Diagnostic organometallic and metallodendritic materials for SO2 gas detection: reversible binding of sulfur dioxide to arylplatinum(II) complexes

A series of square-planar platinum(II) complexes of the N,C,N'-terdentate-coordinating monoanionic "pincer" ligand, [PtX(4-E-2,6-[CH2NRR']2-C6H2](X=Cl, Br, I, tolyl; R, R'=Et, Me; E=H, OH, OSiMe2tBu) has been prepared. In the presence of sulfur dioxide, these complexes spontaneously adsorb this gas to form penta-coordinated adducts. Solid-state crystal-structure analyses of the SO2 adducts 8c (X=I, R=R=Me, E=OSiMe2tBu) and 11 (X=Cl, R=R'=Me, E=OH) show a square-pyramidal geometry around the metal center with SO2 in the apical position. Most interestingly. the adduct 11 forms similar Pt-Cl... H-O hydrogen-bonded alpha-type networks as the corresponding SO2-free complex 5. The conservation of the supramolecular information (hydrogen-bonded self-assembly) throughout a reaction (SO2 adsorption) is unprecedented in crystal engineering. Adduct formation in the solid state or in solution is fast and reversible and is indicated by a characteristic color change of the material from colorless to bright orange. Since facile methods have been developed to remove SO2 from the adducts and to regenerate the square-planar starting complexes, these complexes fulfill several essential prerequisites of sensor materials for repeated diagnostic SO2 detection. The platinum sensors have been found to be highly selective for sulfur dioxide and particularly sensitive for submilimolar to molar gas quantities. Their response capacity is tuneable by electronic and steric modifications of the ligand array by introduction of, for example, different substituents on the nitrogen donors. The periphery of dendrimers is shown to be an appropriate macromolecular support for anchoring the detection-active sites, thus allowing full recovery of the sensor materials for repeated use. By using this concept, metallo-dendrimers 3 and 15 have been prepared. Owing to the dendritic connectivity, these sensors are suitable for repetitive qualitative and quantitative detection of small amounts of SO2.

New antitumor-active azole-bridged dinuclear platinum(II) complexes: synthesis, characterization, crystal structures, and cytotoxic studies

Three new derivatives of the cytotoxic azole-bridged dinuclear platinum(II) complex [(cis-Pt(NH3)2)2(mu-OH)(mu-pz)][NO3]2 (1) have been prepared and structurally characterized. Their formulas are [(cis-Pt(NH3)2)2(mu-OH)(mu-1,2,3-ta)][NO3]2 (2) (1,2,3-ta = 1,2,3-triazolate), [(Pt(R,R-dach))(mu-OH)(mu-pz)(Pt(S,S- dach))][NO3]2 (3) (dach = 1,2-diaminocyclohexane, pz = pyrazolate), and [(Pt(R,R-dach))(mu-1,2,3- ta)2(Pt(S,S-dach))][NO3]2 (4). The compounds were characterized by 1H, 13C, and 195Pt NMR spectroscopy, and elemental analysis, and their crystal structures were determined. Relevant data for 2: triclinic, space group P1, a = 8.5225(15) A, b = 9.1977(18) A, c = 9.9771(7) A, alpha = 66.988(10) degrees, beta = 75.423(9) degrees, gamma = 67.321(13) degrees, Z = 2. 3: orthorhombic, space group Pca2(1), a = 17.7653(3) A, b = 12.4076(3) A, c = 10.7091(3) A, Z = 4. 4: orthorhombic, space group Pbca, a = 13.8944(1) A, b = 17.8668(1) A, c = 20.7647(2) A, Z = 8. In the crystal structures of 2, and 3, the intramolecular distances between the two Pt atoms are 3.4411(6) and 3.4873(5) A, and the dihedral angles between the platinum coordination planes are 14.1(3) and 9.3(4) degrees, respectively. In 2, an intramolecular hydrogen bond is observed between N9 of the ammine ligand and the noncoordinated nitrogen atom (N3) of the triazole ring (N9...N3: 2.962(10) A). 4 has a boat-form structure, and the two coordination planes cross at 83.64(10) degrees. A cytotoxicity assay of these dinuclear platinum(II) compounds on human tumor cell lines was performed. In most of the cell lines, 1 and 2 showed much higher cytotoxicity than those of cisplatin. On the other hand, 3 was found to be moderately active, and 4 was found only marginally cytotoxic. Implications of these findings are discussed in the context of a structure-activity relationship.

