Tissue-resident alveolar macrophages reduce O3-induced inflammation via MerTK mediated efferocytosis.

Lung inflammation, caused by acute exposure to ozone (O3) - one of the six criteria air pollutants - is a significant source of morbidity in susceptible individuals. Alveolar macrophages (AMØs) are the most abundant immune cells in the normal lung and their number increases following O3 exposure. However, the role of AMØs in promoting or limiting O3-induced lung inflammation has not been clearly defined. Here, we used a mouse model of acute O3 exposure, lineage tracing, genetic knockouts, and data from O3-exposed human volunteers to define the role and ontogeny of AMØs during acute O3 exposure. Lineage tracing experiments showed that 12, 24, and 72 h after exposure to O3 (2 ppm) for 3h all AMØs were tissue-resident origin. Similarly, in humans exposed to FA and O3 (200 ppb) for 135 minutes, we did not observe ~21h post-exposure an increase in monocyte-derived AMØs by flow cytometry. Highlighting a role for tissue-resident AMØs, we demonstrate that depletion of tissue-resident AMØs with clodronate-loaded liposomes led to persistence of neutrophils in the alveolar space after O3 exposure, suggesting that impaired neutrophil clearance (i.e., efferocytosis) leads to prolonged lung inflammation. Moreover, depletion of tissue-resident AMØ demonstrated reduced clearance of intratracheally instilled apoptotic Jurkat cells, consistent with reduced efferocytosis. Genetic ablation of MerTK - a key receptor involved in efferocytosis - also resulted in impaired clearance of apoptotic neutrophils followed O3 exposure. Overall, these findings underscore the pivotal role of tissue-resident AMØs in resolving O3-induced inflammation via MerTK-mediated efferocytosis.

[Clinical characteristics and correlative factors of dry eye disease associated with graft-versus-host disease].

Objective: To investigate the clinical features of dry eye disease in patients with graft-versus-host disease (GVHD) and to identify the correlative factors that contribute to its severity. Methods: It was a retrospective case series study. A total of 62 patients with dry eye disease caused by GVHD after allogeneic hematopoietic stem cell transplantation (HSCT) were recruited from the First Affiliated Hospital of Soochow University between 2012 and 2020. The study population comprised 38 males (61%) and 24 females (39%), with an average age of (35.29±11.75) years. Only the right eye of each patient was evaluated. The patients were divided into two groups based on the severity of corneal epitheliopathy: a mild group (15 eyes) and a severe group (47 eyes). Demographic information, including gender, age, primary disease, type of allogeneic HSCT, donor-to-recipient information, source of hematopoietic stem cells, systemic GVHD, and the time from HSCT to the first visit, was collected. Ophthalmologic assessments, including the Schirmer Ⅰ test, tear breakup time, corneal epithelial staining, and eye margin assessment, were performed during the first visit to the ophthalmology department and compared between the two groups. Results: The average time from HSCT to the first visit to the ophthalmology department among the 62 patients was (20.26±13.09) months. The median corneal fluorescein staining score was 4.5 points. In the mild group, the main characteristic of corneal staining was scattered punctate staining in the peripheral region in 80% of cases, while in the severe group, corneal staining fused into clumps in both the peripheral region (64%) and the pupillary zone (28%). Results of the Schirmer Ⅰ test were significantly lower in the severe group compared to the mild group (P<0.05). The median total eyelid margin score in the severe group was higher than that in the mild group [9 (7, 12) points vs. 6 (5, 8) points] (P<0.05). The median eyelid congestion score in the severe group was, also higher than that in the mild group [2 (1, 3) points vs. 1 (0, 2) points] (P<0.05). The compatibility between the blood types of the donor and recipient was found to be statistically significant (P<0.05). There was no significant difference in gender, age, family relationship, human leukocyte antigen matching, gender consistency, source of hematopoietic stem cells, or the occurrence of systemic GVHD between the two groups (P>0.05). Conclusions: Patients in the mild group had scattered punctate corneal staining in the peripheral region, while those in the severe group showed fusion of corneal staining into clumps in both the peripheral and pupillary zones. The severity of dry eye disease caused by GVHD was strongly correlated with eyelid margin lesions. A higher degree of eyelid margin lesions indicated more severe dry eye disease caused by GVHD. Additionally, compatibility between the blood types of the donor and recipient may play a role in the development of GVHD-associated dry eye.

