Double Irradiation Research Articles

Biosynthesis of prodiginines. 13C resonance assignments and enrichment patterns in nonyl-, cyclononyl-, methylcyclodecyl-, and butylcycloheptylprodiginine produced by actinomycete cultures supplemented with 13C-labeled acetate and 15N-labeled nitrate

Resonances in the 13C nmr spectra of nonylprodiginine, cyclononylprodiginine, methylcyclodecylprodiginine, and butylcycloheptylprodiginine were assigned using information from the literature, from high resolution spectra and double irradiation experiments, and from 13C–15N couplings observed in samples of nonylprodiginine enriched with 15N. Supplementation of cultures with sodium [1-13C]- and [1,2-13C]acetate gave 13C-enriched prodiginines and the labeling patterns were established from 13C nmr spectra. These indicated that rings A and B were formed in a similar manner to rings A and B in prodigiosin and other prodiginine pigments. Ring C and the C2-alkyl substituent were derived in part from acetate units that were condensed in a linear 12- or 14-carbon chain. The same pattern of acetate assembly has been found in ail actinomycete prodiginines examined.

Collision induced energy transfer between H2O and NH3 molecules

Energy transfer has been observed in H2ONH3 mixtures irradiated by infrared microwave double irradiation. An interpretation of the energy transfer process in given.

Deuteron quadrupole resonance studies. Part 8.—1H/2H double resonance in some inorganic hydroxy compounds

2 H quadrupole resonance frequencies have been detected in partially deuterated H2SeO3, HIO3, B(OH)3, Te(OH)6, KHSO4, NaHCO3 and KHCO3 using double resonance by level crossing (d.r.l.c.) techniques. Te(OH)6 shows a complex multiplet which has been tentatively assigned using a combination of Zeeman measurements, double irradiation and double quantum methods.The quadrupole coupling constants have been correlated with the H … O hydrogen bond lengths derived from neutron diffraction data, and deviations are attributed to differences in π-bonding to the oxygen atom.

UV-inducible repair II: Its role in various defective mutants of Escherichia coli K-12

Involvement of UV-inducible protein(s) in repair of various E. coli K-12 cell strains has been investigated using a procedure of double UV irradiation and postincubation with chloramphenicol. From the course of dose survival curves the following conclusions concerning significance of a UV-inducible protein have been drawn: 1. It is a very important for wild type cells; in these cells its early occurrence is necessary to prevent killing. 2. It is involved in repair of excision-deficient cells; however, its action early after UV is less urgent. 3. It is not involved at all in repair of lex mutant cells; 4. It exhibits some effect on survival of recA as well as recB mutant cells. We conclude that the protein is involved in excision repair as well as in resumption of DNA replication.

Étude par 13C NMR et 1H NMR du dextrane et de ses dérivés acétylés et benzylés

AbstractA 13C NMR and 1H NMR study has been performed on a bacterial dextrane, its triacetylated derivative and a synthetic tri‐O‐benzyldextrane obtained by polycondensation. The main feature of these three products is their regular linearity of glucose residues linked α‐D‐(1→6). In each of them, the proton signals were assigned by homonuclear double irradiation and the 13C signals by selective proton irradiation.The 13C chemical shifts of isomaltose and gentiobiose are compared with the shifts of the corresponding homopolymers dextrane and pustulane.

A nuclear quadrupole double-resonance study of orthorhombic DC1

A 35Cl 2H double-resonance study of deuterium in the orthorhombic solid phase of deuterium chloride has been made at temperatures below the transition to the cubic phase (105.03 K). The temperature dependence of the deuterium coupling constant was obtained over the range 4.2 to 90 K and the fine structure was resolved. Upon pulsed irradiation of the deuterium transitions, a 35Cl echo envelope modulation is observed, the period of which corresponds to the frequency of the fine structure mentioned above. This establishes the origin of the structure to be due to dipolar coupling between the two spin species, and not due to a nonaxial component in the field gradient at 2H The theory of this echo modulation is given and it leads to an echo structure E DR(2 τ) = E 0(2 τ)[1 + 2 cos (2 δτ)], where δ is the scale constant for the dipolar coupling between 35Cl and 2H. Under double irradiation, the deuterium NQR line is a doublet, and the splitting observed is 2.97 kHz (mean deviation ±0.02) from 4.2 to 77 K. This is substantially smaller than the value of 3.29 kHz calculated from the neutron diffraction bond length of 1.30 Å. The discrepancy is interpreted as arising principally from the averaging of the dipolar interaction by the molecular librational motion. Since the quadrupole coupling and the dipolar interaction depend upon the librational motion through the same angular dependence, one may use the observed decrease in dipole coupling strength to estimate the rigid lattice coupling constant for 2H to be 166.8 kHz (0.2481 a.u.). If one uses instead the librational amplitudes obtained from the neutron diffraction structure, one obtains a value of 155.2 kHz (0.2310 a.u.). These values are discussed as they relate to theoretical estimates, and to measurements in the cubic solid and the liquid phases.