Structure of spheroidene in the photosynthetic reaction center from Y Rhodobacter sphaeroides

The structure of the reaction center of Y Rhodobacter sphaeroides has been solved at 3 A resolution, using the atomic coordinates of the reaction center from the carotenoidless mutant R26 Rhodobacter sphaeroides. The structure has been refined by a stimulated annealing with the computer program X-PLOR, leading to a crystallographic R factor of 0.22 using reflections between 8 and 3 A. The spheroidene molecule which is bound to the Y reaction center has been fitted in the electron density map as a 15-cis isomer with a highly asymmetric structure. The cis-bond is located at proximity from ring 1 of the accessory bacteriochlorophyll on the inactive M side. The nature of the cis-bond was confirmed by resonance Raman spectra obtained from Y reaction center crystals. The structure of spheroidene in Y reaction center is compared to that proposed for 1,2-dihydroneurosporene in Rhodopseudomonas viridis reaction center crystals.

Randomized phase III study of high-dose fluorouracil given as a weekly 24-hour infusion with or without leucovorin versus bolus fluorouracil plus leucovorin in advanced colorectal cancer: European organization of Research and Treatment of Cancer Gastrointestinal Group Study 40952

PURPOSE

This trial was conducted to determine whether high-dose fluorouracil (FU) given as a weekly 24-hour infusion is more active than bolus FU + leucovorin (LV), and whether high-dose infusional FU can be modulated by LV.

PATIENTS AND METHODS

A total of 497 patients with previously untreated metastatic colorectal cancer were randomly assigned to receive bolus FU 425 mg/m2 intravenously + LV 20 mg/m2 on days 1 to 5 and repeated on day 28 (FU + LV), or FU 2600 mg/m2 as a 24-hour infusion alone (FU24h) or in combination with 500 mg/m2 LV (FU24h + LV)-all given weekly x6 followed by a 2-week rest period. Survival was the major study end point.

RESULTS

With a median follow-up of more than 3 years, survival did not differ among the treatment groups (median FU + LV, 11.1 months [95% CI, 10.2 to 15.0 months]; FU24h, 13.0 months [95% CI, 10.4 to 15.4 months]; FU24h + LV, 13.7 months [95% CI, 12.0 to 16.4 months]; P =.724). Progression-free survival (PFS) was significantly longer for FU24h + LV (median FU + LV, 4.0 months [95% CI, 3.4 to 4.9]; FU24h, 4.1 months [95% CI, 3.4 to 5.0]; FU24h + LV 5.6 months [95% CI, 4.4 to 6.7]; P =.029). The response rates in the subgroup of patients with measurable disease were 12%, 10%, and 17% for FU + LV, FU24h, and FU24h + LV, respectively (not significant). Occurrence of grade 3 and 4 diarrhea was higher in the FU24h + LV arm (22%) compared with the FU24h (6%) or FU + LV (9%) arms; however, stomatitis (11% in FU + LV v 3% in FU24h v 5% in FU24h + LV arms) and hematologic toxicity were higher in the bolus FU + LV arm. Global quality of life did not differ within the three arms.

CONCLUSION

Neither FU24h + LV nor FU24h prolong survival, relative to bolus FU + LV. Leucovorin increases PFS if added to FU24h, but increases toxicity.

