ALBERT

Description: Fish sauce is a popular fermented product used in south Asian countries which is made from different small fishes in this research work it was attempted to produce fish sauce from kilka of the Caspian sea, the fish sauce was made from three models of kilka ,such as whole kilka , cooked whole kilka and dressed kilka , each of these models treated it four different fashions of fermentation such as:1- Traditional method, 2- Enzymatic method 3- Microbial method, 4- Mixture of enzyme and microb The results of this investigation showed that time of fermentation for the traditional method was six month, enzymatic method one month, microbial method 3 month and the mixture of enzyme and microb 1 month. The rate of fermentation was least for dressed Kilka, microbial and biochemical changes of Kilka fish sauce were evaluated, total bacterial count was 2.1-6.15 log cfu/ml total volatile nitrogen (TVN) in samples recorded was 250 mg /100g, the amount of protein varied between 10-13 percent, the name of commercial enzymes added was Protamex and Flavourzyme, the bacteria added was L act ob acillus and Pediococous, fish sauce containers fish and 20% salt, temperature of keeping for fermentation was 37 degree c for 6 month.

Description: PhD

Description: Advisors: S. Moini Counsellors: A. keyvan, Gh. Vosoughi

Description: The first aim of this research was to identify fatty acids, amino acids composition of Thunnustonggol roe and their changes during cold storage (-18'C). The second aim was to determinethe changes of moisture, protein, fat and ash contents of the roe during one year cold storage(-18'C). 60 samples of longtail tuna (Thunnus tonggol) ovaries were randomly collected formBandar-e-Abbas landings. The samples were frozen at-30'C and kept in cold store at -18'Cfor one year. According to a time table, the samples were examined for identification offatty acids, amino acids, moisture, protein, fat, ash, peroxide and T.V.N. and their changeswere evaluated during this time. The results showed that 26 fatty acids were identified. Theunsaturated fatty acids (UFA) and saturated fatty acids (SFA) were 62.33 and 37.6%,respectively, in fresh roe. So that, DHA (C22:6) and oleic acid (C18:1) had high amounts(24.79 and 21.88%) among the UFA and palmitic acid (C16:0) was the most content(22.75%) among the SFA. The PUFA/SFA was 0.91. Also, 17 amino acids were identifiedthat essential amino acids (EAA) and nonessential amino acids (NE) were 10478 and 7562mg/100g, respectively, and E/NE was 1.38. Among the EAA and NE, lysine (2110mg/100g)and aspartic acid (1924 mg/100g) were the most contents. Also, results showed that moisture,ash, protein and fat contents were 72.74, 1.8, 19.88 and 4.53%, respectively, in fresh roe. Theeffects of freezing and cold storage on the roes showed that UFA and SFA contents havereached to 49.83 and 48.07%, respectively, at the end of cold storage. It indicated that thesecompounds change to each other during frozen storage. Also, n-3 and n-6 series of fattyacids were 32.75 and 1.61% in fresh roe. But their contents decreased to 22.96 and 1.25% atthe end of period. Among the fatty acids, 22:6 and C16:0 had the most changes. The changesof fatty acids were significantly at 95% level except for C15:1, C18:3(n-3) and C20:4(n-6).All of the amino acids decreased in frozen storage and their changes were significantly(P〈0.05). EAA was 7818 mg/100g and E/NE was 1.27 at the end of storage period. Amongthe amino acids, leucine and lysine had the most changes. Moisture, ash, protein and fatcontents were 70.13, 1.82, 19.4 and 6.51%, respectively, at the end of storage period. Theperoxide value and T.V.N. increased during storage. So that, their contents have reached to5.86 mg/kg and 26.37 mg/100 g, respectively, at the end of frozen storage. The best shelf lifeof Thunnus tonggol roe was 6 or 7 months, because of lipid oxidation and increasing ofperoxide.

Description: PhD

Description: Advisors: S. Moeini Counsellors: A. Keyvan, M. Yousefian

Description: Fish protein concentrate (FPC) is a healthy, sustainable and high nutritiveproduct which sanitized produced from fishes in which, protein and othernutrients are more concentrated than in fresh fishes.The aim of this research is to study on the sustainability of FPC producedfrom Kilka (Clupeonella engrauliformis , C. grimmi and C. cultriventris)in two Vaccum Packaging and Modified Atmosphere Packaging atdifferent environmental factors during six months.In our study the analysis of FPC protein showed 91.2%, lipid: 0.5%, ash:3.6%, moisture: 2.3%, Total Volatile Nitrogen: 10 ml/100gr andperoxide: 5meq/kg. Amino acids and fatty acids were also determined.Bacteria and Fungi were lower than 1000 colony. Samples are kept indifferent condition of temperature (5, 20 and 35 degree centigrade),humidity (25, 40 and 90 percent) and light and dark environment in sixmonth.Lipid rate in FPC after 6 months in VP and MAP (60% C02, 30 % N2 and10% O2), packages was decreased but was not significant (P〉0.05). It wasalso detected that increase temperature lead to more decrease in lipidcontent. Protein rate of FPC was decreased from 91.2% to 73.6% duringsix months at 35°C in VP Package and from 91.2% to 69.4% in MAPpackage. These changes were significant (P〈0.05). TVN and PV rate inFPC after 6 months in VP and MAP packages was increased but wassignificant (P〈0.05). Amino acids and fatty acids were also determined.But more changes in MAP packages was detected.

Description: PhD

Description: Advisors: Abbas Ali Motalebi Counsellors: Wadud Rzvylar, Aliasghar Khanipoor. The full text document is in Farsi only so it has not been possible for AC Editors to check the metadata input.

Description: At the fishing season, in 2000, samples of species persian sturgeon (A. persicus), Severjuga (A. stellatus) and Mullet (L. aurata), were caught from the southern coasts of Caspian Sea and were freezes and preserved in the cold storage for one year They have also become biometery. The tissue's fillet were identified in order to determined the Fatty Acids. This was done during one year, frequently, fresh, two weeks after freezing and then monthly, respectively. So, after the extraction of lipids from the tissues and methylation, was injected to the gas-liquid Chromatography. After calibration, identified Fatty Acids were compared with standards according to their Retention Times. Peroxid value, lipid content and humidity were controlled. The unsaturated Fatty acids had The most amount, and a plenty of Polyunsaturated Fatty acids (PUFA) were observed, so that linoleic (C18:2), a-linolenic (C18:3), Arashidonic (C20:4), EPA (C20:5) and DHA (C22:6) Fatty acids had high amounts. The w-3, PUFA were more in comparison with w-6. The effects of freezing and cold storing on the fish fatty acids , were evaluated by the statistical tests , like SPSS, Tukey, Homogenous and Anova, and showed that in some species, a group of Fatty acids, specially PUFA, had some variation. The peroxide value that indicates the lipid deterioration, increased during toring. So, the best term if preserving in the cold storage, were determined and their Nutrition value and Medical applications due to their consumption were investigated.

