Alkaloidy a pesticídy

Kategorie: Chémia (celkem: 341 referátů a seminárek)

Informace o referátu:

  • Přidal/a: anonymous
  • Datum přidání: 12. března 2007
  • Zobrazeno: 8664×

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Alkaloidy a pesticídy

ALKALOIDY

Alkaloidy sú prírodné dusíkaté zlúčeniny zásaditého charakteru. Vznikajú v malom množstve ako produkty metabolizmu AK, napr. u iskerníkovitých, ľuľkovitých, makovitých rastlinách. V rastlinnom, príp. živočíšnom organizme sa vyskytujú v hotovej forme, v prírode najčastejšie vo forme solí s organickými kyselinami ( jablčná, citrónová, šťavelová, jantárová, octová...). Alkaloidy takmer všetky obsahujú heterocyklický kruh, na ktorý sa viažu ďalšie štruktúry. Sú to kvapaliny alebo kryštalické látky, vo forme solí dobre rozpustné vo vode. Možno ich získať extrakciou z rastlín, alebo pripraviť synteticky. Ich fyziologické účinky sú známe už oddávna. Požitím niektorých z nich nastávajú stavy ako ľahostajnosť, bezstarostnosť, porušenie rovnováhy, znecitlivenie, halucinácia aj agresivita, neskôr môže nastať, hlavne pri požití väčšieho množstva, otrava až smrť. Pri opakovanom požívaní môže vzniknúť závislosť, ktorá sa prejavuje ako narkománia. No pri správnom dávkovaní sú niektoré dôležité liečivá. Je mnoho typov ich delenia, napr. podľa základnej chemickej štruktúry, podľa hlavného reprezentanta skupiny, podľa ich výskytu v rastlinách, alebo podľa typu viazania dusíka (acyklicky, cyklicky).

Najvýznamnejšie alkaloidy:

NIKOTÍN - obs. cyklus pyridínu, je rozpust. vo vode, izoluje sa z listov tabaku, nepriaznivé účinky na srdcové cievy, zvyšuje krvný tlak, zapríčiňuje poruchy dýchania, jeho spalné splodiny pri fajčení podporujú vznik rakoviny pľúc.
ATROPÍN - obs. cyklus tropánu, nach. sa v ľuľkovci zlomocnom a v semenách durmana, veľmi jedovatý, tvorí bezfarebné kryštáliky, nerozpust. vo vode, rozpust. v alkohole, jeho roztoky majú horkú chuť, používa sa v očnom lekárstve, spočiatku povzbudzuje činnosť CNS, postupne vyvoláva halucinácie, až vysilenie, môže zastaviť dýchanie.
KOKAÍN - obs. cyklus tropánu, je obsiahnutý v listoch koky, tvorí bezfarebné kryštáliky málo rozp. vo vode, dobre v alkoh. a éteri. Rastie v Peru, Chile, pestuje sa na Jáve a na niekt. ostrovoch Ind. oceána, použ. sa v lekárstve ako lokálne anestetikum, silné narkotikum, veľmi návykový
ÓPIUM - zdroj viac ako 20 alkaloidov, šťava z nezrelých makovíc, čiastočne rozpust. vo vode, medzi ópiové alkaloidy patrí napr. morfín (jed. látka, kt. odstraňuje subjektívne bolesti), kodeín ( tlmenie kašľa), narkotín, papaverín a pod., obs. cyklus chinolínu, al.

izochinolínu
HEROÍN - polosyntetický derivát morfínu, silne zásaditý charakter, omamná látka, najnebezpečnejšia návyková droga, celosvetovo zakázaná
LSD - derivát lysergid odvodený od kyseliny lysergovej, psychofarmakum - halucinogén, kt. spôsobuje u človeka emočné zmeny až depresie, obs. cyklus indolu
KOFEÍN - obs. cyklus purínu, diuretikum (zasahuje do funkcie obličiek, zvýš. tvorba moču),analeptikum (stimuluje urč. oblasti CNS, pričom neovplyv. psych. funkcie), nach. sa v niektorých rastlinách, napr. kávové zrná al. čajové listy.