Transcriptional repression by the insulator protein CTCF involves histone deacetylases

The highly conserved zinc-finger protein, CTCF, is a candidate tumor suppressor protein that binds to highly divergent DNA sequences. CTCF has been connected to multiple functions in chromatin organization and gene regulation including chromatin insulator activity and transcriptional enhancement and silencing. Here we show that CTCF harbors several autonomous repression domains. One of these domains, the zinc-finger cluster, silences transcription in all cell types tested and binds directly to the co-repressor SIN3A. Two distinct regions of SIN3A, the PAH3 domain and the extreme C-terminal region, bind independently to this zinc-finger cluster. Analysis of nuclear extract from HeLa cells revealed that CTCF is also capable of retaining functional histone deacetylase activity. Furthermore, the ability of regions of CTCF to retain deacetylase activity correlates with the ability to bind to SIN3A and to repress gene activity. We suggest that CTCF driven repression is mediated in part by the recruitment of histone deacetylase activity by SIN3A.

Negative protein 1, which is required for function of the chicken lysozyme gene silencer in conjunction with hormone receptors, is identical to the multivalent zinc finger repressor CTCF

The transcriptional repressor negative protein 1 (NeP1) binds specifically to the F1 element of the chicken lysozyme gene silencer and mediates synergistic repression by v-ERBA, thyroid hormone receptor, or retinoic acid receptor. Another protein, CCCTC-binding factor (CTCF), specifically binds to 50-bp-long sequences that contain repetitive CCCTC elements in the vicinity of vertebrate c-myc genes. Previously cloned chicken, mouse, and human CTCF cDNAs encode a highly conserved 11-Zn-finger protein. Here, NeP1 was purified and DNA bases critical for NeP1-F1 interaction were determined. NeP1 is found to bind a 50-bp stretch of nucleotides without any obvious sequence similarity to known CTCF binding sequences. Despite this remarkable difference, these two proteins are identical. They have the same molecular weight, and NeP1 contains peptide sequences which are identical to sequences in CTCF. Moreover, NeP1 and CTCF specifically recognize each other's binding DNA sequence and induce identical conformational alterations in the F1 DNA. Therefore, we propose to replace the name NeP1 with CTCF. To analyze the puzzling sequence divergence in CTCF binding sites, we studied the DNA binding of 12 CTCF deletions with serially truncated Zn fingers. While fingers 4 to 11 are indispensable for CTCF binding to the human c-myc P2 promoter site A, a completely different combination of fingers, namely, 1 to 8 or 5 to 11, was sufficient to bind the lysozyme silencer site F1. Thus, CTCF is a true multivalent factor with multiple repressive functions and multiple sequence specificities.

Vascularized bone graft from the iliac crest for the treatment of nonunion of the proximal part of the scaphoid with an avascular fragment

BACKGROUND

It was hypothesized that nonunion of the proximal third of the scaphoid associated with avascular necrosis could be treated successfully with a free vascularized bone graft obtained from the iliac crest.

METHODS

Fifteen patients who had a nonunion of the proximal part of the scaphoid that had been present for an average of two years and three months (range, nine months to seven years) were managed with use of a free vascularized bone graft obtained from the iliac crest. Avascularity of the scaphoid, as assessed on preoperative radiographs, was characterized by loss of trabecular structure, collapse of subchondral bone, and formation of bone cysts. The results of the procedure were assessed in terms of osseous union, pain, active motion of the wrist, and osteoarthritis. Postoperatively, vascularity of the scaphoid was evaluated with use of magnetic resonance imaging and color Doppler ultrasonography. The average duration of follow-up was six years and one month (range, two years and one month to eight years and one month).

