Comparison of the electronic and steric structures of 1-vinyl-and 1-(prop-1-en-1-yl)pyrroles according to the <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR data

According to the ¹H and ¹³C NMR data, 1-isopropenylpyrroles are characterized by larger dihedral angles between the heteroring and exocyclic double bond planes, as compared to isostructural 1-vinylpyrroles, due to steric effect of the α-methyl group in the propenyl fragment. As a result, p-π conjugation with the propenyl group is weaker than with the vinyl group. The propenyl group in 1-isopropenylpyrrole having no other substituents in the heteroring is forced out from the heteroring plane, while the 1-vinylpyrrole molecule is planar. If substituents are present in positions 2 and 5 of the pyrrole ring, the propenyl group on the nitrogen atom becomes orthogonal with respect to the pyrrole ring plane, so that no p-π conjugation is possible. The steric structures of (E)-1-(prop-1-en-1-yl)pyrrole and (Z)-1-(prop-1-en-1-yl)pyrrole are different: the propenyl group in the former is turned relative to the heteroring plane, while the latter molecule is planar.     

Crystal structures of a family of layered coordination polymers containing divalent metal ions (Mn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) and the 3-amino 4-methyl benzoate ion

The syntheses and crystal structures of the layered coordination polymers M(C₈H₈NO₂)₂ [M = Mn (1), Co (2), Ni (3) and Zn (4)] are described. These isostructural compounds contain centrosymmetric trans-MN₂O₄ octahedra as parts of infinite sheets; the ligand bonds to three adjacent metal ions in μ³-N,O,O′ mode from both its carboxylate O atoms and its amine N atom. In each case, weak intra-sheet N–H?O and C–H?O hydrogen bonds may help to consolidate the structure. Crystal data: 1, C₁₆H₁₆MnN₂O₄, M _r = 355.25, monoclinic, P2₁/c (No. 14), a = 10.6534(2) Å, b = 4.3990(1) Å, c = 15.5733(5) Å, β = 95.1827(10)°, V = 726.85(3) ų, Z = 2, R(F) = 0.026, wR(F ²) = 0.067. 2, C₁₆H₁₆CoN₂O₄, M _r = 359.24, monoclinic, P2₁/c (No. 14), a = 10.6131(10) Å, b = 4.3374(4) Å, c = 15.3556(17) Å, β = 95.473(4)°, V = 703.65(12) ų, Z = 2, R(F) = 0.041, wR(F ²) = 0.091. 3, C₁₆H₁₆N₂NiO₄, M _r = 359.02, monoclinic, P2₁/c (No. 14), a = 10.6374(4) Å, b = 4.2964(2) Å, c = 15.2827(8) Å, β = 95.9744(14)°, V = 694.66(6) ų, Z = 2, R(F) = 0.028, wR(F ²) = 0.070. 4, C₁₆H₁₆N₂O₄Zn, M _r = 365.68, monoclinic, P2₁/c (No. 14), a = 10.6385(5) Å, b = 4.2967(3) Å, c = 15.2844(8) Å, β = 95.941(3)°, V = 694.89(7) ų, Z = 2, R(F) = 0.038, wR(F ²) = 0.107.     

Formation of mononuclear rhodium(III) sulfates: <Superscript>103</Superscript>Rh and <Superscript>17</Superscript>O NMR study

It was shown that the monomeric rhodium sulfate complexes [Rh(H₂O)₄(SO₄)]⁺, trans-[Rh(H₂O)₂(SO₄)₂]^?, cis-[Rh(H₂O)₂(SO₄)₂]^?, and [Rh(SO₄)₃]^3? were not predominant forms in aqueous solutions. The ¹⁰³Rh NMR chemical shifts of the complexes were assigned, and the conditions for their formation in solutions, concentration parameters, and acidity at which the fraction of the monomers was maximal were determined. The constants of formation of the complexes and ion pair (IP) were estimated: K _IP = 8 ± 3.5, K ₁ ≈ 8, K _2trans ≈ 1, K _2cis ≈ 1, and K ₃ ≈ 2.     

