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Home > E Ffect of C Omplexing a Gents on the P Hotodegradation of R Iboflavin in a Queous S Olution

E Ffect of C Omplexing a Gents on the P Hotodegradation of R Iboflavin in a Queous S Olution

Thesis Info

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Author

A Hmed, S Ofia

Program

PhD

Institute

Baqai Medical University

City

Karachi

Province

Sindh

Country

Pakistan

Thesis Completing Year

2009

Thesis Completion Status

Completed

Subject

Applied Sciences

Language

English

Link

http://prr.hec.gov.pk/jspui/handle/123456789/323

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676725933066

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The present investigation involves a study of the effect of complexing agents, i.e., borate, caffeine and divalent ions (phosphate, sulphate, tartrate, succinate, and malonate) on the photodegradation reactions of riboflavin (RF) in aqueous solutions. RF and its major products of photoreduction, formylmethylflavin (FMF), lumichrome (LC), lumiflavin (LF), and photoaddition, cyclodehydroriboflavin (CDRF), have been determined by a multicomponent spectrophotometric method. In borate buffer (0.1–0.5 M) at pH 8.0–10.5, RF (5 × 10 –5 M) undergoes photolysis by consecutive first-order reactions to yield FMF, LC, LF (major products) and carboxymethylflavin, CMF (minor product). The overall first-order rate constants (k obs ) for the photolysis of RF (1.55–4.36 × 10 –2 min –1 ) and the rate constants for the formation of FMF (1.16–3.52 × 10 –2 min –1 ) and LC (0.24–0.84 × 10 –2 min –1 ) have been determined. The values of all these rate constants decrease with an increase in buffer concentration suggesting the inhibition of the photolysis reaction by borate ions. The kinetic data support the formation of a RF–borate complex involving the ribityl side chain to cause the inhibition of the reaction. The second-order rate constants for the borate inhibited reactions (k ́) range from 1.17–3.94 × 10 –2 M –1 min –1 ). The log k–pH profiles for the reactions at various buffer concentrations indicate a gradual increase in rate, with pH, up to 10 followed by a decrease in rate at pH 10.5 probably due to the ionization of RF and quenching of fluorescence by borate ions (32%). A graph of k ́ against pH is a sigmoid curve showing that the rate of photolysis increases with an increase in pH. The results suggest the involvement of excited singlet state, in addition to excited triplet state, in the formation of LC. ivThe photolysis of RF in the presence of caffeine (0.5–2.5 × 10 –4 M) yields the same products as in the case of borate buffer. The apparent first-order rate constants (k obs ) for the photolysis reactions at pH 2.0–10.5 range from 2.71 × 10 –4 to 4.26 × 10 –2 min –1 . Similar to the effect of borate ions, the values of the rate constants decrease with increasing concentrations of caffeine indicating its inhibitory effect on the reactions. The second-order rate constants (k'') for the photolysis reactions in the presence of caffeine are in the range of 0.13–5.10 × 10 –3 M –1 min –1 . The log k–pH profiles for the photolysis reactions at various caffeine concentrations involve multiple steps indicating a gradual increase in the rate up to pH 10. The lower rates at pH 2.0 and above 10.0 are due to the ionization of RF. The k''–pH profile for the interaction of RF and caffeine represents a bell-shaped curve in the pH range 3–6 followed by a sigmoid curve in the pH range 7–10. The inhibition of RF photolysis in the presence of caffeine appears to be a result of the monomeric interaction and complex formation of RF with caffeine. The photochemical interaction of RF with caffeine suggests that a pH around 6 is most appropriate for the stabilization of the vitamin. At this pH the complex shows the highest stability constant. The photodegradation of RF in the presence of divalent ions (0.2–1.0 M) at pH 6.0–8.0 involves simultaneous photolysis and photoaddition yielding FMF, LC, LF, CMF, and CDRF, respectively, by parallel first-order reactions. The rate–pH curves represent a composite profile for the overall photodegradation of RF by two simultaneous reactions involving changes in the rates of formation of CDRF and LC. The catalytic effect of divalent ions influences the reaction in the order of phosphate > sulphate > tartrate > succinate > malonate to give rise to CDRF. The mode of photodegradation of RF has been explained on the basis of the kinetic data obtained for these reactions.
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وجہ تالیف