[Eltrombopag for thrombocytopenia in 24 children after hematopoietic stem cell transplantation].

Objective: To evaluate the efficacy and safety of eltrombopag for children with thrombocytopenia after hematopoietic stem cell transplantation (HSCT). Methods: Clinical data of 24 patients with thrombocytopenia after HSCT,who were treated with eltrombopag in the Department of Pediatrics, Sun Yat-sen Memorial Hospital, Sun Yat-sen University from August 1, 2018 to April 1, 2019 were analyzed retrospectively. The response rate and adverse reactions of eltrombopag were evaluated. Patients were divided into groups by source of hematopoietic stem cells (umbilical cord blood group and peripheral stem cell group) and type of disease (malignant and non-malignant disease group) and the clinical outcomes between groups were compared. Rank Sum test was used for comparisons between groups. Results: Among 24 cases, 15 were males and 9 females, the age of starting eltrombopag was 7.7 (2.6-13.7) years, the time of eltrombopag treatment after HSCT was 27.5 (8.0-125.0) days, the time from treatment to complete response (CR) was 23.5 (6.0-83.0) days, with the treatment course 36.5 (8.0-90.0) days. The total dose of eltrombopag was 1 400(200-5 900) mg. Complete response rate was 92% (22/24),without eltrombopag related adverse reactions. Comparing with peripheral stem cell group (n=8), the course and total dose of eltrombopag in umbilical cord blood group (n=16) were significantly reduced(24.5 (8.0-81.0) vs. 65.5 (35.0-90.0) d, Z=-3.004, P=0.002; 900.0 (200.0-3 850.0) vs. 2 862.5 (1 175.0-5 900.0) mg, Z=-2.604, P=0.007), but no significant differences were found in the time from treatment to complete response, platelet count after 2 weeks of eltrombopag withdrawal or platelet count at the end point of follow-up (all P>0.05). Comparing malignant patients (n=12) and non-malignant patients (n=12), no significant differences were found in the time from treatment to complete response, course, total dose, platelet count after 2 weeks of eltrombopag withdrawal, and platelet count at the end point of follow-up in non-malignant patients (all P>0.05). Conclusion: Eltrombopag is safe and maybe effective for thrombocytopenia after HSCT, especially for umbilical cord blood transplantation.

MicroRNA-9501 inhibits breast cancer proliferation and metastasis through regulating Wnt/ß-catenin pathway.

OBJECTIVE: This research was designed to explore the expression characteristics of microRNA-9501 in breast cancer (BCa), and to further explore whether it can influence the development of BCa through the regulation of Wnt/ß-Catenin pathway. PATIENTS AND METHODS: QPCR was carried out to examine microRNA-9501 level in tumor tissue samples and paracancerous ones collected from 42 BCa patients, and the interplay between microRNA-9501 expression and the clinical indicators, as well as the prognosis of BCa patients were analyzed. In addition, we detected microRNA-9501 expression in BCa cell lines by qPCR. Subsequently, microRNA-9501 overexpression model was constructed in BCa cell lines MCF-7 and MDA-MB-231. Then, CCK-8, EdU, cell wound healing, as well as transwell assays, were carried out to evaluate the impact of microRNA-9501 on the biological functions of BCa cells. Finally, the Dual-Luciferase reporting test and tumor formation experiment in nude mice were conducted to further clarify the potential molecular mechanism. RESULTS: QPCR results indicated that microRNA-9501 level in tumor tissue specimens of BCa patients was remarkably higher than that in adjacent ones, and the difference was statistically significant. Compared with patients with high expression of microRNA-9501, patients with lowly-expressed microRNA-9501 had higher tumor stage, higher incidence of lymph node or distant metastasis, and lower overall survival rate. In addition, compared with control group, cells in microRNA-9501 overexpression group showed a significant decrease in proliferation rate, invasiveness, and migration ability. Meanwhile, luciferase reporting assay revealed that overexpression of ß-Catenin remarkably attenuated the luciferase activity of the vector containing wild-type microRNA-9501 sequences, further demonstrating that microRNA-9501 can be targeted by ß-Catenin. Meanwhile, qPCR revealed a negative association between ß-Catenin and microRNA-9501 in BCa tissues. Finally, tumor-bearing experiments in nude mice also demonstrated that microRNA-9501 may suppress the malignant growth of breast tumor. CONCLUSIONS: MicroRNA-9501 expression was found remarkably decreased in BCa tissues and cell lines, which was closely relevant to the pathological stage, metastasis incidence, and prognosis of BCa patients. In addition, microRNA-9501 may suppress the malignant progression of BCa via modulating Wnt/ß-Catenin path-way.