RESULTS

Preoperatively, one patient had had pain with any movement of the wrist and fourteen had had pain after strenuous manual labor or sports activity. The average pain score, derived with use of a 10-point visual analog scale, was 2.4 points (range, 1.0 to 6.7 points). Postoperatively, union was achieved in twelve patients; six were pain-free, and six had occasional pain during strenuous manual labor or sports activity, or both. The average pain score for these twelve patients was 1.1 points (range, 0.0 to 4.2 points) on the visual analog scale. Preoperatively, osteoarthritis was limited to the region between the radial styloid process and the distal part of the scaphoid in fourteen patients and to the radioscaphoid region in one patient. Postoperatively, the degree of osteoarthritis remained unchanged in seven of the twelve patients who had union and progressed to the radioscaphoid region in five. Vascularity, as seen on the imaging studies, was restored in all twelve patients who had union. The nonunion persisted in three patients, all of whom had progressive osteoarthritis leading to carpal collapse.

CONCLUSIONS

The index procedure was successful in twelve of the fifteen patients who had a symptomatic nonunion of the proximal part of the scaphoid associated with avascular necrosis and osteoarthritis that was limited to the radioscaphoid joint.

Low-frequency vibrations in resonance Raman spectra of horse heart myoglobin. Iron-ligand and iron-nitrogen vibrational modes

The low-frequency regions (150--700 cm-1) of resonance Raman (RR) spectra of various complexes of oxidized and reduced horse heart myoglobin were examined by use of 441.6-nm excitation. In this frequency range, RR spectra show 10 bands common to all myoglobin derivatives (numbered here for convenience from I to X). Relative intensities of bands IV, V, and X constitute good indicators of the doming state of the heme and, consequently, of the spin state of the iron atom. An additional band is present for several complexes (fluorometmyoglobin, hydroxymetmyoglobin, azidometmyoglobin, and oxymyoglobin). Isotopic substitutions on the exogenous ligands and of the iron atom (56Fe leads to 54Fe) allow us to assign these additional lines to the stretching vibrations of the Fe-sixth ligand bond. Similarly, bands II are assigned to stretching vibrations of the Fe-N-(pyrrole) bonds. An assignment of bands VI to stretching vibrations of the Fe-Nepsilon(proximal histidine) bonds is also proposed. Mechanisms for the resonance enhancement of the main low-frequency bands are discussed on the basis of the excitation profiles and of the dispersion curves for depolarization ratios obtained for fluorometmyoglobin and hydroxymetmyoglobin.

Fixation of nondisplaced scaphoid fractures: making treatment cost effective. Prospective controlled trial

INTRODUCTION

Nondisplaced scaphoid waist fractures treated with prolonged plaster immobilisation often lead in transient joint stiffness and to a delay in return to sport and work activity. The long time off work increases the work off compensation costs. Internal fixation of scaphoid fractures has resulted in a shorter time to union and to return to work and sports. This prospective study compares cast immobilisation with screw fixation and the direct cost with indirect cost of conservative and minimally invasive treatment of undisplaced scaphoid fractures.

MATERIALS AND METHODS

Forty-seven patients with an acute nondisplaced waist fracture of the scaphoid were allocated into either cast immobilisation or internal screw fixation for this study. Cost data concerning the groups of nonoperated and operated patients were analysed. Range of wrist motion, grip strength, DASH-score, time to fracture union, return to work time and the needed physiotherapy at the final follow-up at 6 months were evaluated.

RESULTS

Twenty-one patients were included in the group of screw fixation and 23 patients were included in the group of cast immobilisation. At final follow-up there was no significant difference in the range of motion of the wrist or in grip strength. The operatively treated group had a better mean DASH-score than the conservative group. Fracture union was seen in the screw fixation group at a mean of 43 days and in the cast immobilisation group at a mean of 74 days (P < 0.5). The average time of return to work was 8 days for patients who had an internal screw fixation, while those treated with a cast returned to work at a mean of 55 days (P < 0.5). In total the internal fixation of undisplaced scaphoid fractures is less expensive than conservative treatment.

CONCLUSION

Internal screw fixation of nondisplaced scaphoid fractures had a shorter time to bony union and the patients returned earlier to work compared with cast immobilisation. Although it is assumed that operative treatment is more expensive, in this study the cost was not found to be higher.

