A Study on Auto-Catalysis and Product Inhibition: A Nucleophilic Aromatic Substitution Reaction Catalysed within the Cavity of an Octanuclear Coordination Cage.

The ability of an octanuclear cubic coordination cage to catalyse a nucleophilic aromatic substitution reaction on a cavity-bound guest was studied with 2,4-dinitrofluorobenzene (DNFB) as the guest/substrate. It was found that DNFB undergoes a catalysed reaction with hydroxide ions within the cavity of the cubic cage (in aqueous buffer solution, pH 8.6). The rate enhancement of kcat/kuncat was determined to be 22, with cavity binding of the guest being required for catalysis to occur. The product, 2,4-dinitrophenolate (DNP), remained bound within the cavity due to electrostatic stabilisation and exerts two apparently contradictory effects: it initially auto-catalyses the reaction when present at low concentrations, but at higher concentrations inhibits catalysis when a pair of DNP guests block the cavity. When encapsulated, the UV/Vis absorption spectrum of DNP is red-shifted when compared to the spectrum of free DNP in aqueous solution. Further investigations using other aromatic guests determined that a similar red-shift on cavity binding also occurred for 4-nitrophenolate (4NP) at pH 8.6. The red-shift was used to determine the stoichiometry of guest binding of DNP and 4NP within the cage cavity, which was confirmed by structural analysis with X-ray crystallography; and was also used to perform catalytic kinetic studies in the solution-state.

Studying manganese carbonyl photochemistry in a permanently porous metal-organic framework.

Mn(diimine)(CO)3X (X = halide) complexes are critical components of chromophores, photo- and electrocatalysts, and photoactive CO-releasing molecules (photoCORMs). While these entities have been incorporated into metal-organic frameworks (MOFs), a detailed understanding of the photochemical and chemical processes that occur in a permanently porous support is lacking. Here we site-isolate and study the photochemistry of a Mn(diimine)(CO)3Br moiety anchored within a permanently porous MOF support, allowing for not only the photo-liberation of CO from the metal but also its escape from the MOF crystals. In addition, the high crystallinity and structural flexibility of the MOF allows crystallographic snapshots of the photolysis products to be obtained. We report these photo-crystallographic studies in the presence of coordinating solvents, THF and acetonitrile, showing the changing coordination environment of the Mn species as CO loss proceeds. Using time resolved experiments, we report complementary spectroscopic studies of the photolysis chemistry and characterize the final photolysis product as a possible Mn(ii) entity. These studies inform the chemistry that occurs in MOF-based photoCORMs and where these moieties are employed as catalysts.

The preservation of sarin and O,O'-diisopropyl fluorophosphate inside coordination cage hosts.

The host-guest chemistry of O,O'-diisopropyl fluorophosphate (DFP), a phosphonofluoridate G-series chemical warfare agent simulant, was investigated in the presence of a number of octanuclear cubic coordination cage hosts. The aim was to demonstrate cage-catalysed hydrolysis of DFP at near neutral pH: however, two octanuclear coordination cages, HPEG (containing water-solubilising PEG groups) and HW (containing water-solubilising hydroxymethyl groups), were actually found to increase the lifetime of DFP in aqueous buffer solution (pH 8.7). Crystallographic analysis of DFP with a structurally related host cage revealed that DFP binds to windows in the cage surface, not in the internal cavity. The phosphorus-fluorine bond is directed into the cavity rather than towards the external environment, with the cage/DFP association protecting DFP from hydrolysis. Initial studies with the chemical warfare agent (CWA) sarin (GB) with HPEG cage in a buffered solution also showed a drastically reduced rate of hydrolysis for sarin when bound in the host cage. The ability of these cages to inhibit hydrolysis of these P-F bond containing organophosphorus guests, by encapsulation, may have applications in forensic sample preservation and analysis.

MOF matrix isolation: cooperative conformational mobility enables reliable single crystal transformations.

