Revisiting the mechanism of asymmetric Ni-catalyzed reductive carbo-carboxylation with CO2: The additives affect the product selectivity.

The mechanistic details of the asymmetric Ni-catalyzed reductive cyclization/carboxylation of alkenes with CO2 have been revisited using DFT methods. Emphasis was put on the enantioselectivity and the mechanistic role of Lewis acid additives and in situ formed salts. Our results show that oxidative addition of the substrate is rate-limiting, with the formed Ni(II)-aryl intermediate preferring a triplet spin state. After reduction to Ni(I), enantioselective cyclization of the substrate occurs, followed by inner sphere carboxylation. Our proposed mechanism reproduces the experimentally observed enantiomeric excess and identifies critical C-H/O and C-H/N interactions that affect the selectivity. Further, our results highlight the beneficial effect of Lewis acids on CO2 insertion and suggest that in situ formed salts influence if the 5-exo or 6-endo product will be formed.

Mechanistic Investigations of the Asymmetric Hydrogenation of Enamides with Neutral Bis(phosphine) Cobalt Precatalysts.

The mechanism of the asymmetric hydrogenation of prochiral enamides by well-defined, neutral bis(phosphine) cobalt(0) and cobalt(II) precatalysts has been explored using(R,R)-iPrDuPhos ((R,R)-iPrDuPhos = (+)-1,2-bis[(2R,5R)-2,5-diisopropylphospholano]benzene) as a representative chiral bis(phosphine) ligand. A series of (R,R)-(iPrDuPhos)Co(enamide) (enamide = methyl-2-acetamidoacrylate (MAA), methyl(Z)-α-acetamidocinnamate (MAC), and methyl(Z)-acetamido(4-fluorophenyl)acrylate (4FMAC)) complexes (1-MAA, 1-MAC, and 1-4FMAC), as well as a dinuclear cobalt tetrahydride, [(R,R)-(iPrDuPhos)Co]2(µ2-H)3(H) (2), were independently synthesized, characterized, and evaluated in both stoichiometric and catalytic hydrogenation reactions. Characterization of (R,R)-(iPrDuPhos)Co(enamide) complexes by X-ray diffraction established the formation of the pro-(R) diastereomers in contrast to the (S)-alkane products obtained from the catalytic reaction. In situ monitoring of the cobalt-catalyzed hydrogenation reactions by UV-visible and freeze-quench electron paramagnetic resonance spectroscopies revealed (R,R)-(iPrDuPhos)Co(enamide) complexes as the catalyst resting state for all the three enamides studied. Variable time normalization analysis kinetic studies of the cobalt-catalyzed hydrogenation reactions in methanol established a rate law that is first order in (R,R)-(iPrDuPhos)Co(enamide) and H2 but independent of the enamide concentration. Deuterium-labeling studies, including measurement of an H2/D2 kinetic isotope effect and catalytic hydrogenations with HD, established an irreversible H2 addition step to the bound enamide. Density functional theory calculations support that this step is both rate and selectivity determining. Calculations, as well as HD-labeling studies, provide evidence for two-electron redox cycling involving cobalt(0) and cobalt(II) intermediates during the catalytic cycle. Taken together, these experiments support an unsaturated pathway for the [(R,R)-(iPrDuPhos)Co]-catalyzed hydrogenation of prochiral enamides.

Cobalt-Catalyzed Asymmetric Hydrogenation of Enamides: Insights into Mechanisms and Solvent Effects.

The mechanistic details of the (PhBPE)Co-catalyzed asymmetric hydrogenation of enamides are investigated using computational and experimental approaches. Four mechanistic possibilities are compared: a direct Co(0)/Co(II) redox path, a metathesis pathway, a nonredox Co(II) mechanism featuring an aza-metallacycle, and a possible enamide-imine tautomerization pathway. The results indicate that the operative mechanism may depend on the type of enamide. Explicit solvent is found to be crucial for the stabilization of transition states and for a proper estimation of the enantiomeric excess. The combined results highlight the complexity of base-metal-catalyzed hydrogenations but do also provide guiding principles for a mechanistic understanding of these systems, where protic substrates can be expected to open up nonredox hydrogenation pathways.