Pharmacogenetics of medication-related osteonecrosis of the jaw: a systematic review and meta-analysis.

Medication-related osteonecrosis of the jaw (MRONJ) is a severe complication that can develop in patients treated with anti-resorptive drugs. Although the pathogenesis of MRONJ is still unclear, genetic factors have a demonstrated important role. Thus, the aim of this study was to perform a systematic review on the pharmacogenetics of MRONJ. Studies published until March 2019 were retrieved from eight databases and were selected by two independent reviewers. Evidence on several genetic polymorphisms was summarized and a meta-analysis was conducted when possible. Fourteen studies involving 1515 participants were eligible for systematic review. For CYP2C8 rs1934951, no significant difference was observed between the MRONJ and non-MRONJ groups (odds ratio (OR) 2.04, 95% confidence interval (CI) 0.88-4.73, P=0.09). However, a subgroup analysis based on only multiple myeloma status showed a positive association (OR 3.64, 95% CI 1.29-10.30, P=0.01). PPARG rs1152003 was not differently distributed between groups (OR 0.25, 95% CI 0.01-9.92, P=0.46). Also, VEGF rs3025039 was found to be correlated with the occurrence of MRONJ (OR 0.35, 95% CI 0.15-0.82, P=0.02). CYP2C8 rs1934951 (in multiple myeloma patients) and VEGF rs3025039 are associated with the development of MRONJ in patients treated with bisphosphonates. The results are promising and call for new trials with a larger sample to further explore this growing field.

Validation of spirometry prediction equations in western Kenya.

SETTING: Community of Eldoret, Kenya. OBJECTIVE: To test the performance of three commonly used spirometry prediction equations in a healthy Kenyan population. DESIGN: Cross-sectional assessment of healthy adults in Eldoret. RESULTS: Of the 331 subjects enrolled in the study, 282 subjects aged 18-85 years (45% males, 55% females) produced high-quality spirograms. Lung function predictions were made using the Global Lung Initiative 2012 (GLI 2012) prediction equations for African Americans, the National Health and Nutrition Examination Survey III (NHANES III) prediction equations for African Americans, and the Crapo prediction equation. Bland-Altman analyses were performed to measure the agreement between observed and predicted spirometry parameters. Overall, the GLI 2012 and NHANES equations for African Americans performed similarly for forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1), significantly overestimating FVC while accurately predicting observed FEV1 values. CONCLUSION: The study brings into question the utility of three major spirometry prediction equations in a Kenyan population. The significant overestimation of FVC by the best-performing equations despite accurate prediction of FEV1 suggests poor performance of these equations in our population.

l-citrulline prevents asymmetric dimethylarginine-mediated reductions in nitric oxide and nitrosative stress in primary human airway epithelial cells.