وجہ تالیف
انسان ہر میدان میں روج کا خواہاں دکھائی دیتا ہے ۔زوال نام سے خائف ہے ، معاشی، معاشرتی ، سیاسی یا روحانی میدان ہو خواہش اُ س کی یہی ہوتی ہے کہ ان سب پر اُسی کا قبضہ ہو اور دیگر حضرات اِن میادین میں اُس کی دریوزہ گری کریں ، تحریر ہو، تقریر ہو، خطابت ہو، کتابت ہو،سب میدان اپنے نام کرنا چاہتا ہے ۔ لیکن یہ قانون قدرت ہے کہ ملتا وہی ہے جس کے لیے لیس للانسان الا ماسعٰیکے مصداق وہ جہدِ مسلسل کرتاہے۔ انسانی شخصیت میں جو شعبے نکھار پیدا کرتے ہیں وہ خطابت اور تحریر ہیں ، مقالات و خطابت میں ، انسان اپنا مافی الضمیر یا تواپنی زبان کی حرکت سے بیان کرتا ہے اوریا پھر قلم کو اذنِ خرام دے کر قرطاس ابیض پر کچھ رقم کر کے تخیلات و تصورات کو منصۂ شہود پر لا کر کرتا ہے ۔ ایّام زیست و حیات کے طائر خوش الحان کو محو پرواز رکھنے کے لیے تحریر و تقریر کی فضائے خوشگوار کی اشد ضرورت ہے ۔ اسی فضاء میں زندگی کی گاڑی بطریق احسن اپنی منزل کی طرف رواں دواں ہو سکتی ہے ۔ ان حقائق کو مدِ نظر رکھتے ہوئے عوام النّاس کے لیے بالعموم اور طلباء کے لیے بالخصوص چند عنوانات پر مشتمل مضامین کا انتخاب کیا ہے جو طلباء میں فصاحت و بلاغت کے ساتھ ساتھ اُن کی معاشرتی زندگی میں بھی ممدو معاون ثابت ہوں گے۔ نیز ان کے لیے تحریر و تقریر کے میدان میں مہمیز ثابت ہوں ۔ یہ چنگاری کافی عرصے سے اس وجودِ خاکی میں سلگ رہی تھی کہ کوئی تو ذریعہ ایسا سامنے آئے جس سے نونہالانِ وطن کے دماغ کے دریچوں کو جنبش دی جا سکے اور اُن کی تخلیقی صلاحیتوں کو اُجا گر کیا جا سکے ۔ اِس...

The Gray area Beyond Raised Objections (Sharia’h Perspective) Regarding In-practice Islamic Banking System

Shari‘ah’s teachings are perfect and forever. They leave everlasting impacts on society towards its spiritual as well as material purification (Tazkia) if implemented properly according to Qur’an and Sunnah. Interest (Sood/Rib┐) has been forbidden by Almighty Allah whereas Trade (Ba‘a) has been legitimated. To bring the Muslims of today out of Interest-based Banking System, religious scholars have outlined and introduced Islamic Banking System which, although, has got fast growth in market but still, a number of objections are being raised by different scholars leading to an impression that this system is not working in accordance with Shari‘ah. This not only discourages the entry of new ones to Islamic Banking Sector but also create confusions in the minds of the enlisted customers. Keeping in view the above scenario, need is felt to assess, evaluate and analyze the Objections raised with special emphasis on Islamic Concept of Bank, Charity Fund (Iltez┐m be tasaduq) and Mur┐ba╒a being the major points of objections of the critics. The present study investigates different aspects and dimensions of these objections in the context of Shariah and ground realities in order to know the extent of validity of these objections, highlight the gray areas giving rise to objections and give real picture to the public in general and enhance the satisfactory level of the enlisted Islamic Banking customers in particular.