Description: PhD

Description: Advisors: Sohrab Moeini Counsellors: Amin Keyvan, Mehdi Yousefian

Description: Biodegradable protein-based film was developed by incorporating cinnamon essential oil(CEO) into whey protein concentrate (WPC) at level of 0.8% and 1.5% v/v. Then physicaland mechanical properties of the films were evaluated. Adding CEO to the WPC matrixdecreased the water vapour permeability of the films and water solubility. Films containingCEO showed significant antibacterial activity both gram-positive and gram-negative strainsand exhibited significant inhibitory effect on the studied fungi. In continue, the effect ofwhey coating and whey coating incorporated with 1.5% CEO on quality and shelf life ofHuso huso fillet during refregrated (4±1°C) storage period were also investigated. The controland treated fish samples were analyzed for microbiological (total viable count, psychrophiliccounts), chemical (PV, TBA, FFA, pH, TVB-N), and sensory characteristics in 4-dayintervals up of microbial, chmical and sensoy analyses indicated lower levels of PV, TBA,FFA, pH, TVB-N in coasted sampels and specially, those with CEO while were kept inrefrigerator. Based on results, whey protein edible coating contain 1.5% cinnamon essentialoil could enhance preserving ability Huso huso during storage cold.

Description: PhD

Description: Advisors: M. Rezaei Counsellors: M. Soltioni, A. kamali

Description: The ever-increasing population of the world and the growing need for animal protein has doubled the modern man’s demand for food. Additionally, the improvement in the general public health, and the worsening of environmental/ecological pollution have prompted today’s world to look for ways to procure healthy food. And one such attempt is the use of natural preservatives to decrease the bacterial load in foodstuffs, in other words, to increase their durability.This study evaluates the effects of different concentrations of Zataria multiflora Bioss (EO 0, 0.005, 0.015, 0.045, 0.135, 0.405%) and Nisin (0, 0.25, 0.5, 0.75 μg/ml) and storage time (9 days) on the growth of Lactococcus garvieae Ir-170A(856bp) alone, and their combination in a food model system (fillets of the rainbow trout (Oncorhynchus mykiss). Additionally, the growth of a sample of this bacteria in laboratory conditions was studied.The results of this study showed that different concentrations of Nisin had a significant impact (p〈0.05) on Lactococcus garvieae.With the value of t in 0.75 μg/ml, the effectiveness rose to 65.77%; the biggest effect on Lactococcus garvieae. And the effect at 4 0C exceeded 80C.The study has also demonstrated that all concentrations of Zataria multiflora Bioss were effective against Lactococcus garvieae. However, with the value of t at 0.405%, the effectiveness was 71.91%. This value had the biggest effect on Lactococcus garvieae. At 4 0C, the effect surpassed the one at 80C.The synergistic effects of the EO and Nisin showed that with the value of t at 0.405% EO and 0.75 μg/ml Nisin was 14.62% had the greatest effect on Lactococcus garvieae.In this study, multi-factorial effects for different concentrations of Zataria multiflora Bioss (EO 0, 0.005, 0.015, 0.0025%), three different concentrations of122Nisin (0, 0.25,0.75 μg/ml) and two different levels of PH (5.5 , 7) at two incubation temperatures (15,37) on logp% of Lactococcus garvieae during 43 days in BHI broth were evaluated. Most of the effects on Lactococcus garvieae occurred in PH 5.5 and at a temperature of 150C.

Description: PhD

Description: Advisors: Mehdi Soltani, A. Akhondzadeh Basti. counsellor: A. Kamali

Description: The main aim of this research was to identify fatty acids composition of Caspian sea of White fish Rutilus frisi kutum tissue and their changes during one year cold storage (-18Ċ).The secondary aim was to determine the changes of moisture, ash, protein, fat, and to investigate the effects of storage time on peroxide, TBAi, FFA, and extractability of myofibrillar proteins of the fish tissue during one year cold storage (-18 Ċ). 10 samples of (Rutilus frisi kutum) were randomly collected from Anzali landings. The samples were frozen at -30 Ċ and kept in cold storage at -18Ċ for one year. According to time table, the samples were examined. The results showed that 27 fatty acids were identified. The unsaturated fatty acids (UFA) and saturated fatty acids (SFA) were 74/09 and 21/63 %, respectively, in fresh tissue. So that DHA (C22:6) oleic acid (C18:1c) had high amounts (15/07 ,20/57 ) among the UFA and palmitic acid (C16:0) was the most (13/09 %) among the SFA. The effects of freezing and cold storage on fish tissue showed that UFA and SFA contents have reached to 58/79 and 22/17 %, respectively, at the end of cold storage. It indicated that these compound change to each other during frozen storage. Also ω-3 and ω-6 series of fatty acids was 24/22 and 15/56% in fresh tissue, but their contents decreased to 8/68 and 5/11% at the end of period. Among the fatty acids C22:6, C18:1c and C16:0 had the most changes. The changes of fatty acids were significantly at 95% level expected for C18:0. Results showed that moisture, ash, protein, and fat contents were 75/9±0/03, 1/28±0/012, 21/8±0/2, and 4/1±0/01 % respectively, in fresh tissue. The moisture, ash, protein, and fat contents were 72/3±0/04, 1/83±0/05, 1/91±0/01 and 19/9±0/01 % respectively, at the end of storage period. Lipid damage was measured on the basis of free fatty acids (FFA), peroxide value (PV), and Thiobarbituric acid index (TBA-i). PV, TBARS and FFA concentration of frozen Caspian Sea white fish stored at -18 Ċ the temporal variation of these three variables were statistically significant (p〈0.001). Results of White fish myofibrillar proteins showed aggregation of bound reduced for stored at 12 months. SDS-PAGE analysis revealed that, the intensity of the myosin heavy chain and actin bound was reduced with increasing storage time. SDS-PAGE patterns showed that myosin heavy chain was much more susceptible to hydrolysis than actin.Key words: Rutilus frisi kutum, frozen storage, ω-3, ω-6, protein myofibrillar

Description: PhD

Description: Advisors: Sohrab Moeini, Nasser Ghaemi Counsellors: A.K. Haghdost

Description: In this study microbiological , chemical quality and fatty acid composition ofgrass carp (Ctenopharyngodon idella) fillets treated by dipping in sodiumacetate (%1 and %3), nisin (% 0.1 and % 0.2) and combination of sodiumacetate and nisin was evaluated during 16 days of refrigerated of 4°CAntilisterial effect of nisin was enhanced with the increased concentration ofsodium acetate. At day 12 post storage, Listeria monocytogenese count washigher in the control group than the recommended value, however in sodiumacetate and nisin treated samples, the count was lower (5.17-5.91 log cfu/g).With increasing the concentrations of sodium acetate, mesophilic counts werelower. Regarding nisin, better results was obtained by applying %0.1 nisin.Greater inhibition of mesophile bacteria was observed when combinationtreatment was used. The number of lactobacillus was lower when higherconcentrations of sodium acetate and nisin were used.Total Volatile Nitrogen values at the end of the experiment were lower in thesamples treated with both nisin and sodium acetate and the better results wereobtained in combination treatments. Peroxide (PV) at the end of the experimentwas 1.9 meq/kg in control, and the lowest values were observed for thetreatments 3(%0 sodium acetate +% 0.2 nisin) and 9(%3 sodium acetate +% 0.2nisin) between 1.08 and 1.62 meq/kg without significant difference.Thiobarbituric acid (TBA) levels at the end of experiment have been shown tobe 0.46 mg malonaldehyde per kg in the control. On the other hand treatments 9had the TBA values of 0.19 mg malonaldehyde per kg which was significantlylower than that of control.Polyunsaturated fatty acids increased by increasing the sodium acetate dosesand instead saturated fatty acids and n-6/n-3 ratio decreased. The ratio ofUFA/SFA and also C22:6/C16:0 increased when a higher concentration ofsodium acetate has been used. The best result obtained by using 3% of sodiumacetate but no such relation with nisin was observed.