On the state of carotenoids bound to reaction centers of photosynthetic bacteria: a resonance Raman study

The carotenoids bound to reaction centers of wild, Ga and GIC strains of Rhodopseudomonas spheroides, of Rhodospirrillum rubrum, strain S1 and of Rhodopseudomonas viridis, yield very similar, but unusual resonance Raman spectra. Through a comparison with resonance Raman spectra of 15,15'-cis-beta-carotene, these carotenoids are shown to assume cis conformations, while the corresponding chromatophores contain all-trans forms only. These cis conformations likely are identical for all the carotenoids studied. They remain unaffected by variations of temperature from 20 to 300 K as well as by the redox state of P-870. They are unstable, being rapidly isomerised towards the all-trans forms when extracted from the reaction centers. The possible nature of these conformers is discussed on the basis of their electronic and vibrational spectra.

Method for large scale isolation, culture and cryopreservation of human monocytes suitable for chemotaxis, cellular adhesion assays, macrophage and dendritic cell differentiation

This paper presents an improved method of isolating, culturing and cryopreserving human monocytes in large quantity with high purity using standard laboratory centrifuges. Monocytes were isolated from 300 to 360 ml of heparinized human blood using a Double Density technique employing Ficoll Isopaque and 46% iso-osmotic Percoll. Yields of monocytes ranged from 75 to 205 million (from 300 to 360 ml of blood) with an average purity of 90.6%. The ability of fresh or frozen monocytes to adhere to endothelial cells in the presence of oxidized L-alpha-1-palmitoyl-2-arachidonosyl-sn-glycero-3-phosphocholine (oxPAPC) or lipopolysaccharide (LPS) did not differ and no significant difference in response to the chemotactic stimulant N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) was observed. We define a useful method for the culture and differentiation of fresh or frozen monocytes isolated by this method, into macrophages as judged by morphology, expression of the macrophage marker SRA-1 and induction of inflammatory genes TNF-alpha, IL-6 and COX-2. Also, fresh or frozen Double Density isolated cells can be successfully differentiated into dendritic cells in the presence of GM-CSF and IL-4 as judged by the expression of the hallmark surface proteins CD1a and DC-sign and the absence of CD14. This method also yields a pure population of lymphocytes.

Interaction between SecA and SecYEG in micellar solution and formation of the membrane-inserted state

Preprotein translocation in Escherichia coli is mediated by the translocase with SecA as peripheral ATPase and SecY, SecE, and SecG as membrane domain. To facilitate large-scale purification of the SecYEG heterotrimer, SecY was fused at its amino terminus with a hexahistidine tag and co-overexpressed with SecE and SecG. The presence of the His tag allowed purification of homogeneously pure SecYEG complex by a single anion-exchange chromatographic step starting from octyl glucoside-solubilized inner membranes. Endogenous levels of SecD and SecF copurified with the SecYEG protein. Purified SecYEG complex retained a nativelike, alpha-helical conformation in octyl glucoside and in micellar solution binds SecA with high affinity. In the presence of the nonhydrolyzable nucleotide analogue adenosine 5'-(beta, gamma-imidotriphosphate), octyl glucoside-solubilized SecYEG is nearly as effective as the reconstituted enzyme in inducing the formation of a proteinase K-protected 30 kDa fragment of 125I-labeled SecA, while SecYEG is proteolyzed to fragments smaller than 6 kDa. These data demonstrate that the 30-kDa SecA fragment is not protected by the lipid phase nor by SecYEG but rather indicate that it represents a SecYEG- and nucleotide-induced stable conformational state of a SecA domain.