Synthesis and X-ray diffraction study of ferrites ErM<Superscript>I</Superscript>Fe<Subscript>2</Subscript>O<Subscript>5</Subscript> (M<Superscript>I</Superscript> = Li,Na, K,Cs)

Ferrites of composition ErM^IFe₂O₅ (M^I = Li, Na, K, Cs) were synthesized by a solid-phase method. The structure of the ferrites was for the first time studied by X-ray powder diffraction. Crystal systems, unit cell parameters, and X-ray and pycnometric densities were determined. For ErLiFe₂O₅, a = 10.510 Å, c = 14.270 Å, V°= 1616.16 ų, Z = 16, V _subcell ^° = 101.01 ų, ρ_x = 6.01 g/cm³, ρ_pyc = 5.97 ± 0.04 g/cm³; for ErNaFe₂O₅, a = 10.519 Å, c = 15.510 Å, V° = 1759.56 ų, Z = 16, V _subcell ^° = 109.90 ų, ρ_x = 5.77 g/cm³, ρ_pyc = 5.72 ± 0.08 g/cm³; for ErKFe₂O₅, a = 11.050 Å, c = 15.480 Å, V° = 1937.33 ų, Z = 16, V _subcell ^° = 121.08 ų, ρ_x = 5.46 g/cm³, ρ_pyc = 5.41 ± 0.04 g/cm³; and for ErCsFe₂O₅, a = 10.78 Å, c = 16.01 Å, V° = 1905.37 ų, Z = 16, V _subcell ^° = 119.09 ų, ρ_x = 6.86 g/cm³, ρ_pyc = 6.61 ± 0.01 g/cm³.     

Synthesis,crystal structures,and antibacterial activities of Schiff base zinc(II) complexes [Zn(L<Superscript>1</Superscript>)<Subscript>2</Subscript>] and [Zn(L<Superscript>2</Superscript>)<Subscript>2</Subscript>]

The reaction of cyclopentylamine with 2-hydroxy-1-naphthaldehyde and 5-nitrosalicylaldehyde, respectively, in methanol affords two new Schiff bases, 1-(cyclopentyliminomethyl)naphthalen-2-ol (HL¹) and 4-nitro-2-(cyclopentyliminomethyl)phenol (HL²). Two new zinc(II) complexes, [Zn(L¹)₂] (I) and [Zn(L²)₂] (II), derived from the Schiff bases, have been prepared and characterized by single-crystal X-ray diffraction, FT-IR, and elemental analysis. Complex I crystallizes in the monoclinic space group P2₁/c with a = 17.834(4), b = 14.738(3), c = 9.868(2) Å, β = 91.20(3)°, V = 2593.1(9) ų, Z = 4. Complex II crystallizes in the triclinic space group P \(\bar 1\) with a = 10.206(1), b = 10.502(1), c = 12.554(1) Å, α = 66.771(2)°, β = 78.133(2)°, γ = 76.292(2)°, V = 1191.8(1) ų, Z = 2. The Zn atom in each complex is coordinated by two N and two O atoms from two Schiff base ligands, forming a tetrahedral geometry. The Schiff bases and the complexes were assayed for antibacterial activities.     

Synthesis and crystal structure of EnH<Superscript>2</Superscript>[IrCl<Superscript>6</Superscript>]

The preparation of EnH²[IrCl⁶] is described. Crystal data for C₂H₁₀Cl₆IrN₂ are: a = 6.8972(11) Å, b = 6.9435(16) Å, c = 7.3354(11) Å; α = 88.269(3)°, β = 65.495(2)°, γ = 60.305(2)°, V = 270.76(9) ų, space group P1, Z = 1, d_calc = 2.864 g/cm³. Crystal chemical analysis of the general motif of the structure was performed by the translation sublattice identification technique. It has been found that complex anions [IrCl₆]^2? follow the nodes of a rather regular rhombohedral subcell with the parameters a_c = 7.1 Å, α_c = 64°.     

Crystalline cadmium dialkyl phosphorodithioate complexes: Synthesis and structural organization as probed by multinuclear <Superscript>13</Superscript>C, <Superscript>31</Superscript>P,and <Superscript>113</Superscript>Cd CP/MAS NMR and single-crystal X-ray diffraction

The cadmium O,O′-dethyl (I) and O,O′-di-sec-butyl phosphorodithioate (II) complexes have been synthesized and characterized in detail by ¹³C, ³¹P, and ¹¹³Cd CP/MAS NMR. X-ray crystallography shows that complex II has a binuclear molecular structure [Cd₂{S₂P(O-s-C₄H₉)₂}₄]. For ³¹P and ¹¹³Cd NMR signals, the chemical shift anisotropy δ_aniso and the asymmetry parameter η have been calculated. The ³¹P NMR signals are assigned to the terminal and bridging ligands in the complexes.     