Description: PhD

Description: Advisors: Mehdi Soltani, Abolghasem Kamali Counsellors: Mohammad Reza Ghomi, Seyed Ebrahim Hoseini

Description: Effects of different thawing method i.e. in a refrigerator, in water, at air ambient temperature and in a microwave oven on proximate, chemical (PV, TBA, FFA, TVB-N, SSP, FA), biochemical (pH, WHC,ThL), microbial (total viable, psychrotrophic, coliform, Shewanella and yeast-mould count) and sensory analysis were carried out on frozen whole Caspian sea Kutum (Rutilus frisii kutum) and Rainbow trout (Oncorhynchus mykiss) carcasses. The values of ash, protein, SSP, WHC, PUFA, PUFA/SFA. EPA+DHA/C16:0, pH, and microbial count of thawed samples decreased significantly while fat, PV, TBA, FFA, TVB-N, SFA and MUFA increased compared to the fresh fish (unfrozen) as control samples. Also, sensory evaluation all of thawed samples showed a significant (p〈0.05) quality loss compared to the fresh fish as control samples. The lowest chemical and biochemical values as well as microbial growth were determined in water thawed samples. Therefore, based on this study thawing in water is most suitable for frozen whole rainbow trout.

Description: PhD

Description: Advisors: Masoud Rezaei, Mehdi Soltani Counsellors: Mohammad Haghighi, Reza Pourgholam

Description: There is an increasing demand in developing newer and safer methods in preserving food products.Among which herbal additives seem to attract evermore attention recently.the major advantage of herbal additives is due to their favorable aroma besides their antimicrobial effects and less expensive than chemical additives. Zataria multiflora Boiss is a native Iranian herb which is used vastly as a food preserver essential oils and also medical usage.Metabolites of harmless bacteria, such as Nisin are also known to be safe preservatives that have antimicrobial activity.However to establish the usefulness of natural antimicrobial preservatives, they must be evaluated alone and in combination with other preservation factors to determine whether there are synergistic effects in rigid media .In this study were evaluated the effects of different concentrations of Zataria multiflora (EO 0, 0.005, 0.015, 0.045, 0.135, 0.405 ,0.810 %) and Nisin(0, 0.15, 0.25, 0.75 μg/ml) and Storage time (up to 21 days) on growth of Staphylococcus aureus ATCC 6538 in a food model system(light salted fish of silver carp, Hypophthalmichthys molitrix).The results on growth of S. aureus were evaluated using SPSS 15.0 statistical software (SPSS 15.0 for windows, SPSS Inc.) and analyzed the logarithm of total count of the bacteria by Tukey Test. Results were considered statistically significant when P≤0.05.The growth of Staphylococcus aureus was affected significantly(P〈0.05) by EO and Nisin and also combinations of EO and Nisin.Samples treated with 0.135, 0.405 and 0.810% of thyme essential oil showed a significant decrease on the growth of the bacteria compared with an treated samples(P〈0.05). No significant difference was seen on the growth of S.aureus in samples treated with lower concentrations of Z.multiflora(below 0.045%) and untreated group(P〉0.05).The most inhibitory effects were seen in samples treated with 0.405% and 0.810% of thyme essential oil until 9 and 12 days after storage,respectively.Also there was significant inhibtory effect(P〈0.05) in different concentration of nisin on the organism compared with an treated samples.The synergism effects of the Eo and nisin on the growth rate of the bacteria was significant (P〈0.05) compared with untreated samples and samples treated with the Eo or nisin, only. Synergismic effects was observed at concentration of 0.405 and 0.810% of Z. multiflora essential oil with 0.25 μg/ml Nisin, respectively until 15 days after storage.As expected it is preferred to apply the least possible amounts of additives in food preserving that not only are effective and safe but are economically justifiable.

Description: PhD

Description: Advisors: Afshin Akhondzadeh Basti, Mehdi Soltani counsellors: Abbas Matinfar

