Antifungal efficacy of natural antiseptic products against Candida auris.

Candida auris is an emerging fungal pathogen responsible for healthcare-associated infections and outbreaks with high mortality around the world. It readily colonizes the skin, nares, respiratory and urinary tract of hospitalized patients, and such colonization may lead to invasive Candida infection in susceptible patients. However, there is no recommended decolonization protocol for C. auris by international health authorities. The aim of this study is to evaluate the susceptibility of C. auris to commonly used synthetic and natural antiseptic products using an in vitro, broth microdilution assay. Synthetic antiseptics including chlorhexidine, povidone-iodine, and nystatin were shown to be fungicidal against C. auris. Among the natural antiseptics tested, tea tree oil and manuka oil were both fungicidal against C. auris at concentrations less than or equal to 1.25% (v/v). Manuka honey inhibited C. auris at 25% (v/v) concentrations. Among the commercial products tested, manuka body wash and mouthwash were fungicidal against C. auris at concentrations less than or equal to 0.39% (w/v) and 6.25% (v/v) of products as supplied for use, respectively, while tea tree body wash and MedihoneyTM wound gel demonstrated fungistatic properties. In conclusion, this study demonstrated good in vitro antifungal efficacy of tea tree oil, manuka oil, manuka honey, and commercially available antiseptic products containing these active ingredients. Future studies are warranted to evaluate the effectiveness of these antiseptic products in clinical settings.

Candida auris is an emerging superbug fungus that poses a serious threat to global public health. The excellent antifungal efficacy of natural antiseptics and their commercial hygiene products provide new insights into the development of an alternative decolonization regimen against C. auris.

Stroke caregivers' perception on instant messaging application use for psychological intervention: a qualitative study.

In caring for patients with stroke, the leading cause of death and disability affecting over 80 million people worldwide, caregivers experience substantial psychological and physical burdens and difficulties in help-seeking owing to physical and time-constraints. Social distancing measures imposed during the coronavirus disease 2019 (COVID-19) pandemic further restricted them from using caregiver support services. While the use of telehealth emerged as a global prevailing trend during the COVID-19 pandemic, evidence for utilising instant messaging (IM) applications for psychological intervention is scanty. This study aimed to explore stroke caregivers' perceived potential utility of IM-delivered psychological intervention. Between January and August 2020, 36 adult family stroke caregivers in Hong Kong were recruited to individual telephone semi-structured interviews using purposive sampling. The interviews were audio-recorded, transcribed verbatim and analysed using an interpretive description approach. Three themes of caregivers' perceptions towards IM-delivered psychological intervention emerged: perceived high convenience and ease of use, perceived advantages that overcome existing barriers to services and message delivery tailored to individual needs. Our findings suggested that there is an imminent need among stroke caregivers for personalised psychological interventions and that IM is a potential modality for overcoming existing barriers in delivering accessible support to caregivers in real-time, real-world settings. Our study highlighted caregivers' acceptance and perceived benefits of IM-delivered psychological intervention and provided practical insights into the design of IM-delivered psychological interventions.

Associations of eHealth literacy and knowledge with preventive behaviours and psychological distress during the COVID-19 pandemic: a population-based online survey.