BACKGROUND: Asthma is associated with reduced systemic levels of l-arginine and increased asymmetric dimethylarginine (ADMA). This imbalance leads to nitric oxide synthase (NOS) uncoupling with reduced nitric oxide (NO) formation and greater oxidative and nitrosative stress. Whether this imbalance also occurs in bronchial epitheliumof asthmatics is unknown. OBJECTIVES: We used primary human bronchial epithelial cells (HBECs) from asthmatics and healthy controls to evaluate: (i) ADMA-mediated NOS uncoupling reduces epithelial production of NO and increases oxygen and nitrogen reactive species, and (ii) l-citrulline can reverse this mechanism by recoupling NOS, restoring NO production and reducing oxidative and nitrosative stress. RESULTS: In HBECsIL-13 and INFγ stimulated NOS2 and increased NOx levels. The addition of ADMA reduced NOx and increased H2 O2 levels (p<0.001). Treatment with l-citrulline (800, 1600 µm) rescued NOx when the l-arginine media concentration was 25 µm but failed to do so with higher concentrations (100 µm). Under reduced l-arginine media conditions, HBECs treated with l-citrulline increased the levels of argininosuccinate, an enzyme that metabolizes l-citrulline to l-arginine. l-citrulline prevented the ADMA-mediated increase in nitrotyrosine in HBECs in cells from asthmatics and controls. CONCLUSIONS AND CLINICAL RELEVANCE: Increasing ADMA reduces NO formation and increases oxidative and nitrosative stress in airway epithelial cells. l-citrulline supplementation restores NO formation, while preventing nitrosative stress. These results, suggest that l-citrulline supplementation may indeed be a powerful approach to restore airway NO production and may have a therapeutic potential in diseases in which there is a defective production of NO.

[Effect of hydrocinnamoyl-L-valyl pyrrolidine on healing quality of deep partial-thickness scald wound in mice].