Description: The present study aimed production of a new product with various texture and sensoryproperties in chase of the impetus for increasing human consumption considering suitableresources of Kilka fish in Caspian Sea. Following deheading, gutting, and brining, commonKilka were battered in two different formulations, i.e. simple batter and tempura batter, viaautomated predusting machinery and then, they were fried through flash frying for 30 secondsat 170°C in sunflower oil after they were breaded with bread crumbs flour. The products weresubjected to continuous freezing at -40°C and were kept at -18°C in cold storage for fourmonths once they were packed. Chemical composition (protein, fat, moisture, and ash), fattyacid profiles (29 fatty acids), chemical indices of spoilage (peroxide value, thiobarbituric acid,free fatty acids, and volatile nitrogen), and microbial properties (total bacteria count andcoliform count) were compared in fresh and breaded Kilka at various times before frying (rawbreaded Kilka), after frying (zero-phase), and in various months of frozen storage (phases 1,2, 3, and 4). Organoleptic properties of breaded Kilka (i.e. odor, taste, texture, crispiness,cohesiveness of batter) and general acceptability in the phases 0, 1, 2, 3, and 4 were evaluated.The results obtained from chemical composition and fatty acid profiles in common Kilkadenoted that MUFA, PUFA, and SFA were estimated to be 36.96, 32.85, and 29.12 g / 100glipid, respectively. Levels of ù-3 and ù-6 were 7.6 and 1.12 g / 100 gr lipid, respectively.Docosahexaonoic acid (20.79%) was the highest fatty acid in PUFA group. ù-3/ù-6 andPUFA/SFA ratios were 7.6 and 1.12, respectively. The high rates of the indices and highpercentage of ù-3 fatty acid in common Kilka showed that the fish can be considered asinvaluable nutritional and fishery resources and commonsensical consumption of the speciesmay reduce the risk of cardiovascular diseases. Frying breaded Kilka affected overall fat andmoisture contents so that moisture content in fried breaded Kilka decreased significantlycompared to raw breaded Kilka, while it was absolutely reverse for fat content. Overall fatcontent in tempura batter treatment was significantly lower than that of simple battertreatment (P≤0.05). Presence of hydrocolloids, namely proteins, starch, gum, and otherpolysaccharides, in tempura batter may prohibit moisture evaporation and placement with oilduring frying process in addition to boosting water holding capacity through confining watermolecules. During frying process, fatty acids composition of breaded Kilka with variousbatters changed so that rates of some fatty acids such as Palmitic acid (C16:0), Stearic acid(C18:0), Oleic acid (C18:1 ù-9cis), and linoleic acid (C18:3 ù-3) increased considerablyfollowing frying; however, ù-3/ù-6, PUFA/SFA, and EPA+DHA/C16:0 ratios (Polyan index)decreased significantly after frying. ù-3/ù-6, PUFA/SFA, and EPA+DHA/C16:0 ratios intempura batter treatment were higher than those of simple batter treatment which is anindicator of higher nutritional value of breaded Kilka with tempura batter. Significantelevations were found in peroxide, thiobarbituric acid, and free fatty acids in fried breaded Kilka samples compared to raw samples which points to fat oxidation during cooking process.Overall microorganism count and coliform count decreased following heating process. Bothbreaded Kilka samples were of high sanitation quality at zero-phase according to ICMSFStandard. The results acquired from organoleptic evaluation declared that odor, cohesiveness,and general acceptability indices, among others, had significant differences between thetreatments (P≤0.05). In all evaluated properties, breaded Kilka with tempura batter indifferent phases gained higher scores than breaded Kilka with simple batter. During coldstorage of various treatments of breaded Kilka, total lipid content, PUFA, MUFA, ù-3, ù-3/ù-6, PUFA/SFA, Polyen index decreased significantly. The mentioned reductions inaddition to significant elevation of spoilage indices, namely peroxide, thiobarbituric acid, andfree fatty acids, during frozen storage, indicate to oxidation and enzymatic mechanismactivity during frozen storage of breaded Kilka. Considering sensory evaluation at the end ofthe fourth month and TVB-N contents exceeded eligible rate in the fourth month, shelf life ofthe products during frozen storage was set to be three months at -18°C. The results obtainedfrom statistical tests indicate to better quality of breaded Kilka processed with tempura battercompared to simple batter in terms of organoleptic evaluation, spoilage indices, and highquality of fat in various sampling phases.

Description: PhD

Description: Advisors: Ali Asghar Khanipour, Mehdi Soltani Counsellors: Abbasali Motallebi, Abolghasem Kamali

Description: The purpose of this study, Evaluation the effect of Rosmarinus officinalis and Thymus vulgaris extracts on the stability of poly unsaturated fatty acids in frozen Silver carp minced. Treatments include:Treatment 1 - Control: frozen meat packaged in conventionalTreatment 2: Frozen Silver carp minced+Thyme 300 mg/kg in normal packagingTreatment 3: Frozen Silver carp minced+Rosemary 200 mg/kg in normal packagingTreatment 4: Frozen Silver carp minced+Rosemary compound (100 mg/kg) and Thyme(100 mg/kg) in normal packagingAfter rapid freezing of samples in the spiral freezer by individual quick freezing method, tomaintain the cold temperature (-18) °C were transferred. Sampling and measurements to determine the fatty acid profile of the zero phase beginning in the first month and then every ten days, and 15 days in the second month of the third month after the monthly test.Identifying, defining and measuring the fatty acid profile by gas chromatography was performed. In this study, levels of both saturated and unsaturated fatty acids in threeexperimental and one control were identified as follows:A: saturated fatty acids: Meristic C14: 0/Palmitic C16: 0/Hepta decaenoic C17: 0/Stearic C18: 0/Arashidic C20: 0/B:Mono unsaturated fatty acids: palmitoleic C16: 1-W7/Oleic C18: 1-W9/Gadoleic C20:1-W9C:Poly unsaturated fatty acids: Linoleic C18: 2-W6/α-Linolenic C18: 3-W3D:High unsaturated fatty acids: Arachidonic C20: 4-W6 Eicosapentaenoic acid C20: 5-EPA/W3 Docosahexaenoic C22: 6-DHA/W3Results of this study was to determine, Thyme and rosemary extracts containing silver carpminced stored in freezing conditions, Stability of different types of fatty acids, monounsaturatedfatty acids, poly-unsaturated fatty acids, omega-3 and omega-6 fatty acids are. So that none of the fatty acids measured were not significant 100% increase or decrease,While changes in the fatty acid oxidation during storage time is minimized. The resultsobtained from the fatty acid profiles and indicators of their and statistical tests show that treatment with rosemary extract More stable during storage (-18) ° C In comparison with the control and other treatments are shown; And at relatively low compared to othertreatments and control samples oleic acid and linoleic acid, palmitic more.According to studies,in Silver carp minced that containing rosemary extract, end of the storage period of six months. Were usable, so even rosemary extract the shelf-lifeexamples to increase more than six months.

Description: PhD

Description: Advisors: A. A. Motalebi Moghanjvqy, Seyed Ebrahim Hosseini Counsellors: Ali Asghar Khanipour, Mehdi Soltani

Description: Nisin is a widely used naturally occurring antimicrobial effective against many pathogenic and spoilage microorganisms. It has been proposed thatreduced efficacy of nisin in foods can be improved by technologies such as encapsulation to protect it from interferences by food matrix components. Theaim of this study was using of spray dried encapsulated nisin with zein in concentration of (0.15 and 0.25 g/kg) and sodium citrate (1.5 and 2.5%) and treatments with both of them to extent the shelf life of filleted trouts packagedby Modified Atmosphere Packaging (45% CO2, 50% N2 ,5% O2) and stored at 4±1 °C for 20 days. Furthermore, to evaluate the antimicrobial efficiency of encapsulated nisin and soudium citrate the trouts fillets was inoculated withStaphylococcus aureus as an index pathogenic bacteria. Assessment of chemical spoilage indexes such as (Proxide value, Thiobarbituric acid, total volatile basenitrogen and pH) , microbial parameters (Total Plate Count, Psychrotrophic count, Lactic acid bacteria count), Staphylococcus aureus cont in treatments which were inoculated with 5 logcfu/g of this bacteria and sensory evaluation of fillets including (smell, color, texture and total acceptability) was carried out indays of 0, 4, 8, 12, 16 and 20. The results revealed that treatment with both exposure of nisin and sodium citrate showed significantly lower chemicalspoilage indexes in comparison with controls (vaccum packed and MAP)(P〈0.05). Furthermore, (nisin 0.25 g/kg sodium citrate 2.5%) treatment whichwas exposed to the maximal level used of both materials was significantly thelowest treatment with (Proxide value, Thiobarbituric acid, total volatile basenitrogen and pH) of 9.95 (meq O2/kg) , 1.55 (mgMA/kg), 29.65 (mgN/100g) and 6.65 , respectively and according to the maximal recommended level of this indices , shelf life of fillets in this treatment was esstimated 20 days.The control(vaccum packed) treatment was significantly the highest treatment with (Proxide value, Thiobarbituric acid, total volatile base nitrogen and pH) of 15.17 (meq O2/kg), 3.03 (mgMA/kg), 38.4 (mgN/100g) and 6.95 , respectively and according to the maximal recommended level of this indices , shelf life of filletsin this treatment was estimated 11 days. Also, in microbial point of view (nisin0.25 g/kg- sodium citrate 2.5%) treatment was the lowest treatment with TotalPlate Count, Psychrotrophic count, Lactic acid bacteria count andStaphylococcus aureus count of 6.7, 6.83, 5.25 and 6.04 logcfu/g respectively,and conrol (vaccum packed) treatment was the highest treatment with 9.15, 9.41, 7.7 and 9.01 logcfu/g respectively. According to the lower results of chemicaland microbial indices and higher sensory evaluated scores assessed in this research for encapsulated nisin in comparison with free nisin , it was concludedthat encapsulation of nisin with zein capsules may improve the efficiency of nisin. The measuremented values of Mass yield, Total solids content of capsules, Encapsulation efficiency, In vitro release kinetics in 200 hour for encapsulated nisin in this study was 49.89, 62, 98.31 and 69% respectively and Encapsulated particle size was lower than 674.21 μm for 90% of particles. As a consequence, nisin , in particular encapsulated nisin, and sodium citrate alone or together with and Modified Atmosphere packaging might be considered as effective tools in preventing the quality degradation of the fillets, resulting in an extension of their shelf life.