Reaction of transsilylation of <Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="Italic">N</Emphasis>-trimethylsilylacetamide with silanes ClCH<Subscript>2</Subscript>SiR<Superscript>1</Superscript>R<Superscript>2</Superscript>Cl

The reaction of N-methyl-N-trimethylsilylacetamide with silanes ClCH₂SiR¹R²Cl (R¹, R² = H, Me; H, Ph; Ph₂) leads to the formation of (O→Si) chelate compounds with pentacoordinate silicon: N-[chloro(methyl)-silyl]methyl-, N-[chloro(phenyl)silyl]methyl-, and N-[chloro(diphenyl)silyl]methyl-N-methylacetamides. From the data of multinuclear NMR spectroscopy, the intermediates of the reaction of N-methyl-N-trimethylsilylacetamide with ClCH₂SiPhHCl and ClCH₂SiPh²Cl are stable in CDCl₃ solution at room temperature during several days and slowly rearrange to the final (O–Si) chelate compounds.     

Intrinsic ratios of glucose,fructose, glycerol and ethanol <Superscript>13</Superscript>C/<Superscript>12</Superscript>C isotopic ratio determined by HPLC-<Emphasis Type="Italic">co</Emphasis>-IRMS: toward determining constants for wine authentication

High-performance liquid chromatography linked to isotope ratio mass spectrometry (HPLC-co-IRMS) via a Liquiface© interface has been used to simultaneously determine ¹³C isotope ratios of glucose (G), fructose (F), glycerol (Gly) and ethanol (Eth) in sweet and semi-sweet wines. The data has been used the study of wine authenticity. For this purpose, 20 authentic wines from various French production areas and various vintages have been analyzed after dilution in pure water from 20 to 200 times according to sugar content. If the ¹³C isotope ratios vary according to the production area and the vintage, it appears that internal ratios of ¹³C isotope ratios \(\left( {R_{^{13} C} } \right)\) of the four compounds studied can be considered as a constant. Thus, ratios of isotope ratios are found to be 1.00?±?0.04 and 1.02?±?0.08 for \(R_{^{13} C_{G/F} }\) and \(R_{^{13} C_{Gly/Eth} }\), respectively. Moreover, \(R_{^{13} C_{Eth/Sugar} }\) is found to be 1.15?±?0.10 and 1.16?±?0.08 for \(R_{^{13} C_{Gly/Sugar} }\). Additions of glucose, fructose and glycerol to a reference wine show a variation of the \(R_{^{13} C}\) value for a single product addition as low as 2.5 g/L^?1. Eighteen commercial wines and 17 concentrated musts have been analyzed. Three wine samples are suspicious as the \(R_{^{13} C}\) values are out of range indicating a sweetening treatment. Moreover, concentrated must analysis shows that ¹³C isotope ratio can be also used directly to determine the authenticity of the matrix.

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Figure HPLC-co-IRMS chromatogram of a diluted sweet wine.

     

Ca<Superscript>2+</Superscript> and Mg<Superscript>2+</Superscript> incorporated barium hexaferrites: structural and magnetic properties

BaM hexaferrites substituted with both Ca²⁺ and Mg²⁺ ions, namely, Ba_1-2×Ca_xMg_xFe₁₂O₁₉ (0.0?≤?x?≤?0.1), synthesized during a sol–gel auto-combustion route. The hexaferrite phase and morphology of all samples were investigated using X-ray powder diffraction, a field emission scanning electron microscope, a high-resolution transmission microscope, and Fourier transform infrared spectroscopy. In addition, an M-type hexagonal structure was confirmed using XRD for all samples. FE-SEM and TEM revealed the shape of the hexagonal plate. Measurements of the magnetization versus the field M(H) of Ba_1-2×Ca_xMg_xFe₁₂O₁₉ (0.0?≤?x?≤?0.1) nanohexaferrites were conducted at 300 and 10?K. A hard-ferrimagnetic behavior at both 300 and 10?K was noted for the different products produced. The squareness ratio indicates the uniaxial anisotropy for various products. The deduced values of saturation magnetization (M_s) in all substituted samples are higher than in the pristine sample (x?=?0). The Ba_0.96Ca_0.02Mg_0.02Fe₁₂O₁₉ nanosized hexaferrite showed the highest values of M_s, remanence M_r, magneton number (n_B), and magnetocrystalline anisotropy constant (K_eff). In contrast, the values of the coercive field (H_c) and intrinsic coercivity (H_ci) diminish with the increase in the amount of the substituted Ca and Mg elements.