Objective: To observe the effect of Toll interleukin-1 recptor homology/BB-loop mimetic hydrocinnamoyl-L-valyl pyrrolidine (AS-1) on the healing quality of deep partial-thickness scald wound in mice. Methods: Forty-two adult C57BL/6 mice were divided into sham injury group (SI), scald group (S), early AS-1 treatment group (EAT), early dimethyl sulfoxide (DMSO) control group (EDC), late AS-1 treatment group (LAT), late DMSO control group (LDC) according to the random number table, with 7 mice in each group. Mice in group SI were sham injured without other treatment. Deep partial-thickness scald model with 10% total body surface area was reproduced on the back of the other mice, and the wound was treated by daily wound cleaning with saline and dressing changing with vaseline gauze after injury. Mice in group EAT and those in group LAT were intraperitoneally injected with 20 mg/mL AS-1 50 mg/kg each day respectively from post scald hour (PSH) 8 and post scald day (PSD) 15 on. Mice in group EDC and those in group LDC were intraperitoneally injected with 20 mg/mL DMSO 50 mg/kg each day respectively from PSH 8 and PSD 15 on. On PSD 21, the gross condition of wound healing of mice with scald was observed, and the wound healing rate was calculated. Tissue samples of healed wound were collected and stained with HE and Masson respectively to observe the histomorphological change and fibrosis of collagen, and the percentage of fibrosis of collagen was calculated. The mRNA expressions of interleukin-1ß (IL-1ß), tumor necrosis factor α (TNF-α), transforming growth factor ß1 (TGF-ß1), matrix metalloproteinase-1 (MMP-1), tissue inhibitors of metalloproteinase 1 (TIMP-1), connective tissue growth factor (CTGF), type Ⅰ collagen and type Ⅲ collagen in healed wound tissue were detected by real time fluorescent quantitive reverse transcription polymerase chain reaction. The protein expressions of type Ⅰ collagen and type Ⅲ collagen in healed wound tissue were detected by Western blotting. Skin tissue of mice in group SI at the same area as that observed and collected in mice with scald was performed with the same observation and detection as mentioned above at the same time. Data were processed with one-way analysis of variance and Tukey test. Results: On PSD 21, no abnormal appearance was found in skin tissue of mice in group SI. Wounds of mice in group EAT were healed completely without scar formation, while those in the other four groups were not completely healed with scars formed in different degree. The wound healing rate of mice in group EAT was (97±4)%, close to that of group SI (100%, q=1.753, P>0.05), and both of them were obviously higher than those of groups S, EDC, LAT, and LDC [respectively (83±8)%, (87±6)%, (85±9)%, and (85±7)%, with q values from 4.819 to 6.803, P<0.05 or P<0.01]. On PSD 21, no abnormal appearance was found in morphology of skin tissue of mice in group SI. The morphology of healed wound tissue of mice in group EAT was close to that in group SI, with little epidermis hyalinosis and few newly formed collagen fibers arranged orderly. Epidermis hyalinosis in band- or flake-shape and obvious proliferation of collagen fibers arranged disorderly were observed in healed wound tissue of mice in the other four groups. Much infiltration of inflammatory cells was found in group S. The percentage of fibrosis of collagen in healed wound tissue of mice in group EAT was (30±3)%, close to that of group SI [(30±4)%, q=0.159, P>0.05], and both of them were obviously lower than those of groups S, EDC, LAT, and LDC [respectively (86±9)%, (74±5)%, (82±4)%, and (82±7)%, with q values from 12.080 to 15.530, P values below 0.01]. On PSD 21, compared with those of group SI, the mRNA expressions of IL-1ß, TNF-α, TGF-ß1, MMP-1, and CTGF in healed wound tissue of mice in group S, the mRNA expressions of TGF-ß1 in healed wound tissue of mice in groups EDC and LDC, and the mRNA expression of MMP-1 in healed wound tissue of mice in group LAT were significantly increased (with q values from 4.039 to 5.232, P values below 0.05), while the mRNA expression of TIMP-1 in healed wound tissue of mice in group S was significantly decreased (q=4.921, P<0.05). Compared with those of group S, the mRNA expressions of IL-1ß, TNF-α, TGF-ß1, MMP-1, and CTGF in healed wound tissue of mice in group EAT and the mRNA expressions of IL-1ß and CTGF in healed wound tissue of mice in group LAT were significantly decreased (with q values from 4.418 to 6.402, P<0.05 or P<0.01), while the mRNA expressions of TIMP-1 in healed wound tissue of mice in groups EAT and LAT were significantly increased (with q values respectively 3.929 and 8.299, P<0.05 or P<0.01). Compared with those of group SI, the mRNA and protein expressions of type Ⅲ collagen in healed wound tissue of mice in the other groups and the mRNA and protein expressions of type Ⅰ collagen in healed wound tissue of mice in groups S, EDC, LAT, and LDC were significantly increased (with q values from 7.054 to 11.650, P values below 0.01). Compared with those of group EAT, the mRNA and protein expressions of type Ⅰ collagen in healed wound tissue of mice in groups S, EDC, LAT, and LDC were significantly increased (with q values from 5.156 to 7.451, P<0.05 or P<0.01). Conclusions: AS-1 can effectively promote wound healing and reduce fibrosis degree in the early stage of inflammation response after deep partial-thickness scald in mice, which may be related to its effect in decreasing the expression of inflammation related factors IL-1ß and TNF-α and fibrosis related factors TGF-ß1, MMP-1, CTGF, and type Ⅰ collagen.

Novel inactivating mutation of the calcium-sensing receptor in a young woman with mild hypercalcaemia.

A young woman with mild hypercalcaemia and an inappropriately normal serum parathyroid hormone had parathyroid scintigraphy suggestive of an active ectopic parathyroid tissue in the superior mediastinum. Urinary calcium to creatinine clearance ratio was low, and a subsequent genetic analysis confirmed a novel mutation (Q164K) in the calcium sensing receptor gene, consistent with familial hypocalciuric hypercalcaemia. We propose that this mutation accounts for her clinical and investigational findings, although a double pathology of Q164K and an ectopic parathyroid adenoma is also conceivable.

Acid-stress-induced changes in enterohaemorrhagic Escherichia coli O157 : H7 virulence.