Description: PhD

Description: Advisors: Seyed Ebrahim Hosseini, Aboulghassem Kamali Counsellorrs: Abbasali Motallebi, Resa Pourgholam

Description: The comment and response concerning the report of oxidation of methane to methanol by water (Reports, 5 May 2017, p. 523) do not fully capture the implications of thermodynamic limitations. A nonisothermal process in which each cycle requires a large temperature swing and permits only substoichiometric methane conversion surely could not be carried out on any practical scale.

Description: Labinger argues that stepwise reaction of methane with water to produce methanol and hydrogen will never be commercially feasible because of its substoichiometric basis with respect to the active site and the requirement of a large temperature swing. This comment is not touching any new ground, beyond describing the thermodynamic feasibility, thermal cycling, and the role of water as discussed previously. Most important, it does not have a solid numerical basis.

Description: Vinyl carbocations have been the subject of extensive experimental and theoretical studies over the past five decades. Despite this long history in chemistry, the utility of vinyl cations in chemical synthesis has been limited, with most reactivity studies focusing on solvolysis reactions or intramolecular processes. Here we report synthetic and mechanistic studies of vinyl cations generated through silylium–weakly coordinating anion catalysis. We find that these reactive intermediates undergo mild intermolecular carbon-carbon bond–forming reactions, including carbon-hydrogen (C–H) insertion into unactivated sp 3 C–H bonds and reductive Friedel-Crafts reactions with arenes. Moreover, we conducted computational studies of these alkane C–H functionalization reactions and discovered that they proceed through nonclassical, ambimodal transition structures. This reaction manifold provides a framework for the catalytic functionalization of hydrocarbons using simple ketone derivatives.

Description: It is commonly assumed that recognition and discrimination of chirality, both in nature and in artificial systems, depend solely on spatial effects. However, recent studies have suggested that charge redistribution in chiral molecules manifests an enantiospecific preference in electron spin orientation. We therefore reasoned that the induced spin polarization may affect enantiorecognition through exchange interactions. Here we show experimentally that the interaction of chiral molecules with a perpendicularly magnetized substrate is enantiospecific. Thus, one enantiomer adsorbs preferentially when the magnetic dipole is pointing up, whereas the other adsorbs faster for the opposite alignment of the magnetization. The interaction is not controlled by the magnetic field per se, but rather by the electron spin orientations, and opens prospects for a distinct approach to enantiomeric separations.

Description: Theory has established the importance of geometric phase (GP) effects in the adiabatic dynamics of molecular systems with a conical intersection connecting the ground- and excited-state potential energy surfaces, but direct observation of their manifestation in chemical reactions remains a major challenge. Here, we report a high-resolution crossed molecular beams study of the H + HD -〉 H 2 + D reaction at a collision energy slightly above the conical intersection. Velocity map ion imaging revealed fast angular oscillations in product quantum state–resolved differential cross sections in the forward scattering direction for H 2 products at specific rovibrational levels. The experimental results agree with adiabatic quantum dynamical calculations only when the GP effect is included.

Description: The chemistry of the carbonyl group is essential to modern organic synthesis. The preparation of substituted, enantioenriched 1,3- or 1,5-dicarbonyls is well developed, as their disconnection naturally follows from the intrinsic polarity of the carbonyl group. By contrast, a general enantioselective access to quaternary stereocenters in acyclic 1,4-dicarbonyl systems remains an unresolved problem, despite the tremendous importance of 2,3-substituted 1,4-dicarbonyl motifs in natural products and drug scaffolds. Here we present a broad enantioselective and stereodivergent strategy to access acyclic, polysubstituted 1,4-dicarbonyls via acid-catalyzed [3,3]-sulfonium rearrangement starting from vinyl sulfoxides and ynamides. The stereochemistry at sulfur governs the absolute sense of chiral induction, whereas the double bond geometry dictates the relative configuration of the final products.

Description: With the recent soaring production of natural gas, the use of methane and other light hydrocarbon feedstocks as starting materials in synthetic transformations is becoming increasingly economically attractive, although it remains chemically challenging. We report the development of photocatalytic C–H amination, alkylation, and arylation of methane, ethane, and higher alkanes under visible light irradiation at ambient temperature. High catalytic efficiency (turnover numbers up to 2900 for methane and 9700 for ethane) and selectivity were achieved using abundant, inexpensive cerium salts as photocatalysts. Ligand-to-metal charge transfer excitation generated alkoxy radicals from simple alcohols that in turn acted as hydrogen atom transfer catalysts. The mixed-phase gas/liquid reaction was adapted to continuous flow, enabling the efficient use of gaseous feedstocks in scalable photocatalytic transformations.

Description: Intrigued by the potential of nanoscale machines, scientists have long attempted to control molecular motion. We monitored the individual 0.7-nanometer steps of a single molecular hopper as it moved in an electric field along a track in a nanopore controlled by a chemical ratchet. The hopper demonstrated characteristics desired in a moving molecule: defined start and end points, processivity, no chemical fuel requirement, directional motion, and external control. The hopper was readily functionalized to carry cargos. For example, a DNA molecule could be ratcheted along the track in either direction, a prerequisite for nanopore sequencing.