Ligand and solvent effects on CO2 insertion into group 10 metal alkyl bonds.

The insertion of carbon dioxide into metal element σ-bonds is an important elementary step in many catalytic reactions for carbon dioxide valorization. Here, the insertion of carbon dioxide into a family of group 10 alkyl complexes of the type (RPBP)M(CH3) (RPBP = B(NCH2PR2)2C6H4 -; R = Cy or t Bu; M = Ni or Pd) to generate κ1-acetate complexes of the form (RPBP)M{OC(O)CH3} is investigated. This involved the preparation and characterization of a number of new complexes supported by the unusual RPBP ligand, which features a central boryl donor that exerts a strong trans-influence, and the identification of a new decomposition pathway that results in C-B bond formation. In contrast to other group 10 methyl complexes supported by pincer ligands, carbon dioxide insertion into (RPBP)M(CH3) is facile and occurs at room temperature because of the high trans-influence of the boryl donor. Given the mild conditions for carbon dioxide insertion, we perform a rare kinetic study on carbon dioxide insertion into a late-transition metal alkyl species using ( t BuPBP)Pd(CH3). These studies demonstrate that the Dimroth-Reichardt parameter for a solvent correlates with the rate of carbon dioxide insertion and that Lewis acids do not promote insertion. DFT calculations indicate that insertion into ( t BuPBP)M(CH3) (M = Ni or Pd) proceeds via an SE2 mechanism and we compare the reaction pathway for carbon dioxide insertion into group 10 methyl complexes with insertion into group 10 hydrides. Overall, this work provides fundamental insight that will be valuable for the development of improved and new catalysts for carbon dioxide utilization.

Occurrence of Campylobacter, Salmonella, Yersinia enterocolitica and Listeria monocytogenes in some retail food products in Novi Sad.

The official reporting system in the Province of Vojvodina (PV) indicates that cases of human salmonellosis were partly covered by complete epidemiological investigation including laboratory analysis of the suspected food. Intestinal campylobacteriosis and yersiniosis and four cases of septicemias caused by Listeria monocytogenes were not fully epidemiologically investigated. Actual country legislation on food safety does not include provisions for a routine control of the above mentioned pathogens except for Salmonella. In the PV, there are no other sources of data that contribute to risk assessment of the above food-borne diseases. A pilot investigation, performed in Novi Sad, indicated that 8.17% out of the total number of 257 retail food samples (90 of fresh meat and 167 of ready-to-eat food) had been contaminated with one of the tested bacteria Campylobacter or Salmonella or Listeria monocytogenes. Yersinia enterocolitica was not detected in any of the tested samples. Fresh poultry meat and other fresh meats were the dominant sources of the detected pathogens compared to samples of ready-to-eat food (p < 0.05). Campylobacter was detected in 18.8% and 10.0% samples of fresh poultry and other fresh meat respectively, which was not statistically significant (p > 0.05). Salmonella was detected in 3.3% samples of fresh poultry meat. Listeria monocytogenes was detected in 5.0% samples of fresh poultry and in 3.3% samples of other fresh meat, the difference was not statistically significant (p > 0.05). One sample (0.6%) of ready to eat food was contaminated with Campylobacter and one (0.6%) with Salmonella.

Ochratoxin A and aflatoxin B1 in breakfast cereals marketed in Serbia - occurrence and health risk characterisation.

The present paper reports data on the occurrence of ochratoxin A (OTA) and aflatoxin B1 (AFB1) in breakfast cereals marketed in Serbia and interprets consequent dietary exposure. A total of 136 samples was collected in 2012 and 2015 and analysed using high-performance liquid chromatography with fluorescence detection. OTA was detected in 20.7% of the samples in 2012 and 13.0% in 2015, with 3.6% and 0% of the samples above the EU maximum level, respectively. AFB1 was found in low concentrations in 11.1% of the samples collected in 2015, mainly corn based. Comparison of estimated exposure of Serbian adult population with respective toxicological reference values showed no concern for public health.