OBJECTIVES: To compare the associations of COVID-19 preventive behaviours and depressive and anxiety symptoms with eHealth literacy and COVID-19 knowledge among Korean adults. DESIGN: A cross-sectional online survey was conducted in April 2020. SETTING: Seoul metropolitan area in South Korea. PARTICIPANTS: 1057 Korean adults were recruited. MAIN OUTCOME MEASURES: Associations between eHealth literacy, COVID-19 knowledge, COVID-19 preventive behaviours and psychological distress were computed using Pearson's correlation and logistic regression analyses. eHealth literacy, COVID-19 knowledge, COVID-19 preventive behaviours and psychological distress were weighted by sex and age distribution of the general population in Seoul Metropolitan area. RESULTS: 68.40% (n=723) perceived high eHealth literacy level (eHEALS ≥26), while 57.43% (n=605) had high levels of COVID-19 knowledge (score ≥25). No significant association between eHealth literacy and COVID-19 knowledge was identified (r=0.05, p=0.09). eHealth literacy and COVID-19 knowledge were significantly associated with COVID-19 preventive behaviours (aOR=1.99, 95% CI 1.51 to 2.62 L; aOR=1.81, 95% CI 1.40 to 2.34, respectively). High eHealth literacy was significantly associated with anxiety symptom (aOR=1.71, 95% CI 1.18 to 2.47) and depressive symptom (aOR=1.69, 95% CI 1.24 to 2.30). COVID-19 knowledge had negative and no associations with the symptoms (aOR=0.62, 95% CI 0.46 to 0.86; aOR=0.79, 95% CI 0.60 to 1.03, respectively). High eHealth literacy with low COVID-19 knowledge was positively and significantly associated with COVID-19 preventive behaviours (aOR=2.30, 95% CI 1.52 to 3.43), and anxiety (aOR=1.81, 95% CI 1.09 to 3.01) and depressive symptoms (aOR=2.24, 95% CI 1.41 to 3.55). High eHealth literacy with high COVID-19 knowledge were significantly associated with more preventive behaviours (aOR=3.66, 95% CI 2.47 to 5.42) but no significant associations with anxiety and depressive symptoms. CONCLUSION: We identified that eHealth literacy and COVID-19 knowledge were not associated each other, and differently associated with individuals' COVID-19 preventive behaviours and psychological well-being. Public health strategies should pay attention to enhancing both eHealth literacy and COVID-19 knowledge levels in the public to maximise their COVID-19 preventive behaviours and mitigate their psychological distress during COVID-19 pandemic.

Qualitative Study of Chinese Stroke Caregivers' Caregiving Experience During the COVID-19 Pandemic.

BACKGROUND AND PURPOSE: The coronavirus disease 2019 (COVID-19) outbreak has led to disruptions in health care service delivery worldwide, inevitably affecting stroke survivors requiring ongoing rehabilitation and chronic illness management. To date, no published research has been found on stroke caregiving during the COVID-19 pandemic. This study aimed to explore Hong Kong stroke caregivers' caregiving experiences in the midst of this difficult time. METHODS: Individual semistructured interviews were conducted with 25 Chinese adult primary stroke caregivers from May to June 2020 via telephone. Interviews were transcribed verbatim and analyzed using an interpretive description approach and constant comparison strategy. RESULTS: Five themes of the stroke caregiving experience during the COVID-19 pandemic emerged: care service adversities, additional caregiving workload and strain, threatened relationship between caregiver and stroke survivors, threats to caregivers' physical and psychological well-being, and needs for continuing caregiving roles. Our findings suggested that caregivers have worsened physical and psychological well-being because of increases in care burden with simultaneously reduced formal and informal support. The relationship between caregiver and stroke survivor was subsequently affected, placing some survivors at heightened risk of abuse. CONCLUSIONS: Our study provides valuable findings about stroke caregiving experiences and needs during the pandemic. Delivery of psychological support, telemedicine, and household hygiene resources would be useful to mitigate caregivers' psychological distress during the COVID-19 pandemic.

Withaferin A activates TRIM16 for its anti-cancer activity in melanoma.

Although selective BRAF inhibitors and novel immunotherapies have improved short-term treatment responses in metastatic melanoma patients, acquired resistance to these therapeutics still represent a major challenge in clinical practice. In this study, we evaluated the efficacy of Withaferin A (WFA), derived from the medicinal plant Withania Somnifera, as a novel therapeutic agent for the treatment of melanoma. WFA showed selective toxicity to melanoma cells compared to non-malignant cells. WFA induced apoptosis, significantly reduced cell proliferation and inhibited migration of melanoma cells. We identified that repression of the tumour suppressor TRIM16 diminished WFA cytotoxicity, suggesting that TRIM16 was in part responsible for the cytotoxic effects of WFA in melanoma cells. Together our data indicates that WFA has potent cytopathic effects on melanoma cells through TRIM16, suggesting a potential therapeutic application of WFA in the disease.

Mycophenolate sodium in the treatment of corticosteroid-refractory non-infectious inflammatory uveitis (MySTRI study).