Description: Phosphorothioate nucleotides have emerged as powerful pharmacological substitutes of their native phosphodiester analogs with important translational applications in antisense oligonucleotide (ASO) therapeutics and cyclic dinucleotide (CDN) synthesis. Stereocontrolled installation of this chiral motif has long been hampered by the systemic use of phosphorus(III) [P(III)]–based reagent systems as the sole practical means of oligonucleotide assembly. A fundamentally different approach is described herein: the invention of a P(V)-based reagent platform for programmable, traceless, diastereoselective phosphorus-sulfur incorporation. The power of this reagent system is demonstrated through the robust and stereocontrolled synthesis of various nucleotidic architectures, including ASOs and CDNs, via an efficient, inexpensive, and operationally simple protocol.

Description: Here we report an anomalous porous molecular crystal built of C–H···N-bonded double-layered roof-floor components and wall components of a segregatively interdigitated architecture. This complicated porous structure consists of only one type of fully aromatic multijoint molecule carrying three identical dipyridylphenyl wedges. Despite its high symmetry, this molecule accomplishes difficult tasks by using two of its three wedges for roof-floor formation and using its other wedge for wall formation. Although a C–H···N bond is extremely labile, the porous crystal maintains its porosity until thermal breakdown of the C–H···N bonds at 202°C occurs, affording a nonporous polymorph. Though this nonporous crystal survives even at 325°C, it can retrieve the parent porosity under acetonitrile vapor. These findings show how one can translate simplicity into ultrahigh complexity.

Description: Some of the simplest and most powerful carbon-carbon bond forming strategies take advantage of readily accessible ubiquitous motifs: carbonyls and olefins. Here we report a fundamentally distinct mode of reactivity between carbonyls and olefins that differs from established acid-catalyzed carbonyl-ene, Prins, and carbonyl-olefin metathesis reaction paths. A range of epsilon, zeta-unsaturated ketones undergo Brønsted acid–catalyzed intramolecular cyclization to provide tetrahydrofluorene products via the formation of two new carbon-carbon bonds. Theoretical calculations and accompanying mechanistic studies suggest that this carbocyclization reaction proceeds through the intermediacy of a transient oxetane formed by oxygen atom transfer. The complex polycyclic frameworks in this product class appear as common substructures in organic materials, bioactive natural products, and recently developed pharmaceuticals.

Description: Alkene aminoarylation with a single, bifunctional reagent is a concise synthetic strategy. We report a catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivity to provide 2,2-diarylethylamines. In this process, single-electron alkene oxidation enables carbon-nitrogen bond formation to provide a key benzylic radical poised for a Smiles-Truce 1,5-aryl shift. This reaction is redox-neutral, exhibits broad functional group compatibility, and occurs at room temperature with loss of sulfur dioxide. As this process is driven by visible light, uses readily available starting materials, and demonstrates convergent synthesis, it is well suited for use in a variety of synthetic endeavors.

Description: Photocatalysis based on optically active, "plasmonic" metal nanoparticles has emerged as a promising approach to facilitate light-driven chemical conversions under far milder conditions than thermal catalysis. However, an understanding of the relation between thermal and electronic excitations has been lacking. We report the substantial light-induced reduction of the thermal activation barrier for ammonia decomposition on a plasmonic photocatalyst. We introduce the concept of a light-dependent activation barrier to account for the effect of light illumination on electronic and thermal excitations in a single unified picture. This framework provides insight into the specific role of hot carriers in plasmon-mediated photochemistry, which is critically important for designing energy-efficient plasmonic photocatalysts.

Description: Single-electron reduction of a carbonyl to a ketyl enables access to a polarity-reversed platform of reactivity for this cornerstone functional group. However, the synthetic utility of the ketyl radical is hindered by the strong reductants necessary for its generation, which also limit its reactivity to net reductive mechanisms. We report a strategy for net redox-neutral generation and reaction of ketyl radicals. The in situ conversion of aldehydes to α-acetoxy iodides lowers their reduction potential by more than 1 volt, allowing for milder access to the corresponding ketyl radicals and an oxidative termination event. Upon subjecting these iodides to a dimanganese decacarbonyl precatalyst and visible light irradiation, an atom transfer radical addition (ATRA) mechanism affords a broad scope of vinyl iodide products with high Z -selectivity.

Description: Reactions that form a product with the same reactive functionality as that of one of the starting compounds frequently end in oligomerization. As a salient example, selective aldol coupling of the smallest, though arguably most useful, enolizable aldehyde, acetaldehyde, with just one partner substrate has proven to be extremely challenging. Here, we report a highly enantioselective Mukaiyama aldol reaction with the simple triethylsilyl (TES) and tert -butyldimethylsilyl (TBS) enolates of acetaldehyde and various aliphatic and aromatic acceptor aldehydes. The reaction is catalyzed by recently developed, strongly acidic imidodiphosphorimidates (IDPi), which, like enzymes, display a confined active site but, like small-molecule catalysts, have a broad substrate scope. The process is scalable, fast, efficient (0.5 to 1.5 mole % catalyst loading), and greatly simplifies access to highly valuable silylated acetaldehyde aldols.

Description: Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(Cp i Pr5 )Dy(Cp*)] + (Cp i Pr5 , penta-iso-propylcyclopentadienyl; Cp *, pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of U eff = 1541 wave number is also measured. The magnetic blocking temperature of T B = 80 kelvin for this cation overcomes an essential barrier toward the development of nanomagnet devices that function at practical temperatures.

Description: The development of highly reactive and stereoselective catalytic systems is required not only to improve existing synthetic methods but also to invent distinct chemical reactions. Herein, a homogenized combination of nickel-based Lewis acid–surfactant-combined catalysts and single-walled carbon nanotubes is shown to exhibit substantial activity in water. In addition to the enhanced reactivity, stereoselective performance and long-term stability were demonstrated in asymmetric conjugate addition reactions of aldoximes to furnish chiral nitrones in high yields with excellent selectivities. The practical and straightforward application of the designed catalysts in water provides an expedient, environmentally benign, and highly efficient pathway to access optically active compounds.

Description: Exploration of intermediates that enable chemoselective cycloaddition reactions and expeditious construction of fused- or bridged-ring systems is a continuous challenge for organic synthesis. As an intermediate of interest, the oxyallyl cation has been harnessed to synthesize architectures containing seven-membered rings via (4+3) cycloaddition. However, its potential to access five-membered skeletons is underdeveloped, largely due to the thermally forbidden (3+2) pathway. Here, the combination of a tailored precursor and a Pd(0) catalyst generates a Pd-oxyallyl intermediate that cyclizes with conjugated dienes to produce a diverse array of tetrahydrofuran skeletons. The cycloaddition overrides conventional (4+3) selectivity by proceeding through a stepwise pathway involving a Pd-allyl transfer and ring closure sequence. Subsequent treatment of the (3+2) adducts with a palladium catalyst converts the heterocycles to the carbocyclic cyclopentanones.

Description: Understanding the practical limitations of chemical reactions is critically important for efficiently planning the synthesis of compounds in pharmaceutical, agrochemical, and specialty chemical research and development. However, literature reports of the scope of new reactions are often cursory and biased toward successful results, severely limiting the ability to predict reaction outcomes for untested substrates. We herein illustrate strategies for carrying out large-scale surveys of chemical reactivity by using a material-sparing nanomole-scale automated synthesis platform with greatly expanded synthetic scope combined with ultrahigh-throughput matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry (MALDI-TOF MS).