Clonal persistence of Salmonella enterica serovars Montevideo, Tennessee, and Infantis in feed factories.

INTRODUCTION: Novel molecular techniques applied in biotechnology research have provided sound evidence on clonal persistence of distinct serovars of Salmonella in feed factory environments, over long periods of time (months, even years), which can be responsible for repeated in-house contamination of final products. In this study, we examined the possibility of clonal persistence of isolates of three Salmonella serovars that have been repeatedly identified in animal feed samples from three feed factories throughout a two-year period. METHODOLOGY: The isolates Salmonella enterica serovars Tennessee (n = 7), Montevideo (n = 8), and Infantis (n = 4) were tested for genetic diversity using pulsed-field gel electrophoresis (PFGE) and multicellular behavior patterns by applying the Congo red agar test. RESULTS: SpeI and XbaI macro-restriction profiles indicated that isolates S. Montevideo and S. Infantis were identical, whereas isolates of S. Tennessee demonstrated greater genetic diversity, although the genetic differences did not exceed 10%. All Salmonella serovars demonstrated the ability to produce predominant matrix compounds essential for biofilm formation, curli fimbriae and cellulose. CONCLUSIONS: The identification of identical clones of S. Montevideo and S. Infantis, as well as the minor genetic diversity of S. Tennessee, which have been repeatedly isolated from animal feed in three production plants throughout a two-year period, indirectly suggests the possibility of their persistence in feed factory environments. Their ability to express the key biofilm matrix components further supports this hypothesis.

[Phenotypic detection of beta-lactamases production in Enterobacteriaceae].

INTRODUCTION: Beta-lactam antibiotics are the most commonly used antibacterial drugs. However, many bacteria have developed resistance to these antibiotics, and the most common form of resistance is the production of beta-lactamase enzymes. Many members of the Enterobacteriaceae family produce different types of these enzymes. OBJECTIVE: The aim of this study was to perform phenotypic detection of production and identification of beta-lactamase type in Enterobacteriaceae isolated from different clinical specimens from patients hospitalized in the Clinical Center of Serbia. METHODS: The strains of Enterobacteriaceae were collected between November 2011 and January 2012 in the laboratory of the Clinical Center of Serbia.The isolates were identified according to the standard microbiology procedures and confirmed by the Vitek2 automated system. Antimicrobial susceptibility testing was performed by the disk diffusion method, and the phenotypic detection of production and identification of beta-lactamases was performed according to previously described methodologies. RESULTS: In this study, a total of 172 Enterobacteriaceae strains were isolated. Further testing was performed on 54/145 (37.2%) strains showing decreased susceptibility to beta-lactam antibiotics: 13/85 (15.3%) Escherichia coli, 31/46 (67.4%) Klebsiella pneumoniae and 10/14 (71.4%) Proteus mirabilis. Among them, 40/145 (27.6%) strains produced extended spectrum beta-lactamases (ESBLs), 9/145 (6.2%)--AmpC, 1/145 (0.7%)--K1 beta-lactamase and 4/145 (2.8%)--carbapenemases. Carbapenemases were predominantly detected in K. pneumoniae (75%). CONCLUSION: Enterobacteriaceae produce different types of beta-lactamases, and the most common type in our study was ESBLs. Production of carbapenemases detected in Enterobacteriaceae is also an associated problem.

Prevalence of macrolide resistance in Streptococcus pyogenes collected in Serbia.

The purpose of our study was to determine the prevalence of macrolide resistance in 3,188 pharyngeal Streptococcus pyogenes isolates collected at the Institute of Public Health of Serbia during the period 2006-2008. The disk diffusion tests were used to determine the susceptibility of the isolates. Two hundred and sixteen S. pyogenes isolates (6.8%) were resistant to erythromycin, with 9 isolates coresistant to tetracycline: 181 isolates harbored mefA gene, 19 ermB gene, 11 ermA(TR) gene, 5 ermB and mefA genes, and 7 tetM gene. Although the prevalence of macrolide resistance in pharyngeal S. pyogenes isolates is low in Serbia, monitoring of the emergence of resistance is advisable.