Enterohaemorrhagic Escherichia coli (EHEC) O157 : H7 is naturally exposed to a wide variety of stresses including gastric acid shock, and yet little is known about how this stress influences virulence. This study investigated the impact of acid stress on several critical virulence properties including survival, host adhesion, Shiga toxin production, motility and induction of host-cell apoptosis. Several acid-stress protocols with relevance for gastric passage as well as external environmental exposure were included. Acute acid stress at pH 3 preceded by acid adaptation at pH 5 significantly enhanced the adhesion of surviving organisms to epithelial cells and bacterial induction of host-cell apoptosis. Motility was also significantly increased after acute acid stress. Interestingly, neither secreted nor periplasmic levels of Shiga toxin were affected by acid shock. Pretreatment of bacteria with erythromycin eliminated the acid-induced adhesion enhancement, suggesting that de novo protein synthesis was required for the enhanced adhesion of acid-shocked organisms. DNA microarray was used to analyse the transcriptome of an EHEC O157 : H7 strain exposed to three different acid-stress treatments. Expression profiles of acid-stressed EHEC revealed significant changes in virulence factors associated with adhesion, motility and type III secretion. These results document profound changes in the virulence properties of EHEC O157 : H7 after acid stress, provide a comprehensive genetic analysis to substantiate these changes and suggest strategies that this pathogen may use during gastric passage and colonization in the human gastrointestinal tract.

Bisphosphonate space measurement and dosage requirement for intravenous clodronate treatment of Paget's disease.

It has been claimed that the bisphosphonate space, a scintigraphic technique which simultaneously estimates bone uptake and renal clearance of bisphosphonate, can be used to predict the dose of bisphosphonate required to induce biochemical remission in Paget's disease. In a prospective study of 15 newly diagnosed patients with Paget's disease, bisphosphonate space measurements were made prior to treatment with intravenous clodronate. Treatment with clodronate 0.6 g was given four times weekly until the alkaline phosphatase (ALP) suppressed below the upper level of the reference range (120 u/l) or reached a plateau, and the cumulative dose required (1.8-7.8 g) was calculated. Overall, the bisphosphonate space correlated poorly with the total dose requirement (r = 0.441, P = 0.100), but the relationship was weakened by an outlier, who had the poorest renal function. Excluding this subject improved the correlation coefficient (r = 0.852, P <0.0001). The relationship between dose requirement and log10 initial ALP was not as strong (r = 0.672, P <0.01). However, for both ALP and the bisphosphonate space the 95% prediction intervals were wide. We conclude that the bisphosphonate space does relate to dose requirements for intravenous bisphosphonates, but that it is unreliable when renal function is poor, and may not offer much gain over the pretreatment ALP levels. Both ALP and the bisphosphonate space have wide prediction intervals, and are therefore poor guides to dose requirement.

Electronic structure of high-spin iron(III)-alkylperoxo complexes and its relation to low-spin analogues: reaction coordinate of O-O bond homolysis.

The spectroscopic properties of the high-spin Fe(III)-alkylperoxo model complex [Fe(6-Me(3)TPA)(OH(x))(OO(t)Bu)](x)(+) (1; TPA = tris(2-pyridylmethyl)amine, (t)Bu = tert-butyl, x = 1 or 2) are defined and related to density functional calculations of corresponding models in order to determine the electronic structure and reactivity of this system. The Raman spectra of 1 show four peaks at 876, 842, 637, and 469 cm(-1) that are assigned with the help of normal coordinate analysis, and corresponding force constants have been determined to be 3.55 mdyn/A for the O-O and 2.87 mdyn/A for the Fe-O bond. Complex 1 has a broad absorption feature around 560 nm that is assigned to a charge-transfer (CT) transition from the alkylperoxo to a t(2g) d orbital of Fe(III) with the help of resonance Raman profiles and MCD spectroscopy. An additional contribution to the Fe-O bond arises from a sigma interaction between and an e(g) d orbital of iron. The electronic structure of 1 is compared to the related low-spin model complex [Fe(TPA)(OH(x))(OO(t)Bu)](x)(+) and the reaction coordinate for O-O homolysis is explored for both the low-spin and the high-spin Fe(III)-alkylperoxo systems. Importantly, there is a barrier for homolytic cleavage of the O-O bond on the high-spin potential energy surface that is not present for the low-spin complex, which is therefore nicely set up for O-O homolysis. This is reflected by the electronic structure of the low-spin complex having a strong Fe-O and a weak O-O bond due to a strong Fe-O sigma interaction. In addition, the reaction coordinate of the Fe-O homolysis has been investigated, which is a possible decay pathway for the high-spin system, but which is thermodynamically unfavorable for the low-spin complex.