Agricultural Trade Between Pakistan and United Arab Emirates: Performance, Competitiveness and Determinants

Major trading partners of Pakistan are China, United Arab Emirates, Saudi Arabia and Unites States of America. United Arab Emirate is the trading partner of Pakistan with 10.9 percent share of total trade. Export share of Pakistan to United Arab Emirates is 8.5 percent of its total exports. Import share of Pakistan from United Arab Emirates is about 12 percent of its total imports. Major agricultural export products of Pakistan to UAE are rice, meat and cotton yarn. Major imports of agricultural products include dried vegetables, sugar and dairy products. Objective of the study was to elaborate the trade of major agricultural products between Pakistan and United Arab Emirates, with a focus on analysis of major factors affecting the agricultural trade, competitiveness and comparative advantage of major agricultural products traded between Pakistan and United Arab Emirates. Impact of different variable was determined by the application of gravity model by using the panel data methods. Variables that were used are total trade, population, GDP, distance between trading partners, and dummies for border and cultural similarities. Competitiveness in agricultural trade was estimated by nominal protection coefficient (NPC). To estimate the comparative advantage of Pakistan for specific products, approaches of revealed comparative advantage (RCA) and revealed systematic comparative advantage (RSCA) were used. For this purpose data for analysis were obtained from suitable sources. According to the results of gravity model of trade GDP of Pakistan has a positive and significant impact on agricultural trade with United Arab Emirates. GDP of United Arab Emirates has a positive and significant impact on agricultural trade between Pakistan and United Arab Emirates. Population of United Arab Emirates has positive and significant Impact on agricultural trade. Increasing Population of Pakistan has a negative and significant impact on agricultural trade with United Arab Emirates. It implies that population variable has the trade inhibiting affect. It implies that a larger population size may be treated as large resource endowments and thus an indication of selfsufficiency and thereby less reliance on international trade. Dummy variable of cultural similarities has a significant and positive impact on agricultural trade and the joint border has negative and significant impact on trade of Pakistan. Distance between trading partners has a negative impact on agricultural trade but this was not significant. The value of NPC 11 shows that Pakistan is losing its competitiveness in basmati exports. So there was need to find other markets where its competitiveness is more as compared to United Arab Emirates. Furthermore the basmati growers should be given proper subsidies and the policies should be made to keep the domestic prices of basmati low, to make Pakistani basmati rice more competitive in international markets as compared to its main competitors. Increasing values of RCA index of basmati rice shows that Instead of losing competitiveness of basmati rice Pakistan has comparative advantage in basmati rice. There is need to maintain both the competitiveness and comparative advantage at the same time and for this purpose the government should play its role by changing the existing price policies. NPC of beef remained less as compared to Mutton that means Pakistani beef is more competitive as compared to mutton. It was concluded that Pakistan should focus more on beef for its exports growth as compared to mutton. The analysis increasing trend of RCA indices for the previous 10 years of both mutton and beef shows that the Pakistani beef has more comparative advantage as compared to mutton. Pakistani beef is more competitive having more comparative advantage showing that there are some issues in the mutton exports as compared to beef. Pakistan should try to find other markets for its mutton. Pakistan should focus on the both the mutton and beef to enlarge in export value. Pakistan has competitiveness in the cotton yarn but it is not a strong competitiveness. Pakistan has comparative advantage in export of cotton yarn. Pakistan can produce milk at low cost and can export to get high margin but due to the domestic demand it is not possible. Pakistan has strong competitiveness in milk but still is not able to export the milk to the other countries. There is need to make more growth in dairy sector and government should give more attention toward this sector. Value of NPC of sugar more than unity was showing that international prices were less than the domestic prices and Pakistan has no competitiveness in the sugar. Pakistan is an exporter of fresh vegetables but at the same time Pakistan is also importer of the dried vegetables. There is lack of value addition in vegetables. There is need of value addition in the sector of vegetable as there is demand of dried vegetables in Pakistan but there is lack of supply of the dried vegetables to fulfill its demand. Dried vegetables are imported and the Pakistani consumers pay more for these products. There is also lack of adoption of value addition in this sector.