Obtaining structural information for highly reactive metal-based species can provide valuable insight into important chemical transformations or catalytic processes. Trapping these metal-based species within the cavities of porous crystalline hosts, such as metal-organic frameworks (MOFs), can stabilise them, allowing detailed structural elucidation by single crystal X-ray diffraction. Previously, we have used a bespoke flexible MOF, [Mn3L2L'] (MnMOF-1, where L = bis-(4-carboxyphenyl-3,5-dimethylpyrazolyl)methane and L = L', but L' has a vacant N,N'-chelation site), which has a chelating site capable of post-synthetically binding metal ions, to study organometallic transformations and fundamental isomerisation processes. This manuscript will report the underlying conformational flexibility of the framework, demonstrate the solvent dependency of post-synthetic metalation, and show that the structural flexibility of the linker site and framework are critical to controlling and achieving high levels of metal loading (and therefore site occupancy) during chemical transformations. From these results, a set of design principles for linker-based "matrix isolation" and structure determination in MOFs are derived.

Isolating reactive metal-based species in Metal-Organic Frameworks - viable strategies and opportunities.

Structural insight into reactive species can be achieved via strategies such as matrix isolation in frozen glasses, whereby species are kinetically trapped, or by confinement within the cavities of host molecules. More recently, Metal-Organic Frameworks (MOFs) have been used as molecular scaffolds to isolate reactive metal-based species within their ordered pore networks. These studies have uncovered new reactivity, allowed observation of novel metal-based complexes and clusters, and elucidated the nature of metal-centred reactions responsible for catalysis. This perspective considers strategies by which metal species can be introduced into MOFs and highlights some of the advantages and limitations of each approach. Furthermore, the growing body of work whereby reactive species can be isolated and structurally characterised within a MOF matrix will be reviewed, including discussion of salient examples and the provision of useful guidelines for the design of new systems. Novel approaches that facilitate detailed structural analysis of reactive chemical moieties are of considerable interest as the knowledge garnered underpins our understanding of reactivity and thus guides the synthesis of materials with unprecedented functionality.

Characterisation of two self-sufficient CYP102 family monooxygenases from Ktedonobacter racemifer DSM44963 which have new fatty acid alcohol product profiles.

BACKGROUND: Two self-sufficient CYP102 family encoding genes (Krac_0936 and Krac_9955) from the bacterium Ktedonobacter racemifer DSM44963, which possesses one of the largest bacterial genomes, have been identified. METHODS: Phylogenetic analysis of both the encoded cytochrome P450 enzymes, Krac0936 and Krac9955. Both enzymes were produced and their turnovers with fatty acid substrates assessed in vitro and using a whole-cell oxidation system. RESULTS: Krac0936 hydroxylated straight chain, saturated fatty acids predominantly at the ω-1 and ω-2 positions using NADPH as the cofactor. Krac0936 was less active towards shorter unsaturated fatty acids but longer unsaturated acids were efficiently oxidised. cis,cis-9,12-Octadecadienoic and pentadecanoic acids were the most active substrates tested with Krac0936. Unusually Krac9955 showed very low levels of NAD(P)H oxidation activity though coupling of the reducing equivalents to product formation was high. The product distribution of tridecanoic, tetradecanoic and pentadecanoic acid oxidation by Krac9955 favoured oxidation at the ω-4, ω-5 and ω-6 positions, respectively. CONCLUSION: Krac0936 and Krac9955 are self-sufficient P450 monooxygenases. Krac0936 has a preference for pentadecanoic acid over other straight chain fatty acids and showed little or no activity with dodecanoic or octadecanoic acids. Krac9955 preferably oxidised shorter fatty acids compared to Krac0936 with tridecanoic having the highest levels of product formation. Unlike Krac0936 and P450Bm3, Krac9995 showed lower activities with unsaturated fatty acids. GENERAL SIGNIFICANCE: In this study of two of the CYP enzymes from K. racemifer we have shown that this bacterium from the Chloroflexi phylum contains genes which encode new proteins with novel activity.

A retrospective, case-control pilot study of the natural history of pediatric gastroesophageal reflux.

