coordinating group which prevents acetonitrile full coordination, thus forming the cationic complexes [(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂-κO,κC,κN)Pd]⁺ (4b), [(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂- κO,κC,κN)Pd(CH₃CN)]⁺ (4c) and [(C₆H₄ (o-MeO)CC(Cl)CH₂N(CH₃)₂-κO, κC,κN)Pd-Cl-Pd(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂-κO,κC,κN)]⁺ (4a). ESI-MS spectra analysis of acetonitrile solutions of the monomeric palladacycles Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Cl)(Py) (5, Y=H and 6, Y=CF₃) allows the detection of some of the same species observed in the spectra of the dimeric palladacycles, i.e., monometallic cationic 2d-3d, 2e-3e and {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Py)}⁺ (5a, 6a) and {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)(Py)}⁺ (5b, 6b) and the bimetallic 2a, 3a, 2b, 3b, 2c and 3c. In all cationic complexes detected by ESI-MS, the cyclometallated moiety was intact indicating the high stability of the four or six electron anionic chelate ligands. The anionic (chloride) or neutral (pyridine) ligands are, however, easily replaced by the acetonitrile solvent.     

X-ray structure of the curare alkaloid (+) - tubocurarine dibromide

X-ray structure determination of the compound (C₃₇H₄₂N₂O₆)²⁺. 2Br⁻. 4CH₃OH, confirms that (+) - tubocurarine is a monoquarternary salt and has established that the molecule adopts different conformations in crystals of the dibromide and dichloride salts. The crystal structure is stabilised by a number of hydrogen bonds involving the two free hydroxyl groups and the tertiary nitrogen of the tubocurarine molecule, the bromide ions and the solvent molecules. The absolute configuration of the molecule, determined by X-ray anomalous scattering, confirms the configuration assigned earlier by chemical studies.     

Synthesis,structural characterization,and properties of the organothorium alkylthiolate complex [(CH3)5C5]2Th(SCH2CH2CH3)2

This contribution reports the synthesis and characterization of the organothorium alkylthiolate complex [(CH₃)₅C₅]₂Th(SCH₂CH₂CH₃)₂. This compound crystallizes in the monoclinic space group C2/c (#15) with four molecules in a cell of dimensions a=19.066(2), b=11.603(1), c=16.379(2) Å, and β=130.08(1)°. Least-squares refinement led to a value for the conventional R index (on F_o) of 0.040 for 132 variables and 2030 observations having F_o²⩾3σ(F_o²). The molecular structure consists of an unexceptional ‘bent sandwich’ [(CH₃)₅C₅]₂Th fragment coordinated to two n-propylthiolate ligands. The ThS bond distance is 2.718(3) Å; the SC(α) distance, 1.78(2) Å; the ThSC(α) angle, 108.3(5)°; and the SThS′ angle, 102.5(2)°. Contrasts are drawn with the structures of analogous actinide alkoxides     

Raman Spectroscopy Analysis of Botryococcene Hydrocarbons from the Green Microalga Botryococcus braunii

Botryococcus braunii, B race is a unique green microalga that produces large amounts of liquid hydrocarbons known as botryococcenes that can be used as a fuel for internal combustion engines. The simplest botryococcene (C₃₀) is metabolized by methylation to give intermediates of C₃₁, C₃₂, C₃₃, and C₃₄, with C₃₄ being the predominant botryococcene in some strains. In the present work we have used Raman spectroscopy to characterize the structure of botryococcenes in an attempt to identify and localize botryococcenes within B. braunii cells. The spectral region from 1600–1700 cm⁻¹ showed ν(C=C) stretching bands specific for botryococcenes. Distinct botryococcene Raman bands at 1640 and 1647 cm⁻¹ were assigned to the stretching of the C=C bond in the botryococcene branch and the exomethylene C=C bonds produced by the methylations, respectively. A Raman band at 1670 cm⁻¹ was assigned to the backbone C=C bond stretching. Density function theory calculations were used to determine the Raman spectra of all botryococcenes to compare computed theoretical values with those observed. The analysis showed that the ν(C=C) stretching bands at 1647 and 1670 cm⁻¹ are actually composed of several closely spaced bands arising from the six individual C=C bonds in the molecule. We also used confocal Raman microspectroscopy to map the presence and location of methylated botryococcenes within a colony of B. braunii cells based on the methylation-specific 1647 cm⁻¹ botryococcene Raman shift.     

Laser Raman spectroscopic analysis of angiotensin peptides' conformation

In this study we examined the conformation and side chain environments of angiotensins I, II, III, and [Sar¹-Ile⁵-Ala⁸]angiotensin II using laser Raman spectroscopy. The positions of the amide I bands for all four peptides were found between 1664 and 1673 cm^?1. D₂O exchange studies confirmed the positions of the amide I and amide III bands. The positions of the amide I bands for all the angiotensins were found at approximately 1665 cm^?1 and the amide III bands were all located between 1265 and 1278 cm^?1. From the positions and intensities of the amide I and III bands we concluded that all peptides share the same overall conformation consisting of β-turn structure. Spectral analysis indicated that although the spectra for all the peptides were qualitatively identical there was evidence that the angiotensin conformations were more flexible in the aqueous phase than the solid phase. Examination of the $\text{850}\text{830}$ cm^?1 tyrosine doublet suggested that the tyrosine residue in the peptides is exposed to the solvent environment and becomes more exposed as the peptide length is decreased. Therefore, there are some localized conformational differences among the angiotensins. The conformational data yielded by this study leads us to conclude that the various biological properties ascribed to the angiotensins are not due to different conformations of the peptides. The biological differences could perhaps be attributed to localized interactions of the individual amino acid residues with themselves and with the hormone receptors.     

Synthesis and characterization of metallatranes with phenyl substituents in atrane cage

A new series of mono- and diphenylsubstituted silatranes and boratranes N(CH₂CH₂O)₂(CHR³CR¹R²O)MZ (M = Si, Z = CH₂Cl, CCPh, H, OMenth, R¹, R², R³ = H, Ph; M = B, Z = nothing, R¹, R², R³ = H, Ph) have been synthesized. Both transalkoxylation and stepwise modification of a preformed metallatrane skeleton were used. The chloromethyl derivatives N(CH₂CH₂O)₂(CHRCHRO)SiCH₂Cl (R = H, Ph) react with tert-BuOK under intramolecular cycle expansion to give 1-tert-butoxy-2-carba-3-oxahomosilatranes N(CH₂CH₂O)(CH₂CH₂OCH₂)(CHRCHRO)SiO^tBu (R = H, Ph). The treatment of boratranes N(CH₂CH₂O)₂(CH₂CR¹R²O)B (R¹,R² = H, Ph) with triflic acid and trimethylsilyl triflate results in the products of electrophilic attack at the nitrogen atom. The molecular structures of four silatranes and one boratrane bearing phenyl groups in the atrane skeleton were determined by the X-ray structure analysis.