OBJECTIVES: To evaluate the therapeutic effect and safety profile of next generation mycophenolate sodium (MPS), which is different from mycophenolate mofetil with an enteric-coated formulation, in corticosteroid-refractory non-infectious inflammatory uveitis (CRU) patients. METHODS: Prospective, uncontrolled, open-label interventional case series. Forty consecutive patients at a tertiary uveitis referral centre received 6 months of oral MPS as the treatment regimen with follow-up 12 months. The main outcome measures were best-corrected visual acuity (BCVA), inflammatory index, steroid-sparing effect of tapering prednisone to ≤10 mg daily and side effects. RESULTS: Mean age of enroled patients was 49 (49 ± 13) years and 29 (72.5%) were female. Thirty-six (90.0%) had bilateral disease. There were 0 (0%) anterior uveitis, 2 (5.0%) intermediate uveitis, 22 (55.0%) posterior uveitis, and 16 (40.0%) panuveitis. Vogt-Koyanagi-Harada disease was the most common diagnosis (17/40, 42.5%), followed by idiopathic panuveitis (8/40, 20%) and idiopathic retinal vasculitis (5/40, 12.5%). LogMAR BCVA improved from 0.9 (SD = 0.09) to 0.31 (SD = 0.08) after 6 months of MPS with good steroid-sparing effect (p = 0.012). Further maintenance in LogMAR BCVA was evident after MPS discontinuation from 6th month to 12th month, from 0.31 (SD = 0.08) to 0.33 (SD = 0.07), respectively (p = 0.81). MPS was the only immunosuppressive drug needed to reach quiescent state in 29 patients (72.5%). The drug-related safety profile was satisfactory. CONCLUSION: MPS is an effective steroid-sparing drug for the treatment of CRU. The effect seen was not only during the 6 months of therapy, but also extended to 12 months to maintain BCVA and inflammation control. The side effects were acceptable.

Icaritin enhances mESC self-renewal through upregulating core pluripotency transcription factors mediated by ERα.

Utilization of small molecules in modulation of stem cell self-renewal is a promising approach to expand stem cells for regenerative therapy. Here, we identify Icaritin, a phytoestrogen molecule enhances self-renewal of mouse embryonic stem cells (mESCs). Icaritin increases mESCs proliferation while maintains their self-renewal capacity in vitro and pluripotency in vivo. This coincides with upregulation of key pluripotency transcription factors OCT4, NANOG, KLF4 and SOX2. The enhancement of mESCs self-renewal is characterized by increased population in S-phase of cell cycle, elevation of Cylin E and Cyclin-dependent kinase 2 (CDK2) and downregulation of p21, p27 and p57. PCR array screening reveals that caudal-related homeobox 2 (Cdx2) and Rbl2/p130 are remarkably suppressed in mESCs treated with Icaritin. siRNA knockdown of Cdx2 or Rbl2/p130 upregulates the expression of Cyclin E, OCT4 and SOX2, and subsequently increases cell proliferation and colony forming efficiency of mESCs. We then demonstrate that Icaritin co-localizes with estrogen receptor alpha (ERα) and activates its nuclear translocation in mESCs. The promotive effect of Icaritin on cell cycle and pluripotency regulators are eliminated by siRNA knockdown of ERα in mESCs. The results suggest that Icaritin enhances mESCs self-renewal by regulating cell cycle machinery and core pluripotency transcription factors mediated by ERα.

Fabrication of injectable high strength hydrogel based on 4-arm star PEG for cartilage tissue engineering.

Hydrogels prepared from poly(ethylene glycol) (PEG) are widely applied in tissue engineering, especially those derived from a combination of functional multi-arm star PEG and linear crosslinker, with an expectation to form a structurally ideal network. However, the poor mechanical strength still renders their further applications. Here we examined the relationship between the dynamics of the pre-gel solution and the mechanical property of the resultant hydrogel in a system consisting of 4-arm star PEG functionalized with vinyl sulfone and short dithiol crosslinker. A method to prepare mechanically strong hydrogel for cartilage tissue engineering is proposed. It is found that when gelation takes place at the overlap concentration, at which a slow relaxation mode just appears in dynamic light scattering (DLS), the resultant hydrogel has a local maximum compressive strength ∼20 MPa, while still keeps ultralow mass concentration and Young's modulus. Chondrocyte-laden hydrogel constructed under this condition was transplanted into the subcutaneous pocket and an osteochondral defect model in SCID mice. The in vivo results show that chondrocytes can proliferate and maintain their phenotypes in the hydrogel, with the production of abundant extracellular matrix (ECM) components, formation of typical chondrocyte lacunae structure and increase in Young's modulus over 12 weeks, as indicated by histological, immunohistochemistry, gene expression analyses and mechanical test. Moreover, newly formed hyaline cartilage was observed to be integrated with the host articular cartilage tissue in the defects injected with chondrocytes/hydrogel constructs. The results suggest that this hydrogel is a promising candidate scaffold for cartilage tissue engineering.