Anti-CD2 antibodies induce T cell unresponsiveness in vivo

The CD2 receptor functions as an adhesion and signal molecule in T cell recognition. Multimeric binding of CD2 on T cells to its physiologic ligand LFA-3 on cognate partner cells in vitro efficiently augments the antigen-specific T cell signal delivered by the T cell receptor/CD3 complex. The precise contribution of the antigen-nonspecific CD2-LFA-3 interactions to T cell immune responses in vivo, however, has been difficult to assess. Here we analyzed the role of CD2 in the murine immune response using a nondepleting anti-CD2 monoclonal antibody that induces a marked, reversible modulation of CD2 expression on murine T and B cells in situ. This modulation is dose and time dependent, specific for CD2, and does not require the Fc portion of the antibody. Anti-CD2 antibodies [rat IgG1 or F(ab')2] significantly inhibit the CD4+ T cell-mediated response to hen egg lysozyme and the cytotoxic CD8+ T cell response to a syngeneic tumor cell line. In both cases, anti-CD2 antibodies are only effective when administered before or within 24 h after antigen priming. The suppression of the antitumor response corresponds to a sixfold reduction of specific cytotoxic T lymphocyte precursor cells and results in the abrogation of protective antitumor immunity. Anti-CD2 antibodies also affect the humoral immune response to oxazolone: the isotype switch from specific IgM to IgG1 antibodies is delayed, whereas the IgM response is unaltered. In addition, a single antibody injection results in sustained polyclonal unresponsiveness of T cells irrespective of antigen priming and CD2 modulation. These results document that CD2-mediated signals induce a state of T cell unresponsiveness in vivo.

Primary donor structure and interactions in bacterial reaction centers from near-infrared Fourier transform resonance Raman spectroscopy

Preresonance Raman and resonance Raman spectra of the primary donor (P) from reaction centers of the Rhodobacter (Rb.) sphaeroides R26 carotenoidless strain in the P and P+ states, respectively, were obtained at room temperature with 1064-nm excitation and a Fourier transform spectrometer. These spectra clearly indicate that the chromophore modes are observable over those of the protein with no signs of interference below 1800 cm-1. The chromophore modes are dominated by those of the bacteriochlorophylls (BChl a), and it is estimated that, in the P state, ca. 65% of the Raman intensity of the BChl a modes arises from the primary donor. This permits the direct observation of a vibrational spectrum of the primary donor at preresonance with the excitonic 865-nm band. The Raman spectrum of oxidized reaction centers in the presence of ferricyanide clearly exhibits bands arising from a BChl a+ species. The magnitude of the frequency shift of a keto carbonyl of neutral P from 1691 to 1717 cm-1 upon P+ formation strongly suggests that one BChl molecule in P+ carries nearly the full +1 charge. Our results indicate that the unpaired electron in P.+ does not share a molecular orbital common to the two components of the dimer on the time scale of the resonance Raman effect (ca. 10(-13) s).

Distinct immunological signatures discriminate severe COVID-19 from non-SARS-CoV-2-driven critical pneumonia

Immune profiling of COVID-19 patients has identified numerous alterations in both innate and adaptive immunity. However, whether those changes are specific to SARS-CoV-2 or driven by a general inflammatory response shared across severely ill pneumonia patients remains unknown. Here, we compared the immune profile of severe COVID-19 with non-SARS-CoV-2 pneumonia ICU patients using longitudinal, high-dimensional single-cell spectral cytometry and algorithm-guided analysis. COVID-19 and non-SARS-CoV-2 pneumonia both showed increased emergency myelopoiesis and displayed features of adaptive immune paralysis. However, pathological immune signatures suggestive of T cell exhaustion were exclusive to COVID-19. The integration of single-cell profiling with a predicted binding capacity of SARS-CoV-2 peptides to the patients' HLA profile further linked the COVID-19 immunopathology to impaired virus recognition. Toward clinical translation, circulating NKT cell frequency was identified as a predictive biomarker for patient outcome. Our comparative immune map serves to delineate treatment strategies to interfere with the immunopathologic cascade exclusive to severe COVID-19.