Použitá literatúra: Chémia pre 3. ročník gymnázií, Malá encyklopédia chémie

Poznámka: AK = aminokyseliny
CNS = centrálna nervová sústava

PESTICÍDY



Sú to chemické látky, ktoré sa v poľnohospodárstve a v lesníctve používajú v boji proti chorobám a škodcom rastlín a proti burine. Rozdeľujú sa na fungicídy, insekticídy, herbicídy, rodenticídy, akaricídy a nematocídy. Fungicídy sú skupinou pesticídov používaných na zamedzenie vývoja alebo na ničenie cudzopasných húb na úžitkových rastlinách. Z chemického hľadiska sa delia na meďnaté, sírnaté, organické a kombinované. Insekticídy sú chemické prípravky na ničenie hmyzu. Podľa toho, na ktoré vývojové štádium hmyzu účinkujú, rozdeľujú sa na ovicídy (ničia vajíčka), larvycídy (ničia larvy) a imagocídy (ničia dospelý hmyz). Podľa fyziologického účinku sa delia na plazmatické, leptavé, nervové a dýchacie. Podľa spôsobu vnikania do tela hmyzu zase dotykové (kontaktné), perorálne a dýchacie. Z chemického hľadiska ich možno rozdeliť na chlórované uhľovodíky, napr. DDT, prestávajú sa používať, pretože sa hromadia v živočíšnom organizme. Ďalej sú to organofosfáty - estery kyseliny fosforečnej a jej tioderivátov, v súčasnosti najčastejšie používané. Karbamáty - estery kyseliny karbamovej, sa používajú menej. Pre vysokú toxicitu sa ako insekticíd používa kyanovodík. Ďalším významným insekticídom je pirimicarb. Hubí vošky a šetrí lienky, zlatoočky a včely. Keď sa ním vošky postriekajú, molekuly pirimicarbu padnú ako uliate na molekuly životne dôležitého enzýmu v tele vošiek, zvaného acetylcholinesteráza. Ten odbúrava jedovaté látky vznikajúce v nervovej sústave hmyzu. Zastavenie jeho pôsobenia spôsobuje rýchlu smrť. Zlatoočky a lienky majú iný druh enzýmu. Pirimicarb preniká aj listami a zahubí aj vošky pod nimi, navyše jeho výpary sú jedovaté. Dostáva sa do miazgy rastlín, takže hubí vošky, ktoré sa ňou živia , ešte 2 týždne po postreku. Môže však mať nepriaznivý účinok na ľudí, zvieratá a vtáky.

Herbicídy sú chemické látky, ktoré zabraňujú rastu rastlín. Obyčajne sa používajú na ničenie buriny. Selektívne herbicídy účinkujú na 1 rastlinu alebo na skupinu rastlín.

Totálne herbicídy ničia všetky druhy rastlín. Kontaktné ničia rastlinu pri jej dotyku s látkou, koreňové klíčiacu rastlinu cez jej korene a herbicídy stimulujúce rast bránia rastu rastliny. Dnes herbicídy ničia burinu tak, že ťažia z jej vlastného rastu. Používajú sa chemické látky, ktoré sa správajú ako hormóny buriny - jej prirodzené rastové látky - a vyprovokujú taký rýchly rast, že sa rastliny rýchle vyčerpajú a skoro hynú. Medzi takéto 2 najpoužívanejšie herbicídy patria látky MCPA a 2,4-D. Sú selektívne, ničia rastliny so širokými listami. Ovos hluchý, divo rastúci medzi obilninami, sa nedá zničiť ani 1 z týchto herbicídov, lebo jeho hormóny sú podobné hormónom pestovaných rastlín. Pre tento prípad vedci vyvinuli herbicíd, ktorý využíva rozdiely v tom, ako divoké a pestované rastliny vyrastajú zo semena. Herbicíd PCP sa po osiatí uloží do vrchnej vrstvy pôdy. Ovos hluchý klíči skoro a jeho konček prenikne do tejto vrstvy v čase, keď je najjedovatejšia. Herbicíd zaútočí na klíčok a rastlinu zahubí.

Rodenticídy sú látky, ktoré sa používajú v boji proti hlodavcom v poľnohospodárstve alebo domácnostiach. Sú založené na báze fosforovodíka, fosfidov alebo warfarínu. Tieto pesticídy sú jedovaté aj pre človeka.

Akaricídy sa používajú v boji proti roztočom a roztočcom. Sú založené na báze malatiónu al. meoinphosu.

Nematocídy sú skupinou pesticídov, ktoré sa používajú v boji proti voľne žijúcim a cystotvorným háďatkám v pôde. Patria k nim látky na báze N-metyl-ditiokarbamátov, 1,2-dibrómchlórpropánu. Použitá literatúra: Malá encyklopédia chémie (Obzor, 1981), Ako funguje svet? (Reader´s Digest Výber, 1998).

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