Description: Researchers around the world have observed the formation of molecularly ordered structures of unknown origin on the surface of titanium dioxide (TiO 2 ) photocatalysts exposed to air and solution. Using a combination of atomic-scale microscopy and spectroscopy, we show that TiO 2 selectively adsorbs atmospheric carboxylic acids that are typically present in parts-per-billion concentrations while effectively repelling other adsorbates, such as alcohols, that are present in much higher concentrations. The high affinity of the surface for carboxylic acids is attributed to their bidentate binding. These self-assembled monolayers have the unusual property of being both hydrophobic and highly water-soluble, which may contribute to the self-cleaning properties of TiO 2 . This finding is relevant to TiO 2 photocatalysis, because the self-assembled carboxylate monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.

Description: The alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) typically engage in chemical bonding as classical main-group elements through their n s and n p valence orbitals, where n is the principal quantum number. Here we report the isolation and spectroscopic characterization of eight-coordinate carbonyl complexes M(CO) 8 (where M = Ca, Sr, or Ba) in a low-temperature neon matrix. Analysis of the electronic structure of these cubic O h -symmetric complexes reveals that the metal–carbon monoxide (CO) bonds arise mainly from [M(d )] -〉 (CO) 8 backdonation, which explains the strong observed red shift of the C-O stretching frequencies. The corresponding radical cation complexes were also prepared in gas phase and characterized by mass-selected infrared photodissociation spectroscopy, confirming adherence to the 18-electron rule more conventionally associated with transition metal chemistry.

Description: Mystery surrounds the transition from gas-phase hydrocarbon precursors to terrestrial soot and interstellar dust, which are carbonaceous particles formed under similar conditions. Although polycyclic aromatic hydrocarbons (PAHs) are known precursors to high-temperature carbonaceous-particle formation, the molecular pathways that initiate particle formation are unknown. We present experimental and theoretical evidence for rapid molecular clustering–reaction pathways involving radicals with extended conjugation. These radicals react with other hydrocarbon species to form covalently bound complexes that promote further growth and clustering by regenerating resonance-stabilized radicals through low-barrier hydrogen-abstraction and hydrogen-ejection reactions. Such radical–chain reaction pathways may lead to covalently bound clusters of PAHs and other hydrocarbons that would otherwise be too small to condense at high temperatures, thus providing the key mechanistic steps for rapid particle formation and surface growth by hydrocarbon chemisorption.

Description: Basic heteroarenes are a ubiquitous feature of pharmaceuticals and bioactive molecules, and Minisci-type additions of radical nucleophiles are a leading method for their elaboration. Despite many Minisci-type protocols that result in the formation of stereocenters, exerting control over the absolute stereochemistry at these centers remains an unmet challenge. We report a process for addition of prochiral radicals, generated from amino acid derivatives, to pyridines and quinolines. Our method offers excellent control of both enantioselectivity and regioselectivity. An enantiopure chiral Brønsted acid catalyst serves both to activate the substrate and induce asymmetry, while an iridium photocatalyst mediates the required electron transfer processes. We anticipate that this method will expedite access to enantioenriched small-molecule building blocks bearing versatile basic heterocycles.

Description: Primary amines are essential constituents of biologically active molecules and versatile intermediates in the synthesis of drugs and agrochemicals. However, their preparation from easily accessible alkenes remains challenging. Here, we report a general strategy to access primary amines from alkenes through an operationally simple iron-catalyzed aminochlorination reaction. A stable hydroxylamine derivative and benign sodium chloride act as the respective nitrogen and chlorine sources. The reaction proceeds at room temperature under air; tolerates a large scope of aliphatic and conjugated alkenes, including densely functionalized substrates; and provides excellent anti-Markovnikov regioselectivity with respect to the amino group. The reactivity of the 2-chloroalkylamine products, an understudied class of amphoteric molecules, enables facile access to linear or branched aliphatic amines, aziridines, aminonitriles, azido amines, and homoallylic amines.

Description: Despite the enormous potential for the use of stereospecific cross-coupling reactions to rationally manipulate the three-dimensional structure of organic molecules, the factors that control the transfer of stereochemistry in these reactions remain poorly understood. Here we report a mechanistic and synthetic investigation into the use of enantioenriched alkylboron nucleophiles in stereospecific Pd-catalyzed Suzuki cross-coupling reactions. By developing a suite of molecular descriptors of phosphine ligands, we could apply predictive statistical models to select or design distinct ligands that respectively promoted stereoinvertive and stereoretentive cross-coupling reactions. Stereodefined branched structures were thereby accessed through the predictable manipulation of absolute stereochemistry, and a general model for the mechanism of alkylboron transmetallation was proposed.

Description: Heterobiaryls composed of pyridine and diazine rings are key components of pharmaceuticals and are often central to pharmacological function. We present an alternative approach to metal-catalyzed cross-coupling to make heterobiaryls using contractive phosphorus C–C couplings, also termed phosphorus ligand coupling reactions. The process starts by regioselective phosphorus substitution of the C–H bonds para to nitrogen in two successive heterocycles; ligand coupling is then triggered via acidic alcohol solutions to form the heterobiaryl bond. Mechanistic studies imply that ligand coupling is an asynchronous process involving migration of one heterocycle to the ipso position of the other around a central pentacoordinate P(V) atom. The strategy can be applied to complex drug-like molecules containing multiple reactive sites and polar functional groups, and also enables convergent coupling of drug fragments and late-stage heteroarylation of pharmaceuticals.

Description: Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF 3 I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF 3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.

Description: Common anionic nucleophiles such as those derived from inorganic salts have not been used for enantioselective catalysis because of their insolubility. Here, we report that merging hydrogen bonding and phase-transfer catalysis provides an effective mode of activation for nucleophiles that are insoluble in organic solvents. This catalytic manifold relies on hydrogen bonding complexation to render nucleophiles soluble and reactive, while simultaneously inducing asymmetry in the ensuing transformation. We demonstrate the concept using a chiral bis-urea catalyst to form a tridentate hydrogen bonding complex with fluoride from its cesium salt, thereby enabling highly efficient enantioselective ring opening of episulfonium ion. This fluorination method is synthetically valuable considering the scarcity of alternative protocols and points the way to wider application of the catalytic approach with diverse anionic nucleophiles.

Description: Carbon dioxide (CO 2 ) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO 2 to ethylene with 70% faradaic efficiency at a potential of –0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO 2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at –0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.