[Medical nutrition therapy planning].

INTRODUCTION: Diet has vital, preventive and therapeutic functions. Medical nutrition therapy is a part of the Standardized Nutrition Care Process integrated in health care systems. MATERIAL AND METHODS: An overview of the Nutrition Care Process model and the application of nutrition guidelines based on literature, reports, documents and programmes of international health, food and physical activity authorities was done. RESULTS: The Nutrition Care Process model requires registered dieticians, standardized terminology as well as nutrition diagnosis categorization. It consists of four distinct, but interrelated and connected steps: (a) nutrition assessment, (b) nutrition diagnosis, (c) nutrition intervention, and (d) nutrition monitoring and evaluation. An individual approach is essential for successful medical nutrition therapy. Nutrition guidelines facilitate the process of understanding and application of medical nutrition therapy. CONCLUSION: The Nutrition Care process provides dietetic professionals information on high-quality client nutrition care. The success of medical nutrition therapy rests not only upon the advice of the dietician, but also upon the client's compliance.

Analysis of salt content in meals in kindergarten facilities in Novi Sad.

INTRODUCTION: Investigations have brought evidence that salt intake is positively related to systolic blood pressure and that children with higher blood pressure are more susceptible to hypertension in adulthood. In developed countries the main source of salt is processed food. OBJECTIVE: The aim of this paper was to determine total sodium chloride (NaCl) in average daily meal (breakfast, snack and dinner) and in each of three meals children receive in kindergarten. METHODS: From kindergarten, in the meal time, 88 samples of daily meals (breakfast, snacks and dinner) offered to children aged 4-6 years were taken. Standardized laboratory methods were applied to determine proteins, fats, ash and water in order to calculate energy value of meal. The titrimetric method with AgNO3, and K2CrO4 as indicator, was applied in order to determine chloride ion. Content of NaCl was calculated as %NaCl = mlAgNO3 x 0.05844 x 5 x 100/g tested portion. NaCl content in total daily meal and each meal and in 100 kcal of each meal was calculated using descriptive statistical method. Student's t-test was applied to determine statistical differences of NaCl amount among meals. RESULTS: NaCl content in average daily meal was 5.2 +/- 1.7 g (CV 31.7%), in breakfast 1.5 +/- 0.6 g (CV 37.5%), in dinner 3.5 +/- 1.6 g (CV 46.1%) and in snack 0.3 +/- 0.4 g (CV 163.3%). NaCl content per 100 kcal of breakfast was 0.4 +/- 0.1 g (CV 29.5%), dinner 0.7 +/- 0.2 g (CV 27.8%) and snack 0.13 +/- 0.19 g (CV 145.8%). The difference of NaCl content among meals was statistically significant (p < 0.01). CONCLUSION: Children in kindergarten, through three meals, received NaCl in a quantity that exceeded internationally established population nutrient goal for daily salt intake. The main source of NaCl was dinner, a meal that is cooked at place.

How a routine checking of Escherichia coli in retailed food of animal origin can protect consumers against exposition to Campylobacter spp. and Listeria monocytogenes?