Flavonoid Compound Icariin Activates Hypoxia Inducible Factor-1α in Chondrocytes and Promotes Articular Cartilage Repair.

Articular cartilage has poor capability for repair following trauma or degenerative pathology due to avascular property, low cell density and migratory ability. Discovery of novel therapeutic approaches for articular cartilage repair remains a significant clinical need. Hypoxia is a hallmark for cartilage development and pathology. Hypoxia inducible factor-1alpha (HIF-1α) has been identified as a key mediator for chondrocytes to response to fluctuations of oxygen availability during cartilage development or repair. This suggests that HIF-1α may serve as a target for modulating chondrocyte functions. In this study, using phenotypic cellular screen assays, we identify that Icariin, an active flavonoid component from Herba Epimedii, activates HIF-1α expression in chondrocytes. We performed systemic in vitro and in vivo analysis to determine the roles of Icariin in regulation of chondrogenesis. Our results show that Icariin significantly increases hypoxia responsive element luciferase reporter activity, which is accompanied by increased accumulation and nuclear translocation of HIF-1α in murine chondrocytes. The phenotype is associated with inhibiting PHD activity through interaction between Icariin and iron ions. The upregulation of HIF-1α mRNA levels in chondrocytes persists during chondrogenic differentiation for 7 and 14 days. Icariin (10-6 M) increases the proliferation of chondrocytes or chondroprogenitors examined by MTT, BrdU incorporation or colony formation assays. Icariin enhances chondrogenic marker expression in a micromass culture including Sox9, collagen type 2 (Col2α1) and aggrecan as determined by real-time PCR and promotes extracellular matrix (ECM) synthesis indicated by Alcian blue staining. ELISA assays show dramatically increased production of aggrecan and hydroxyproline in Icariin-treated cultures at day 14 of chondrogenic differentiation as compared with the controls. Meanwhile, the expression of chondrocyte catabolic marker genes including Mmp2, Mmp9, Mmp13, Adamts4 and Adamts5 was downregulated following Icariin treatment for 14 days. In a differentiation assay using bone marrow mesenchymal stem cells (MSCs) carrying HIF-1α floxed allele, the promotive effect of Icariin on chondrogenic differentiation is largely decreased following Cre recombinase-mediated deletion of HIF-1α in MSCs as indicated by Alcian blue staining for proteoglycan synthesis. In an alginate hydrogel 3D culture system, Icariin increases Safranin O positive (SO+) cartilage area. This phenotype is accompanied by upregulation of HIF-1α, increased proliferating cell nuclear antigen positive (PCNA+) cell numbers, SOX9+ chondrogenic cell numbers, and Col2 expression in the newly formed cartilage. Coincide with the micromass culture, Icariin treatment upregulates mRNA levels of Sox9, Col2α1, aggrecan and Col10α1 in the 3D cultures. We then generated alginate hydrogel 3D complexes incorporated with Icariin. The 3D complexes were transplanted in a mouse osteochondral defect model. ICRS II histological scoring at 6 and 12 weeks post-transplantation shows that 3D complexes incorporated with Icariin significantly enhance articular cartilage repair with higher scores particularly in selected parameters including SO+ cartilage area, subchondral bone and overall assessment than that of the controls. The results suggest that Icariin may inhibit PHD activity likely through competition for cellular iron ions and therefore it may serve as an HIF-1α activator to promote articular cartilage repair through regulating chondrocyte proliferation, differentiation and integration with subchondral bone formation.

Unimolecular Rate Expression for Cyclohexene Decomposition and Its Use in Chemical Thermometry under Shock Tube Conditions.

The methods used in deriving the rate expressions from comparative rate single-pulse shock tube studies, recent direct shock tube studies, and high-pressure flow experiments bearing on the data for the reverse Diels-Alder decomposition of cyclohexene to form ethylene and 1,3-butadiene are reviewed. This current interest is due to the increasing need for accurate kinetics and physical data (particularly the temperature) for realistic simulations in practical areas such as combustion. The rate constants derived from the direct shock tube studies and high-pressure flow experiments are somewhat larger than those used in comparative rate single-pulse shock tube experiments. For the latter, it is shown that they have been derived from a variety of independent experiments that include rate constants for unimolecular decomposition and isomerization processes that are considered to be well understood. The possibility of non-Arrhenius behavior in the unimolecular rate constants as a consequence of the large range covered in rate constants (as much as 12 orders of magnitude) for the comparative rate experiments has been examined and ruled out as a source of the discrepancy. Our analysis shows that there is the need to consider the possibility of radical-induced decompositions for verifying the correctness of the reaction mechanisms in studying unimolecular reactions. In the case of cyclohexene decomposition, recent experiments demonstrating the presence of residual amounts of H atoms in shock tube experiments suggest that addition to the double bond can also lead to the formation of ethylene and 1,3-butadiene and hence to rate constants larger than the true values. This possibility is even more likely to occur in high-pressure flow experiments. As a result, the internal standard method must be used with care and a radical inhibitor should always be present in sufficiently large quantities to suppress possible chain reactions. The present analysis results have important implications for the determination of temperatures in shock tubes.