Description: White phosphorus, generated in the legacy thermal process for phosphate rock upgrading, has long been the key industrial intermediate for the synthesis of phosphorus-containing chemicals, including herbicides, flame-retardants, catalyst ligands, battery electrolytes, pharmaceuticals, and detergents. In contrast, phosphate fertilizers are made on a much larger scale from phosphoric acid, obtained by treating phosphate rock with sulfuric acid. Dehydration of phosphoric acid using sodium chloride gives trimetaphosphate, and here we report that trichlorosilane, primarily used for the production of high-purity silicon, reduces trimetaphosphate to the previously unknown bis(trichlorosilyl)phosphide anion. This anion offers an entry point to value-added organophosphorus chemicals such as primary and secondary alkyl phosphines, and thus to organophosphinates, and can also be used to prepare phosphine gas and the hexafluorophosphate anion, all previously available only downstream from white phosphorus.

Description: Cross-coupling chemistry is widely applied to carbon-carbon bond formation in the synthesis of medicines, agrochemicals, and other functional materials. Recently, single-electron–induced variants of this reaction class have proven particularly useful in the formation of C(sp 2 )–C(sp 3 ) linkages, although certain compound classes have remained a challenge. Here, we report the use of sulfones to activate the alkyl coupling partner in nickel-catalyzed radical cross-coupling with aryl zinc reagents. This method’s tolerance of fluoroalkyl substituents proved particularly advantageous for the streamlined preparation of pharmaceutically oriented fluorinated scaffolds that previously required multiple steps, toxic reagents, and nonmodular retrosynthetic blueprints. Five specific sulfone reagents facilitate the rapid assembly of a vast set of compounds, many of which contain challenging fluorination patterns.

Description: Plasmon-induced chemical reactions of molecules adsorbed on metal nanostructures are attracting increased attention for photocatalytic reactions. However, the mechanism remains controversial because of the difficulty of direct observation of the chemical reactions in the plasmonic field, which is strongly localized near the metal surface. We used a scanning tunneling microscope (STM) to achieve real-space and real-time observation of a plasmon-induced chemical reaction at the single-molecule level. A single dimethyl disulfide molecule on silver and copper surfaces was dissociated by the optically excited plasmon at the STM junction. The STM study combined with theoretical calculations shows that this plasmon-induced chemical reaction occurred by a direct intramolecular excitation mechanism.

Description: Identifying catalyst activation modes that exploit one-electron chemistry and overcome associated deactivation pathways will be transformative for developing first-row transition metal catalysts with performance equal or, ideally, superior to precious metals. Here we describe a zinc-activation method compatible with high-throughput reaction discovery that identified scores of cobalt-phosphine combinations for the asymmetric hydrogenation of functionalized alkenes. An optimized catalyst prepared from ( R , R )-Ph-BPE {Ph-BPE, 1,2-bis[(2 R ,5 R )-2,5-diphenylphospholano]ethane} and cobalt chloride [CoCl 2 ·6H 2 O] exhibited high activity and enantioselectivity in protic media and enabled the asymmetric synthesis of the epilepsy medication levetiracetam at 200-gram scale with 0.08 mole % catalyst loading. Stoichiometric studies established that the cobalt (II) catalyst precursor ( R , R )-Ph-BPECoCl 2 underwent ligand displacement by methanol, and zinc promoted facile one-electron reduction to cobalt (I), which more stably bound the phosphine.

Description: Transition metal–catalyzed arene functionalization has been widely used for molecular synthesis over the past century. In this arena, copper catalysis has long been considered a privileged platform due to the propensity of high-valent copper to undergo reductive elimination with a wide variety of coupling fragments. However, the sluggish nature of oxidative addition has limited copper’s capacity to broadly facilitate haloarene coupling protocols. Here, we demonstrate that this copper oxidative addition problem can be overcome with an aryl radical–capture mechanism, wherein the aryl radical is generated through a silyl radical halogen abstraction. This strategy was applied to a general trifluoromethylation of aryl bromides through dual copper-photoredox catalysis. Mechanistic studies support the formation of an open-shell aryl species.

Description: The activation of olefins for asymmetric chemical synthesis traditionally relies on transition metal catalysts. In contrast, biological enzymes with Brønsted acidic sites of appropriate strength can protonate olefins and thereby generate carbocations that ultimately react to form natural products. Although chemists have recently designed chiral Brønsted acid catalysts to activate imines and carbonyl compounds, mimicking these enzymes to protonate simple olefins that then engage in asymmetric catalytic reactions has remained a substantial synthetic challenge. Here, we show that a class of confined and strong chiral Brønsted acids enables the catalytic asymmetric intramolecular hydroalkoxylation of unbiased olefins. The methodology gives rapid access to biologically active 1,1-disubstituted tetrahydrofurans, including (–)-Boivinianin A.

Description: Machine learning methods are becoming integral to scientific inquiry in numerous disciplines. We demonstrated that machine learning can be used to predict the performance of a synthetic reaction in multidimensional chemical space using data obtained via high-throughput experimentation. We created scripts to compute and extract atomic, molecular, and vibrational descriptors for the components of a palladium-catalyzed Buchwald-Hartwig cross-coupling of aryl halides with 4-methylaniline in the presence of various potentially inhibitory additives. Using these descriptors as inputs and reaction yield as output, we showed that a random forest algorithm provides significantly improved predictive performance over linear regression analysis. The random forest model was also successfully applied to sparse training sets and out-of-sample prediction, suggesting its value in facilitating adoption of synthetic methodology.

Description: Chiral amines are widely used as catalysts in asymmetric synthesis to activate carbonyl groups for α-functionalization. Carbonyl catalysis reverses that strategy by using a carbonyl group to activate a primary amine. Inspired by biological carbonyl catalysis, which is exemplified by reactions of pyridoxal-dependent enzymes, we developed an N-quaternized pyridoxal catalyst for the asymmetric Mannich reaction of glycinate with aryl N -diphenylphosphinyl imines. The catalyst exhibits high activity and stereoselectivity, likely enabled by enzyme-like cooperative bifunctional activation of the substrates. Our work demonstrates the catalytic utility of the pyridoxal moiety in asymmetric catalysis.

Description: Deconstructive functionalizations involving scission of carbon-carbon double bonds are well established. In contrast, unstrained C(sp 3 )–C(sp 3 ) bond cleavage and functionalization have less precedent. Here we report the use of deconstructive fluorination to access mono- and difluorinated amine derivatives by C(sp 3 )–C(sp 3 ) bond cleavage in saturated nitrogen heterocycles such as piperidines and pyrrolidines. Silver-mediated ring-opening fluorination using Selectfluor highlights a strategy for cyclic amine functionalization and late-stage skeletal diversification, establishing cyclic amines as synthons for amino alkyl radicals and providing synthetic routes to valuable building blocks.

Description: Transformation of simple precursors into structurally complex cyclobutanes, present in many biologically important natural products and pharmaceuticals, is of considerable interest in medicinal chemistry. Starting from 1,3-enynes and ethylene, both exceptionally inexpensive starting materials, we report a cobalt-catalyzed route to vinylcyclobutenes, as well as the further enantioselective addition of ethylene to these products to form complex cyclobutanes with all-carbon quaternary centers. These reactions can proceed in discrete stages or in a tandem fashion to achieve three highly selective carbon-carbon bond formations in one pot using a single chiral cobalt catalyst.