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Synthesis,scope, <Superscript>1</Superscript>H and <Superscript>13</Superscript>C spectral assignments of isomeric dibenzofuran carboxaldehydes

Two isomeric dibenzofuran carboxaldehydes, namely 2-methoxydibenzo[b,d]furan-1-carbaldehyde (4) and 2-methoxydibenzo[b,d]furan-3-carbaldehyde (5), were synthesized. Formylation of 2-methoxydibenzo[b,d]furan (3) with α,α-dichloromethyl methyl ether and tin(IV) chloride gave a mixture of aldehydes 4 and 5 in 95 % yield and in a 35:65 ratio. Their ¹H and ¹³C NMR spectral signals were not sufficiently resolved in CDCl₃ solution to achieve their complete assignment, but this was possible in DMSO-d ₆ with the help of 2D-NMR techniques: NOESY for ¹H–¹H interactions and HSQC and HMQC experiments for ¹H–¹³C correlations. These aldehydes were used in the synthesis of novel β-phenylethylamines and NBOMe derivatives, which are undergoing biological evaluation.     

Preparation of stereochemically pure <Emphasis Type="Italic">E</Emphasis>- and <Emphasis Type="Italic">Z</Emphasis>-alkenoic acids and their methyl esters from bicyclo[<Emphasis Type="Italic">n</Emphasis>.1.0]alkan-1-ols. Application in the synthesis of insect pheromones

Oxidative cleavage of exo- and endo-alkyl- and hydroxyalkyl-substituted bicyclo[n.1.0]alkan-1-ols with (diacetoxy-λ³-iodanyl)benzene gave the corresponding methyl alkenoates exclusively with E or Z configuration of the double bond. This reaction was used as the key stage in the syntheses of stereoisomerically pure components of pest insect pheromones: (E)-dodec-9-en-1-yl acetate (European pine shoot moth Rhyacionia buoliana), (Z)-tetradec-11-en-1-yl acetate (European oak leafroller Tortrix viridana), and (3E,8Z,11Z)-tetradeca-3,8,11-trien-1-yl acetate (tomato leafminer Tuta absoluta).     

Synthesis and crystal structure of (<Emphasis Type="Italic">o</Emphasis>-Diaminobenzene)<Subscript>2</Subscript> Zn(OAc)<Subscript>2</Subscript>

The treatment of o-diaminobenzene with Zn ( OAc )₂ · 2H₂O in alcohol results in the formation of mononuclear bis(o-diaminobenzene)diacetate Zinc, Zn[C₈H₁₁N₂O₂]₂. Its structure was determined by X-ray diffraction analysis. The complex is also characterized by elemental analysis, ¹H NMR and IR. The crystal is monoclinic space group C2, parameters: a = 16.297(5), b = 4.775(3), c = 11.664(5) Å, β = 97.646(5)°, λ = 1.54184 Å, V = 899.6(7) ų, Z = 2, ρ _c = 1.476 g/cm³, M _r = 399.75, F(000) = 416.0, R ₁ = 0.0594, wR ₂ = 0.1439 for 995 observed reflections with I > 2σ(I).     

Crystal structure and <Superscript>121,123</Superscript>Sb NQR parameters of ammonium tridecafluorotetraantimonate(III) NH<Subscript>4</Subscript>Sb<Subscript>4</Subscript>F<Subscript>13</Subscript>

(NH₄)Sb₄F₁₃ crystals (I) are synthesized and their crystal structure (tetragonal crystal system: a = 9.6431(2) Å, c = 6.5503(2) Å, V = 609.11(3) ų, Z = 2, d _calc = 4.100 g/cm³, F(000) = 664, space group I4?) is determined. The main structural units of I are tetranuclear anionic [Sb₄F₁₃]^? complexes and [NH₄]⁺ cations. The anionic complexes are built of four SbF₃ groups linked together by tetrahedral bridging fluorine atom. At room temperature the (NH₄)Sb₄F₁₃ crystals are isostructural to previously studied МSb₄F₁₃ (М = K, Rb, Cs, and Tl). The study of ^121,123Sb NQR spectra of compound I is performed in a range of 77-370 K, which shows that when the temperature decreases (<250 K) the substance exhibits piezoelectric properties, as do other compounds of this group, but with a violation of their isostructurality.     