Isomerization of cis-1,2-dimethylcyclohexane in single-pulse shock tube experiments.

Cyclic hydrocarbons are major constituents of jet fuels and reference compounds in jet fuel surrogates. The kinetic and thermal stability and reaction mechanisms of fuel molecules are essential input parameters in the models and simulations used in the design of novel fuels, renewable energy technologies, and devices. A detailed study and analysis of the pyrolytic chemistry of cis-1,2-dimethylcyclohexane has been performed in single-pulse shock tube experiments. The investigations are carried out over the temperature range of 1100 to 1200 K at about 2.5 atm pressure. The isomeric products are trans-1,2-dimethylcyclohexane, 1-octene, and (cis + trans)-2-octene. The three octene isomers can be attributed to internal disproportionation processes. Assuming a diradical mechanism and that cis-1,2-dimethylcyclohexane is formed in equal amount with respect to its trans isomer, the total rate expression for isomerization is kC-C = 10(15.5±0.8) exp(-38,644 ± 2061 K/T) s(-1). The rate constants are over an order of magnitude smaller than the equivalent noncyclic hydrocarbon system. The presence of the isomeric octenes suggests that internal disproportionation is an important component of the isomerization process.

EPO promotes bone repair through enhanced cartilaginous callus formation and angiogenesis.

Erythropoietin (EPO)/erythropoietin receptor (EPOR) signaling is involved in the development and regeneration of several non-hematopoietic tissues including the skeleton. EPO is identified as a downstream target of the hypoxia inducible factor-α (HIF-α) pathway. It is shown that EPO exerts a positive role in bone repair, however, the underlying cellular and molecular mechanisms remain unclear. In the present study we show that EPO and EPOR are expressed in the proliferating, pre-hypertrophic and hypertrophic zone of the developing mouse growth plates as well as in the cartilaginous callus of the healing bone. The proliferation rate of chondrocytes is increased under EPO treatment, while this effect is decreased following siRNA mediated knockdown of EPOR in chondrocytes. EPO treatment increases biosynthesis of proteoglycan, accompanied by up-regulation of chondrogenic marker genes including SOX9, SOX5, SOX6, collagen type 2, and aggrecan. The effects are inhibited by knockdown of EPOR. Blockage of the endogenous EPO in chondrocytes also impaired the chondrogenic differentiation. In addition, EPO promotes metatarsal endothelial sprouting in vitro. This coincides with the in vivo data that local delivery of EPO increases vascularity at the mid-stage of bone healing (day 14). In a mouse femoral fracture model, EPO promotes cartilaginous callus formation at days 7 and 14, and enhances bone healing at day 28 indexed by improved X-ray score and micro-CT analysis of microstructure of new bone regenerates, which results in improved biomechanical properties. Our results indicate that EPO enhances chondrogenic and angiogenic responses during bone repair. EPO's function on chondrocyte proliferation and differentiation is at least partially mediated by its receptor EPOR. EPO may serve as a therapeutic agent to facilitate skeletal regeneration.

Insulin exerts direct, IGF-1 independent actions in growth plate chondrocytes.