Catalysis research of relevance to carbon management: progress, challenges, and opportunities.

The goal of the "Opportunities for Catalysis Research in Carbon Management" workshop was to review within the context of greenhouse gas/carbon issues the current state of knowledge, barriers to further scientific and technological progress, and basic scientific research needs in the areas of H2 generation and utilization, light hydrocarbon activation and utilization, carbon dioxide activation, utilization, and sequestration, emerging techniques and research directions in relevant catalysis research, and in catalysis for more efficient transportation engines. Several overarching themes emerge from this review. First and foremost, there is a pressing need to better understand in detail the catalytic mechanisms involved in almost every process area mentioned above. This includes the structures, energetics, lifetimes, and reactivities of the species thought to be important in the key catalytic cycles. As much of this type of information as is possible to acquire would also greatly aid in better understanding perplexing, incomplete/inefficient catalytic cycles and in inventing new, efficient ones. The most productive way to attack such problems must include long-term, in-depth fundamental studies of both commercial and model processes, by conventional research techniques and, importantly, by applying various promising new physicochemical and computational approaches which would allow incisive, in situ elucidation of reaction pathways. There is also a consensus that more exploratory experiments, especially high-risk, unconventional catalytic and model studies, should be undertaken. Such an effort will likely require specialized equipment, instrumentation, and computational facilities. The most expeditious and cost-effective means to carry out this research would be by close coupling of academic, industrial, and national laboratory catalysis efforts worldwide. Completely new research approaches should be vigorously explored, ranging from novel compositions, fabrication techniques, reactors, and reaction conditions for heterogeneous catalysts, to novel ligands and ligation geometries (e.g., biomimetic), reaction media, and activation methods for homogeneous ones. The interplay between these two areas involving various hybrid and single-site supported catalyst systems should also be productive. Finally, new combinatorial and semicombinatorial means to rapidly create and screen catalyst systems are now available. As a complement to the approaches noted above, these techniques promise to greatly accelerate catalyst discovery, evaluation, and understanding. They should be incorporated in the vigorous international research effort needed in this field.

Spectroscopic properties and electronic structure of low-spin Fe(III)-alkylperoxo complexes: homolytic cleavage of the O-O bond.

The spectroscopic properties, electronic structure, and reactivity of the low-spin Fe(III)-alkylperoxo model complex [Fe(TPA)(OH(x))(OO(t)Bu)](x+) (1; TPA = tris(2-pyridylmethyl)amine, (t)Bu = tert-butyl, x = 1 or 2) are explored. The vibrational spectra of 1 show three peaks that are assigned to the O-O stretch (796 cm(-1)), the Fe-O stretch (696 cm(-)(1)), and a combined O-C-C/C-C-C bending mode (490 cm(-1)) that is mixed with upsilon(FeO). The corresponding force constants have been determined to be 2.92 mdyn/A for the O-O bond which is small and 3.53 mdyn/A for the Fe-O bond which is large. Complex 1 is characterized by a broad absorption band around 600 nm that is assigned to a charge-transfer (CT) transition from the alkylperoxo pi*(upsilon) to a t(2g) d orbital of Fe(III). This metal-ligand pi bond is probed by MCD and resonance Raman spectroscopies which show that the CT state is mixed with a ligand field state (t(2g) --> e(g)) by configuration interaction. This gives rise to two intense transitions under the broad 600 nm envelope with CT character which are manifested by a pseudo-A term in the MCD spectrum and by the shapes of the resonance Raman profiles of the 796, 696, and 490 cm(-1) vibrations. Additional contributions to the Fe-O bond arise from sigma interactions between mainly O-O bonding donor orbitals of the alkylperoxo ligand and an e(g) d orbital of Fe(III), which explains the observed O-O and Fe-O force constants. The observed homolytic cleavage of the O-O bond of 1 is explored with experimentally calibrated density functional (DFT) calculations. The O-O bond homolysis is found to be endothermic by only 15 to 20 kcal/mol due to the fact that the Fe(IV)=O species formed is highly stabilized (for spin states S = 1 and 2) by two strong pi and a strong sigma bond between Fe(IV) and the oxo ligand. This low endothermicity is compensated by the entropy gain upon splitting the O-O bond. In comparison, Cu(II)-alkylperoxo complexes studied before [Chen, P.; Fujisawa, K.; Solomon, E. I. J. Am. Chem. Soc. 2000, 122, 10177] are much less suited for O-O bond homolysis, because the resulting Cu(III)=O species is less stable. This difference in metal-oxo intermediate stability enables the O-O homolysis in the case of iron but directs the copper complex toward alternative reaction channels.

