An infrared study of various nitrated polysaccharides and their structural characterisation

Infrared absorption spectra for a number of polysaccharides and their nitrated derivatives have been obtained. The frequency range 730–960 cm^?1 is useful for identification of the polysaccharides, and the region 900–1350 cm^?1 is more suitable for distinguishing the nitrated materials. The strong intensity of the nitrate bands limits the interpretation of spectra below 960 cm^?1, but above this frequency the absorption bands of nitrated polysaccharides are generally sharper and more clearly defined than the corresponding bands of the parent polysaccharides. Data on the COC bridge, CC ring, CO, and COH frequencies and on the CH deformation and stretching frequencies have been obtained. The use of i.r. spectroscopy for the quantitative determination of nitrate groups in nitrated polysaccharides is discussed.     

Multinuclear NMR of cis-dicarbonylbis(dithiocarbamato)iron(II) complexes in chloroform solution

The ¹³C and ¹⁵SN NMR spectra of eleven cis-Fe(S₂CNRR′)₂(CO)₂ complexes, where R and R′ are organic substituents, have been measured at ambient temperature in CDCl₃ (0.08–0.16 M). The ¹³C absorptions for the carbonyl ligands correlate well with the force constants for the CO stretching vibrations in CHCl₃ solution. Each of the parameters (¹³CO absorption and k_cis for CO) correlate well with the aqueous solution pK_a for⁺H₂NRR′, corrected for the phenyl-containing substituents, high pK_a values corresponding to high ¹³CO absorptions and low k_cis CO force constants. [p ]Evidence was found in the ¹³C NMR spectra for hindered rotation about the CN bond in S₂CNC₂ in complexes with higher pK_a(corr) values and in the ¹³C spectra of the corresponding thiuram disulfides. [p ]The ¹⁵N (natural abundance) NMR spectra for each of the complexes was determined. Each revealed a single sharp absorption in a region of the ¹⁵N NMR spectrum which indicates substantial CN double bond character, as one would expect for coordinated dithiocarbamate ligands.     

Force constants and fundamental frequencies of the fare earth trihalide molecules

The effective nuclear charge model has been applied to the rare earth trihalides. A set of the effective nuclear charge values of the rare earth atoms has been evaluated from the bond stretch force constants obtained by normal coordinate analysis of the infrared spectra of the lanthanide trifluorides.The force constants and the fundamental frequencies of all the lanthanide trihalides have been calculated by means of the effective nuclear charge model. The calculated results are in agreement with the experimental data. The results show that the most probable configuration of the lanthanide trihalides is pyramidal with C_3ν symmetry, although the geometry of the lanthanide trifluoride molecules is very close to planar. It is also found that the frequency ν₂ (symmetric deformation) and the frequency ν₄ (antisymmetric deformation) will vary with the bond angle (XLnX).     

Main group metal halide complexes with sterically hindered thioureas. IX. New complexes of selected post-transition metals and 1,3-dimethyl-2(3H)-imidazolethione and a structural investigation of infrared peak shifts associated with coordination

Five new complexes of sterically hindered 1,3- dimethyl-2(3H)-imidazolethione (dmit) with the chlorides of Cd(II), Hg(II), Te(II), Sn(IV) and Sb(V) have been synthesized and characterized. The previously reported Zn(II) adduct was also synthesized and further characterized. These complexes were of the general formula MX_n(dmit)_m where n = 2 and m = 2 when M = Zn, Cd, Hg and Sn; and n = 2 and m = 4 for Te(II). The only 1:1 adduct observed was SbCl₅dmit, and its chemistry is more complex giving rise to unique redox products upon heating in solution. Solid state spectra of these complexes as well as for dmit complexes are reported and discussed with regard to the coordination sensitive NCN asymmetric stretch and the CS stretch observed not only for dmit complexes but for tetramethylthiourea (tmtu) complexes reported in the literature as well. Greatest shifts on coordination are observed with the NCN asymmetric stretch for tmtu causing shifts to higher wave numbers ranging from 55 to 95 cm⁻¹ relative to free tmtu. Shifts are explained on the basis of observed crystal structures of tmtu adducts showing a greater CN double bond character. Dmit adducts show much smaller shifts both to higher and lower wave numbers for this mode relative to free ligand, and the CS stretch shows little change also. Comparison to known crystal structures show little change in the bond distances of the dmit ligand upon coordination. Inductive effects based on correlations of shift magnitude to the Sanderson group electronegativity (SGEN) of the acceptor seem to be unrelated with the exception of a small positive correlation observed for the NCN asymmetric stretch of tmtu.     