Insufficient insulin production or action in diabetic states is associated with growth retardation and impaired bone healing, while the underling mechanisms are unknown. In this study, we sought to define the role of insulin signaling in the growth plate. Insulin treatment of embryonic metatarsal bones from wild-type mice increased chondrocyte proliferation. Mice lacking insulin receptor (IR) selectively in chondrocytes (CartIR (-/-)) had no discernable differences in total femoral length compared to control littermates. However, CartIR (-/-) mice exhibited an increase in chondrocyte numbers in the growth plate than that of the controls. Chondrocytes lacking IR had elevated insulin-like growth factor (IGF)-1R mRNA and protein levels. Subsequently, IGF-1 induced phosphorylation of Akt and ERK was enhanced, while this action was eliminated when the cells were treated with IGF-1R inhibitor Picropodophyllin. Deletion of the IR impaired chondrogenic differentiation, and the effect could not be restored by treatment of insulin, but partially rescued by IGF-1 treatment. Intriguingly, the size of hypertrophic chondrocytes was smaller in CartIR (-/-) mice when compared with that of the control littermates, which was associated with upregulation of tuberous sclerosis complex 2 (TSC2). These results suggest that deletion of the IR in chondrocytes sensitizes IGF-1R signaling and action, IR and IGF-1R coordinate to regulate the proliferation, differentiation and hypertrophy of growth plate chondrocytes.

CD146+ human umbilical cord perivascular cells maintain stemness under hypoxia and as a cell source for skeletal regeneration.

The human umbilical cord perivascular cells (HUCPVCs) have been considered as an alternative source of mesenchymal progenitors for cell based regenerative medicine. However, the biological properties of these cells remain to be well characterized. In the present study, HUCPVCs were isolated and sorted by CD146(+) pericyte marker. The purified CD146(+) HUCPVCs were induced to differentiate efficiently into osteoblast, chondrocyte and adipocyte lineages in vitro. Six weeks following subcutaneous transplantation of CD146(+) HUCPVCs-Gelfoam-alginate 3D complexes in severe combined immunodeficiency (SCID) mice, newly formed bone matrix with embedded osteocytes of donor origin was observed. The functional engraftment of CD146(+) HUCPVCs in the new bone regenerates was further confirmed in a critical-sized bone defect model in SCID mice. Hypoxic conditions suppressed osteogenic differentiation while increased cell proliferation and colony-forming efficiency of CD146(+) HUCPVCs as compared to that under normoxic conditions. Re-oxygenation restored the multi-differentiation potential of the CD146(+) HUCPVCs. Western blot analysis revealed an upregulation of HIF-1α, HIF-2α, and OCT-4 protein expression in CD146(+) HUCPVCs under hypoxia, while there was no remarkable change in SOX2 and NANOG expression. The gene expression profiles of stem cell transcription factors between cells treated by normoxia and hypoxic conditions were compared by PCR array analysis. Intriguingly, PPAR-γ was dramatically downregulated (20-fold) in mRNA expression under hypoxia, and was revealed to possess a putative binding site in the Hif-2α gene promoter region. Chromatin immunoprecipitation assays confirmed the binding of PPAR-γ protein to the Hif-2α promoter and the binding was suppressed by hypoxia treatment. Luciferase reporter assay showed that the Hif-2α promoter activity was suppressed by PPAR expression. Thus, PPAR-γ may involve in the regulation of HIF-2α for stemness maintenance and promoting the expansion of CD146(+) HUCPVCs in response to hypoxia. CD146(+) HUCPVCs may serve as a potential autologous cell source for bone regeneration.

Bond cleavage during isobutanol thermal decomposition and the breaking of C-C bonds in alcohols at high temperatures.

Isobutanol was thermally decomposed in a single pulse shock tube under conditions where chain processes were suppressed. The main reaction is the breaking of C-C bonds. Literature rate expressions, experimentally determined, are found in some cases to be in disagreement. The rate expressions for the decomposition processes at temperatures of 1090 to 1240 K and pressures of 1.5 and 6 atm are k(isobutanol → isopropyl + hydroxymethyl) + k(isobutanol → methyl + 1-hydroxypropyl-2) = 10(16.7±0.3) exp(-41097 ± 750) s(-1), where k(isobutanol → isopropyl + hydroxymethyl) = 10(16.45 ±0.3) exp(-40910 ± 750/T) s(-1) and k(isobutanol → methyl + 1-hydroxypropyl-2) = 10(16.38±0.3) exp(-41560 ± 750/T) s(-1). These values permit comparisons with recent estimates including those from ab initio calculations. A new procedure is presented that uses information on the kinetics of bond breaking reactions of alkanes and the effect of OH substitution to derive rate coefficients for similar reactions of alcohols. This leads to the following rate expression for the smaller alcohols, at temperatures of 1090 to 1240 K and pressures of 1.5 and 6 atm, k(ethanol → methyl + hydroxymethyl) = 10(16.42±0.3) exp(-43496 ± 750 K/T) s(-1), k(isopropanol → methyl + 1-hydroxyethyl) = 10(16.54±0.3) exp(-42495 ± 750 K/T) s(-1), k(n-propanol → ethyl + hydroxymethyl) = 10(16.43±0.3) exp(-41696 ± 750 K/T) s(-1), and k(n-propanol → methyl + 2-hydroxymethyl) = 10(16.53±0.3) exp(-42945 ± 750 K/T) s(-1). Extension of this approach to other alcohols is straightforward. The resulting correlations along with the data on dehydration of alcohols provide novel information of the kinetic stability of alcohols.