Double-strand hydrolysis of plasmid DNA by dicerium complexes at 37 degrees C.

Significant effort has been made to develop synthetic metal complexes that hydrolyze DNA. Here we report a new dicerium complex, Ce(2)(HXTA) (HXTA = 5-methyl-2-hydroxy-1,3-xylene-alpha,alpha-diamine-N,N,N',N'-tetraacetic acid), which can hydrolyze DNA at pH 8 and 37 degrees C. This complex hydrolyzes DNA restriction fragments to give products with high regioselectivity, affording >90% 5'-OPO(3) and 3'-OH ends, like the products of DNA hydrolyzing enzymes. Ce(2)(HXTA) also hydrolyzes Litmus 29 plasmid DNA to afford both nicked and linear DNA. Analysis of the relative amounts of supercoiled, nicked, and linear DNA present show that there is one double-strand cleavage per ten single-strand cleavages, indicating that the linear DNA formed cannot be the result of two random single-strand cleavage events. The kinetics of nicked and linear DNA formation are comparable, both being associated with apparent first-order rate constants of approximately 1 x 10(-)(4) s(-)(1) for complex concentrations of 10(-)(5)-10(-)(4) M. These observations suggest that similar factors affect the hydrolysis of the first and second DNA strands and that cleaving the phosphodiester bond is likely the rate determining step in both cases. This is the first detailed study of a metal complex shown to mimic DNA hydrolases in their capability to effect double-strand DNA hydrolysis regioselectively at the 3'-O-P bond.

Resonance Raman studies of the iron(II)--alpha-keto acid chromophore in model and enzyme complexes.

The bidentate coordination of an alpha-keto acid to an iron(II) center via the keto group and the carboxylate gives rise to metal-to-ligand charge-transfer transitions between 400 and 600 nm in model complexes and in alpha-ketoglutarate-dependent dioxygenases. Excitation into these absorption bands of the Fe(II)TauD(alpha-KG) complex (TauD = taurine/alpha-ketoglutarate dioxygenase, alpha-KG = alpha-ketoglutarate) elicits two resonance Raman features at 460 and 1686 cm(-1), both of which are sensitive to (18)O labeling. Corresponding studies of model complexes, the six-coordinate [Fe(II)(6-Me(3)-TPA)(alpha-keto acid)](+) and the five-coordinate [Fe(II)(Tp(Ph2))(alpha-keto acid)] (6-Me(3)-TPA = tris[(6-methyl-2-pyridyl)methyl]amine, Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate), lead to the assignment of these two features to the Fe(II)(alpha-keto acid) chelate mode and the nu(C==O) of the keto carbonyl group, respectively. Furthermore, the chelate mode is sensitive to the coordination number of the metal center; binding of a sixth ligand to the five-coordinate [Fe(II)(Tp(Ph2))(benzoylformate)] elicits a 9--20 cm(-1) downshift. Thus, the 10 cm(-1) upshift of the chelate mode observed for Fe(II)TauD(alpha-KG) upon the addition of the substrate, taurine, is associated with the conversion of the six-coordinate metal center to a five-coordinate center, as observed for the iron center of clavaminate synthase from X-ray crystallography (Zhang, Z.; et al. Nat. Struct. Biol. 2000, 7, 127-133) and MCD studies (Zhou, J.; et al. J. Am. Chem. Soc. 1998, 120, 13539--13540). These studies provide useful insights into the initial steps of the oxygen activation mechanism of alpha-ketoglutarate-dependent dioxygenases.