Cooperative reactivity of early-late heterodinuclear transition metal complexes with polar organic substrates

A comprehensive investigation into the cooperative reactivity of two chemically complementary metal-complex fragments in early-late heterodinuclear complexes has been carried out. Reaction of the partially fluorinated tripodal amidozirconium complexes [HC-(SiMe2NR)3Zr(mu-Cl)2Li(OEt2)2] (R = 2-FC6H4: 2a, 2,3,4-F3C6H4: 2b) with K[CpM(CO)2] (M=Fe, Ru) afforded the stable metal-metal bonded heterodinuclear complexes [HC[SiMe2NR]3-Zr-MCp(CO)2] (3-6). Reaction of the dinuclear complexes with methyl isonitrile as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Two of these complexes, [HC[SiMe2N(2-FC6-H4)]3Zr(S2C)Fe(CO)2Cp] (9a) and [HC-[SiMe2N(2-FC2H4)]3Zr-(SCNPh)Fe(CO)2-Cp] (12), have been structurally characterized by a single crystal X-ray structure analysis, proving the structural situation of the inserted substrate as a bridging ligand between the early and late transition metal centre. The reactivity towards organic carbonyl derivatives proved to be varied. Reaction of the heterobimetallic complexes with benzyl and ethylbenzoate led to the cleavage of the ester generating the respective alkoxozirconium complexes [HC[SiMe2N(2-FC6H4)]3ZrOR] (R = Ph-CH2: 13a, Et: 13b) along with [CpFe-[C(O)Ph](CO)2], whereas the analogous reaction with ethyl formate gave 13b along with [CpFeH(CO)2]; this latter complex results from the instability of the formyliron species initially formed. Aryl aldehydes were found to react with the Zr-M complexes according to a Cannizzaro disproportionation pattern yielding the aroyliron and ruthenium complexes along with the respective benzoxyzirconium species. The transfer of the aldehyde hydrogen atom in the course of the reaction was established in a deuteriation experiment. [HC[SiMe2-N(2-FC6H4)]3Zr-M(CO)2Cp] reacted with lactones to give the ring-opened species containing an alkoxozirconium and an acyliron or acylruthenium fragment; the latter binds to the early transition metal centre through the acyl oxygen atom, as evidenced from the unusuallly low-field shifted 13C NMR resonances of the RC(O)M units. Ketones containing a-CH units react with the Zr-Fe complexes cooperatively to yield the aldol coupling products coordinated to the zirconium complex fragment along with the hydridoiron compound [CpFeH(CO)2], whereas 1,2-diphenylcyclopropenone underwent an oxygen transfer from the keto group to a CO ligand to give a linking CO2 unit and a cyclopropenylidene ligand coordinated to the iron fragment in [HC-[Si(CH3)2N(2,3,4-F3C6H2)]3Zr(mu-O2C)-Fe(CO)[C3Ph2)Cp] (19). The atom transfer was established by 17O and 13C labelling studies. Similar oxygen-transfer processes were observed in the reactions with pyridine N-oxide, dimethylsulfoxide and methylphenylsulfoxide.

Chemistry of porphyrin-appended cellulose strands with a helical structure: spectroscopy, electrochemistry, and in situ circular dichroism spectroelectrochemistry

Around 100 porphyrin units have been selectively linked at C(6)-O to a cellulose (Avicel). The properties of the metal-free and zincated porphyrin-celluloses 2 and Zn-2 have been determined by optical and electrochemical methods. Circular dichroism indicates a helical arrangement of the porphyrin units and reveals intra-chain coupling reminiscent, in the broadest sense, of strands of nucleic acids. Cyclic voltammetry and spectroelectrochemistry have been used to characterize the radical ions and dianions. The electrochromism of the oxidation of cellulose 2 to porphyrin radical cations of 2 has been employed for both molecular switching and the transduction of an electrochemical input into chiroptical signal expression.