Synthesis of 4,5-dideoxy-4-C-[(R,S)-phenylphosphinyl]-d-ribo- and l-lyxo-furanose and their 1,2,3-triacetates

2,3-O-Isopropylidene-d-ribose diethyl dithioacetal, prepared from d-ribose, was converted in three steps into the corresponding dimethyl acetal, which was monotosylated at O-5, and the ester oxidized at C-4 with pyridinium chlorochromate; addition of methyl phenylphosphinate to the resulting pentos-4-ulose derivative then provided (4R,S)-4,5-anhydro-2,3-O-isopropylidene-4-C-[(R,S)-(methoxy)phenylphosphinyl]-d-erythro-pentose dimethyl acetal. Hydrogenation of this compound in the presence of Raney Ni, followed by reduction with SDMA, hydrolysis, and acetylation, yielded the title compounds (seven kinds), the structures of which were established on the basis of their 400-MHz, ¹H-n.m.r. and mass spectra. A general dependence of the ²J_PH and ³J_PH values on the OPCH and PCCH dihedral angles provided an effective method for the assignment of the configurations and conformations of these 4-deoxy-4-phosphinyl-pentofuranoses.     

Infrared absorption and raman scattering of sulfate groups of heparin and related glycosaminoglycans in aqueous solution

The i.r. spectra for aqueous solutions of sulfated glycosaminoglycans and model compounds in the transmittance “window” region of the solvent (1400-950 cm^?1) are dominated by the strong and complex absorption centered at ～1230 cm^?1 and associated with the antisymmetric stretching vibrations of the SO groups. Primary and secondary O-sulfate groups absorb at somewhat higher frequencies (1260-1200 cm^?1) than N-sulfates (～1185 cm^?1). Each sulfate band lends itself to quantitative applications, especially within a given class of sulfated polysaccharide. Laser-Raman spectra of heparin and model compounds have been obtained in aqueous solution and in the solid state. The most-prominent Raman peak (at ～1060 cm^?1) is attributable to the symmetrical vibration of the SO groups, with N-sulfates emitting at somewhat lower frequencies (～1040 cm^?1) than O-sulfates. The Raman pattern in the 950-800 cm^?1 region (currently used in the i.r. for distinguishing between types of sulfate groups) also involves vibrations that are not localized only in the COS bonds.     

G.L.C.-M.S. of the oxidation products of pentitols and hexitols as O-butyloxime trifluoroacetates

Chemical ionisation (c.i.) mass spectra of trifluoroacetylated O-butyloximes of 2- and 3-pentuloses, 2- and 3-hexuloses, and 2,5-hexodiuloses (products of the oxidation of the pentitols and hexitols with bromine) are reported. Small amounts of 2-pentosuloses and 2,3- and 2,4-pentodiuloses could be detected by using selected ion monitoring at m/z 579 (M + 1). The mass spectra comprise few signals, with those for (M + 1) or (M + 1 ? 2 F₃CCOO) being the most intense.     

PtL3 X-ray absorption studies of Pt model compounds and [(NH3)2Pt(OH)2Pt(NH3)2]2+ bound to DNA

The Pt L₃ X-ray absorption spectra of a series of Pt compounds have been recorded and their extended fine structure (EXAFS) analysed to investigate the sensitivity of EXAFS to non-first-shell PtPt distances. The Pt L₃ EXAFS spectra of complexes formed between [(NH₃)₂Pt(OH)₂Pt(NH₃)₂]²⁺ and calf thymus DNA were also recorded. PtPt vectors could not be detected in these spectra. When combined with the model compound studies, this result rules out Pt dimer structures for the PtDNA complex which involve rigidly bridged, adjacent Pt atoms. Such structures, based on dimeric bonding of a hydroxo dimer intermediate to DNA, have been proposed as models for cisplatin antitumor activity. These types of models now seem unlikely.     