High-field solid-state <Superscript>35</Superscript>Cl NMR in selenium(IV) and tellurium(IV) hexachlorides

We report solid-state ³⁵Cl NMR spectra in three hexachlorides, (NH₄)₂SeCl₆, (NH₄)₂TeCl₆ and Rb₂TeCl₆. The C_Q(³⁵Cl) quadrupole coupling constants in the three compounds were found to be 41.4±0.1 MHz, 30.3±0.1 MHz and 30.3±0.1 MHz, respectively, some of the largest C_Q(³⁵Cl) quadrupole coupling constants ever measured in polycrystalline powdered solids directly via ³⁵Cl NMR spectroscopy. The ³⁵Cl EFG tensors are axial in all three cases reflecting the C_4v point group symmetry of the chlorine sites. ³⁵Cl NMR experiments in these compounds were only made possible by employing the WURST-QCPMG pulse sequence in the ultrahigh magnetic field of 21.1 T. ³⁵Cl NMR results agree with the earlier reported ³⁵Cl NQR values and with the complementary plane-wave DFT calculations. The origin of the very large C_Q(³⁵Cl) quadrupole coupling constants in these and other main-group chlorides lies in the covalent-type chlorine bonding. The ionic bonding in the ionic chlorides results in significantly reduced C_Q(³⁵Cl) values as illustrated with triphenyltellurium chloride Ph₃TeCl. The high sensitivity of ³⁵Cl NMR to the chlorine coordination environment is demonstrated using tetrachlorohydroxotellurate hydrate K[TeCl₄(OH)]?0.5H₂O as an example. ¹²⁵Te MAS NMR experiments were performed for tellurium compounds to support ³⁵Cl NMR findings.     

Rh<Subscript>2</Subscript>(OAc)<Subscript>4</Subscript>-catalyzed reaction of 2-(2-carbonylvinyl)-3-phenyl-2<Emphasis Type="Italic">H</Emphasis>-azirines with diazo esters

Rh₂(OAc)₄-catalyzed reaction of 2-(2-carbonylvinyl)-3-phenyl-2H-azirines with diazo esters proceeds through an intermediate generation of azirinium ylide suffering a nonstereoselective ring opening to form (3Z)- and (3E)-2-azahexa-1,3,5-trienes. The former depending on configuration of the C ⁵ =C ⁶ bond may undergo cyclization either in derivative of 2,3-dihydropyridine, or in pyrrolium ylide that isomerizes into a derivative of 1H-pyrrole. According to DFT calculation, the preferred formation of pyrroles at increasing volume of Z-substituent at the atom C ⁶ and of substituents at the atom C ¹ of 2-azahexatriene occurs due to the destabilization of more sterically loaded transition states of 1,6-cyclization.     

Difference of Electron Capture and Transfer Dissociation Mass Spectrometry on Ni<Superscript>2+</Superscript>-, Cu<Superscript>2+</Superscript>-, and Zn<Superscript>2+</Superscript>-Polyhistidine Complexes in the Absence of Remote Protons

Electron capture dissociation (ECD) and electron transfer dissociation (ETD) in metal-peptide complexes are dependent on the metal cation in the complex. The divalent transition metals Ni²⁺, Cu²⁺, and Zn²⁺ were used as charge carriers to produce metal-polyhistidine complexes in the absence of remote protons, since these metal cations strongly bind to neutral histidine residues in peptides. In the case of the ECD and ETD of Cu²⁺-polyhistidine complexes, the metal cation in the complex was reduced and the recombination energy was redistributed throughout the peptide to lead a zwitterionic peptide form having a protonated histidine residue and a deprotonated amide nitrogen. The zwitterion then underwent peptide bond cleavage, producing a and b fragment ions. In contrast, ECD and ETD induced different fragmentation processes in Zn²⁺-polyhistidine complexes. Although the N–C_α bond in the Zn²⁺-polyhistidine complex was cleaved by ETD, ECD of Zn²⁺-polyhistidine induced peptide bond cleavage accompanied with hydrogen atom release. The different fragmentation modes by ECD and ETD originated from the different electronic states of the charge-reduced complexes resulting from these processes. The details of the fragmentation processes were investigated by density functional theory.