BACKGROUND/AIM: According to the literature that has been published over the last two decades Campylobacter spp i Listeria monocitogens can be identified as causes of numerous diseases derived by consuming food of animal origin. The purpose of this paper was to find out how established national microbiological criteria of the Republic of Serbia on food safety in retailed food of animal origin could contribute to consumer's protection against exposition to foodborne pathogens such as Campylobacter spp. and Listeria monocytogenes. METHODS: During a routine microbiological safety control of randomly selected 60 samples of fresh poultry meat, 30 samples of other fresh meat readymade for grilling, 30 samples of sausage products, 37 samples of heat-treated meat, 39 samples of toppings for fast food of animal origin and 31 samples of dairy products a national food safety criteria (Escherichia coli, aerobic plate count, Salmonella spp., coagulasa positive Staphylococcus, Proteus spp., sulphito-reducting Clostridia) were applied and, as well as, testing to Campylobacter spp. and Listeria monocitogens. In determination of Campylobacter spp. and Listeria monocytogenes, food quality control methods of the Food and Agriculture Organization (FAO) were applied, while in determination of the other above motioned bacteria, national provisions on microbiological methods were applied who are adjusted to the FAO ones. RESULTS: Related to the national criteria on microbiological food safety, 88 (38.8%) samples, out of the total 227 tested, were rejected. When to these results, the results of laboratory tests on Listeria monocytogens were added, a terminal number of rejected samples were not changed. When to these results, the results of Campylobacter spp. testing were added, 91 (40.1%) out of the 227 samples were unsatisfied. Results of logistic regression model with occurrence of Escherichia coli as dependent variable indicated that Escherichia coli was 4.5 times likely to occur among samples with Campylobacter spp. than among samples without Campylobacter spp. (OR = 4.515, 95% CI: 1.019-20.002). Sensitivity of the fitted model (Hosmer-Lemeshowp = 0.268) was 76.8% and its specificity was 75.0%. At the same time Escherichia coli was confound in all (100%) food samples that were contaminated by Listeria monocytogenes. CONCLUSION: Statistical analysis indicated that Escherichia coli was completely sensitive to identify all samples contaminated with Listeria monocytogenas and highly sensitive to identify samples contaminated with Campylobacter spp. Nevertheless, 3 (1.3%) of the tested samples were not covered with Escherichia coli.

[Medical nutrition prevention and medical nutrition therapy of lipid metabolism disorder].

High energetic density of nutrition, insufficient physical activity and smoking are the most common causes of obesity and lipid metabolism disorders (hyperlipoproteinemia and dyslipoproteinemia). Hyperlipoproteinemia and dislipoproteinemia are mass noncommunicable diseases and at the same time they are main causes of atherosclerotic cardiovascular diseases and cerebrovascular diseases, metabolic syndrome, hepatic diseases and some localization of malignant diseases. Cardiovascular diseases and malignant diseases are the leading causes of mortality in the world. Global Strategy on Diet, Physical Activity and Health Nutrition and The Second European Action Plan for Food and Nutrition Policy represent the World Health Organisation approach in prevention of risks of development, and treatment of mass noncommunicable diseases, first of all for hyperlipoproteinemia, cardiovascular diseases and cerebrovascular diseases. According to the previously mentioned health programmes, medical nutrition therapy of hyperlipoproteinemia and dislipoproteinemia should be applied on whole population and individual level as well. Medical nutrition therapy is managed on individual level. Eminent international organizations, such as the European Society of Atherosclerosis and the American Heart Association, give priority to medical nutrition prevention and medical nutrition therapy in their guides for prevention and therapy of hyperlipoproteinemia, cardiovascular diseases and cerebrovascular diseases.

[Health and environment].

INTRODUCTION: The Department of Hygiene, Faculty of Medicine, University of Novi Sad, is responsible for undergraduate and graduate courses in the field of preventive medicine. The principal task of physicians in the 21st century is to provide health promotion and desease prevention. In the future, evaluation of physician knowledge and competence will be predominantly based on patients' health conditions. HEALTH AND ENVIRONMENT: Human health is a result of long-term interaction between human genome and the environment. Good human health requires permanent control of health conditions as well as control of environmental health hazards. Various environmental factors, such as physical, chemical, biological, social and economic, affect the population health. Air, drinking water and food are fundamental to the existence of life of all living beings on Earth, and therefore they have enormous influence on the health of individuals and populations. CONCLUSION: The significance of the above mentioned requirements, essential for human health, is the reason why the Department of Hygiene conducted an investigation on the quality of air, food and water (water is a foodstuff as well) in Vojvodina.