Dehydration of isobutanol and the elimination of water from fuel alcohols.

Rate coefficients for the dehydration of isobutanol have been determined experimentally from comparative rate single pulse shock tube measurements and calculated via multistructural transition state theory (MS-TST). They are represented by the Arrhenius expression, k(isobutanol → isobutene + H2O)(experimental) = 7.2 × 10(13) exp(-35300 K/T) s(-1). The theoretical work leads to the high pressure rate expression, k(isobutanol → isobutene + H2O)(theory) = 3.5 × 10(13) exp(-35400 K/T) s(-1). Results are thus within a factor of 2 of each other. The experimental results cover the temperature range 1090-1240 K and pressure range 1.5-6 atm, with no discernible pressure effects. Analysis of these results, in combination with earlier single pulse shock tube work, made it possible to derive the governing factors that control the rate coefficients for alcohol dehydration in general. Alcohol dehydration rate constants depend on the location of the hydroxyl group (primary, secondary, and tertiary) and the number of available H-atoms adjacent to the OH group for water elimination. The position of the H-atoms in the hydrocarbon backbone appears to be unimportant except for highly substituted molecules. From these correlations, we have derived k(isopropanol → propene + H2O) = 7.2 × 10(13) exp(-33000 K/T) s(-1). Comparison of experimental determination with theoretical calculations for this dehydration, and those for ethanol show deviations of the same magnitude as for isobutanol. Systematic differences between experiments and theoretical calculations are common.

Shock tube study on the thermal decomposition of n-butanol.

Dilute concentrations of normal-butanol has been decomposed in single pulse shock tube studies in the presence of large quantities of a chemical inhibitor that suppresses contributions from chain decomposition. Reaction temperatures and pressures are in the range of [1126-1231] K and [1.3-6.5] bar. Ethylene and 1-butene are the only products. The mechanism of the initial decomposition steps involves direct elimination of water and C-C bond cleavage. The fundamental high pressure unimolecular decomposition rate expressions are k(C(4)H(9)OH → CH(3) + CH(2)CH(2)CH(2)OH) = 10(16.4±0.4) exp(42410 ± 800 [K]/T) s(-1); k(C(4)H(9)OH → CH(3)CH(2) + CH(2)CH(2)OH) = 10(16.4±0.4) exp(-41150 ± 800 [K]/T) s(-1); k(C(4)H(9)OH → CH(3)CH(2)CH(2) + CH(2)OH) = 10(16.4±0.4) exp(-41150 ± 800 [K]/T) s(-1); and k(C(4)H(9)OH → CH(3)CH(2)CH═CH(2) + H(2)O) = 10(14.0±0.4) exp(-35089 ± 800 [K]/T) s(-1), where the rate expressions for C-C bond cleavage are based on assumptions regarding the relative rates of the three processes derived from earlier studies on the effect of an OH group on rate expressions. All reactions are in the high pressure limit and suggest that the step size down in the presence of argon is at least 1300 cm(-1). These rate expressions are consistent with the following H-C bond dissociation energies: BDE(H-CH(2)CH(2)CH(2)OH) = 417.2 ± 7 kJ/mol, BDE(H-CH(2)CH(2)OH) = 419.2 ± 7 kJ/mol, and BDE(H-CH(2)OH) = 401.7 ± 9 kJ/mol, with an estimated uncertainty of 6 kJ/mol. The kinetics and thermodynamic results are compared with estimates used in the building of combustion kinetics databases.

Shock tube studies on the decomposition of 2-butanol.