Measurements of 15N, 1H, and 13C, 1H direct couplings in natural abundance from proton NMR spectra of s-triazine in the nematic phase

A method using proton FT NMR and double irradiation has been used in order to obtain 1H– 15N and 1H– 13C direct couplings of unlabelled s-triazine in the nematic phase. These couplings allow a complete structural determination. Large distortions of the aromatic ring with respect to hexagonal geometry are observed.

Solution Conformation of the Antibiotic 3823A (Monensin A)‐Sodium Salt

AbstractExtensive double irradiation experiments allowed the almost complete unraveling and extraction of the parameters in the 1H‐nmr spectrum of Na+‐Monensin (1). From this it is concluded that the solution conformation is in its details highly similar to the crystal state of the Ag+ salt. Thus rings A and E are in a somewhat distorted chair, both rings B and D are in an envelope (with the flap at respectively C‐10 and C‐18) while ring C is in a 1514T(wist). An unusual high screening and consequently low rate of proton exchange was observed for some hydroxyl protons, especially in C6D6. The small couplings observed where OH‐protons are involved allow a further deeper insight in their spatial arrangement and in their participation as ligand and hydrogen bonding. Some differences with the solid state are noted here.

Solution Conformation of the Ionophore A204A Na+‐Salt

AbstractMost of the parameters of the Na+‐salt of A204A could be extracted from its 300 MHz H‐nmr spectrum in CDCl3, by consecutive double irradiation and INDOR experiments. A comparison of the so‐obtained solution conformation (Figure 4) with that reported2 for the solid state disclose their striking analogy. The backbone forms a pseudocyclic structure, closed by head‐to‐tail hydrogen bond between OH‐15 and COOθ (1). The cation is fixed in the center by at least six ligands, forming an irregular octahedron. Rather OH‐3 or 0‐4 (instead of the second oxygen atom of the carboxylic function as proposed2 for the crystaline state) seems to be involved as one of the ligands. Also, the rotameric states of some side chains (methoxy groupings and ring G) behave presumably different in solution. The outside periphery of the pseudo cycle is not entirely hydrophobic and four methoxy groups, OH‐15 and at least three ether/acetal oxygen atoms point away from the central cavity into the surroundings. Most of these ambident functions are concentrate around one region, e. g. the dangling sugar‐like ring G. This is a chemically mobile entity and attached via an acetal function to the remaining architecture, the latter thus being the sole skeleton responsible for chelation.

1H Nmr studies at 360 MHz of the methyl groups in native and chemically modified basic pancreatic trypsin inhibitor (BPTI).

In the 1H NMR spectra obtained at 360 MHz after digital resolution enhancement, the multiplet resonances of the methyl groups in the basic pancreatic trypsin inhibitor (BPTI) were resolved. With suitable double irradiation techniques the individual methyl resonances were assigned to the different types of aliphatic amino acid residues. Furthermore, from pH titration and comparison of the native protein with chemically modified BPTI, the resonance lines of Ala 16 in the active site and Ala 58 at the C-terminus were identified. Potential applications of the resolved methyl resonances as natural NMR probes for studies of the molecular conformation are discussed.

Attribution des signaux de résonance magnétique nucléaire- 13c de disaccharides peracétylés dans la série du D-glucose

Selective, double irradiation allows the assignment of most 13C-n.m.r. signals in a series of per- O-acetyl disaccharides composed of two D-glucose residues linked α-(1→3), β-(1→3), α-(1→4), β-(1→4), α-(1→6), β-(1→6), and α,α-(1→1). The main influences that affect the chemical shifts are discussed and the spectra of β-cellobiose octaacetate and β-maltose octaacetate are compared to those of cellulose and amylose triacetate, respectively, to show the possibilities and limitations of a disaccharide model for the interpretation of the 13C-spectrum of a polymer.

13C n.m.r. spectra of some thiobenzamides. Correlation between 13C and 1H n.m.r. spectra and signal assignments of syn and anti CH2 groups

Abstract13C n.m.r. spectra of a series of N,N‐disubstituted thioamides have been recorded and signal assignments were performed. Separate signals are observed for methylene groups fixed on the nitrogen atom. Since the carbon atom syn to the thiocarbonyl sulfur resonates at higher field than the anti carbon, the syn‐anti assignment in 1H n.m.r. is easily obtained by selective double irradiation. This method, which is rapid and reliable, affords a rather general solution to the interesting problem of resonance assignments in tertiary amides and thioamides (and in analogous molecules such as oximes and nitrosamines).