Synthesis and characterization of some aminoarsonium chlorides

R₃As reacts with NR′R″Cl to give good yields of a new homologous series of aminoarsonium chlorides, [R₃AsNR′R″]Cl, in which R = Me, Et, n-Pr, and Ph; R′ and/or R″ = H, Me. IR, NMR, mass, and X-ray spectral data suggest that the arsenic is tetra- coordinate. Electfical conductivity and temperature and concentration dependent NMR studies suggest that hydrogen-bonding interactions are important in solution. Quaternization of the arsenic produces a downfield ¹H NMR chemical shift for the protons in the alkyl chains and a change from non-equivalence to equivalence of the C-1 protons. The NMR data are compared with those for the analogous phosphorus compounds. The electron impact, chemical ionization, and negative ion mass spectral data and fragment ion identities are given for the compounds. Ions corresponding to a variety of AsCl containing species, in addition to those associated .with fragmentation of the R₃As moieties, are observed in the EI mass spectra. AsN, AsNAs, and AsNAsN containing fragments are observed in the Cl mass spectra and AsCl bonding species in the NI mass spectra. A preliminary X-ray diffraction study of [n-Pr₃AsNH₂]Cl indicates near tetrahedral geometry about the arsenic atom.     

Raman spectroscopic analysis of the sodium salt of kappa-carrageenan and related compounds in solution

Laser-Raman spectra of Na⁺ kappa-carrageenan, Na⁺ neocarrabiose 4-sulphate, and neocarrabiose in the region 700–1500 cm⁻¹ are reported for solutions in H₂O and D₂O. The C-1-H-1α vibration, coupled with COH related modes, is assigned to a band at 840 cm⁻¹, close to the maximum of the symmetrical COS stretching (∼850 cm⁻¹). The symmetrical SO stretch is proposed to occur near 1040 cm⁻¹ and is probably coupled with COH vibrations which give rise to strong bands in the region 1000–1100 cm⁻¹. The intense band in the region 730–740 cm⁻¹ is ascribed to a complex ring vibration.     

Raman study of crystalline peptides containing beta turns

The Raman spectra of crystalline H-ProLeuGlyNH₂ which has a type II β turn, crystalline S-benzylCysProLeuGlyNH₂ which has a type I β-turn, and crystalline gramicidin S which has two β turns and β-sheet structure in its conformation, were investigated. The amide I and amide III bands of the peptides with β turns were generally different from those which are diagnostic for α-helix and β-sheet conformations. The patterns of the amide I and amide III bands, when examined together, indicate that Raman spectra can provide diagnostic evidence for β-turn structure in peptides.     

31P n.m.r. studies of complexes of NADPH and NADP+ with Escherichia coli dihydrofolate reductase

We have measured the ³¹P n.m.r. spectra of NADP⁺ and NADPH in their binary complexes with Escherichia coli dihydrofolate reductase and in ternary complexes with the enzyme and folate or methotrexate. The ³¹P chemical shift of the 2′ phosphate group is the same in all complexes; its value indicates that it is binding in the dianionic state and its pH independence suggests that it is interacting strongly with cationic residue(s) on the enzyme. Similar behaviour has been noted previously for the complexes with the Lactobacillus casei enzyme although the ³¹P shift is somewhat different in this complex, possibly due to an interaction between the 2′ phosphate group and His 64 which is not conserved in the E. coli enzyme. For the coenzyme complexes with both enzymes ³¹POC₂¹H_2′ spin-spin interactions were detected (7.5–7.8 Hz) on the 2′ phosphate resonances, indicating a POC₂H_2′ dihedral angle of 30 or 330 : this is in good agreement with the value of 330° measured in crystallographic studies¹ (Matthews et al., 1978) on the L. casei enzyme. NADPH-MTX complex. The pyrophosphate resonances are shifted to different extents in the various complexes and there is evidence that there is more OPO bond angle distortion in the E. coli enzyme complexes than in those with the L. casei enzyme. The effects of ³¹POC₅¹H_5′ spin coupling were detected on one pyrophosphate resonance and indicate that the POC₅H_5′ torsion angle has changed by at least ～30° on binding to the E. coli enzyme: this is considerably less than the distortion (～50°) observed previously in the L. casei enzyme complex.     