The duration of gastroesophageal reflux disease (GERD) is an important factor in the development of esophageal complications. The objective of this study was to examine in a retrospective, case-controlled manner the prevalence of GERD in adults who were diagnosed with GERD in infancy or early childhood. Infants and children with nonsyndromic GERD diagnosed by an experienced pediatric gastroenterologist from 1976 to 1980 and control subjects seen for well-child care from 1980 to 1985 were included in this study. The subjects were located and contacted by telephone or mail and administered a brief structured questionnaire relating to their current history of GERD. GERD-A was defined as weekly heartburn or regurgitation of any severity, and GERD-B was defined as monthly heartburn or regurgitation greater than mild in severity. Sixty-five participants (31 patients and 34 controls) returned completed questionnaires and were subdivided into the three study groups as follows: Infant (15), Child (16), and Control (34). The prevalence of adulthood GERD-A was 13, 31, and 21% in the Infant, Child, and Control groups, respectively. Similarly, the prevalence of adulthood GERD-B was 20%, 44%, and 24%, respectively. The Child group tended to report more severe heartburn than the other groups. The Infant group tended to report more frequent regurgitation, and the Child group also reported a higher prevalence of nocturnal heartburn and more frequent use of GERD medications, although these were not statistically significant. These data suggest that pediatric GER is a heterogeneous disorder and that GERD occurring after infancy may be more predictive of the presence of GERD during adulthood. Longitudinal follow-up of a larger number of children is needed to answer the question of when classic adulthood GERD begins.

Diagnosis and management of gastrointestinal polyps: pediatric considerations.

Painless, bright red, rectal bleeding with normal stool frequency and consistency is the hallmark presentation of colorectal polyps at any age. Most polyps in children are sporadic, usually isolated, colorectal juvenile polyps that do not require any further surveillance after they are removed. There is, however, increasing recognition of syndromes, including familial adenomatous polyposis, juvenile polyposis coli, Peutz-Jeghers syndrome, and infrequent conditions, such as PTEN hamartoma and hereditary mixed polyposis syndromes. The aim of this review is to allow the reader to correctly identify the patients who do not require follow-up and the smaller group of patients who do require follow-up because of syndromic polyp conditions.

Enteric microbial flora, bacterial overgrowth, and short-bowel syndrome.

Small intestinal bacterial overgrowth (SIBO) occurs commonly in short-bowel syndrome (SBS) and, in some instances, may result in significant problems. SIBO is characterized by a variety of signs and symptoms resulting from nutrient malabsorption caused by an increased number and/or type of bacteria in the small intestine. The anatomic and physiologic changes that occur in SBS together with medications commonly used in these patients facilitate the development of SIBO. Because many aspects related to SIBO in the SBS population remain poorly understood, it was our aim to review the current understanding of the gut flora and issues related to SIBO occurring in SBS.

Neonatal and infant feeding: effect on bone density at 4 years.

OBJECTIVE: The aim of this study was to determine whether the type of feeding during the first 4 months of life affects bone mineral density at 4 years of age. METHODS: Healthy 4-year-old children were recruited from the offices of primary health care providers. After confirming the type of infant feeding by history, dual energy x-ray absorptiometry analysis was obtained at the University of Nebraska Medical Center and evaluated by a radiologist blinded as to feeding type. RESULTS: One hundred and seventy-eight children completed the study (58% male, 85% Caucasian; mean age, 4.5 years). All children had exclusively consumed human milk (n = 57), an infant formula containing no palm olein oil (n = 56) or an infant formula containing palm olein oil (n = 65) during the first 4 months of life. At 4 years of age, no significant differences were noted in bone mineral content or bone mineral density (P = 0.51 and 0.89, respectively) among the three feeding groups as measured by dual energy x-ray absorptiometry. Total body bone mineral content and bone mineral density varied by gender, with males having significantly higher values than females regardless of feeding type (P = 0.028 and P < 0.001, respectively). CONCLUSION: There is no association between the use of palm olein formula during the first 4 months of life and subsequent bone mineral content and bone mineral density in healthy 4-year-old children.

Current and potential uses of probiotics.

OBJECTIVE: To present data that support the current and potential use of probiotics in treating or preventing allergic disorders of the gastrointestinal tract and other disorders. DATA SOURCES: Case reports, double-blind studies, and animal studies were reviewed. STUDY SELECTION: Studies were selected based on the expert opinion of the authors. CONCLUSIONS: Well-designed research studies suggest that supplementary consumption of certain probiotic strains may temporarily alter the intestinal microflora of infants and children to produce a beneficial effect. However, generalization of probiotic effects must not be made and critical scientific evaluation must be used in directing patients to select the appropriate probiotic.