Phobic Reactions between two Adjacent Monochromatic Light Fields

Trichoms of the blue-green alga Phormidium uncinatum undergo a phobic reaction when they traverse by random movement from a field of photosystem II light (557 nm) to an adjacent field with light of a variable wavelength. According to the electron pool hypothesis, the wavelength dependency curve of organism accumulations resulting from repeated phobic reactions must be regarded as an action spectrum of photosystem I. This action spectrum is compared to one obtained with a double irradiation technique.

Azobilirubin isomers: NMR structure determination using a shift reagent

AbstractThe isomeric benzeneazodipyrromethene derivatives, obtained from the reaction of bilirubin and a phenyldiazonium salt were separated as their corresponding methyl esters. The lanthanide‐induced chemical shifts, coupling constants and double irradiation experiments permit direct assignment of methyl and vinyl substituent positions in these bilirubin‐derived isomers.

The application of the forsén-hoffman method of measuring rates of exchange to the 13C NMR spectrum of cis-decalin

The Forsén-Hoffman double irradiation method of relating exchange rates to T 1 has been applied to the 13C NMR spectrum of cis-decalin. The rate of exchange can be determined for a two-site exchange problem by measuring the size of the signal at one site in the absence and presence of a radiofrequency magnetic field at the second site and by measuring T 1 of the first site by the conventional ( T d - π- τ- π/2) n pulse sequence. It is shown that the use of this method in conjunction with line-shape analysis provides a powerful method of accurately determining activation parameters.

Orientation Effects and the Sign of Two-bond 13C–1H Coupling

Signs of two bond (2J) 13C–1H coupling in 13C–enriched carbohydrates have been determined from proton spectra by the double irradiation technique. Instances of both positive and negative 2J values are given and are characterized in terms of the relative orientations of the coupled proton and of oxygen appended to the 13C nucleus; e.g., an oxygen anti to the proton appears to make a positive contribution to 2J and a gauche oxygen a negative one. Theoretical calculations, using ethanol and 1,1-ethanediol as model compounds, are in accord with these experimental observations.

Synthesis and structure of edulans I and II

Eculans I and II have been shown by synthesis to be the epimeric 3,5,6,8a-tetrahydro-2,5,5,8a-tetramethyl-2H-1-benzopyrans (11) and (10). Diels–Alder addition of penta-1,3-diene to bromomesityl oxide, elimination of hydrogen bromide, and aldol condensation with acetaldehyde produced the hydroxy-ketone (1) already used in the synthesis of β-damascenone, reduction of which gave 1-(2,6,6-trimethylcyclohexa-1,3-dienyl)butane-1,3-diol (3). Cyclisation of this diol (3) with acid led to (±)-edulan II, isomerised to (±)-edulan I by further treatment with acid. N.m.r. spectrometry at 100 MHz, including use of double irradiation, INDOR, and lanthanide shifts, confirmed the structures of the edulans.

Spin echo double resonance: a novel method for detecting decoupling in Fourier transform nuclear magnetic resonance

It is shown that the combination of double irradiation and a simple two-pulse spin echo sequence is a powerful and sensitive method for detecting homonuclear decoupling in a complex spectrum.

Theory of line narrowing by double-frequency irradiation in NQR

It is shown that the standard time-dependent perturbation theory is inadequate to treat the problem of line narrowing by double-frequency irradiation in NQR. We show here that a semiclassical treatment which avoids the secular terms provides results in agreement with the radiation field quantization method, which is here extended for the first time to NQR problems. As an application, we consider a hypothetical 14N NQR double irradiation experiment and we determine the conditions which lead to line narrowing.

Studies Relating to Aziridine Antitumor Antibiotics. Part II. 13C and 1H Nuclear Magnetic Resonance Spectra of Mitomycin C and Structurally Related Streptonigrin

Double irradiation experiments in the 100 MHz n.m.r. spectrum of mitomycin C allowed determination of vicinal coupling constants which provide information on the conformation of the antibiotic in solution. The natural abundance 13C spectrum and comparison with selected model compounds allowed assignment of the carbon resonances of mitomycin C. The 13C chemical shifts of the quinone ring carbons in mitomycin C have a bearing on the proposed stabilization in vivo. Similar studies on the antitumor antibiotic streptonigrin bearing the common aminoquinone moiety gave indications of conjugative interactions similar to those established for mitomycin C.