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Graphical Abstract ?

     

Imidazolium-based ionic liquid derivative/Cu<Superscript>II</Superscript> complexes as efficient catalysts of the lucigenin chemiluminescence system and its application to H<Subscript>2</Subscript>O<Subscript>2</Subscript> and glucose detection

The effects of six synthetic imidazolium-based ionic liquids (ILs) on the Cu^II-catalyzed chemiluminescence of lucigenin (Luc-CL) in the pH range 6.0–11 were investigated. Preliminary experiments found that the CL emission was strongly enhanced or inhibited in the presence of the ILs. The degree of enhancement or inhibition of the CL intensity in the presence of each IL was related to the molecular structure of the IL, the medium used, and the pH. The maximum enhancement of the CL intensity was observed at pH 9.0 (amplification factor?=?443). This decrease in the pH at which maximum CL enhancement occurred and the substantial signal amplification of the Luc-CL may be related to a strong interaction between Cu^II and the imidazolium ring of superior ILs at this pH. Additionally, the formation of IL microdomains in semi-aqueous media permitted more solubility of the product yielded by the Luc-CL reaction (N-methylacridone), which could increase the CL intensity. To obtain consistent data on the catalytic efficiency of Cu^II in the presence of various ILs as well as the corresponding CL emission intensities, fluorescence quantum yields (Φ _F) of lucigenin were measured under the same conditions. Comparison of the data pointed to the mechanism that controls the properties of Luc-CL in the presence of the Cu^II/IL complexes. Based on the catalytic effect of the Cu^II/IL complex and the measurement of the enzymatically generated H₂O₂, a novel, simple, and sensitive CL method for determining glucose with a detection limit (LoD) of 6.5 μM was developed. Moreover, this method was satisfactorily applied to the determination of glucose in human serum and urine samples.

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Graphical Abstract The lucigenin chemiluminescence assay for H₂O₂ and glucose using imidazolium–based ionic liquid derivatives/Cu^II complexes as efficient catalysts at pH 9.0

     

Riboflavin synthase of <Emphasis Type="Italic">Schizosaccharomyces pombe.</Emphasis> Protein dynamics revealed by <Superscript>19</Superscript>F NMR protein perturbation experiments

Background

Riboflavin synthase catalyzes the transformation of 6,7-dimethyl-8-ribityllumazine into riboflavin in the last step of the riboflavin biosynthetic pathway. Gram-negative bacteria and certain yeasts are unable to incorporate riboflavin from the environment and are therefore absolutely dependent on endogenous synthesis of the vitamin. Riboflavin synthase is therefore a potential target for the development of antiinfective drugs.

Results

A cDNA sequence from Schizosaccharomyces pombe comprising a hypothetical open reading frame with similarity to riboflavin synthase of Escherichia coli was expressed in a recombinant E. coli strain. The recombinant protein is a homotrimer of 23 kDa subunits as shown by sedimentation equilibrium centrifugation. The protein sediments at an apparent velocity of 4.1 S at 20°C. The amino acid sequence is characterized by internal sequence similarity indicating two similar folding domains per subunit. The enzyme catalyzes the formation of riboflavin from 6,7-dimethyl-8-ribityllumazine at a rate of 158 nmol mg^-1 min^-1 with an apparent K_M of 5.7 microM. ¹⁹F NMR protein perturbation experiments using fluorine-substituted intermediate analogs show multiple signals indicating that a given ligand can be bound in at least 4 different states. ¹⁹F NMR signals of enzyme-bound intermediate analogs were assigned to ligands bound by the N-terminal respectively C-terminal folding domain on basis of NMR studies with mutant proteins.

Conclusion

Riboflavin synthase of Schizosaccharomyces pombe is a trimer of identical 23-kDa subunits. The primary structure is characterized by considerable similarity of the C-terminal and N-terminal parts. Riboflavin synthase catalyzes a mechanistically complex dismutation of 6,7-dimethyl-8-ribityllumazine affording riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione. The ¹⁹F NMR data suggest large scale dynamic mobility in the trimeric protein which may play an important role in the reaction mechanism.