Intestinal rehabilitation and the short bowel syndrome: part 2.

The management of patients with intestinal failure due to short bowel syndrome is complex, requiring a comprehensive approach that frequently necessitates long-term, if not life-long, use of parenteral nutrition. Despite tremendous advances in the provision of parenteral nutrition over the past three decades, which have allowed significant improvements in the survival and quality of life of these patients, this mode of nutritional support carries with it significant risks to the patient, is very costly, and ultimately, does not attempt to improve the function of the remaining bowel. Intestinal rehabilitation refers to the process of restoring enteral autonomy, and thus, allowing freedom from parenteral nutrition, usually by means of dietary, medical, and occasionally, surgical strategies. While recent investigations have focused on the use of trophic substances to increase the absorptive function of the remaining gut, whether intestinal rehabilitation occurs as a consequence of enhanced bowel adaptation or is simply a result of an optimized, comprehensive approach to the care of these patients remains unclear. In Part 1 of this review, we provided an overview of short bowel syndrome and pathophysiological considerations related to the remaining bowel anatomy in these patients. We also reviewed intestinal adaptation and factors that may enhance the adaptive process, focusing on evidence derived from animal studies. In Part 2, relevant data on the development of intestinal adaptation in humans are reviewed as is the general management of short bowel syndrome. Lastly, the potential benefits of a multidisciplinary intestinal rehabilitation program in the care of these patients are also discussed.

Intestinal rehabilitation and the short bowel syndrome: part 1.

The management of patients with intestinal failure due to short bowel syndrome (SBS) is complex, requiring a comprehensive approach that frequently necessitates long-term, if not life-long, use of parenteral nutrition (PN). Despite tremendous advances in the provision of PN over the past three decades, which have allowed significant improvements in the survival and quality of life of these patients, this mode of nutritional support carries with it significant risks to the patient, is very costly and, ultimately, does not attempt to improve the function of the remaining bowel. Intestinal rehabilitation refers to the process of restoring enteral autonomy and, thus, allowing freedom from parenteral nutrition, usually by means of dietary, medical, and, occasionally, surgical strategies. While recent investigations have focused on the use of trophic substances to increase the absorptive function of the remaining gut, whether intestinal rehabilitation occurs as a consequence of enhanced bowel adaptation or is simply a result of an optimized, comprehensive approach to the care of these patients remains unclear. In Part 1 of this review, an overview of SBS and pathophysiological considerations related to the remaining bowel anatomy in these patients will be provided. Additionally, a review of intestinal adaptation and factors that may enhance the adaptive process, focusing on evidence derived from animal studies, will also be discussed. In Part 2, relevant data on the development of intestinal adaptation in studies involving humans will be reviewed as will the general management of SBS. Lastly, the potential benefits of a multidisciplinary intestinal rehabilitation program in the care of these patients will also be discussed.

Enteral and parenteral nutrition in the care of patients with short-bowel syndrome.

Short-bowel syndrome is a challenging entity for the gastroenterologist, requiring integration of medical, nutritional, surgical and psychological therapies. Treatment must be based on the patient's age, remaining gastrointestinal anatomy, baseline nutritional status and underlying general health as well as the numerous complications which may arise. This chapter reviews physiological alterations that occur with short-bowel syndrome and how therapies can be tailored to most adequately meet the needs of these patients. Emphasis on early stages of therapy to enhance intestinal adaptation is focused on as management during this time has a significant impact on the long-term outcome of these patients.

Probiotic use in children.

Interest in nutritional supplements and functional foods has risen significantly in recent years. Many of the products that are marketed to consumers tout the benefits of probiotics for general good health and for a wide variety of conditions and situations. Although most of these products have been used safely for years, careful analysis of scientific research should be conducted before routinely recommending these products, especially for children. A basic understanding of intestinal flora, properties of probiotics, and clinical research findings is necessary for clinicians to delineate the role of probiotic agents in the pediatric population.