The thermal decomposition of 2-butanol have been studied at temperatures of 1045-1221 K and pressures of 1.5-6 bar using the single pulse shock tube technique. Dilute concentrations of 2-butanol have been decomposed in the presence of large quantities of a radical inhibitor. The mechanism for decomposition involves direct elimination of water producing cis- and trans-2-butene, and 1-butene, and C-C bond fission producing ethylene. Acetaldehyde, propionaldehyde, and propene were also observed in much smaller yields from C-C bond fission. The respective unimolecular rate expressions are as follows: k(C(3)H(6)(OH)CH(3) → cis-CH(3)CH═CHCH(3) + H(2)O) = 10(13.1 ± 0.3) exp(-33414 ± 755 K/T) s(-1); k(C(3)H(6)(OH)CH(3) → trans-CH(3)CH═CHCH(3) + H(2)O) = 10(13.5 ± 0.3) exp(-33820 ± 755 K/T) s(-1); k(C(3)H(6)(OH)CH(3) → CH(3)CH(2)CH═CH(2) + H(2)O) = 10(13.6 ± 0.3) exp(-33002 ± 755 K/T) s(-1); k(C(3)H(6)(OH)CH(3) → C(2)H(5)(•) + (•)CH(OH)CH(3)) = 10(15.9 ± 0.3) exp(-39252 ± 755 K/T) s(-1). These rate expressions are compared with analogous reactions for primary and tertiary butanols. They form a basis for the prediction of those for related systems. Comparison with estimated values used in the simulation of butanol combustion is indicative of the uncertainties in the rate constants that are used in such models. The activation energy of 326 kJ/mol leads to a bond dissociation energy of the CH(OH)CH(3) radical (H-CH(OH)CH(3)) of 400 kJ/mol, in excellent agreement with earlier calculated results from theory and disagreement with the experimental results from iodination studies in the expected range.

Proton transfer from C-6 of uridine 5'-monophosphate catalyzed by orotidine 5'-monophosphate decarboxylase: formation and stability of a vinyl carbanion intermediate and the effect of a 5-fluoro substituent.

The exchange for deuterium of the C-6 protons of uridine 5'-monophosphate (UMP) and 5-fluorouridine 5'-monophosphate (F-UMP) catalyzed by yeast orotidine 5'-monophosphate decarboxylase (ScOMPDC) at pD 6.5-9.3 and 25 °C was monitored by (1)H NMR spectroscopy. Deuterium exchange proceeds by proton transfer from C-6 of the bound nucleotide to the deprotonated side chain of Lys-93 to give the enzyme-bound vinyl carbanion. The pD-rate profiles for k(cat) give turnover numbers for deuterium exchange into enzyme-bound UMP and F-UMP of 1.2 × 10(-5) and 0.041 s(-1), respectively, so that the 5-fluoro substituent results in a 3400-fold increase in the first-order rate constant for deuterium exchange. The binding of UMP and F-UMP to ScOMPDC results in 0.5 and 1.4 unit decreases, respectively, in the pK(a) of the side chain of the catalytic base Lys-93, showing that these nucleotides bind preferentially to the deprotonated enzyme. We also report the first carbon acid pK(a) values for proton transfer from C-6 of uridine (pK(CH) = 28.8) and 5-fluorouridine (pK(CH) = 25.1) in aqueous solution. The stabilizing effects of the 5-fluoro substituent on C-6 carbanion formation in solution (5 kcal/mol) and at ScOMPDC (6 kcal/mol) are similar. The binding of UMP and F-UMP to ScOMPDC results in a greater than 5 × 10(9)-fold increase in the equilibrium constant for proton transfer from C-6, so that ScOMPDC stabilizes the bound vinyl carbanions, relative to the bound nucleotides, by at least 13 kcal/mol. The pD-rate profile for k(cat)/K(m) for deuterium exchange into F-UMP gives the intrinsic second-order rate constant for exchange catalyzed by the deprotonated enzyme as 2300 M(-1) s(-1). This was used to calculate a total rate acceleration for ScOMPDC-catalyzed deuterium exchange of 3 × 10(10) M(-1), which corresponds to a transition-state stabilization for deuterium exchange of 14 kcal/mol. We conclude that a large portion of the total transition-state stabilization for the decarboxylation of orotidine 5'-monophosphate can be accounted for by stabilization of the enzyme-bound vinyl carbanion intermediate of the stepwise reaction.

Asymmetric hydroalkynylation of norbornadienes promoted by chiral iridium catalysts.

Across bonds: The first successful iridium-catalyzed asymmetric hydroalkynylation of nonpolar alkenes with good to excellent enantioselectivity is described (see scheme; cod = 1,5-cyclooctadiene, DCE = 1,2-dichloroethane). This catalytic system exhibits good functional group compatibility as NH(2), OH, Br, F, and SiMe(3) groups remain intact during the reaction.