Resonance Raman studies of the peroxotitanate(IV) complexes K2(Ti(O2)(SO4)2)·5H2O and K2(Ti(O2)(C2O4)2)·3H2O

The resonance Raman spectra of K₂(Ti(O₂)(SO₄)₂)·5H₂O and K₂(Ti(O₂)(C₂O₄)₂)·3H₂O are recorded. The results are consistent with the triangular structure of the peroxotitanium unit, Ti(O₂), with C_2ν symmetry. The ν(OO), ν_s(TiO) and ν_as(TiO) are observed around 890, 610 and 535 cm⁻¹, respectively. The resonance effects are shown to be associated with the 425 nm absorption band. This band is assigned to the O₂²⁻ → Ti(IV) charge-transfer transition. The calculated force constant values for the O₂²⁻ and TiO bonds are 320 and 275 N m⁻¹, respectively.     

New stoichiometric and catalytic organometallic chemistry with actinides. CH activation and phosphine/phosphite coordination chemistry

This short review highlights two areas of recent activity in organoactinide chemistry: actinide-centered homogeneous chemistry in which intra- and intermolecular CH activation takes place on hydrocarbon fragments, and actinide coordination chemistry involving phosphine and phosphite ligands. It is shown that new metal-ligand bond enthalpy data afford a far greater understanding of observed CH activation patterns, and, moreover, support the design of successful new strategies for CH activation on exogenous hydrocarbon molecules. For example, the strain energy of a thoracyclobutane provides the driving force for ring-opening reactions that involve attack on a alkane or arene carbon-hydrogen bond. While phosphines have been shown to be rather unexceptional ligands for organoactinides, the reaction of trialkylphosphites with the organoactinide hydrides {M[(CH₃)₅C₅]₂H₂}₂, M = Th, U takes a different course. In the case of P(OCH₃)₃, quantitative demethoxylation of the phosphite occurs under mild conditions to yield μ-phosphinidine complexes of the type {M[(CH₃)₅C₅]₂(OCH₃)}PH.     

13C-n.m.r. spectra of some ribitol teichoic acids

Proton-decoupled ¹³C-n.m.r. spectra were determined for D₂O solutions of several wall teichoic acids containing glycosylated ribitol 1,5-diphosphate residues and for their dephosphorylated repeating-units. Assignments were made by correlating the chemical shift values observed with those reported for isolated constituents, allowing for perturbations of the latter resonances because of the presence of O-glycosyl or phosphodiester bonds. Anomeric configurations of hexopyranosyl residues and their position of substitution on ribitol were indicated from the distinctive chemical shifts of the carbons concerned. Three-bond ¹³C³¹P couplings (6–8 Hz) were observed, and two-bond ¹³C³¹P couplings were indicated by broadened signals. The lack of resolution for the latter resonances is probably due to the heterogeneous nature of the polymers.     

Infrared-spectral characteristics of some acetylated,anomeric glycosides

Barker and co-workers had described the C-1-H deformation bands in the ranges 844 ±8 cm^?1 and 891 ±7 cm^?1 as characteristic bands for the α and β anomers, respectively, of hexo- and pento-pyranoses and -pyranosides, and their derivatives. Later, Audichya and co-workers reported the presence of the 844 ±8-cm^?1 band for both anomers of some aryl d-glucoside derivatives, making the applicability of the earlier findings doubtful. Examination by us of the i.r. spectra of some aryl glycoside derivatives suggested that the origin of the band at 844 ±8 cm^?1 for the β anomers of the p-substituted-aryl glycoside derivatives studied by Audichya et al. could be a CH, out-of-plane deformation-mode of the substituted aromatic ring. Also, their further claim of a characteristic band in the region 961-957 cm^?1 for α anomers is shown to be of little diagnostic value. The relative intensities of bands in the COC stretching region, 1100-1000 cm^?1, and a band near 300 cm^?1 in the COC deformation region, found only for the β anomers, are shown to be helpful in differentiating the anomers of some peracetylated alkyl and aryl glycosides.     

Kinetic studies on the chymotrypsin Aα-catalyzed hydrolysis of a series of N-acetyl-l-phenylalanyl peptides

A series of N-acetyl-l-phenylalanyl peptides of general formula Ac-Phe-(Gly)_n-NH₂ (n = 0–2) has been synthesized to study the effect of leaving group chain length on the efficiency of chymotrypsin A_α amidase and peptidase activities. The effect upon catalysis of hydrophobic side chains on the leaving group was investigated using similar substrates with one of the glycine residues selectively substituted by an alanine residue as in AcPheAlaNH₂, AcPheAlaGlyNH₂, and AcPheGlyAlaNH₂. Values of k_cat and K_m have been obtained from kinetic measurements at pH 8.00 and 25 °C. The results are shown to be consistent with binding schemes postulated from published model building studies. The catalytic reactions were studied over a range of temperature (15–35 °C) and in each case the Arrhenius law was obeyed. It was thus possible to obtain meaningful values for the thermodynamic functions of activation for the acylation step of the catalytic reaction. The results are shown to confirm the findings of postulated binding schemes but indicate that conclusions drawn from kinetic measurements at a single temperature may sometimes be misleading.     

Synthesis,characterization and study of the PtPt interaction in cis-[(aa)(bb)FCrNCPt(CN)3] (aa,bb=bidentate amine)

Two new dinuclear μ-cyano complexes, cis-[(en)(tn)FCrNCPt(CN)₃] and cis-[(chxn)(tn)FCrNCPt(CN)₃] en=ethylenediamine, tn=1,3-diaminepropane and chxn=1,2-cyclohexanediamine) have been obtained by solid state heating of the trans[Cr(aa)(bb)F(H₂O)][Pt(CN)₄] salts. These complexes have been characterized by chemical analysis, electronic and IR spectra. The dinuclear complexes show strong PtPt interaction both in the solid state and in solution. The association constant of the oligomers formed has been calculated and correlated with the size of the amine ligands. An orbital explanation is proposed to account for the enhancement of the PtPt interaction in the dinuclear complexes relative to the complex salts.     

Complexes of formamidines and ethyl formimidate

Formamidines and formimidates (L = (p-MeC₆H₄ NH)(p-MeC₆H₄N=)CH; L′ = (p-MeC₆H₄N=) (EtO)CH are shown to yield metal complexes, not obtained directly before. The following complexes were characterized through spectral and magnetic data: L₂Ag⁺, L₂AgNO₃, L₂ZnBr₂, L₂CdBr₂, L₃Cd₂Br₄, LHgCl₂, L₂CoCl₂, [LH]₂[CoCl₄], cis-(CO)₂RhClL as well as L′₂Ag⁺ and cis-(CO)₂RhClL′. I.r. and n.m.r. spectra allow to distinguish these complexes from the derivatives of the isomer carbene ligands, (RNH)₂C: and (RNH)(R′O)C:.     

Resonance Raman spectroscopy of chemically modified retinals: Assigning the carbon-methyl vibrations in the resonance Raman spectrum of rhodopsin

To assign the observed vibrationsl modes in the resonance Raman spectrum of the retinylidene chromophore of rhodopsin, we have studied chemically modified retinals. The series of analogs investigated are the n-butyl retinals substituted at C₉ and C₁₃. The results obtained for the 11-cis isomer have clearly assigned the CCH₃ vibrational frequencies observed in the spectrum of the retinylidene chromophore. The data show that the C₍₉₎CH₃ stretching vibration can be assigned to the vibrational mode observed in the 1017 cm^?1 region, and the vibration detected at 997 cm^?1 can be assigned to the C₍₁₃CH₃ vibration. The C₍₅₎CH₃ stretching mode does not contribute to the vibrations observed in this region. The splitting in the C_(n)CH₃ (n = 9, 13) vibration is characteristic of the 11-cis conformation. The results on the modified retinals do not support the hypothesis that the splitting arises from equilibrium mixtures of 11-cis, 12-s-cis and 11-cis, 12-s-trans in solution. Thus, this splitting cannot be used to determine whether the chromophore in rhodopsin is in a 12-s-cis or 12-s-trans conformation. However, our results demonstrate that there are other vibrational modes in the spectra which are sensitive to this conformational equilibrium and we use the presence of a strong ~ 1271 cm^?1 mode in bovine and squid rhodopsin spectra as an indication that the chromophore in these pigments is 11-cis, 12-s-trans.